WO2023218558A1

WO2023218558A1 - Gallium nitride single crystal substrate and method for producing same

Info

Publication number: WO2023218558A1
Application number: PCT/JP2022/019935
Authority: WO
Inventors: 拓司岡久; 俊佑西野
Original assignee: 住友電気工業株式会社
Priority date: 2022-05-11
Filing date: 2022-05-11
Publication date: 2023-11-16
Also published as: JP7409556B1; JPWO2023218558A1; TW202347827A

Abstract

This gallium nitride single crystal substrate comprises a first main surface and a second main surface. The diameter of the gallium nitride single crystal substrate is 50 mm or more. The first main surface is a gallium polar face, and the second main surface is a nitrogen polar face. The first main surface and the second main surface have a circular shape. In the gallium nitride single crystal substrate, the (0001) plane of the gallium nitride single crystal constituting the same is a spherical curved surface that is convex from the first main surface side toward the second main surface side and has a curvature radius of 6 m or more. The first main surface has a plurality of pit marks, and the density of the pit marks is 0.1/cm² to 100/cm² inclusive.

Description

Gallium nitride single crystal substrate and its manufacturing method

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

One of the gallium nitride single crystal substrates useful for forming nitride semiconductor devices has two main surfaces that are parallel or substantially parallel to the C plane (hereinafter also referred to as the "(0001) plane") of the gallium nitride single crystal. A C-plane gallium nitride single crystal substrate (hereinafter also simply referred to as a "GaN single crystal substrate") is well known. The two main surfaces of the C-plane GaN single crystal substrate refer to the gallium polar plane, which is the main surface on the [0001] direction side, and the nitrogen polar plane, which is the main surface on the [000-1] direction side, respectively. In a C-plane GaN single crystal substrate, various nitride semiconductor devices are usually formed on the gallium polar plane. C-plane GaN single crystal substrates are generally made of gallium nitride single crystals (hereinafter referred to as "GaN single crystals") obtained by applying the HVPE (Hydride Vapor Phase Epitaxy) method using gallium chloride (GaCl) gas and ammonia (NH ₃ ) gas. (also referred to as "crystal"). It is known that when a GaN single crystal is grown using the C-plane as a growth surface by the HVPE method, inverted hexagonal pyramid-shaped depressions called pits are formed on the growth surface.

The following non-patent document 1 discloses that when a GaN single crystal is obtained by using the HVPE method and leaving the pits, the GaN single crystal is caused by dislocations, which are structural defects of the crystal, concentrating at the bottom of the pits. reported that the dislocations are reduced around the pits. JP2016-074549A (Patent Document 1) and International Publication No. 2005/050709 (Patent Document 2) disclose that in the process of obtaining a gallium nitride single crystal using the above HVPE, dislocations are generated on the growth plane under predetermined growth conditions. It is proposed that after forming the pits in which GaN is concentrated, almost all of the pits are filled with GaN single crystal under other growth conditions to produce a GaN single crystal substrate with a low dislocation density.

Japanese Patent Application Publication No. 2016-074549 International Publication No. 2005/050709

A gallium nitride single crystal substrate according to the present disclosure is a gallium nitride single crystal substrate comprising a first main surface and a second main surface, wherein the diameter of the gallium nitride single crystal substrate is 50 mm or more, and the gallium nitride single crystal substrate has a diameter of 50 mm or more. The first main surface is a gallium polar surface, the second main surface is a nitrogen polar surface, the first main surface and the second main surface have a circular shape, and the nitride In the gallium single crystal substrate, the (0001) plane of the gallium nitride single crystal constituting the substrate is a spherical curved surface that is convex from the first main surface side to the second main surface side, and has a radius of curvature of 6 m or more, the first main surface has a plurality of pit traces, and the density of the pit traces is 0.1 pieces/cm ² or more and 100 pieces/cm ² or less.

A 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 first main surface and a second main surface, the method comprising forming a gallium nitride film on at least a portion of the surface. a step of forming a first layer on the gallium nitride film by growing a gallium nitride single crystal under first growth conditions in the gallium nitride film; in the first layer, forming a second layer on the first layer by growing the gallium nitride single crystal under second growth conditions; and forming the gallium nitride single crystal by cutting out the second layer. obtaining a substrate, the growth surface of the first layer has a pit density of more than 100 pits/cm2, and the growth surface of the second layer has a pit density of 0.1 pits/ ^cm2 ^{or more} and 100 pits/cm2 or more. / ^cm2 or less, having a pit density of
The above first growth condition is
A gallium chloride gas partial pressure of 0.1 kPa or more and 20 kPa or less,
Ammonia gas partial pressure of 0.5 kPa or more and 50 kPa or less,
A growth temperature of 900°C or higher and 1100°C or lower,
has a growth rate of 10 μm/hour or more and 300 μm/hour or less,
The above second growth condition is
Gallium chloride gas partial pressure of 1 kPa or more and 50 kPa or less,
Ammonia gas partial pressure of 1 kPa or more and 100 kPa or less,
A growth temperature of 900°C or higher and 1100°C or lower,
has a growth rate of 50 μm/hour or more and 500 μm/hour or less,
The growth temperature under the first growth condition is lower than the growth temperature under the second growth condition.

FIG. 1 is a schematic cross-sectional view illustrating a gallium nitride single crystal substrate according to this embodiment. FIG. 2 relates to the gallium nitride single crystal substrate according to the present embodiment, and shows measurement points used in XRD analysis to determine the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrate (i.e. measurement points irradiated with X-rays). FIG. FIG. 3 is an explanatory diagram illustrating the reason why pit traces exist in the gallium nitride single crystal substrate according to the present embodiment. FIG. 4 is a schematic diagram schematically showing the distribution of pit traces existing on the first main surface of the gallium nitride single crystal substrate according to the present embodiment. FIG. 5 is a photograph substituted for a drawing showing a fluorescence microscopic image of pit traces. FIG. 6 is a photograph substituted for a drawing, which is an enlarged fluorescence microscopic image of the pit trace shown in FIG. FIG. 7 is a flowchart illustrating an example of a method for manufacturing a gallium nitride single crystal substrate according to this embodiment. FIG. 8 is a schematic cross-sectional diagram illustrating how a mask is placed on a base substrate in order to perform the step of forming a first layer on a gallium nitride film in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment. It is a diagram. FIG. 9 is a schematic cross-sectional view illustrating how a first layer (GaN single crystal) is formed on a gallium nitride film in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment. FIG. 10 is a schematic cross-sectional view illustrating how a second layer (GaN single crystal) is formed on the first layer in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment.

[Problems that this disclosure seeks to solve]
Non-Patent Document 1, Patent Document 1, and Patent Document 2 mentioned above all focus on providing a GaN single-crystal substrate whose main surface has low dislocations. In particular, Patent Document 1 and Patent Document 2 disclose that after forming pits where dislocations are concentrated on the growth surface as described above, dislocations are reduced by filling almost all of the pits with GaN single crystal using other growth conditions. I am proposing to do so. However, when the pits are filled with GaN single crystals, the dislocations concentrated at the bottom of the pits diffuse to the periphery, generating stress (particularly tensile stress), which causes the GaN single crystals cut from the ingot to warp. A phenomenon occurs in which the (0001) plane of the GaN single crystal is curved.

A GaN single crystal substrate having a flat main surface can be obtained from a warped GaN single crystal by surface processing such as polishing the surface. Since the (0001) plane is curved, the characteristics may change for each region of the main surface, which may adversely affect the device characteristics. Therefore, a GaN single crystal substrate that can improve device characteristics by achieving both low dislocations on the main surface and suppression of warping of the GaN single crystal has not yet been obtained, and its development is highly desired. has been done.

In view of the above points, the present disclosure provides a gallium nitride single crystal substrate that can increase the radius of curvature of the (0001) plane of the GaN single crystal by suppressing warpage of the GaN single crystal, thereby improving device characteristics. , and a manufacturing method thereof.

[Effects of this disclosure]
According to the above, a gallium nitride single crystal substrate that can increase the radius of curvature of the (0001) plane of the GaN single crystal by suppressing warpage of the GaN single crystal, thereby improving device characteristics, and a method for manufacturing the same can be provided.

