Gallium arsenide single crystal substrate and method for producing same

Abstract

Provided is a gallium arsenide single crystal substrate having a main surface having a circular shape and having a first integrated intensity ratio, a second integrated intensity ratio of 0.9-1.05, a third integrated intensity ratio of 0.9-1.05, a fourth integrated intensity ratio of 0.9-1.05, and a fifth integrated intensity ratio of 0.9-1.05. The third integrated intensity ratio and the fourth integrated intensity ratio are 1.0 or less, the fifth integrated intensity ratio is 0.8 or less, and the ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5-1.

Description

Technical Field

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

[0002] Japanese Patent Laid-Open No. 06-045318 (Patent Document 1) proposes a gallium arsenide single crystal substrate (hereinafter also referred to as "GaAs single crystal substrate") capable of performing a thermal cleaning operation for removing an oxide film at a low temperature and in a short time. This GaAs single crystal substrate can be realized by artificially forming an As-rich interfacial transition layer having the following thickness on its surface. Japanese Patent Laid-Open No. 2008-300747 (Patent Document 2) proposes to provide a GaAs wafer cleaned to the following extent: by thermally cleaning at least the surface of the GaAs single crystal substrate, impurities and oxides on the surface can be removed by the thermal cleaning.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 06-045318;

[0006] Patent Document 2: Japanese Patent Laid-Open No. 2008-300747. Summary of the Invention

[0007] The gallium arsenide single crystal substrate of the present invention is a gallium arsenide single crystal substrate having a main surface, and the main surface has a circular shape. The gallium arsenide single crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio. The first integrated intensity ratio and the third integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 30°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The fourth integrated intensity ratio is obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The first integrated intensity ratio and the second integrated intensity ratio are: the ratio of the sum of the integrated intensity of arsenic present as arsenic pentoxide, the integrated intensity of arsenic present as arsenic trioxide, the integrated intensity of arsenic present as gallium arsenide, and the integrated intensity of arsenic present as metallic arsenic to the sum of the integrated intensity of gallium present as gallium monoxide, the integrated intensity of gallium present as gallium trioxide, and the integrated intensity of gallium present as gallium arsenide. The third integrated intensity ratio, the fourth integrated intensity ratio, and the fifth integrated intensity ratio are: the ratio of the sum of the integrated intensity of arsenic present as the arsenic pentoxide and the integrated intensity of arsenic present as the arsenic trioxide to the sum of the integrated intensity of gallium present as the gallium monoxide and the integrated intensity of gallium present as the gallium trioxide. The second integrated intensity ratio is 0.9 or more and 1.05 or less. The third integrated intensity ratio and the fourth integrated intensity ratio are 1.0 or less. The fifth integrated intensity ratio is 0.8 or less. The ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or more and 1 or less.

[0008] The manufacturing method of the gallium arsenide single crystal substrate of the present invention is a manufacturing method of a gallium arsenide single crystal substrate having a main surface, and the main surface has a circular shape. The manufacturing method includes: a step of preparing a gallium arsenide single crystal substrate precursor having a surface and the surface having a circular shape; and a cleaning step for obtaining the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor. The cleaning step includes: a step of polishing the surface of the gallium arsenide single crystal substrate precursor to make the surface a polished surface; a step of cleaning the polished surface with a first alkaline cleaning solution to make the polished surface an alkaline cleaning surface; a step of cleaning the alkaline cleaning surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid to make the alkaline cleaning surface an acid cleaning surface; a step of cleaning the acid cleaning surface while rotating the acid cleaning surface at a rotational speed of 1000 rpm or more in the circumferential direction and supplying a second alkaline cleaning solution to the acid cleaning surface at a flow rate of 0.1 L / minute or more and 5 L / minute or less for 30 seconds or more and 5 minutes or less to make the acid cleaning surface a second alkaline cleaning surface; a step of heat-treating the second alkaline cleaning surface under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less in an inert gas environment to make the second alkaline cleaning surface the main surface. The first alkaline cleaning solution contains 0.1 mass% or more and 10 mass% or less of a first base. The first base contains at least any one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. The second alkaline cleaning solution contains 0.3 mass ppm or more and 0.5 mass% or less of a second base. The second base contains at least any one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An example of a graph showing the relationship between the measurement depth (horizontal axis) from the main surface of the GaAs single crystal substrate of the present embodiment, the ratio of the integrated intensity of the entire arsenic element to the integrated intensity of the entire gallium element (vertical axis), and the ratio of the integrated intensity of the arsenic element present as arsenic oxide to the integrated intensity of the gallium element present as gallium oxide (vertical axis).

[0010] Figure 2 An explanatory diagram schematically illustrating the structure of an analysis system using X-ray Photoelectron Spectroscopy (XPS).

[0011] Figure 3A An example of a graph showing the background-corrected Ga3d spectrum obtained by XPS with X-rays irradiated to the center of the main surface of the GaAs single crystal substrate of the present embodiment.

[0012] Figure 3BA graph showing an example of an As3d spectrum after background correction obtained by XPS with the center of the main surface of the GaAs single crystal substrate of the present embodiment irradiated with X-rays.

[0013] Figure 4 An explanatory diagram showing five measurement points set on a GaAs single crystal substrate with a diameter of 75 mm or more and less than 150 mm in the present embodiment.

[0014] Figure 5 An explanatory diagram showing nine measurement points set on a GaAs single crystal substrate with a diameter of 150 mm or more and 205 mm or less in the present embodiment.

[0015] Figure 6 A flowchart showing a manufacturing method of the GaAs single crystal substrate of the present embodiment. Detailed implementation manners

[0016] [Problems to be solved by the present invention]

[0017] Haze is known as a method for evaluating the specularity (i.e., the presence or absence of height differences) of the surface of an epitaxial film, and an increase in its value is associated with a decrease in device characteristics. Haze refers to the irregularities of the above surface and the amount of scattered light scattered by minute defects and foreign substances present on the above surface when laser light is irradiated onto the surface of the epitaxial film. Haze is expressed as the ratio of the amount of scattered light to the amount of laser light incident on the above surface. Haze is expressed in parts per million (ppm). Haze is evaluated such that the smaller its value, the more specular the above surface and the fewer height differences. Such height differences, for example, result from stacking defects (stacking faults) generated when an epitaxial film grows on a GaAs single crystal substrate. Such stacking defects depend on the specularity of the main surface of the GaAs single crystal substrate, and therefore, it is required to reduce the value of haze by realizing a GaAs single crystal substrate having a highly specular main surface.

[0018] As means for realizing a GaAs single crystal substrate having a highly specular main surface by removing the oxide film on the main surface, the above-mentioned thermal cleaning and wet etching are known. The above-mentioned wet etching is a means for removing the oxide film on the main surface using a sulfuric acid-based aqueous solution containing sulfuric acid and hydrogen peroxide, or an NH4OH-based aqueous solution containing ammonium hydroxide and hydrogen peroxide. However, since the above-mentioned oxide film has poor wettability, there are cases where the oxide film cannot be sufficiently removed by the above-mentioned wet etching. In this case, it is impossible to obtain a GaAs single crystal substrate having a sufficiently highly specular main surface, and therefore, it is also difficult to sufficiently reduce the value of haze of the epitaxial film grown on its main surface.

[0019] In view of the above problems, an object of the present invention is to provide a gallium arsenide single crystal substrate and a method for manufacturing the same, which can improve device characteristics by using an epitaxial film with a reduced haze value.

[0020] [Effects of the present invention]

[0021] According to the present invention, it is possible to provide a gallium arsenide single crystal substrate and a method for manufacturing the same, which can improve device characteristics by using an epitaxial film with a reduced haze value.

[0022] [Outline of the embodiment]

[0023] First, the outline of the embodiment of the present invention will be described. The inventors of the present invention have repeatedly conducted in-depth research to solve the above problems, and thus completed the present invention. That is, the inventors focused on: by implementing a new cleaning method on a gallium arsenide single crystal substrate precursor cut from a gallium arsenide single crystal and having a surface with a circular shape, a main surface with high specularity is obtained in the gallium arsenide single crystal substrate. Specifically, in addition to performing the liquid-phase treatment of both the alkali cleaning using an alkaline solution and the acid cleaning using an acidic solution, which are publicly known, a second alkali cleaning is newly performed and a heat treatment is newly performed. As a result, it was found that the wettability of the oxide film is improved when the GaAs single crystal substrate obtained by the above new cleaning method has a composition in which gallium is more abundant than arsenic in the entire oxide film and this tendency continues to the interface between the oxide film and the GaAs single crystal constituting the gallium arsenide single crystal substrate. Thus, a GaAs single crystal substrate having a main surface with high specularity can be obtained by wet etching, and a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value is realized, and the present invention is completed.

[0024] Next, the embodiments of the present invention will be listed and described.

[0025] [1]One type of gallium arsenide single crystal substrate of the present invention is a gallium arsenide single crystal substrate having a main surface, and the main surface has a circular shape. The gallium arsenide single crystal substrate has a first integral intensity ratio, a second integral intensity ratio, a third integral intensity ratio, a fourth integral intensity ratio, and a fifth integral intensity ratio. The first integral intensity ratio and the third integral intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 30°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The second integral intensity ratio and the fifth integral intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The fourth integral intensity ratio is obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate. The first integral intensity ratio and the second integral intensity ratio are: The ratio of the sum of the integral intensities of arsenic elements present as arsenic pentoxide, arsenic elements present as arsenic trioxide, arsenic elements present as gallium arsenide, and arsenic elements present as metallic arsenic to the sum of the integral intensities of gallium elements present as gallium monoxide, gallium elements present as gallium trioxide, and gallium elements present as gallium arsenide. The third integral intensity ratio, the fourth integral intensity ratio, and the fifth integral intensity ratio are: The ratio of the sum of the integral intensities of arsenic elements present as the arsenic pentoxide and arsenic elements present as the arsenic trioxide to the sum of the integral intensities of gallium elements present as the gallium monoxide and gallium elements present as the gallium trioxide. The second integral intensity ratio is 0.9 or more and 1.05 or less. The third integral intensity ratio and the fourth integral intensity ratio are 1.0 or less. The fifth integral intensity ratio is 0.8 or less. The ratio of the first integral intensity ratio to the second integral intensity ratio is 0.5 or more and 1 or less.

[0026] A gallium arsenide single crystal substrate having such characteristics can effectively remove the oxide film by wet etching and has a main surface with high specularity, so an epitaxial film with a reduced haze value can be formed.

[0027] [2] The above second integral intensity ratio is preferably 0.9 or more and less than 1.04. Thus, the above oxide film can be removed more effectively by wet etching.

[0028] [3] The above gallium arsenide single crystal substrate preferably has an oxide film with a thickness of 2 nm or less on the above main surface. Thus, the above oxide film can be removed more effectively by wet etching.

[0029] [4] The contact angle of the above oxide film is preferably 20 degrees or less. Thus, the oxide film with good wettability can be removed effectively by wet etching.

[0030] [5] The above gallium arsenide single crystal substrate preferably has a diameter of 75 mm or more and 205 mm or less. Thus, the gallium arsenide single crystal substrate with a diameter of 75 mm or more and 205 mm or less can have a main surface with high specularity, and thus an epitaxial film with a reduced haze value can be formed.

[0031] [6]The above-mentioned gallium arsenide single crystal substrate preferably has the following characteristics. The above-mentioned gallium arsenide single crystal substrate has a diameter of 75 mm or more and less than 150 mm. The above-mentioned gallium arsenide single crystal substrate has a sixth integrated intensity ratio and a seventh integrated intensity ratio. The above-mentioned sixth integrated intensity ratio and the above-mentioned seventh integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are respectively irradiated to 5 measurement points on the above-mentioned main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensity of the 3d electrons of gallium and arsenic is obtained with respect to the binding energy of the photoelectrons released to the outside of the above-mentioned gallium arsenide single crystal substrate. The above-mentioned sixth integrated intensity ratio is the ratio of the sum of the integrated intensity of arsenic elements present as the above-mentioned arsenic pentoxide, the integrated intensity of arsenic elements present as the above-mentioned arsenic trioxide, the integrated intensity of arsenic elements present as the above-mentioned gallium arsenide, and the integrated intensity of arsenic elements present as the above-mentioned metallic arsenic to the sum of the integrated intensity of gallium elements present as the above-mentioned gallium monoxide, the integrated intensity of gallium elements present as the above-mentioned gallium trioxide, and the integrated intensity of gallium elements present as the above-mentioned gallium arsenide. The above-mentioned seventh integrated intensity ratio is the ratio of the sum of the integrated intensity of arsenic elements present as the above-mentioned arsenic pentoxide and the integrated intensity of arsenic elements present as the above-mentioned arsenic trioxide to the sum of the integrated intensity of gallium elements present as the above-mentioned gallium monoxide and the integrated intensity of gallium elements present as the above-mentioned gallium trioxide. The standard deviation and the average value of the ratio of the above-mentioned seventh integrated intensity ratio to the above-mentioned sixth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.039. When the above-mentioned diameter is represented by D and two axes orthogonal to each other on the above-mentioned main surface passing through the center of the above-mentioned main surface are taken as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the above-mentioned 5 measurement points are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4). The units of D and X and Y in the above-mentioned coordinates (X, Y) are mm. Thus, in a gallium arsenide single crystal substrate having a diameter of 75 mm or more and less than 150 mm, by effectively removing the oxide film using wet etching, a main surface with high specularity can be obtained without deviation in the plane, and thus an epitaxial film with a reduced haze value can be formed.

[0032] [7] The above-mentioned gallium arsenide single crystal substrate preferably has the following characteristics. The above-mentioned gallium arsenide single crystal substrate has a diameter of 150 mm or more and 205 mm or less. The above-mentioned gallium arsenide single crystal substrate has an eighth integral intensity ratio and a ninth integral intensity ratio. The above-mentioned eighth integral intensity ratio and the above-mentioned ninth integral intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are respectively irradiated to 9 measurement points on the above-mentioned main surface under the conditions of an X-ray incident energy of 600 eV and a take-off angle of 85° of the photoelectrons, the detection intensity of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the above-mentioned gallium arsenide single crystal substrate is obtained as a spectrum. The above-mentioned eighth integral intensity ratio is: the ratio of the sum of the integral intensity of arsenic element present as the above-mentioned arsenic pentoxide, the integral intensity of arsenic element present as the above-mentioned arsenic trioxide, the integral intensity of arsenic element present as the above-mentioned gallium arsenide, and the integral intensity of arsenic element present as the above-mentioned metallic arsenic to the sum of the integral intensity of gallium element present as the above-mentioned gallium monoxide, the integral intensity of gallium element present as the above-mentioned gallium trioxide, and the integral intensity of gallium element present as the above-mentioned gallium arsenide. The above-mentioned ninth integral intensity ratio is: the ratio of the sum of the integral intensity of arsenic element present as the above-mentioned arsenic pentoxide and the integral intensity of arsenic element present as the above-mentioned arsenic trioxide to the sum of the integral intensity of gallium element present as the above-mentioned gallium monoxide and the integral intensity of gallium element present as the above-mentioned gallium trioxide. The relationship that the standard deviation and the average value of the ratio of the above-mentioned ninth integral intensity ratio to the above-mentioned eighth integral intensity ratio satisfy standard deviation / average value ≤ 0.022. When the above-mentioned diameter is represented by D and two axes orthogonal to each other on the above-mentioned main surface passing through the center of the above-mentioned main surface are taken as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the above-mentioned 9 measurement points are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (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 above-mentioned coordinates (X, Y) are mm. Thus, in a gallium arsenide single crystal substrate having a diameter of 150 mm or more and 205 mm or less, by effectively removing the oxide film using wet etching, a main surface with high specularity can be obtained without deviation in the plane, and thus an epitaxial film with a reduced haze value can be formed.

