Gallium nitride single crystal substrate and method for producing gallium nitride single crystal substrate

Abstract

Provided is a high-resistance gallium nitride single crystal substrate which is uniformly doped with Mn. The gallium nitride single crystal substrate has a diameter of 50 mm or more, the low-index crystal plane closest to the principal surface is a (0001) plane, the concentration of Mn in the substrate is 5 * 1017 cm-3 or more, and the variation in Mn concentration when a plurality of arbitrary points on the principal surface are subjected to secondary ion mass spectrometry is within an average value of + / -20%.

Description

Technical Field

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

[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. To improve the quality (semiconductor properties, etc.) of semiconductor devices composed of Group III nitride semiconductors, it is desirable to manufacture semiconductor stacks or nitride semiconductor self-supporting substrates with high crystal quality.

[0003] As a method for manufacturing a GaN single crystal substrate, for example, Patent Document 1 discloses a method for manufacturing a gallium nitride single crystal substrate using the VAS (Void-Assisted Separation) method. Furthermore, Patent Document 2 discloses a method comprising a step of epitaxially growing a semiconductor layer composed of GaN on a substrate and a step of slicing the GaN layer to produce a GaN self-supporting substrate.

[0004] Furthermore, for applications such as manufacturing high-frequency semiconductor devices, semi-insulating GaN single crystal substrates with high electrical resistance are sought. Iron (Fe), manganese (Mn), and carbon (C) are used as dopants for achieving semi-insulating GaN single crystal substrates. Using manganese (Mn) results in the production of substrates with the highest electrical resistance. For example, Patent Document 3 discloses a method for producing a nitride crystal substrate by epitaxially growing a crystal layer composed of a single crystal of a Group III nitride semiconductor containing manganese on a base substrate using hydride vapor phase epitaxy (HVPE).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-178984

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-156189

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2021-109813 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, it is known that Mn-doped GaN substrates, particularly large-diameter GaN substrates (eg, with a diameter of 50 mm or more), have a problem in that the Mn concentration distribution within the substrate surface varies significantly.

[0012] An object of the present invention is to provide a high-resistance gallium nitride single crystal substrate uniformly doped with Mn.

[0013] Solutions to Problems

[0014] One embodiment of the present invention provides a gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0015] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0016] When secondary ion mass spectrometry is performed on a plurality of arbitrary points on the main surface, the deviation of the Mn concentration is within ±20% of the average value.

[0017] In addition, another embodiment of the present invention provides a gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0018] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0019] When the resistivity is measured at a plurality of arbitrary points on the main surface, the deviation is within ±20% of the average value.

[0020] In another embodiment of the present invention, there is provided a gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0021] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0022] When the Vickers hardness was measured at a plurality of arbitrary points on the main surface, the deviation was within ±2% of the average value.

[0023] In another embodiment of the present invention, there is provided a gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0024] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0025] When the surface roughness is measured at a plurality of arbitrary points on the main surface, the deviation of the arithmetic mean height Sa is within ±20% of the average value.

[0026] In another embodiment of the present invention, there is provided a gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0027] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0028] At a plurality of arbitrary points on the main surface, a deviation in the minimum value of the light transmittance in the wavelength range of 700 nm to 900 nm is within ±20% of the average value.

[0029] In addition, another embodiment of the present invention provides a method for manufacturing a gallium nitride single crystal substrate, wherein:

[0030] The method for manufacturing the gallium nitride single crystal substrate comprises:

[0031] Step (a) of preparing a base substrate composed of a gallium nitride single crystal whose low-index crystal plane closest to the main surface is the (0001) plane;

[0032] Step (b): the Mn concentration is set to 5×10 17 cm -3 The above gallium nitride single crystal is epitaxially grown on the main surface of the base substrate; and

[0033] 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);

[0034] In the step (b), a gas containing HCl is intermittently introduced to periodically etch the growth interface, thereby uniformly doping the crystal with Mn.

[0035] Effects of the Invention

[0036] According to the present invention, a high-resistance gallium nitride single crystal substrate uniformly doped with Mn can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flowchart showing a method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present invention.

[0038] Figure 2A This is a schematic cross-sectional view showing a portion of a method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present invention.

[0039] Figure 2B This is a schematic cross-sectional view showing a portion of a method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present invention.

[0040] Figure 2CThis is a schematic cross-sectional view showing a portion of a method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present invention.

[0041] Figure 3A This is a photograph of a region uniformly doped with Mn on the primary surface of a gallium nitride single crystal substrate.

