WO2024095449A1

WO2024095449A1 - Gallium nitride single crystal substrate and method for producing same

Info

Publication number: WO2024095449A1
Application number: PCT/JP2022/041170
Authority: WO
Inventors: 俊佑西野; 拓司岡久
Original assignee: 住友電気工業株式会社
Priority date: 2022-11-04
Filing date: 2022-11-04
Publication date: 2024-05-10

Abstract

This gallium nitride single crystal substrate has a circular main surface. The main surface has first dislocation density and second dislocation density comprising two or more values. The average value of the second dislocation density is 5.0×10⁶cm^-2 or less. The standard deviation and average value of the second dislocation density satisfy the following relationship: standard deviation/average value ≤ 0.40. The first dislocation density is obtained by measuring the number of dislocations in each of nine first measurement regions on the main surface, and converting the sum of the number of dislocations into the number of dislocations per 1 cm², wherein the first measurement regions are each a square 100 μm on a side. The second dislocation density is obtained by obtaining a reference area expressed as a value obtained by dividing 100 by the first dislocation density, forming a virtual lattice in which 2-mm squares are laid out on the main surface so that the squares do not overlap each other and the number of the squares arranged in parallel is maximized, measuring the number of dislocations in a second measurement region that has an area of 30% of the reference area and that is set at the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per 1 cm² for each second measurement region.

Description

Gallium nitride single crystal substrate and method for producing same

This disclosure relates to a gallium nitride single crystal substrate and a method for manufacturing the same.

　JP Patent Publication No. 2006-052102 (Patent Document 1) and JP Patent Publication No. 2007-519591 (Patent Document 2) disclose a method for manufacturing a gallium nitride single crystal substrate (hereinafter also referred to as "GaN single crystal substrate") having the following surface. In the above manufacturing method, a mask with a predetermined opening is first placed on a base substrate, and a gallium nitride single crystal (hereinafter also referred to as "GaN single crystal") having irregularities including pits that are triangular cross-sectional depressions on the surface is grown from the opening. Next, the GaN single crystal is grown under conditions that flatten the irregularities. Finally, the GaN single crystal is processed to manufacture a GaN single crystal substrate. It is said that this concentrates dislocations in the pits and annihilates them, and uniformly disperses the remaining dislocations, thereby making it possible to obtain a surface with low dislocation density and a substantially uniform dislocation density distribution. JP 2021-031329 A (Patent Document 3) discloses a c-plane GaN single crystal substrate that achieves low dislocation density by using a manufacturing method similar to those described in Patent Documents 1 and 2 above.

JP 2006-052102 A JP 2007-519591 A JP 2021-031329 A

A gallium nitride single crystal substrate according to the present disclosure is a gallium nitride single crystal substrate having a circular main surface, the main surface having a first dislocation density and two or more second dislocation densities, the average value of the second dislocation density being 5.0×10 ⁶ cm ⁻² or less, the standard deviation and the average value of the second dislocation density satisfy the relationship of standard deviation/average value≦0.40, the standard deviation being in cm ⁻² , and the first dislocation density being determined by measuring the number of dislocations in nine first measurement regions on the main surface, the first measurement regions being squares each having a side of 100 μm, and calculating the sum of the number of dislocations per cm of the dislocations. The second dislocation density is obtained by converting the number of dislocations per ^square meter into the number of dislocations per square meter, the second dislocation density being obtained by obtaining a reference area represented by dividing 100 by the first dislocation density, forming a virtual lattice on the main surface in which squares each having a side length of 2 mm are laid out in parallel as many times as possible without overlapping each other, and measuring the number of dislocations in second measurement regions each having an area that is 30% of the reference area and set in the center of each of the squares constituting the lattice, and measuring the number of dislocations in each of the second measurement regions. ² , and when the diameter of the gallium nitride single crystal substrate is represented by D and two axes on the main surface that pass through the center of the main surface and are orthogonal to each other at the center are represented by the X-axis and Y-axis, the X-axis and Y-axis coordinates (X, Y) of the center point of the first measurement region are (0, 0), (D/4-5, 0), (0, D/4-5), (-(D/4-5), 0), (0, -(D/4-5)), (D/2-10, 0), (0, D/2-10), (-(D/2-10), 0) and (0, -(D/2-10)), and the units of D and X and Y in the coordinates (X, Y) are mm.

The method for manufacturing a gallium nitride single crystal substrate according to the present disclosure is a method for manufacturing a gallium nitride single crystal substrate having a circular main surface, and includes the steps of: preparing a base substrate including a growth substrate and a gallium nitride film to be disposed on the growth substrate; disposing a mask having a structure in which shielding portions and openings are repeated in the width direction on the base substrate; growing a first layer made of a gallium nitride single crystal having a facet structure from the base substrate by a hydride vapor phase epitaxy method; and growing a second layer made of the gallium nitride single crystal having a {0001} growth surface on the first layer. and a step of obtaining the gallium nitride single crystal substrate by removing the base substrate and the first layer from the structure and processing the second layer, the thickness of the mask being 0.2 μm or less, the width of one pitch of the mask, which is composed of the width of the shielding portion and the width of the opening, being 10 μm or less, the percentage of the width of the opening relative to the width of one pitch of the mask being 10% or more and 50% or less, and the thickness of the first layer being 20 μm or less.

FIG. 1 is a schematic diagram illustrating the distribution of dislocations in a gallium nitride single crystal substrate according to this embodiment. FIG. 2 is a schematic diagram illustrating the distribution of dislocations in a conventional gallium nitride single crystal substrate. FIG. 3 is an explanatory diagram illustrating nine first measurement regions on a main surface set to determine a reference area in a gallium nitride single crystal substrate according to this embodiment, and the coordinates (X, Y) of their center points. FIG. 4 is an explanatory diagram illustrating a virtual lattice in which squares, each 2 mm on a side, are arranged in parallel on the main surface so as to maximize the number of squares without overlapping each other, in order to determine the second dislocation density in the gallium nitride single crystal substrate according to this embodiment, and a second measurement region. FIG. 5 is a flow chart showing an example of a method for manufacturing a gallium nitride single crystal substrate according to this embodiment. FIG. 6 is a schematic diagram illustrating the structure of a mask used to obtain a gallium nitride single crystal substrate according to this embodiment. FIG. 7 is a schematic cross-sectional view illustrating the state in which the mask of FIG. 6 is disposed on the base substrate. FIG. 8 is a schematic cross-sectional view illustrating a state in which a first layer (single crystal GaN) is formed on a gallium nitride film in the method for manufacturing a gallium nitride single crystal substrate according to this embodiment. FIG. 9 is a schematic cross-sectional view illustrating a structure in which a base substrate, a first layer, and a second layer are laminated in this order in the method for producing a gallium nitride single crystal substrate according to this embodiment.

[Problem to be solved by this disclosure]
In the GaN single crystal substrates of Patent Documents 1 and 2, dislocations are concentrated in the pits as described above, and the remaining dislocations are uniformly dispersed to grow the GaN single crystal, so that a surface layer with a substantially uniform dislocation density distribution can be obtained. However, according to Non-Patent Document 1, it is reported that the inclination at which dislocations are dispersed as the crystal grows is about several degrees with respect to the direction of crystal growth. Therefore, a sufficient crystal thickness is required to obtain a surface layer with a substantially uniform dislocation density distribution. On the other hand, according to Patent Documents 1 and 2, it is difficult to say that the GaN single crystal substrate is obtained after growing a GaN single crystal with a thickness necessary for uniform dispersion of dislocations. Therefore, it is considered that the dislocation density distribution on the surface of the GaN single crystal substrates of Patent Documents 1 and 2 is substantially uneven and non-uniform. In particular, although the above substrates have relatively high dislocation regions periodically generated on their surfaces, it is understood that the "substantially uniform dislocation density distribution" is mentioned by arbitrarily setting the unit area used to measure the dislocation density. The GaN single crystal substrate of Patent Document 3 is manufactured by a method similar to that of the GaN single crystal substrates of Patent Documents 1 and 2, and is therefore considered to have the same inherent problems.

In addition, in most of the GaN single crystal substrates described in Patent Documents 1 to 3, pits do not occur uniformly within the surface during the manufacturing process. It is generally known that pits occur randomly (non-uniformly) within the surface, except for the FIELO method used in Example 4 of Patent Document 1. When pits occur non-uniformly within the surface, the dislocation density distribution also tends to be non-uniform. Therefore, a gallium nitride single crystal substrate with a uniform dislocation density distribution within the surface, which enables stable improvement of device characteristics, has not yet been obtained, and its development is eagerly awaited.

In view of the above, the present disclosure aims to provide a gallium nitride single crystal substrate that has a uniform in-plane dislocation density distribution and can stably improve device characteristics, and a method for manufacturing the same.

[Effects of the present disclosure]
According to the above, it is possible to provide a gallium nitride single crystal substrate having a uniform in-plane dislocation density distribution and capable of stably improving device characteristics, and a method for manufacturing the same.

