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

Abstract

The present invention suppresses the occurrence of cracks due to growth and processing when manufacturing a gallium nitride single crystal substrate having a low dislocation density. The gallium nitride single crystal substrate has a diameter of 50 mm or more, the low-index crystal plane closest to the main surface is a (0001) plane, the average density of etch pits formed when the main surface is etched is less than 1 * 106 cm <-2 >, and histograms of the diameters of the etch pits are created in a plurality of different regions on the main surface. When the diameter of a first peak having the smallest diameter among peaks appearing in the histogram is a, the diameter of a second peak having the second smallest diameter is b, the frequency of the first peak is A, the frequency of the second peak is B, the number of erosion pits constituting the first peak is alpha, and the number of erosion pits constituting the second peak is beta, (1) the deviation of the value a / b is within + / -5% of the average value; (2) the deviation of the A / B value is within + / -15% of the average value, and (3) the deviation of the alpha / beta value is within + / -30% of the average value.

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] For example, Patent Document 1 discloses a method for manufacturing a gallium nitride single crystal substrate, wherein the method comprises: a step of preparing a base substrate, wherein the base substrate is composed of a single crystal of a group III nitride semiconductor, has a mirrored main surface, and the low-index crystal plane closest to the main surface is the (0001) plane; a first step of growing a first layer, wherein a single crystal of a group III nitride semiconductor having a top surface with the (0001) plane exposed is directly epitaxially grown on the main surface of the base substrate, and a plurality of layers other than the (0001) plane are generated on the top surface. The concave portion formed by the inclined interface gradually expands as it progresses upward from the main surface of the base substrate, causing the (0001) plane to disappear from the top surface, thereby forming a surface composed only of the inclined interface; and a second step of growing a second layer having a mirrored surface, causing a single crystal of a group III nitride semiconductor to epitaxially grow on the first layer, thereby causing the inclined interface to disappear. In the first step, multiple concave portions are generated on the top surface of the single crystal, and the (0001) plane disappears, thereby forming multiple valleys and multiple tops on the surface of the first layer.

[0003] Furthermore, for example, Non-Patent Document 1 discloses a method for manufacturing a gallium nitride single crystal substrate by a VAS (Void-Assisted Separation) method.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-33211

[0007] Non-patent literature

[0008] Non-patent document 1: Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1-L3 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] An object of the present invention is to suppress cracks generated by growth and processing when producing a gallium nitride single crystal substrate having a low dislocation density.

[0011] Solutions to Problems

[0012] 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:

[0013] The average density of the etch pits formed when the main surface is etched with an alkaline etching solution is less than 1×10 6 cm -2 ,

[0014] When a histogram of the diameter of the pits is prepared in each of the plurality of different regions on the main surface, and the diameter of the first peak with the smallest diameter among the peaks appearing in the histogram is set to a, the diameter of the second peak with the second smallest diameter is set to b, the frequency of the first peak (the number of pits) is set to A, the frequency of the second peak is set to B, the number of the pits constituting the first peak is set to α, and the number of the pits constituting the second peak is set to β, at least any one of the following conditions (1), (2), and (3) is satisfied.

[0015] (1) The deviation of the a / b values in the plurality of histograms is within ±5% of the average value.

[0016] (2) The deviation of the A / B values in the plurality of histograms is within ±15% of the average value.

[0017] (3) The deviation of the values of α / β in the plurality of histograms is within ±30% of the average value.

[0018] In addition, another embodiment of the present invention provides a method for manufacturing a gallium nitride single crystal substrate.

[0019] The method for manufacturing the gallium nitride single crystal substrate comprises:

[0020] Step (a) of preparing a base substrate composed of a gallium nitride single crystal, wherein the low-index crystal plane closest to the main surface is the (0001) plane and the dislocation density of the main surface is uniformly distributed within the surface;

[0021] Step (b), epitaxially growing a gallium nitride single crystal on the main surface of the base substrate; and

[0022] 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);

[0023] In the step (b), during the entire growth period, no tilted interface other than the (0001) plane is generated, and the gallium nitride single crystal is epitaxially grown using only the (0001) plane as a growth plane.

[0024] The gallium nitride single crystal substrate obtained in the step (c) is used as a new base substrate, and the steps (b) and (c) are repeated at least once.

[0025] Effects of the Invention

[0026] According to the present invention, when manufacturing a gallium nitride single crystal substrate having a low dislocation density, cracks generated by growth and processing can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Figure 2C 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.

[0031] Figure 3 This is an SEM image showing an example of an etch pit formed on the main surface of a gallium nitride single crystal substrate according to one embodiment of the present invention.

[0032] Figure 4 It is a histogram of the diameter of the etch pit of the VAS substrate.

[0033] Figure 5 This is a histogram of the diameters of the etch pits on the substrate of Example 1.

[0034] Figure 6 This is a histogram of the diameters of the etch pits of the substrate of Comparative Example 1.

[0035] Description of Reference Numerals

[0036] 10. Substrate

[0037] 30 Growth Layer

[0038] 50 Gallium nitride single crystal substrate (substrate)

[0039] S100 Substrate Preparation Process

[0040] S110 2D growth process

[0041] S120 Slicing / Processing DETAILED DESCRIPTION

[0042] Insights Gained by the Inventors

[0043] First, the findings obtained by the inventors will be described.

[0044] It is known that when etching the c-plane of a gallium nitride (GaN) single crystal substrate using an alkaline etchant, for example, forms etch pits corresponding to dislocations. While techniques for identifying the type of dislocation (edge-shaped, mixed, or screw) based on the size (diameter) of the etch pit are known to those skilled in the art, this approach is not necessarily universally applicable. The size of the etch pit formed by alkaline etching corresponds to the amount of strain in the crystal lattice surrounding the dislocation core. This is because, in addition to the type of dislocation, the size of the etch pit is also influenced by factors such as impurities trapped in the dislocation, precipitates on the dislocation, and the distance to other nearby dislocations.

