Gallium nitride single crystal substrate, and gallium nitride single crystal substrate production method

Abstract

To provide a gallium nitride single crystal substrate having high resistance with Mn doped uniformly.SOLUTION: A gallium nitride single crystal substrate has a diameter of 50 mm or more, and a crystal face with a low index nearest a main plane is a (0001) face. An Mn concentration in the substrate is 5×1017 cm-3 or more. Variation of the Mn concentration when secondary ion-mass analysis is applied to plural arbitrary points on the main plane is within an average value of ±20%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a gallium nitride single crystal substrate and a method for manufacturing a gallium nitride single crystal substrate. [Background technology]

[0002] Group III nitride semiconductors, typified by gallium nitride (GaN), are widely used as materials for semiconductor devices such as light-emitting devices and electronic devices. In order to improve the quality (semiconductor characteristics, etc.) of semiconductor devices made of Group III nitride semiconductors, it is desirable to manufacture semiconductor stacks or nitride semiconductor freestanding substrates for use in manufacturing semiconductor devices with good crystal quality.

[0003] As a method for producing a GaN single crystal substrate, for example, Patent Document 1 discloses a method for producing a gallium nitride single crystal substrate by a VAS (Void-Assisted Separation) method. Also, Patent Document 2 discloses a method including a step of epitaxially growing a semiconductor layer made of GaN on a substrate and a step of slicing the GaN layer to produce a GaN freestanding substrate.

[0004] Furthermore, for applications such as manufacturing high-frequency semiconductor devices, semi-insulating GaN single crystal substrates with high resistance are required. Iron (Fe), manganese (Mn), and carbon (C) are used as dopants to obtain semi-insulating GaN single crystal substrates, and among these, manganese (Mn) can be used to produce substrates with the highest resistance. For example, Patent Document 3 discloses a method for manufacturing a nitride crystal substrate, in which a crystal layer made of a single crystal of a group-III nitride semiconductor containing manganese is epitaxially grown on the base substrate by hydride vapor phase epitaxy (HVPE). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-178984 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-156189 [Patent Document 3] Patent Publication No. 2021-109813 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has become clear that Mn-doped GaN substrates, especially large-diameter GaN substrates (eg, diameters of 50 mm or more), have a problem in that the Mn concentration distribution within the substrate surface varies widely.

[0007] An object of the present invention is to provide a high-resistivity gallium nitride single crystal substrate that is uniformly doped with Mn. [Means for solving the problem]

[0008] According to one aspect of the present invention, A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate is provided in which the variation in Mn concentration when secondary ion mass spectrometry is performed on a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0009] According to another aspect of the present invention, A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate is provided in which the variation in resistivity measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0010] According to yet another aspect of the present invention, A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate is provided in which the variation in Vickers hardness measured at a plurality of arbitrary points on the main surface is within ±2% of the average value.

[0011] According to yet another aspect of the present invention, A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate is provided in which the variation in arithmetic mean height Sa when surface roughness is measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0012] According to yet another aspect of the present invention, A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, The gallium nitride single crystal substrate is provided in which the variation in the minimum value of light transmittance in the wavelength range of 700 nm to 900 nm at any given point on the main surface is within ±20% of the average value.

[0013] According to yet another aspect of the present invention, A step (a) of preparing a base substrate made of gallium nitride single crystal, the low-index crystal plane closest to the primary surface being the (0001) plane; On the main surface of the base substrate, a Mn concentration of 5×10 17 cm -3a step (b) of epitaxially growing the above-described gallium nitride single crystal; and step (c) of obtaining a gallium nitride single crystal substrate having a diameter of 50 mm or more from the gallium nitride single crystal epitaxially grown in step (b), In the step (b), a gas containing HCl is intermittently introduced and the growth interface is periodically etched, thereby doping Mn uniformly into the crystal, thereby providing a method for producing a gallium nitride single crystal substrate. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a gallium nitride single crystal substrate that is uniformly doped with Mn and has high resistance. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present invention. [Figure 2] 2(a) to 2(c) are schematic cross-sectional views showing a part of a method for producing a gallium nitride single crystal substrate according to one embodiment of the present invention. [Figure 3] FIG. 3(a) is a photograph of a region on the primary surface of a gallium nitride single crystal substrate that is uniformly doped with Mn, and FIG. 3(b) is a photograph of a region that is non-uniformly doped with Mn. [Figure 4] FIG. 4(a) is a photograph of the substrate of Example 1 according to the present invention, and FIG. 4(b) is a photograph of the substrate of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Insights gained by the inventor> First, the findings of the inventors will be described.

