JP2022132823A - Semiconductor substrate, and method for producing semiconductor substrate - Google Patents

Abstract

To improve the crystallinity of a gallium nitride single crystal.SOLUTION: A semiconductor substrate 100 has a sapphire substrate 110 composed of a sapphire single crystal, a buffer layer 120 provided on the sapphire substrate 110, and a gallium nitride single crystal layer 130 that is provided on the buffer layer 120 and is composed of a gallium nitride single crystal. The buffer layer 120 is an alterated layer formed on the surface of the sapphire substrate 110 on the gallium nitride single crystal layer 130 side, the crystal structure of the sapphire single crystal has been turned into a spinel-type crystal structure of a specific metal oxide. The buffer layer 120 has a thickness of 10 nm or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor substrate and a method for manufacturing a semiconductor substrate.

Gallium nitride (GaN) is attracting attention as a semiconductor material that constitutes light-emitting diodes, semiconductor lasers, high-voltage, high-frequency power supply transistors, and the like.

When gallium nitride is deposited as a single crystal thin film on a sapphire substrate or the like, vapor phase growth methods such as hydride vapor phase epitaxial growth method and metalorganic vapor phase growth method are generally used. In the hydride vapor phase epitaxial growth method, ammonia gas and gallium chloride vapor are reacted on the substrate.

In such a vapor deposition method, a gallium nitride crystal is grown on a substrate made of a different material such as sapphire. For this reason, there is known a technique of providing a buffer layer between the substrate and the gallium nitride crystal in order to alleviate the difference in thermal expansion coefficient between the substrate and the gallium nitride or the lattice mismatch (see, for example, Patent Documents 1, 2).

However, even when the techniques disclosed in Patent Documents 1 and 2 are adopted, the gallium nitride crystal synthesized by vapor growth has many crystal defects, so that the desired characteristics cannot be achieved when incorporated into a device. was difficult to obtain. In addition, since the vapor phase growth method uses highly reactive ammonia gas as a nitrogen source, equipment for removing harmful gases is required, and the manufacturing process and manufacturing equipment are likely to be complicated, resulting in high manufacturing costs.

Therefore, as a method for producing a gallium nitride crystal in which crystal defects are less likely to occur, a method for producing a gallium nitride crystal using liquid phase epitaxy has been studied (for example, Patent Document 3). In such a method, the gallium nitride crystal can be grown stepwise in layers by crystal precipitation from the liquid phase, so lattice mismatch is less likely to occur, and the occurrence of crystal defects in the gallium nitride crystal can be suppressed. It is said.

JP-A-8-310900 Japanese Patent Application Laid-Open No. 2000-269605 JP 2019-151542 A

However, even when the technique disclosed in Patent Document 3 is employed, it is still difficult to form a gallium nitride single crystal with sufficiently improved crystallinity.

In view of such problems, an object of the present invention is to further improve the crystallinity of gallium nitride single crystals.

In order to solve the above problems, according to one aspect of the present invention, a sapphire substrate composed of a sapphire single crystal, a buffer layer provided on the sapphire substrate, a gallium nitride single layer provided on the buffer layer, a gallium nitride single crystal layer composed of crystals, wherein the buffer layer is an altered layer formed on the surface of the sapphire substrate on the gallium nitride single crystal layer side, and the crystal structure of the sapphire single crystal is a specific metal Provided is a semiconductor substrate converted to an oxide spinel crystal structure, wherein the thickness of the buffer layer is greater than or equal to 10 nm.

In addition, the (0001) plane of the sapphire single crystal constituting the sapphire substrate, the (111) plane of the specific metal oxide crystal layer of the spinel crystal structure constituting the buffer layer, and the gallium nitride single crystal layer The (0001) plane of the gallium nitride single crystal may be substantially parallel.

In addition, the [1-100] axis on the (0001) plane of the sapphire single crystal constituting the sapphire substrate and the [1 −10] axis and the [11-20] axis of the (0001) plane of the gallium nitride single crystal forming the gallium nitride single crystal layer may be substantially parallel.

In addition, 1/(2√2) times the lattice constant a _spi of the crystal layer of the specific metal oxide with the spinel crystal structure that constitutes the buffer layer is the lattice constant a _sap of the sapphire single crystal that constitutes the sapphire substrate. It may be a value between 1/√3 and the lattice constant a _gan of the gallium nitride single crystal forming the gallium nitride single crystal layer.

Further, the lattice constant a _spi of the crystal layer of the specific metal oxide having a spinel crystal structure that constitutes the buffer layer may be 8.050 to 8.338 Å.

In addition, the orientation variation of the [111] axis normal to the (111) plane of the specific metal oxide crystal layer of the spinel crystal structure forming the buffer layer may be less than 6°.

Further, the absolute value of the lattice mismatch amount between the crystal layer of the specific metal oxide having the spinel crystal structure forming the buffer layer and the gallium nitride single crystal forming the gallium nitride single crystal layer is 10.8. may be less than %.

Also, the specific metal oxide is a composite oxide represented by the chemical formula AB ₂ O ₄ , where A is +2 selected from the group consisting of Mg, Fe, Mn, Ni, Co, Cu, and Zn. is a valent metal atom, and B may be a +3 valent metal atom of either or both of Al and Ga.

Also, the specific metal oxide may contain one or more complex oxides selected from the group consisting of MgAl ₂ O ₄ , MgGa ₂ O ₄ , MnAl ₂ O ₄ and MnGa ₂ O ₄ .

Also, the buffer layer may contain a total of 1 at % or more of specific metal atoms other than Al contained in the specific metal oxide.

In order to solve the above problems, according to another aspect of the present invention, a step of melting a reaction material containing metallic gallium, iron nitride, and a specific metallic material in a nitrogen atmosphere to obtain a melt; immersing the sapphire substrate in the melt; and holding the sapphire substrate immersed in the melt at 700° C. to 1000° C. for 20 hours or more. A method for manufacturing a semiconductor substrate is provided, which may be a specific metal itself or a compound of a specific metal.

The method further includes the step of forming a film of the oxide of the specific metal on the surface of the sapphire substrate, and the step of immersing the sapphire substrate on which the film of the oxide of the specific metal is formed is immersed in the melt. may

According to the present invention, it is possible to further improve the crystallinity of gallium nitride single crystals.

1 is a cross-sectional view showing a cross-sectional configuration of a semiconductor substrate cut in a thickness direction according to an embodiment of the present invention; FIG. FIG. 4 is a diagram showing an X-ray diffraction measurement method for evaluating the tilt of the gallium nitride single crystal film according to the same embodiment. It is a figure which shows the measuring method of the X-ray diffraction for evaluating the twist of the gallium nitride single crystal film which concerns on the same embodiment. FIG. 4 is a diagram illustrating the crystal axis orientation of a sapphire single crystal forming a sapphire substrate and a gallium nitride single crystal forming a gallium nitride single crystal layer according to the same embodiment. FIG. 3 is a diagram illustrating the orientation of the crystal axis of a crystal layer of a metal oxide having a spinel crystal structure that constitutes the buffer layer according to the same embodiment. The sapphire single crystal constituting the sapphire substrate according to the embodiment, the metal oxide crystal layer having a spinel crystal structure constituting the buffer layer, and the crystal axis orientation of the gallium nitride single crystal constituting the gallium nitride single crystal layer It is a figure explaining about. FIG. 2 is a schematic diagram showing the configuration of a reactor used for producing gallium nitride single crystals according to the same embodiment. It is a flow chart explaining the flow of processing of a manufacturing method of a semiconductor substrate concerning the embodiment. 1 is a bright-field image of a cross-sectional TEM observation of a sapphire substrate on which a buffer layer and a gallium nitride single crystal layer are laminated according to Example 1. FIG. Results of in-plane wide-angle 2θχ-φ measurement at an incident angle of 0.25° and an incident angle of 0.8° for the sapphire substrate on which the buffer layer and the gallium nitride single crystal layer are laminated according to Example 1. It is a figure which shows. FIG. 10 is a diagram showing out-of-plane wide-angle 2θ-ω measurement results for a sapphire substrate having a buffer layer and a gallium nitride single crystal layer stacked thereon according to Example 1; FIG. 2 is a diagram showing the results of line analysis of each element of nitrogen, oxygen, magnesium, aluminum, and gallium on the sapphire substrate on which the buffer layer and the gallium nitride single crystal layer are laminated according to Example 1; FIG. 10 is a bright-field image of a cross-sectional TEM observation of a sapphire substrate on which a buffer layer and a gallium nitride single crystal layer are laminated according to Example 2. FIG. 10 is a bright-field image of a cross-sectional TEM observation of a sapphire substrate on which a buffer layer and a gallium nitride single crystal layer are laminated according to Example 3. FIG. FIG. 10 is a diagram showing reciprocal lattice map measurement results of a sapphire substrate on which a buffer layer and a gallium nitride single crystal layer are laminated according to Example 4;

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in these embodiments are merely examples for facilitating understanding of the invention, and do not limit the invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are given the same reference numerals to omit redundant description, and elements that are not directly related to the present invention are omitted from the drawings. do.

In addition, in each drawing referred to in the following description, for convenience of description, the size of some of the constituent members may be exaggerated. Therefore, the relative sizes of the constituent members illustrated in each drawing do not necessarily accurately represent the actual size relationship between the constituent members.

[Semiconductor substrate 100]
FIG. 1 is a cross-sectional view showing a cross-sectional configuration of a semiconductor substrate 100 cut in the thickness direction according to one embodiment of the present invention. As shown in FIG. 1, the semiconductor substrate 100 includes a sapphire substrate 110, a buffer layer 120, and a gallium nitride single crystal layer .

The sapphire substrate 110 is, for example, a plate-like support made of single crystal sapphire (single crystal sapphire). A sapphire single crystal is a crystal with a corundum structure composed of α-alumina (α-Al ₂ O ₃ ). Sapphire single crystals have excellent mechanical and thermal properties, chemical stability, and optical transparency. Therefore, the sapphire substrate 110 is used as a substrate for manufacturing, for example, a light-emitting diode, a semiconductor laser, or a transistor for high-voltage/high-frequency power supply. The thickness of the sapphire substrate 110 is, for example, approximately 0.4 mm.

A buffer layer 120 is provided directly on the sapphire substrate 110 . The buffer layer 120 is an altered layer formed on the surface (c-plane) of the sapphire single crystal forming the sapphire substrate 110 . The buffer layer 120 is obtained by converting the crystal structure of the sapphire single crystal that constitutes the sapphire substrate 110 into the spinel crystal structure of a specific metal oxide. The buffer layer 120 is a crystal layer composed of metal oxide microcrystals having a spinel crystal structure, and the orientation of each microcrystal is substantially oriented in [111]. The microcrystals may have twin crystals rotated by 30° in the plane of the buffer layer 120 while maintaining the substantially [111] orientation.

