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, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio, the third integrated intensity ratio being 1.05-1.2, and the sixth integrated intensity ratio being 1.05-1.2. The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all 0.9 or more, and the ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9-1.3 (inclusive). The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all 0.7-1.1.

Description

Technical Field

[0001] The invention relates to a gallium arsenide single crystal substrate and a manufacturing method thereof. Background Art

[0002] Japanese Patent Application Laid-Open No. 06-045318 (Patent Document 1) proposes a gallium arsenide single crystal substrate (hereinafter also referred to as a "GaAs single crystal substrate") capable of thermally cleaning an oxide film at low temperature and in a short time. This GaAs single crystal substrate can be achieved by artificially forming an As-rich interface transition layer with a thickness of 3 or less on its surface. Japanese Patent Application Laid-Open No. 2008-300747 (Patent Document 2) proposes a GaAs wafer that is cleaned by thermally cleaning at least the surface of the GaAs single crystal substrate to a degree that allows the removal of impurities and oxides from the surface.

[0003] Prior art literature

[0004] Patent Literature

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

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

[0007] A gallium arsenide single crystal substrate according to the present invention comprises a main surface having 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, a fifth integrated intensity ratio, and a sixth integrated intensity ratio. The first and fourth integrated intensity ratios are obtained by determining a spectrum of the detected intensity of gallium and arsenic 3d electrons relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which involves irradiating the center of the main surface with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining a spectrum of the detected intensities of 3d electrons of gallium and arsenic relative to the binding energies of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which is performed by irradiating the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 45 degrees. The third integrated intensity ratio and the sixth integrated intensity ratio are obtained by determining a spectrum of the detected intensities of 3d electrons of gallium and arsenic relative to the binding energies of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which is performed by irradiating the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 85 degrees. The first, second, and third integrated intensity ratios are the ratios of the sum of the integrated intensities of arsenic present as arsenic pentoxide, arsenic present as arsenic trioxide, arsenic present as gallium arsenide, and arsenic present as metallic arsenic to the sum of the integrated intensities of gallium present as gallium monoxide, gallium present as gallium trioxide, and gallium present as gallium arsenide. The fourth, fifth, and sixth integrated intensity ratios are the ratios of the sum of the integrated intensities of arsenic present as arsenic pentoxide and arsenic present as arsenic trioxide to the sum of the integrated intensities of gallium present as gallium monoxide and gallium present as gallium trioxide. The third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are all 0.9 or greater. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.9 and less than or equal to 1.3. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all greater than or equal to 0.7 and less than or equal to 1.1.

[0008] The present invention provides a method for manufacturing a gallium arsenide single crystal substrate having a main surface with a circular shape. The method includes preparing a gallium arsenide single crystal substrate precursor having a surface with a circular shape, and cleaning the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor. The cleaning step includes: polishing the surface of the gallium arsenide single crystal substrate precursor to form a polished surface; cleaning the polished surface with an alkaline cleaning solution to form an alkaline cleaned surface; immersing the alkaline cleaned surface in a first acid cleaning solution containing 0.3 mass ppm to 0.5 mass % of a first acid to clean the alkaline cleaned surface to form an acid cleaned surface; supplying a second acid cleaning solution containing 0.3 mass ppm to 0.5 mass % of a second acid to the acid cleaned surface at a flow rate of 0.1 L / min to 5 L / min for 30 seconds to 5 minutes while rotating the acid cleaned surface in a circumferential direction at a rotation speed of 1000 rpm or more to clean the acid cleaned surface to form a second acid cleaned surface; and heat-treating the second acid cleaned surface in an inert gas atmosphere at atmospheric pressure and at 150° C. to 300° C. to form the second acid cleaned surface to form the main surface. The first acid contained in the first acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. The second acid contained in the second acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 2 This is an explanatory diagram schematically illustrating the configuration of an analysis system using X-ray photoelectron spectroscopy (XPS).

[0011] Figure 3A This is a graph showing an example of a background-corrected Ga3d spectrum obtained by XPS in which the center of the main surface of the GaAs single crystal substrate of this embodiment is irradiated with X-rays.

[0012] Figure 3BThis is a graph showing an example of a background-corrected As3d spectrum obtained by XPS in which the center of the main surface of the GaAs single crystal substrate of this embodiment is irradiated with X-rays.

[0013] Figure 4 This figure is an explanatory diagram for explaining five measurement points set on a GaAs single crystal substrate having a diameter of 75 mm or more and less than 150 mm in this embodiment.

[0014] Figure 5 This figure is an explanatory diagram for explaining nine measurement points set on a GaAs single crystal substrate having a diameter of 150 mm to 205 mm in this embodiment.

[0015] Figure 6 This is a flowchart showing the method for manufacturing a GaAs single crystal substrate according to this embodiment. DETAILED DESCRIPTION

[0016] [Problems to be Solved by the Invention]

[0017] It is known that haze is a method for evaluating the mirror surface of an epitaxial film (i.e., whether there is a height difference), and an increase in its value is associated with a decrease in device characteristics. Haze refers to the amount of scattered light that is scattered due to the irregularity of the surface and the tiny defects and foreign matter present on the surface when the surface of the epitaxial film is irradiated with a laser. Haze is expressed as the ratio of the amount of scattered light to the amount of laser light incident on the surface. Haze is expressed in parts per million (ppm). The smaller the haze value, the more mirror-like the surface is and the less the height difference. The height difference comes from, for example, stacking defects (stacking faults) generated when the epitaxial film is grown on a GaAs single crystal substrate. The stacking defect depends on the mirror surface of the main surface of the GaAs single crystal substrate, and therefore it is required to reduce the value of the haze by realizing a GaAs single crystal substrate with a high mirror surface on the main surface.

[0018] Thermal cleaning is highly anticipated as a means of achieving a GaAs single crystal substrate having a main surface with a high mirror finish by removing an oxide film from the main surface. However, for GaAs single crystal substrates having a mirror finish on the main surface using thermal cleaning, as described in Patent Document 1, there is a need to further reduce the haze value of the epitaxial film grown on the main surface.

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

[0020] [Effects of the Invention]

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

[0022] [Overview of Embodiments]

[0023] First, an overview of the embodiments of the present invention will be described. The present inventors conducted extensive research to address the aforementioned issues and ultimately achieved the present invention. Specifically, the present inventors focused on applying a novel cleaning method to a GaAs single crystal substrate precursor having a rounded surface, cut from a GaAs single crystal, to obtain a primary surface with high mirror finish in the GaAs single crystal substrate. Specifically, in addition to the conventionally known liquid phase treatments of alkaline cleaning with an alkaline solution and acid cleaning with an acidic solution, they also implemented an acid cleaning method using a second acid and a heat treatment. As a result, they discovered that in the GaAs single crystal substrate obtained using the novel cleaning method, the oxide film not only has an arsenic-rich composition, but also, due to the reduction of metallic arsenic generated during the cleaning process using the novel cleaning method, has a composition rich in gallium monoxide and arsenic trioxide. This oxide film composition, which readily sublimates gallium monoxide and arsenic trioxide, can be effectively removed using thermal cleaning. As a result, a GaAs single crystal substrate having a main surface with high mirror properties can be obtained, and a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value can be realized, thereby completing the present invention.

[0024] Next, embodiments of the present invention will be described by way of examples.

[0025] [1] A gallium arsenide single crystal substrate according to one embodiment of the present invention has a main surface having 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, a fifth integrated intensity ratio, and a sixth integrated intensity ratio. The first integrated intensity ratio and the fourth integrated intensity ratio are obtained by determining a spectrum of the detected intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which irradiates the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 30°. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining a spectrum of the detected intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which irradiates the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 45°. The third and sixth integrated intensity ratios are obtained by determining a spectrum of the detected intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which involves irradiating the center of the main surface with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron takeoff angle of 85 degrees. The first, second, and third integrated intensity ratios are the ratios of the sum of the integrated intensities of arsenic as arsenic pentoxide, arsenic as arsenic trioxide, arsenic as gallium arsenide, and arsenic as metallic arsenic to the sum of the integrated intensities of gallium as gallium monoxide, gallium trioxide, and gallium arsenide. The fourth, fifth, and sixth integrated intensity ratios are the ratios of the sum of the integrated intensity of arsenic present as arsenic pentoxide and the integrated intensity of arsenic present as arsenic trioxide to the sum of the integrated intensity of gallium present as gallium monoxide and the integrated intensity of gallium present as gallium trioxide. The third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are all 0.9 or greater. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or greater and 1.3 or less. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all 0.7 or greater and 1.1 or less.

[0026] A gallium arsenide single crystal substrate having such characteristics can have a main surface with high mirror finish by effectively removing the oxide film using thermal cleaning, and thus can form an epitaxial film with a reduced haze value.

[0027] [2] The ratio of the first integrated intensity ratio to the third integrated intensity ratio is preferably 0.95 or more and 1.2 or less. This allows the oxide film to be removed more efficiently using thermal cleaning.

[0028] [3] The third integrated intensity ratio is preferably not less than 1.05 and not more than 1.1. This allows the oxide film to be removed more efficiently using thermal cleaning.

[0029] [4] The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are preferably all 1.2 or less. This allows the oxide film to be removed more effectively using thermal cleaning.

[0030] [5] The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are preferably not less than 0.75 and not more than 1.05. This allows the oxide film to be removed more effectively using thermal cleaning.

[0031] [6] The gallium arsenide single crystal substrate preferably has a diameter of 75 mm to 205 mm. This allows the gallium arsenide single crystal substrate having a diameter of 75 mm to 205 mm to have a main surface with high mirror finish, thereby enabling the formation of an epitaxial film with a reduced haze value.

[0032] [7] The gallium arsenide single crystal substrate preferably has the following characteristics. 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 seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio, and a tenth integrated intensity ratio. The seventh integrated intensity ratio and the ninth integrated intensity ratio are obtained by irradiating five measurement points on the main surface with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, and obtaining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate. The eighth and tenth integrated intensity ratios are obtained by determining a spectrum of detected intensities of 3d electrons of gallium and arsenic relative to the binding energies of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which involves irradiating five measurement points on the main surface with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron takeoff angle of 85 degrees. The seventh and eighth integrated intensity ratios are the ratios of the sum of the integrated intensities of arsenic present as arsenic pentoxide, arsenic present as arsenic trioxide, arsenic present as gallium arsenide, and arsenic present as metallic arsenic to the sum of the integrated intensities of gallium present as gallium monoxide, gallium present as gallium trioxide, and gallium present as gallium arsenide. The ninth and tenth integrated intensity ratios are the ratios of the sum of the integrated intensity of arsenic present as arsenic pentoxide and the integrated intensity of arsenic present as arsenic trioxide to the sum of the integrated intensity of gallium present as gallium monoxide and the integrated intensity of gallium trioxide. The standard deviation and average of the eighth integrated intensity ratio satisfy the relationship: standard deviation / average value ≤ 0.01. The standard deviation and average of the ratio R1 of the ninth integrated intensity ratio to the seventh integrated intensity ratio and R2 of the tenth integrated intensity ratio to the eighth integrated intensity ratio, i.e., R1 / R2, satisfy the relationship: standard deviation / average value ≤ 0.07. When D represents the diameter and the two axes passing through the center of the main surface and orthogonal to each other on the main surface are defined as the X-axis and Y-axis, the X-axis and Y-axis coordinates (X, Y) of the five 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 coordinates (X, Y) are mm. Thus, for a gallium arsenide single crystal substrate having a diameter of 75 mm or more and less than 150 mm, the oxide film can be effectively removed by thermal cleaning to obtain a main surface with no in-plane deviation and high mirror finish, thereby enabling the formation of an epitaxial film with a reduced haze value.

[0033] [8] The gallium arsenide single crystal substrate preferably has the following characteristics. The gallium arsenide single crystal substrate has a diameter of not less than 150 mm and not more than 205 mm. The gallium arsenide single crystal substrate has an eleventh integrated intensity ratio, a twelfth integrated intensity ratio, a thirteenth integrated intensity ratio, and a fourteenth integrated intensity ratio. The eleventh integrated intensity ratio and the thirteenth integrated intensity ratio are obtained by irradiating nine measurement points on the main surface with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, and obtaining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate. The twelfth and fourteenth integrated intensity ratios are obtained by determining a spectrum of the detected intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate using X-ray photoelectron spectroscopy, which involves irradiating nine measurement points on the main surface with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 85 degrees. The eleventh and twelfth integrated intensity ratios are the ratios of the sum of the integrated intensity of arsenic present as arsenic pentoxide, arsenic present as arsenic trioxide, arsenic present as gallium arsenide, and arsenic present as metallic arsenic to the sum of the integrated intensity of gallium present as gallium monoxide, gallium present as gallium trioxide, and gallium present as gallium arsenide. The thirteenth and fourteenth integrated intensity ratios are the ratios of the sum of the integrated intensity of arsenic present as arsenic pentoxide and the integrated intensity of arsenic present as arsenic trioxide to the sum of the integrated intensity of gallium present as gallium monoxide and the integrated intensity of gallium present as gallium trioxide. The standard deviation and average of the twelfth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.015. The standard deviation and average of the ratio R3 of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio and the ratio R4 of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio, i.e., R3 / R4, satisfy the relationship of standard deviation / average value ≤ 0.078. When the diameter is represented by D and two axes passing through the center of the main surface and perpendicular to each other on the main surface are defined as the X-axis and the Y-axis, the X-axis and Y-axis coordinates (X, Y) 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, for a gallium arsenide single crystal substrate having a diameter of 150 mm to 205 mm, the oxide film can be effectively removed by thermal cleaning to obtain a main surface with no in-plane deviation and high mirror finish, thereby forming an epitaxial film with reduced haze.

[0034] [9] The gallium arsenide single crystal substrate preferably has an epitaxial film on the main surface, wherein the maximum haze value of the surface of the epitaxial film is 350 ppm or less, and the average haze value of the surface of the 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.