[0042] Figure 3B This is a photograph of a region unevenly doped with Mn on the primary surface of a gallium nitride single crystal substrate.

[0043] Figure 4A This is a photograph of the substrate of Example 1 according to the embodiment of the present invention.

[0044] Figure 4B This is a photograph of the substrate of Comparative Example 1 according to the embodiment of the present invention.

[0045] Description of Reference Numerals

[0046] 10. Substrate

[0047] 30 Growth Layer

[0048] 50 Gallium nitride single crystal substrate (substrate)

[0049] S100 Substrate Preparation Process

[0050] S110 Growth Process

[0051] S120 Slicing / Processing DETAILED DESCRIPTION

[0052] Insights Gained by the Inventors

[0053] First, the findings obtained by the inventors will be described.

[0054] The inventors discovered the following phenomenon during repeated trials of growing GaN crystals doped with Mn: 17 cm -3 When Mn exceeds 50%, the performance of devices manufactured on the substrate varies.

[0055] It was also found that the main reason for the performance deviation of the above-mentioned equipment is related to the Mn concentration entering the crystal.

[0056] The amount of Mn that enters the crystal is susceptible to changes depending on the tilt of the crystal plane orientation on the surface during crystal growth. Therefore, if a slightly tilted surface slightly tilted from the c-plane appears on the surface during crystal growth, the amount of Mn that enters this area changes, and Mn concentration is easily uneven within the crystal plane. This morphology is affected by the internal residual stress during crystal growth and the warping of the c-plane of the crystal. In particular, in GaN crystal growth, the growing crystal is prone to warping. Therefore, especially when manufacturing large-diameter GaN substrates with a diameter exceeding 50mm, the warping of the crystal c-plane affects the growth surface, causing it to tilt from the original growth plane orientation, namely the (0001) plane. A tilted morphology that depends on the growth plane orientation at that position appears within the crystal growth surface, and therefore it is more likely to produce areas with different Mn concentrations.

[0057] The inventors have conducted in-depth research on the above-mentioned problems. The deviation in the way Mn enters the GaN crystal is caused by the formation of a micro-inclined surface slightly tilted from the c-plane on the growth surface during crystal growth. It is believed that the reason for the formation of the micro-inclined surface at the growth interface is that the density and orientation of the atomic steps formed are deviated due to defects such as dislocations and the deviation of the crystal surface from the c-plane. Therefore, in the process of growing the Mn-doped GaN layer, a gas containing HCl is intermittently introduced into the growth interface, and the surface of the growing crystal is regularly etched to maintain the flatness and cleanliness of the interface, thereby suppressing the formation of tiny facets at the growth interface and preventing the growth surface from showing the aforementioned morphology, thereby establishing a technology for uniformly doping Mn into GaN crystals.

[0058] <One embodiment of the present invention>

[0059] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0060] It should be noted that, hereinafter, in GaN crystals having a wurtzite structure, the <0001> axis is referred to as the "c-axis," and the (0001) plane is referred to as the "c-plane." It should be noted that the (0001) plane is sometimes referred to as the "+c-plane (gallium polar plane)," and the (000-1) plane is sometimes referred to as the "-c-plane (nitrogen polar plane)." Furthermore, the <1-100> axis is referred to as the "m-axis," and the {1-100} plane is referred to as the "m-plane." It should be noted that the m-axis can also be expressed as the <10-10> axis. Furthermore, the <11-20> axis is referred to as the "a-axis," and the {11-20} plane is referred to as the "a-plane."

[0061] (1) Method for manufacturing gallium nitride single crystal substrate

[0062] First, a method for manufacturing a gallium nitride single crystal substrate according to this embodiment will be described. Figure 11 is a flowchart showing a method for manufacturing a gallium nitride single crystal substrate according to this embodiment. Figure 2A to Figure 2C This is a schematic cross-sectional view showing a part of the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment.

[0063] like Figure 1 As shown, the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment includes, for example, a base substrate preparation step S100 , a growth step S110 , and a slicing / processing step S120 .

[0064] (S100: Base substrate preparation process)

[0065] like Figure 2A As shown, in the base substrate preparation step S100, a base substrate 10 composed of a gallium nitride single crystal is prepared, wherein 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 (a free-standing substrate, not a template) can be used as the base substrate 10, or a base substrate 10 composed of a gallium nitride single crystal can be produced using the VAS (Void-Assisted Separation) method described in Patent Document 1. It should be noted that the base substrate 10 can be either Mn-doped or undoped, with Mn doping being particularly preferred. This can reduce the lattice constant difference caused by the Mn concentration difference between the base substrate 10 and the growth layer 30 described later.