[Overview of the embodiment]
The following is an outline of an embodiment of the present disclosure. The present inventors have made extensive studies to solve the above problems, and have completed the present disclosure. First, the present inventors have focused on the structure of a mask used for epitaxially growing a GaN single crystal, and on growing the GaN single crystal under specific growth conditions during the epitaxial growth. Specifically, in a mask having a structure in which a shielding portion and an opening are repeated in the width direction, the inventors have come up with the idea of narrowing the width of one pitch consisting of the width of the shielding portion and the width of the opening (specifically, the width of one pitch is set to 10 μm or less), and setting the percentage of the width of the opening to 10 to 50%. Furthermore, the conditions for growing a GaN single crystal (first layer) on whose surface the pits are formed using a mask having the above structure were controlled so that the thickness of the first layer was thin, specifically, so that the thickness was 20 μm or less. The researchers discovered that this makes it possible to uniformly generate pits on the growth surface of the first layer and to control the degree to which dislocations are concentrated in the pits, thereby completing a gallium nitride single crystal substrate according to the present disclosure having a uniform in-plane dislocation density distribution.

Next, embodiments of the present disclosure will be listed and described.
[1] A gallium nitride single crystal substrate according to one aspect of the present disclosure is a gallium nitride single crystal substrate having a circular main surface, the main surface having a first dislocation density and two or more second dislocation densities, the average value of the second dislocation density being 5.0 × 10 ⁶ cm ^-2 or less, the standard deviation and the average value of the second dislocation density satisfy a relationship of standard deviation/average value≦0.40, the standard deviation being in cm ^-2 , and the first dislocation density being determined by measuring the number of dislocations in nine first measurement regions on the main surface, the first measurement region being a square with one side measuring 100 μm, and calculating the sum of the number of dislocations per cm of the dislocations. The second dislocation density is obtained by converting the number of dislocations per ^square meter into the number of dislocations per square meter, the second dislocation density being obtained by obtaining a reference area represented by dividing 100 by the first dislocation density, forming a virtual lattice on the main surface in which squares each having a side length of 2 mm are laid out in parallel as many times as possible without overlapping each other, and measuring the number of dislocations in second measurement regions each having an area that is 30% of the reference area and set in the center of each of the squares constituting the lattice, and measuring the number of dislocations in each of the second measurement regions. ² , and when the diameter of the gallium nitride single crystal substrate is represented by D and two axes on the main surface that pass through the center of the main surface and are orthogonal to each other at the center are represented by the X-axis and Y-axis, the X-axis and Y-axis coordinates (X, Y) of the center point of the first measurement region are (0, 0), (D/4-5, 0), (0, D/4-5), (-(D/4-5), 0), (0, -(D/4-5)), (D/2-10, 0), (0, D/2-10), (-(D/2-10), 0) and (0, -(D/2-10)), and the units of D and X and Y in the coordinates (X, Y) are mm.

Gallium nitride single crystal substrates with these characteristics have a uniform in-plane dislocation density distribution, which allows for stable improvement of device characteristics.

[2] The diameter of the gallium nitride single crystal substrate is preferably 50 mm or more and 155 mm or less. This allows the gallium nitride single crystal substrate with a diameter of 50 mm or more and 155 mm or less to have a uniform in-plane dislocation density distribution, thereby providing the effect of stably improving device characteristics.

[3] The gallium nitride single crystal substrate preferably contains impurity atoms, the impurity atoms being either or both of silicon and germanium, and the concentration of the impurity atoms is 1.0×10 ¹⁸ cm ^-3 or more and 5.0×10 ¹⁸ cm ^-3 or less. This makes it possible to provide an effect of stably improving device characteristics by providing a uniform in-plane dislocation density distribution in an n-type (electron donor type) gallium nitride single crystal substrate containing either or both of silicon and germanium.

[4] It is preferable that the main surface has two or more third dislocation densities, the standard deviation and average value of the third dislocation densities satisfy the relationship of standard deviation/average value≦0.35, and the third dislocation density is determined by measuring the number of dislocations in third measurement regions each having an area of 50% of the reference area set in the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per ^cm2 for each of the third measurement regions. This makes the in-plane dislocation density distribution more uniform, thereby making it possible to more stably improve device characteristics.

[5] It is preferable that the main surface has a fourth dislocation density of 2 or more, the standard deviation and average value of the fourth dislocation density satisfy the relationship of standard deviation/average value≦0.53, and the fourth dislocation density is determined by measuring the number of dislocations in fourth measurement regions having an area of 10% of the reference area set in the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per ^cm2 for each of the fourth measurement regions. This makes the in-plane dislocation density distribution more uniform, thereby making it possible to more stably improve device characteristics.

[6] A method for manufacturing a gallium nitride single crystal substrate according to one embodiment of the present disclosure is a method for manufacturing a gallium nitride single crystal substrate having a circular main surface, comprising the steps of: preparing a base substrate including a growth substrate and a gallium nitride film to be disposed on the growth substrate; disposing a mask having a structure in which shielding portions and openings are repeated in the width direction on the base substrate; growing a first layer made of a gallium nitride single crystal having a facet structure from the base substrate by a hydride vapor phase epitaxy method; and growing a first layer made of the gallium nitride single crystal having a facet structure on the first layer, the first layer being made of the gallium nitride single crystal whose growth surface is a {0001} plane. The method includes a step of growing a second layer on the mask to obtain a structure including the base substrate, the first layer, and the second layer in this order, and a step of removing the base substrate and the first layer from the structure and processing the second layer to obtain the gallium nitride single crystal substrate, in which the thickness of the mask is 0.2 μm or less, the width of one pitch of the mask consisting of the width of the shielding portion and the width of the opening is 10 μm or less, the percentage of the width of the opening relative to the width of one pitch of the mask is 10% to 50%, and the thickness of the first layer is 20 μm or less. A manufacturing method having such characteristics can obtain a gallium nitride single crystal substrate having a uniform in-plane dislocation density distribution and capable of stably improving device characteristics.

[7] The length direction of the mask is preferably parallel to the <11-20> or <1-100> direction of the gallium nitride single crystal that constitutes the gallium nitride film on the base substrate. This makes it possible to obtain a gallium nitride single crystal substrate with a more uniform in-plane dislocation density distribution, enabling more stable improvement of device characteristics.

[8] The thickness of the second layer is preferably 1000 μm or less. This makes it possible to obtain a gallium nitride single crystal substrate from a GaN single crystal having a relatively thin second layer, which has a uniform in-plane dislocation density distribution and can stably improve device characteristics.

[Details of the embodiment]
Hereinafter, one embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described in more detail, but the present disclosure is not limited thereto. In the following description, the drawings may be referred to, and the same or corresponding elements in this specification and the drawings will be given the same reference numerals, and the same description will not be repeated. Furthermore, in the drawings, the scale is appropriately adjusted to make each component easy to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

In this specification, expressions in the form "A-B" refer to the upper and lower limits of a range (i.e., greater than or equal to A and less than or equal to B). If no unit is stated for A, and only B, the units of A and B are the same. Furthermore, when compounds are expressed in chemical formulas in this specification, if the atomic ratio is not specifically limited, this includes all conventionally known atomic ratios and should not necessarily be limited to only those within the stoichiometric range.

In this specification, the "main surface" of a gallium nitride single crystal substrate means both of the two circular faces of the GaN single crystal substrate. In the above gallium nitride single crystal substrate, if at least one of the two faces satisfies the scope of the claims of this disclosure, it falls within the technical scope of the present invention. Furthermore, in this specification, the "face" used in the term "in-plane" means the "main surface." Furthermore, when the diameter of a gallium nitride single crystal substrate is described as "50 mm," this means that the diameter is approximately 50 mm (approximately 50 to 55.5 mm), or that it is 2 inches. When the diameter is described as "100 mm," this means that the diameter is approximately 100 mm (approximately 95 to 105 mm), or that it is 4 inches. When the diameter is described as "150 mm," this means that the diameter is approximately 150 mm (approximately 145 to 155 mm), or that it is 6 inches. The diameter can be measured using a conventionally known outer diameter measuring device such as a caliper.

In this specification, "dislocation" and "dislocation density" refer to "threading dislocations" identified by applying a multiphoton excitation photoluminescence method to the main surface, and "the number of threading dislocations per ¹ cm2 of the main surface," respectively. The above-mentioned "threading dislocations" are known to be non-radiative recombination centers in gallium nitride single crystals, and appear as dark spots when the main surface of a GaN single crystal substrate is observed using a multiphoton excitation microscope or the like. The above-mentioned "threading dislocations" are not academically synonymous with crystal defects, but can be regarded as equivalent to crystal defects in this technical field.

In this specification, a "pit" refers to an inverted hexagonal pyramid or inverted dodecagonal pyramid shaped depression that is formed by being surrounded by flat growth surfaces ((0001) surfaces) when a GaN single crystal is grown by hydride vapor phase epitaxy using the (0001) surface as the growth surface. In this specification, a "facet structure" refers to a surface structure that includes the growth surface ((0001) surface) of the GaN single crystal and the slope of the pit, called a facet surface, when a GaN single crystal is grown by hydride vapor phase epitaxy using the (0001) surface as the growth surface.