[0033] [8] The above-mentioned gallium arsenide single crystal substrate preferably has: an epitaxial film on the above-mentioned main surface, the maximum value of the haze of the surface of the above-mentioned epitaxial film is 100 ppm or less, and the average value of the haze of the surface of the above-mentioned epitaxial film is 2.5 ppm or less. Thus, a gallium arsenide single crystal substrate having an epitaxial film with a reduced haze value formed on the main surface can be provided.

[0034] [9]A method for manufacturing a gallium arsenide single crystal substrate according to one aspect of the present invention is a method for manufacturing a gallium arsenide single crystal substrate having a main surface, and the main surface has a circular shape. The manufacturing method includes a step of preparing a gallium arsenide single crystal substrate precursor having a surface and the surface having a circular shape, and a cleaning step for obtaining the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor. The cleaning step includes: a step of polishing the surface of the gallium arsenide single crystal substrate precursor to make the surface a polished surface; a step of cleaning the polished surface with a first alkaline cleaning solution to make the polished surface an alkali-cleaned surface; a step of cleaning the alkali-cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid to make the alkali-cleaned surface an acid-cleaned surface; a step of cleaning the acid-cleaned surface while rotating the acid-cleaned surface at a rotational speed of 1000 rpm or more in the circumferential direction and supplying a second alkaline cleaning solution to the acid-cleaned surface at a flow rate of 0.1 L / min or more and 5 L / min or less for 30 seconds or more and 5 minutes or less to make the acid-cleaned surface a second alkali-cleaned surface; a step of heat-treating the second alkali-cleaned surface under conditions of 1.1 atm or more and 3 atm or less and 150 °C or more and 300 °C or less in an inert gas atmosphere to make the second alkali-cleaned surface the main surface. The first alkaline cleaning solution contains 0.1 mass% or more and 10 mass% or less of a first alkali. The first alkali contains at least one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. The second alkaline cleaning solution contains 0.3 mass ppm or more and 0.5 mass% or less of a second alkali. The second alkali contains at least one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. By the method for manufacturing a gallium arsenide single crystal substrate having such characteristics, a gallium arsenide single crystal substrate having a main surface with high specularity can be obtained.

[0035]

[10] Preferably, it includes a step of forming an epitaxial film on the main surface. Thereby, an epitaxial film with a reduced haze value can be formed on the main surface.

[0036] [Details of the Embodiment]

[0037] Hereinafter, one embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in further detail, but the present invention is not limited thereto. There are cases where explanations are made while referring to the attached Figure 1 figures. In this specification and the drawings, the same or corresponding elements are denoted by the same reference numerals, and the same explanations for them will not be repeated. In addition, in the drawings, for the convenience of understanding each component, the scale is appropriately adjusted and shown, and the scale of each component shown in the drawings is not necessarily the same as the scale of the actual component.

[0038] In this specification, a notation in the form of "A to B" represents the upper and lower limits of a range (i.e., A or more and B or less). When no unit is described for A and a unit is described only for B, the unit of A is the same as the unit of B. Further, in the case where a compound or the like is represented by a chemical formula in this specification, when the atomic ratio is not particularly limited, it is regarded as including all known atomic ratios and is not necessarily limited to the atomic ratios within the stoichiometric range.

[0039] In this specification, the "main surface" of a gallium arsenide single crystal substrate means both of the two circular surfaces of the above substrate. In a gallium arsenide single crystal substrate, when at least one of these two surfaces satisfies the scope of the claims of the present invention, it belongs to the scope of the present invention. There is a case where an epitaxial film is disposed on the "main surface" of the gallium arsenide single crystal substrate. Further, in this specification, the "plane" used in the term "in-plane" means the "main surface". Further, when the diameter of the gallium arsenide single crystal substrate is denoted as "75 mm", it means that the above diameter is around 75 mm (75 to 76.5 mm), or it means 3 inches. When the above diameter is denoted as "100 mm", it means that the above diameter is around 100 mm (95 to 105 mm), or it means 4 inches. When the above diameter is denoted as "150 mm", it means that the above diameter is around 150 mm (145 to 155 mm), or it means 6 inches. When the above diameter is denoted as "200 mm", it means that the above diameter is around 200 mm (195 to 205 mm), or it means 8 inches. In addition, the above diameter can be measured by using a known external diameter measuring instrument such as a vernier caliper.

[0040] In the crystallographic descriptions in this specification, [] is used to represent a single crystal orientation, <> is used to represent a crystal orientation family, () is used to represent a single crystal plane, and {} is used to represent a crystal plane family. Further, a negative crystallographic index is usually represented by attaching "- (dash)" to the number, and when this notation is made in this specification, a negative sign is attached before the number.

[0041] [Gallium Arsenide Single Crystal Substrate]

[0042] The gallium arsenide single crystal substrate (GaAs single crystal substrate) of this embodiment is a GaAs single crystal substrate having a main surface, and the main surface has a circular shape. The GaAs single crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio. The first integrated intensity ratio and the third integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 30°, the detection intensities of the 3d electrons of gallium (Ga) and arsenic (As) are determined with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate to obtain a spectrum. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensities of the 3d electrons of Ga and As are determined with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate to obtain a spectrum. The fourth integrated intensity ratio is obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, the detection intensities of the 3d electrons of Ga and As are determined with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate to obtain a spectrum.

[0043] The first integrated intensity ratio and the second integrated intensity ratio are: The integrated intensity of the As element present as arsenic pentoxide (As2O5) (hereinafter, for convenience, there is a case where it is denoted as "As 5+ "), the integrated intensity of the As element present as arsenic trioxide (As2O3) (hereinafter, for convenience, there is a case where it is denoted as "As 3+ "), the integrated intensity of the As element present as gallium arsenide (GaAs) (hereinafter, for convenience, there is a case where it is denoted as "As-Ga"), and the integrated intensity of the As element present as metallic arsenic (metallic As) (hereinafter, for convenience, there is a case where it is denoted as "metallic As") with respect to the integrated intensity of the Ga element present as gallium monoxide (Ga2O) (hereinafter, for convenience, there is a case where it is denoted as "Ga + "), the integrated intensity of the Ga element present as gallium trioxide (Ga2O3) (hereinafter, for convenience, there is a case where it is denoted as "Ga 3+The ratio of the integrated intensity of the case of “ 5 + ) to the sum of the integrated intensities of the Ga element present as gallium arsenide (GaAs) (hereinafter, for convenience, there is a case where it is denoted as “Ga-As”). The above third integrated intensity ratio, the above fourth integrated intensity ratio, and the above fifth integrated intensity ratio are: the integrated intensity of the As element present as the above As2O5 (As 3+ ) and the integrated intensity of the As element present as the above As2O3 (As + ) with respect to the sum of the integrated intensity of the Ga element present as the above Ga2O (Ga 3+ ) and the integrated intensity of the Ga element present as the above Ga2O3 (Ga

[0044] ) The ratio of the sum of the integrated intensities. In the above GaAs single crystal substrate, the above second integrated intensity ratio is 0.9 or more and 1.05 or less. The above third integrated intensity ratio and the above fourth integrated intensity ratio are 1.0 or less. The above fifth integrated intensity ratio is 0.8 or less. Further, the ratio of the above first integrated intensity ratio to the above second integrated intensity ratio is 0.5 or more and 1 or less.

[0045] <Principal surface>

[0046] As described above, the above-mentioned GaAs single crystal substrate has a main surface, and the main surface has a circular shape. In this specification, the "circular shape" representing the shape of the main surface includes, in addition to the geometrically circular shape, a shape in which the main surface does not form a geometrically circular shape by forming at least any one of a notch, an orientation flat (hereinafter also referred to as "OF"), or an index flat (hereinafter also referred to as "IF"). That is, the "shape when the main surface does not form a geometrically circular shape" means: among the line segments extending from an arbitrary point on the outer periphery of the main surface to the center of the main surface, the shape when the length of the line segment extending from an arbitrary point on the notch, OF, and IF to the center of the main surface becomes short. In other words, in this specification, based on the shape before forming the notch, OF, and IF, the shape of the main surface is called a "circular shape". Therefore, regarding the center of the main surface and the diameter of the substrate, their positions and sizes (lengths) are obtained based on the circular shape before forming the notch, OF, and IF, etc. In addition, the "shape when the main surface does not form a geometrically circular shape" also includes a shape in which the lengths of all line segments extending from an arbitrary point on the outer periphery of the main surface to the center of the main surface are not necessarily equal due to the shape of the GaAs single crystal before being cut out as the GaAs single crystal substrate. In this case, for the center of the main surface, it refers to the position of the center of gravity, and for the diameter of the substrate, it refers to the length of the longest line segment among the line segments extending from a point on the outer periphery of the substrate through the center of the main surface to another point on the outer periphery of the substrate.

[0047] <X-ray Photoelectron Spectroscopy (XPS) Using Radiation Light>

[0048] In the development of a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value, the inventors focused on X-ray Photoelectron Spectroscopy (XPS) using radiation light that can analyze the state of the main surface of the GaAs single crystal substrate with high precision. Specifically, the following attempts were made: By performing XPS using radiation light, in the GaAs single crystal substrate, the cause of the deterioration of the specularity of the main surface was determined, and by eliminating the above cause, a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value was realized. Here, XPS refers to the following analysis method: irradiating a sample with X-rays and measuring the distribution of the kinetic energy of photoelectrons released from the sample, thereby obtaining information about the types, abundances, chemical bonding states, etc. of the elements present on the surface of the sample.

[0049] Generally speaking, when analyzing the main surface of a GaAs single crystal substrate by XPS, most of the X-rays with energy fixed at about 1.487keV are used for implementation. However, when using X-rays with incident energy fixed at about 1.487keV and the photoelectron flight angle set to 30°, information about the state of the main surface of the GaAs single crystal substrate can be obtained after averaging the area from the above-mentioned main surface to a depth of about 5nm. If the above-mentioned area is converted into atomic layers, it is equivalent to about 20 atomic layers. Therefore, it is difficult for the above-mentioned XPS to analyze the state of the main surface of the GaAs single crystal substrate with high precision. Furthermore, in XPS, if you want to use X-rays with incident energy fixed at about 1.487keV and stagger the photoelectron flight angle to obtain information about the state of the main surface of the GaAs single crystal substrate, the measurement error relative to the angle will become too large, and the ionization efficiency of the photoelectron intensity is small, so the measurement error becomes large, so it is still difficult to perform high-precision analysis.

[0050] In contrast, in the present invention, as described above, X-rays with an incident energy of 600 eV are used and XPS is performed under the condition that the photoelectron escape angle is set to 30°, 45° or 85°, thereby being able to analyze the state of the main surface of the GaAs single crystal substrate.

[0051] As a condition for implementing the above-mentioned XPS, when the X-ray incident energy is set to 600eV and the photoelectron flight angle is set to 30°, information about the state of the main surface of the GaAs single crystal substrate can be obtained after averaging the area from the above-mentioned main surface to a depth of about 2.25nm. As a condition for implementing the above-mentioned XPS, when the X-ray incident energy is set to 600eV and the photoelectron flight angle is set to 45°, information about the state of the main surface of the GaAs single crystal substrate can be obtained after averaging the area from the above-mentioned main surface to a depth of about 3.18nm. As a condition for implementing the above-mentioned XPS, when the X-ray incident energy is set to 600eV and the photoelectron flight angle is set to 85°, information about the state of the main surface of the GaAs single crystal substrate can be obtained after averaging the area from the above-mentioned main surface to a depth of about 4.48nm. That is, the region from the main surface of the GaAs single crystal substrate to a depth of about 5 nm can be analyzed in detail every about 1 to 3 atomic layers (about 20 atomic layers), so the state of the main surface can be analyzed with higher precision than before.

[0052] Regarding a GaAs single crystal substrate, it is known that after cleaning through a cleaning process, an oxide film with a thickness of about 1 to 2 nm is formed on the main surface. Therefore, the following attempt has been made: after removing this oxide by wet etching, an epitaxial film is formed on the above-mentioned main surface, thereby reducing the haze value on the surface of the above-mentioned epitaxial film. However, even after the above-mentioned wet etching, a part of the oxide film still remains on the above-mentioned main surface, etc., and thus the haze value on the surface of the above-mentioned epitaxial film increases to a certain extent. In contrast, the present inventors focused on the interface (i.e., the region from the main surface of the GaAs single crystal substrate to a depth of about 2 to 5 nm) between the oxide film occupying the outermost surface of the main surface of the above-mentioned GaAs single crystal substrate and the layer composed of gallium (Ga) and arsenic (As) (hereinafter also referred to as the "main layer" of the GaAs single crystal substrate) directly below this oxide film through detailed XPS analysis using the above-mentioned radiation light. As a result, it was found that when the GaAs single crystal substrate has a composition in which gallium is more abundant than arsenic throughout the oxide film and this tendency persists up to the interface between the oxide film and GaAs single crystal, the wettability of the surface of the above-mentioned oxide film becomes good, and thus the above-mentioned oxide film can be effectively removed by wet etching. That is, it was conceived that by appropriately controlling the gallium composition in the above-mentioned oxide film, a main surface with high specularity can be obtained. In addition, in this specification, the "surface" of the oxide film refers to the surface of the above-mentioned oxide film opposite to the GaAs single crystal substrate side.

[0053] <First integral intensity ratio, second integral intensity ratio, third integral intensity ratio, fourth integral intensity ratio, and fifth integral intensity ratio>

[0054] The GaAs single crystal substrate of the present embodiment has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio. The above-mentioned first integrated intensity ratio and the above-mentioned third integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 30°, the detection intensities of the 3d electrons of Ga and As are obtained with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate. The above-mentioned second integrated intensity ratio and the above-mentioned fifth integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensities of the 3d electrons of Ga and As are obtained with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate. The above-mentioned fourth integrated intensity ratio is obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, the detection intensities of the 3d electrons of Ga and As are obtained with respect to the binding energy of the photoelectrons released to the outside of the GaAs single crystal substrate.

[0055] The above-mentioned first integrated intensity ratio and the above-mentioned second integrated intensity ratio are: The sum of the integrated intensities of As elements (As 5+ ) present as As2O5, As elements (As 3+ ) present as As2O3, As elements (As-Ga) present as GaAs, and As elements (metallic As) present as metallic As with respect to the sum of the integrated intensities of Ga elements (Ga + ) present as Ga2O, Ga elements (Ga 3+ ) present as Ga2O3, and Ga elements (Ga-As) present as GaAs. The above-mentioned third integrated intensity ratio, the above-mentioned fourth integrated intensity ratio, and the above-mentioned fifth integrated intensity ratio are: The sum of the integrated intensities of As elements (As 5+ ) present as As2O5 and As elements (As 3 + ) present as As2O3 with respect to the sum of the integrated intensities of Ga elements (Ga + ) present as Ga2O and Ga elements (Ga 3+ ) present as Ga2O3.

