Group III nitride crystals, Group III nitride semiconductors, Group III nitride substrates, and methods for manufacturing Group III nitride crystals.

Abstract

The group III nitride crystal substrate has a main surface and a rear surface opposite the main surface. Also, the average dislocation density of the main surface and the average dislocation density of the rear surface are 6.0×105cm-2 or less. Furthermore, the difference in the average dislocation density of the main surface and the average dislocation density of the rear surface is 5.0×104cm-2 or less. The curve of the crystal axis of the main surface has a radius of curvature of 30 m or more.

Description

[Technical Field]

[0001] This disclosure relates to group III nitride crystals, group III nitride semiconductors, group III nitride substrates, and methods for manufacturing group III nitride crystals. [Background technology]

[0002] Group III nitride crystals are used in optical semiconductor devices such as light-emitting diodes (LEDs) and semiconductor lasers (LDs) because they can cover a wide band gap by changing the composition of Group III elements (Ga, Al, In). Furthermore, Group III nitride crystals have a dielectric breakdown field of 3.3 MV / cm². -3 Because of its high crystalline properties (GaN), it is widely used in electronic devices for high-frequency and high-power applications. Optical and electronic devices grown homoepitaxially on a Group III nitride crystal substrate exhibit high crystallinity, resulting in significantly improved device characteristics compared to devices formed on dissimilar substrates such as sapphire. Therefore, devices using Group III nitride crystals are highly anticipated and are being widely researched and developed.

[0003] For the group III nitride crystals used in these high-performance devices, a method is known in which thick group III nitride crystals are grown on dissimilar substrates such as sapphire using hydride vapor phase epitaxy (HVPE), and the thick group III nitride crystals are sliced ​​to form self-supporting nitride substrates. HVPE is a method of growing GaN crystals by introducing GaCl gas and ammonia gas into a growth chamber and reacting them. For example, Patent Document 1 discloses a technique in which a mask or uneven pattern is formed on dissimilar substrates and selective growth is performed using HVPE. This intentionally forms nitride semiconductor crystal nuclei with facets that are angled relative to the substrate surface, and then nitride crystals are grown laterally on top of them to achieve a density of 5.0 × 10⁻¹⁶ 6 cm -2 We have obtained nitride semiconductor crystals with a certain degree of dislocation density.

[0004] However, in the technology of Patent Document 1, from the relationship between the film thickness and the dislocation density of the nitride crystal disclosed in Non-Patent Document 1, as shown in FIG. 1, in the initial stage of growth, it is approximately 10 7 cm -2 and has a high dislocation density. FIG. 1 is a graph showing the relationship between the film thickness and the dislocation density of the group III nitride crystal grown on the sapphire substrate disclosed in Non-Patent Document 1. Therefore, even if the growth of a film thickness of about 1 mm is performed, as shown in FIG. 1, the surface dislocation density is at most 5.0×10 6 cm -2 or so.

[0005] In addition, when the distribution of the dislocation density with respect to the film thickness direction is large, the curvature of the +c axis of the nitride crystal becomes about 5 m in radius and the warpage becomes large. In FIG. 2, similar to FIG. 1, the nitride crystal grown on the sapphire substrate is sliced in a region of a specific growth film thickness from the surface side, and the nitride crystal is cut out with a thickness of 500 μm toward the sapphire substrate side, and when it is formed into a thickness of 400 μm, the difference between the dislocation density on the surface side and the dislocation density on the back side of the crystal is shown. In the graph of FIG. 2, the plot indicated by the arrow shows the value of the dislocation density difference between the front and back surfaces when the nitride crystal in the region of 1.5 mm to 2 mm from the surface side is sliced and a nitride crystal with a thickness of 500 μm is cut out and formed into a thickness of 400 μm. Specifically, the dislocation densities on the surface (2.0 mm) and the back surface (1.6 mm) are 1.0×10 6 cm -2 , 1.25×10 6 cm -2 or so, respectively, indicating that there is a dislocation density difference of about 2.5×10 5 cm -2 ]>existing between the front and back surfaces. The dislocation density difference in the film thickness direction inside the nitride crystal induces the warpage of the crystal axis on the surface of the nitride crystal (FIG. 3(a)). Therefore, when processed to be flat for use as a wafer, there is a possibility that the inclination of the crystal axis of the main surface as shown in FIG. 3(b) changes within the wafer surface. Such a distribution of the crystal axis within the wafer surface is likely to cause variations in composition and film thickness in the growth of the nitride mixed crystal used for the device, which may lead to a decrease in quality. Therefore, the coexistence of further improvement in dislocation density and reduction of crystal warpage is required.

[0006] Patent Document 2 discloses a method for obtaining high-quality nitride crystals by growing nitride crystals on a nitride species substrate by liquid-phase growth such as the Na flux method and then slicing and polishing the nitride crystals. Further, it is disclosed that the nitride crystals obtained by the Na flux method have a good dislocation density of 6.0×10 5 cm -2 or less and a crystal warp of the c-axis has a radius of curvature of 30 m or more.