The specific metal oxide is preferably a multiple oxide represented by the chemical formula AB ₂ O ₄ . A is a +2 valent metal atom selected from the group consisting of Mg, Fe, Mn, Ni, Co, Cu, and Zn. In addition, the above B is a +3 valent metal atom of either one or both of Al and Ga. The specific metal oxide preferably contains, for example, one or more complex oxides selected from the group consisting of MgAl ₂ O ₄ , MgGa ₂ O ₄ , MnAl ₂ O ₄ and MnGa ₂ O ₄ . Thereby, a spinel-type crystal structure suitable for the buffer layer 120 can be realized, and the buffer function of the buffer layer 120 can be preferably exhibited.

A gallium nitride single crystal layer 130 is provided on the buffer layer 120 . The gallium nitride single crystal layer 130 according to this embodiment is composed of a gallium nitride single crystal doped with iron (Fe) atoms and magnesium (Mg) atoms or manganese atoms (Mn). That is, the gallium nitride single crystal layer 130 is stacked on the buffer layer 120 as a single crystal film of gallium nitride doped with iron atoms and magnesium atoms or manganese atoms. For example, by epitaxially growing a gallium nitride single crystal on the sapphire substrate 110 provided with the buffer layer 120, a gallium nitride single crystal layer 130 made of gallium nitride single crystal is provided on the sapphire substrate 110 with the buffer layer 120 interposed therebetween. be done. The thickness of the gallium nitride single crystal layer 130 is, for example, about several μm. Here, the gallium nitride single crystal layer 130 may have a microcrystalline layer with crystal orientation deviation or impurity grain boundaries as an initial growth layer. If a uniform single crystal layer can be confirmed even in part of the layer, it is expressed as a single crystal layer.

A plurality of gallium nitride single crystal layers 130 may be provided on the buffer layer 120 . In other words, the gallium nitride single crystal layer 130 may be laminated in two or more layers on the buffer layer 120 . Although there is no upper limit to the number of gallium nitride single crystal layers 130 to be stacked, if the number of gallium nitride single crystal layers 130 to be stacked is too large, the semiconductor substrate 100 may warp in the stacking direction of the gallium nitride single crystal layers 130 . . Therefore, the upper limit of the number of gallium nitride single crystal layers 130 to be stacked is, for example, 10 layers.

[Characteristics of sapphire substrate 110, buffer layer 120, and gallium nitride single crystal layer 130]
Next, the characteristics of the sapphire substrate 110, the buffer layer 120, and the gallium nitride single crystal layer 130 that constitute the semiconductor substrate 100 according to this embodiment will be described.

[Crystallinity of Gallium Nitride Single Crystal Layer 130]
As described above, the gallium nitride single crystal layer 130 according to this embodiment is composed of a gallium nitride single crystal doped with iron atoms and magnesium atoms or manganese atoms. The crystallinity of such a single crystal film can be evaluated, for example, by X-ray diffraction. The X-ray diffraction measurement can be performed by, for example, a fully automatic horizontal multi-purpose X-ray analyzer "SmartLab 3XG 9MTP" manufactured by Rigaku Corporation.

FIG. 2 is a diagram showing an X-ray diffraction measurement method for evaluating the tilt of the gallium nitride single crystal film according to this embodiment. The crystallinity in the crystal stacking direction (growth direction), that is, the index indicating the alignment of the crystal orientations in the crystal stacking direction (tilt of the crystal orientation) is generally referred to as tilt. Tilt can be evaluated by X-ray diffraction measured by the X-ray analyzer 10 shown in FIG.

As shown in FIG. 2, the X-ray analysis apparatus 10 has an X-ray source XG and a detector SC. In FIG. 2, the white arrow indicates the scanning direction of the X-ray source XG and the detector SC.

The X-ray source XG makes X-rays incident on the surface H of the sample SP. The detector SC detects diffracted X-rays emitted from the surface H of the sample SP.

As shown in FIG. 2, when evaluating the tilt, an out-of-plane measurement is performed in which X-ray incidence and diffraction detection are performed in a plane perpendicular to the surface H of the sample SP. will be The out-of-plane measurement is also called symmetric reflection measurement because the X-ray incidence and exit angles with respect to the surface H of the sample SP are equal. The out-of-plane measurement measures lattice planes parallel to the surface H of the sample SP. Specifically, as shown in FIG. 2, the angle 2θ between the detector SC and the incident X-ray is fixed at the diffraction peak position, and the angle ω between the surface H of the sample SP and the incident X-ray is changed. and measure the diffraction intensity (ω scan). The inclination (tilt) of the crystal orientation in the stacking direction of the crystal, which is the sample SP, can be evaluated from the measured diffraction intensity variation.

In the out-of-plane measurement, the penetration depth of X-rays into the sample SP is about several tens of μm. Therefore, it is inferred that the peak intensity value in the out-of-plane measurement depends on, for example, the volume (average thickness) of the gallium nitride single crystal layer 130 (that is, gallium nitride single crystal) present in the X-ray irradiation region.

FIG. 3 is a diagram showing an X-ray diffraction measurement method for evaluating the twist of the gallium nitride single crystal film according to this embodiment. The crystallinity in the in-plane direction of a crystal, that is, an index indicating the alignment of crystal orientations in the in-plane direction of a crystal is generally called twist. Twist can be evaluated by the X-ray analysis device 20 shown in FIG.

As shown in FIG. 3, when evaluating twist, in-plane measurement is performed in which X-ray incidence and diffraction detection are performed in a plane parallel to the surface H of the sample SP. In-plane measurement is performed by fixing the incident angle of X-rays near the critical angle of total reflection. The in-plane measurement measures lattice planes orthogonal to the surface H of the sample SP. Specifically, as shown in FIG. 3, the detector SC is fixed at a value of 2θχ calculated from the lattice spacing of the sample SP to be measured using Bragg's formula, and the sample SP is rotated in-plane. The diffraction intensity is measured by swinging around the angle φ axis (scan around the C axis (in-plane φ scan)). From the variation in the measured diffraction intensity, the variation (twist) of the crystal orientation in the in-plane direction of the crystal, which is the sample SP, can be evaluated.

In the in-plane measurement, the peak intensity values can be relatively compared by unifying the conditions of the measurement optical system such as the incident angle, the entrance slit width, and the length limiting slit width, and matching the X-ray irradiation area. . In this case, the peak intensity value is presumed to depend, for example, on the volume (average thickness) of the gallium nitride single crystal layer 130 (that is, gallium nitride single crystal) present in the X-ray irradiation region.

In the gallium nitride single crystal film, the growth anisotropy greatly differs between the lamination direction and the in-plane direction. Therefore, when evaluating the crystallinity of the gallium nitride single crystal layer 130 composed of a gallium nitride single crystal, it is important to separate the stacking direction (tilt) and the in-plane direction (twist) of the crystal for precise analysis. be. The full width at half maximum (FWHM) of the tilt peak of the gallium nitride single crystal film (gallium nitride single crystal layer 130) is 0.05° or more and 1.1°. or less, preferably 0.05° or more and 0.94° or less, more preferably 0.05° or more and 0.22° or less.

Further, the full width at half maximum of the twist peak of the gallium nitride single crystal film (gallium nitride single crystal layer 130) (hereinafter also simply referred to as “twist width”) is 0.1° or more and 0.78° or less, preferably , 0.1° or more and 0.42° or less, more preferably 0.1° or more and 0.3° or less.

Thus, it can be understood that the semiconductor substrate 100 according to the present embodiment has high crystallinity because the tilt width and twist width of the gallium nitride single crystal layer 130 are small.

[Characteristics of sapphire substrate 110, buffer layer 120, and gallium nitride single crystal layer 130]
As described above, the sapphire substrate 110 is made of sapphire single crystal, the buffer layer 120 is made of a metal oxide crystal layer with a spinel crystal structure, and the gallium nitride single crystal layer 130 is made of gallium nitride single crystal. Configured. The crystal axis orientations of the sapphire single crystal, the metal oxide crystal layer having the spinel crystal structure, and the gallium nitride single crystal in the semiconductor substrate 100 will be described below.

The orientation of the crystal axis of the sapphire single crystal forming the sapphire substrate 110, the metal oxide crystal layer having a spinel crystal structure forming the buffer layer 120, and the gallium nitride single crystal forming the gallium nitride single crystal layer 130 is For example, it can be obtained from the results of in-plane measurement (2θχ-φ measurement and φ scan (twist measurement)) by the X-ray analysis device 20 and out-of-plane measurement by the X-ray analysis device 10 .

More specifically, diffraction from a lattice plane orthogonal to the surface of the sample SP is measured by in-plane wide-angle 2θχ-φ measurement by the X-ray analyzer 20 shown in FIG. By increasing the incident angle of the X-rays with respect to the surface of the sample SP, the penetration depth of the X-rays is increased, and signals from deeper layers can be obtained. For this reason, in the X-ray analysis apparatus 20, measurements are performed by greatly changing the incident angle of X-rays with respect to the surface of the sample SP. The X-ray penetration depth is determined by the X-ray incident angle and the X-ray linear absorption coefficient of the sample SP.

The X-ray analysis apparatus 20 uses a parallel beam optical system, and performs measurement in an in-plane arrangement that includes X-ray incidence and diffraction in the plane of the sample SP (semiconductor substrate 100). In addition, unlike the twist measurement shown in FIG. 3, the in-plane diffraction angle (2θχ) and the in-plane rotation axis (φ) are interlocked so as to satisfy Bragg's diffraction formula. Note that the 2θχ-φ measurement is performed multiple times while changing the incident angle of the X-rays with respect to the surface of the sample SP. From the variation in the diffraction intensity at this time, the diffraction from the lattice plane orthogonal to the surface of the sample SP is detected, and the lattice spacing is determined from the in-plane diffraction angle (2θχ).

Then, the detector SC is fixed at the value of the obtained diffraction peak (2θχ) from the lattice plane, and the sample SP is oscillated around the in-plane rotation angle φ axis to measure the diffraction intensity (twist measurement (in-plane φ scan)). Based on the position of the obtained diffraction intensity peak, the symmetry of the lattice plane of the single crystal is confirmed.

By in-plane measurement (2θχ-φ measurement and φ scan (twist measurement)) by such an X-ray analysis device 20, the buffer layer The (110) plane of the spinel crystal structure metal oxide crystal layer forming 120 and the (11-20) plane of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 are substantially parallel. I can confirm. Here, "substantially parallel" includes not only the case where the normal directions of the two surfaces are the same, but also the case where the normal directions of the two surfaces are deviated within a predetermined angle range. Here, the predetermined angle range refers to the (110) plane of the metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120 and the gallium nitride single crystal layer in the in-plane 2θχ-φ measurement and φ scan. It is the range of angular variation including the angular error of the measurement system in which the diffraction peak of the (11-20) plane of the gallium nitride single crystal forming 130 is detected. The same applies to "substantially parallel" in the following description.