[0045] While it's difficult to identify the type of dislocation (edge, mixed, or screw) based on pit size for the reasons mentioned above, it can be argued that dislocations that form larger pits tend to have larger strain fields around their cores. Dislocations with larger strain fields are more likely to have larger Burgers vectors, and such dislocations become micropipe defects with hollow cores, making them more likely to serve as anomalous diffusion pathways for impurities.

[0046] The size of the etch pits also depends greatly on the etching conditions. Therefore, it is meaningless to discuss the absolute value of the etch pit size. However, among the several etch pits of different sizes detected by etching, the smallest etch pit is very likely to correspond to an edge dislocation with the smallest strain field around the dislocation core. Therefore, the inventors have discovered the following technology: by investigating the histogram of the diameter of the etch pits, the diameter and number of other etch pits are investigated based on the diameter of the peak with the smallest diameter among the peaks appearing in the histogram, thereby understanding the presence or absence of dislocation defects that adversely affect the characteristics of devices manufactured on gallium nitride single crystal substrates. Furthermore, it was found that when the diameter of the etch pit that will serve as the benchmark is set to a, etch pits with a diameter exceeding 4a correspond to dislocations that have accumulated the above-mentioned large strain, and such dislocations are more likely to adversely affect the device characteristics.

[0047] Furthermore, as described in Patent Document 1, when growth with an inclined interface as the growth plane (hereinafter also referred to as 3D growth) forcibly changes the propagation direction of dislocations, thereby canceling them and reducing the dislocation density, it is known that while the overall dislocation density of the substrate is reduced, the type and density of dislocations tend to vary within the surface. When the type and density of dislocations vary within the surface, a locally large stress field is generated, making it easier for cracks to be introduced into the crystal.

[0048] The inventors conducted in-depth research on the relationship between histograms of pit diameters formed by alkaline etching and crack generation. They discovered that by creating diameter histograms for multiple different regions within a surface, with the diameter of the smallest first peak represented by a, the diameter of the second peak represented by b, the frequency of the first peak (number of pits) represented by A, the frequency of the second peak represented by B, the number of pits constituting the first peak represented by α, and the number of pits constituting the second peak represented by β, crack generation can be significantly reduced if the variations in the values of a / b, A / B, or α / β across the multiple histograms fall within a specified range.

[0049] Furthermore, the inventors conducted intensive research into methods for producing substrates with the aforementioned uniform in-plane histogram (i.e., substrates with uniformly reduced dislocations within the plane). As a result, they discovered that by using a substrate with a uniform in-plane dislocation density distribution as a starting seed substrate, a gallium nitride single crystal can be grown exclusively with the (0001) plane as the growth plane (hereinafter also referred to as 2D growth), without generating tilted interfaces other than the (0001) plane throughout the entire growth period. Furthermore, this method utilizes successive growth rather than a single thick film growth (details of which will be described later), thereby enabling the production of substrates with a uniform in-plane histogram.

[0050] <One embodiment of the present invention>

[0051] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0052] 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 (N) 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."

[0053] (1) Method for manufacturing gallium nitride single crystal substrate

[0054] use Figure 1 as well as Figure 2A to Figure 2C , a method for manufacturing a gallium nitride single crystal substrate according to this embodiment is described. Figure 1 1 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.

[0055] like Figure 1As 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 2D growth step S110 , and a slicing / processing step S120 .

[0056] (S100: Base substrate preparation process)

[0057] 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 10c), and the dislocation density of the primary surface 10s is uniformly distributed within the plane. Specifically, the base substrate 10 composed of a gallium nitride single crystal is preferably produced using the VAS (Void-Assisted Separation) method described in Non-Patent Document 1. GaN substrates produced using the VAS method are characterized by a uniform dislocation density distribution within the plane. However, the c-plane in the crystal exhibits warpage, with the primary surface 10s side becoming concave. To produce a substrate with a uniform distribution of dislocation seeds, which is a characteristic of the gallium nitride single crystal substrate of this embodiment, the base substrate 10, serving as the starting substrate, must not undergo a 3D growth process such as the ELO (Epitaxial Lateral Overgrowth) method, so that dislocations do not accumulate locally and are uniformly distributed within the plane. The VAS method is a suitable method for obtaining such substrates. However, substrates produced using the VAS method exhibit considerable c-plane warpage, and the magnitude of this warpage is in a trade-off relationship with the in-plane uniformity of dislocation density. In this embodiment, emphasis is placed on in-plane uniformity of dislocation density, and treatment is performed to mitigate c-plane warpage during a subsequent crystal growth step (e.g., the generational growth described below). This allows for c-plane warpage in the base substrate 10.

[0058] It should be noted that the base substrate 10 may be a substrate doped with dopants such as germanium (Ge), silicon (Si), and oxygen (O), or may be a so-called undoped substrate that is intentionally not doped with dopants.

[0059] (S110: 2D growth process)

[0060] In the 2D growth step S110, as Figure 2B As shown, a GaN single crystal is epitaxially grown on the primary surface 10s of the substrate 10 prepared in the substrate preparation step S100, using the c-plane 30c as the growth plane. Specifically, for example, GaCl gas and NH3 gas are supplied to the heated substrate 10 by the HVPE method, thereby epitaxially growing the growth layer 30 directly on the primary surface 10s of the substrate 10.

