Group III nitride crystal and method for producing same

Abstract

Provided is a group III nitride crystal with which it is possible to improve productivity when producing a group III nitride crystal. The group III nitride crystal is obtained by crystal growth on a seed substrate, and has a base part that is crystal-grown from the seed substrate up to a growth surface of a growth pit having a recess, and a buried part in which the recess of the growth pit is buried by the group III nitride crystal in the growth surface.

Description

Technical Field

[0001] This disclosure relates to group III nitride crystals and methods for manufacturing the same. Background Technology

[0002] Vertical GaN power devices require GaN substrates with low resistance and low dislocation density. For example, in the case of fabricating n-type low-resistance GaN substrates, the traditional approach has been to increase carrier concentration and reduce dislocation density by forming pits while growing (see, for example, Patent Document 1).

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-50107 Summary of the Invention

[0004] The problem that the invention aims to solve

[0005] However, the manufacturing method described in Patent Document 1 has the following problems: cracking and fissures occur during cooling after growth, reducing the productivity of Group III nitride crystals. The cracking and fissures are caused by the following: the growth surface is covered with pits (growth pits), and there is a difference in the coefficient of thermal expansion between the seed substrate and the growth layer.

[0006] Figure 1 (a) is a schematic cross-sectional view showing the vertical cross-sectional structure at high temperature immediately after GaN crystal growth on the seed substrate using the OVPE method, and (b) is a schematic cross-sectional view showing the vertical cross-sectional structure after cooling to room temperature as shown in (a). According to the OVPE method described in Patent Document 1, when n-type low-resistivity GaN is fabricated by adding a higher concentration of oxygen than the seed substrate, the coefficient of thermal expansion of the n-type low-resistivity GaN becomes greater than that of the seed substrate. In this case, during cooling after growth, if... Figure 1 As shown in (b), the growth layer shrinks more significantly compared to the seed substrate, thus deforming the convex shape. Furthermore, if pits exist on the surface, compared to a flat surface, as... Figure 1 As indicated by the arrow in (b), the stress generated on the surface increases. Therefore, the probability of cracking or fissures increases.

[0007] This disclosure is made in view of the above-mentioned problems, and its purpose is to provide a group III nitride crystal and a method for manufacturing group III nitride crystals that can improve the productivity of manufacturing group III nitride crystals.

[0008] means for solving problems

[0009] The group III nitride crystal disclosed herein is a group III nitride crystal obtained by crystal growth on a seed substrate, which has: a substrate portion from which crystal growth occurs from the seed substrate to a growth surface having a growth pit with a recess, and an embedded portion in which the recess of the growth pit in the growth surface is buried by the group III nitride crystal.

[0010] The method for manufacturing group III nitride crystals disclosed herein includes the following steps: a step of preparing a seed substrate; a step of supplying group III element oxide gas and nitrogen-containing gas to the seed substrate and growing group III nitride crystals in a three-dimensional manner on the seed substrate; and a step of growing group III nitride crystals in a two-dimensional manner and burying growth pits on the surface of group III nitride crystals to smooth the surface.

[0011] Invention Effects

[0012] The group III nitride crystal and its manufacturing method disclosed herein can improve the productivity of manufacturing group III nitride crystals and produce high-quality group III nitride crystals. Attached Figure Description

[0013] Figure 1 (a) is a schematic cross-sectional view showing the vertical cross-sectional structure of GaN crystals grown on a seed substrate using the OVPE method at high temperature. Figure 1 (b) is a schematic cross-sectional view showing the vertical cross-sectional structure after (a) has been cooled to room temperature.

[0014] Figure 2 (a) is a schematic cross-sectional view showing the vertical cross-sectional structure of GaN crystals grown on a seed substrate using the OVPE method at high temperature. Figure 2 (b) is a schematic cross-sectional view showing the vertical surface of a group III nitride crystal with a buried portion of a growth pit having a buried growth surface after a smoothing process is performed in the manufacturing method of group III nitride crystal in embodiment 1.

[0015] Figure 3 (a) is a time-series flowchart of the method for manufacturing group III nitride crystals according to Embodiment 1. Figure 3 (b) is a diagram showing the functional units from upstream to downstream within the manufacturing apparatus used in this manufacturing method as processes.