[Overview of embodiment]
First, an overview of an embodiment of the present disclosure will be described. The present inventors have made extensive studies to solve the above problems and have completed the present disclosure. First, the present inventors focused on the growth conditions when growing a GaN single crystal using the above HVPE method. Specifically, a first growth condition in which many pits are formed on a growth surface that is a (0001) plane and dislocations are concentrated at the bottom of the pits to reduce dislocations around the pits; A GaN single crystal ingot was manufactured by employing a growth process including second growth conditions for growing a gallium nitride single crystal while controlling the filling ratio with the GaN single crystal. In this case, a GaN single crystal ingot in which the pits remained at a predetermined density on the growth surface of the GaN single crystal was obtained under the second growth conditions. Furthermore, it has been found that warping of the GaN single crystal cut from the above ingot can be suppressed. In particular, the present disclosure was completed by obtaining a GaN single crystal substrate made of GaN single crystal with a flat (0001) plane with a radius of curvature of 6 m or more from a GaN single crystal with suppressed warpage.

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 including a first main surface and a second main surface, and the diameter of the gallium nitride single crystal substrate is 50 mm or more, the first main surface is a gallium polar surface, the second main surface is a nitrogen polar surface, and the first main surface and the second main surface are circular. In the gallium nitride single crystal substrate, the (0001) plane of the gallium nitride single crystal constituting the substrate has a spherical shape that is convex from the first main surface side to the second main surface side. and has a radius of curvature of 6 m or more, the first main surface has a plurality of pit marks, and the density of the pit marks is 0.1 pieces/cm 2 or more and 100 pieces/cm ² or more. ^cm2 or less. A gallium nitride single crystal substrate having such characteristics has uniform characteristics in each region of the first main surface, so that device characteristics can be improved.

[2] The diameter of the pit trace is preferably 200 μm or less, and the polarity of the region corresponding to the pit trace on the first main surface is preferably gallium polarity. This makes it possible to avoid excessive concentration of dislocations in the region corresponding to the pit traces on the first main surface, thereby making it possible to form a device in the region corresponding to the pit traces.

[3] The (0001) plane preferably has a radius of curvature of 11 m or more. Thereby, device characteristics can be further improved.

[4] The density of the pit traces is preferably 1 piece/cm ² or more and 100 pieces/cm ² or less. Thereby, device characteristics can be further improved.

[5] The diameter of the gallium nitride single crystal substrate is preferably 50 mm or more and 155 mm or less. Thereby, device characteristics can be improved in the gallium nitride single crystal substrate having a diameter of 50 mm or more and 155 mm or less.

[6] A method for manufacturing a gallium nitride single crystal substrate according to one aspect of the present disclosure is a method for manufacturing a gallium nitride single crystal substrate having a first main surface and a second main surface, the method comprising: forming a first layer on the gallium nitride film by preparing a base substrate on which a gallium nitride film is disposed, and growing a gallium nitride single crystal under first growth conditions in the gallium nitride film; forming a second layer on the first layer by growing the gallium nitride single crystal under second growth conditions in the first layer; and cutting out the second layer. obtaining the gallium nitride single crystal substrate by, the growth surface of the first layer having a pit density of more than 100 pits/cm ² , and the growth surface of the second layer having a pit density of more than 0.1 pits/cm 2 . The ^first growth condition is a gallium chloride gas partial pressure of 0.1 kPa or more and 20 kPa or ^less , and an ammonia gas partial pressure of 0.5 kPa or more and 50 kPa or less. , a growth temperature of 900° C. or more and 1100° C. or less, and a growth rate of 10 μm/hour or more and 300 μm/hour or less, and the second growth conditions include a gallium chloride gas partial pressure of 1 kPa or more and 50 kPa or less, and 1 kPa or more and 100 kPa or less. It has the following ammonia gas partial pressure, a growth temperature of 900°C or more and 1100°C or less, and a growth rate of 50 μm/hour or more and 500 μm/hour or less, and the growth temperature of the first growth condition is the same as the second growth condition. lower than the growth temperature of By the method of manufacturing a gallium nitride single crystal substrate having such characteristics, a gallium nitride single crystal substrate is obtained in which the characteristics of each region of the first main surface are uniform without variation and device characteristics can be improved. be able to.

[7] The first growth conditions are a gallium chloride gas partial pressure of 1 kPa or more and 5 kPa or less, an ammonia gas partial pressure of 5 kPa or more and 20 kPa or less, a growth temperature of 950°C or more and 1050°C or less, and 10 μm/hour or more and 200 μm/hour or more. The second growth conditions include a gallium chloride gas partial pressure of 3 kPa or more and 10 kPa or less, an ammonia gas partial pressure of 5 kPa or more and 50 kPa or less, and a growth temperature of 1000°C or more and 1100°C or less. , and a growth rate of 50 μm/hour or more and 400 μm/hour or less. This makes it possible to make the characteristics of each region of the first main surface more uniform with less variation.

[Details of embodiment]
Hereinafter, one embodiment (hereinafter also referred to as "this embodiment") according to the present disclosure will be described in more detail, but the present disclosure is not limited thereto. Although the following description may be made with reference to the drawings, 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. Further, in the drawings, the scale of each component is adjusted appropriately to make it easier 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, the notation in the format "A to B" means the upper and lower limits of the range (i.e., from A to B), and when there is no unit described in A and only in B, The units of and the units of B are the same. Furthermore, when a compound or the like is expressed by a chemical formula in this specification, it includes all conventionally known atomic ratios unless the atomic ratio is specifically limited, and should not necessarily be limited to only those in the stoichiometric range. For example, when expressed as "GaN", the ratio of the number of atoms constituting GaN includes all conventionally known atomic ratios. This also applies to the description of compounds other than "GaN".

In this specification, the GaN single crystal substrate is the so-called "C-plane GaN single-crystal substrate" mentioned above, and has two main surfaces parallel or substantially parallel to the C-plane ((0001) plane), the first main surface and the second main surface. It has two main surfaces. Among these, the first main surface is the main surface on the [0001] direction side, and is a gallium polar surface. The second main surface is the main surface on the [000-1] direction side and is a nitrogen polar surface. Various nitride semiconductor devices may be formed on the first main surface of the GaN single crystal substrate. Further, in this specification, the "plane" used in the term "in-plane" means the above-mentioned "first main surface" unless otherwise specified below. In this specification, when it is stated that the diameter of the GaN single crystal substrate is "50 mm", it means that the diameter is around 50 mm (about 50 to 55.5 mm), or it means that it is 2 inches. When the above-mentioned diameter is described as "100 mm", it means that the above-mentioned diameter is around 100 mm (about 95 to 105 mm), or 4 inches. When the above-mentioned diameter is described as "150 mm", it means that the above-mentioned diameter is around 150 mm (about 145 to 155 mm), or 6 inches. Note that the diameter of the main surface can be measured using a conventionally known outer diameter measuring device such as a caliper.

The first main surface and the second main surface of the GaN single crystal substrate have a "circular shape". In this specification, the "circular shape" expressing the shape of the main surface includes a geometric circular shape, as well as a notch, an orientation flat (hereinafter also referred to as "OF"), or an index on the outer periphery of the main surface. By forming at least one of flats (hereinafter also referred to as "IF"), shapes in which the main surface does not form a geometric circular shape are included. Here, "the shape when the main surface does not form a geometric circular shape" refers to the notch, OF, and IF of the line segment extending from any point on the outer periphery of the main surface to the center of the main surface. It means a shape in which the length of a line segment extending from any point above to the center of the main surface becomes shorter. Furthermore, the "shape when the main surface does not form a geometric circular shape" includes the length of all line segments extending from any point on the outer periphery of the main surface to the center of the main surface of the GaN single crystal substrate. This also includes shapes that are not necessarily the same due to the shape of the GaN single crystal that is the raw material.

In the crystallographic descriptions in this specification, individual orientations are indicated by [], collective orientations are indicated by <>, individual planes are indicated by (), and collective planes are indicated by {}, respectively. Also, the fact that the crystallographic index is negative is usually expressed by adding a "- (bar)" above the number, but in this specification, a negative sign is added in front of the number. .