[0035]

[10] One embodiment of the present invention provides a method for manufacturing a gallium arsenide single crystal substrate having a main surface with a circular shape. The method includes preparing a gallium arsenide single crystal substrate precursor having a surface with a circular shape, and cleaning the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor. The cleaning step includes: polishing the surface of the gallium arsenide single crystal substrate precursor to form a polished surface; cleaning the polished surface with an alkaline cleaning solution to form an alkaline cleaned surface; immersing the alkaline cleaned surface in a first acid cleaning solution containing 0.3 mass ppm to 0.5 mass % of a first acid to clean the alkaline cleaned surface to form an acid cleaned surface; supplying a second acid cleaning solution containing 0.3 mass ppm to 0.5 mass % of a second acid to the acid cleaned surface at a flow rate of 0.1 L / min to 5 L / min for 30 seconds to 5 minutes while rotating the acid cleaned surface in a circumferential direction at a rotation speed of 1000 rpm or more to clean the acid cleaned surface to form a second acid cleaned surface; and heat-treating the second acid cleaned surface in an inert gas atmosphere at atmospheric pressure and at 150° C. to 300° C. to form the second acid cleaned surface to form the main surface. The first acid contained in the first acid cleaning solution is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. The second acid contained in the second acid cleaning solution is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. This manufacturing method having these characteristics enables the production of a gallium arsenide single crystal substrate having an oxide film on its main surface that can be effectively removed using thermal cleaning.

[0036]

[11] It is preferable to include a step of forming an epitaxial film on the main surface. This allows the epitaxial film with a reduced haze value to be formed on the main surface.

[0037] [Details of the implementation method]

[0038] Hereinafter, an 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. Figure 1 In the present specification and the drawings, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated. In addition, in the drawings, the scales of the components are appropriately adjusted to facilitate understanding, and the scales of the components shown in the drawings are not necessarily consistent with the scales of the actual components.

[0039] In this specification, expressions such as "A to B" refer to the upper and lower limits of a range (i.e., greater than A and less than B). When units are not described for A but only for B, the units for A are the same as those for B. Furthermore, when compounds are expressed as chemical formulas in this specification, unless the atomic ratio is particularly limited, all conventionally known atomic ratios are included and the atomic ratios are not necessarily limited to those within the stoichiometric range.

[0040] In this specification, the "main surface" of a gallium arsenide single crystal substrate refers to both of the two circular surfaces of the substrate. In a gallium arsenide single crystal substrate, if at least one of these two surfaces meets the requirements of the claims of the present invention, it falls within the scope of the present invention. The "main surface" of the gallium arsenide single crystal substrate may be provided with an epitaxial film. In addition, in this specification, the "surface" used in the term "in-plane" refers to the "main surface." Furthermore, when the diameter of a gallium arsenide single crystal substrate is described as "75 mm," it means that the diameter is approximately 75 mm (approximately 75 to 76.5 mm), or it means 3 inches. When the diameter is described as "100 mm," it means that the diameter is approximately 100 mm (approximately 95 to 105 mm), or it means 4 inches. When the diameter is described as "150 mm," it means that the diameter is approximately 150 mm (approximately 145 to 155 mm), or it means 6 inches. When the diameter is described as "200 mm", it means that the diameter is about 200 mm (about 195 to 205 mm), or 8 inches. The diameter can be measured using a conventionally known outer diameter measuring instrument such as a vernier caliper.

[0041] In the crystallographic descriptions in this specification, individual crystal directions are represented by [], families of crystal directions are represented by <>, individual crystal planes are represented by (), and families of crystal planes are represented by {}. Furthermore, negative crystallographic indices are usually indicated by appending "- (bar)" to a number; however, in this specification, a minus sign is appended before the number.

[0042] [Gallium arsenide single crystal substrate]

[0043] 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, a fifth integrated intensity ratio, and a sixth integrated intensity ratio. The first integrated intensity ratio and the fourth integrated intensity ratio are obtained as follows: based on X-ray photoelectron spectroscopy, which irradiates the center of the main surface with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, a spectrum of the detection intensity of 3d electrons of gallium (Ga) and arsenic (As) relative to the binding energy of photoelectrons released outside the GaAs single crystal substrate is obtained. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining a spectrum of the detected intensities of 3d electrons of Ga and As relative to the binding energies of photoelectrons released outside the GaAs single crystal substrate using X-ray photoelectron spectroscopy, which is performed by irradiating the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 45°. The third integrated intensity ratio and the sixth integrated intensity ratio are obtained by determining a spectrum of the detected intensities of 3d electrons of Ga and As relative to the binding energies of photoelectrons released outside the GaAs single crystal substrate using X-ray photoelectron spectroscopy, which is performed by irradiating the center of the main surface with X-rays at an incident energy of 600 eV and a photoelectron escape angle of 85°.

[0044] The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are: As element (hereinafter referred to as "As" for convenience) present as arsenic pentoxide (As2O5) 5+ ”) and the integrated intensity of the As element (hereinafter referred to as “As” for the sake of convenience) present as arsenic trioxide (As2O3) 3+ The sum of the integrated intensities of the As element as gallium arsenide (GaAs) (hereinafter referred to as “As-Ga” for the sake of convenience) and the As element as metallic arsenic (metallic As) (hereinafter referred to as “metallic As” for the sake of convenience) relative to the integrated intensities of the Ga element as gallium monoxide (Ga2O) (hereinafter referred to as “Ga + "), the integrated intensity of the Ga element existing as gallium trioxide (Ga2O3) (hereinafter referred to as "Ga 3+The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are the sum of the integrated intensities of the As element (As present as the As2O5) and the Ga element (hereinafter referred to as "Ga-As" for convenience). 5+ ) and the integral intensity of the As element (As 3+ ) relative to the integrated intensity of the Ga element (Ga + ) and the integrated intensity of Ga element (Ga 3+ ) to the sum of the integrated intensities of the above-mentioned GaAs single crystal substrate. In the above-mentioned GaAs single crystal substrate, the above-mentioned third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.2. The above-mentioned fourth integrated intensity ratio, the above-mentioned fifth integrated intensity ratio, and the above-mentioned sixth integrated intensity ratio are all greater than or equal to 0.9. The ratio of the above-mentioned first integrated intensity ratio to the above-mentioned third integrated intensity ratio is greater than or equal to 0.9 and less than or equal to 1.3. The ratio of the above-mentioned fourth integrated intensity ratio to the above-mentioned first integrated intensity ratio, the ratio of the above-mentioned fifth integrated intensity ratio to the above-mentioned second integrated intensity ratio, and the ratio of the above-mentioned sixth integrated intensity ratio to the above-mentioned third integrated intensity ratio are all greater than or equal to 0.7 and less than or equal to 1.1.

[0045] The GaAs single crystal substrate having such characteristics can effectively remove the oxide film by thermal cleaning, thereby having a main surface with high mirror finish. Therefore, the GaAs single crystal substrate can form an epitaxial film with reduced haze.

[0046] <Main surface>

[0047] As described above, the 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 a geometric circular shape, a shape in which the main surface does not form a geometric circular shape by forming at least one of a notch, an orientation flat (hereinafter also referred to as "OF"), or an index flat (hereinafter also referred to as "IF") . That is, "a shape in which the main surface does not form a geometric circular shape" refers to a shape in which, among the line segments extending from any point on the periphery of the main surface to the center of the main surface, the length of the line segment extending from any point on the notch, OF, and IF to the center of the main surface becomes shorter. In other words, in this specification, the main surface is a "circular shape" based on the shape before the notch, OF, and IF are formed. Therefore, with respect to the center of the main surface and the diameter of the substrate, their position and size (length) are determined based on the circular shape before the notch, OF, IF, etc. are formed. Furthermore, the term "shape in which the main surface does not form a geometrically circular shape" also includes shapes in which, due to the shape of the GaAs single crystal before being cut out as a GaAs single crystal substrate, the lengths of line segments extending from any point on the periphery of the main surface to the center of the main surface are not necessarily all equal. In such cases, the center of the main surface is referred to as the position of the center of gravity, and the diameter of the substrate is the length of the longest line segment extending from a point on the periphery of the substrate through the center of the main surface to another point on the periphery of the substrate.

[0048] X-ray Photoelectron Spectroscopy (XPS) Using Radiation

[0049] In the process of developing a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value, the present inventors have focused on X-ray photoelectron spectroscopy (XPS) using radiant light that can analyze the state of the main surface of a GaAs single crystal substrate with high precision. Specifically, the following attempt was made: by implementing XPS using radiant light, the cause of the deterioration of the mirror surface of the main surface in the GaAs single crystal substrate was determined, and the above cause was eliminated, thereby realizing a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value. Here, XPS refers to an analysis method in which a sample is irradiated with X-rays and the distribution of the kinetic energy of the photoelectrons released from the sample is measured, thereby obtaining information on the type, amount, chemical bond state, etc. of the elements present on the surface of the sample.

[0050] In general, when analyzing the main surface of a GaAs single crystal substrate by XPS, most of the time, X-rays with an energy fixed at around 1.487 keV are used for the analysis. However, when using X-rays with an incident energy fixed at around 1.487 keV and the photoelectron take-off angle set to 30°, information about the state of the main surface of the GaAs single crystal substrate is obtained by averaging the area from the above-mentioned main surface to a depth of about 5 nm. The above-mentioned area is equivalent to about 20 atomic layers if converted into 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, if you want to obtain information about the state of the main surface of the GaAs single crystal substrate by using X-rays with an incident energy fixed at around 1.487 keV in XPS and changing the photoelectron take-off angle, the angle measurement error will become too large, and the ionization efficiency of the photoelectron intensity is small, so the measurement error also becomes large, so it is still difficult to perform high-precision analysis.

[0051] 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 conditions where the photoelectron escape angle is set to 30°, 45°, or 85°, thereby enabling analysis of the state of the main surface of the GaAs single crystal substrate.

[0052] When the XPS is performed under the conditions of 600 eV X-ray incident energy and 30° photoelectron escape angle, information on the state of the main surface of the GaAs single crystal substrate is obtained by averaging the region from the main surface to a depth of approximately 2.25 nm. When the XPS is performed under the conditions of 600 eV X-ray incident energy and 45° photoelectron escape angle, information on the state of the main surface of the GaAs single crystal substrate is obtained by averaging the region from the main surface to a depth of approximately 3.18 nm. When the XPS is performed under the conditions of 600 eV X-ray incident energy and 85° photoelectron escape angle, information on the state of the main surface of the GaAs single crystal substrate is obtained by averaging the region from the main surface to a depth of approximately 4.48 nm. That is, the region from the main surface of the GaAs single crystal substrate to a depth of about 5 nm (about 20 atomic layers) can be analyzed in detail every about 1 to 3 atomic layers, thereby enabling analysis of the state of the main surface with higher precision than before.

[0053] It is known that after cleaning a GaAs single crystal substrate, an oxide film with a thickness of approximately 1 to 2 nm forms on the main surface. Therefore, attempts have been made to reduce the haze of the epitaxial film by removing the oxide through thermal cleaning and then forming an epitaxial film on the main surface. However, even after thermal cleaning, a portion of the oxide film remains on the main surface, increasing the haze of the epitaxial film to a certain extent. To address this issue, the present inventors conducted detailed XPS analysis using the aforementioned radiation light to analyze the interface (i.e., the region from the main surface of the GaAs single crystal substrate to a depth of approximately 2 to 5 nm) between the oxide film, the outermost layer of the main surface of the GaAs single crystal substrate, and the layer composed of gallium (Ga) and arsenic (As) directly beneath it (hereinafter referred to as the "main layer" of the GaAs single crystal substrate). They found that when the oxide film on the GaAs single crystal substrate has an As-rich composition and an As₂O₃-rich composition, the oxide film can be effectively removed by thermal cleaning due to its easy sublimation properties. In particular, they discovered that when metallic As is generated near the interface, the reduction of this As promotes the formation of Ga2O and As2O3 in the oxide film. This suggests that by appropriately controlling the composition of arsenic and oxides in the oxide film, a primary surface with high mirror finish can be obtained. In this specification, the "surface" of the oxide film refers to the surface of the oxide film facing the GaAs single crystal substrate.

[0054] <First Integrated Intensity Ratio, Second Integrated Intensity Ratio, Third Integrated Intensity Ratio, Fourth Integrated Intensity Ratio, Fifth Integrated Intensity Ratio, and Sixth Integrated Intensity Ratio>

[0055] The GaAs single crystal substrate of this embodiment has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio. The first integrated intensity ratio and the fourth integrated intensity ratio are obtained by: based on X-ray photoelectron spectroscopy in which the center of the main surface is irradiated with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, a spectrum of the detection intensity of 3d electrons of Ga and As relative to the binding energy of photoelectrons released to the outside of the GaAs single crystal substrate is obtained. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by: based on X-ray photoelectron spectroscopy in which the center of the main surface is irradiated with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 45°, a spectrum of the detection intensity of 3d electrons of Ga and As relative to the binding energy of photoelectrons released to the outside of the GaAs single crystal substrate is obtained. The above-mentioned third integrated intensity ratio and the above-mentioned sixth integrated intensity ratio are obtained as follows: based on the X-ray photoelectron spectroscopy method of irradiating the center of the above-mentioned main surface with X-rays under the conditions of X-ray incident energy of 600eV and photoelectron escape angle of 85°, a spectrum of the detection intensity of 3d electrons of Ga and As relative to the binding energy of photoelectrons released to the outside of the above-mentioned GaAs single crystal substrate is obtained.

[0056] The first integrated intensity ratio, the second integrated intensity ratio and the third integrated intensity ratio are: As element (As 5+ ) integrated intensity, the As element (As 3+ ), the integrated intensity of the As element as GaAs (As-Ga), and the integrated intensity of the As element as metallic As (metallic As) relative to the integrated intensity of the Ga element as Ga2O (Ga + ) integrated intensity, Ga element (Ga 3+ ) and the integrated intensity of Ga element (Ga-As) existing as GaAs. The fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio are: As element (As 5+ ) and the integral intensity of As element (As 3+ ) relative to the integrated intensity of Ga element (Ga + ) and the integrated intensity of Ga element (Ga 3+ ) is the ratio of the sum of the integrated intensities.

[0057] Among the above-mentioned first integrated intensity ratio, second integrated intensity ratio, third integrated intensity ratio, fourth integrated intensity ratio, fifth integrated intensity ratio and sixth integrated intensity ratio, when the above-mentioned first integrated intensity ratio and fourth integrated intensity ratio are representatively represented by In1 and In4 respectively, the above-mentioned In1 and In4 can be respectively expressed by the following mathematical formulas.

[0058] [Mathematical formula 1]

[0059]

[0060] In the GaAs single crystal substrate, the third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.2. The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all greater than or equal to 0.9. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.9 and less than or equal to 1.3. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all greater than or equal to 0.7 and less than or equal to 1.1.