[0016] Figure 4 This is a schematic cross-sectional view of the apparatus for manufacturing group III nitride crystals according to Embodiment 1.

[0017] Figure 5 This is a graph showing the relationship between the oxygen concentration during the smoothing process and the stress generated in the embedded part. Detailed Implementation

[0018] The group III nitride crystal of the first embodiment is a group III nitride crystal obtained by crystal growth on a seed substrate, which has: a substrate portion from which crystal growth occurs from the seed substrate to a growth surface having a growth pit with a recess, and an embedded portion in which the recess of the growth pit in the growth surface is buried by the group III nitride crystal.

[0019] The second method uses a group III nitride crystal that, in the first method described above, is such that the growth pit is buried by the group III nitride crystal, and the oxygen concentration in the substrate is 1 × 10⁻⁶. 20 atoms / cm 3 above.

[0020] The third method involves a group III nitride crystal that, in the first or second method described above, is buried by a group III nitride crystal, and the oxygen concentration in the substrate is 1 × 10⁻⁶. 21 atoms / cm 3 The oxygen concentration in the embedded part is 4.8 × 10⁴. 20 atoms / cm 3 above.

[0021] The fourth type of group III nitride crystal can be any of the first to third types described above, where the growth pits are buried by the group III nitride crystal, and the dislocation density is 5 × 10⁻⁶. 5 cm -2 the following.

[0022] The fifth method for manufacturing a group III nitride crystal includes the following steps: a step of preparing a seed substrate; a step of supplying a group III element oxide gas and a nitrogen-containing gas to the seed substrate and growing a group III nitride crystal in a three-dimensional manner on the seed substrate; and a step of smoothing the surface by burying the growth pits on the surface of the group III nitride crystal in a two-dimensional manner.

[0023] The method for manufacturing group III nitride crystals in the sixth manner can be as follows: in the fifth manner described above, the process of smoothing the surface is carried out by controlling the supplied group III element oxide gas and nitrogen-containing element gas to make the V / III ratio more than 5 times.

[0024] The method for manufacturing the group III nitride crystal in the seventh aspect can be that, in the fifth aspect described above, the process of smoothing the surface is performed by raising the temperature of the substrate by 50°C or more compared to the growth process.

[0025] The method for manufacturing a group-III nitride crystal according to the eighth aspect may be such that, in any of the fifth to seventh aspects described above, in the step of smoothing the surface of the group-III nitride crystal, the oxygen concentration in the region covering the surface irregularities is 4.8×10 20 atoms / cm 3 or more.

[0026] Hereinafter, the group-III nitride crystal and the method for manufacturing the same according to the embodiment will be described in detail with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to these embodiments.

[0027] (Embodiment 1)

[0028] <Group-III Nitride Crystal>

[0029] Figure 2 (a) of < > shows a schematic cross-sectional view of a vertical plane at a high temperature just after GaN crystal growth by the OVPE method on a seed substrate, and (b) shows a schematic cross-sectional view of a vertical plane of a group-III nitride crystal having a buried portion of a growth pit that fills a recess on the growth surface after a smoothing process is performed after (a) in the method for manufacturing a group-III nitride crystal according to Embodiment 1.

[0030] Refer to Figure 2 to explain the outline of the group-III nitride crystal of Embodiment 1. The group-III nitride crystal of Embodiment 1 is a group-III nitride crystal obtained by crystal growth on a seed substrate. This group-III nitride crystal has: a base portion from crystal growth on the seed substrate up to a growth surface having a recess, and a buried portion in which the recess of the growth pit is buried by the group-III nitride crystal within the growth surface.

[0031] It should be noted that, as a method for burying the growth pit, it is necessary to switch the growth mode of the group-III nitride crystal to two-dimensional growth. As a method for switching from a three-dimensional growth mode to a two-dimensional growth mode in normal crystal growth, for example, it can be cited: compared with Figure 2 during the growth of the base portion shown in (b) of < >, increasing the growth temperature and increasing the V / III ratio (the ratio of the group-V source to the group-III source). As a means for increasing the V / III ratio, it can be cited: increasing the supply amount of the group-V source or reducing the supply amount of the group-III source. By controlling the growth conditions of the buried portion, the oxygen concentration of the buried portion can be controlled, and the difference in the thermal expansion coefficient from the base portion can be controlled.