[Gallium nitride single crystal substrate]
The gallium nitride single crystal substrate according to this embodiment is a GaN single crystal substrate including a first main surface and a second main surface. The diameter of the GaN single crystal substrate is 50 mm or more. The first main surface is a gallium polar surface, and the second main surface is a nitrogen polar surface. The first main surface and the second main surface have circular shapes. In the GaN single crystal substrate, the (0001) plane of the GaN single crystal constituting the substrate is a spherical curved surface that is convex from the first main surface side to the second main surface side, and has a radius of curvature of 6 m or more. Additionally, the first major surface has a plurality of pit marks. The density of the pit traces is 0.1 pieces/cm ² or more and 100 pieces/cm ² or less. In a GaN single crystal substrate having such characteristics, the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrate is as large as 6 m or more, so that the characteristics of each region of the first main surface are uniform without variation. , thereby improving device characteristics.

In the GaN single crystal substrate according to this embodiment, the reason why the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrate can be increased to 6 m or more is as follows. That is, in the present disclosure, the present inventors grew a GaN single crystal constituting the GaN single crystal substrate using the HVPE method including the following first growth conditions and second growth conditions. The first growth conditions described above are for the purpose of obtaining a GaN single crystal layer in which pits are formed at a density of more than 100 pits/cm ² on the growth surface. These are the conditions for growing a GaN single crystal layer (first layer) under the following conditions: gallium chloride gas partial pressure, ammonia gas partial pressure, growth temperature, and growth rate. The above second growth conditions are such that a predetermined chloride concentration is applied to the first layer in order to obtain a GaN single crystal layer in which pits are formed on the growth surface at a density of 0.1 pits/cm ² to 100 pits/cm ² . The conditions are a gallium gas partial pressure, an ammonia gas partial pressure, a growth temperature, and a growth rate to grow a GaN single crystal layer (second layer). Here, in this specification, the term "growth surface" refers to the surface of the GaN single crystal located in the growth direction (eg, [0001] direction) in which the GaN single crystal grows by performing the HVPE method.

In the GaN single crystal (first layer) obtained under the above first growth conditions, dislocations concentrate at the bottoms of the pits, and dislocations around the pits are reduced, so that the single crystal as a whole has a low dislocation level. can. Furthermore, the GaN single crystal (second layer) obtained under the second growth condition has pits remaining at the above-mentioned density on its growth surface, making it difficult for stress to occur. Warpage of the cut GaN single crystal can be suppressed. In particular, the GaN single crystal (second layer) inherits the dislocation density of the GaN single crystal (first layer), and as it grows, the dislocation density is further reduced. Therefore, the GaN single crystal cut out from the GaN single crystal (second layer) can be characterized by suppressed warpage and low dislocation.

From the above, in the present disclosure, by manufacturing a GaN single crystal using the HVPE method employing the first growth condition and the second growth condition, the GaN single crystal has low dislocations and its warpage is suppressed. ) The radius of curvature of the surface can be increased to 6 m or more. Thereby, it is possible to obtain a GaN single crystal substrate in which the characteristics of each region of the first main surface are uniform without variation from the GaN single crystal, thereby improving device characteristics in the GaN single crystal substrate.

(diameter)
The diameter of the GaN single crystal substrate is 50 mm or more. 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 GaN single crystal substrate 1 is preferably 2 to 6 inches. Here, regarding the above-mentioned diameter, even if the above-mentioned substrate does not have a geometric circular shape due to the influence of OF, IF, etc., the substrate has a circular shape before the above-mentioned OF, IF, etc. are formed. The size (diameter) shall be determined by assuming that it has a diameter.

<First main surface and second main surface>
(Gallium polar surface and nitrogen polar surface)
FIG. 1 is a schematic cross-sectional view illustrating a gallium nitride single crystal substrate according to this embodiment. As shown in FIG. 1, gallium nitride single crystal substrate 1 according to this embodiment includes a first main surface 11 and a second main surface 21. The first main surface 11 is a gallium polar surface, and the second main surface 21 is a nitrogen polar surface. That is, first main surface 11 is the main surface of gallium nitride single crystal substrate 1 located on the [0001] direction side of the gallium nitride single crystal that constitutes this. The second main surface 21 is a main surface located on the [000-1] direction side of the gallium nitride single crystal constituting the gallium nitride single crystal substrate 1. The gallium nitride single crystal substrate 1 has a plurality of pit traces on the first main surface 11. In particular, the polarity of the region corresponding to the pit trace on the first main surface 11 is preferably gallium polarity. In other words, it is preferable that the region corresponding to the pit trace on the first main surface 11 be maintained as a gallium polar plane without being reversed to a nitrogen polar plane due to concentration of dislocations or the like during the manufacturing process. This makes it possible to form various nitride semiconductor devices on the first main surface 11 regardless of whether the region of the first main surface 11 is a pit trace region or not. The pit traces will be described later.

((0001) plane)
As shown in FIG. 1, in the GaN single crystal substrate 1, the (0001) plane 31 of the GaN single crystal constituting the substrate has a spherical shape that is convex from the first main surface 11 side to the second main surface 21 side. It is a curved surface with a radius of curvature of 6 m or more. Preferably, the (0001) plane 31 has a radius of curvature of 11 m or more. This makes the characteristics of each region of the first main surface 11 uniform without variation, thereby improving device characteristics.

Here, in this specification, a "spherical curved surface" that is convex from the first main surface 11 side to the second main surface 21 side refers to whether or not the curved surface exhibits a strictly spherical surface. First, it means a curved surface that is convex from the first main surface 11 side toward the center of the second main surface 21 side. Therefore, in this specification, the radius of curvature of the (0001) plane 31 of the GaN single crystal is not an exact value that can be obtained when the curved surface exhibits a strictly spherical surface, but an approximate value that can be obtained by the following method. is shown as

Hereinafter, a method for determining the radius of curvature of the (0001) plane 31 of the GaN single crystal in the GaN single crystal substrate will be explained based on FIG. 2. FIG. 2 relates to the gallium nitride single crystal substrate according to the present embodiment, and shows measurement points used in XRD analysis to determine the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrate (i.e. measurement points irradiated with X-rays). FIG. Note that the above-mentioned "XRD analysis" is an abbreviation for analysis using X-ray diffraction method.

First, a GaN single crystal substrate 1 to be measured is prepared, for example, by obtaining a GaN single crystal substrate 1 having a first main surface 11 and a second main surface according to a manufacturing method described later. Analysis using an X-ray diffraction method (XRD analysis) is performed on this GaN single crystal substrate 1 under the following conditions. Specifically, XRD analysis under the following conditions was performed at a measurement point M0 at the center O of the first main surface 11 of the GaN single crystal substrate 1, and at a point 5 mm inside from each outer peripheral end in the [1-100] direction from the center O. By performing the above measurement for a total of 5 points, 2 measurement points M1 and M2, and 2 measurement points M3 and M4 5 mm inside from each outer peripheral edge in the [11-20] direction from the center O. The inclination angle with respect to the (0001) plane of the GaN single crystal at five points is measured. Here, the above-mentioned "tilt angle" refers to a straight line (vector) extending in a direction parallel to the <0001> direction of the GaN single crystal, and the above-mentioned five measurement points M0, M1, M2 on the first main surface 11, It means the intersection angle with the normal (vector) to the first main surface 11 in each of M3 and M4.

Next, the inclination angle at the measurement point M0 obtained from the XRD analysis and the four measurement points M1, M2, M3, and M4 located 5 mm inside from each outer peripheral edge in the [1-100] direction and the [11-20] direction. Numerical values (curvature radius values) corresponding to the four radii of curvature are calculated from each of the inclination angles at , based on a conventionally known formula using trigonometric functions. That is, the first radius of curvature value is calculated from each inclination angle at the measurement point M0 and measurement point M1 based on the above calculation formula, and the second radius of curvature value is calculated from each inclination angle at the measurement point M0 and measurement point M2 in the same way. A third radius of curvature value from each inclination angle at the measurement point M0 and measurement point M3, and a fourth radius of curvature value from each inclination angle at the measurement point M0 and measurement point M4, respectively. calculate. Finally, the value obtained by averaging the four radius of curvature values (first radius of curvature value to fourth radius of curvature value) is calculated using the (0001) plane 31 of the GaN single crystal in the GaN single crystal substrate. It can be found as the radius of curvature of

The conditions of the XRD analysis used to determine the radius of curvature are as follows. Note that the diffraction plane is a (0002) plane. This is because the (0001) plane does not appear due to forbidden reflection under the following conditions. The above inclination angle is determined by rotating the GaN single crystal substrate 1 to be measured in the θ direction (ω scan) under the following conditions, and obtaining X-ray diffraction peaks at a total of 5 points from the above measurement point M0 to measurement point M4. By specifying the respective diffraction angles, it is possible to determine based on the diffraction angles.
Analysis device: Product name (product number) "X'pert PRO MDR", manufactured by PANalytical X-ray light source: Cu-Kα ray (wavelength: 1.5405 Å)
X-ray incident angle on the first main surface: θ (17.28°)
Incidence slit width: 0.1mm x 0.1mm
Monochromator/collimator crystal: Uses 4 Ge(220) crystals.

