GaN substrate, method for manufacturing GaN crystal, and method for manufacturing GaN substrate

Abstract

A method for manufacturing a GaN substrate and a GaN substrate obtained by the method, wherein the method includes: growing a GaN crystal by an ammonia thermal method through a mask opening portion of a first pattern mask provided on a first base substrate having the first pattern mask on a nitrogen-polarity surface, to obtain a layered structure in which the GaN crystal is layered on the nitrogen-polarity surface of the first base substrate through the first pattern mask; separating a GaN crystal from the layered structure to use as a second base substrate; providing a second pattern mask on the nitrogen-polarity surface so that at least a part of a region of the nitrogen-polarity surface grown above the mask opening portion of the first pattern mask is covered with a mask portion of the second pattern mask; and growing a GaN crystal by an ammonia thermal method through a mask opening portion of the second pattern mask. The GaN substrate achieves improvement in yield or reduction in crystal defects in a wide range when used as a c-plane GaN substrate in device manufacturing.

Description

Technical Field

[0001] This invention relates to a gallium nitride (GaN) substrate, a method for manufacturing GaN crystals, and a method for manufacturing GaN substrates. Background Technology

[0002] GaN substrates obtained from GaN crystals are used as substrates for manufacturing laser diodes (LDs). Recently, GaN substrates have been highly anticipated as substrates for vertical power semiconductor devices (PDs).

[0003] As GaN substrates for LDs and vertical PDs, GaN substrates with reduced crystal defects are required to improve device performance.

[0004] Patent Document 1 describes a method for growing GaN crystals using an ammonothermal method on a GaN seed crystal with a patterned mask, and the resulting GaN crystal. Patent Document 2 describes a method for obtaining GaN crystals using the HVPE method with a GaN crystal obtained by the ammonothermal method as a seed crystal.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: WO2018 / 030311

[0008] Patent Document 2: WO2020 / 036047

[0009] Non-patent literature

[0010] Non-patent literature 1: Fukuzawa Riyuki, Dissertation "Research on the Photoelastic Evaluation of Compound Semiconductors", Kyoto Institute of Technology and Fiberglass University (1997).

[0011] Non-Patent Literature 2: M. Fukuzawa, T. Chu, and M. Yamada, J. Soc. Mat. Sci., Japan., 51, 9, 966, (2002).

[0012] Non-patent literature 3: M. Fukuzawa, R. Kashiwagi, and M. Yamada, Phys. Status Solidi C 8, No. 2, 432, (2011). Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] As described above, there is room for improvement in the yield of GaN crystals obtained by growing GaN crystals using an ammonothermal method on GaN seed crystals with patterned masks, and GaN crystals obtained by growing them using HVPE method on GaN seed crystals. This can be considered from the perspective of yield when used as c-plane GaN substrates in device manufacturing.

[0015] Furthermore, as mentioned above, the GaN crystals obtained by growing GaN crystals using the ammonothermal method on GaN seed crystals with patterned masks have room for improvement in reducing crystal defects over a wide range.

[0016] Therefore, the objective of the first aspect of the present invention is to provide a GaN substrate that can improve the yield when used as a c-plane GaN substrate in device manufacturing.

[0017] Furthermore, the second aspect of the present invention aims to provide a GaN crystal and a GaN substrate that significantly reduce crystal defects.

[0018] Solution for solving the problem

[0019] To address the aforementioned problems, the inventors conducted in-depth research and discovered that one of the main reasons for the decrease in yield is the localized strain present in the main facets of the GaN crystal, thus completing the first aspect of the present invention. Furthermore, to address the aforementioned problems, the inventors conducted in-depth research and discovered that, through a desired manufacturing method, GaN crystals with significantly reduced crystal defects can be achieved, thus completing the second aspect of the present invention.

[0020] The embodiments of the present invention include the following.

[0021] <1> A GaN substrate having an inclination of 0–20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The above main face, among which,

[0022] At least one 0.275cm exists within the aforementioned main surface. 2 The observation area is defined as the region of the observation, and the dislocation density of the observed area is less than 1.0 × 10⁻⁶. 4 cm -2 .

[0023] <2> according to <1> The GaN substrate, wherein,

[0024] The observation area described above includes unit region A and unit region B.

[0025] The dislocation density per unit area A is less than 1.0 × 10⁻⁶. 2 cm -2 ,

[0026] The dislocation density per unit area B is 1.0 × 10⁻⁶. 3 cm -2 above.

[0027] <3> according to <1> or <2> The GaN substrate, wherein the observation region is a 5.5mm × 5.0mm observation region, and the dislocation density in a unit region of 5.5mm × 0.5mm obtained by dividing the observation region into 10 parts is less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is more than one.

[0028] <4> according to <1> ~ <3> The GaN substrate described in any one of the above-mentioned main surface has an (004) XRD rocking curve FWHM of less than 20 arcsec.

[0029] <5> according to <1> ~ <4> The GaN substrate described in any one of the following examples, wherein,

[0030] Set the normal direction of the aforementioned principal face to the z-direction.

[0031] When the two directions orthogonal to and mutually orthogonal to the z-direction are respectively designated as the x-direction and the y-direction.

[0032] The variation range of the x-direction component of the tangent angle passing through the center of the main surface and extending along the first line in the x-direction, and the variation range of the y-direction component of the tangent angle passing through the center of the main surface and extending along the y-direction, are both less than 0.2 degrees within a length of 40 mm.

[0033] <6> according to <1> ~ <5> In any one of the GaN substrates, the concentrations of Li, Na, K, Mg, and Ca are all less than 1 × 10⁻⁶. 16 atoms / cm 3 .

[0034] <7> according to <1> ~ <6> The GaN substrate according to any one of the following, wherein the GaN substrate contains F.

[0035] <8> according to <7> The GaN substrate, in addition to containing F, contains one or more halogens selected from Cl, Br and I.

[0036] <9> according to <8> The GaN substrate, wherein the GaN substrate contains F and I.

[0037] <10> according to <7> The GaN substrate, wherein the GaN substrate substantially contains only F as a halogen element.

[0038] <11> according to <1> ~ <10> In any one of the GaN substrates, the H concentration is 5 × 10⁻⁶. 17 atoms / cm 3 Above and 1×10 20 atoms / cm 3 the following.

[0039] <12> according to <1> ~ <11> The GaN substrate described in any one of the following examples, wherein the GaN substrate is formed from materials with a thickness of 3140–3200 cm⁻¹ -1 GaN crystals with infrared absorption peaks attributable to gallium vacancy-hydrogen complexes are formed.

[0040] <13> A method for manufacturing a GaN crystal includes the following steps:

[0041] The process of preparing a first substrate having a nitrogen-polar surface;

[0042] A process of configuring a first pattern mask comprising a mask portion and a mask opening on the nitrogen polar surface of the first substrate;

[0043] The process of growing GaN crystals using the ammonothermal method through the mask opening of the first pattern mask to obtain a stacked structure in which GaN crystals are stacked on the nitrogen polar surface of the first substrate through the first pattern mask.

[0044] The process of separating at least a portion of the GaN crystal grown on the nitrogen polar surface of the first substrate from the stacked structure.

[0045] The process of planarizing the nitrogen polar surface of the separated GaN crystal;

[0046] The process of using the separated GaN crystal as a second substrate and configuring a second pattern mask on the planarized nitrogen-polar surface, wherein the second pattern mask is configured such that at least a portion of the region grown above the mask opening of the first pattern mask on the nitrogen-polar surface of the GaN crystal serving as the second substrate is covered by a mask portion of the second pattern mask; and

[0047] The process of growing GaN crystals using the ammonothermal method through the mask opening of the second pattern mask.

[0048] <14> according to <13> In the method for manufacturing GaN crystal, the second pattern mask is configured such that the merging surface formed on the mask portion of the first pattern mask and the region grown thereon in the nitrogen polar surface of the GaN crystal, which serves as the second substrate, are covered by the mask portion of the second pattern mask.

[0049] <15> according to <13> or <14> In the method for manufacturing GaN crystal, the second pattern mask is configured such that the region grown above the mask opening of the first pattern mask (the substrate mask opening region) and the region overlapping the substrate mask opening region and the mask opening of the second pattern mask (the substrate opening exposed region) in the nitrogen polar surface of the GaN crystal, which serves as the second substrate substrate, satisfy the following relationship (I).

[0050] The area of ​​the exposed region of the substrate opening / the area of ​​the opening region of the substrate mask ≤ 10% ······(I)

[0051] <16> according to <13> ~ <15> According to any one of the methods for manufacturing a GaN crystal, the second pattern mask is configured such that the region grown on the mask opening of the first pattern mask and the mask opening of the second pattern mask in the nitrogen polar surface of the GaN crystal, which serves as the second substrate, do not overlap.

[0052] <17> A method for manufacturing a GaN crystal, wherein the crystal is produced by means of... <13> ~ <16> The GaN crystal manufactured by any one of the GaN crystal manufacturing methods is used as a third substrate, and the GaN crystal is grown on a gallium polar surface by the HVPE method.

[0053] <18> A method for manufacturing a GaN substrate, wherein the substrate is manufactured by means of... <13> ~ <17> The GaN crystal manufactured by any one of the GaN crystal manufacturing methods is sliced ​​to obtain a GaN substrate.

[0054] <19> A GaN substrate having an inclination of 0–20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The above main face, among which,

[0055] The dislocation density of the principal surface is 5.0 × 10⁻⁶. 4 cm -2 the following,

[0056] For the main surface, the strain evaluation value measured by photoelasticity and calculated based on the following equation (1) exceeds 5 × 10⁻⁶. -5 The area (S1) is less than 2.5% of the total area of ​​the main surface;

[0057]

[0058] The terms in equation (1) are represented by equations (2) and (3) below.

[0059]

[0060] In the formula, δ and ψ are the phase difference and principal axis azimuth angle, respectively, which are birefringence quantities originating from strain; λ is the wavelength of the light source in the photoelasticity measuring device; d is the sample thickness; n0 is the strain-free refractive index relative to the light source wavelength; |p 11 -p 12 | represents the components of the photoelastic tensor, where λ, n0, and |p are... 11 -p 12 The following conditions must be met.

[0061] λ=633nm;

[0062] n0 = 2.355;

[0063] |p 11 -p 12 |=0.13.

[0064] <20> according to <19> The GaN substrate, wherein, for the main surface, the strain evaluation value measured by photoelasticity and calculated based on equation (1) exceeds 1 × 10⁻⁶. -4 The area (S2) is less than 1% of the total area of ​​the main surface.

[0065] <21> according to <19> or <20> The GaN substrate wherein the (004) XRD rocking curve FWHM of the main surface is less than 20 arcsec.

[0066] <22> according to <19> ~ <21> The GaN substrate described in any one of the following examples, wherein,

[0067] Set the normal direction of the principal surface to the z-direction.

[0068] When the two directions orthogonal to the z-direction and mutually orthogonal are respectively designated as the x-direction and y-direction.

[0069] The variation range of the x-direction component of the tangent angle passing through the center of the main surface and extending along the first line in the x-direction, and the variation range of the y-direction component of the tangent angle passing through the center of the main surface and extending along the second line in the y-direction, are both less than 0.2 degrees within a length of 40 mm.

[0070] <23> according to <19> ~ <22> The GaN substrate in any one of the following embodiments satisfies the following condition (a) regarding the impurity concentration.

[0071] Condition (a): O concentration is 3 × 10 16 atoms / cm 3 the following.

[0072] <24> according to <19> ~ <23> The GaN substrate in any one of the following embodiments satisfies the following condition (b) regarding the impurity concentration.

[0073] Condition (b): H concentration is 1×10 17 atoms / cm 3 the following.

[0074] Invention Effects

[0075] According to one aspect of the present invention, a GaN substrate with reduced dislocations on the main surface and reduced strain locally present within the main surface can be obtained. Therefore, when used as a c-plane GaN substrate in device manufacturing, yield degradation can be reduced. Furthermore, according to one aspect of the present invention, a GaN crystal with significantly reduced crystal defects can be obtained through a desired manufacturing method. Therefore, when such a GaN crystal is used as a c-plane GaN substrate for device manufacturing, yield degradation caused by device performance deterioration can be suppressed. Attached Figure Description

[0076] Figure 1 This is a perspective view showing an example of a c-plane GaN substrate according to this embodiment.

[0077] Figure 2 The attached figure illustrates the case where the offset angle of a c-plane GaN substrate can be decomposed into components in two mutually perpendicular directions.

[0078] Figure 3 This is a top view of the GaN substrate used in the embodiment.

[0079] Figure 4 This is a top view of the GaN substrate used in the embodiment.

[0080] Figure 5 A flowchart illustrating the GaN crystal growth method.

[0081] Figure 6 (a) is a three-dimensional view of the substrate. Figure 6 (b) is a perspective view of the substrate after the pattern mask has been disposed on the nitrogen polar surface.

[0082] Figure 7 This is a top view showing a portion of the nitrogen polar surface side of the substrate after a patterned mask has been applied.

[0083] Figure 8 This is a top view showing a portion of the nitrogen polar surface side of the substrate after a patterned mask has been applied.

[0084] Figure 9 (a) to (d) are top views of a substrate with a patterned mask disposed on a nitrogen polar surface.

[0085] Figure 10 (e) to (h) are top views of a substrate on which a patterned mask is disposed on a nitrogen polar surface.

[0086] Figure 11 (i) to (l) are top views of a substrate on which a patterned mask is disposed on a nitrogen polar surface.

[0087] Figure 12 (a) to (f) are top views of a portion of a pattern mask formed on the nitrogen polar surface of a substrate.

[0088] Figure 13 (a) to (f) are top views of a portion of a pattern mask formed on the nitrogen polar surface of a substrate.

[0089] Figure 14 (a) to (e) are schematic cross-sectional views representing the growth process of GaN crystals.

[0090] Figure 15 This indicates the crystal growth apparatus that can be used in GaN crystal growth using the ammonothermal method.

[0091] Figure 16 (a) is a schematic cross-sectional view of a GaN crystal grown by ammonothermal method through the mask opening of a patterned mask formed on the nitrogen polar surface of a substrate. Figure 16 (b) is a schematic cross-sectional view showing the patterned substrate and the separated GaN crystal after the GaN crystal has been separated from the patterned substrate.

[0092] Figure 17 (a) is a schematic cross-sectional view of a GaN crystal grown by ammonothermal method through the mask opening of a patterned mask formed on the nitrogen polar surface of a substrate. Figure 17 (b) is to Figure 17 A schematic cross-sectional view of the GaN crystal grown in (a) obtained by separating the GaN crystal from the substrate with the patterned mask. Figure 17 (c) is in Figure 17 (b) is a schematic cross-sectional view of a GaN crystal with a second pattern mask disposed thereon. Figure 17 (d) is configured with Figure 17 (c) is a schematic cross-sectional view of a stacked structure obtained by growing GaN crystal through the mask opening of the second pattern mask on the nitrogen polar surface of the GaN crystal using the ammonothermal method.

[0093] Figure 18(a) to (b) are schematic diagrams showing a second pattern mask disposed on the nitrogen polar surface of the second substrate.

[0094] Figure 19 This is a schematic cross-sectional view showing the basic structure of an HVPE device.

[0095] Figure 20 (a) is a schematic cross-sectional view showing the seed crystal and edge shield placed on the substrate. Figure 20 (b) represents GaN crystal in Figure 20 (a) is a schematic cross-sectional view of the growth state on the seed crystal.

[0096] Figure 21 This is a schematic cross-sectional view showing the seed crystal and edge shield placed on the base.