[0032] The first effect brought about by forming the buried portion is that by smoothing the irregularities on the surface formed by the growth pits, stress concentration during the generation of load on the substrate portion can be reduced. For example, when a group III nitride crystal grown on a certain substrate grows with rotation during the growth process, contact with the substrate pedestal cannot be avoided, and a load on the grown crystal is generated from the substrate pedestal. Therefore, by forming the buried portion, cracking and fissures can be suppressed. Furthermore, as the second effect, by forming a buried portion with a thermal expansion coefficient difference similar to that of the substrate portion, stress concentration during cooling due to the thermal expansion coefficient difference can be reduced. Thus, by providing a buried portion with a similar thermal expansion coefficient difference, further suppression of cracking and fissures can be achieved.

[0033] <Outline of the manufacturing method of group III nitride crystal>

[0034] Figure 3 (a) of is a time-sequence flowchart of the manufacturing method of the group III nitride crystal of Embodiment 1, and (b) is a diagram showing each functional unit from upstream to downstream in the manufacturing apparatus used in this manufacturing method as processes. Figure 4 is a schematic cross-sectional view of the manufacturing apparatus of the group III nitride crystal of Embodiment 1.

[0035] Refer to Figure 3 the flowchart of and Figure 4 To explain the outline of the manufacturing method of the group III nitride crystal of this Embodiment 1. The manufacturing method of the group III nitride crystal includes the following processes: a process of preparing a seed substrate; a process of supplying a group III element oxide gas and a nitrogen-containing element gas to grow a group III nitride crystal on the seed substrate; and a process of burying the growth pits in the later stage of the process of growing the group III nitride crystal to smooth the surface.

[0036] In the seed substrate preparation process of preparing the seed substrate 116, the seed substrate 116 is placed on the substrate pedestal 117.

[0037] In this embodiment, the manufacturing method of the group III nitride crystal has a heating process. In the heating process, the cultivation chamber 111 is heated to 100 °C or higher and lower than 500 °C in an inert gas atmosphere.

[0038] In this embodiment, the manufacturing method of the group III nitride crystal has a decomposition protection heating process 1. In the decomposition protection heating process 1, the cultivation chamber 111 is heated to 500 °C or higher and lower than 1100 °C in an NH3 gas atmosphere.

[0039] In this embodiment, the manufacturing method of the group III nitride crystal has a decomposition protection heating process 2. In the decomposition protection heating process 2, the cultivation chamber 111 is heated to 1100 °C or higher and lower than 1500 °C in an NH3 gas and Ga2O gas atmosphere.

[0040] In the growth process of growing group III nitride crystals on seed substrate 116, group III element oxide gas is generated in raw material chamber 100 and supplied to cultivation chamber 111, and nitrogen-containing gas is supplied to cultivation chamber 111 to grow group III nitride crystals on seed substrate 116.

[0041] The growth process also includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen-containing gas supply process, a group III nitride crystal formation process, and a residual gas removal process. It should be noted that all the steps within the growth process can be performed simultaneously within the group III nitride crystal manufacturing apparatus.

[0042] The reactive gas supply process supplies reactive gas to the raw material reaction chamber.

[0043] The process for generating group III element oxide gases involves reacting a starting group III element source with a reactive gas (a reducing gas if the starting group III element source is an oxide, and an oxidizing gas if the starting group III element source is a metal) to generate group III element oxide gases.

[0044] The Group III element oxide gas supply process supplies the Group III element oxide gas produced in the Group III element oxide gas generation process to the incubation chamber.

[0045] The nitrogen-containing gas supply process supplies nitrogen-containing gas to the cultivation chamber.

[0046] The group III nitride crystal growth process involves reacting the group III element oxide gas supplied to the cultivation chamber in the group III element oxide gas supply process with the nitrogen-containing gas supplied to the cultivation chamber in the nitrogen-containing gas supply process, thereby growing group III nitride crystals on the seed substrate.

[0047] The residual gas venting process removes unreacted gases that do not contribute to the formation of Group III nitride crystals to the outside.