[0061] Figure 1 This is an example of a graph showing the relationship between the measurement depth from the main surface of the GaAs single crystal substrate of this embodiment (horizontal axis), 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 existing as arsenic oxide to the integrated intensity of the gallium element existing as gallium oxide (vertical axis). Figure 1 In the figure, the points indicated by circles near the measurement depth (horizontal axis) of approximately 2.25 nm correspond to the first integrated intensity ratio, the points indicated by circles near the measurement depth (horizontal axis) of approximately 3.18 nm correspond to the second integrated intensity ratio, and the points indicated by circles near the measurement depth (horizontal axis) of approximately 4.48 nm correspond to the third integrated intensity ratio. The points indicated by rectangles near the measurement depth (horizontal axis) of approximately 2.25 nm correspond to the fourth integrated intensity ratio, the points indicated by rectangles near the measurement depth (horizontal axis) of approximately 3.18 nm correspond to the fifth integrated intensity ratio, and the points indicated by rectangles near the measurement depth (horizontal axis) of approximately 4.48 nm correspond to the sixth integrated intensity ratio. Figure 1 In the above, “Ga overall” refers to Ga + The integrated intensity of Ga 3+ The sum of the integrated intensity of As and the integrated intensity of Ga-As. 5+ The integrated intensity, As 3+ The sum of the integrated intensity of Ga, the integrated intensity of As-Ga and the integrated intensity of metallic As. + The integrated intensity and Ga 3+The sum of the integrated intensities of 5+ The integral intensity and As 3+ The sum of the integrated intensities.

[0062] exist Figure 1 , the first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are 1.24, 1.24, and 1.16, respectively. The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are 1.14, 1.1, and 1.06, respectively. The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all greater than 0.9. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 1.07. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio is 0.92. The ratio of the fifth integrated intensity ratio to the second integrated intensity ratio is 0.89. The ratio of the sixth integrated intensity ratio to the third integrated intensity ratio is 0.91. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all greater than 0.7 and less than 1.1.

[0063] This relationship means that the entire oxide film from the main surface to a depth of approximately 1 to 2 nm has an As-rich composition, and the composition becomes increasingly rich in arsenic oxide as it approaches the surface of the oxide film from the interface between the main layer and the oxide film (at a depth of approximately 2 to 5 nm from the main surface). Specifically, this means that by setting the third integrated intensity ratio to be greater than 1.05 and less than 1.2, arsenic is sufficiently present in the entire oxide film for practical purposes. This means that by setting the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio to be greater than 0.9, arsenic oxide is sufficiently present at the interface between the main layer and the oxide film, within the oxide film, and on the surface of the oxide film for practical purposes. This means that by setting the ratio of the first integrated intensity ratio to the third integrated intensity ratio to be greater than 0.9 and less than 1.3, the composition becomes increasingly rich in arsenic as it approaches the surface of the oxide film from the interface between the main layer and the oxide film. This means that by further making the ratio of the fourth integrated intensity ratio relative to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio relative to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio relative to the third integrated intensity ratio all greater than 0.7 and less than 1.1, arsenic oxide is sufficiently present throughout the entire thickness direction of the oxide film, thereby achieving an excellent balance in the ratio of metal As to the oxide film. It is speculated that in this case, the oxide film is rich in Ga2O and As2O3, which are easily sublimated, and therefore the oxide film can be effectively removed by thermal cleaning. Therefore, when an epitaxial film is grown on the main surface of the GaAs single crystal substrate of this embodiment after thermal cleaning, both the maximum value and the average value of the haze of the surface of the epitaxial film can be made smaller than before (for example, the maximum value of the haze of the surface of the epitaxial film can be made less than 350 ppm, and the average value of the haze can be made less than 2.5 ppm). 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.

[0064] On the other hand, when the first, second, third, fourth, fifth, and sixth integrated intensity ratios are obtained by performing the above-mentioned XPS on an existing GaAs single crystal substrate, none of the following relationships is satisfied. Specifically, the relationship that the third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.2 is not satisfied, or the relationship that at least any one of the fourth, fifth, and sixth integrated intensity ratios is greater than or equal to 0.9 is not satisfied, or the relationship that the ratio of the first integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.9 and less than or equal to 1.3 is not satisfied, or the relationship that at least any one of the ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.7 and less than or equal to 1.1 is not satisfied. In such a GaAs single crystal substrate, there is a possibility that a portion of the oxide film remains on the main surface even after thermal cleaning. Therefore, when an epitaxial film is formed on the main surface of the GaAs single crystal substrate after thermal cleaning, there is a possibility that a difference in height will occur on the surface, and the maximum value and average value of the haze may increase.

[0065] As described above, the present inventors discovered for the first time that the surface haze of the epitaxial film formed on the main surface of a GaAs single crystal substrate depends on the amount of arsenic, arsenic oxide, and gallium oxide in the above-mentioned oxide film (occupying the region from the main surface to a depth of about 1 to 2 nm) and near the interface between the above-mentioned oxide film and the main layer (the region from the main surface to a depth of 2 to 5 nm).

[0066] Here, the ratio of the first integrated intensity ratio to the third integrated intensity ratio is preferably 0.95 or more and 1.2 or less. This optimizes the uniformity of the arsenic content in the oxide film, allowing the oxide film to be removed more efficiently using thermal cleaning.

[0067] The third integrated intensity ratio is preferably not less than 1.05 and not more than 1.1. This optimizes the arsenic content, and thus enables the oxide film to be removed more efficiently using thermal cleaning.

[0068] The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are preferably all 1.2 or less. This ensures that the arsenic oxide content in the oxide film is necessary and sufficient, and thus the oxide film can be removed more effectively using thermal cleaning.

[0069] The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are preferably all greater than 0.75 and less than 1.05. This prevents excessive metallic arsenic from forming in the oxide film, allowing the oxide film to be removed more efficiently using thermal cleaning.

[0070] <Diameter>

[0071] 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, for a GaAs single crystal substrate having a diameter of 75 mm or more and 205 mm or less, the oxide film can be removed by using thermal cleaning, thereby obtaining a main surface with high mirror finish. Here, regarding the above-mentioned diameter, even if the above-mentioned substrate does not become a geometrically circular shape due to the influence of OF, IF, etc., the substrate is regarded as having a circular shape before the formation of the above-mentioned OF, IF, etc. to determine its size (diameter). The above-mentioned GaAs single crystal substrate preferably has a diameter of 100 mm or more and 205 mm or less, and preferably has a diameter of 150 mm or more and 205 mm or less.

[0072] Analyzing GaAs Single Crystal Substrates Using X-ray Photoelectron Spectroscopy (XPS) Using Radiated Light

[0073] Hereinafter, the analysis method of the GaAs single crystal substrate by XPS using radiant light will be described in further detail.

[0074] (Analysis System)

[0075] Figure 2 This is an explanatory diagram schematically illustrating the structure of an analysis system using X-ray photoelectron spectroscopy. Figure 2 As shown, the analysis system 100 includes an X-ray generating device 10, a vacuum container 20, and an electron spectrometer 30. The X-ray generating device 10, the vacuum container 20, and the electron spectrometer 30 are connected in this order. The internal spaces of the X-ray generating device 10, the vacuum container 20, and the electron spectrometer 30 are maintained at an ultra-high vacuum. The pressure of the internal spaces of the X-ray generating device 10, the vacuum container 20, and the electron spectrometer 30 is, for example, 4×10 -7 Pa.

[0076] The X-ray generator 10 generates X-rays called radiation light. As the X-ray generator 10, for example, beamline "BL17" in the Saga Prefectural Kyushu Synchrotron Light Research Center can be used.

[0077] The X-ray generator 10 can generate X-rays of any energy within the range of 50 to 2000 eV in the aforementioned “BL17” and irradiate the GaAs single crystal substrate 1 placed in the vacuum container 20 with the X-rays. Figure 2 The illustrated X-ray generating device 10 includes an X-ray source 11, a slit 12, a slit 14, and a grating 13. The slits 12 and 14 are respectively arranged upstream and downstream of the grating (spectrometer) 13. The slits 12 and 14 are, for example, four-quadrant slits.

[0078] The X-ray source 11 bends the traveling direction of high-energy electrons by using a magnetic field generated by a deflection electromagnet in a circular accelerator, thereby outputting radiation light (X-rays) radiated in a direction tangential to the traveling direction.

[0079] The X-rays emitted from the X-ray source 11 are of high brightness. Specifically, the number of X-ray photons emitted from the X-ray source 11 per second is 10 9 However, the brightness (intensity) of X-rays emitted from the X-ray source 11 decays over time. For example, the brightness of X-rays emitted 11 hours after the X-ray source 11 is activated is 1 / 3 of the brightness of the X-rays emitted immediately after activation.

[0080] X-rays emitted from an X-ray source 11 are collimated by a collimating mirror (not shown). A slit 12 allows a portion of the collimated X-rays to pass through. The X-rays that pass through the slit 12 are monochromatized by a grating 13. The slit 14 limits the spread of the monochromatized X-rays.

[0081] The energy of the X-rays emitted from the X-ray generator 10 is determined by the slit widths of the slits 12 and 14 and the line density of the grating 13. For example, by setting the slit widths of the slits 12 and 14 to 30 μm, using the grating 13 with a center line density of 400 1 / mm, and adjusting the grating's exit angle, the X-ray generator 10 emits 600 eV X-rays.

[0082] When X-rays from the X-ray generating device 10 are irradiated onto the GaAs single crystal substrate 1 disposed in the vacuum container 20 , photoelectrons are released from the GaAs single crystal substrate 1 .

[0083] The electron spectrometer 30 measures the kinetic energy distribution of photoelectrons emitted from the GaAs single crystal substrate 1. The electron spectrometer 30 includes a hemispherical analyzer and a detector. The hemispherical analyzer separates the photoelectrons. The detector counts the number of photoelectrons of each energy.

[0084] The angle θ1 formed between the propagation direction of X-rays incident on the GaAs single crystal substrate 1 from the X-ray generator 10 and the main surface 1m of the GaAs single crystal substrate 1 is variable. Furthermore, the angle (hereinafter also referred to as "emission angle θ2") formed between the propagation direction of photoelectrons released from the GaAs single crystal substrate 1 and captured by the electron spectrometer 30 and the main surface 1m of the GaAs single crystal substrate 1 is also variable. In this 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.

[0085] As the electron spectrometer 30 , for example, a high-resolution XPS analyzer “R3000” manufactured by Scienta Omicron Corporation can be used.

[0086] (Depth from the main surface to be analyzed)

[0087] A portion of the photoelectrons released to the outside of the GaAs single crystal substrate 1 by X-ray irradiation loses energy due to inelastic scattering. Therefore, only a portion of the photoelectrons generated in the GaAs single crystal substrate 1 escapes into the vacuum while maintaining the energy state at the time of generation and reaches the electron spectrometer 30. The photoelectrons escaping from the surface are generated at a depth equivalent to about 3 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 escape angle.

[0088] [Mathematical formula 2]

[0089] d=3λsinθ2

[0090] Furthermore, as shown in "Estimation of the Inelastic Mean Free Path of Electrons Based on the Tpp-2M Formula", Journal of Surface Analysis, Vol. 1, No. 2, 1995, It is expressed by the following mathematical formulas.

[0091] [Mathematical formula 3]

[0092]

[0093] γ=0.191p -0.50

[0094] C=1.97-0.94U

[0095] D=53.4-20.8U

[0096]

[0097] In the above mathematical formulas, A W Indicates atomic weight or molecular weight, N v Indicates the number of valence electrons per atom or molecule, E p represents the plasma energy of free electrons (eV), and ρ represents the density (g / cm 3 ), E g = represents the band gap energy (eV). E represents the kinetic energy of the photoelectron (eV), which is calculated from the energy of the irradiated X-ray (eV) and the binding energy between the electron and the nucleus (eV).

[0098] By using the above formulas, the depth d (nm) from the main surface of the GaAs single crystal substrate being analyzed can be calculated. Specifically, the depth d (nm) from the main surface of the GaAs single crystal substrate can be calculated using the above formulas, various parameter values ​​for 3d electrons of Ga and As elements, and the X-ray energy (600 eV). The depths d (nm) are as follows.

[0099] When the X-ray incident energy is 600 eV and the photoelectron escape angle is 30°, the depth d is approximately 2.25 nm. When the X-ray incident energy is 600 eV and the photoelectron escape angle is 45°, the depth d is approximately 3.18 nm. When the X-ray incident energy is 600 eV and the photoelectron escape angle is 85°, the depth d is approximately 4.48 nm.

[0100] (Calculation Method of First Integrated Intensity Ratio, Second Integrated Intensity Ratio, Third Integrated Intensity Ratio, Fourth Integrated Intensity Ratio, Fifth Integrated Intensity Ratio, and Sixth Integrated Intensity Ratio)

[0101] Below, regarding the method of calculating the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio of the above-mentioned main surface based on the above-mentioned XPS, the calculation method of the first integrated intensity ratio and the fourth integrated intensity ratio is first illustrated. In this case, the above-mentioned 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 flight angle of the photoelectron is 30°. Thus, the kinetic energy distribution of the photoelectrons released from the GaAs single crystal substrate can be obtained.

[0102] The kinetic energy E of the photoelectrons released from the GaAs single crystal substrate is calculated using the energy hν (eV) of the irradiated X-rays and the electron binding energy E in the GaAs single crystal substrate. B (eV) and work function φ (eV) are expressed by the following mathematical formula.

[0103] E=hv-E B -φ.

[0104] 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 the GaAs single crystal substrate. In this embodiment, a Ga3d spectrum and an As3d spectrum representing the binding energy distribution of photoelectrons are generated based on the kinetic energy distribution of photoelectrons released from a position at a depth d (nm) from the main surface of the above-mentioned GaAs single crystal substrate. Here, in this specification, the "Ga3d spectrum" refers to a spectrum representing the detection intensity of photoelectrons released from the 3d orbital of the Ga element (Ga2O, Ga2O3, and GaAs). The "As3d spectrum" refers to a spectrum representing the detection intensity of photoelectrons released from the 3d orbital of the As element (As2O5, As2O3, metallic As, and As contained in GaAs).

[0105] In particular, in XPS analysis, for high-precision measurement, narrow scanning within a defined binding energy range allows for the generation of Ga and As 3d spectra. Specifically, by narrowing the binding energy range from 16 to 26 eV, the Ga 3d spectra can be plotted on a graph with the aforementioned range on the horizontal axis and the detection intensity on the vertical axis. By narrowing the binding energy range from 39 to 49 eV, the As 3d spectra can be plotted on a graph with the aforementioned range on the horizontal axis and the detection intensity on the vertical axis.