[0061] At this time, sometimes, due to the growth conditions, an inclined interface other than the c-plane is generated on the growth surface, as described in Patent Document 1, thereby generating 3D growth. There are three modes of crystal growth in the early stage of epitaxial crystal growth, and these modes change depending on the crystal growth conditions. Among the above three modes, the VW (Volmer-Weber) mode and the SK (Stranski-Krastanov) mode are growth modes that cause 3D growth. In contrast, in the 2D growth step S110, it is necessary to not generate inclined interfaces other than the c-plane during the entire growth period, and to use only the c-plane as the growth surface to cause the GaN single crystal to undergo epitaxial growth (i.e., 2D growth). In order to achieve 2D growth, the crystal growth conditions can be adjusted in such a way that it becomes an FM (Frank-van der Merwe) mode that is different from the above growth mode.

[0062] During 3D growth, the propagating dislocations are forcibly bent and locally concentrated. This allows multiple dislocations to combine, effectively reducing dislocation density. However, this also tends to generate dislocations with large Burgers vectors, distributing dislocation seeds with various crystal strains within the substrate surface. In such areas, localized, large stress fields form, sometimes leading to cracks during crystal growth or cooling.

[0063] In 2D growth, the direction of propagation of dislocations is not forcibly bent, but even so, in the process of growing the crystal thicker, propagation dislocations with tilted directions of propagation will converge with each other with a certain probability and disappear, or form dislocation loops and stop propagating, thereby gradually reducing the dislocation density.

[0064] Thus, while 2D growth takes time to reduce dislocations compared to 3D growth, it does not cause changes in the propagation direction of dislocations or forced synthesis of dislocations, thus enabling uniform reduction of dislocations within the surface. Furthermore, it has the advantage of being less likely to produce dislocations with large Burgers vectors, which arise from the synthesis of multiple dislocations.

[0065] In the 2D growth step S110, the growth layer 30 is grown under predetermined growth conditions in a manner that allows crystal growth to be performed in the FM mode. In this embodiment, the growth temperature is preferably set to, for example, 980°C or higher and 1200°C or lower. Furthermore, in the 2D growth step S110, the ratio of the supply rate of NH3 gas, which is a nitriding gas, to the supply rate of GaCl gas, which is a Group III source gas (hereinafter also referred to as the "V / III ratio") is preferably set to, for example, 0.1 or higher and 5 or lower.

[0066] In the 2D growth step S110, GaCl gas, NH3 gas, and dichlorosilane (SiH2Cl2) gas as an n-type dopant gas may be supplied to the base substrate 10 to epitaxially grow a Si-doped GaN layer as the growth layer 30. Alternatively, germanium tetrachloride (GeCl4) gas may be supplied as an n-type dopant gas instead of SiH2Cl2 gas to epitaxially grow a Ge-doped GaN layer. It should be noted that a GaN layer doped with iron (Fe), manganese (Mn), carbon (C), or the like may also be epitaxially grown as the growth layer 30.

[0067] It should be noted that other growth conditions in the 2D growth step S110 are as follows, for example.

[0068] Growth pressure: 90~105kPa, preferably 90~95kPa

[0069] Partial pressure of GaCl gas: 1.5~15kPa

[0070] N2 gas flow rate / H2 gas flow rate: 0~1

[0071] In the 2D growth step S110, the thickness of the growth layer 30 is preferably set to, for example, 3 mm or more and 20 mm or less. If the thickness of the growth layer 30 is less than 3 mm, the effect of reducing dislocations may not be fully achieved. Furthermore, the warpage of the c-plane of the base substrate 10 is also inherited by the growth layer 30 grown thereon. Therefore, by growing the growth layer 30 thicker than a certain level, stress is generated that causes the warpage to return to the crystal, flattening the c-plane, and gradually reducing the magnitude of the c-plane warpage. If the thickness of the growth layer 30 is less than 3 mm, the stress required to return the warpage of the c-plane may not be sufficient. 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 3 mm, dislocations can be uniformly reduced within the surface, and the c-plane warpage can be reduced. Furthermore, a GaN single crystal substrate of sufficient thickness can be obtained in the subsequent slicing / processing step S120. On the other hand, if the thickness of the growth layer 30 exceeds 20 mm, the force attempting to reverse the warping of the c-plane accumulates excessive strain in the crystal, potentially causing dislocations to multiply or microcracks to form. Furthermore, the internal residual stress of the GaN crystal increases, making it more susceptible to crystal fracture during the slicing / processing step S120. In contrast, by reducing the thickness of the growth layer 30 to 20 mm or less, the internal residual stress of the GaN crystal can be reduced, suppressing cracks and breakage.

[0072] (S120: Slicing / Processing Process)

[0073] 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 (c-plane 30c) 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, 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 to 500 μm.

[0074] As described above, by growing the growth layer 30 to a relatively thick thickness, stress is generated during growth that counteracts the warping of the c-plane. Consequently, the radius of curvature of the c-plane 50c of the substrate 50 cut from the growth layer 30 is greater than the radius of curvature of the c-plane 10c of the base substrate 10. Furthermore, by separating the growth layer 30 from the base substrate 10 in the slicing / processing step S120, the growth layer 30 is freed from the constraints imposed by the warping of the c-plane on the base substrate 10. Consequently, the radius of curvature of the c-plane 50c of the cut substrate 50 is further increased compared to that before separation from the base substrate 10. Consequently, residual stress within the cut substrate 50 is also reduced.

[0075] Specifically, the radius of curvature of the c-plane 50c of the substrate 50 is preferably 60 μm or greater, and more preferably 80 μm or greater. This allows the variation in the off-angle θ of the c-axis relative to the normal to the primary surface 50s of the substrate 50 (the range of the off-angle θ within the substrate surface) to be smaller than the variation in the off-angle of the c-axis of the base substrate 10.

[0076] 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.