[0048] In this embodiment, the method for manufacturing group III nitride crystals includes a surface smoothing process. The surface smoothing process smooths the surface of the group III nitride crystals grown on the seed substrate 116, promotes the two-dimensional growth of the group III nitride crystals (in the case of growth on the +c surface, growth with the +c surface as the surface), and reduces surface unevenness.

[0049] In this embodiment, the method for manufacturing a group-III nitride crystal has a decomposition protection temperature reduction process. In the decomposition protection temperature reduction process, in order to suppress the decomposition of the group-III nitride crystal grown on the seed substrate 116, while supplying NH3 gas, the temperatures of the raw material chamber 100 and the cultivation chamber 111 are reduced to 500 °C.

[0050] In this embodiment, the method for manufacturing a group-III nitride crystal has a temperature reduction process. In the temperature reduction process, the temperatures of the raw material chamber 100 and the cultivation chamber 111 are reduced to below 100 °C in an inert gas atmosphere.

[0051] In this embodiment, the method for manufacturing a group-III nitride crystal has a taking-out process. In the taking-out process, the seed substrate 116 on which the group-III nitride crystal has grown is taken out from the cultivation chamber 111.

[0052] <Outline of the manufacturing apparatus for group-III nitride crystals>

[0053] Refer to Figure 4 The outline of the manufacturing apparatus used in the method for manufacturing a group-III nitride crystal according to Embodiment 1 will be described.

[0054] In Figure 4 , the sizes, ratios, etc. of the respective constituent members may be different from the actual ones. In the manufacturing apparatus for group-III nitride crystals, a raw material reaction chamber 101 is arranged in the raw material chamber 100, and a raw material boat 104 on which a starting group-III element source 105 is placed is arranged in the raw material reaction chamber 101. The raw material reaction chamber 101 is connected to a reactive gas supply pipe 103 for supplying a gas that reacts with the starting group-III element source 105. The raw material reaction chamber 101 has a group-III element oxide gas discharge port 107 for discharging the generated group-III element oxide gas. When the starting group-III source is an oxide, a reducing gas is used as the reactive gas. When the starting group-III source is a metal, an oxidizing gas is used as the reactive gas. In addition, the raw material chamber 100 is connected to a first carrier gas supply port 102 for supplying a first carrier gas. The first carrier gas supplied from the first carrier gas supply port 102 and the group-III element oxide gas discharged from the group-III element oxide gas discharge port 107 flow into the cultivation chamber 111 through a gas discharge port 108 via a connection pipe 109 and are supplied to the cultivation chamber 111 from a gas supply port 118 connected to the cultivation chamber 111. The cultivation chamber 111 has a gas supply port 118, a third carrier gas supply port 112, a nitrogen-containing element gas supply port 113, a second carrier gas supply port 114, and an exhaust port 119. The cultivation chamber 111 includes a substrate pedestal 117 for setting the seed substrate 116.

[0055] <Details of the manufacturing method and the manufacturing apparatus>

[0056] Refer to Figure 3 and Figure 4 The method for manufacturing group III nitride crystals according to Embodiment 1 will be described in detail.

[0057] In this embodiment, Ga metal is used as the starting group III element source 105, but it is not limited to this; for example, Al or In can be used.

[0058] First, a seed substrate 116 is prepared. For example, gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, or ScAlMgO4 can be used as the seed substrate 116. In this embodiment, gallium nitride is used as the seed substrate 116.

[0059] The heating process involves heating the incubation chamber in an inert gas atmosphere until the seed substrate 116 reaches a temperature at which it does not decompose. In the manufacture of group III nitride crystals based on the OVPE method, heating is carried out in an inert gas atmosphere (e.g., N2 gas) until approximately 500°C.

[0060] The decomposition protection heating process 1 involves heating in a nitrogen-containing gas atmosphere while suppressing the decomposition of the seed substrate 116. In the manufacture of Group III nitride crystals based on the OVPE method, heating is performed at temperatures above 500°C and below 1100°C in a mixture of an inert gas and a nitrogen-containing gas (NH3). The reason for mixing NH3 is to prevent the decomposition of the seed substrate 116 due to the removal of N atoms. Furthermore, heating can be performed with an additional mixture of H2 gas.