[0106] Narrow scanning was performed under the following conditions: energy interval was set to 0.05 eV, the integration time for each energy value was set to 100 ms, the number of integrations was set to 1 or more, and the energy resolution E / ΔE was 3480.

[0107] Through the above methods, we can obtain Figure 3A The Ga3d spectrum LG and Figure 3B As3d map LA shown. Figure 3A This is a graph showing an example of a background-corrected Ga3d spectrum obtained by XPS in which the center of the main surface of the GaAs single crystal substrate of this embodiment is irradiated with X-rays. Figure 3B This is a graph showing an example of a background-corrected As3d spectrum obtained by XPS in which the center of the main surface of the GaAs single crystal substrate of this embodiment is irradiated with X-rays. Figure 3A and Figure 3B, an example of a background-corrected Ga3d spectrum and As3d spectrum is shown, respectively. Specifically, when obtaining the Ga3d spectrum LG and As3d spectrum LA, background correction is performed using the Shirley method (Reference: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, No. 6, pp. 243-247). Thus, the background-corrected Ga3d spectrum LG can be determined based on the difference between the measured Ga3d spectrum and the background. Furthermore, the background-corrected As3d spectrum LA can be determined based on the difference between the measured As3d spectrum and the background.

[0108] When the Ga3d spectrum LG is obtained, the Ga element (Ga + ) is fixed at the position of the binding energy of 19.9 eV, and the Ga element (Ga 3+ ) is fixed at a binding energy of 20.7 eV. Furthermore, the peak of the detection intensity of the Ga element (Ga-As), present as GaAs, is positioned at a binding energy of approximately 19.2 to 19.7 eV and has a width. This is because, when performing the aforementioned X-ray photoelectron spectroscopy on a GaAs single crystal, there is a possibility of a charge shift, causing the aforementioned Ga3d spectrum to shift to the high-energy side by a maximum of approximately 1 eV. Furthermore, the peak of the detection intensity of Ga-As is affected by the main layer composed of GaAs, making it difficult to fix it to a single value. Therefore, as described above, the peak has a width of 0.5 eV.

[0109] When the As3d spectrum LA is obtained, the As element (As 5+ ) is fixed at the position of the binding energy of 45.57 eV, and the As element (As 3+ ) is fixed at a position with a binding energy of 44.07 eV. Furthermore, the peak of the detection intensity of the As element (metallic As) present as metallic As is positioned at a binding energy of approximately 41.62 to 42.12 eV and has a width, and the peak of the detection intensity of the As element (As-Ga) present as GaAs is positioned at a binding energy of approximately 40.77 to 41.27 eV and has a width. This is because, when the above-mentioned X-ray photoelectron spectroscopy is performed on a GaAs single crystal, there is a possibility that a charging shift occurs, and the above-mentioned As3d spectrum may shift to the high energy side by a maximum of about 1 eV. In addition, each peak of metallic As and As-Ga is affected by the main layer composed of GaAs, so it is difficult to fix it to a single value. Therefore, as described above, the peak position has a width of 0.5 eV.

[0110] Next, the background-corrected Ga3d spectrum LG obtained above is separated into the following three Gaussian functions Y1, Y2, and Y3 (hereinafter referred to as "peak separation"). Thus, within the binding energy range of 16 to 26 eV, the Ga element (Ga2O) present as Ga2O can be obtained by peak separation. + ), Ga element (Ga 3+ ), and three spectra of Ga element existing as GaAs (Ga-As).

[0111] Y1=a1*exp{(-(X-b1) 2 ) / c 12}

[0112] Y2=a2*exp{(-(X-b2) 2 ) / c2 2}

[0113] Y3=a3*exp{(-(X-b3) 2 ) / c3 2}.

[0114] The units of the above-mentioned Gaussian functions Y1, Y2 and Y3 are dimensionless. In the above-mentioned 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.

[0115] The above Gaussian functions Y1 to Y3 are obtained by the following method: 2 ) / Wi 2} represents the i-th component of Ga3d, the square of the difference with the measured value ([measured-ΣGi] 2 ) is minimized. + 、Ga 3+ and the binding energy value of the peak of the detection intensity of Ga-As.

[0116] That is, the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) are as follows.

[0117] a1, a2, and a3 are real numbers greater than or equal to 0.

[0118] b1=19.9eV

[0119] b2=20.7eV

[0120] 19.2eV≤b3≤19.7eV

[0121] 0.2eV≤c1≤0.95eV

[0122] 0.2eV≤c2≤0.95eV

[0123] 0.2eV≤c3≤0.95eV.

[0124] Thus, the Gaussian functions Y1, Y2 and Y3 can be expressed as follows, for example, Figure 3A The Ga3d spectrum of LG is separated from the Ga + Spectrum L2, Ga 3+ Spectrum L1 and Ga-As spectrum L3.

[0125] Furthermore, the As3d spectrum LA obtained after background correction can be expressed by separating its peaks into the following four Gaussian functions Y4, Y5, Y6 and Y7. Thus, in the range of binding energy of 39 to 49 eV, the As element (As2O5) can be obtained by peak separation. 5+ ), As element (As 3+ ), four spectra of the As element existing as metallic As (metallic As) and the As element existing as GaAs (As-Ga).

[0126] Y4=a4*exp{(-(X-b4) 2 ) / c4 2}

[0127] Y5=a5*exp{(-(X-b5) 2 ) / c5 2}

[0128] Y6=a6*exp{(-(X-b6) 2 ) / c6 2}

[0129] Y7=a7*exp{(-(X-b7) 2 ) / c7 2}

[0130] The units of the above-mentioned Gaussian functions Y4, Y5, Y6 and Y7 are dimensionless. In the above-mentioned 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.

[0131] The above Gaussian functions Y4 to Y7 are obtained by the following method:2 ) / Wi 2} represents the i-th component of As3d, the square of the difference with the measured value ([measured - ΣGi] 2 ) is minimized. Optimize each variable (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) by substituting the above-mentioned As for b4 to b7. 5+ 、As 3+ , the binding energy values ​​of the peaks of the signal intensities of metal As and As-Ga.

[0132] That is, the variables (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) are as follows.

[0133] a4, a5, a6, and a7 are real numbers greater than or equal to 0.

[0134] b4=45.57eV

[0135] b5=44.07eV

[0136] 41.62eV≤b6≤42.12eV

[0137] 40.77eV≤b7≤41.27eV

[0138] 0.2eV≤c4≤0.95eV

[0139] 0.2eV≤c5≤0.95eV

[0140] 0.2eV≤c6≤0.95eV

[0141] 0.2eV≤c7≤1.2eV.

[0142] Thus, the Gaussian functions Y4, Y5, Y6 and Y7 can be expressed as follows, for example, Figure 3B As3d spectrum LA peak separated As 5+ Spectrum L4, As 3+ Spectrum L5, metallic As spectrum L6, and As-Ga spectrum L7. Here, metallic As is generated from the oxide film and the main layer by the reaction of 2GaAs+As2O3→Ga2O3+4As, and is therefore detected as intensity by the XPS.

[0143] To determine the peak positions of the Gaussian functions Y1 to Y7, the following calibration can be performed. First, the probability of generating photoelectrons from X-rays, known as the photoionization efficiency (η), varies depending on the element and X-ray energy. Therefore, the value of η is used as the data published on the following website. Specifically, the photoionization efficiency (η) for X-rays with an incident energy of 600 eV is set to 0.28 for Ga3d and 0.42 for As3d.

[0144] https: / / vuo.elettra.eu / services / elements / WebElements.html (In addition, the literature used as the basis for the data is JJ Yeh, Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993 and JJ Yeh and I. Lindau, Atomic Data and Nuclear Data Tables, 32, 1-155 (1985)).

[0145] In addition, since the irradiation intensity of X-rays used in the above-mentioned radiation light equipment will decay over time, a standard sample of gold (Au) is measured at regular intervals to calculate the attenuation ratio of the Au4f photoelectron intensity, and the X-ray irradiation amount is corrected based on this ratio.

[0146] exist Figure 3A Medium, Ga 3+ The area between the spectrum L1 and the horizontal axis (X axis) corresponds to the area from Ga 3+ The number of photoelectrons released from the 3d orbital of Ga 3+ The integrated intensity of Ga + The area between the spectrum L2 and the horizontal axis (X axis) corresponds to the area from Ga + The number of photoelectrons released from the 3d orbital 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 orbital of Ga-As and thus refers to the integrated intensity of Ga-As.

[0147] exist Figure 3B As 5+ The area between the spectrum L4 and the horizontal axis (X axis) corresponds to the area from As 5+ The number of photoelectrons released from the 3d orbital of As 5+ The integrated intensity of As3+ The area between the spectrum L5 and the horizontal axis (X axis) corresponds to the area from As 3+ The number of photoelectrons released from the 3d orbital of As 3+ The area between the metal As spectrum L6 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbital of metal As and thus refers to the integrated intensity of metal As. The area between the As-Ga spectrum L7 and the horizontal axis (X-axis) corresponds to the number of photoelectrons released from the 3d orbital of As-Ga and thus refers to the integrated intensity of As-Ga.

[0148] Therefore, based on the areas obtained from the above-mentioned graphs and the horizontal axis, As can be obtained. 5+ The integrated intensity, As 3+ The sum of the integrated intensity of As-Ga, the integrated intensity of As-Ga and the integrated intensity of metal As relative to Ga + The integrated intensity of Ga 3+ The ratio of the integrated intensity of Ga-As to the integrated intensity of Ga-As is taken as the first integrated intensity ratio. 5+ The integrated intensity of As 3+ The sum of the integrated intensities relative to Ga + The integrated intensity of Ga 3+ The ratio of the sum of the integrated intensities is used as the fourth integrated intensity ratio.

[0149] According to this 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 escape angle of 45°. In addition, the second integrated intensity ratio and the fifth integrated intensity ratio can be calculated using the same method as the method for calculating the first integrated intensity ratio and the fourth integrated intensity ratio. 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 escape angle of 85°. In addition, the third integrated intensity ratio and the sixth integrated intensity ratio can be calculated using the same method as the method for calculating the first integrated intensity ratio and the fourth integrated intensity ratio.

[0150] Uniformity of the Main Surface of a GaAs Single Crystal Substrate

[0151] The properties of the GaAs single crystal substrate of this embodiment are preferably uniform within the plane of the main surface. In other words, the GaAs single crystal substrate of this embodiment is preferably capable of forming an epitaxial film with a reduced haze value, regardless of the position within the plane of the main surface. Specific embodiments of such a preferred GaAs single crystal substrate include the following embodiments (a first embodiment and a second embodiment).

[0152] (First Method)

[0153] The GaAs single crystal substrate of the first embodiment has a diameter of not less than 75 mm and less than 150 mm. The above-mentioned GaAs single crystal substrate preferably has a diameter of not less than 75 mm and not more than 105 mm. The above-mentioned GaAs single crystal substrate has a seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio and a tenth integrated intensity ratio. The above-mentioned seventh integrated intensity ratio and the above-mentioned ninth integrated intensity ratio are obtained as follows: based on X-ray photoelectron spectroscopy in which X-rays are irradiated to five measurement points on the above-mentioned main surface under the conditions of X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, a spectrum of the detection intensity of 3d electrons of Ga and As relative to the binding energy of photoelectrons released to the outside of the above-mentioned GaAs single crystal substrate is obtained. The eighth integrated intensity ratio and the tenth integrated intensity ratio are obtained as follows: based on X-ray photoelectron spectroscopy in which X-rays are irradiated on five measuring points on the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 85°, a spectrum of the detection intensity of 3d electrons of Ga and As relative to the binding energy of photoelectrons released to the outside of the GaAs single crystal substrate is obtained.

[0154] The seventh integrated intensity ratio and the eighth integrated intensity ratio are: As element (As 5+ ) integrated intensity, the As element (As 3+ ), the integrated intensity of the As element as GaAs (As-Ga), and the integrated intensity of the As element as metallic As (metallic As) relative to the integrated intensity of the Ga element as Ga2O (Ga + ) integrated intensity, Ga element (Ga 3+ ) and the integrated intensity of Ga element (Ga-As) existing as GaAs. The ninth integrated intensity ratio and the tenth integrated intensity ratio are: As element (As 5+ ) and the integral intensity of As element (As 3+ ) relative to the integrated intensity of Ga element (Ga + ) and the integrated intensity of Ga element (Ga 3+). The standard deviation and average value of the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.01, and the standard deviation and average value of the ratio R1 of the ninth integrated intensity ratio to the seventh integrated intensity ratio and R2 of the tenth integrated intensity ratio to the eighth integrated intensity ratio, i.e., R1 / R2, satisfy the relationship of standard deviation / average value ≤ 0.07. The lower limit of the standard deviation and average value of the eighth integrated intensity ratio is an ideal value of 0. For example, the standard deviation and average value of the eighth integrated intensity ratio may also satisfy the relationship of standard deviation / average value ≥ 0.008. The lower limit of the standard deviation and average value of the ratio R1 of the ninth integrated intensity ratio to the seventh integrated intensity ratio and R2 of the tenth integrated intensity ratio to the eighth integrated intensity ratio, i.e., R1 / R2, satisfy the relationship of standard deviation / average value ≥ 0.056.

[0155] The fact that the standard deviation and average value of the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.01 indicates that a desired amount of arsenic is present within the oxide film. The fact that the standard deviation and average value of the ratio R1 (the ninth integrated intensity ratio relative to the seventh integrated intensity ratio) and the ratio R2 (the tenth integrated intensity ratio relative to the eighth integrated intensity ratio), i.e., R1 / R2, satisfy the relationship of standard deviation / average value ≤ 0.07 indicates that arsenic is dispersed within the oxide film with desired uniformity without segregation.

[0156] When the diameter is represented by D and two axes passing through the center of the main surface and orthogonal to each other on the main surface are defined as the X-axis and the Y-axis, the coordinates (X, Y) of the X-axis and the Y-axis of the five 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 coordinates (X, Y) are mm. Thus, for a GaAs single crystal substrate having a diameter of 75 mm or more and less than 150 mm, it is possible to effectively remove the oxide film by thermal cleaning to obtain a main surface with no in-plane deviation and high mirror finish. Therefore, the above-mentioned GaAs single crystal substrate can form an epitaxial film with a reduced haze value.