In addition, lattice planes parallel to the surface of the sample SP in the stacking direction are detected by wide-angle 2θ-ω measurement in an out-of-plane arrangement using the X-ray analysis apparatus 10 shown in FIG. As shown in FIG. 2, the X-ray analysis apparatus 10 uses a parallel beam optical system, and an out-of-plane system in which X-ray incidence and diffraction detection are performed in a plane perpendicular to the surface of the sample SP. Measurements are taken at placement. In addition, unlike the tilt measurement shown in FIG. 2, the angle (diffraction angle, 2θ) formed by the detector SC and the incident X-ray, the surface H of the sample SP and the incident X-ray are measured so as to satisfy Bragg's diffraction formula. Measurement is performed by interlocking the angle ω with the line. In the out-of-plane measurement, the penetration depth of X-rays into the sample SP is about several tens of μm. Then, the diffraction from the grating plane parallel to the surface of the sample SP is detected from the fluctuation of the diffraction intensity at this time, and the grating interval is determined from the diffraction angle (2θ).

By out-of-plane measurement (2θ-ω measurement) by such an X-ray analysis apparatus 10, the (111) plane of the metal oxide crystal layer of the spinel-type crystal structure constituting the buffer layer 120 and the gallium nitride single crystal layer It can be confirmed that the (0001) plane of the gallium nitride single crystal forming the 130 and the (0001) plane of the sapphire single crystal forming the sapphire substrate 110 are substantially parallel. Here, "substantially parallel" includes not only the case where the normal directions of the three surfaces are the same, but also the case where the normal directions of the three surfaces are deviated within a predetermined angle range. Here, in the out-of-plane 2θ-ω measurement, the predetermined angle range is the (111) plane of the metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120 in the same measurement, and the gallium nitride single crystal. The range of angular variation including the angular error of the measurement system in which the diffraction peaks of the (0001) plane of the gallium nitride single crystal forming the layer 130 and the (0001) plane of the sapphire single crystal forming the sapphire substrate 110 are detected. is. The same applies to "substantially parallel" in the following description.

Next, the orientation of crystal axes in the sapphire single crystal, the metal oxide crystal layer having the spinel crystal structure, and the gallium nitride single crystal in the semiconductor substrate 100 will be specifically described.

FIG. 4 is a diagram for explaining the crystal axis orientation of the sapphire single crystal forming the sapphire substrate 110 and the gallium nitride single crystal forming the gallium nitride single crystal layer 130 according to the present embodiment. In FIG. 4, the solid line indicates the sapphire single crystal, and the dashed line indicates the gallium nitride single crystal.

As shown in FIG. 4, sapphire single crystals and gallium nitride single crystals are hexagonal crystals. 4, in the semiconductor substrate 100, the (0001) plane (c-plane, (0001) sap in FIG. 4) of the sapphire single crystal of the sapphire substrate 110 and the gallium nitride single crystal layer 130 of the gallium nitride single crystal layer 130 The (0001) plane (c-plane, (0001) GaN in FIG. 4) of the single crystal is substantially parallel.

In the semiconductor substrate 100, the [1-100] axis ([1-100] sap in FIG. 4) of the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and the gallium nitride single crystal of the gallium nitride single crystal layer 130 The [11-20] axis ([11-20] GaN in FIG. 4) on the (0001) plane of the crystal is substantially parallel.

Similarly, in the semiconductor substrate 100, the [01-10] axis ([01-10] sap in FIG. 4) of the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and the gallium nitride of the gallium nitride single crystal layer 130 The [1-210] axis ([1-210] GaN in FIG. 4) on the (0001) plane of the single crystal is substantially parallel.

In the semiconductor substrate 100, the [−1010] axis ([−1010] sap in FIG. 4 ) in the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and the gallium nitride single crystal of the gallium nitride single crystal layer 130 The [−2110] axis ([−2110] GaN in FIG. 4) in the (0001) plane is substantially parallel.

FIG. 5 is a diagram for explaining the orientation of the crystal axis of the crystal layer of the metal oxide having the spinel crystal structure that constitutes the buffer layer 120 according to the present embodiment. As shown in FIG. 5, a single crystal with a spinel crystal structure is a cubic crystal.

Therefore, as shown in FIG. 5, in the semiconductor substrate 100, the (111) plane ((111) spi in FIG. ) are indicated by equilateral triangles. Moreover, each direction of [1-10] spi, [-101] spi, and [01-1] spi forms 120° in the (111) plane, and there is a 3-fold symmetry relationship.

In the semiconductor substrate 100, the (111) plane of the metal oxide crystal layer of the spinel crystal structure forming the buffer layer 120 is the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and the nitride of the gallium nitride single crystal layer 130. It is substantially parallel to the (0001) plane of the gallium single crystal.

FIG. 6 shows a sapphire single crystal forming the sapphire substrate 110 according to the present embodiment, a metal oxide crystal layer having a spinel crystal structure forming the buffer layer 120, and a gallium nitride forming the gallium nitride single crystal layer 130. It is a figure explaining the direction of the crystal axis of a single crystal.

As described above, in the semiconductor substrate 100, the (111) plane of the metal oxide crystal layer of the spinel crystal structure forming the buffer layer 120 is the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and the gallium nitride single crystal layer. It is substantially parallel to the (0001) plane of the gallium nitride single crystal of the crystal layer 130 . Therefore, as shown in FIG. 6, in the semiconductor substrate 100, the [111] axis ( , [111] spi) is the [0001] axis normal to the (0001) plane of the sapphire substrate 110 ([0001] sap in FIG. 6), and the nitridation of the gallium nitride single crystal layer 130 It is substantially parallel to the [0001] axis ([0001] GaN in FIG. 6) normal to the (0001) plane of the gallium single crystal.

That is, the semiconductor substrate 100 according to the present embodiment has the (0001) plane of the sapphire single crystal forming the sapphire substrate 110 and the (111) plane of the specific metal oxide crystal layer of the spinel crystal structure forming the buffer layer 120 . ) plane and the (0001) plane of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 are substantially parallel to each other. As noted above, near-parallel is the range of angular variation over which diffraction peaks are detected in out-of-plane 2θ-ω measurements.

Further, in the semiconductor substrate 100, the [1-10] axis ([1-10] spi in FIG. [1-100] axis ([1-100] sap in FIG. 6) on the (0001) plane of the sapphire single crystal of the sapphire substrate 110 and on the (0001) plane of the gallium nitride single crystal of the gallium nitride single crystal layer 130 It is substantially parallel to the [11-20] axis ([11-20] GaN in FIG. 6). As noted above, near-parallel is the range of angular variation over which diffraction peaks are detected in in-plane 2θχ-φ measurements and φ scans.

Similarly, in the semiconductor substrate 100, the [01-1] axis ([01-1] spi in FIG. , the [01-10] axis ([01-10] sap in FIG. 6) on the (0001) plane of the sapphire single crystal of the sapphire substrate 110, and the (0001) plane of the gallium nitride single crystal of the gallium nitride single crystal layer 130 is substantially parallel to the [1-210] axis ([1-210] GaN in FIG. 6) in .

In the semiconductor substrate 100, the [−101] axis ([−101] spi in FIG. 6) in the (111) plane of the metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120 is the sapphire substrate. [−1010] axis ([−1010] sap in FIG. 6) on the (0001) plane of the sapphire single crystal of 110 and [−2110] on the (0001) plane of the gallium nitride single crystal of the gallium nitride single crystal layer 130 It is substantially parallel to the axis ([−2110] GaN in FIG. 6).

In addition, the [111] axis in the normal direction of the (111) plane of the specific metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120, relative to the (0001) plane of the sapphire single crystal of the sapphire substrate 110 The azimuth variation is 0° or more and less than 6°. As a result, in addition to the effect of alleviating lattice mismatch due to the formation of the buffer layer 120, the microcrystals of the metal oxide with the spinel crystal structure that constitute the buffer layer 120 have angular variations, so that the orientation is inherited. , can enhance the buffer effect.

In addition, the orientation variation of the [0002] axis normal to the (0002) plane of the gallium nitride single crystal layer 130 with respect to the (0001) plane of the sapphire single crystal of the sapphire substrate 110 is 0°. more than or equal to less than 1.2°. It is believed that the initial growth layer of gallium nitride is formed while inheriting the orientation along the angular variation of the metal oxide microcrystals of the spinel crystal structure that constitutes the buffer layer 120. It can enhance the buffer effect.

Thus, in the semiconductor substrate 100 according to this embodiment, the [111] is substantially parallel to the [0001] axis normal to the (0001) plane of the sapphire single crystal. Therefore, the [0001] direction normal to the (0001) plane of the gallium nitride single crystal (gallium nitride single crystal layer 130) grown starting from the metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120 The axis is substantially parallel to the [111] axis normal to the (111) plane of the metal oxide crystal layer of the spinel crystal structure forming the buffer layer 120 . Therefore, the [0001] axis normal to the (0001) plane of the gallium nitride single crystal layer 130 grown on the buffer layer 120 is the ( 0001) plane is substantially parallel to the [0001] axis in the normal direction of the plane. That is, the buffer layer 120 can inherit the orientation (3-fold in-plane symmetry) of the sapphire single crystal of the sapphire substrate 110 to the gallium nitride single crystal of the gallium nitride single crystal layer 130 .

[Thickness of buffer layer 120]
In the semiconductor substrate 100 according to this embodiment, the thickness of the buffer layer 120 is, for example, 10 nm or more and 250 nm or less. If the thickness of the buffer layer 120 is less than 10 nm, it is considered that the sufficient effect of the buffer layer 120 is not exhibited. It is difficult to uniformly inherit the gallium nitride single crystal of the gallium nitride single crystal layer 130 over the entire area of . On the other hand, when the thickness of the buffer layer 120 exceeds 250 nm, the microcrystalline layer of the metal oxide having a spinel-type crystal structure that constitutes the buffer layer 120 grows thick, resulting in large steps and angle variations at the interface of the crystal layers. The inheritance of the orientation of the sapphire single crystal of the sapphire substrate 110 to the gallium nitride single crystal of the gallium nitride single crystal layer 130 is deteriorated.

Therefore, by setting the thickness of the buffer layer 120 to 10 nm or more and 250 nm or less, the buffer layer 120 ensures that the gallium nitride single crystal of the gallium nitride single crystal layer 130 inherits the orientation of the sapphire single crystal of the sapphire substrate 110. becomes possible.

[Lattice Constant of Crystal Layer of Metal Oxide with Spinel Crystal Structure Constituting Buffer Layer 120]
As described above, the buffer layer 120 is composed of a metal oxide crystal layer having a spinel crystal structure, and the gallium nitride single crystal layer 130 is composed of a gallium nitride single crystal. The lattice constant of such a single crystal can be calculated, for example, by X-ray diffraction using the X-ray analysis apparatus 10 described above. The X-ray diffraction measurement can be performed, for example, by the fully automatic horizontal multi-purpose X-ray analyzer "SmartLab 3XG 9MTP" manufactured by Rigaku Corporation.