[0061] In the decomposition protection heating process 2, the temperature is increased while suppressing the decomposition of the seed substrate 116 under an atmosphere of Group III oxide gas and nitrogen-containing gas. In the manufacture of Group III nitride crystals based on the OVPE method, heating is performed at a temperature above 1100°C and below 1500°C in an atmosphere containing H2 gas, an inert gas, Group III oxide gas, and nitrogen-containing NH3 gas. The reason for mixing Group III oxide gas is that decomposition cannot be suppressed by nitrogen-containing gas alone. By providing a driving force for the growth of the Group III nitride crystal, decomposition can be suppressed.

[0062] The growth process generates Group III element oxide gas in the raw material chamber 100 and supplies it to the cultivation chamber 111. Nitrogen-containing gas is also supplied to the cultivation chamber 111, resulting in the three-dimensional formation of Group III nitride crystals on the seed substrate 116. Specifically, the growth process includes a reactive gas supply process, a Group III element oxide gas generation process, a Group III element oxide gas supply process, a nitrogen-containing gas supply process, a Group III nitride crystal formation process, and a residual gas removal process.

[0063] The reactive gas supply process supplies reactive gas from the reactive gas supply pipe 103 to the raw material reaction chamber 101 within the raw material chamber 100. As described above, either a reducing gas or an oxidizing gas can be used as the reactive gas, depending on the need. In this embodiment, since metallic Ga is used as the Group III element source 105, H2O gas is used as the reactive gas.

[0064] The Group III element oxide gas generation process involves reacting the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supply process with Ga, which serves as the starting Group III element source 105, to generate Ga₂O gas, which is a Group III element oxide gas. The generated Ga₂O gas is discharged from the raw material reaction chamber 101 to the raw material chamber 100 via the Group III element oxide gas outlet 107. The discharged Ga₂O gas is mixed with the first carrier gas supplied to the raw material chamber from the first carrier gas supply port 102 and supplied to the gas outlet 108. In this embodiment, the raw material chamber 100 is heated by the first heater 106. When heating the raw material chamber 100, from the perspective of the boiling point of Ga₂O gas, it is preferable that the temperature of the raw material chamber 100 is 800°C or higher. Furthermore, it is preferable that the temperature of the raw material chamber 100 is lower than that of the incubation chamber 111. When heating the incubation chamber by the second heater 115 as described later, it is preferable that the temperature of the raw material chamber 100 is, for example, lower than 1800°C. The starting group III element source 105 is placed in a feed boat 104 disposed within the feed reaction chamber 101. The feed boat 104 is preferably shaped to allow for a large contact area between the reactive gas and the starting group III element source. For example, to prevent the starting group III element source 105 from passing through the feed reaction chamber 101 without contact with the reactive gas, the feed boat 104 is preferably a multi-stage vessel shape.

[0065] It should be noted that the methods for generating Group III element oxide gases can be broadly categorized into methods of reducing the starting Group III element source 105 and methods of oxidizing the starting Group III element source 105. For example, in the reduction method, an 105 oxide (e.g., Ga₂O₃) is used as the starting Group III element source, and a reducing gas (e.g., H₂, CO, CH₄, C₂H₆, H₂S, SO₂) is used as the reactive gas. Conversely, in the oxidation method, a non-oxide (e.g., liquid Ga) is used as the starting Group III element source 105, and an oxidizing gas (e.g., H₂O, O₂, CO, CO₂, NO, N₂O, NO₂) is used as the reactive gas. Furthermore, in addition to the starting Group III element source 105, In and Al sources can also be used as starting Group III elements. As the first carrier gas, inert gases such as H₂ can be used.

[0066] The Group III oxide gas supply process supplies Ga₂O gas generated in the Group III oxide gas generation process to the incubation chamber 111 via gas outlet 108, connecting pipe 109, and gas supply port 118. If the temperature of the connecting pipe 109 connecting the raw material chamber 100 and the incubation chamber 111 is lower than the temperature of the raw material chamber 100, a reverse reaction of the Group III oxide gas generation reaction will occur, and the initial Ga source 105 will precipitate within the connecting pipe 109. Therefore, the connecting pipe 109 is preferably heated to a higher temperature than the first heater 106 by a third heater 110 so that it does not decrease compared to the temperature of the raw material chamber 100.