[0017] The inventors have repeatedly grown Mn-doped GaN crystals, and have found that the Mn content is increased to, for example, 5×10 17 cm -3When doped to this extent, we found that variations occurred in the performance of devices fabricated on the substrate. It has also become clear that the factors that cause variations in device performance mentioned above are correlated with the concentration of Mn incorporated into the crystal. The amount of Mn incorporated into a crystal tends to vary depending on the inclination of the crystal plane orientation on the surface during crystal growth. Therefore, when a morphology with a slightly inclined plane from the c-plane appears on the surface during crystal growth, the amount of Mn incorporated in that region changes, easily resulting in uneven Mn concentration within the crystal plane. This morphology is caused by the influence of internal residual stress during crystal growth and warpage of the crystal's c-plane. In particular, GaN crystal growth is prone to warpage during growth. When large-diameter GaN substrates (e.g., those with diameters exceeding 50 mm) are manufactured, warpage of the crystal's c-plane can cause the growth surface to tilt from the original growth plane orientation (0001). This results in the appearance of morphology within the crystal growth surface that depends on the inclination of the growth plane orientation, making it more likely that regions with uneven Mn concentrations will occur.

[0018] The inventors have conducted extensive research into the above-mentioned problems. Variations in the incorporation of Mn into GaN crystals occur due to the formation of vicinal planes on the growth surface during crystal growth, which are slightly tilted from the c-plane. The formation of vicinal planes at the growth interface is thought to be due to variations in the density and orientation of atomic steps formed due to defects such as dislocations and deviations of the crystal surface from the c-plane. Therefore, during the process of growing a Mn-doped GaN layer, a gas containing HCl is intermittently introduced to the growth interface, and the surface of the growing crystal is periodically etched to maintain the flatness and cleanliness of the interface. This suppresses the formation of minute facets at the growth interface, preventing the appearance of the aforementioned morphology on the growth surface, and thereby establishing a technology for uniformly doping Mn into GaN crystals.

[0019] <One embodiment of the present invention> Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] In the following, in a GaN crystal having a wurtzite structure, <0001> The axis is called the "c-axis" and the (0001) plane is called the "c-plane." The (0001) plane is sometimes called the "+c-plane (gallium polarity plane)" and the (000-1) plane is sometimes called the "-c-plane (nitrogen polarity plane)." The <1-100> axis is called the "m-axis" and the {1-100} plane is called the "m-plane." The m-axis can also be written as the <10-10> axis. The <11-20> axis is called the "a-axis" and the {11-20} plane is called the "a-plane."

[0021] (1) Method for manufacturing gallium nitride single crystal substrate First, a method for manufacturing a gallium nitride single crystal substrate according to this embodiment will be described. Fig. 1 is a flowchart showing a method for manufacturing a gallium nitride single crystal substrate according to this embodiment. Figs. 2(a) to 2(c) are schematic cross-sectional views showing a part of the method for manufacturing a gallium nitride single crystal substrate according to this embodiment.

[0022] As shown in FIG. 1, the method for manufacturing a gallium nitride single crystal substrate according to this embodiment includes, for example, a base substrate preparation step S100, a growth step S110, and a slicing and processing step S120.

[0023] (S100: Base board preparation process) As shown in FIG. 2(a), in the base substrate preparation step S100, a base substrate 10 made of a gallium nitride single crystal is prepared, in which the low-index crystal plane closest to the primary surface 10s is the (0001) plane (c-plane). Specifically, a commercially available gallium nitride single crystal substrate (not a template, but a freestanding substrate) may be used as the base substrate 10, or the base substrate 10 made of a gallium nitride single crystal may be fabricated by the Void-Assisted Separation (VAS) method described in Patent Document 1. The base substrate 10 may be either Mn-doped or undoped, but is preferably Mn-doped. This reduces the lattice constant difference caused by the Mn concentration difference between the base substrate 10 and the growth layer 30 described below.

[0024] (S110: Growth process) In the growth step S110, a GaN single crystal is epitaxially grown on the primary surface 10s of the base substrate 10 prepared in the base substrate preparation step S100, as shown in Fig. 2(b). Specifically, for example, by supplying GaCl gas and NH gas to the heated base substrate 10 using the HVPE method, epitaxial growth is performed directly on the primary surface 10s of the base substrate 10, thereby growing a growth layer 30.

