JP2005183524A - Epitaxial substrate and its manufacturing method, and method of reducing dislocation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group-III nitride epitaxial substrate having a low dislocation density. <P>SOLUTION: The epitaxial substrate 1 is made by depositing an underlying layer 12, a buffer layer 13, and a designed group-III nitride layer 14 on a base material 11 in order by epitaxial growth using the MOCVD method. By annealing the epitaxial substrate 1 prior to the epitaxial growth of the group-III nitride layer 14, the dislocation density in the group-III nitride layer 14 is reduced half or less than in a case where no annealing is conducted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an epitaxial substrate obtained by epitaxially forming a group III nitride on a base material, a method for manufacturing the epitaxial substrate, and a dislocation reduction method.

  Group III nitride semiconductors have different characteristics from other semiconductors, such as a large band gap, a large dielectric breakdown electric field, and a high saturation electron mobility. For this reason, group III nitride semiconductors are optical devices such as LEDs (light emitting diodes), LDs (laser diodes) and light receiving elements in the ultraviolet to green region, and HEMTs (high frequency characteristics) that have excellent high frequency characteristics. It has been studied as a material for electronic devices such as electron mobility transistors (High Electron Mobility Transistors) and HBTs (Hetero Bipolar Transistors) and materials for field emitters.

  However, since it is currently difficult to produce a large-sized bulk single crystal of a group III nitride semiconductor, substrates used in the above optical devices and electronic devices are, for example, MOCVD (metal organic chemical vapor phase). It is obtained by heteroepitaxially growing a group III nitride semiconductor on a single crystal substrate such as sapphire or SiC using a growth method (Metal Organic Chemical Vapor Deposition).

  However, in heteroepitaxial growth, dislocations are caused by lattice mismatch with the substrate, and various attempts have been made to reduce dislocations.

  For example, Patent Document 1 discloses a technique in which a base layer and a buffer layer are provided between a substrate and a semiconductor layer group made of a GaN-based semiconductor.

JP 2002-252177 A

  However, although the technique of Patent Document 1 is effective in reducing dislocations, the influence of manufacturing conditions and manufacturing equipment is large, and sufficient dislocation reducing effects are often not obtained.

  The present invention has been made to solve this problem, and an object thereof is to provide a group III nitride epitaxial substrate having a low dislocation density.

In order to solve the above-mentioned problems, the invention of claim 1 is a method for manufacturing an epitaxial substrate, which is based on all group III elements contained therein having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 mm or less. A first forming step of epitaxially forming a first group III nitride layer having a molar fraction of Al of 50% or more on a substrate; and an in-plane lattice constant larger than that of the first group III nitride layer; A second forming step of epitaxially forming a second group III nitride layer having a layer thickness of 100 nm or less on the first group III nitride layer; an annealing step of performing an annealing process after the second forming step; A third forming step of epitaxially forming a third group III nitride layer having an in-plane lattice constant larger than that of the second group III nitride layer on the second group III nitride layer after the annealing step. It is characterized by providing.

  According to a second aspect of the present invention, in the epitaxial substrate manufacturing method according to the first aspect, the temperature of the annealing treatment is equal to or higher than the epitaxial formation temperature of the third formation step.

  The invention according to claim 3 is the method for producing an epitaxial substrate according to claim 1 or 2, wherein the molar fraction of Al with respect to all group III elements contained in the first group III nitride layer is 80. % Or more.

  According to a fourth aspect of the present invention, in the method for manufacturing an epitaxial substrate according to the first or second aspect, the group III nitride related to the first group III nitride layer is AlN. .

  The invention of claim 5 provides the epitaxial substrate manufacturing method according to any one of claims 1 to 4, wherein the annealing step includes at least one of an inert gas and a nitrogen element-containing gas. It is performed in gas.

  The invention according to claim 6 is the method for producing an epitaxial substrate according to claim 5, wherein the pressure of the atmospheric gas is equal to or higher than the epitaxial formation pressure in the third formation step.

  The invention of claim 7 is the method of manufacturing an epitaxial substrate according to any one of claims 1 to 6, wherein the first to third group III nitride layers are C-plane group III nitride layers. It is characterized by being.