[0157] (Second Method)

[0158] The GaAs single crystal substrate of the second embodiment has a diameter of not less than 150 mm and not more than 205 mm. The GaAs single crystal substrate has an eleventh integrated intensity ratio, a twelfth integrated intensity ratio, a thirteenth integrated intensity ratio, and a fourteenth integrated intensity ratio. The eleventh integrated intensity ratio and the thirteenth integrated intensity ratio are obtained by X-ray photoelectron spectroscopy, which irradiates nine measurement points on the main surface with X-rays under the conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°, and obtains a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the GaAs single crystal substrate. The above-mentioned twelfth integrated intensity ratio and the above-mentioned fourteenth integrated intensity ratio are obtained as follows: based on the X-ray photoelectron spectroscopy method of irradiating 9 measurement points on the above-mentioned main surface with X-rays under the conditions of X-ray incident energy of 600eV and photoelectron escape angle of 85°, a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released to the outside of the above-mentioned GaAs single crystal substrate is obtained.

[0159] The eleventh integrated intensity ratio and the twelfth integrated intensity ratio are: As element (As 5 + ) integrated intensity, the As element (As 3+ ), the integrated intensity of the As element as GaAs (As-Ga), and the integrated intensity of the As element as metallic As (metallic As) relative to the integrated intensity of the Ga element as Ga2O (Ga + ) integrated intensity, Ga element (Ga 3+ ) and the integrated intensity of Ga element (Ga-As) existing as GaAs. The above-mentioned thirteenth integrated intensity ratio and the above-mentioned fourteenth integrated intensity ratio are: As element (As 5+ ) and the integral intensity of As element (As 3+ ) relative to the integrated intensity of Ga element (Ga + ) and the integrated intensity of Ga element (Ga 3+) to the sum of the integrated intensities of the above-mentioned twelfth integrated intensity ratio. The standard deviation and the average value of the above-mentioned twelfth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.015, and the standard deviation and the average value of the ratio R3 of the above-mentioned thirteenth integrated intensity ratio to the above-mentioned eleventh integrated intensity ratio and the ratio R4 of the above-mentioned fourteenth integrated intensity ratio to the above-mentioned twelfth integrated intensity ratio, that is, R3 / R4, satisfy the relationship of standard deviation / average value ≤ 0.078. The lower limit of the standard deviation and the average value of the above-mentioned twelfth integrated intensity ratio is an ideal value, that is, 0. For example, the standard deviation and the average value of the above-mentioned twelfth integrated intensity ratio may also satisfy the relationship of standard deviation / average value ≥ 0.010. The lower limit of the standard deviation and the average value of the ratio R3 of the above-mentioned thirteenth integrated intensity ratio to the above-mentioned eleventh integrated intensity ratio and the ratio R4 of the above-mentioned fourteenth integrated intensity ratio to the above-mentioned twelfth integrated intensity ratio, that is, R3 / R4, is an ideal value, that is, 0. For example, the standard deviation and average value of the ratio R3 of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio and the ratio R4 of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio, i.e., R3 / R4, may also satisfy the relationship of standard deviation / average value ≥ 0.061.

[0160] The fact that the standard deviation and average value of the twelfth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.015 indicates that a desired amount of arsenic is present within the oxide film. The fact that the standard deviation and average value of the ratio R3 (the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio) and the ratio R4 (the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio), i.e., R3 / R4, satisfy the relationship of standard deviation / average value ≤ 0.078 indicates that arsenic is dispersed within the oxide film with desired uniformity without segregation.

[0161] When the diameter is represented by D and two axes passing through the center of the main surface and orthogonal to each other on the main surface are defined 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, for a GaAs single crystal substrate having a diameter of 150 mm or more and 205 mm or less, it is possible to effectively remove the oxide film by thermal cleaning to obtain a main surface with no in-plane deviation and high mirror finish. Therefore, the above-mentioned GaAs single crystal substrate can form an epitaxial film with a reduced haze value.

[0162] In the above-mentioned first and second methods, the specific analysis method for obtaining the seventh integrated intensity ratio to the fourteenth integrated intensity ratio is the same as the method described in the above-mentioned item "Analysis method of GaAs single crystal substrate based on X-ray photoelectron spectroscopy (XPS) using radiant light", so it will not be repeated.

[0163] (5 measuring points and 9 measuring points)

[0164] The GaAs single crystal substrate of the first embodiment has a diameter of 75 mm or more and less than 150 mm. In this case, five measurement points are set in the following manner on the main surface of the GaAs single crystal substrate of the first embodiment. That is, in order to evaluate the effect of reducing the haze value of the epitaxial film brought about by the uniformity of the in-plane distribution of the eighth integrated intensity ratio and the R1 / R2 value, it is preferred to set the five measurement points with the greatest possible distance from each other, and measure the haze value generated by the epitaxial film grown in the vicinity of each of the five measurement points. In this case, it is preferred to measure the haze value of an area with a diameter of 20 mm or more. Therefore, five circular measurement objects with a diameter of 20 mm are set in the main surface of the GaAs single crystal substrate with the greatest possible distance from each other. Moreover, the center of each measurement object is set as a measurement point.

[0165] First, assuming that two axes passing through the center of the main surface and intersecting orthogonally on the main surface are the X and Y axes, the X and Y coordinates (X, Y) of the first of the five measurement points are set to (0, 0). Furthermore, the X and Y axes are set so that the notch formed in the GaAs single crystal substrate is located in the third quadrant of the XY coordinate plane and that a ray passing through the notch makes a general angle of 225° with respect to a ray extending from the origin in the positive direction of the X axis.

[0166] Furthermore, the second, third, fourth, and fifth measurement points of the five measurement points are equally spaced on a circumference formed by a set of points at a distance D / 4 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). D represents the diameter of the GaAs single crystal substrate, and the units of D and X and Y in the coordinates (X, Y) are in mm.

[0167] The GaAs single crystal substrate of the second embodiment has a diameter of 150 mm to 205 mm. In this case, four additional measurement points are set on the main surface of the GaAs single crystal substrate of the second embodiment, in addition to the five measurement points set in the GaAs single crystal substrate of the first embodiment, for a total of nine measurement points. Specifically, in addition to the second, third, fourth, and fifth measurement points set above, four measurement points with a diameter of 20 mm are set on the main surface of the GaAs single crystal substrate of the second embodiment, located further outward from these measurement points and not overlapping with the measurement points included in the second, third, fourth, and fifth measurement points. Furthermore, the center of each measurement point is set as a measurement point, and X-rays are irradiated at each measurement point. Specifically, the coordinates (X, Y) of the sixth of the four additional 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)). D represents the diameter of the GaAs single crystal substrate, and the units of D and X and Y in the coordinates (X, Y) are mm.

[0168] It is known that in a large-diameter main surface with a diameter of 150 mm to 205 mm, such as the second embodiment of the GaAs single crystal substrate, characteristics tend to vary in the outermost regions. Therefore, in order to evaluate the haze reduction effect of the epitaxial film achieved by achieving uniform in-plane distribution of the twelfth integrated intensity ratio and the R3 / R4 value, it is desirable to measure the haze generated by the epitaxial film grown in the outermost regions in addition to the five measurement points described above. To address this, in addition to the five measurement points described above, four measurement points with a diameter of 20 mm and a measurement point at their center were set in the outermost regions of the main surface of the GaAs single crystal substrate, with the greatest possible distance between them.

[0169] Figure 4 This figure is an explanatory diagram for explaining five measurement points set on a GaAs single crystal substrate having a diameter of 75 mm or more and less than 150 mm in this embodiment. Figure 5 This figure is an explanatory diagram for explaining nine measurement points set on a GaAs single crystal substrate having a diameter of 150 mm to 205 mm in this embodiment.

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

[0171] Next, a second measurement point P2, a third measurement point P3, a fourth measurement point P4, and a fifth measurement point P5 were set on a circumference formed by a collection of points at a distance D / 4 from the center of the GaAs single crystal substrate. Furthermore, circular areas with a diameter of 20 mm, namely measurement objects A2, A3, A4, and A5, were set, centered on these second, third, fourth, and fifth measurement points P2, P3, P4, and P5, respectively.

[0172] For example, in Figure 4 In the example shown, for a GaAs single crystal substrate with a diameter of 75 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 (the units of X and Y are all mm, the same applies hereinafter) are set to (18.75, 0), (0, 18.75), (-18.75, 0), and (0, -18.75), respectively. In this case, in the 75 mm diameter GaAs single crystal substrate, measurement object A1 partially overlaps with measurement objects A2, A3, A4, and A5. However, from the perspective of evaluating the uniformity of the main surface of the GaAs single crystal substrate, this overlap does not cause problems and is therefore permissible.

[0173] like Figure 5 As shown, in the GaAs single crystal substrate of the second embodiment, in addition to the first to fifth measurement points P1 to P5 set in the GaAs single crystal substrate of the first embodiment, four further measurement points, namely, sixth measurement point P6, seventh measurement point P7, eighth measurement point P8, and ninth measurement point P9, are set at equal intervals on the circumference of a circle located 10 mm inward from the outer periphery of the GaAs single crystal substrate, further outward from the second, third, fourth, and fifth measurement points P2, P3, P4, and P5. Furthermore, circular areas with a diameter of 20 mm centered on the sixth, seventh, eighth, and ninth measurement points P8 and P9, namely, measurement objects A6, A7, A8, and A9, are set.

[0174] For example, in Figure 5In the example shown, for 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. Furthermore, 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 GaAs single crystal substrate preferably has an epitaxial film disposed on the main surface. In this case, the maximum haze value of the epitaxial film is preferably 350 ppm or less, and the average haze value of the epitaxial film is preferably 2.5 ppm or less. The maximum haze value of the epitaxial film is more preferably 100 ppm or less, and the average haze value of the epitaxial film is more preferably 2.0 ppm or less. The lower limits of the maximum and average haze values ​​of the epitaxial film are ideally 0.

[0177] For example, there are cases where the epitaxial film is made of Al 1-y-z Ga y In z In the compound film composed of As, the above y is 0 or more and 1 or less, the above z is 0 or more and 1 or less, and the sum of the above y and the above z is 0 or more and 1 or less. That is, this embodiment can be applied to the compound film composed of Al 1-y-z Ga y In z As (0≤y≤1, 0≤z≤1, 0≤y+z≤1) compound film is formed as an epitaxial film on the main surface of the GaAs single crystal substrate. 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 within the above range, the GaAs single crystal substrate can be used in a wide range of applications. More preferably, the epitaxial film has a thickness of 1 to 5 μm.

[0179] The haze value of the epitaxial film disposed on the main surface of the GaAs single crystal substrate can be determined using a conventionally known surface foreign matter inspection device (e.g., "Surfscan 6420" manufactured by KLA-TENCOR). The device can measure the haze value of the epitaxial film on the entire surface of the epitaxial film (excluding the area from the outer periphery of the substrate to 2 mm inside) every 1 cm. 2 The haze value of the surface (amount of scattered light (ppm)) can be obtained. Based on the results of such measurements, the maximum value and average value of the haze of the surface of the epitaxial film can be obtained.

[0180] [Method for manufacturing a gallium arsenide single crystal substrate]

[0181] The method for manufacturing a gallium arsenide single crystal substrate (GaAs single crystal substrate) of the present embodiment is preferably a method for manufacturing the above-mentioned GaAs single crystal substrate having a main surface and the main surface having a circular shape. For example, the above-mentioned manufacturing method includes: a step of preparing a gallium arsenide single crystal substrate precursor (hereinafter also referred to as "GaAs single crystal substrate precursor") having a surface and the surface having a circular shape (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 above-mentioned 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 an alkaline cleaning solution to make the above-mentioned polished surface an alkaline cleaned surface (alkaline cleaning step); a step of immersing the above-mentioned alkaline cleaned surface in a first acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass % of a first acid to clean the above-mentioned alkaline cleaned surface to make the above-mentioned acid cleaned surface (first acid cleaning step); a step of rotating the above-mentioned acid cleaned surface at a rotation speed of 0.000 rpm or more in the circumferential direction while rotating the above-mentioned acid cleaned surface at a rotation speed of 0.000 rpm or more. The process comprises supplying a second acid cleaning solution containing 0.3 mass ppm to 0.5 mass % of a second acid to the acid cleaning surface at a flow rate of 1 L / min to 5 L / min for 30 seconds to 5 minutes to clean the acid cleaning surface, thereby converting the acid cleaning surface into the second acid cleaning surface (second acid cleaning process); and heat-treating the second acid cleaning surface for 1 minute to 30 minutes under an inert gas atmosphere at atmospheric pressure and 150°C to 300°C to convert the second acid cleaning surface into the main surface (heat treatment process). The first acid contained in the first acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. The second acid contained in the second acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid.

[0182] By using a manufacturing method having such characteristics, a GaAs single crystal substrate having an oxide film on the main surface that can be effectively removed using thermal cleaning 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). Thus, 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, "gallium arsenide single crystal substrate precursor (GaAs single crystal substrate precursor)" refers to a GaAs single crystal substrate with a circular surface cut from a gallium arsenide single crystal (hereinafter also referred to as "GaAs single crystal") manufactured using an existing well-known manufacturing method such as the vertical wafer boat method, and in particular refers to a GaAs single crystal substrate that is the object of the various steps included in the above-mentioned cleaning step.

[0184] Based on information obtained from XPS analysis using the aforementioned radiation, the present inventors aimed to improve the conventionally known cleaning process for obtaining the aforementioned GaAs single crystal substrate. In particular, it is known that the oxide film of the aforementioned GaAs single crystal substrate is formed by surface oxidation during an acid cleaning process, which is a process for removing impurities in the alkaline cleaning agent that adheres to the surface of the GaAs single crystal substrate precursor after alkaline cleaning. Therefore, the inventors aimed to treat the oxide film after the acid cleaning process to obtain an As-rich composition, thereby generating metallic arsenic near the interface between the oxide film and the GaAs layer of the aforementioned GaAs single crystal substrate, and reducing the metallic arsenic to obtain an As₂O₃-rich composition. Specifically, after cleaning the surface of the GaAs single crystal substrate precursor in the order of the alkali cleaning step and the acid cleaning step, a second acid cleaning step of spin cleaning is performed, that is, a step of supplying an acid cleaning solution to the surface while rotating the surface to clean it, thereby further promoting the oxidation reaction of GaAs and causing an As-rich oxide film to segregate on the surface. Subsequently, the surface is heat-treated to promote the reduction of metallic arsenic near the interface, thereby modifying the oxide film to a composition rich in As2O3. Since As2O3 has the property of being easily sublimated, such an oxide film can be effectively removed using thermal cleaning. Thus, the inventors were able to obtain a GaAs single crystal substrate having a main surface with high mirror finish, and realized a method for manufacturing a GaAs single crystal substrate capable of forming an epitaxial film with a reduced haze value.