[0025] In the growth step S110, the growth layer 30 is grown under predetermined growth conditions, for example. In this embodiment, the growth conditions preferably include a growth temperature of 980° C. or higher and 1200° C. or lower. In addition, in the growth step S110, the supply partial pressure ratio of NH gas as a nitriding agent gas to GaCl gas as a Group III source gas (hereinafter also referred to as "V / III ratio") is preferably 0.1 or higher and 5.0 or lower.

[0026] In the growth step S110, GaCl gas, NH gas, and a Mn dopant gas, such as manganese chloride (MnCl) gas, are supplied to the base substrate 10, so that the Mn concentration becomes 5×10 17 cm -3 More than 1×10 20 cm -3 The following Mn-doped GaN layer is epitaxially grown. MnCl2 gas can be obtained, for example, by reacting solid Mn with HCl gas. Either H2 gas or N2 gas, or both, can be used as the carrier gas. In either case, it is preferable to control the flow rate using a mass flow controller so that the partial pressure of the MnCl2 gas is 0.1 to 2.2 Pa.

[0027] Other growth conditions in the growth step S110 are, for example, as follows: Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa Partial pressure of MnCl2 gas: 0.1 to 2.2 Pa N2 gas flow rate / H2 gas flow rate: 0 to 1

[0028] In the growth step S110, a gas containing HCl is intermittently introduced to periodically etch the growth interface (hereinafter also referred to as intermittent etching), thereby doping the crystal uniformly with Mn. Specifically, for example, during growth using the c-plane as the growth surface, the supply of GaN source gas and dopant gas is temporarily stopped, and HCl gas and a carrier gas (e.g., H2 gas) are introduced. This suppresses the formation of minute facets on the growth surface, allowing for uniform doping with Mn. Note that the introduction of the gas containing HCl is preferably carried out, for example, at intervals of 5 to 10 minutes, for 0.5 to 1 minute per introduction.

[0029] In the growth step S110, the thickness of the growth layer 30 is preferably, for example, 1 mm or more and 20 mm or less. When a GaN substrate fabricated using the VAS method described above is used as the base substrate 10, the c-plane of the base substrate 10 often has a concave warp toward the surface (crystal growth surface). Even GaN substrates fabricated using other methods may have a curved c-plane due to stress generated within the crystal during growth. The c-plane warp of the base substrate 10 is inherited by the growth layer 30 grown on it. However, by growing the growth layer 30 to a certain thickness or more, stress is generated within the crystal to reverse the warp and flatten the c-plane. The magnitude of the c-plane warp gradually decreases, resulting in a c-plane warp corresponding to the thickness of the growth layer 30. If the growth layer 30 is less than 1 mm thick, the stress required to reverse the c-plane warp may be insufficient. Furthermore, in the subsequent slicing and processing step S120, it is difficult to obtain a GaN single crystal substrate with sufficient thickness. By setting the thickness of the growth layer 30 to 1 mm or more, the c-plane warpage can be reduced. Furthermore, a GaN single crystal substrate of sufficient thickness can be obtained in the subsequent slicing and processing step S120. On the other hand, if the thickness of the growth layer 30 exceeds 20 mm, excessive strain accumulates in the crystal due to the force attempting to restore the c-plane warpage, which can lead to the proliferation of dislocations and the occurrence of microcracks. Furthermore, the internal residual stress of the GaN crystal increases, making the crystal more susceptible to cracking in the slicing and processing step S120. By setting the thickness of the growth layer 30 to 20 mm or less, the internal residual stress of the GaN crystal can be reduced, suppressing cracking and breakage.

[0030] (S120: Slicing and processing process) 1(c), in the slicing and processing step S120, the growth layer 30 is sliced, for example, using a wire saw or the like along a cutting plane substantially parallel to the main surface 30s of the growth layer 30. This results in at least one gallium nitride single crystal substrate 50 (also referred to as substrate 50) having a diameter of 50 mm or more as an as-sliced ​​substrate. At this time, it is preferable to slice the substrate 50 so that the thickness is, for example, 300 μm or more and 1200 μm or less.

[0031] When a GaN substrate fabricated by the VAS method is used as the base substrate 10, the c-plane of the base substrate 10 typically has a curvature radius of approximately 5 m, with the surface facing in a concave direction. The radius of curvature of the c-plane of the substrate 50 cut out from the growth layer 30 is larger than that of the c-plane of the base substrate 10. Furthermore, because the substrate 50 is released from the stress applied by the base substrate 10 upon being cut out from the base substrate 10, the radius of curvature of the c-plane tends to be even larger than that of the base substrate 10 with the growth layer 30 formed thereon, as shown in FIG. 2( b). Specifically, the radius of curvature of the c-plane of the substrate 50 is preferably, for example, 10 m or more, and more preferably 20 m or more. This allows the variation in the off-angle θ of the c-axis of the substrate 50 relative to the normal to the primary surface 50s (the maximum and minimum difference between the off-angle θ within the substrate plane) to be smaller than the variation in the off-angle of the c-axis of the base substrate 10.