[0077] (Replacement growth)

[0078] In the present embodiment, the substrate 50 obtained by the slicing / processing step S120 is used as a new base substrate 10, and the 2D growth step S110 and the slicing / processing step S120 are repeated at least once (preferably 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. By this method, even when a substrate with a uniform dislocation density distribution that sacrifices the warping of the c-plane is used as the base substrate 10, its shortcomings can be eliminated. In addition, by performing replacement growth, the internal residual stress of the obtained GaN crystal can be further reduced. By reducing the internal residual stress, it is easy to maintain the propagation direction of the dislocation even in the new 2D growth step S110 using the substrate 50 as the base substrate 10, so it is easy to reduce the dislocation uniformly within the plane. Specifically, by repeatedly performing replacement growth to make the cumulative growth thickness of the growth layer 30 more than 12 mm, the dislocation density can be reduced to 5×10 5 cm -3 It should be noted that the upper limit of the number of times the generation growth is performed is not particularly limited, but is preferably set to 10 times or less from the viewpoint of efficiently manufacturing a large-diameter GaN single crystal substrate, for example.

[0079] Through the above steps, the substrate 50 of this embodiment is manufactured.

[0080] (Process for Manufacturing a Semiconductor Stack and Process for Manufacturing a Semiconductor Device)

[0081] After fabricating 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 fabricating the semiconductor stack, electrodes and other processes can be further formed on the semiconductor stack, and the semiconductor stack can be diced to produce chips of a predetermined size. This can also be used to fabricate semiconductor devices. Because dislocations in substrate 50 are uniformly reduced within the surface, the characteristics of semiconductor devices (devices) fabricated on substrate 50 are uniform within the surface, thereby improving reliability.

[0082] (2) Gallium nitride single crystal substrates (nitride semiconductor self-supporting substrates, nitride crystal substrates)

[0083] Next, the gallium nitride single crystal substrate 50 of this embodiment will be described.

[0084] 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.

[0085] 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.

[0086] The conductivity of the substrate 50 is not particularly limited. However, when a semiconductor device as a vertical Schottky barrier diode (SBD) is manufactured using the substrate 50, the substrate 50 is, for example, n-type, the n-type impurities in the substrate 50 are, for example, Si or Ge, and the n-type impurity concentration in the substrate 50 is, for example, 1.0×10 18 cm -3 Above and 1.0×10 20 cm -3 the following.

[0087] 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 c-plane 50c.

[0088] It should be noted that the principal surface 50 s of the substrate 50 is, for example, mirror-finished, and the root mean square roughness RMS of the principal surface 50 s of the substrate 50 is, for example, less than 1 nm.

[0089] 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.

[0090] Specifically, the hydrogen 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 concentration in the substrate 50 is, for example, 5×10 16 cm -3 Below, preferably 3×10 16 cm -3 the following.

[0091] (C-plane curvature and deviation of the off-angle)

[0092] In this embodiment, the substrate 50 is manufactured by generational growth, and therefore the radius of curvature of the c-plane 50c of the substrate 50 is, for example, larger than the radius of curvature of the c-plane 10c of the base substrate 10 used in the above-described method for manufacturing the substrate 50. Specifically, the radius of curvature of the c-plane 50c of the substrate 50 is preferably, for example, 60 μm or greater, and more preferably 80 μm or greater.

[0093] In this embodiment, the upper limit of the curvature radius of the c-plane 50c of the substrate 50 is preferably as large as possible and is not particularly limited. When the c-plane 50c of the substrate 50 is substantially flat, the curvature radius of the c-plane 50c may be considered to be infinite.

[0094] In this embodiment, the c-plane 50 c of the substrate 50 has a large curvature radius, so that the deviation of 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 deviation of the off angle of the c-axis of the base substrate 10 .

[0095] 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, 0.024°, and preferably less than 0.018°.

[0096] 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 50c 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°.

[0097] Furthermore, in the present embodiment, the curvature of the c-plane 50 c is isotropically reduced with respect to the principal surface 50 s of the substrate 50 , and therefore the direction dependence of the radius of curvature of the c-plane 50 c is small.

[0098] Specifically, the difference between the curvature radius of the c-plane 50c along the a-axis and the curvature radius of the c-plane 50c 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%.

[0099] (Dislocation density)

[0100] In the present embodiment, by the above-described manufacturing method, the dislocation density in the surface of the substrate 50 is reduced compared to the dislocation density in the main surface 10 s of the base substrate 10 .

[0101] When the substrate 50 is manufactured using the base substrate 10 composed of a high-purity GaN single crystal produced by the VAS method, the substrate 50 contains fewer non-luminescent centers caused by foreign matter or point defects.

[0102] Therefore, when observing the main surface of the substrate 50 of the present application using a multiphoton excitation microscope or the like, more than 95% (preferably more than 99%) of the dark spots observed are not non-luminescent centers caused by foreign matter or point defects, but rather correspond to dislocations. It should be noted that "multiphoton excitation microscopy" is sometimes also referred to as two-photon excitation microscopy.

[0103] In this embodiment, the above-described manufacturing method uniformly reduces dislocations within the surface, thereby preventing the formation of regions with an exceptionally high dislocation density due to the concentration of dislocations, and instead uniformly forming regions with a low dislocation density. Specifically, in this embodiment, when the main surface 50s of the substrate 50 is observed in a 250 μm square field of view using a multiphoton excitation microscope and the dislocation density is determined from the dark spot density, no regions with a dislocation density exceeding 1×10 6 cm -2 In the region, the dislocation density is less than 5×10 5 cm -2 The region exists on 80% or more of the main surface 50 s, preferably exists on 90% or more, and more preferably exists on 95% or more.

