Indium phosphide substrate and method for manufacturing indium phosphide substrate

Abstract

The ratio of the integrated intensity of indium element that is present as an oxide to the integrated intensity of indium element that is present as indium phosphide is denoted as a first integrated intensity ratio. The ratio of the integrated intensity of indium element that is present as metal indium to the integrated intensity of indium element that is present as indium phosphide is denoted as a second integrated intensity ratio. The ratio of the integrated intensity of phosphorus element that is present as an oxide to the integrated intensity of phosphorus element that is present as indium phosphide is denoted as a third integrated intensity ratio. The ratio of the integrated intensity of indium element to the integrated intensity of phosphorus element is denoted as a fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 to 3.20 inclusive. The second integrated intensity ratio is 0.05 to 0.30 inclusive. The third integrated intensity ratio is 2.90 to 11.00 inclusive. The fourth integrated intensity ratio is 1.15 to 2.00 inclusive.

Description

Indium phosphide substrate and method for manufacturing the same

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to indium phosphide substrates and methods for making indium phosphide substrates.

[0002] Japanese Patent Laid-Open Publication No. 62-252140 (Patent Document 1) describes a cleaning method in which a mirror-polished InP wafer is cleaned with a mixed solution containing phosphoric acid or hydrogen fluoride.

[0003] Japanese Patent Application Publication No. 62-252140

[0004] The indium phosphide substrate according to the present disclosure is an indium phosphide substrate having a main surface. X-rays are irradiated onto the center of the main surface under conditions of an X-ray incident energy of 200 eV and a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy, in which photoelectrons emitted to the outside of the indium phosphide substrate are captured, and a spectrum of the detected intensity of indium 4d electrons and a spectrum of the detected intensity of phosphorus 2p electrons are obtained. The ratio of the integrated intensity of indium element present as oxide to the integrated intensity of indium element present as indium phosphide is defined as a first integrated intensity ratio. The ratio of the integrated intensity of indium element present as metallic indium to the integrated intensity of indium element present as indium phosphide is defined as a second integrated intensity ratio. The ratio of the integrated intensity of phosphorus element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a third integrated intensity ratio. The ratio of the integrated intensity of indium element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 or more and 3.20 or less, the second integrated intensity ratio is 0.05 or more and 0.30 or less, the third integrated intensity ratio is 2.90 or more and 11.00 or less, and the fourth integrated intensity ratio is 1.15 or more and 2.00 or less.

[0005] FIG. 1 is a plan view schematic diagram showing the configuration of an indium phosphide substrate according to this embodiment. FIG. 2 is a cross-sectional view schematic diagram taken along line II-II in FIG. 1. FIG. 3 is an enlarged cross-sectional view schematic diagram showing region III in FIG. 2. FIG. 4 is a cross-sectional view schematic diagram showing the configuration of an analysis system used in X-ray photoelectron spectroscopy. FIG. 5 is a cross-sectional view schematic diagram showing the In4d spectrum of an indium phosphide substrate according to this embodiment. FIG. 6 is a cross-sectional view schematic diagram showing the P2p spectrum of an indium phosphide substrate according to this embodiment. FIG. 7 is a flow chart showing an outline of a method for producing an indium phosphide substrate according to this embodiment. FIG. 8 is a cross-sectional view schematic diagram showing an enlarged cross-sectional view illustrating a step of immersing an indium phosphide single crystal substrate in an acidic solution. FIG. 9 is a cross-sectional view schematic diagram showing an enlarged cross-sectional view illustrating a step of immersing an indium phosphide single crystal substrate in ozone water. FIG. 10 is a cross-sectional view schematic diagram showing the surface state of an indium phosphide substrate when the amount of phosphorus present is excessively high. FIG. 11 is a cross-sectional view schematic diagram showing a state in which metaphosphoric acid has collapsed. Fig. 12 is an enlarged cross-sectional schematic view showing a state in which indium oxide is formed on an indium phosphide single crystal substrate. Fig. 13 is a graph showing a first integrated intensity ratio and the yield of the epitaxial substrate of the indium phosphide substrates according to Samples 1 to 11. Fig. 14 is a graph showing a second integrated intensity ratio and the yield of the epitaxial substrate of the indium phosphide substrates according to Samples 1 to 11. Fig. 15 is a graph showing a third integrated intensity ratio and the yield of the epitaxial substrate of the indium phosphide substrates according to Samples 1 to 11. Fig. 16 is a graph showing a fourth integrated intensity ratio and the yield of the epitaxial substrate of the indium phosphide substrates according to Samples 1 to 11.

[0006] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide an indium phosphide substrate and a method for manufacturing an indium phosphide substrate that can improve the yield of epitaxial substrates.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an indium phosphide substrate and a method for manufacturing an indium phosphide substrate that can improve the yield of epitaxial substrates.

[0008] [Outline of the embodiment] First, an outline of the embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described.

[0009] (1) The indium phosphide substrate according to the present disclosure is an indium phosphide substrate having a main surface. X-rays are irradiated onto the center of the main surface under conditions of an X-ray incident energy of 200 eV and a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy, where photoelectrons emitted to the outside of the indium phosphide substrate are captured, and a spectrum of the detected intensity of indium 4d electrons and a spectrum of the detected intensity of phosphorus 2p electrons are obtained. The ratio of the integrated intensity of indium element present as oxide to the integrated intensity of indium element present as indium phosphide is defined as a first integrated intensity ratio. The ratio of the integrated intensity of indium element present as metallic indium to the integrated intensity of indium element present as indium phosphide is defined as a second integrated intensity ratio. The ratio of the integrated intensity of phosphorus element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a third integrated intensity ratio. The ratio of the integrated intensity of indium element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 or more and 3.20 or less, the second integrated intensity ratio is 0.05 or more and 0.30 or less, the third integrated intensity ratio is 2.90 or more and 11.00 or less, and the fourth integrated intensity ratio is 1.15 or more and 2.00 or less.

[0010] As described above, in the indium phosphide substrate according to this embodiment, the amounts of indium oxide, metallic indium, and phosphate in the surface layer are prevented from becoming excessively large or small, thereby improving the yield of epitaxial substrates.

[0011] (2) A method for producing an indium phosphide substrate according to the present disclosure includes the following steps: immersing an indium phosphide single crystal substrate in an acidic solution; cleaning the indium phosphide single crystal substrate using ultrapure water after the step of immersing the indium phosphide single crystal substrate in the acidic solution; cleaning the indium phosphide single crystal substrate using ultrapure water after the step of cleaning the indium phosphide single crystal substrate using ultrapure water; cleaning the indium phosphide single crystal substrate using ultrapure water after the step of immersing the indium phosphide single crystal substrate in ozone water; The hydrogen ion exponent of the acidic solution is 2.0 or more and 4.0 or less, and the ozone concentration in the ozone water is 3 ppm or more and 30 ppm or less, or the hydrogen ion exponent of the acidic solution is 1.0 or more and 5.0 or less, and the ozone concentration in the ozone water is 10 ppm or more and 30 ppm or less. This can improve the yield of epitaxial substrates.