[0066] (S110: Growth process)

[0067] In the growth step S110, the GaN single crystal is grown as Figure 2B As shown, epitaxial growth is performed on the main surface 10s of the base substrate 10 prepared in the base substrate preparation step S100. Specifically, for example, by supplying GaCl gas and NH3 gas to the heated base substrate 10 using the HVPE method, epitaxial growth is performed directly on the main surface 10s of the base substrate 10, thereby growing the growth layer 30.

[0068] In the growth step S110, for example, the growth layer 30 is grown under predetermined growth conditions. In this embodiment, the growth conditions are preferably set at a growth temperature of, for example, 980° C. to 1200° C. Furthermore, in the growth step S110, the supply partial pressure ratio of NH 3 gas, which is a nitriding gas, to GaCl gas, which is a Group III source gas (hereinafter also referred to as a "V / III ratio") is preferably set at, for example, 0.1 to 5.0.

[0069] In the growth step S110 , for example, GaCl gas, NH 3 gas, and manganese chloride (MnCl 2 ) gas as a Mn doping gas are supplied to the base substrate 10 so that the Mn concentration is 5×1017 cm -3 Above and 1×10 20 cm -3 The following is the epitaxial growth of a Mn-doped GaN layer. MnCl₂ gas can be obtained, for example, by reacting solid Mn with HCl gas. The carrier gas can be either H₂ gas or N₂ gas, or both. In either case, the flow rate of the MnCl₂ gas is preferably controlled by a mass flow controller to maintain a partial pressure of 0.1 to 2.2 Pa.

[0070] It should be noted that other growth conditions in the growth step S110 are as follows, for example.

[0071] Growth pressure: 90~105kPa, preferably 90~95kPa

[0072] Partial pressure of GaCl gas: 1.5~15kPa

[0073] Partial pressure of MnCl2 gas: 0.1~2.2Pa

[0074] N2 gas flow rate / H2 gas flow rate: 0~1

[0075] 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 uniformly doping Mn into the crystal. Specifically, for example, during the growth with the c-plane as the growth plane, the supply of GaN raw material gas and doping gas is temporarily stopped, and HCl gas and carrier gas (such as H2 gas) are introduced. As a result, the formation of tiny facets generated on the growth surface is suppressed, so that Mn can be uniformly doped. It should be noted that the introduction of the gas containing HCl is preferably performed at intervals of 0.5 to 1 minute per time at intervals of 5 to 10 minutes per time, for example.

[0076] In the growth step S110, the thickness of the growth layer 30 is preferably set to, for example, 1 mm to 20 mm. When a GaN substrate produced using the aforementioned VAS method is used as the base substrate 10, the c-plane of the base substrate 10 often exhibits concave curvature toward the surface (crystal growth plane). Furthermore, even GaN substrates produced using other methods may experience c-plane curvature due to stress generated within the crystal during growth. The c-plane curvature of the base substrate 10 is also inherited by the growth layer 30 grown thereon. However, by growing the growth layer 30 to a certain thickness, stress is generated that returns the warp to the crystal, flattening 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 thickness of the growth layer 30 is less than 1 mm, sufficient stress may not be generated to return the c-plane warp. Furthermore, it is difficult to obtain a GaN single crystal substrate of sufficient thickness in the subsequent slicing / processing step S120. In contrast, by making the thickness of the growth layer 30 greater than 1 mm, the warping of the c-plane can be reduced. In addition, in the subsequent slicing / processing step S120, a GaN single crystal substrate of sufficient thickness can be obtained. On the other hand, when the thickness of the growth layer 30 exceeds 20 mm, excessive strain accumulates in the crystal due to the force to return the warping of the c-plane, sometimes causing dislocations to multiply or microcracks to form in the crystal. In addition, since the internal residual stress of the GaN crystal increases, the crystal is easily broken in the slicing / processing step S120. In contrast, by making the thickness of the growth layer 30 less than 20 mm, the internal residual stress of the GaN crystal can be reduced, suppressing cracks and breakage.

[0077] (S120: Slicing / Processing Process)

[0078] In the slicing / processing step S120, as Figure 2C As shown, for example, the growth layer 30 is sliced using a wire saw or the like along a cut plane substantially parallel to the primary 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 greater being obtained as an as-cut substrate. At this time, the slicing is preferably performed so that the thickness of the substrate 50 is, for example, 300 μm or more and 1200 μm or less.