[0104] In other words, in this embodiment, the dislocation density averaged over the entire principal surface 50s of the substrate 50 is, for example, less than 1×10 6 cm -2 , preferably less than 5.5×10 5 cm -2 , more preferably 3×10 5 cm -2 the following.

[0105] (Erosion pit histogram)

[0106] When the main surface 50s of the substrate 50 is etched with an alkaline etching solution, Figure 3 In this embodiment, the substrate 50 is immersed in a solution (temperature 470°C) of potassium hydroxide (KOH) and sodium hydroxide (NaOH) mixed in a ratio of 1:1 for 20 minutes and then etched. Then, the main surface 50s of the etched substrate 50 is observed using an SEM, and the diameter of each etch pit is calculated by image analysis. A histogram of the diameter of the etch pit is produced based on the data of the diameter of the etch pit obtained. It should be noted that the diameter of the etch pit can be the maximum diameter of each etch pit area obtained by image analysis, or it can be the equivalent circle diameter. In this embodiment, the diameter of the peak that appears on the side with the smallest diameter (hereinafter also referred to as the first peak) in the histogram of the diameter of the etch pit is set to a and standardized, and the level (scale width) of the horizontal axis is set to 0.1a scale. The vertical axis is the number (frequency) of etch pits in the measurement area.

[0107] The average density (number per unit area) of etch pits formed when etching the principal surface 50s of the substrate 50 of this embodiment under the aforementioned conditions roughly matches the dislocation density determined by observation using a multiphoton excitation microscope. The size of the etch pits can vary depending on the etching conditions, but if the etch pits are present at an excessively high density, adjacent etch pits overlap, making it difficult to measure the pit diameter. Therefore, for meaningful measurement, the average density of the etch pits is preferably less than 1×10 6 cm -2 , more preferably less than 5.5×10 5 cm -2 , more preferably 3×10 5 cm -2 It should be noted that the average density of the pits and the histogram of the pit diameter are preferably calculated based on an area of 1 mm. 2 The above area measurement.

[0108] When a histogram of the diameter of the etching pits is prepared for each of the plurality of different regions on the main surface 50s of the substrate 50, and the diameter of the first peak with the smallest diameter among the peaks appearing in the histogram is set to a, the diameter of the second peak with the second smallest diameter is set to b, the frequency of the first peak (the number of etching pits) is set to A, the frequency of the second peak is set to B, the number of etching pits constituting the first peak is set to α, and the number of etching pits constituting the second peak is set to β, the substrate 50 of this embodiment satisfies at least any one of the following conditions (1), (2), and (3).

[0109] (1) The deviation of the a / b values in multiple histograms is within ±5% of the average value.

[0110] (2) The deviation of the A / B values in multiple histograms is within ±15% of the average value.

[0111] (3) The deviation of the α / β values in multiple histograms is within ±30% of the mean value.

[0112] The dislocations of the substrate 50 that obtains such a histogram are uniformly reduced within the surface, and it can be said that the substrate is less likely to crack during crystal growth or processing. On the other hand, a substrate with deviations exceeding conditions (1), (2), and (3) generates a large stress field locally, and it can be said that cracks are easily generated during crystal growth or processing. It should be noted that, from the perspective of accurately determining conditions (1), (2), and (3), it is preferable to prepare a histogram of the diameter of the etch pit in different regions of three or more locations (more preferably five or more locations) on the main surface 50s.

[0113] The substrate 50 preferably satisfies two of the conditions (1), (2), and (3), and more preferably satisfies all of the conditions (1), (2), and (3). This can significantly reduce the incidence of cracks during crystal growth and processing.

[0114] In addition, the substrate 50 preferably satisfies at least one of the following conditions (4), (5), and (6), more preferably satisfies two of the conditions, and particularly preferably satisfies all of the conditions.

[0115] (4) The difference between the maximum and minimum values of a / b in multiple histograms is less than 0.1.

[0116] (5) The difference between the maximum and minimum values of A / B in multiple histograms is less than 0.5.

[0117] (6) The difference between the maximum and minimum values of α / β in multiple histograms is less than 0.8.

[0118] In addition, the substrate 50 preferably satisfies at least one of the following conditions (7), (8), and (9), more preferably satisfies two of the conditions, and particularly preferably satisfies all of the conditions.

[0119] (7) The standard deviation of a / b in multiple histograms is less than 0.03.

[0120] (8) The standard deviation of A / B in multiple histograms is less than 0.20.

[0121] (9) The standard deviation of β / α in multiple histograms is less than 0.3.

[0122] In addition, the substrate 50 preferably satisfies at least one of the following conditions (10) and (11), and more preferably satisfies both of them.

[0123] (10) In a plurality of histograms, A / α is 0.5 or greater, more preferably 0.7 or greater.

[0124] (11) In a plurality of histograms, B / β is 0.5 or greater, more preferably 0.7 or greater.

[0125] Furthermore, for the substrate 50 , in a plurality of histograms, α+β is preferably 90% or more of the total number of etch pits, and more preferably 95% or more.

[0126] For the substrate 50 of this embodiment, the total number (total count) of etch pits with a diameter exceeding 4 Å is preferably α / 1000 or less. This can be translated as the absence of etch pits with a diameter exceeding 4 Å. However, larger etch pits may form due to damage or foreign matter on the substrate 50, so the number is expressed as α / 1000 or less. Because dislocations in the substrate 50 of this embodiment are less likely to combine with each other due to the aforementioned manufacturing method, it can be said that there are virtually no dislocation seeds or regions of dislocation concentration that could locally generate significant stress. Consequently, the generation of cracks during crystal growth and processing can be suppressed.