[0012] (3) According to the method for manufacturing an indium phosphide substrate according to (2) above, the acidic solution may contain any of an organic acid, hydrochloric acid, and hydrofluoric acid.

[0013] (4) According to the method for manufacturing an indium phosphide substrate according to (2) or (3), in the step of immersing the indium phosphide single crystal substrate in the acidic solution, the temperature of the acidic solution may be room temperature. The time for immersing the indium phosphide single crystal substrate in the acidic solution may be 10 seconds or more and 5 minutes or less. This effectively improves the yield of epitaxial substrates.

[0014] (5) In the method for manufacturing an indium phosphide substrate according to any one of (2) to (4) above, in the step of immersing the indium phosphide single crystal substrate in ozone water, the temperature of the ozone water may be room temperature. The time for immersing the indium phosphide single crystal substrate in ozone water may be 10 seconds or more and 5 minutes or less. This effectively improves the yield of epitaxial substrates.

[0015] [Details of the Embodiments] Hereinafter, details of the embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the following drawings are given the same reference numerals, and their description will not be repeated. In the crystallographic description in this specification, individual orientations are indicated by [ ], collective orientations by < >, individual planes by ( ), and collective planes by {}. Furthermore, for negative indices, in crystallography, a "-" (bar) is placed above the number, but in this specification, a negative sign is placed before the number.

[0016] <Indium Phosphide Substrate> First, the configuration of an indium phosphide substrate 100 (hereinafter also referred to as an InP substrate 100) according to this embodiment will be described. FIG. 1 is a plan view schematically showing the configuration of the InP substrate 100 according to this embodiment. FIG. 2 is a cross-sectional view schematically showing the configuration of the InP substrate 100 along line II-II in FIG. 1. As shown in FIGS. 1 and 2, the InP substrate 100 has a first main surface 1, a second main surface 2, and an outer peripheral surface 9.

[0017] The first main surface 1 is, for example, planar. When viewed along a line perpendicular to the first main surface 1 (hereinafter also referred to as a planar view), the shape of the first main surface 1 is, for example, circular. The first main surface 1 includes a center O. The first main surface 1 extends along each of a first direction 101 and a second direction 102.

[0018] The first main surface 1 is, for example, a {100} plane of single-crystal indium phosphide constituting the InP substrate 100. The first direction 101 and the second direction 102 are, for example, the <011> direction. The second direction 102 is a direction perpendicular to the first direction 101.

[0019] As shown in FIG. 2 , the second main surface 2 is opposite the first main surface 1. The direction from the second main surface 2 toward the first main surface 1 is referred to as a third direction 103. The third direction 103 is the growth direction of the indium phosphide single crystal when the InP substrate 100 is manufactured. The third direction 103 is, for example, the <100> direction. The outer peripheral surface 9 is continuous with each of the first main surface 1 and the second main surface 2. The ridge between the first main surface 1 and the outer peripheral surface 9 is referred to as an outer edge 8. Hereinafter, the first main surface 1 and the second main surface 2 will also be referred to simply as the main surfaces.

[0020] 1, the diameter W1 of the first main surface 1 is, for example, 75 mm or more and 300 mm or less. The diameter W1 is the longest distance between two different points on the outer edge 8.

[0021] At least one of a notch, an orientation flat, and an index flat may be provided on the outer peripheral surface 9. When at least one of a notch, an orientation flat, and an index flat is provided on the outer peripheral surface 9, the center O is defined as the center of a circle that includes an arc along the arc-shaped portion of the outer peripheral surface 9 in a plan view.

[0022] The InP substrate 100 may contain, for example, sulfur (S), iron (Fe), or tin (Sn) as an impurity. The InP substrate 100 may not contain, for example, an impurity. In other words, the InP substrate 100 may be non-doped.

[0023] Fig. 3 is an enlarged schematic cross-sectional view showing region III in Fig. 2. As shown in Fig. 3, the InP substrate 100 has an indium phosphide single crystal substrate 10 (hereinafter also referred to as an InP single crystal substrate 10), a first surface layer 11, and a second surface layer 12.

[0024] The InP single crystal substrate 10 is made of single crystal indium phosphide. The InP single crystal substrate 10 has a third main surface 3 and a fourth main surface 4. In a plan view, the third main surface 3 has, for example, a circular shape. The fourth main surface 4 is located opposite the third main surface 3. The third main surface 3 is located in a third direction 103 relative to the fourth main surface 4.

[0025] The first surface layer 11 is on the third main surface 3. The first surface layer 11 covers the third main surface 3. The first surface layer 11 constitutes the first main surface 1. The first surface layer 11 contains indium phosphide (InP), indium oxide, metallic indium, and phosphorus oxide. The thickness of the first surface layer 11 in the third direction 103 is, for example, 2 nm or less.

[0026] The second surface layer 12 is on the fourth main surface 4. From another perspective, the InP single crystal substrate 10 is between the first surface layer 11 and the second surface layer 12. The second surface layer 12 covers the fourth main surface 4. The second surface layer 12 constitutes the second main surface 2. The second surface layer 12 contains indium phosphide, indium oxide, metallic indium, and phosphorus oxide. The thickness of the second surface layer 12 in the third direction 103 is, for example, 2 nm or less. Hereinafter, the first surface layer 11 and the second surface layer 12 will also be simply referred to as surface layers.

[0027] (X-ray Photoelectron Spectroscopy) Next, a method for analyzing the surface state of the InP substrate 100 using X-ray photoelectron spectroscopy (XPS) will be described.

[0028] <Analysis System> Fig. 4 is a schematic diagram showing the configuration of an analysis system used in X-ray photoelectron spectroscopy. As shown in Fig. 4, the analysis system 200 mainly includes an X-ray generating facility 20, a vacuum chamber 30, and an electron spectrometer 40.

[0029] The X-ray generating facility 20 generates X-rays. X-rays are also called synchrotron radiation. The X-ray generating facility 20 can generate X-rays with an energy of, for example, 50 eV or more and 2000 eV or less. For example, the beamline "BL17" at the Saga Prefectural Kyushu Synchrotron Light Research Center can be used as the X-ray generating facility 20.

[0030] 4, the X-ray generating equipment 20 has an X-ray source 21, a first slit 22, a grating 23, and a second slit 24. The X-ray source 21 outputs X-rays in the direction of arrow A.

[0031] The first slit 22 is disposed in the direction of arrow A relative to the X-ray source 21. The first slit 22 is, for example, a four-quadrant slit. The first slit 22 allows a portion of the X-rays to pass through. The slit width of the first slit 22 is, for example, 30 μm.