[0067] The nitrogen-containing gas supply process supplies nitrogen-containing gas from nitrogen-containing gas supply port 113 to the cultivation chamber 111. Examples of nitrogen-containing gases include NH3 gas, NO gas, NO2 gas, N2O gas, N2H2 gas, and N2H4 gas.

[0068] The group III nitride crystal growth process involves reacting the raw material gases supplied to the growth chamber via various feeding processes to grow group III nitride crystals on the seed substrate 116. The growth chamber 111 is preferably heated to the temperature at which group III oxide gases and nitrogen-containing gases react, via a second heater 115. To prevent the reverse reaction that generates group III oxide gases, the temperature of the growth chamber 111 is preferably controlled so that it does not decrease compared to the temperature of the raw material chamber 100. The temperature of the growth chamber 111 heated by the second heater 115 is preferably 1000°C or higher and 1800°C or lower. Furthermore, to suppress temperature fluctuations in the growth chamber 111 caused by the Ga₂O gas generated in the raw material chamber 100 and the first carrier gas, it is ideal to have the temperatures of the second heater 115 and the third heater 111 be the same.

[0069] By mixing the Group III element oxide gas supplied to the growth chamber 111 via the Group III element oxide supply process and the nitrogen-containing gas supplied to the growth chamber 111 via the nitrogen-containing gas supply process upstream of the seed substrate 116, Group III nitride crystals can be grown on the seed substrate 116.

[0070] It should be noted that the reactive gas supply process, the group III element oxide gas generation process, the group III element oxide gas supply process, the nitrogen-containing gas supply process, the group III nitride crystal generation process, and the residual gas discharge process included in the growth process can be carried out simultaneously.

[0071] As the second carrier gas, an inert gas or H2 gas can be used.

[0072] The residual gas discharge process discharges unreacted Group III element oxide gases and nitrogen-containing element gases, as well as the first carrier gas, the second carrier gas, and the third carrier gas, from the exhaust port 119.

[0073] Furthermore, from the perspective of increasing carrier concentration, the oxygen concentration in the substrate portion of the group III nitride crystal formed through the growth process is preferably 1 × 10⁻⁶. 20 atoms / cm 3 The above further optimizes the oxygen concentration to 1×10⁻⁶. 21 atoms / cm 3 above.

[0074] Furthermore, the growth pits generated during the growth process have the effect of merging and eliminating dislocations in the seed substrate. Therefore, from the perspective of improving the quality of the substrate, the density of growth pits is preferably 5 × 10⁻⁶. 5 cm -2 Hereinafter, 1×10 is further preferred. 5 cm -2 the following.

[0075] The surface smoothing process smooths out growth pits and other unevenness generated during the growth process. Instead of three-dimensional growth, the final stage of growth promotes two-dimensional growth of group III nitride crystals. By promoting two-dimensional growth, growth pits and other unevenness are buried, forming embedded portions and smoothing the surface. It should be noted that there are generally two methods to promote two-dimensional growth. One is to increase the growth temperature. The other is to increase the V / III ratio (the ratio of group V sources to group III sources). Either or both of these methods can bury surface unevenness. Specifically, ideally, the V / III ratio should be increased to more than 5 times. Furthermore, ideally, the growth temperature should be at least 50°C higher than the temperature of the substrate in the aforementioned growth process. These conditions can be selectively applied individually or simultaneously.

[0076] The decomposition protection cooling process involves cooling the crystals while suppressing their decomposition in a nitrogen-containing gas atmosphere. In the manufacture of Group III nitride crystals based on the OVPE method, cooling is performed to below 500°C in a mixture of inert gas and nitrogen-containing gas (NH3).

[0077] The cooling process is carried out in an inert gas atmosphere to cool the crystals to a temperature at which the Group III nitride crystals can be removed from the growth chamber.

[0078] In this embodiment, after a cooling process, the seed substrate 116 on which group III nitride crystals have grown is taken out from the cultivation chamber 111.