[0185] The following is based on Figure 6 Each step included in the method for manufacturing a GaAs single crystal substrate according to this embodiment will be described in detail. Figure 6 This is a flowchart showing the method for manufacturing a GaAs single crystal substrate according to this embodiment.

[0186] <Preparation Step S100>

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

[0188] <Cleaning Step S200>

[0189] The manufacturing method of the above-mentioned GaAs single crystal substrate includes a cleaning step S200 for obtaining the above-mentioned GaAs single crystal substrate from the above-mentioned GaAs single crystal substrate precursor. Through the cleaning step S200, a GaAs single crystal substrate having an oxide film on the main surface that can be effectively removed by thermal cleaning can be obtained from the above-mentioned GaAs single crystal substrate precursor. The cleaning step S200 includes: a step of polishing the above-mentioned surface of the above-mentioned GaAs single crystal substrate precursor, thereby making the above-mentioned surface a polished surface (surface polishing step S210); a step of cleaning the above-mentioned polished surface with an alkaline cleaning solution, thereby making the above-mentioned polished surface an alkaline cleaned surface (alkaline cleaning step S220); a step of immersing the above-mentioned alkaline cleaned surface in a first acid cleaning solution containing a first acid of not less than 0.3 mass ppm and not more than 0.5 mass %, thereby cleaning the above-mentioned alkaline cleaned surface to make the above-mentioned acid cleaned surface an acid cleaned surface (first acid cleaning step S230); while rotating the above-mentioned acid cleaned surface at a rotation speed of not less than 1000 rpm in the circumferential direction, The steps of supplying a second acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass % or less of a second acid to the acid cleaning 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 clean the acid cleaning surface, thereby converting the acid cleaning surface into the second acid cleaning surface (second acid cleaning step S240); and heat-treating the second acid cleaning surface for 1 minute or more and 30 minutes or less under the conditions of atmospheric pressure and 150° C. or more and 300° C. or less in an inert gas atmosphere, thereby converting the second acid cleaning surface into the main surface (heat treatment step S250). The steps included in the cleaning step S200 are described in detail below.

[0190] (Surface Polishing Step S210)

[0191] The surface polishing step S210 is a step of polishing the surface of the GaAs single crystal substrate precursor to a polished surface. The surface polishing step S210 provides the surface of the GaAs single crystal substrate precursor with a mirror-like polished surface. For example, the surface polishing step S210 can also provide the surface of the GaAs single crystal substrate precursor with a surface roughness of 0.3 nm or less, as expressed in terms of arithmetic mean roughness Ra. Various polishing methods, such as conventionally known mechanical polishing and chemical mechanical polishing, can be used as the polishing method in the surface polishing step S210.

[0192] (Alkali Cleaning Step S220)

[0193] The alkaline cleaning step S220 is a step of cleaning the polished surface with an alkaline cleaning solution to make the polished surface an alkaline-cleaned surface. The alkaline cleaning step S220 can remove foreign matter, impurities, etc. attached to the polished surface of the GaAs single crystal substrate precursor using the alkaline cleaning solution. The alkaline cleaning solution is not particularly limited, but preferably uses an aqueous solution containing 0.1 to 10% by mass of an organic alkaline compound that does not contain a metal element that affects electrical properties, such as choline, a quaternary ammonium hydroxide such as tetramethylammonium hydroxide (TMAH), or a quaternary pyridinium hydroxide.

[0194] (First Acid Cleaning Step S230)

[0195] The first acid cleaning step S230 is a step of cleaning the alkali cleaned surface by immersing it in an acid cleaning solution containing a first acid of 0.3 mass ppm or more and 0.5 mass % or less, so that the alkali cleaned surface becomes an acid cleaned surface. Through the first acid cleaning step S230, impurities in the alkali cleaning solution attached to the alkali cleaned surface of the GaAs single crystal substrate precursor can be removed by utilizing the oxidation reaction of the first acid cleaning solution (etching of the alkali cleaned surface). In particular, in the first acid cleaning step S230, the alkali cleaned surface is immersed in a first acid cleaning solution containing a first acid of 0.3 mass ppm or more and 0.5 mass % or less. As a result, the ratio of Ga atoms to As atoms on the main surface is optimized, so that the oxide film can be effectively removed by thermal cleaning. The first acid cleaning step S230 is further preferably cleaned with a first acid cleaning solution containing a first acid of 0.3 mass ppm or more and 0.3 mass % or less.

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

[0197] About the acid included in the above-mentioned acid cleaning solution, there is no particular restriction, preferably the following acid component: cleaning power is high, does not include the element (such as metallic element, sulphur etc.) that has an impact on electrical properties, and when the droplets are scattered in the equipment, the acid component also evaporates together with the water and is not easy to produce serious secondary pollution, equipment degradation. For example, the acid included in the acid cleaning solution preferably includes at least one inorganic acid selected from hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO 3 ) and nitrous acid (HNO 2 ). As the above-mentioned acid, organic acids such as acetic acid, citric acid, malic acid can also be preferably used. In addition, these acid combinations of more than two kinds can also be used, for example, hydrochloric acid and nitric acid can be used in combination.

[0198] From the perspective of cleaning performance, the first acid cleaning solution more preferably contains 0.3 ppm to 0.3% by mass of hydrogen peroxide (H₂O₂). If the H₂O₂ concentration is less than 0.3 ppm by mass, the effect of dissolved oxygen in the first acid cleaning solution may be increased, potentially reducing the effectiveness of promoting impurity removal. If the H₂O₂ concentration is greater than 0.3% by mass, the etching rate may be excessively high, potentially causing uneven etching on the acid-cleaned surface.

[0199] It is preferred that the following is performed: after the first acid cleaning step S230, the acid cleaning surface of the GaAs single crystal substrate precursor is cleaned with pure water immediately after the first acid cleaning step S230. There is no particular limitation on the cleaning method using pure water, but it is preferred to use pure water with a dissolved oxygen concentration (DO) of 100 ppb or less to clean the acid cleaning surface of the GaAs single crystal substrate precursor for a time of 5 minutes or less. In this way, the excessive oxidation of the acid cleaning surface can be suppressed. Here, from the viewpoint of further suppressing the excessive oxidation, the dissolved oxygen concentration of the above-mentioned pure water is more preferably 50 ppb or less. From the viewpoint of less impurities, the total organic carbon (TOC) of the above-mentioned pure water is preferably 40 ppb or less. The above-mentioned cleaning method using pure water can also be performed in the following manner: while the GaAs single crystal substrate precursor is kept horizontal with its main surface and rotated in a circumferential direction at 100 to 800 rpm, the above-mentioned pure water is supplied to the above-mentioned acid cleaning surface.

[0200] (Second Acid Cleaning Step S240)

[0201] The second acid cleaning step S240 involves supplying a second acid cleaning solution to the acid-cleaned surface at a flow rate of 0.1 L / min to 5 L / min for 30 seconds to 5 minutes while rotating the acid-cleaned surface circumferentially at a speed of 1000 rpm or higher. This cleans the acid-cleaned surface, converting it into a second acid-cleaned surface. The second acid cleaning step S240 further promotes the oxidation reaction of GaAs in the acid-cleaned surface, thereby promoting the acid-cleaned surface to have an As-rich composition. This effectively promotes the reduction of metallic arsenic near the interface between the oxide film and the main layer in the subsequent heat treatment step S250, modifying the oxide film to have an As2O3-rich composition.

[0202] In particular, the second acid contained in the second acid cleaning solution is at least one selected from hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3) and nitrous acid (HNO2). These acids have high cleaning power, do not contain elements that affect electrical properties (such as metal elements, sulfur, etc.), and when droplets are scattered into the equipment, the acid component also evaporates together with the water and is not easy to produce serious secondary pollution or acid component that deteriorates the equipment, so it is preferred. The above-mentioned second acid cleaning solution also preferably contains organic acids such as acetic acid, citric acid, and malic acid. In addition, it is also possible to combine these acids of more than two kinds, for example, it is also possible to use hydrochloric acid and nitric acid in combination. Furthermore, the concentration of the second acid in the second acid cleaning solution is preferably more than 0.3 mass ppm and less than 0.5 mass %. When the concentration of the second acid in the second acid cleaning solution is less than 0.3 mass ppm, the effect of promoting the oxidation process of the above-mentioned acid cleaning surface becomes smaller. On the other hand, if the concentration of the second acid in the second acid cleaning solution exceeds 0.5 mass %, the deviation of the acid-cleaned surface from the stoichiometric composition becomes larger, and there is a tendency for the chemical composition of the acid-cleaned surface (and thus the main surface in the subsequent process) to deviate. The concentration of the second acid in the second acid cleaning solution is more preferably 0.3 mass ppm or more and 0.3 mass % or less.

[0203] In addition, in the above-mentioned first acid cleaning process S230, as described above, the first acid contained in the example first acid cleaning solution is at least one selected from hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3) and nitrous acid (HNO2). The first acid and the second acid may include at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid, and the second acid is an acid of the same type as the first acid. The first acid and the second acid may include at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid, and the second acid is an acid of a different type from the first acid. That is, the first acid and the second acid can include at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid, and the second acid is an acid of the same or different type as the first acid.

[0204] In the second acid cleaning step S240, the acid-cleaned surface is preferably rotated circumferentially at a speed of 1500 rpm or higher. The upper limit of the speed at which the acid-cleaned surface is rotated circumferentially is not particularly limited, but is preferably 2500 rpm. The flow rate of the second acid cleaning solution supplied to the acid-cleaned surface is preferably 0.1 L / min or higher and 1 L / min or lower. The time for supplying the second acid cleaning solution to the acid-cleaned surface is preferably 30 seconds or higher and 1 minute or lower. This allows for more appropriate control of the oxidation reaction of GaAs on the acid-cleaned surface.

[0205] Furthermore, after the second acid cleaning step S240, it is preferred that pure water be used to clean the second acid cleaning surface of the GaAs single crystal substrate precursor immediately after the second acid cleaning step S240. There is no particular limitation on the cleaning method using pure water, and it is preferred to use pure water having a dissolved oxygen concentration (DO) of 100 ppb or less to clean the second acid cleaning surface of the GaAs single crystal substrate precursor for a period of less than 5 minutes. In this way, impurities attached to the second acid cleaning surface can be removed. Here, from the viewpoint of further suppressing the progress of excessive oxidation, the dissolved oxygen concentration of the above-mentioned pure water is more preferably 50 ppb or less. From the viewpoint of having few impurities, the total organic carbon (TOC) of the above-mentioned pure water is preferably 40 ppb or less. The above-mentioned cleaning method using pure water can also be carried out in the following manner: while the GaAs single crystal substrate precursor is kept horizontal on its main surface and rotated at more than 100 rpm, the above-mentioned pure water is supplied to the above-mentioned second acid cleaning surface.

[0206] (Heating Process S250)

[0207] The heat treatment step S250 is a step in which the second acid-cleaned surface is heat-treated in an inert gas atmosphere at atmospheric pressure and at a temperature of 150°C to 300°C for 1 minute to 30 minutes, thereby converting the second acid-cleaned surface into the main surface. The heat treatment step S250 promotes the reduction of metallic arsenic in the oxide film on the second acid-cleaned surface, thereby modifying the oxide film to a composition rich in As₂O₃. As₂O₃ readily sublimes, the oxide film can be effectively removed by thermal cleaning.

[0208] In the heat treatment step S250, the second acid-cleaned surface is heat-treated in an inert gas atmosphere at atmospheric pressure and at a temperature of 150°C to 300°C for a period of 1 minute to 30 minutes. The type of inert gas is not particularly limited, but is preferably argon or nitrogen. Furthermore, the temperature for the heat treatment is preferably 150 to 200°C. The time for the heat treatment is preferably 1 to 5 minutes. By performing the heat treatment under the conditions in the above range, the composition of the oxide film can be properly controlled. When the temperature for the heat treatment is less than 150°C or the time for the heat treatment is less than 1 minute, there is a tendency for the oxide film to be insufficiently modified. When the temperature for the heat treatment exceeds 300°C or the time for the heat treatment exceeds 30 minutes, there is a possibility that the GaAs single crystal substrate may be adversely affected due to excessive heating.

[0209] <Film Forming Step S300>

[0210] (Thermal Cleaning Process S310)

[0211] According to the above description, the manufacturing method of the GaAs single crystal substrate of this embodiment can obtain a GaAs single crystal substrate having the following main surface, wherein the main surface includes an oxide film having a composition rich in As and rich in As2O3. It is preferable to perform a thermal cleaning step S310 and a later-described epitaxial film forming step S320 on the GaAs single crystal substrate as the film forming step S300. In the thermal cleaning step S310, even if the GaAs single crystal substrate is thermally cleaned under conventionally known conditions (e.g., a heat treatment at 550°C for 5 minutes), the oxide film can be effectively removed because Ga2O and As2O3 have the property of easily sublimating.

[0212] <Epitaxial Film Formation Step S320>

[0213] Furthermore, in the manufacturing method of the GaAs single crystal substrate of this embodiment, it is preferable to include a step of forming an epitaxial film on the main surface (epitaxial film forming step S320) as described above. Through the epitaxial film forming step S320, 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 haze value of the surface of the epitaxial film can be less than 350 ppm, and the average haze value of the surface can be less than 2.5 ppm, thereby improving device characteristics.

[0214] In the epitaxial film forming step S320, the epitaxial film is formed on the main surface of the GaAs single crystal substrate using a conventionally known method. The properties of the epitaxial film obtained in this step are already described in the "Epitaxial Film" section above, and therefore will not be repeated here. The GaAs single crystal substrate having the epitaxial film formed on its main surface has a sufficiently low haze value, making it suitable for use in devices such as field-effect transistors, microwave diodes, and other integrated circuits.

[0215] Example

[0216] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The GaAs single crystal substrates of Samples 1 to 6 described below are examples, and the GaAs single crystal substrates of Samples 11 to 13 are comparative examples.