[0079] When a GaN substrate produced 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 μm in the direction in which the surface becomes concave. The c-plane of the substrate 50 cut from the growth layer 30 has a larger curvature radius than the c-plane of the base substrate 10.

[0080] In addition, since the substrate is separated from the base substrate 10, the stress applied to the substrate 10 is relieved, and thus the substrate has a better Figure 2BAs shown, the c-plane curvature radius tends to be larger when the growth layer 30 is formed on the base substrate 10. Specifically, the curvature radius of the c-plane of the substrate 50 is preferably 10 μm or greater, and more preferably 20 μm or greater. This allows the variation in the off-angle θ of the c-axis relative to the normal to the primary surface 50 s of the substrate 50 (the range of 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.

[0081] After the substrate 50 is obtained as an as-cut substrate, both surfaces of the substrate 50 may be polished using a polishing device, for example.

[0082] It should be noted that, in the present embodiment, the substrate 50 obtained by the slicing / processing step S120 can also be used as a new base substrate 10, and the growth step S110 and the slicing / processing step S120 can be repeated multiple times (for example, more than 4 times). In this specification, such a growth method is referred to as replacement growth. By performing replacement growth instead of thick film growth at one time, the warping of the c-plane is alleviated each time the substrate 50 is cut out, so that the internal residual stress of the GaN crystal can be reduced. Since the internal residual stress is reduced, the generation of morphology is suppressed, making it easy to uniformly dope Mn. It should be noted that the upper limit of the number of times replacement growth is performed is not particularly limited. From the perspective of efficiently manufacturing large-diameter GaN single crystal substrates, it is preferably set to 10 times or less.

[0083] Through the above steps, the substrate 50 of this embodiment is manufactured.

[0084] (Process for Manufacturing a Semiconductor Stack and Process for Manufacturing a Semiconductor Device)

[0085] After manufacturing substrate 50, a semiconductor functional layer composed of, for example, a Group III nitride semiconductor can be epitaxially grown on substrate 50 to produce a semiconductor stack. After the semiconductor stack is produced, electrodes and other components are further formed on the semiconductor stack, and the semiconductor stack is cut into chips of a predetermined size. Semiconductor devices can also be produced in this manner. Since substrate 50 is uniformly doped with Mn, it is suitable for the production of high-frequency semiconductor devices, etc.

[0086] (2) Gallium nitride single crystal substrates (nitride semiconductor self-supporting substrates, nitride crystal substrates)

[0087] Next, the gallium nitride single crystal substrate 50 of this embodiment will be described.

[0088] In the present embodiment, the substrate 50 obtained by the above-described manufacturing method is a self-supporting substrate composed of a GaN single crystal.

[0089] The diameter of the substrate 50 is, for example, not less than 50 mm. The thickness of the substrate 50 is, for example, not less than 300 μm and not more than 1 mm.

[0090] The Mn concentration in the substrate 50 is, for example, 5×10 17 cm -3 Above and 1.0×10 20 cm -3 Below, preferably 5×10 17 cm -3 Above and 5.0×10 19 cm -3 Below, more preferably 1×10 18 cm -3 Above and 5.0×10 19 cm -3 The following. The thinner the Mn concentration in the substrate 50 is within the range of high resistance, the more likely it is that the deviation of the Mn concentration in the substrate 50 will affect the substrate resistance value. Therefore, the lower the Mn doping level of the substrate, the more effective it is to frequently perform intermittent etching during Mn doping growth. It should be noted that the Mn concentration is likely to vary within the substrate surface, but the substrate 50 of this embodiment is uniformly doped with Mn by intermittent etching. Therefore, when performing secondary ion mass spectrometry (SIMS) on multiple arbitrary points on the main surface 50s, the Mn concentration is, for example, within 5×10 17 cm -3 Above and 1.0×10 20 cm -3 The following ranges converged within ±20% of the average value.

[0091] The substrate 50 has, for example, a principal surface 50s serving as an epitaxial growth surface. In this embodiment, the low-index crystal plane closest to the principal surface 50s is, for example, the (0001) plane.

[0092] Note that the principal surface 50 s of the substrate 50 is mirror-finished by, for example, polishing, and the root mean square roughness RMS of the principal surface 50 s of the substrate 50 is, for example, less than 1 nm.