(Pit trace)
The first main surface has a plurality of pit traces. The density of the pit traces is 0.1 pieces/cm ² or more and 100 pieces/cm ² or less. The density of the pit traces is preferably 1 piece/cm ² or more and 100 pieces/cm ² or less. This allows the radius of curvature of the (0001) plane of the GaN single crystal constituting the GaN single crystal substrate to be 6 m or more.

In this specification, the term "pit" in the term "pit trace" refers to a gap between the so-called facet structures on the growth plane when a GaN single crystal is grown using the (0001) plane as the growth plane by the HVPE method. A concavity formed by being surrounded by an inverted hexagonal pyramid or an inverted dodecagonal pyramid. Furthermore, "pit traces" refer to regions on the first main surface corresponding to pits formed on the growth surface when the first main surface of the GaN single crystal substrate is observed using a fluorescence microscope. This refers to an approximately regular hexagonal or approximately regular dodecagonal image that appears as a trace of the pit. Here, the first main surface is the main surface on the [0001] direction side of the GaN single crystal substrate, as described above, by performing surface processing such as grinding, polishing, and dry etching on the growth surface. It can be obtained as a gallium polar plane. Details of the "pit traces" in the GaN single crystal substrate according to this embodiment will be described below with reference to FIGS. 3 to 6.

FIG. 3 is an explanatory diagram illustrating the reason why pit traces exist in the gallium nitride single crystal substrate according to the present embodiment. FIG. 4 is a schematic diagram schematically showing the distribution of pit traces existing on the first main surface of the gallium nitride single crystal substrate according to the present embodiment. FIG. 5 is a photograph substituted for a drawing showing a fluorescence microscopic image of pit traces. FIG. 6 is a photograph substituted for a drawing, which is an enlarged fluorescence microscopic image of the pit trace shown in FIG.

The GaN single-crystal substrate according to the present embodiment is produced by passing through a manufacturing process including the following growth conditions using the HVPE method, as explained in the section [Manufacturing method of gallium nitride single-crystal substrate] described below. By obtaining the crystal, a GaN single crystal substrate made of the GaN single crystal can be obtained. The manufacturing process includes first growth conditions that reduce dislocations around the pits by concentrating dislocations at the bottoms of the pits, and growing GaN single crystals while controlling the ratio of filling the pits with GaN single crystals. and a second growth condition. In particular, as shown by the double-dashed line in FIG. The growth surface (hereinafter, the growth surface of the second layer is also referred to as "second growth surface") has pits P at a density of 0.1 pits/cm ² or more and 100 pits/cm ² or less. . Here, the GaN single crystal 100 shown by the two-dot chain line in FIG. 3 represents a state in which it has been separated from the underlying substrate by conventionally known means after the growth process under the second growth condition has been performed.

Furthermore, by performing surface processing such as grinding, polishing, and dry etching on the second growth surface 10 of the GaN single crystal 100, the first main surface 11 and the second main surface 21 shown by solid lines in FIG. A GaN single crystal substrate 1 can be obtained. When the first main surface 11 of this GaN single crystal substrate 1 is observed using a fluorescence microscope, a plurality of There are pit traces T. In particular, the pit traces T on the first main surface 11 correspond to the pits P formed on the second growth surface 10, so the density of the pit traces T on the first main surface 11 is equal to the density of the pits P. Correspondingly, it is 0.1 pieces/cm ² or more and 100 pieces/cm ² or less. For example, the pit traces T on the first main surface 11 exhibit a distribution as shown in FIG. When the density of the pit traces T is within the above-mentioned range, it is difficult to generate stress in the GaN single crystal 100 as described above. The radius of curvature of the (0001) plane of the GaN single crystal can be set to 6 m or more. When the density of pit traces T is less than 0.1 pieces/cm ² , the stress generated in the GaN single crystal 100 causes the radius of curvature of the (0001) plane of the GaN single crystal forming the GaN single crystal substrate 1 to be 6 m or more. It becomes difficult to do so. If the density of pit traces T exceeds 100 pieces/cm ² , the dislocation density increases due to the large number of pits in the GaN single crystal constituting the GaN single crystal substrate 1, so it is difficult to improve device characteristics. It becomes difficult.

Here, the pit trace T has a substantially regular hexagonal shape or a substantially regular dodecagonal shape, as shown in FIGS. 5 and 6. The diameter of the pit trace T is preferably 200 μm or less. This prevents dislocations from excessively concentrating on the pits in the GaN single crystal corresponding to the pit traces T, making it easy to improve device characteristics. The diameter of the pit trace T is more preferably 100 μm or less. The lower limit of the diameter of the pit trace T is not particularly limited, but in view of obtaining this type of GaN single crystal substrate 1, it is realistic to set it to 5 μm or more. In this specification, the "diameter" of the pit trace T shall mean the distance between two points that are farthest apart on the outline of the substantially regular hexagonal shape or the substantially regular dodecagonal shape of the pit trace T.

Hereinafter, a measurement method (hereinafter also referred to as "fluorescence microscope image mapping measurement") for identifying both the pit trace and its diameter in a GaN single crystal substrate will be described. It has been known that the concentration of impurities is different between the region where pit traces exist and the other regions on the gallium polar plane of the main surface of a GaN single crystal substrate manufactured using the above-mentioned HVPE method. It will be done. For this reason, by using the above-mentioned fluorescence microscope image mapping measurement and irradiating the first main surface, which is the gallium polar surface, with fluorescence having a wavelength under the following conditions, the first main surface can be measured using the density of the impurity as an index. It becomes possible to identify the upper pit trace and its diameter.

First, a GaN single-crystal substrate to be measured is prepared by obtaining a GaN single-crystal substrate having a first main surface and a second main surface, for example, according to a manufacturing method described later. Next, the first main surface of the GaN single crystal substrate was scanned using a fluorescence microscope image mapping device (for example, product name: "LEICA DM6000M", manufactured by Leica) under the following conditions and with a field of view of 2.5 mm. Observe at a magnification of x1.9 mm. The above observation is carried out by moving the GaN single crystal substrate so that there is no overlap and setting a complete field of view, covering the entire first main surface. For example, when the diameter of the GaN single crystal substrate is 105 mm, the total number of fields of view is 41×54 (=2214 fields of view). However, if the outer periphery of the first main surface and its outside appear within one field of view, that field of view shall be excluded from the targets for specifying both the pit trace and its diameter. This is because the region near the outer periphery of the GaN single crystal substrate is usually not used as a material for semiconductor devices.

The conditions for the fluorescence microscopic image mapping measurement are as follows.
Irradiation light: Ultraviolet excitation using a mercury lamp (wavelength 365 nm)
Fluorescence wavelength range: 365-650nm
Temperature: room temperature (25°C).

As described above, the density and diameter of pit traces per cm ² on the first main surface of the GaN single crystal substrate can be determined from the number of pit traces identified in each field of view and their diameters.

(dislocation density)
The maximum value of the dislocation density on the first main surface of the GaN single crystal substrate according to this embodiment is preferably 3.0×10 ⁶ /cm ² or less. The maximum value of the dislocation density on the first main surface of the GaN single crystal substrate is more preferably 2.5×10 ⁶ /cm ² or less, and preferably 2.0×10 ⁶ /cm ² or less. More preferred. As a result, it is possible to achieve low dislocations on the first main surface of a GaN single crystal substrate in which the radius of curvature of the (0001) plane of the GaN single crystal that constitutes the substrate is as large as 6 m or more.

In this specification, "dislocations" and "dislocation density" refer to "defects" which are threading dislocations identified by applying multiphoton excitation photoluminescence to the first main surface, and "defects" which are threading dislocations identified by applying multiphoton excitation photoluminescence to the first main surface, and The number of pieces per 1 cm ² of the main surface of 1. The above-mentioned "defects" appear as dark spots when the first main surface of the GaN single crystal substrate is observed using a multiphoton excitation microscope or the like. Although the above-mentioned "defect" is not academically synonymous with dislocation, it can be regarded as equivalent to dislocation in this technical field.

