JP2020189762A - Method for manufacturing nitride semiconductor substrate, nitride semiconductor substrate and laminated structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the crystal quality of a nitride semiconductor substrate. SOLUTION: A step of preparing a base substrate, a step of forming a first base layer on the base substrate, a step of forming a metal layer on the first base layer, and a heat treatment are performed in the first base layer. Group III having a step of forming voids, a step of epitaxially growing a second base layer above the first base layer and mirroring the main surface of the second base layer, and a top surface with an exposed (0001) surface. A single crystal of a nitride semiconductor is epitaxially grown directly on the main surface of the second base layer to generate a plurality of recesses composed of inclined interfaces other than the (0001) plane on the top surface, and above the second base layer. A three-dimensional growth step in which the inclined interface is gradually expanded, the (0001) plane disappears from the top surface, and the first layer whose surface is composed of only the inclined interface is grown, and on the first layer. It has a flattening step of epitaxially growing a single crystal of a group III nitride semiconductor, eliminating the inclined interface, and growing a second layer having a mirrored surface. [Selection diagram] Fig. 1

Description

The present invention relates to a method for manufacturing a nitride semiconductor substrate, a nitride semiconductor substrate and a laminated structure.

Various methods have been disclosed in order to obtain a self-supporting substrate (hereinafter, also referred to as “nitride semiconductor substrate”) made of a single crystal of a group III nitride semiconductor (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-1789884

An object of the present invention is to improve the crystal quality of a nitride semiconductor substrate.

According to one aspect of the invention
The process of preparing the base substrate and
A step of forming a first base layer made of a group III nitride semiconductor on the base substrate, and
The step of forming a metal layer on the first base layer and
A step of performing heat treatment to form a void in the first base layer, and
A second base layer composed of a single crystal of a group III nitride semiconductor and having a main surface whose closest low index crystal plane is the (0001) plane is epitaxially grown above the first base layer, and the second lower layer is formed. The process of mirroring the main surface of the stratum and
A single crystal of a group III nitride semiconductor having a top surface with an exposed (0001) plane is epitaxially grown directly on the main surface of the second base layer, and is composed of an inclined interface other than the (0001) plane. A plurality of recesses are formed on the top surface, the inclined interface is gradually expanded toward the upper side of the second base layer, the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. A three-dimensional growth process that grows the first layer composed of
A flattening step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, eliminating the inclined interface, and growing a second layer having a mirrored surface.
A method for manufacturing a nitride semiconductor substrate having the above is provided.

According to another aspect of the invention
In the method for manufacturing a nitride semiconductor substrate according to the above aspect, the nitride semiconductor substrate obtained by slicing the second layer is provided.

According to still another aspect of the invention.
A nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
When the main surface is irradiated with X-rays of Cu Kα1 through a two-crystal monochromator and a slit on the Ge (220) surface and the X-ray locking curve of (0002) surface diffraction is measured, the slit. The half-value width FWHMb of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm is subtracted from the half-value width FWHMa of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm. A nitride semiconductor substrate having a difference of FWHMa-FWHMb of 30% or less of FWHMa is provided.

According to another aspect of the invention
A nitride semiconductor substrate having a diameter of 2 inches or more.
When the main surface of the nitride semiconductor substrate is observed with a multiphoton excitation microscope with a field of view of 250 μm square and the dislocation density is obtained from the dark spot density, the region where the dislocation density exceeds 3 × 10 ⁶ cm- ² is the main surface. Provided is a nitride semiconductor substrate in which a region that is not present on the surface and has a dislocation density of less than 1 × 10 ⁶ cm- ² is present at 80% or more of the main surface.

According to still another aspect of the invention.
A nitride semiconductor substrate having a main plane in which the closest low index crystal plane is the (0001) plane.
The X-ray locking curve of the (0002) plane is measured at each position on the straight line passing through the center in the main plane, and the peak angle ω formed by the X-ray incident on the main plane and the main plane is measured on the straight line. When plotted against the position of and the peak angle ω is approximated by the linear function of the position,
The radius of curvature of the (0001) plane obtained by the reciprocal of the slope of the linear function is 10 m or more.
A nitride semiconductor substrate is provided in which the measured error of the peak angle ω with respect to the linear function is 0.05 ° or less.

According to still another aspect of the invention.
A base layer composed of a single crystal of a group III nitride semiconductor, having a mirrored main surface, and having a low index crystal plane closest to the main plane as the (0001) plane.
A plurality of single crystals of group III nitride semiconductors having a top surface with an exposed (0001) plane are epitaxially grown directly on the main surface of the base layer, and are composed of inclined interfaces other than the (0001) plane. The concave surface is formed on the top surface, the inclined interface is gradually expanded toward the upper side of the base layer, and the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. The first layer composed of
A single crystal of a group III nitride semiconductor is epitaxially grown on the first layer to eliminate the inclined interface, and a second layer having a mirrored surface is formed.
A laminated structure having the above is provided.

According to the present invention, the crystal quality of a nitride semiconductor substrate can be improved.

It is a flowchart which shows the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. It is a flowchart which shows the base structure manufacturing process. (A) to (e) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention. (A)-(c) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. It is a schematic perspective view which shows a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. (A)-(b) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. (A)-(b) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. (A) is a schematic cross-sectional view showing a growth process under reference growth conditions in which each of the inclined interface and the c-plane does not expand or contract, and (b) is a th-order view in which the inclined interface expands and the c-plane shrinks. 1 It is a schematic cross-sectional view which shows the growth process under the growth condition. It is a schematic cross-sectional view which shows the growth process under the 2nd growth condition that the inclined interface shrinks and the c plane expands. (A) is a schematic top view showing a nitride semiconductor substrate according to an embodiment of the present invention, and (b) is a schematic cross section of the nitride semiconductor substrate according to an embodiment of the present invention along the m-axis. FIG. 3C is a schematic cross-sectional view taken along the a-axis of the nitride semiconductor substrate according to the embodiment of the present invention. (A) is a schematic cross-sectional view showing the diffraction of X-rays with respect to the curved c-plane, and (b) and (c) are diagrams showing the fluctuation of the diffraction angle of the (0002) plane with respect to the radius of curvature of the c-plane. Is. It is a figure which shows the observation image which observed the cross section of the laminated structure of an Example with a fluorescence microscope. It is a figure which observed the main surface of the nitride semiconductor substrate of an Example using a multiphoton excitation microscope. FIG. (A) is a diagram showing the results of X-ray locking curve measurement of (0002) plane diffraction along the m-axis direction for each of the nitride semiconductor substrates of Example and Comparative Example 1. Is a diagram showing the results of X-ray locking curve measurement of (0002) plane diffraction along the a-axis direction for each of the nitride semiconductor substrates of Example and Comparative Example 1. (A) is a diagram showing a standardized X-ray diffraction pattern when the X-ray locking curve is measured with different slits for the nitride semiconductor substrate of the example, and (b) is a comparative example. It is a figure which shows the standardized X-ray diffraction pattern at the time of performing the same measurement as the Example about the nitride semiconductor substrate of 1.

<Knowledge obtained by inventors>
First, the findings obtained by the inventors will be described.

The method in Patent Document 1 described above is called a VAS (Void-assisted Spalation Method). The VAS method is performed, for example, as follows.

First, a first crystal layer made of a group III nitride semiconductor is formed on a predetermined substrate. After forming the first crystal layer, a metal layer is formed on the first crystal layer. After the metal layer is formed, heat treatment is performed in an atmosphere containing a predetermined gas to form fine holes in the metal layer and voids in the first crystal layer through the mesh (nanonet) of the metal layer. To form. After forming voids in the first crystal layer, a second crystal layer made of a group III nitride semiconductor is formed above the first crystal layer. At this time, a part of the above-mentioned void remains. After the second crystal layer is formed, when the temperature is lowered from the growth temperature of the second crystal layer, the second crystal layer is peeled off from the base substrate due to the above-mentioned remaining voids. After the second crystal layer is peeled off, the second crystal layer is sliced and polished to obtain a nitride semiconductor substrate having high crystal quality.

Here, when a crystal layer composed of a single crystal of a group III nitride semiconductor is grown thick with the c-plane as a growth plane, the dislocation density on the surface of the crystal layer tends to be inversely proportional to the thickness of the crystal layer. is there.

Therefore, in the above-mentioned VAS method, in order to reduce the dislocation density of the second crystal layer, it is conceivable to grow the second crystal layer thickly above the first crystal layer.

However, in the above-mentioned VAS method, tensile stress generated by attracting the initial nuclei of the crystal is accumulated on the substrate side of the second crystal layer. On the other hand, due to the tensile stress generated in the second crystal layer, the c-plane of the second crystal layer is curved like a concave spherical surface. When the second crystal layer is grown thickly on the concavely curved c-plane, the stress applied to the second crystal layer gradually changes to compressive stress as the second crystal layer becomes thicker. Therefore, the stress difference between the base substrate side and the surface side of the second crystal layer gradually increases. If the stress difference becomes excessive, cracks may occur in the second crystal layer.

As described above, in the VAS method, it is difficult to grow the second crystal layer thickly with the c-plane as the growth plane.

The present invention is based on the above findings found by the inventor.

<One Embodiment of the present invention>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(1) Method for Manufacturing Nitride Semiconductor Substrate A method for manufacturing a nitride semiconductor substrate according to the present embodiment will be described with reference to FIGS. 1 to 8. FIG. 1 is a flowchart showing a method for manufacturing a nitride semiconductor substrate according to the present embodiment. FIG. 2 is a flowchart showing a base structure manufacturing process. 3 (a) to (e), FIGS. 4 (a) to 4 (c), and 6 (a) to 8 are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to the present embodiment. Is. FIG. 5 is a schematic perspective view showing a part of the method for manufacturing a nitride semiconductor substrate according to the present embodiment. In addition, in FIGS. 3A to 3E, the lower side of the base substrate 1 is omitted. Further, FIG. 5 corresponds to the perspective view at the time of FIG. 4B, and shows a part of the first layer 30 growing on the base structure 10. Further, in FIG. 6 (b), the fine solid line in the second layer 40 indicates a crystal plane during growth, and in FIGS. 4 (c) and 6 (a) to 8, the dotted line indicates a dislocation. ..

In the following, in a crystal of a group III nitride semiconductor having a wurtzite structure, the <0001> axis (for example, [0001] axis) is referred to as “c-axis”, and the (0001) plane is referred to as “c-plane”. The (0001) plane may be referred to as "+ c plane (Group III element polar plane)", and the (000-1) plane may be referred to as "-c plane (nitrogen (N) polar plane)". Further, the <1-100> axis (for example, the [1-100] axis) is referred to as an "m axis", and the {1-100} plane is referred to as an "m plane". The m-axis may be expressed as the <10-10> axis. Further, the <11-20> axis (for example, the [11-20] axis) is referred to as an "a axis", and the {11-20} plane is referred to as an "a plane".

As shown in FIG. 1, the method for manufacturing a nitride semiconductor substrate according to the present embodiment includes, for example, a base structure manufacturing step S100, a three-dimensional growth step S200, a flattening step S300, a slicing step S400, and polishing. It has a step S500.

(S100: Substrate structure manufacturing process)
First, for example, the base structure 10 is produced by the above-mentioned VAS method.

Specifically, the base structure manufacturing step S100 includes, for example, a base substrate preparation step S110, a first base layer forming step S120, a metal layer forming step S130, a void forming step S140, and a second base layer forming step. It has S150 and.

(S110: Base substrate preparation process)
First, as shown in FIG. 3A, the base substrate 1 is prepared. The base substrate 1 is made of, for example, a material different from that of the group III nitride semiconductor. Specifically, the base substrate 1 is, for example, a sapphire substrate. The base substrate 1 may be, for example, a Si substrate or a gallium arsenide (GaAs) substrate.

The diameter of the base substrate 1 is, for example, 2 inches (50.8 mm) or more. The thickness of the base substrate 1 is, for example, 300 μm or more and 1 mm or less.

The base substrate 1 has, for example, a main surface 1s which is an epitaxial growth surface. The crystal plane with the lowest index closest to the main plane 1s is, for example, the c plane.

In the present embodiment, the c-plane of the base substrate 1 is inclined with respect to the main surface 1s. The c-axis of the base substrate 1 is inclined at a predetermined off angle with respect to the normal of the main surface 1s. The off angle of the base substrate 1 in the main surface 1s is uniform over the entire main surface 1s. The size of the off angle at the center of the main surface 1s of the base substrate 1 is set to, for example, more than 0 ° and 1 ° or less. The off angle of the base substrate 1 in the main surface 1s affects the off angle at the center of the main surface 6s of the second base layer 6, which will be described later.

(S120: First base layer forming step)
Next, as shown in FIG. 3B, a first base layer (first crystal layer) 2 made of a group III nitride is formed on the main surface 1s of the base substrate 1.

Specifically, for example, a group III raw material gas and a nitrogen raw material gas are supplied to the base substrate 1 heated to a predetermined growth temperature by the organic metal vapor phase growth (MOVPE) method. For example, by supplying trimethylgallium (TMG) gas as a group III raw material gas and ammonia gas (NH ₃ ) as a nitrogen raw material gas, a low-temperature growth GaN buffer layer and GaN are used as the first base layer 2. The layers and the layers are grown on the main surface 1s of the base substrate 1 in this order. When the GaN layer is grown, for example, an n-type impurity may be doped into the GaN layer by supplying a monosilane (SiH ₄ ) gas as an n-type dopant gas.

At this time, the growth conditions of the low-temperature growth GaN buffer layer as the first base layer 2 are adjusted so that the desired crystal quality of the GaN layer can be obtained. Specifically, the growth temperature of the low-temperature growth GaN buffer layer is, for example, 400 ° C. or higher and 600 ° C. or lower.

Further, at this time, the growth conditions of the GaN layer as the first base layer 2 are adjusted so that a desired void is formed in the void forming step S140 described later. Specifically, the growth temperature of the GaN layer is, for example, 1,000 ° C. or higher and 1,200 ° C. or lower.

At this time, for example, the surface of the first base layer 2 is mirrored. The "mirror surface" here means a surface in which the difference in surface irregularities is equal to or less than the wavelength of visible light, and the surface of the first base layer 2 is a hillock in which facets other than the c surface are exposed. May occur. Specifically, the root mean square roughness RMS of the surface of the first base layer 2 is set to, for example, less than 10 nm, preferably less than 1 nm. By mirroring the surface of the first base layer 2 in this way, the appearance of voids can be made substantially uniform over the entire main surface 1s of the base substrate 1 in the void forming step S140 described later.

(S130: Metal layer forming step)
Next, as shown in FIG. 3C, the metal layer 3 is formed on the first base layer 2. For example, the metal layer 3 is formed by vacuum deposition or sputtering.

The metal layer 3 is configured to form fine holes in itself by heat treatment in the void forming step S140 described later, promote decomposition of the first base layer 2, and form voids in the first base layer 2. It is preferably made of a material. Specifically, examples of the metal layer 3 satisfying this condition include titanium (Ti), scandium (Sc), ittrium (Y), zirconium (Zr), hafnium (Hf), vanadium (V), and niobium (Nb). ), Tantal (Ta), Chromium (Cr), Molybdenum (Mo), Tungsten (W), Rhenium (Re), Iron (Fe), Ruthenium (Ru), Osmium (Os), Cobalt (Co), Rodium (Rh) ), Iridium (Ir), nickel (Ni), palladium (Pd), manganese (Mn), copper (Cu), platinum (Pt), gold (Au) and the like. In the present embodiment, the metal layer 3 is, for example, a Ti layer.

At this time, the thickness of the metal layer 3 is set to, for example, 1 μm or less, preferably 300 nm or less, and more preferably 100 nm or less. By setting the thickness of the metal layer 3 to 1 μm or less, preferably 300 nm or less, more preferably 100 nm or less, it is possible to suppress a decrease in flatness of the metal layer 3 (metal nitride layer 5) in the void forming step S140 described later. Can be done. As a result, deterioration of the crystal quality of the second base layer 6 formed on the metal nitride layer 5 can be suppressed. The lower limit of the thickness of the metal layer 3 is not particularly limited. However, from the viewpoint of stably forming the metal nitride layer 5 in the void forming step S140 described later, the thickness of the metal layer 3 is preferably 0.5 nm or more, for example.