Specifically, using the 2D wide area reciprocal lattice map analysis package of the fully automatic horizontal multipurpose X-ray analyzer "SmartLab 3XG 9MTP" manufactured by Rigaku Corporation, [0001] of the sapphire single crystal constituting the sapphire substrate 110 The semiconductor substrate 100 is tilted with the axis toward the (11-20) plane orientation flat (χ direction scanning), 2θ/ω is in the range of 18° to 80°, and χ is in the range of -7.5° to 67.5°. , to measure the distribution of reciprocal lattice points. Then, the image data obtained by the detector SC is converted into data for creating a reciprocal lattice map, and the coordinates are transformed into the orthogonal coordinate system (Qx, Qz) of the reciprocal lattice space to obtain the reciprocal lattice map. Next, the correspondence between the sapphire single crystal in the sapphire substrate 110, the metal oxide crystal layer of the spinel crystal structure in the buffer layer 120, and the stacking axis of the gallium nitride single crystal in the gallium nitride single crystal layer 130, and the X-ray A reciprocal lattice simulation is performed taking into consideration the incident and outgoing methods of , and is displayed superimposed on the reciprocal lattice map. The reciprocal lattice points obtained from the reciprocal lattice map are allocated from the reciprocal lattice simulation results, and the reciprocal lattice points (Qx, Qz) coordinates of the (111) plane of the metal oxide crystal layer of the spinel crystal structure in the buffer layer 120 are , the lattice constant a _spi of the metal oxide crystal layer of the spinel crystal structure is calculated.

The lattice constant a _spi of the metal oxide crystal layer of the spinel crystal structure in the buffer layer 120 calculated by X-ray diffraction is 8.050 to 8.338 Å. Specifically, the lattice constant a _spi of MgAl ₂ O ₄ with a spinel crystal structure is 8.094 Å. The lattice constant a _spi of (MgMn)Al ₂ O ₄ with a spinel crystal structure is 8.141 Å. The lattice constant a _spi of MnAl ₂ O ₄ with spinel crystal structure is 8.170-8.338 Å.

Further, the lattice constant a _spi of NiAl ₂ O ₄ having a spinel crystal structure is 8.050 Å. The lattice constant a _spi of ZnAl ₂ O ₄ with spinel crystal structure is 8.062 Å. The lattice constant a _spi of CuAl ₂ O ₄ with spinel crystal structure is 8.064 Å. The lattice constant a _spi of FeAl ₂ O ₄ with spinel crystal structure is 8.119 Å. The lattice constant a _spi of CoAl ₂ O ₄ with a spinel crystal structure is 8.080 Å.

Also, the lattice constant a _spi of MgGa ₂ O ₄ with a spinel crystal structure is 8.280 Å. The lattice constant a _spi of ZnGa ₂ O ₄ with spinel crystal structure is 8.330 Å.

The lattice constant a _spa of the sapphire single crystal forming the sapphire substrate 110 is 4.758 Å. The lattice constant a _gan of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 is 3.189 Å.

That is, 1/(2√2) times the lattice constant a _spi of the specific metal oxide crystal layer of the spinel crystal structure that constitutes the buffer layer 120 is the lattice constant a of the sapphire single crystal that constitutes the sapphire substrate 110. It is a value between 1/√3 times _sap and the lattice constant a _gan of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 .

In other words, the lattice constant a _spi of the crystal layer of the specific metal oxide with the spinel crystal structure forming the buffer layer 120, the lattice constant a _sap of the sapphire single crystal forming the sapphire substrate 110, and the gallium nitride single crystal layer 4. The semiconductor substrate according to claim 2, wherein the gallium nitride single crystal forming 130 has a lattice constant a _gan that satisfies the following formula (1).
(1/√3)×a _sap <(1/(2√2))×a _spi <a _gan (Formula 1)

From the lattice constant calculated in this way, using the following (Equation 2), the crystal layer of a specific metal oxide with a spinel crystal structure that constitutes the buffer layer 120 and the nitride that constitutes the gallium nitride single crystal layer 130 The amount of lattice mismatch (mismatch) with the gallium single crystal is calculated.
Lattice mismatch amount = [(lattice constant a _spi )/(2√2)-(lattice constant a _gan )]/(lattice constant a _gan ) (Formula 2)

For example, if the specific metal oxide is MgAl ₂ O ₄ , the lattice mismatch amount will be −10.30%. Also, when the specific metal oxide is (MgMn)Al ₂ O ₄ , the amount of lattice mismatch is −10.3% to −8.30%. If the specific metal oxide is MnAl ₂ O ₄ , the amount of lattice mismatch is −8.30%.

That is, since the lattice constant a _spi of the crystal layer of the metal oxide with the spinel crystal structure in the buffer layer 120 is 8.050 to 8.338 Å, the specific metal oxide with the spinel crystal structure that constitutes the buffer layer 120 The absolute value of the amount of lattice mismatch between the crystal layer of the material and the gallium nitride single crystal forming the gallium nitride single crystal layer 130 is less than 10.8%. On the other hand, the amount of lattice mismatch between the sapphire single crystal and the gallium nitride single crystal is about -13.8%.

As described above, in the semiconductor substrate 100 according to the present embodiment, the gallium nitride single crystal layer 130 and the spinel-type crystal structure metal oxide crystal layer forming the buffer layer 120 serving as the starting point for the growth of the gallium nitride single crystal are formed. The amount of lattice mismatch with the constituting gallium nitride single crystal is smaller than the amount of lattice mismatch between the sapphire single crystal and the gallium nitride single crystal. Therefore, when the gallium nitride single crystal layer 130 is indirectly grown on the sapphire substrate 110 through the buffer layer 120 as in the present embodiment, the gallium nitride single crystal layer 130 is directly grown on the sapphire substrate 110. , the crystallinity of the gallium nitride single crystal layer 130 can be improved.

[Concentration of Specific Metal Atoms Other than Al in Buffer Layer 120]
The buffer layer 120 according to the present embodiment contains a total of 1 at % (atomic %) of specific metal atoms other than Al contained in metal oxides with a spinel crystal structure.

This promotes ion exchange and promotes the development of a spinel structure.

[Threading dislocation density of gallium nitride single crystal layer 130]
Next, the threading dislocation density of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 according to this embodiment will be described. The threading dislocation density of such a single crystal can be calculated from an image obtained by a transmission electron microscope (TEM). The threading dislocation density can be calculated from an image obtained by a transmission electron microscope "JEM-ARM200" manufactured by JEOL Ltd., for example.

Specifically, first, a sample for cross-sectional observation of the gallium nitride single crystal layer 130 is cut out from the semiconductor substrate 100 using a focused ion beam apparatus (FIB). Note that the cutting orientation and observation orientation are aligned so that the thickness direction of the sample coincides with the [1-100] axis orientation of the gallium nitride single crystal composing the gallium nitride single crystal layer 130 . The growth direction of the sample corresponds to the [0001] axis orientation of the gallium nitride single crystal forming the gallium nitride single crystal layer 130, and the longitudinal (width) direction corresponds to the [11-20] axis orientation.

Thus, the cut sample is observed by TEM, and the number of dislocations is determined from the bright-field image. The threading dislocation density is evaluated by the number of dislocations per unit area (cm ² ) obtained by dividing the number of threading dislocations vertically in the growth direction by the cross-sectional area of the sample. For example, if the thickness of the sample is 100 nm and one threading dislocation with a width of 10 μm is confirmed, the threading dislocation density is calculated as 1×10 ⁸ [cm ⁻² ].

The threading dislocation density of the gallium nitride single crystal forming the gallium nitride single crystal layer 130 in the semiconductor substrate 100 according to the present embodiment is 5.7×10 ⁹ [cm ⁻² ] or less, for example, 8.4×10 ⁷ [cm −2 ] or less. cm ⁻² ] or more and 5.7×10 ⁹ [cm ⁻² ] or less.

Thus, it can be understood that the semiconductor substrate 100 according to the present embodiment has high crystallinity because the threading dislocation density of the gallium nitride single crystal layer 130 is low.

[Manufacturing method of semiconductor substrate 100]
Next, a method for manufacturing the semiconductor substrate 100 according to this embodiment will be described.

In the method for manufacturing the semiconductor substrate 100 according to the present embodiment, metal gallium, iron nitride, and a specific metal material are heated and melted, and the nitriding action of the iron nitride is used to obtain, on the sapphire substrate 110 as a crystal growth substrate, A method for manufacturing a buffer layer 120 and a gallium nitride single crystal layer 130. FIG. According to the above method, the buffer layer 120 is formed on the sapphire substrate 110 under a lower pressure (for example, normal pressure) environment compared to the conventional liquid phase growth, and the gallium nitride single crystal (nitride A gallium single crystal layer 130) can be liquid phase epitaxially grown on the buffer layer 120. FIG.

[Reaction material]
First, reaction materials used in the method for producing a gallium nitride single crystal according to this embodiment will be described. Metallic gallium, iron nitride, and certain metallic materials are used as reactive materials.

It is preferable to use metal gallium of high purity. For example, commercially available metal gallium with a purity of 99.99% or more can be used.

Iron nitride can be specifically tetrairon mononitride (Fe ₄ N), triiron mononitride (Fe ₃ N), diiron mononitride (Fe ₂ N), or a mixture of two or more thereof. can. It is preferable to use high-purity iron nitride, and for example, commercially available iron nitride with a purity of 99.9% or more can be used.

The iron atoms in the iron nitride are mixed with metallic gallium and heated to function as a catalyst to generate active nitrogen from nitrogen atoms in the iron nitride or nitrogen molecules in the melt. The generated active nitrogen reacts with metal gallium to form a gallium nitride single crystal.

Specifically, when tetrairon mononitride is used as the iron nitride, iron nitride and metal gallium react with the nitriding action of tetrairon mononitride to form gallium nitride (reaction formula 1).
Fe ₄ N+13Ga→GaN+4FeGa ₃ Reaction Formula 1

Nitrogen and metallic gallium dissolved in a nitrogen atmosphere or in a melt from iron nitride react with each other as iron atoms function as catalysts to form gallium nitride (reaction formula 2).
2Ga+N ₂ +Fe→2GaN+Fe Reaction formula 2

The proportion of iron nitride in the reaction material is preferably 2 mol % or less with respect to the total number of moles of metallic gallium, iron nitride, and the specific metal material. If the proportion of iron nitride exceeds 2 mol %, the amount of alloying between the iron atoms in the iron nitride and metallic gallium increases, and the viscosity of the melt obtained by melting the reaction material increases. As a result, the growth rate of the gallium nitride single crystal decreases, so it is not preferable for the proportion of iron nitride to exceed 2 mol %.

The specific metal material is a specific metal itself or a compound of a specific metal that has a spinel crystal structure. Specific metals are, for example, one or more selected from the group consisting of Mg, Fe, Mn, Ni, Co, Cu, and Zn.

When the specific metal itself is used as the specific metal material, it is preferable to use a specific metal material of high purity, for example, a commercially available product with a purity of 99.9% or more can be used.