  According to an eighth aspect of the present invention, in the method for manufacturing an epitaxial substrate according to any one of the first to seventh aspects, an X-ray rocking curve half-value width of an epitaxial growth surface of the first group III nitride layer is 200. It is less than second.

  The invention according to claim 9 is the method of manufacturing an epitaxial substrate according to any one of claims 1 to 8, wherein the annealing temperature is 1100 ° C. or higher.

  The invention of claim 10 is the method of manufacturing an epitaxial substrate according to any one of claims 1 to 9, wherein the annealing temperature is higher by 50 ° C. or more than the epitaxial formation temperature of the third formation step. It is characterized by being.

Further, the invention of claim 11 is a dislocation reduction method for a target group III nitride layer epitaxially formed on an epitaxial substrate, and prior to the epitaxial formation of the target group III nitride layer, A first group III nitride layer having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 μm or less and having a mole fraction of Al with respect to all the group III elements contained is 50% or more on the substrate. A first forming step for epitaxial formation; an in-plane lattice constant larger than that of the first group III nitride layer; an in-plane lattice constant smaller than that of the target group III nitride layer; and a layer thickness of 100 nm or less A second forming step of epitaxially forming the second group III nitride layer on the first group III nitride layer, and an annealing step of performing an annealing process after the second forming step. And

The invention of claim 12 is an epitaxial substrate comprising a base material and an epitaxially formed dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 μm or less. From a first group III nitride layer containing 50% or more of Al with respect to a group III element, and the first group III nitride layer formed epitaxially on the first group III nitride layer A second group III nitride layer having a large in-plane lattice constant and a layer thickness of 100 nm or less, and the second group III nitride layer formed epitaxially on the second group III nitride layer. A third group III nitride layer having a large in-plane lattice constant, and the second group III nitride layer is annealed prior to the epitaxial formation of the third group III nitride layer. An epitaxial substrate characterized by that.

Further, the invention of claim 13 is an epitaxial substrate provided for epitaxial formation of a target group III nitride layer, wherein the substrate and the dislocation density formed epitaxially on the substrate are 1 ×. A first group III nitride layer having a molar fraction of Al of not less than 10 ¹¹ / cm ² and having a surface roughness of 3 mm or less and having a mole fraction of Al of 50% or more, and the first group III nitride Epitaxially formed on the layer, the in-plane lattice constant is larger than that of the first group III nitride layer, the in-plane lattice constant is smaller than that of the target group III nitride layer, and the layer thickness is 100 nm or less. And a second group III nitride layer, wherein the second group III nitride layer is annealed.

  According to the first to thirteenth inventions, a low dislocation density group III nitride epitaxial substrate can be obtained.

  According to the third to fourth aspects of the present invention, a higher quality group III nitride epitaxial substrate can be obtained.

  According to the sixth and ninth to tenth aspects of the present invention, since the effect of the annealing treatment can be improved, a higher-quality group III nitride epitaxial substrate can be obtained.

  According to the invention of claim 8, a higher quality group III nitride epitaxial substrate can be obtained.

<Laminated structure of epitaxial substrate>
FIG. 1 is a schematic cross-sectional view showing a laminated structure of epitaxial substrate 1 according to the present embodiment. The epitaxial substrate 1 is obtained by sequentially epitaxially growing the base layer 12, the buffer layer 13, and the target group III nitride layer 14 on the base material 11 using various thin film forming methods. For example, a CVD method (chemical vapor deposition method) such as MOCVD method, HVPE method (hydride vapor phase epitaxy), MBE method (molecular beam epitaxy), or molecular beam epitaxy is used. be able to. As the CVD method, a PALE method (Pulsed Atomic Layer Epitaxy), a plasma assist method, a laser assist method, or the like can be applied, and the same technology can be used in combination with the MBE method. It is. In the epitaxial substrate 1, annealing is performed prior to the epitaxial growth of the group III nitride layer 14, thereby reducing the dislocation density of the group III nitride layer 14 to less than half that when the annealing process is not performed.