Further, the number of defects per 1 cm ² of the first main surface can be determined by the following method. First, a GaN single crystal substrate is manufactured by a manufacturing method described later. Next, the first main surface of the GaN single crystal substrate is observed using a multiphoton excitation microscope. The above observation can be performed by forming an image on the CCD with a 5x objective lens. In this case, the size of one field of view is 2.5 mm x 2.0 mm, so the defects that appear in the enlarged image of the central part (size of 0.1 mm x 0.1 mm) are counted and this is calculated as a unit. Convert it to the area of 1 cm ² (that is, multiply by 10,000). However, if the image quality of the enlarged image is poor, a high magnification image can be obtained by increasing the magnification of the objective lens to 100 times, and defects in the central part (0.1 mm x 0.1 mm size) of the high magnification image can be detected. and convert it to the size of 1 cm ² , which is the unit area. As described above, the "number of defects per 1 cm ² of the first main surface" in the observed field of view can be determined. Note that the magnification of the objective lens when imaging defects is preferably changed as appropriate so that the number of defects per field of view is approximately 100, for example. The number of defects mentioned above per 1 cm ² of the first main surface is calculated by moving the GaN single crystal substrate so that there are no duplications and setting a complete field of view, covering the entire main surface. . However, if the outer periphery of the first main surface and the outside thereof appear within one field of view, that field of view shall be excluded from the calculation of the number of defects per 1 cm ² of the first main surface. This is because the region near the outer periphery of a GaN single crystal substrate has large variations in the number of defects from substrate to substrate, and is usually a region that is not used as a material for semiconductor devices.

As described above, it is possible to grasp the in-plane distribution of the number of defects per 1 cm ² of the first main surface in the GaN single crystal substrate from the number of defects per 1 cm ² of the first main surface determined in each field of view. , the maximum value of dislocation density in the GaN single crystal substrate (first main surface) can be determined.

[Method for manufacturing gallium nitride single crystal substrate]
The method for manufacturing a gallium nitride single crystal substrate (GaN single crystal substrate) according to this embodiment is preferably a method for manufacturing a GaN single crystal substrate having the above-described first main surface and second main surface. The above manufacturing method includes a step of preparing a base substrate having a gallium nitride film disposed on at least a portion of the surface thereof, and growing a gallium nitride single crystal in the gallium nitride film under first growth conditions. a step of forming a first layer on the gallium film; and a step of forming a second layer on the first layer by growing the gallium nitride single crystal under second growth conditions in the first layer. and obtaining the gallium nitride single crystal substrate by cutting out the second layer. The growth surface of the first layer has a pit density of more than 100 pits/cm ² . The growth surface of the second layer has a pit density of 0.1 pits/cm ² or more and 100 pits/cm ² or less. The first growth conditions are a gallium chloride gas partial pressure of 0.1 kPa or more and 20 kPa or less, an ammonia gas partial pressure of 0.5 kPa or more and 50 kPa or less, a growth temperature of 900°C or more and 1100°C or less, and a growth rate of 10 μm/hour or more and 300 μm or less. It has a growth rate of less than /hour. The second growth conditions are a gallium chloride gas partial pressure of 1 kPa or more and 50 kPa or less, an ammonia gas partial pressure of 1 kPa or more and 100 kPa or less, a growth temperature of 900°C or more and 1100°C or less, and a growth temperature of 50 μm/hour or more and 500 μm/hour or less. growth rate. The growth temperature under the first growth condition is lower than the growth temperature under the second growth condition.

In particular, the first growth conditions are a gallium chloride gas partial pressure of 1 kPa or more and 5 kPa or less, an ammonia gas partial pressure of 5 kPa or more and 20 kPa or less, a growth temperature of 950° C. or more and 1050° C. or less, and 10 μm/hour or more and 200 μm/hour or less. It is preferable to have a growth rate of . The second growth conditions are a gallium chloride gas partial pressure of 3 kPa or more and 10 kPa or less, an ammonia gas partial pressure of 5 kPa or more and 50 kPa or less, a growth temperature of 1000°C or more and 1100°C or less, and a growth temperature of 50 μm/hour or more and 400 μm/hour or less. It is preferable to have a growth rate. By using a manufacturing method having such characteristics, it is possible to obtain a GaN single crystal substrate in which the characteristics of each region of the first main surface are uniform without variation, and the device characteristics can be improved.

The method for manufacturing a GaN single crystal substrate described above preferably includes steps as shown in the flowchart of FIG. 7, for example, from the viewpoint of manufacturing a GaN single crystal substrate having the above-mentioned effects with a high yield. FIG. 7 is a flowchart illustrating an example of a method for manufacturing a gallium nitride single crystal substrate according to this embodiment. In other words, the method for manufacturing the GaN single crystal substrate includes step S10 (first step) of preparing a base substrate on which a gallium nitride film is disposed on at least a portion of the surface, and a step of first growing a GaN single crystal in the gallium nitride film. Step S20 (second step) of forming a first layer on the gallium nitride film by growing it under conditions, and growing the GaN single crystal under second growth conditions in the first layer. This includes a step S30 (third step) of forming a second layer on the first layer, and a step S40 (fourth step) of obtaining the GaN single crystal substrate by cutting out the second layer. Each step will be explained in order below.

<First step>
The first step is step S10 of preparing a base substrate on which a gallium nitride film is disposed on at least a portion of the surface. This process will be explained below using FIG. 8. FIG. 8 is a schematic cross-sectional diagram illustrating how a mask is placed on a base substrate in order to perform the step of forming a first layer on a gallium nitride film in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment. It is a diagram. As shown in FIG. 8, the first step consists of a growth substrate 41 and a gallium nitride film (hereinafter also referred to as "GaN film") 42 disposed on at least a part of the surface of the growth substrate 41. Base substrate 40 is prepared. The material of the growth substrate 41 is not particularly limited as long as it is a material that allows the growth of the GaN film 42. For example, as the growth substrate 41, a heterogeneous substrate using a material different from GaN (different material) such as a sapphire substrate or a gallium arsenide (GaAs) substrate can be prepared, and a homogeneous substrate using GaN (the same material) can be prepared. You can also prepare. In addition, the growth substrate 41 includes 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 or the like may also be used. These growth substrates 41 can be obtained from the market or manufactured by conventionally known methods. The GaN film 42 can be disposed on at least a portion of the surface of the growth substrate 41 by a conventionally known method such as MOCVD (metal organic chemical vapor deposition).

Further, a mask 43 may be disposed on the GaN film 42 of the base substrate 40 to suppress generation of an excessive number of dislocations in the GaN single crystal that will be the first layer to be described later. The mask 43 can be formed on the GaN film 42 using a conventionally known method. Here, the pattern of the mask 43 is not particularly limited as long as it is a pattern that can suppress generation of an excessive number of dislocations in the GaN single crystal. The pattern of the mask 43 can be a conventionally known pattern, such as a grid, dot or stripe pattern formed by alternately arranging shielding parts and openings. I can do it. Furthermore, the mask 43 can be formed, for example, by the following method. First, a chemical vapor deposition film (for example, a silicon-based chemical vapor deposition film) is formed on the entire surface of the base substrate 40 by a plasma CVD (Chemical Vapor Deposition) method or the like. Thereafter, a resist patterned by photolithography is formed on the chemical vapor deposition film, and etching is performed using the resist as an etching mask, thereby forming the mask 43.

<Second process>
The second step is a step S20 in which a first layer is formed on the GaN film by growing a GaN single crystal under first growth conditions. In this process, the aim is to obtain a GaN single crystal (first layer) having a pit density exceeding 100 pits/ ^cm2 on the growth surface, and the growth surface (hereinafter referred to as , the growth surface in the first layer is also referred to as "first growth surface"), and the first growth conditions are such that dislocations are reduced around the pits by concentrating dislocations at the bottoms of the pits. Execute the adopted HVPE method.

