Gallium arsenide single crystal substrate and method for its preparation

Abstract

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

Description

Technical field

[0001] The present disclosure relates to a gallium arsenide single crystal substrate and a process for its preparation. Background technology

[0002] Japanese Patent Publication No. 06-045318 (PTL 1) proposes a gallium arsenide single-crystal substrate (hereinafter also referred to as a "GaAs single-crystal substrate") with which thermal cleaning, i.e., the removal of an oxide layer, can be carried out at low temperatures in a short time. Such a GaAs single-crystal substrate can be created such that an As-rich interfacial transition layer with a thickness of 3 Å or less is artificially formed on its surface. Japanese Patent Publication No. 2008-300747 (PTL 2) proposes the provision of a GaAs wafer which is cleaned by thermally cleaning at least one surface of a GaAs single-crystal substrate to such an extent that impurities and oxides on its surface can be removed by thermal cleaning. List of oppositions patent literature PTL 1: Japanese Patent Publication No. 06-045318 PTL 2: Japanese Patent Publication No. 2008-300747 Summary of the invention

[0003] A gallium arsenide single-crystal substrate according to the present disclosure is a gallium arsenide single-crystal substrate with a major surface in a circular shape. The gallium arsenide single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio.Both the first integrated intensity ratio and the third integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°.Both the second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The fourth integrated intensity ratio is obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.Both the first integrated intensity ratio and the second integrated intensity ratio are each a ratio of the sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metal arsenic to the sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide.The third, fourth, and fifth integrated intensity ratios each correspond to the ratio of the sum of the integrated intensities of arsenic (present as diarsenic pentoxide) and arsenic (present as diarsenic trioxide) to the sum of the integrated intensities of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). The second integrated intensity ratio is 0.9 or greater and 1.05 or less. Both the third and fourth integrated intensity ratios are 1.0 or less. The fifth integrated intensity ratio is 0.8 or less. The ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or greater and 1 or less.

[0004] A process for producing a gallium arsenide single-crystal substrate according to the present disclosure is a process for producing a gallium arsenide single-crystal substrate having a major surface in a circular shape. The process comprises: preparing a gallium arsenide single-crystal substrate precursor having a circular surface; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining the substrate comprises: converting the surface of the gallium arsenide single-crystal substrate precursor to a polished surface by polishing the surface; converting the polished surface to an alkaline-cleaned surface by cleaning the polished surface with a first alkaline cleaning fluid; and converting the alkaline-cleaned surface to an acid-cleaned surface by cleaning the alkaline-cleaned surface with an acidic cleaning fluid containing 0.Containing 3 ppm by mass or more and 0.5% by mass or less of an acid; converting the acid-cleaned surface to a second alkaline-cleaned surface by cleaning the acid-cleaned surface through the application of a second alkaline cleaning fluid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more; and converting the second alkaline-cleaned surface into the main surface by performing a heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere under the conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less. The first alkaline cleaning fluid contains 0.1% by mass or more and 10% by mass or less of a first base. The first base contains at least either quaternary ammonium hydroxide and / or quaternary pyridinium hydroxide. The second alkaline cleaning fluid contains 0.3 ppm by mass or more and 0.5% by mass or less of a second base. The second base contains at least either quaternary ammonium hydroxide or quaternary pyridinium hydroxide. Brief description of the drawings Fig.Figure 1 shows an exemplary diagram illustrating the relationship between a measurement depth (horizontal axis) of a main surface of a GaAs single-crystal substrate according to the present embodiment and a ratio (vertical axis) of an integrated intensity of a total arsenic element to an integrated intensity of the total gallium element and a ratio (vertical axis) of an integrated intensity of an arsenic element present as arsenic oxide to an integrated intensity of a gallium element present as gallium oxide. Fig. Figure 2 is an explanatory diagram that schematically illustrates the setup of an analysis system using X-ray photoelectron spectroscopy (XPS). Fig.3A is an exemplary Ga3d spectrum after background correction, obtained on the basis of XPS, in which X-ray radiation was applied to the center of the main surface of the GaAs single crystal substrate according to the present embodiment. Fig. 3B is an exemplary As3d spectrum after background correction, obtained on the basis of XPS, in which X-ray radiation was applied to the center of the main surface of the GaAs single crystal substrate according to the present embodiment. Fig. Figure 4 is an explanatory diagram showing five measurement points placed on a GaAs single-crystal substrate with a diameter of 75 mm or more and 150 mm or less in the present embodiment. Fig.Figure 5 is an explanatory diagram showing nine measurement points placed on a GaAs single-crystal substrate with a diameter of 150 mm or more and 205 mm or less in the present embodiment. Fig. Figure 6 is a flowchart showing a process for producing the GaAs single crystal substrate according to the present embodiment. Detailed description [The problem to be solved by the present disclosure]

[0005] One method used to evaluate the mirror surface properties (i.e., the presence or absence of a height difference) of an epitaxial layer surface is turbidity, and it is known that an increase in turbidity correlates with a deterioration of the device properties. Turbidity refers to the amount of scattered light generated due to surface irregularities, fine defects, and foreign matter on the surface when laser light is applied to the epitaxial layer. Turbidity is expressed as the ratio of the amount of scattered light to the amount of laser light incident on the surface. It is given in ppm (parts per million). It is generally accepted that the lower the turbidity value, the better the mirror surface properties and the smaller the height difference.The height difference results, for example, from a stacking fault that arises during the growth of an epitaxial layer on a GaAs single-crystal substrate. Since the stacking fault depends on the mirror surface property of the main surface of the GaAs single-crystal substrate, it is necessary to create a GaAs single-crystal substrate with a main surface exhibiting high mirror surface property in order to reduce the haze value.

[0006] In addition to the thermal purification described above, wet etching is also a known method for producing such a GaAs single-crystal substrate with a highly reflective main surface by removing an oxide layer from the main surface. Wet etching is a method for removing the oxide layer from the main surface using a sulfuric acid-based aqueous solution containing sulfuric acid and hydrogen peroxide, or by using an NH4OH-based aqueous solution containing ammonium hydroxide and hydrogen peroxide. However, due to poor wettability, wet etching may not sufficiently remove the oxide layer.In this case, it is not possible to obtain a GaAs single-crystal substrate with a main surface having a sufficiently high mirror surface property, which makes it difficult to sufficiently reduce the turbidity value of the epitaxial layer grown on the main surface.

[0007] Against this background, the purpose of the present disclosure is to provide a gallium arsenide single-crystal substrate which improves the device properties by forming an epitaxial layer with a reduced turbidity value; and a method for producing the gallium arsenide single-crystal substrate. [Advantageous effects of the present disclosure]

[0008] According to the present disclosure, it is possible to provide a gallium arsenide single-crystal substrate that improves the device properties by forming an epitaxial layer with a reduced turbidity value; and a method for producing the gallium arsenide single-crystal substrate. [Description of the embodiments]

[0009] First, an overview of an embodiment of the present disclosure is described. To solve the problem described above, the inventors hereby prepared the present disclosure after careful investigation. They focused on obtaining a primary surface with a high mirror surface property in a gallium arsenide single-crystal substrate by carrying out a novel purification process on a circular-surface gallium arsenide single-crystal substrate precursor cut from a gallium arsenide single crystal. In addition to the known liquid-phase treatment, which includes both alkaline purification with an alkaline solution and acidic purification with an acidic solution, a second alkaline purification and a heat treatment were newly performed.As a result, the inventors have gained the following insights: the wettability of the oxide layer of the GaAs single-crystal substrate obtained by the novel purification process described above improves when the GaAs single-crystal substrate has a composition that is generally richer in gallium than in arsenic, and this tendency is also maintained at the interface between the oxide layer and the GaAs single crystal of the gallium arsenide single-crystal substrate. In this way, by wet etching, the GaAs single-crystal substrate with the main surface exhibiting high mirror surface properties can be obtained, in order to obtain a GaAs single-crystal substrate on which an epitaxial layer with a reduced turbidity value can be formed, thus completing the present disclosure.

[0010] The following are embodiments of the present disclosure listed and described. A gallium arsenide single-crystal substrate according to an embodiment of the present disclosure is a gallium arsenide single-crystal substrate having a major surface in a circular shape. The gallium arsenide single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio.The first integrated intensity ratio and the third integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°.Both the second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The fourth integrated intensity ratio is obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.Both the first and the second integrated intensity ratio are each a ratio of a sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide and an integrated intensity of an arsenic element present as metal arsenic to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide and an integrated intensity of a gallium element present as gallium arsenide.The third, fourth, and fifth integrated intensity ratios each correspond to a ratio of the sum of the integrated intensity of arsenic (present as diarsenic pentoxide) and arsenic (present as diarsenic trioxide) to the sum of the integrated intensity of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). The second integrated intensity ratio is 0.9 or greater and 1.05 or less. Both the third and fourth integrated intensity ratios are 1.0 or less. The fifth integrated intensity ratio is 0.8 or less. The ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or greater and 1 or less.

[0011] The gallium arsenide single crystal substrate with such a property has a main surface with a high mirror surface property, since the oxide layer can be effectively removed by wet etching, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0012] [2] The second integrated intensity ratio is preferably 0.9 or more and less than 1.04. This makes it possible to remove the oxide layer more effectively by wet etching.

[0013] [3] The gallium arsenide single-crystal substrate preferably has an oxide layer with a thickness of 2 nm or less on the main surface. This makes it easier to remove the oxide layer by wet etching.

[0014] [4] The contact angle of the oxide layer is preferably 20° or less. This allows the oxide layer to be removed more effectively by wet casting with excellent wettability.

[0015] [5] The gallium arsenide single-crystal substrate preferably has a diameter of 75 mm or more and 205 mm or less. Thus, the gallium arsenide single-crystal substrate with a diameter of 75 mm or more and 205 mm or less can be provided with a main surface having a high mirror surface property, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0016] [6] The gallium arsenide single-crystal substrate preferably has the following feature: The gallium arsenide single-crystal substrate has a diameter of 75 mm or more and less than 150 mm. The gallium arsenide single-crystal substrate has a sixth integrated intensity ratio and a seventh integrated intensity ratio. Both the sixth integrated intensity ratio and the seventh integrated intensity ratio are each obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-rays are applied to each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The sixth integrated intensity ratio is a ratio of a sum of an integrated intensity of the arsenic element present as diarsene pentoxide, an integrated intensity of the arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide and an integrated intensity of the arsenic element present as metal arsenic to a sum of an integrated intensity of the gallium element present as digallium monoxide, an integrated intensity of the gallium element present as digallium trioxide and an integrated intensity of the gallium element present as gallium arsenide.The seventh integrated intensity ratio is the ratio of the sum of the integrated intensity of arsenic (present as diarsene pentoxide) and arsenic (present as diarsene trioxide) to the sum of the integrated intensity of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). A standard deviation and a mean value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio satisfy a relationship where standard deviation / mean value ≤ 0.039.If the diameter is specified by D, and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as an X-axis and a Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4), respectively. The units of D and of both X and Y in the coordinates (X, Y) are mm. Since the oxide layer in the gallium arsenide single-crystal substrate with a diameter of 75 mm or more and less than 150 mm is effectively removed using wet processes, it is therefore possible to obtain a main surface with high mirror surface properties and no in-plane variations, allowing the formation of an epitaxial layer with reduced haze on it.

[0017] [7] The gallium arsenide single-crystal substrate preferably has the following feature. The gallium arsenide single-crystal substrate has a diameter of 150 mm or more and 205 mm or less. The gallium arsenide single-crystal substrate has an eighth integrated intensity ratio and a ninth integrated intensity ratio. Both the eighth integrated intensity ratio and the ninth integrated intensity ratio are each obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy, in which X-rays are applied to each of the nine measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The eighth integrated intensity ratio is a ratio of the sum of an integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide, and an integrated intensity of the arsenic element present as metal arsenic to the sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of the gallium element present as digallium trioxide, and an integrated intensity of the gallium element present as gallium arsenide.The ninth integrated intensity ratio is the ratio of the sum of the integrated intensity of arsenic (present as diarsene pentoxide) and arsenic (present as diarsene trioxide) to the sum of the integrated intensity of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). A standard deviation and a mean value of a ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy a relationship where standard deviation / mean value ≤ 0.022.If the diameter is specified by D and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as an X-axis and a Y-axis, the coordinates (X, Y) of the nine measurement points on the X-axis and Y-axis 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)), respectively. The units of D and of both X and Y in the coordinates (X, Y) are mm. Since the oxide layer in the gallium arsenide single-crystal substrate with a diameter of 150 mm or more and 205 mm or less is effectively removed using wet processes, it is therefore possible to obtain a main surface with high To obtain a mirror surface property without fluctuations in the plane, thereby allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0018] [8] Preferably, the gallium arsenide single-crystal substrate has an epitaxial layer on the main surface, wherein the maximum turbidity value of the surface of the epitaxial layer is 100 ppm or less and the average turbidity value of the surface of the epitaxial layer is 2.5 ppm or less. Thus, it is possible to provide a gallium arsenide single-crystal substrate with a main surface on which the epitaxial layer with a reduced turbidity value is formed.

[0019] [9] A process for producing a gallium arsenide single-crystal substrate according to one embodiment of the present disclosure is a process for producing a gallium arsenide single-crystal substrate having a major circular surface. The process comprises: preparing a gallium arsenide single-crystal substrate precursor having a circular surface; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining the substrate comprises: converting the surface of the gallium arsenide single-crystal substrate precursor to a polished surface by polishing the surface; converting the polished surface to an alkaline-cleaned surface by cleaning the polished surface with a first alkaline cleaning fluid; and converting the alkaline-cleaned surface to an acid-cleaned surface by cleaning the alkaline-cleaned surface with anacidic cleaning fluid containing 0.3 ppm or more and 0.5 percent or less by mass of an acid; converting the acid-cleaned surface to a second alkaline-cleaned surface by cleaning the acid-cleaned surface through the application of a second alkaline cleaning fluid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more; and converting the second alkaline-cleaned surface into the main surface by performing a heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less. The first alkaline cleaning fluid contains0.1 wt% or more and 10 wt% or less of a first base. The first base contains at least one quaternary ammonium hydroxide and / or one quaternary pyridinium hydroxide. The second alkaline cleaning fluid contains 0.3 wt% or more and 0.5 wt% or less of a second base. The second base contains at least either the quaternary ammonium hydroxide or the quaternary pyridinium hydroxide. A gallium arsenide single-crystal substrate with a major surface exhibiting high mirror surface properties can be obtained by the process for preparing a gallium arsenide single-crystal substrate with such properties.