Examples of the material of the base material 11 include various oxide materials such as sapphire, ZnO, LiAlO ₂ , LiGaO ₂ , MgAl ₂ O ₄ , (LaSr) (AlTa) O ₃ , NdGaO ₃ , and MgO, and various IV groups such as Si and Ge. A single crystal, various IV-IV group compounds such as SiC and SiGe, various III-V group compounds such as GaAs, AlN, GaN, and AlGaN and single crystals of various borides such as ZrB ₂ are appropriately selected. The epitaxial growth surface 15 of the substrate 11 is desirably a surface on which a C-group III nitride layer can be epitaxially grown in order to ensure surface flatness of the layer to be epitaxially grown. In particular, the materials of the epitaxial growth surface 15 and the base material 11 improve the crystal quality of the layer to be epitaxially grown. It is desirable to select from physical single crystals. The A plane and the C plane here mean the (11-20) plane and the (0001) plane of the crystal plane, respectively. Although the thickness of the base material 11 is not restrict | limited, The range of 100 micrometers-3000 micrometers is suitable.

The underlayer 12, the general formula constituted of group III nitride represented by _{B w Al x Ga y In z} N (w + x + y + z = 1). The underlayer 12 has a mole fraction of Al element with respect to all group III elements of 50% or more (x ≧ 0.5), preferably 80% or more (x ≧ 0.8). More preferably, the underlayer 12 is made of AlN (x = 1). However, it is not prevented that the underlayer 12 contains contamination that is inevitably mixed in the manufacturing process. Since the crystal quality of the group III nitride layer 14 is adversely affected when the crystal quality of the base layer 12 is lowered, it is desirable that the crystal quality of the base layer 12 is good. Specifically, the epitaxial growth surface of the underlayer 12 is an X-ray rocking curve half-value width (hereinafter referred to simply as “rocking curve half-value width”) in the X-ray rocking curve measurement of the (002) plane, which is an index of crystal orientation fluctuation. (Also referred to as “also”) is 200 seconds or less, preferably 100 seconds or less. The underlayer 12 is desired to have atomic level flatness such that the surface roughness is 3 mm or less. Here, the surface roughness is an arithmetic average roughness in a square area of 5 μm × 5 μm measured by AFM (atomic force microscope) (the same applies to the following). The thickness of the underlayer 12 is 0.3 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. The upper limit of the thickness of the underlayer 12 is not particularly limited, but is appropriately determined in consideration of prevention of occurrence of cracks and peeling.

Buffer layer 13 is represented by the general formula constituted of group III nitride represented by _{B w Al x Ga y In z} N (w + x + y + z = 1). The specific composition of the buffer layer 13 is selected so that the in-plane lattice constant of the buffer layer 13 is larger than the in-plane lattice constant of the underlayer 12. Further, from the viewpoint of suppressing cracks, it is more desirable to select so as to be not more than the in-plane lattice constant of the group III nitride layer 14. As a result, compressive stress due to lattice mismatch occurs at the interface 16 between the underlayer 12 and the buffer layer 13 and at the interface 17 between the buffer layer 13 and the group III nitride layer 14. Since this compressive stress promotes the dislocation reduction effect, it is desirable that the in-plane lattice constant difference be larger in the combination of the underlayer 12 and the group III nitride layer 14 where the compressive stress works more greatly. It is desirable that the mole fraction of Al element with respect to all group III elements is large. Note that if the thickness of the buffer layer 13 exceeds 100 nm, the effect of reducing the dislocation of the group III nitride layer 14 due to annealing is lowered, so that the thickness is preferably 100 nm or less.