[0056] When the above first integral intensity ratio, second integral intensity ratio, third integral intensity ratio, fourth integral intensity ratio, and fifth integral intensity ratio are represented by In1, In2, In3, In4, and In5 respectively, the above In1, In2, In3, In4, and In5 can be represented by the following mathematical expressions respectively.

[0057] [Mathematical Expression 1]

[0058]

[0059] In the above GaAs single crystal substrate, the above second integral intensity ratio is 0.9 or more and 1.05 or less. The above third integral intensity ratio and the above fourth integral intensity ratio are 1.0 or less. The above fifth integral intensity ratio is 0.8 or less. Further, the ratio of the above first integral intensity ratio to the above second integral intensity ratio is 0.5 or more and 1 or less. The above second integral intensity ratio is preferably 0.9 or more and less than 1.04.

[0060] Figure 1 As an example of a graph showing the relationship between the measurement depth (horizontal axis) from the main surface of the GaAs single crystal substrate of the present embodiment, the ratio of the integral intensity of the entire arsenic element to the integral intensity of the entire gallium element (vertical axis), and the ratio of the integral intensity of the arsenic element present as arsenic oxide to the integral intensity of the gallium element present as gallium oxide (vertical axis). In Figure 1 , the point represented by a circle near the measurement depth (horizontal axis) of about 2.25 nm corresponds to the first integral intensity ratio, and the point represented by a circle near the measurement depth (horizontal axis) of about 4.48 nm corresponds to the second integral intensity ratio. The point represented by a rectangle near the measurement depth (horizontal axis) of about 2.25 nm corresponds to the third integral intensity ratio, the point represented by a rectangle near the measurement depth (horizontal axis) of about 3.18 nm corresponds to the fourth integral intensity ratio, and the point represented by a rectangle near the measurement depth (horizontal axis) of about 4.48 nm corresponds to the fifth integral intensity ratio.

[0061] In Figure 1 , the first integral intensity ratio, second integral intensity ratio, third integral intensity ratio, fourth integral intensity ratio, and fifth integral intensity ratio are 0.99, 1.01, 0.9, 0.83, and 0.76 respectively. Further, the ratio of the above first integral intensity ratio to the above second integral intensity ratio is 0.98 (=0.99 / 1.01).

[0062] Such a relationship means that: the composition of the oxide film occupying the whole region from the main surface to a depth of about 1 to 2 nm is richer in gallium than in arsenic, and this tendency is maintained up to the interface between the main layer and the oxide film (a depth of about 2 to 5 nm from the main surface). Specifically, it means that: the above second integral intensity ratio is 0.9 or more and 1.05 or less, whereby the oxide film has a desired thickness and the thickness of the oxide film does not exceed the desired thickness. It means that: the above third integral intensity ratio and the above fourth integral intensity ratio are 1.0 or less, whereby gallium is richer than arsenic in the whole oxide film. It means that: the above fifth integral intensity ratio is 0.8 or less, and the ratio of the above first integral intensity ratio to the above second integral intensity ratio is 0.5 or more and 1 or less, whereby the change in composition at the interface between the main layer and the oxide film is sharp, and up to the vicinity of the interface, the oxide film maintains a composition richer in gallium than in arsenic. It is speculated that in this case, the wettability of the surface of the above oxide film becomes good, so that the above oxide film can be effectively removed by wet etching. Thus, when an epitaxial film is grown on the main surface of the GaAs single crystal substrate of the present embodiment after wet etching, both the maximum value and the average value of the haze on the surface of the epitaxial film can be made smaller than in the past (for example, the maximum value of the haze on the surface of the epitaxial film can be made 100 ppm or less, and the average value of the above haze can be made 2.5 ppm or less). In this specification, the "surface" of the epitaxial film refers to the surface of the epitaxial film opposite to the GaAs single crystal substrate side.

[0063] On the other hand, for an existing GaAs single crystal substrate, when the first integral intensity ratio, the second integral intensity ratio, the third integral intensity ratio, the fourth integral intensity ratio, and the fifth integral intensity ratio are obtained by performing the above XPS, none of the following relationships are satisfied. That is, the relationship that the above second integral intensity ratio is 0.9 or more and 1.05 or less is not satisfied, or the relationship that the above third integral intensity ratio and the above fourth integral intensity ratio are 1.0 or less is not satisfied, or the relationship that the above fifth integral intensity ratio is 0.8 or less is not satisfied, or the relationship that the ratio of the above first integral intensity ratio to the above second integral intensity ratio is 0.5 or more and 1 or less is not satisfied. In such a GaAs single crystal substrate, a part of the above oxide film may remain on the main surface even after wet etching. Therefore, when an epitaxial film is formed on the main surface of the above GaAs single crystal substrate after wet etching, there is a possibility that height differences and the maximum value and the average value of the haze are increased on its surface.

[0064] As described above, the present inventors have first discovered that the haze on the surface of the epitaxial film formed on the main surface of the GaAs single crystal substrate depends on the above oxide film (the region occupying from the main surface to a depth of about 1 to 2 nm), and the amount of gallium relative to arsenic and the amount of gallium oxide relative to arsenic oxide in the vicinity of the interface between the above oxide film and the main layer (the region at a depth of 2 to 5 nm from the main surface).

[0065] <Oxide film>

[0066] The above-mentioned GaAs single crystal substrate preferably has an oxide film with a thickness of 2 nm or less on the above-mentioned main surface. Thereby, the above-mentioned oxide film can be removed more effectively by wet etching. The thickness of the above-mentioned oxide film is more preferably 1.5 nm or less. There is no particular limitation on the lower limit of the thickness of the above-mentioned oxide film, for example, it is 0.5 nm.

[0067] The thickness of the above-mentioned oxide film can be obtained by analyzing the main surface of the above-mentioned GaAs single crystal substrate using a scanning transmission electron microscope (STEM: Scanning Transmission Electron Microscope, for example, trade name (product number): "JEM-ARM300F2", manufactured by JEOL Ltd.) equipped with an energy dispersive X-ray analyzer (EDX: Energy Dispersive X-ray Spectroscopy). Specifically, under the condition of an acceleration voltage of 200 kV, by irradiating an electron beam on the center of the main surface of the above-mentioned GaAs single crystal substrate, spectroscopic analysis is performed using the above-mentioned EDX, and characteristic X-rays inherent to the elements generated at the center of the above-mentioned main surface are detected, thereby performing composition analysis. By performing line analysis in the depth direction of the above-mentioned main surface, the compositions corresponding to the analysis depths from the surface of the above-mentioned main surface are respectively obtained.

[0068] Furthermore, the thickness of the oxide film can be obtained from the above-mentioned composition analysis in the following manner. That is, first, the difference in the contents of As and Ga is obtained along the analysis depth from the surface of the above-mentioned main surface, and a spectrum with the above-mentioned analysis depth as the horizontal axis and the above-mentioned difference as the vertical axis is plotted as a curve. Then, since the above-mentioned spectrum shows a shape with a peak similar to a Gaussian distribution, the full width at half maximum of this shape can be obtained, and this full width at half maximum is taken as the thickness of the oxide film. As described above, the GaAs single crystal substrate of the present embodiment has a composition rich in gallium (especially gallium oxide) in the above-mentioned oxide film and in the vicinity of the interface between the above-mentioned oxide film and the main layer (the region from the main surface to a depth of 1 to 5 nm). Therefore, along the analysis depth from the surface of the above-mentioned main surface, the contents of As and Ga differ, and based on this situation, the thickness of the oxide film can be obtained from the spectrum representing the above-mentioned difference.

[0069] <Wettability (contact angle)>

[0070] The contact angle of the above-mentioned oxide film is preferably 20 degrees or less. Thereby, the wettability of the oxide film becomes good and it can be removed more effectively by wet etching. The contact angle of the above-mentioned oxide film is more preferably 10 degrees or less. There is no particular limitation on the lower limit value of the contact angle of the above-mentioned oxide film, for example, it is 1 degree.

[0071] The contact angle of the above-mentioned oxide film can be obtained by measuring the contact angle of a droplet of distilled water formed at the center of the main surface (the surface of the oxide film) to which 2 μL of distilled water has been added, using the θ / 2 method, in an environment of room temperature (20 to 25 °C) and relative humidity of 40 to 60%. In the observation of the above-mentioned droplet, a contact angle meter (for example, trade name (product number): "Drop Master500", manufactured by Kyowa Interface Science Co., Ltd.) can be used.

[0072] <Diameter>

[0073] The above-mentioned GaAs single crystal substrate preferably has a diameter of 75 mm or more and 205 mm or less. In other words, the diameter of the above-mentioned GaAs single crystal substrate is preferably 3 to 8 inches. Thus, in a GaAs single crystal substrate having a diameter of 75 mm or more and 205 mm or less, by effectively removing the oxide film using wet etching, a main surface with high specularity can be obtained. Here, regarding the above-mentioned diameter, even if the substrate has a shape that does not become a geometrically circular shape due to the influence of OF, IF, etc., the substrate is regarded as having the circular shape before the formation of the above-mentioned OF, IF, etc., and its size (diameter) is obtained. The above-mentioned GaAs single crystal substrate preferably has a diameter of 100 mm or more and 205 mm or less, and also preferably has a diameter of 150 mm or more and 205 mm or less.

[0074] <Analysis method of GaAs single crystal substrate based on X-ray photoelectron spectroscopy (XPS) using radiation light>

[0075] Hereinafter, the analysis method of the GaAs single crystal substrate based on XPS using radiation light will be described in further detail.

[0076] (Analysis system)

[0077] Figure 2 It is an explanatory diagram for schematically explaining the structure of an analysis system using X-ray photoelectron spectroscopy. As Figure 2 shown, the analysis system 100 includes an X-ray generating device 10, a vacuum chamber 20, and an electron spectrometer 30. The X-ray generating device 10, the vacuum chamber 20, and the electron spectrometer 30 are connected in this order. The internal spaces of the X-ray generating device 10, the vacuum chamber 20, and the electron spectrometer 30 are maintained at ultra-high vacuum. The pressure in the internal spaces of the X-ray generating device 10, the vacuum chamber 20, and the electron spectrometer 30 is, for example, 4 × 10 -7 Pa.

[0078] The X-ray generating device 10 generates X-rays called radiation light. As the X-ray generating device 10, for example, the beamline "BL17" in the Saga Prefectural Kyushu Synchrotron Light Research Center can be used.

[0079] The X-ray generating device 10 can generate X-rays with any energy in the range of 50 to 2000 eV in the above-mentioned "BL17" and irradiate the GaAs single crystal substrate 1 disposed in the vacuum chamber 20 with the X-rays. Figure 2 The illustrated X-ray generating device 10 includes an X-ray source 11, slits 12, 14, and a grating 13. The slits 12, 14 are respectively arranged on the upstream side and the downstream side of the grating (spectrometer) 13. The slits 12, 14 are, for example, four-quadrant slits.

[0080] The X-ray source 11 bends the traveling direction of high-energy electrons by the magnetic field generated by the deflection electromagnet in the circular accelerator, thereby outputting radiation light (X-rays) radiated in the direction of the tangent along the traveling direction.

[0081] The X-rays emitted from the X-ray source 11 are of high brightness. Specifically, the number of photons of the X-rays emitted from the X-ray source 11 per second is 10 9 photons / s. However, the brightness (intensity) of the X-rays emitted from the X-ray source 11 decays with time. For example, the brightness of the X-rays emitted 11 hours after starting the X-ray source 11 is 1 / 3 of the brightness of the X-rays emitted just after starting.

[0082] The X-rays emitted from the X-ray source 11 are collimated by a collimating mirror (not shown) or the like. The slit 12 allows a part of the collimated X-rays to pass through. The X-rays passing through the slit 12 are monochromatized by the grating 13. The slit 14 limits the divergence of the monochromatized X-rays.

[0083] The energy of the X-rays irradiated from the X-ray generating device 10 is determined by the slit widths of the slits 12, 14 and the grating density of the grating 13. For example, by setting the slit widths of the slits 12, 14 to 30 μm, using a grating 13 with a central grating density of 400 l / mm, and adjusting the exit angle of the grating, X-rays of 600 eV are irradiated from the X-ray generating device 10.

[0084] When the X-rays from the X-ray generating device 10 irradiate the GaAs single crystal substrate 1 disposed in the vacuum chamber 20, photoelectrons are released from the GaAs single crystal substrate 1.

[0085] The electron spectrometer 30 measures the kinetic energy distribution of the photoelectrons released from the GaAs single crystal substrate 1. The electron spectrometer 30 includes a hemispherical analyzer and a detector. The hemispherical analyzer disperses the photoelectrons. The detector counts the number of photoelectrons with each energy.

[0086] The angle θ1 formed by the traveling direction of the X-rays incident on the GaAs single crystal substrate 1 from the X-ray generating device 10 and the main surface 1m of the GaAs single crystal substrate 1 is variable. In addition, the angle (hereinafter also referred to as "emission angle θ2") formed by the traveling direction of the photoelectrons captured by the electron spectrometer 30 among the photoelectrons released from the GaAs single crystal substrate 1 and the main surface 1m of the GaAs single crystal substrate 1 is also variable. In the present embodiment, the emission angle θ2 is set to 30°, 45°, or 85°. The angle θ1 is not particularly limited and is set to 85°, for example.

[0087] As the electron spectrometer 30, for example, a high-resolution XPS analysis device "R3000" manufactured by Scienta Omicron can be used.

[0088] (Depth from the main surface to be analyzed)

[0089] By the irradiation of X-rays, a part of the photoelectrons released to the outside of the GaAs single crystal substrate 1 loses energy due to inelastic scattering. Therefore, only a part of the photoelectrons generated in the GaAs single crystal substrate 1 escapes into the vacuum while maintaining the energy at the time of generation and reaches the electron spectrometer 30. The photoelectrons escaping from the surface are generated at a depth of about three times the inelastic mean free path (IMFP) of the photoelectrons. Therefore, the depth d (nm) from the main surface of the GaAs single crystal substrate to be analyzed is expressed by the following mathematical formula. In the following mathematical formula, λ (nm) is the IMFP value, and θ2 is the emission angle.

[0090] [Mathematical formula 2]

[0091] d = 3λsinθ2.

[0092] Furthermore, as shown in "Estimation Method of Inelastic Mean Free Path of Electrons Based on the Tpp-2M Equation, Journal of Surface Analysis, Vol. 1, No. 2, 1995", It is expressed by the following mathematical formulas.

[0093] [Mathematical formula 3]

[0094]

[0095] γ = 0.191ρ -0.50

[0096] C = 1.97 - 0.94U

[0097] D = 53.4 - 20.8U

[0098]

[0099] In each of the above mathematical expressions, A W represents the atomic weight or molecular weight, N v represents the number of valence electrons per 1 atom or per 1 molecule, E p represents the plasma energy of free electrons (eV), ρ represents the density (g / cm 3 ), E g represents the band gap energy (eV). E represents the kinetic energy of photoelectrons (eV), which is calculated from the energy of the irradiated X-ray (eV) and the binding energy between the electron and the atomic nucleus (eV).