[0097] Figure 22 This is a schematic diagram used to illustrate a 5.5mm × 5.0mm observation area (OE) and a 5.5mm × 0.5mm unit area (UE) obtained by dividing the above observation area into 10 parts.

[0098] Figure 23 This is a schematic diagram illustrating the apparatus used for photoelasticity measurement. Detailed Implementation

[0099] Unless otherwise specified, the GaN crystals mentioned in this specification refer to hexagonal GaN crystals with a wurtzite-type crystal structure.

[0100] In GaN crystals, the crystal axes parallel to

[0001] and [000-1] are called c-axis, the crystal axis parallel to <10-10> is called m-axis, and the crystal axis parallel to <11-20> is called a-axis. Crystal planes orthogonal to the c-axis are called c-planes, crystal planes orthogonal to the m-axis are called m-planes, and crystal planes orthogonal to the a-axis are called a-planes. In this specification, the (0001) and (000-1) crystal planes are collectively referred to as c-planes.

[0101] In the following context, when referring to crystal axes, crystal planes, crystal orientations, etc., unless otherwise specified, it refers to the crystal axes, crystal planes, crystal orientations, etc. of GaN crystals.

[0102] The Miller index (hkil) of a hexagonal crystal has the relationship h + k = -i, so it is sometimes represented by a three-digit number (hkl). For example, if it is represented by a three-digit number (0004), then it is (004).

[0103] Unless otherwise specified, in this specification, "dislocation" refers to a threading dislocation. In this specification, screw dislocations, mixed dislocations, and edge dislocations are not distinguished, and are collectively referred to as dislocations.

[0104] Hereinafter, embodiments of the present invention will be described with appropriate reference to the accompanying drawings.

[0105] 1.GaN substrate

[0106] 1.1. First Implementation Method

[0107] The GaN substrate of the first embodiment has an inclination angle of 0 to 20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The dislocation density of the above principal plane (first principal plane) is 5.0 × 10⁻⁶. 4 cm -2 Hereinafter, for the first principal surface mentioned above, the strain evaluation value calculated by photoelastic measurement and based on the following formula (1) exceeds 5 × 10⁻⁶. -5 The area (S1) is less than 2.5% of the total area of ​​the main surface.

[0108]

[0109] It should be noted that each term in equation (1) is represented by the following equations (2) and (3).

[0110]

[0111] Here, δ and ψ are the phase difference and principal axis azimuth, respectively, representing the birefringence quantities derived from strain; λ is the wavelength of the light source in the photoelasticity measuring device; d is the sample thickness; n0 is the strain-free refractive index relative to the light source wavelength; and |p 11 -p 12 | represents the components of the photoelastic tensor, where λ, n0, and |p are... 11 -p 12 The following conditions must be met.

[0112] λ=633nm;

[0113] n0 = 2.355;

[0114] |p 11 -p 12 |=0.13.

[0115] If photoelasticity is used, the local strain existing within the main surface of the GaN substrate can be quantitatively measured. The strain is expressed as the magnitude of the strain evaluation value.

[0116] The principle of photoelasticity measurement will be explained in detail below.

[0117] Birefringence occurs in crystals due to photoelasticity when strain caused by residual stress exists or when an external force is applied. If the phase difference δ and principal axis azimuth angle ψ in the strain of the crystal substrate are measured as birefringence quantities using photoelasticity, and the anisotropic elastic constants of the crystal are used, then a quantitative evaluation of the strain components can be performed.

[0118] Gallium nitride (GaN) crystals are uniaxial crystals, exhibiting both strain-induced birefringence and natural birefringence. However, natural birefringence does not occur for incident light along the c-plane normal. Therefore, measurements of the c-plane substrate of GaN can be performed to quantitatively evaluate in-plane strain without being affected by natural birefringence.

[0119] The photoelastic method primarily uses linear and circular polarimeters. These instruments allow light to pass through by placing a sample between orthogonal polarizers and analyzers, and then observing the patterns of bright and dark fringes—such as isoclinic fringes that appear when the principal axis of birefringence is aligned with the birefringence, and isochromatic fringes that appear when the phase difference of birefringence is 2πn (where n is an integer)—to evaluate the amount of birefringence. Furthermore, the phase difference of birefringence is also proportional to the sample thickness (the length of the light transmission path).

[0120] However, the aforementioned stripe patterns cannot be observed when the strain that produces the photoelastic effect is minute, or when the sample thickness is thin (compound semiconductor substrates are typically hundreds of μm thick), or when the phase difference caused by strain is less than 2π. On the other hand, birefringence can be measured using a rotating polarizer method with a circular cyclotor.

[0121] This measurement and strain analysis utilized the photoelastic method published in Non-Patent Literature 1 and Non-Patent Literature 2. This method is identical to a linear polarimeter, but with the following structure: the polarizer and analyzer rotate synchronously while accurately maintaining an arbitrary relative angle, allowing the intensity of transmitted light from the sample to be collected as a function of the polarization angle φ. By analyzing this polarization characteristic, a quantitative evaluation of strain taking into account the elastic anisotropy of the crystal can be performed. Furthermore, it has the advantage of being unaffected by the polarization characteristics of the light used in this measurement or the reflectivity of the sample.

[0122] The determination method is described below.

[0123] If the intensity of transmitted light from the sample when the polarizer and detector are orthogonal is set as I... ⊥ (φ), let the intensity of transmitted light from the sample in the parallel state be I. || (φ), then the intensity of transmitted light is equal to I. r (φ) is expressed by the following formula using the phase difference δ and principal axis azimuth angle ψ, which are birefringence quantities derived from strain.

[0124]

[0125] In actual transmitted light measurements, the polarization angle φ is measured at intervals of 2π / J (where J is the division number), and the respective I values ​​are obtained. r (φ) j Here, φ j =2πj / J (j=0, 1, 2, ..., J-1), the more the number of segments J increases, the higher the measurement accuracy.

[0126] According to the above formula, by I r (φ) By performing sin and cos transformations as shown below, δ and ψ can be obtained.

[0127]

[0128] Next, the relationship between the strain component and the refractive index in the crystal caused by the photoelastic effect is expressed by the following formula.

[0129]

[0130] In the above formula, n ij p is the refractive index tensor. ijkl S is the photoelastic constant. kl For strain tensor.

[0131] However, as pointed out in the aforementioned non-patent document 1, due to the anisotropy of the photoelastic effect, sometimes δ is not simply proportional to the strain in the crystal. Even if the strain is the same value, if the strain tensor components are different, the resulting δ and ψ will also be different. Therefore, it is appropriate to convert them into in-plane strain components instead of δ and ψ.

[0132] Therefore, in Non-Patent Document 3, through tensor analysis of the photoelastic effect generated by incident light in the c-plane normal direction of gallium nitride, the phase difference δ and principal axis azimuth angle ψ, which are birefringence quantities originating from strain, are transformed into |S| as shown in the following equation. yy -S xx |and 2|S xy |

[0133]

[0134] |S yy -S xx | is the strain difference along the x-axis and y-axis, which are the crystal axes, 2|S xy | represents the shear strain between the x and y axes. Furthermore, λ is the wavelength of the light source in the photoelasticity measuring device, d is the sample thickness, and n0 is the strain-free refractive index relative to the light source wavelength. Additionally, in the experiment described in Non-Patent Document 3, for a light source wavelength of 630 nm, the photoelastic tensor component |p 11 -p12 The value is determined to be 0.13.

[0135] In the case of a substrate that has undergone circular machining, the difference in strain |S| between the radial and tangential directions in the cylindrical coordinate system. r -S t |Use|S yy -S xx |and 2|S xy |It is represented by the following formula.

[0136]

[0137] The inventors set the above formula as formula (1), and expressed |S| as therefrom. r -S t The value of | is used as the strain evaluation value. The specific structure and method of the measuring device used to determine the strain evaluation value can be described later.

[0138] It is known that when GaN substrates are used as device substrates, especially as substrates for LDs (particularly long-wavelength LDs), a low dislocation density on the main surface of the substrate is generally required. However, if local strain exists within the main surface, the desired end face cannot be formed when separating the wafer into strips. The end face shape has a significant impact on device characteristics, and therefore local strain leads to a deterioration in device manufacturing yield. In contrast, the GaN substrate of this embodiment has a reduced dislocation density and effectively reduced local strain within the main surface, thus significantly reducing the deterioration in device manufacturing yield when used as a c-plane substrate for devices.

[0139] From the perspective of suppressing the deterioration of device manufacturing yield, it is preferable to have a smaller area of ​​regions with large local strain within the main surface. Therefore, strain evaluation values ​​measured by photoelasticity measurement exceed 5 × 10⁻⁶. -5 The area (S1) is preferably 2% or less of the total area of ​​the main surface, more preferably 1% or less, and particularly preferably 0.5% or less.

[0140] Furthermore, from the viewpoint of suppressing the deterioration of device manufacturing yield, the strain evaluation value of the GaN substrate in the first embodiment, measured by photoelasticity measurement, exceeds 1×10⁻⁶. -4 The area (S2) is preferably less than 1% of the total area of ​​the main surface, more preferably less than 0.5%, further preferably less than 0.1%, particularly preferably less than 0.1%, and most preferably 0%.

[0141] Furthermore, from the viewpoint of suppressing the deterioration of device manufacturing yield, the maximum value of the strain evaluation value in the main plane of the GaN substrate in the first embodiment is preferably 1×10⁻⁶. -4Below. For the same reason, the maximum value of the strain evaluation value within the principal plane is more preferably 8 × 10⁻⁶. -5 The following is a further preference for values ​​less than 5×10 -5 .

[0142] 1.2. Second Implementation Method

[0143] The GaN substrate of the second embodiment of the present invention has an inclination of 0 to 20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The above principal face (first principal face) must contain at least one element with a diameter of 0.275 cm. 2 The area of ​​the observation region, and the dislocation density of the aforementioned area of ​​the observation region is less than 1.0 × 10⁻⁶. 4 cm -2 .

[0144] At least one 0.275cm as defined above exists within the aforementioned principal plane. 2 The dislocation density of the observation region, and the aforementioned area of ​​the observation region, is less than 1.0 × 10⁻⁶. 4 cm -2 This means that crystal defects are reduced to a minimum over a very large area within the main surface of the GaN substrate. By confirming the presence of at least one of the aforementioned observation areas on the main surface of the GaN crystal substrate, it can be confirmed that crystal defects are reduced to a minimum over a very large area.

[0145] Preferably, it can be confirmed that there are two or more observation areas at non-overlapping locations; more preferably, any 0.275cm within the main surface... 2 When the observation area (excluding areas less than 5 mm from the outer periphery of the substrate and small planar growth areas) is used, the dislocation density is less than 1.0 × 10⁻⁶. 4 cm -2 .

[0146] When GaN substrates are used as substrates for LDs or power devices, dislocations in the main surface of the substrate can lead to a decrease in the yield of LDs and electronic devices, or a decrease in the breakdown voltage of electronic devices. In contrast, the dislocation density of the GaN substrate in this embodiment is reduced to an extremely low level over a wide range. Therefore, when used as a C-plane substrate for LDs or C-plane substrates for power devices, it can reduce the deterioration of device manufacturing yield and suppress device performance degradation.

[0147] From the above perspective, it is more preferable that at least one dislocation density of 8.0 × 10⁻⁶ exists within the aforementioned principal plane. 3 cm -2The observation area described above is further preferred. Furthermore, it is even more preferable that at least one dislocation density of 5.0 × 10⁻⁶ exists within the aforementioned main surface. 3 cm -2 The observation area mentioned above is as follows.

[0148] Furthermore, preferably, the observation region contains a dislocation density of less than 1.0 × 10⁻⁶. 2 cm -2 The unit region A has a dislocation density of less than 1.0 × 10⁻⁶. 2 cm -2 This means that there are almost no dislocations in this unit area. The more such areas there are, the less the yield deterioration in device manufacturing can be reduced when using C-plane substrates for LDs and C-plane substrates for power devices, and the more the device performance degradation can be suppressed.

[0149] Furthermore, when the aforementioned observation region includes a unit region A, it typically includes a unit region with a higher dislocation density than unit region A. For example, it could include a unit region with a dislocation density greater than 1.0 × 10⁻⁶ units of A. 2 cm -2 Above, 1.0×10 2 cm -3 Above, or 1.0 × 10 4 cm -2 The above refers to the unit region. More specifically, the observation region described above, when including unit region A, can contain a dislocation density of 1.0 × 10⁻⁶. 3 cm -2 The above refers to unit region B. Higher dislocation densities can be generated in unit regions that include merged regions, but in the GaN substrate of this embodiment, it can be configured such that dislocations are almost non-existent in regions other than this.

[0150] It should be noted that, in this specification, "unit region" refers to each region when the observation area is divided into 2 to 100 equal parts in one or two dimensions. Unit region A and unit region B are each composed of one of the aforementioned divided regions, and multiple unit regions A and B may exist in the observation area. Furthermore, multiple unit regions A and multiple unit regions B may have different dislocation densities.

[0151] For example, in the substantial whole of the aforementioned main surface (e.g., all areas except for regions less than 5 mm from the outer periphery of the substrate and the small-facet growth regions), unit region A can exist periodically. The term "periodicity" here does not necessarily mean a strictly equal-interval period, nor does it imply that unit region A alternates with other unit regions. Furthermore, the period can be one-dimensional or two-dimensional.

[0152] As an example of a unit region A existing periodically, one could exemplify this by having a unit region A existing along a periodic opening pattern of a pattern mask used in the GaN substrate manufacturing method described later. When the GaN substrate is manufactured using the GaN substrate manufacturing method described later, the dislocation density is less than 1.0 × 10⁻⁶. 2 cm -2 The unit region A is formed corresponding to the periodic opening pattern of the pattern mask disposed on the second substrate. According to the manufacturing method described later, fewer dislocation defects are inherited from the second substrate, thus achieving a dislocation density of less than 1.0 × 10⁻⁶. 2 cm -2 The unit area.

[0153] Furthermore, preferably, the observation area is a rectangular observation area of ​​5.5mm × 5.0mm, and the dislocation density in the ten 5.5mm × 0.5mm sub-regions obtained by dividing the observation area into ten sub-regions is less than 1.0 × 105. 2 cm -2 The number of segmented regions is one or more. In other words, preferably, on the main surface of the GaN substrate in the second embodiment of the present invention, as a dislocation density of less than 1.0 × 10⁻⁶, 2 cm -2 Within unit region A, at least one 5.5mm × 0.5mm region can be found, and within a 5.5mm × 5.0mm region, which includes this region as one of 10 segmented regions, there exists a dislocation density of less than 1.0 × 10⁻⁶. 4 cm -2 The region. Within the aforementioned 5.5mm × 5.0mm rectangular observation area, the dislocation density is less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is more preferably three or more, and even more preferably five or more.

[0154] 1.3. GaN substrates of the first and second embodiments

[0155] The GaN substrates of the two embodiments described above will be further explained below.

[0156] The inclination of the first main surface relative to the (0001) surface is 0 to 20 degrees, or it can be more than 0.2 degrees. In addition, it can be less than 10 degrees, less than 5 degrees, less than 2.5 degrees, less than 1.5 degrees, less than 1.0 degrees, or less than 0.5 degrees.

[0157] In addition, the area of ​​the first main surface is 15cm. 2 That's all, it can be 18cm. 2 The above can also be 400cm 2 the following.

[0158] Figure 1 An example of a GaN substrate according to this embodiment is shown.

[0159] Figure 1 The substrate 100 shown is a self-supporting GaN wafer with two main surfaces (large area surfaces) facing opposite directions, namely the first main surface 101 and the second main surface 102.

[0160] The first main surface 101 and the second main surface 102 are preferably parallel to each other.