The annealing process performed on the buffer layer 13 is performed at a temperature equal to or higher than the epitaxial growth temperature of the group III nitride layer 14. Preferably, the annealing process is performed at a temperature of 1100 ° C. or higher or 50 ° C. or higher than the epitaxial growth temperature of the group III nitride layer 14. In particular, when the Al composition of the buffer layer 13 is high, the kinetic energy of dislocation increases, so it is desirable to anneal at a higher temperature. Even when the annealing process is performed at a temperature lower than the epitaxial growth temperature of the group III nitride layer 14, a dislocation reduction effect can be obtained by extending the annealing process time. The annealing process is performed in a state where an inert gas or a nitrogen element-containing gas is added in order to prevent the buffer layer 13 from being lost. The higher the amount of the inert gas or nitrogen element-containing gas added, the higher the effect of preventing the loss of the buffer layer 13, and the total amount of the inert gas or nitrogen element-containing gas in the atmospheric gas is such that the molar fraction is 50% or more. Desirably, the effect can be maximized by setting it to 100%. Typical examples of the nitrogen element-containing gas include nitrogen (N ₂ ) gas and ammonia (NH ₃ ) gas. Increasing the pressure of the atmospheric gas more than during the epitaxial formation of the group III nitride layer 14 is also effective for enhancing the annealing effect. Furthermore, this effect can be further enhanced by setting the atmospheric gas pressure to 1 atm or higher.

The group III nitride layer 14 is made of a group III nitride having a general formula represented by B _w Al _x Ga _y In _z N (w + x + y + z = 1). The group III nitride is doped with a donor or acceptor such as Mg, Be, Zn, Si, Ge, and P, if necessary. In FIG. 1, the group III nitride layer 14 is expressed as a single layer, but the group III nitride layer 14 may be composed of a plurality of layers.

  In the epitaxial substrate 1, the stress described above is used to reduce dislocations, and the dislocations are facilitated by annealing to facilitate the reduction of dislocations. For this reason, when the flatness of the underlayer 12 is impaired, stress relaxation occurs due to the rough interface shape, and the dislocation reduction effect due to the annealing treatment decreases. Also, when the thickness of the buffer layer 13 exceeds the above limit, the dislocation movement is hindered and the dislocation reduction effect by the annealing process is reduced.

<Manufacturing equipment>
FIG. 2 is a schematic cross-sectional view of manufacturing apparatus 2 for epitaxial substrate 1 according to the present embodiment. The manufacturing apparatus 2 is a so-called “MOCVD apparatus” that uses a group III organometallic gas as a source gas and forms a group III nitride film by chemical vapor deposition. The manufacturing apparatus 2 is configured such that a raw material gas for producing the epitaxial substrate 1 can flow on the main surface of the base material 11.

  The manufacturing apparatus 2 includes a reactive gas introduction pipe 31 for introducing a reactive gas into the main surface of the substrate 11. The reactive gas introduction pipe 31 is installed inside an airtight reaction vessel 21, and two external ends thereof are a reactive gas introduction port 22 and an exhaust port 24, respectively. Further, the reactive gas introduction pipe 31 is provided with an opening 31 h for contacting the reactive gas on the main surface of the substrate 11.

  Piping systems L 1 and L 2 are connected to the introduction port 22.

The piping system L1 is a piping system for supplying ammonia gas (NH ₃ ), nitrogen gas (N ₂ ), and hydrogen gas (H ₂ ).

On the other hand, the piping system L2 is TEB (triethylboron; B (C ₂ H ₅ ) ₃ ), (← Please deal with the drawing.) TMA (trimethylaluminum; Al (CH ₃ ) ₃ ), TMG (trimethylgallium Ga (CH ₃ ) ₃ ), TMI (trimethylindium; In (CH ₃ ) ₃ ), CP ₂ Mg (cyclopentadienylmagnesium; Mg (C ₅ H ₅ ) ₂ ), silane gas (SiH ₄ ), nitrogen gas And a piping system for supplying hydrogen gas. Since CP ₂ Mg and silane gas are raw materials of Mg and Si, respectively, which will be an acceptor and a donor in the group III nitride, they can be appropriately changed depending on the acceptor and donor to be used.

The TEB, TMA, TMG, TMI, and CP ₂ Mg supply sources 24d to 24h are connected to a nitrogen gas supply source 24b for bubbling. Similarly, TEB, TMA, TMG, TMI and CP ₂ Mg supply sources 24d to 24h are connected to a hydrogen gas supply source 24c.

  In the manufacturing apparatus 2, hydrogen gas, nitrogen gas, or a mixed gas thereof is a carrier gas. All gas supply systems can control the gas flow rate with a flow meter. In the manufacturing apparatus 2, group III nitrides having various mixed crystal compositions including a single phase can be epitaxially grown by appropriately controlling the flow rate of each gas.