[0020]

[10] Preferably, the method comprises forming an epitaxial layer on the main surface. This allows an epitaxial layer with a reduced turbidity value to be formed on the main surface. [Details of embodiments]

[0021] In the following, an embodiment (hereinafter also referred to as "the present embodiment") according to the present disclosure is described in more detail, although the present disclosure is not limited to it. Although the explanation in the description is given with reference to figures, identical or corresponding elements in the present description and the figures are designated by the same reference numerals, and the same explanation is therefore not repeated. In addition, in each of the figures, the scale of the individual components has been adjusted for better understanding, and the scale of the elements shown in each of the figures does not necessarily correspond to the actual scale.

[0022] In the present description, the expression "A to B" represents a range of lower to upper limits (i.e., A or more and B or less), and if no unit is specified for A but only for B, then the unit of A is the same as the unit of B. Furthermore, if a compound or the like is expressed in the present description by a chemical formula and the atomic ratio is not subject to any particular restriction, then it is assumed that all generally known atomic ratios are included and that the atomic ratio is not necessarily restricted to a ratio within the stoichiometric range.

[0023] In this description, the term "main surface" of a gallium arsenide single-crystal substrate refers to each of the two circular surfaces of the substrate. If at least one of the two surfaces satisfies the scope of protection of the claims with respect to the present disclosure of the gallium arsenide single-crystal substrate, then the gallium arsenide single-crystal substrate falls within the scope of the present invention. An epitaxial layer may be deposited on the "main surface" of the gallium arsenide single-crystal substrate. In this description, the term "plane" used in connection with the expression "in the plane" means the "main surface". If the diameter of the gallium arsenide single-crystal substrate is "75 mm", this means that the diameter is approximately 75 mm (approximately 75 to 76.5 mm), or 3 inches. When the diameter is described as "100 mm", this means a diameter of approximately 100 mm (approx. 95-105 mm) or 4 inches.When a diameter is described as "150 mm," this means a diameter of approximately 150 mm (about 145 to 155 mm) or 6 inches. When a diameter is described as "200 mm," this means a diameter of approximately 200 mm (about 195 to 205 mm) or 8 inches. It should be noted that the diameter can be measured using a conventional outside diameter measuring device, such as a caliper.

[0024] With regard to the crystallographic information in this description, an individual orientation is represented by [], a group orientation by <>, an individual plane by (), and a group plane by {}. A negative crystallographic index is usually expressed by a '-' (line) over a number. However, in this description, a negative sign is placed before the number when specified in the description. [Gallium arsenide single crystal substrate]

[0025] The gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is a GaAs single-crystal substrate with a circular main surface. The GaAs single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio.Both the first integrated intensity ratio and the third integrated intensity ratio are obtained by determining the spectra of the detection intensities of 3d electrons of gallium (Ga) and arsenic (As) with respect to the binding energy of a photoelectron emitted externally onto the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°.Both the second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted externally onto the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The fourth integrated intensity ratio is obtained by determining each of the spectra of the detection intensities of 3 electrons of Ga and As with respect to the binding energy of a photoelectron emitted externally onto the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.

[0026] Both the first integrated intensity ratio and the second integrated intensity ratio are each a ratio of a sum of an integrated intensity of an As element present as diarsene pentoxide (As2O5) (hereinafter referred to simply as "As"). s+“designated), an integrated intensity of an As element present as diarsenic trioxide (As2O3) (hereinafter also referred to as “A” for the sake of simplicity S 3+ “ denoted), an integrated intensity of an As element present as gallium arsenide (GaAs) (hereinafter also referred to as “As-Ga” for simplicity), and an integrated intensity of an As element present as metal arsenic (metal-As) (hereinafter also referred to as “metal-As” for simplicity) to a sum of an integrated intensity of a Ga element present as digallium monoxide (Ga2O) (hereinafter also referred to as “Ga” for simplicity). + “designated), an integrated intensity of a Ga element present as digallium trioxide (Ga2O3) (hereinafter also referred to as “Ga” for simplicity) 3+“ denoted) and an integrated intensity of a Ga element present as gallium arsenide (GaAs) (hereinafter also referred to as “Ga-As” for the sake of simplicity). The third, fourth, and fifth integrated intensity ratios are each a ratio of the sum of an integrated intensity of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ) to a sum of an integrated intensity of the Ga element present as Ga2O (Ga + ) and an integrated intensity of the Ga element present as Ga2O3 (Ga 3 +In the GaAs single-crystal substrate, the second integrated intensity ratio is 0.9 or greater and 1.05 or less. Both the third and fourth integrated intensity ratios are 1.0 or less. The fifth integrated intensity ratio is 0.8 or less. The ratio of the first integrated intensity ratio to the second integrated intensity ratio remains 0.5 or greater and 1 or less.

[0027] By effectively removing an oxide layer using wet etching, the GaAs single-crystal substrate can exhibit a primary surface with high mirror-like properties. This allows for the formation of an epitaxial layer with reduced turbidity. <Hauptoberfläche>

[0028] The GaAs single-crystal substrate has the circular primary surface described above. In this description, the “circular shape” representing the primary surface includes not only a geometric circle but also a shape where the primary surface is not geometrically circular due to the formation of at least one notch, orientation surface (hereinafter also referred to as “OF”), or index surface (hereinafter also referred to as “IF”). That is to say, the “shape where the primary surface is not geometrically circular” refers to a shape where the length of a line segment extending from any point on the notch, orientation surface, or index surface to the center of the primary surface is short compared to the line segments extending from any point on the outer circumference of the primary surface to the center of the primary surface.In other words, in the present description, the main surface is referred to as a "circular shape" based on its shape before the formation of the notch, orientation surface, and index surface. Therefore, the position of the main surface's center and the size (length) of the substrate's diameter are determined based on the circular shape before the formation of the notch, orientation surface, index surface, etc. It should be noted that the "shape where the main surface is not geometrically circular" also includes a shape where the lengths of all line segments extending from any point on the outer circumference of the main surface to its center are not necessarily equal due to the shape of the GaAs single crystal before it is cut out as a GaAs single-crystal substrate.In this case, the center of the main surface refers to the position of the center of gravity, and the diameter of the substrate refers to the length of the longest line segment among the line segments that each run from a point on the outer circumference of the substrate, through the center of the main surface, to another point on the outer circumference of the substrate. < X-ray photoelectron spectroscopy (XPS) using synchrotron radiation>

[0029] In developing a GaAs single-crystal substrate on which an epitaxial layer with reduced turbidity can be formed, the inventors investigated X-ray photoelectron spectroscopy (XPS) using synchrotron radiation, which allows for highly precise analysis of the condition of the main surface of the GaAs single-crystal substrate. Specifically, the synchrotron XPS was performed to identify and eliminate the cause of the deterioration of the mirror surface properties of the main surface of the GaAs single-crystal substrate, in order to obtain a GaAs single-crystal substrate on which an epitaxial layer with reduced turbidity can be formed.XPS refers here to an analytical method in which a sample is irradiated with X-rays and the kinetic energy distribution of the photoelectrons emitted by the sample is measured in order to gain insights into the type, abundance, chemical bonding states and similar properties of the elements present on the surface of the sample.

[0030] When the main surface of a GaAs single-crystal substrate is analyzed by XPS, XRP is typically used with X-rays with a fixed energy of approximately 1.487 keV. However, using X-rays with a fixed incidence energy of approximately 1.487 keV and a photoelectron exit angle of 30° yields the state of the main surface of the GaAs single-crystal substrate as an average state over a region extending from the main surface to a depth of approximately 5 nm. This region corresponds to about 20 atomic layers. Therefore, it is difficult to analyze the state of the main surface of the GaAs single-crystal substrate with high precision using XPS.If the X-ray beam is used with a fixed incidence energy of about 1.487 keV and the photoelectron exit angle is changed in the XPS analysis to gain insights into the state of the main surface of the GaAs single crystal substrate, the measurement error with respect to the angle becomes too large, and a measurement error also becomes large due to the low ionization efficiency of the photoelectron intensity, which makes a highly precise analysis difficult.

[0031] In contrast, in the present disclosure the state of the main surface of the GaAs single crystal substrate can be analyzed, since XPS is carried out under the condition that the X-ray beam with an X-ray incident energy of 600 eV is used and the photoelectron exit angle is set to 30°, 45° or 85° as described above.

[0032] When XPS is performed under X-ray incident energy of 600 eV and a photoelectron exit angle of 30°, information about the state of the main surface of the GaAs single-crystal substrate can be obtained as an average state in a region from the main surface to a depth of approximately 2.25 nm. When XPS is performed under X-ray incident energy of 600 eV and a photoelectron exit angle of 45°, information about the state of the main surface of the GaAs single-crystal substrate can be obtained as an average state in a region from the main surface to a depth of approximately 3.18 nm.When the X-ray incident energy is set to 600 eV and the photoelectron exit angle to 85° as the conditions for conducting XPS, insights into the state of the main surface of the GaAs single-crystal substrate can be obtained as an average state in a region from the main surface to a depth of approximately 4.48 nm. This means that the region from the main surface of the GaAs single-crystal substrate to a depth of approximately 5 nm (corresponding to about 20 atomic layers) can be analyzed in detail for about every third atomic layer, resulting in a more precise analysis of the main surface state than is possible with prior art methods.

[0033] It is known that after purification in a cleaning step, an oxide layer approximately 1 to 2 nm thick forms on the main surface of the GaAs single-crystal substrate. Therefore, attempts were made to form an epitaxial layer on the main surface after removing the oxide by wet etching in order to reduce the haze value of the epitaxial layer's surface. However, even after wet etching, some of the oxide layer remains on the main surface, resulting in a partially high haze value of the epitaxial layer's surface. To solve this problem, the inventors have optimized the environment around an interface (i.e.,The area at a depth of approximately 2 to 5 nm from the main surface of the GaAs single-crystal substrate between the oxide layer occupying the upper surface of the main surface of the GaAs single-crystal substrate and a layer (hereinafter also referred to as the "main layer" of the GaAs single-crystal substrate) of gallium (Ga) and arsenic (As) located directly beneath the oxide layer was analyzed in detail using synchrotron radiation as described above using XPS. The inventors obtained the following findings: The wettability of the oxide layer is excellent when the GaAs single-crystal substrate has a composition that is richer overall in gallium than in arsenic, and this tendency persists at the interface between the oxide layer and the GaAs single-crystal substrate, with the result that the oxide layer can be effectively removed by wet etching.The inventors therefore devised a method to appropriately control the gallium composition of the oxide layer to obtain a primary surface with a high mirror-like surface property. It should be noted that in this description, "surface" of the oxide layer refers to the surface of the oxide layer facing the side of the GaAs single-crystal substrate. <Erstes integriertes Intensitätsverhältnis, Zweites integriertes Intensitätsverhältnis, Drittes integriertes Intensitätsverhältnis, Viertes integriertes Intensitätsverhältnis und Fünftes integriertes Intensitätsverhältnis>

[0034] The GaAs single-crystal substrate according to the present embodiment has the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, and the fifth integrated intensity ratio. Both the first integrated intensity ratio and the third integrated intensity ratio are obtained by determining the detection intensities of 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted externally onto the GaAs single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-rays are applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°.Both the second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining the spectra of the detection intensities of 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted externally onto the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The fourth integrated intensity ratio is obtained by determining each of the spectra of the detection intensities of 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted externally onto the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.

[0035] Both the first integrated intensity ratio and the second integrated intensity ratio are each the ratio of the sum of the integrated intensities of the As element present as As2O5 (As 5+ ), the integrated intensity of the As element present as As2O3 (As 3+), the integrated intensity of the As element present as GaAs (As-Ga) and the integrated intensity of the As element present as metal As (Metal As) to the sum of the integrated intensity of the Ga element present as Ga2O (Ga + ), the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ) and the integrated intensity of the Ga element present as GaAs (Ga-As). The third, fourth, and fifth integrated intensity ratios are each the ratio of the sum of the integrated intensities of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ) to the sum of an integrated intensity of the Ga element present as Ga2O (Ga + ) and an integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ).

[0036] If the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio and the fifth integrated intensity ratio are each expressed by In1, In2, In3, In4 and In5, then In1, In2, In3, In4 and In5 can each be represented by the following mathematical formulas. In1=I(As2O5)+I(As2O3)+I(As_Ga)+I(As)I(Ga2O)+I(Ga2O3)+I(Ga_As)In2=I(As2O5)+I(As2O3)+I(As_Ga)+I(As)I(Ga2O)+I(Ga2O3)+I( Ga_As)In3=I(As2O5)+I(As2O3)I(Ga2O)+I(Ga2O3)In4=I(As2O5)+I(As2O3)I(Ga2O)+I(Ga2O3)In5=I(As2O5)+I(As2O3)I(Ga2O)+I(Ga2O3)

[0037] In the GaAs single-crystal substrate, the second integrated intensity ratio is 0.9 or more and 1.05 or less. Both the third and fourth integrated intensity ratios are 1.0 or less. The fifth integrated intensity ratio is 0.8 or less. The ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or more and 1 or less. The second integrated intensity ratio is preferably 0.9 or more and less than 1.04.

[0038] Fig.Figure 1 shows an exemplary diagram illustrating the relationship between the measurement depth (horizontal axis) from the main surface of the GaAs single-crystal substrate according to the present embodiment and each ratio (vertical axis) of the integrated intensity of the total arsenic element to the integrated intensity of the total gallium element, as well as the ratio (vertical axis) of the integrated intensity of the arsenic element present as arsenic oxide to the integrated intensity of the gallium element present as gallium oxide. Fig.A point marked by a circle around a measurement depth (horizontal axis) of approximately 2.25 nm corresponds to the first integrated intensity ratio; a point marked by a circle around a measurement depth (horizontal axis) of approximately 4.48 nm corresponds to the second integrated intensity ratio; a point marked by a rectangle around a measurement depth (horizontal axis) of approximately 2.25 nm corresponds to the third integrated intensity ratio; a point marked by a rectangle around a measurement depth (horizontal axis) of approximately 3.18 nm corresponds to the fourth integrated intensity ratio; and a point marked by a rectangle around a measurement depth (horizontal axis) of approximately 4.48 nm corresponds to the fifth integrated intensity ratio.