[0161] The first main surface 101 is the main surface used for epitaxial growth of nitride semiconductors during the manufacture of nitride semiconductor devices, i.e., the "front side". The second main surface 102 is the "back side".

[0162] In this specification, the first principal surface 101 is Ga polarity, and the other second principal surface 102 is N polarity.

[0163] The tilt angle of the second principal plane 102 relative to the (000-1) crystal plane is preferably 0 degrees or more and 20 degrees or less. The tilt angle may also be 0.2 degrees or more, or it may be 10 degrees or less, less than 5 degrees, less than 2.5 degrees, less than 1.5 degrees, less than 1.0 degrees or less than 0.5 degrees.

[0164] The diameter of the substrate 100 is only required to be 15 cm² in area of ​​the first main surface 101. 2 There are no specific limitations on the above. It is usually 45mm or more, but can be 95mm or more or 145mm or more. Typical values ​​are 50-55mm (about 2 inches), 100-105mm (about 4 inches), 150-155mm (about 6 inches), etc.

[0165] The thickness of the substrate 100 is designed so that the substrate 100 can be self-supporting and can be operated.

[0166] When the diameter of the substrate 100 is about 2 inches, its thickness is preferably 250 μm or more, more preferably 300 μm or more, and preferably 500 μm or less, more preferably 450 μm or less.

[0167] When the diameter of the substrate 100 is about 4 inches, its thickness is preferably 400 μm or more, more preferably 500 μm or more, and preferably 800 μm or less, more preferably 650 μm or less.

[0168] When the diameter of the substrate 100 is about 6 inches, its thickness is preferably 500 μm or more, more preferably 600 μm or more, and preferably 850 μm or less, more preferably 750 μm or less.

[0169] The offset angle of substrate 100 can be decomposed into components in two mutually orthogonal directions within the first main surface 101, namely, an x-direction component and a y-direction component. This will be referred to... Figure 2 The description is as follows.

[0170] When the normal direction of the first principal surface 101 is set as the z-direction, and the vector parallel to the c-axis is set as vector Vc, the offset angle of the wafer 20 is equal to the tilt angle θ of vector Vc in the z-direction. This vector Vc can be decomposed into vector Vc as the x-direction component. x and the vector Vc as the y-direction component y The orthographic projection of vector Vc onto the xz plane is vector Vc. x The orthographic projection of vector Vc onto the yz plane is vector Vc. y .

[0171] When decomposing vector Vc in this way, vector Vc x The tilt in the z-direction is the x-direction component θ of the tangent angle θ. x Vector Vc y The tilt in the z-direction is the y-direction component of the tangent angle θ. y .

[0172] Preferably, in the substrate 100, the variation range of the x-direction component of the tangent angle on the first line extending in the x-direction through the center of the first main surface 101 and the variation range of the y-direction component of the tangent angle on the second line extending in the y-direction through the center of the first main surface 101 are both less than 0.2 degrees within a length range of 40 mm. The x-direction may also be parallel to one of the a-planes, in which case the y-direction is parallel to one of the m-planes.

[0173] The so-called variation range here refers to the difference between the maximum and minimum values ​​of the shear angle. The variation range is less than 0.2 degrees. In other words, the variation of the shear angle relative to the central value is within ±0.1 degrees.

[0174] The smaller the variation range of the x-direction component of the tangent angle on the first line and the y-direction component of the tangent angle on the second line, the better. These variation ranges can be less than 0.16 degrees, further less than 0.14 degrees, further less than 0.12 degrees, further less than 0.10 degrees, further less than 0.08 degrees, further less than 0.06 degrees, and further less than 0.04 degrees within a length range of 40 mm.

[0175] When evaluating the variation range of the offset angle, the portion less than 5 mm from the outer periphery of the substrate can be excluded.

[0176] The first main surface 101 of the substrate 100 is usually mirror-finished, and its root mean square (RMS) roughness, as measured by atomic force microscopy (AFM), is preferably less than 2 nm within a measurement range of 2 μm × 2 μm, but may also be less than 1 nm or less than 0.5 nm.

[0177] The second surface 102, which serves as the back surface, can be either mirror-finished or matte-finished.

[0178] The edges of the substrate 100 can also be chamfered.

[0179] Various markings, such as orientation flats or notches for displaying the orientation of crystals, and index flats for making the surface and back sides easily identifiable, can be implemented in the substrate 100 as needed.

[0180] The main surface of the substrate 100 is circular, but it is not limited to a circle. It can be changed to a square, rectangle, hexagon, octagon, or any other arbitrary shape.

[0181] The substrate 100 can be a GaN crystal grown by HVPE.

[0182] For GaN grown using a conventional HVPE apparatus equipped with a quartz reactor, the impurity concentration can meet one or more of the following conditions (a) to (c).

[0183] Condition (a): Si concentration is 5 × 10⁻⁶ 16 atoms / cm 3 above.

[0184] Condition (b): O concentration is 3 × 10 16 atoms / cm 3 the following.

[0185] Condition (c): H concentration is 1×10 17 atoms / cm 3 the following.

[0186] The substrate 100 may satisfy two or more of the conditions (a) to (c) above. In some cases, it may satisfy both conditions (a) and (b), both conditions (b) and (c), or both conditions (a) and (c). In some cases, the substrate 100 may satisfy all of the conditions (a) to (c) above.

[0187] The substrate 100 can be composed of GaN crystals obtained by ammonium thermal growth in a Pt (platinum) capsule using ammonium halides such as NH4F, NH4Cl (ammonium chloride), NH4Br (ammonium bromide), and NH4I as mineralizing agents. In the aforementioned GaN crystals, unless intentionally added, the concentrations of alkali metals such as Li (lithium), Na (sodium), and K (potassium), and alkaline earth metals such as Mg (magnesium) and Ca (calcium) are typically less than 1 × 10⁻⁶ for each element. 16 atoms / cm 3 .

[0188] GaN crystals obtained by ammonium-thermal growth using ammonium halides as mineralizing agents may contain halogens from the mineralizing agent. For example, GaN crystals obtained by growth using NH4F as a mineralizing agent sometimes have a density of 5 × 10⁻⁶. 14 atoms / cm 3 Above and less than 1×10 16 atoms / cm 3 1×10 16 atoms / cm 3 Above and less than 1×10 17 atoms / cm 3 It contains F (fluorine) at the same concentration.

[0189] The inventors have experimentally confirmed that the I (iodine) concentration in GaN crystals obtained by ammonothermal growth using NH4F and NH4I as mineralizing agents is typically less than 1 × 10⁻⁶. 16 atoms / cm 3 .

[0190] GaN crystals obtained by ammonium halide as a mineralizing agent through ammothermal growth may have a crystal density of 5 × 10⁻⁶. 17 atoms / cm 3 The above concentrations contain H (hydrogen). The H concentration of the GaN crystals described above is typically 10. 21 atoms / cm 3 The following can be 5×10 20 atoms / cm 3 Below, 1×10 20 atoms / cm 3 Below, or 5×10 19 atoms / cm 3 the following.

[0191] GaN crystals grown via the ammonothermal method typically have a diameter of 3140–3200 cm⁻¹. -1The infrared absorption peak at this location is attributed to the gallium vacancy-hydrogen complex. This infrared absorption peak is not observed in GaN crystals grown via the HVPE method or the Na flux method.

[0192] The concentration of alkali metals and alkaline earth metals in the substrate 100 is preferably less than 1 × 10⁻⁶. 16 atoms / cm 3 More preferably less than 1×10 15 atoms / cm 3 .

[0193] The substrate 100 can be formed from unintentionally doped GaN (UID-GaN). Due to unintentional donor impurity doping, UID-GaN typically exhibits n-type conductivity.

[0194] In UID-GaN, the carrier concentration can be as high as 5 × 10⁻⁶. 17 atoms / cm 3 The resistivity can be as low as approximately 0.04 Ω·cm at room temperature. This is because the Si concentration in UID-GaN can be as high as 5 × 10⁻⁶. 17 atoms / cm 3 Around 2 × 10⁻⁶, in addition, the O concentration can be as high as 2 × 10⁻⁶. 17 atoms / cm 3 about.

[0195] In one example, intentional doping can reduce the room temperature resistivity of the substrate 100. This room temperature resistivity can be set to less than 0.03 Ω·cm, further less than 0.02 Ω·cm, further less than 0.015 Ω·cm, and further less than 0.010 Ω·cm. To achieve a sufficient reduction in resistivity, it is preferable to set the carrier concentration of the substrate 100 at room temperature to 1 × 10⁻⁶. 18 atoms / cm 3 The above is further optimized to be 2×10 18 atoms / cm 3 That's all. The carrier concentration can be set to 3 × 10⁻⁶. 18 atoms / cm 3 The above can be further set to 4×10 18 atoms / cm 3 That concludes the discussion. From an electrical perspective, there is no specific upper limit to this carrier concentration. However, to avoid degrading the productivity of substrate 100, it is ideal to set this carrier concentration to 1 × 10⁻⁶. 19 atoms / cm 3 The following can be set to 8×10 18 atoms / cm3 The following can be further set to 5×10 18 atoms / cm 3 The following is because strong doping increases the frequency of abnormal growth in GaN crystals.

[0196] The dopant used to reduce the resistivity of the substrate by 100 ohms is preferably a donor impurity. This is because donor impurities typically exhibit a higher activation rate than acceptor impurities. Activation rate refers to the ratio of carrier concentration in doped GaN to the concentration of the dopant.

[0197] Elements that act as donors in GaN crystals include Group 14 elements such as Si (silicon) and Ge (germanium), and Group 16 elements such as O (oxygen) and S (sulfur). Si and Ge are preferred as intentional dopants. GaN crystals intentionally doped with Ge can contain Si as an unintentional dopant at a concentration on the same order of magnitude as Ge.

[0198] When evaluating the dislocation density on the first principal surface 101 of the substrate 100, it is preferable to observe a 360μm×360μm (129600μm) area at each measurement point. 2 A rectangular region with an area of ​​360μm × 360μm or more. When the observed area is 360μm × 360μm or more, the maximum value of the dislocation density within the first principal surface 101 will not exceed 4 times the minimum value, and is generally less than 3 times, and further less than 2 times.

[0199] In the first embodiment, the dislocation density of the first principal surface 101 of the substrate 100 is 5.0 × 10⁻⁶. 4 cm -2 The following is a preferred embodiment. In any implementation, 4.0 × 10⁻⁶ is preferred. 4 cm -2 Hereinafter, 3.0 × 10 is preferred. 4 cm -2 The following is a further preferred value: 2.0 × 10 4 cm -2 Hereinafter, 1.0 × 10 is even more preferred. 4 cm -2 The dislocation density is typically 10 cm⁻¹. -2 That's all. In the second embodiment, the dislocation density of the first principal surface 101 is preferably 1.0 × 10⁻⁶. 4 cm -2 the following.

[0200] In photoluminescence (PLI) imaging of GaN crystals, dislocations appear as dark spots, so the dislocation density can be determined by observing the PLI image. When the first main surface 101 is Ga polar, the density of the etch pits in the first main surface 101 after etching the substrate 100 with 89% sulfuric acid heated to 270°C for 1 hour can be regarded as the dislocation density.

[0201] When evaluating the dislocation density of the first principal surface 101, regions with a distance of less than 5 mm from the outer periphery of the substrate and small planar growth regions can be excluded as exceptions. In this specification, a small planar growth region refers to a closed region obtained by crystal growth on a plane orientation different from that of the principal surface 1. The small planar growth region is concave in shape and typically has a diameter of 100 to several hundred μm, thus allowing it to be observed with the naked eye or under a microscope.

[0202] Specifically, the dislocation density can be determined using the following methods.

[0203] The normal direction of the principal surface is set as the z-direction, and the direction orthogonal to the z-direction and parallel to one of the a-faces is selected as the x-direction. A first line extending along the x-direction and passing through the center of the principal surface is defined, as well as a second line extending along the y-direction perpendicular to the x-direction and passing through the center of the principal surface. Dislocation density is measured at all 17 points: the intersection of the first and second lines (which is the center of the principal surface), 8 points on the first line excluding this intersection, and 8 points on the second line excluding this intersection, observed using PLI images. The interval between adjacent measurement points is 5 mm.

[0204] Observe a 360μm × 360μm square region at each measurement point. Divide the number of dislocations appearing within the square region by its area (129600μm). 2 The dislocation density is calculated for each measurement point. The average value across the 17 measurement points is taken as the dislocation density of the main surface of the c-plane GaN substrate.

[0205] The quality of crystal 100 can be evaluated using the (004) XRD rocking curve FWHM (Full Width at Half Maximum) determined by ω-scanning with CuKα1 radiation. The better the crystal quality, the narrower the (004) XRD rocking curve FWHM.

[0206] In the (004) XRD rocking curve determination, the X-ray tube was operated at a voltage of 45kV and a current of 40mA. The CuK crystal, after being monochromated using a Ge(440)4 crystal symmetric monochromator, was then used. αThe X-rays are incident on the first principal plane 11. There is no particular limitation on the direction in which the X-rays are incident on the first principal plane 11; for example, the incident plane of the X-rays can be perpendicular to the a-axis.

[0207] The X-ray beam size is set as follows: when the incident angle (the angle between the reflecting surface and the X-ray) is set to 90°, that is, when the X-ray is incident perpendicularly onto the (004) surface which serves as the reflecting surface, the size of the irradiated area on the first principal surface 11 is 5 mm in the direction parallel to the ω-axis and 1 mm in the direction perpendicular to the ω-axis. The ω-axis refers to the rotation axis of the sample in the rocking curve measurement.

[0208] With the X-ray beam size set in this manner, ω is approximately 36.5° in the (004) XRD rocking curve measurement of GaN, therefore the size of the irradiated area on the first principal surface 11 is approximately 1.7 × 5 mm. 2 .

[0209] The (004) XRD swing curve FWHM thus measured can be below 20 arcsec, further below 18 arcsec, further below 16 arcsec, further below 14 arcsec, and further below 12 arcsec.

[0210] When the diameter of the first main surface 11 exceeds 40mm, such as Figure 3 As shown, ω scanning is performed every 1 mm along a line L on the first main surface 101 under the above conditions, within a length of 40 mm. This yields 40 measurement points P arranged at 1 mm intervals along the line L. M The XRD swing curve at (004) is shown. At this time, at each measurement point P... M During the ω-scan, the ω-axis is made perpendicular to line L. That is, the X-rays are incident on crystal 10 with the X-ray incident surface parallel to line L.

[0211] In a preferred embodiment, when the above measurement is performed along at least one line on the first main surface 101, the maximum value of the (004) XRD rocking curve FWHM between all measurement points can be less than 20 arcsec.

[0212] The average value of the (004) XRD swing curve FWHM between all the measurement points can be less than 18 arcsec, further less than 16 arcsec, further less than 14 arcsec, further less than 12 arcsec, and further less than 10 arcsec.

[0213] When the diameter of the first main surface 101 exceeds 40mm, further, along the first main surface 101 respectively, as shown in the figure... Figure 4The example illustrates two mutually perpendicular lines L1 and L2. Under the aforementioned conditions, ω-scans are performed every 1 mm over a length of 40 mm, thereby obtaining (004) XRD oscillation curves at 40 measurement points arranged at 1 mm intervals on each line L1 and L2. In this case, during the ω-scan at each measurement point on line L1, the ω-axis is made perpendicular to line L1, and during the ω-scan at each measurement point on line L2, the ω-axis is made perpendicular to line L2.

[0214] In a preferred embodiment, when the above measurements are performed on the first main surface 101 along at least two mutually perpendicular lines, the maximum value of the (004) XRD swing curve FWHM between all measurement points on each line can be less than 20 arcsec. That is, the maximum value between 40 measurement points on one side of the two lines and the maximum value between 40 measurement points on the other side can both be less than 20 arcsec.