[0093] Furthermore, in the present embodiment, the impurity concentration in the substrate 50 obtained by the above-described manufacturing method is lower than that in a substrate obtained by liquid phase growth such as a flux method or an ammonothermal method.

[0094] Specifically, the hydrogen (H) concentration in the substrate 50 is, for example, less than 1×10 17 cm- 3 , preferably 5×10 16 cm -3 Below. In addition, the oxygen (O) concentration in the substrate 50 is, for example, 5×10 16 cm -3 Below, preferably 3×1016 cm -3 the following.

[0095] The total content of silicon (Si) and oxygen (O) in the substrate 50 is preferably 1×10 17 cm -3 In addition, it is preferable that the total content of Fe and carbon (C) in the substrate 50 is, for example, 1×10 17 cm -3 Furthermore, it is more preferable that the total content of Si, O, Fe, and C in the substrate 50 is, for example, 1×10 17 cm -3 the following.

[0096] The substrate 50 is doped with Mn, and the contents of Si and O as n-type impurities are lower than the Mn concentration, thus forming a high-resistance substrate. The average resistivity of the substrate 50 is preferably, for example, 1×10 8 Ωcm or more.

[0097] (C-plane curvature and deviation of the off-angle)

[0098] The radius of curvature of the c-plane of substrate 50 is, for example, greater 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 preferably greater than 10 μm, and more preferably greater than 20 μm. The intermittent etching described above can minimize the distribution of impurities in the crystal in substrate 50, thereby reducing the internal residual stress of the crystal. As a result, compared to a case where intermittent etching is not performed, even thicker growth is less likely to cause cracks and breakage, thereby further increasing the radius of curvature of the c-plane.

[0099] In this embodiment, the upper limit of the curvature radius of the c-plane of the substrate 50 is preferably as large as possible, and is therefore not particularly limited. When the c-plane of the substrate 50 is substantially flat, the curvature radius of the c-plane may be considered to be infinite.

[0100] In this embodiment, since the curvature radius of the c-plane of the substrate 50 is large, the variation in the off angle θ of the c-axis with respect to the normal to the principal surface 50 s of the substrate 50 can be made smaller than the variation in the off angle of the c-axis of the base substrate 10 .

[0101] Specifically, when an X-ray rocking curve of the (0002) plane of the substrate 50 is measured and the deviation angle θ of the c-axis relative to the normal of the main surface 50s is measured based on the diffraction peak angle of the (0002) plane, the deviation calculated based on the extreme difference in the magnitude of the deviation angle θ from the center of the main surface 50s to within a diameter of 25 mm is, for example, less than 0.14°, preferably less than 0.07°, and more preferably less than 0.05°.

[0102] In this embodiment, the lower limit of the deviation of the off angle θ of the c-axis of the substrate 50 is preferably as small as possible and is not particularly limited. When the c-plane of the substrate 50 is substantially flat, the deviation of the off angle θ of the c-axis of the substrate 50 is considered to be 0°.

[0103] Furthermore, in the present embodiment, the curvature of the c-plane is isotropically reduced with respect to the principal surface 50 s of the substrate 50 , and the direction dependence of the radius of curvature of the c-plane is small.

[0104] Specifically, the difference between the curvature radius of the c-plane along the a-axis and the curvature radius of the c-plane along the m-axis obtained by the above-mentioned measurement method is, for example, less than 50% of the larger curvature radius, preferably less than 20%.

[0105] (Dislocation density)

[0106] In the present embodiment, the dislocation density in the surface of the substrate 50 is lower than the dislocation density in the main surface 10 s of the base substrate 10 .

[0107] In this embodiment, since crystal growth is performed while maintaining the flatness of the crystal growth interface, the mechanism of localized concentration of propagating dislocations does not operate. Consequently, regions with exceptionally high dislocation density due to concentration of dislocations do not form, and the dislocation density distribution is uniform across the substrate surface. It should be noted that observation of etch pits corresponding to dislocations formed by etching in molten alkali confirmed that even with high Mn doping concentrations, the dislocation density in the GaN crystal does not increase.

[0108] (In-plane uniformity)

[0109] In the substrate 50 of the present embodiment, the Mn concentration in the surface and various properties described later are made uniform in the surface by the intermittent etching described above.