[0100] By using each of the above mathematical expressions, the depth d (nm) from the main surface of the GaAs single crystal substrate to be analyzed can be obtained. That is, using each of the above mathematical expressions, various parameter values of the 3d electrons of the Ga element and the As element, and the energy of the X-ray (600 eV), the depth d (nm) from the main surface of the GaAs single crystal substrate is calculated. The above depth d (nm) is as follows respectively.

[0101] In the case of an X-ray incident energy of 600 eV and a photoelectron emission angle of 30°, the above depth d is approximately 2.25 nm. In the case of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, the above depth d is approximately 3.18 nm. In the case of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the above depth d is approximately 4.48 nm.

[0102] (Calculation methods for the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, and the fifth integrated intensity ratio)

[0103] Hereinafter, regarding the method for calculating the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, and the fifth integrated intensity ratio of the main surface based on the above XPS, first, the calculation methods for the first integrated intensity ratio and the third integrated intensity ratio will be exemplified. In this case, the above XPS is performed on the center of the main surface of the GaAs single crystal substrate using X-rays with an energy of 600 eV. At this time, the photoelectron emission angle is 30°. Thus, the kinetic energy distribution of the photoelectrons released from the GaAs single crystal substrate can be obtained.

[0104] The kinetic energy E of the photoelectrons released from the GaAs single crystal substrate is represented by the following mathematical expression using the energy hν (eV) of the irradiated X-ray, the binding energy E B (eV) of the electrons in the GaAs single crystal substrate, and the work function as follows.

[0105] E = hv - E B - φ.

[0106] Using the above mathematical formula, a spectrum representing the binding energy distribution of photoelectrons is generated from the kinetic energy distribution of photoelectrons released from a GaAs single crystal substrate. In the present embodiment, based on the kinetic energy distribution of photoelectrons released from a position at a depth d (nm) from the main surface of the above GaAs single crystal substrate, a Ga3d spectrum and an As3d spectrum representing the binding energy distribution of photoelectrons are generated. Here, in this specification, the "Ga3d spectrum" refers to a spectrum representing the detection intensity of photoelectrons released from the 3d orbit of Ga element (Ga contained in Ga2O, Ga2O3, and GaAs). The "As3d spectrum" refers to a spectrum representing the detection intensity of photoelectrons released from the 3d orbit of As element (As contained in As2O5, As2O3, metallic As, and GaAs).

[0107] Especially in the analysis following the above XPS, from the viewpoint of high-precision measurement, the Ga3d spectrum and the As3d spectrum are obtained by narrow-scanning a specified binding energy range. Specifically, by narrow-scanning the range of the binding energy from 16 to 26 eV, the Ga3d spectrum can be represented in a graph with the above range as the horizontal axis and the detection intensity as the vertical axis. The As3d spectrum can be represented in a graph with the above range as the horizontal axis and the detection intensity as the vertical axis by narrow-scanning the range of the binding energy from 39 to 49 eV.

[0108] The narrow-scanning is performed under the following conditions: the energy interval is set to 0.05 eV, the accumulation time for each energy value is set to 100 ms, and the number of accumulations is set to 1 or more. In addition, the energy resolution E / ΔE is 3480.

[0109] In the above manner, it is possible to obtain Figure 3A the Ga3d spectrum LG shown in Figure 3B and the As3d spectrum LA shown in Figure 3A is a graph showing an example of the background-corrected Ga3d spectrum obtained by XPS irradiating the center of the main surface of the GaAs single crystal substrate of the present embodiment with X-rays. Figure 3B is a graph showing an example of the background-corrected As3d spectrum obtained by XPS irradiating the center of the main surface of the GaAs single crystal substrate of the present embodiment with X-rays. Here, as described above, in Figure 3A and Figure 3BAn example of the background-corrected Ga3d spectrum and As3d spectrum is shown respectively. That is, when obtaining the above-mentioned Ga3d spectrum LG and As3d spectrum LA, the background was corrected by using the Shirley method (Reference: Kazuhiro Yoshihara, Journal of the Vacuum Society of Japan, Vol. 56, No. 6, 2013, p. 243-247). Thus, based on the difference between the measured Ga3d spectrum and the background, the background-corrected Ga3d spectrum LG can be determined. In addition, based on the difference between the measured As3d spectrum and the background, the background-corrected As3d spectrum LA can be determined.

[0110] When obtaining the above-mentioned Ga3d spectrum LG, the peak of the detection intensity of the Ga element (Ga + ) existing as Ga2O was fixed at the position with a binding energy of 19.9 eV, and the peak position of the detection intensity of the Ga element (Ga 3+ ) existing as Ga2O3 was fixed at the position with a binding energy of 20.7 eV. Furthermore, the peak of the detection intensity of the Ga element (Ga-As) existing as GaAs was located at the position with a binding energy of about 19.2 - 19.7 eV and had a width. This is because when the above-mentioned X-ray photoelectron spectroscopy is performed on a GaAs single crystal as the object, a charging offset occurs, and there is a possibility that the above-mentioned Ga3d spectrum can be offset by up to about 1 eV on the high-energy side. In addition, since the peak of the detection intensity of Ga-As is affected by the main layer composed of GaAs, it is difficult to fix it to a single value, so as described above, it has a width of 0.5 eV at the peak position.

[0111] When obtaining the above-mentioned As3d spectrum LA, the peak of the detection intensity of the As element (As 5+ ) existing as As2O5 was fixed at the position with a binding energy of 45.57 eV, and the peak position of the detection intensity of the As element (As 3+ ) existing as As2O3 was fixed at the position with a binding energy of 44.07 eV. Furthermore, the peak of the detection intensity of the As element (metallic As) existing as metallic As was located at the position with a binding energy of about 41.62 - 42.12 eV and had a width, and the peak of the detection intensity of the As element (As-Ga) existing as GaAs was located at the position with a binding energy of about 40.77 - 41.27 eV and had a width. This is because when the above-mentioned X-ray photoelectron spectroscopy is performed on a GaAs single crystal as the object, a charging offset occurs, and there is a possibility that the above-mentioned As3d spectrum can be offset by up to about 1 eV on the high-energy side. In addition, since the peaks of metallic As and As-Ga are affected by the main layer composed of GaAs, it is difficult to fix them to a single value, so as described above, they have a width of 0.5 eV at the peak position.

[0112] Next, the background-corrected Ga3d spectrum LG obtained as described above is separated into the following three Gaussian functions Y1, Y2, and Y3 (this operation will also be denoted as "peak separation" hereinafter) for representation. Thus, in the range of binding energy from 16 to 26 eV, through peak separation, the Ga element existing as Ga2O (Ga + ), the Ga element existing as Ga2O3 (Ga 3+ ), and the three spectra of the Ga element existing as GaAs (Ga-As) can be obtained.

[0113] Y1 = a1*exp{(-(X - b1) 2 ) / c1 2}

[0114] Y2 = a2*exp{(-(X - b2) 2 ) / c2 2}

[0115] Y3 = a3*exp{(-(X - b3) 2 ) / c3 2}.

[0116] The units of the above Gaussian functions Y1, Y2, and Y3 are dimensionless. In the above Gaussian functions Y1, Y2, and Y3, the units of X, b1, b2, b3, c1, c2, and c3 are eV, and the units of a1, a2, and a3 are dimensionless.

[0117] The above Gaussian functions Y1 to Y3 are obtained as follows: On the premise that the Ga3d's i-th component is represented by the Gaussian function Gi = Ai*exp{(-(E - E1) 2 ) / Wi 2}, each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) is optimized in such a way that the square of the difference from the measured value ([measured - ΣGi] 2 ) reaches the minimum. Among them, the binding energy values of the peaks of the detection intensities of the above-mentioned Ga + , Ga 3+ and Ga-As are substituted into b1 to b3 respectively.

[0118] That is, each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) is as follows.

[0119] a1, a2, a3 are real numbers greater than or equal to 0.

[0120] b1 = 19.9 eV

[0121] b2 = 20.7 eV

[0122] 19.2 eV ≤ b3 ≤ 19.7 eV

[0123] 0.2 eV ≤ c1 ≤ 0.95 eV

[0124] 0.2 eV ≤ c2 ≤ 0.95 eV

[0125] 0.2 eV ≤ c3 ≤ 0.95 eV.

[0126] Thus, the Gaussian functions Y1, Y2, and Y3 can be respectively expressed as, for example, the Ga Figure 3A spectrum L2, Ga + spectrum L1, and Ga-As spectrum L3 obtained by peak separation from the Ga3d spectrum LG of 3+ as described above.

[0127] Furthermore, regarding the background-corrected As3d spectrum LA obtained as described above, it can be peak-separated and expressed as the following four Gaussian functions Y4, Y5, Y6, and Y7. Thus, in the range of binding energy from 39 to 49 eV, four spectra of the As element present as As2O5 (As 5+ ), the As element present as As2O3 (As 3+ ), the As element present as metallic As (metallic As), and the As element present as GaAs (As-Ga) can be obtained by peak separation.

[0128] Y4 = a4 * exp{(-(X - b4) 2 ) / c4 2}

[0129] Y5 = a5 * exp{(-(X - b5) 2 ) / c5 2}

[0130] Y6 = a6 * exp{(-(X - b6) 2 ) / c6 2}

[0131] Y7 = a7 * exp{(-(X - b7) 2 ) / c7 2}.

[0132] The above Gaussian functions Y4, Y5, Y6, and Y7 are dimensionless. In the above Gaussian functions Y4, Y5, Y6, and Y7, the units of X, b4, b5, b6, b7, c4, c5, c6, and c7 are eV, and the units of a4, a5, a6, and a7 are dimensionless.

[0133] The above Gaussian functions Y4 to Y7 are obtained by the following method: In the case of the Gaussian function Gi = Ai * exp{(-(E - E1) 2) / Wi 2} Assuming it represents the i-th component of As3d, optimize each variable (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) in such a way that the sum of the squares of the differences from the measured values ([measured - ΣGi] 2 ) reaches the minimum. Among them, substitute the above-mentioned As into b4 to b7 respectively 5+ 、As 3+ 、the binding energy values of the peaks of the signal intensities of metallic As and As-Ga.

[0134] That is, each variable (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) is as follows.

[0135] a4, a5, a6, a7 are real numbers greater than or equal to 0.

[0136] b4 = 45.57 eV

[0137] b5 = 44.07 eV

[0138] 41.62 eV ≤ b6 ≤ 42.12 eV

[0139] 40.77 eV ≤ b7 ≤ 41.27 eV

[0140] 0.2 eV ≤ c4 ≤ 0.95 eV

[0141] 0.2 eV ≤ c5 ≤ 0.95 eV

[0142] 0.2 eV ≤ c6 ≤ 0.95 eV

[0143] 0.2 eV ≤ c7 ≤ 1.2 eV.

[0144] Thus, the Gaussian functions Y4, Y5, Y6, and Y7 can be respectively expressed as, for example, the As Figure 3B spectra L4, As 5+ spectra L5, metallic As spectra L6, and As-Ga spectra L7 obtained by peak separation from the As3d spectrum LA of 3+ . Here, since metallic As is generated from the oxide film and the above-mentioned main layer through the reaction 2GaAs + As2O3 → Ga2O3 + 4As, it is detected as an intensity in the above XPS.

[0145] In addition, in order to determine the peak positions of the Gaussian functions Y1 to Y7, the following correction can be performed. First, the probability of generating photoelectrons by X-rays, known as the photoionization efficiency (η), varies depending on the element, X-ray energy, etc. Therefore, the data published on the following website is used as the value of the above η. Specifically, the photoionization efficiency (η) of X-rays with an incident energy of 600 eV is 0.28 for Ga 3d and 0.42 for As 3d.

[0146] https: / / vuo.elettra.eu / services / elements / WebElements.html (It should be noted that the literature on which the data is based is J.J. Yeh, Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993 and J.J. Yeh and I. Lindau, Atomic Data and Nuclear Data Tables, 32, 1 - 155 (1985)).

[0147] In addition, since the irradiation intensity of the X-rays used in the above radiation light device decays over time, a standard sample of gold (Au) is measured every certain time, and from this, the decay ratio of the Au 4f photoelectron intensity is obtained, and the X-ray irradiation dose is corrected based on this ratio.

[0148] In Figure 3A Ga 3+ The area between the spectrum L1 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of Ga 3+ and thus refers to the integrated intensity of Ga 3+ . The area between the spectrum L2 of Ga + and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of Ga + and thus refers to the integrated intensity of Ga + . The area between the Ga - As spectrum L3 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of Ga - As and thus refers to the integrated intensity of Ga - As.

[0149] In Figure 3B As 5+ The area between the spectrum L4 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of As 5+ and thus refers to the integrated intensity of As 5+ As3+ The area between the spectrum L5 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of As 3+ and thus represents the integrated intensity of As 3+ The area between the spectrum L6 of metallic As and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of metallic As, and thus represents the integrated intensity of metallic As. The area between the spectrum L7 of As-Ga and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbit of As-Ga, and thus represents the integrated intensity of As-Ga.

[0150] Therefore, based on the respective areas obtained from the above-mentioned spectra and the horizontal axis, the integrated intensity of As 5+ the integrated intensity of As 3+ the sum of the integrated intensity of As-Ga and the integrated intensity of metallic As relative to the integrated intensity of Ga + the integrated intensity of Ga 3+ the integrated intensity of Ga 5+ the integrated intensity of As and the integrated intensity of As 3+ the sum of the integrated intensity of As relative to the integrated intensity of Ga + the integrated intensity of Ga and the integrated intensity of Ga 3+ the sum of the integrated intensity of Ga is used as the third integrated intensity ratio.

[0151] According to the present embodiment, the above-mentioned XPS is performed on the center of the main surface of the GaAs single crystal substrate under the conditions of an incident energy of 600 eV and a photoelectron emission angle of 85°. In addition, by the same method as the method for calculating the above-mentioned first integrated intensity ratio and third integrated intensity ratio, the second integrated intensity ratio and the fifth integrated intensity ratio can be obtained. For the center of the main surface of the above-mentioned GaAs single crystal substrate, the above-mentioned XPS is performed under the conditions of an incident energy of 600 eV and a photoelectron emission angle of 45°. In addition, by the same method as the method for calculating the above-mentioned first integrated intensity ratio and third integrated intensity ratio, the fourth integrated intensity ratio can also be obtained.

[0152] <Uniformity of the main surface of the GaAs single crystal substrate>

[0153] The characteristics of the GaAs single crystal substrate of the present embodiment are preferably uniform in the plane of the main surface. That is, the GaAs single crystal substrate of the present embodiment preferably enables the formation of an epitaxial film with a reduced haze value regardless of the in-plane position of the main surface. As specific forms of such a preferred GaAs single crystal substrate, the following forms (the first form and the second form) can be exemplified.

[0154] (First form)

[0155] The GaAs single crystal substrate of the first mode has a diameter of 75 mm or more and less than 150 mm. Preferably, the GaAs single crystal substrate has a diameter of 75 mm or more and 105 mm or less. The above GaAs single crystal substrate has a sixth integrated intensity ratio and a seventh integrated intensity ratio. The above sixth integrated intensity ratio and the above seventh integrated intensity ratio can be obtained by the following method: Based on X-ray photoelectron spectroscopy in which X-rays are respectively irradiated on 5 measurement points on the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the detection intensity of the 3d electrons of Ga and As is obtained with respect to the binding energy of the photoelectrons released to the outside of the above GaAs single crystal substrate to obtain a spectrum.