  The exhaust port 24 is connected to a vacuum pump 27 that forcibly exhausts the gas inside the reactive gas introduction pipe 31.

  Inside the reaction vessel 21, a substrate stand (susceptor) 28 on which the substrate 11 is placed and a support leg 29 that supports the substrate stand 28 inside the reaction vessel 21 are provided. The temperature of the base 28 can be controlled using a heater 30 provided immediately below. The heater 30 is, for example, a resistance heating type heater. In the manufacturing apparatus 2, it is possible to change the growth temperature of the epitaxial layer by changing the temperature of the base plate 28 that is in close contact with the base material 11. In other words, the epitaxial growth temperature in the MOCVD method is variable by the heater 30.

  Examples 1 to 3 below show a method for manufacturing epitaxial substrate 1 according to the present embodiment and a quality evaluation result of epitaxial substrate 1 manufactured by the manufacturing method. Moreover, the following comparative examples 1-3 show the manufacturing method of the epitaxial substrate which becomes out of the scope of the present invention and the quality evaluation result of the epitaxial substrate manufactured by the manufacturing method.

<Example 1>
FIG. 3 is a diagram illustrating a process flow of the method for manufacturing the epitaxial substrate 100 according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing the laminated structure of the epitaxial substrate 100 obtained by the manufacturing method.

  In Example 1, a substantially circular C-plane sapphire single crystal having a diameter of 2 inches and a thickness of 430 μm was used as the substrate 101. The epitaxial growth surface is the (001) plane of a C-plane sapphire single crystal (the same applies to Examples 2-3 and Comparative Examples 1-3).

  In Example 1, the composition of the foundation layer, the buffer layer, and the group III nitride layer is AlN, GaN, and GaN, respectively. The composition of the buffer layer is selected so that the in-plane lattice constant is larger than that of the underlayer and smaller than that of the buffer layer.

First, the surface of the base material 101 which becomes an epitaxial growth surface was washed (step S1). For the cleaning, an organic solvent and a mixed solution of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) were used.

  Next, the substrate 101 was placed on the substrate stand 28 (step S2), and the surface of the substrate 101 was thermally cleaned (step S3). Thermal cleaning is performed by flowing hydrogen gas over the main surface of the substrate 101 at a flow rate of 2 m / sec while maintaining the internal pressure of the reactive gas introduction pipe 31 at 10 Torr, and holding the substrate 101 at 1200 ° C. for 10 minutes. went. In the subsequent processing, the hydrogen gas flow rate was adjusted to maintain a total gas flow rate of 2 m / sec. By the thermal cleaning, the surface of the substrate 101 can be cleaned and recrystallization (hydrogen annealing) can also proceed.

After completion of the thermal cleaning, the substrate temperature was changed to 1200 ° C., and the AlN layer 102 was formed epitaxially (step S4). Formation of AlN layer 102, NH ₃ and the molar fraction of the TMA is NH _3: TMA = 10~1000: were performed by a reactive gas is introduced into the reaction gas inlet tube 31. As a result, an AlN layer 102 having a thickness of 0.7 μm was formed on the substrate 101. When the surface roughness and rocking curve half-value width of the AlN layer 102 obtained by this process were measured, they were 1.5 mm and 60 sec, respectively.

Subsequently, the substrate temperature was changed to 1050 ° C., and the GaN layer 103 was epitaxially formed (step S5). Formation of the GaN layer 103, NH ₃ and mole fraction NH with _{TMG 3: TMG = 500~5000: 1} : the reactive gas was carried out by introducing into the reaction gas inlet tube 31. As a result, a GaN layer 103 having a thickness of 50 nm was formed.

  Next, the GaN layer 103 is annealed (step S6). Prior to the annealing treatment, the atmosphere inside the reactive gas introduction pipe 31 was replaced with nitrogen gas. Thereafter, the pressure was set to 1 atm, the substrate temperature was raised to 1150 ° C., and the substrate temperature was maintained for 10 minutes.