When using a specific metal compound as the specific metal material, the specific metal material is a nitride, oxide, or chloride of the specific metal. When the specific metal is magnesium, magnesium compounds are, for example, magnesium nitride _{( Mg3N2} ), magnesium oxide, magnesium chloride. When the specific metal is manganese, manganese compounds are, for example, manganese nitride, manganese oxide (MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ ), manganese chloride.

The specific metal material in the reaction material is preferably one or both of a specific metal and a specific metal nitride. By using one or both of the specific metal and the nitride of the specific metal as the reaction material, impurities contained in the gallium nitride single crystal layer 130 can be reduced.

The proportion of the specific metal material in the reaction material is preferably less than 0.5 mol % with respect to the total number of moles of metallic gallium, iron nitride and the specific metal material. If the ratio of the specific metal material is 0.5 mol % or more, the crystallinity of the gallium nitride single crystal is lowered, which is not preferable.

[Reactor]
Next, with reference to FIG. 7, the reactor used in the method for producing a gallium nitride single crystal according to this embodiment will be described. FIG. 7 is a schematic diagram showing the configuration of a reactor 200 used for producing gallium nitride single crystals according to this embodiment.

As shown in FIG. 7 , the reactor 200 includes an electric furnace 210 , a heater 212 provided on the side of the electric furnace 210 , a gas introduction port 220 , a gas exhaust port 222 and a rotating shaft 230 . Further, inside the electric furnace 210, a frame 242 is provided for mounting a reaction vessel 240 containing the raw material melt M of the reaction material. A sapphire substrate 110 on which a gallium nitride single crystal is grown is horizontally attached to the lower end of the rotating shaft 230 . That is, the reaction apparatus 200 is an apparatus for epitaxially growing a gallium nitride single crystal layer 130 (gallium nitride single crystal film) on a sapphire substrate 110 immersed in a raw material melt M obtained by melting a reaction material.

The electric furnace 210 has a closed structure and accommodates a reaction vessel 240 inside. The electric furnace 210 is, for example, a tubular structure with an inner diameter (diameter) of about 200 mm and a height of about 800 mm.

The heater 212 is arranged on the longitudinal side of the electric furnace 210 and heats the inside of the electric furnace 210 .

A gas introduction port 220 is provided in the upper portion of the electric furnace 210 . The gas inlet 220 introduces atmospheric gas into the electric furnace 210 . The atmosphere gas is, for example, nitrogen (N ₂ ) gas or argon (Ar). A gas exhaust port 222 is provided in the lower portion of the electric furnace 210 . The gas exhaust port 222 exhausts the ambient gas from inside the electric furnace 210 . Gas introduction port 220 and gas exhaust port 222 keep the pressure inside electric furnace 210 at substantially normal pressure (that is, atmospheric pressure).

The pedestal 242 is a member that supports the reaction vessel 240 . Specifically, the pedestal 242 supports the reaction vessel 240 so that the reaction vessel 240 is evenly heated by the heater 212 . For example, the height of the pedestal 242 is such that the reaction vessel 240 is positioned at the center of the heater 212 .

The reaction vessel 240 is a vessel that holds the raw material melt M in which the reaction material is melted. The reaction container 240 is, for example, a cylindrical container with an outer diameter (diameter) of about 100 mm, a height of about 90 mm, and a thickness of about 5 mm. The reaction vessel 240 is made of carbon, for example. By forming the reaction vessel 240 from carbon, it is possible to avoid a situation in which impurities such as oxygen are mixed into the reaction material. Note that the reaction vessel 240 is not limited to carbon, and may be made of a material that does not react with metal gallium at a high temperature of about 1000° C., such as aluminum oxide.

The raw material melt M is a liquid obtained by melting the reaction material. Specifically, the raw material melt M is a liquid obtained by heating and melting reaction materials such as metal gallium, iron nitride, and a specific metal material by the heater 212 . In addition, as described above, the mixing ratio of metal gallium, iron nitride, and the specific metal material as reaction materials is such that the number of moles of iron nitride is 2% or less with respect to the total number of moles of metal gallium and iron nitride. , the number of moles of the specific metal material is preferably less than 0.5%.

The sapphire substrate 110 is a substrate on which a gallium nitride single crystal film can be laminated. The sapphire substrate 110 may be, for example, a flat plate shape such as a disk or rectangular plate. However, the shape of the sapphire substrate 110 is not limited to this example.

A rotating shaft 230 is provided on the upper portion of the electric furnace 210 . The rotating shaft 230 has, for example, a plurality of hooks for holding the sapphire substrate 110 at its lower end, and holds the sapphire substrate 110 horizontally. In this embodiment, the sapphire substrate 110 attached to the rotating shaft 230 is immersed in the raw material melt M or pulled up from the raw material melt M by vertically moving the rotating shaft 230 .

Note that the rotating shaft 230 may be provided rotatably around the axis. By rotating the rotating shaft 230, the sapphire substrate 110 can be rotated and the raw material melt M can be stirred. Thereby, the nitrogen concentration distribution in the raw material melt M can be made more uniform, and a more uniform gallium nitride single crystal film can be grown on the sapphire substrate 110 .

Further, as described above, the rotating shaft 230 according to the present embodiment holds the sapphire substrate 110 horizontally with respect to the liquid surface of the raw material melt M. As shown in FIG. Thereby, the influence of the nitrogen concentration distribution in the depth direction of the raw material melt M on the sapphire substrate 110 can be reduced. Therefore, the reactor 200 can grow a gallium nitride single crystal film on the sapphire substrate 110 more uniformly.

The rotating shaft 230 is made of carbon, for example, like the reaction vessel 240 . By forming the rotating shaft 230 from carbon, it is possible to avoid a situation in which impurities such as oxygen are mixed into the reaction material. The rotary shaft 230 is not limited to carbon, and may be made of other materials such as aluminum oxide that do not react with metallic gallium at high temperatures around 1000°C.

As described above, the reactor 200 moves the rotating shaft 230 up and down to immerse the sapphire substrate 110 in the raw material melt M, thereby forming a gallium nitride single crystal film (gallium nitride single crystal layer 130) on the sapphire substrate 110. can grow.

As a result, the reaction apparatus 200 can stack a gallium nitride single-crystal film (gallium nitride single-crystal layer 130) having the same crystal orientation as the sapphire substrate 110 (that is, epitaxially grown) on the sapphire substrate 110. Become.

[Production method]
Next, the flow of the method for manufacturing the semiconductor substrate 100 according to this embodiment will be described. FIG. 8 is a flow chart for explaining the flow of processing in the method for manufacturing the semiconductor substrate 100 according to this embodiment. The manufacturing method of the semiconductor substrate 100 according to this embodiment includes a melt generation step S110, an immersion step S120, a holding step S130, and a purification step S140. Each step will be described below.

[Melt generation step S110]
First, metal gallium, iron nitride, and powders of a specific metal material are mixed and filled in the reaction vessel 240 described above, and the reaction vessel 240 is placed in the electric furnace 210 .

Subsequently, the atmosphere gas is introduced into the electric furnace 210 through the gas inlet 220 to create a nitrogen atmosphere in the electric furnace 210 , and the reaction material in the reaction vessel 240 is heated by the heater 212 . Since the atmosphere gas introduced into the electric furnace 210 through the gas inlet 220 is discharged through the gas exhaust port 222, the pressure inside the electric furnace 210 is maintained at substantially normal pressure.

Here, the reaction materials in reaction vessel 240 are heated to at least the reaction temperature at which metallic gallium, iron nitride, and certain metal materials react. Specifically, such a reaction temperature is 300° C. or higher and 1000° C. or lower, preferably 700° C. or higher and 1000° C. or lower.

Thus, under the nitrogen atmosphere, the reaction material in the reaction vessel 240 is melted, and the raw material melt M is produced.

[Immersion step S120]
The sapphire substrate 110 held by the rotating shaft 230 is immersed in the raw material melt M by operating the rotating shaft 230 .

[Holding step S130]
With the sapphire substrate 110 held by the rotary shaft 230 immersed in the raw material melt M, the raw material melt M in the reaction vessel 240 is held within the reaction temperature range for 20 hours or more and 100 hours or less. As a result, the buffer layer 120 and a uniform single crystal film of gallium nitride can be grown on the sapphire substrate 110 immersed in the raw material melt M.

In the holding step S130, the temperature of the raw material melt M (reaction material) does not need to be constant as long as it is within the reaction temperature range (for example, 300° C. or higher and 1000° C. or lower). may be

[Purification step S140]
However, the reaction products obtained by executing the melt generation step S110 to the holding step S130 include by-products such as intermetallic compounds of iron and gallium, and intermetallic compounds of specific metals and gallium. It may contain objects. Therefore, the sapphire substrate 110 on which the gallium nitride single crystal is deposited is subjected to the refining step S140 to remove the by-products.

For the purification step S140, for example, acid washing using an acid such as aqua regia can be used. As a result, an intermetallic compound of iron and gallium, an intermetallic compound of a specific metal and gallium, and the like can be dissolved in acid to refine the gallium nitride single crystal (gallium nitride single crystal layer 130).

As described above, the method for manufacturing the semiconductor substrate 100 according to the present embodiment can efficiently manufacture a gallium nitride single crystal by liquid phase epitaxy in a low-pressure nitrogen atmosphere such as normal pressure.

In addition, the method of manufacturing the semiconductor substrate 100 according to the present embodiment may perform a step of forming a specific metal oxide film on the surface of the sapphire substrate 110 before performing the immersion step S120. In this case, in the immersion step S120, the sapphire substrate 110 on which the specific metal oxide film is formed is immersed in the melt. In addition, the process of forming a film is performed by sputtering or the like.

Examples and comparative examples of the present invention will be specifically described below. It should be noted that the embodiments shown below are merely examples, and the semiconductor substrate and the method for manufacturing the semiconductor substrate according to the present invention are not limited to the following examples.

Further, in the following examples and comparative examples, in common, metallic gallium with a purity of 7N (manufactured by DOWA Electronics Co., Ltd.), triiron mononitride with a purity of 99% or more (manufactured by Kojundo Chemical Laboratory Co., Ltd.), purity 99 % or higher magnesium nitride (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and manganese nitride with a purity of 99% or higher (manufactured by Kojundo Chemical Laboratory Co., Ltd.). As the sapphire substrate 110, a sapphire substrate (manufactured by Shinko Co., Ltd.) has a diameter of about 2 inches and a thickness of 0.4 mm, and has a (0001) plane (c-plane) on which a single crystal film of gallium nitride is laminated. ) was used.

[Example 1]
First, in a reaction vessel 240 installed inside the reaction device ₂₀₀ , each raw material of metallic gallium (Ga), triiron mononitride ( _Fe3N ), and magnesium nitride ( _Mg3N2 ) was charged into Ga: _Fe3N . :Mg ₃ N ₂ =99.75 mol %:0.2 mol %:0.05 mol % were mixed and charged. Also, the sapphire substrate 110 having the (0001) plane for forming the gallium nitride single crystal layer 130 was placed on the rotating shaft 230 .

Subsequently, by controlling the internal temperature of the reactor 200 according to the following temperature profile, metal gallium, triiron mononitride, and magnesium nitride were reacted to produce a gallium nitride single crystal.