[0032] The grating 23 is disposed in the direction of arrow A relative to the first slit 22. The grating 23 is a spectroscope. The grating 23 monochromatizes the X-rays. The ruling density at the center of the grating 23 is, for example, 400 l / mm.

[0033] The second slit 24 is disposed in the direction of arrow A relative to the grating 23. From another perspective, the grating 23 is disposed between the first slit 22 and the second slit 24. The second slit 24 is, for example, a four-quadrant slit. The second slit 24 limits the spread of the monochromated X-rays. The slit width of the second slit 24 is, for example, 30 μm.

[0034] The vacuum vessel 30 is connected to the X-ray generating facility 20. The vacuum vessel 30 is arranged in the direction of arrow A relative to the X-ray generating facility 20. The vacuum vessel 30 is the portion where the InP substrate 100 is arranged.

[0035] The electron spectrometer 40 is connected to the vacuum vessel 30. The electron spectrometer 40 is connected to the X-ray generating equipment 20 via the vacuum vessel 30. The electron spectrometer 40 has a hemispherical analyzer (not shown) and a detector (not shown). The hemispherical analyzer separates the photoelectrons. The detector calculates the number of photoelectrons of each kinetic energy. For example, a high-resolution XPS analyzer "R3000" manufactured by Scienta Omicron can be used as the electron spectrometer 40.

[0036] The internal spaces of the X-ray generating facility 20, the vacuum vessel 30, and the electron spectrometer 40 are maintained at an ultra-high vacuum. Specifically, the pressure in the internal spaces of the X-ray generating facility 20, the vacuum vessel 30, and the electron spectrometer 40 is, for example, 4×10 －７ It is Pa.

[0037] <Analysis Method> Next, a method for analyzing the surface state of the InP substrate 100 using the analysis system 200 will be described.

[0038] First, an InP substrate 100 is placed in a vacuum chamber 30. X-rays are irradiated from an X-ray generating facility 20 toward the InP substrate 100. Specifically, an X-ray source 21 uses a magnetic field generated by a bending electromagnet (not shown) to bend the traveling direction of high-energy electrons in a circular accelerator (not shown). As a result, synchrotron radiation (X-rays) is emitted in a direction tangent to the traveling direction of the high-energy electrons. The X-ray source 21 outputs the X-rays along the arrow A.

[0039] The X-rays emitted from the X-ray source 21 have high brightness. Specifically, the number of X-ray photons emitted from the X-ray source 21 per second is, for example, 10 ９ The X-rays emitted from the X-ray source 21 are collimated using a collimating mirror (not shown) or the like. A portion of the collimated X-rays passes through the first slit 22. The X-rays that have passed through the first slit 22 are monochromatized by the grating 23. The spread of the monochromatized X-rays is limited by the second slit 24.

[0040] The energy of the X-rays irradiated from the X-ray generating equipment 20 onto the InP substrate 100 is determined by the slit width of the first slit 22 , the slit width of the second slit 24 , and the ruling density of the grating 23 .

[0041] For example, when the slit width of each of the first slit 22 and the second slit 24 is 30 μm and the ruling density at the center of the grating 23 is 400 l / mm, 200 eV X-rays are irradiated from the X-ray generating facility 20 .

[0042] The angle (incident angle θ1) formed between the traveling direction of the X-rays irradiated onto the InP substrate 100 from the X-ray generating equipment 20 and the first main surface 1 of the InP substrate 100 is not particularly limited, but is set to, for example, 5°. When the InP substrate 100 is irradiated with the X-rays, photoelectrons are emitted from the InP substrate 100.

[0043] Some of the photoelectrons emitted from the InP substrate 100 lose energy due to inelastic scattering, so only some of the photoelectrons generated in the InP substrate 100 escape into vacuum while retaining the energy they had when they were generated, and are captured by the electron spectrometer 40.

[0044] The angle (take-off angle θ2) formed between the traveling direction B of the photoelectrons reaching the electron spectrometer 40 and the first main surface 1 of the InP substrate 100 is set to 45°. The electron spectrometer 40 measures the kinetic energy distribution of the photoelectrons emitted from the InP substrate 100.

[0045] The brightness (intensity) of the X-rays emitted from the X-ray source 21 decays over time. For example, the brightness of the X-rays emitted from the X-ray source 21 11 hours after the X-ray source 21 is turned on is one-third of the brightness of the X-rays emitted from the X-ray source 21 immediately after the X-ray source 21 is turned on. The Au4f photoelectron intensity is measured at regular intervals using a standard sample made of gold (Au). The decay ratio of the Au4f photoelectron intensity is calculated based on the measured Au4f photoelectron intensity. The X-ray exposure dose is corrected based on the calculated decay ratio.

[0046] <Analysis Target Region> Photoelectrons that can escape from the surface of the InP substrate 100 are generated in a region up to a depth equivalent to approximately three times the inelastic mean free path (IMFP) of the photoelectrons. This depth is the depth of the region of the InP substrate 100 that is the analysis target. Hereinafter, this depth will also be referred to as the measurement depth.

[0047] The measurement depth is calculated based on parameters related to 4d electrons of indium (In) in InP, indium oxide, and metallic indium, parameters related to 2p electrons of phosphorus (P) in InP and phosphorus oxide, and the X-ray incident energy. For example, when the X-ray incident energy is 200 eV and the photoelectron take-off angle θ2 is 45°, the measurement depth in the InP substrate 100 is approximately 1.0 nm to 1.5 nm.

[0048] (Method of Calculating Integrated Intensity Ratio) Next, a method of calculating the integrated intensity ratio at the first main surface 1 of the InP substrate 100 based on the kinetic energy distribution of photoelectrons measured by the above-mentioned XPS will be described.

[0049] <In4d Spectrum and P2p Spectrum> The kinetic energy E of photoelectrons emitted from the InP substrate 100 is the sum of the energy hν of the irradiated X-rays and the binding energy E of the photoelectrons in the InP substrate 100. Ｂ and the work function φ, E is expressed by the following formula 1: E=hν−E Ｂ −φ (Formula 1) Using the above formula 1, a spectrum indicating the binding energy distribution of photoelectrons is calculated based on the kinetic energy distribution of photoelectrons emitted from the InP substrate 100. Specifically, an In4d spectrum and a P2p spectrum are obtained by narrow scanning a predetermined range of binding energies.

[0050] In this specification, the term "In4d spectrum" refers to a spectrum representing the detected intensity of photoelectrons emitted from the 4d orbital of In contained in indium oxide, InP, and metallic indium. The term "P2p spectrum" refers to a spectrum representing the detected intensity of photoelectrons emitted from the 2p orbital of P contained in phosphate and InP.