[0156] The above sixth integrated intensity ratio is: The integrated intensity of As element (As 5+ ) existing as As2O5, the integrated intensity of As element (As 3+ ) existing as As2O3, the integrated intensity of As element (As-Ga) existing as GaAs, and the sum of the integrated intensities of As element (metallic As) existing as metallic As with respect to the integrated intensity of Ga element (Ga + ) existing as Ga2O, the integrated intensity of Ga element (Ga 3+ ) existing as Ga2O3, and the integrated intensity of Ga element (Ga-As) existing as GaAs. The above seventh integrated intensity ratio is: The integrated intensity of As element (As 5+ ) existing as As2O5 and the integrated intensity of As element (As 3+ ) existing as As2O3 with respect to the integrated intensity of Ga element (Ga + ) existing as Ga2O and the integrated intensity of Ga element (Ga 3+ ) existing as Ga2O3. The standard deviation and the average value of the ratio of the above seventh integrated intensity ratio to the above sixth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.039. The fact that the standard deviation and the average value of the ratio of the above seventh integrated intensity ratio to the above sixth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.039 means that the oxide film has a gallium-rich composition without deviation in the plane, so that the oxide film on the main surface can be removed without deviation in the plane by wet etching. The lower limit of the standard deviation and the average value of the ratio of the above seventh integrated intensity ratio to the above sixth integrated intensity ratio is the ideal value of 0. For example, the standard deviation and the average value of the ratio of the above seventh integrated intensity ratio to the above sixth integrated intensity ratio can satisfy the relationship of standard deviation / average value ≥ 0.026.

[0157] When the above diameter is represented by D and two axes orthogonal to each other on the above main surface passing through the center of the above main surface are taken as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the above five measurement points are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4). The units of the above D and X and Y in the above coordinates (X, Y) are mm. Thus, in a GaAs single crystal substrate having a diameter of 75 mm or more and less than 150 mm, the oxide film can be effectively removed by wet etching, and a main surface with high specularity can be obtained without deviation in the plane, so that an epitaxial film with a reduced haze value can be formed.

[0158] (Second method)

[0159] Furthermore, the GaAs single crystal substrate of the second method has a diameter of 150 mm or more and 205 mm or less. The above GaAs single crystal substrate has an eighth integral intensity ratio and a ninth integral intensity ratio. The above eighth integral intensity ratio and the above ninth integral intensity ratio can be obtained by the following method: Based on X-ray photoelectron spectroscopy in which X-rays are respectively irradiated to five measurement points on the above main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, the spectra of the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of the photoelectrons released to the outside of the above GaAs single crystal substrate are obtained.

[0160] The above eighth integral intensity ratio is: the integral intensity of the As element (As 5+ ) present as As2O5, the integral intensity of the As element (As 3+ ) present as As2O3, the integral intensity of the As element (As-Ga) present as GaAs, and the sum of the integral intensities of the As element (metallic As) present as metallic As with respect to the integral intensity of the Ga element (Ga + ) present as Ga2O, the integral intensity of the Ga element (Ga 3+ ) present as Ga2O3, and the integral intensity of the Ga element (Ga-As) present as GaAs. The above ninth integral intensity ratio is: the sum of the integral intensity of the As element (As 5+ ) present as As2O5 and the integral intensity of the As element (As 3+ ) present as As2O3 with respect to the integral intensity of the Ga element (Ga + ) present as Ga2O and the integral intensity of the Ga element (Ga 3+The ratio of the sum of the integrated intensities. The standard deviation and the average value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.022. The fact that the standard deviation and the average value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.022 means that the oxide film has a gallium-rich composition without deviation in the plane, so that the oxide film on the main surface can be removed by wet etching without deviation in the plane. The lower limit of the standard deviation and the average value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio is the ideal value of 0. For example, the standard deviation and the average value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio can satisfy the relationship of standard deviation / average value ≥ 0.009.

[0161] When the diameter is represented by D and two axes orthogonal to each other on the main surface passing through the center of the main surface are used as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the nine measurement points are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (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. Thus, in a GaAs single crystal substrate having a diameter of 150 mm or more and 205 mm or less, the oxide film can be effectively removed by wet etching, and a main surface with high specularity can be obtained without deviation in the plane, so that an epitaxial film with a reduced haze value can be formed.

[0162] In the first and second modes, the specific analysis methods for obtaining the sixth integrated intensity ratio, the seventh integrated intensity ratio, the eighth integrated intensity ratio, and the ninth integrated intensity ratio are the same as those described in the item of <Analysis method of GaAs single crystal substrate based on X-ray photoelectron spectroscopy (XPS) using radiation light>, so the description will not be repeated.

[0163] (Five measurement points and nine measurement points)

[0164] The GaAs single crystal substrate of the first mode has a diameter of 75 mm or more and less than 150 mm. In this case, five measurement points are set on the main surface of the GaAs single crystal substrate of the first mode in the following manner. That is, in order to evaluate the reduction effect of the haze value of the epitaxial film due to the uniform in-plane distribution of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio, it is preferable to set five measurement points in such a way that the distance between them is as large as possible, and measure the haze value generated by the epitaxial film grown in the vicinity of each of the five measurement points. At this time, the haze value is preferably measured for a region with a diameter of 20 mm or more. Therefore, in the main surface of the GaAs single crystal substrate, five circular measurement objects with a diameter of 20 mm are set in such a way that the distance between them is as large as possible. Moreover, the center of each measurement object is set as the measurement point.

[0165] First, when two axes orthogonal to each other on the main surface passing through the center of the main surface are taken as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the first measurement point among the five measurement points are set to (0, 0). In addition, the X-axis and the Y-axis are set in the following manner: the notch formed in the GaAs single crystal substrate is located in the third quadrant of the XY coordinate plane, and the general angle of the ray passing through the notch with respect to the ray extending from the origin to the positive direction of the X-axis is 225°.

[0166] Furthermore, the second measurement point, the third measurement point, the fourth measurement point, and the fifth measurement point among the five measurement points are arranged at equal intervals on the circumference formed by the set of points that are only D / 4 away from the center of the GaAs single crystal substrate. Specifically, the coordinates (X, Y) of the second measurement point are set to (D / 4, 0). The coordinates (X, Y) of the third measurement point are set to (0, D / 4). The coordinates (X, Y) of the fourth measurement point are set to (-D / 4, 0). The coordinates (X, Y) of the fifth measurement point are set to (0, -D / 4). The above D represents the diameter of the GaAs single crystal substrate, and the units of X and Y in the above D and the coordinates (X, Y) are mm.

[0167] The GaAs single crystal substrate of the second method has a diameter of 150 mm or more and 205 mm or less. In this case, in the main surface of the GaAs single crystal substrate of the second method, together with the 5 measurement points set in the GaAs single crystal substrate of the first method, 4 more measurement points are further added, and a total of 9 measurement points are set in the following manner. That is, 4 measurement objects with a diameter of 20 mm are set on the main surface of the GaAs single crystal substrate of the second method in the following manner: in addition to the above-mentioned second measurement point, third measurement point, fourth measurement point, and fifth measurement point, on the outer peripheral side of these measurement points and not overlapping with the measurement objects including the second measurement point, third measurement point, fourth measurement point, and fifth measurement point. Moreover, the center of each measurement object is set as a measurement point, and X-rays are irradiated onto the measurement point. Specifically, the coordinates (X, Y) of the sixth measurement point among the above-mentioned 4 added measurement points are set to (0, D / 2 - 10). The coordinates (X, Y) of the seventh measurement point are set to (D / 2 - 10, 0). The coordinates (X, Y) of the eighth measurement point are set to (-(D / 2 - 10), 0). The coordinates (X, Y) of the ninth measurement point are set to (0, -(D / 2 - 10)). The above D represents the diameter of the GaAs single crystal substrate, and the units of X and Y in the above D and the coordinates (X, Y) are mm.

[0168] It is known that in the large-diameter main surface of the GaAs single crystal substrate of the second method having a diameter of 150 mm or more and 205 mm or less, there is a tendency for characteristics to deviate in the region closer to the outer periphery. Therefore, in order to evaluate the effect of reducing the haze value of the epitaxial film brought about by the in-plane distribution uniformity of the ratio of the above-mentioned ninth integrated intensity ratio to the above-mentioned eighth integrated intensity ratio, it is preferable to measure the haze value generated by the epitaxial film grown in the region closer to the outer periphery in addition to the above-mentioned 5 measurement points. To correspond to this, in the main surface of the GaAs single crystal substrate, in addition to the above-mentioned 5 measurement points, 4 measurement objects with a diameter of 20 mm and the measurement points as their centers are also set in the region closer to the outer periphery in such a way that the distance between them is as large as possible.

[0169] Figure 4 Explanation diagram of the 5 measurement points set on the GaAs single crystal substrate with a diameter of 75 mm or more and less than 150 mm in this embodiment. Figure 5 Explanation diagram of the 9 measurement points set on the GaAs single crystal substrate with a diameter of 150 mm or more and 205 mm or less in this embodiment.

[0170] As Figure 4As shown, in the GaAs single crystal substrate of the first method, the X-axis and Y-axis are set as follows: the general angle of the ray passing through the notch 50 with respect to the ray extending from the origin to the positive direction of the X-axis is 225°. Next, a first measurement point P1 is set at the center of the GaAs single crystal substrate, that is, the origin (0, 0), and a circular region A1 to be measured with a diameter of 20 mm centered on this first measurement point P1 is set.

[0171] Next, on the circumference formed by the set of points that are only D / 4 away from the center of the GaAs single crystal substrate, a second measurement point P2, a third measurement point P3, a fourth measurement point P4, and a fifth measurement point P5 are set. Furthermore, circular regions A2, A3, A4, and A5 to be measured with a diameter of 20 mm centered on the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 respectively are set.

[0172] For example, in Figure 4 In the shown example of a GaAs single crystal substrate with a diameter of 75 mm, the coordinates (X, Y) (the units of X and Y are both mm, the same below) of the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 are set to (18.75, 0), (0, 18.75), (-18.75, 0), and (0, -18.75) respectively. Here, in the GaAs single crystal substrate with a diameter of 75 mm, the measurement objects A1, A2, A3, A4, and A5 overlap in part of the region. However, from the perspective of evaluating the uniformity of the main surface of the GaAs single crystal substrate, this overlap does not cause any problems and is therefore permissible.

[0173] As Figure 5 shown, in the GaAs single crystal substrate of the second method, in addition to the first measurement point P1 to the fifth measurement point P5 set in the GaAs single crystal substrate of the first method, 4 measurement points, namely a sixth measurement point P6, a seventh measurement point P7, an eighth measurement point P8, and a ninth measurement point P9, are equally spaced on the circumference that is closer to the outer periphery than the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 and is located 10 mm inside from the outer periphery of the GaAs single crystal substrate. Furthermore, circular regions A6, A7, A8, and A9 to be measured with a diameter of 20 mm centered on the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 respectively are set.

[0174] For example, in Figure 5In the case of the illustrated example of a GaAs single crystal substrate with a diameter of 150 mm, the coordinates (X, Y) of the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 are set to (37.5, 0), (0, 37.5), (-37.5, 0), and (0, -37.5), respectively. Further, the coordinates (X, Y) of the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 are set to (65, 0), (0, 65), (-65, 0), and (0, -65), respectively.

[0175] <Epitaxial film>

[0176] The above GaAs single crystal substrate preferably has an epitaxial film disposed on the main surface. In this case, the maximum value of the haze on the surface of the epitaxial film is preferably 100 ppm or less, and the average value of the haze on the surface of the epitaxial film is preferably 2.5 ppm or less. The maximum value of the haze on the surface of the epitaxial film is more preferably 20 ppm or less, and the average value of the haze on the surface of the epitaxial film is more preferably 2.0 ppm or less. The lower limits of the maximum value and the average value of the haze on the surface of the epitaxial film are ideal values, i.e., 0.

[0177] The epitaxial film exists, for example, in the following cases: a compound film composed of Al 1-y-z Ga y In z As, where y is 0 or more and 1 or less, z is 0 or more and 1 or less, and the sum of y and z is 0 or more and 1 or less. That is, this embodiment can apply a compound film composed of Al 1-y-z Ga y In z As (0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ y + z ≤ 1) as an epitaxial film formed on the main surface of the GaAs single crystal substrate. Further, the epitaxial film can also be Al x Ga 1-x N (0 ≤ x ≤ 1) or Al x Ga 1-x As (0 ≤ x ≤ 1) compound film.

[0178] The epitaxial film is formed to have a thickness of, for example, 0.5 to 10 μm. When the thickness of the epitaxial film is in the above range, the above GaAs single crystal substrate can be applied to a wide range of uses. The epitaxial film more preferably has a thickness of 1 to 5 μm.

[0179] The haze value of the epitaxial film disposed on the main surface of the above-mentioned GaAs single crystal substrate can be obtained by a conventionally known surface foreign matter inspection device (for example, trade name: "Surfscan6420", manufactured by KLA-TENCOR Corporation). The above-mentioned device can take the entire surface of the above-mentioned epitaxial film (except for the area 2 mm inside from the outer periphery of the above-mentioned substrate) as the object and measure the haze value (light quantity of scattered light (ppm)) per 1 cm of the above-mentioned surface. Based on the results of such measurements, the maximum value and the average value of the haze of the above-mentioned epitaxial film surface can be obtained respectively. 2

[0180] [Manufacturing Method of Gallium Arsenide Single Crystal Substrate]

[0181] The manufacturing method of the gallium arsenide single crystal substrate (GaAs single crystal substrate) of the present embodiment is preferably a manufacturing method for manufacturing the above-mentioned GaAs single crystal substrate. For example, the above-mentioned manufacturing method includes a step of preparing a gallium arsenide single crystal substrate precursor having a surface and the surface having a circular shape (hereinafter also referred to as "GaAs single crystal substrate precursor") (preparation step), and a cleaning step for obtaining the above-mentioned GaAs single crystal substrate from the above-mentioned GaAs single crystal substrate precursor. The above-mentioned cleaning step includes: a step of polishing the above-mentioned surface of the GaAs single crystal substrate precursor to make the above-mentioned surface a polished surface (surface polishing step); a step of cleaning the above-mentioned polished surface with a first alkaline cleaning solution to make the above-mentioned polished surface an alkaline cleaning surface (first alkaline cleaning step); a step of cleaning the above-mentioned alkaline cleaning surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid to make the above-mentioned alkaline cleaning surface an acid cleaning surface (acid cleaning step); a step of cleaning the above-mentioned acid cleaning surface while rotating the above-mentioned acid cleaning surface at a rotational speed of 1000 rpm or more in the circumferential direction and supplying a second alkaline cleaning solution to the above-mentioned acid cleaning surface at a flow rate of 0.1 L / minute or more and 5 L / minute or less for 30 seconds or more and 5 minutes or less to make the above-mentioned acid cleaning surface a second alkaline cleaning surface (second alkaline cleaning step); a step of heat-treating the above-mentioned second alkaline cleaning surface in an inert gas environment under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less to make the above-mentioned second alkaline cleaning surface the above-mentioned main surface (heat treatment step). The above-mentioned first alkaline cleaning solution contains 0.1 mass% or more and 10 mass% or less of a first alkali. The above-mentioned first alkali contains at least one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. The above-mentioned second alkaline cleaning solution contains 0.3 mass ppm or more and 0.5 mass% or less of a second alkali. The above-mentioned second alkali contains at least one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide.