Specifically, first, nitrogen gas (99.99% purity) was introduced into the reaction device 200 at a flow rate of 3000 mL/min, and the internal atmosphere of the reaction device 200 was set to approximately 100% nitrogen and 1 atmosphere. After manually raising the internal temperature of the reactor 200 to 200° C., the internal temperature was raised to 700° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was kept at 700° C. for 10 hours. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was raised to 880° C. at a rate of 5° C./hour and held at 880° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metallic gallium, an intermetallic compound of iron and gallium, an intermetallic compound of magnesium and gallium, and the like.

Subsequently, the above tilt measurement and twist measurement were performed on the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 laminated according to Example 1. FIG. Tilt measurement (ω scan) measures the change or dispersion of crystal orientation in the stacking direction of crystals, and the narrower the width of the peak, the smaller the dispersion of crystal orientation and the better the crystallinity.

Using the Rigaku fully automatic horizontal multi-purpose X-ray analyzer "SmartLab 3XG 9MTP" described above, X-ray incidence and diffraction detection are performed in a plane perpendicular to the surface of the sample, 2θ = 34.6 (a value calculated from the lattice spacing of the (0002) plane of gallium nitride using Bragg's equation), and the measurement was performed by ω scanning. The penetration depth of X-rays into the sample at this time is about several tens of μm.

The twist measurement (φ scan) measures the change or dispersion of the crystal orientation in the in-plane direction of the crystal, and the narrower the peak width, the smaller the dispersion of the crystal orientation and the better the crystallinity.

Using the fully automatic horizontal multipurpose X-ray analyzer "SmartLab 3XG 9MTP" manufactured by Rigaku Co., Ltd., in an arrangement in which X-ray incidence and diffraction detection are performed in a plane parallel to the sample surface, X-rays were incident at a very shallow angle with respect to . The penetration depth of the X-rays into the sample at this time is about several μm. In the twist measurement, an incident angle of 0.25°, an incident slit width of 0.1 mm, and a longitudinal limiting slit width of 5 mm were used as the conditions of the measurement optical system, and 2θχ = 57.91° (gallium nitride (11-20) plane A value calculated from the lattice spacing using Bragg's equation) was placed in the detector and measurement was performed by φ scanning.

As a result, the semiconductor substrate 100 of Example 1 had a tilt width of 0.218° and a twist width of 0.296°.

In addition, intensity peaks were observed at six-fold symmetrical positions (every 60° in-plane rotation).

Subsequently, for the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated, according to Example 1, the in-plane 2θχ-φ measurement, φ scan, and out-of-plane 2θ-ω measurement and crystallinity analysis was performed. For the measurement, the fully automatic horizontal multi-purpose X-ray analyzer "SmartLab 3XG 9MTP" manufactured by Rigaku was used.

FIG. 10 shows in-plane sapphire substrate 110 having buffer layer 120 and gallium nitride single crystal layer 130 stacked thereon according to Example 1 at an incident angle of 0.25° and at an incident angle of 0.8°. is a diagram showing wide-angle 2θχ-φ measurement results. In FIG. 10, the horizontal axis indicates the in-plane diffraction angle 2θχ, and the vertical axis indicates the X-ray intensity value. Note that the vertical axis is logarithmic. Also, for ease of comparison, the data for the incident angle of 0.25° and the data for the incident angle of 0.8° are shown shifted in the vertical axis direction.

First, a peak (diffraction A) common to the incident angle (2θ=ω=) of 0.25° and the incident angle (2θ=ω=) of 0.8° can be confirmed near 2θχ=57.9°. This corresponds to the (11-20) diffraction of gallium nitride. On the other hand, at an incident angle of 0.8°, a peak near 2θχ=31.3° (diffraction B) and a peak near 2θχ=65.7° (diffraction C) were remarkably confirmed.

Diffraction conditions near 2θχ = 31.3° (diffraction B) and near 2θχ = 65.7° (diffraction C) were searched from the ICDD card data as constituent element candidates Ga, N, Al, O, and Mg. rice field. As a result, diffraction B is the (220) plane of MgAl ₂ O ₄ having a spinel crystal structure, 2θ=31.25°, and diffraction C is the (440) plane of MgAl ₂ O ₄ having a spinel crystal structure, 2θ=65. .70° was found to be a candidate.

Next, focusing on the peak (diffraction C) near 2θχ = 65.7° that was conspicuous at an incident angle of 0.8°, the detector was placed at 2θχ = 65.7° at an incident angle of 0.8°. When a twist measurement (φ scan) was performed with the SC arranged, intensity peaks were observed at six-fold symmetrical positions (in-plane rotation at 60° intervals). Furthermore, the lattice plane obtained from the twist measurement is estimated to be the (110) plane (more precisely, the (1-10) plane) of MgAl ₂ O ₄ of the spinel crystal structure, and the (11-20) plane of gallium nitride. It was confirmed that the plane was parallel to the (10-10) plane of sapphire.

Subsequently, wide-angle 2θ-ω measurements were performed in an out-of-plane configuration to detect lattice planes parallel to the surface of the sample in the stacking direction. FIG. 11 is a diagram showing out-of-plane wide-angle 2θ-ω measurement results for the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 (gallium nitride single crystal) stacked thereon according to Example 1. . In FIG. 11, the horizontal axis indicates the diffraction angle 2θ, and the vertical axis indicates the X-ray intensity value. Note that the vertical axis is logarithmic. In order to facilitate comparison, the data of Example 1 and the data of a comparative example, which will be described later, are shown shifted in the direction of the vertical axis.

In FIG. 11, the peak (diffraction E) seen near 2θ = 34.6° is the diffraction of the (0002) plane of gallium nitride, and the peak (diffraction F) seen near 2θ = 41.7° is the diffraction of sapphire. They correspond to the diffraction of the (0006) plane, respectively. A diffraction peak (diffraction D) could be detected near 2θ=19.2° although the intensity was three orders of magnitude lower than that of diffraction E and diffraction F. As a result of peak search of diffraction D, it was found that the (111) plane of MgAl ₂ O ₄ with a spinel crystal structure, 2θ=19.20°, is a candidate for diffraction D.

The lattice plane of diffraction D is presumed to be the (111) plane of MgAl ₂ O ₄ with a spinel crystal structure, and since the measurement results in FIG. 11 are out-of-plane symmetric reflection measurements, the (0001) plane of gallium nitride (c-plane) and the (0001) plane (c-plane) of sapphire.

From the above results, according to Example 1, the sapphire single crystal forming the sapphire substrate 110, the MgAl ₂ O ₄ having a spinel crystal structure forming the buffer layer 120, and the gallium nitride forming the gallium nitride single crystal layer 130 The correspondence relationship between the axes of the single crystal is arranged as shown in the following formula (3).
[11-20] (0001) GaN // [1-10] (111) MgAl ₂ O ₄ // [1-100] (0001) Al ₂ O ₃ Formula (3)
In the above formula (3), [11-20](0001)GaN represents the [11-20] axis of the (0001) plane of the gallium nitride single crystal. [1-10](111)MgAl ₂ O ₄ indicates the [1-10] axis of the (111) plane of MgAl ₂ O ₄ in the spinel crystal structure. [1-100](0001)Al ₂ O ₃ indicates the [1-100] axis of the (0001) plane of the sapphire single crystal. Also, "//" indicates a parallel relationship.

Subsequently, the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 (gallium nitride single crystal) stacked thereon according to Example 1 was subjected to cross-sectional TEM observation to measure the threading dislocation density. For cross-sectional TEM observation, a transmission electron microscope "JEM-ARM200" manufactured by JEOL Ltd. was used.

FIG. 9 is a bright-field image of a cross-sectional TEM observation of the sapphire substrate 110 on which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated according to Example 1. FIG. As shown in FIG. 9, the gallium nitride single crystal layer 130 had a thickness of about 1.9 μm, and a discolored portion was observed on the surface of the sapphire substrate 110 . The discolored portion was confirmed to be MgAl ₂ O ₄ with a spinel crystal structure from the crystallinity analysis results shown below. That is, it was confirmed that the discolored portion was the buffer layer 120 . The thickness of the buffer layer 120 was 30 nm to 65 nm. Further, the threading dislocation density of Example 1 was 5.7×10 ⁹ [cm ⁻² ].

Subsequently, about a 200 nm region spanning from the sapphire substrate 110 to the gallium nitride single crystal layer 130, the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 (gallium nitride single crystal) are laminated according to Example 1, Line analysis was performed with an EDS (energy dispersive X-ray spectrometer).

FIG. 12 shows each element of nitrogen, oxygen, magnesium, aluminum, and gallium for the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 (gallium nitride single crystal) are stacked according to Example 1. It is a figure which shows the result of having carried out the line analysis.

As shown in FIG. 12, oxygen (O) changes at about 63 at % from the 0 point (0 nm position) of the distance on the sapphire substrate 110 side to the 100 nm position, but decreases sharply to about 4 at % toward the 110 nm position. do. Correspondingly, nitrogen (N) and gallium (Ga) rapidly increase from about 1 at% to about 65 at% from 100 nm to 110 nm. To increase. Also, aluminum (Al) changes at about 35 at % from the 0 point to about 90 nm, but its abundance gradually decreases to about 1 at % toward 110 nm. Magnesium (Mg) is present at a maximum of about 16 at % from the 90 nm position to the 110 nm position. The sum of the existing amounts of Al and Mg changes at about 35 atomic %. In addition, there is a gap between the decrease of oxygen and the decrease of Al, but since Mg is present so as to correspond to the amount of deviation, it can be said that part of Al on the sapphire surface is replaced with Mg. It is suggested.

[Example 2]
A buffer layer 120 and a gallium nitride single crystal layer 130 were grown on a sapphire substrate 110 in the same manner as in Example 1, except that the temperature profile was set under the following conditions.

Specifically, first, the internal temperature of the reactor 200 was manually raised to 200° C., and then the internal temperature was raised to 950° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was held at 950° C. for 1 hour. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was kept at 950° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metallic gallium, an intermetallic compound of iron and gallium, an intermetallic compound of magnesium and gallium, and the like.

Similar to Example 1, tilt measurement and twist measurement were performed on the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 stacked thereon according to Example 2. FIG. As a result, the semiconductor substrate 100 of Example 2 had a tilt width of 1.1° and a twist width of 0.42°. Also in Example 2, intensity peaks were observed at six-fold symmetrical positions (every 60° in-plane rotation).

Further, the sapphire substrate 110 laminated with the buffer layer 120 and the gallium nitride single crystal layer 130 according to Example 2 was subjected to cross-sectional TEM observation in the same manner as in Example 1, and the threading dislocation density was measured.