The HVPE method based on the first growth conditions can be performed, for example, in the following manner. First, a base substrate is placed on a quartz sample holder in a hot wall reactor, and at least the GaN film in the base substrate is heated to about 1000°C. Next, gallium chloride gas is generated by spraying hydrogen chloride (HCl) gas with hydrogen (H ₂ ) gas as a carrier gas onto metal Ga installed in an upstream boat in the reactor. Furthermore, ammonia gas is introduced into the reactor. Subsequently, by supplying the above-mentioned gallium chloride gas and ammonia gas to the GaN film in the base substrate through the opening of the mask using hydrogen gas as a carrier gas, a GaN film is formed on the side of the base substrate where the mask is formed. The crystal can be grown under the following first growth conditions. The thickness of the GaN single crystal (first layer) can be adjusted by controlling the amount or time of supply of gallium chloride gas and ammonia gas.

The specific first growth conditions are as follows.
Gallium chloride gas partial pressure: 0.1-20kPa
Ammonia gas partial pressure: 0.5-50kPa
Growth temperature: 900-1100℃
Growth rate: 10-300 μm/hour V/III (ammonia gas/gallium chloride gas) ratio: 1-10.

Here, the gallium chloride gas partial pressure under the first growth condition is preferably 1 to 5 kPa, and the ammonia gas partial pressure is preferably 5 to 20 kPa. The growth temperature under the first growth condition is preferably 950 to 1050°C, and the growth rate is preferably 10 to 200 μm/hour.

Further, the gallium chloride gas partial pressure under the first growth condition is more preferably 2 to 4 kPa, and the ammonia gas partial pressure is more preferably 10 to 15 kPa. The growth temperature under the first growth condition is more preferably 950 to 1000° C., and the growth rate is more preferably 20 to 100 μm/hour. Note that the growth temperature under the first growth condition is lower than the growth temperature under the second growth condition, which will be described later.

FIG. 9 is a schematic cross-sectional view illustrating how a first layer (GaN single crystal) is formed on a gallium nitride film in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment. As shown in FIG. 9, in the second step, a first layer 44 made of GaN single crystal and having a thickness of 0.05 to 0.5 mm can be formed on the mask 43. The first growth surface 5 of the first layer 44 has many pits P, and the pit density exceeds 100/cm ² . Here, the pit density on the first growth surface 5 of the first layer 44 can be determined in the same manner as the method for determining the "pit trace density" described above.

<3rd process>
The third step is step S30 of forming a second layer on the first layer by growing the GaN single crystal under second growth conditions in the first layer. In this process ^{, the purpose is to obtain a GaN single crystal (second layer) having a pit density of 0.1 to 100 pits/cm 2} ^on ^the growth surface; The HVPE method employing second growth conditions for controlling and reducing the pit density is performed on the first layer having the pit density on the first growth surface.

The HVPE method based on the above second growth conditions is the same as the HVPE method based on the above first growth conditions, except for the specific gas partial pressure, growth temperature and growth rate conditions based on the second growth conditions described below. This can be done according to the guidelines. Thereby, a GaN single crystal (second layer) can be grown on the first layer, specifically on the first growth surface side of the first layer. The thickness of the GaN single crystal (second layer) can be adjusted by controlling the amount or time of supply of gallium chloride gas and ammonia gas.

The specific second growth conditions are as follows.
Gallium chloride gas partial pressure: 1-50kPa
Ammonia gas partial pressure: 1-100kPa
Growth temperature: 900-1100℃
Growth rate: 50 to 500 μm/hour V/III (ammonia gas/gallium chloride gas) ratio: 1 to 5
However, as described above, the growth temperature under the second growth condition is set higher than the growth temperature under the first growth condition.

Here, the gallium chloride gas partial pressure under the second growth condition is preferably 3 to 10 kPa, and the ammonia gas partial pressure is preferably 5 to 50 kPa. The growth temperature under the first growth condition is preferably 1000 to 1100°C, and the growth rate is preferably 50 to 400 μm/hour.

Furthermore, the gallium chloride gas partial pressure under the second growth condition is more preferably 3 to 10 kPa, and the ammonia gas partial pressure is more preferably 5 to 50 kPa. The growth temperature under the second growth condition is more preferably 1020 to 1080°C, and the growth rate is more preferably 50 to 300 μm/hour.

FIG. 10 is a schematic cross-sectional view illustrating how a second layer (GaN single crystal) is formed on the first layer in the method for manufacturing a gallium nitride single crystal substrate according to the present embodiment. As shown in FIG. 10, in the third step, a second layer 45 made of GaN single crystal and having a thickness of 1 to 10 mm can be formed on the first layer 44. The second growth surface 10 of ^the second layer 45 has a pit density of 0.1 to 100/cm ² by controlling the number of pits P. The pit density is preferably 1 pit/cm ² or more and 100 pits/cm ² or less. Here, the pit density on the second growth surface 10 of the second layer 45 can also be determined in the same manner as the method for determining the "pit trace density" described above.

<4th step>
The fourth step is step S40 of obtaining the GaN single crystal substrate by cutting out the second layer. In this step, referring to FIG. 10, first, in a structure including a growth substrate 41, a GaN film 42, a mask 43, a first layer 44, and a second layer 45, the first layer 44 side of the second layer 45 is ground. do. As a result, the growth substrate 41, the underlying substrate including the GaN film 42, the mask 43, and the first layer 44 can be separated from the structure. Furthermore, a disk-shaped GaN single crystal is cut out with a predetermined thickness from the ingot made of the second layer 45. The surface of the GaN single crystal substrate is flattened by grinding, and then both or at least one of polishing and dry etching is performed. Thereby, a GaN single crystal substrate having a first main surface and a second main surface can be obtained. The GaN single crystal substrate has a plurality of pit traces in a region on the first main surface corresponding to the pits formed on the second growth surface 10 of the second layer 45. That is, the density of the pit traces corresponds to the pit density of the second growth surface 10 of the second layer 45, and is 0.1 pieces/cm ² or more and 100 pieces/cm ² or less (see also FIG. 3).

<Effect>
Through the above steps, the GaN single crystal substrate according to this embodiment can be manufactured. In the GaN single crystal substrate, the (0001) plane of the GaN single crystal constituting the substrate is a spherical curved surface that is convex from the first main surface side to the second main surface side, And it can have a radius of curvature of 6 m or more. Therefore, by the above manufacturing method, since the radius of curvature of the (0001) plane of the GaN single crystal is large, the characteristics of each region of the first main surface are uniform without variation, so that a GaN single crystal with improved device characteristics can be obtained. A substrate can be obtained.

Hereinafter, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited thereto. In this example, one sample of each GaN single crystal substrate was obtained by carrying out the following GaN single crystal substrate manufacturing method.

[Sample 1: Production of a GaN single crystal substrate with a diameter of 50.8 mm (2 inches)]
<First step>
A base substrate was prepared by obtaining a commercially available sapphire substrate with a diameter of 50.8 mm and forming a GaN film on the sapphire substrate using the MOCVD method. The plane orientation of the main surface of the GaN film was a (0001) plane. Subsequently, a mask having a structure in which shielding portions and opening portions were alternately repeated was formed on the GaN film side of the base substrate. Specifically, a plasma CVD method is applied to the GaN film side of the base substrate to form a chemical vapor deposited film (thickness 200 nm) made of silicon oxide, and then a resist patterned by photolithography is applied on the chemical vapor deposited film. A mask was formed by etching using the resist as an etching mask.

<Second process>
By applying the HVPE method, a GaN single crystal (first layer) having a so-called facet structure was grown in the GaN film of the base substrate through the opening of the mask under the following first growth conditions. Specifically, a base substrate was placed on a quartz sample holder in a hot wall reactor, and after heating the inside of the reactor to 980°C, a metal Ga was placed in a boat on the upstream side of the reactor. Then, gallium chloride gas was generated and supplied by spraying HCl gas, and then ammonia gas was supplied into the reactor. Further, the reactor was maintained at 980° C. for 2.5 hours. As the first growth conditions, the partial pressure of gallium chloride gas was 3.0×10 ³ Pa, and the partial pressure of ammonia gas was 12×10 ³ Pa. Further, the growth rate of the growth surface (first growth surface) of the GaN single crystal was set to 40 μm/hour. As a result, a GaN single crystal (first layer) was obtained whose growth plane (first growth plane) was the (0001) plane and whose thickness was 0.1 mm as measured with a stylus-type film thickness meter. Furthermore, the pit density on the growth surface measured by the method described above exceeded 100 pits/cm ² . Gallium chloride gas is generated by spraying hydrogen chloride (HCl) gas with hydrogen (H ₂ ) gas as a carrier gas onto metal Ga installed in an upstream boat in the reactor.