[0039] In the Fig.The first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, and the fifth integrated intensity ratio are 0.99, 1.01, 0.9, 0.83, and 0.76, respectively. Furthermore, the ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.98 (= 0.99 / 1.01).

[0040] Such a ratio means achieving a composition such that the oxide layer, from the main surface to a depth of about 1 to 2 nm, is overall richer in gallium than arsenic, and this tendency is maintained up to the interface (about 2 to 5 nm from the main surface) between the main layer and the oxide layer. Specifically, if the second integrated intensity ratio is 0.9 or greater and 1.05 or less, this means that the oxide layer thickness is the desired thickness and is not greater than the desired thickness. If the third and fourth integrated intensity ratios are each 1.0 or less, this means that the oxide layer is overall richer in gallium than arsenic.If the fifth integrated intensity ratio is 0.8 or less, and the ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or more or 1 or less, respectively, this indicates that the composition at the interface between the main layer and the oxide layer changes significantly, and the composition in which the oxide layer is richer in gallium than in arsenic is maintained near the interface. In this case, the oxide layer is assumed to be effectively removed by wet etching due to its excellent wettability.Therefore, if, according to the present embodiment, an epitaxial layer is grown on the main surface of the GaAs single-crystal substrate after wet settling, both the maximum and average values ​​of the surface haze of the epitaxial layer can be lower than in the prior art (for example, the maximum value of the surface haze of the epitaxial layer can be 100 ppm or less and the average value of the haze 2.5 ppm or less). In this description, the “surface” of the epitaxial layer refers to a surface of the epitaxial layer facing the side of the GaAs single-crystal substrate.

[0041] However, if the first, second, third, fourth, and fifth integrated intensity ratios are obtained by performing XPS on a conventional GaAs single-crystal substrate, one of the following ratios is not satisfied: the second integrated intensity ratio does not meet the condition of 0.9 or more and 1.05 or less; neither the third nor the fourth integrated intensity ratio meets the condition of 1.0 or less; the fifth integrated intensity ratio does not meet the condition of 0.8 or less; or the ratio of the first integrated intensity ratio to the second integrated intensity ratio does not meet the condition of 0.5 or more and 1 or less.With such a GaAs single-crystal substrate, even after wet settling, part of the oxide layer can remain on the main surface. If an epitaxial layer forms on the main surface of the GaAs single-crystal substrate after wet settling, a height difference in the surface arises, which can lead to high maximum and average turbidity values.

[0042] As described above, the inventors first determined that the turbidity of the surface of the epitaxial layer formed on the main surface of the GaAs single-crystal substrate depends on the ratio of gallium to arsenic and the ratio of gallium oxide to arsenic oxide in both the oxide layer (area from the main surface to a depth of about 1 to 2 nm) and the vicinity of the interface (area at a depth of 2 to 5 nm from the main surface) between the oxide layer and the main layer. <oxidschicht>

[0043] The GaAs single-crystal substrate preferably has an oxide layer with a thickness of 2 nm or less on the main surface. This allows for more effective removal of the oxide layer by wet etching. The thickness of the oxide layer is preferably 1.5 nm or less. The lower limit of the oxide layer thickness is not subject to any particular restriction, but is, for example, 0.5 nm.

[0044] The thickness of the oxide layer can be determined by analyzing the main surface of the GaAs single-crystal substrate using a scanning transmission electron microscope (STEM; e.g., trade name (product number): "JEM-ARM300F2" from JEOL) in combination with an energy-dispersive X-ray spectrometer (EDX). By applying an electron beam to the center of the main surface of the GaAs single-crystal substrate under an accelerating voltage of 200 kV, the element-specific X-ray beam generated at the center of the main surface is split and detected by EDX, thus performing a composition analysis. By conducting a line analysis along the depth direction of the main surface, the composition is determined according to the respective analysis depth from the surface of the main surface.

[0045] The thickness of the oxide layer can be determined from the composition analysis described above as follows. First, the difference between the As content and the Ga content is determined along each analysis depth from the surface of the main layer, and a spectrum is plotted graphically, with the horizontal axis representing the analysis depth and the vertical axis representing the difference. Since the spectrum has a peaked shape similar to a Gaussian distribution, the full width at half maximum (FWHM) of this shape is determined and can be considered the thickness of the oxide layer. As described above, the GaAs single-crystal substrate according to the present embodiment has a composition that is rich in gallium (especially gallium oxide) both in the oxide layer and near the interface (region up to a depth of 1 to 5 nm from the main surface) between the oxide layer and the main layer.From the difference between the As content and the Ga content along the analysis depth from the surface of the main surface, the thickness of the oxide layer can therefore be determined based on the spectrum that indicates the difference. <Benetzbarkeit (Kontaktwinkel)>

[0046] The contact angle of the oxide layer is preferably 20° or less. This gives the oxide layer excellent wettability and allows for more effective removal by wet etching. The contact angle of the oxide layer is preferably 10° or less. The lower limit of the contact angle of the oxide layer is not subject to any particular restriction, but is, for example, 1°.

[0047] The contact angle of the oxide layer can be determined as follows: 2 µl of distilled water are dropped onto the center of the main surface (the surface of the oxide layer) at room temperature (20 to 25 °C) in an environment with a relative humidity of 40 to 60%. The contact angle of a drop of distilled water forming in the center of the main surface is then measured using the θ / 2 method. A contact angle measuring device (e.g., trade name (product number): "Drop Master 500" from Kyowa Interface Science) can be used to observe the drop. <durchmesser>

[0048] The 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 GaAs single-crystal substrate is preferably 3 to 8 inches. Thus, with a GaAs single-crystal substrate having a diameter of 75 mm or more and 205 mm or less, the main surface can be obtained with high mirror surface properties by effectively removing the oxide layer using wet casting. Even if the substrate has a shape other than a geometric circle due to the influence of OF, IF, or the like, the size (diameter) of the substrate is determined under the assumption that the substrate has a circular shape before the formation of OF, IF, or the like. The GaAs single-crystal substrate preferably has a diameter of 100 mm or more and 205 mm or less, and more preferably a diameter of 150 mm or more and 205 mm or less. <Verfahren zur Analyse des GaAs-Einkristall-Substrats mittels Röntgen-Photoelektronenspektroskopie (XPS) unter Verwendung von Synchrotronstrahlung>

[0049] The following section explains in more detail the method for analyzing the GaAs single crystal substrate using XPS with synchrotron radiation. (Analysis system)

[0050] The Fig. Figure 2 is an explanatory diagram that schematically illustrates the setup of an analysis system using X-ray photoelectron spectroscopy. As shown in the Fig. As shown in Figure 2, an analysis system 100 comprises an X-ray generator 10, a vacuum chamber 20, and an electron spectrometer 30. The X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 are coupled to each other in this order. The interior of the X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 is each maintained under ultra-high vacuum. The pressure inside the X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 is, for example, 4 × 10⁻⁶. -7 Pa.

[0051] The X-ray generation unit 10 generates X-rays, which are referred to as synchrotron radiation. For example, the beamline “BL17” of the SAGA Light Source can be used as the X-ray generation unit 10.

[0052] The X-ray generation device 10 can generate X-rays with any energy in the range of 50 to 2000 eV in the “BL17” to apply the X-ray beam to a GaAs single-crystal substrate 1 placed in the vacuum chamber 20. Fig. The X-ray generating device 10 shown in Figure 2 has an X-ray source 11, slots 12, 14 and a grating 13. The slots 12 and 14 are located upstream and downstream, respectively, with respect to the grating (spectrometer) 13. Each of the slots 12 and 14 is, for example, a four-quadrant slot.

[0053] By deflecting the direction of propagation of high-energy electrons by means of a magnetic field generated by a deflection electromagnet in a circular accelerator, the X-ray source 11 emits synchrotron radiation (X-rays) that is emitted tangentially to the direction of propagation.

[0054] The X-ray beam emitted by X-ray source 11 has a high luminance. In particular, the number of photons of the X-ray beam emitted by X-ray source 11 per second is 10 9 Photons / s. However, the luminance (intensity) of the X-ray beam emitted by the X-ray source 11 decreases over time. For example, the luminance of the X-ray beam emitted 11 hours after activation of the X-ray source 11 is one-third of the luminance of the X-ray beam emitted immediately after activation.

[0055] The X-ray beam emitted by the X-ray source 11 is collimated by a collimating mirror (not shown) or the like. The slot 12 allows a portion of the collimated X-ray beam to pass through. The X-ray beam passing through the slot 12 is monochromatized by the grating 13. The slot 14 limits the width of the monochromatized X-ray beam.

[0056] The energy of the X-ray beam emitted by the X-ray beam generator 10 is determined by the slot widths of slots 12 and 14 and the line density of the grating 13. For example, the 600 eV X-ray beam is emitted by the X-ray beam generator 10 by setting an emission angle in the grating using grating 13, in which the slot width of each of slots 12 and 14 is 30 µm and the line density in the center is 400 I / mm.

[0057] When the X-ray beam of the X-ray generating device 10 is applied to the GaAs single crystal substrate 1 placed in the vacuum container 20, photoelectrons are emitted from the GaAs single crystal substrate 1.

[0058] An electron spectrometer 30 measures the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate 1. The electron spectrometer 30 has a hemispherical analyzer and a detector. The hemispherical analyzer separates the photoelectrons. The detector counts the number of photoelectrons of each energy.

[0059] The angle θ1, formed by the propagation direction of the X-ray beam 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. Likewise, the angle (hereinafter referred to as the "exit angle θ2") formed by the propagation direction of the photoelectrons detected by the electron spectrometer 30 between the photoelectrons emitted by the GaAs single-crystal substrate 1 and the main surface 1m of the GaAs single-crystal substrate 1 is variable. In the present embodiment, the exit angle θ2 is set to 30°, 45°, or 85°. The angle θ1 is not subject to any particular restriction but is, for example, 85°.

[0060] For example, a high-resolution XPS analyzer “R3000” from Scienta Omicron can be used as an electron spectrometer 30. (Depth from the main surface for analysis)

[0061] Some of the photoelectrons emitted outwards from the GaAs single-crystal substrate 1 in response to the X-ray beam lose energy due to inelastic scattering. Therefore, only a portion of the photoelectrons generated in the GaAs single-crystal substrate 1 escape into the vacuum, retaining the same energy as during generation, and reach the electron spectrometer 30. The photoelectrons emerging from the surface are generated at a depth approximately three times the inelastic mean free path (IMFP) of the photoelectrons. The depth d (nm) from the main surface of the GaAs single-crystal substrate for analysis is thus expressed by the following mathematical formula: In the following mathematical formula, λ (nm) represents the IMFP value and θ2 represents the exit angle. d=3λ sin θ2

[0062] As described in “Method of Estimating Inelastic Mean Free Path of Electrons by Tpp-2M Formula”, Journal of Surface Analysis, Vol. 1, No. 2, 1995, λ (Å) is represented by the following mathematical formulas. λ=EEp2[β ln(γE)−C / E+D / E2]Ep=28.8(NvρAw)1 / 2β=−0.10+0.944(Ep2+Eg2)12+0, 069ρ0.1γ=0.191ρ−0.50C=1.97−0.94UD=53.4−20.8UU=NvρAw=Ep2829.4

[0063] In each of the mathematical formulas above, A W for the atomic weight or molecular weight, N v stands for the number of valence electrons per atom or molecule, E p represents the plasmon energy (eV) of free electrons, ρ represents the density (g / cm³). 3 ) and E g E stands for the band gap energy (eV). E stands for the kinetic energy (eV) of the photoelectrons and is calculated from the energy (eV) of the applied X-ray beam and the binding energy (eV) between electron and atomic nucleus.

[0064] The depth d (nm) from the main surface of the GaAs single-crystal substrate for analysis can be determined using the mathematical formulas above. Specifically, the depth d (nm) from the main surface of the GaAs single-crystal substrate is calculated using each of the above mathematical formulas, various parameter values ​​for the 3d electrons of the Ga and As elements, and the X-ray energy (600 eV). The depth d (nm) is obtained as follows: At an X-ray incidence energy of 600 eV and a photoelectron emission angle of 30°, the depth d is approximately 2.25 nm. At an X-ray incidence energy of 600 eV and a photoelectron emission angle of 45°, the depth d is approximately 3.18 nm. At an X-ray incidence energy of 600 eV and a photoelectron emission angle of 85°, the depth d is approximately 4.48 nm.

[0065] (Method for calculating the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio and the fifth integrated intensity ratio.

[0066] Regarding the method for calculating the first, second, third, fourth, and fifth integrated intensity ratios at the main surface based on the XPS described above, an exemplary method for calculating the first and third integrated intensity ratios is described below. In this case, the XPS is performed using X-rays with an energy of 600 eV at the center of the main surface of the GaAs single-crystal substrate. The photoelectron emission angle is 30°. This yields the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate.

[0067] The kinetic energy E of the photoelectrons emitted from the GaAs single-crystal substrate is calculated using the energy hv (eV) of the applied X-ray beam and the binding energy E. B The electron density (eV) of the GaAs single-crystal substrate and a work function φ (eV) are expressed by the following mathematical formula: E = hv - E B -φ.

[0068] From the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate, a spectrum is generated using the mathematical formula above, which indicates the binding energy distribution of the photoelectrons. In the present embodiment, a Ga3d spectrum and an As3d spectrum, each indicating the binding energy distribution of the photoelectrons, are generated based on the kinetic energy distribution of the photoelectrons emitted from the position at depth d (nm) from the main surface of the GaAs single-crystal substrate. In this description, the “Ga3d spectrum” refers to a spectrum representing the detection intensity of each photoelectron emitted from the 3d orbital of the Ga element (Ga2O, Ga2O3, and the Ga contained in GaAs).The “As3d spectrum” refers to a spectrum that represents the detection intensity of each photoelectron emitted from the 3d orbital of the As element (As2O5, As2O3, metallic As and As contained in GaAs).

[0069] In XPS analysis, both the Ga3d and As3d spectra are obtained for precise measurement through close sampling within a predefined binding energy range. Close sampling within a binding energy range of 16 to 26 eV allows the Ga3d spectrum to be plotted in a graph, with the horizontal axis representing the range and the vertical axis the detection intensity. Similarly, close sampling within a binding energy range of 39 to 49 eV allows the As3d spectrum to be plotted in a graph, with the horizontal axis representing the range and the vertical axis the detection intensity.