[0127] In the substrate 50 of this embodiment, the total number of etch pits with a diameter of 2 Å or greater is preferably 1 / 10 or less, and more preferably 1 / 100 or less, of the number of etch pits constituting the first peak. Since etch pits with a diameter of 2 Å or greater may correspond to dislocations that locally generate high stress, cracking can be suppressed by limiting the total number of etch pits with a diameter of 2 Å or greater to 1 / 10 or less (more preferably 1 / 100 or less) of the number of etch pits constituting the first peak.

[0128] For substrate 50 of this embodiment, the number of etch pits forming the first peak preferably accounts for at least 50% (more preferably at least 70%) of the total substrate. As described above, in this embodiment, since dislocation synthesis is less likely to occur, the proportion of dislocations with smaller strain fields is higher. This can suppress the occurrence of cracks.

[0129] For the substrate 50 of this embodiment, when the frequency of the first peak is set to A, the peaks appearing in the diameter histogram with a frequency of A / 10 or greater are preferably the first peak and the second peak. The number of peaks appearing in the pit histogram can be said to correspond to the number of types of dislocation defects corresponding to the pits. For crystals in which multiple peaks are observed, in addition to simple edge and mixed dislocations, there are many deformations of impurities or point defects that are combined with these dislocations in a complex manner. In other words, this is a crystal with a high probability of generating impurity energy levels or defect energy levels, which locally generates a large stress field and can be said to be prone to cracking during crystal growth or processing. In contrast, for crystals in which the peaks appearing in the histogram with a frequency of A / 10 or greater are the first peak and the second peak, it is taught that the dislocations present in the crystal are only simple edge dislocations and mixed dislocations. In other words, this is a substrate that is not prone to cracking during crystal growth or processing.

[0130] Furthermore, substrate 50 of this embodiment preferably has a second peak within a diameter range exceeding a and less than 2a, and the number of pits β constituting the second peak is less than the number of pits α constituting the first peak. A pit diameter exceeding a and less than 2a in the second peak indicates a high probability of corresponding to simple mixed dislocations. A smaller number of pits constituting the second peak, or in other words, a larger number of pits constituting the first peak, indicates that the dislocations in the crystal are primarily composed of dislocations with less strain surrounding the dislocation core. These characteristics mean that substrate 50 is less susceptible to cracking during crystal growth or processing.

[0131] <Another embodiment>

[0132] 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.

[0133] While the above embodiments primarily describe substrate 50 as being n-type, substrate 50 may also be p-type or have semi-insulating properties. For example, when using substrate 50 to manufacture a semiconductor device serving as a high electron mobility transistor (HEMT), it is preferable that substrate 50 have semi-insulating properties.

[0134] In the above embodiment, a case where a wire saw is used to slice the growth layer 30 in the slicing / machining step S120 is described. However, for example, an outer peripheral blade slicer, an inner peripheral blade slicer, an electric discharge machine, or the like may be used.

[0135] [Example]

[0136] 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.

[0137] (1) Fabrication of GaN single crystal substrate

[0138] Gallium nitride single crystal substrates of Example 1 and Comparative Example 1 were produced as follows.

[0139] [Conditions for Fabricating Gallium Nitride Single Crystal Substrate in Example 1] (Base Substrate)

[0140] Material: GaN

[0141] Production method: VAS method

[0142] Diameter: 2 inches

[0143] Thickness: 400μm

[0144] Low-index crystal plane closest to the main surface: c-plane

[0145] There is no patterning of a mask layer or the like on the main surface.

[0146] Root mean square roughness RMS of the main surface: 2nm

[0147] Offset angle of the main surface: 0.4° in the m direction

[0148] Curvature radius of the main surface: 5m

[0149] Dislocation density of the main surface: 3×10 6 cm -2 (Growth layer)

[0150] Material: GaN

[0151] Growth method: HVPE method, 2D growth

[0152] Growth temperature: above 980℃ and below 1200℃

[0153] V / III ratio: 0.1 or more and 5 or less

[0154] Thickness of growth layer: 3mm (slicing conditions)

[0155] Thickness of GaN single crystal substrate: 400μm (generation growth)

[0156] Number of replacement growth: 4 times

[0157] [Conditions for Fabricating Gallium Nitride Single Crystal Substrate in Comparative Example 1] (Base Substrate)

[0158] Same as Example 1.

[0159] (First floor)

[0160] Material: GaN

[0161] Growth method: HVPE method, 3D growth

[0162] First growth conditions:

[0163] The growth temperature is set to 980° C. or higher and 1020° C. or lower, and the V / III ratio is set to 2 or higher and 20 or lower.

[0164] Thickness from the main surface of the base substrate to the surface of the first layer: 1mm (second layer)

[0165] Material: GaN

[0166] Growth method: HVPE method, 2D growth

[0167] Second growth conditions:

[0168] The growth temperature is set to 1050° C. or higher and 1080° C. or lower, and the V / III ratio is set to 2 or higher and 5 or lower.

[0169] Thickness from the main surface of the base substrate to the surface of the second layer: 2 mm (slicing conditions)

[0170] Same as Example 1.

[0171] (Replacement growth)

[0172] In Comparative Example 1, no generational growth was performed.

[0173] (2) Evaluation of the pit histogram

[0174] The main surfaces of the base substrate (VAS substrate), the gallium nitride single crystal substrate of Example 1, and the gallium nitride single crystal substrate of Comparative Example 1 were etched with an alkaline etching solution under the following conditions to form etch pits.

[0175] Etching solution: Alkaline solution consisting of 500g KOH and 500g NaOH

[0176] Melt temperature: 470°C

[0177] Soaking time: 20 minutes

[0178] The main surface of the substrate with etch pits was observed using an SEM (manufactured by Hitachi High-Technologies Corporation, SU5000). The measurement field of view was set to 127μm×95.3μm (magnification 1000 times), and the image (1143μm×1048μm) formed by combining 9 horizontal × 11 vertical SEM images (a total of 99 images) was analyzed to measure the etch pits. Specifically, the image was binarized using image processing software (Image J), the etch pit area was filled, and the larger of the width and height of the etch pit area was calculated as the diameter of the etch pit. It should be noted that when filling the etch pit area, areas representing smaller garbage or linear pit areas caused by processing damage were removed.