After the annealing process, the GaN layer 104 was formed epitaxially. Formation of the GaN layer 104 lowers the substrate temperature to 1050 ° C., NH ₃ and mole fraction NH with TMG _3: TMG = 500~5000: 1 of the reactive gas into the reaction gas inlet tube 31 Done by introducing. As a result, a 3 μm thick GaN layer 104 was formed. When the dislocation density of the GaN layer 104 was measured by counting the dark spots in the cathodoluminescence image, it was 2 × 10 ⁷ / cm ² , confirming that a high-quality GaN layer 104 with a low dislocation density was obtained. It was.

<Example 2>
In the second embodiment, only the specific processing method of the annealing process (step S6) in the process flow shown in FIG. 3 is different from the first embodiment, and the remaining processes are the same as the first embodiment. Specifically, after the epitaxial formation of the GaN layer 102 is completed, the epitaxial substrate 100 is moved to an atmosphere heating apparatus different from the manufacturing apparatus 2. The epitaxial substrate 100 is heated to 1150 ° C. and held for 10 minutes inside the atmosphere heating apparatus replaced with an argon atmosphere pressurized to 2 atm. Thereafter, the epitaxial substrate 100 is naturally allowed to cool and is returned to the base plate 28 of the manufacturing apparatus 2 again. Then, the GaN layer 104 is formed as in the first embodiment (step S7). When the dislocation density of the GaN layer 104 was measured for the epitaxial substrate 100 according to Example 2, it was 2 × 10 ⁷ / cm ² , and it was confirmed that a high-quality GaN layer 104 with a low dislocation density was obtained.

<Example 3>
In Example 3, the composition of the buffer layer and the group III nitride layer is Al _0.4 Ga _0.6 N and Al _0.4 Ga _0.6 N, respectively, which is different from Example 1 (see the inside of FIG. 4), and the process flow is It is the same as that of Example 1 (refer in FIG.3 ()).

After forming the AlN underlayer, the substrate temperature was changed to 1150 ° C., and the Al _0.4 Ga _0.6 N layer 103 was formed epitaxially (step S5). The Al _0.4 Ga _0.6 N layer 103 is formed by reacting a reactive gas having a NH ₃ : TMA: TMG = 50 to 5000: 0.5: 1 molar ratio of NH ₃ , TMA and TMG with a reactive gas introduction pipe 31. It was done by introducing it. As a result, an Al _0.4 Ga _0.6 N layer 103 having a thickness of 15 nm was formed.

Next, annealing treatment of the Al _0.4 Ga _0.6 N layer 103 is performed (step S6). Prior to the annealing treatment, the atmosphere inside the reactive gas introduction pipe 31 was replaced with nitrogen gas. Thereafter, the pressure was set to 1 atm, the substrate temperature was raised to 1350 ° C., and the substrate temperature was maintained for 10 minutes.

After the annealing treatment, an Al _0.4 Ga _0.6 N layer 104 was formed epitaxially. Formation of the Al _0.4 Ga _0.6 N layer 104 is a reaction in which the substrate temperature is lowered to 1150 ° C., and the molar fraction of NH ₃ and TMG is NH ₃ : TMA: TMG = 50 to 5000: 0.5: 1. This was performed by introducing a reactive gas into the reactive gas introduction pipe 31. As a result, an Al _0.4 Ga _0.6 N layer 104 having a thickness of 2 μm was formed. When the dislocation density of the Al _0.4 Ga _0.6 N layer 104 was measured by counting the dark spots in the cathodoluminescence image, it was 5 × 10 ⁸ / cm ² , and a high quality Al _0.4 Ga _0.6 N layer 104 with a low dislocation density was obtained. It was confirmed that it was obtained.

<Comparative Example 1>
FIG. 5 is a diagram showing a process flow of the method for manufacturing epitaxial substrate 100 according to Comparative Example 1. Steps S11 to S16 in the process flow shown in FIG. 5 correspond to steps S1 to S5 and S7 in the process flow shown in FIG. That is, the process flow according to Comparative Example 1 corresponds to the process flow of Example 1 in which the annealing process (Step S6) is omitted. With respect to the epitaxial substrate 100 according to Comparative Example 1, the dislocation density of the GaN layer 104 was measured and found to be 7 × 10 ⁷ / cm ² .