[0110] Specifically, for example, when performing secondary ion mass spectrometry (SIMS) analysis on multiple arbitrary points on the main surface 50s, the deviation in Mn concentration is within ±20% of the average value. It should be noted that when selecting multiple arbitrary points on the main surface 50s, for example, three or more points are preferred, five or more points are more preferred, and ten or more points are even more preferred. Furthermore, since the periphery of the substrate 50 is susceptible to the effects of polishing, for example, multiple arbitrary points are preferably selected in an area of the main surface 50s excluding the area 5 mm inward from the outer periphery.

[0111] Furthermore, for example, when the resistivity is measured at a plurality of arbitrary points on the primary surface 50s, the deviation is preferably within ±20% of the average value. A uniform resistivity value within the surface indicates that Mn is uniformly doped within the surface. It should be noted that the method for selecting the plurality of arbitrary points on the primary surface 50s is as described above.

[0112] Furthermore, for example, when measuring the Vickers hardness at a plurality of arbitrary points on the main surface 50s, the deviation is preferably within ±2% of the average value. A uniform Vickers hardness value within the surface indicates that Mn is uniformly doped within the surface. It should be noted that the method for selecting the plurality of arbitrary points on the main surface 50s is as described above.

[0113] In addition, for example, when the surface roughness is measured at a plurality of arbitrary points on the main surface 50s, the deviation of the arithmetic mean height Sa is preferably within ±20% of the average value. If the Mn concentration in the crystal is different, the mechanical strength and chemical reactivity of the crystal will deviate. Therefore, during the grinding process, the amount of removal will deviate accordingly with the concentration deviation of Mn, and its influence will be reflected in the deviation of the Sa value. The value of the arithmetic mean height Sa is uniform in the surface, indicating that Mn is uniformly doped in the surface. It should be noted that the selection method of the plurality of arbitrary points on the main surface 50s is as described above.

[0114] Furthermore, in the region where the Mn concentration is non-uniform on the main surface 50 s , color non-uniformity corresponding to the intensity of the Mn concentration is observed. Figure 3A This is a photograph of a region uniformly doped with Mn. Figure 3B This is a photograph of a region unevenly doped with Mn. Figure 3A As shown in FIG, in the region uniformly doped with Mn, no color unevenness is observed. Figure 3B As shown in FIG. 1 , color unevenness is observed in the region where Mn concentration is unevenly doped. Specifically, the color of the region Z1 where the Mn concentration is locally increased becomes darker, and the color of the region Z2 where the Mn concentration is locally decreased becomes lighter. For the substrate 50 of this embodiment, Mn is uniformly doped in the surface, so the entire surface of the main surface 50s becomes Figure 3A There are no areas of uneven color as shown.

[0115] Furthermore, the aforementioned color unevenness can also be investigated by measuring the transmittance of the substrate 50. For example, for a plurality of arbitrary points on the main surface 50s, the deviation of the minimum transmittance in the wavelength range of 700 nm to 900 nm is preferably within ±20% of the average value. A uniform transmittance value within the surface indicates that there is no color unevenness and that Mn is uniformly doped within the surface. It should be noted that the method for selecting the plurality of arbitrary points on the main surface 50s is as described above.

[0116] In addition, the light reflectivity and light absorption coefficient of the substrate 50 can also be measured to evaluate the color unevenness. For example, for a plurality of arbitrary points on the main surface 50s, the deviation of the maximum value of the light reflectivity in the wavelength range of more than 600nm and less than 700nm is preferably within ±20% of the average value. In addition, for example, for a plurality of arbitrary points on the main surface 50s, the deviation of the minimum value of the light absorption coefficient in the wavelength range of more than 600nm and less than 700nm is preferably within ±20% of the average value. The values of the light reflectivity and the light absorption coefficient are uniform in the surface and indicate that there is no color unevenness, and Mn is uniformly doped in the surface. It should be noted that the selection method of a plurality of arbitrary points on the main surface 50s is as described above.

[0117] <Another embodiment>

[0118] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and various modifications can be made without departing from the spirit and scope of the present invention.

[0119] In the above-described embodiment, in the growth step S110, epitaxial growth of the growth layer 30 is described using the c-plane as the growth plane. However, for example, a growth step using an inclined interface other than the c-plane as the growth plane can also be performed midway through the growth step S110. This allows dislocations to propagate, converge, and disappear in a curved manner. However, during growth using an inclined interface as the growth plane, Mn tends to become uneven. Therefore, it is preferable to not dope Mn during the growth using the inclined interface, return the growth interface to a flat surface using the c-plane as the growth plane, then perform intermittent etching while performing Mn-doped growth, and obtain the substrate 50 from the crystal region subjected to the intermittent etching.