[0070] Close sampling is performed under the conditions that the energy interval is 0.05 eV, the integration time for each energy value is 100 ms, and the number of integrations is one or more. Furthermore, the energy resolution E / ΔE is 3480.

[0071] In this way, a Ga3d spectrum LG (in the Fig. 3A shown) and an As3d spectrum LA (in the Fig. 3B) will be obtained. Fig. Figure 3A is an exemplary Ga3d spectrum after background correction, obtained on the basis of XPS, in which the center of the main surface of the GaAs single-crystal substrate was irradiated with X-rays according to the present embodiment. Fig. Figure 3B is an exemplary As3d spectrum after background correction, obtained based on the XPS in which the center of the main surface of the GaAs single-crystal substrate was irradiated with X-rays according to the present embodiment. As described above, the Fig. 3A and the Fig. Figure 3B shows the exemplary Ga3d spectrum and the As3d spectrum after background correction. This means that when obtaining the Ga3d spectrum LG and the As3d spectrum LA, a background correction is performed using the Shirley method (reference document: Kazuhiro Yoshihara: "Journal of the Vacuum Society of Japan", 2013, Vol. 56, No. 6, pp. 243-247). Thus, the Ga3d spectrum LG after background correction can be determined based on the difference between the Ga3d spectrum obtained from the actual measurement and the background. Furthermore, the As3d spectrum LA after background correction can be determined based on the difference between the measured As3d obtained from the actual measurement and the background.

[0072] When obtaining the Ga3d spectrum LG, the peak of the detection intensity of the Ga element present as Ga2O (Ga) is + ) fixed at a position corresponding to a binding energy of 19.9 eV and the peak position of the detection intensity of the Ga element present as Ga2O3 (Ga 3+ The peak of the detection intensity of the GaAs element (Ga-As) is fixed at a position corresponding to a binding energy of 20.7 eV. This peak corresponds to a binding energy of approximately 19.2 to 19.7 eV and thus has a width. This is because, during X-ray photoelectron spectroscopy of the GaAs single crystal, a charge shift can occur, shifting the Ga3d spectrum at its maximum by about 1 eV towards the higher energy. Since the peak of the Ga-As detection intensity is also influenced by the GaAs main layer, it is difficult to fix the peak at a single value, and therefore, as described above, the peak is fixed to a width of 0.5 eV.

[0073] When obtaining the As3d spectrum LA, the peak of the detection intensity of the As element present as As2O5 (As) 5+ ) fixed at a position corresponding to a binding energy of 45.57 eV and the peak of the detection intensity of the As element present as As2O3 (As 3+ The peak detection intensity of the As element present as metal As (Metal As) is fixed at a position corresponding to a binding energy of approximately 44.07 eV. The peak detection intensity of the As element present as GaAs (As-Ga) is fixed at a position corresponding to a binding energy of approximately 41.62 to 42.12 eV, resulting in a broad detection range. The peak detection intensity of the As element present as GaAs (As-Ga) is fixed at a position corresponding to a binding energy of approximately 40.77 to 41.27 eV. This is because, during X-ray photoelectron spectroscopy of the GaAs single crystal, a charge shift can occur, which shifts the As3d peak at its maximum by about 1 eV towards the higher energy. Since the peak detection intensity of the metal As and the As-Ga is also influenced by the main layer consisting of GaAs, it is difficult to fix the peak to a value and the maximum position is therefore set to a width of 0.5 eV as described above.

[0074] The Ga3d spectrum LG is then expressed, according to the background correction described above, by separating the Ga3d spectrum LG into the three Gaussian functions Y1, Y2, and Y3 (hereinafter also referred to as "peak separation"). In this way, the three spectra of the Ga element present as Ga2O (Ga) can be determined. + ), of the Ga element present as Ga2O3 (Ga 3+ ) and the Ga element present as GaAs (Ga-As) by tip separation in the range of binding energy from 16 to 26 eV. Y1=a1*exp{(−(X−b1)2) / c12} Y2=a2*exp{(−(X−b2)2) / c22} Y3=a3*exp{(−(X−b3)2) / c32}

[0075] The unit of the Gaussian functions Y1, Y2 and Y3 is dimensionless, the unit of X, b1, b2, b3, c1, c2 and c3 in the Gaussian functions Y1, Y2 and Y3 is eV, and the unit of both a1, a2 and a3 is dimensionless.

[0076] The Gaussian functions Y1 to Y3 are determined by optimizing each of the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) such that the square ([actual measured value - ΣGi] 2 ) a difference to the actual measured value becomes minimal, provided that the i-th component of Ga3d is given by the Gaussian function Gi = Ai*exp{(-(E-E1) 2 ) / Wi 2 } is expressed. This includes the binding energy values ​​at the peaks of the Ga detection intensities described above. + , Ga 3+ and Ga-As are each substituted to b1 to b3.

[0077] This means that each of the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) is as follows: a1, a2 and a3 are all real numbers of 0 or greater. b1=19.9eV b2=20.7eV 19.2 eV ≤ b3 ≤ 19.7 eV 0.2eV≤c1≤0.95eV 0.2eV≤c2≤0.95eV 0.2eV≤c3≤0.95eV.

[0078] Thus, the Gaussian functions Y1, Y2, and Y3 can each be expressed as Ga + -Spectrum L2, Ga 3+ -Spectrum L1 and Ga-As spectrum L3 are represented, for example by tip separation from the Ga3d spectrum LG in the Fig. 3A will be won.

[0079] The As3d spectrum LA after the background correction described above can be represented by peak separation into the following four Gaussian functions Y4, Y5, Y6, and Y7. In this way, the four spectra of the As element present as As2O5 (As) can be determined. 5+ ), of the As element present as As2O3 (As 3+ ), of the As element present as metal-As (Metal-As) and of the As element present as GaAs (As-Ga) by tip separation in the binding energy range of 39 to 49 eV. Y4=a4*exp{(−(X−b4)2) / c42} 0.2eV≤c1≤0.95eV 0.2eV≤c2≤0.95eV 0.2eV≤c3≤0.95eV.

[0080] The unit of each Gaussian function Y4, Y5, Y6 and Y7 is dimensionless, the unit of X, b4, b5, b6, b7, c4, c5, c6, and c7 in the Gaussian functions Y4, Y5, Y6 and Y7 is eV, and the unit of both a1, a2 and a3 is dimensionless.

[0081] The Gaussian functions Y4 to Y7 are determined by optimizing each of the variables (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) such that the square ([actual measured value - ΣGi] 2 ) a difference to the actual measured value becomes minimal, provided that the i-th component of As3d is given by the Gaussian function Gi-Ai*exp{(-(E-E1) 2 ) / Wi 2 ) is expressed. The values ​​of the binding energy at the peaks of the signal intensities of As 5+ , As 3+ , of metal As and As-Ga, which were described above, are each substituted as b4 to b7.

[0082] This means that each of the variables (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) is as follows: a4, a5, a6 and a7 are all real numbers of 0 or greater. b4=45.57eV b5=44.07eV 41.62 eV ≤ b6 ≤ 42.12 eV 41.77 eV ≤ b7 ≤ 41.27 eV 0.2eV≤c4≤0.95eV 0.2eV≤c5≤0.95eV 0.2eV≤c6≤0.95eV 0.2eV≤c7≤1.2eV.

[0083] Thus, the Gaussian functions Y4, Y5, Y6, and Y7 can each be described as an ace. 5+ -Spectrum L4, an As 3+ -Spectrum L5 and a metal-As spectrum L6 and an As-Ga spectrum L7, which are represented, for example, by tip separation from the As3d spectrum LA in the Fig. 3A are obtained. Since the metal As is produced from the oxide layer and the main layer by the reaction 2GaAs+As2O3---*Ga2O3+4As, the metal As is detected as the intensity by the XPS.

[0084] It should be noted that the following correction can be made to fix the peak positions of the Gaussian functions Y1 to Y7. First, the probability of photoelectron generation by X-rays, known as the photoionization efficiency (η), varies depending on the element, the X-ray energy, and other factors. Therefore, the data published on the following website are used as the value for η. Specifically, the photoionization efficiency (η) of X-rays with an incident energy of 600 eV is 0.28 for Ga3d and 0.42 for As3d.

[0085] https: / / vuo.elettra.eu / services / elements / WebElements.html (Note that the data is based on the following documents: 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)).

[0086] Since the intensity of the X-ray beam used in the synchrotron radiation facility decreases over time, the attenuation ratio of the Au4f photoelectron intensity is determined by measuring a gold standard sample (Au) at regular intervals and the dose of the X-ray beam used is corrected based on this ratio.

[0087] In the Fig. 3A corresponds to an area between the Ga 3+ -Spectrum L1 and the horizontal axis (X-axis) of the number of particles from the 3d orbital of Ga 3+ emitted photoelectrons and therefore represents the integrated intensity of the Ga 3+ This represents an area between the Ga + -Spectrum L2 and the horizontal axis (X-axis) corresponds to the number of ions from the 3d orbital of Ga + emitted photoelectrons and thus represents the integrated intensity of the Ga + The area between the Ga-As spectrum L3 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of Ga-As and thus represents the integrated intensity of Ga-As.

[0088] In the Fig. 3B corresponds to an area between the As 5+ The spectrum L4 and the horizontal axis (X-axis) represent the number of photoelectrons emitted from the 3d orbital and therefore represent the integrated intensity. An area between the As 3+ -Spectrum L5 and the horizontal axis (X-axis) corresponds to the number of ions from the 3d orbital of As 3+ emitted photoelectrons and thus represents the integrated intensity of the As 3+ The area between the metal-As spectrum L6 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted by the 3d orbital of the metal-As and thus represents the integrated intensity of the metal-As. Similarly, the area between the AS-Ga spectrum L7 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted by the 3d orbital of the AS-Ga and thus represents the integrated intensity of the AS-Ga.

[0089] Therefore, the ratio of the sum of the integrated intensity of the As can be 5+ , the integrated intensity of the ace 3+ , the integrated intensity of As-Ga and the integrated intensity of metal-As to the sum of the integrated intensity of Ga + , the integrated intensity of the Ga 3+ and the integrated intensity of Ga-As is determined as the first integrated intensity ratio based on the areas obtained from the spectra above and the horizontal axis. The ratio of the sum of the integrated intensities of the As 5+ and the integrated intensity of the acetylcholine 3+ to the sum of the integrated intensity of the Ga + and the integrated intensity of the Ga 3+ can be determined as a third integrated intensity ratio based on the areas obtained from the spectra above and the horizontal axis.

[0090] According to the present embodiment, the second integrated intensity ratio and the fifth integrated intensity ratio can be determined in the same way as in the calculation of the first integrated intensity ratio and the third integrated intensity ratio described above, except that the XPS is carried out on the center of the main surface of the GaAs single crystal substrate under conditions of an incident energy of 600 eV and a photoelectron exit angle of 85°.The fourth integrated intensity ratio can also be determined in the same way as the procedure described above for calculating the first and third integrated intensity ratios, except that the XPS is performed on the center of the main surface of the GaAs single crystal substrate under conditions of an incident energy of 600 eV and a photoelectron exit angle of 45°. <Gleichmäßigkeit der Hauptoberfläche des GaAs-Einkristall-Substrats>

[0091] The properties of the GaAs single-crystal substrate according to the present embodiment are preferably uniform in the plane of the main surface. The GaAs single-crystal substrate according to the present embodiment is preferably such that an epitaxial layer with a reduced turbidity value can form on it, regardless of its position in the plane of the main surface. The following implementations (a first implementation and a second implementation) can be cited as examples of such a preferred GaAs single-crystal substrate. (First implementation)

[0092] A GaAs single-crystal substrate according to the first implementation has a diameter of 75 mm or more and less than 150 mm. The GaAs single-crystal substrate preferably has a diameter of 75 mm or more and 105 mm or less. The gallium arsenide single-crystal substrate has a sixth integrated intensity ratio and a seventh integrated intensity ratio.Both the sixth and seventh integrated intensity ratios are obtained by determining each of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy, in which X-ray radiation is applied to each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.

[0093] The sixth integrated intensity ratio is a ratio of the sum of the integrated intensities of the As element present as As2O5 (As 5+ ), an integrated intensity of the As element present as As2O3 (As 3+ ), an integrated intensity of the As element present as GaAs (As-Ga) and an integrated intensity of the As element present as metal-As (Metal-As) to a sum of an integrated intensity of the Ga element present as Ga2O (Ga + ), an integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ) and an integrated intensity of the Ga element present as GaAs (Ga-As). The seventh integrated intensity ratio is a ratio of the sum of the integrated intensities of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ) to a sum of the integrated intensity of the Ga element present as Ga2O (Ga + ) and the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ The standard deviation and mean value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio satisfy a standard deviation / mean value ≤ 0.039 relationship. If the standard deviation and mean value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio satisfy the standard deviation / mean value ≤ 0.039 relationship, then this means that a composition has been achieved in which the oxide layer is rich in gallium and exhibits no in-plane variations, and therefore the oxide layer on the main surface can be removed by wet etching without in-plane variations. The lower limit of both the standard deviation and the mean value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio is 0, which corresponds to an ideal value.For example, the standard deviation and the mean value of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio can satisfy the relationship standard deviation / mean value ≥ 0.026.

[0094] If the diameter is specified by D, and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as an X-axis and a Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4), respectively. The units of D and of both X and Y in the coordinates (X, Y) are mm. Since the oxide layer can be effectively removed by wet etching in the GaAs single-crystal substrate with a diameter of 75 mm or more and less than 150 mm, it is therefore possible to obtain a main surface with high mirror surface properties and no in-plane variations, allowing for the formation of an epitaxial layer with reduced turbidity on it. (Second implementation)

[0095] Furthermore, according to the first implementation, a GaAs single-crystal substrate has a diameter of 150 mm or more and 205 mm or less. The GaAs single-crystal substrate exhibits an eighth integrated intensity ratio and a ninth integrated intensity ratio. Both the eighth integrated intensity ratio and the ninth integrated intensity ratio are obtained by determining each of the 3d electron detection intensities spectra of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate. This determination is based on X-ray photoelectron spectroscopy, in which X-rays are applied to each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.