[0051] An In4d spectrum can be obtained by narrow scanning the binding energy range of 14 eV to 24 eV. Similarly, a P2p spectrum can be obtained by narrow scanning the binding energy range of 127 eV to 137 eV. Narrow scanning can improve the measurement accuracy of both the In4d spectrum and the P2p spectrum.

[0052] In the narrow scan, the conditions that can be used are an energy interval of 0.05 eV, an accumulation time at each energy value of 100 ms, and an accumulation number of 2 to 5. The energy resolution E / ΔE is 3480.

[0053] <Background Correction> Background correction is performed on the obtained In4d spectrum and P2p spectrum by using the Shirley method (Reference: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, No. 6, pp. 243-247). As a result, a background-corrected In4d spectrum is calculated based on the difference between the In4d spectrum obtained by the narrow scan and the background. Similarly, a background-corrected P2p spectrum is calculated based on the difference between the P2p spectrum obtained by the narrow scan and the background.

[0054] <Charge Shift Correction> When the above-mentioned X-ray photoelectron spectroscopy is performed on an InP crystal, a charge shift may occur. In this case, each of the above-mentioned In4d spectrum and P2p spectrum may shift to the high energy side by up to about 1 eV. Therefore, the charge shift correction is performed by fixing the peak positions of each of the In4d spectrum and P2p spectrum.

[0055] Specifically, the peak positions of the detection intensities of the In element present as an oxide (In—O), the In element present as InP (In—P), and the In element present as metallic In (In—In) contained in the In4d spectrum are fixed. More specifically, the binding energy at the peak of the detection intensity of In—O is set to 17.9 eV. The binding energy at the peak of the detection intensity of In—P is set to approximately 17.0 eV or more and 17.5 eV or less. The binding energy at the peak of the detection intensity of In—In is set to approximately 16.0 eV or more and 16.5 eV or less. Note that the peaks of the detection intensities of In—P and In—In are affected by the InP single crystal substrate 10 (see FIG. 3 ). Therefore, it is difficult to fix them to a single value. Therefore, as described above, the peak positions of the detection intensities of In—P and In—In are set to have a width of 0.5 eV.

[0056] Similarly, the peak positions of the detection intensities of P element present as an oxide (P—O) and P element present as InP (P—In) contained in the P2p spectrum are fixed. Specifically, the binding energy at the peak of the detection intensity of P—O is assumed to be 132.82 eV. The binding energy at the peak of the detection intensity of P-In is assumed to be approximately 128.2 eV or more and 128.7 eV or less. Note that, like In—P and In—In, the peak of the detection intensity of P-In is affected by the InP single crystal substrate 10 (see FIG. 3). Therefore, it is difficult to fix it to a single value. Therefore, as described above, the peak position of the detection intensity of P-In is given a width of 0.5 eV.

[0057] As a result of the above, a corrected In4d spectrum LI and a corrected P2p spectrum LP are obtained. FIG. 5 is a schematic diagram showing the In4d spectrum LI of the InP substrate 100 according to this embodiment. FIG. 6 is a schematic diagram showing the P2p spectrum LP of the InP substrate 100 according to this embodiment. In each of FIGS. 5 and 6 , the horizontal axis represents binding energy. The vertical axis represents the detected intensity of photoelectrons. FIG. 5 shows the detected intensity in the binding energy range of 14 eV to 24 eV. FIG. 6 shows the detected intensity in the binding energy range of 127 eV to 137 eV. In FIG. 5 , each spectrum is normalized with the photoelectron intensity value at the maximum peak of the In4d spectrum LI set to 1. In FIG. 6 , each spectrum is normalized with the photoelectron intensity value at the maximum peak of the P2p spectrum LP set to 1.

[0058] <Peak Separation> Next, an operation is performed in which each of the In4d spectrum LI and the P2p spectrum LP is separated into a plurality of Gaussian functions and expressed. In this specification, this operation is also referred to as "peak separation."

[0059] Specifically, it is assumed that the In4d spectrum L after the above correction is expressed as the sum of multiple Gaussian functions. The In4d spectrum L is expressed by separating it into the following three equations (Equation 2, Equation 3, and Equation 4). Equation 2, Equation 3, and Equation 4 correspond to the In—O spectrum, the In—P spectrum, and the In—In spectrum, respectively.

[0060]

[0061]

[0062]

[0063] The spectrum of In4d has two sub-peaks (In4d ３／２ and In4d ５／２ ) (peak splitting). ３／２ Intensity and In4d ５／２ The intensity ratio of In4d to In4d is 2:3. ３／２ The binding energy in In4d ５／２ The binding energy is smaller than that in In4d. ３／２ Binding energy in In4d ５／２ The absolute value of the difference (energy difference) between the binding energy at In4d and that at In4d is set to 0.90 eV. Therefore, the In-O spectrum (Equation 2), the In-P spectrum (Equation 3), and the In-In spectrum (Equation 4) are each expressed as In4d ３／２ and In4d ５／２ In the spectrum of In—O, the peaks are blunted and do not appear to be split, but they are approximately represented by two subpeaks, similar to those of In—P and In—In.

[0064] In the above Equations 2, 3, and 4, Y1, Y2, and Y3 each represent photoelectron intensity. The units of Y1, Y2, and Y3 are dimensionless. X represents binding energy. The unit of X is eV. a1, a2, a3, b1, b2, b3, c1, c2, and c3 are variables. The units of a1, a2, and a3 are dimensionless. The units of b1, b2, b3, c1, c2, and c3 are eV.

[0065] The square of the difference between the measured value of the In4d spectrum LI after the above correction and the sum of Y1, Y2, and Y3 ([measured value - (Y1 + Y2 + Y3)] ２ Each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) is optimized so that the value of the binding energy at the peak of the detected intensity of In—O, In—P, and In—In is minimized.

[0066] The numerical values ​​or numerical ranges of each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) are as follows: a1, a2, and a3 are real numbers equal to or greater than 0. b1=19.9 eV 17.0 eV≦b2≦17.5 eV 16.0 eV≦b3≦16.5 eV 0.3 eV≦c1≦1.05 eV 0.3 eV≦c2≦1.05 eV 0.3 eV≦c3≦1.05 eV As described above, peak separation allows the spectra of In—O, In—P, and In—In to be obtained in the binding energy range of 14 eV to 24 eV. In FIG. 5, In—O spectrum L1 indicates the obtained In—O spectrum. In-P spectrum L2 indicates the obtained In-P spectrum. In—In spectrum L3 indicates the obtained In—In spectrum.

[0067] Similarly, it is assumed that the P2p spectrum LP after the above correction is expressed as the sum of multiple Gaussian functions. The P2p spectrum LP is expressed separately in the following two equations (Equation 5 and Equation 6). Equations 5 and 6 correspond to the P-O and P-In spectra, respectively.