[0007] However, the growth temperature used in the HVPE method is usually about 1050°C. When nitride crystals are grown at a growth temperature of 1050°C by the HVPE method on a seed substrate obtained by liquid-phase growth disclosed in Patent Document 2, good nitride crystals cannot be obtained. This is considered to be due to the influence of Na (Na inclusion) present inside the nitride species substrate obtained by the Na flux method. In the Na flux method, Na present in the melt is incorporated into the seed substrate and becomes Na inclusion. Na inclusion is observed as having white cavities inside the crystal as shown in the optical microscope photographs of the nitride crystals by liquid-phase growth in (a) and (b) of FIG. 4, and exists in a streak shape shown in (a) of FIG. 4 or a circular shape shown in (b) of FIG. 4. Under the high temperature of 1030 to 1050°C used in the HVPE method, it is considered that this Na inclusion expands inside the seed substrate and causes rupture as shown in FIG. 5. Due to the rupture, as shown in FIG. 6, large depressions can form on the seed substrate. Further, the ruptured Na inclusion not only contaminates the surface of the seed substrate with Na, but also the nitride crystals of the seed substrate scattered by the rupture remain on the surface of the seed substrate as foreign substances. For this reason, the growth of nitride crystals on the seed substrate in the HVPE method is inhibited. Then, it is considered that the crystallinity of the nitride crystals on the seed substrate grown by the HVPE method deteriorates and good nitride crystals cannot be obtained.

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] Patent No. 4396816 [Patent Document 2] Patent No. 6578570 [Non-patent literature]

[0009] [Non-Patent Document 1] Sumitomo Chemical Technical Report - "Development of GaN Single Crystal Substrates" - 2018 [Overview of the Initiative]

[0010] A group III nitride crystal according to one aspect of this disclosure has a principal surface and a back surface opposite to the principal surface, wherein the average dislocation density of the principal surface and the average dislocation density of the back surface are 6.0 × 10⁻⁶. 5 cm -2 The following is true: the difference between the average dislocation density of the main surface and the average dislocation density of the back surface is 5.0 × 10⁻⁶. 4 cm -2 The following conditions apply, and the curvature of the crystal axis of the main plane is greater than or equal to a radius of curvature of 30m.

[0011] The method for producing a group III nitride crystal according to this disclosure comprises a preparation step of preparing a group III nitride species substrate containing Na, and a growth step of growing a group III nitride crystal on the group III nitride species substrate by vapor phase growth, wherein the starting temperature of the growth step is 950°C or higher and 970°C or lower, and the growth of the group III nitride crystal in the growth step is carried out at a temperature of 950°C or higher and 1020°C or lower. [Effects of the Invention]

[0012] The group III nitride crystals described herein can provide high-quality group III nitride crystals. [Brief explanation of the drawing]

[0013] [Figure 1] This graph shows the relationship between film thickness and dislocation density of a group III nitride crystal grown on a sapphire substrate using conventional technology. [Figure 2]This graph shows the relationship between the film thickness of a group III nitride crystal grown on a sapphire substrate using conventional technology, and the difference in dislocation density between the front and back surfaces of group III nitride crystals cut out in regions of each film thickness and formed to a thickness of 400 μm. [Figure 3] This is a conceptual diagram showing the crystal warping of group III nitride crystals that occurs in conventional technology. [Figure 4] This is an optical microscope image of a Na inclusion in a group III nitride crystal produced using conventional techniques. [Figure 5] This is an optical microscope image of a fractured Na inclusion in a group III nitride crystal produced using conventional techniques. [Figure 6] This is an electron microscope image of a fractured Na inclusion in a group III nitride crystal produced using conventional techniques. [Figure 7A] A graph showing the in-plane distribution of the full width at half maximum of the X-ray ω-SCAN rocking curve for a group III nitride substrate in the example. [Figure 7B] A graph showing the in-plane distribution of the full width at half maximum of the X-ray ω-SCAN rocking curve for a group III nitride substrate in the example. [Figure 8] This is a schematic diagram of a manufacturing apparatus for Group III nitride crystals according to Embodiment 1. [Figure 9] This is a graph showing the growth sequence of a group III nitride crystal according to Embodiment 1. [Figure 10] This is an atomic force microscope image of the surface of a group III nitride substrate after the surface treatment process in the example. [Figure 11] This is a photograph of a group III nitride crystal after the initial growth process in the example. [Figure 12A] This is the X-ray ω-SCAN rocking curve after the initial growth process at 950°C in the example. [Figure 12B] This is the X-ray ω-SCAN rocking curve after the initial growth process at 950°C in the example. [Figure 13A] This is the X-ray ω-SCAN rocking curve after the initial growth process at 970°C in the example. [Figure 13B]This is the X-ray ω-SCAN rocking curve after the initial growth process at 970°C in the example. [Figure 14] This is a photograph of a 1.1 mm thick group III nitride crystal from the example. [Figure 15A] This is the X-ray ω-SCAN rocking curve of a 1.1 mm thick group III nitride crystal in the example. [Figure 15B] This is the X-ray ω-SCAN rocking curve of a 1.1 mm thick group III nitride crystal in the example. [Figure 16] This is a photograph of a group III nitride crystal in the example. [Figure 17A] This graph shows the in-plane distribution of the full width at half maximum (FWHM) of the X-ray ω-SCAN rocking curve for the group III nitride crystals in the examples. [Figure 17B] This graph shows the in-plane distribution of the full width at half maximum (FWHM) of the X-ray ω-SCAN rocking curve for the group III nitride crystals in the examples. [Figure 18] This is a photograph showing the cathodoluminescence results of the surface dislocation density of a group III nitride crystal in the example. [Figure 19] This table shows the in-plane distribution of surface dislocation density in the group III nitride crystals in the examples. [Figure 20] This graph shows the relationship between the film thickness and dislocation density of a group III nitride crystal grown on a nitride substrate with a surface dislocation density of 2.0 × 10⁵ cm⁻², according to Embodiment 1. [Figure 21] This graph shows the relationship between the film thickness of a group III nitride crystal grown on a group III nitride substrate with a surface dislocation density of 2.0 × 10⁵ cm⁻² in the example, and the difference in dislocation density between the front and back surfaces of group III nitride crystals cut out in each film thickness region and formed to a thickness of 400 μm. [Figure 22] This graph shows the relationship between film thickness and dislocation density of a group III nitride crystal grown on a nitride substrate with a surface dislocation density of 6.0 × 10⁵ cm⁻² in the example. [Figure 23]This graph shows the relationship between the film thickness of a group III nitride crystal grown on a group III nitride substrate with a surface dislocation density of 6.0 × 10⁵ cm⁻² in the example, and the difference in dislocation density between the front and back surfaces of group III nitride crystals cut out in 400 μm thicknesses from each film thickness region. [Figure 24] This is a photograph of a comparative example of a group III nitride crystal with a thickness of 1.1 mm. [Figure 25] This is a cross-sectional SEM image of a group III nitride crystal grown on a group III nitride substrate as a comparative example. [Figure 26] Table 1 summarizes the results of our investigation into the crystallinity of GaN-grown films in relation to their growth rate and growth temperature. [Modes for carrying out the invention]