[0096] The eighth integrated intensity ratio is a ratio of a sum of an integrated intensity of the As element present as As2O5 (As 5+ ), an integrated intensity of the As element present as As2O3 (As 3+ ), an integrated intensity of the As element present as GaAs (As-Ga) and an integrated intensity of the As element present as metal-As (Metal-As) to a sum of an integrated intensity of the Ga element present as Ga2O (Ga + ), an integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ) and an integrated intensity of the Ga element present as GaAs (Ga-As). The ninth integrated intensity ratio is a ratio of the sum of the integrated intensities of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ) to a sum of the integrated intensity of the Ga element present as Ga2O (Ga + ) and the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ The standard deviation and mean value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy a standard deviation / mean value ≤ 0.022 relationship. If the standard deviation and mean value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy the standard deviation / mean value ≤ 0.022 relationship, then this means that a composition has been achieved in which the oxide layer is rich in gallium and exhibits no in-plane variations, and therefore the oxide layer on the main surface can be removed by wet etching without in-plane variations. The lower limit of both the standard deviation and the mean value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio is 0, which corresponds to an ideal value.For example, the standard deviation and the mean value of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio can satisfy the relationship standard deviation / mean value ≥ 0.009.

[0097] If the diameter is given by D and two axes, each passing through the center of the main surface, lying on the main surface and orthogonal to each other, are defined as an X-axis and a Y-axis, then the coordinates (X, Y) of the nine measurement points on the X-axis and the Y-axis 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)), respectively. The units of D and of both X and Y in the coordinates (X, Y) are mm. Therefore, in the Ga-As single crystal substrate with a diameter of 150 mm or more and 205 mm or less, the oxide layer can be effectively removed by wet etching to obtain the main surface with high mirror surface properties without fluctuations in the plane, allowing an epitaxial layer with reduced turbidity to be formed on it.

[0098] In both the first implementation described above and the second implementation, the specific analytical procedure for determining the sixth integrated intensity ratio, the seventh integrated intensity ratio, the eighth integrated intensity ratio and the ninth integrated intensity ratio corresponds to the procedure described in the section “Method for analyzing a GaAs single crystal substrate by X-ray photoelectron spectroscopy (XPS) using synchrotron radiation”, and therefore a repetition is omitted. (Five measuring points and nine measuring points)

[0099] The GaAs single-crystal substrate according to the first implementation has a diameter of 75 mm or more and less than 150 mm. In this case, five measurement points are placed on the main surface of the GaAs single-crystal substrate according to the first embodiment as follows. To evaluate the reduction of the turbidity value of the epitaxial layer due to the uniform distribution of the ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio in the plane, it is preferable that the five measurement points are preferably positioned so that the distances between them are as large as possible, and that the turbidity value generated in the epitaxial layer be measured near each of the five measurement points. The turbidity value is preferably measured over a region with a diameter of 20 mm or more.Therefore, five circular measurement targets, each with a diameter of 20 mm, are placed on the main surface of the GaAs single-crystal substrate such that the distances between them are as large as possible. The center of each measurement target is designated as the measurement point.

[0100] If the two axes, each passing through the center of the main surface, are initially laid on the main surface and are orthogonal to each other, and are defined as the X and Y axes, the coordinates (X, Y) of the first of the five measurement points on the X and Y axes are set to (0, 0). It should be noted that the X and Y axes are each positioned such that a notch formed in the GaAs single-crystal substrate lies in the third quadrant of the XY coordinate plane, and the general angle of a semiline passing through the notch is 225° with respect to a semiline emanating from the origin in the positive direction of the X-axis.

[0101] Of the five measurement points, the second, third, fourth, and fifth are arranged at equal intervals on a circle consisting of a series of points, each located D / 4 from the center of the GaAs single-crystal substrate. 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 of both X and Y in the coordinates (X, Y) are mm.

[0102] The GaAs single-crystal substrate according to the second implementation has a diameter of 150 mm or more and 205 mm or less. In this case, four additional measurement points are added to the main surface of the GaAs single-crystal substrate according to the second implementation, in addition to the five measurement points of the GaAs single-crystal substrate according to the first implementation. The total of nine measurement points are positioned as follows. This means that, in addition to the second, third, fourth, and fifth measurement points described above, four measurement targets, each with a diameter of 20 mm, are placed on the main surface of the GaAs single-crystal substrate according to the second implementation such that they are located on the outer side of the circumference of these measurement points and do not overlap with the measurement targets, including the second, third, fourth, and fifth measurement points.The center of each measurement target is defined as the measurement point, and X-rays are applied to this point. Specifically, the coordinates (X, Y) of the sixth measurement point of the four added measurement points are set to (0, D / 2-10). The coordinates (X, Y) of the seventh measurement point are set to (D / 2-10, 0). The coordinates (X, Y) of the eighth measurement point are set to (D / 2-10, 0). The coordinates (X, Y) of the ninth measurement point are set to (0, -(D / 2-10)). D represents the diameter of the GaAs single-crystal substrate, and the units of D and of both X and Y in the coordinates (X, Y) are mm.

[0103] It is known that in a primary surface with a diameter of 150 mm or more and 205 mm or less, such as the primary surface of the GaAs single-crystal substrate according to the second implementation, the property is subject to greater fluctuations in a region on the outer periphery. Therefore, to evaluate the effect of the reduction in the turbidity value of the epitaxial layer due to the uniform distribution of the ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio in the plane, it is desirable, in addition to the five measurement points described above, to measure the turbidity value that has grown in the epitaxial layer in a region located on the outer periphery.To achieve this, in addition to the five measuring points described above on the main surface of the GaAs single crystal substrate, four measuring targets with a diameter of 20 mm and the measuring points serving as the corresponding centers of the measuring targets were placed in the area of ​​the outer circumferential side in such a way that the distances between them are as large as possible.

[0104] The Fig. Figure 4 is an explanatory diagram showing five measurement points placed in a GaAs single-crystal substrate with a diameter of 75 mm or more and less than 150 mm in the present embodiment. Fig. Figure 5 is an explanatory diagram showing nine measurement points placed in a GaAs single-crystal substrate with a diameter of 150 mm or more and 205 mm or less in the present embodiment.

[0105] As in the Fig. As shown in Figure 4, in the GaAs single-crystal substrate, according to the first implementation, the X-axis and Y-axis are set such that the general angle of the semiline passing through notch 50 with respect to a semiline extending from the origin in the positive X-axis direction is 225°. Next, a first measurement point P1 is set at the origin (0, 0), representing the center of the GaAs single-crystal substrate, and a measurement target A1, which is a circular area with a diameter of 20 mm and centered on the first measurement point P1, is set.

[0106] Subsequently, a second measurement point P2, a third measurement point P3, a fourth measurement point P4, and a fifth measurement point P5 are placed on a circumference consisting of a series of points, each located D / 4 from the center of the GaAs single-crystal substrate. Furthermore, a measurement target A2, a measurement target A3, a measurement target A4, and a measurement target A5 are placed, each a circular area with a diameter of 20 mm, centered on the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5, respectively.

[0107] For example, in the example in the Fig. Figure 4, which shows a GaAs single-crystal substrate with a diameter of 75 mm, shows the coordinates (X, Y) (the units of X and Y are mm; the same applies for the following description) of the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 set to (18.75, 0), (0, 18.75), (-18.75, 0), and (0, -18.75), respectively. In this GaAs single-crystal substrate with a diameter of 75 mm, measurement target A1 partially overlaps measurement targets A2, A3, A4, and A5. This overlap is acceptable, however, as it does not affect the evaluation of the uniformity of the main surface of the GaAs single-crystal substrate.

[0108] As in the Fig. As shown in Figure 5, in the GaAs single-crystal substrate according to the second embodiment, in addition to the first measuring point P1 to the fifth measuring point P5 of the first embodiment, a sixth measuring point P6, a seventh measuring point P7, an eighth measuring point P8, and a ninth measuring point P9, comprising the four measuring points in total, are positioned at regular intervals on the outer circumference relative to the second measuring point P2, the third measuring point P3, the fourth measuring point P4, and the fifth measuring point P5, respectively, and are located 10 mm inwards from the outer circumference of the GaAs single-crystal substrate. Furthermore, a measuring target A6, a measuring target A7, a measuring target A8, and a measuring target A9 are defined, each being a circular area with a diameter of 20 mm, centered on the sixth measuring point P6, the seventh measuring point P7, the eighth measuring point P8, and the ninth measuring point P9, respectively.

[0109] For example, in the example in the Fig. Figure 5, which shows a GaAs single-crystal substrate with a diameter of 150 mm, sets 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 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. <epitaxialschicht>

[0110] The GaAs single-crystal substrate preferably has an epitaxial layer on its main surface. In this case, the maximum turbidity of the epitaxial layer surface is preferably 100 ppm or less, and the average turbidity of the epitaxial layer surface is preferably 2.5 ppm or less. The maximum turbidity of the epitaxial layer surface is preferably 20 ppm or less, and the average turbidity of the epitaxial layer surface is preferably 2.0 ppm or less. The lower limit of both the maximum and average turbidity of the epitaxial layer surface is 0, which corresponds to an ideal value.

[0111] The epitaxial layer, for example, is a composite layer made of Al 1-y-z Ga y In z As, where y can be 0 or greater and 1 or less, z can be 0 or greater and 1 or less, and the sum of y and z can be greater than or equal to 0 and less than 1. This means that in the present embodiment, a composite layer of Al 1-y-z Ga y In z As (0≤y≤1, 0≤z≤1, 0≤y+z≤1) can be deposited as an epitaxial layer on the main surface of the GaAs single-crystal substrate. The epitaxial layer can further be a composite layer of Al x Ga 1-x N (0≤x≤1) or Al x Ga 1-x As (0≤x≤1).

[0112] The epitaxial layer is formed with a thickness of, for example, 0.5 to 10 µm. If the thickness of the epitaxial layer lies within this range, the GaAs single-crystal substrate can be used for a wide variety of applications. Preferably, the epitaxial layer has a thickness of 1 to 5 µm.

[0113] The turbidity value on the main surface of the epitaxial layer located on the GaAs single-crystal substrate can be determined using a known instrument for surface inspection for foreign matter (e.g., the "Surfscan6420" from KLA-Tencor Corporation). The instrument can perform measurements across the entire surface of the epitaxial layer (except for a 2 mm inward zone from the substrate edge) and determine the turbidity value (amount of scattered light (ppm)) per cm². 2 Measure the turbidity on the surface of the epitaxial layer. The maximum and average values ​​of the surface turbidity of the epitaxial layer can be determined from the measurement results. [Method for the preparation of a gallium arsenide single crystal substrate]

[0114] The process for producing a gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is preferably a process for producing the GaAs single-crystal substrate described above. The production process comprises, for example: a preparation step of preparing a gallium arsenide single-crystal substrate precursor (hereinafter also referred to as the "GaAs single-crystal substrate precursor") with a circular surface; and a purification step for obtaining the GaAs single-crystal substrate from the GaAs single-crystal substrate precursor. The purification step comprises a surface polishing step of converting the surface of the GaAs single-crystal substrate precursor to a polished surface.a step (first alkaline cleaning step) of converting the polished surface to an alkaline cleaned surface by cleaning the polished surface with a first alkaline cleaning fluid; a step (acid cleaning step) of converting the alkaline cleaned surface to an acid cleaned surface by cleaning the alkaline cleaned surface with an acidic cleaning fluid containing 0.3 ppm by mass or more and 0.5 percent by mass or less of an acid;a step (second alkaline cleaning step) of converting the acid-cleaned surface to a second alkaline-cleaned surface by cleaning the acid-cleaned surface by applying a second alkaline cleaning fluid to the acid-cleaned surface at a flow rate of 0.1 l / minute or higher and 5 l / minute or less for 30 seconds or longer and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more;and a step (heat treatment step) of converting the second alkaline-cleaned surface to the main surface by performing a heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less. The first alkaline cleaning fluid contains 0.1 wt% or more and 10 wt% or less of a first base. The first base contains at least a quaternary ammonium hydroxide and / or a quaternary pyridinium hydroxide. The second alkaline cleaning fluid contains 0.3 wt% or more and 0.5 wt% or less of a second base. The second base contains at least either the quaternary ammonium hydroxide or the quaternary pyridinium hydroxide.

[0115] The manufacturing process with this property yields a GaAs single-crystal substrate whose main surface exhibits an oxide layer that can be effectively removed by wet etching. The manufacturing process preferably includes a step (epitaxial layer formation step) for the formation of an epitaxial layer on the main surface. Thus, it is possible to provide a GaAs single-crystal substrate with a main surface on which the epitaxial layer forms with a reduced turbidity value.

[0116] In the present description, the term ‘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’) produced by a conventional known manufacturing process, such as a vertical boat process, and refers in particular to a GaAs single crystal substrate that is subjected to each step included in the purification step.

[0117] The inventors have dedicated themselves to improving a known purification step for the production of a GaAs single-crystal substrate, based on insights gained from analysis using synchrotron radiation XPS described above. Specifically, it is known that the oxide layer of the GaAs single-crystal substrate is formed by surface oxidation during the acid purification step to remove impurities in an alkaline cleaning agent that adhere to the surface of the GaAs single-crystal substrate precursor after the alkaline cleaning. It was therefore noted that after acid purification, a process is required to maintain a gallium-rich composition (gallium oxide, hereinafter also referred to as "Ga oxide") both within the oxide layer and near the interface between the oxide layer and the GaAs layer contained in the GaAs single-crystal substrate.In particular, the progression of oxide layer oxidation was further suppressed by performing a second alkaline cleaning step, a so-called spin cleaning. This involved applying an alkaline cleaning fluid to the surface of the GaAs single-crystal substrate precursor for cleaning purposes, while the surface was rotated after cleaning in the sequence of the alkaline and acid cleaning steps. Furthermore, the surface that had undergone the second alkaline cleaning step was subjected to heat treatment to modify the composition of the oxide layer so that Ga oxide predominated. In this way, it was found that a Ga oxide-rich composition could be obtained both in the oxide layer and near the interface between the oxide layer and the GaAs layer contained in the GaAs single-crystal substrate.In the GaAs single-crystal substrate that has undergone such a purification process, an oxide layer with excellent wettability is formed on the main surface, which can then be effectively removed by wet etching. In this way, the present inventors were able to obtain a GaAs single-crystal substrate with a main surface exhibiting high mirror surface properties and thus arrived at a method for producing a GaAs single-crystal substrate on which an epitaxial layer with a reduced turbidity value can be formed.