(S140: void forming step)
After the metal layer 3 is formed, a predetermined heat treatment is performed to form voids in the first base layer 2.

Specifically, the above-mentioned base substrate 1 is put into an electric furnace, and the base substrate 1 is placed on a susceptor having a predetermined heater. After the base substrate 1 is placed on the susceptor, the base substrate 1 is heated by a heater and heat-treated in an atmosphere containing a predetermined gas.

At this time, for example, the heat treatment is performed in an atmosphere containing at least one of nitrogen (N ₂ ) gas and nitrogen-containing gas. Examples of the nitrogen-containing gas include at least one of NH ₃ gas and hydrazine (N ₂ H ₄ ) gas. As a result, the metal layer 3 can be nitrided while being aggregated to form a mesh-like metal nitride layer 5 (also referred to as a nanonet of the metal nitride layer 5) having high-density fine holes (through holes) on the surface. it can.

Further, at this time, for example, the heat treatment is performed in an atmosphere containing at least one of hydrogen (H ₂ ) gas and hydrogen-containing gas. Examples of the hydrogen-containing gas include at least one of the above-mentioned NH ₃ gas and N ₂ H ₄ gas. As a result, a part of the first base layer 2 can be etched through the mesh of the metal nitride layer 5 to form high-density voids in the first base layer 2.

At this time, the step of forming the nanonet of the metal nitride layer 5 and the step of forming voids in the first base layer 2 may be performed at the same time, or may be performed separately in different atmospheres. Good.

Further, at this time, the heat treatment conditions are adjusted so that a predetermined void ratio of the first base layer 2 can be obtained. Specifically, the partial pressure ratio of the hydride gas in the atmosphere is, for example, 10% or more and 95% or less, preferably 50% or less. The heat treatment temperature is, for example, 1,000 ° C. or higher and 1,100 ° C. or lower. The heat treatment time is, for example, 1 minute or more and 100 minutes or less.

From the above void forming step S140, as shown in FIG. 3D, the void-containing first base layer 4 is formed.

(S150: Second base layer forming step)
After the void-containing first base layer 4 is formed, as shown in FIG. 3 (e), a second base layer (second crystal) composed of a single crystal of a group III nitride semiconductor is formed above the void-containing first base layer 4. Layer) 6 is epitaxially grown.

Specifically, for example, the base substrate 1 is carried into a predetermined vapor phase growth apparatus. Next, the group III raw material gas and the nitrogen raw material gas are supplied to the base substrate 1 heated to a predetermined growth temperature by the hydride vapor phase growth (HVPE) method. For example, by supplying gallium chloride (GaCl) gas and NH ₃ gas, the GaN layer as the second base layer 6 is epitaxially grown on the void-containing first base layer 4 and the metal nitride layer 5. When the GaN layer as the second base layer 6 is grown, for example, at least one of dichlorosilane (SiH ₂ Cl ₂ ) gas and tetrachlorogerman (GeCl ₄ ) gas as the n-type dopant gas is supplied. , N-type impurities may be doped in the GaN layer.

In the early stage of growth of the second base layer 6, initial nuclei of island-shaped crystals are generated. At this time, the frequency of the island-shaped crystals of the second base layer 6 depends on the degree of supersaturation when growing on the nanonet of the metal nitride layer 5 and the variation in the opening width of the nanonet. As the second base layer 6 is grown, the initial nuclei of the island-shaped crystals grow laterally. After that, when the distance from the adjacent early nuclei is approached, it is energetically stable that the surfaces of the early nuclei are bound to one rather than the two surfaces of the early nuclei are present. Therefore, adjacent early nuclei are forcibly attracted (meeted). The main surface 6s of the second base layer 6 is formed by associating the initial nuclei with each other over the entire second base layer 6.

At this time, for example, the main surface 6s of the second base layer 6 is mirrored. As described above, the "mirror surface" here means a surface in which the difference in surface irregularities is equal to or less than the wavelength of visible light, and the main surface 6s of the second base layer 6 is other than the c surface. There may be hillocks with exposed facets. Specifically, the root mean square roughness RMS of the main surface 6s of the second base layer 6 is set to, for example, less than 10 nm, preferably less than 1 nm. Details will be described later in (4), but by mirroring the main surface 6s of the second base layer 6, the growth form of the first layer 30 described later is changed to an island shape generated in the early stage of growth of the second base layer 6. It can be changed from the growth form of the crystal. As a result, the average distance between the closest apex portions of the first layer 30 described later can be controlled based on the first growth condition in the three-dimensional growth step S200, and the distance between the closest apex portions can be increased.

At this time, since the crystal plane having a low index closest to the main surface 1s of the base substrate 1 is set as the c-plane, the crystal plane having a low index closest to the mirrored main surface 6s of the second base layer 6 is also c. It becomes a face.

At this time, the growth conditions of the second base layer 6 are adjusted so that the initial nuclei of the crystals that grow in an island shape are generated at a predetermined frequency. Specifically, the growth temperature of the second base layer 6 is set to, for example, 1,000 ° C. or higher and 1,100 ° C. or lower. Further, the ratio of the partial pressure of the flow rate of the NH ₃ gas as the nitrogen raw material gas to the partial pressure of the GaCl gas as the group III raw material gas during the growth of the second base layer 6 (hereinafter, also referred to as “V / III ratio”). For example, 1 or more and 50 or less.

At this time, the thickness of the second base layer 6 is set to, for example, 100 μm or more and 1.5 mm or less, preferably 200 μm or more and 500 μm or less. If the thickness of the second base layer 6 is less than 100 μm, it becomes difficult to mirror the main surface 6s of the second base layer 6. On the other hand, by setting the thickness of the second base layer 6 to 100 μm or more, the main surface 6s of the second base layer 6 can be easily mirrored. As a result, the growth form of the first layer 30 is surely changed from the growth form of the island-shaped crystals generated in the initial stage of growth of the second base layer 6, and the first layer grows three-dimensionally in the three-dimensional growth step S200 described later. The distance between the nearest apexes of 30 can be easily increased. Further, by setting the thickness of the second base layer 6 to 200 μm or more, the main surface 6s of the second base layer 6 can be stably mirrored. On the other hand, if the thickness of the second base layer 6 is more than 1.5 mm, cracks may occur in the second base layer 6. On the other hand, by setting the thickness of the second base layer 6 to 1.5 mm or less, the occurrence of cracks in the second base layer 6 can be suppressed. Further, by setting the thickness of the second base layer 6 to 500 μm or less, the occurrence of cracks in the second base layer 6 can be stably suppressed.

At this time, the second base layer 6 grows from the void-containing first base layer 4 onto the void-containing first base layer 4 and the metal nitride layer 5 through the holes in the metal nitride layer 5. A part of the voids in the void-containing first base layer 4 is embedded by the second base layer 6, but the other part of the voids in the void-containing first base layer 4 remains. A flat void is formed between the second base layer 6 and the metal nitride layer 5 due to the voids remaining in the void-containing first base layer 4. This void causes peeling of the second base layer 6 in the peeling step S380 described later.

Further, at this time, tensile stress is introduced into the second base layer 6 by attracting the initial nuclei generated in the growth process to each other. Therefore, due to the tensile stress generated in the second base layer 6, the internal stress acts so that the c-plane of the second base layer 6 is recessed. Further, the dislocation density on the main surface 6s side of the second base layer 6 is low, while the dislocation density on the base substrate 1 side of the second base layer 6 is high. Therefore, even if the dislocation density difference in the thickness direction of the second base layer 6 is caused, the internal stress acts so that the c-plane of the second base layer 6 is recessed. Therefore, the c-plane of the second base layer 6 is curved in a concave spherical shape with respect to the main surface 6s. The term "spherical" as used herein means a curved surface that is approximated by a spherical surface. Further, the "spherical approximation" referred to here means that the spherical surface or the elliptical spherical surface is approximated within a predetermined error. Since the c-plane is curved as described above, the off-angle formed by the c-axis with respect to the normal of the center of the main surface 6s of the second base layer 6 has a predetermined distribution.

The base structure 10 is obtained by the above base structure manufacturing step S100.

(S200: 3D growth step (1st layer growth step))
Then, as shown in FIGS. 4 (b), 4 (c), and 5, a single crystal of a group III nitride semiconductor having a top surface 30u with an exposed c-plane 30c is mainly used for the second base layer 6. Epitaxially grow directly on the surface 6s. As a result, the first layer (three-dimensional growth layer) 30 is grown.

At this time, a plurality of recesses 30p formed by being surrounded by the inclined interface 30i other than the c-plane are formed on the top surface 30u of the single crystal, and the inclined interface 30i is gradually formed toward the upper side of the second base layer 6. And gradually reduce the c-plane 30c. As a result, the c-plane 30c disappears from the top surface 30u. As a result, the first layer 30 whose surface is composed of only the inclined interface 30i is grown.

That is, in the three-dimensional growth step S200, the first layer 30 is three-dimensionally grown so as to intentionally roughen the main surface 6s of the mirrored second base layer 6. Even if the first layer 30 forms such a growth form, it is grown as a single crystal as described above. In this respect, the first layer 30 is different from the so-called low temperature growth buffer layer formed as an amorphous or polycrystal on the dissimilar substrate before epitaxially growing the group III nitride semiconductor on the dissimilar substrate such as sapphire. is there.

In the present embodiment, as the first layer 30, for example, a layer made of the same group III nitride semiconductor as the group III nitride semiconductor constituting the base substrate 1 is epitaxially grown. Specifically, for example, by HVPE, the underlying substrate 1 is heated, by supplying the GaCl gas and NH ₃ gas to the underlying substrate 1, which is the heat, epitaxially growing a GaN layer as the first layer 30 ..

Here, in the three-dimensional growth step S200, in order to express the above-mentioned growth process, for example, the first layer 30 is grown under predetermined first growth conditions.

First, the reference growth conditions in which the inclined interface 30i and the c-plane 30c do not expand or contract will be described with reference to FIG. 9A. FIG. 9A is a schematic cross-sectional view showing a growth process under reference growth conditions in which the inclined interface and the c-plane are neither expanded nor contracted.

In FIG. 9A, the thick solid line shows the surface of the first layer 30 for each unit time. The inclined interface 30i shown in FIG. 9A is the inclined interface most inclined with respect to the c-plane 30c. Further, in FIG. 9 (a), the growth rate of the c-plane 30c of the first layer 30 and _{G c0,} the growth rate of the graded interface 30i of the first layer 30 and _{G i,} in the first layer 30 Let α be the angle formed by the c-plane 30c and the inclined interface 30i. Further, in FIG. 9A, it is assumed that the first layer 30 grows while maintaining the angle α formed by the c-plane 30c and the inclined interface 30i. It is assumed that the off angle of the c-plane 30c of the first layer 30 is negligible as compared with the angle α formed by the c-plane 30c and the inclined interface 30i.

As shown in FIG. 9A, when each of the inclined interface 30i and the c-plane 30c does not expand or contract, the locus of the intersection of the inclined interface 30i and the c-plane 30c is perpendicular to the c-plane 30c. .. From this, the reference growth condition in which each of the inclined interface 30i and the c-plane 30c does not expand or contract satisfies the following formula (a).
_{G c0 = G i / cosα ···} (a)

Next, with reference to FIG. 9B, the first growth condition in which the inclined interface 30i expands and the c-plane 30c shrinks will be described. FIG. 9B is a schematic cross-sectional view showing a growth process under the first growth condition in which the inclined interface expands and the c-plane shrinks.

In FIG. 9B, as in FIG. 9A, the thick solid line indicates the surface of the first layer 30 for each unit time. Further, the inclined interface 30i shown in FIG. 9B is also the inclined interface most inclined with respect to the c-plane 30c. Further, in FIG. 9B, the growth rate of the c-plane 30c of the first layer 30 is set to G _c1, and the progress rate of the locus of the intersection of the inclined interface 30i and the c-plane 30c of the first layer 30 is set. and R _1. Further, the narrower angle between the locus of the intersection of the inclined interface 30i and the c-plane 30c and the c-plane 30c is defined as α _R1 . 'When the, alpha' an angle between R ₁ direction and _{G i} direction alpha is a = α + 90-α _R1. It is assumed that the off angle of the c-plane 30c of the first layer 30 is negligible as compared with the angle α formed by the c-plane 30c and the inclined interface 30i.

As shown in FIG. 9 (b), the traveling rate _{R 1} of the locus of the intersection between the inclined surface 30i and the c-plane 30c is represented by the following formula (b).
_{R 1 = G i / cosα '} ··· (b)

The growth rate G _c1 of the c-plane 30c of the first layer 30 is represented by the following formula (c).
G _c1 = R ₁ sinα _R1 ... (c)

By substituting equation (b) in formula _{(c), G c1,} using the _{G i,} is expressed by the following formula (d).
_{G c1 = G i sinα R1 /} cos (α + 90-α R1) ··· (d)

In order for the inclined interface 30i to expand and the c-plane 30c to shrink, it is preferable that α _R1 <90 °. Therefore, it is preferable that the first growth condition in which the inclined interface 30i expands and the c-plane 30c shrinks satisfies the following equation (1) according to the equation (d) and α _R1 <90 °.
_{G c1> G i / cosα ···} (1)
However, as described above, _{G i} is the growth rate of the inclined surface 30i of the most inclined relative to the c plane 30c, alpha is an inclined surface 30i of the most inclined relative to the c plane 30c, and the c-plane 30c The angle between the two.

_{Alternatively,} it can be considered that G _c1 under the first growth condition is preferably larger than G _c0 under the reference growth condition. From this as well, the equation (1) can be derived by substituting the equation (a) for G _c1 > G _c0 .

Since the growth condition for expanding the most inclined inclined interface 30i with respect to the c-plane 30c is the strictest condition, if the first growth condition satisfies the equation (1), the other inclined interface 30i is also expanded. Is possible.

Specifically, for example, when the inclined interface 30i most inclined with respect to the c surface 30c is the {10-11} surface, α = 61.95 °. Therefore, it is preferable that the first growth condition satisfies, for example, the following formula (1').
G _c1 > 2.13G _i ... (1')

Alternatively, as will be described later, for example, when the inclined interface 30i is a {11-2m} surface with m ≧ 3, the inclined interface 30i most inclined with respect to the c surface 30c is the {11-23} surface. Therefore, α = 47.3 °. Therefore, it is preferable that the first growth condition satisfies, for example, the following formula (1 ″).
G _c1 > 1.47G _i ... (1 ")

As the first growth condition of the present embodiment, for example, the growth temperature in the three-dimensional growth step S200 is made lower than the growth temperature in the flattening step S300 described later. Specifically, the growth temperature in the three-dimensional growth step S200 is, for example, 980 ° C. or higher and 1,020 ° C. or lower, preferably 1,000 ° C. or higher and 1,020 ° C. or lower.

Further, as the first growth condition of the present embodiment, for example, the V / III ratio in the three-dimensional growth step S200 may be larger than the V / III ratio in the flattening step S300 described later. Specifically, the V / III ratio in the three-dimensional growth step S200 is, for example, 2 or more and 20 or less, preferably 2 or more and 15 or less.

Actually, as the first growth condition, at least one of the growth temperature and the V / III ratio is adjusted within the above range so as to satisfy the formula (1).

The other conditions of the first growth condition of the present embodiment are as follows, for example.
Growth pressure: 90-105 kPa, preferably 90-95 kPa
Partial pressure of GaCl gas: 1.5 to 15 kPa
Flow rate of N ₂ gas / Flow rate of H ₂ gas: 0 to 1

Here, the three-dimensional growth step S200 of the present embodiment is classified into two steps based on, for example, the growing form of the first layer 30. Specifically, the three-dimensional growth step S200 of the present embodiment includes, for example, an inclined interface expanding step S220 and an inclined interface maintaining step S240. By these steps, the first layer 30 has, for example, an inclined interface expanding layer 32 and an inclined interface maintaining layer 34.