[0217] [Manufacturing of GaAs Single Crystal Substrates]

[0218] Sample 1

[0219] (Preparation process)

[0220] Semi-insulating GaAs single crystals to which carbon (C) atoms were added, grown by the Vertical Bridgman (VB) method, were sliced ​​and chamfered to prepare a plurality of GaAs single crystal substrate precursors having a diameter of 6 inches (150 mm) and a thickness of 675 μm.

[0221] (Surface polishing process)

[0222] The surface of the GaAs single crystal substrate precursor was subjected to conventional mechanical polishing and chemical mechanical polishing to produce 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 an off angle of 2° relative to the (100) plane.

[0223] (Alkali cleaning process)

[0224] The polished surface of the GaAs single crystal substrate precursor was immersed in an aqueous solution (alkaline cleaning solution) containing 0.5 mass% tetramethylammonium hydroxide at room temperature (25°C) in a vertical batch process for 10 minutes. The GaAs single crystal substrate precursor was then rinsed with ultrapure water (resistivity (specific resistivity) of 18 MΩ·cm or greater, TOC (total organic carbon) of less than 10 μg / L, and a particle count of less than 100 particles / L, the same applies hereinafter) for 3 minutes.

[0225] (First Acid Cleaning Step)

[0226] The alkali-cleaned surface of the GaAs single crystal substrate precursor was immersed in a hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the first acid cleaning solution) at room temperature (25°C) for 2 minutes in a vertical batch process. Furthermore, the GaAs single crystal substrate precursor was rinsed for 3 minutes with the same ultrapure water used in the alkali cleaning step. This converted the alkali-cleaned surface into an acid-cleaned surface.

[0227] (Second Acid Cleaning Step)

[0228] The acid-cleaned surface of the GaAs single crystal substrate precursor is acid-cleaned using a second acid-cleaning solution in a rotational cleaning manner. Specifically, a hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid-cleaning solution) is supplied to the acid-cleaned surface of the GaAs single crystal substrate precursor while the substrate is rotated at 1500 rpm in the circumferential direction for 1 minute. Thereafter, the GaAs single crystal substrate precursor is rinsed for 3 minutes using the same ultrapure water as used in the first acid-cleaning step. This makes the acid-cleaned surface the second acid-cleaned surface.

[0229] (Heat treatment process)

[0230] The second acid-cleaned surface of the GaAs single crystal substrate precursor was heat-treated under argon atmosphere at atmospheric pressure, 200°C, and for one minute. This resulted in the second acid-cleaned surface becoming the main surface having the specified oxide film. As described above, the required number of GaAs single crystal substrates for Sample 1 were obtained. These GaAs single crystal substrates maintained the diameter and thickness of the GaAs single crystal substrate precursor.

[0231] (Epitaxial Film Formation Step)

[0232] The GaAs single crystal substrates were thermally cleaned at 550°C for 5 minutes. Furthermore, an Al layer with a thickness of 5 μm was grown on the main surface of one of the thermally cleaned GaAs single crystal substrates by metal organic vapor phase epitaxy (MOVPE). 0.5 Ga 0.5 The As layer was used as the epitaxial layer (the GaAs single crystal substrate on which the epitaxial layer was grown will hereinafter be referred to as "epitaxial substrate"). Thus, the epitaxial substrate of Sample 1 was obtained. When growing the epitaxial layer, the GaAs single crystal substrate was heated to 550°C.

[0233] Sample 2

[0234] The required number of GaAs single crystal substrates of Sample 2 were obtained by the same procedure as Sample 1, except that the acid cleaning was performed by spin cleaning under the following conditions in the second acid cleaning step and the heat treatment step was performed under the following conditions. Furthermore, Al was grown on the main surface of one of the GaAs single crystal substrates in the same procedure as Sample 1 to a thickness of 5 μm. 0.5 Ga 0.5 The As layer was used as the epitaxial layer. The acid cleaning conditions for obtaining Sample 2 using a spin cleaning method were as follows: A hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid cleaning solution) was supplied at a flow rate of 1 L / min for 30 seconds to the acid-cleaned surface of the GaAs single crystal substrate precursor, which was rotated in the circumferential direction at 2500 rpm. The heat treatment conditions for obtaining Sample 2 were a heat treatment at atmospheric pressure and 150°C for 5 minutes in an argon atmosphere.

[0235] Sample 3

[0236] The required number of GaAs single crystal substrates of Sample 3 were obtained in the same manner as Sample 1, except that the acid cleaning was performed by spin cleaning under the following conditions in the second acid cleaning step and the heat treatment step was performed under the following conditions. Furthermore, for one of the above-mentioned GaAs single crystal substrates, an Al layer with a thickness of 5 μm was grown on its main surface in the same manner as Sample 1. 0.5 Ga 0.5 The As layer served as the epitaxial layer. The spin-cleaning acid cleaning conditions used to obtain Sample 3 were as follows: A hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid cleaning solution) was supplied at a flow rate of 5 L / min for 5 minutes to the acid-cleaned surface of the GaAs single crystal substrate precursor, which was rotated circumferentially at 1500 rpm. The heat treatment step used to obtain Sample 3 was performed under an argon atmosphere at atmospheric pressure and 200°C for 1 minute.

[0237] <Sample 4>

[0238] The required number of GaAs single crystal substrates of Sample 4 were obtained in the same manner as Sample 1, except that the acid cleaning was performed by spin cleaning under the following conditions in the second acid cleaning step and the heat treatment step was performed under the following conditions. Furthermore, for one of the above-mentioned GaAs single crystal substrates, an Al layer with a thickness of 5 μm was grown on its main surface in the same manner as Sample 1. 0.5 Ga 0.5The As layer served as the epitaxial layer. The spin-cleaning acid cleaning conditions used to obtain Sample 4 were as follows: A hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid cleaning solution) was supplied at a flow rate of 0.1 L / min for 5 minutes to the acid-cleaned surface of the GaAs single crystal substrate precursor, which was rotated circumferentially at 1500 rpm. The heat treatment step used to obtain Sample 4 was performed under an argon atmosphere at atmospheric pressure and 300°C for 1 minute.

[0239] Sample 5

[0240] The required number of GaAs single crystal substrates of Sample 5 were obtained in the same manner as Sample 1, except that the acid cleaning was performed by spin cleaning under the following conditions in the second acid cleaning step and the heat treatment step was performed under the following conditions. Furthermore, for one of the above-mentioned GaAs single crystal substrates, an Al layer with a thickness of 5 μm was grown on its main surface in the same manner as Sample 1. 0.5 Ga 0.5 The As layer was used as the epitaxial layer. The acid cleaning conditions for obtaining Sample 5 using a spin cleaning method were as follows: A hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid cleaning solution) was supplied at a flow rate of 0.1 L / min for 1 minute to the acid-cleaned surface of the GaAs single crystal substrate precursor, which was rotated in the circumferential direction at 1500 rpm. The heat treatment step for obtaining Sample 5 was performed under an argon atmosphere at atmospheric pressure and 150°C for 30 minutes.

[0241] Sample 6

[0242] The required number of GaAs single crystal substrates of Sample 6 were obtained in the same manner as Sample 1, except that the acid cleaning was performed by spin cleaning under the following conditions in the second acid cleaning step and the heat treatment step was performed under the following conditions. Furthermore, for one of the above-mentioned GaAs single crystal substrates, an Al layer with a thickness of 5 μm was grown on its main surface in the same manner as Sample 1. 0.5 Ga 0.5 The As layer served as the epitaxial layer. The spin-cleaning acid cleaning conditions used to obtain Sample 6 were as follows: A hydrochloric acid aqueous solution containing 0.3 mass ppm of hydrochloric acid (the second acid cleaning solution) was supplied at a flow rate of 0.1 L / min for 5 minutes to the acid-cleaned surface of the GaAs single crystal substrate precursor, which was rotated circumferentially at 1500 rpm. The heat treatment step used to obtain Sample 6 was performed under an argon atmosphere at atmospheric pressure and 300°C for 30 minutes.

[0243] Sample 11

[0244] The required number of GaAs single crystal substrates of Sample 11 were obtained by the same procedure as Sample 1 except that the above-mentioned heat treatment step was not performed. Furthermore, on one of the above-mentioned GaAs single crystal substrates, an Al layer with a thickness of 5 μm was grown on its main surface in the same procedure as Sample 1. 0.5 Ga 0.5 The As layer serves as the epitaxial layer.

[0245] Sample 12

[0246] The required number of GaAs single crystal substrates of Sample 12 were obtained by the same procedure as Sample 1 except that the second acid cleaning step was not performed. Furthermore, Al2O3 with a thickness of 5 μm was grown on the main surface of one of the GaAs single crystal substrates in the same procedure as Sample 1. 0.5 Ga 0.5 The As layer serves as the epitaxial layer.

[0247] Sample 13

[0248] The required number of GaAs single crystal substrates of Sample 13 were obtained by the same procedure as Sample 1 except that the second acid cleaning step and the heat treatment step were not performed. Furthermore, Al was grown on the main surface of one of the GaAs single crystal substrates in the same procedure as Sample 1 to a thickness of 5 μm. 0.5 Ga 0.5 The As layer serves as the epitaxial layer.

[0249] [First Test]

[0250] Analysis of GaAs Single Crystal Substrates Using X-ray Photoelectron Spectroscopy

[0251] X-rays with an energy of 600 eV were prepared using "BL17," one of Sumitomo Electric Industries, Ltd.'s dedicated beamlines within the Kyushu Synchrotron Light Research Center at Saga Prefectural University. These X-rays were irradiated onto the center of the main surface of each of the GaAs single crystal substrates for Samples 1 to 6 and Samples 11 to 13, and analysis was performed using X-ray photoelectron spectroscopy. Furthermore, since the entire GaAs single crystal substrates for Samples 1 to 6 and Samples 11 to 13 could not be placed on a sample stand, test pieces were cut from each of the GaAs single crystal substrates for Samples 1 to 6 and Samples 11 to 13, and these test pieces were analyzed.

[0252] The analysis conditions are as follows.

[0253] Condition 1: X-ray incident energy 600 eV and photoelectron escape angle 30°

[0254] Condition 2: X-ray incident energy 600 eV and photoelectron escape angle 45°

[0255] Condition 3: X-ray incident energy 600 eV and photoelectron escape angle 85°.

[0256] The size of the test piece under each condition: 10mm×10mm

[0257] Pressure around the test piece under each condition: 4×10 -7 Pa

[0258] High-resolution XPS analyzer used under each condition (trade name: "R3000", manufactured by Scienta Omicron)

[0259] Energy resolution E / ΔE: 3480

[0260] Bond energy plot interval: 0.02 eV

[0261] The accumulation time and number of accumulation times for each energy value are: 100ms and 50 times.

[0262] Based on the Ga3d spectra and As3d spectra obtained by XPS analysis under the above conditions (conditions 1 to 3), the As 5+ The integrated intensity, As 3+ The sum of the integrated intensity of As-Ga, the integrated intensity of As-Ga and the integrated intensity of metal As relative to Ga + The integrated intensity of Ga 3+ The ratio of the integrated intensity of Ga-As to the sum of the integrated intensity of Ga-As is the first integrated intensity ratio (In1), the second integrated intensity ratio (In2), and the third integrated intensity ratio (In3). Furthermore, based on the Ga3d spectrum and As3d spectrum obtained by the analysis of the above conditions (conditions 1 to 3), the As 5+ The integrated intensity of As 3+ The sum of the integrated intensities relative to Ga + The integrated intensity of Ga 3+The ratio of the sum of the integrated intensities is the fourth integrated intensity ratio (In4), the fifth integrated intensity ratio (In5) and the sixth integrated intensity ratio (In6). The ratio (In1 / In3) of the first integrated intensity ratio (In1) of samples 1 to 6 and samples 11 to 13 to the third integrated intensity ratio (In3) is also calculated. Furthermore, the ratio (In4 / In1) of the fourth integrated intensity ratio (In4) to the first integrated intensity ratio (In1) of samples 1 to 6 and samples 11 to 13, the ratio (In5 / In2) of the fifth integrated intensity ratio (In5) to the second integrated intensity ratio (In2), and the ratio (In6 / In3) of the sixth integrated intensity ratio (In6) to the third integrated intensity ratio (In3) are also calculated. The results are shown in Tables 1 and 2. In Tables 1 and 2, "Ga as a whole" refers to Ga + The integrated intensity of Ga 3+ The sum of the integrated intensity of As and the integrated intensity of Ga-As. "As as a whole" refers to As 5+ The integrated intensity, As 3+ The sum of the integrated intensity of As, the integrated intensity of As-Ga and the integrated intensity of metal As.

[0263] <Maximum and average values ​​of haze on the surface of the epitaxial film>

[0264] The surfaces of the epitaxial films on the epitaxial substrates of Samples 1 to 6 and Samples 11 to 13 were inspected using a surface foreign matter inspection device (trade name: "Surfscan 6420", manufactured by KLA-TENCOR Corporation) to determine the maximum and average haze values ​​of the epitaxial films in each sample. The results are shown in Tables 1 and 2.

[0265] Furthermore, the quality of the epitaxial substrates of Samples 1 to 6 and Samples 11 to 13 was evaluated based on the maximum and average values ​​of the haze of the epitaxial film surface according to the following criteria.

[0266] A: The maximum haze value is 100 ppm or less and the average haze value is 2.0 ppm or less;

[0267] B: The maximum haze value is greater than 100 ppm and less than 350 ppm, and the average haze value is less than 2.5 ppm;

[0268] C: At least the maximum value of the haze is greater than 350 ppm, or the average value of the haze is greater than 2.5 ppm.

[0269] [Table 1]

[0270] Table 1

[0271]

[0272] [Table 2]

[0273] Table 2

[0274]

[0275] <Inspection>

[0276] According to Table 1, the epitaxial substrates of Samples 1 to 6 that met all of the following relationships were rated A or B: In3 was 1.05 or higher and 1.2 or lower, In4, In5, and In6 were all 0.9 or higher, In1 / In3 was 0.9 or higher and 1.3 or lower, and In4 / In1, In5 / In2, and In6 / In3 were all 0.7 or higher and 1.1 or lower. In contrast, according to Table 2, the epitaxial substrates of Samples 11 to 13, which did not meet at least one of the above relationships, were rated C.

[0277] [Second Test]

[0278] <Manufacturing of GaAs Single Crystal Substrates>

[0279] (Sample 7)

[0280] In the above preparation process, the semi-insulating GaAs single crystal to which carbon (C) atoms are added is 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 sample 3 is obtained according to the same key points as sample 2.