[0014] This disclosure aims to provide high-quality group III nitride crystals, group III nitride semiconductors and group III nitride substrates having the same, and a method for manufacturing the group III nitride crystals.

[0015] The group III nitride crystal according to the first embodiment has a main surface and a back surface opposite to the main surface, and the average dislocation density of the main surface and the average dislocation density of the back surface are 6.0 × 10 5 cm -2 The following is true: the difference between the average dislocation density of the main surface and the average dislocation density of the back surface is 5.0 × 10⁻⁶. 4 cm -2 The following conditions apply, and the curvature of the crystal axis of the main plane is greater than or equal to a radius of curvature of 30m.

[0016] The group III nitride crystal according to the second embodiment has an average dislocation density of 2.0 × 10⁻¹⁰ on the main surface and an average dislocation density of 2.0 × 10⁻¹⁰ on the back surface, according to the first embodiment. 5 cm -2 The following is true: the difference between the average dislocation density of the main surface and the average dislocation density of the back surface is 2.0 × 10⁻⁶. 4 cm -2 The following is also acceptable.

[0017] In the third embodiment, the thickness of the group III nitride crystal may be 0.3 mm or more and 1.0 mm or less, as in the first or second embodiment described above.

[0018] The fourth embodiment of the group III nitride semiconductor comprises a group III nitride crystal according to any of the first to third embodiments described above, and a group III nitride semiconductor element laminated on the group III nitride crystal.

[0019] The group III nitride substrate according to the fifth embodiment includes a group III nitride species substrate containing Na and a group III nitride crystal according to any of the first to third embodiments, laminated on the group III nitride species substrate.

[0020] In the sixth embodiment, the group III nitride substrate may have a group III nitride crystal film thickness of 0.5 mm or more, as in the fifth embodiment.

[0021] A method for producing a group III nitride crystal according to the seventh embodiment comprises a preparation step of preparing a group III nitride species substrate containing Na, and a growth step of growing a group III nitride crystal on the group III nitride species substrate by vapor phase growth, wherein the starting temperature of the growth step is 950°C or higher and 970°C or lower, and the growth of the group III nitride crystal in the growth step is carried out at a temperature of 950°C or higher and 1020°C or lower.

[0022] The eighth embodiment of the method for producing a group III nitride crystal may further include a surface treatment step of surface treating a group III nitride species substrate containing Na at a temperature of 720°C to 900°C, as described in the seventh embodiment.

[0023] In the ninth embodiment, the method for producing a group III nitride crystal may be such that the surface treatment step is performed at a temperature of 720°C or higher and 750°C or lower, as in the eighth embodiment described above.

[0024] In the method for manufacturing a group-III nitride crystal according to the tenth aspect, in any of the seventh to ninth aspects described above, the growth of the group-III nitride crystal in the growth step may be performed at a growth rate of 100 μm / hour or more by controlling the supply amount and temperature of the source gas.

[0025] In the method for manufacturing a group-III nitride crystal according to the eleventh aspect, in any of the seventh to tenth aspects described above, the growth step may be performed until the film thickness of the group-III nitride crystal reaches 0.5 mm or more.

[0026] In the method for manufacturing a group-III nitride crystal according to the twelfth aspect, in any of the seventh to eleventh aspects described above, the method may further include a processing step of slicing and polishing the group-III nitride crystal grown on the group-III nitride species substrate.

[0027] Hereinafter, a group-III nitride crystal, a method for manufacturing the same, and a group-III nitride substrate according to an embodiment will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.

[0028] (Embodiment 1) A method for manufacturing a group-III nitride crystal according to Embodiment 1 will be described in detail with reference to FIGS. 8 and 9.