[0215] The average value of the (004) XRD swing curve FWHM between all measurement points on each line can be less than 18 arcsec, further less than 16 arcsec, further less than 14 arcsec, further less than 12 arcsec, and further less than 10 arcsec.

[0216] In the Lang method-based X-ray morphology method, an X-ray transmission image of at least one 10 mm × 10 mm square region can be obtained from crystal 10.

[0217] In the Langmuir method, an X-ray source is placed on one main side of a plate-shaped test piece, and an X-ray detector is placed on the other main side.

[0218] Anomalous X-ray transmission, also known as the Borrmann effect, is the phenomenon where X-rays pass through a crystal of a thickness that would normally be impenetrable due to absorption. For example, in X-ray topography using MoKα (wavelength 0.71073 Å) as the X-ray source, a transmission image obtained from a 344 μm thick GaN crystal exhibits anomalous transmission. This is because, with a MoKα X-ray source, the absorption coefficient μ of GaN is 290.40 cm⁻¹. -1 When the thickness t of the wafer is 344 μm, μ・t = 10.0. If there is no abnormal transmission, a transmission image cannot be obtained under the condition that μ・t ≥ 10.

[0219] When the crystal integrity is low, abnormal transmission images cannot be observed. Therefore, it can be said that GaN crystals that produce abnormal transmission images in X-ray morphology are of good quality.

[0220] Preferably, an X-ray anomalous transmission image of at least a square region of 15 mm × 15 mm is obtained from the crystal 10, and more preferably, an X-ray anomalous transmission image of at least a square region of 20 mm × 20 mm is obtained.

[0221] 2. Manufacturing method of GaN substrate

[0222] 2.1. GaN Crystal Growth Methods

[0223] A method for growing GaN crystals, which is preferably used in the fabrication of the GaN substrate in the embodiments, will be described. A flowchart of this GaN crystal growth method is shown below. Figure 5 As shown, it includes the following three processes S1 to S6.

[0224] S1: The process of preparing a first substrate having a nitrogen-polar surface.

[0225] S2: A process of depositing a first pattern mask, including a mask portion and a mask opening portion, on the nitrogen polar surface of the first substrate prepared in process S1.

[0226] S3: The process of growing GaN crystals using the ammonothermal method through the mask opening of the first pattern mask.

[0227] S4: The process of separating GaN crystals from a first substrate with a first pattern mask.

[0228] S5: A process of using a separated GaN crystal as a second substrate and configuring a second pattern mask on a nitrogen-polar surface.

[0229] S6: The process of growing GaN crystals using the ammonothermal method through the mask opening of the second pattern mask.

[0230] The following is a detailed explanation of each process.

[0231] (1) Process S1

[0232] In process S1, a first substrate having a nitrogen-polar surface is prepared.

[0233] The preferred substrate is a C-plane GaN substrate obtained by processing bulk GaN crystals grown by HVPE or acidic ammonium thermal method. In the C-plane GaN substrate, the main surface on the

[0001] side is a gallium polar surface, and the main surface on the [000-1] side is a nitrogen polar surface.

[0234] The orientation of the nitrogen polar surface of the substrate is preferably within 2° relative to [000-1], and more preferably within 1° relative to [000-1].

[0235] The area of ​​the nitrogen-polar surface of the substrate is preferably 15 cm².2 The above can be 15cm 2 Above and below 50cm 2 50cm 2 Above and below 100cm 2 100cm 2 Above and below 200cm 2 200cm 2 Above and below 350cm 2 350cm 2 Above and below 500cm 2 500cm 2 Above and below 750cm 2 wait.

[0236] When the nitrogen-polar surface of the substrate is circular, its diameter is preferably 45 mm or more. Typical diameters are 45–55 mm (about 2 inches), 95–105 mm (about 4 inches), 145–155 mm (about 6 inches), 195–205 mm (about 8 inches), 295–305 mm (about 12 inches), etc.

[0237] For example, when the substrate is a C-plane GaN substrate with a diameter of 50 mm, its thickness is preferably 300 μm or more. If the diameter is greater than 50 mm, the preferred lower limit of its thickness also becomes larger. There is no particular upper limit to the thickness of the substrate, which is usually 20 mm or less.

[0238] The size of the substrate will be determined by the size of the GaN crystal grown in subsequent processes S3 and S6.

[0239] For example, when it is desired to cut a C-plane GaN substrate with dimensions of 45 mm in the [1-100] direction, [10-10] direction, and [01-10] direction from a grown GaN crystal, it is necessary to grow the GaN crystal to have dimensions of 45 mm or more in the [1-100] direction, [10-10] direction, and [01-10] direction. In order to grow a GaN crystal with dimensions of 45 mm in the [1-100] direction, [10-10] direction, and [01-10] direction, it is preferable to use a substrate substrate with dimensions of 45 mm or more in the [1-100] direction, [10-10] direction, and [01-10] direction.

[0240] The nitrogen-polar surface of the substrate is planarized by grinding or polishing. Preferably, the damage layer introduced by the planarization process is removed from the nitrogen-polar surface by CMP (Chemical Mechanical Polishing) and / or etching.

[0241] (2) Process S2

[0242] In step S2, a first pattern mask comprising a mask portion and a mask opening is disposed on the nitrogen polar surface of the first substrate prepared in step S1.

[0243] The material for the surface forming the patterned mask is preferably a platinum group metal, i.e., a metal selected from Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium), and Pt (platinum), with Pt being particularly preferred. The patterned mask can be a single-layer film formed of a platinum group metal or its alloy, but is preferably a multilayer film formed by stacking platinum group metal layers as a surface layer on a substrate layer made of a metal with better adhesion to GaN crystals than platinum group metals. Examples of materials for the substrate layer include W (tungsten), Mo (molybdenum), Ti (titanium), and alloys containing one or more of these, but are not limited thereto.

[0244] A patterned mask includes: a mask portion that covers the nitrogen-polar surface of a substrate; and a mask opening that exposes the nitrogen-polar surface of the substrate when the mask is not present. The mask opening is typically formed as a linear opening. Because the mask has a pattern of periodic openings, it is called a patterned mask. (See reference...) Figure 6 and Figure 7 Let's illustrate with an example.

[0245] Figure 6 (a) is a perspective view of the substrate. The substrate 20 is a disk-shaped C-plane GaN substrate with a gallium polar surface 21, a nitrogen polar surface 22, and a side surface 23.

[0246] Figure 6 (b) is a perspective view of the substrate 20 after the pattern mask 30 is disposed on the nitrogen polar surface 22. Multiple linear mask openings 31 are provided on the pattern mask 30 and arranged parallel to each other. The periodic opening pattern formed by the linear mask openings 31 is a stripe pattern.

[0247] Figure 7 It is a top view showing a portion of the nitrogen polar surface 22 side of the substrate 20 after the pattern mask 30 is configured.

[0248] Reference Figure 7 In the pattern mask 30, a plurality of linear mask openings 31 are arranged parallel to each other at a fixed spacing P, and the nitrogen polar surface 22 of the substrate 20 is exposed inside each linear mask opening 31. The spacing refers to the distance between the center lines of adjacent parallel linear mask openings separated by a non-opening portion (i.e., mask portion) of the pattern mask.

[0249] To reduce dislocation defects inherited from the substrate 20 by the GaN crystal grown in the subsequent process S3, it is advantageous to have a narrow linewidth W of the linear mask opening 31. Therefore, the linewidth W is preferably 0.5 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less.

[0250] From a manufacturing efficiency perspective, it is preferable that the linewidth W of the linear mask opening 31 is moderately wide. This is because this results in a higher initial growth rate during GaN crystal growth in the subsequent process S3. Therefore, the linewidth W is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more.

[0251] To reduce dislocation defects inherited from the substrate 20 by the GaN crystal grown in the subsequent process S3, a large spacing P between the linear mask openings 31 is advantageous. Therefore, this spacing P is preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and more preferably 4 mm or more.

[0252] On the other hand, the larger the spacing P between the openings 31 of the linear mask, the longer the time it takes for the through-hole generated above the mask portion of the patterned mask to close during the GaN crystal growth process in the subsequent step S3. Therefore, from the viewpoint of manufacturing efficiency, this spacing P is preferably set to 10 mm or less, and can also be set to 4 mm or less, 3 mm or less, or even 2 mm or less.

[0253] When the direction of the intersection line between the nitrogen polar surface 22 in the substrate 20 and the A-plane [(11-20) plane, (2-1-10) plane, or (1-210) plane] is taken as the reference direction, the angle θ between the longitudinal direction of the linear mask opening 31 and this reference direction is preferably 0°±5°. This angle θ can also be 0°±3°, 0°±2°, or 0°±1°. If the linear mask opening is oriented in this way, the probability of dislocation defects penetrating the substrate can be reduced.

[0254] A patterned mask can be configured with a linear mask opening and include intersecting periodic opening patterns. (See reference...) Figure 8 Let's illustrate with an example.

[0255] Figure 8 This is a top view showing a portion of the nitrogen polar surface 22 side of the substrate 20 after the patterned mask 30 is configured.

[0256] A linear mask opening 31 is provided on the pattern mask 30, and the nitrogen polar surface 22 of the substrate is exposed inside the linear mask opening 31.

[0257] The linear mask openings 31 provided on the pattern mask 30 are of two types: first linear mask openings 311 and second linear mask openings 312, which are different in length direction. A square grid pattern is formed by a plurality of the first linear mask openings 311 and a plurality of the second linear mask openings 312.

[0258] The spacing P1 between the first linear mask openings 311 and the spacing P2 between the second linear mask openings 312 are both fixed. The spacing refers to the distance between the center lines of adjacent, parallel linear mask openings separated by a pattern mask.

[0259] The spacing P1 and spacing P2 can be the same. However, the inventors have found through experiments that when the spacing P1 and spacing P2 are different, the through-holes generated above the mask portion of the pattern mask tend to become clogged during GaN crystal growth in the subsequent process S3. Therefore, it is preferable that one of the spacings P1 and P2 is at least 1.5 times the other, and more preferably at least 2 times the other.

[0260] The square grid pattern disposed on the pattern mask 30 includes intersections K formed between the first linear mask opening 311 and the second linear mask opening 312. As will be described later, the presence of intersections in the opening pattern facilitates the sealing of through-holes generated above the mask portion of the pattern mask during GaN crystal growth in the subsequent process S3. From the above viewpoint, the number density of intersections contained in the pattern mask is preferably 1 cm⁻¹. -2 above.

[0261] On the other hand, in order to increase the number density of the crossovers, it is necessary to increase the density of the openings in the linear mask. However, as the density of the openings in the linear mask increases, the dislocation defects inherited from the substrate by the GaN crystal grown in the subsequent process S3 also increase. Considering this, the number density of the crossovers is preferably 20 cm⁻¹. -2 The following is a preferred value: 15cm -2 The following is more preferably 10cm -2 the following.

[0262] To reduce dislocation defects inherited from the substrate 20 by the GaN crystal grown in the subsequent process S3, it is advantageous to have narrow linewidths W1 of the first linear mask opening 311 and W2 of the second linear mask opening 312. Therefore, these linewidths W1 and W2 are preferably 0.5 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. The linewidths W1 and W2 can be the same or different.

[0263] From a manufacturing efficiency perspective, it is preferable that the linewidth W1 of the first linear mask opening 311 and the linewidth W2 of the second linear mask opening 312 are moderately wide. This is because this will result in a higher growth rate in the initial stage during GaN crystal growth in the subsequent process S3. Therefore, the linewidths W1 and W2 are preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more.

[0264] To reduce dislocation defects inherited from the substrate 20 by the GaN crystal grown in the subsequent process S3, it is advantageous to have a large spacing P1 between the first linear mask openings 311 and P2 between the second linear mask openings 312. Therefore, these spacings P1 and P2 are preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and more preferably 4 mm or more.

[0265] On the other hand, the smaller the spacings P1 and P2, the less time is required for the GaN crystal to grow in the subsequent process S3 until the through-hole generated above the mask portion of the pattern mask is closed. Therefore, from the viewpoint of manufacturing efficiency, it is preferable to set at least one of the spacings P1 and P2 to 10 mm or less. In one example, one or both of the spacings P1 and P2 can be set to 4 mm or less, 3 mm or less, or further to 2 mm or less.

[0266] In a preferred example, considering both reducing inherited dislocation defects and improving manufacturing efficiency, either the spacing P1 or P2 can be set to less than 4 mm, less than 3 mm, or less than 2 mm.

[0267] Regarding the orientation of the first linear mask opening 311 and the second linear mask opening 312, it is convenient to designate one of the directions of the intersection line between the nitrogen polar surface 22 and the A surface as the first reference direction and the other as the second reference direction. For example, when the first reference direction is the direction of the intersection line between the nitrogen polar surface 22 and the (11-20) surface, the second reference direction is the direction of the intersection line between the (2-1-10) surface or the (1-210) surface and the nitrogen polar surface 22.

[0268] In a preferred embodiment, at least one of the angle θ1 formed by the longitudinal direction of the first linear mask opening 311 and the first reference direction and the angle θ2 formed by the longitudinal direction of the second linear mask opening 312 and the second reference direction can be set to 0°±5°.

[0269] Preferably, when the total extension of the first linear mask opening 311 is equal to or greater than the total extension of the second linear mask opening 312, the angle θ1 is at least 0°±5°. In other words, preferably, the longitudinal direction of more than 50% of the total extension of the linear mask opening 31 forms an angle of 0°±5° with respect to the direction of the intersection of the nitrogen polar surface of the substrate and surface A.

[0270] In a more preferred example, both angles θ1 and θ2 are 0°±5°, that is, the longitudinal direction of all portions of the linear mask opening 31 is at an angle of 0°±5° relative to the direction of the intersection of the nitrogen polar surface of the substrate and surface A.

[0271] Angles θ1 and θ2 can be 0°±3°, 0°±2°, or 0°±1°.

[0272] If the opening of the linear mask is oriented as described above, the through-hole generated above the mask portion of the patterned mask will be easily blocked during GaN crystal growth in the subsequent process S3.

[0273] In process S2, the periodic opening pattern of the pattern mask disposed on the nitrogen polar surface of the substrate is not limited to the striped pattern or the square grid pattern described above.

[0274] Figures 9-11 The accompanying drawings are top views of the substrate 20 after the pattern mask 30 is disposed on the nitrogen polar surface 22, illustrating various periodic opening patterns that can be provided on the pattern mask, but the opening patterns that can be used are not limited to these.

[0275] exist Figure 9 In (a), the linear mask opening 31 forms a sawtooth stripe pattern.

[0276] exist Figure 9 In (b), the linear mask opening 31 forms a grid pattern.

[0277] exist Figure 9 In (c), the opening 31 of the linear mask forms an inclined brick-patterned grid pattern.

[0278] exist Figure 9 In (d), the linear mask opening 31 forms an inclined square grid pattern.

[0279] exist Figure 10 In (e), the linear mask opening 31 forms a herringbone grid pattern.

[0280] exist Figure 10 In (f), the linear mask opening 31 forms a grid pattern that folds the inclined brick-pattern grid and the inclined square grid.

[0281] exist Figure 10 In (g), the linear mask opening 31 forms a triangular grid pattern.

[0282] exist Figure 10 In (h), the linear mask opening 31 forms a flat honeycomb grid pattern.

[0283] exist Figure 11 In (i), the linear mask opening 31 forms a Vaisravana tortoise shell grid pattern.