[0032] Once the substrate 50 is obtained as an as-sliced ​​substrate, both surfaces of the substrate 50 may be polished using, for example, a polishing device.

[0033] In this embodiment, the substrate 50 obtained in the slicing and processing step S120 may be used as a new base substrate 10, and the growing step S110 and the slicing and processing step S120 may be repeated multiple times (e.g., four or more times). This type of growth method is referred to herein as "alternate-generation growth." By performing alternate-generation growth rather than growing a thick film all at once, the warpage of the c-plane is alleviated each time the substrate 50 is sliced, thereby reducing the internal residual stress of the GaN crystal. The reduction in internal residual stress suppresses the occurrence of morphology and facilitates uniform Mn doping. The upper limit of the number of times alternate-generation growth can be performed is not particularly limited, but from the perspective of efficiently producing large-diameter GaN single crystal substrates, it is preferable to perform the growth step 10 times or less.

[0034] Through the above steps, the substrate 50 according to this embodiment is manufactured.

[0035] (Process for manufacturing semiconductor laminates and process for manufacturing semiconductor devices) After the substrate 50 is manufactured, a semiconductor functional layer made of, for example, a group III nitride semiconductor may be epitaxially grown on the substrate 50 to produce a semiconductor laminate. After the semiconductor laminate is produced, electrodes and the like may be formed on the semiconductor laminate, and the semiconductor laminate may be diced to cut out chips of a predetermined size. In this manner, a semiconductor device may be produced. Because the substrate 50 is uniformly doped with Mn, it is suitable for producing high-frequency semiconductor devices and the like.

[0036] (2) Gallium nitride single crystal substrate (freestanding nitride semiconductor substrate, nitride crystal substrate) Next, the gallium nitride single crystal substrate 50 according to this embodiment will be described.

[0037] In this embodiment, the substrate 50 obtained by the above-described manufacturing method is a free-standing substrate made of single crystal GaN.

[0038] The diameter of the substrate 50 is, for example, 50 mm or more, and the thickness of the substrate 50 is, for example, 300 μm or more and 1 mm or less.

[0039] The Mn concentration in the substrate 50 is, for example, 5×10 17 cm -3 Over 1.0 x 10 20 cm -3 less than or equal to 5 × 10 17 cm -3 Over 5.0 x 10 19 cm -3 or less, more preferably 1×10 18 cm -3 Over 5.0 x 10 19 cm -3The more diluted the Mn concentration in the substrate 50 is in the range where the resistance increases, the greater the influence that variations in the Mn concentration in the substrate 50 have on the substrate resistance value. Therefore, the lower the Mn doping level of the substrate, the more effective it is to perform intermittent etching frequently during Mn doping growth. Note that although the Mn concentration is prone to vary within the substrate surface, the substrate 50 of this embodiment is uniformly doped with Mn by intermittent etching. Therefore, when secondary ion mass spectrometry (SIMS) is performed on a plurality of arbitrary points on the main surface 50s, the Mn concentration can be measured at, for example, 5×10 17 cm -3 Over 1.0 x 10 20 cm -3 The results are within the range below, within ±20% of the average value.

[0040] The substrate 50 has, for example, a primary surface 50s that serves as an epitaxial growth surface. In this embodiment, the crystal plane with a low index closest to the primary surface 50s is, for example, the (0001) plane.

[0041] The main surface 50s of the substrate 50 is polished to a mirror finish, for example, and the root mean square roughness RMS of the main surface 50s of the substrate 50 is, for example, less than 1 nm.

[0042] Furthermore, in this embodiment, the impurity concentration in the substrate 50 obtained by the above-described manufacturing method is lower than that of a substrate obtained by liquid phase growth such as a flux method or an ammonothermal method.

[0043] Specifically, the hydrogen (H) concentration in the substrate 50 is, for example, 1×10 17 cm -3 Less than 5 x 10 16 cm -3 The oxygen (O) concentration in the substrate 50 is, for example, 5×10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0044] The total content of silicon (Si) and oxygen (O) in the substrate 50 is, for example, 1×10 17cm -3 The total content of Fe and carbon (C) in the substrate 50 is preferably, for example, 1×10 17 cm -3 Furthermore, the total content of Si, O, Fe, and C in the substrate 50 is preferably, for example, 1×10 17 cm -3 More preferably, it is:

[0045] The substrate 50 is doped with Mn, and the content of Si and O as n-type impurities is low compared to the Mn concentration, making it a high-resistivity substrate. The average resistivity of the substrate 50 is, for example, 1×10 8 It is preferable that the resistivity is Ωcm or more.