[0029] <Group-III nitride species substrate> In the first embodiment, a GaN crystal seed substrate produced by the Na flux method is used as the group-III nitride species substrate 101. The GaN crystal seed substrate can be formed by shaping and polishing a GaN ingot produced by the Na flux method and subjecting the surface to chemical mechanical polishing treatment (CMP treatment). The film thickness of the GaN crystal seed substrate used in this embodiment is 400 μm, but it is not limited thereto, and may be, for example, 300 μm or more and 2000 μm or less.

[0030] <Manufacturing apparatus for group-III nitride crystal> Fig. 8 shows a schematic diagram of a manufacturing apparatus 100 for a group-III nitride crystal used in the method for manufacturing a group-III nitride crystal according to Embodiment 1. This manufacturing apparatus 100 for a group-III nitride crystal includes a reaction chamber 110 in which a group-III nitride seed substrate 101 for growing a group-III nitride crystal is disposed, a first nozzle 111 for introducing a group-III-based reaction gas into the reaction chamber 110, a second nozzle 112 for introducing a group-V-based reaction gas into the reaction chamber 110, and a third nozzle 113 for introducing a carrier gas into the reaction chamber 110. The group-III-based reaction gas is generated by introducing a chloride-based gas from a chloride-based gas introduction nozzle 115 into a group-III raw material chamber 114 in which a group-III metal is disposed, and is supplied from the first nozzle 111 to the group-III nitride seed substrate 101. The substrate 101 disposed in the reaction chamber 110 is held by a susceptor 116, and the susceptor 116 is larger in size than the group-III nitride seed substrate 101. The susceptor 116 may further have a heating mechanism, a rotation mechanism, and the like. The gas introduced into the reaction chamber 110 is exhausted from an exhaust section 117.

[0031] <Method for Manufacturing Group-III Nitride Crystal> Fig. 9 shows a growth sequence of a group-III nitride crystal according to Embodiment 1. As shown in Fig. 9, the method for manufacturing a group-III nitride crystal includes a surface treatment step and a growth step having an initial growth step and a main growth step.

[0032] (Surface Treatment Step) In the heat treatment process, oxides such as oxide films and carbon deposits are removed from the surface of the group III nitride substrate 101, resulting in a clean crystalline surface. However, it is necessary to suppress the rupture of Na inclusions within the group III nitride substrate 101. In this embodiment 1, surface treatment at a temperature of 720°C to 900°C can suppress the rupture of Na inclusions and sufficiently improve the surface condition of the group III nitride substrate 101. If the surface treatment temperature is lower than 720°C, the etching effect of H2 and the decomposition of NH3 are insufficient, making it impossible to adequately clean the surface of the group III nitride substrate 101. Also, if the surface treatment temperature is higher than 900°C, it exceeds the growth temperature of the group III nitride substrate 101, making it impossible to adequately suppress the rupture of Na inclusions. Therefore, it is even more preferable to perform the surface treatment process at a temperature of 720°C to 800°C, and most preferably at a temperature of 720°C to 750°C.

[0033] (Initial growth process) The initial growth process is necessary to grow high-quality group III nitride crystals on the group III nitride substrate 101, inheriting the crystallinity of the highly crystalline group III nitride substrate 101. The initial growth process is a vapor phase growth process of group III nitride crystals on the group III nitride substrate 101, and is carried out at a temperature of 950°C to 970°C. That is, the starting temperature of the growth process is set to 950°C to 970°C. In the initial growth process, since group III nitride crystals have not yet grown on the surface of the group III nitride substrate 101 and the surface of the group III nitride substrate 101 is exposed, if the temperature is raised above 970°C, there is a risk that the Na inclusions in the plane of the group III nitride substrate 101 will rupture. On the other hand, at temperatures below 950°C, it is not possible to start the growth of group III nitride crystals on the group III nitride substrate 101. The initial growth process is carried out at a temperature of 950°C to 970°C to prevent the rupture of Na inclusions and to initiate the growth of group III nitride crystals. The initial growth process is preferably carried out until the film thickness of the group III nitride crystals growing on the group III nitride species substrate 101 reaches 30 μm or more, and more preferably until the film thickness reaches 100 μm or more. After the initial growth process, initial growth crystals 102 of group III nitride crystals are formed on the group III nitride species substrate 101. This is thought to fill in the Na inclusions exposed on the surface and to suppress the rupture of Na inclusions even when the growth temperature is raised to a certain extent during the subsequent main growth.

[0034] (Main training process) This growth process is carried out at a temperature of 950 °C or higher and 1020 °C or lower. When cutting out the III-nitride crystal grown on the III-nitride substrate 101 to form a wafer, it is desirable to perform this growth so that the growth film thickness becomes 0.5 mm or more. By extending the growth time of this growth process, it is possible to achieve a desired growth film thickness. For example, it is also possible to obtain the growth of a III-nitride crystal with a film thickness of about 10 mm. In order to achieve thick film growth of 0.5 mm or more, from the viewpoint of the efficiency of crystal growth, it is preferable to perform this growth at a growth rate of 100 μm / h or more, and a growth rate of 150 μm / h or more is more preferable.