[0068]

[0069]

[0070] Similar to the In4d spectrum, the P2p spectrum has two subpeaks (P2p １／２ and P2p ３／２ ) (peak splitting). １／２ Intensity and P2p ３／２ The intensity ratio of P2p to P2p is 1:2. １／２ The binding energy at P2p ３／２ The binding energy is smaller than that at １／２ The binding energy at P2p ３／２ The absolute value of the difference (energy difference) between the binding energy at P2p and the P-In spectrum (Equation 5) is set to 0.85 eV. １／２ and P2p ３／２ In the spectrum of P-O, the peak is blunted and does not appear to be split, but it is approximately represented by two sub-peaks, just like P-In.

[0071] In the above Equations 5 and 6, Y4 and Y5 each represent photoelectron intensity. The units of Y4 and Y5 are dimensionless. X represents binding energy. The unit of X is eV. a4, a5, b4, b5, c4, and c5 are each variables. The units of a4 and a5 are dimensionless. The units of b4, b5, c4, and c5 are eV.

[0072] The square of the difference between the measured value of the P2p spectrum LP after the above correction and the sum of Y4 and Y5 ([measured value - (Y4 + Y5)] ２ Each variable (a4, a5, b4, b5, c4, c5) is optimized so that the above-mentioned binding energy values ​​at the peaks of P-O and P-In detection intensities are respectively substituted for b4 and b5.

[0073] The numerical values ​​or numerical ranges of each variable (a4, a5, b4, b5, c4, c5) are as follows: a4 and a5 are real numbers equal to or greater than 0. b4=132.82 eV 128.2 eV≦b5≦128.7 eV 0.3 eV≦c4≦1.05 eV 0.3 eV≦c5≦1.05 eV As described above, peak separation allows for the acquisition of spectra of P-O and P-In in the binding energy range of 127 eV to 137 eV. In FIG. 6, P-O spectrum L4 shows the obtained P-O spectrum. P-In spectrum L5 shows the obtained P-In spectrum.

[0074] The following correction is made to determine the peak intensities Y1 to Y5 described above. The probability of photoelectrons being generated by X-ray irradiation is called the photoionization efficiency (η). η varies depending on the element, orbital, and incident energy of the X-rays. The unit of η is dimensionless. The correction is made by dividing the detected intensities of the In4d spectrum LI and the P2p spectrum LP obtained by actual measurements by η. This makes it possible to compare the abundances of the In element and the P element in the InP substrate 100.

[0075] The data published on the following website is used as the value of η. Specifically, the photoionization efficiency (η) of In4d when the incident X-ray energy is 200 eV is set to 0.68. The photoionization efficiency (η) of P2p when the incident X-ray energy is 200 eV is set to 3.49.

[0076] (Website) https: / / vuo.elettra.eu / services / elements / WebElements.html (The data is based on the following literature: J.J. Yeh, Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993, and J.J. Yeh and I. Lindau, Atomic Data and Nuclear Data Tables, 32, 1-155 (1985).) <Integrated Intensity Ratio> In FIG. 5, the area of ​​the region surrounded by the In—O spectrum L1 and the horizontal axis is taken as the integrated intensity of In—O. The integrated intensity of In—O corresponds to the number of photoelectrons emitted from the 4d orbital of In—O. From another perspective, the integrated intensity of In—O corresponds to the amount of indium oxide present in the region being analyzed by XPS.

[0077] 5, the area of ​​the region surrounded by the In-P spectrum L2 and the horizontal axis is the integrated intensity of In-P. The integrated intensity of In-P corresponds to the number of photoelectrons emitted from the 4d orbital of In-P. From another perspective, the integrated intensity of In-P corresponds to the amount of indium phosphide present in the region analyzed by XPS.

[0078] In Figure 5, the area of ​​the region surrounded by the In-In spectrum L3 and the horizontal axis is the integrated intensity of In-In. The integrated intensity of In-In corresponds to the number of photoelectrons emitted from the 4d orbital of In-In. From another perspective, the integrated intensity of In-In corresponds to the amount of metallic indium present in the region analyzed by XPS.

[0079] 5, the area enclosed by the In4d spectrum LI and the horizontal axis is the integrated intensity of indium. The integrated intensity of indium corresponds to the number of photoelectrons emitted from the 4d orbital of indium. From another perspective, the integrated intensity of indium corresponds to the amount of indium present in the region analyzed by XPS.

[0080] 6, the area of ​​the region surrounded by the P-O spectrum L4 and the horizontal axis is the integrated intensity of P-O. The integrated intensity of P-O corresponds to the number of photoelectrons emitted from the 2p orbital of P-O. From another perspective, the integrated intensity of P-O corresponds to the amount of phosphate present in the region being analyzed by XPS.

[0081] 6, the area of ​​the region surrounded by the P-In spectrum L5 and the horizontal axis is the integrated intensity of P-In. The integrated intensity of P-In corresponds to the number of photoelectrons emitted from the 2p orbital of P-In. From another perspective, the integrated intensity of P-In corresponds to the amount of indium phosphide present in the region analyzed by XPS.

[0082] 6, the area of ​​the region surrounded by the P2p spectrum LP and the horizontal axis is the integrated intensity of phosphorus. The integrated intensity of phosphorus corresponds to the number of photoelectrons emitted from the 2p orbital of phosphorus. From another perspective, the integrated intensity of phosphorus corresponds to the amount of phosphorus present in the region to be analyzed by XPS.

[0083] The ratio of the integrated intensity of In—O to the integrated intensity of In—P is defined as a first integrated intensity ratio. In other words, the first integrated intensity ratio is the value obtained by dividing the integrated intensity of In—O by the integrated intensity of In—P. When the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 according to this embodiment, the first integrated intensity ratio is 1.10 or more and 3.20 or less. The first integrated intensity ratio may be, for example, 1.30 or more, or 1.50 or more. The first integrated intensity ratio may be, for example, 3.00 or less, or 2.50 or less.

[0084] The ratio of the In—In integrated intensity to the In—P integrated intensity is defined as the second integrated intensity ratio. In other words, the second integrated intensity ratio is the value obtained by dividing the In—In integrated intensity by the In—P integrated intensity. When the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 according to this embodiment, the second integrated intensity ratio is 0.05 or more and 0.30 or less. The second integrated intensity ratio may be, for example, 0.10 or more, or 0.15 or more. The second integrated intensity ratio may be, for example, 0.25 or less, or 0.20 or less.

[0085] The ratio of the integrated intensity of P-O to the integrated intensity of P-In is defined as a third integrated intensity ratio. In other words, the third integrated intensity ratio is the value obtained by dividing the integrated intensity of P-O by the integrated intensity of P-In. When the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 according to this embodiment, the third integrated intensity ratio is 2.90 or more and 11.00 or less. The third integrated intensity ratio may be, for example, 3.00 or more, or 5.50 or more. The third integrated intensity ratio may be, for example, 10.00 or less, or 6.00 or less.