(S220: Inclined interface expansion step)
First, as shown in FIGS. 4 (b), 4 (c) and 5, the inclined interface expansion layer 32 of the first layer 30 made of a single crystal of a group III nitride semiconductor is subjected to the above-mentioned first growth condition. Then, it is epitaxially grown on the second base layer 6.

In the initial stage in which the inclined interface expanding layer 32 grows, the inclined interface expanding layer 32 grows in the normal direction (direction along the c-axis) of the main surface 1s of the base substrate 1 with the c-plane 30c as the growth surface.

By gradually growing the inclined interface expansion layer 32 under the first growth condition, as shown in FIGS. 4 (c) and 5, the c-plane 30c of the inclined interface expansion layer 32 is exposed to the top surface 30u. , A plurality of recesses 30p composed of an inclined interface 30i other than the c-plane are formed. A plurality of recesses 30p formed by the inclined interface 30i other than the c-plane are randomly formed on the top surface 30u. As a result, the inclined interface expansion layer 32 in which the c-plane 30c and the inclined interface 30i other than the c-plane are mixed on the surface is formed.

The "inclined interface 30i" here means a growth interface inclined with respect to the c-plane 30c, and has a low exponential facet other than the c-plane, a high exponential facet other than the c-plane, or a surface index. Includes slopes that cannot be represented by. The facets other than the c-plane are, for example, {11-2m}, {1-10n} and the like. However, m and n are integers other than 0.

In the present embodiment, the inclined interface expansion layer 32 is grown on the mirrored second base layer 6 described above, and the first growth condition is adjusted so as to satisfy the formula (1), thereby forming the inclined interface 30i. For example, a {11-2m} plane where m ≧ 3 can be generated. As a result, the inclination angle of the {11-2m} plane with respect to the c plane 30c can be made gentle. Specifically, the inclination angle can be 47.3 ° or less.

By further growing the inclined interface expanding layer 32 under the first growth condition, as shown in FIG. 4C, the inclined interface expanding layer 32 is formed in the inclined interface expanding layer 32 other than the c-plane as it goes above the second base layer 6. The inclined interface 30i of the above is gradually expanded, and the c-plane 30c is gradually reduced. At this time, the inclination angle formed by the inclined interface 30i with respect to the main surface 1s of the underlying substrate 1 gradually decreases toward the upper side of the second underlying layer 6. As a result, most of the inclined interface 30i finally becomes the {11-2m} plane of m ≧ 3 described above.

When the inclined interface expanding layer 32 is further grown, the c-plane 30c of the inclined interface expanding layer 32 disappears from the top surface 30u, and the surface of the inclined interface expanding layer 32 is composed of only the inclined interface 30i. As a result, the inclined interface expansion layer 32 in which the cones are continuously connected is formed.

As shown in FIG. 4C, by forming a plurality of recesses 30p composed of the inclined interface 30i other than the c surface on the top surface 30u of the inclined interface expanding layer 32 and eliminating the c surface 30c in this way, as shown in FIG. In addition, a plurality of valleys 30v and a plurality of tops 30t are formed on the surface of the inclined interface expansion layer 32. Each of the plurality of valleys 30v is an inflection point that is convex downward on the surface of the inclined interface expansion layer 320, and is formed above the position where each of the inclined interfaces 30i other than the c-plane is generated. On the other hand, each of the plurality of tops 30t is an inflection point that is convex upward on the surface of the inclined interface expanding layer 320, and is a c-plane sandwiching a pair of inclined interfaces 30i that are enlarged in directions opposite to each other. 30c is formed at or above the (last) disappearance position. The valley portion 30v and the top portion 30t are formed alternately in the direction along the main surface 1s of the base substrate 1.

In the present embodiment, in the second base layer forming step S150, the second base layer 6 having the mirrored main surface 6s is grown on the main surface 1s of the base substrate 1, and then in the inclined interface expansion step S220. , An inclined interface 30i other than the c-plane is generated on the surface of the inclined interface expansion layer 32. As a result, the plurality of valley portions 30v are formed at positions separated upward from the main surface 6s of the second base layer 6.

Due to the growth process of the inclined interface expansion layer 32 as described above, the dislocations are bent and propagated as follows. Specifically, as shown in FIG. 4C, a plurality of dislocations extending in the direction along the c-axis in the second base layer 6 are formed from the second base layer 6 to the inclined interface expansion layer 32. Propagate in the direction along the c-axis of. In the region of the inclined interface expansion layer 32 that has grown with the c-plane 30c as the growth surface, dislocations propagate in the direction along the c-axis of the inclined interface expansion layer 32. However, when the dislocations propagated in the direction along the c-axis of the inclined interface expansion layer 32 are exposed to the inclined interface 30i, the dislocations are substantially perpendicular to the inclined interface 30i at the position where the inclined interface 30i is exposed. It bends in the direction and propagates. That is, the dislocations are bent and propagated in a direction inclined with respect to the c-axis. As a result, in the steps after the inclined interface expansion step S220, dislocations are locally collected above the substantially center between the pair of tops 30t. As a result, the dislocation density on the surface of the second layer 40, which will be described later, can be reduced.

At this time, in the present embodiment, when an arbitrary cross section perpendicular to the main surface 1s of the base substrate 1 is viewed, one of the plurality of valleys 30v is sandwiched between the plurality of tops 30t and the closest is the closest. The average distance L (also referred to as “the average distance between the most recent apex portions”) L in which the pair of top portions 30t are separated from each other in the direction along the main surface 1s of the base substrate 1 is set to, for example, more than 100 μm. When the average distance L between the most recent apex parts is 100 μm or less, as in the case where fine hexagonal cone-shaped crystal nuclei are formed on the second base layer 6 from the initial stage of the inclined interface expansion step S220, the inclined interface expansion In the steps after step S220, the distance at which dislocations are bent and propagated is shortened. For this reason, dislocations are not sufficiently collected above the substantially center between the pair of tops 30t of the inclined interface expansion layer 32. As a result, the dislocation density on the surface of the second layer 40, which will be described later, may not be sufficiently reduced. On the other hand, in the present embodiment, by setting the average distance L between the most recent apex parts to more than 100 μm, the distance at which dislocations bend and propagate in the steps after the inclined interface expansion step S220 is secured at least more than 50 μm. be able to. As a result, dislocations can be sufficiently collected above the substantially center between the pair of tops 30t in the inclined interface expansion layer 32. As a result, the dislocation density on the surface of the second layer 40, which will be described later, can be sufficiently reduced.

In the present embodiment, for example, in the first layer 30, it is preferable that there is no portion where the distance between the nearest apex portions is 100 μm or less. In other words, when an arbitrary cross section perpendicular to the main surface 1s of the base substrate 1 is viewed, it is preferable that the distance between the most recent apex portions is more than 100 μm over the entire surface of the first layer 30. As a result, the dislocation density can be reduced substantially uniformly over the entire surface of the second layer 40 described later.

On the other hand, in the present embodiment, the average distance L between the most recent apex portions is set to less than 800 μm. When the average distance L between the most recent apex portions is 800 μm or more, the height from the valley portion 30v to the apex portion 30t of the inclined interface expansion layer 32 becomes excessively high. Therefore, in the flattening step S300 described later, the thickness of the second layer 40 until it becomes a mirror surface becomes thicker. On the other hand, in the present embodiment, the height from the valley portion 30v to the top portion 30t of the inclined interface expansion layer 32 can be lowered by setting the average distance L between the most recent apex portions to less than 800 μm. As a result, in the flattening step S300 described later, the second layer 40 can be quickly mirrored.

Further, at this time, the inclined interface expansion layer 320 is provided with the first c-plane growth region 60 grown with the c-plane 30c as the growth plane and the inclined interface 30i other than the c-plane based on the difference in the growth plane in the growth process. An inclined interface growth region 70 (gray portion in the figure) grown as a growth surface is formed.

At this time, in the first c-plane growth region 60, a valley portion 60a is formed at a position where the inclined interface 30i is generated, and a mountain portion 60b is formed at a position where the c-plane 30c disappears. Further, in the first c-plane growth region 60, a pair of inclined portions 60i are formed on both sides of the mountain portion 60b as a locus of intersections between the c-plane 30c and the inclined interface 30i.

Further, at this time, when the first growth condition satisfies the equation (1), the angle β formed by the pair of inclined portions 60i is set to, for example, 70 ° or less.

Details of these areas will be described later.

(S240: Inclined interface maintenance step)
After the c-plane 30c disappears from the surface of the inclined interface expansion layer 32, as shown in FIG. 6A, the inclined interface 30i occupies more than the c-plane 30c on the surface, and the predetermined thickness is maintained. The growth of the first layer 30 is continued over the period. As a result, the inclined interface maintenance layer 34 having a surface in which the inclined interface 30i occupies more than the c-plane 30c is formed on the inclined interface expanding layer 32. By forming the inclined interface maintenance layer 34, the c-plane 30c can be reliably eliminated over the entire surface of the first layer 30.

At this time, the c-plane 30c may reappear on a part of the surface of the inclined interface maintenance layer 34, but the area ratio occupied by the inclined interface growth region 70 in the creepage cross section along the main surface 1s of the base substrate 1 is 80. It is preferable to mainly expose the inclined interface 30i on the surface of the inclined interface maintaining layer 34 so as to be% or more. The area ratio occupied by the inclined interface growth region 70 in the creepage cross section is better, and preferably 100%.

Further, at this time, the growth conditions in the inclined interface maintaining step S240 are maintained under the above-mentioned first growth conditions in the same manner as in the inclined interface expanding step S220. As a result, the inclined interface maintenance layer 34 can be grown with the inclined interface 30i as the growth surface.

Further, at this time, by growing the inclined interface maintaining layer 34 with the inclined interface 30i as the growth surface under the first growth condition, as described above, at the position where the inclined interface 30i is exposed in the inclined interface expanding layer 32. The dislocations that are bent and propagated in the direction inclined with respect to the c-axis continue to propagate in the same direction in the inclined interface maintenance layer 34.

By the above three-dimensional growth step S200, the first layer 30 having the inclined interface expanding layer 32 and the inclined interface maintaining layer 34 is formed.

In the three-dimensional growth step S200 of the present embodiment, the height from the main surface 6s of the second base layer 6 to the top 30t of the first layer 30 (the maximum height in the thickness direction of the first layer 30) is set, for example. It shall be more than 100 μm and less than 1.5 mm.

(S300: Flattening step (second layer growth step))
After the first layer 30 in which the c-plane 30c has disappeared is grown, a single crystal of a group III nitride semiconductor is further epitaxially grown on the first layer 30 as shown in FIGS. 6 (b) and 7 (a). Let me.

At this time, the inclined interface 40i is gradually reduced and the c-plane 40c is gradually expanded toward the upper side of the first layer 30. As a result, the inclined interface 30i formed on the surface of the first layer 30 disappears. As a result, the second layer (flattening layer) 40 having a mirrored surface is grown.

In the present embodiment, as the second layer 40, for example, a layer containing the same group III nitride semiconductor as the group III nitride semiconductor constituting the first layer 30 as a main component is epitaxially grown. In flattening step S300, by supplying to and from the bottom substrate 1 heated to a predetermined growth temperature, GaCl gas, _SiH 2 Cl ₂ gas as the NH ₃ gas and the n-type dopant gas, a second layer As 40, the silicon (Si) -doped GaN layer is epitaxially grown. As the n-type dopant gas, GeCl ₄ gas or the like may be supplied instead of SiH ₂ Cl ₂ gas.

Here, in the flattening step S300, in order to express the above-mentioned growth process, for example, the second layer 40 is grown under a predetermined second growth condition.

The second growth condition in which the inclined interface 40i is reduced and the c-plane 40c is expanded will be described with reference to FIG. FIG. 10 is a schematic cross-sectional view showing a growth process under a second growth condition in which the inclined interface is reduced and the c-plane is expanded. FIG. 10 shows a process in which the second layer 40 grows on the first layer 30 where the inclined interface 30i most inclined with respect to the c-plane 30c is exposed.

Also in FIG. 10, as in FIG. 9A, the thick solid line indicates the surface of the second layer 40 for each unit time. Further, in FIG. 10, the growth rate of the c-plane 40c of the second layer 40 and _{G c2,} the growth rate of the graded interface 40i of the second layer 40 and _{G i,} the inclination of the second layer 40 Let R _{2 be} the progress rate of the locus of the intersection of the interface 40i and the c-plane 40c. Further, the narrower angle between the locus of the intersection of the inclined interface 40i and the c-plane 40c and the c-plane 30c is defined as α _R2 . "When set to, alpha" the angle between R ₂ direction and _{G i} direction alpha = a α- (90-α _R2). Further, in FIG. 10, it is assumed that the second layer 40 grows while maintaining the angle α formed by the c-plane 30c in the first layer 30 and the inclined interface 30i. It is assumed that the off angle of the c-plane 40c of the second layer 40 is negligible as compared with the angle α formed by the c-plane 30c and the inclined interface 30i.

As shown in FIG. 10, the traveling rate _{R 2} of the locus of the intersection between the inclined surface 40i and the c-plane 40c is represented by the following formula (e).
_{R 2 = G i / cosα "} ··· (e)

The growth rate G _c2 of the c-plane 40c of the second layer 40 is represented by the following formula (f).
G _c2 = R ₂ sinα _R2 ... (f)

By substituting equation (e) in the formula _{(f), G c2,} using the _{G i,} is represented by the following formula (g).
_{G c2 = G i sinα R2 /} cos (α + α R2 -90) ··· (g)

In order for the inclined interface 40i to shrink and the c-plane 40c to expand, it is preferable that α _R2 <90 °. Therefore, it is preferable that the second growth condition in which the inclined interface 40i is reduced and the c-plane 40c is expanded satisfies the following formula (2) according to the formula (g) and α _R2 <90 °.
G _c2 <G _i / cos α ・ ・ ・ (2)
However, as described above, _{G i} is the growth rate of the inclined surface 40i of the most inclined relative to the c plane 40c, alpha is an inclined surface 40i of the most inclined relative to the c plane 40c, and the c-plane 40c The angle between the two.

Alternatively, when the growth rate of the c-plane 30c of the second layer 40 under the reference growth condition is G _c0 , G _c2 under the second growth condition is smaller than G _c0 under the reference growth condition. Can also be considered preferable. From this as well, the equation (2) can be derived by substituting the equation (a) for G _c2 <G _c0 .

Since the growth condition for reducing the most inclined inclined interface 40i with respect to the c-plane 40c is the strictest condition, if the second growth condition satisfies the equation (2), the other inclined interface 40i is also reduced. Is possible.

Specifically, when the inclined interface 40i most inclined with respect to the c-plane 40c is the {10-11} plane, the second growth condition preferably satisfies the following formula (2').
G _c2 <2.13G _i ... (2')

Alternatively, for example, when the inclined interface 30i is a {11-2m} plane with m ≧ 3, the most inclined inclined interface 30i with respect to the c-plane 30c is the {11-23} plane, so that the second growth occurs. The conditions preferably satisfy, for example, the following equation (2 ").
G _c2 <1.47G _i ... (2 ")

As the second growth condition of the present embodiment, the growth temperature in the flattening step S300 is set higher than, for example, the growth temperature in the three-dimensional growth step S200. Specifically, the growth temperature in the flattening step S300 is, for example, 990 ° C. or higher and 1,120 ° C. or lower, preferably 1,020 ° C. or higher and 1,100 ° C. or lower.

Further, as the second growth condition of the present embodiment, the V / III ratio in the flattening step S300 may be adjusted. For example, the V / III ratio in the flattening step S300 may be smaller than the V / III ratio in the three-dimensional growth step S200. Specifically, the V / III ratio in the flattening step S300 is, for example, 1 or more and 10 or less, preferably 1 or more and 5 or less.

Actually, as the second growth condition, at least one of the growth temperature and the V / III ratio is adjusted within the above range so as to satisfy the formula (2).