[0035] Note that the growth rate can be set by controlling the supply amount of the source gas and the growth temperature (the temperature of the III-nitride crystal). In particular, the growth rate is substantially determined by the supply amount of the source gas. For example, in the case of a supply amount of 0.07 slm of HCl gas and 0.6 slm of NH3 gas, the growth rate is 28 μm / h. In the case of a supply amount of 0.13 slm of HCl gas and 1.2 slm of NH3 gas, the growth rate is 88 μm / h. In the case of a supply amount of 0.20 slm of HCl gas and 1.8 slm of NH3 gas, the growth rate is 159 μm / h. Also, in the case of a supply amount of 0.26 slm of HCl gas and 1.8 slm of NH3 gas, the growth rate is 200 μm / h.

[0036] In this growth process, if necessary, an n-type dopant such as Si, an n-type dopant such as O or Ge, or a p-type dopant such as Mg may be doped.

[0037] Through this growth process, a main growth crystal 103 of a III-nitride crystal is further formed on the initial growth crystal 102. Thereby, a III-nitride substrate on which a III-nitride crystal has grown on the III-nitride substrate 101 can be obtained.

[0038] <III-nitride substrate> In the group-III nitride substrate according to Embodiment 1, the grown group-III nitride crystal inherits the characteristics of the group-III nitride seed substrate 101. Therefore, by using a high-quality group-III nitride seed substrate 101 in which the rupture of Na inclusion is suppressed, the quality of the group-III nitride crystal can be improved. In Embodiment 1, the group-III nitride crystal on the group-III nitride seed substrate 101 has an average dislocation density on the front and back surfaces of 6.0×10 5 cm -2 or less, and the difference in the average dislocation density between the front and back surfaces is 5.0×10 4 cm -2 or less, and furthermore, a high quality with a radius of curvature of 30 m or more is realized. Moreover, even for a size of 2 inches or more in diameter, it is possible to obtain such a high-quality group-III nitride crystal with a thickness of 0.5 mm or more. Also, it is possible to realize an even higher quality where the average dislocation density on the front and back surfaces of the group-III nitride crystal on the group-III nitride seed substrate 101 is 3.0×10 5 cm -2 or less.

[0039] (Processing step) In Embodiment 1, the method for manufacturing a group-III nitride crystal may further include a processing step of slicing and polishing the group-III nitride crystal grown on the group-III nitride seed substrate 101. The group-III nitride crystal can be cut out from the group-III nitride substrate using a grinding machine, a wire saw, or the like. Then, if necessary, by performing ori-fla processing, mirror polishing, chemical mechanical polishing treatment, or the like on the surface of the cut-out group-III nitride crystal, a group-III nitride crystal can be obtained.

[0040] <Group-III nitride crystal> The wafer of the group-III nitride crystal thus obtained has a dislocation density on the front and back surfaces of 6.0×10 5 cm -2 or less, and the difference in the average dislocation density between the front and back surfaces is 5.0×10 4 cm -2The following is achieved, and moreover, a high quality with a radius of curvature of 30 m or more is realized. Moreover, even for a size of 2 inches or more in diameter, a wafer of a group III nitride crystal with such high quality and a thickness of 0.3 mm or more and 1.0 mm or less can be produced. The dislocation density on the front and back surfaces of the group III nitride crystal is 2.0×10 5 cm -2 or less, and the difference in the average dislocation density between the front and back surfaces is 2.0×10 4 cm -2 or less, and it is also possible to realize an even higher quality group III nitride crystal.

[0041] <Group III Nitride Semiconductor> By laminating a group III nitride semiconductor element on the wafer of the group III nitride crystal obtained above, a group III nitride semiconductor can be produced.

[0042] (Example) A GaN crystal seed substrate was produced using a template substrate on which a GaN thin film was grown on a sapphire substrate by the Na flux method.

[0043] (1) Na and Ga were introduced into the crucible in the liquid phase apparatus at a molar ratio of about 50:50, and the temperature of the crucible was set to 800°C or more and 1000°C or less.

[0044] (2) Next, nitrogen gas was fed into the liquid phase apparatus, and the gas pressure in the liquid phase apparatus was set to 1×10 6 Pa or more and 1×10 7 Pa or less, so that nitrogen was dissolved in the molten Na at a high temperature, and GaN crystals were grown on the template substrate immersed in the melt. The GaN crystal seed substrate grown by liquid phase growth (sometimes referred to as a liquid phase substrate or a liquid phase seed substrate) was regular hexagonal, and the inscribed circle was Φ60 mm. The obtained GaN crystal seed substrate grown by liquid phase growth was used as the group III nitride seed substrate 101.

[0045] Figure 7A shows the full width at half maximum (FWHM) of the X-ray ω-SCAN rocking curve of the (0002) plane in the liquid-phase grown GaN crystal species substrate. The FWHM at five points in the plane was 27.4 arcsec for the (0002) plane. Figure 7B shows the FWHM of the X-ray ω-SCAN rocking curve of the (10-12) plane in the liquid-phase grown GaN crystal species substrate of this embodiment 1. The FWHM at five points in the plane was 23.6 arcsec for the (10-12) plane. As shown in Figures 7A and 7B, the liquid-phase grown GaN crystal species substrate exhibits uniform and good crystallinity in the plane. Furthermore, the radius of curvature of the c plane, estimated from the peak angle of the (0002) plane in the plane, was approximately 60 m, indicating a flat surface. The liquid-phase grown GaN crystal species substrate used in the examples had a full width at half maximum (FWHM) of 32 arcsec or less in the (0002) plane and 33 arcsec or less in the (10-12) plane of the X-ray ω-SCAN rocking curve, and a radius of curvature of approximately 30 m or more.