[0120] In the above embodiment, the case where the growth layer 30 is sliced using a wire saw in the slicing / processing step S120 has been described. However, for example, an outer peripheral blade slicer, an inner peripheral blade slicer, or the like may be used.

[0121] [Example]

[0122] Next, examples of the present invention will be described. These examples are examples of the present invention, and the present invention is not limited to these examples.

[0123] (1) Fabrication of GaN single crystal substrate

[0124] Gallium nitride single crystal substrates of Example 1 and Comparative Example 1 were produced as follows.

[0125] [Conditions for Fabricating Gallium Nitride Single Crystal Substrate in Example 1] (Base Substrate)

[0126] Material: GaN

[0127] Production method: VAS method

[0128] Diameter: 2 inches

[0129] Thickness: 400μm

[0130] Low-index crystal plane closest to the main surface: c-plane

[0131] There is no patterning of a mask layer or the like on the main surface.

[0132] Root mean square roughness RMS of the main surface: 2nm

[0133] Offset angle of the main surface: 0.4° in the m direction (growth layer)

[0134] Material: GaN

[0135] Growth method: HVPE method

[0136] Growth temperature: above 980℃ and below 1020℃

[0137] V / III ratio: 2 or more and 20 or less

[0138] Mn doping method: MnCl2 gas

[0139] Partial pressure of MnCl2 gas: 0.65Pa

[0140] Growth layer thickness: 4500 μm (intermittent etching conditions)

[0141] Etching gas: HCl gas

[0142] Etching interval: 10 minutes / time

[0143] Etching time: 0.5 minutes / time (slicing / processing conditions)

[0144] Thickness of GaN single crystal substrate: 400μm

[0145] Kerf loss: 200 μm

[0146] [Conditions for Fabricating Gallium Nitride Single Crystal Substrate in Comparative Example 1] (Base Substrate)

[0147] Same as Example 1.

[0148] (Growth layer)

[0149] Same as Example 1.

[0150] (Intermittent etching)

[0151] In Comparative Example 1, intermittent etching was not performed.

[0152] (Slicing / Processing Conditions)

[0153] Same as Example 1.

[0154] (2) Evaluation of in-plane uniformity

[0155] On the main surfaces of the gallium nitride single crystal substrates of Example 1 and Comparative Example 1, three arbitrary points (a, b, and c) were selected from the main surfaces, excluding an area 5 mm inward from the outer periphery. SIMS measurements, resistivity measurements, Vickers hardness measurements, surface roughness measurements, and light transmittance measurements were performed at each point. The measurement conditions for each measurement were as follows.

[0156] (SIMS measurement)

[0157] SIMS measurement was performed in a range of 10 μm in depth from the main surface side of the substrate.

[0158] (Resistivity measurement)

[0159] Equipment: Hiresta-UX (MCP-HT800), manufactured by Nitto Seiko Analytical Science Co., Ltd.

[0160] Method: Surface-back contact measurement (with guide ring)

[0161] Probe model: URS

[0162] Probe size: φ5.9mm (guide ring inner diameter φ11mm)

[0163] Applied voltage: 500V

[0164] Measurement method: average value of 10 times

[0165] (Vickers hardness test)

[0166] Device: Shimadzu Corporation, HMV-G31-FA-D

[0167] Measurement method: average value of 5 times

[0168] (Surface roughness measurement)

[0169] Device: VertScan manufactured by Myoka Systems Co., Ltd.

[0170] Measurement method: Irradiate white light and observe the interference at 530nm

[0171] (Transmittance measurement)

[0172] Equipment: SolidSpec-3700DUV UV-visible-infrared spectrophotometer manufactured by Shimadzu Corporation

[0173] Slit width: 20nm

[0174] Light source: halogen lamp

[0175] Detector: PMT

[0176] Angle of incidence: 0 degrees

[0177] Table 1 shows the results of the above-described measurements at various points (a, b, and c) on the main surfaces of the substrates of Example 1 and Comparative Example 1. The transmittance values are the minimum values within the wavelength range of 700 nm to 900 nm. The deviation column in Table 1 shows the deviation from the average value for each measurement.