The other conditions of the second growth condition of the present embodiment are as follows, for example.
Growth pressure: 90-105 kPa, preferably 90-95 kPa
Partial pressure of GaCl gas: 1.5 to 15 kPa
Flow rate of N ₂ gas / Flow rate of H ₂ gas: 1 to 20

Here, the flattening step S300 of the present embodiment is classified into two steps based on, for example, the growing form of the second layer 40. Specifically, the flattening step S300 of the present embodiment includes, for example, a c-plane expanding step S320 and a main growth step S340. By these steps, the second layer 40 has, for example, a c-plane expansion layer 42 and a main growth layer 44.

(S320: c-plane expansion process)
As shown in FIG. 6B, the c-plane enlarged layer 42 of the second layer 40 made of a single crystal of a group III nitride semiconductor is epitaxially grown on the first layer 30 under the above-mentioned second growth conditions.

At this time, the inclined interface 40i other than the c-plane is reduced while expanding the c-plane 40c toward the upper side of the first layer 30.

Specifically, due to the growth under the second growth condition, the c-plane expansion layer 42 is directed from the inclined interface 30i of the inclined interface maintenance layer 34 along the direction perpendicular to the c-axis with the inclined interface 40i as the growth surface. It grows in the creepage or lateral direction (ie, creeping or lateral). When the c-plane expansion layer 42 is grown in the lateral direction, the c-plane 40c of the c-plane expansion layer 42 begins to be exposed again above the top 30t of the inclined interface maintenance layer 34. As a result, the c-plane expansion layer 42 in which the c-plane 40c and the inclined interface 40i other than the c-plane are mixed on the surface is formed.

When the c-plane expansion layer 42 is further grown in the lateral direction, the c-plane 40c gradually expands and the inclined interface 40i of the c-plane expansion layer 42 gradually shrinks. As a result, the recess 30p formed by the plurality of inclined interfaces 30i is gradually embedded in the surface of the first layer 30.

After that, when the c-plane expansion layer 42 is further grown, the inclined interface 40i of the c-plane expansion layer 42 disappears completely, and the recesses 30p composed of the plurality of inclined interfaces 30i are completely embedded on the surface of the first layer 30. Is done. As a result, the surface of the c-plane expansion layer 42 becomes a mirror surface (flat surface) composed of only the c-plane 40c.

At this time, the dislocation density can be reduced by locally collecting dislocations in the growth process of the first layer 30 and the c-plane expansion layer 42. Specifically, the dislocations that are bent and propagated in the direction inclined with respect to the c-axis in the first layer 30 continue to propagate in the same direction in the c-plane expansion layer 42. As a result, dislocations are locally collected at the meeting portion of the adjacent inclined interface 40i above the center of the c-plane enlarged layer 42 between the pair of tops 30t. Of the plurality of dislocations collected at the meeting portion of the adjacent inclined interface 40i in the c-plane expansion layer 42, the dislocations having Burgers vectors opposite to each other disappear at the time of association. Further, a part of the plurality of dislocations collected at the meeting portion of the adjacent inclined interface 40i may form a loop and propagate in the direction along the c-axis (that is, the surface side of the c-plane expansion layer 42). It is suppressed. The other portion of the plurality of dislocations collected at the meeting portion of the adjacent inclined interface 40i in the c-plane enlarged layer 42 is propagated in a direction along the c-axis from a direction inclined with respect to the c-axis. It is changed again and propagates to the surface side of the second layer 40. By eliminating some of the plurality of dislocations and suppressing the propagation of some of the plurality of dislocations to the surface side of the c-plane expansion layer 42 in this way, the dislocation density on the surface of the second layer 40 Can be reduced. Further, by locally collecting the dislocations, a low dislocation density region can be formed above the portion of the second layer 40 in which the dislocations propagate in the direction inclined with respect to the c-axis.

Further, at this time, in the c-plane expansion layer 42, the c-plane 40c gradually expands, so that the second c-plane growth region 80, which will be described later and has grown with the c-plane 40c as the growth plane, goes upward in the thickness direction. Therefore, it is formed while gradually expanding.

On the other hand, in the c-plane expansion layer 42, the inclined interface 40i gradually shrinks, so that the inclined interface growth region 70 gradually shrinks toward the upper side in the thickness direction and ends at a predetermined position in the thickness direction. .. Due to the growth process of the c-plane expansion layer 42, a valley portion 70a of the inclined interface growth region 70 is formed at a position where the c-plane 40c is generated again in a cross-sectional view. Further, in the process of gradually embedding the recess formed by the inclined interface 40i, a mountain portion 70b of the inclined interface growth region 70 is formed at a position where the inclined interface 40i disappears in a cross-sectional view.

In the c-plane expansion step S320, the surface of the c-plane expansion layer 42 is a mirror surface composed of only the c-plane 40c, so that the height of the c-plane expansion layer 42 in the thickness direction (maximum height in the thickness direction) is For example, the height of the inclined interface maintenance layer 34 is equal to or higher than the height from the valley portion 30v to the top portion 30t.

(S340: Main growth step (c-plane growth step))
When the inclined interface 40i disappears in the c-plane expansion layer 42 and the surface is mirror-finished, as shown in FIG. 7A, the c-plane 40c is set to a predetermined thickness on the c-plane expansion layer 42 as a growth surface. The main growth layer 44 is formed over the entire surface. As a result, the main growth layer 44 having only the c-plane 40c on the surface without having the inclined interface 40i is formed.

At this time, the growth conditions in the main growth step S340 are maintained under the above-mentioned second growth conditions in the same manner as in the c-plane expansion step S320. As a result, the main growth layer 44 can be step-flow-grown with the c-plane 40c as the growth plane.

Further, at this time, by growing the main growth layer 44 with only the c-plane 40c as the growth plane without exposing the inclined interface 40i, the entire main growth layer 44 becomes the second c-plane growth region 80 described later. Become.

In the main growth step S340, the thickness of the main growth layer 44 is set to, for example, 300 μm or more and 10 mm or less. By setting the thickness of the main growth layer 44 to 300 μm or more, at least one or more substrates 50 can be sliced from the main growth layer 44 in the slicing step S400 described later. On the other hand, by setting the thickness of the main growth layer 44 to 10 mm, the final thickness is set to 650 μm, and when slicing the substrate 50 having a thickness of 700 μm from the main growth layer 44, even if about 200 μm of carfloss is taken into consideration. , At least 10 substrates 50 can be obtained.

As described above, the second layer 40 having the c-plane expansion layer 42 and the main growth layer 44 is formed.

(S380: Peeling step)
After the growth of the second layer 40 is completed, as shown in FIG. 7B, the laminated structure 90 having the second base layer 6, the first layer 30, and the second layer 40 is peeled off from the base substrate 1. ..

Specifically, in the process of cooling the inside of the chamber of the vapor phase growth apparatus, stress is generated between the above-mentioned laminated structure 90 and the base substrate 1 due to the difference in linear expansion coefficient. For example, since the base substrate 1 made of sapphire has a coefficient of linear expansion larger than that of the laminated structure 90 mainly made of GaN, stress is generated to shrink the base substrate 1 with respect to the laminated structure 90.

As a result, the above-mentioned laminated structure 90 is naturally peeled from the base substrate 1 due to the flat voids formed between the metal nitride layer 5 and the second base layer 6. As a result, the laminated structure 90 can be peeled off from the base substrate 1 without causing cracks in the laminated structure 90.

By the above steps, the laminated structure 90 of this embodiment is obtained.

The above steps from the second base layer forming step S150 to the flattening step S300 are continuously performed in the same vapor phase growth apparatus without exposing the base substrate 1 to the atmosphere. As a result, at the interface between the second base layer 6 and the first layer 30 and the interface between the first layer 30 and the second layer 40, an unintended high oxygen concentration region (more than the inclined interface growth region 70). It is possible to suppress the formation of a region having an excessively high oxygen concentration).

(S400: Slicing process)
Next, as shown in FIG. 8, for example, the main growth layer 44 is sliced by a wire saw along a cut surface substantially parallel to the surface of the main growth layer 44. As a result, at least one nitride semiconductor substrate 50 (also referred to as substrate 50) as an asslice substrate is formed. At this time, the thickness of the substrate 50 is set to, for example, 300 μm or more and 700 μm or less.

At this time, when the radius of curvature of the c-plane 50c of the substrate 50 is such that the second base layer is grown to the same thickness as the second layer and the second base layer is sliced without performing the three-dimensional growth step and the flattening step. It can be made larger than the radius of curvature of the c-plane of the nitride semiconductor substrate (that is, the nitride semiconductor substrate obtained by the conventional VAS method). As a result, the variation in the off-angle θ of the c-axis 50ca with respect to the normal of the main surface 50s of the substrate 50 can be made smaller than the variation in the c-axis off-angle of the nitride semiconductor substrate obtained by the conventional VAS method.

(S500: Polishing process)
Next, both sides of the substrate 50 are polished by a polishing device. At this time, the thickness of the final substrate 50 is set to, for example, 250 μm or more and 650 μm or less.

The substrate 50 according to the present embodiment is manufactured by the above steps S100 to S500.

(Semiconductor laminate manufacturing process and semiconductor device manufacturing process)
After the substrate 50 is manufactured, for example, a semiconductor functional layer made of a group III nitride semiconductor is epitaxially grown on the substrate 50 to produce a semiconductor laminate. After producing the semiconductor laminate, electrodes and the like are formed using the semiconductor laminate, the semiconductor laminate is diced, and a chip having a predetermined size is cut out. As a result, a semiconductor device is manufactured.

(2) Laminated Structure Next, the laminated structure 90 according to the present embodiment will be described with reference to FIG. 7B.

The laminated structure 90 of the present embodiment has, for example, a second base layer 6, a first layer 30, and a second layer 40. The second base layer 6 can be simply rephrased as a "base layer".

The second base layer 6 is made of, for example, a single crystal of a group III nitride. The second base layer 6 has, for example, a mirrored main surface 6s (trace). The crystal plane with the lowest index closest to the main plane 6s of the second base layer is, for example, the c plane.

The first layer 30 grows on, for example, the second base layer 6.

The first layer 30 is formed, for example, by forming a plurality of recesses 30p composed of inclined interfaces 30i other than the c-plane on the top surface 30u of a single crystal of a group III nitride semiconductor and eliminating the c-plane 30c. It has a plurality of valleys 30v and a plurality of tops 30t to be formed. When looking at an arbitrary cross section perpendicular to the main surface 6s of the second base layer 6, the average distance between the nearest apex portions is, for example, more than 100 μm.

Further, the first layer 30 includes, for example, the first c-plane growth region (first low oxygen concentration region) 60 and the inclined interface growth region (high oxygen concentration region) 70 based on the difference in the growth plane in the growth process. ,have.

The first c-plane growth region 60 is a region that has grown with the c-plane 30c as the growth plane. The first c-plane growth region 60 has, for example, a plurality of valley portions 60a and a plurality of peak portions 60b in a cross-sectional view. Each of the valley portion 60a and the peak portion 60b referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and the first layer. It does not mean a part of the outermost surface shape that occurs during the growth of 30. Each of the plurality of valleys 60a is a downwardly convex inflection point in the first c-plane growth region 60 in a cross-sectional view, and is formed at a position where an inclined interface 30i is generated. At least one of the plurality of valley portions 60a is provided at a position separated upward from the main surface 6s of the second base layer 6. On the other hand, each of the plurality of mountain portions 60b is an inflection point that is convex upward in the first c-plane growth region 60 in a cross-sectional view, and has a pair of inclined interfaces 30i that are enlarged in directions opposite to each other. The c-plane 30c is formed at a position where it disappears (finally). The valley portions 60a and the mountain portions 60b are formed alternately in the direction along the main surface 6s of the second base layer 6.

The first c-plane growth region 60 has a pair of inclined portions 60i provided as a locus of an intersection between the c-plane 30c and the inclined interface 30i on both sides of one of the plurality of mountain portions 60b in a cross-sectional view. doing. The inclined portion 60i referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and is generated during the growth of the first layer 30. It does not mean the inclined interface 30i on the outermost surface.

In cross-sectional view, the angle β formed by the pair of inclined portions 60i is, for example, 70 ° or less, preferably 20 ° or more and 65 ° or less. It angle β of the pair of inclined portions 60i is 70 ° or less, in the first growth condition, on the growth rate G _i of the inclined surface 30i of the most inclined relative to the c plane 30c of the first layer 30, means that the ratio _G c1 / _{G i} of growth rate _{G c1} of c plane 30c of the first layer 30 was high. Thereby, the inclined interface 30i other than the c-plane can be easily generated. As a result, the dislocations can be easily bent at the position where the inclined interface 30i is exposed. Further, by setting the angle β formed by the pair of inclined portions 60i to 70 ° or less, a plurality of valley portions 30v and a plurality of top portions 30t can be easily generated above the second base layer 6. Further, by setting the angle β formed by the pair of inclined portions 60i to 65 ° or less, an inclined interface 30i other than the c-plane can be more easily generated, and a plurality of valley portions are formed above the second base layer 6. 30v and a plurality of tops 30t can be generated more easily. By setting the angle β formed by the pair of inclined portions 60i to 20 ° or more, it is possible to prevent the height from the valley portion 30v to the top portion 30t of the first layer 30 to increase, and the second layer 40 is mirrored. It is possible to prevent the thickness from becoming thicker.

On the other hand, the inclined interface growth region 70 is a region where the inclined interface 30i other than the c-plane is used as the growth surface. The lower surface of the inclined interface growth region 70 is formed, for example, following the shape of the first c-plane growth region 60. The inclined interface growth region 70 is continuously provided along the main surface 6s of the second base layer 6.

In the inclined interface growth region 70, oxygen is easily taken in as compared with the first c-plane growth region 60. Therefore, the oxygen concentration in the inclined interface growth region 70 is higher than the oxygen concentration in the first c-plane growth region 60. The oxygen taken into the inclined interface growth region 70 is, for example, oxygen unintentionally mixed in the vapor phase growth apparatus, oxygen released from a member (quartz member or the like) constituting the vapor phase growth apparatus, or the like. Is.

The oxygen concentration in the first c-plane growth region 60 is, for example, 5 × 10 ¹⁶ cm ^-3 or less, preferably 3 × 10 ¹⁶ cm ^-3 or less. On the other hand, the oxygen concentration in the inclined interface growth region 70 is, for example, 3 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less.

The second layer 40 has, for example, an inclined interface growth region 70 and a second c-plane growth region (second hypoxia concentration region) 80 based on the difference in the growth plane in the growth process.

The upper surface of the inclined interface growth region 70 in the second layer 40 has, for example, a plurality of valleys 70a and a plurality of peaks 70b in a cross-sectional view. Each of the valley portion 70a and the peak portion 70b referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and the second layer. It does not mean a part of the outermost surface shape that occurs during the growth of 40. As described above, the plurality of valleys 70a of the inclined interface growth region 70 are formed at positions where the c-plane 40c is generated again in the cross-sectional view. Further, the plurality of valleys 70a of the inclined interface growth region 70 are formed above the plurality of peaks 60b of the first c-plane growth region 60, respectively, in cross-sectional view. On the other hand, the plurality of mountain portions 70b of the inclined interface growth region 70 are formed at positions where the inclined interface 40i disappears in the cross-sectional view as described above. Further, each of the plurality of peaks 70b of the inclined interface growth region 70 is formed above the plurality of valleys 60a of the first c-plane growth region 60 in cross-sectional view.

Further, the surface of the second layer 40 that is substantially parallel to the main surface 6s of the second base layer 6 at the upper end of the inclined interface growth region 70 becomes the boundary surface 40b at the position where the inclined interface 40i disappears in the second layer 40. ..

The second c-plane growth region 80 is a region that has grown with the c-plane 40c as the growth plane. In the second c-plane growth region 80, the uptake of oxygen is suppressed as compared with the inclined interface growth region 70. Therefore, the oxygen concentration in the second c-plane growth region 80 is lower than the oxygen concentration in the inclined interface growth region 70. The oxygen concentration in the second c-plane growth region 80 is, for example, 5 × 10 ¹⁶ cm ^-3 or less, preferably 3 × 10 ¹⁶ cm ^-3 or less.