[0182] By means of a manufacturing method having such characteristics, a GaAs single crystal substrate having an oxide film on the main surface that can be effectively removed by wet etching can be obtained. The above manufacturing method preferably includes a step of forming an epitaxial film on the above main surface (epitaxial film forming step). Thereby, a GaAs single crystal substrate having an epitaxial film with a reduced haze value formed on the main surface can be obtained.

[0183] In this specification, "GaAs single crystal substrate precursor" refers to a GaAs single crystal substrate having a circular surface cut out from a GaAs single crystal (hereinafter also referred to as "GaAs single crystal") manufactured by a conventionally known manufacturing method such as the vertical boat method, and particularly refers to a GaAs single crystal substrate that is the object of each step included in the above cleaning step.

[0184] Based on the information obtained from the analysis of XPS using the above-mentioned radiation light, the inventors focused on improving the conventionally known cleaning process for obtaining the above GaAs single crystal substrate. In particular, it is known that the oxide film of the above GaAs single crystal substrate is formed by oxidizing the surface in the pickling process, which is a process for removing impurities in the alkali cleaning agent attached to the surface of the GaAs single crystal substrate precursor after alkali cleaning. Therefore, the inventors focused on performing a treatment to form a composition rich in gallium (gallium oxide, hereinafter also referred to as "Ga oxide") near the interface between the above oxide film and the GaAs single crystal substrate layer composed of GaAs after the above acid cleaning process. Specifically, by performing a second alkali cleaning process called spin cleaning, the oxidation process of the oxide film is suppressed. The spin cleaning is performed by cleaning the surface of the GaAs single crystal substrate precursor in the order of the above alkali cleaning process and acid cleaning process, and then supplying an alkali cleaning solution to the surface while rotating the surface. Further, the surface after the second alkali cleaning process is heat-treated, thereby modifying the composition of the oxide film to be mainly Ga oxide. As a result, it was found that a composition rich in Ga oxide can be formed near the interface between the above oxide film and the GaAs single crystal substrate layer composed of GaAs. The GaAs single crystal substrate obtained through such a cleaning method has a well-wettable oxide film formed on its main surface, so that the above oxide film can be effectively removed by wet etching. Therefore, the inventors were able to obtain a GaAs single crystal substrate having a highly mirror-like main surface and achieved a manufacturing method for a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value.

[0185] The following is based on Figure 6 Specifically, each step included in the manufacturing method of the GaAs single crystal substrate of the present embodiment will be described. Figure 6 FIG. is a flowchart showing the manufacturing method of the GaAs single crystal substrate of the present embodiment.

[0186] <Preparation process S100>

[0187] The manufacturing method of the above GaAs single crystal substrate includes a process (preparation process S100) of preparing a GaAs single crystal substrate precursor having a surface and the surface having a circular shape. In the preparation process S100, a necessary GaAs single crystal substrate precursor is prepared for implementing the above cleaning process. The preparation process S100 can include a process of implementing a known manufacturing method of a GaAs single crystal substrate precursor. That is, the preparation process S100 can include a process of manufacturing GaAs single crystal using a known manufacturing method such as the vertical boat method and cutting out a GaAs single crystal substrate precursor having a surface and the surface having a circular shape from the above GaAs single crystal. In addition, for example, in the case of manufacturing a GaAs single crystal substrate precursor whose main surface is the (100) plane, it can be obtained by cutting out a GaAs single crystal grown with the growth direction as the <100> direction in such a way that the (100) plane becomes the main surface. The preparation process S100 can also include a process of processing the GaAs single crystal substrate precursor cut out from the GaAs single crystal into a desired size (for example, a disk shape with a diameter of 2 to 8 inches and a thickness of 250 to 1500 μm). As the processing method, known methods such as slicing and chamfering can be used.

[0188] <Cleaning process S200>

[0189] The manufacturing method of the above-mentioned GaAs single crystal substrate includes a cleaning process S200 for obtaining the above-mentioned GaAs single crystal substrate from the above-mentioned GaAs single crystal substrate precursor. Through this cleaning process S200, a GaAs single crystal substrate having an oxide film on the main surface can be obtained from the above-mentioned GaAs single crystal substrate precursor, and the above-mentioned oxide film can be effectively removed using wet etching. The cleaning process S200 includes: a process of polishing the above-mentioned surface of the GaAs single crystal substrate precursor to make the above-mentioned surface a polished surface (surface polishing process S210); a process of cleaning the above-mentioned polished surface with a first alkaline cleaning solution to make the above-mentioned polished surface an alkaline cleaned surface (first alkaline cleaning process S220); a process of cleaning the above-mentioned alkaline cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid to make the above-mentioned alkaline cleaned surface an acid cleaned surface (acid cleaning process S230); a process of cleaning the above-mentioned acid cleaned surface while rotating the above-mentioned acid cleaned surface at a rotational speed of 1000 rpm or more in the circumferential direction and supplying a second alkaline cleaning solution to the above-mentioned acid cleaned surface at a flow rate of 0.1 L / minute or more and 5 L / minute or less for 30 seconds or more and 5 minutes or less to make the above-mentioned acid cleaned surface a second alkaline cleaned surface (second alkaline cleaning process S240); a process of heat-treating the above-mentioned second alkaline cleaned surface under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150°C or more and 300°C or less in an inert gas environment to make the above-mentioned second alkaline cleaned surface the above-mentioned main surface (heat treatment process S250). Each process included in the cleaning process S200 will be described in detail below.

[0190] (Surface polishing process S210)

[0191] The surface polishing process S210 is a process of polishing the above-mentioned surface of the GaAs single crystal substrate precursor to make the above-mentioned surface a polished surface. Through the surface polishing process S210, the surface of the above-mentioned GaAs single crystal substrate precursor becomes a polished surface that is mirror-finished. For example, through the surface polishing process S210, the surface of the above-mentioned GaAs single crystal substrate precursor can be made into a polished surface with a surface roughness represented by the arithmetic mean roughness Ra of 0.3 nm or less. As the polishing method in the surface polishing process S210, various polishing methods such as conventionally known mechanical polishing and chemical mechanical polishing can be used.

[0192] (First alkaline cleaning process S220)

[0193] The first alkali cleaning step S220 is a step of cleaning the polished surface with a first alkali cleaning solution, thereby making the polished surface into an alkali-cleaned surface. Through the first alkali cleaning step S220, foreign matters, impurities, etc. attached to the polished surface of the above-mentioned GaAs single crystal substrate precursor can be removed using the first alkali cleaning solution. The first alkali cleaning solution is not particularly limited, and an aqueous solution containing 0.1 to 10% by mass of an organic base compound that does not contain metal elements that affect electrical properties, such as choline, quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH), and quaternary pyridinium hydroxides, is preferably used.

[0194] (Acid cleaning step S230)

[0195] The acid cleaning step S230 is a step of cleaning the alkali-cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid, thereby making the alkali-cleaned surface into an acid-cleaned surface. Through this acid cleaning step S230, impurities in the first alkali cleaning solution on the alkali-cleaned surface of the above-mentioned GaAs single crystal substrate precursor can be removed by utilizing the oxidation reaction (etching of the alkali-cleaned surface) of the above-mentioned acid cleaning solution. In particular, the acid cleaning step S230 cleans the alkali-cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid. Thereby, the ratio of Ga atoms to As atoms on the main surface is optimized, and the formation of the remaining oxide film is suppressed, so that the oxide film can be effectively removed by wet etching. The acid cleaning step S230 preferably cleans the alkali-cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.1 mass% or less of an acid.

[0196] When the acid concentration of the acid in the above-mentioned acid cleaning solution is less than 0.3 mass ppm, the modification effect on the alkali-cleaned surface becomes smaller. On the other hand, the influence of carbon dioxide (CO2) gas dissolved from the atmospheric environment into the acid cleaning solution becomes larger, so that the chemical composition of the acid-cleaned surface after the acid cleaning step S230 deviates. When the acid concentration of the acid in the above-mentioned acid cleaning solution is greater than 0.5 mass%, the deviation of the acid-cleaned surface from stoichiometry becomes larger due to the action of the above-mentioned acid, so there is a tendency for the chemical composition of the acid-cleaned surface (and thus the main surface in subsequent steps) to deviate. Here, "stoichiometry" means that when a certain compound exists, the ratio (composition) of the number of atoms constituting the compound exists as in the chemical formula.

[0197] There is no particular limitation on the acid contained in the above acid cleaning solution. Preferably, it is the following acid components: having high cleaning ability, not containing elements that affect electrical properties (such as metal elements, sulfur, etc.), and in the case where droplets fly into the equipment, since the acid component evaporates together with moisture, it is difficult to cause serious secondary pollution and equipment deterioration. For example, the acid contained in the acid cleaning solution preferably contains at least one inorganic acid selected from hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and nitrous acid (HNO2). As the above acid, organic acids such as acetic acid, citric acid, and malic acid can also be preferably used. In addition, two or more of these acids can be combined. For example, hydrochloric acid and nitric acid can be used in combination.

[0198] From the viewpoint of cleaning performance, the above acid cleaning solution more preferably contains 0.3 mass ppm to 0.3 mass% of hydrogen peroxide (H2O2). When the concentration of the above H2O2 is less than 0.3 mass ppm, the influence of dissolved oxygen in the acid cleaning solution may become larger and the effect of promoting impurity removal may be reduced. When the concentration of the above H2O2 is greater than 0.3 mass%, the etching rate may become too large and an etching height difference may occur on the acid cleaning surface.

[0199] In the acid cleaning step S230, while keeping the surface of the GaAs single crystal substrate precursor horizontal and rotating it at 100 to 800 rpm in the circumferential direction, the above acid cleaning solution can be supplied to the alkali cleaning surface. Thereby, a film of the acid cleaning solution can be formed on the alkali cleaning surface, suppressing excessive oxidation of the alkali cleaning surface while performing efficient acid cleaning. When the rotation speed of the GaAs single crystal substrate precursor is lower than 100 rpm, it may be difficult to improve the cleaning efficiency. When the rotation speed is higher than 800 rpm, it may be impossible to form a film of the acid cleaning solution and the effect of suppressing oxidation may be reduced.

[0200] Furthermore, after the acid cleaning step S230, it is preferable to immediately clean the acid cleaning surface of the GaAs single crystal substrate precursor with pure water after the acid cleaning step S230. There is no particular limitation on the cleaning method using this pure water. Preferably, the acid cleaning surface of the GaAs single crystal substrate precursor is cleaned with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less for a time of 5 minutes or less. Thereby, the progress of excessive oxidation of the acid cleaning surface can be suppressed. Here, from the viewpoint of further suppressing the progress of excessive oxidation, the dissolved oxygen concentration of the above pure water is more preferably 50 ppb or less. From the viewpoint of having few impurities, the total organic carbon (TOC) of the above pure water is preferably 40 ppb or less. Regarding the cleaning method using the above pure water, it can also be carried out by the following method: while keeping the main surface of the GaAs single crystal substrate precursor horizontal and rotating it at 100 to 800 rpm in the circumferential direction, the above pure water is supplied to the acid cleaning surface.

[0201] (Second alkali cleaning process S240)

[0202] The second alkali cleaning process S240 is a process in which while rotating the acid cleaning surface at a rotational speed of 1000 rpm or more in the circumferential direction, a second alkali cleaning liquid is supplied to the acid cleaning surface at a flow rate of 0.1 L / minute or more and 5 L / minute or less for 30 seconds or more and 5 minutes or less, thereby cleaning the acid cleaning surface and making the acid cleaning surface into a second alkali cleaning surface. Through the second alkali cleaning process S240, it is possible to suppress the excessive progress of the oxidation reaction of GaAs in the acid cleaning surface, and thus it is possible to suppress the acid cleaning surface from becoming a composition rich in As oxide. Thereby, in the subsequent heat treatment process S250, it is possible to efficiently modify the oxide film into a composition rich in Ga oxide.

[0203] In particular, the second alkali cleaning liquid contains 0.3 mass ppm or more and 0.5 mass% or less of an alkali. The alkali is an organic base compound that does not contain metal elements that affect electrical properties. There is no particular limitation on such an organic base compound, and for example, choline, quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH), and quaternary pyridinium hydroxides can be exemplified. Thereby, it is possible to suppress the excessive progress of the oxidation reaction of GaAs in the acid cleaning surface. When the concentration of the alkali in the second alkali cleaning liquid is less than 0.3 mass ppm, the effect of suppressing excessive oxidation of the acid cleaning surface becomes smaller. On the other hand, when the concentration of the alkali in the second alkali cleaning liquid exceeds 0.5 mass%, there is a possibility that dissolution occurs in the acid cleaning surface and the surface flatness is lost. The concentration of the alkali in the second alkali cleaning liquid is preferably 0.3 mass ppm or more and 0.1 mass% or less.

[0204] In addition, as described above, as the first alkali cleaning liquid used in the first alkali cleaning process S220, an aqueous solution containing 0.1 to 10 mass% of choline, quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH), and quaternary pyridinium hydroxides can be exemplified. The first alkali cleaning liquid and the second alkali cleaning liquid contain at least one alkali selected from quaternary ammonium hydroxides and quaternary pyridinium hydroxides, and the first alkali cleaning liquid may also contain the same type of alkali as the second alkali cleaning liquid. The first alkali cleaning liquid and the second alkali cleaning liquid contain at least one alkali selected from quaternary ammonium hydroxides and quaternary pyridinium hydroxides, and the first alkali cleaning liquid may also contain a different type of alkali from the second alkali cleaning liquid. That is, the first alkali cleaning liquid and the second alkali cleaning liquid contain at least one alkali selected from quaternary ammonium hydroxides and quaternary pyridinium hydroxides, and the first alkali cleaning liquid can contain the same or different type of alkali as the second alkali cleaning liquid.

[0205] In the second alkali cleaning step S240, it is preferred that the above acid cleaning surface rotates at a speed of 1500 rpm or more in the circumferential direction. There is no particular limitation on the upper limit of the rotation speed of the above acid cleaning surface in the circumferential direction, and it is preferably 2000 rpm. Regarding the flow rate of the second alkali cleaning solution supplied to the above acid cleaning surface, it is preferably 0.5 L / min or more and 3 L / min or less. Regarding the time for supplying the second alkali cleaning solution to the above acid cleaning surface, it is preferably 30 seconds or more and 3 minutes or less. Thereby, the excessive oxidation reaction of GaAs in the acid cleaning surface can be more effectively suppressed.

[0206] Furthermore, after the second alkali cleaning step S240, preferably immediately after the second alkali cleaning step S240, the above second alkali cleaning surface is cleaned with pure water in a very short time without adversely affecting the GaAs single crystal substrate precursor. Regarding the cleaning method using this pure water, it is preferred to clean the second alkali cleaning surface of the GaAs single crystal substrate precursor with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less within 30 seconds. Thereby, the impurities adhering to the second alkali cleaning surface can be removed. Here, from the viewpoint of further suppressing the progress of excessive oxidation, the dissolved oxygen concentration of the above pure water is more preferably 50 ppb or less. From the viewpoint of less impurities, the total organic carbon (TOC) of the above pure water is preferably 40 ppb or less. Regarding the cleaning method using the above pure water, it can also be carried out by the following method: while keeping the main surface of the GaAs single crystal substrate precursor horizontal and rotating at 100 - 800 rpm, the above pure water is supplied to the above second alkali cleaning surface.