<3rd process>
By continuing to apply the HVPE method, a GaN single crystal (second layer) was grown on the first growth surface of the first layer under the following second growth conditions. Specifically, after heating the inside of the reactor to 1030°C, 1 mass of HCl gas was applied to the first growth surface of the first layer placed on a quartz sample holder in a hot wall reactor. Gallium chloride gas and iron chloride gas, which were generated by reacting with Ga to which % of Fe was added, and ammonia gas were supplied into the reactor. Further, the reactor was maintained at 1030° C. for 37.5 hours. The second growth conditions include a gallium chloride gas partial pressure of 4.0×10 ³ Pa, an iron chloride gas partial pressure of 1/100 of the gallium chloride gas, and an ammonia gas partial pressure of 8.0×10 3 Pa. ³ Pa. Further, the growth rate of the GaN single crystal growth surface (second growth surface) was set to 80 μm/hour. Thereafter, the temperature inside the reactor was lowered to room temperature, and a GaN single crystal (second layer) was obtained on the first layer. The second layer had a (0001) growth surface (second growth surface) and a thickness of 3 mm as measured with a stylus-type film thickness meter. Furthermore, the pit density on the second growth surface measured by the method described above was 0.1 pits/cm ² .

<4th step>
In the structure including the base substrate, the mask, the first layer, and the second layer, by grinding the first layer side (one of the two main surfaces and the side that becomes the nitrogen polar surface) of the second layer. Then, the second layer was separated from the underlying substrate, GaN film, and mask. Furthermore, a disk-shaped GaN single crystal was cut out at a predetermined thickness from the ingot made of the second layer. Subsequently, the surfaces of the GaN single crystal (both the gallium polar surface and the nitrogen polar surface) were flattened by grinding, and then polished. As described above, a GaN single crystal substrate of Example 1 having a diameter of 50.8 mm (2 inches), a thickness of 350 μm, and a circular first main surface and a second main surface was manufactured.

[Sample 2: Production of a GaN single crystal substrate with a diameter of 101.6 mm (4 inches)]
In the first step, a commercially available sapphire substrate with a diameter of 101.6 mm was obtained, and a GaN film was formed on the sapphire substrate by MOCVD, the growth temperature, growth rate, and gallium chloride gas of the first growth conditions in the second step. Same as sample 1 except that the partial pressure and ammonia gas partial pressure, and the growth temperature, growth rate, gallium chloride gas partial pressure, and ammonia gas partial pressure of the second growth conditions in the third step were changed as shown in Table 1. According to the procedure, a GaN single crystal substrate of Example 2 having a diameter of 101.6 mm (4 inches), a thickness of 450 μm, and a circular first main surface and a second main surface was manufactured. The thicknesses (mm) of the first layer and second layer in Sample 2 are shown in Table 1. The pit density on the first growth surface of Sample 2 measured by the method described above was over 100 pits/cm ² , and the pit density on the second growth surface was 0.2 pits/cm ² .

[Samples 3 to 7: Production of GaN single crystal substrates with a diameter of 101.6 mm (4 inches)]
Growth temperature, growth rate, gallium chloride gas partial pressure and ammonia gas partial pressure under the first growth conditions in the second step, and growth temperature, growth rate, gallium chloride gas partial pressure and ammonia gas under the second growth conditions in the third step. A second main surface having a diameter of 101.6 mm (4 inches), a thickness of 450 μm, and a circular first main surface and a second main surface was prepared in the same manner as Sample 2 except that the partial pressure was changed as shown in Table 1. GaN single crystal substrates of Samples 3 to 7 were manufactured, respectively. The thicknesses (mm) of the first layer and second layer in Samples 3 to 7 are shown in Table 1. The pit density on the first growth surface of Samples 3 to 7 measured by the method described above exceeded 100 pits/cm ² . The pit density on the second growth surface in Sample 3 is 0.5/cm ² , the pit density on the second growth surface in Sample 4 is 1/cm ² , and the pit density on the second growth surface in Sample 5 was 2.55 pits/cm ² , the pit density on the second growth surface in Sample 6 was 10 pits/cm ² , and the pit density on the second growth surface in Sample 7 was 100 pits/cm ² .

[Example 8: Production of a GaN single crystal substrate with a diameter of 152.4 mm (6 inches)]
In the first step, a commercially available sapphire substrate with a diameter of 152.4 mm was obtained, and a GaN film was formed on the sapphire substrate by MOCVD, the growth temperature, growth rate, and gallium chloride gas of the first growth conditions in the second step. Same as sample 1 except that the partial pressure and ammonia gas partial pressure, and the growth temperature, growth rate, gallium chloride gas partial pressure, and ammonia gas partial pressure of the second growth conditions in the third step were changed as shown in Table 1. According to the procedure, a GaN single crystal substrate of sample 8 having a diameter of 152.4 mm (6 inches), a thickness of 675 μm, and a circular first main surface and a second main surface was manufactured. The thicknesses (mm) of the first layer and second layer in Sample 8 are shown in Table 1. The pit density on the first growth surface of sample 8 measured by the method described above was over 100 pits/cm ² , and the pit density on the second growth surface was 90 pits/cm ² .

[Sample 11 and Sample 12: Production of 50.8 mm (2 inch) diameter GaN single crystal substrate]
Growth temperature, growth rate, gallium chloride gas partial pressure and ammonia gas partial pressure under the first growth conditions in the second step, and growth temperature, growth rate, gallium chloride gas partial pressure and ammonia gas under the second growth conditions in the third step. A circular first main surface and a second main surface with a diameter of 50.8 mm (2 inches) and a thickness of 350 μm were prepared in the same manner as Sample 1 except that the partial pressure was changed as shown in Table 1. GaN single crystal substrates of Sample 11 and Sample 12 were manufactured. The thicknesses (mm) of the first layer and second layer in Sample 11 and Sample 12 are shown in Table 1. The pit density on the first growth surface of Samples 11 and 12 measured by the method described above exceeded 100 pits/cm ² . The pit density on the second growth surface in sample 11 was 0.05 pits/cm ² , and the pit density on the second growth surface in sample 12 was 300 pits/cm ² .

[Sample 13: Production of a GaN single crystal substrate with a diameter of 50.8 mm (2 inches)]
According to the description of the method for manufacturing a GaN single crystal substrate disclosed as Example 1 in Patent Document 1, the density of pit-embedded regions (corresponding to "pit traces" in this specification) is 1.0 x 10 ^-2 pieces. A GaN single crystal substrate was manufactured so that the number of particles/cm ² or more and 0.9 pieces/cm ² or less was obtained, and this was used as the GaN single crystal substrate of sample 13.

In manufacturing the GaN single crystal substrate of Sample 13, referring to Patent Document 1 mentioned above, a silicon (Si)-doped gallium nitride layer is formed as the first stage of growth (corresponding to the "second step" in this specification). A GaN single crystal having a multilayer structure in which 20 undoped gallium nitride layers (thickness: 700 nm) and undoped gallium nitride layers (thickness: 500 nm) were grown alternately was manufactured. Furthermore, as a second stage of growth (corresponding to the "third step" in this specification), after growing a GaN single crystal that will become an undoped gallium nitride layer (thickness 0.2 mm), a Si-doped gallium nitride layer (thickness A GaN single crystal with a thickness of 3 mm) was grown.

Thereafter, the GaN single crystal is separated from the base substrate, and surface processing is performed on the GaN single crystal (corresponding to the "fourth step" in this specification), so that the diameter is 50.8 mm (2 inches). A GaN single crystal substrate of sample 13 having a thickness of 350 μm and a circular shape was manufactured. The conditions regarding the growth temperature, growth rate, various gas partial pressures, etc. in the first and second stages of growth are as shown in Table 1. Furthermore, the thicknesses (mm) of the first layer and second layer in Sample 13 are shown in Table 1. The pit density on the first growth surface of sample 13 measured by the method described above was over 100 pits/cm ² , and the pit density on the second growth surface was 0.9 pits/cm ² .