In the present embodiment, in the growth process of the first layer 30, dislocations are bent and propagated in a direction substantially perpendicular to the inclined interface 30i at a position where the inclined interface 30i other than the c-plane is exposed. Therefore, in the second layer 40, a part of the plurality of dislocations disappears, and a part of the plurality of dislocations is suppressed from propagating to the surface side of the c-plane expansion layer 42. As a result, the dislocation density on the surface of the second layer 40 is lower than the dislocation density on the main surface 6s of the second base layer 6.

In addition, in the present embodiment, the entire surface of the second layer 40 is composed of + c planes, and the first layer 30 and the second layer 40 do not include a polarity reversal zone (inversion domain), respectively. In this respect, the laminated structure 90 of the present embodiment is different from the laminated structure formed by the so-called DEEP (Dislocation Elimination by the Epitaxyal-growth with inverse-pyramidal Pits) method, that is, it is located at the center of the pit. It is different from the laminated structure in which the core contains a polarity reversal section.

(3) Nitride semiconductor substrate (nitride semiconductor self-supporting substrate, nitride crystal substrate)
Next, the nitride semiconductor substrate 50 according to the present embodiment will be described with reference to FIG. FIG. 11A is a schematic top view showing a nitride semiconductor substrate according to the present embodiment, and FIG. 11B is a schematic cross-sectional view taken along the m-axis of the nitride semiconductor substrate according to the present embodiment. (C) is a schematic cross-sectional view along the a-axis of the nitride semiconductor substrate according to the present embodiment.

In the present embodiment, the substrate 50 obtained by slicing the second layer 40 by the above-mentioned manufacturing method is, for example, a self-standing substrate made of a single crystal of a group III nitride semiconductor. In the present embodiment, the substrate 50 is, for example, a GaN free-standing substrate.

The diameter of the substrate 50 is, for example, 2 inches or more. The thickness of the substrate 50 is, for example, 300 μm or more and 1 mm or less.

The conductivity of the substrate 50 is not particularly limited, but when the substrate 50 is used to manufacture a semiconductor device as a vertical Schottky barrier diode (SBD), the substrate 50 is, for example, n-type. The n-type impurity in the substrate 50 is, for example, Si or germanium (Ge), and the n-type impurity concentration in the substrate 50 is, for example, 1.0 × 10 ¹⁸ cm ^-3 or more and 1.0 × 10 ²⁰ cm ^-3 or less. ..

The substrate 50 has, for example, a main surface 50s which is an epitaxial growth surface. In the present embodiment, the crystal plane having the lowest index closest to the main plane 50s is, for example, the c plane 50c.

The main surface 50s of the substrate 50 is mirrored, for example, and the root mean square roughness RMS of the main surface 50s of the substrate 50 is, for example, less than 1 nm.

Further, in the present embodiment, the impurity concentration in the substrate 50 obtained by the above-mentioned manufacturing method is lower than that of the substrate obtained by the flux method, the amonothermal method, or the like.

Specifically, the hydrogen concentration in the substrate 50 is, for example, less than 1 × 10 ¹⁷ cm ^-3 , preferably 5 × 10 ¹⁶ cm ^-3 or less.

Further, in the present embodiment, since the substrate 50 is formed by slicing the main growth layer 44 grown with the c-plane 40c as the growth surface, the inclined interface growth grown with the inclined interface 30i or the inclined interface 40i as the growth surface. Does not include region 70. That is, the entire substrate 50 is composed of a low oxygen concentration region.

Specifically, the oxygen concentration in the substrate 50 is, for example, 5 × 10 ¹⁶ cm ^-3 or less, preferably 3 × 10 ¹⁶ cm ^-3 or less.

(C-plane curvature and variation in off-angle)
As shown in FIGS. 11B and 11C, in the present embodiment, the c-plane 50c as the crystal plane having the lowest index closest to the main plane 50s of the substrate 50 is, for example, the production of the substrate 50 described above. Due to the method, it is curved in a concave spherical shape with respect to the main surface 50s.

In the present embodiment, the c-plane 50c of the substrate 50 has, for example, a curved surface that approximates a spherical surface in each of a cross section along the m-axis and a cross-section along the a-axis.

In the present embodiment, since the c-plane 50f of the substrate 50 is curved in a concave spherical shape as described above, at least a part of the c-axis 50ca is inclined with respect to the normal of the main surface 50s. .. The off-angle θ, which is the angle formed by the c-axis 50ca with respect to the normal of the main surface 50s, has a predetermined distribution within the main surface 50s.

Of the off-angle θ of the c-axis 50ca with respect to the normal of the main surface 50s, the directional component along the m-axis is defined as “θ _m ”, and the directional component along the a-axis is defined as “θ _a ”. It should be noted that θ ² = θ _m ² + θ _a ² .

In the present embodiment, since the c-plane 50c of the substrate 50 is curved in a concave spherical shape as described above, the off-angle m-axis component θ _m and the off-angle a-axis component θ _a are 1 of x, respectively. It can be approximately represented by a linear function and a linear function of y.

Specifically, for example, the X-ray locking curve of the (0002) plane is measured at each position on a straight line passing through the center within the main plane 50s, and the peak formed by the X-ray incident on the main plane 50s and the main plane 50s. When the angle ω is plotted against a position on a straight line, the peak angle ω can be approximated by a linear function of the position. The "peak angle ω" referred to here is an angle formed by an X-ray incident on the main surface 50s and the main surface 50s, and means an angle at which the diffraction intensity is maximized. The radius of curvature of the c-plane 50c can be obtained from the reciprocal of the slope of the linear function approximated as described above.

In the present embodiment, the radius of curvature of the c-plane 50c of the substrate 50 is larger than, for example, the radius of curvature of the c-plane of the nitride semiconductor substrate obtained by the conventional VAS method described above.

Specifically, when the peak angle ω is approximated by the linear function of the position in the X-ray locking curve measurement of the c-plane 50c, the radius of curvature of the c-plane 50c obtained by the reciprocal of the slope of the linear function is, for example. It is 10 m or more, preferably 15 m or more, more preferably 19 m or more, and further preferably 40 m or more.

In the present embodiment, the upper limit of the radius of curvature of the c-plane 50c of the substrate 50 is not particularly limited as it is larger. When the c-plane 50c of the substrate 50 is substantially flat, it may be considered that the radius of curvature of the c-plane 50c is infinite.

In the present embodiment, since the radius of curvature of the c-plane 50c of the substrate 50 is large, the variation of the off-angle θ of the c-axis 50ca with respect to the normal of the main surface 50s of the substrate 50 is made larger than that of the nitride semiconductor substrate of the conventional VAS method. It can be made smaller than the variation in the off angle of the c-axis.

Further, in the present embodiment, when the peak angle ω is approximated by the linear function of the position in the X-ray locking curve measurement of the c-plane 50c, the error of ω with respect to the linear function of the position is small. When the error of ω in the present embodiment is not eliminated in the substrate obtained from the crystal layer grown on the base substrate processed by the ELO method using a mask layer, or in the three-dimensional growth step. It can be made smaller than the substrate obtained from the second layer.

Specifically, the error of the measured peak angle ω with respect to the linear function approximated as described above is, for example, 0.05 ° or less, preferably 0.02 ° or less, more preferably 0.01 ° or less. Is. Since at least a part of the peak angle ω may match the linear function, the minimum value of the error is 0 °.

(Dark spot)
Next, a dark spot on the main surface 50s of the substrate 50 of the present embodiment will be described. The "dark spot" here means a point where the emission intensity observed in the observation image of the main surface 50s or the cathode luminescence image of the main surface 50s in a multiphoton excitation microscope is low, and only dislocations occur. It also contains non-luminescent centers due to foreign matter or point defects. The "multiphoton excitation microscope" may also be referred to as a two-photon excitation fluorescence microscope.

In the present embodiment, since the substrate 50 is manufactured by using the base structure 10 produced by the VAS method, there are few non-emission centers in the substrate 50 due to foreign matter or point defects. Therefore, 95% or more, preferably 99% or more of the dark spots when the main surface of the substrate 50 is observed with a multi-photon excitation microscope or the like are dislocations rather than non-emission centers due to foreign matter or point defects.

Further, in the present embodiment, the dislocation density on the surface of the second layer 40 is reduced by the above-mentioned manufacturing method as compared with the dislocation density in the nitride semiconductor substrate obtained by the conventional VAS method. As a result, dislocations are also reduced on the main surface 50s of the substrate 50 formed by slicing the second layer 40.

Further, in the present embodiment, the second layer 40 is sliced by performing the three-dimensional growth step S200 and the flattening step S300 using the base structure 10 in the unprocessed state by the above-mentioned manufacturing method. On the main surface 50s of the substrate 50 formed by the above, a region having a high dislocation density due to the concentration of dislocations is not formed, and a region having a low dislocation density is uniformly formed.

Specifically, in the present embodiment, when the main surface 50s of the substrate 50 is observed with a multiphoton excitation microscope in a field of view of 250 μm square and the dislocation density is obtained from the dark spot density, the dislocation density is 3 × 10 ⁶ cm ^−. There is no region exceeding ² and a region having a dislocation density of less than 1 × 10 ⁶ cm- ² exists in an amount of 80% or more, preferably 90% or more, more preferably 95% or more of the main surface 50s.

In other words, in the present embodiment, the dislocation density obtained by averaging the entire main surface 50s of the substrate 50 is, for example, less than 1 × 10 ⁶ cm- ² , preferably less than 5.5 × 10 ⁵ cm- ² . , More preferably 3 × 10 ⁵ cm- ² or less.

Further, the main surface 50s of the substrate 50 of the present embodiment includes, for example, a dislocation-free region of at least 50 μm square based on the average distance L between the closest apex portions in the above-mentioned three-dimensional growth step S200. Further, the main surface 50s of the substrate 50 of the present embodiment has, for example, 100 non-dislocation-free regions of 50 μm square that do not overlap at a density of 100 pieces / cm ² or more.

Next, the Burgers vector of dislocations in the substrate 50 of the present embodiment will be described.

In the present embodiment, since the dislocation density on the main surface 6s of the second base layer 6 used in the above-mentioned manufacturing method is low, when the first layer 30 and the second layer 40 are grown on the second base layer 6, the first layer 30 and the second layer 40 are grown. Multiple dislocations are less likely to combine (mix). This makes it possible to suppress the formation of dislocations having a large Burgers vector in the substrate 50 obtained from the second layer 40.

Specifically, in the substrate 50 of the present embodiment, for example, there are many dislocations in which the Burgers vector is any one of <11-20> / 3, <0001>, and <11-23> / 3. The "Burgers vector" here can be measured by, for example, a large-angle converged electron diffraction method (LACBED method) using a transmission electron microscope (TEM). A dislocation having a Burgers vector <11-20> / 3 is a blade dislocation, a dislocation having a Burgers vector <0001> is a spiral dislocation, and a dislocation having a Burgers vector <11-23> / 3. One dislocation is a mixed dislocation that is a mixture of edge dislocations and spiral dislocations.

In this embodiment, when 100 dislocations on the main surface 50s of the substrate 50 are randomly extracted, the Burgers vector is any one of <11-20> / 3, <0001>, and <11-23> / 3. The ratio of the number of dislocations is, for example, 50% or more, preferably 70% or more, and more preferably 90% or more. In addition, dislocations having a Burgers vector of 2 <11-20> / 3 or <11-20> may be present in at least a part of the main surface 50s of the substrate 50.

(About X-ray locking curve measurement with different slit width)
Here, the inventor performs the X-ray locking curve measurement with different slit widths on the incident side to obtain the mosaicity of the crystals constituting the substrate 50 of the present embodiment and the curvature (warp) of the c-plane 50c described above. And found that both can be evaluated at the same time.

First, the effect of crystal mosaicity on X-ray locking curve measurement will be described.

The "crystal mosaicity" here means a variation in crystal plane orientation. In a crystal, the more dislocations there are, the more randomly the crystal plane orientation tends to tilt, and the higher the crystal faceability tends to be. In particular, when a plurality of dislocations are linearly arranged to form lineage, the crystal plane orientations of adjacent subcrystal grains are displaced via the lineage, and the crystal faceability tends to increase. When the crystal mothity is high as described above, when the X-ray locking curve measurement is performed, the fluctuation (fluctuation, distribution width) of the diffraction angle of the crystal plane becomes large due to the mothity.

Next, the influence of the curvature of the c-plane 50c on the X-ray locking curve measurement will be described with reference to FIG. 12 (a). FIG. 12A is a schematic cross-sectional view showing the diffraction of X-rays with respect to the curved c-plane.

When the width of the slit on the incident side of the X-ray is a, the irradiation width (footprint) of the X-ray irradiated to the main surface of the substrate is b, and the Bragg angle of the crystal is θ _B , the main surface of the substrate The X-ray irradiation width b is calculated by the following formula (h).
b = a / sinθ _B ... (h)

As shown in FIG. 12A, when the c-plane of the substrate is curved, the radius of curvature of the c-plane is R, and the central angle formed by the curved c-plane within the range of the X-ray irradiation width b. When half is γ, the radius of curvature R of the c-plane is very large with respect to the X-ray irradiation width b. From this, the angle γ can be obtained by the following equation (i).
γ = sin ^-1 (b / 2R) ≒ b / 2R ... (i)

At this time, at the incident-side end (right end in the figure) of the region of the c-plane of the substrate on which X-rays are irradiated, the diffraction angle with respect to the main surface of the substrate is θ _B + γ = θ _B + b / 2R. Become.

On the other hand, at the end of the c-plane of the substrate on the light receiving side (left end in the figure) of the region irradiated with X-rays, the diffraction angle with respect to the main surface of the substrate is θ _B −γ = θ _B −b / 2R. It becomes.

Therefore, it is curved by the difference between the diffraction angle of the c-plane of the substrate with respect to the main surface of the substrate at the incident side end and the diffraction angle of the c-plane of the substrate with respect to the main surface of the substrate at the light receiving side end. The fluctuation of the diffraction angle of the X-ray with respect to the c-plane is b / R.

12 (b) and 12 (c) are diagrams showing fluctuations in the diffraction angle of the (0002) plane with respect to the radius of curvature of the c plane. The vertical axis of FIG. 12B is a logarithmic scale, and the vertical axis of FIG. 12C is a linear scale.

As shown in FIGS. 12B and 12C, when the width a of the slit on the incident side of the X-ray is increased, that is, the irradiation width b of the X-ray is increased, the irradiation width b of the X-ray is increased. , The fluctuation of the diffraction angle of the (0002) plane becomes large. Further, as the radius of curvature R of the c-plane becomes smaller, the fluctuation of the diffraction angle of the (0002) plane gradually increases. Further, the difference in the fluctuation of the diffraction angle of the (0002) plane when the X-ray irradiation width b is different becomes larger as the radius of curvature R of the c plane becomes smaller.

In fact, when the X-ray locking curve of a substrate having a low crystal mosaicity is measured, when the width a of the slit on the incident side is narrow, the component of the fluctuation of the diffraction angle of the (0002) plane due to the curvature of the c plane. Is small, and the component due to the mosaicity of the crystal is dominant. However, when the width a of the slit on the incident side is wide, both the component due to the mosaicity of the crystal and the component due to the curvature of the c-plane are superimposed on the fluctuation of the diffraction angle of the (0002) plane. Therefore, if the X-ray locking curve measurement is performed with different slit widths a on the incident side, it is possible to evaluate both the crystal mosaicity and the curvature (warp) of the c-plane at the same time.

Here, the features of the substrate 50 of the present embodiment when the X-ray locking curve is measured will be described.

In the following, the main surface 50s of the substrate 50 is irradiated with X-rays of Cu Kα1 via a two-crystal monochromator and a slit on the Ge (220) surface, and the X-ray locking curve of (0002) surface diffraction is measured. In this case, the half-value width of the (0002) plane diffraction when the width of the slit in the ω direction is 1 mm is "FWHMa", and the width of the (0002) plane diffraction when the width of the slit in the ω direction is 0.1 mm. The half width is defined as "FWHMb". The "ω direction" is the rotation direction (circumferential direction) when the substrate 50 is rotated about the axis passing through the center of the substrate 50 and parallel to the main surface of the substrate 50 in the X-ray locking curve measurement. Say that.