[0046] (Curving of the c-plane and variation in off-angle) The radius of curvature of the c-plane of substrate 50 is, for example, larger than the radius of curvature of the c-plane of base substrate 10. Specifically, the radius of curvature of the c-plane of substrate 50 is, for example, preferably 10 m or more, and more preferably 20 m or more. The intermittent etching described above can minimize the impurity distribution in the crystal of substrate 50 and reduce the internal residual stress of the crystal. As a result, cracks and breaks are less likely to occur even when the crystal is grown thicker than when intermittent etching is not performed, and the radius of curvature of the c-plane can be further increased.

[0047] In this embodiment, the upper limit of the radius of curvature of the c-plane of the substrate 50 is not particularly limited, and the larger the radius, the better. When the c-plane of the substrate 50 is substantially flat, the radius of curvature of the c-plane can be considered to be infinite.

[0048] Furthermore, in this embodiment, since the radius of curvature of the c-plane of the substrate 50 is large, the variation in the off-angle θ of the c-axis relative to the normal to the main surface 50s of the substrate 50 can be made smaller than the variation in the off-angle of the c-axis of the base substrate 10.

[0049] Specifically, when an X-ray rocking curve measurement is performed on the (0002) plane of the substrate 50 and the off-angle θ of the c-axis relative to the normal to the main surface 50s is measured based on the diffraction peak angle of the (0002) plane, the variation calculated as the maximum / minimum difference in the magnitude of the off-angle θ within a diameter of 25 mm from the center of the main surface 50s is, for example, 0.14° or less, preferably 0.07° or less, and more preferably 0.05° or less.

[0050] In this embodiment, the lower limit of the variation in the off-angle θ of the c-axis of the substrate 50 is not particularly limited, and the smaller the better. When the c-plane of the substrate 50 is substantially flat, the variation in the off-angle θ of the c-axis of the substrate 50 can be considered to be 0°.

[0051] Furthermore, in this embodiment, the curvature of the c-plane is isotropically reduced relative to the main surface 50s of the substrate 50, so the radius of curvature of the c-plane has little directional dependency.

[0052] Specifically, the difference between the radius of curvature of the c-plane in the direction along the a-axis and the radius of curvature of the c-plane in the direction along the m-axis, as determined by the above-mentioned measurement method, is, for example, 50% or less, preferably 20% or less, of the larger of these radii of curvature.

[0053] (dislocation density) In this embodiment, the dislocation density at the surface of the substrate 50 is reduced compared to the dislocation density at the major surface 10s of the base substrate 10.

[0054] In this embodiment, crystal growth is carried out so as to maintain the flatness of the crystal growth interface, so a mechanism that causes localized concentration of propagating dislocations does not work. Therefore, no regions with particularly high dislocation density due to dislocation concentration are formed, and the distribution of dislocation density is uniform within the substrate surface. Furthermore, it has been confirmed by observing etch pits corresponding to dislocations formed by etching in molten alkali that the dislocation density in GaN crystals does not increase even when Mn is doped at a high concentration.

[0055] (In-plane uniformity) The substrate 50 of this embodiment has a uniform Mn concentration in the plane and various properties described below due to the intermittent etching described above.

[0056] Specifically, for example, when secondary ion mass spectrometry (SIMS) is performed on a plurality of arbitrary points on the main surface 50s, the variation in Mn concentration is within ±20% of the average value. When selecting a plurality of arbitrary points on the main surface 50s, it is preferable to select, for example, three or more points, more preferably five or more points, and even more preferably ten or more points. Furthermore, because the vicinity of the outer periphery of the substrate 50 is susceptible to the effects of polishing and the like, it is preferable to select a plurality of arbitrary points excluding, for example, a region extending 5 mm inward from the outer periphery of the main surface 50s.

[0057] Furthermore, for example, it is preferable that the variation in resistivity measured at a plurality of arbitrary points on the main surface 50s is within ±20% of the average value. A uniform resistivity value in the plane indicates that Mn is doped uniformly in the plane. The method for selecting a plurality of arbitrary points on the main surface 50s is as described above.