<Comparative example 2>
In Comparative Example 2, an epitaxial substrate was fabricated under the same conditions as in Example 1 except that the thickness of the GaN layer 103 serving as the buffer layer in Example 1 was increased to 200 nm. When the dislocation density of the GaN layer 104 of the epitaxial substrate 100 according to Comparative Example 2 was measured, it was 7 × 10 ⁷ / cm ² .

  As is clear from comparison between Examples 1 and 2 and Comparative Examples 1 and 2, the epitaxial substrate according to the present embodiment is a high-quality substrate in which the target group III nitride layer has a low dislocation density. ing. That is, by introducing the buffer layer 13 and performing annealing at a temperature higher than the epitaxial formation temperature of the target group III nitride layer in an inert atmosphere or a nitrogen element-containing gas atmosphere, the target group III nitride is obtained. The dislocation density of the layer can be reduced.

<Comparative Example 3>
The process flow according to Comparative Example 3 corresponds to a process flow obtained by omitting the annealing process (Step S6) from the process flow of Example 3 (see FIG. 5). With respect to the epitaxial substrate 100 according to Comparative Example 3, the dislocation density of the Al _0.6 Ga _0.4 N layer 104 was measured and found to be 3 × 10 ⁹ / cm ² .

As is clear from comparison between Example 3 and Comparative Example 3, the epitaxial substrate according to the present embodiment is a high-quality substrate in which the target group III nitride layer has a low dislocation density. That is, by introducing the buffer layer 13 and performing annealing at a temperature higher than the epitaxial formation temperature of the target group III nitride layer in an inert atmosphere or a nitrogen element-containing gas atmosphere, the target group III nitride is obtained. The dislocation density of the layer can be reduced. That is, in Examples 1 and 2, the composition of the group III nitride layer 14 was GaN, but the same is true even if the composition is a composition represented by the general formula Al _x Ga _y N (x + y = 1). Dislocation reduction effect can be obtained.

<Modification>
In Examples 1 to 3, the composition of the group III nitride layer 14 was Al _x Ga _y N (x + y = 1), but the composition was the general formula B _w Al _x Ga _y In _z N (w + x + y + z = 1). The same dislocation reduction effect can be obtained even with a composition expressed by: In addition, when a group III nitride having a composition expressed by B _w Al _x Ga _y In _z N (w + x + y + z = 1) contains donors and acceptors such as Mg, Be, Zn, Si, Ge, and P The same dislocation reduction effect can be obtained.

  In Examples 1 and 2, the atmospheric gas during the annealing treatment was nitrogen gas or argon gas. However, even if the atmospheric gas is changed to an inert gas such as neon or ammonia gas, an equivalent dislocation reduction effect is obtained. It is done.

It is a cross-sectional schematic diagram which shows the laminated structure of the epitaxial substrate 1 which concerns on this Embodiment. It is a cross-sectional schematic diagram of the manufacturing apparatus 2 of the epitaxial substrate 1 which concerns on embodiment. It is a figure which shows the process flow of the manufacturing method of the epitaxial substrate 100 which concerns on Example 1 (Example 3). 3 is a schematic cross-sectional view showing a laminated structure of an epitaxial substrate 100 according to Example 1 (Example 3). FIG. It is a figure which shows the process flow of the manufacturing method of the epitaxial substrate 100 which concerns on the comparative example 1 (comparative example 3).

Explanation of symbols

1,100 Epitaxial substrate 11 Base material 15 Epitaxial growth surface 16, 17 Interface 27 Vacuum pump 28 Base plate 29 Support leg 30 Heater 31 Reactive gas introduction tube

Claims (13)