In the substrate 50 of the present embodiment, as described above, there are few dislocations and the crystal mosaicity is low over a wide range of the main surface 50s.

As a result, (0002) surface diffraction X-ray locking curve measurement is performed at a plurality of measurement points set at intervals of 5 mm in the main surface 50s of the substrate 50 of the present embodiment, with the width of the slit in the ω direction set to 0.1 mm. Then, for example, at 95% or more, preferably 100% of all measurement points, the half width FWHMb of (0002) plane diffraction is 80 arcsec or less, preferably 50 arcsec or less.

Further, in the substrate 50 of the present embodiment, the diffraction spectrum of the (0002) plane when the X-ray locking curve measurement is performed by widening the slit width on the incident side narrows the slit width on the incident side for X-ray locking. It tends to be less likely to be narrower than the diffraction spectrum of the (0002) plane when the curve measurement is performed.

As a result, in the substrate 50 of the present embodiment, the full width at half maximum of (0002) plane diffraction when the width of the slit in the ω direction is 1 mm is, for example, when the width of the slit in the ω direction is 0.1 mm. (0002) The half width of surface diffraction can be FWHMb or more.

Further, in the substrate 50 of the present embodiment, as described above, there are few dislocations and the crystal mosaicity is low over a wide range of the main surface 50s. Further, the curvature of the c-plane 50c of the substrate 50 is small, and the radius of curvature of the c-plane 50c is large. As a result, in the substrate 50 of the present embodiment, even if the slit width on the incident side is widened and the X-ray locking curve measurement is performed, the fluctuation of the diffraction angle of the (0002) plane is not so large, and the fluctuation of the diffraction angle on the incident side is not so large. Even if the X-ray locking curve measurement is performed with different slit widths, the difference in the fluctuation of the diffraction angle of the (0002) plane becomes small.

As a result, at a predetermined measurement point (for example, the center of the main surface) of the substrate 50 of the present embodiment, the half-value width of (0002) plane diffraction when the width of the slit in the ω direction is 1 mm, the ω direction of the slit. The difference FWHMa-FWHMb obtained by subtracting the full width at half maximum FWHMb of the (0002) plane diffraction when the width is 0.1 mm is, for example, 30% or less, preferably 22% or less of FWHMa.

Further, when (0002) X-ray locking curve measurement of surface diffraction is performed at a plurality of measurement points set at intervals of 5 mm in the main surface 50s of the substrate 50 of the present embodiment with different widths in the ω direction of the slits. In addition, for example, at 95% or more, preferably 100% of all measurement points, FWHMa-FWHMb is, for example, 30% or less, preferably 22% or less of FWHMa.

In the substrate 50 of the present embodiment, even if FWHMa <FWHMb, | FWHMa-FWHMb | is 30% or less.

For reference, in the above-mentioned conventional VAS nitride semiconductor substrate, the curvature of the c-plane 10c is relatively large and the radius of curvature of the c-plane 10c is small. Therefore, the difference FWHMa-FWHMb in the nitride semiconductor substrate obtained by the conventional VAS method is, for example, 50% or more of FWHMa.

(4) Effects obtained by the present embodiment According to the present embodiment, one or more of the following effects can be obtained.

(A) A stress canceling effect (stress relaxation) in which the tensile stress accumulated in the second base layer 6 of the base structure 10 is canceled by the first layer 30 by three-dimensionally growing the first layer 30 on the base structure 10. Effect) can be obtained.

As one of the reasons why the stress canceling effect of the first layer 30 can be obtained, for example, the following reasons can be considered.

As described above, in the three-dimensional growth step S200, the inclined interface growth region 70 is formed by three-dimensionally growing the first layer 30 with the inclined interface 30i other than the c-plane as the growth surface. In the inclined interface growth region 70, oxygen is easily taken in as compared with the first c-plane growth region 60. Therefore, the oxygen concentration in the inclined interface growth region 70 is higher than the oxygen concentration in the first c-plane growth region 60. That is, the inclined interface growth region 70 can be considered as a high oxygen concentration region.

By incorporating oxygen into the high oxygen concentration region in this way, the lattice constant of the high oxygen concentration region can be made larger than the lattice constant of other regions other than the high oxygen concentration region (Reference: Chris G. et al. Van de Walle, Physical Review B vol.68, 165209 (2003)). In the second base layer 6 or the first c-plane growth region 60 grown with the c-plane 30c as the growth plane of the first layer 30, the curvature of the c-plane of the second base layer 6 is directed toward the center of curvature of the c-plane. The stress that concentrates is applied. On the other hand, by relatively increasing the lattice constant in the high oxygen concentration region, it is possible to generate a stress in the high oxygen concentration region that spreads the c-plane 30c outward in the creepage direction. As a result, the stress concentrated toward the center of curvature of the c-plane 30c below the high oxygen concentration region and the stress of spreading the c-plane 30c of the high oxygen concentration region outward in the creepage direction can be offset.

By obtaining the stress canceling effect of the first layer 30 in this way, even if the second layer 40 is thickly grown with the tensile stress accumulated in the second base layer 6, the base of the second layer 400 It is possible to suppress the occurrence of a stress difference between the structure 10 side and the surface side. As a result, it is possible to prevent cracks and the like from being generated in the second layer 40.

(B) In the present embodiment, by obtaining the stress canceling effect of the first layer 30 described above, the radius of curvature of the c-plane 50c of the substrate 50 obtained from the second layer 40 can be obtained by the conventional VAS method. It can be larger than the radius of curvature of the semiconductor substrate. As a result, the variation in the off-angle θ of the c-axis 50ca with respect to the normal of the main surface 50s of the substrate 50 can be made smaller than the variation in the off-angle of the c-axis of the nitride semiconductor substrate obtained by the conventional VAS method. ..

(C) In the three-dimensional growth step S200, by creating an inclined interface 30i other than the c-plane on the surface of the single crystal constituting the first layer 30, the inclined interface 30i is exposed to the inclined interface 30i. The dislocations can be bent and propagated in a substantially vertical direction. This allows dislocations to be collected locally. By locally collecting dislocations, dislocations having Burgers vectors that are opposite to each other can be eliminated. Alternatively, the locally collected dislocations form a loop to prevent the dislocations from propagating to the surface side of the second layer 40. In this way, the dislocation density on the surface of the second layer 40 can be reduced. As a result, it is possible to obtain a substrate 50 having a reduced dislocation density as compared with the nitride semiconductor substrate obtained by the conventional VAS method.

(D) As described above, in the growth process of the second layer 40, some of the plurality of dislocations may be eliminated, or some of the plurality of dislocations may be suppressed from propagating to the surface side of the second layer 40. By doing so, the dislocation density can be reduced rapidly and faster than in the case where the crystal layer composed of a single crystal of a group III nitride semiconductor is grown with only the c-plane as the growth plane. As a result, the substrate 50 having a reduced dislocation density can be efficiently obtained, and its productivity can be improved.

(E) In the three-dimensional growth step S200, the c-plane 30c disappears from the top surface 30u of the first layer 30. As a result, a plurality of valley portions 30v and a plurality of top portions 30t can be formed on the surface of the first layer 30. As a result, the dislocations propagating from the second base layer 6 can be reliably bent at the position where the inclined interface 30i in the first layer 30 is exposed.

Here, consider the case where the c-plane remains in the three-dimensional growth step. In this case, in the portion where the c-plane remains, the dislocations propagated from the base substrate propagate substantially vertically upward without being bent and reach the surface of the second layer. Therefore, dislocations are not reduced and a high dislocation density region is formed above the portion where the c-plane remains.

On the other hand, according to the present embodiment, in the three-dimensional growth step S200, by eliminating the c-plane 30c from the top surface 30u of the first layer 30, the surface of the first layer 30 is an inclined interface 30i other than the c-plane. It is possible to form a plurality of valleys 30v and a plurality of tops 30t on the surface of the first layer 30. As a result, the dislocations propagating from the second base layer 6 can be reliably bent over the entire surface of the first layer 30. By reliably bending the dislocations, it is possible to easily eliminate some of the plurality of dislocations, or to make it difficult for some of the plurality of dislocations to propagate to the surface side of the second layer 40. As a result, it becomes possible to reduce the dislocation density over the entire main surface 1s of the substrate 50 obtained from the second layer 40.

(F) In the present embodiment, the second base layer forming step S150 is performed between the void forming step S140 and the three-dimensional growth step S200 to mirror the main surface 6s of the second base layer 6. As a result, the growth form of the first layer 30 can be changed from the growth form of the island-shaped crystals generated in the early stage of growth of the second base layer 6.

Here, if the three-dimensional growth step S200 is performed without performing the second base layer forming step S150 immediately after the void forming step S140, a metal nitride layer is formed above the void-containing first base layer from the initial stage of growth of the first layer. Through this, the first layer grows as island-like crystals. In this case, the frequency of the island-shaped crystals in the first layer depends on the degree of supersaturation when growing on the nanonet of the metal nitride layer and the variation in the opening width of the nanonet, as described above. Therefore, the tops of the first layer are densely formed, and the average distance between the closest tops of the first layer is shortened. When the average distance between the nearest apexes of the first layer becomes short, dislocations are not sufficiently collected. As a result, it may not be possible to sufficiently reduce the dislocation density on the surface of the second layer.

On the other hand, in the present embodiment, by mirroring the main surface 6s of the second base layer 6 after the void forming step S140, the growth form of the first layer 30 is changed to the second base layer 6 as described above. It can be changed from the growth morphology of the island-shaped crystals generated in the early stage of growth.

That is, the first layer 30 that grows on the mirrored second base layer 6 is not grown as an island-shaped crystal from the initial stage of growth, but depends on the above-mentioned first growth condition in the three-dimensional growth step S200. It can be grown three-dimensionally. In this case, the nearest apex average distance between the first layer 30, as a first growth conditions described above, the growth rate G _i in the inclination direction of the c-axis direction between the growth rate G _c0 graded interface 30i of the c-plane 30c Depends on the difference. As a result, the average distance between the closest apex parts of the first layer 30 can be controlled based on the first growth condition, and the distance between the closest apex parts can be increased.

Further, in the present embodiment, by mirroring the main surface 6s of the second base layer 6 after the void forming step S140, the second lower layer is irrespective of the state of the void-containing first base layer 4 and the metal nitride layer 5. The morphology of the main surface 6s of the formation 6 can be made substantially uniform throughout. By making the morphology of the main surface 6s of the second base layer 6 substantially uniform, the generation state of the inclined interface 30i in the three-dimensional growth step S200 can be made substantially uniform over the entire surface of the first layer 30. .. As a result, it is possible to prevent the formation of a region having a short distance between the nearest apex portions on a part of the surface of the first layer 30, and to make the distance between the closest apex portions substantially uniform over the entire surface of the first layer 30. Can be lengthened.

As a result, in the present embodiment, the formation of a region having a high dislocation density on a part of the surface of the second layer 40 is suppressed, and the dislocation density is lowered over the entire surface of the second layer 40. be able to.

(G) The number of steps of the present embodiment is larger than that of the case where the three-dimensional growth step and the flattening step are performed using the self-supporting substrate obtained by slicing and polishing the crystal layer composed of a single crystal of the group III nitride semiconductor. Can be reduced. That is, the slicing step and the polishing step for obtaining the self-supporting substrate can be omitted. As a result, the manufacturing cost can be reduced while improving the yield of the present embodiment.

(H) In the present embodiment, the base structure 10 in a state in which any of the formation of the mask layer on the main surface 6s of the second base layer 6 and the formation of the uneven pattern on the main surface 6s is not performed. On the other hand, the three-dimensional growth step S200 is performed. The term "mask layer" as used herein means, for example, a mask layer used in the so-called ELO (Epitaxial Lateral Overgrowth) method, which is made of silicon oxide or the like and has a predetermined opening. Further, the "concavo-convex pattern" referred to here means, for example, at least one of a trench and a ridge in which the main surface is directly patterned, which is used in the so-called pendeo epitaxy method. The height difference of the uneven pattern referred to here is, for example, 100 nm or more.

Due to the concentration of dislocations on the main surface 50s of the substrate 50 formed by slicing the second layer 40 by performing the three-dimensional growth step S200 and the flattening step S300 without having the above-mentioned structure. It is possible to suppress the formation of a region having a high dislocation density and uniformly form a region having a low dislocation density.

Further, by performing the three-dimensional growth step S200 and the flattening step S300 without having the above-mentioned structure, a predetermined processing step (mask layer forming step, photolithography step, etc.) can be eliminated. , The number of steps of this embodiment can be reduced. As a result, the manufacturing cost can be reduced while improving the yield of the present embodiment.

(I) In the present embodiment, the first layer 30 is grown on the mirrored second base layer 6 described above, and the first growth condition is adjusted so as to satisfy the formula (1) in the three-dimensional growth step S200. By doing so, in the three-dimensional growth step S200, a {11-2m} plane having m ≧ 3 can be generated as the inclined interface 30i. As a result, the inclination angle of the {11-2m} plane with respect to the c plane 30c can be made gentle. Specifically, the inclination angle can be 47.3 ° or less. By making the inclination angle of the {11-2m} plane with respect to the c-plane 30c gentle, the period of the plurality of tops 30t can be lengthened. Specifically, when an arbitrary cross section perpendicular to the main surface 1s of the base substrate 1 is viewed, the average distance L between the nearest apex portions can be set to more than 100 μm.

For reference, usually, when an etch pit is formed on a nitride semiconductor substrate using a predetermined etchant, an etch pit composed of {1-10n} planes is formed on the surface of the substrate. On the other hand, on the surface of the first layer 30 grown under predetermined conditions in the present embodiment, a {11-2 m} surface having m ≧ 3 can be generated. Therefore, it is considered that the inclined interface 30i peculiar to the manufacturing method is formed in the present embodiment as compared with the normal etch pit.

(J) In the present embodiment, when an arbitrary cross section perpendicular to the main surface 1s of the base substrate 1 is viewed, the dislocation is bent and propagated by setting the average distance L between the nearest apex portions to exceed 100 μm. Can be secured at least over 50 μm. As a result, dislocations can be sufficiently collected above the substantially center between the pair of tops 30t in the first layer 30. As a result, the dislocation density on the surface of the second layer 40 can be sufficiently reduced.

(K) In the three-dimensional growth step S200, after the c-plane 30c disappears from the surface of the first layer 30, a predetermined thickness is maintained while maintaining a state in which the inclined interface 30i occupies more than the c-plane 30c on the surface. The growth of the first layer 30 is continued over the period. As a result, after the c-plane 30c disappears, it is possible to secure a sufficient time to bend the dislocation at the position where the inclined interface 30i is exposed. Here, if the c-plane grows immediately after the c-plane disappears, the dislocations may not be sufficiently bent and propagate in a substantially vertical direction toward the surface of the second layer. On the other hand, in the present embodiment, by securing a sufficient time to bend the dislocation at the position where the inclined interface 30i other than the c-plane is exposed, the dislocation in the vicinity of the top 30t of the first layer 30 is surely bent. This makes it possible to suppress the propagation of dislocations in the substantially vertical direction from the second base layer 6 toward the surface of the second layer 40. As a result, the concentration of dislocations above the top 30t of the first layer 30 can be suppressed.

<Other embodiments>
The embodiments of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist thereof.

In the above-described embodiment, the case where the substrate 50 is a GaN free-standing substrate has been described, but the substrate 50 is not limited to the GaN free-standing substrate, and for example, aluminum nitride (AlN), aluminum gallium nitride (AlGaN), and indium nitride (InN). ), Indium gallium nitride (InGaN), aluminum nitride indium gallium (AlInGaN), and other group III nitride semiconductors, that is, Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, It may be a self-supporting substrate made of a group III nitride semiconductor represented by the composition formula of 0 ≦ x + y ≦ 1).

In the above-described embodiment, the case where the substrate 50 is n-type has been described, but the substrate 50 may be p-type or may have semi-insulating properties. For example, when a semiconductor device as a high electron mobility transistor (HEMT) is manufactured using the substrate 50, the substrate 50 preferably has a semi-insulating property.