[0118] The following describes the individual steps of the process for producing the GaAs single-crystal substrate according to the present embodiment with reference to the Fig. 6 described in detail. Fig. Figure 6 is a flowchart showing a process for producing the GaAs single crystal substrate according to the present embodiment. <Vorbereitungs-Schritt S100>

[0119] The process for producing the GaAs single-crystal substrate includes the preparation step (S100) of preparing the GaAs single-crystal substrate precursor with a circular surface. In preparation step S100, the GaAs single-crystal substrate precursor required for the purification step is prepared. Preparation step S100 may involve carrying out a conventional method for producing a GaAs single-crystal substrate precursor. This means that preparation step S100 may include fabricating a GaAs single crystal using a known method, such as a vertical boat process, and cutting out a GaAs single-crystal substrate precursor with a circular surface from the GaAs single crystal.It should be noted that when preparing a GaAs single-crystal substrate precursor with a (100) plane as its main surface, the GaAs single-crystal substrate precursor is obtained, for example, by cutting it out of a substrate in a <100> The direction of the grown GaAs single crystal can be obtained, such that the (100) plane becomes the main surface. The preparation step S100 can also include processing the GaAs single-crystal substrate precursor cut from the GaAs single crystal to the desired size (e.g., a wafer with a diameter of 2 to 8 inches and a thickness of 250 to 1500 µm). A known method such as cutting or chamfering can be used as the processing method. <Reinigungs-Schritt S200>

[0120] The process for producing the GaAs single-crystal substrate includes the purification step S200, in which the GaAs single-crystal substrate is obtained from the GaAs single-crystal substrate precursor. This purification step S200 allows the GaAs single-crystal substrate precursor to be obtained, the main surface of which has an oxide layer that can be effectively removed by wet etching. The purification step S200 comprises: the step (surface polishing step S210), in which the surface of the GaAs single-crystal substrate precursor is converted into a polished surface by polishing; the step (first alkaline cleaning step S220), in which the polished surface is converted into an alkaline-cleaned surface by cleaning it with the first alkaline cleaning fluid.and the step (acid cleaning step S230) in which the alkaline cleaned surface is converted into an acid-cleaned surface by cleaning the alkaline cleaned surface with an acidic cleaning fluid containing 0.3 ppm by mass or more and 0.5 percent by mass or less acid; the step (second alkaline cleaning step S240) of converting the acid-cleaned surface into the second alkaline cleaned surface by cleaning the acid-cleaned surface by applying the second alkaline cleaning fluid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more;and the step (heat treatment step S250) of converting the second alkaline-cleaned surface into the main surface by performing heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere under conditions of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less. Each of the steps of cleaning step S200 is described in detail below. (Surface polishing step S210)

[0121] Surface polishing step S210 is the step in which the surface of the GaAs single-crystal substrate precursor is transformed into a polished surface. This step results in a mirror-smooth, polished surface. For example, surface polishing step S210 can achieve a surface roughness of 0.3 nm or less, expressed as the arithmetic mean roughness Ra. Various polishing methods can be used in surface polishing step S210, such as conventional mechanical polishing and chemical-mechanical polishing. (First alkaline cleaning step S220)

[0122] The first alkaline cleaning step, S220, is the step in which the polished surface is converted into an alkaline-cleaned surface by cleaning with the first alkaline cleaning fluid. This first alkaline cleaning step, S220, removes foreign substances, impurities, or similar contaminants adhering to the polished surface of the GaAs single-crystal substrate precursor. The first alkaline cleaning fluid is not subject to any particular restrictions; however, an aqueous solution containing 0.1 to 10% by mass of an organic alkaline compound that does not contain any metallic element affecting the electrical properties is preferably used. Examples of such organic alkaline compounds include quaternary ammonium hydroxides such as choline or tetramethylammonium hydroxide (TMAH), as well as quaternary pyridinium hydroxides or similar compounds. (Acid purification step S230)

[0123] Acid cleaning step S230 is the step in which the alkaline-cleaned surface is converted to an acid-cleaned surface by cleaning with the acidic cleaning fluid containing 0.3 ppm or more by mass and 0.5% or less by mass of acid. Acid cleaning step S230 removes contaminants present in the initial alkaline cleaning fluid and adhering to the alkaline-cleaned surface of the GaAs single-crystal substrate precursor through an oxidation reaction (etching of the alkaline-cleaned surface) with the acidic cleaning fluid. Specifically, in acid cleaning step S230, the alkaline-cleaned surface is cleaned with the acidic cleaning fluid containing 0.3 ppm or more by mass and 0.5% or less by mass of acid.This optimizes the ratio of Ga atoms to As atoms on the main surface and suppresses excessive oxide layer formation, resulting in efficient removal of the oxide layer by wet etching. In acid cleaning step S230, the alkaline-cleaned surface is preferably cleaned with an acidic cleaning fluid containing 0.3 ppm by mass or more and 0.1 percent by mass or less of the acid.

[0124] If the acid concentration in the acidic cleaning fluid is less than 0.3 ppm by mass, the modifying effect on the alkaline-cleaned surface will be minimal. However, the influence of carbon dioxide (CO2) dissolved in the acidic cleaning fluid from the atmosphere will be significant, leading to fluctuations in the chemical composition of the acid-cleaned surface after acid cleaning step S230. If the acid concentration in the acidic cleaning fluid exceeds 0.5% by mass, the chemical composition of the acid-cleaned surface (and the main surface in the subsequent step) will tend to fluctuate because the deviation of the acid-cleaned surface from stoichiometry due to the acid's action will be substantial.Here, the term "stoichiometry" means that the ratio (the composition) of the number of atoms that make up a particular compound corresponds to the ratio given in the chemical formula.

[0125] The acid contained in the acidic cleaning fluid is not subject to any particular restrictions, but should preferably be an acid component that has high cleaning power, does not contain any element (e.g., a metallic element, sulfur, or the like) that affects the electrical properties, and is less likely to cause serious secondary contamination or equipment damage when the acid component evaporates with water and droplets are dispersed throughout the equipment. For example, the acid contained in the acidic cleaning fluid preferably contains at least one inorganic acid selected from the group consisting of hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and nitrous acid (HNO2). An organic acid such as acetic acid, citric acid, or malic acid may also preferably be used.Furthermore, two or more of these acids can be used in combination; for example, hydrochloric acid and nitric acid can be used together.

[0126] From a cleaning perspective, the acidic cleaning fluid preferably contains 0.3 ppm to 0.3% hydrogen peroxide (H₂O₂) by mass. If the H₂O₂ concentration is less than 0.3 ppm by mass, the influence of dissolved oxygen in the acidic cleaning fluid can be significant, thereby reducing its effectiveness in removing the contaminant. If the H₂O₂ concentration is greater than 0.3% by mass, the etching rate can become too high, potentially resulting in uneven etching on the acid-cleaned surface.

[0127] In acid cleaning step S230, the acidic cleaning fluid can be applied to the alkaline-cleaned surface while the GaAs single-crystal substrate precursor rotates circumferentially at 100 to 800 rpm and its surface is held horizontally. This allows a layer of the acidic cleaning fluid to form on the alkaline-cleaned surface, thus performing efficient acid cleaning while suppressing excessive oxidation of the alkaline-cleaned surface. If the rotational speed of the GaAs single-crystal substrate precursor is less than 100 rpm, the cleaning efficiency may not be improved, whereas at a rotational speed of more than 800 rpm, the formation of a layer of acidic cleaning fluid can be prevented, thereby reducing the oxidation suppression effect.

[0128] Furthermore, the acid-cleaned surface of the GaAs single-crystal substrate precursor is cleaned with pure water after acid cleaning step S230, preferably immediately thereafter. The pure water cleaning process is not subject to any particular restrictions; however, the acid-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned with pure water for 5 minutes or less, provided the water has a dissolved oxygen concentration (DO) of no more than 100 ppb. This helps to suppress excessive oxidation of the acid-cleaned surface. For this purpose, the dissolved oxygen concentration of the pure water is preferably 50 ppb or less to suppress excessive oxidation. The total organic carbon (TOC) content of the pure water is preferably 40 ppb or less to minimize impurities.The purification process with pure water can also be carried out by applying the pure water to the acid-cleaned surface while the GaAs single-crystal substrate precursor rotates circumferentially at 100 to 800 rpm and its main surface is held horizontally. (Second alkaline cleaning step S240)

[0129] The second alkaline cleaning step, S240, is the step in which the acid-cleaned surface is converted into a second alkaline-cleaned surface by cleaning with the second alkaline cleaning fluid. This is achieved by applying the second alkaline cleaning fluid at a flow rate of 0.1 L / minute or more and 5 L / minute or less for a duration of 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more. The second alkaline cleaning step, S240, suppresses the progression of excessive oxidation of GaAs on the acid-cleaned surface, thus preventing it from acquiring an As oxide-rich composition.This allows the oxide layer to be efficiently modified to a gas oxide-rich composition in the heat treatment step S250 described later.

[0130] In particular, the second alkaline cleaning solution contains 0.3 ppm or more and 0.5% or less of the base by mass. The base is an organic alkali compound without metallic elements that affect electrical properties. Such an organic alkali compound is not subject to any particular restrictions, and examples include quaternary ammonium hydroxides such as choline or tetramethylammonium hydroxide (TMAH), quaternary pyridinium hydroxide, and similar compounds. This can suppress the progression of excessive oxidation of GaAs on the acid-cleaned surface. If the concentration of the base in the second alkaline cleaning solution is less than 0.3 ppm by mass, its effect on suppressing excessive oxidation on the acid-cleaned surface will be minimal.On the other hand, if the base concentration in the second alkaline cleaning solution exceeds 0.5% by mass, the acid-cleaned surface may dissolve, leading to a loss of surface flatness. The base concentration in the second alkaline cleaning solution is preferably 0.3 ppm by mass or more and 0.1% by mass or less.

[0131] It should be noted that examples of the first alkaline cleaning fluid used in the first alkaline cleaning step S220, as described above, include an aqueous solution containing 0.1 to 10 wt% of a quaternary ammonium hydroxide such as choline or tetramethylammonium hydroxide (TMAH), a quaternary pyridinium hydroxide, or the like. Both the first alkaline cleaning fluid and the second alkaline cleaning fluid may contain at least one base selected from a group consisting of quaternary ammonium hydroxide and quaternary pyridinium hydroxide, and the first alkaline cleaning fluid may contain the same base as the second alkaline cleaning fluid.Both the first alkaline cleaning solution and the second alkaline cleaning solution may contain at least one base selected from the group consisting of quaternary ammonium hydroxide and quaternary pyridinium hydroxide, and the first alkaline cleaning solution may contain a base that differs from that of the second alkaline cleaning solution. That is to say, both the first alkaline cleaning solution and the second alkaline cleaning solution may each contain at least one base selected from the group consisting of quaternary ammonium hydroxide and quaternary pyridinium hydroxide, and the first alkaline cleaning solution may contain the same base as the second alkaline cleaning solution or it may contain a different base than that of the second alkaline cleaning solution.

[0132] In the second alkaline cleaning step S240, the acid-cleaned surface is preferably rotated circumferentially at a speed of 1500 rpm or more. The upper limit of the rotational speed of the acid-cleaned surface in the circumferential direction is not subject to any particular restriction, but is preferably 2000 rpm. The flow rate of the second alkaline cleaning fluid applied to the acid-cleaned surface is preferably 0.5 l / min or more and 3 l / min or less. The application time of the second alkaline cleaning fluid to the acid-cleaned surface is preferably 30 seconds or more and 3 minutes or less. This allows excessive oxidation of the GaAs on the acid-cleaned surface to be suppressed more effectively.

[0133] Furthermore, the second alkaline-cleaned surface can be cleaned with pure water for a very short time after the second alkaline cleaning step S240, preferably immediately thereafter, without adversely affecting the GaAs single-crystal substrate precursor. In the pure-water cleaning process, the second alkaline-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned for 30 seconds or less with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less. This removes impurities adhering to the alkaline-cleaned surface. To suppress excessive oxidation, the dissolved oxygen concentration of the pure water is preferably 50 ppb or less.The total organic carbon (TOC) content of the pure water is preferably 40 ppb or less, considering the low level of impurities. The purification process with pure water can also be carried out by applying the pure water to the second alkaline-cleaned surface while the GaAs single-crystal substrate precursor is rotated at 100 to 800 rpm and its main surface is held horizontally. (Heat treatment step S250)

[0134] Heat treatment step S250 is the step in which the second alkaline-cleaned surface is converted into the main surface by performing heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere at conditions of 1.1 atmospheres or more and 3 atmospheres or less, and 150 °C or more and 300 °C or less. Heat treatment step S250 can modify the composition of the oxide layer on the second alkaline-cleaned surface so that Ga oxide predominates. In this way, a Ga oxide-rich composition can be obtained both in the oxide layer and near the interface between the oxide layer and the GaAs layer contained in the GaAs single-crystal substrate. As a result, the oxide layer in the GaAs single-crystal substrate exhibits excellent surface wettability, allowing it to be effectively removed by wet etching.

[0135] In heat treatment step S250, the heat treatment is carried out on the second alkaline-cleaned surface in an inert gas atmosphere under conditions of 1.1 atmospheres or more and 3 atmospheres, or 150 °C or more and 300 °C or less. The type of inert gas is not subject to any particular restrictions; however, argon or nitrogen are preferred. The temperature at which the heat treatment is carried out is preferably 175 to 275 °C. The pressure at which the heat treatment is carried out is preferably 1.5 to 2.5 atmospheres. By carrying out the heat treatment under the conditions within the aforementioned ranges, the composition of the oxide layer can be suitably made gallium-rich. If the temperature of the heat treatment is below 150 °C or the atmospheric pressure during the heat treatment is 1.1 atmospheres, the oxide layer tends to be insufficiently modified.If the heat treatment temperature exceeds 300 °C or the atmospheric pressure is more than 3 atmospheres, the GaAs single-crystal substrate may be damaged by excessive heating. The heat treatment time is preferably 1 to 30 minutes. <Nassätz-Schritt>

[0136] As described above, the method for producing the GaAs single-crystal substrate according to the present embodiment yields a GaAs single-crystal substrate with a major surface exhibiting an oxide layer with the following characteristic: The oxide layer has a composition rich in Ga oxide, both within the oxide layer itself and near the interface between the oxide layer and the GaAs layer contained in the GaAs single-crystal substrate. With such a GaAs single-crystal substrate, the oxide layer can be effectively removed even during a wet etching step under conventional conditions (e.g., conditions in which the GaAs single-crystal substrate is cleaned with a sulfuric acid-hydrogen peroxide mixture (H₂SO₄:H₂O₂:H₂O = 7:1:1) for one minute, then exposed to running water, and subsequently dried), because the wettability of the oxide layer surface is excellent. <Epitaxialschichtbildungs-Schritt S300>

[0137] The method for producing the GaAs single-crystal substrate according to the present embodiment preferably comprises a step (epitaxial layer formation step S300) for forming an epitaxial layer on the main surface. Epitaxial layer formation step S300 enables the GaAs single-crystal substrate to be obtained whose main surface exhibits an epitaxial layer with a reduced turbidity value. For example, the maximum turbidity value of a surface of the epitaxial layer can be 100 ppm or less, and the average turbidity value of the surface can be 2.5 ppm or less, thereby achieving improved device properties.