[0284] exist Figure 11 In each of (j) and (k), the linear mask opening 31 forms a cubic pattern.

[0285] exist Figure 11 In (l), the opening 31 of the linear mask forms a Y-shaped pattern.

[0286] exist Figures 9-11 In any of the examples shown, the periodic opening patterns provided on the pattern mask 30 all include intersections. Figure 12 (a) to (f) and Figure 13 Several types of crosses are shown in (a) to (f).

[0287] This specification will include Figure 12 The intersection between two or more linear mask openings with different longitudinal dimensions, as shown in (a) to (f), is called a continuous intersection.

[0288] Unless otherwise specified, the term "intersection" in this manual includes not only consecutive intersections, but also... Figure 13 The discontinuous crossings illustrated in (a) to (f) are examples. A discontinuous crossing can be considered as a crossing created by applying a change to a continuous crossing that breaks the connection between the openings of the linear mask.

[0289] At discontinuous intersections, the distance between two linear mask openings separated by the mask portion is 300 μm or less, preferably 200 μm or less.

[0290] exist Figures 9-11 In addition to Figure 9 In all examples other than (b), the configuration of the intersections contained in the periodic opening pattern is two-dimensional.

[0291] If the periodic opening pattern contains intersections, the through-holes generated above the mask portion of the pattern mask are prone to blockage during GaN crystal growth in the subsequent process S3. This effect is more pronounced when the intersections in the periodic opening pattern are configured in two dimensions, and becomes even more significant by increasing the number density of the intersections.

[0292] Therefore, the arrangement of intersections in the periodic opening pattern is preferably two-dimensional, in which case the number density of intersections contained in the pattern mask is preferably 1 cm⁻¹. -2 That's all. However, to increase the crossover number density, it is necessary to increase the density of the linear mask openings. Furthermore, as the density of the linear mask openings increases, the dislocation defects inherited from the substrate by the GaN crystal grown in the subsequent process S3 increase. Considering this, the crossover number density is preferably 20 cm⁻¹. -2 The following is a preferred value: 15cm -2 The following is more preferably 10cm -2 the following.

[0293] In Figures 9-11 The preferred designs for various periodic opening patterns when set on a pattern mask, related to the orientation, line width, and spacing of the openings in the linear mask, are as follows.

[0294] Preferably, at least a portion of the linear mask opening has its longitudinal direction at an angle of 0°±5° relative to the direction of the intersection of the nitrogen polar surface of the substrate and surface A. More preferably, in a portion accounting for more than 50% of the total extension of the linear mask opening, and further in the entire portion of the linear mask opening, the longitudinal direction has an angle of 0°±5° relative to the direction of the intersection of the nitrogen polar surface of the substrate and surface A.

[0295] The linewidth of the opening in the linear mask is preferably 0.5 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. Furthermore, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The linewidth does not need to be the same in all portions of the opening in the linear mask.

[0296] (3) Process S3

[0297] In step S3, GaN crystals are grown on the nitrogen-polar surface of the first substrate prepared in step S1 by using an ammonothermal method through the mask opening of the first pattern mask formed in step S2, to obtain a stacked structure in which GaN crystals are stacked on the nitrogen-polar surface of the first substrate across the first pattern mask.

[0298] Reference Figure 14 The growth process of GaN crystal in step S3 is described.

[0299] Figure 14 (a) is a cross-sectional view showing the state before crystal growth begins. A patterned mask 30 with a linear mask opening 31 is provided on the nitrogen polar surface 22 of the substrate 20.

[0300] Figure 14(b) shows the situation where GaN crystal 40 begins to grow on the nitrogen polar surface 22 exposed inside the linear mask opening 31 of the pattern mask 30.

[0301] After passing through pattern mask 30, as Figure 14 As shown in (c), the GaN crystal 40 grows not only in the [000-1] direction but also in the lateral direction (parallel to the nitrogen polar surface 22), but a gap G is formed between the GaN crystal 40 and the pattern mask 30. As a result, orientation disorder of the GaN crystal 40 that might be caused by contact with the pattern mask 30 is suppressed.

[0302] exist Figure 14 In the growth stage shown in (c), the GaN crystal 40 has a through hole T above the mask portion of the pattern mask 30.

[0303] As GaN crystal 40 is further grown, the interstitial G is gradually filled, but not completely, such as... Figure 14 As shown in (d), the through hole T is closed while the void V remains.

[0304] After the through hole T is closed, as Figure 14 As shown in (e), the GaN crystal 40 is further grown in the [000-1] direction. It can be considered that the stress occurring between the substrate 20 and the GaN crystal 40 is mitigated by the voids V, thereby reducing the strain of the GaN crystal 40.

[0305] The growth amount of the GaN crystal 40 in the [000-1] direction after the through hole T is blocked is preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and there is no particular upper limit.

[0306] Note that in process S3, GaN crystals are also grown on the gallium polar surface 21 of the substrate 20, but... Figure 14 Not shown in the image.

[0307] exist Figure 14 During the (d) stage, when the through hole T is closed, due to any one or both of the following reasons—dislocation occurring at the merging surface, or dislocations at the merging surface bending together in the [000-1] direction—it is possible to prevent the through hole from... Figure 14 In stage (e), a dislocation array will appear on the main surface of the C-plane GaN substrate cut from the GaN crystal formed during the process. The shape of this dislocation array is roughly the shape of the intersection line formed by the extension of the merged surface in the [000-1] direction and the main surface of the C-plane GaN substrate. This intersection line may include straight portions, curved portions, bends, and forks.

[0308] It should be noted that, here, "merging surface" refers to the surface where GaN crystals growing from two adjacent mask openings further grow laterally on the mask portion of the patterned mask and eventually join together. In this specification, such joining is sometimes referred to as merging. Furthermore, the region grown above the merging surface is sometimes referred to as the merging region.

[0309] The aforementioned merging surface is formed above the mask portion of the pattern mask. Therefore, when the pattern mask has multiple closed mask portions, multiple dislocation arrays discretely appear on the main surface of the C-plane GaN substrate. When the arrangement of the multiple closed mask portions in the pattern mask is periodic, the arrangement of the multiple dislocation arrays on the main surface of the C-plane GaN substrate is also periodic. When the arrangement of the multiple closed mask portions in the pattern mask is two-dimensional, the arrangement of the multiple dislocation arrays on the main surface of the C-plane GaN substrate is also two-dimensional.

[0310] A closed mask portion refers to a mask portion surrounded by linear mask openings, or a mask portion whose own outline forms a ring. Figures 9-11 The pattern masks shown in the various examples have examples with closed mask portions. Figure 9 (c) and (d) Figure 10 (e) ~ (h) Figure 11 (i) to (j). In these examples, the arrangement of closed mask portions in the pattern mask is periodic and two-dimensional.

[0311] In process S3, the ammonothermal method can be preferred for growing GaN crystals. Figure 15 Crystal growth apparatus of the type shown.

[0312] Reference Figure 15 The crystal growth apparatus 200 includes an autoclave 201 and a sealed container 202 made of Pt disposed therein.

[0313] The sealed container 202 has a raw material dissolution zone 202a and a crystal growth zone 202b, which are separated by baffles 203 made of Pt. The raw material FS is placed in the raw material dissolution zone 202a. The seed crystal S is suspended by Pt wires 204 in the crystal growth zone 202b.

[0314] The gas pipeline, which connects to the vacuum pump 205, ammonia cylinder 206, and nitrogen cylinder 207, is connected to the autoclave 201 and the sealed container 202 via valve 208. When adding NH3 (ammonia) to the sealed container 202, the amount of NH3 supplied from the ammonia cylinder 206 can be confirmed using mass flow meter 209.

[0315] The raw material can preferably be polycrystalline GaN prepared by the following method: HCl (hydrogen chloride) gas is brought into contact with elemental Ga (metallic gallium) under heating to obtain gaseous GaCl, and then the gaseous GaCl is reacted with NH3 gas.

[0316] The mineralizing agent used to promote the dissolution of raw materials is preferably a combination of one or more ammonium halides selected from NH4Cl (ammonium chloride), NH4Br (ammonium bromide), and NH4I (ammonium iodide) with NH4F (ammonium fluoride). It is particularly preferred to use NH4F and NH4I together.

[0317] When using growth temperatures below 650℃, it is not recommended to use ammonium halides other than NH4F as mineralizers. This is because the growth direction of GaN crystals is essentially only the [000-1] direction, and lateral growth does not occur.

[0318] On the other hand, when NH4F is used alone as a mineralizing agent, it strongly promotes lateral growth. However, if the lateral growth of GaN crystals is excessively promoted, it becomes difficult to achieve optimal growth. Figure 14 The method shown makes it difficult to grow GaN crystals by creating gaps between them and the pattern mask.

[0319] When GaN crystals are grown on seed crystal S, NH3 is also added to the space between autoclave 201 and sealed container 202. Then, the autoclave 201 is heated from the outside by a heater (not shown) to make the sealed container 202 a supercritical or subcritical state.

[0320] During the period from when the raw material FS is fully dissolved and the solvent reaches saturation, etching also occurs on the surface of the seed crystal S. If necessary, before growth begins, in order to promote the etchback of the seed crystal S, a temperature reversal period can be set so that the temperature gradient between the raw material dissolution zone 202a and the crystal growth zone 202b is opposite to that during crystal growth.

[0321] The optimal growth temperature is 550℃ or higher. While growth temperatures above 1000℃ are acceptable, high-quality GaN crystals can be grown even at temperatures below 700℃.

[0322] The growth pressure can be set in the range of 100 to 250 MPa, but is not limited to this.

[0323] As an example, GaN can be grown under the following conditions: using NH4F and NH4I as mineralizers with molar ratios of 0.5% and 4.0% relative to NH3, respectively, at a pressure of approximately 220 MPa, with an average temperature Ts in the raw material dissolution zone and an average temperature Tg in the crystal growth zone of approximately 600 °C, and a temperature difference Ts-Tg between the two zones of approximately 5 °C (Ts>Tg).

[0324] Increasing the temperature difference between the raw material dissolution zone and the crystal growth zone can improve the growth rate of GaN crystals. However, if the growth rate is too high, the growth of GaN crystals may become difficult. Figure 14 Phase (c) enters Figure 14 The (d) stage, namely the problem of the difficulty in closing the through-holes in GaN crystals.

[0325] In process S3, each time the raw material is used up, the sealed container can be replaced and the GaN crystal regrowth can be repeated.

[0326] (4) Process S4

[0327] In step S4, at least a portion of the GaN crystal grown in step S3 is separated from the stacked structure obtained in step S3.

[0328] Reference Figure 16 The separation process in step S4 is described.

[0329] Figure 16 (a) is a schematic cross-sectional view of a stacked structure obtained by growing GaN crystals through the mask opening of the first pattern mask formed in step S2 on the nitrogen polar surface of the substrate prepared in step S1 via step S3. Figure 16 (b) is a schematic cross-sectional view showing the substrate with the patterned mask and the separated GaN crystal after the GaN crystal grown in step S3 is separated from the substrate with the first patterned mask in step S4.

[0330] That is, in step S3, a stacked structure in which GaN crystals are stacked on the nitrogen-polar surface of the first substrate with a first pattern mask in between is obtained. In step S4, a portion consisting only of the GaN crystals stacked as described above is separated from this stacked structure. The separated GaN crystals need to be at least a portion of the GaN crystals grown using the ammonothermal method in step S3. The separated portion is not particularly limited, but is preferably a portion of the stacked structure farther from the first substrate. This is because it can further reduce dislocation defects inherited from the substrate 20. Furthermore, the GaN crystals are preferably separated in a sheet shape. The number of separated GaN crystals is not particularly limited; for example, one or more can be separated in a sheet shape, but one is preferred.

[0331] By separating the GaN crystal grown using the ammonothermal method in step S3, the GaN crystal grown in step S3 can be used as a substrate, and the ammonothermal method can be appropriately implemented, especially... Figure 15 The ammonothermal method in a crystal growth apparatus as shown.

[0332] The separation method can use known methods of slicing GaN crystals; for example, it is also preferred to use a wire saw to slice only the GaN crystal from the stacked structure. As the wire saw, a single-wire saw or a multi-wire saw can be used.

[0333] Preferably, the shape and area of ​​the nitrogen polar surface of the GaN crystal to be separated are substantially the same as the shape and area of ​​the nitrogen polar surface of the substrate prepared in step S1.

[0334] The area of ​​the nitrogen polar surface of the GaN crystal to be separated is preferably 15 cm². 2 The above can be 15cm 2 Above and below 50cm 2 50cm 2 Above and below 100cm 2 100cm 2 Above and below 200cm 2 200cm 2 Above and below 350cm 2 350cm 2 Above and below 500cm 2 500cm 2 Above and below 750cm 2 wait.

[0335] When the nitrogen polar surface of the GaN crystal to be separated is circular, its diameter is preferably 45 mm or more. Typical diameters are 45–55 mm (about 2 inches), 95–105 mm (about 4 inches), 145–155 mm (about 6 inches), 195–205 mm (about 8 inches), 295–305 mm (about 12 inches), etc.

[0336] For the GaN crystal to be separated, for example when the nitrogen polar surface is a circle with a diameter of about 50 mm, its thickness is preferably 300 μm or more. If the diameter is larger than this value, the preferred lower limit of its thickness also becomes larger. There is no particular upper limit to the thickness of the GaN crystal to be separated, and it is usually less than 20 mm.

[0337] In step S5 described later, a second pattern mask is disposed on the nitrogen-polar surface of the separated GaN crystal. Before disposing the second pattern mask on the nitrogen-polar surface of the separated GaN crystal, a step of planarizing the nitrogen-polar surface is performed. By planarizing the nitrogen-polar surface, the second pattern mask can be easily and accurately formed on the surface. Preferably, the nitrogen-polar surface is planarized by grinding or polishing. More preferably, the damage layer introduced by the planarization process is removed from the nitrogen-polar surface by CMP (Chemical Mechanical Polishing) and / or etching.

[0338] It should be noted that the planarization process is performed after the separation process. By performing it after the separation process, the nitrogen polar surface can be accurately planarized without being affected by issues such as the strength of the stacked structure containing the substrate with the pattern mask and the GaN crystal grown thereon. By separating at least a portion of the GaN crystal grown from the stacked structure and grinding the nitrogen polar surface of the separated GaN crystal, a second pattern mask can be accurately formed.

[0339] (5) Process S5

[0340] In step S5, a GaN crystal separated from a first substrate substrate in step S4, on which a first pattern mask is disposed, is used as a second substrate substrate, and a second pattern mask is disposed on its nitrogen polar surface.

[0341] The second pattern mask can be the same as that described in section (2) S2. The second pattern mask can be the same as the first pattern mask, or it can be a different mask.

[0342] The second pattern mask is configured such that at least a portion of the region (substrate mask opening region) grown on the nitrogen polar surface of the GaN crystal grown in step S2, on the mask opening of the first pattern mask, is covered by the mask portion of the second pattern mask. Furthermore, it is preferable that at least 50% of the aforementioned substrate mask opening region is covered by the mask portion of the second pattern mask. More preferably, it is preferable that at least 80% of the aforementioned substrate mask opening region is covered by the mask portion of the second pattern mask. Even more preferably, it is preferable that the entire aforementioned substrate mask opening region is covered by the mask portion of the second pattern mask.

[0343] By covering the substrate mask opening region of the nitrogen polar surface configured as a GaN crystal with the mask portion of a second pattern mask, the GaN crystal obtained by growing it using the ammonothermal method through the mask opening of the second pattern mask in the subsequent process S6 can become a GaN crystal with fewer dislocations and fewer regions with large local strain. Furthermore, the GaN crystal obtained in this way can reduce dislocation density over a large area of ​​the main surface.