[0281] (Sample 8)

[0282] In the above preparation process, the semi-insulating GaAs single crystal to which carbon (C) atoms are added 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, the GaAs single crystal substrate of sample 4 is obtained according to the same key points as sample 2.

[0283] (Sample 9)

[0284] In the above preparation process, the semi-insulating GaAs single crystal to which carbon (C) atoms are added 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, the GaAs single crystal substrate of sample 5 is obtained according to the same key points as sample 3.

[0285] (Sample 10)

[0286] In the above preparation process, the semi-insulating GaAs single crystal to which carbon (C) atoms are added 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, the GaAs single crystal substrate of sample 6 is obtained according to the same key points as sample 3.

[0287] Analysis of the Uniformity of the Main Surface of a GaAs Single Crystal Substrate

[0288] (Sample 7 and Sample 8)

[0289] Five test pieces cut from each main surface of the GaAs single crystal substrate of Sample 7 and Sample 8 were analyzed according to the same procedure as in the first experiment [Analysis of GaAs single crystal substrate using X-ray photoelectron spectroscopy]. As obtained by the XPS analysis under Conditions 1 and 3, the As 5+ The integrated intensity, As 3+ The sum of the integrated intensity of As-Ga, the integrated intensity of As-Ga and the integrated intensity of metal As relative to Ga + The integrated intensity of Ga 3+ The ratio of the sum of the integrated intensity of Ga-As and the integrated intensity of Ga-As is the seventh integrated intensity ratio (In7) and the eighth integrated intensity ratio (In8). In addition, the As obtained based on the XPS analysis under the above conditions 1 and 3 are also obtained. 5+ The integrated intensity of As 3+ The sum of the integrated intensities relative to Ga + The integrated intensity of Ga 3+ The ratio of the sum of the integrated intensities is the ninth integrated intensity ratio (In9) and the tenth integrated intensity ratio (In10).

[0290] Next, the standard deviation / average value of the eighth integrated intensity ratio (In8) is calculated from the standard deviation and average value of the eighth integrated intensity ratio (In8). The standard deviation / average value of R1 / R2 is calculated from the standard deviation and average value of the ratio R1 (In9 / In7) of the ninth integrated intensity ratio (In9) to the seventh integrated intensity ratio (In7) and the ratio R2 (In10 / In8) of the tenth integrated intensity ratio (In10) to the eighth integrated intensity ratio (In8).

[0291] The above five test pieces contain Figure 4The 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 are shown. Furthermore, five test pieces were set in a high-resolution XPS analysis device in such a manner 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 3 and 4. Table 3 shows the standard deviation and average value of In8, In8, R1 / R2, and the standard deviation and average value of R1 / R2 of the GaAs single crystal substrate of sample 7. Table 4 shows the standard deviation and average value of In8, In8, R1 / R2, and the standard deviation and average value of R1 / R2 of the GaAs single crystal substrate of sample 8. The smaller the value of the standard deviation / average value shown in Tables 3 and 4, the more uniform the characteristics of the GaAs single crystal substrate are within the plane of the main surface.

[0292] (Sample 9 and Sample 10)

[0293] Nine test pieces cut from each main surface of the GaAs single crystal substrate of Sample 9 and Sample 10 were analyzed according to the same procedure as in the first experiment [Analysis of GaAs single crystal substrate using X-ray photoelectron spectroscopy]. As obtained by the XPS analysis under Conditions 1 and 3, the As 5+ The integrated intensity, As 3+ The sum of the integrated intensity of As-Ga, the integrated intensity of As-Ga and the integrated intensity of metal As relative to Ga + The integrated intensity of Ga 3+ The ratio of the sum of the integrated intensity of Ga-As and the integrated intensity of Ga-As is the eleventh integrated intensity ratio (In11) and the twelfth integrated intensity ratio (In12). In addition, the As obtained based on the XPS analysis under the above conditions 1 and 3 are also obtained. 5+ The integrated intensity of As 3+ The sum of the integrated intensities relative to Ga + The integrated intensity of Ga 3+ The ratio of the sum of the integrated intensities is the thirteenth integrated intensity ratio (In13) and the fourteenth integrated intensity ratio (In14).

[0294] Next, the standard deviation / average value of the twelfth integrated intensity ratio (In12) is calculated from the standard deviation and average value of the twelfth integrated intensity ratio (In12). The standard deviation / average value of R3 / R4 is also calculated from the standard deviation and average value of the ratio R3 (In13 / In11) of the thirteenth integrated intensity ratio (In13) to the eleventh integrated intensity ratio (In11) and the ratio R4 (In14 / In12) of the fourteenth integrated intensity ratio (In14) to the twelfth integrated intensity ratio (In12).

[0295] The above 9 test pieces contain Figure 5 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 are shown. Furthermore, nine test pieces were placed in a high-resolution XPS analyzer so that X-rays were irradiated at 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, respectively. The results are shown in Tables 5 and 6. Table 5 shows the standard deviation and average value of In₁₂, In₁₂, R₃ / R₄, and the standard deviation and average value of R₃ / R₄ for the GaAs single crystal substrate of Sample 9. Table 6 shows the standard deviation and average value of In₁₂, In₁₂, R₃ / R₄, and the standard deviation and average value of R₃ / R₄ for the GaAs single crystal substrate of Sample 10. The smaller the value of the standard deviation / average value shown in Tables 5 and 6, the more uniform the characteristics of the GaAs single crystal substrate are within the plane of the main surface.

[0296] [Table 3]

[0297] Table 3

[0298]

[0299] [Table 4]

[0300] Table 4

[0301]

[0302] [Table 5]

[0303] Table 5

[0304]

[0305] [Table 6]

[0306] Table 6

[0307]

[0308] <Inspection>

[0309] According to Tables 3 and 4, in the GaAs single crystal substrates of Samples 7 and 8, the standard deviation / average value of In8 satisfies the relationship of standard deviation / average value ≤ 0.01, and the standard deviation and average value of R1 / R2 satisfy the relationship of standard deviation / average value ≤ 0.07. According to Tables 5 and 6, in the GaAs single crystal substrates of Samples 9 and 10, the standard deviation / average value of In12 satisfies the relationship of standard deviation / average value ≤ 0.015, and the standard deviation and average value of R3 / R4 satisfy the relationship of standard deviation / average value ≤ 0.078. In other words, it can be understood that the characteristics of the GaAs single crystal substrates of Samples 7 to 10 are sufficiently uniform within the plane of the main surface. Therefore, the mirror properties are high across the entire main surface of the GaAs single crystal substrates of Samples 7 to 10, and it is expected that an epitaxial film with a reduced haze value can be formed.

[0310] As described above, the embodiments and examples of the present invention have been described. However, it has been intended from the outset that the configurations of the above-described embodiments and examples may be appropriately combined.

[0311] The embodiments and examples disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0312] Description of Reference Numerals

[0313] 1: GaAs single crystal substrate; 1m: main surface; 10: X-ray generating device; 11: X-ray source; 12, 14: slits; 13: grating; 20: vacuum container; 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: metal As spectrum; L7: As-Ga spectrum; P1: first measuring point; P2: second measuring point; P3: third measuring point; P4: fourth measuring point; P5: fifth measuring point; P6: sixth measuring point; P7: seventh measuring point; P8: eighth measuring point; P9: ninth measuring point; A1~A9: measuring objects; S100: preparation process; S200: cleaning process; S210: surface polishing process; S220: first alkaline cleaning process; S230: acid cleaning process; S240: second alkaline cleaning process; S250: heat treatment process; S300: epitaxial film formation process.

Claims

1. A gallium arsenide single crystal substrate having a main surface, the main surface having 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, a fifth integrated intensity ratio, and a sixth integrated intensity ratio, The first integrated intensity ratio and the fourth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which the center of the main surface is irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°. The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which the center of the main surface is irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 45 degrees. The third integrated intensity ratio and the sixth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which the center of the main surface is irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 85°. The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are ratios 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 fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are ratios of the sum of the integrated intensity of arsenic element present as arsenic pentoxide and the integrated intensity of arsenic element present as arsenic trioxide to the sum of the integrated intensity of gallium element present as gallium monoxide and the integrated intensity of gallium element present as gallium trioxide. The third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.2, The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all greater than 0.9, The ratio of the first integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.9 and less than or equal to 1.3, The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all 0.7 or more and 1.1 or less.

2. The gallium arsenide single crystal substrate according to claim 1, wherein A ratio of the first integrated intensity ratio to the third integrated intensity ratio is greater than or equal to 0.95 and less than or equal to 1.

2.

3. The gallium arsenide single crystal substrate according to claim 1 or 2, wherein: The third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.

1.

4. The gallium arsenide single crystal substrate according to any one of claims 1 to 3, wherein The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all less than or equal to 1.

2.

5. The gallium arsenide single crystal substrate according to any one of claims 1 to 4, wherein The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all 0.75 or more and 1.05 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 205 mm or less.

7. The gallium arsenide single crystal substrate according to any one of claims 1 to 6, wherein The gallium arsenide single crystal substrate has a diameter of not less than 75 mm and less than 150 mm, The gallium arsenide single crystal substrate has a seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio, and a tenth integrated intensity ratio, The seventh integrated intensity ratio and the ninth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which five measurement points on the main surface are irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°. The eighth integrated intensity ratio and the tenth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which five measurement points on the main surface are irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 85°. The seventh integrated intensity ratio and the eighth integrated intensity ratio are ratios of the sum of the integrated intensity of arsenic element present as arsenic pentoxide, the integrated intensity of arsenic element present as arsenic trioxide, the integrated intensity of arsenic element present as gallium arsenide, and the integrated intensity of arsenic element present as metallic arsenic to the sum of the integrated intensity of gallium element present as gallium monoxide, the integrated intensity of gallium element present as gallium trioxide, and the integrated intensity of gallium element present as gallium arsenide. The ninth integrated intensity ratio and the tenth integrated intensity ratio are ratios of the sum of the integrated intensity of arsenic element present as arsenic pentoxide and the integrated intensity of arsenic element present as arsenic trioxide to the sum of the integrated intensity of gallium element present as gallium monoxide and the integrated intensity of gallium element present as gallium trioxide. The standard deviation and average value of the eighth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.01, and The standard deviation and average value of the ratio R1 of the ninth integrated intensity ratio to the seventh integrated intensity ratio and the ratio R2 of the tenth integrated intensity ratio to the eighth integrated intensity ratio, i.e., R1 / R2, satisfy the relationship of standard deviation / average value ≤ 0.

07. When the diameter is represented by D and two axes passing through the center of the main surface and orthogonal to each other on the main surface are defined as the X-axis and the Y-axis, the X-axis and Y-axis coordinates (X, Y) of the five measurement points 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.

8. The gallium arsenide single crystal substrate according to any one of claims 1 to 6, 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 eleventh integrated intensity ratio, a twelfth integrated intensity ratio, a thirteenth integrated intensity ratio, and a fourteenth integrated intensity ratio, The eleventh integrated intensity ratio and the thirteenth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which nine measurement points on the main surface are irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 30°. The twelfth integrated intensity ratio and the fourteenth integrated intensity ratio are obtained by determining a spectrum of the detection intensity of 3d electrons of gallium and arsenic relative to the binding energy of photoelectrons released outside the gallium arsenide single crystal substrate based on X-ray photoelectron spectroscopy in which nine measurement points on the main surface are irradiated with X-rays under conditions of an X-ray incident energy of 600 eV and a photoelectron escape angle of 85°. The eleventh integrated intensity ratio and the twelfth integrated intensity ratio are ratios of the sum of the integrated intensity of arsenic element present as arsenic pentoxide, the integrated intensity of arsenic element present as arsenic trioxide, the integrated intensity of arsenic element present as gallium arsenide, and the integrated intensity of arsenic element present as metallic arsenic to the sum of the integrated intensity of gallium element present as gallium monoxide, the integrated intensity of gallium element present as gallium trioxide, and the integrated intensity of gallium element present as gallium arsenide. The thirteenth integrated intensity ratio and the fourteenth integrated intensity ratio are ratios of the sum of the integrated intensity of arsenic element present as arsenic pentoxide and the integrated intensity of arsenic element present as arsenic trioxide to the sum of the integrated intensity of gallium element present as gallium monoxide and the integrated intensity of gallium element present as gallium trioxide. The standard deviation and average value of the twelfth integrated intensity ratio satisfy the relationship of standard deviation / average value ≤ 0.015, and The standard deviation and average value of the ratio R3 of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio and the ratio R4 of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio, i.e., R3 / R4, satisfy the relationship of standard deviation / average value ≤ 0.

078. When the diameter is represented by D and two axes passing through the center of the main surface and orthogonal to each other on the main surface are defined as the X-axis and the Y-axis, the X-axis and Y-axis coordinates (X, Y) 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.

9. The gallium arsenide single crystal substrate according to any one of claims 1 to 8, wherein The gallium arsenide single crystal substrate has an epitaxial film disposed on the main surface, The maximum haze value of the surface of the epitaxial film is 350 ppm or less, The average haze value of the surface of the epitaxial film is 2.5 ppm or less.

10. 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 with a rounded shape, and a cleaning step for obtaining the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor. The cleaning process comprises: 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 an alkaline cleaning solution, thereby making the polished surface an alkaline cleaned surface; The alkali-cleaned surface is immersed in a first acid cleaning solution containing 0.3 mass ppm or more and 0.5 mass % or less of a first acid to thereby clean the alkali-cleaned surface to become an acid-cleaned surface; a step of supplying a second acid cleaning liquid containing 0.3 mass ppm to 0.5 mass % of a second acid to the acid cleaning surface at a flow rate of 0.1 L / min to 5 L / min for 30 seconds to 5 minutes while rotating the acid cleaning surface in a circumferential direction at a rotation speed of 1000 rpm or higher, thereby cleaning the acid cleaning surface to form a second acid cleaning surface; and a step of heating the second acid-cleaned surface for 1 minute to 30 minutes in an inert gas atmosphere at atmospheric pressure and 150° C. to 300° C., thereby making the second acid-cleaned surface the main surface; The first acid contained in the first acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid, The second acid contained in the second acid cleaning solution is at least one selected from hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid.

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

12. The gallium arsenide single crystal substrate according to claim 2, wherein The third integrated intensity ratio is greater than or equal to 1.05 and less than or equal to 1.1, The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are all less than 1.2, The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are all 0.75 or more and 1.05 or less.

Images