[0179] A histogram of pit diameters was created based on the obtained pit diameter data. In this example, the diameter of the peak with the smallest diameter (the first peak) in the pit diameter histogram was normalized to 1, and the horizontal axis was scaled to 0.1. The histogram was created for five regions: the substrate center (0 mm, 0 mm), the right side (20 mm, 0 mm), the left side (-20 mm, 0 mm), the upper side (0 mm, 20 mm), and the lower side (0 mm, -20 mm), with the substrate center as the origin, the left and right directions in top view as the x-direction, and the vertical directions in top view as the y-direction.

[0180] exist Figure 4 The histogram of the VAS substrate is shown in Figure 5 The histogram of Example 1 is shown in Figure 6 The histograms for Comparative Example 1 are shown in Table 1. In each histogram, the horizontal axis represents the normalized pit diameter, and the vertical axis represents the number (frequency) of pits within the measurement area. Table 1 also summarizes the average pit density, a / b ratio, A / B ratio, α / β ratio, and other values for each histogram for the VAS substrate, Example 1, and Comparative Example 1.

[0181]

Table 1

[0182]

[0183] like Figure 4 As shown in Table 1, the shape of the histogram is uniform within the surface of the VAS substrate, satisfying the aforementioned conditions (2) and (3). In other words, the VAS substrate can be said to be a substrate in which the dislocation density is uniform within the surface, although the average density of etch pits (in other words, the dislocation density) is relatively high.

[0184] In addition, if Figure 5 As shown in Table 1, the histogram shape of the substrate of Example 1 is uniform within the surface, satisfying all of the above-mentioned conditions (1), (2), and (3). Furthermore, the average density of etch pits is lower than that of the VAS substrate. In other words, the substrate of Example 1 can be said to have uniformly reduced dislocations within the surface. Furthermore, the deviations from the average values of a / b, A / B, and α / β for the substrate of Example 1 are smaller than those for the VAS substrate.

[0185] In addition, if Figure 6 As shown in Table 1, the shape of the histogram fluctuates within the plane of the substrate of Comparative Example 1, and the above-mentioned conditions (1), (2), and (3) are not satisfied. In other words, the substrate of Comparative Example 1 can be said to be a substrate in which the density and type of dislocations vary within the plane, although the dislocation density is reduced.

[0186] Table 2 shows the incidence rates of cracks during substrate fabrication (growth cracks) and cracks during substrate processing (processing cracks) for the VAS substrate, the substrate of Example 1, and the substrate of Comparative Example 1. As shown in Table 2, the higher the in-plane uniformity of the histogram, the lower the incidence rate of cracks.

[0187]

Table 2

[0188]

[0189] (3) Evaluation of the curvature radius of the c-surface

[0190] The c-plane curvature radius was measured for the base substrate (VAS substrate), the substrate of Example 1, and the substrate of Comparative Example 1. The results showed that the curvature radius of the c-plane was 5 μm for the VAS substrate, 60 μm for the substrate of Example 1, and 40 μm for the substrate of Comparative Example 1.

[0191] Based on the above, it was confirmed that by using a VAS substrate with a uniform dislocation density distribution within the plane as the base substrate and repeatedly performing 2D growth and generational growth, a substrate with uniformly reduced dislocations within the plane can be produced. Furthermore, it was confirmed that the higher the in-plane uniformity of the histogram of the substrate, the lower the incidence of cracks. Furthermore, it was confirmed that the c-plane radius of curvature of the substrate of Example 1, which underwent repeated generational growth, was larger than that of the VAS substrate used as the starting seed substrate and the substrate of Comparative Example 1, which did not undergo generational growth.

[0192] <Preferred embodiment of the present invention>

[0193] Preferred embodiments of the present invention are described below.

[0194] (Note 1)

[0195] 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:

[0196] The average density of the etch pits formed when the main surface is etched with an alkaline etching solution is less than 1×10 6 cm -2 ,

[0197] When a histogram of the diameter of the pits is prepared in each of the plurality of different regions on the main surface, and the diameter of the first peak with the smallest diameter among the peaks appearing in the histogram is set to a, the diameter of the second peak with the second smallest diameter is set to b, the frequency of the first peak (the number of pits) is set to A, the frequency of the second peak is set to B, the number of the pits constituting the first peak is set to α, and the number of the pits constituting the second peak is set to β, at least any one of the following conditions (1), (2), and (3) is satisfied.

[0198] (1) The deviation of the a / b values in the plurality of histograms is within ±5% of the average value.

[0199] (2) The deviation of the A / B values in the plurality of histograms is within ±15% of the average value.

[0200] (3) The deviation of the values of α / β in the plurality of histograms is within ±30% of the average value.

[0201] (Note 2)

[0202] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0203] The gallium nitride single crystal substrate satisfies two of the conditions (1), (2) and (3).

[0204] (Note 3)

[0205] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0206] The gallium nitride single crystal substrate satisfies all of the conditions (1), (2) and (3).

[0207] (Note 4)

[0208] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0209] The gallium nitride single crystal substrate satisfies at least any one of the following conditions (4), (5) and (6).

[0210] (4) The difference between the maximum value and the minimum value of a / b in the plurality of histograms is 0.1 or less.

[0211] (5) The difference between the maximum value and the minimum value of A / B in the plurality of histograms is 0.5 or less.

[0212] (6) The difference between the maximum value and the minimum value of α / β in the plurality of histograms is 0.8 or less.