[0079] (The relationship between oxygen concentration in the embedded part and stress in the embedded part)

[0080] The relationship between the oxygen concentration in the buried section and the stress caused by the difference in the coefficient of thermal expansion generated in the region of the buried growth pit (the buried section) is shown in the figure. Figure 5 It should be noted that, Figure 5 The result is the analytical value of thermal stress, with an oxygen concentration of 1×10⁻⁶ in the substrate. 21 atoms / cm 3 The result at that time. Figure 5 The dashed lines represent the stress in the growth pits before the surface smoothing process. This indicates that the oxygen concentration in the embedded portion exceeds 4.8 × 10⁻⁶. 20 atoms / cm 3 Within this range, compared to the case where no embedded portion is formed, the stress generated in the embedded portion can be reduced. Therefore, from the perspective of suppressing stress caused by the difference in thermal expansion coefficients, it is preferable to have an oxygen concentration of 4.8 × 10⁻⁶ in the embedded portion. 20 atoms / cm 3 In conclusion, it should be noted that burying the crystal further suppresses cracking and fissures. Therefore, it can be seen that even forming only an embedded portion can suppress the load on the growth crystal, effectively reducing cracking and fissures. This is because during growth and cooling, the substrate (growth crystal) is rotated to ensure uniform gas pressure on the crystal surface. Therefore, with rotation, the growth crystal sometimes comes into contact with the substrate base. This contact applies a load to the growth crystal, and without an embedded portion, cracking and fissures are more likely to occur.

[0081] Industrial availability According to the group III nitride crystal disclosed herein, it is possible to improve the productivity of manufacturing group III nitride crystals and produce high-quality group III nitride crystals.

[0082] Symbol Explanation 100 Raw Material Room 101 Raw Material Reaction Chamber 102 First Carrier Gas Supply Port 103 Reactive gas supply pipe 104 Raw Material Boat 105 Initial Group III Elemental Source 106 First Heater 107 Group III element oxide gas exhaust outlet 108 Gas Exhaust Port 109 Connecting pipe 110 Third Heater 111 Cultivation Room 112 Third Carrier Gas Supply Port 113 Nitrogen-containing gas supply port 114 Second Carrier Gas Supply Port 115 Second Heater 116 types of substrates 117 Substrate Base 118 Gas supply port 119 Exhaust port

Claims

1. A group III nitride crystal, which is a group III nitride crystal obtained by crystal growth on a seed substrate. It has the following characteristics: The substrate portion from which crystal growth occurs, up to the growth surface with the recessed growth pits, and The recessed portion of the growth pit within the growth surface is buried by a group III nitride crystal.

2. The group III nitride crystal according to claim 1, wherein, The growth pits were buried by group III nitride crystals. The oxygen concentration of the substrate is 1×10⁻⁶. 20 atoms / cm 3 above.

3. The group III nitride crystal according to claim 1, wherein, The growth pits were buried by group III nitride crystals. The oxygen concentration of the substrate is 1×10⁻⁶. 21 atoms / cm 3 above, The oxygen concentration in the embedded part is 4.8 × 10⁻⁶. 20 atoms / cm 3 above.

4. The group III nitride crystal according to claim 1, wherein, The growth pits are buried by group III nitride crystals, with a dislocation density of 5 × 10⁻⁶. 5 cm -2 the following.

5. A method for manufacturing a group III nitride crystal, comprising the following steps: The process of preparing the seed substrate; The process of supplying group III element oxide gas and nitrogen-containing gas to the seed substrate, and growing group III nitride crystals in a three-dimensional manner on the seed substrate; and, The process of growing a group III nitride crystal in a two-dimensional manner and smoothing the surface by burying the growth pits on the surface of the group III nitride crystal.

6. The method for manufacturing group III nitride crystals according to claim 5, wherein, The surface smoothing process is carried out by controlling the supplied group III element oxide gas and nitrogen-containing gas to achieve a V / III ratio of more than 5.

7. The method for manufacturing group III nitride crystals according to claim 5, wherein, The surface smoothing process is performed by raising the temperature of the substrate by 50°C or more compared to the growth process.

8. The method for manufacturing group III nitride crystals according to any one of claims 5 to 7, wherein, In the process of smoothing the surface of the group III nitride crystal, the oxygen concentration in the uneven areas of the buried surface is 4.8 × 10⁻⁶. 20 atoms / cm 3 above.

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