[0046] (3) Next, the obtained liquid-phase grown GaN crystal seed substrate was subjected to heat treatment at 720°C. Specifically, the liquid-phase grown GaN crystal seed substrate was placed in the reaction chamber 110 of the group III nitride crystal manufacturing apparatus, and the temperature was raised to 720°C at a heating rate of 20°C / min under an N2 atmosphere. Then, while maintaining the temperature of the liquid-phase grown GaN crystal seed substrate, an NH3 flow rate of 3.5 slm was introduced into the reaction chamber 110 from the second nozzle 112, and an N2 flow rate of 4.0 slm and an H2 flow rate of 16.0 slm were introduced from the third nozzle 113, and heat treatment was performed for 60 minutes. The rotation speed of the susceptor 116 was set to 500 rpm.

[0047] Figure 10 shows the results of atomic force microscopy evaluation of a 3 μm × 3 μm region of a GaN crystal species substrate grown in the liquid phase after heat treatment. Good atomic steps were observed on the surface, indicating that the surface was well cleaned. The roughness value Ra estimated from the surface was 0.43 nm. Na inclusions were also examined using an optical microscope, but no rupture was observed.

[0048] (4) Next, initial growth was carried out at a growth temperature of 950°C. After heat treatment at 720°C, the liquid-phase grown GaN crystal species substrate was heated to 950°C at a rate of 10°C / min while maintaining a rotation speed of 500 rpm, under the conditions of NH3 flow rate of 5.0 slm, N2 flow rate of 45.0 slm, and H2 flow rate of 3.0 slm. After reaching 950°C, HCl gas was supplied to the reaction chamber 110 at a rate of 0.07 slm from the chloride gas introduction nozzle 115, NH3 gas at a rate of 0.6 slm from the second nozzle 112, and N2 gas at a rate of 44.0 slm and H2 gas at a rate of 12.0 slm from the third nozzle 113. The HCl gas supplied from the chloride gas introduction nozzle 115 becomes GaCl gas in the Group III raw material chamber 114 where Ga metal is installed, and is supplied to the reaction chamber 110 from the first nozzle 111. The growth rate of GaN, a group III nitride crystal, on a GaN crystal species substrate grown in the liquid phase was 28 μm / hour.

[0049] Figure 11 shows a photograph of a 110 μm thick GaN crystal grown on a triangular liquid-phase grown GaN crystal species substrate. It can be seen that a flat GaN crystal without surface roughness has been grown, indicating that the effect of Na inclusions has been suppressed.

[0050] Figures 12A and 12B show the results of the X-ray ω-SCAN rocking curves of the GaN crystal obtained in Figure 11. The estimated full width at half maximum (FWHM) was 26.6 arcsec in the (0002) plane in Figure 12A and 24.6 arcsec in the (10-12) plane in Figure 12B, which are almost the same as the values ​​for the liquid-phase grown GaN crystal substrate shown in Figures 7A and 7B, confirming good crystallinity inheritance. In addition, the radius of curvature of the crystal warpage estimated from the diffraction angle of the (0002) plane peak was 148 m, which is almost flat.

[0051] Figures 13A and 13B show the X-ray ω-SCAN rocking curve results when only the initial growth temperature is changed to 970°C under similar conditions. Even in this case, a full width at half maximum (FMAX) of 24.6 arcsec in the (0002) plane in Figure 13A and 22.3 arcsec in the (10-12) plane in Figure 13B, with a radius of curvature of 67 m, can be obtained, indicating good crystallinity.

[0052] (5) After initial growth at 950°C, the substrate was heated to 1020°C at a rate of 10°C / min while maintaining the initial growth conditions, and the main growth was carried out. After the temperature rise, a high growth rate was achieved by changing the supply gas flow rates to HCl gas 0.26 slm, NH3 gas 1.8 slm, carrier gas N2 gas 44.0 slm, and H2 gas 10.5 slm. In addition, to dope with Si, SiH2Cl2 gas was supplied at 90 sccm from the chloride-based gas introduction nozzle 115. The growth rate was 200 μm / hour, and the rotation speed was 500 rpm. The growth time was 5 hours, and the grown film thickness was 1.1 mm. The Si concentration in the grown GaN crystal was 5 × 10⁻⁶. 17 cm 3 That was the case.

[0053] Figure 14 shows a photograph of the GaN crystal on the liquid-phase grown GaN crystal seed substrate after growth. From Figure 14, it can be seen that the growth was successful, with no significant surface roughness, which is thought to be due to Na inclusions. Furthermore, the X-ray ω-SCAN rocking curve results for this substrate, as shown in Figure 15A, yielded a full width at half maximum of 26.5 arcsec in the (0002) plane and 25.9 arcsec in the (10-12) plane, as shown in Figure 15B, with a radius of curvature of 60 m, indicating good crystallinity. These results indicate that the quality of the liquid-phase grown GaN crystal seed substrate is carried over from the initial growth to the main growth, suggesting that there is almost no difference in crystallinity in the film thickness direction.