FIG. 13 is a bright-field image of cross-sectional TEM observation of the sapphire substrate 110 on which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated according to Example 2. FIG. In FIG. 3, arrows indicate threading dislocations. As shown in FIG. 13, the gallium nitride single crystal layer 130 had an average thickness of about 0.3 μm. Moreover, it was confirmed that the gallium nitride single crystal layer 130 was formed on almost the entire surface of the sapphire substrate 110 . The average thickness of buffer layer 120 was 80 nm. The threading dislocation density of Example 2 was 5.4×10 ⁹ [cm ⁻² ]. It was also confirmed that many threading dislocations tended to be formed at locations where the thickness of the buffer layer 120 was thin.

Further, the reciprocal lattice map measurement was performed for the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 laminated according to Example 2. FIG. First, reciprocal lattice points (hereinafter referred to as “spinel 111 (reciprocal lattice points)”) of the (111) plane of MgAl ₂ O ₄ having a spinel crystal structure were extracted in accordance with the reciprocal lattice simulation results. The lattice constant of MgAl ₂ O ₄ with a spinel crystal structure calculated based on the extracted reciprocal lattice points was 8.094 Å. The amount of lattice mismatch with respect to the gallium nitride single crystal in this case was −10.3%.

[Example 3]
A buffer layer 120 and a gallium nitride single crystal layer 130 were grown on a sapphire substrate 110 in the same manner as in Example 1, except that the sapphire substrate 110 was pretreated and the temperature profile was set under the following conditions. let me

Specifically, a sputtering apparatus was used to pre-process a magnesium oxide (MgO) film of 20 nm on the sapphire substrate 110 in advance. Then, on the sapphire substrate 110 on which the magnesium oxide film was formed, the buffer layer 120 and the gallium nitride single crystal layer 130 were grown with the following temperature profile.

Specifically describing the temperature profile, first, the internal temperature of the reactor 200 was manually raised to 200°C, and then the internal temperature was raised to 975°C at a rate of 100°C per hour. After that, the internal temperature of the reactor 200 was held at 975° C. for 1 hour. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was kept at 975° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metallic gallium, an intermetallic compound of iron and gallium, an intermetallic compound of magnesium and gallium, and the like.

Similar to Example 1, tilt measurement and twist measurement were performed on the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 stacked thereon according to Example 3. FIG. As a result, the semiconductor substrate 100 of Example 3 had a tilt width of 0.94° and a twist width of 0.78°. Also in Example 3, intensity peaks were observed at six-fold symmetrical positions (every 60° in-plane rotation).

Further, the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 are stacked according to Example 3 was subjected to cross-sectional TEM observation in the same manner as in Example 1, and the threading dislocation density was measured.

FIG. 14 is a bright-field image of cross-sectional TEM observation of the sapphire substrate 110 on which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated according to Example 3. FIG. In FIG. 14, arrows indicate threading dislocations. As shown in FIG. 14, the gallium nitride single crystal layer 130 had an average thickness of about 1.7 μm. Moreover, it was confirmed that the gallium nitride single crystal layer 130 was formed on almost the entire surface of the sapphire substrate 110 . The thickness of the buffer layer 120 was 150 nm to 250 nm. Further, the threading dislocation density of Example 3 was 1.4×10 ⁸ [cm ⁻² ]. It was also confirmed that many threading dislocations tended to be formed at locations where the thickness of the buffer layer 120 was thin.

Further, the reciprocal lattice map measurement was performed on the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 laminated according to Example 3. First, the spinel 111 (reciprocal lattice point) of MgAl ₂ O ₄ having a spinel crystal structure was extracted in accordance with the results of the reciprocal lattice simulation. The lattice constant of MgAl ₂ O ₄ with a spinel crystal structure calculated based on the extracted reciprocal lattice points was 8.094 Å. The amount of lattice mismatch with respect to the gallium nitride single crystal in this case was −10.3%.

[Example 4]
First, a manganese oxide (Mn ₃ O ₄ ) film of 5 nm was formed in advance on the sapphire substrate 110 using a sputtering apparatus, and heat treatment was performed at 975° C. for 1 hour in an air atmosphere. Then, the buffer layer 120 and the gallium nitride single crystal layer 130 were grown on the sapphire substrate 110 on which the manganese oxide film was formed by the reactor 200 .

Specifically, in a reaction vessel 240 installed inside the reaction device 200, each raw material of metallic gallium (Ga), triiron mononitride (Fe ₃ N), and magnesium nitride (Mg ₃ N ₂ ) is added to Ga. :Fe ₃ N:Mg ₃ N ₂ =99.85 mol %:0.1 mol %:0.05 mol %. Also, the sapphire substrate 110 having the (0001) plane for forming the gallium nitride single crystal layer 130 was placed on the rotating shaft 230 .

Subsequently, by controlling the internal temperature of the reactor 200 according to the following temperature profile, metal gallium, triiron mononitride, and magnesium nitride were reacted to produce a gallium nitride single crystal.

Specifically, first, nitrogen gas (99.99% purity) was introduced into the reaction device 200 at a flow rate of 3000 mL/min, and the internal atmosphere of the reaction device 200 was set to approximately 100% nitrogen and 1 atmosphere. After manually raising the internal temperature of the reactor 200 to 200° C., the internal temperature was raised to 975° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was held at 975° C. for 1 hour. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was kept at 975° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metal gallium, an intermetallic compound of iron and gallium, an intermetallic compound of magnesium and gallium, or an intermetallic compound of manganese and gallium.

For the buffer layer 120 according to Example 4, the in-plane 2θχ-φ measurement was performed in the same manner as in Example 1. FIG. In the 2θχ-φ measurement, when the X-ray incident angle (2θ=ω) is larger than 0.4°, the diffraction of the (440) plane of MnAl ₂ O ₄ with a spinel crystal structure can be captured at 2θχ=65.8°. did it. It was also confirmed that the (440) plane of MnAl ₂ O ₄ with a spinel-type crystal structure exhibits 6-fold symmetry with in-plane φ rotation. In the case of a single crystal with a single spinel crystal structure, the (440) plane should be confirmed three times at intervals of 120° around the [111] axis (three-fold symmetry). However, since six-fold symmetry is confirmed in Example 4, this is considered to be a result suggesting the existence of twin crystals shifted by 30° in the plane.

Further, the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 are stacked according to Example 4 was subjected to cross-sectional TEM observation in the same manner as in Example 1, and the threading dislocation density was measured.

As a result, the gallium nitride single crystal layer 130 had an average thickness of about 0.28 μm. Moreover, it was confirmed that the gallium nitride single crystal layer 130 was formed on almost the entire surface of the sapphire substrate 110 . The average thickness of buffer layer 120 was 70 nm. The threading dislocation density of Example 4 was 2.2×10 ⁹ [cm ⁻² ].

Subsequently, the reciprocal lattice map measurement was performed on the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 were laminated according to Example 4. FIG. FIG. 15 is a diagram showing reciprocal lattice map measurement results of the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 stacked thereon according to Example 4. FIG.

The reciprocal lattice simulation was performed with the lamination axis correspondence relationship and the X-ray incident and outgoing direction of the gallium nitride single crystal, MnAl ₂ O ₄ having a spinel crystal structure, and the sapphire single crystal in the relationship shown in the following formula (4).
[−1100] (0001) GaN // [010] (111) MnAl ₂ O ₄ // [11-20] (0001) Al ₂ O ₃ Formula (4)
In the above formula (4), [−1100](0001)GaN represents the [−1100] axis of the (0001) plane of the gallium nitride single crystal. [010] (111) MnAl ₂ O ₄ indicates the [010] axis of the (111) plane of MnAl ₂ O ₄ in the spinel crystal structure. [11-200](0001)Al ₂ O ₃ indicates the [11-20] axis of the (0001) plane of the sapphire single crystal. Also, "//" indicates a parallel relationship. It shows that the X-ray incident direction in this case is also parallel.

Each reciprocal lattice point of the reciprocal map measurement was assigned from the reciprocal lattice simulation results. First, corresponding to the reciprocal lattice simulation results, the spinel 111 (reciprocal lattice point) of MnAl ₂ O ₄ having a spinel crystal structure and the reciprocal lattice point (nitriding point) of the (0002) plane of gallium nitride on the line of Qx=0 Gallium 0002 (reciprocal lattice point)) and the reciprocal lattice point of the (0006) plane of sapphire (sapphire 0006 (reciprocal lattice point)) were confirmed, and they were confirmed to exist parallel to the stacking direction of the substrate. As a result of extracting the spinel 111 (reciprocal lattice point) of MnAl ₂ O ₄ having a spinel crystal structure, a diffraction peak was detected at the position of Qz=0.2127 corresponding to 2θ=18.88°. The lattice constant of MnAl ₂ O ₄ with a spinel crystal structure was calculated to be 8.141 Å from the relational expression of d=1/Qz. The amount of lattice mismatch with respect to gallium nitride in this case was -9.7%.

In addition, as shown in FIG. 15, in comparison with the reciprocal lattice simulation results, in the spinel crystal structure, the reciprocal lattice point of the (131) plane of MnAl ₂ O ₄ of the spinel crystal structure (spinel 131 (reciprocal lattice point) ) and a reciprocal lattice point (spinel 040 (reciprocal lattice point)) of the (040) plane of MnAl ₂ O ₄ having a spinel crystal structure.

Since the reciprocal lattice points of sapphire, MnAl ₂ O ₄ having a spinel crystal structure, and gallium nitride are confirmed in accordance with the results of the reciprocal lattice simulation, the set stack axis correspondence relationship and the X-ray incident/exit relationship can be calculated. It can be said that the inheritance of the orientation relationship is in a good state. On the other hand, the reciprocal lattice point (spinel 202 (reciprocal lattice point)) of the (202) plane of MnAl ₂ O ₄ with the spinel crystal structure and the (reciprocal lattice point) of MnAl ₂ O ₄ with the spinel crystal structure, which do not exist in the reciprocal lattice simulation results, 404) plane reciprocal lattice points (spinel 404 (reciprocal lattice points)) were also confirmed. This reciprocal lattice point appears when the X-ray incident direction is parallel to the MnAl ₂ O ₄ [0-10] axis of the spinel crystal structure. It shows that it exists.

[Example 5]
A buffer layer 120 and a gallium nitride single crystal layer 130 were grown on a sapphire substrate 110 in the same manner as in Example 4, except that the mixing ratio of raw materials and the temperature profile were set as follows.

Raw materials of metallic gallium (Ga), triiron mononitride (Fe ₃ N), and metallic manganese (Mn) were placed in a reaction vessel 240 installed inside the reactor 200 in a ratio of Ga:Fe ₃ N:Mn=97. They were mixed at a ratio of 9 mol %:0.1 mol %:2 mol % and charged.

Specifically describing the temperature profile, first, the internal temperature of the reactor 200 was manually raised to 200° C., and then the internal temperature was raised to 880° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was held at 880° C. for 1 hour. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was maintained at 880° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metallic gallium, an intermetallic compound of iron and gallium, an intermetallic compound of manganese and gallium, and the like.

Further, the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated according to Example 5 was subjected to cross-sectional TEM observation in the same manner as in Example 1, and the threading dislocation density was measured.