In the crystallographic descriptions in this specification, individual orientations are indicated with [ ], collective orientations with < >, individual faces with ( ), and collective faces with { }. In addition, when a crystallographic index is negative, it is usually indicated by placing a "- (bar)" above the number, but in this specification, a negative sign is placed before the number.

[Gallium nitride single crystal substrate]
The gallium nitride single crystal substrate (GaN single crystal substrate) according to this embodiment is a GaN single crystal substrate having a circular main surface. The main surface has a first dislocation density and a second dislocation density of 2 or more. The average value of the second dislocation density is 5.0×10 ⁶ cm ⁻² or less. The standard deviation and the average value of the second dislocation density satisfy the relationship of standard deviation/average value≦0.40, and the unit of the standard deviation is cm ⁻² . The first dislocation density is obtained by measuring the number of dislocations in nine first measurement regions on the main surface, each of which is a square with one side of 100 μm, and converting the sum of the number of dislocations into the number of dislocations per cm ² . The second dislocation density is determined by obtaining a reference area expressed as a value obtained by dividing 100 by the first dislocation density, forming a virtual lattice on the main surface in which squares, each having a side length of 2 mm, are laid out in parallel as many times as possible without overlapping each other, measuring the number of dislocations in second measurement regions having an area of 30% of the reference area set in the centers of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per ^cm2 for each of the second measurement regions. When the diameter of the gallium nitride single crystal substrate is represented by D and two axes on the main surface that pass through the center of the main surface and intersect at right angles at the center are represented by the X-axis and Y-axis, the X-axis and Y-axis coordinates (X, Y) of the center point of the first measurement region are (0, 0), (D/4-5, 0), (0, D/4-5), (-(D/4-5), 0), (0, -(D/4-5)), (D/2-10, 0), (0, D/2-10), (-(D/2-10), 0) and (0, -(D/2-10)), and the units of D and X and Y in the coordinates (X, Y) are mm.

It is preferable that the main surface has two or more third dislocation densities, and the standard deviation and average value of the third dislocation densities satisfy the relationship of standard deviation/average value≦0.35. The third dislocation density is determined by measuring the number of dislocations in third measurement regions having an area of 50% of the reference area set in the centers of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per ^cm2 for each of the third measurement regions.

Furthermore, it is preferable that the main surface has a fourth dislocation density of 2 or more, and the standard deviation and average value of the fourth dislocation density satisfy the relationship of standard deviation/average value≦0.53. The fourth dislocation density is determined by measuring the number of dislocations in fourth measurement regions having an area of 10% of the reference area set in the centers of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per ^cm2 for each of the fourth measurement regions.

A GaN single crystal substrate with these characteristics has a uniform in-plane dislocation density distribution, making it possible to stably improve device characteristics. For example, when a light-emitting device is constructed by stacking a light-emitting layer on the GaN single crystal substrate, the variation in the light-emitting intensity of the light-emitting device can be suppressed. The reason why the GaN single crystal substrate according to this embodiment provides the above-mentioned effects is presumably based on the following characteristics of the GaN single crystal that constitutes the GaN single crystal substrate.

1 is a schematic diagram illustrating the distribution of dislocations in the gallium nitride single crystal substrate according to this embodiment. As shown in FIG. 1, the GaN single crystal substrate 1 according to this embodiment has a uniform distribution of dislocations t on the main surface 11. The reason for this is presumably because the GaN single crystal constituting the GaN single crystal substrate 1 is epitaxially grown in the order of the first layer and the second layer on the base substrate based on the method described in the section [Method of manufacturing a gallium nitride single crystal substrate] below. In this epitaxial growth, the first layer is first formed on a mask arranged on the base substrate. The mask has a structure in which a shielding portion and an opening are repeated in the width direction, and is characterized in that the width of one pitch consisting of the width of the shielding portion and the width of the opening is narrow (specifically, the width of one pitch is 10 μm or less). As a result, the first layer can promote the generation of regular pits on the growth surface of the GaN single crystal, thereby contributing to the uniform distribution of dislocations t on the main surface 11. Furthermore, the mask has a small percentage of the width of the opening relative to the width of one pitch, at 10-50%. This suppresses the amount of dislocations propagating from the base substrate to the first layer. In addition, because the thickness of the mask is 0.2 μm or less, the number of new dislocations that are generated during the growth of the first layer can also be suppressed.

In addition, in the epitaxial growth, the growth conditions are changed when the thickness of the first layer is thin (specifically, 20 μm or less), so that a second layer with a flat growth surface is formed on the first layer. This allows the second layer to be grown on the first layer before dislocations are concentrated in the pits more than necessary. In other words, from the early stage of the epitaxial growth, dislocations can be dispersed in a direction perpendicular to the direction of crystal growth, thereby contributing to a uniform distribution of dislocations t on the main surface 11. In the GaN single crystal constituting the GaN single crystal substrate 1, the amount of dislocations propagating from the base substrate to the first layer is suppressed as described above, and the number of dislocations newly generated during the growth of the first layer is also suppressed, so there is no need to concentrate dislocations more than necessary in the pits and annihilate them for the purpose of reducing dislocations. From the above, it is considered that the GaN single crystal substrate 1 according to this embodiment has a uniform in-plane dislocation density distribution based on the characteristics of the GaN single crystal described above.

On the other hand, in the conventional GaN single crystal substrate 101 as shown in FIG. 2, there are scattered regions (i.e., high dislocation regions) in which dislocations t are concentrated like clusters on the main surface 11, and it is understood that the dislocation density distribution is non-uniform. The reason is that the GaN single crystal constituting the GaN single crystal substrate 101 is different from that constituting the GaN single crystal substrate 1 according to this embodiment. FIG. 2 is a schematic diagram explaining the distribution of dislocations in a conventional gallium nitride single crystal substrate. That is, the GaN single crystal constituting the conventional GaN single crystal substrate 101 in the above-mentioned Patent Documents 1 and 2, etc., is epitaxially grown in the order of a first layer and a second layer on a base substrate, like that constituting the GaN single crystal substrate 1 according to this embodiment, but first, the structure of the mask used for the epitaxial growth is different. Alternatively, the first layer and the second layer made of GaN single crystal are epitaxially grown without placing a mask on the base substrate. For this reason, the GaN single crystal that constitutes the conventional GaN single crystal substrate 101 randomly develops pits during the growth process, and the amount of dislocations that propagate from the base substrate to the first layer can be significant.

Secondly, in the conventional GaN single crystal substrate 101, dislocations are concentrated in the pits formed on the surface of the first layer and annihilated, and then the remaining dislocations are dispersed in the growth of the second layer, so that regions with relatively high dislocation density are periodically generated. As a result, it is estimated that the conventional GaN single crystal substrate 101 has a distribution of dislocations t as shown in FIG. 2. In this case, even if the average value of the second dislocation density is 5.0×10 ⁶ cm ⁻² or less, the main surface 11 of the conventional GaN single crystal substrate 101 cannot satisfy the relationship of standard deviation/average value≦0.40 for the standard deviation and average value of the second dislocation density. The GaN single crystal substrate according to this embodiment will be described in detail below. The term second dislocation density is defined as a density obtained by a calculation method described later.

<Diameter>
The diameter of the GaN single crystal substrate is preferably 50 mm or more and 155 mm or less. In other words, the diameter of the GaN single crystal substrate is preferably 2 inches or more and 6 inches or less. Here, regarding the diameter of the GaN single crystal substrate, even if the main surface has a shape that is not geometrically circular due to the influence of OF, IF, etc., the main surface is considered to have a circular shape before the OF, IF, etc. are formed, and the size (diameter) of the main surface is determined.

<Main surface>
The GaN single crystal substrate according to this embodiment has a circular main surface as described above. In this specification, the term "circular shape" representing the shape of the main surface includes a geometric circular shape, as well as a shape in which the main surface does not form a geometric circular shape by forming at least one of a notch, an orientation flat (hereinafter also referred to as "OF"), or an index flat (hereinafter also referred to as "IF") on the periphery of the main surface. Here, the term "shape in which the main surface does not form a geometric circular shape" refers to a shape in which, among the line segments extending from any point on the periphery of the main surface to the center of the main surface, the line segments extending from any point on the notch, OF, and IF to the center of the main surface have shorter lengths. Furthermore, the term "shape in which the main surface does not form a geometric circular shape" also includes a shape in which the lengths of all the line segments extending from any point on the periphery of the main surface to the center of the main surface are not necessarily the same due to the shape of the gallium nitride single crystal (hereinafter also referred to as "GaN single crystal") that is the raw material of the GaN single crystal substrate. In this case, the center of the main surface refers to the position of the center of gravity, and the diameter of the GaN single crystal substrate refers to the length of the longest line segment that extends from any point on the outer periphery of the GaN single crystal substrate, passing through the center of the main surface, to another point on the outer periphery.