[0086] The ratio of the integrated intensity of indium to the integrated intensity of phosphorus is defined as a fourth integrated intensity ratio. In other words, the fourth integrated intensity ratio is the value obtained by dividing the integrated intensity of indium by the integrated intensity of phosphorus. When the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 according to this embodiment, the fourth integrated intensity ratio is 1.15 or more and 2.00 or less. The fourth integrated intensity ratio may be, for example, 1.30 or more, or 1.50 or more. The fourth integrated intensity ratio may be, for example, 1.80 or less, or 1.60 or less.

[0087] In addition, when the above-mentioned XPS analysis is performed on the second main surface 2 of the InP substrate 100 according to this embodiment, the numerical ranges of the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, and the fourth integrated intensity ratio may be the same as the above-mentioned numerical ranges.

[0088] <Method for Manufacturing Indium Phosphide Substrate> Next, a method for manufacturing the InP substrate 100 according to this embodiment will be described. Fig. 7 is a flow chart that schematically shows the method for manufacturing the InP substrate 100 according to this embodiment. As shown in Fig. 7, the method for manufacturing the InP substrate 100 according to this embodiment mainly includes a step (S10) of preparing an indium phosphide single crystal substrate, a step (S20) of immersing the indium phosphide single crystal substrate in an acidic solution, a first cleaning step (S30), a step (S40) of immersing the indium phosphide single crystal substrate in ozone water, and a second cleaning step (S50).

[0089] First, a step (S10) of preparing an indium phosphide single crystal substrate is carried out. An InP single crystal substrate 10 is prepared. Specifically, an indium phosphide single crystal is manufactured using, for example, a vertical boat method. The indium phosphide single crystal is sliced ​​using, for example, a wire saw, to form the InP single crystal substrate 10.

[0090] For example, the InP single crystal substrate 10 is polished at each of the third main surface 3 and the fourth main surface 4. Specifically, the InP single crystal substrate 10 is polished so that the surface of the InP single crystal substrate 10 becomes a mirror finish. In order to remove abrasives and the like adhering to the polished InP single crystal substrate 10, the InP single crystal substrate 10 is cleaned using, for example, hydrofluoric acid. The cleaned InP single crystal substrate 10 is boiled using, for example, IPA (Isopropyl Alcohol). This dries the surface of the InP single crystal substrate 10. In this way, the above-mentioned InP single crystal substrate 10 (see FIG. 3 ) is prepared.

[0091] Next, a step (S20) of immersing the indium phosphide single crystal substrate in an acidic solution is carried out. Fig. 8 is an enlarged cross-sectional schematic view showing the step (S20) of immersing the indium phosphide single crystal substrate in an acidic solution. As shown in Fig. 8, the InP single crystal substrate 10 is immersed in an acidic solution 81. The acidic solution 81 covers, for example, the third main surface 3 and the fourth main surface 4 of the InP single crystal substrate 10.

[0092] The acidic solution 81 contains, for example, any of an organic acid, hydrochloric acid, or hydrofluoric acid. The organic acid is, for example, acetic acid or citric acid. The hydrogen ion exponent of the acidic solution 81 is 1.0 or more and 5.0 or less. The hydrogen ion exponent of the acidic solution 81 may be, for example, 1.8 or more, or 2.5 or more. The hydrogen ion exponent of the acidic solution 81 may be, for example, 4.7 or less, or 3.5 or less.

[0093] The temperature of the acidic solution 81 is, for example, room temperature (e.g., 25°C). The time (first time) for immersing the InP single crystal substrate 10 in the acidic solution 81 is, for example, 10 seconds or more and 300 seconds (5 minutes) or less. The first time may be, for example, 60 seconds or more, or 120 seconds or more. The first time may be, for example, 240 seconds or less, or 180 seconds or less.

[0094] A rotor (not shown) may be placed in the acidic solution 81. The rotor may be rotated in the acidic solution 81 using magnetic force, thereby stirring the acidic solution 81. This can promote the reaction between the acidic solution 81 and the InP single crystal substrate 10.

[0095] As shown in FIG. 8, the In atoms at the third main surface 3 react with the H of the acidic solution 81. ＋ The P atoms react with the ions. This ionizes the In atoms. The ionized In atoms dissolve into the acidic solution 81. Therefore, there is an excess of P atoms at the third main surface 3. The P atoms react with, for example, water molecules in the acidic solution 81, thereby forming phosphorus oxide 71 on the third main surface 3.

[0096] After the first time period has elapsed, the InP single crystal substrate 10 is removed from the acid solution 81. Phosphate 71 is formed on the third main surface 3 by reaction of the P atoms with oxygen in the atmosphere.

[0097] Next, a first cleaning step (S30) is carried out. Ultrapure water (not shown) is prepared. The dissolved oxygen concentration of the ultrapure water is, for example, 100 ppb or less. The InP single crystal substrate 10 is cleaned using the ultrapure water. This removes the acid solution 81 adhering to the InP single crystal substrate 10.

[0098] Next, a step (S40) of immersing the indium phosphide single crystal substrate in ozone water is carried out. Fig. 9 is an enlarged cross-sectional schematic view showing the step (S40) of immersing the indium phosphide single crystal substrate in ozone water. As shown in Fig. 9, the InP single crystal substrate 10 is immersed in ozone water 82. The ozone water 82 covers, for example, the third main surface 3 and the fourth main surface 4 of the InP single crystal substrate 10.

[0099] The ozone concentration in ozone water 82 is 3 ppm or more and 30 ppm or more. The ozone concentration in ozone water 82 may be, for example, 5 ppm or more, 8 ppm or more, or 10 ppm or more. The ozone concentration in ozone water 82 may be, for example, 25 ppm or less, 20 ppm or less, 18 ppm or less, or 15 ppm or less.

[0100] In the manufacturing method of the InP substrate 100 according to this embodiment, the hydrogen ion exponent of the acidic solution 81 and the ozone concentration in the ozone water 82 each satisfy the following condition 1 or 2. (Condition 1) The hydrogen ion exponent of the acidic solution 81 is 2.0 or more and 4.0 or less, and the ozone concentration in the ozone water 82 is 3 ppm or more and 30 ppm or less. (Condition 2) The hydrogen ion exponent of the acidic solution 81 is 1.0 or more and 5.0 or less, and the ozone concentration in the ozone water 82 is 10 ppm or more and 30 ppm or less.

[0101] The temperature of the ozone water 82 is, for example, room temperature (e.g., 25°C). The time (second time) for immersing the InP single crystal substrate 10 in the ozone water 82 is, for example, 10 seconds or more and 300 seconds (5 minutes) or less. The second time may be, for example, 60 seconds or more, or 120 seconds or more. The second time may be, for example, 240 seconds or less, or 180 seconds or less.