[0344] The inventors have considered the following reasons. The explanation will be provided with appropriate reference to the accompanying drawings.

[0345] Figure 17 (a) is a schematic cross-sectional view of a stacked structure obtained by growing GaN crystals through the mask opening of a first pattern mask on the nitrogen polar surface of a substrate in process S3 using the ammonothermal method. Figure 17 (b) is to process S4 to Figure 17 A schematic cross-sectional view of the GaN crystal obtained by separating the GaN crystal grown in (a).

[0346] In process S3, the GaN crystal β300 grown on the nitrogen polar surface of the substrate β100 through the mask opening of the first pattern mask β200 has a region (substrate mask opening region) β301 grown above the mask opening of the first pattern mask and a region (substrate mask region) β302 grown above the mask portion of the first pattern mask.

[0347] As described in section S3, the GaN crystal β300 grown on the nitrogen-polar surface exposed inside the mask opening of the pattern mask grows not only in the GaN [000-1] direction but also in the lateral direction (parallel to the nitrogen-polar surface) after passing through the pattern mask, and also grows above the mask portion. Therefore, the GaN crystal in the substrate mask opening region β301 mainly grows from the nitrogen-polar surface of the substrate β100 exposed from the mask opening in the [000-1] direction, while the GaN crystal in the substrate mask region β302 grown above the mask portion mainly grows simultaneously from the mask opening in both the GaN [000-1] direction and the lateral direction (parallel to the nitrogen-polar surface). That is, the growth environments of the substrate mask opening region β301 and the substrate mask region β302 are different. However, according to the inventors' research, the residual strain of the GaN crystal in the substrate mask opening region β301 is larger than that in the substrate mask region β302. As a result, the dislocation density of the GaN crystal β300 obtained in process S3 can be effectively reduced using the mechanism described in this section. On the other hand, a large residual strain is still retained in the substrate mask opening region β301.

[0348] Figure 17 (c) is in Figure 17 (b) is a schematic cross-sectional view of a GaN crystal with a second pattern mask disposed thereon. Figure 17 (d) is configured with Figure 17 (c) is a schematic cross-sectional view of a stacked structure obtained by growing GaN crystal through the mask opening of the second pattern mask on the nitrogen polar surface of the GaN crystal using the ammonothermal method.

[0349] Using the GaN crystal β300 obtained in step S3 as a substrate, a mask portion β400 of a second pattern mask is formed on its nitrogen polar surface, and the mask portion β400 of the second pattern mask covers part or all of the opening region β301 of the substrate mask, so that the opening region β301 of the GaN crystal substrate mask is not exposed due to the opening region β401 of the second pattern mask. As a result, the GaN crystal β500 grown through the opening region β401 of the second pattern mask can reduce the residual strain originating from the opening region β301 of the substrate mask and has fewer dislocations.

[0350] In the GaN crystal β500 grown through the mask opening β401 of the second pattern mask, from the viewpoint of reducing residual strain originating from the substrate mask opening region β301, it is preferable that, after the second pattern mask is configured, the area of ​​the substrate mask opening region β301 exposed through the mask opening β401 of the second pattern mask on the nitrogen polar surface of the GaN crystal is as small as possible.

[0351] Reference Figure 18 Please provide an explanation. Figure 18 (a) is a schematic cross-sectional view of a second pattern mask disposed on the nitrogen-polar surface of a second substrate. Figure 18 In (a), the entire substrate mask opening region β301 on the nitrogen polar surface of the GaN crystal β300, which serves as the second substrate, is covered by the mask portion β400 of the second pattern mask. That is, in Figure 18 In (a), there is no region where the base mask opening region overlaps with the mask opening of the second pattern mask (hereinafter also referred to as the "base opening exposed region").

[0352] On the other hand, Figure 18 In (b), a portion of the substrate mask opening region β301 on the nitrogen polar surface of the GaN crystal β300, which serves as the second substrate, is exposed through the mask opening β401 of the second pattern mask. That is, in Figure 18 In (b), there is an exposed area of ​​the base opening.

[0353] Therefore, the second pattern mask is preferably configured such that the region grown on the mask opening of the first pattern mask in the nitrogen polar surface of the GaN crystal obtained in step S4, i.e. the region where the substrate mask opening region overlaps with the substrate mask opening region and the mask opening of the second pattern mask (the exposed region of the substrate opening), satisfies the following relationship (I).

[0354] The area of ​​the exposed region of the substrate opening / the area of ​​the opening region of the substrate mask ≤ 10% ······(I)

[0355] From the same point of view, the second pattern mask is more preferably configured to satisfy the following relationship (II).

[0356] The area of ​​the exposed region of the substrate opening / the area of ​​the opening region of the substrate mask ≤ 1% ······(II)

[0357] From the same perspective, the second pattern mask is further preferably configured such that there is no exposed area of ​​the substrate opening. It should be noted that the absence of an exposed area of ​​the substrate opening has the same meaning as satisfying the following relationship (III).

[0358] Area of ​​exposed region of substrate opening / Area of ​​substrate mask opening = 0 ······(III)

[0359] As described above, when a second pattern mask is disposed on the nitrogen polar surface of the GaN crystal in step S5, it is preferable that part or all of the substrate mask opening region of the GaN crystal is covered by the mask portion of the second pattern mask. However, in this case, it is preferable to confirm the position of the substrate mask opening region of the GaN crystal before disposing of the second pattern mask, and use the information of the confirmed position of the substrate mask opening region to determine the placement position of the second pattern mask.

[0360] Since the GaN crystal grown in step S3 is separated from the substrate with the first pattern mask disposed in step S4, the location of the substrate mask opening region of the GaN crystal is not always clear. Therefore, it is more preferable to estimate the location of the substrate mask opening region based on the location of large residual strain on the nitrogen polar surface of the GaN crystal through photoelastic measurement, or to estimate the location of the substrate mask opening region based on the location of relatively large residual strain on the nitrogen polar surface of the GaN crystal from the surrounding area through orthogonal Nicol images observed by a polarized strain detector, or to confirm the positional relationship of the substrate mask opening region of the GaN crystal by using the shape of the substrate as a marker.

[0361] Furthermore, it is also preferable that the second pattern mask is configured such that, in the nitrogen polar surface of the GaN crystal grown in step S2, the merging surface formed above the mask portion of the first pattern mask and the area where information is grown on the merging surface (merging region) are covered by the mask portion of the second pattern mask.

[0362] The second pattern mask is configured such that the merging surface formed above the mask portion of the first pattern mask and the information growth area (merging region) on the nitrogen polar surface of the GaN crystal are covered by the mask portion of the second pattern mask. As a result, the GaN crystal obtained by growing it through the mask opening of the second pattern mask using the ammonothermal method in the subsequent process S6 can achieve a significant reduction in dislocation density over a large area of ​​the main surface.

[0363] Regarding the reasons, the inventors considered the following.

[0364] Refer again Figure 17 In step (a), the GaN crystal β300 grown in step S3 has a substrate mask opening region β301 and a substrate mask region β302, as described above. Here, the substrate mask region β302 grows simultaneously from the mask opening of the first pattern mask in both the GaN [000-1] direction and the lateral direction (parallel to the nitrogen polar surface), but a merging surface is formed above the mask region where GaN crystals grown in the lateral direction merge with each other. As detailed in step S3, dislocation arrays appear in the merging surface and the GaN crystal grown above it (merging region β303). Therefore, in the merging region β303 of the GaN crystal β300 grown in step S3, a dislocation array corresponding to the merging surface sometimes exists.

[0365] In contrast, refer to Figure 17 In (c) and (d), the GaN crystal β300 obtained in process S3 is used as a substrate, and a mask portion β400 of a second pattern mask is formed on its nitrogen polar surface. The second pattern mask is configured to cover the merging region β303 with the mask portion β400, so that the merging region β303 of the GaN crystal β300 is not exposed through the mask opening β401 of the second pattern mask. As a result, the GaN crystal β500 grown through the mask opening β401 of the second pattern mask can reduce the dislocation array originating from the merging region β303 and has very few dislocations over a large area.

[0366] Based on the above reasons, the second pattern mask is preferably configured such that at least a portion of the substrate mask opening region and the substrate merging region are covered by the mask portion of the second pattern mask on the nitrogen polar surface of the GaN crystal grown in process S2. This results in a GaN crystal with reduced areas of high residual strain and reduced dislocation density over a large area of ​​the main surface.

[0367] (6) Process S6

[0368] In step S6, GaN crystals are grown on the nitrogen polar surface of the second substrate on which the second pattern mask is disposed in step S5 using an ammonothermal method through the mask opening of the second pattern mask.

[0369] The specific method for growing GaN crystals in step S6 can be the same as that described in step S3 above.

[0370] The GaN crystal grown in step S6 can be further used as a third substrate for growing new GaN crystals. For example, the GaN crystal grown in step S6 can also be used as a third substrate, and the GaN crystal can be grown on the main surface of the GaN crystal using the HVPE method to obtain a new GaN crystal. The new GaN crystal obtained in this way can also yield the GaN substrate of the first embodiment or the GaN crystal of the second embodiment described above.

[0371] 3. GaN crystal growth method based on HVPE method

[0372] The following describes the preferred method for growing GaN crystals based on the HVPE method.

[0373] 3.1.HVPE device

[0374] The basic structure of an HVPE device that can be used in the fabrication of GaN crystals is shown below. Figure 19 .

[0375] Reference Figure 19 The HVPE apparatus 300 includes: a hot-wall reactor 301, a gallium storage section 302 and a base 303 disposed within the reactor, and a first heater 304 and a second heater 305 disposed outside the reactor. The first heater 304 and the second heater 305 respectively surround the reactor 301 in an annular shape.

[0376] Reactor 301 is a quartz tubular chamber. Within reactor 301 are a first zone Z1 primarily heated by a first heater 304 and a second zone Z2 primarily heated by a second heater 305. Exhaust pipe P E It is connected to the reactor end on the Z2 side of the second zone.

[0377] The gallium storage unit 302, located in the first zone Z1, is a quartz container with a gas inlet and a gas outlet.

[0378] The base 303, located in the second zone Z2, is made of graphite, for example. A mechanism for rotating the base 103 can be arbitrarily configured.

[0379] Seed crystals are placed on base 303.

[0380] Preferably, such as Figure 20 As shown in (a), the edge cover covering the edge of the seed crystal is disposed on the base together with the seed crystal.

[0381] The edge shield is, for example, formed of graphite, such as Figure 20 As shown in (b), its height h is set such that the position of the upper surface of the GaN thick film grown on the seed crystal does not reach above the upper end of the edge shield when its growth ends.

[0382] like Figure 21 As shown, the edge cover can cover not only the edge of the seed crystal, but also the outer periphery of the main surface of the seed crystal.

[0383] Back to Figure 19 During GaN crystal growth, reactor 301 is heated using a first heater 304 and a second heater 305. NH3 (ammonia), diluted with a carrier gas, is supplied to the second region Z2 through ammonia inlet pipe P1, and HCl (hydrogen chloride), diluted with a carrier gas, is supplied to the gallium storage section 302 through hydrogen chloride inlet pipe P2. The HCl reacts with metallic gallium in the gallium storage section 302, and the resulting GaCl (gallium chloride) is transported to the second region Z2 through gallium chloride inlet pipe P3. In the second region Z2, NH3 reacts with GaCl, and the resulting GaN crystallizes on a seed crystal placed on a substrate 303.

[0384] When growing a GaN crystal on a seed crystal with impurities, the dopant gas diluted with carrier gas is introduced into the second region Z2 of reactor 301 through dopant introduction pipe P4.

[0385] The ammonia inlet tube P1, hydrogen chloride inlet tube P2, gallium chloride inlet tube P3, and dopant inlet tube P4 may be formed from quartz and disposed within reactor 301.

[0386] exist Figure 19 In this case, the distance from the nozzle to the base 303 is the same in both the ammonia inlet tube P1 and the gallium chloride inlet tube P3, but it is not limited to this. The nozzle of the ammonia inlet tube P1 can also be opened at a position further away from the base 303 (upstream side) than the nozzle of the gallium chloride inlet tube P3.

[0387] Alternatively, it can also be in Figure 19 The nozzle of the independent ammonia inlet tube P1 is integrated with the nozzle of the gallium chloride inlet tube P3, forming a double-tube nozzle with the former as the outer tube and the latter as the inner tube.

[0388] exist Figure 19 In this paper, the nozzles of the gallium chloride inlet tube P3 and the dopant inlet tube P4 are depicted as independent nozzles, but this is not a limitation. For example, in order to uniformly dope the grown GaN crystal, the nozzle of the dopant inlet tube P4 can be made to open inside the gallium chloride inlet tube P3 so that GaCl is mixed with the dopant gas and then released into the second region Z2 through a shared nozzle.

[0389] When doping the grown GaN crystal with Si, the preferred doping gases are SiH4 (silane), SiH3Cl (monochlorosilane), and SiH2Cl. s (Dichlorosilane), SiHCl3 (trichlorosilane), or SiCl4 (tetrachlorosilane).

[0390] When doping the grown GaN crystal with Ge, the doping gas can preferably be GeH4 (germanane), GeH3Cl (monochlorogermanane), GeH2Cl2 (dichlorogermanane), GeHCl3 (trichlorogermanane) or GeCl4 (tetrachlorogermanane).

[0391] When doping the grown GaN crystal with Sn, SnH4 (stanane), SnH3Cl (monochlorostanane), SnH2Cl2 (dichlorostanane), SnHCl3 (trichlorostanane) or SnCl4 (tetrachlorostanane) are preferred.

[0392] Although the grown GaN crystals are unintentionally doped, they may sometimes contain O and Si. It is estimated that the unintentional Si comes from the quartz that makes up the reactor or piping, and the unintentional O comes from either or both of the quartz and moisture that has infiltrated the reactor from the outside.

[0393] Included Figure 19 The components arranged within reactor 301, including those omitted in the text, can be made of quartz and carbon, as well as SiC (silicon carbide) and SiN. x Components are formed from silicon nitride, boron nitride (BN), aluminum oxide, tungsten (W), molybdenum (Mo), etc. By doing so, as long as the doping is unintentional, the concentration of impurities other than Si, O, and H in the GaN crystal grown on the seed crystal can be 5 × 10⁻⁶. 15 atoms / cm 3 the following.

[0394] 3.2. Substrate

[0395] The substrate used in the growth of GaN crystals is as described above, which is a GaN crystal obtained through processes S1 to S6.

[0396] 3.3. Growth conditions

[0397] The preferred conditions for growing GaN crystals on the above-mentioned substrate using HVPE are as follows.

[0398] The temperature of the gallium storage section is, for example, 500 to 1000°C, preferably 700°C or higher, and more preferably 900°C or lower.

[0399] The base temperature is, for example, 900 to 1100°C, preferably 930°C or higher, more preferably 950°C or higher, and preferably 1080°C or lower, more preferably 1050°C or lower.

[0400] The V / III ratio, which is the ratio of the partial pressure of NH3 to the partial pressure of GaCl in the reactor, can be set to, for example, 1 to 20, preferably 2 or more, more preferably 3 or more, and even more preferably 10 or less.

[0401] An excessively large or small V / III ratio can both lead to a deterioration in the surface morphology of the grown GaN. This deterioration in surface morphology results in a decrease in crystal quality or an increase in the oxygen concentration unintentionally incorporated into the GaN crystal.

[0402] The growth rate of GaN crystals can be controlled by using the product of the partial pressure of NH3 and the partial pressure of GaCl in the reactor as a parameter. This rate is, for example, 20 to 300 μm / h, preferably 30 μm / h or more, more preferably 40 μm / h or more, and further preferably 200 μm / h or less, more preferably 150 μm / h or less, and even more preferably 100 μm / h or less.