In the above-described embodiment, the case where the growth temperature is mainly adjusted as the first growth condition in the three-dimensional growth step S200 has been described, but if the first growth condition satisfies the equation (1), the first growth condition is satisfied. , Growth conditions other than the growth temperature may be adjusted, or the growth temperature and the growth conditions other than the growth temperature may be combined and adjusted.

In the above-described embodiment, the case where the growth temperature is mainly adjusted as the second growth condition in the flattening step S300 has been described, but if the second growth condition satisfies the equation (2), the second growth condition is The growth conditions other than the growth temperature may be adjusted, or the growth temperature and the growth conditions other than the growth temperature may be combined and adjusted.

In the above-described embodiment, the case where the growth conditions in the inclined interface maintenance step S240 are maintained under the above-mentioned first growth conditions as in the inclined interface expansion step S220 has been described, but the growth conditions in the inclined interface maintenance step S240 have been described. If the first growth condition is satisfied, the growth condition in the inclined interface maintenance step S240 may be different from the growth condition in the inclined interface expansion step S220.

In the above-described embodiment, the case where the growth conditions in the main growth step S340 are maintained under the above-mentioned second growth conditions as in the c-plane expansion step S320 has been described, but the growth conditions in the main growth step S340 are the first. If the two growth conditions are satisfied, the growth conditions in the main growth step S340 may be different from the growth conditions in the c-plane expansion step S320.

In the above-described embodiment, the case where the main growth layer 44 is sliced by using a wire saw in the slicing step S400 has been described, but for example, an outer peripheral blade slicer, an inner peripheral blade slicer, an electric discharge machine, or the like may be used.

In the above-described embodiment, the case where the substrate 50 is obtained by slicing the main growth layer 44 of the laminated structure 90 has been described, but the present invention is not limited to this case. For example, the laminated structure 90 may be used as it is to manufacture a semiconductor laminate for manufacturing a semiconductor device. Specifically, after the laminated structure 90 is produced, the semiconductor functional layer is epitaxially grown on the laminated structure 90 in the semiconductor laminate manufacturing step to prepare the semiconductor laminate. After producing the semiconductor laminate, the back surface side of the laminate structure 90 is polished to remove the second base layer 6, the first layer 30, and the c-plane expansion layer 42 of the laminate structure 90. As a result, a semiconductor laminate having the main growth layer 44 and the semiconductor functional layer can be obtained as in the above-described embodiment. According to this case, the slicing step S400 and the polishing step S500 for obtaining the substrate 50 can be omitted.

Hereinafter, various experimental results supporting the effects of the present invention will be described.

(1) Experiment 1
(1-1) Preparation of Nitride Semiconductor Substrate The nitride semiconductor substrate of Examples and Comparative Example 1 and the laminated structure of Comparative Example 2 were prepared as follows. In the examples, a laminated structure before slicing the nitride semiconductor substrate was also produced. Further, in the following, the "nitride semiconductor substrate" may be abbreviated as a substrate.

[Conditions for Fabrication of Nitride Semiconductor Substrate in Examples]
(Base board)
Material: Sapphire Diameter: 2 inches Thickness: 400 μm
Crystal plane with the lowest index closest to the main surface: c-plane No processing such as mask layer on the main surface.
(First base layer)
Low temperature growth buffer layer:
Material: GaN
Growth temperature: 550 ° C
Thickness: 50 nm
GaN layer:
Material: Undoped (Unintensionally Doped) GaN
Growth temperature: 1,050 ° C
Thickness: 350 nm
The surface of the GaN layer was mirrored.
(Metal layer)
Material: Ti
Thickness: 20 nm
(Heat treatment conditions)
A two-step heat treatment was performed.
First heat treatment:
Atmosphere: N ₂ gas 80%, NH ₃ gas 20%
Temperature: 1,050 ° C
Time: 10 minutes Second heat treatment:
Atmosphere: H ₂ gas 80%, NH ₃ gas 20%
Temperature: 1,050 ° C
Time: 20 minutes (second base layer)
Material: Undoped (Unintensionally Doped) GaN
Growth temperature: 1,050 ° C
Thickness: Approximately 200 μm
The main surface of the second base layer was mirrored.
(1st layer)
Material: GaN
Growth method: HVPE method First growth condition:
The growth temperature was 980 ° C. or higher and 1,020 ° C. or lower, and the V / III ratio was 2 or higher and 20 or lower. At this time, at least one of the growth temperature and the V / III ratio was adjusted within the above range so that the first growth condition satisfies the formula (1).
Height from the main surface of the second base layer to the top of the first layer: Approximately 450 μm
(2nd layer)
Material: GaN
Growth method: HVPE method Growth temperature: 1,050 ° C
V / III ratio: 2
The second growth condition satisfies the formula (2).
Thickness from the top of the first layer to the surface of the second layer: about 800 μm
(Peeling condition)
Natural peeling when the temperature drops from the second layer growth temperature.
(Slicing and polishing conditions)
Slice position: Main growth layer of the second layer Calfros at the time of slicing: 200 μm
Double-sided polishing Final thickness of nitride semiconductor substrate: 400 μm

In the examples, a plurality of nitride semiconductor substrates were produced under the same conditions.

[Conditions for Fabrication of Nitride Semiconductor Substrate in Comparative Example 1]
In Comparative Example 1, a substrate was prepared under the same conditions as the conventional VAS method.
(Base board)
Same as the embodiment.
(First crystal layer, metal layer, and heat treatment conditions)
Same as the first base layer, metal layer, and heat treatment conditions of the examples.
(Second crystal layer)
The conditions other than the point that the thickness is 600 μm are the same as those of the second base layer of the example.
(1st layer and 2nd layer)
None.
(Peeling condition)
Natural exfoliation when the temperature drops from the growth temperature of the second crystal layer.
(Slicing and polishing conditions)
The conditions other than the point where the slice position is the second crystal layer are the same as in the examples.

[Conditions for Fabrication of Nitride Semiconductor Substrate in Comparative Example 2]
(Base board)
Same as the embodiment.
(First crystal layer, metal layer, and heat treatment conditions)
Same as the first base layer, metal layer, and heat treatment conditions of the examples.
(Second crystal layer)
The conditions other than the point that the thickness is 1700 μm are the same as those of the second base layer of the example.
(1st layer and 2nd layer)
None.

(1-2) Evaluation (observation with a fluorescence microscope)
In the examples, the cross section of the laminated structure before slicing the nitride semiconductor substrate was observed using a fluorescence microscope.

(Observation with multi-photon excitation microscope)
Using a multi-photon excitation microscope, the main surfaces of the nitride semiconductor substrates of Examples and Comparative Example 1 were observed. At this time, the dislocation density was measured by measuring the dark spot density over the entire main surface every 250 μm of the visual field. It is confirmed that all the dark spots on these substrates are dislocations by measuring the focus in the thickness direction. At this time, the ratio of the number of regions having a dislocation density of less than 1 × 10 ⁶ cm- ² (low dislocation density region) to the total number of measurement regions in a field of view of 250 μm was determined.

(X-ray locking curve measurement)
The following two types of X-ray locking curve measurements were performed on each of the nitride semiconductor substrates of Example and Comparative Example 1.

For the X-ray locking curve measurement, "X'Pert-PRO MRD" manufactured by Spectris was used, and as the monochromator on the incident side, "Hybrid monochromator" manufactured by the same company was used. The hybrid monochromator has an X-ray mirror and two crystals on the Ge (220) plane in this order from the X-ray light source side. In the measurement, first, the X-rays emitted from the X-ray light source are made into parallel light by an X-ray mirror. This makes it possible to increase the number of X-ray photons used (ie, X-ray intensity). Next, the parallel light from the X-ray mirror is converted into monochromatic light of Kα1 of Cu by two crystals on the Ge (220) plane. Next, monochromatic light from the two crystals on the Ge (220) plane is narrowed to a predetermined width through the slit and incident on the substrate. The resolution when the hybrid monochromator is used is about 24 arcsec.

In the measurement, the X-ray incident on the substrate is parallel light toward the substrate in the cross section along the ω direction, but in the cross section along the direction orthogonal to the ω direction (the direction of the rotation axis of the substrate). It is not parallel light. Therefore, the width of the X-ray in the ω direction is substantially constant from the slit to the substrate, but the width of the X-ray in the direction orthogonal to the ω direction increases. Therefore, in the X-ray locking curve measurement, the full width at half maximum of the X-ray diffracted at the predetermined crystal plane depends on the width of the slit on the incident side in the ω direction in which the X-ray becomes parallel light.

(X-ray locking curve measurement 1)
The width of the slit on the incident side in the ω direction was set to 0.1 mm, and the X-ray locking curve of the (0002) plane of each of the nitride semiconductor substrates of Examples and Comparative Example 1 was measured. At this time, the measurement was performed at a plurality of measurement points set at 5 mm intervals on a straight line passing through the center in the main surface of each substrate and along each of the m-axis direction and the a-axis direction. As a result of the measurement, the peak angle ω formed by the X-ray incident on the main surface and the main surface was obtained. Then, the peak angle ω was plotted against the position on the straight line, and the peak angle ω was approximated by the linear function of the position. The radius of curvature of the c-plane was obtained from the reciprocal of the slope of the linear function.

Further, at each measurement point, the full width at half maximum FWHMb of the (0002) plane diffraction when the width of the slit on the incident side in the ω direction was 0.1 mm was obtained.

(X-ray locking curve measurement 2)
The width of the slit on the incident side in the ω direction was set to 1 mm, and the X-ray locking curve measurement was performed for each of the nitride semiconductor substrates of Example and Comparative Example 1. The measurement was performed at the center of the main surface of each substrate. As a result of the measurement, the full width at half maximum FWHMa of the (0002) plane diffraction when the width of the slit on the incident side in the ω direction was 1 mm was obtained. Further, the ratio of FWHMa-FWHMb to FWHMa was determined at the center of the main surface of each substrate.

In the X-ray locking curve measurements 1 and 2, when X-rays are incident on the main surface of each substrate at a Bragg angle of 17.28 ° on the (0002) surface, the width of the slit in the ω direction is 0.1 mm. At this time, the X-ray footprint is about 0.337 mm, and when the width of the slit in the ω direction is 1 mm, the X-ray footprint is about 3.37 mm.

(1-3) Results The results are shown in Table 1.

(Comparison between Example and Comparative Example 2)
First, Example and Comparative Example 2 are compared.

In Comparative Example 2, when it was confirmed that the temperature was lowered to room temperature after the crystal layer had grown, the second crystal layer was finely cracked. In addition, crystals were abnormally grown from the cracked cross section of the second crystal layer. From this, it is considered that the second crystal layer was cracked during the growth of the second crystal layer. In Comparative Example 2, since the second crystal layer having a sufficient thickness and diameter could not be obtained, the nitride semiconductor substrate was not manufactured.

On the other hand, in the example, when the temperature was lowered to room temperature after the growth of the second layer was completed, the laminated structure was peeled off from the base substrate at the boundary between the metal nitride layer and the second base layer. .. No cracks were found in the laminated structure after peeling.

(Comparison between Example and Comparative Example 1)
Examples and Comparative Example 1 are compared with reference to Table 1, FIGS. 13 to 16. FIG. 13 is a diagram showing an observation image obtained by observing a cross section of the laminated structure of the example with a fluorescence microscope. FIG. 14 is a view of observing the main surface of the nitride semiconductor substrate of the example using a multi-photon excitation microscope. FIG. 15A is a diagram showing the results of X-ray locking curve measurement of (0002) plane diffraction along the m-axis direction for each of the nitride semiconductor substrates of Example and Comparative Example 1. b) is a diagram showing the results of X-ray locking curve measurement of (0002) plane diffraction along the a-axis direction for each of the nitride semiconductor substrates of Example and Comparative Example 1. In FIGS. 15A and 15B, the black circle mark is an example, and the white circle mark is Comparative Example 1. FIG. 16A is a diagram showing a standardized X-ray diffraction pattern when the X-ray locking curve is measured with different slits in the nitride semiconductor substrate of the embodiment, and FIG. 16B is a diagram showing a standardized X-ray diffraction pattern. It is a figure which shows the standardized X-ray diffraction pattern when the same measurement as the Example was performed about the nitride semiconductor substrate of the comparative example 1. FIG. 16 (a) and 16 (b) show the measurement results in the direction along the m-axis. Further, in the figure, "Line width" means the above-mentioned X-ray footprint.

As shown in FIG. 13, in the laminated structure of the example, the first layer was grown with the c-plane as the growth interface based on the difference in the growth interface during the growth process (that is, the difference in oxygen concentration). It had a surface growth region and an inclined interface growth region grown with the inclined interface as a growth surface. The first c-plane growth region had a plurality of concave portions and a plurality of convex portions. The average value of the angles formed by the pair of inclined portions in the first c-plane growth region was approximately 45.1 °. In addition, the average distance between the most recent apex parts was about 109 μm. Further, the inclined interface growth region was continuously formed along the main surface of the base substrate.

As shown in Table 1, in the substrate of Example, the average dislocation density in the main surface, as compared with the substrate of Comparative Example 1, is greatly reduced, it was less than 5.5 × 10 ⁵ cm ^-2.

Further, in the substrate of the example, there was no region where the dislocation density exceeded 3 × 10 ⁶ cm- ² . Even the highest region dislocation density, the dislocation density was less than 1.6 × ¹⁰ 6 ^{cm -2.} Further, in the substrate of the example, a region having a dislocation density of less than 1 × 10 ⁶ cm- ² (low dislocation density region) was present at 90% or more of the main surface 50s. The dislocation density in the low dislocation density region was 1.3 × 10 ^{5 to} 7.6 × 10 ⁵ cm- ² .

Further, as shown by the square frame in FIG. 14, the main surface of the substrate of the example contained a dislocation-free region of at least 50 μm square. Further, the main surface of the substrate of the example had 100 non-dislocation-free regions of 50 μm square which did not overlap at a density of 100 pieces / cm ² or more.

Further, as shown in Table 1, FIGS. 15 (a) and 15 (b), in the substrate of the example, the radius of curvature of the c-plane was larger than that of the substrate of the comparative example 1, and was 19 m or more.

In the substrate of the example, since the radius of curvature of the c-plane is obtained, the error with respect to the linear function when the peak angle ω is approximated by the linear function of the position in the X-ray locking curve measurement of the c-plane is small. Specifically, the error of the measured peak angle ω with respect to the linear function approximated as described above was 0.01 ° or less.

Further, as shown in Table 1, FIGS. 15 (a) and 15 (b), in the substrate of the example, when the width of the slit in the ω direction was 0.1 mm at all measurement points (that is, 100%) ( 0002) The half width FWHMb of surface diffraction was 50 arcsec or less.

As shown in FIG. 16B, in the substrate of Comparative Example 1, when the width of the slit in the ω direction was 0.1 mm, the X-ray diffraction spectrum was narrow, but the width of the slit in the ω direction was 1 mm. At that time, the diffraction spectrum of the X-ray was widened.

Therefore, as shown in Table 1, in the substrate of Comparative Example 1, FWHMa-FWHMb was 50% or more of FWHMa.

On the other hand, as shown in FIG. 16A, in the substrate of the example, even when the width of the slit in the ω direction is widened from 0.1 mm to 1 mm, the X-ray diffraction spectrum is slightly widened. , The spread was small.

As a result, as shown in Table 1, in the substrate of the example, FWHMa-FWHMb was 0% or more and 30% or less of FWHMa.

(Summary)
According to the above examples, the stress canceling effect of the first layer can be obtained by three-dimensionally growing the first layer on the underlying structure. By obtaining the stress canceling effect of the first layer, it is possible to suppress the occurrence of cracks or the like in the second layer even if the second layer is grown thick with the tensile stress accumulated in the second base layer. I confirmed that I was able to do it.

Further, according to the examples, in the three-dimensional growth step, the first growth condition was adjusted so as to satisfy the formula (1). As a result, the c-plane could be reliably eliminated during the growth process of the first layer. By surely eliminating the c-plane, the dislocations could be reliably bent at the position where the inclined interface in the first layer was exposed. As a result, it was confirmed that the dislocation density on the main surface of the nitride semiconductor substrate could be efficiently reduced.