[0102] As shown in FIG. 9 , P atoms present as indium phosphide and P atoms present as oxide react with hydroxyl radicals (OH) in the ozone water 82. This ionizes the P atoms. The ionized P atoms dissolve into the ozone water 82. Therefore, In atoms become excessive. This causes In atoms 73 to migrate on the third main surface 3. Some of the In atoms 73 are oxidized to form indium oxide 72. A plurality of In atoms 73 aggregate to form tiny indium droplets 74. Hereinafter, the indium droplets 74 will also be referred to as metallic indium 74.

[0103] After the second time has elapsed, the InP single crystal substrate 10 is removed from the ozone water 82. The In atoms 73 react with oxygen in the atmosphere to form indium oxide 72 on the third main surface 3.

[0104] Next, the second cleaning step (S50) is carried out. Ultrapure water (not shown) having substantially the same composition as the ultrapure water used in the first cleaning step (S30) is prepared. The InP single crystal substrate 10 is cleaned using the ultrapure water. As a result, the ozone water 82 adhering to the InP single crystal substrate 10 is removed.

[0105] As a result of the above, phosphorus oxide 71, indium oxide 72, and indium droplets 74 are formed on the third main surface 3. For convenience of explanation, the phosphorus oxide 71, indium oxide 72, and indium droplets 74 are each illustrated as an independent object in Figures 8 and 9. In reality, the phosphorus oxide 71, indium oxide 72, and indium droplets 74 constitute the first surface layer 11 (see Figure 3) on the third main surface 3.

[0106] Similarly, phosphorus oxide 71, indium oxide 72, and indium droplets 74 are formed on the fourth main surface 4. The phosphorus oxide 71, indium oxide 72, and indium droplets 74 constitute the second surface layer 12 (see FIG. 3 ) on the fourth main surface 4. In this way, the InP substrate 100 according to this embodiment is manufactured.

[0107] Next, the effects of the indium phosphide substrate and the method for manufacturing the indium phosphide substrate according to this embodiment will be described.

[0108] When an epitaxial substrate is manufactured using an InP substrate 100, the yield of the epitaxial substrate may be lower than expected. Specifically, haze may increase on the surface of the epitaxial substrate. Haze is a value obtained by dividing the amount of scattered light when light is irradiated onto the surface of an object to be measured by the amount of incident light. Furthermore, the number of LPDs (Light Point Defects) may increase in the epitaxial substrate. LPDs are surface defects detected by measuring scattered light generated by irradiating the surface of the epitaxial substrate with light.

[0109] The haze and the number of LPDs are each used as an index for evaluating the surface condition of an epitaxial substrate. If the haze is excessively high, the characteristics of a semiconductor device manufactured using the epitaxial substrate will deteriorate. If the number of LPDs is excessively high, the characteristics of a semiconductor device manufactured using the epitaxial substrate will deteriorate.

[0110] While investigating ways to improve the surface condition of an epitaxial substrate, the inventors focused on the structure of the InP substrate 100 near the main surface. For example, cleaning of the InP substrate 100 can result in the formation of oxides on the surface of the InP substrate 100. Conventional XPS instruments emit incident X-rays with high energy (e.g., approximately 2 keV), so they can only measure average information for a region approximately 9 nm deep from the substrate surface. Therefore, conventional XPS instruments cannot extract information only from a region very close to the surface. Therefore, if a very thin layer composed of an oxide or the like is present on the main surface of the InP substrate 100, conventional XPS instruments cannot quantitatively and accurately analyze the layer.

[0111] The inventors have come up with the idea of ​​analyzing a region very close to the main surface by performing XPS under conditions where the X-ray incident energy is 200 eV and the photoelectron take-off angle θ2 is 45°. By performing XPS under these conditions, it is possible to extract information about a region up to a depth of about 1.5 nm from the main surface. Based on the information about this region, the inventors have made the following findings.

[0112] The inventors have found that the abundance of indium elements (In—O, In—P, and In—In) and phosphorus elements (P—O and P—In) in the surface layer of the InP substrate 100 affect the haze and the number of LPDs in the epitaxial substrate.

[0113] FIG. 10 is an enlarged cross-sectional schematic diagram showing the surface state of the InP substrate 100 when the amount of phosphorus element (P—O, P—In) present is excessively large. When P—O is excessively large, the first surface layer 11 contains an excessive amount of phosphorus oxide. As shown in FIG. 10, in this case, the phosphorus oxide reacts with moisture in the air. As a result, a metaphosphate portion 75 is formed. The metaphosphate portion 75 is formed by reacting metaphosphate ((HPO ３ ) ｎ ) is composed of

[0114] FIG. 11 is an enlarged cross-sectional schematic diagram showing a state in which the metaphosphate portion 75 has collapsed. As shown in FIG. 11 , the metaphosphate portion 75 is formed so that it covers the first surface layer 11. The metaphosphate portion 75 has relatively low physical strength. Therefore, the metaphosphate portion 75 may collapse when the InP substrate 100 is transported into the epitaxial growth furnace. When the metaphosphate portion 75 collapses, minute irregularities and holes 79 are formed in the first surface layer 11. As a result, a portion of the InP single crystal substrate 10 is exposed from the first surface layer 11.

[0115] 12 is an enlarged schematic view showing a state in which indium oxide 72 has been formed on the InP single crystal substrate 10. As shown in FIG. 12, the exposed portion of the InP single crystal substrate 10 reacts with moisture and oxygen in the atmosphere, thereby forming indium oxide 72.

[0116] As described above, it is believed that the main surface of the InP substrate 100 becomes non-uniform. When an epitaxial layer is formed on the non-uniform main surface, irregularities are formed on the surface of the epitaxial layer. This increases the haze and the number of LPDs in the epitaxial substrate.

[0117] When the abundance of indium (In—O, In—P, and In—In) and phosphorus (P—O and P—In) in the surface layer of the InP substrate 100 is appropriate, the surface layer can be removed by heating the InP substrate 100 in a hydrogen atmosphere during epitaxial growth. However, when the abundance of indium (In—O, In—P, and In—In) is excessively high, the thickness of the surface layer becomes excessively large. In this case, heating the InP substrate 100 in a hydrogen atmosphere may not be sufficient to remove the surface layer. As a result, the surface layer inhibits epitaxial growth. As a result, an increase in haze and an increase in the number of LPDs occur in the epitaxial substrate.