[0403] The inventors have discovered that when growing GaN crystals using HVPE on a substrate with high crystal quality formed from GaN crystals grown through processes S1 to S6, if the growth rate is too low, a problem occurs where a region of localized growth cessation forms on the growth surface.

[0404] When a low growth rate of 20 μm / h to 60 μm / h is used, it is preferable to prevent new through-dislocations from occurring at the interface between the GaN crystal substrate obtained in processes S1 to S6 and the GaN crystal grown on the substrate using HVPE.

[0405] To improve production efficiency, the growth rate can be increased midway through the growth process. Experiments conducted by the inventors show that when the initial growth rate is set to 40 μm / h, and the growth rate is increased to 80 μm / h or 120 μm / h midway through the process, the through-dislocation density of the GaN crystal grown at 80 μm / h is the same as that of the substrate formed from the GaN crystal obtained in processes S1 to S6. Even in the GaN crystal grown at 120 μm / h, the through-dislocation density is at most twice that of the substrate.

[0406] The carrier gas used to dilute NH3, HCl and the dopant gas can preferably be H2 (hydrogen), N2 (nitrogen) or a mixture of H2 and N2.

[0407] The molar ratio of H2 in the carrier gas affects the impurity concentration of the grown GaN crystal. It should be noted that the molar ratio of H2 in the carrier gas mentioned here is calculated based on the flow rates of each type of gas supplied from outside the reactor to the reactor as carrier gas.

[0408] 4. Applications of GaN substrates

[0409] The c-side GaN substrate of the embodiment can be used to manufacture various nitride semiconductor devices, including light-emitting diodes (LEDs), laser diodes (LDs), and other light-emitting devices, as well as electronic devices such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (High Electron Mobility Transistors).

[0410] Nitride semiconductors, also known as group III-V nitride compound semiconductors, group III nitride compound semiconductors, GaN-based semiconductors, etc., are compounds in which gallium, in addition to GaN, is partially or completely replaced by other group 13 elements (B, Al, In, etc.) of the periodic table.

[0411] Nitride semiconductor devices are semiconductor devices whose main structure is formed by nitride semiconductors.

[0412] Example

[0413] The following records the results of the experiments conducted by the inventors.

[0414] <Example 1-1>

[0415] As the first substrate, a C-plane GaN substrate is prepared, cut from a GaN crystal grown using the HVPE method. This C-plane GaN substrate has a nitrogen-polar surface and a gallium-polar surface, both of which have undergone CMP finishing. The orientation of the nitrogen-polar surface is within 1° relative to [000-1].

[0416] On the nitrogen-polar surface of the C-side GaN substrate, a first pattern mask is formed using a lift-off method, consisting of a 150nm thick Pt layer on a 50nm thick TiW layer. A stripe pattern formed by linear mask openings is formed on this pattern mask. The linewidth of the linear openings is set to 20μm, and the spacing between the linear openings is set to 2mm. The stripe direction is parallel to the intersection line of the A-side and the nitrogen-polar surface of the first substrate.

[0417] After forming the first pattern mask, use Figure 15 The crystal growth apparatus of the type shown grows GaN crystals on the nitrogen polar surface of the substrate through the mask opening of a first pattern mask using an acidic ammonothermal method.

[0418] The raw material used is polycrystalline GaN synthesized by the following method: HCl gas is brought into contact with elemental Ga under heating to obtain gaseous GaCl, and then the gaseous GaCl is reacted with NH3 gas.

[0419] The mineralizing agents used were NH4F and NH4I. The molar ratios of NH4F and NH4I relative to NH3 were 5.0% and 3.5%, respectively. NH4I was synthesized by introducing HI (hydrogen iodide) into a closed Pt container after the addition of NH3.

[0420] The growth conditions are as follows: the average temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone are set to 598℃, the temperature difference between the crystal growth zone and the raw material dissolution zone is set to 15℃ (Ts>Tg), and the pressure is set to 220MPa.

[0421] The sealed container was opened 40 days after the start of growth, and the stacked structure consisting of a substrate with a first pattern mask and GaN crystals grown thereon was taken out.

[0422] The GaN crystal is separated from the aforementioned stacked structure. Separation is performed by slicing the GaN crystal on a substrate with a first pattern mask disposed thereon using a wire saw.

[0423] The GaN crystals separated in the above steps are processed to fabricate a first C-plane GaN substrate with a thickness of 500 μm. Specifically, the GaN crystals are sliced ​​parallel to the C-plane using a multi-wire saw. The two main surfaces of the resulting blank substrate are ground to planarize them, and then further CMP finishing is performed to remove the damaged layer.

[0424] Next, the first C-side GaN substrate is used as the second substrate, and GaN crystals are grown using the acidic ammonothermal method.

[0425] A second pattern mask is formed on the nitrogen-polar surface of the second substrate by a lift-off method, consisting of a stacked film of a 150 nm thick Pt layer on a 50 nm thick TiW layer. A stripe pattern formed by linear mask openings is formed on this pattern mask. The linewidth of the linear openings is set to 20 μm, and the spacing between the linear openings is set to 2 mm. The stripe direction is parallel to the intersection line of the A-plane and the nitrogen-polar surface in the second substrate.

[0426] Before configuring the second pattern mask, the location of the region (substrate mask opening region) grown on the mask opening of the first pattern mask was confirmed by observing orthogonal Nicol images using a polarized strain detection device and an LED ultraviolet projection emitter (manufactured by MeCan Imaging Co., Ltd.). Using the confirmed location information of the substrate mask opening region, the position of the second pattern mask was adjusted and determined such that at least a portion of the substrate mask opening region was covered by the mask portion of the second pattern mask, and the second pattern mask was configured. The exposure rate of the area where the substrate mask opening region overlaps with the mask opening of the second pattern mask (substrate opening exposed area), i.e., (area of ​​substrate opening exposed area) / (area of ​​substrate mask opening region), was 0%.

[0427] After forming the second pattern mask, use Figure 15 The crystal growth apparatus of the type shown grows GaN crystals on the nitrogen polar surface of a second substrate through the mask opening of a second pattern mask using an acidic ammonothermal method.

[0428] The raw material used is polycrystalline GaN synthesized by the following method: HCl gas is brought into contact with elemental Ga under heating to obtain gaseous GaCl, and then the gaseous GaCl is reacted with NH3 gas.

[0429] The mineralizing agents used are NH4F and NH4I. The molar ratio of NH4F and NH4I to NH3 is set to 1.0%. NH4I is synthesized by introducing HI into a Pt-made sealed container after the addition of NH3.

[0430] The growth conditions are as follows: the average temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone are set to 605-610℃, the temperature difference between the crystal growth zone and the raw material dissolution zone is set to 15-20℃ (Ts>Tg), and the pressure is set to 220MPa.

[0431] Through 28 days of growth, GaN crystals were grown to 1.8 mm in the [000-1] direction on the nitrogen polar surface of the second substrate.

[0432] Next, the grown GaN crystal was processed to fabricate a second C-plane GaN substrate with a diameter of 50 mm (hereinafter referred to as "sample E-1"). The main surface of the GaN substrate was planarized by grinding on both sides, and then further CMP finishing was performed to remove the damaged layer. The final substrate thickness was set to 350 μm.

[0433] The dislocation density of the main surface on the Ga polar side of sample E-1 was investigated by measuring the pit density (EPD). The substrate was etched with 89% sulfuric acid heated to 270°C for 1 hour, and the pits were observed using an optical microscope. Figure 22 This is a schematic diagram used to illustrate the observation area (OE) of 5.5mm × 5.0mm and the unit area (UE) of 5.5mm × 0.5mm obtained by dividing the above observation area into 10 parts.

[0434] A rectangular area of ​​5.5mm × 5.0mm was defined as the observation area. This observation area was divided into 10 parts, and the resulting rectangular areas of 5.5mm × 0.5mm were used as unit areas. The observation area was positioned 5mm inward from the outer periphery of the substrate, with the long side (5.5mm) of the rectangle parallel to the direction of the stripes used as the first pattern mask during manufacturing. The dislocation density of each unit area was calculated by measuring the pit density. Then, the average dislocation density of each of the 10 unit areas constituting the observation area was taken as the 5.5mm × 5.0mm (area: 0.275cm²) unit area. 2 The dislocation density of the observed region is calculated.

[0435] The dislocation density in the 5.5mm × 5.0mm observation area is 2.4 × 10⁻⁶. 3 cm -2 Furthermore, the dislocation densities of the 10 unit regions constituting the observation area, from one end to the other (unit regions 1 to 10), are as shown below, with the dislocation density of each unit region being less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is 5.

[0436] Unit area 1: 0cm -2 .

[0437] Unit area 2: 0cm -2 .

[0438] Unit area 3: 1.3 × 10 4 cm -2 .

[0439] Unit area 4: 6.2 × 10 2 cm -2 .

[0440] Unit area 5:0cm -2 .

[0441] Unit area 6:0cm -2 .

[0442] Unit area 7: 1.0 × 10 4 cm -2 .

[0443] Unit area 8: 2.9 × 10 2 cm -2.

[0444] Unit area 9:0cm -2 .

[0445] Unit area 10: 1.1 × 10 2 cm -2 .

[0446] For sample E-1, the dislocation density was also measured in the same manner for observation areas located at different positions than those described above. The dislocation density of the 5.5 mm × 5.0 mm observation area was 4.8 × 10⁻⁶. 3 cm -2 That is, in sample E-1, it was confirmed that there were more than two observation regions at non-overlapping locations. Furthermore, the dislocation densities of the 10 unit regions constituting the observation region, from one end to the other (unit regions 1 to 10), are as shown below, with the dislocation density per unit region being less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is four.

[0447] Unit area 1: 0cm -2 .

[0448] Unit area 2: 3.6 × 10 1 cm -2 .

[0449] Unit area 3: 1.9 × 10 4 cm -2 .

[0450] Unit area 4: 1.8 × 10 2 cm -2 .

[0451] Unit area 5:0cm -2 .

[0452] Unit area 6:0cm -2 .

[0453] Unit area 7: 2.9 × 10 4 cm -2 .

[0454] Unit area 8: 3.6 × 10 2 cm -2 .

[0455] Unit area 9:0cm -2 .

[0456] Unit area 10: 7.3 × 10 1 cm -2 .

[0457] <Comparative Example 1-1>

[0458] A C-face GaN substrate identical to the first C-face GaN substrate used in the manufacturing process of Example 1 is obtained. In other words, a C-face GaN substrate is obtained from a GaN crystal obtained by a manufacturing method comprising: a step of preparing a first substrate having a nitrogen-polar surface; a step of disposing a first pattern mask comprising a mask portion and a mask opening portion on the nitrogen-polar surface of the first substrate; a step of growing a GaN crystal through the mask opening portion of the first pattern mask using an ammonothermal method; and a step of separating the GaN crystal from the first substrate having the first pattern mask disposed thereon, but excluding the step of disposing a second pattern mask on the nitrogen-polar surface using the separated GaN crystal as a second substrate, and the step of growing a GaN crystal through the mask opening portion of the second pattern mask using an ammonothermal method.

[0459] Regarding the observation area, a 5.5mm × 5.0mm observation area was positioned on the inner side of the rectangle, parallel to the direction of the stripes used as the first pattern mask during manufacturing, at a distance of 5mm from the outer periphery of the substrate. The dislocation density of the observation area was calculated similarly to that in Example 1-1, and the result was 1.4 × 10⁻⁶. 4 cm -2 Furthermore, the dislocation densities of the 10 unit regions constituting the observation area, from one end to the other (unit regions 1 to 10), are as shown below, with the dislocation density of each unit region being less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is 0.

[0460] Unit area 1: 1.9 × 10 4 cm -2 .

[0461] Unit area 2: 1.3 × 10 4 cm -2 .

[0462] Unit area 3: 4.4 × 10 4 cm -2 .

[0463] Unit area 4: 5.5 × 10 3 cm -2 .

[0464] Unit area 5: 7.6 × 10 3 cm -2 .

[0465] Unit area 6: 2.9 × 10 3 cm -2 .

[0466] Unit area 7: 3.2 × 10 4 cm -2 .

[0467] Unit area 8: 6.4 × 10 3 cm -2 .

[0468] Unit area 9: 9.4 × 10 3 cm -2 .

[0469] Unit area 10: 2.4 × 10 3 cm -2 .

[0470] <Example 2-1>

[0471] A C-plane GaN substrate, fabricated using the same method as the second C-plane GaN substrate in Embodiments 1-1 above, is used as a seed crystal (third substrate). On its Ga polarity surface, a substrate having the same... Figure 19 The HVPE apparatus shown is a basic vapor-phase growth apparatus with a common structure, used to grow GaN thick films via HVPE. The process is roughly as follows.

[0472] First, seed crystals are placed on the substrate. No edge shielding is used.

[0473] Next, N2, H2 and NH3 are supplied to the reactor at partial pressures of 0.80 atm, 0.15 atm and 0.05 atm, respectively, while the reactor is heated by a heater located on the outside of the reactor.

[0474] After the substrate temperature reached 1020°C, the substrate temperature was kept constant to allow GaN growth. The temperature of the Ga storage section was set to 800°C. The carrier gas supplied to the reactor was 51% H2 and the remainder N2 in a molar ratio.

[0475] Within 60 minutes of the start of growth, GaCl and NH3 were reacted at their respective partial pressures to form a mixture of 7.2 × 10⁻⁶ g / L. -3 atm and 6.9×10 - 2 The gas is supplied to the reactor via ATM without any intentional doping.

[0476] Sixty minutes after the start of growth, GeCl4 (germanium tetrachloride) was introduced into the reactor. The supply rate of GeCl4 was gradually increased over 10 minutes.

[0477] After the GeCl4 supply rate reaches the specified value, GaCl, NH3, and GeCl4 are supplied at their respective partial pressures of 1.1 × 10⁻⁶. -2 atm, 8.0×10 -2 atm and 2.1×10 -5 The material is supplied to the reactor via atm, allowing a Ge-doped GaN film to grow to approximately 5.4 mm thick.

[0478] The growth rate of the Ge-doped GaN thick film, calculated based on the thickness and growth time, is approximately 83 μm / hr.

[0479] Next, the GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar side of the resulting wafer was planarized by grinding and subsequently CMP finishing. Slicing damage on the N polar side of the wafer was removed by etching. A wafer with a thickness of 400 μm and a main surface area of ​​approximately 20 cm² was successfully produced. 2 The third C-side GaN substrate (hereinafter also referred to as "sample E-2").

[0480] For the Ga polarity side of the third C-plane GaN substrate (sample E-2), the photoelastic strain within the main surface was measured by photoelasticity measurement. The conditions for photoelasticity measurement are as follows.

[0481] The photoelastic device uses a device developed by the authors of Non-Patent Documents 1 to 3. A schematic diagram of the device is shown below. Figure 22 .

[0482] In photoelasticity measurements, an LED with a wavelength of 633 nm is used as the incident light source. The light, after being processed by a rotating polarizer, is incident along the c-plane normal of the gallium nitride substrate (which serves as the substrate under test). The intensity of transmitted light at various points within the surface is detected using a CCD camera by rotating a polarizer. The substrate under test requires double-sided polishing to allow light transmission.

[0483] It should be noted that when the GaN substrate on the c-side of the sample is unpolished on both sides or polished on only one side, the incident light may not pass through the GaN substrate, making proper measurement impossible. In this case, polishing the unpolished side of the GaN substrate allows the incident light to pass through, thus enabling photoelasticity measurement.