(Dislocation Density)
The main surface has a first dislocation density and a second dislocation density of 2 or more. The average value of the second dislocation density is 5.0×10 ⁶ cm ⁻² or less. The standard deviation and the average value of the second dislocation density satisfy the relationship of standard deviation/average value≦0.40. The unit of the standard deviation is cm ⁻² . Furthermore, it is preferable that the main surface has a third dislocation density of 2 or more, and the standard deviation and average value of the third dislocation density satisfy the relationship of standard deviation/average value≦0.35. It is also preferable that the main surface has a fourth dislocation density of 2 or more, and the standard deviation and average value of the fourth dislocation density satisfy the relationship of standard deviation/average value≦0.53.

In the above GaN single crystal substrate, the standard deviation and average value of the second dislocation density satisfying the relationship of standard deviation/average value≦0.40 means that the in-plane dislocation density distribution is uniform. In addition to the above, the standard deviation and average value of the third dislocation density satisfying the relationship of standard deviation/average value≦0.35 and the standard deviation and average value of the fourth dislocation density satisfying the relationship of standard deviation/average value≦0.53 are preferable because they mean that the in-plane dislocation density distribution is more uniform in the above GaN single crystal substrate. Here, the standard deviation/average value of the second dislocation density, the third dislocation density, and the fourth dislocation density (hereinafter also referred to as "coefficient of variation") are indices that the present inventors have found in order to appropriately evaluate the uniformity of the in-plane dislocation density distribution. On the other hand, the first dislocation density is necessary to determine the reference area used to calculate the above second dislocation density, third dislocation density, and fourth dislocation density.

The inventors have noticed that if the in-plane dislocation density distribution is uniform in a GaN single crystal substrate, the coefficient of variation of the dislocation density is consistently low, regardless of the size of the unit area used to calculate the dislocation density. In other words, if the in-plane dislocation density distribution is uniform in a GaN single crystal substrate, the coefficient of variation of one dislocation density calculated based on one unit area is comparable to the coefficient of variation of another dislocation density calculated based on another unit area, and both are low. Under such a premise, in order to properly evaluate the uniformity of the in-plane dislocation density distribution, the inventors first set an area on the main surface where 100 dislocations exist as a reference area for calculating the dislocation density (hereinafter also referred to as the "reference area"), and calculated the dislocation density in a unit area smaller than the reference area (for example, an area that is 50%, 30%, or 10% of the reference area), and calculated the above-mentioned coefficient of variation from the average value and standard deviation. As a result, it was discovered that when the above-mentioned coefficient of variation of the dislocation density calculated for a unit area smaller than the reference area is equal to or less than a predetermined value described below, the in-plane dislocation density distribution in the GaN single crystal substrate becomes uniform, and device characteristics can be stably improved.

For example, it has been found that when the dislocation density (corresponding to the second dislocation density) of the GaN single crystal substrate according to this embodiment is calculated using an area that is 30% of the reference area as a unit area, if the coefficient of variation is 0.40 or less, the in-plane dislocation density distribution is uniform and the device characteristics can be stably improved. In addition, in order to obtain the above effect, it has been found that when the dislocation density (corresponding to the third dislocation density) of the GaN single crystal substrate is calculated using an area that is 50% of the reference area as a unit area, the coefficient of variation is preferably 0.35 or less, and when the dislocation density (corresponding to the fourth dislocation density) of the GaN single crystal substrate is calculated using an area that is 10% of the reference area as a unit area, the coefficient of variation is preferably 0.53 or less. Specific methods for calculating the second dislocation density, the third dislocation density, and the fourth dislocation density are described below.

FIG. 3 is an explanatory diagram illustrating nine first measurement regions on the main surface set to determine the reference area in the gallium nitride single crystal substrate according to this embodiment, and the coordinates (X, Y) of their center points. FIG. 4 is an explanatory diagram illustrating a virtual lattice in which squares with sides of 2 mm are laid out on the main surface in such a way that the greatest number of squares are arranged in parallel without overlapping each other, and the second measurement regions, in order to determine the second dislocation density in the gallium nitride single crystal substrate according to this embodiment. The second dislocation density can be determined as follows, with reference to FIGS. 3 and 4.

First, as shown in FIG. 3, nine first measurement areas A1 are set on the main surface 11, and the number of dislocations is measured in each of the first measurement areas A1. In FIG. 3, the first measurement area A1 is a square area with one side of 100 μm. If the diameter of the GaN single crystal substrate 1 is represented by D, and the two axes on the main surface 11 that pass through the center of the main surface and are perpendicular to each other at the center are the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the center point C of the first measurement area A1 are (0, 0), (D/4-5, 0), (0, D/4-5), (-(D/4-5), 0), (0, -(D/4-5)), (D/2-10, 0), (0, D/2-10), (-(D/2-10), 0), and (0, -(D/2-10)). The units of D and X and Y in the coordinates (X, Y) are mm.

The number of dislocations can be obtained by the following method. A multiphoton excitation photoluminescence method is applied to the main surface 11 of the GaN single crystal substrate, and the above-mentioned first measurement area A1 set on the main surface 11 is observed using a multiphoton excitation microscope. The above observation can be performed, for example, by forming an image on a CCD with a 5x objective lens. In this case, the image (one field of view) displayed on an external monitor connected to this microscope corresponds to a 2.5 mm x 2.0 mm range including the first measurement area A1 on the main surface 11 of the GaN single crystal substrate 1. Therefore, the number of dark spots that appear in an image obtained by electronically enlarging the central part of the image (a size of 0.1 mm x 0.1 mm that can be considered to be the first measurement area A1), that is, the number of dislocations, is counted. However, if the image quality of the magnified image is poor, a high-magnification image can be obtained by setting the magnification of the objective lens to 10 to 100 times, and further combining electronic magnification to count the number of dark spots in the central part of the high-magnification image (a size of 0.1 mm x 0.1 mm that can be considered as the first measurement area A1). Next, the total number of dark spots measured in the nine first measurement areas A1 is calculated, and this is converted into the number of dislocations per ^cm2 to obtain the first dislocation density. Furthermore, the above-mentioned reference area can be calculated by dividing 100 by the first dislocation density. The unit of the reference area can be, for example, ^μm2 .

Next, as shown in FIG. 4, a virtual lattice G is formed on the main surface 11 in which squares with sides of 2 mm are laid out in the greatest number of parallel rows without overlapping each other. Here, "squares laid out in the greatest number of parallel rows without overlapping each other" on the main surface 11 means that when the squares are laid out in the greatest number of parallel rows without overlapping each other on the main surface 11, if the squares overlap with the periphery of the main surface 11 and its outside, the squares are excluded from being elements that make up the virtual lattice G. This is because the number of dislocations varies greatly from substrate to substrate in the region near the periphery, including the periphery of the main surface 11 of the GaN single crystal substrate 1, and is generally not used as a material for semiconductor devices.

Furthermore, a second measurement area A2 is set in the center of each of the squares constituting the lattice G. The second measurement area A2 has an area of 30% of the reference area. Next, the second measurement area A2 is observed using the multiphoton excitation microscope described above. In this observation, the magnification of the objective lens is appropriately selected so that at least the size of the second measurement area A2 is included in an image (one field of view) displayed on an external monitor connected to this microscope. Then, the number of dark spots, i.e., dislocations, that appear in the second measurement area A2 observed using the multiphoton excitation microscope are counted, and the number of dark spots is converted into the number of dislocations per ^cm2 to calculate the second dislocation density. For example, when the dislocation density in the reference area is 1.0 x ¹⁰⁶ cm ^-2 , the size of the second measurement area A2, which is 30% of the reference area, is 0.05 mm x 0.05 mm. In this case, a high-magnification image (size of 0.125 mm x 0.1 mm) is projected on an external monitor using a 100x objective lens, the number of dark spots in the central part (size of 0.05 mm x 0.05 mm) of the high-magnification image is counted, and the number of dark spots is converted into the number of dislocations per ^cm2 , whereby the second dislocation density can be calculated. Next, the above-mentioned observation is performed every time the GaN single crystal substrate 1 is moved at a pitch of 2 mm in the vertical and horizontal directions, thereby calculating the second dislocation density for all the second measurement areas A2 set in the virtual lattice G on the main surface 11. Finally, the average value and standard deviation of the second dislocation density are calculated from the second dislocation density calculated for each of the second measurement areas A2, and thus the fluctuation rate can also be calculated.

The third dislocation density and the fourth dislocation density can be calculated in the same manner as the second dislocation density calculation method, except that the areas of the third measurement region and the fourth region, which are set in the center of the squares that make up the virtual lattice G, are 50% and 10% of the reference area, respectively. Furthermore, the average value, standard deviation and coefficient of variation of the third dislocation density can be calculated from the third dislocation density and the fourth dislocation density calculated for each third measurement region and each fourth measurement region, and the average value, standard deviation and coefficient of variation of the fourth dislocation density can be calculated.