Further, according to the embodiment, in the second base layer forming step, the main surface of the second base layer is mirror-finished, so that the growth form of the first layer is changed to the island generated in the early stage of the growth of the second base layer. It was possible to increase the distance between the nearest apex portions of the first layer that grows three-dimensionally in the three-dimensional growth process by changing from the growth form of the crystalline crystal. As a result, it was confirmed that the formation of a high dislocation density region on a part of the main surface of the substrate was suppressed, and the dislocation density could be lowered over the entire main surface of the substrate.

Further, according to the embodiment, the first layer is grown on the above-mentioned mirrored second base layer, and the first growth condition is adjusted so as to satisfy the equation (1). The average distance could be over 100 μm. As a result, it was confirmed that the dislocation density on the main surface of the substrate could be sufficiently reduced. In addition, it was confirmed that a dislocation-free region of at least 50 μm square could be formed by setting the average distance between the most recent ridges to more than 100 μm.

Further, according to the embodiment, by obtaining the stress canceling effect of the first layer described above, the radius of curvature of the c-plane of the substrate of the embodiment is changed to the c-plane of the substrate of Comparative Example 1 corresponding to the conventional VAS method. It was confirmed that it was possible to make it larger than the radius of curvature of.

Further, according to the examples, as described above, there were few dislocations over a wide range of the main surface of the substrate, and the crystal mosaicity on the substrate was low. As a result, it was confirmed that the FWHMb of the substrate of the example was 50 arcsec or less over a wide range of the main surface.

Further, according to the examples, as described above, the crystal mobility was low and the radius of curvature of the c-plane of the substrate was large. From these, it was confirmed that in the Example, the difference in half-value width FWHMa-FWHMb was 30% or less of FWHMa when the X-ray locking curve measurement was performed with different slit widths on the incident side.

<Preferable Aspect of the Present Invention>
Hereinafter, preferred embodiments of the present invention will be added.

(Appendix 1)
The process of preparing the base substrate and
A step of forming a first base layer made of a group III nitride semiconductor on the base substrate, and
The step of forming a metal layer on the first base layer and
A step of performing heat treatment to form a void in the first base layer, and
A second base layer composed of a single crystal of a group III nitride semiconductor and having a main surface whose closest low index crystal plane is the (0001) plane is epitaxially grown above the first base layer, and the second lower layer is formed. The process of mirroring the main surface of the stratum and
A single crystal of a group III nitride semiconductor having a top surface with an exposed (0001) plane is epitaxially grown directly on the main surface of the second base layer, and is composed of an inclined interface other than the (0001) plane. A plurality of recesses are formed on the top surface, the inclined interface is gradually expanded toward the upper side of the second base layer, the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. A three-dimensional growth process that grows the first layer composed of
A flattening step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, eliminating the inclined interface, and growing a second layer having a mirrored surface.
A method for manufacturing a nitride semiconductor substrate having.

(Appendix 2)
In the three-dimensional growth step,
By creating the plurality of recesses on the top surface of the single crystal and eliminating the (0001) surface, a plurality of valleys and a plurality of tops are formed on the surface of the first layer.
When looking at an arbitrary cross section perpendicular to the main surface, the direction in which the pair of tops closest to each other across the plurality of valleys are along the main surface. The method for manufacturing a nitride semiconductor substrate according to Appendix 1, wherein the average distance separated from the above is 100 μm or more.

(Appendix 3)
In the three-dimensional growth step,
The method for manufacturing a nitride semiconductor substrate according to Appendix 2, wherein the average distance between the pair of tops that are closest to each other is less than 800 μm.

(Appendix 4)
In the three-dimensional growth step,
After the (0001) plane is eliminated from the surface, the first layer is grown over a predetermined thickness while maintaining a state in which the inclined interface occupies more than the (0001) plane on the surface. The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary notes 1 to 3 to be continued.

(Appendix 5)
After the flattening step, there is a step of slicing at least one nitride semiconductor substrate from the second layer.
In the step of slicing the nitride semiconductor substrate,
The radius of curvature of the (0001) plane of the nitride semiconductor substrate is such that the second base layer is grown to have the same thickness as the second layer, and the three-dimensional growth step and the flattening step are not performed. 2. The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary note 1 to 4, wherein the radius of curvature of the (0001) plane of the nitride semiconductor substrate when the base layer is sliced is made larger.

(Appendix 6)
The method for manufacturing a nitride semiconductor substrate according to Appendix 5, wherein the radius of curvature of the (0001) plane of the nitride semiconductor substrate is 10 m or more.

(Appendix 7)
After the flattening step, any one of Supplementary notes 1 to 6 further comprising a peeling step of peeling the laminated structure having the second base layer, the first layer and the second layer from the base substrate. The method for manufacturing a nitride semiconductor substrate according to the description.

(Appendix 8)
In the three-dimensional growth step,
The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary note 1 to 7, wherein a {11-2 m} surface having m ≧ 3 is generated as the inclined interface.

(Appendix 9)
In the three-dimensional growth step, the first layer is grown under the first growth condition satisfying the formula (1).
The method for producing a nitride semiconductor substrate according to any one of Supplementary note 1 to 8, wherein in the flattening step, the second layer is grown under the second growth condition satisfying the formula (2).
_{G c1> G i / cosα ···} (1)
G _c2 <G _i / cos α ・ ・ ・ (2)
(However, the growth rate of the (0001) plane of the first layer is G _c1 , the growth rate of the (0001) plane of the second layer is G _c2, and the first layer and the first layer are wherein within each of the two layers (0001) the most inclined growth rate of the inclined surface with respect to surface and G _i, most inclined with respect to the (0001) plane in each of the first layer and the second layer Let α be the angle formed by the inclined interface and the (0001) plane.

(Appendix 10)
The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary note 1 to 9, wherein the steps from forming the second base layer to the flattening step are continuously performed in the same vapor phase growth apparatus.

(Appendix 11)
The nitride semiconductor substrate obtained by slicing the second layer in the method for manufacturing a nitride semiconductor substrate according to any one of Supplementary note 1 to 10.

(Appendix 12)
A nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
When the main surface is irradiated with X-rays of Cu Kα1 through a two-crystal monochromator and a slit on the Ge (220) surface and the X-ray locking curve of (0002) surface diffraction is measured, the slit. The half-value width FWHMb of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm is subtracted from the half-value width FWHMa of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm. The difference FWHMa-FWHMb is a nitride semiconductor substrate having 30% or less of FWHMa.

(Appendix 13)
When the dislocation density was obtained from the dark spot density by observing the main surface with a field of view of 250 μm square with a multiphoton excitation microscope, there was no region on the main surface where the dislocation density exceeded 3 × 10 ⁶ cm- ^2. The nitride semiconductor substrate according to Appendix 12, wherein a region having a dislocation density of less than 1 × 10 ⁶ cm- ² exists in 80% or more of the main surface.

(Appendix 14)
A nitride semiconductor substrate having a diameter of 2 inches or more.
When the main surface of the nitride semiconductor substrate is observed with a multiphoton excitation microscope in a field of view of 250 μm and the dislocation density is obtained from the dark spot density, the region where the dislocation density exceeds 3 × 10 ⁶ cm- ² is the main surface. A nitride semiconductor substrate in which a region that does not exist on the surface and has a dislocation density of less than 1 × 10 ⁶ cm- ² exists in 80% or more of the main surface.

(Appendix 15)
The nitride semiconductor substrate according to any one of Appendix 12 to 14, wherein the main surface includes a dislocation-free region of at least 50 μm square.

(Appendix 16)
The X-ray locking curve of the (0002) plane is measured at each position on the straight line passing through the center in the main plane, and the peak angle ω formed by the X-ray incident on the main plane and the main plane is measured on the straight line. When plotted against the position of and the peak angle ω is approximated by the linear function of the position,
The radius of curvature of the (0001) plane obtained by the reciprocal of the slope of the linear function is 10 m or more.
The nitride semiconductor substrate according to any one of Supplementary note 12 to 15, wherein the measured error of the peak angle ω with respect to the linear function is 0.05 ° or less.

(Appendix 17)
A nitride semiconductor substrate having a main plane in which the closest low index crystal plane is the (0001) plane.
The X-ray locking curve of the (0002) plane is measured at each position on the straight line passing through the center in the main plane, and the peak angle ω formed by the X-ray incident on the main plane and the main plane is measured on the straight line. When plotted against the position of and the peak angle ω is approximated by the linear function of the position,
The radius of curvature of the (0001) plane obtained by the reciprocal of the slope of the linear function is 10 m or more.
A nitride semiconductor substrate in which the measured error of the peak angle ω with respect to the linear function is 0.05 ° or less.

(Appendix 18)
A base layer composed of a single crystal of a group III nitride semiconductor, having a mirrored main surface, and having a low index crystal plane closest to the main plane as the (0001) plane.
A plurality of single crystals of group III nitride semiconductors having a top surface with an exposed (0001) plane are epitaxially grown directly on the main surface of the base layer, and are composed of inclined interfaces other than the (0001) plane. The concave surface is formed on the top surface, the inclined interface is gradually expanded toward the upper side of the base layer, and the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. The first layer composed of
A single crystal of a group III nitride semiconductor is epitaxially grown on the first layer to eliminate the inclined interface, and a second layer having a mirrored surface is formed.
Laminated structure having.

(Appendix 19)
The first layer is
The first c-plane growth region grown with the (0001) plane as the growth plane,
An inclined interface growth region grown with the inclined interface as a growth surface,
Have,
The laminated structure according to Appendix 18, wherein the second layer has a second c-plane growth region grown with the (0001) plane as a growth plane.

(Appendix 20)
The laminated structure according to Appendix 19, wherein the inclined interface growth region is continuously provided along the main surface of the base layer.

(Appendix 21)
The first c-plane growth region is
A convex portion provided at a position where the (0001) surface disappears,
A pair of inclined portions provided as a locus of an intersection between the (0001) plane and the inclined interface on both sides of the convex portion.
Have,
The laminated structure according to Appendix 19 or 20, wherein the angle formed by the pair of inclined portions is 70 ° or less.

1 Underground board 2 First underlayer 3 Metal layer 4 Void-containing first underlayer 5 Metal nitride layer 6 Second underlayer 10 Underlay structure 30 First layer 40 Second layer 50 Nitride semiconductor substrate (substrate)

Claims (14)

The process of preparing the base substrate and
A step of forming a first base layer made of a group III nitride semiconductor on the base substrate, and
The step of forming a metal layer on the first base layer and
A step of performing heat treatment to form a void in the first base layer, and
A second base layer composed of a single crystal of a group III nitride semiconductor and having a main surface whose closest low index crystal plane is the (0001) plane is epitaxially grown above the first base layer, and the second lower layer is formed. The process of mirroring the main surface of the stratum and
A single crystal of a group III nitride semiconductor having a top surface with an exposed (0001) plane is epitaxially grown directly on the main surface of the second base layer, and is composed of an inclined interface other than the (0001) plane. A plurality of recesses are formed on the top surface, the inclined interface is gradually expanded toward the upper side of the second base layer, the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. A three-dimensional growth process that grows the first layer composed of
A flattening step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, eliminating the inclined interface, and growing a second layer having a mirrored surface.
A method for manufacturing a nitride semiconductor substrate having. In the three-dimensional growth step,
By creating the plurality of recesses on the top surface of the single crystal and eliminating the (0001) surface, a plurality of valleys and a plurality of tops are formed on the surface of the first layer.
When looking at an arbitrary cross section perpendicular to the main surface, the direction in which the pair of tops closest to each other across the plurality of valleys are along the main surface. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the average distance separated from the above is 100 μm or more. In the three-dimensional growth step,
The method for manufacturing a nitride semiconductor substrate according to claim 2, wherein the average distance between the pair of tops that are closest to each other is less than 800 μm. In the three-dimensional growth step,
After the (0001) plane is eliminated from the surface, the first layer is grown over a predetermined thickness while maintaining a state in which the inclined interface occupies more than the (0001) plane on the surface. The method for manufacturing a nitride semiconductor substrate according to any one of claims 1 to 3 to be continued. After the flattening step, there is a step of slicing at least one nitride semiconductor substrate from the second layer.
In the step of slicing the nitride semiconductor substrate,
The radius of curvature of the (0001) plane of the nitride semiconductor substrate is such that the second base layer is grown to have the same thickness as the second layer, and the three-dimensional growth step and the flattening step are not performed. 2. The method for manufacturing a nitride semiconductor substrate according to any one of claims 1 to 4, wherein the radius of curvature of the (0001) plane of the nitride semiconductor substrate when the base layer is sliced is made larger. The method for manufacturing a nitride semiconductor substrate according to claim 5, wherein the radius of curvature of the (0001) plane of the nitride semiconductor substrate is 10 m or more. The nitride semiconductor substrate obtained by slicing the second layer in the method for producing a nitride semiconductor substrate according to any one of claims 1 to 6. A nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
When the main surface is irradiated with X-rays of Cu Kα1 through a two-crystal monochromator and a slit on the Ge (220) surface and the X-ray locking curve of (0002) surface diffraction is measured, the slit. The half-value width FWHMb of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm is subtracted from the half-value width FWHMa of the (0002) surface diffraction when the width in the ω direction of the slit is 0.1 mm. The difference FWHMa-FWHMb is a nitride semiconductor substrate having 30% or less of FWHMa. When the dislocation density was obtained from the dark spot density by observing the main surface with a field of view of 250 μm square with a multiphoton excitation microscope, there was no region on the main surface where the dislocation density exceeded 3 × 10 ⁶ cm- ^2. The nitride semiconductor substrate according to claim 8, wherein a region having a dislocation density of less than 1 × 10 ⁶ cm- ² exists in 80% or more of the main surface. A nitride semiconductor substrate having a diameter of 2 inches or more.
When the main surface of the nitride semiconductor substrate is observed with a multiphoton excitation microscope in a field of view of 250 μm and the dislocation density is obtained from the dark spot density, the region where the dislocation density exceeds 3 × 10 ⁶ cm- ² is the main surface. A nitride semiconductor substrate in which a region that does not exist on the surface and has a dislocation density of less than 1 × 10 ⁶ cm- ² exists in 80% or more of the main surface. The nitride semiconductor substrate according to any one of claims 8 to 10, wherein the main surface includes a dislocation-free region of at least 50 μm square. The X-ray locking curve of the (0002) plane is measured at each position on the straight line passing through the center in the main plane, and the peak angle ω formed by the X-ray incident on the main plane and the main plane is measured on the straight line. When plotted against the position of and the peak angle ω is approximated by the linear function of the position,
The radius of curvature of the (0001) plane obtained by the reciprocal of the slope of the linear function is 10 m or more.
The nitride semiconductor substrate according to any one of claims 8 to 11, wherein the measured error of the peak angle ω with respect to the linear function is 0.05 ° or less. A nitride semiconductor substrate having a main plane in which the closest low index crystal plane is the (0001) plane.
The X-ray locking curve of the (0002) plane is measured at each position on the straight line passing through the center in the main plane, and the peak angle ω formed by the X-ray incident on the main plane and the main plane is measured on the straight line. When plotted against the position of and the peak angle ω is approximated by the linear function of the position,
The radius of curvature of the (0001) plane obtained by the reciprocal of the slope of the linear function is 10 m or more.
A nitride semiconductor substrate in which the measured error of the peak angle ω with respect to the linear function is 0.05 ° or less. A base layer composed of a single crystal of a group III nitride semiconductor, having a mirrored main surface, and having a low index crystal plane closest to the main plane as the (0001) plane.
A plurality of single crystals of group III nitride semiconductors having a top surface with an exposed (0001) plane are epitaxially grown directly on the main surface of the base layer, and are composed of inclined interfaces other than the (0001) plane. The concave surface is formed on the top surface, the inclined interface is gradually expanded toward the upper side of the base layer, and the (0001) surface is eliminated from the top surface, and the surface is only the inclined interface. The first layer composed of
A single crystal of a group III nitride semiconductor is epitaxially grown on the first layer to eliminate the inclined interface, and a second layer having a mirrored surface is formed.
Laminated structure having.