[0484] In photoelasticity measurement, the intensity of transmitted light is measured while the rotating polarizer and rotating detector are rotated synchronously under orthogonal and parallel conditions. The light intensity is adjusted so that the transmitted light intensity does not exceed the detection intensity of the CCD camera and saturate. The polarization angle division number of the rotating polarizer and rotating detector is set to 25 or higher. In addition, the in-plane resolution of the CCD camera, the so-called pixel size, is 167 μm in both the longitudinal and transverse directions.

[0485] By using the polarization analysis described above, the birefringence at various points in the plane, namely the phase difference δ and the principal axis azimuth angle ψ, is determined.

[0486]

[0487] Then, the strain-free refractive index of gallium nitride relative to the thickness of the substrate under test and the wavelength of the light source (633 nm) was set to 2.355, and the photoelastic tensor component |p 11 -p 12 Given |=0.13, calculate |S, which is the strain evaluation value expressed by the following formula. r -S t The in-plane distribution of | is evaluated.

[0488]

[0489] Measurements were performed at room temperature (around 25°C). It is known that the refractive index of gallium nitride is temperature-dependent; if the measurement temperature deviates significantly from room temperature, proper measurements may not be possible. Therefore, photoelasticity measurements are preferably performed at room temperature (around 25°C).

[0490] In addition, the dislocation density of the principal facet on the Ga polar side of sample E-2 was investigated by PL imaging (PLI) image observation.

[0491] The normal direction of the principal surface is set as the z-direction, and the direction orthogonal to the z-direction and parallel to one of the a-faces is selected as the x-direction. Dislocation density is measured on a first line extending in the x-direction through the center of the principal surface and on a second line extending in the y-direction perpendicular to the x-direction.

[0492] Measurements were taken at all 17 points: the intersection of the first and second lines (the center of the main surface), 8 points on the first line excluding the intersection, and 8 points on the second line excluding the intersection. The interval between adjacent measurement points was 5 mm.

[0493] Observe a 360μm × 360μm square region at each measurement point. Divide the number of dislocations appearing within the square region by its area (129600μm). 2 The dislocation density was calculated for each measurement point. The average value among the 17 measurement points was taken as the dislocation density of the main surface of the c-plane GaN substrate.

[0494] In addition, using an X-ray diffraction apparatus [manufactured by Spectris Co., Ltd., PANalytical X'Pert ProMRD], the variation of the x-direction component of the off-cut angle within a 40 mm interval on the first line and the variation of the y-direction component of the off-cut angle within a 40 mm interval on the second line were investigated.

[0495] The (004) XRD rocking curve of sample E-2 was determined at a position far from the edge on the Ga polar surface.

[0496] During the measurement, the line-focusing CuKα X-ray source of the X-ray diffraction apparatus [Spectris Corporation, PANalytical X'Pert Pro MRD] was operated at 45 kV and 40 mA, and CuKα1 rays were obtained using a Ge(440)4 crystal symmetric monochromator. The optical system used was a parallel optical system, employing a 1 / 2 slit, an X-ray mirror, and a cross slit of w1 mm × h1 mm on the incident side. The detector used was a PIXcel semiconductor pixel detector. 3D (Registered trademark) 0D mode. Angular resolution is 5–6 arcsec.

[0497] The beam size of the X-rays is set as follows: when the incident angle is set to 90°, that is, when the X-rays are incident perpendicularly on the Ga polar surface of the sample substrate, the size of the irradiated area on the Ga polar surface is 5 mm in the direction parallel to the ω axis and 1 mm in the direction perpendicular to the ω axis.

[0498] In the rocking curve determination, X-rays are incident on the sample from a direction perpendicular to the a-axis of the GaN crystal. In other words, the incident surface of the X-rays is parallel to the a-plane of the GaN crystal.

[0499] <Example 2-2>

[0500] As the seed crystal for growing GaN thick films via HVPE, the following seed crystal was used: GaN thick films were grown under the same conditions as in Example 2-1, and the main surface was planarized and reused after the growth layer was separated. This process was performed twice. In other words, a material that had been used three times was used as the seed crystal. Except for the above aspects, the C-side GaN substrate was fabricated in the same manner as in Example 2-1.

[0501] <Example 2-3>

[0502] As a seed crystal for growing GaN thick films via HVPE, a C-plane GaN substrate obtained under the same conditions as in Example 2-1 was used, and the C-plane GaN substrate was fabricated in the same manner as in Example 2-1.

[0503] <Comparative Example 2-1>

[0504] As the seed crystal for growing GaN thick films via HVPE, a C-plane GaN substrate obtained by the same method as the first C-plane GaN substrate used in the manufacturing process of Example 1-1 is used. In other words, a GaN crystal obtained by a manufacturing method comprising: preparing a first substrate having a nitrogen-polar surface; disposing a first pattern mask including a mask portion and a mask opening on the nitrogen-polar surface of the first substrate; growing the GaN crystal through the mask opening of the first pattern mask using an ammonothermal process; and separating the GaN crystal from the first substrate with the first pattern mask disposed thereon, but excluding the steps of disposing a second pattern mask on the nitrogen-polar surface using the separated GaN crystal as a second substrate, and growing the GaN crystal through the mask opening of the second pattern mask using an ammonothermal process. Regarding the HVPE growth conditions, the C-plane GaN substrate is fabricated in the same manner as in Example 2-1.

[0505] The evaluation results of the C-plane GaN substrates obtained in Examples 2-1 to 2-3 and Comparative Example 2-1 are shown in Table 1 below.

[0506] [Table 1]

[0507]

[0508] As shown in Table 1, the GaN substrates of Examples 2-1 to 2-3 have low dislocation densities, and the local strain within the main plane is significantly reduced when fabricating c-plane GaN substrates. In other words, they can be considered GaN crystals that balance reduced local strain within the main plane with excellent crystal quality. Therefore, when the GaN substrates of Examples 2-1 to 2-3 are used as substrates for devices, the manufacturing yield can be improved. It can be considered that the GaN substrates of Examples 2-1 to 2-3 can improve the manufacturing yield, especially for long-wavelength LDs. On the other hand, although the GaN substrate of Comparative Example 2-1 has a low dislocation density, there are more areas with large local strain within the main plane.

[0509] It should be noted that the variation range of the tangent angle in Table 1 records the maximum variation range of the x-direction component and the y-direction component.

[0510] The present invention has been described above with reference to specific embodiments, but these embodiments are presented as examples and do not limit the scope of the invention. The embodiments described in this specification can be modified in various ways without departing from the spirit of the invention, and can be combined with features described through other embodiments within the scope of implementation.

[0511] This application is based on Japanese Patent Application No. 2024-048031, dated March 25, 2024, the contents of which are incorporated herein by reference.

[0512] Explanation of reference numerals in the attached figures

[0513] 100: substrate;

[0514] 101: First Main Page;

[0515] 102: Second main face;

[0516] L: line segment;

[0517] LS1: First line segment;

[0518] LS2: Second line segment;

[0519] 20: Substrate;

[0520] 21: Gallium polar surface;

[0521] 22: Nitrogen polar surface;

[0522] 23: Side view;

[0523] 30: Pattern mask;

[0524] 31: Linear mask opening;

[0525] 40: GaN crystal;

[0526] G: Gap;

[0527] T: Through hole;

[0528] V: gap;

[0529] K: Cross;

[0530] 200: Crystal growth apparatus;

[0531] 201: Autoclave;

[0532] 202: Closed container;

[0533] 202a: Raw material dissolution zone;

[0534] 202b: Crystal growth region;

[0535] 203: Baffle;

[0536] 204: Pt line;

[0537] 205: Vacuum pump;

[0538] 206: Ammonia cylinder;

[0539] 207: Nitrogen cylinder;

[0540] 208: Valve;

[0541] 209: Mass flow meter;

[0542] S: Seed crystal;

[0543] FS: Raw materials;

[0544] β100: Substrate;

[0545] β200: The mask portion of the first pattern mask;

[0546] β300: GaN crystal;

[0547] β301: The opening region of the substrate mask;

[0548] β302: Substrate mask region;

[0549] β303: Merged region;

[0550] β400: The mask portion of the second pattern mask;

[0551] β401: The mask opening of the second pattern mask;

[0552] β403: Exposed area at the base opening;

[0553] β500: GaN crystal;

[0554] 300: HVPE device;

[0555] 301: Reactor;

[0556] 302: Gallium storage unit;

[0557] 303: Base;

[0558] 304: First heater;

[0559] 305: Second heater.

Claims

1. A GaN substrate having an inclination of 0 to 20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The above main face, among which, At least one 0.275cm exists within the main surface. 2 The observation region is an area with a dislocation density of less than 1.0 × 10⁻⁶. 4 cm -2 .

2. The GaN substrate according to claim 1, wherein, The observation area comprises unit region A and unit region B. The dislocation density per unit area A is less than 1.0 × 10⁻⁶. 2 cm -2 , The dislocation density per unit area B is 1.0 × 10⁻⁶. 3 cm -2 above.

3. The GaN substrate according to claim 1, wherein, The observation area is 5.5mm × 5.0mm. In a unit region of 5.5mm × 0.5mm obtained by dividing the observation area into 10 parts, the dislocation density is less than 1.0 × 10⁻⁶. 2 cm -2 The number of unit regions is more than one.

4. The GaN substrate according to any one of claims 1 to 3, wherein, The half-width at half-maximum (WHM) of the (004) XRD oscillation curve of the main face is less than 20 arcsec.

5. The GaN substrate according to any one of claims 1 to 3, wherein, Set the normal direction of the principal surface to the z-direction. When the two directions orthogonal to the z-direction and mutually orthogonal are respectively designated as the x-direction and y-direction. The variation range of the x-direction component of the tangent angle passing through the center of the main surface and extending along the first line in the x-direction, and the variation range of the y-direction component of the tangent angle passing through the center of the main surface and extending along the second line in the y-direction, are both less than 0.2 degrees within a length of 40 mm.

6. The GaN substrate according to any one of claims 1 to 3, wherein, The concentrations of Li, Na, K, Mg, and Ca are all less than 1 × 10⁻⁶. 16 atoms / cm 3 .

7. The GaN substrate according to any one of claims 1 to 3, wherein, The GaN substrate contains F.

8. The GaN substrate according to claim 7, wherein, In addition to F, the GaN substrate contains one or more halogens selected from Cl, Br and I.

9. The GaN substrate according to claim 8, wherein, The GaN substrate contains F and I.

10. The GaN substrate according to claim 7, wherein, The GaN substrate actually contains only F as a halogen element.

11. The GaN substrate according to any one of claims 1 to 3, wherein, H concentration is 5×10 17 atoms / cm 3 Above and 1×10 20 atoms / cm 3 the following.

12. The GaN substrate according to any one of claims 1 to 3, wherein, The GaN substrate is made of material with a thickness of 3140-3200 cm⁻¹ -1 GaN crystals with infrared absorption peaks attributable to gallium vacancy-hydrogen complexes are formed.

13. A method for manufacturing a GaN crystal, comprising the following steps: The process of preparing a first substrate having a nitrogen-polar surface; A process of configuring a first pattern mask comprising a mask portion and a mask opening on the nitrogen polar surface of the first substrate; The process of growing GaN crystals using the ammonothermal method through the mask opening of the first pattern mask to obtain a stacked structure in which GaN crystals are stacked on the nitrogen polar surface of the first substrate through the first pattern mask. The process of separating at least a portion of the GaN crystal grown on the nitrogen polar surface of the first substrate from the stacked structure. The process of planarizing the nitrogen polar surface of the separated GaN crystal; The process of using the separated GaN crystal as a second substrate and configuring a second pattern mask on the planarized nitrogen polar surface, wherein the second pattern mask is configured such that at least a portion of the region grown above the mask opening of the first pattern mask in the nitrogen polar surface of the GaN crystal, which is the second substrate, is covered by the mask portion of the second pattern mask. as well as The process of growing GaN crystals using the ammonothermal method through the mask opening of the second pattern mask.

14. The method for manufacturing GaN crystal according to claim 13, wherein, The second pattern mask is configured such that the merging surface formed on the mask portion of the first pattern mask and the region grown thereon are covered by the mask portion of the second pattern mask in the nitrogen polar surface of the GaN crystal, which serves as the second substrate.

15. The method for manufacturing a GaN crystal according to claim 13, wherein, The second pattern mask is configured such that, in the nitrogen polar surface of the GaN crystal serving as the second substrate, the region grown above the mask opening of the first pattern mask (i.e., the substrate mask opening region) and the region overlapping the substrate mask opening region and the mask opening of the second pattern mask (i.e., the exposed substrate opening region) satisfy the following relationship (I): The area of ​​the exposed region of the substrate opening / the area of ​​the opening region of the substrate mask ≤ 10% ······(I).

16. The method for manufacturing a GaN crystal according to claim 13, wherein, The second pattern mask is configured such that the region grown on the mask opening of the first pattern mask in the nitrogen polar surface of the GaN crystal, which serves as the second substrate, does not overlap with the mask opening of the second pattern mask.

17. A method for manufacturing a GaN crystal, wherein, Using the GaN crystal manufactured by the GaN crystal manufacturing method according to claim 13 as a third substrate, the GaN crystal is grown on a gallium polar surface by the HVPE method.

18. A method for manufacturing a GaN substrate, wherein, A GaN substrate is obtained by slicing a GaN crystal manufactured by the manufacturing method of GaN crystal according to any one of claims 13 to 17.

19. A GaN substrate having an inclination of 0 to 20 degrees relative to the (0001) plane and an area of ​​15 cm². 2 The above main face, among which, The dislocation density of the principal surface is 5.0 × 10⁻⁶. 4 cm -2 the following, For the main surface, the strain evaluation value measured by photoelasticity and calculated based on the following equation (1) exceeds 5 × 10⁻⁶. -5 The area S1 is less than 2.5% of the total area of ​​the main surface; The terms in equation (1) are represented by equations (2) and (3) below. In the formula, δ and ψ are the phase difference and principal axis azimuth angle, respectively, which are birefringence quantities originating from strain; λ is the wavelength of the light source in the photoelasticity measuring device; d is the sample thickness; n0 is the strain-free refractive index relative to the light source wavelength; |p 11 -p 12 | represents the components of the photoelastic tensor, where λ, n0, and |p are... 11 -p 12 |The following conditions must be met: λ=633nm; n0=2.355； |p 11 -p 12 |=0.13。 20. The GaN substrate according to claim 19, wherein, For the main surface, the strain evaluation value measured by photoelasticity and calculated based on equation (1) exceeds 1 × 10⁻⁶. -4 The area S2 is less than 1% of the total area of ​​the main surface.

21. The GaN substrate according to claim 19, wherein, The half-width at half-maximum (WHM) of the (004) XRD oscillation curve of the main face is less than 20 arcsec.

22. The GaN substrate according to claim 19, wherein, Set the normal direction of the principal surface to the z-direction. When the two directions orthogonal to the z-direction and mutually orthogonal are respectively designated as the x-direction and y-direction. The variation range of the x-direction component of the tangent angle passing through the center of the main surface and extending along the first line in the x-direction, and the variation range of the y-direction component of the tangent angle passing through the center of the main surface and extending along the second line in the y-direction, are both less than 0.2 degrees within a length of 40 mm.

23. The GaN substrate according to any one of claims 19 to 22, wherein, Regarding the impurity concentration, the following condition (a) must be met; Condition (a): O concentration is 3 × 10 16 atoms / cm 3 the following.

24. The GaN substrate according to any one of claims 19 to 22, wherein, Regarding the impurity concentration, the following condition (b) must be met; Condition (b): H concentration is 1×10 17 atoms / cm 3 the following.

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