Here, as described above, the average value of the second dislocation density is 5.0×10 ⁶ cm ⁻² or less. The average value of the second dislocation density is preferably 3.5×10 ⁶ cm ⁻² or less. The lower limit of the average value of the second dislocation density is ideally 0 cm ⁻² , but it is realistic to set it to at least 1.0×10 ³ cm ⁻² or more from the physical properties of the GaN single crystal. Furthermore, the average value of the third dislocation density and the average value of the fourth dislocation density can be approximately the same as the average value of the second dislocation density, taking into account the effects of the present disclosure. Therefore, the average values of the third dislocation density and the fourth dislocation density are preferably 5.0×10 ⁶ cm ⁻² or less, and more preferably 3.5×10 ⁶ cm ⁻² or less. This makes it possible to provide a GaN single crystal substrate with reduced dislocation density.

Furthermore, in the above GaN single crystal substrate, from the viewpoint of making the in-plane dislocation density distribution more uniform, it is preferable that the standard deviation and average value of the second dislocation density satisfy the relationship of standard deviation/average value≦0.40 (i.e., the coefficient of variation is 0.40 or less). It is more preferable that the standard deviation and average value of the third dislocation density satisfy the relationship of standard deviation/average value≦0.34 (i.e., the coefficient of variation is 0.34 or less), and that the standard deviation and average value of the fourth dislocation density satisfy the relationship of standard deviation/average value≦0.50 (i.e., the coefficient of variation is 0.50 or less). Here, the lower limit of the coefficient of variation of the above second dislocation density, third dislocation density, and fourth dislocation density is ideally 0, but it is realistic that it is at least 0.10 or more due to the physical properties of GaN single crystal.

(impurity atoms: dopants)
The GaN single crystal substrate preferably contains impurity atoms. In this case, the impurity atoms are both or either of silicon (Si) and germanium (Ge), and the concentration of the impurity atoms is 1.0×10 ¹⁸ cm ⁻³ or more and 5.0×10 ¹⁸ cm ⁻³ or less. This can provide an effect of stably improving device characteristics in an n-type (electron-donating) GaN single crystal substrate containing both or either of Si and Ge. In particular, by containing impurity atoms in the above-mentioned concentration range, it is possible to provide a GaN single crystal substrate suitable for device formation, for example, because it is easy to form an n-type electrode. The atomic concentration of the impurity atoms can be measured by using GDMS (glow discharge mass spectrometry). Furthermore, the carrier concentration of the GaN single crystal substrate can be calculated based on the measured value of the resistivity of the GaN single crystal substrate obtained by the Van der Pauw method.

The GaN single crystal substrate can be made into an n-type GaN single crystal substrate with a high carrier concentration by introducing a gas containing the above-mentioned impurity atoms during epitaxial growth of the GaN single crystal constituting the substrate. For example, in the case of Si doping, the gas containing the impurity atoms can be _{tetrachlorosilane} ( _SiCl4 ) gas, dichlorosilane ( _SiH2Cl2 ) gas, or silane ( _SiH4 ) gas. In the case of Ge doping, the gas can be tetrachlorogermane ( _GeCl4 ) gas, _{dichlorogermane} ( _GeH2Cl2 ) gas, or germane ( _GeH4 ) gas.

[Method for manufacturing gallium nitride single crystal substrate]
The manufacturing method of the gallium nitride single crystal substrate (GaN single crystal substrate) according to this embodiment is preferably a manufacturing method of the GaN single crystal substrate having the circular main surface described above, and may include, for example, the following steps. That is, the manufacturing method of the GaN single crystal substrate includes the steps of preparing a base substrate including a growth substrate and a gallium nitride film disposed on the growth substrate, disposing a mask having a structure in which a shielding portion and an opening portion are repeated in the width direction on the base substrate, growing a first layer made of a gallium nitride single crystal having a facet structure from the base substrate by hydride vapor phase epitaxy, growing a second layer made of the gallium nitride single crystal having a {0001} plane on the first layer to obtain a structure including the base substrate, the first layer, and the second layer in this order, and removing the base substrate and the first layer from the structure and processing the second layer to obtain the GaN single crystal substrate. In particular, the thickness of the mask is 0.2 μm or less. The width of one pitch formed by the width of the shielding portion of the mask and the width of the opening is 10 μm or less. The percentage of the width of the opening to the width of one pitch of the mask is 10% to 50%. The thickness of the first layer is 20 μm or less. By using a manufacturing method having such characteristics, it is possible to obtain a GaN single crystal substrate having a uniform in-plane dislocation density distribution and capable of stably improving device characteristics.

From the viewpoint of producing GaN single crystal substrates having the above-mentioned effects with a high yield, the method for producing the GaN single crystal substrate preferably has the steps shown in the flowchart of FIG. 5, for example. FIG. 5 is a flowchart showing an example of a method for producing a gallium nitride single crystal substrate according to this embodiment. That is, the method for producing the GaN single crystal substrate includes the steps of: preparing a base substrate S10 (first step: base substrate preparation step) including a growth substrate and a gallium nitride film (hereinafter also referred to as "GaN film") to be placed on the growth substrate; arranging a mask having a structure in which shielding portions and openings are repeated in the width direction on the base substrate S20 (second step: mask placement step); and growing a first layer of gallium nitride single crystal having a facet structure from the base substrate by hydride vapor phase epitaxy (hereinafter also referred to as "HVPE method"). It is preferable that the method includes a step S30 of growing a layer (third step: step of growing the first layer), a step S40 of growing a second layer made of the gallium nitride single crystal having a {0001} growth surface on the first layer to obtain a structure including the base substrate, the first layer, and the second layer in this order (fourth step: step of obtaining a structure), and a step S50 of removing the base substrate and the first layer from the structure and processing the second layer to obtain the GaN single crystal substrate (fifth step: step of obtaining a GaN single crystal substrate). Each step will be described in order below.

<First step>
The first step is a step S10 of preparing a base substrate including a growth substrate and a GaN film disposed on the growth substrate. The purpose of this step is to prepare a base substrate necessary for growing a GaN single crystal constituting a GaN single crystal substrate that can obtain the effects of the present disclosure by disposing the GaN film on the growth substrate. The material of the growth substrate is not particularly limited as long as it is a substrate on which a GaN film can be grown. For example, a heterogeneous substrate using a material (heterogeneous material) different from GaN, such as a sapphire substrate or a gallium arsenide (GaAs) substrate, can be prepared as the growth substrate, and a homogeneous substrate using GaN (homogeneous material) can also be prepared. In addition, an aluminum nitride (AlN) substrate, a silicon carbide (SiC) substrate, a zirconium boride (ZrB ₂ ) substrate, a silicon oxide/aluminum oxide (SiO ₂ /Al ₂ O ₃ ) sintered body substrate, a molybdenum (Mo) substrate, etc. can also be applied as the growth substrate. These growth substrates can be commercially available or can be manufactured by conventional methods. The GaN film can be disposed on at least a portion of the surface of the growth substrate by conventional methods such as MOCVD (metal organic chemical vapor deposition).

<Second step>
The second step is step S20 of arranging a mask having a structure in which a shielding portion and an opening are repeated in the width direction on the base substrate. The purpose of this step is to arrange the mask 21 on the base substrate by forming a mask 21 having a structure (pattern) in which a shielding portion 21a and an opening 21b are repeated in the width direction as shown in Fig. 6 on the base substrate using a conventionally known method. Fig. 6 is a schematic diagram illustrating the structure of the mask used to obtain the gallium nitride single crystal substrate according to this embodiment.

The mask 21 has a rectangular shape in plan view, and has a structure in which the shielding portion 21a and the opening 21b are repeated in the width direction as described above. Furthermore, the shielding portion 21a and the opening 21b have a structure in which they are continuous in the length direction of the mask 21. The pattern of the mask 21 has a pitch width P consisting of the width W1 of the shielding portion 21a and the width W2 of the opening 21b, which is 10 μm or less. Furthermore, the percentage of the width of the opening 21b to the width P of one pitch of the mask 21 (hereinafter also referred to as the "opening rate") is 10 to 50% or less. The thickness of the mask 21 is 0.2 μm or less. The pitch width P consisting of the width W1 of the shielding portion 21a of the mask 21 and the width W2 of the opening 21b is preferably 5 to 8 μm or less, the opening rate of the mask 21 is preferably 14 to 50%, and the thickness of the mask 21 is preferably 0.1 μm or less. For structural reasons, it is practical for the thickness of the mask 21 to be 10 μm or more.

By having the width P of one pitch, which is composed of the width W1 of the shielding portion 21a and the width W2 of the opening portion 21b in the mask 21, be 10 μm or less, it is possible to promote the generation of regular pits on the growth surface of the first layer (GaN single crystal) in step S30, which is described below, for growing the first layer. Furthermore, by having the opening ratio of the mask 21 be 10-50% or less, it is possible to suppress the amount of dislocations propagating from the base substrate to the first layer in step S30, which is described below, for growing the first layer. By having the thickness of the mask 21 be 0.2 μm or less, it is possible to suppress the number of new dislocations that are generated during the growth of the first layer.