[0054] Table 1 in Figure 26 summarizes the results of the study on the crystallinity of GaN grown films in relation to the growth rate and growth temperature. The study of these growth conditions was conducted after heat-treating a GaN crystal seed substrate grown in the liquid phase at 740°C and then growing an initial layer of 110 μm thickness at 950°C. In Table 1, "Improvement" indicates that the change in the full width at half maximum of the X-ray ω-SCAN rocking curve after growth is improved or kept within +1.0 arcsec compared to the GaN crystal seed crystal grown in the liquid phase. "Degradation" indicates that the crystallinity was not inherited from the GaN crystal seed crystal and was degraded. "-" indicates conditions that were not tested. From Table 1, it can be concluded that for this growth method, a growth rate of 28 μm / hour is suitable, and the temperature should be between 950°C and 1020°C. It can be seen that a temperature of 1000°C to 1020°C is good for growth rates between 88 μm / hour and 200 μm / hour, and that a temperature of 1000°C to 1020°C is good for achieving growth rates of 200 μm / hour or higher. In Table 1, under the conditions in the upper right, the crystallinity of the GaN crystal seed crystal grown in the liquid phase cannot be inherited after growth, and the crystallinity tends to deteriorate. On the other hand, under the conditions in the lower left of Table 1, the crystallinity of the GaN crystal seed crystal grown in the liquid phase can be inherited after growth, or can even be improved.

[0055] The crystallinity of Group III nitride crystals is largely dependent on the crystallinity of the liquid-phase grown GaN substrate, which serves as the seed substrate. Even in the GaN substrate with low crystallinity among the liquid-phase grown GaN crystals in this embodiment, the full width at half maximum of the X-ray ω-SCAN rocking curve was 32 arcsec or less on the (0002) plane and 33 arcsec or less on the (10-12) plane, with a radius of curvature of approximately 30 m, and the estimated surface dislocation density was 6.0 × 10⁻¹⁰. 5 cm -2 Compared to conventional GaN substrates, the dislocation density is nearly an order of magnitude smaller.

[0056] (6) Next, the thick GaN crystals on the liquid-phase grown GaN crystal seed substrate prepared in this embodiment were sliced ​​to cut out 2-inch GaN crystals. A grinding machine was used for processing to circularize the hexagonal GaN crystals to a diameter of approximately 52 mm, and then slicing was performed using a wire saw to produce multiple HVPE-grown GaN freestanding wafers with a thickness of 650 μm. Furthermore, orientation flattening and mirror polishing of the front and back surfaces were performed, and finally the surface was chemically and mechanically polished (CMP) to obtain GaN freestanding substrates with a thickness of 400 μm and a diameter of 2 inches.

[0057] A photograph of the fabricated GaN freestanding substrate is shown in Figure 16. Figure 16 shows a GaN substrate cut from a region near the interface of a seed crystal / HVPE grown crystal grown in the liquid phase. It can be seen that a 2-inch substrate without through-pits due to the rupture of Na inclusions has been formed.

[0058] Figures 17A and 17B show the in-plane distribution of the full width at half maximum (FWHM) of the X-ray ω-SCAN rocking curve of a 2-inch GaN freestanding substrate. The average FWHM values ​​for the (0002) plane in Figure 17A and the (10-12) plane in Figure 17B were 22.8 arcsec and 19.4 arcsec, respectively. HVPE growth resulted in better FWHM values ​​than those for liquid-phase grown GaN crystal species substrates. Furthermore, the radius of curvature of the crystal estimated from the diffraction peak of the (0002) plane was a good 66 m, which was comparable to that of liquid-phase grown GaN crystal species substrates.

[0059] Figure 18 shows the results of cathodoluminescence measurement of the surface of the fabricated GaN freestanding substrate. In Figure 18, the dark spots enclosed by the white dotted line correspond to dislocations. The density of dark spots corresponding to dislocations was calculated from Figure 18 to be 5.5 × 10⁻⁶. 4 cm -2 The average dislocation density obtained from random measurements across the substrate surface was 1.7 × 10⁻⁶. 5 cm -2 That was the case.

[0060] Figure 19 shows the numerical value of the in-plane dislocation density of the GaN freestanding substrate shown in Figure 16, obtained from images obtained by two-photon photoluminescence measurements. The measurements in Figure 19 were taken in five in-plane regions, one at the center and two at 20 mm from the center, each measuring a 1 mm × 1 mm area (inset in Figure 19). Each measurement covered a 0.25 mm × 0.25 mm region, and these were measured continuously in a 4 × 4 pattern to obtain the 1 mm × 1 mm region. The numerical values ​​shown in Figure 19 represent the dislocation density observed in each 0.25 mm × 0.25 mm region. The average value at each point is also shown in the figure. The estimated dislocation density in a 0.25 mm × 0.25 mm region is at most 3.9 × 10⁻¹⁰. 5 cm -2 The in-plane uniformity was relatively good. The average dislocation density was 1.2 × 10⁻⁶. 5 cm -2 This resulted in a value more than an order of magnitude lower than that obtained for GaN freestanding substrates fabricated using the conventional HVPE method. This value was close to the cathodoluminescence measurement result shown in Figure 18. The dislocation density on the back surface of the GaN freestanding substrate of the example was also measured and evaluated using two-photon photoluminescence. The dislocation density on the back surface was 1.3 × 10⁻⁶. 5 cm -2 It is almost equivalent to the surface, and the difference in dislocation density between the surface and the back surface is 4.8 × 10⁻⁶. 3 cm -2 The difference was slight. Generally, GaN freestanding substrates fabricated by the HVPE method tend to show a decrease in dislocation density in the stacking direction, as shown in Figure 1. However, large changes in dislocation density can induce crystal warping, so a small difference in dislocation density is preferable.