[0058] Furthermore, for example, when measuring the Vickers hardness at a plurality of arbitrary points on the main surface 50s, it is preferable that the variation is within ±2% of the average value. A uniform Vickers hardness value in the plane indicates that Mn is doped uniformly in the plane. The method for selecting the plurality of arbitrary points on the main surface 50s is as described above.

[0059] Furthermore, for example, when surface roughness is measured at multiple arbitrary points on the main surface 50s, it is preferable that the variation in the arithmetic mean height Sa is within ±20% of the average value. Differences in the Mn concentration in the crystal cause variations in the mechanical strength and chemical reactivity of the crystal, which in turn causes variations in the amount of removal during the polishing process depending on the Mn concentration variation, and this effect is reflected in the variation in the Sa value. A uniform value of the arithmetic mean height Sa indicates that Mn is doped uniformly within the surface. The method for selecting multiple arbitrary points on the main surface 50s is as described above.

[0060] Furthermore, in regions of the main surface 50s where the Mn concentration is non-uniform, color unevenness corresponding to the intensity of the Mn concentration is observed. FIG. 3(a) is a photograph of a region where Mn is uniformly doped, and FIG. 3(b) is a photograph of a region where Mn is non-uniformly doped. As shown in FIG. 3(a), color unevenness is not observed in the region where Mn is uniformly doped. On the other hand, as shown in FIG. 3(b), color unevenness is observed in the region where Mn is non-uniformly doped. Specifically, the region Z1 where the Mn concentration is locally high becomes darker in color, and the region Z2 where the Mn concentration is locally low becomes lighter in color. In the substrate 50 of this embodiment, Mn is doped uniformly within the plane, so the entire in-plane area of ​​the main surface 50s is a region without color unevenness as shown in FIG. 3(a).

[0061] The color unevenness can also be investigated by measuring the light transmittance of the substrate 50. For example, it is preferable that the variation in the minimum light transmittance in the wavelength range of 700 nm to 900 nm for multiple arbitrary points on the main surface 50s is within ±20% of the average value. A uniform light transmittance value in the plane indicates that there is no color unevenness and that Mn is doped uniformly in the plane. The method for selecting multiple arbitrary points on the main surface 50s is as described above.

[0062] Alternatively, the optical reflectance and optical absorption coefficient of the substrate 50 may be measured to evaluate color unevenness. For example, it is preferable that the variation in the maximum value of optical reflectance in the wavelength range of 600 nm to 700 nm for multiple arbitrary points on the main surface 50s is within ±20% of the average value. Also, it is preferable that the variation in the minimum value of optical absorption coefficient in the wavelength range of 600 nm to 700 nm for multiple arbitrary points on the main surface 50s is within ±20% of the average value. Uniform values ​​of optical reflectance and optical absorption coefficient in the plane indicate that there is no color unevenness and that Mn is doped uniformly in the plane. The method for selecting multiple arbitrary points on the main surface 50s is as described above.

[0063] <Other embodiments> Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention.

[0064] In the above embodiment, the case where the growth layer 30 is epitaxially grown using the c-plane as the growth surface in the growth step S110 has been described. However, for example, a growth step using an inclined interface other than the c-plane as the growth surface may be interposed during the growth step S110. This allows dislocations to bend, propagate, meet, and disappear. However, since Mn tends to become non-uniform during growth using an inclined interface as the growth surface, it is preferable not to dope Mn during growth at the inclined interface, but to return the growth interface to a flat surface using the c-plane as the growth surface, and then perform Mn-doped growth while performing intermittent etching, and obtain the substrate 50 from the crystalline region where intermittent etching has been performed.

[0065] In the above embodiment, the case where the growth layer 30 is sliced ​​using a wire saw in the slicing and processing step S120 has been described, but for example, an outer diameter blade slicer, an inner diameter blade slicer, or the like may also be used. [Example]

[0066] Next, examples of the present invention will be described. These examples are merely examples of the present invention, and the present invention is not limited to these examples.

[0067] (1) Preparation of gallium nitride single crystal substrate Gallium nitride single crystal substrates of Example 1 and Comparative Example 1 were fabricated as follows.