[0207] (Heat treatment step S250)

[0208] The heat treatment step S250 is a step of heat-treating the above second alkali cleaning surface under the conditions of 1.1 atm or more and 3 atm or less and 150°C or more and 300°C or less in an inert gas atmosphere, thereby forming the above second alkali cleaning surface into the above main surface. Through the heat treatment step S250, the oxide film on the second alkali cleaning surface can be modified so that its composition is mainly Ga oxide. Thereby, a composition rich in Ga oxide can be formed near the interface between the above oxide film and the layer composed of GaAs of the above GaAs single crystal substrate. Thereby, in the above GaAs single crystal substrate, an oxide film with good surface wettability is formed, so that the above oxide film can be more effectively removed by wet etching.

[0209] In the heat treatment step S250, the second alkali-cleaned surface is heat-treated in an inert gas atmosphere under the conditions of 1.1 atm or more and 3 atm or less and 150°C or more and 300°C or less. The type of the inert gas is not particularly limited, and argon or nitrogen is preferred. Further, regarding the temperature at which the heat treatment is performed, it is preferably 175 to 275°C. Regarding the atmospheric pressure at which the heat treatment is performed, it is preferably 1.5 to 2.5 atm. By performing the heat treatment under the conditions within the above ranges, the composition of the oxide film can be made to be a composition appropriately rich in gallium. When the temperature at which the heat treatment is performed is less than 150°C or the atmospheric pressure at which the heat treatment is performed is 1.1 atm, there is a tendency that the modification of the oxide film is insufficient. When the temperature at which the heat treatment is performed exceeds 300°C or the atmospheric pressure at which the heat treatment is performed exceeds 3 atm, there is a possibility of adversely affecting the GaAs single crystal substrate due to overheating. Regarding the time for performing the heat treatment, it is preferably 1 to 30 minutes.

[0210] <Wet etching step>

[0211] In summary, the method for manufacturing a GaAs single crystal substrate according to the present embodiment can obtain a GaAs single crystal substrate having a main surface, and the main surface includes an oxide film having the following characteristics. That is, the oxide film has the following composition: near the interface between the oxide film and the layer made of GaAs of the GaAs single crystal substrate, it is rich in Ga oxide. In such a GaAs single crystal substrate, even when the wet etching step is performed under the conditions known in the art (for example, after cleaning with sulfuric acid and water (H2SO4:H2O2:H2O = 7:1:1) for 1 minute and then rinsing and drying), the wettability of the surface of the oxide film is good, and thus the oxide film can be effectively removed.

[0212] <Epitaxial film formation step S300>

[0213] In the method for manufacturing a GaAs single crystal substrate according to the present embodiment, it preferably includes a step of forming an epitaxial film on the main surface (epitaxial film formation step S300). By the epitaxial film formation step S300, a GaAs single crystal substrate having an epitaxial film with a reduced haze value formed on the main surface can be obtained. For example, the maximum value of the haze of the epitaxial film surface can be 100 ppm or less, and the average value of the haze of the surface can be 2.5 ppm or less, and thus the device characteristics can be improved.

[0214] In the above-described epitaxial film forming step S300, a method for forming an epitaxial film on the main surface of a GaAs single crystal substrate can use a conventionally well-known method. Regarding the characteristics of the epitaxial film obtained in this step, as described in the item of <epitaxial film> above, it will not be repeated here. Since the haze value of the GaAs single crystal substrate having the epitaxial film formed on its main surface is very small, it can be applied to devices such as field effect transistors and microwave diodes, and other integrated circuits, etc., in terms of usage.

[0215] Examples

[0216] Examples are given below to explain the present invention in more detail, but the present invention is not limited to these examples. The GaAs single crystal substrates of Specimens 1 to 6 described below are examples, and the GaAs single crystal substrates of Specimens 11 to 13 are comparative examples.

[0217] [Manufacture of GaAs Single Crystal Substrate]

[0218] <Specimen 1>

[0219] (Preparation Step)

[0220] A semi-insulating GaAs single crystal doped with carbon (C) atoms grown by the vertical Bridgman (VB) method was sliced and chamfered to prepare a plurality of GaAs single crystal substrate precursors with a diameter of 6 inches (150 mm) and a thickness of 675 μm.

[0221] (Surface Polishing Step)

[0222] The surface of the above GaAs single crystal substrate precursor was polished by a conventionally well-known mechanical polishing and chemical mechanical polishing. Thus, a GaAs single crystal substrate precursor having a polished surface with an arithmetic mean roughness Ra of 0.3 nm or less as specified in JIS B0601:2001 and a deviation angle of 2° with respect to the (100) plane was fabricated.

[0223] (First Alkaline Cleaning Step)

[0224] At room temperature (25 °C), the polished surface of the above GaAs single crystal substrate precursor was immersed in an aqueous solution (first alkaline cleaning solution) containing 0.5 mass% of tetramethylammonium hydroxide in a vertical-batch manner for 10 minutes. Then, the GaAs single crystal substrate precursor was rinsed with ultrapure water (resistivity (specific resistance) of 18 MΩ·cm or more, TOC (total organic carbon) less than 10 μg / L, and the number of particles less than 100 / L, the same hereinafter) for 3 minutes.

[0225] (Acid Cleaning Step)

[0226] For the alkali-cleaned surface of the above-mentioned GaAs single crystal substrate precursor, acid cleaning is performed in a vertical-batch manner using an acid cleaning solution. In the above acid cleaning, the alkali-cleaned surface of the GaAs single crystal substrate precursor is immersed in an aqueous hydrochloric acid solution containing 0.3 mass ppm of hydrochloric acid as the acid cleaning solution at room temperature (25 °C) for 2 minutes. Further, the GaAs single crystal substrate precursor is rinsed with the same ultrapure water as that used in the above alkali cleaning process for 3 minutes. Thus, the alkali-cleaned surface is made into an acid-cleaned surface.

[0227] (Second alkali cleaning process)

[0228] For the acid-cleaned surface of the above-mentioned GaAs single crystal substrate precursor, alkali cleaning is performed in a spin-cleaning manner using a second alkali cleaning solution. Specifically, for the acid-cleaned surface of the above-mentioned GaAs single crystal substrate precursor rotating at 1500 rpm in the circumferential direction, an aqueous solution containing 0.3 mass ppm of tetramethylammonium hydroxide as the alkali is supplied at a flow rate of 3 L / min for 3 minutes. Then, the GaAs single crystal substrate precursor is rinsed with the same ultrapure water as that used in the acid cleaning process for 3 minutes. Thus, the acid-cleaned surface is made into a second alkali-cleaned surface.

[0229] (Heat treatment process)

[0230] For the second alkali-cleaned surface of the above-mentioned GaAs single crystal substrate precursor, heat treatment is performed under the conditions of an argon atmosphere, 3 atmospheres, 300 °C, and 5 minutes. Thus, the second alkali-cleaned surface is made into a main surface with a specified oxide film. Through the above, a GaAs single crystal substrate of the required number of samples 1 is obtained. This GaAs single crystal substrate maintains the diameter and thickness of the above-mentioned GaAs single crystal substrate precursor.

[0231] (Epitaxial film formation process)

[0232] Wet etching is carried out under the following conditions: After cleaning the above-mentioned GaAs single crystal substrate with sulfuric acid diluted with water (H2SO4:H2O2:H2O = 7:1:1) for 1 minute, it is rinsed and dried. Further, for one of the GaAs single crystal substrates subjected to the above wet etching, an Al 0.5 Ga 0.5 As layer with a thickness of 1 μm is grown on its main surface as an epitaxial layer (hereinafter, the GaAs single crystal substrate with an epitaxial layer grown on its main surface is also referred to as an "epitaxial substrate"). Thus, an epitaxial substrate of sample 1 is obtained. When growing the above epitaxial layer, the GaAs single crystal substrate is heated to 550 °C.

[0233] <Sample 2>

[0234] In the above second alkali cleaning process, for the acid cleaning surface of the above GaAs single crystal substrate precursor rotating at 1500 rpm in the circumferential direction, an aqueous solution containing 0.1 mass% of tetramethylammonium hydroxide as an alkali is supplied at a flow rate of 0.5 L / minute for 30 seconds, and in the above heat treatment process, heat treatment is performed under an argon atmosphere at 1.1 atmospheres, 150 °C, and for 1 minute. In addition, according to the same points as in Sample 1, GaAs single crystal substrates of Sample 2 in the required number are obtained. Further, for one of the above GaAs single crystal substrates, according to the same points as in Sample 1, an Al 0.5 Ga 0.5 As layer is grown as an epitaxial layer on its main surface.

[0235] <Sample 11>

[0236] The above second alkali cleaning process and heat treatment process are not performed. In addition, according to the same points as in Sample 1, GaAs single crystal substrates of Sample 11 in the required number are obtained. Further, for one of the above GaAs single crystal substrates, according to the same points as in Sample 1, an Al 0.5 Ga 0.5 As layer is grown as an epitaxial layer on its main surface.

[0237] <Sample 12>

[0238] The above second alkali cleaning process is not performed. In addition, according to the same points as in Sample 1, GaAs single crystal substrates of Sample 12 in the required number are obtained. Further, for one of the above GaAs single crystal substrates, according to the same points as in Sample 1, an Al 0.5 Ga 0.5 As layer is grown as an epitaxial layer on its main surface.

[0239] [Sample 13]

[0240] The above heat treatment process is not performed. In addition, according to the same points as in Sample 1, GaAs single crystal substrates of Sample 13 in the required number are obtained. Further, for one of the above GaAs single crystal substrates, according to the same points as in Sample 1, an Al 0.5 Ga 0.5 As layer is grown as an epitaxial layer on its main surface.

[0241] [First Experiment]

[0242] <Analysis of GaAs Single Crystal Substrate Using X-ray Photoelectron Spectroscopy>

[0243] By using "BL17", one of the dedicated beamlines of Sumitomo Electric Industries, Ltd. in the Saga Prefectural Kyushu Synchrotron Light Research Center, X-rays with an energy of 600 eV were prepared. The main surfaces of the GaAs single crystal substrates of Specimens 1 to 2 and Specimens 11 to 13 were irradiated with the X-rays at the centers, and thus analysis using X-ray photoelectron spectroscopy was performed. In addition, regarding the GaAs single crystal substrates of Specimens 1 to 2 and Specimens 11 to 13, since it was impossible to place all of them on the specimen stage, test pieces were cut out from the GaAs single crystal substrates of Specimens 1 to 2 and Specimens 11 to 13, and the test pieces were analyzed.

[0244] The analysis conditions are as follows.

[0245] Condition 1: X-ray incident energy of 600 eV and photoelectron emission angle of 30°

[0246] Condition 2: X-ray incident energy of 600 eV and photoelectron emission angle of 45°

[0247] Condition 3: X-ray incident energy of 600 eV and photoelectron emission angle of 85°

[0248] Dimensions of the test pieces under each condition: 10 mm × 10 mm

[0249] Pressure around the test pieces under each condition: 4×10 -7 Pa

[0250] High-resolution XPS analysis apparatus (trade name: "R3000", manufactured by Scienta Omicron) used under each condition

[0251] Energy resolution E / ΔE: 3480

[0252] Plotting interval of binding energy: 0.02 eV

[0253] Integration time and number of integrations for each energy value: 100 ms, 50 times.

[0254] Based on the Ga3d spectra and As3d spectra obtained by XPS analysis under the above respective conditions (Condition 1 to Condition 3), the integral intensity of As, the integral intensity of As, the integral intensity of As-Ga, and the sum of the integral intensities of metallic As relative to the integral intensity of Ga 5+ of Specimens 1 to 2 and Specimens 11 to 13 were respectively obtained. 3+ of Specimens 1 to 2 and Specimens 11 to 13 were respectively obtained. + of Specimens 1 to 2 and Specimens 11 to 13 were respectively obtained. 3+The ratio of the sum of the integrated intensities of [[]] and the integrated intensity of Ga-As is the first integrated intensity ratio (In1) and the second integrated intensity ratio (In2). Furthermore, based on the Ga3d spectrum and As3d spectrum obtained by the analysis of the above respective conditions (Condition 1 to Condition 3), the As in Specimens 1 to 2 and Specimens 11 to 13 is determined respectively 5+ of the integrated intensity and As 3+ of the integrated intensity sum with respect to Ga + of the integrated intensity and Ga 3+ of the integrated intensity sum is the third integrated intensity ratio (In3), the fourth integrated intensity ratio (In4), and the fifth integrated intensity ratio (In5). The ratio (In1 / In2) of the first integrated intensity ratio (In1) to the second integrated intensity ratio (In2) in Specimens 1 to 2 and Specimens 11 to 13 is also calculated. The results are shown in Table 1. Table 1 also shows: Based on the Ga3d spectrum and As3d spectrum obtained by XPS analysis under Condition 2, the integrated intensity of As 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga, and the ratio of the sum of the integrated intensities of metallic As with respect to the integrated intensity of Ga + , the integrated intensity of Ga 3+ , and the sum of the integrated intensities of Ga-As. In Table 1, "total Ga" means the integrated intensity of Ga + , the integrated intensity of Ga 3+ , and the sum of the integrated intensities of Ga-As, and "total As" means the integrated intensity of As 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga, and the sum of the integrated intensities of metallic As.

[0255] <Maximum and average values of haze on the surface of the epitaxial film>

[0256] For the surface of the epitaxial film of the epitaxial substrate of Specimens 1 to 2 and Specimens 11 to 13, by using a surface foreign matter inspection device (trade name: "Surfscan6420", manufactured by KLA-TENCOR Corporation), the maximum value and average value of the haze on the surface of the epitaxial film in each specimen are determined. The results are shown in Table 1.

[0257] Furthermore, based on the values of the maximum value and average value of the haze on the surface of the epitaxial film, the quality of the epitaxial substrates of Specimens 1 to 2 and Specimens 11 to 13 is determined based on the following criteria. The results are shown in Table 1.

[0258] A: The maximum value of the haze is 20 ppm or less, and the average value of the haze is 2.0 ppm or less

[0259] B: The maximum value of haze is greater than 20 ppm and 100 ppm or less, and the average value of haze is greater than 2.0 ppm and 2.5 ppm or less.

[0260] C: At least the maximum value of haze is greater than 100 ppm, or the average value of haze is greater than 2.5 ppm.

[0261] <Wettability (contact angle)>

[0262] In an environment of room temperature (20 to 25 °C) and relative humidity of 40 to 60%, 2 μL of distilled water was dropped onto the center of the main surface of the GaAs single crystal substrates of Specimens 1 to 2 and Specimens 11 to 13, and the contact angle of the droplet of the distilled water formed on the main surface was measured using the θ / 2 method. In the observation of the droplet, a contact angle meter (for example, trade name (product number): "Drop Master500", manufactured by Kyowa Interface Science Co., Ltd.) was used. The results are shown in Table 1.