The mask 21 can be formed, for example, by the following method. First, a chemical vapor deposition film (for example, a silicon-based chemical vapor deposition film, particularly a chemical vapor deposition film of silicon oxide (SiO ₂ ), silicon carbide (SiC), silicon nitride (SiN), etc.) is formed on the entire surface of the base substrate by plasma CVD (Chemical Vapor Deposition) or the like. After that, a resist patterned by photolithography is formed on the chemical vapor deposition film, and etching is performed using the resist as an etching mask. As a result, as shown in FIG. 7, the mask 21 can be formed on the GaN film 32 of the base substrate 30 consisting of the growth substrate 31 and the GaN film 32 disposed on the growth substrate 31. FIG. 7 is a schematic cross-sectional view illustrating the state in which the mask of FIG. 6 is disposed on the base substrate. In FIG. 7, the symbol Mt represents the thickness (0.2 μm or less) of the mask 21.

The length direction of the mask 21 is preferably parallel to the <11-20> or <1-100> direction of the GaN single crystal that constitutes the GaN film 32 on the base substrate 30. In other words, the direction in which the shielding portions 21a and openings 21b of the mask 21 continue is preferably parallel to the <11-20> or <1-100> direction of the GaN single crystal that constitutes the GaN film 32. This makes it possible to make the in-plane dislocation density distribution more uniform when a GaN single crystal substrate is obtained from the GaN single crystal.

<Third step>
The third step is step S30 of growing a first layer made of gallium nitride single crystal having a facet structure from the base substrate by hydride vapor phase epitaxy (HVPE). The purpose of this step is to form a first layer (GaN single crystal) having a facet structure with pits regularly generated on the growth surface on the base substrate. Such a first layer can be formed, for example, in the following manner.

First, a base substrate with a mask placed on it is placed on a quartz or carbon sample holder in a hot wall type reactor, and at least the GaN film in the base substrate is heated to about 1000°C. Next, hydrogen chloride (HCl) gas is sprayed onto metal Ga placed in an upstream boat in the reactor, using nitrogen ( _N2 ) gas and hydrogen ( _H2 ) gas as carrier gases, to generate gallium chloride (GaCl) gas. Furthermore, ammonia ( _NH3 ) gas is introduced into the reactor. Next, the GaCl gas and _NH3 gas are supplied to the GaN film in the base substrate through the opening of the mask, using _H2 gas as carrier gas, so that a first layer (GaN single crystal) can be grown on the side of the base substrate where the mask is placed, under the following first growth conditions. Furthermore, the thickness of the first layer can be controlled to 20 μm or less by adjusting the amount or time of supplying GaCl gas and _NH3 gas under the first growth conditions.

The specific first growth conditions are as follows.
GaCl gas partial pressure: 0.8 to 7 kPa
_NH3 gas partial pressure: 1.5 to 36 kPa
GaCl gas flow rate: 50 to 400 SCCM
_NH3 gas flow rate: 100 to 2000 SCCM
Growth temperature: 900 to 1100°C
Growth rate: 20-80 μm/hour V/III (NH ₃ gas/GaCl gas) ratio: 2-20.

Here, under the first growth conditions, the GaCl gas partial pressure is preferably 2.5 to 5 kPa, and the _NH3 gas partial pressure is preferably 3 to 14 kPa. The GaCl gas flow rate is preferably 150 to 300 SCCM, and the _NH3 gas flow rate is preferably 200 to 800 SCCM. Under the first growth conditions, the growth temperature is preferably 1010 to 1060° C., and the growth rate is preferably 40 to 60 μm/hour.

FIG. 8 is a schematic cross-sectional view illustrating the state in which the first layer (GaN single crystal) is formed on the gallium nitride film in the manufacturing method of the gallium nitride single crystal substrate according to this embodiment. As shown in FIG. 8, this process can form the first layer 41 made of GaN single crystal with a thickness d1 of 20 μm or less on the mask 21. The thickness d1 of the first layer 41 is preferably 10 μm or less. By proceeding to the next process (the fourth process) before dislocations are unnecessarily concentrated in the pits 41a, dislocations can be dispersed in a direction perpendicular to the direction of crystal growth from the early stage of epitaxial growth of the GaN single crystal. Furthermore, on the growth surface of the first layer 41, the pits 41a can be generated regularly as described above based on the structure of the mask 21. The thickness of the first layer 41 refers to the thickness between the flat portion of the growth surface of the first layer 41 and the base substrate 30, and can be measured by cross-sectional observation using a fluorescent microscope image mapping device (for example, product name: "LEICA DM6000M", manufactured by Leica). Specifically, by irradiating the first layer 41 with fluorescent light having the wavelengths described below, it is possible to measure the thickness of the first layer 41 using the concentration of the above impurities as an index.

Here, the average area of one pit 41a formed on the growth surface of the first layer 41 (hereinafter also referred to as "pit area") is preferably ¹⁰⁰ μm2 or less. This makes it possible to prevent dislocations from concentrating more than necessary in the pit 41a. The pit area is more preferably ⁵⁰ μm2 or less. The pit area is naturally determined by the width P of one pitch, which is composed of the width W1 of the shielding portion 21a of the mask 21 and the width W2 of the opening 21b.

The pit area can also be determined by irradiating the first layer 41 with fluorescence of the wavelength under the following conditions using the above-mentioned fluorescence microscope image mapping device, based on the difference in impurity concentration between the area where the pit 41a exists and the other areas in the first layer 41. First, a crystal piece corresponding to the first layer 41 is obtained by cutting it from the GaN single crystal, and the surface of the crystal piece is polished to obtain a measurement sample. Next, the measurement sample is observed using the above-mentioned fluorescence microscope image mapping device under the following conditions and at a magnification such that the size of one field of view is 2.5 mm x 1.9 mm. The above observation is performed by moving the measurement sample, etc., to set the field of view without overlapping and without leaving anything out, and covers the entire surface of the first layer 41. For example, if the diameter of the first layer 41 is 105 mm, the total number of fields of view is 41 x 54 (= 2214 fields of view). However, if the outer periphery of the first layer 41 and a place corresponding to the outside thereof appear within one field of view, that field of view is excluded from the target for determining the pit area. This is because this area is not normally used as material for semiconductor devices.

The conditions for the above-mentioned fluorescence microscope image mapping measurement are as follows.
Irradiation light: ultraviolet excitation by a mercury lamp (wavelength 365 nm)
Fluorescence wavelength range: 365 to 650 nm
Temperature: room temperature (25°C).

<Fourth step>
The fourth step is step S40 of growing a second layer made of GaN single crystal whose growth surface is the {0001} plane on the first layer to obtain a structure including the base substrate, the first layer, and the second layer in this order. The purpose of this step is to grow a second layer (GaN single crystal) having a flat growth surface on the first layer. Specifically, the HVPE method is performed on the first layer having pits on its growth surface, employing the following second growth condition. This allows for the obtaining of a structure including the base substrate, the first layer, and the second layer in this order.

The HVPE method based on the second growth conditions can be performed in the same manner as the HVPE method based on the first growth conditions, except for the specific gas partial pressure, growth temperature, and growth rate conditions described below. Furthermore, when GaCl gas is generated by spraying HCl gas, for example, tetrachlorosilane (SiCl ₄ ) gas can be added to dope Si into the second layer. This allows a second layer (GaN single crystal) whose growth surface is a {0001} surface to be grown on the first layer, specifically on the growth surface side of the first layer. The thickness of the second layer can be adjusted by controlling the amount or time of supplying GaCl gas and NH ₃ gas. Here, the thickness of the second layer is preferably 1000 μm or less. It is more preferable that the thickness of the second layer is 500 μm or less. According to the method for producing a GaN single crystal substrate in this embodiment, even when a GaN single crystal substrate is obtained from a second layer (GaN single crystal) that is grown to a relatively thin thickness of 1000 μm or less, the in-plane dislocation density distribution is uniform, and device characteristics can be stably improved.

The specific second growth conditions are as follows.
GaCl gas partial pressure: 3 to 18 kPa
_NH3 gas partial pressure: 3 to 36 kPa
_SiCl4 gas partial pressure: 2.5 to 12.5 Pa
GaCl gas flow rate: 200 to 1000 SCCM
_NH3 gas flow rate: 200 to 2000 SCCM
_SiCl4 gas flow rate: 1.5 to 7.5 SCCM
Growth temperature: 1000 to 1100° C.
Growth rate: 50-150 μm/hour V/III (NH ₃ gas/GaCl gas) ratio: 1-10.

Here, under the second growth conditions, the GaCl gas partial pressure is preferably 5 to 9 kPa, and the _NH3 gas partial pressure is preferably 5 to 18 kPa. The GaCl gas flow rate is preferably 300 to 500 SCCM, and the _NH3 gas flow rate is preferably 300 to 1000 SCCM. Under the second growth conditions, the growth temperature is preferably 1010 to 1060° C., and the growth rate is preferably 80 to 120 μm/hour.