[0068] [Conditions for producing a gallium nitride single crystal substrate in Example 1] (Base substrate) Material: GaN Preparation method: VAS method Diameter: 2 inches Thickness: 400 μm The closest low-index crystal plane to the main plane: c-plane No patterning of the main surface, such as a mask layer, is required. Root mean square roughness RMS of main surface: 2nm Off-angle of the main surface: 0.4° in the m direction (growth layer) Material: GaN Growth method: HVPE method Growth temperature: 980℃ or higher and 1,020℃ or lower V / III ratio: 2 or more and 20 or less Mn doping method: MnCl2 gas Partial pressure of MnCl2 gas: 0.65 Pa Growth layer thickness: 4500 μm (Intermittent etching conditions) Etching gas: HCl gas Etching interval: 10 minutes / time Etching time: 0.5 minutes / cycle (Slicing and processing conditions) Gallium nitride single crystal substrate thickness: 400 μm Kerf loss: 200 μm

[0069] [Conditions for producing gallium nitride single crystal substrate in Comparative Example 1] (Base substrate) Same as Example 1. (growth layer) Same as Example 1. (intermittent etching) In Comparative Example 1, intermittent etching was not performed. (Slicing and processing conditions) Same as Example 1.

[0070] (2) Evaluation of in-plane uniformity On the main surface of the gallium nitride single crystal substrates of Example 1 and Comparative Example 1, excluding the region extending from the outer periphery of the main surface to within 5 mm, three arbitrary points (a, b, c) were selected, and SIMS measurement, resistivity measurement, Vickers hardness measurement, surface roughness measurement, and light transmittance measurement were performed for each point. The measurement conditions for each measurement were as follows:

[0071] (SIMS measurement) SIMS measurement was carried out within a range of 10 μm depth from the main surface side of the substrate.

[0072] (Resistivity measurement) Equipment: Hiresta-UX (MCP-HT800), manufactured by Nitto Seiko Analytech Co., Ltd. Method: Front and back contact measurement (with guide ring) Probe type: URS Probe size: φ5.9mm (guide ring inner diameter φ11mm) Applied voltage: 500V Measurement method: 10 times average value

[0073] (Vickers hardness measurement) Equipment: Shimadzu Corporation, HMV-G31-FA-D Measurement method: Average value of 5 measurements

[0074] (surface roughness measurement) Equipment: VertScan, manufactured by Ryoka Systems Co., Ltd. Measurement method: Irradiate with white light and observe interference at 530 nm

[0075] (Light transmittance measurement) Equipment: Shimadzu Corporation, SolidSpec-3700DUV ultraviolet-visible-infrared spectrophotometer Slit width: 20 nm Light source: Halogen lamp Detector: PMT Incident angle: 0 degrees

[0076] The results of the above measurements performed on each point (a, b, c) on the main surface of the substrate of Example 1 and Comparative Example 1 are shown in Table 1. The light transmittance value was the minimum value in the wavelength range of 700 nm to 900 nm. The "variation" column in Table 1 shows the variation from the average value of each measurement.

[0077] [Table 1]

[0078] As shown in Table 1, in Example 1, in which intermittent etching was performed and Mn was uniformly doped, the Mn concentration variation was within ±20% of the average value, the resistivity variation was within ±20% of the average value, the Vickers hardness variation was within ±2% of the average value, the arithmetic mean height variation was within ±20% of the average value, and the light transmittance variation was within ±20% of the average value. On the other hand, in Comparative Example 1, in which intermittent etching was not performed, the variation of each measurement value was greater than in Example 1. Also, FIG. 4(a) shows a photograph of the substrate of Example 1, and FIG. 4(b) shows a photograph of the substrate of Comparative Example 1. When the substrates of Example 1 and Comparative Example 1 were visually inspected, the substrate of Example 1 had no color unevenness, as shown in FIG. 4(a). On the other hand, color unevenness was observed in the substrate of Comparative Example 1, as shown in FIG. 4(b).

[0079] From the above, we confirmed that Mn can be doped uniformly within the surface by performing intermittent etching during the growth of the growth layer. Furthermore, we confirmed that the variations in resistivity, Vickers hardness, arithmetic mean height, and transmittance of the substrate with uniform Mn doping within the surface are within the specified ranges.

[0080] <Preferred embodiment of the present invention> Preferred embodiments of the present invention will be described below.

[0081] (Appendix 1) A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate, wherein the variation in Mn concentration when secondary ion mass spectrometry is performed on a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0082] (Appendix 2) A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3That's all, A gallium nitride single crystal substrate, wherein the variation in resistivity measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0083] (Appendix 3) A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate, wherein the variation in Vickers hardness measured at a plurality of arbitrary points on the main surface is within ±2% of the average value.