[0213] It is more preferred that two of the conditions (4), (5) and (6) are satisfied, and it is particularly preferred that all of the conditions (4), (5) and (6) are satisfied.

[0214] (Note 5)

[0215] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0216] The gallium nitride single crystal substrate satisfies at least any one of the following conditions (7), (8) and (9).

[0217] (7) The standard deviation of a / b in the plurality of histograms is 0.03 or less.

[0218] (8) The standard deviation of A / B in the plurality of histograms is 0.20 or less.

[0219] (9) The standard deviation of β / α in the plurality of histograms is 0.3 or less.

[0220] It is more preferred that two of the conditions (7), (8) and (9) are satisfied, and it is particularly preferred that all of the conditions (7), (8) and (9) are satisfied.

[0221] (Note 6)

[0222] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0223] The gallium nitride single crystal substrate satisfies at least one of the following conditions (10) and (11).

[0224] (10) In the plurality of histograms, A / α is equal to or greater than 0.5, and more preferably equal to or greater than 0.7.

[0225] (11) In the plurality of histograms, B / β is equal to or greater than 0.5, and more preferably equal to or greater than 0.7.

[0226] More preferably, both conditions (10) and (11) are satisfied.

[0227] (Note 7)

[0228] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0229] In a plurality of the histograms, α+β accounts for more than 90% of all etch pit numbers.

[0230] More preferably, α+β accounts for 95% or more of all etch pits.

[0231] (Note 8)

[0232] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0233] In the histogram, the total number of etch pits having a diameter exceeding 4 Å is α / 1000 or less.

[0234] (Note 9)

[0235] Based on the gallium nitride single crystal substrate described in Supplementary Note 1,

[0236] The curvature radius of the (0001) plane is greater than 60 m.

[0237] (Note 10)

[0238] In the case of the gallium nitride single crystal substrate described in any one of Supplementary Notes 1 to 9,

[0239] The average density of the pits and the histogram according to the area of 1mm 2 The above area measurement.

[0240] (Note 11)

[0241] A method for manufacturing a gallium nitride single crystal substrate, wherein:

[0242] The method for manufacturing the gallium nitride single crystal substrate comprises:

[0243] Step (a) of preparing a base substrate composed of a gallium nitride single crystal, wherein the low-index crystal plane closest to the main surface is the (0001) plane and the dislocation density of the main surface is uniformly distributed within the surface;

[0244] Step (b), epitaxially growing a gallium nitride single crystal on the main surface of the base substrate; and

[0245] 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);

[0246] In the step (b), during the entire growth period, no tilted interface other than the (0001) plane is generated, and the gallium nitride single crystal is epitaxially grown using only the (0001) plane as a growth plane.

[0247] The gallium nitride single crystal substrate obtained in the step (c) is used as a new base substrate, and the steps (b) and (c) are repeated at least once.

[0248] (Note 12)

[0249] Based on the method for manufacturing a gallium nitride single crystal substrate described in Supplementary Note 11,

[0250] The base substrate prepared in the step (a) is a substrate produced by the VAS method.

[0251] (Note 13)

[0252] Based on the method for manufacturing a gallium nitride single crystal substrate described in Supplementary Note 11,

[0253] In the step (b), the gallium nitride single crystal is grown to at least 3 mm.

[0254] (Note 14)

[0255] Based on the method for manufacturing a gallium nitride single crystal substrate described in Supplementary Note 11,

[0256] Each time the steps (b) and (c) are repeated, the obtained gallium nitride single crystal substrate has a lower dislocation density than the base substrate and a larger curvature radius of the (0001) plane than the base substrate.

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 average density of the etch pits formed when the main surface is etched with an alkaline etching solution is less than 1×10 6 cm -2 , When a histogram of the diameter of the etch pits is prepared for each of the plurality of different regions on the main surface, and the diameter of the first peak with the smallest diameter among the peaks appearing in the histogram is set to a, the diameter of the second peak with the second smallest diameter is set to b, the frequency of the first peak is set to A, the frequency of the second peak is set to B, the number of the etch pits constituting the first peak is set to α, and the number of the etch pits constituting the second peak is set to β, at least any one of the following conditions (1), (2), and (3) is satisfied: (1) The deviation of the a / b values in the multiple histograms is within ±5% of the mean value; (2) The deviation of the A / B values in the multiple histograms is within ±15% of the mean value; (3) The deviation of the values of α / β in the plurality of histograms is within ±30% of the average value.

2. The gallium nitride single crystal substrate according to claim 1, wherein The gallium nitride single crystal substrate satisfies two of the conditions (1), (2) and (3).

3. The gallium nitride single crystal substrate according to claim 1, wherein The gallium nitride single crystal substrate satisfies all of the conditions (1), (2) and (3).

4. The gallium nitride single crystal substrate according to claim 1, wherein In the histogram, the total number of etch pits having a diameter exceeding 4 Å is α / 1000 or less.

5. The gallium nitride single crystal substrate according to claim 1, wherein The curvature radius of the (0001) plane is greater than 60 m.

6. The gallium nitride single crystal substrate according to any one of claims 1 to 5, wherein The average density of the pits and the histogram according to the area of 1mm 2 The above area measurement.

7. 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, wherein the low-index crystal plane closest to the main surface is the (0001) plane and the dislocation density of the main surface is uniformly distributed within the surface; Step (b), epitaxially growing a gallium nitride single crystal 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), during the entire growth period, no tilted interface other than the (0001) plane is generated, and the gallium nitride single crystal is epitaxially grown using only the (0001) plane as a growth plane. The gallium nitride single crystal substrate obtained in the step (c) is used as a new base substrate, and the steps (b) and (c) are repeated at least once.

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