9 is a schematic cross-sectional view illustrating a structure in which a base substrate, a first layer, and a second layer are laminated in this order in the manufacturing method of a gallium nitride single crystal substrate according to this embodiment. As shown in FIG. 9, the fourth step can form a second layer (GaN single crystal) 42 having a thickness d2 of, for example, 1000 μm or less on the first layer 41. By growing the second layer 42 under the second growth conditions, no pits are formed on the growth surface ({0001} surface) of the second layer 42, resulting in a flat surface. Note that in the manufacturing method of a GaN single crystal substrate according to this embodiment, the thickness d2 of the second layer 42 does not exclude being greater than 1000 μm. For example, the upper limit of the thickness d2 of the second layer 42 can be 7 mm. The thickness of the second layer 42 can be measured using a stylus-type film thickness gauge (for example, the product name "ABS Digimatic Indicator ID-F125", manufactured by Mitutoyo Corporation).

<Fifth step>
The fifth step is a step S50 of removing the base substrate and the first layer from the structure and processing the second layer to obtain the GaN single crystal substrate. The purpose of this step is to obtain a GaN single crystal substrate having the effect of the present disclosure from the structure. In this step, referring to FIG. 9, first, in the structure including the growth substrate 31, the GaN film 32, the mask 21, the first layer 41 and the second layer 42, the first layer 41 side of the second layer 42 is ground. This separates the growth substrate 31, the base substrate 30 including the GaN film 32, the mask 21, and the first layer 41 from the structure, thereby obtaining an ingot of GaN single crystal consisting of the second layer 42. Furthermore, a disk-shaped GaN single crystal is cut out to a predetermined thickness from the ingot of GaN single crystal consisting of the second layer 42, and the surface of the GaN single crystal is flattened by grinding, followed by both or at least one of polishing and dry etching. This allows a GaN single crystal substrate to be obtained.

<Action and effect>
The above steps allow the manufacture of the GaN single crystal substrate according to this embodiment. The GaN single crystal substrate can have a uniform dislocation density distribution on the main surface by using a mask structure used in the manufacturing process and reducing the thickness of the first layer, thereby stably improving device characteristics.

The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these. In the examples, one each of the GaN single crystal substrate samples was obtained by carrying out the following GaN single crystal substrate manufacturing method.

[Production of GaN Single Crystal Substrate]
<Sample 1>
(First step)
A commercially available sapphire substrate having a diameter of 50.8 mm was obtained, and a GaN film was formed on the sapphire substrate by MOCVD to prepare a base substrate. The main surface of the GaN film had a (0001) plane orientation.

(Second step)
A mask was formed on the GaN film side of the base substrate, in which shielding portions and openings were alternately repeated in the width direction, and which had a thickness, pattern, opening rate, opening width, and shielding portion width as shown in Table 1 below. Here, "<1-100> direction stripes" in the "Pattern" section in Table 1 means that the length direction of the mask is parallel to the <1-100> direction of the GaN single crystal that constitutes the GaN film. Specifically, a plasma CVD method was applied to the GaN film side of the base substrate to form a chemical vapor deposition film made of silicon oxide, and then a resist patterned by photolithography was formed on the chemical vapor deposition film, and etching was performed using the resist as an etching mask to form a mask.

(Third process)
By applying the HVPE method, a first layer made of a GaN single crystal having a facet structure was grown from the GaN film of the base substrate through the opening of the mask under the following first growth conditions. Specifically, the base substrate was placed on a carbon sample holder in a hot-wall type reactor, and the reactor was heated to 1050° C., after which HCl gas was sprayed onto metallic Ga placed in an upstream boat in the reactor to generate and supply GaCl gas, and then NH ₃ gas was supplied into the reactor. The reactor was then held at 1050° C. for 15 minutes. The first growth conditions were a GaCl gas partial pressure of 3.2×10 ³ Pa and an ammonia gas partial pressure of 6.9×10 ³ Pa. Furthermore, the growth rate of the growth surface of the first layer was 40 μm/hour. As a result of the above, a first layer made of a GaN single crystal whose growth surface was the (0001) plane and whose thickness measured by the fluorescence microscope was 10 μm was obtained. Furthermore, the pit area of the first layer was determined to be 49 μm ² .

(Fourth step)
By continuing to apply the HVPE method, a second layer made of GaN single crystal with a growth surface of the {0001} surface was grown on the first layer. As a result, a structure including the base substrate, the first layer, and the second layer in this order was obtained. Specifically, the inside of the hot-wall type reactor was heated to 1050° C., and then GaCl gas generated by reacting HCl gas with Ga, NH 3 gas, and SiCl ₄ gas were supplied into the reactor with respect to the growth surface of the first layer placed on a carbon sample holder in the hot-wall type reactor. The reactor was then held at 1050° C. for 16 hours. The second growth conditions were GaCl gas partial pressure of 5.7×10 ³ Pa, SiCl ₄ _gas partial pressure of 11.7 Pa, and NH ₃ gas partial pressure of 6.0×10 ³ Pa. Furthermore, the growth rate of the growth surface of the second layer was set to 100 μm/hour. The temperature inside the reactor was then lowered to room temperature. This resulted in a second layer made of single crystal GaN being grown on the first layer. The growth surface of the second layer was the (0001) plane, and the thickness measured with a stylus-type thickness gauge was 1600 μm.

(Fifth step)
In the structure including the base substrate, the mask, the first layer, and the second layer, the first layer side of the second layer was ground to separate the second layer from the base substrate, the GaN film, the mask, and the first layer, thereby obtaining an ingot consisting of the second layer. Furthermore, a disk-shaped GaN single crystal was cut out at a predetermined thickness from the ingot consisting of the second layer. The surface of the GaN single crystal was then flattened by grinding, and then polished to a mirror surface. In this manner, a GaN single crystal substrate of Example 1 having a diameter of 50.8 mm (2 inches), a thickness of 400 μm, and a circular main surface was produced. The Si concentration and carrier concentration of the GaN single crystal substrate were measured by the above-mentioned measuring method, and were found to be the concentrations shown in Table 1.

<Samples 2 to 12>
The GaN single crystal substrates of Samples 2 to 12 were manufactured in the same manner as the manufacturing method of the GaN single crystal substrate of Sample 1, except that a mask having the mask structure shown in Table 1 was formed on the base substrate, the first and second growth conditions were changed so that the thicknesses and pit areas of the first and second layers were as shown in Table 1, and the substrate size was changed as shown in Table 1. The Si concentration and carrier concentration of each of the above GaN single crystal substrates were measured by the above-mentioned measuring method, and were found to be the concentrations shown in Table 1. The "<11-20> direction stripes" in the "Pattern" section in Table 1 means that the length direction of the mask is parallel to the <11-20> direction of the GaN single crystal constituting the GaN film.

<Samples 101 to 105>
The GaN single crystal substrates of Samples 101 to 105 were manufactured in the same manner as the manufacturing method of the GaN single crystal substrate of Sample 1, except that a mask having the mask structure shown in Table 2 was formed on the base substrate, the first and second growth conditions were changed so that the thicknesses and pit areas of the first and second layers were as shown in Table 2, and the substrate size was changed as shown in Table 2. The Si concentration and carrier concentration of each of the above GaN single crystal substrates were measured by the above-mentioned measuring method, and were found to be the concentrations shown in Table 2.

<Sample 106>
A GaN single crystal substrate of sample 106 was manufactured according to Example 4 of the above-mentioned Patent Document 1. The size of the substrate was 50.8 mm (2 inches) in diameter. The structure of the mask used in manufacturing the GaN single crystal substrate, the thicknesses of the first and second layers obtained in the above-mentioned manufacturing, the pit area, and the Si concentration and carrier concentration are as shown in Table 2.

<Sample 107>
A GaN single crystal substrate of sample 107 was manufactured according to Example 3 of the above-mentioned Patent Document 1. The size of the substrate was 50.8 mm (2 inches) in diameter. The structure of the mask used in manufacturing the GaN single crystal substrate, the thicknesses of the first and second layers obtained in the above-mentioned manufacturing, the pit area, and the Si concentration and carrier concentration are as shown in Table 2.

<Sample 108>
A GaN single crystal substrate of sample 108 was manufactured according to Example 1 of Patent Document 2. The size of the substrate was 50.8 mm (2 inches) in diameter. The structure of the mask used in manufacturing the GaN single crystal substrate, the thicknesses of the first and second layers obtained in the above manufacturing, the pit area, and the Si concentration and carrier concentration are as shown in Table 2.

<Sample 109>
The GaN single crystal substrate of sample 109 was manufactured according to Example 3 of Patent Document 1. The size of the substrate was 50.8 mm (2 inches) in diameter. The structure of the mask used in manufacturing the GaN single crystal substrate, the thicknesses of the first and second layers obtained in the above manufacturing, the pit area, and the Si concentration and carrier concentration are as shown in Table 2. The GaN single crystal substrate of sample 109 has a thicker second layer than the GaN single crystal substrate of sample 107.