[0061] The surface dislocation density of the liquid-phase grown GaN crystal species substrate used in this example was 2.0 × 10⁻⁶. 5 cm -2As shown in Figure 20, the change in dislocation density in a GaN freestanding substrate due to HVPE growth tends to change inversely proportional to the film thickness of the grown GaN crystal. The plots in Figure 20 show the results of this embodiment. The dotted line indicates the dislocation density that changes inversely proportional to the film thickness. From the results in Figure 20, it is considered that when a GaN freestanding substrate with a thickness of 400 μm is fabricated by slicing and forming many GaN crystals, the difference in dislocation density between the front and back surfaces will be as shown in Figure 21. Therefore, the difference in dislocation density between the front and back surfaces is 2.0 × 10⁻⁶ in all film thickness ranges, as shown by the dotted line in Figure 21. 4 cm -2 The following applies.

[0062] Under exactly the same conditions as above, only the surface dislocation density of the liquid-phase grown GaN crystal species substrate was measured to 6.0 × 10⁻⁶. 5 cm -2 When a GaN freestanding substrate is fabricated by changing the method, the change in dislocation density in the GaN freestanding substrate due to HVPE growth follows the trend shown in Figure 22. From the results in Figure 22, when a 400 μm thick GaN freestanding substrate is fabricated by slicing and shaping a large number of GaN crystals, as in the case of Figure 21, the difference in dislocation density between the front and back surfaces is as shown in Figure 23. Even in this case, the difference in dislocation density between the front and back surfaces is 5.0 × 10⁻⁶, as indicated by the dotted line in Figure 23. 4 cm -2 The following applies.

[0063] As in the example, when the difference in dislocation density between the front and back surfaces is small, the radius of curvature of the crystal axis of the GaN freestanding substrate is 30m or more, mainly inheriting the characteristics of the liquid-phase grown GaN crystal species substrate.

[0064] (Comparative example - Main training) The same surface dislocation density used in the example is 2.0 × 10 5 cm -2On a GaN crystal seed substrate grown in the liquid phase, heat treatment was performed at 740°C under the same conditions as in the example. After initial growth to a thickness of 110 μm at 950°C, the temperature was increased to 1035°C at a rate of 10°C / min while maintaining the initial growth conditions. Subsequently, the gases were changed to HCl gas (0.26 slm), NH3 gas (1.8 slm), carrier gas (N2 gas (44.0 slm), H2 gas (10.5 slm)) and supplied to grow a GaN crystal with a thickness of 1.1 mm. The growth rate was 200 μm / hour and the rotation speed was 500 rpm.

[0065] Figure 24 shows a photograph of GaN crystals on a GaN crystal species substrate grown in the liquid phase in the comparative example. Unlike the example, in the comparative example, the growth temperature was set to a high temperature of 1035°C during this growth process, which prevented the rupture of Na inclusions and resulted in surface roughness.

[0066] Furthermore, an electron microscope image of the cross-section of the comparative example GaN crystal shown in Figure 25 confirmed that the GaN growth film above the Na inclusion was growing in three dimensions. An attempt was made to measure the X-ray ω-SCAN rocking curve, but the surface roughness was too great and the crystallinity was poor, making measurement impossible. In addition, because the surface was so rough, it cracked during the surface planarization process, making it impossible to cut and shape the material.

[0067] Furthermore, this disclosure includes appropriately combining any of the various embodiments and / or examples described above, and the effects of each embodiment and / or example can be achieved. [Industrial applicability]

[0068] Because the Group III nitride crystals relating to this disclosure are of high quality, they can be used in high-performance Group III nitride devices. [Explanation of Symbols]

[0069] Apparatus for manufacturing Group III nitride crystals 101 Group III nitride seed substrate 102 Initial Growth Crystals 103 Growth Crystals 110 Reaction Chamber 111 Nozzle No. 1 112 Nozzle No. 2 113 Third Nozzle 114 Group III raw material room 115 Chloride-based gas introduction nozzle 116 Susceptor 117 Exhaust section

Claims

1. Preparation steps for preparing a group III nitride species substrate containing Na, A surface treatment step of surface-treating the aforementioned Na-containing group III nitride substrate at a temperature of 720°C to 900°C, The process includes a growth step of growing a group III nitride crystal on the group III nitride substrate by vapor phase growth, The starting temperature for the growth process is 950°C or higher and 970°C or lower. The growth of the group III nitride crystal in the aforementioned growth process is carried out at a temperature of 950°C to 1020°C. A method for producing Group III nitride crystals.

2. The surface treatment step is performed at a temperature of 720°C to 750°C. A method for producing a group III nitride crystal according to claim 1.

3. The growth of the group III nitride crystal in the aforementioned growth process is carried out at a growth rate of 100 μm / hour or more by controlling the supply amount of the raw material gas and the temperature of the group III nitride crystal. A method for producing a group III nitride crystal according to claim 1 or 2.

4. The growth process is carried out until the thickness of the group III nitride crystal reaches 0.5 mm or more. A method for producing a group III nitride crystal according to any one of claims 1 to 3.

5. The process further includes slicing and polishing the group III nitride crystals grown on the group III nitride substrate. A method for producing a group III nitride crystal according to any one of claims 1 to 4.

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