[0138] A conventional method can be used to form the epitaxial layer on the main surface of the GaAs single-crystal substrate in the epitaxial layer formation step S300. The properties of the epitaxial layer obtained in this step are the same as those described in the section above. <epitaxialschicht>As already described, further explanation is omitted. Since the GaAs single-crystal substrate, with its main surface on which the epitaxial layer is formed, exhibits a sufficiently low turbidity value, it can be used for applications such as field-effect transistors, microwave diodes, other integrated circuits, and the like. Examples

[0139] An embodiment according to the present disclosure is described in more detail below with reference to examples; however, the present disclosure is not limited to such examples. The GaAs single-crystal substrates of samples 1 to 6 described below serve as examples of the present disclosure, and the GaAs single-crystal substrates of samples 11 to 13 are comparative examples. [Production of the GaAs single crystal substrate]<Probe 1> (Preparation step)

[0140] A variety of GaAs single-crystal substrate precursors, each 6 inches (150 mm) in diameter and 675 µm thick, were prepared by cutting and chamfering a semi-insulating GaAs single crystal with added carbon atoms (C) grown using the Vertical Bridgman (VB) method. (Surface polishing step)

[0141] One surface of each GaAs single-crystal substrate precursor was subjected to a known mechanical and chemical-mechanical polishing process. Thus, the GaAs single-crystal substrate precursor was produced with a polished surface and an arithmetic mean roughness Ra of 0.3 nm or less according to JIS B0601:2001, as well as a deviation angle of 2° to the (100) plane. (First alkaline cleaning step S220)

[0142] The polished surface of the GaAs single-crystal substrate precursor was immersed in an aqueous solution (first alkaline cleaning fluid) containing 0.5 wt% tetramethylammonium hydroxide for 10 minutes at room temperature (25 °C) using a vertical batch process. The GaAs single-crystal substrate precursor was then rinsed with ultrapure water for 3 minutes (electrical resistance of 18 MΩ·cm or more, TOC [total carbon content] below 10 µg / L, and the number of fine particles less than 100 per L; this also applies to the subsequent description). (Acid purification step)

[0143] The alkaline-cleaned surface of the GaAs single-crystal substrate precursor was subjected to acid cleaning in a vertical batch process using an acidic cleaning solution. For the acid cleaning, the alkaline-cleaned surface of the GaAs single-crystal substrate precursor was immersed for 2 minutes at room temperature (25 °C) in an aqueous hydrochloric acid solution containing 0.3 ppm hydrochloric acid. Subsequently, the GaAs single-crystal substrate precursor was rinsed for 3 minutes with the same ultrapure water used in the alkaline cleaning step. This process converted the alkaline-cleaned surface to an acid-cleaned surface. (Second alkaline cleaning step S240)

[0144] The alkaline-cleaned surface of the GaAs single-crystal substrate precursor was subjected to a second alkaline cleaning process using a spin cleaning solution. Specifically, an aqueous solution containing 0.3 wt ppm tetramethylammonium hydroxide as a base was applied to the acid-cleaned surface of the rotating GaAs single-crystal substrate precursor, which was spinning at 1500 rpm, for three minutes at a flow rate of 3 l / min. The GaAs single-crystal substrate precursor was then rinsed for three minutes with the same ultrapure water used in the acid cleaning step. This process transformed the acid-cleaned surface into a second alkaline-cleaned surface. (Heat treatment step)

[0145] The second alkaline-cleaned surface of the GaAs single-crystal substrate precursor was subjected to a heat treatment for 5 minutes in an argon gas atmosphere at 3 atmospheres and 300 °C. This transformed the second alkaline-cleaned surface into a primary surface with a predetermined oxide layer. In this way, the required number of GaAs single-crystal substrates of sample 1 were obtained. The diameter and thickness of the GaAs single-crystal substrate precursor were maintained in each of the GaAs single-crystal substrates. (Epitaxial layer formation step)

[0146] Wet etching was performed under the following conditions: the GaAs single-crystal substrate was cleaned for 1 minute with sulfuric acid and hydrogen peroxide (H₂SO₄:H₂O₂:H₂O = 7:1:1), exposed to running water, and dried. Furthermore, a 1 µm thick Al 0·5 Ga 0·5 An As layer was grown as an epitaxial layer on the main surface of one of the GaAs single-crystal substrates, each of which had undergone wet etching (hereinafter, the GaAs single-crystal substrate with the main surface on which the epitaxial layer grew is also referred to as the "epitaxial substrate"). In this way, the epitaxial substrate of sample 1 was obtained. During the growth of the epitaxial layer, the GaAs single-crystal substrate was heated to 550 °C. <Probe 2>

[0147] The required number of GaAs single-crystal substrates of sample 2 were obtained in the same manner as for sample 1, except that: in the second alkaline cleaning step, an aqueous solution containing 0.1 wt% tetramethylammonium hydroxide as a base was applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which was rotated at 1500 rpm in the direction of rotation, at a flow rate of 0.5 L / min for 30 seconds; and in the heat treatment step, the heat treatment was carried out under an argon gas atmosphere at 1.1 atmospheres, 150 °C, for 1 minute. Furthermore, a 1 µm thick Al 0·5 Ga 0·5 The As layer was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. <Probe 11>

[0148] The required number of GaAs single-crystal substrates of sample 11 were obtained in the same manner as for sample 1, except that the second alkaline purification step and the heat treatment step were omitted. Furthermore, a 1 µm thick Al 0·5 Ga 0·5 The As layer was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. <Probe 12>

[0149] The required number of GaAs single-crystal substrates of sample 12 were obtained in the same manner as for sample 1, except that the second alkaline purification step was omitted. Furthermore, a 1 µm thick Al 0·5 Ga 0·5 The As layer was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. [Sample 13]

[0150] The required number of GaAs single-crystal substrates of sample 13 were obtained in the same manner as for sample 1, except that the heat treatment step was omitted. Furthermore, a 1 µm thick Al 0.5 Ga 0.5 The As layer was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. [First test] <Analyse eines GaAs-Einkristall-Substrats mittels Röntgen-Photoelektronenspektroskopie>

[0151] X-rays with an energy of 600 eV were prepared using "BL17," one of the beamlines exclusively for Sumitomo Electric Industries at SAGA Light Source. The X-ray beam was directed onto the center of the main surface of each of the GaAs single-crystal substrates of samples 1 and 2, as well as samples 11 to 13, enabling analysis by X-ray photoelectron spectroscopy. Since the GaAs single-crystal substrates of samples 1 and 2, as well as samples 11 to 13, could not be fully placed on a sample stage, a specimen was cut from each of the GaAs single-crystal substrates of samples 1 and 2, as well as samples 11 to 13, and the analysis was performed on this specimen. The analysis conditions are as follows. Condition 1: X-ray incident energy of 600 eV and photoelectron exit angle of 30° Condition 2: X-ray incident energy of 600 eV and photoelectron exit angle of 45° Condition 3: X-ray incident energy of 600 eV and photoelectron exit angle of 85°

[0152] Test specimen size under all conditions: 10 mm × 10 mm

[0153] Pressure around the test specimen under all conditions: 4×10 -7 Pa

[0154] High-resolution XPS analyzer (trade name: "R3000" from Scienta Omicron) used under all conditions

[0155] Energy resolution E / ΔE: 3480

[0156] Plot interval for the coupling energy: 0.02 eV

[0157] Integration time and number of integrations for each energy value: 100 ms and 50 times.

[0158] Based on a Ga3d spectrum and an As3d spectrum obtained by XPS analysis under all of the above conditions (conditions 1 to 3), a first integrated intensity ratio (In1) and a second integrated intensity ratio (In2) were obtained, each of which is a ratio of a sum of an integrated intensity of the As 5+ , an integrated intensity of the ace 3+ , an integrated intensity of the As-Ga and an integrated intensity of the metal-As to a sum of an integrated intensity of the Ga + , an integrated intensity of the Ga 3+ and an integrated intensity of the Ga-As in each of samples 1 and 2, as well as samples 11 to 13. Further, based on a Ga3d spectrum and an As3d spectrum obtained by XPS analysis under all of the above conditions (conditions 1 to 3), a third integrated intensity ratio (In3), a fourth integrated intensity ratio (In4), and a fifth integrated intensity ratio (In5) were obtained, each of which represents a ratio of a sum of an integrated intensity of the As 5+ and an integrated intensity of the acetylcholine 3+ to a sum of an integrated intensity of the Ga + and an integrated intensity of the Ga 3+ in each of samples 1 and 2, as well as samples 11 to 13. A ratio (In1 / In2) of the first integrated intensity ratio (In1) to the second integrated intensity ratio (In2) in each of samples 1 and 2 and samples 11 to 13 was also calculated. The results are shown in Table 1. Table 1 also shows a ratio of the sum of the integrated intensity of the As 5+ , the integrated intensity of the ace 3+ , the integrated intensity of As-Ga and the integrated intensity of metal-As to a sum of the integrated intensity of Ga+, the integrated intensity of Ga 3+ and the integrated intensity of the Ga-As based on the Ga3d spectrum obtained from the XPS analysis under condition 2 and the As3d spectrum. In Table 1, “Total Ga” means the sum of the integrated intensity of the Ga + , the integrated intensity of the Ga 3+ and the integrated intensity of the Ga-As and “Total-As” means the sum of the integrated intensity of the As 5+ , the integrated intensity of the ace 3+ , the integrated intensity of the As-Ga and the integrated intensity of the metal As. <Maximalwert und Durchschnittswert der Trübung der Oberfläche der Epitaxialschicht>

[0159] The maximum and average surface turbidity of the epitaxial layer in each of the epitaxial substrates of samples 1 and 2, as well as samples 11 to 13, were determined using a surface foreign particle inspection instrument (trade name: "Surfscan 6420" by KLA-Tencor Corporation). The results are shown in Table 1.

[0160] Furthermore, the quality of the epitaxial substrate of each of samples 1 and 2, as well as samples 11 to 13, was determined based on the maximum and average values ​​of the surface turbidity of the epitaxial layer according to the following criteria. The results are shown in Table 1. A: The maximum turbidity value is 20 ppm or less and the average turbidity value is 2.0 ppm or less; B: The maximum turbidity value is more than 20 ppm and 100 ppm or less, and the average turbidity value is more than 2.0 ppm and 2.5 ppm or less; and C: The maximum turbidity value is more than 100 ppm or the average turbidity value is more than 2.5 ppm. <Benetzbarkeit (Kontaktwinkel)>

[0161] In an environment at room temperature (20 to 25 °C) and a relative humidity of 40 to 60%, 2 µL of distilled water was dropped onto the center of the main surface of each GaAs single-crystal substrate of samples 1 and 2, as well as samples 11 to 13. The contact angle of the distilled water droplet formed on the main surface was measured using the θ / 2 method. A contact angle measuring device (e.g., the Kyowa Interface Science Drop Master 500, trade name (product number)) can be used to observe the droplet. The results are shown in Table 1. Table 1 <bewertung>

[0162] According to Table 1, the quality of each of the epitaxial substrates of samples 1 and 2 was determined to be A or B, where each met all the following conditions: that the second integrated intensity ratio is 0.9 or greater and 1.05 or less; that both the third and fourth integrated intensity ratios are 1.0 or less; that the fifth integrated intensity ratio is 0.8 or less; and that the ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or 1 or less. Conversely, the quality of each of the epitaxial substrates of samples 11 to 13, which each failed to meet at least one of the aforementioned conditions, was determined to be C. [Second test]<Herstellung eines GaAs-Einkristall-Substrats> (Sample 3)

[0163] A GaAs single-crystal substrate of sample 3 was obtained in the same way as sample 1, except that in the preparation step a semi-insulating GaAs single crystal with added carbon (C) atoms was cut and chamfered to prepare a GaAs single-crystal substrate precursor with a diameter of 3 inches (76 mm) and a thickness of 350 µm. (Sample 4)

[0164] A GaAs single-crystal substrate of sample 4 was obtained in the same way as sample 1, except that in the preparation step a semi-insulating GaAs single crystal with added carbon (C) atoms was cut and chamfered to prepare a GaAs single-crystal substrate precursor with a diameter of 4 inches (100 mm) and a thickness of 350 µm. (Sample 5)

[0165] A GaAs single-crystal substrate of sample 5 was obtained in the same way as in sample 1, except that in the preparation step a semi-insulating GaAs single crystal with added carbon (C) atoms was cut and chamfered to prepare a GaAs single-crystal substrate precursor with a diameter of 6 inches (150 mm) and a thickness of 675 µm. (Sample 6)

[0166] A GaAs single-crystal substrate of sample 6 was obtained in the same way as sample 1, except that in the preparation step a semi-insulating GaAs single crystal with added carbon (C) atoms was cut and chamfered to prepare a GaAs single-crystal substrate precursor with a diameter of 8 inches (200 mm) and a thickness of 675 µm. <Analyse der Gleichmäßigkeit der Hauptoberfläche des GaAs-Einkristall-Substrats> (Samples 3 and 4)

[0167] Five test specimens cut from each of the main surfaces of the GaAs single-crystal substrates of samples 3 and 4 were prepared in the same manner as in the<Analyse eines GaAs-Einkristall-Substrats mittels Röntgen-Photoelektronenspektroskopie> analyzed in the first test. In this way, a sixth integrated intensity ratio (In6) was determined, which is a ratio of a sum of an integrated intensity of the As. 5+ , an integrated intensity of the ace 3+ , an integrated intensity of the As-Ga and an integrated intensity of the metal-As to a sum of an integrated intensity of the Ga + , an integrated intensity of the Ga 3+ and represents an integrated intensity of the Ga-As. Furthermore, a seventh integrated intensity ratio (In7) was obtained, which is a ratio of a sum of the integrated intensity of the As. 5+ and the integrated intensity of the acetylcholine 3+ to a sum of the integrated intensity of the Ga + and the integrated intensity of the Ga 3+ This represents the seventh integrated intensity ratio (In7) to the sixth integrated intensity ratio (In6). Furthermore, a ratio (In7 / In6) of the seventh integrated intensity ratio (In7) to the sixth integrated intensity ratio (In6) was calculated. Subsequently, the standard deviation and mean value of In7 / In6 were calculated to determine the standard deviation / mean value.