<Sample 110>
The GaN single crystal substrate of sample 110 was manufactured according to Example 3 of Patent Document 1. The size of the substrate was 50.8 mm (2 inches) in diameter. The structure of the mask used in manufacturing the GaN single crystal substrate, the thicknesses of the first and second layers obtained in the above manufacturing, the pit area, and the Si concentration and carrier concentration are as shown in Table 2. The GaN single crystal substrate of sample 110 differs in the thickness of the second layer from the GaN single crystal substrates of samples 107 and 109.

[Evaluation of GaN Single Crystal Substrate]
<Evaluation of uniformity of in-plane dislocation density distribution>
For the GaN single crystal substrates of Samples 1 to 12 and Samples 101 to 110, the first dislocation density (cm ^-2 ), reference area (μm ² ), average value (cm ^-2 ) and coefficient of variation (standard deviation/average value) of the second dislocation density, the coefficient of variation (standard deviation/average value) of the third dislocation density, and the coefficient of variation (standard deviation/average value) of the fourth dislocation density were obtained based on the above-mentioned measurement method and calculation method. The results are shown in Tables 3 and 4. The smaller the value of the coefficient of variation of the second dislocation density, the coefficient of variation of the third dislocation density, and the coefficient of variation of the fourth dislocation density, respectively, the more uniform the in-plane dislocation density distribution is. In this evaluation, a 20x objective lens was used to obtain the second dislocation density and the like using a multiphoton excitation microscope. However, any field area was obtained by combining digital zoom on the software. For example, when the digital zoom is 1x, the measurement area of one field of view is about 640x640μm ² . When the magnification is 5 times, the measurement area of one visual field is approximately 130 x 130 μm ² , and when the magnification is 12.5 times, the measurement area of one visual field is approximately 50 x 50 μm ² .

<Evaluation of variation in luminescence intensity>
(Fabrication of Light-Emitting Element)
On the main surface of the GaN single crystal substrate of Samples 1 to 12 and Samples 101 to 110, an n-AlGaN cladding layer/(InGaN/GaN) 4-period multiple quantum well layer/p-AlGaN cladding layer structure was grown by metal organic vapor phase epitaxy (MOVPE), thereby forming a light emitting device structure having an emission wavelength of about 440 nm. In this way, the light emitting devices of Samples 1 to 12 and Samples 101 to 110 were obtained. Then, PL mapping evaluation was performed on the light emitting device of each sample to evaluate the variation in emission intensity of each sample. Here, the PL mapping evaluation is the following evaluation method. That is, a PL imaging device (trade name: "VerteX", manufactured by Nanometrics) was used to perform spectrum measurement on the entire surface of the light emitting device structure at 2 mm pitch, and the emission intensity of the multiple quantum well layer around 440 nm at each measurement position was obtained. Next, the difference between the maximum and minimum emission intensities was divided by the average value to calculate the variation in emission intensity for each sample. The variation in emission intensity was expressed as a percentage (%), and the smaller the value, the less the variation in device characteristics, and therefore the better the product. The results are shown in Tables 3 and 4.

[Considerations]
The GaN single crystal substrates of samples 1 to 12 have an average second dislocation density of 5.0×10 ⁶ cm ^-2 or less and a coefficient of variation of the second dislocation density of 0.40 or less, so it is understood that the in-plane dislocation density distribution is more uniform than that of the GaN single crystal substrates of samples 101 to 110. Furthermore, the light emitting devices manufactured from samples 1 to 12 all have a variation in emission intensity suppressed to less than 35.0%, suggesting that the GaN single crystal substrates of samples 1 to 12 can stably improve device characteristics. The GaN single crystal substrates of samples 101 to 110 all have a variation in emission intensity exceeding 35.0%.

Although the embodiments and examples of the present disclosure have been described above, it is also planned from the beginning to combine the configurations of the above-mentioned embodiments and examples as appropriate.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope.

1 Gallium nitride single crystal substrate (GaN single crystal substrate), 101 Conventional gallium nitride single crystal substrate (GaN single crystal substrate), 11 Main surface, 21 Mask, 21a Shielding portion, 21b Opening, 30 Base substrate, 31 Growth substrate, 32 GaN film, 41 First layer, 41a Pit, 42 Second layer, t Dislocation, OF Orientation flat, G Virtual lattice, A1 First measurement area, A2 Second measurement area, C Center point of first measurement area, P 1 pitch, W1 Width of shielding portion, W2 Width of opening, Mt Mask thickness, d1 Thickness of first layer, d2 Thickness of first layer, S10 Step of preparing base substrate, S20 Step of placing mask, S30 Step of growing first layer, S40 Step of obtaining structure, S50 Step of obtaining GaN single crystal substrate.

Claims

A gallium nitride single crystal substrate having a circular main surface,
the main surface has a first dislocation density and a second dislocation density that is two or more;
the second average dislocation density is 5.0×10 6 cm −2 or less;
the standard deviation of the second dislocation density and the average value satisfy a relationship of standard deviation/average value≦0.40, and the unit of the standard deviation is cm
the first dislocation density is determined by measuring the number of dislocations in nine first measurement regions on the main surface, each of which is a square with one side measuring 100 μm, and converting the sum of the numbers of dislocations into the number of dislocations per cm2 ;
the second dislocation density is obtained by obtaining a reference area expressed as a value obtained by dividing 100 by the first dislocation density, forming a virtual lattice on the main surface in which squares each having a side length of 2 mm are laid out in parallel as many times as possible without overlapping each other, measuring the number of dislocations in second measurement regions each having an area of 30% of the reference area and set in the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per cm2 for each of the second measurement regions;
a gallium nitride single crystal substrate, wherein a diameter of the gallium nitride single crystal substrate is represented by D, and two axes on the main surface that pass through the center of the main surface and intersect at the center are represented by X-axis and Y-axis, respectively, and the X-axis and Y-axis coordinates (X, Y) of the center point of the first measurement region are (0, 0), (D/4-5, 0), (0, D/4-5), (-(D/4-5), 0), (0, -(D/4-5)), (D/2-10, 0), (0, D/2-10), (-(D/2-10), 0) and (0, -(D/2-10)), and the units of D and X and Y in the coordinates (X, Y) are mm.
The gallium nitride single crystal substrate according to claim 1, wherein the diameter of the gallium nitride single crystal substrate is 50 mm or more and 155 mm or less.
The gallium nitride single crystal substrate contains impurity atoms,
the impurity atoms are silicon and/or germanium;
3. The gallium nitride single crystal substrate according to claim 1, wherein a concentration of said impurity atoms is not less than 1.0×10 18 cm −3 and not more than 5.0×10 18 cm −3 .
the main surface has a third dislocation density of 2 or greater;
the standard deviation and average value of the third dislocation density satisfy the relationship of standard deviation/average value≦0.35;
4. The gallium nitride single crystal substrate according to claim 1, wherein the third dislocation density is determined by measuring the number of dislocations in a third measurement region having an area that is 50% of the reference area set in the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per cm2 for each of the third measurement regions.
the main surface has a fourth dislocation density of 2 or greater;
the standard deviation and average value of the fourth dislocation density satisfy a relationship of standard deviation/average value≦0.53;
5. The gallium nitride single crystal substrate according to claim 1, wherein the fourth dislocation density is determined by measuring the number of dislocations in fourth measurement regions having an area of 10% of the reference area set in the center of each of the squares constituting the lattice, and converting the number of dislocations into the number of dislocations per cm2 for each of the fourth measurement regions.
A method for producing a gallium nitride single crystal substrate having a circular main surface, comprising the steps of:
preparing a base substrate including a growth substrate and a gallium nitride film disposed on the growth substrate;
A step of disposing a mask having a structure in which a shielding portion and an opening portion are repeated in a width direction on the base substrate;
growing a first layer made of a gallium nitride single crystal having a facet structure from the base substrate by hydride vapor phase epitaxy;
growing a second layer made of the gallium nitride single crystal, the growth surface of which is a {0001} plane, on the first layer to obtain a structure including the base substrate, the first layer, and the second layer in this order;
removing the base substrate and the first layer from the structure and processing the second layer to obtain the gallium nitride single crystal substrate;
The thickness of the mask is 0.2 μm or less,
a width of one pitch of the mask, which is formed by a width of the shielding portion and a width of the opening, is 10 μm or less;
a percentage of a width of the opening with respect to a width of one pitch of the mask is 10% or more and 50% or less;
A method for producing a gallium nitride single crystal substrate, wherein the first layer has a thickness of 20 μm or less.
The method for manufacturing a gallium nitride single crystal substrate according to claim 6, wherein the length direction of the mask is parallel to the <11-20> direction or the <1-100> direction of the gallium nitride single crystal that constitutes the gallium nitride film on the base substrate.
The method for manufacturing a gallium nitride single crystal substrate according to claim 6 or 7, wherein the thickness of the second layer is 1000 μm or less.