An epitaxial substrate manufacturing method comprising:
a) Base material is a first group III nitride layer having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 mm or less, and a molar fraction of Al with respect to all group III elements contained is 50% or more. A first forming step of epitaxially forming on,
b) Epitaxially forming a second group III nitride layer having an in-plane lattice constant larger than that of the first group III nitride layer and having a thickness of 100 nm or less on the first group III nitride layer. 2 forming process;
c) An annealing step for performing an annealing process after the second forming step;
d) After the annealing step, a third group III nitride layer having an in-plane lattice constant larger than that of the second group III nitride layer is epitaxially formed on the second group III nitride layer. Forming process;
An epitaxial substrate manufacturing method comprising:   2. The method for manufacturing an epitaxial substrate according to claim 1, wherein a temperature of the annealing treatment is equal to or higher than an epitaxial formation temperature in the third forming step. 3. In the manufacturing method of the epitaxial substrate of Claim 1 or Claim 2,
A method for producing an epitaxial substrate, wherein the molar fraction of Al with respect to all group III elements contained in the first group III nitride layer is 80% or more. In the manufacturing method of the epitaxial substrate of Claim 1 or Claim 2,
A method for producing an epitaxial substrate, wherein the group III nitride related to the first group III nitride layer is AlN. In the manufacturing method of the epitaxial substrate in any one of Claims 1 thru | or 4,
The method of manufacturing an epitaxial substrate, wherein the annealing step is performed in an atmosphere gas containing at least one of an inert gas and a nitrogen element-containing gas. In the manufacturing method of the epitaxial substrate according to claim 5,
The method for manufacturing an epitaxial substrate, wherein the pressure of the atmospheric gas is equal to or higher than the epitaxial formation pressure in the third formation step. In the manufacturing method of the epitaxial substrate in any one of Claims 1 thru | or 6,
The method of manufacturing an epitaxial substrate, wherein the first to third group III nitride layers are C-plane group III nitride layers. In the manufacturing method of the epitaxial substrate in any one of Claims 1 thru | or 7,
An epitaxial substrate manufacturing method, wherein an X-ray rocking curve half-value width of an epitaxial growth surface of the first group III nitride layer is 200 seconds or less. In the manufacturing method of the epitaxial substrate in any one of Claims 1 thru | or 8,
The method of manufacturing an epitaxial substrate, wherein the annealing temperature is 1100 ° C. or higher. In the manufacturing method of the epitaxial substrate in any one of Claims 1 thru | or 9,
The method for manufacturing an epitaxial substrate, wherein the annealing temperature is 50 ° C. or more higher than the epitaxial formation temperature in the third formation step. A method for reducing dislocations in a target group III nitride layer epitaxially formed on an epitaxial substrate,
Prior to the epitaxial formation of the desired group III nitride layer,
a) Base material is a first group III nitride layer having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 mm or less, and a molar fraction of Al with respect to all group III elements contained is 50% or more. A first forming step of epitaxially forming on,
b) A second group III nitride having a larger in-plane lattice constant than the first group III nitride layer, a smaller in-plane lattice constant than the target group III nitride layer, and a layer thickness of 100 nm or less. A second forming step of epitaxially forming a material layer on the first group III nitride layer;
c) An annealing step for performing an annealing process after the second forming step;
The dislocation reduction method characterized by performing. An epitaxial substrate,
A substrate;
A first group III, which is epitaxially formed on the substrate and contains 50% or more of Al with respect to all group III elements having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 mm or less. A nitride layer;
A second group III nitride layer epitaxially formed on the first group III nitride layer, having a larger in-plane lattice constant than the first group III nitride layer and having a layer thickness of 100 nm or less;
A third group III nitride layer epitaxially formed on the second group III nitride layer and having a larger in-plane lattice constant than the second group III nitride layer;
With
An epitaxial substrate, wherein the second group III nitride layer is annealed prior to epitaxial formation of the third group III nitride layer. An epitaxial substrate provided for epitaxial formation of a target group III nitride layer,
A substrate;
A first epitaxial layer formed on the base material, having a dislocation density of 1 × 10 ¹¹ / cm ² or less and a surface roughness of 3 μm or less, and a molar fraction of Al with respect to all group III elements contained is 50% or more. A group III nitride layer;
The in-plane lattice constant is larger than that of the first group III nitride layer epitaxially formed on the first group III nitride layer, and the in-plane lattice constant is larger than that of the target group III nitride layer. A second Group III nitride layer having a small layer thickness of 100 nm or less;
With
An epitaxial substrate, wherein the second group III nitride layer is annealed.

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