As a result, the gallium nitride single crystal layer 130 had an average thickness of about 1.1 μm. Moreover, the average thickness of the buffer layer 120 was 50 nm. The threading dislocation density of Example 5 was 8.4×10 ⁷ [cm ⁻² ].

Subsequently, the above reciprocal lattice map measurement was performed in the same manner as in Example 4 for the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 laminated according to Example 5. First, the spinel 111 (reciprocal lattice point) of MnAl ₂ O ₄ having a spinel crystal structure was extracted in accordance with the results of the reciprocal lattice simulation. The lattice constant of MnAl ₂ O ₄ with a spinel crystal structure calculated based on the extracted reciprocal lattice points was 8.170 Å. The amount of lattice mismatch with respect to the gallium nitride single crystal in this case was −9.4%.

[Example 6]
A buffer layer 120 and a gallium nitride single crystal layer 130 were grown on a sapphire substrate 110 in the same manner as in Example 5, except that the temperature profile was set under the following conditions.

Specifically, first, the internal temperature of the reactor 200 was manually raised to 200° C., and then the internal temperature was raised to 700° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was held at 700° C. for 1 hour. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was raised to 880° C. at a rate of 100° C./hour and held at 880° C. for 20 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction container 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metallic gallium, an intermetallic compound of iron and gallium, an intermetallic compound of manganese and gallium, and the like.

Further, the sapphire substrate 110 in which the buffer layer 120 and the gallium nitride single crystal layer 130 are laminated according to Example 6 was subjected to cross-sectional TEM observation in the same manner as in Example 1, and the threading dislocation density was measured.

As a result, the gallium nitride single crystal layer 130 had an average thickness of about 1.3 μm. Moreover, the average thickness of the buffer layer 120 was 40 nm. Further, the threading dislocation density of Example 5 was 1.3×10 ⁸ [cm ⁻² ].

Subsequently, the above-described reciprocal lattice map measurement was performed in the same manner as in Example 5 for the sapphire substrate 110 having the buffer layer 120 and the gallium nitride single crystal layer 130 laminated according to Example 6. First, the spinel 111 (reciprocal lattice point) of MnAl ₂ O ₄ having a spinel crystal structure was extracted in accordance with the results of the reciprocal lattice simulation. The lattice constant of MnAl ₂ O ₄ with a spinel crystal structure calculated based on the extracted reciprocal lattice points was 8.454 Å. The amount of lattice mismatch with respect to the gallium nitride single crystal in this case was -6.3%.

[Comparative example]
Metallic gallium (Ga) and triiron mononitride (Fe ₃ N) were added to a reaction vessel 240 installed inside the reactor 200 at a ratio of Ga:Fe ₃ N = 99.95 mol%: 0.05 mol%. The sapphire substrate 110 having the (0001) plane for forming the gallium nitride single crystal layer 130 was placed on the rotating shaft 230 .

Subsequently, by controlling the internal temperature of the reactor 200 according to the following temperature profile, metallic gallium and triiron mononitride were reacted to produce a gallium nitride single crystal.

Specifically, first, nitrogen gas (99.99% purity) was introduced into the reaction device 200 at a flow rate of 3000 mL/min, and the internal atmosphere of the reaction device 200 was set to approximately 100% nitrogen and 1 atmosphere. After manually raising the internal temperature of the reactor 200 to 200° C., the internal temperature was raised to 700° C. at a rate of 100° C. per hour. After that, the internal temperature of the reactor 200 was kept at 700° C. for 20 hours. During this time, the sapphire substrate 110 was held above the raw material melt M. After that, the sapphire substrate 110 was immersed in the raw material melt M, and the internal temperature of the reactor 200 was raised to 900° C. at a rate of 100° C./hour and held at 900° C. for 40 hours. At this time, the raw material melt M was stirred by rotating the sapphire substrate 110 at a speed of 10 revolutions per minute about the rotating shaft 230 . After that, the inside of the reaction vessel 240 was allowed to cool down to room temperature by natural heat release. The removed semiconductor substrate 100 was washed with aqua regia to remove remaining metal gallium, an intermetallic compound of iron and gallium, and the like.

A tilt measurement and a twist measurement were performed in the same manner as in Example 1 for a sapphire substrate having a gallium nitride single crystal layer laminated thereon according to a comparative example. As a result, the semiconductor substrate of the comparative example had a tilt width of 0.13° and a twist width of 0.42°.

In addition, wide-angle 2θ-ω measurement was performed in the same out-of-plane arrangement as in Example 1 for the sapphire substrate on which the gallium nitride single crystal layer according to the comparative example was laminated. In FIG. 11, the peak (diffraction E) seen near 2θ = 34.6° is the diffraction of the (0002) plane of gallium nitride, and the peak (diffraction F) seen near 2θ = 41.7° is the diffraction of sapphire. They correspond to the diffraction of the (0006) plane, respectively.

However, unlike Example 1, in the comparative example, no diffraction peak (diffraction D) was observed near 2θ=19.2°. In addition, since the measurement result of FIG. 11 is an out-of-plane symmetrical reflection measurement, the (0001) plane (c-plane) of gallium nitride and the (0001) plane (c-plane) of sapphire are parallel to each other. I understand.

The results measured in Examples 1 to 6 and Comparative Example are summarized in Table 1 below.

Referring to the results in Table 1, it can be seen that the buffer layer 120 is formed in each of Examples 1 to 6. In addition, the amount of lattice mismatch between the metal oxide crystal layer of the spinel crystal structure in the buffer layer 120 in Examples 2 to 6 and the gallium nitride single crystal constituting the gallium nitride single crystal layer 130 was the same as the nitride in the comparative example. It was confirmed to be smaller than the amount of lattice mismatch between the gallium single crystal and the sapphire single crystal. In other words, it was found that the semiconductor substrate 100 according to the present embodiment provided with the buffer layer 120 improved the crystallinity of the gallium nitride single crystal layer 130 as compared with the comparative example without the buffer layer 120 .

In addition, since Examples 1 to 6 have low threading dislocation densities, the yield can be improved when a device is produced from the gallium nitride single crystal (gallium nitride single crystal layer 130) of Examples 1 to 6. In addition, since Examples 1 to 6 have low threading dislocation densities, the luminous efficiency can be improved when LEDs are produced from the gallium nitride single crystals (gallium nitride single crystal layer 130) of Examples 1 to 6. It becomes possible.

As described above, according to the present embodiment, it is possible to obtain a gallium nitride single crystal with excellent crystallinity and high in-plane uniformity for gallium nitride formed on the sapphire substrate 110 using the liquid phase method. is possible.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the claims, and it should be understood that these also belong to the technical scope of the present invention. be done.

In the above embodiment, the configuration in which the gallium nitride single crystal layer 130 is directly provided on the buffer layer 120 is taken as an example. However, an intermediate layer may be provided between buffer layer 120 and gallium nitride single crystal layer 130 . The intermediate layer is made of gallium nitride, for example, in which the [0001] axis in the direction normal to the (0001) plane of the gallium nitride single crystal has a predetermined orientation variation range and the orientation of the [0001] axis is random. be.

REFERENCE SIGNS LIST 100 semiconductor substrate 110 sapphire substrate 120 buffer layer 130 gallium nitride single crystal layer

Claims (12)

a sapphire substrate composed of a sapphire single crystal;
a buffer layer provided on the sapphire substrate;
A gallium nitride single crystal layer provided on the buffer layer and made of gallium nitride single crystal;
with
The buffer layer is an altered layer formed on the surface of the sapphire substrate on the gallium nitride single crystal layer side, and the crystal structure of the sapphire single crystal is converted to a spinel crystal structure of a specific metal oxide. is a
The semiconductor substrate, wherein the buffer layer has a thickness of 10 nm or more. (0001) plane of the sapphire single crystal constituting the sapphire substrate, (111) plane of the specific metal oxide crystal layer of the spinel crystal structure constituting the buffer layer, and the gallium nitride single crystal 2. The semiconductor substrate according to claim 1, wherein the (0001) plane of the gallium nitride single crystal forming the layer is substantially parallel. [1-100] axis on the (0001) plane of the sapphire single crystal constituting the sapphire substrate, and (111) plane of the crystal layer of the specific metal oxide of the spinel crystal structure constituting the buffer layer 3. The semiconductor substrate according to claim 2, wherein the [1-10] axis of and the [11-20] axis of the (0001) plane of the gallium nitride single crystal constituting the gallium nitride single crystal layer are substantially parallel to each other. . 1/(2√2) times the lattice constant a _spi of the crystal layer of the specific metal oxide having the spinel crystal structure that constitutes the buffer layer is the lattice constant of the sapphire single crystal that constitutes the sapphire substrate. 4. The semiconductor substrate according to claim 2, wherein the value is between 1/√3 times a _sap and the lattice constant a _gan of the gallium nitride single crystal forming the gallium nitride single crystal layer. 5. The crystal layer of the specific metal oxide having the spinel crystal structure that constitutes the buffer layer has a lattice constant a _spi of 8.050 to 8.338 Å according to any one of claims 1 to 4. semiconductor substrate. Claims 1 to 1, wherein the orientation variation of the [111] axis in the direction normal to the (111) plane of the specific metal oxide crystal layer of the spinel crystal structure constituting the buffer layer is less than 6°. 6. The semiconductor substrate according to any one of 5. The absolute value of the amount of lattice mismatch between the crystal layer of the specific metal oxide having the spinel crystal structure that constitutes the buffer layer and the gallium nitride single crystal that constitutes the gallium nitride single crystal layer is The semiconductor substrate according to any one of claims 1 to 6, which is less than 10.8%. The specific metal oxide is a composite oxide represented by the chemical formula AB ₂ O ₄ ,
A is a +2 valent metal atom selected from the group consisting of Mg, Fe, Mn, Ni, Co, Cu, and Zn;
8. The semiconductor substrate according to claim 1, wherein said B is a +3 valent metal atom of either one or both of Al and Ga. _2. The specific metal oxide comprises one or _more complex _oxides selected from the group _consisting of _MgAl2O4 , _MgGa2O4 , _MnAl2O4 and _MnGa2O4 . 8. The semiconductor substrate according to any one of items 1 to 7. 10. The semiconductor substrate according to claim 1, wherein said buffer layer contains a total of 1 at % or more of specific metal atoms other than Al contained in said specific metal oxide. a step of melting a reaction material containing metallic gallium, iron nitride, and a specific metallic material in a nitrogen atmosphere to obtain a melt;
a step of immersing a sapphire substrate in the melt;
a step of holding the sapphire substrate immersed in the melt at 700° C. to 1000° C. for 20 hours or more;
including
The method of manufacturing a semiconductor substrate, wherein the specific metal material is a specific metal itself having a spinel crystal structure or a compound of the specific metal. further comprising the step of forming an oxide film of the specific metal on the surface of the sapphire substrate;
12. The method of manufacturing a semiconductor substrate according to claim 11, wherein in said immersing step, said sapphire substrate on which said specific metal oxide film is formed is immersed in said melt.

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