[Sample 14: Production of a GaN single crystal substrate with a diameter of 50.8 mm (2 inches)]
According to the description of the method for manufacturing a GaN single crystal substrate disclosed as Comparative Example 1 in Patent Document 1, the density of pit-embedded regions (corresponding to "pit traces" in this specification) is 1 piece/cm ² or more. A GaN single crystal substrate was manufactured so that the number of GaN single crystals was 9 pieces/cm ² or less, and this was used as a GaN single crystal substrate of sample 14.

In manufacturing the GaN single crystal substrate of sample 14, a GaN single crystal to become a Si-doped gallium nitride layer (thickness: 3 mm) was grown directly on the base substrate by referring to Patent Document 1 mentioned above (in this specification). This corresponds to the "third step." Therefore, in sample 14, crystal growth corresponding to the "second step" in this specification is not performed.) Thereafter, the GaN single crystal is separated from the base substrate, and surface processing is performed on the GaN single crystal (corresponding to the "fourth step" in this specification), so that the diameter is 50.8 mm (2 inches). A GaN single crystal substrate of sample 14 having a thickness of 350 μm and a circular shape was manufactured. The conditions regarding the growth temperature, growth rate, various gas partial pressures, etc. in the first and second stages of growth are as shown in Table 1. The thickness (mm) of the second layer in sample 14 is shown in Table 1. Further, the density of the pit-embedded region in Sample 14 was 1.9 pits/cm ² .

[Sample 15: Production of a GaN single crystal substrate with a diameter of 50.8 mm (2 inches)]
According to the description regarding the method for manufacturing a GaN single crystal substrate disclosed in Patent Document 2 above, a GaN single crystal is manufactured so that the pit density (corresponding to the density of "pits" in this specification) is 10 pieces/cm ² or less. Then, a GaN single crystal substrate of Sample 15 was obtained by manufacturing a GaN single crystal substrate from the GaN single crystal.

In manufacturing the GaN single crystal substrate of sample 15, the first stage of growth (corresponding to the "second step" in this specification) and the second stage of growth (corresponding to (corresponding to the "third step" in Table 1), a GaN single crystal was grown under conditions such as growth temperature, growth rate, various gas partial pressures, and V/III ratio as shown in Table 1.

Thereafter, the GaN single crystal is separated from the underlying substrate and subjected to surface processing (corresponding to the "fourth step" in this specification), resulting in a circular shape with a diameter of 50.8 mm (2 inches) and a thickness of 350 μm. A GaN single crystal substrate of Sample 15 was manufactured. The thicknesses (mm) of the first layer and second layer in sample 15 are shown in Table 1. The pit density on the first growth surface of sample 15 measured by the method described above was over 100 pits/cm ² , and the pit density on the second growth surface was 1 pit/cm ² .

[Evaluation of GaN single crystal substrate]
For the GaN single crystal substrates of Samples 1 to 8 and Samples 11 to 15, the density of pit traces (pieces/cm ² ) on the first main surface and the configuration of the GaN single crystal substrates were determined based on the method described above. The radius of curvature (m) of the (0001) plane of the GaN single crystal, the diameter (μm) of the pit trace, and the maximum value of the dislocation density (pieces/cm ² ) were calculated. The results are shown in Table 2. Note that the density of pit traces (pieces/cm ² ) on the first main surface has the same value as the pit density (pieces/cm ² ) on the second growth surface. Samples 1 to 8 are examples, and samples 11 to 15 are comparative examples.

[Consideration]
In the GaN single crystal substrates of Samples 1 to 8, the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrate is as large as 6 m or more, so that the characteristics are uniform in each region of the first main surface. It is suggested. Furthermore, the density of pit traces in the GaN single crystal substrates of Samples 1 to 8 is between 0.1 pieces/cm ² and 100 pieces/cm ² , so there are no pit traces in the GaN single crystal constituting the GaN single crystal substrates. The dislocation density does not become high due to the large number of dislocations. On the other hand, in the GaN single crystal substrates of Sample 11 and Samples 13 to 15, the radius of curvature of the (0001) plane of the GaN single crystal constituting the substrates was 5 m or less. In the GaN single crystal substrate of sample 12, the density of pit traces was 300 pieces/cm ² and exceeded 100 pieces/cm ² .

Therefore, it is suggested that the GaN single crystal substrate according to this example can provide good device characteristics because the in-plane specific resistance value is uniform without variation.

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

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and it is intended that equivalent meanings to the claims and all changes within the scope are included.

1 Gallium nitride single crystal substrate (GaN single crystal substrate), 5 First growth surface, 10 Second growth surface, 100 Gallium nitride single crystal (GaN single crystal), 11 First main surface, 21 Second main surface, 31 (0001) plane, 40 base substrate, 41 growth substrate, 42 gallium nitride film (GaN film), 43 mask, M0 to M4 measurement points, P pit, T pit trace, S10 step of preparing base substrate S20 GaN film Step of forming a first layer on the top, S30 Step of forming a second layer on the first layer, S40 Step of obtaining a GaN single crystal substrate.

Claims

A gallium nitride single crystal substrate comprising a first main surface and a second main surface,
The diameter of the gallium nitride single crystal substrate is 50 mm or more,
the first main surface is a gallium polar surface,
The second main surface is a nitrogen polar surface,
The first main surface and the second main surface have a circular shape,
In the gallium nitride single crystal substrate, the (0001) plane of the gallium nitride single crystal constituting the substrate is a spherical curved surface that is convex from the first main surface side to the second main surface side. and has a radius of curvature of 6 m or more,
The first main surface has a plurality of pit traces,
The gallium nitride single crystal substrate has a density of the pit traces of 0.1 pieces/cm 2 or more and 100 pieces/cm 2 or less.
The diameter of the pit trace is 200 μm or less,
The gallium nitride single crystal substrate according to claim 1, wherein the polarity of the region corresponding to the pit trace on the first main surface is gallium polarity.
The gallium nitride single crystal substrate according to claim 1 or 2, wherein the (0001) plane has a radius of curvature of 11 m or more.
The gallium nitride single crystal substrate according to any one of claims 1 to 3, wherein the density of the pit traces is 1 piece/cm 2 or more and 100 pieces/cm 2 or less.
The gallium nitride single crystal substrate according to any one of claims 1 to 4, wherein the gallium nitride single crystal substrate has a diameter of 50 mm or more and 155 mm or less.
A method for manufacturing a gallium nitride single crystal substrate having a first main surface and a second main surface, the method comprising:
preparing a base substrate with a gallium nitride film disposed on at least a portion of the surface;
forming a first layer on the gallium nitride film by growing a gallium nitride single crystal under first growth conditions in the gallium nitride film;
forming a second layer on the first layer by growing the gallium nitride single crystal under second growth conditions in the first layer;
obtaining the gallium nitride single crystal substrate by cutting out the second layer,
The growth surface of the first layer has a pit density of more than 100 pits/cm 2 ,
The growth surface of the second layer has a pit density of 0.1 pits/cm 2 or more and 100 pits/cm 2 or less,
The first growth condition is
A gallium chloride gas partial pressure of 0.1 kPa or more and 20 kPa or less,
Ammonia gas partial pressure of 0.5 kPa or more and 50 kPa or less,
A growth temperature of 900°C or higher and 1100°C or lower,
has a growth rate of 10 μm/hour or more and 300 μm/hour or less,
The second growth condition is
Gallium chloride gas partial pressure of 1 kPa or more and 50 kPa or less,
Ammonia gas partial pressure of 1 kPa or more and 100 kPa or less,
A growth temperature of 900°C or higher and 1100°C or lower,
has a growth rate of 50 μm/hour or more and 500 μm/hour or less,
A method for manufacturing a gallium nitride single crystal substrate, wherein the growth temperature under the first growth condition is lower than the growth temperature under the second growth condition.
The first growth condition is
A gallium chloride gas partial pressure of 1 kPa or more and 5 kPa or less,
Ammonia gas partial pressure of 5 kPa or more and 20 kPa or less,
A growth temperature of 950°C or more and 1050°C or less,
has a growth rate of 10 μm/hour or more and 200 μm/hour or less,
The second growth condition is
Gallium chloride gas partial pressure of 3 kPa or more and 10 kPa or less,
Ammonia gas partial pressure of 5 kPa or more and 50 kPa or less,
A growth temperature of 1000°C or more and 1100°C or less,
The method for manufacturing a gallium nitride single crystal substrate according to claim 6, having a growth rate of 50 μm/hour or more and 400 μm/hour or less.