[0084] (Appendix 4) A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate, wherein the variation in arithmetic mean height Sa when surface roughness is measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0085] (Appendix 5) A gallium nitride single crystal substrate having a diameter of 50 mm or more, and having a low-index crystal plane closest to the primary surface as the (0001) plane, The Mn concentration in the substrate is 5×10 17 cm -3 That's all, A gallium nitride single crystal substrate, wherein the variation in the minimum value of light transmittance in the wavelength range of 700 nm or more and 900 nm or less at a plurality of arbitrary points on the main surface is within ±20% of the average value. Preferably, the variation in maximum value of light reflectance in the wavelength range of 600 nm to 700 nm for a plurality of arbitrary points on the main surface is within ±20% of the average value. Also preferably, the variation in the minimum value of the light absorption coefficient in the wavelength range of 600 nm to 700 nm for a plurality of arbitrary points on the main surface is within ±20% of the average value.

[0086] (Appendix 6) The average resistivity is 1×10 8 6. The gallium nitride single crystal substrate according to any one of claims 1 to 5, having a resistivity of Ωcm or more.

[0087] (Appendix 7) The total content of Si and O is 1×10 17 cm -3 A gallium nitride single crystal substrate according to any one of Supplementary Note 1 to Supplementary Note 5, which is:

[0088] (Appendix 8) A step (a) of preparing a base substrate made of gallium nitride single crystal, the low-index crystal plane closest to the primary surface being the (0001) plane; On the main surface of the base substrate, a Mn concentration of 5×10 17 cm -3 a step (b) of epitaxially growing the above-described gallium nitride single crystal; and step (c) of obtaining a gallium nitride single crystal substrate having a diameter of 50 mm or more from the gallium nitride single crystal epitaxially grown in step (b), In the step (b), a gas containing HCl is intermittently introduced and the growth interface is periodically etched, thereby doping Mn uniformly into the crystal. [Explanation of symbols]

[0089] 10 Base substrate 30 growth layer 50 Gallium nitride single crystal substrate (substrate) S100 Base board preparation process S110 Growth process S120 Slicing and Processing

Claims

1. A gallium nitride single crystal substrate having a diameter of 50 mm or more, and a low-index crystal plane closest to the primary surface being the (0001) plane, The Mn concentration in the substrate is 5×10 １７ cm －３ That's all, A gallium nitride single crystal substrate, wherein the variation in Mn concentration when secondary ion mass spectrometry is performed on a plurality of arbitrary points on the main surface is within ±20% of the average value.

2. A gallium nitride single crystal substrate having a diameter of 50 mm or more, and a low-index crystal plane closest to the primary surface being the (0001) plane, The Mn concentration in the substrate is 5×10 １７ cm －３ That's all, A gallium nitride single crystal substrate, wherein the variation in resistivity measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

3. A gallium nitride single crystal substrate having a diameter of 50 mm or more, and a low-index crystal plane closest to the primary surface being the (0001) plane, The Mn concentration in the substrate is 5×10 １７ cm －３ That's all, A gallium nitride single crystal substrate, wherein the variation in Vickers hardness measured at a plurality of arbitrary points on the main surface is within ±2% of the average value.

4. A gallium nitride single crystal substrate having a diameter of 50 mm or more, and a low-index crystal plane closest to the primary surface being the (0001) plane, The Mn concentration in the substrate is 5×10 １７ cm －３ That's all, A gallium nitride single crystal substrate, wherein the variation in arithmetic mean height Sa when surface roughness is measured at a plurality of arbitrary points on the main surface is within ±20% of the average value.

5. A gallium nitride single crystal substrate having a diameter of 50 mm or more, and a low-index crystal plane closest to the primary surface being the (0001) plane, The Mn concentration in the substrate is 5×10 １７ cm －３ That's all, A gallium nitride single crystal substrate, wherein the variation in the minimum value of light transmittance in the wavelength range of 700 nm or more and 900 nm or less at a plurality of arbitrary points on the main surface is within ±20% of the average value.

6. The average resistivity is 1 x 10 ８ The gallium nitride single crystal substrate according to claim 1 , wherein the resistivity is Ωcm or more.

7. The total content of silicon and oxygen is 1×10 １７ cm －３ 6. The gallium nitride single crystal substrate according to claim 1, wherein:

8. a step (a) of preparing a base substrate made of gallium nitride single crystal, the low-index crystal plane closest to the primary surface being the (0001) plane; On the main surface of the base substrate, a Mn concentration of 5×10 １７ cm －３ a step (b) of epitaxially growing the above-described gallium nitride single crystal; and step (c) of obtaining a gallium nitride single crystal substrate having a diameter of 50 mm or more from the gallium nitride single crystal epitaxially grown in step (b), In the step (b), a gas containing HCl is intermittently introduced to periodically etch the growth interface, thereby doping Mn uniformly into the crystal.

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