[0178]

Table 1

[0179]

[0180] As shown in Table 1, for Example 1 in which intermittent etching was performed and Mn was uniformly doped, the deviation of the Mn concentration was within ±20% of the average value, the deviation of the resistivity was within ±20% of the average value, the deviation of the Vickers hardness was within ±2% of the average value, the deviation of the arithmetic mean height was within ±20% of the average value, and the deviation of the transmittance was within ±20% of the average value. On the other hand, for Comparative Example 1 in which intermittent etching was not performed, the deviation of each measured value was larger than that of Example 1. In addition, Figure 4A A photograph of the substrate of Example 1 is shown in FIG. Figure 4B The photo of the substrate of Comparative Example 1 is shown in FIG. When the substrates of Example 1 and Comparative Example 1 were visually confirmed, the substrate of Example 1 was as shown in FIG. Figure 4A On the other hand, the substrate of Comparative Example 1 is as shown in FIG. Figure 4B Color unevenness was observed as shown.

[0181] The above results confirm that intermittent etching during the growth of the growth layer allows for uniform in-plane Mn doping. Furthermore, for substrates uniformly doped with Mn, the variations in resistivity, Vickers hardness, arithmetic mean height, and transmittance also fell within the specified ranges.

[0182] <Preferred embodiment of the present invention>

[0183] Preferred embodiments of the present invention are described below.

[0184] (Note 1)

[0185] A gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0186] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0187] When secondary ion mass spectrometry is performed on a plurality of arbitrary points on the main surface, the deviation of the Mn concentration is within ±20% of the average value.

[0188] (Note 2)

[0189] A gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0190] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0191] When the resistivity is measured at a plurality of arbitrary points on the main surface, the deviation is within ±20% of the average value.

[0192] (Note 3)

[0193] A gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0194] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0195] When the Vickers hardness was measured at a plurality of arbitrary points on the main surface, the deviation was within ±2% of the average value.

[0196] (Note 4)

[0197] A gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0198] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0199] When the surface roughness is measured at a plurality of arbitrary points on the main surface, the deviation of the arithmetic mean height Sa is within ±20% of the average value.

[0200] (Note 5)

[0201] A gallium nitride single crystal substrate having a diameter of 50 mm or more, wherein the low-index crystal plane closest to the main surface is the (0001) plane, wherein:

[0202] The Mn concentration in the substrate is 5×10 17 cm -3 above,

[0203] At a plurality of arbitrary points on the main surface, a deviation in the minimum value of the light transmittance in the wavelength range of 700 nm to 900 nm is within ±20% of the average value.

[0204] Preferably, at a plurality of arbitrary points on the main surface, a deviation in the maximum value of the light reflectance in the wavelength range of 600 nm to 700 nm is within ±20% of the average value.

[0205] Furthermore, it is preferable that, for a plurality of arbitrary points on the main surface, a deviation from a minimum value of the light absorption coefficient in a wavelength range of 600 nm to 700 nm is within ±20% of an average value.

[0206] (Note 6)

[0207] The gallium nitride single crystal substrate according to any one of Supplementary Notes 1 to 5, wherein

[0208] The average resistivity is 1×10 8 Ωcm or more.

[0209] (Note 7)

[0210] The gallium nitride single crystal substrate according to any one of Supplementary Notes 1 to 5, wherein

[0211] The total content of Si and O is 1×10 17 cm -3 the following.

[0212] (Note 8)

[0213] A method for manufacturing a gallium nitride single crystal substrate, wherein:

[0214] The method for manufacturing the gallium nitride single crystal substrate comprises:

[0215] Step (a) of preparing a base substrate composed of a gallium nitride single crystal whose low-index crystal plane closest to the main surface is the (0001) plane;

[0216] Step (b): the Mn concentration is set to 5×10 17 cm -3 The above gallium nitride single crystal is epitaxially grown on the main surface of the base substrate; and

[0217] 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);

[0218] In the step (b), a gas containing HCl is intermittently introduced to periodically etch the growth interface, thereby uniformly doping the crystal with Mn.

Claims

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

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

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

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

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

6. The gallium nitride single crystal substrate according to any one of claims 1 to 5, wherein The average resistivity is 1×10 8 Ωcm or more.

7. The gallium nitride single crystal substrate according to any one of claims 1 to 5, wherein The total content of silicon and oxygen is 1×10 17 cm -3 the following.

8. A method for manufacturing a gallium nitride single crystal substrate, wherein: The method for manufacturing the gallium nitride single crystal substrate comprises: Step (a) of preparing a base substrate composed of a gallium nitride single crystal whose low-index crystal plane closest to the main surface is the (0001) plane; Step (b): the Mn concentration is set to 5×10 17 cm -3 The above gallium nitride single crystal is epitaxially grown on the main surface of the base substrate; 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 uniformly doping the crystal with Mn.

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