[0263] [Table 1]

[0264] Table 1

[0265]

[0266] <Discussion>

[0267] According to Table 1 above, in the epitaxial substrates of Specimens 1 to 2 that satisfy all of the following relationships, the quality is judged as A or B: the second integrated intensity ratio is 0.9 or more and 1.05 or less, the third integrated intensity ratio and the fourth integrated intensity ratio are 1.0 or less, the fifth integrated intensity ratio is 0.8 or less, and the ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or more and 1 or less. In contrast, the quality of the epitaxial substrates of Specimens 11 to 13 that do not satisfy at least any one of the above relationships is judged as C.

[0268] [Second Test]

[0269] <Manufacture of GaAs Single Crystal Substrate>

[0270] (Specimen 3)

[0271] In the above preparation process, a semi-insulating GaAs single crystal doped with carbon (C) atoms was sliced and chamfered to prepare a GaAs single crystal substrate precursor with a diameter of 3 inches (76 mm) and a thickness of 350 μm. In addition, the GaAs single crystal substrate of Specimen 3 was obtained by the same procedure as Specimen 1.

[0272] (Specimen 4)

[0273] In the above preparation process, a semi-insulating GaAs single crystal doped with carbon (C) atoms is sliced and chamfered to prepare a GaAs single crystal substrate precursor with a diameter of 4 inches (100 mm) and a thickness of 350 μm. In addition, a GaAs single crystal substrate of Sample 4 is obtained by the same key points as Sample 1.

[0274] (Sample 5)

[0275] In the above preparation process, a semi-insulating GaAs single crystal doped with carbon (C) atoms is sliced and chamfered to prepare a GaAs single crystal substrate precursor with a diameter of 6 inches (150 mm) and a thickness of 675 μm. In addition, a GaAs single crystal substrate of Sample 5 is obtained by the same key points as Sample 1.

[0276] (Sample 6)

[0277] In the above preparation process, a semi-insulating GaAs single crystal doped with carbon (C) atoms is sliced and chamfered to prepare a GaAs single crystal substrate precursor with a diameter of 8 inches (200 mm) and a thickness of 675 μm. In addition, a GaAs single crystal substrate of Sample 6 is obtained by the same key points as Sample 1.

[0278] <Analysis of the uniformity of the main surface of the GaAs single crystal substrate>

[0279] (Samples 3 and 4)

[0280] Five test pieces cut from the main surfaces of the GaAs single crystal substrates of Samples 3 and 4 are analyzed by the same key points as [Analysis of the GaAs single crystal substrate using X-ray photoelectron spectroscopy] in the above first test. From this, the integrated intensity of As 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga, and the ratio of the sum of the integrated intensities of metallic As to the integrated intensity of Ga + , the integrated intensity of Ga 3+ , and the sum of the integrated intensities of Ga-As, that is, the sixth integrated intensity ratio (In6), are obtained. In addition, the ratio of the sum of the integrated intensities of As 5+ and As 3+ to the sum of the integrated intensities of Ga + and Ga 3+ , that is, the seventh integrated intensity ratio (In7), is obtained. Furthermore, the ratio of the seventh integrated intensity ratio (In7) to the sixth integrated intensity ratio (In6) (In7 / In6) is calculated. Then, by calculating the standard deviation and average value of this In7 / In6, their standard deviation / average value is obtained.

[0281] Each of the above five test pieces containsFigure 4 The first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 shown in the figure. Furthermore, five test pieces were set in a high-resolution XPS analyzer in such a way that the first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 were irradiated with X-rays respectively. The results are shown in Tables 2 and 3. Table 2 shows In7 / In6 of the GaAs single crystal substrate of Specimen 3, as well as its standard deviation and average value. Table 3 shows In7 / In6 of the GaAs single crystal substrate of Specimen 4, as well as its standard deviation and average value. The smaller the value of the standard deviation / average value shown in Tables 2 and 3, the more uniform the characteristics of the GaAs single crystal substrate are in-plane on the main surface.

[0282] (Specimen 5 and Specimen 6)

[0283] Nine test pieces cut from the respective main surfaces of the GaAs single crystal substrates of Specimen 5 and Specimen 6 were analyzed by the same key points as in the above First Experiment [Analysis of GaAs single crystal substrate using X-ray photoelectron spectroscopy]. From this, the integrated intensity of As 5+ was obtained, the integrated intensity of As 3+ was obtained, the integrated intensity of As-Ga, and the ratio of the sum of the integrated intensities of metallic As to the integrated intensity of Ga + was obtained, the integrated intensity of Ga 3+ was obtained, the integrated intensity of Ga 5+ was obtained, and the ratio of the sum of the integrated intensities of As 3+ to the sum of the integrated intensities of Ga + was obtained, which is the eighth integrated intensity ratio (In8). In addition, the ratio of the sum of the integrated intensities of As 3+ to the sum of the integrated intensities of Ga

[0284] The above nine test pieces each contain Figure 5The first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, the fifth measurement point P5, the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 shown. Further, nine test pieces are set in a high-resolution XPS analysis apparatus by irradiating the first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, the fifth measurement point P5, the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 with X-rays, respectively. The results are shown in Tables 4 and 5. Table 4 shows In9 / In8 of the GaAs single crystal substrate of Specimen 5, and its standard deviation and average value. Table 5 shows In9 / In8 of the GaAs single crystal substrate of Specimen 6, and its standard deviation and average value. The smaller the value of the standard deviation / average value shown in Tables 4 and 5, the more uniform the characteristics of the GaAs single crystal substrate are in-plane on the main surface.

[0285] [Table 2]

[0286] Table 2

[0287]

[0288] [Table 3]

[0289] Table 3

[0290]

[0291] [Table 4]

[0292] Table 4

[0293]

[0294] [Table 5]

[0295] Table 5

[0296]

[0297] [Consideration]

[0298] According to Tables 2 and 3, in the GaAs single crystal substrates of Specimen 3 and Specimen 4, the standard deviation and the average value of the ratio (In7 / In6) of the seventh integrated intensity ratio (In7) to the sixth integrated intensity ratio (In6) satisfy the relationship of standard deviation / average value ≤ 0.039. According to Tables 4 and 5, in the GaAs single crystal substrates of Specimen 5 and Specimen 6, the standard deviation and the average value of the ratio (In9 / In8) of the ninth integrated intensity ratio (In9) to the eighth integrated intensity ratio (In8) satisfy the relationship of standard deviation / average value ≤ 0.022. That is to say, the characteristics of the GaAs single crystal substrates of Specimen 3 to Specimen 6 are very uniform in the plane of the main surface. Therefore, the GaAs single crystal substrates of Specimen 3 to Specimen 6 have high specularity over the entire main surface, and thus it is expected that an epitaxial film with a reduced haze value can be formed.

[0299] As described above, the embodiments and examples of the present invention have been described, but appropriate combinations of the configurations of the above-described respective embodiments and examples were also initially contemplated.

[0300] All aspects of the embodiments and examples disclosed this time should be considered illustrative and not restrictive. The scope of the present invention is represented by the scope of the claims rather than by the above-described embodiments and examples, and all changes within the meaning and scope equivalent to the scope of the claims are included in the scope of the present invention.

[0301] Description of Reference Numerals

[0302] 1: GaAs single crystal substrate; 1m: main surface; 10: X-ray generating device; 11: X-ray source; 12, 14: slits; 13: grating; 20: vacuum chamber; 30: electron spectrometer; 50: notch; 100: analysis system; LA: As3d spectrum; LG: Ga3d spectrum; L1: Ga 3+ spectrum; L2: Ga + spectrum; L3: Ga-As spectrum; L4: As 5+ spectrum; L5: As 3+ spectrum; L6: metallic As spectrum; L7: As-Ga spectrum; P1: first measurement point; P2: second measurement point; P3: third measurement point; P4: fourth measurement point; P5: fifth measurement point; P6: sixth measurement point; P7: seventh measurement point; P8: eighth measurement point; P9: ninth measurement point; A1 to A9: measurement objects; S100: preparation process; S200: cleaning process; S210: surface polishing process; S220: first alkali cleaning process; S230: acid cleaning process; S240: second alkali cleaning process; S250: heat treatment process; S300: epitaxial film formation process.

Claims

1. A gallium arsenide single crystal substrate having a main surface with a circular shape, The gallium arsenide single crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio. The first integrated intensity ratio and the third integrated intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a take-off angle of photoelectrons of 30°, a spectrum of the detection intensity of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate is obtained. The second integral intensity ratio and the fifth integral intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, a spectrum of the detection intensity of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate is obtained; The fourth integral intensity ratio is obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto the center of the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 45°, a spectrum of the detection intensity of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate is obtained; The first integral intensity ratio and the second integral intensity ratio are: the ratio of the sum of the integral intensities of arsenic elements present as arsenic pentoxide, arsenic elements present as arsenic trioxide, arsenic elements present as gallium arsenide, and arsenic elements present as metallic arsenic to the sum of the integral intensities of gallium elements present as gallium monoxide, gallium elements present as gallium trioxide, and gallium elements present as gallium arsenide; The third integral intensity ratio, the fourth integral intensity ratio, and the fifth integral intensity ratio are: the ratio of the sum of the integral intensities of arsenic elements present as the arsenic pentoxide and the integral intensities of arsenic elements present as the arsenic trioxide to the sum of the integral intensities of gallium elements present as the gallium monoxide and the integral intensities of gallium elements present as the gallium trioxide; The second integral intensity ratio is 0.9 or more and 1.05 or less, The third integral intensity ratio and the fourth integral intensity ratio are 1.0 or less, The fifth integral intensity ratio is 0.8 or less, and The ratio of the first integral intensity ratio to the second integral intensity ratio is 0.5 or more and 1 or less.

2. The gallium arsenide single crystal substrate according to claim 1, wherein The second integral intensity ratio is 0.9 or more and less than 1.

04.

3. The gallium arsenide single crystal substrate according to claim 1 or 2, wherein The gallium arsenide single crystal substrate has an oxide film with a thickness of 2 nm or less on the main surface.

4. The gallium arsenide single crystal substrate according to claim 3, wherein The contact angle of the oxide film is 20 degrees or less.

5. The gallium arsenide single crystal substrate according to any one of claims 1 to 4, wherein The gallium arsenide single crystal substrate has a diameter of 75 mm or more and 205 mm or less.

6. The gallium arsenide single crystal substrate according to any one of claims 1 to 5, wherein The gallium arsenide single crystal substrate has a diameter of 75 mm or more and less than 150 mm, The gallium arsenide single crystal substrate has a sixth integral intensity ratio and a seventh integral intensity ratio, The sixth integral intensity ratio and the seventh integral intensity ratio are obtained as follows: Based on X-ray photoelectron spectroscopy in which X-rays are irradiated onto 5 measurement points on the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron emission angle of 85°, a spectrum of the detection intensity of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate is obtained; The sixth integrated intensity ratio is: the ratio of the sum of the integrated intensities of arsenic elements present as arsenic pentoxide, arsenic elements present as arsenic trioxide, arsenic elements present as gallium arsenide, and arsenic elements present as metallic arsenic to the sum of the integrated intensities of gallium elements present as gallium monoxide, gallium elements present as gallium trioxide, and gallium elements present as gallium arsenide; The seventh integrated intensity ratio is: the ratio of the sum of the integrated intensities of arsenic elements present as arsenic pentoxide and arsenic elements present as arsenic trioxide to the sum of the integrated intensities of gallium elements present as gallium monoxide and gallium elements present as gallium trioxide; The standard deviation and the average value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.039; When using D to represent the diameter and taking two axes orthogonal to each other on the main surface passing through the center of the main surface as the X-axis and the Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and the Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4), and the units of D and X and Y in the coordinates (X, Y) are mm.

7. The gallium arsenide single crystal substrate according to any one of claims 1 to 5, wherein The gallium arsenide single crystal substrate has a diameter of 150 mm or more and 205 mm or less; The gallium arsenide single crystal substrate has an eighth integrated intensity ratio and a ninth integrated intensity ratio; The eighth integrated intensity ratio and the ninth integrated intensity ratio are obtained by the following method: based on X-ray photoelectron spectroscopy in which X-rays are respectively irradiated to nine measurement points on the main surface under the conditions of an X-ray incident energy of 600 eV and a take-off angle of photoelectrons of 85°, the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of the photoelectrons released to the outside of the gallium arsenide single crystal substrate are obtained; The eighth integrated intensity ratio is: the ratio of the sum of the integrated intensities of arsenic elements present as arsenic pentoxide, arsenic elements present as arsenic trioxide, arsenic elements present as gallium arsenide, and arsenic elements present as metallic arsenic to the sum of the integrated intensities of gallium elements present as gallium monoxide, gallium elements present as gallium trioxide, and gallium elements present as gallium arsenide; The ninth integrated intensity ratio is: the ratio of the sum of the integrated intensities of arsenic elements present as arsenic pentoxide and arsenic elements present as arsenic trioxide to the sum of the integrated intensities of gallium elements present as gallium monoxide and gallium elements present as gallium trioxide; The standard deviation and the average value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.022; When the diameter is represented by D and two axes orthogonal to each other on the main surface passing through the center of the main surface are taken as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the nine measurement points are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (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.

8. The gallium arsenide single crystal substrate according to any one of claims 1 to 7, wherein, The gallium arsenide single crystal substrate has an epitaxial film disposed on the main surface. The maximum value of the haze of the surface of the epitaxial film is 100 ppm or less. The average value of the haze of the surface of the epitaxial film is 2.5 ppm or less.

9. A method for manufacturing a gallium arsenide single crystal substrate, the gallium arsenide single crystal substrate having a main surface, the main surface having a circular shape, The manufacturing method includes a step of preparing a gallium arsenide single crystal substrate precursor having a surface and the surface having a circular shape, and a cleaning step for obtaining the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor, The cleaning step includes: A step of polishing the surface of the gallium arsenide single crystal substrate precursor to thereby form a polished surface on the surface. A step of cleaning the polished surface with a first alkaline cleaning solution to thereby form an alkali-cleaned surface on the polished surface. A step of cleaning the alkali-cleaned surface with an acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass% or less of an acid to thereby form an acid-cleaned surface on the alkali-cleaned surface. A step of cleaning the acid-cleaned surface to thereby form a second alkali-cleaned surface on the acid-cleaned surface by rotating the acid-cleaned surface at a rotational speed of 1000 rpm or more in the circumferential direction and supplying a second alkaline cleaning solution to the acid-cleaned surface at a flow rate of 0.1 L / minute or more and 5 L / minute or less for 30 seconds or more and 5 minutes or less. A step of heat-treating the second alkali-cleaned surface under conditions of 1.1 atm or more and 3 atm or less and 150°C or more and 300°C or less in an inert gas atmosphere to thereby form the main surface on the second alkali-cleaned surface. The first alkaline cleaning solution contains 0.1 mass% or more and 10 mass% or less of a first alkali. The first alkali contains at least any one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide. The second alkaline cleaning solution contains 0.3 mass ppm or more and 0.5 mass% or less of a second alkali. The second alkali contains at least any one of quaternary ammonium hydroxide and quaternary pyridinium hydroxide.

10. The method for manufacturing a gallium arsenide single crystal substrate according to claim 9, wherein, It includes a step of forming an epitaxial film on the main surface.

11. The gallium arsenide single crystal substrate according to claim 2, wherein, The gallium arsenide single crystal substrate has an oxide film with a thickness of 2 nm or less on the main surface. The contact angle of the oxide film is 20 degrees or less.

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