[0168] Each of the five test specimens includes a first measuring point P1, a second measuring point P2, a third measuring point P3, a fourth measuring point P4 and a fifth measuring point P5 (see the Fig. 4) Each of the five test specimens was placed in a high-resolution XPS analyzer to irradiate 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 with X-rays. The results are presented in Tables 2 and 3. Table 2 shows In7 / In6 in the GaAs single-crystal substrate of specimen 3, along with its standard deviation and mean value. Table 3 shows In7 / In6 in the GaAs single-crystal substrate of specimen 4, along with its standard deviation and mean value. Since the standard deviation and mean value are smaller in Tables 2 and 3, respectively, the property of the GaAs single-crystal substrate is more uniform in the plane of the main surface. (Samples 5 and 6)

[0169] Nine test specimens cut from each of the main surfaces of the GaAs single-crystal substrates of samples 5 and 6 were prepared in the same manner as in<Analyse eines GaAs-Einkristall-Substrats mittels Röntgen-Photoelektronenspektroskopie> analyzed in the first test. In this way, an eighth integrated intensity ratio (In6) was determined, which is the ratio of a sum of an integrated intensity of the As. 5+ , an integrated intensity of the ace 3+ , an integrated intensity of the As-Ga and an integrated intensity of the metal-As to a sum of an integrated intensity of the Ga + , an integrated intensity of the Ga 3+ and represents an integrated intensity of the Ga-As. Furthermore, a ninth integrated intensity ratio (In7) was obtained, which is a ratio of the sum of the integrated intensity of the As. 5+ and the integrated intensity of the acetylcholine 3+ to a sum of the integrated intensity of the Ga + and the integrated intensity of the Ga 3+ This represents the ninth integrated intensity ratio (In9) to the eighth integrated intensity ratio (In8). Furthermore, the ratio (In9 / In8) of the ninth integrated intensity ratio (In9) to the eighth integrated intensity ratio (In8) was calculated. Subsequently, the standard deviation and mean value of In9 / In8 were calculated to determine the standard deviation / mean value.

[0170] Each of the nine test specimens comprises a first measuring point P1, a second measuring point P2, a third measuring point P3, a fourth measuring point P4, a fifth measuring point P5, a sixth measuring point P6, a seventh measuring point P7, an eighth measuring point P8 and a ninth measuring point P9 (see the Fig. 5) Each of the nine test specimens was placed in a high-resolution XPS analyzer to irradiate the first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, the fifth measurement point P5, the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 with X-rays. The results are shown in Tables 4 and 5. Table 4 shows In9 / In8 in the GaAs single-crystal substrate of sample 5, along with its standard deviation and mean value. Table 5 shows In9 / In8 in the GaAs single-crystal substrate of sample 6, along with its standard deviation and mean value. Since the standard deviation / mean value is smaller in each case, as shown in Tables 4 and 5, the property of the GaAs single-crystal substrate is more uniform in the plane of the main surface. [Table 2] Measuring point Coordinates (X,Y) In7 / In6 600eV 85° P1 (0,0) 0,75 P2 (19,0) 0,77 P3 (0, 19) 0,72 P4 (-19,0) 0,80 P5 (0,-19) 0,75 Average / Standard deviation σσ / Average 0,76 0,029 0,039 Table 3 Measuring point Coordinates(X,Y) In7 / In6 600eV 85° P1 (0,0) 0,79 P2 (25,0) 0,79 P3 (0,25) 0,80 P4 (25,0) 0.75 P5 (0,25) 0,80 Average / Standard deviation σσ / Average 0,79 0,021 0,026 Table 4 Measuring point Coordinates(X,Y) In9 / In8 600eV 85° P1 (0,0) 0,79 P2 (37.5,0) 0,78 P3 (0,37.5) 0,79 P4 (-37.5,0) 0,78 P5 (0,-37.5) 0,79 P6 (65,0) 0,79 P7 (0,65) 0,77 P8 (-65,0) 0,79 P9 (0,-65) 0,79 Average / Standard deviation σ 0,79 0,007 σ / average 0,009 Table 5 Measuring point Coordinates(X,Y) In9 / In8 600eV 85° P1 (0,0) 0,79 P2 (50,0) 0,78 P3 (0, 50) 0,78 P4 (-50,0) 0,78 P5 (0,-50) 0,78 P6 (90,0) 0,77 P7 (0,90) 0,74 P8 (-90,0) 0,79 P9 (0,-90) 0,80 Average / Standard deviation σσ / Average 0,78 0,017 0,022 <bewertung>

[0171] According to Tables 2 and 3, for each of the GaAs single-crystal substrates of samples 3 and 4, the standard deviation and the mean value of the ratio (In7 / In6) of the seventh integrated intensity ratio (In7) to the sixth integrated intensity ratio (In6) meet a standard deviation / mean value ratio ≤ 0.039. According to Tables 4 and 5, for each of the GaAs single-crystal substrates of samples 5 and 6, the standard deviation and the mean value of the ratio (In9 / In8) of the ninth integrated intensity ratio (In9) to the eighth integrated intensity ratio (In8) meet a standard deviation / mean value ratio ≤ 0.022. Thus, it is understood that the property of each of the GaAs single-crystal substrates of samples 3 to 6 is sufficiently uniform in the plane of the main surface.Since each of the GaAs single-crystal substrates of samples 3 to 6 has a high mirror surface property over its entire main surface, it is expected that an epitaxial layer with a reduced turbidity value can be formed on it.

[0172] The embodiments and examples of the present disclosure have been explained so far, but it was initially expected that the configurations of the embodiments and examples would be suitably combined.

[0173] The embodiments and examples disclosed herein serve only for illustration and are in no way limiting. The scope of protection of the present invention is defined by the claims and not by the embodiments and examples described above, and is intended to encompass all modifications within the scope and meaning that correspond to the claims. Reference symbol list

[0174] 1 GaAs single-crystal substrate; 1 m main area; 10 X-ray generation device; 11 X-ray source; 12, 14 slit; 13 grating; 20 vacuum chamber; 30 electron spectrometer; 50 notch; 100 analysis system; LA As3d spectrum; LG Ga3d spectrum; L1 Ga 3+ -Spectrum; L2 Ga + -Spectrum; L3 Ga-As spectrum; L4 As 5+ -Spectrum; L5 As 3+ -Spectrum; L6 Metal-As spectrum; L7 As-Ga spectrum; P1 First measurement point; P2 Second measurement point; P3 Third measurement point; P4 Fourth measurement point; P5 Fifth measurement point; P6 Sixth measurement point; P7 Seventh measurement point; P8 Eighth measurement point; P9 Ninth measurement point; A1 to A9 Measurement target; S100 Preparation step; S200 Cleaning step; S210 Surface polishing step; S220 First alkaline cleaning step; S230 Acid cleaning step; S240 Second alkaline cleaning step; S250 Heat treatment step; S300 Epitaxial layer formation step. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2008-300747

[0002] JP 06-045318

[0002] Cited non-patent literature

[0000] Method of Estimating Inelastic Mean Free Path of Electrons by Tpp-2M Formula", Journal of Surface Analysis, Vol. 1, No. 2, 1995

[0062] Kazuhiro Yoshihara: "Journal of the Vacuum Society of Japan", 2013, Volume 56, No. 6, pp. 243-247

[0071] J.J. Yeh, „Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters", Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993 und J.J. Yeh und I. Lindau, „Atomic Data and Nuclear Data Tables", 32, 1-155 (1985

[0085] < / bewertung> < / bewertung> < / epitaxialschicht> < / epitaxialschicht> < / durchmesser> < / oxidschicht>

Claims

[1] A gallium arsenide single crystal substrate comprising a main surface in circular form, wherein the gallium arsenide single-crystal substrate exhibits a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, and a fifth integrated intensity ratio. Both the first integrated intensity ratio and the third integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°. Both the second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-rays are applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°. the fourth integrated intensity ratio is obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°, Both the first integrated intensity ratio and the second integrated intensity ratio each correspond to a ratio of the sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metal arsenic to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide. Both the third integrated intensity ratio, the fourth integrated intensity ratio and the fifth integrated intensity ratio each correspond to a ratio of a sum of an integrated intensity of the arsenic element present as diarsene pentoxide and an integrated intensity of the arsenic element present as diarsene trioxide to a sum of an integrated intensity of the gallium element present as digallium monoxide and an integrated intensity of the gallium element present as digallium trioxide. the second integrated intensity ratio is 0.9 or more and 1.05 or less, both the third intensity ratio and the fourth integrated intensity ratio are 1.0 or less, the fifth integrated intensity ratio is 0.8 or less, and a ratio of the first integrated intensity ratio to the second integrated intensity ratio is 0.5 or more and 1 or less. [2] The gallium arsenide single crystal substrate according to claim 1, wherein the second integrated intensity ratio is 0.9 or more and less than 1.

04. [3] The gallium arsenide single crystal substrate according to claim 1 or 2, wherein the gallium arsenide single crystal substrate has an oxide layer with a thickness of 2 nm or less on the main surface. [4] The gallium arsenide single crystal substrate according to claim 3, wherein the contact angle of the oxide layer is 20° or less. [5] The gallium arsenide single crystal substrate according to any one of claims 1 to 4, wherein the gallium arsenide single crystal substrate has a diameter of 75 mm or more and 205 mm or less. [6] The gallium arsenide single crystal substrate according to claim 1, according to any one of claims 1 to 5, wherein. the gallium arsenide single crystal substrate has a diameter of 75 mm or more and less than 150 mm, the gallium arsenide single crystal substrate exhibits a sixth integrated intensity ratio and a seventh integrated intensity ratio, Both the sixth integrated intensity ratio and the seventh integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to each of the five measurement points on the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°. the sixth integrated intensity ratio is a ratio of the sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide and an integrated intensity of an arsenic element present as metallic arsenic to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide and an integrated intensity of a gallium element present as gallium arsenide, the seventh integrated intensity ratio is a ratio of the sum of the integrated intensity of the arsenic element present as diarsene pentoxide and the integrated intensity of the arsenic element present as diarsene trioxide to the sum of the integrated intensity of a gallium element present as digallium monoxide and the integrated intensity of a gallium element present as digallium trioxide. a standard deviation and an average value of a ratio of the seventh integrated intensity ratio to the sixth integrated intensity ratio satisfy a relationship standard deviation / average value ≤ 0.039, and if the diameter is specified by D and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as an X-axis and a Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and the Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0) and (0, -D / 4) respectively, and the units of D and of both X and Y are in the coordinates (X, Y) mm. [7] The gallium arsenide single crystal substrate according to any one of claims 1 to 5, wherein. the gallium arsenide single crystal substrate has a diameter of 150 mm or more and 205 mm or less, the gallium arsenide single crystal substrate exhibits an eighth integrated intensity ratio and a ninth integrated intensity ratio, Both the eighth integrated intensity ratio and the ninth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted externally onto the gallium arsenide single-crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to each of the nine measurement points on the main surface under the conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°. the eighth integrated intensity ratio is a ratio of the sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metallic arsenic to the sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide. the ninth integrated intensity ratio is a ratio of the sum of the integrated intensity of the arsenic element present as diarsene pentoxide and the integrated intensity of the arsenic element present as diarsene trioxide, to the sum of the integrated intensity of a gallium element present as digallium monoxide and the integrated intensity of a gallium element present as digallium trioxide. a standard deviation and an average value of a ratio of the ninth integrated intensity ratio to the eighth integrated intensity ratio satisfy a relationship standard deviation / average value ≤ 0.022, and if the diameter is specified by D and two axes, each passing through the center of the main surface, each lie on the main surface and are orthogonal to each other, are defined as an X-axis and a Y-axis, the coordinates (X, Y) of the nine measurement points on the X-axis and the Y-axis are respectively (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 as well as of both X and Y are in the coordinates (X, Y) mm. [8] The gallium arsenide single crystal substrate according to any one of claims 1 to 7, wherein. the gallium arsenide single-crystal substrate has an epitaxial layer on its main surface, a maximum turbidity value of an epitaxial layer surface is 100 ppm or less and an average value of the turbidity of the surface of the epitaxial layer is 2.5 ppm or less. [9] A method for producing a gallium arsenide single crystal substrate having a main surface in a circular shape, the method comprising: the preparation of a gallium arsenide single-crystal substrate precursor with a circular surface; and the obtaining of the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor, wherein, the comprehensive preservation the conversion of the surface of the gallium arsenide single crystal substrate precursor to a polished surface by polishing the surface, The conversion of the polished surface to an alkaline cleaned surface by cleaning the polished surface with a first alkaline cleaning fluid, Converting an alkaline-cleaned surface to an acid-cleaned surface by cleaning the alkaline-cleaned surface with an acidic cleaning fluid containing 0.3 ppm by mass or more and 0.5 percent by mass or less of an acid, Converting the acid-cleaned surface to a second alkaline-cleaned surface by cleaning the acid-cleaned surface by applying a second alkaline cleaning fluid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more, and Converting the second alkaline-cleaned surface into the main surface by performing a heat treatment on the second alkaline-cleaned surface in an inert gas atmosphere at a pressure of 1.1 atmospheres or more and 3 atmospheres or less and 150 °C or more and 300 °C or less, the first alkaline cleaning fluid contains 0.1% by mass or more and 10% by mass or less of a first base, the first base contains at least either quaternary ammonium hydroxide and / or quaternary pyridinium hydroxide, the second alkaline cleaning fluid contains 0.3 ppm by mass or more and 0.5 percent by mass or less of a second base, and The second base contains at least either quaternary ammonium hydroxide or quaternary pyridinium hydroxide. [10] The method for producing a gallium arsenide single crystal substrate according to claim 9, comprising forming an epitaxial layer on the main surface. [11] The gallium arsenide single crystal substrate according to claim 2, wherein the gallium arsenide single-crystal substrate has an oxide layer with a thickness of 2 nm or less on the main surface, and a contact angle of the oxide layer is 20° or less.

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