[0118] When the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 according to this embodiment, the first integrated intensity ratio is 1.10 or more and 3.20 or less. The second integrated intensity ratio is 0.05 or more and 0.30 or less. The third integrated intensity ratio is 2.90 or more and 11.00 or less. The fourth integrated intensity ratio is 1.15 or more and 2.00 or less. As described above, the InP substrate 100 according to this embodiment prevents the indium oxide 72 and metallic indium 74 from becoming excessively abundant in the first surface layer 11. This prevents the first surface layer 11 from becoming excessively thick, which would be caused by an excessively high amount of indium element. As a result, when growing an epitaxial layer on the first main surface 1, the first surface layer 11 can be sufficiently removed by heating the InP substrate 100 in a hydrogen atmosphere. Therefore, when growing an epitaxial layer, it is possible to prevent the epitaxial growth from being hindered by the first surface layer 11. As a result, it is possible to improve the yield of epitaxial substrates.

[0119] Furthermore, in the InP substrate 100 according to this embodiment, the first surface layer 11 is prevented from containing an excessive amount of phosphate 71. This prevents the first surface layer 11 from reacting with moisture in the atmosphere to form metaphosphate portions 75. This prevents the first surface layer 11 from collapsing due to shocks applied to the InP substrate 100 during transportation. This prevents an increase in haze and an increase in the number of LPDs in the epitaxial substrate when an epitaxial layer is grown on the first main surface 1. As a result, the yield of epitaxial substrates can be improved.

[0120] To grow an epitaxial film on the first main surface 1 of the InP substrate 100, it is necessary to heat the InP substrate 100 inside an epitaxial growth furnace, decompose the source gas on the first main surface 1, and react and deposit the decomposed source gas. However, if the amounts of indium oxide 72, metallic indium 74, and phosphorus oxide 71 in the first surface layer 11 are each excessively small, the phosphorus constituting the InP substrate 100 is released upon heating, causing the first main surface 1 to become rough. In this case, it is not possible to grow a good epitaxial film.

[0121] In the InP substrate 100 according to this embodiment, the indium oxide 72, the metallic indium 74, and the phosphorus oxide 71 are prevented from becoming excessively small in the first surface layer 11. Therefore, the presence of an appropriate amount of indium oxide 72, the metallic indium 74, and the phosphorus oxide 71 can improve the yield of the epitaxial substrate.

[0122] While studying ways to improve the yield of epitaxial substrates, the inventors came up with the idea of ​​immersing an indium phosphide single crystal substrate in each of an acidic solution and ozone water. After further intensive research, the inventors discovered that by optimizing the hydrogen ion exponent of the acidic solution and the ozone concentration in the ozone water, it is possible to prevent the indium oxide 72, metallic indium 74, and phosphorus oxide 71 from becoming excessively large or small in the first surface layer 11 of the InP substrate 100.

[0123] The method for manufacturing the InP substrate 100 according to this embodiment includes a step (S20) of immersing the indium phosphide single crystal substrate in an acidic solution and a step (S40) of immersing the indium phosphide single crystal substrate in ozone water. The hydrogen ion exponent of the acidic solution 81 is 2.0 or more and 4.0 or less, and the ozone concentration of the ozone water 82 is 3 ppm or more and 30 ppm or less, or the hydrogen ion exponent of the acidic solution 81 is 1.0 or more and 5.0 or less, and the ozone concentration of the ozone water 82 is 10 ppm or more and 30 ppm or less.

[0124] This is thought to prevent the chemical reaction caused by immersing the InP single crystal substrate 10 in the acid solution 81 and the chemical reaction caused by immersing the InP single crystal substrate 10 in the ozone water 82 from proceeding excessively. This prevents the indium oxide 72, metallic indium 74, and phosphorus oxide 71 from becoming excessively large or small in the first surface layer 11 of the InP substrate 100. This improves the yield of epitaxial substrates as described above.

[0125] According to the method for manufacturing the InP substrate 100 of this embodiment, the time for immersing the InP single crystal substrate 10 in the acid solution 81 is from 10 seconds to 300 seconds (5 minutes) inclusive. This is thought to prevent excessive progress of chemical reactions caused by immersion of the InP single crystal substrate 10 in the acid solution 81. This effectively prevents the amounts of indium oxide 72, metallic indium 74, and phosphorus oxide 71 from becoming excessively large or small. This improves the yield of epitaxial substrates, as described above.

[0126] According to the method for manufacturing the InP substrate 100 of this embodiment, the time for immersing the InP single crystal substrate 10 in the ozone water 82 is from 10 seconds to 300 seconds (5 minutes). This is thought to prevent excessive progress of chemical reactions caused by immersion of the InP single crystal substrate 10 in the ozone water 82. This effectively prevents the amounts of indium oxide 72, metallic indium 74, and phosphorus oxide 71 from becoming excessively large or small. This improves the yield of epitaxial substrates, as described above.

[0127] (Sample Preparation) First, InP substrates 100 according to Samples 1 to 11 were prepared. The InP substrates 100 according to Samples 1 to 7 are comparative examples. The samples according to Samples 8 to 11 are examples. The InP substrates 100 according to Samples 1 to 11 were manufactured according to the above-described method for manufacturing the InP substrate 100. Specifically, the InP substrates 100 were manufactured using the conditions shown in Table 1 below.

[0128]

[0129] Table 1 shows the manufacturing conditions for the InP substrate 100 according to Samples 1 to 11. In Sample 1, the step of immersing the indium phosphide single crystal substrate in ozone water (S40) and the second cleaning step (S50) were not performed. In Sample 2, the step of immersing the indium phosphide single crystal substrate in an acidic solution (S20) and the first cleaning step (S30) were not performed. In Samples 3 to 11, all steps of the above-described method for manufacturing the InP substrate 100 were performed.

[0130] In samples 1, 5, 10, and 11, the acid solution 81 contained hydrochloric acid and was adjusted to have a pH of 3. In samples 3, 4, and 9, the acid solution contained hydrofluoric acid and was adjusted to have a pH of 1. In samples 6, 7, and 8, the acid solution contained citric acid and was adjusted to have a pH of 5.

[0131] The immersion time in the acid solution was 300 seconds for Samples 3, 6, and 10. The immersion time in the acid solution was 60 seconds for Samples 1, 7, 9, and 11. The immersion time in the acid solution was 10 seconds for Samples 4, 5, and 8.

[0132] The ozone concentration in the ozone water 82 was adjusted to 100 ppm in Samples 3, 5, and 7. The ozone concentration in the ozone water 82 was adjusted to 20 ppm in Samples 2, 8, 9, and 10. The ozone concentration in the ozone water 82 was adjusted to 5 ppm in Samples 4, 6, and 11.

[0133] The immersion time in ozone water 82 for samples 3, 8, and 11 was 300 seconds. The immersion time in ozone water 82 for samples 2, 5, 6, and 9 was 60 seconds. The immersion time in ozone water 82 for samples 4, 7, and 10 was 10 seconds.

[0134] (Evaluation Method) The above-described XPS analysis was performed on the first main surface 1 of the InP substrate 100 according to Samples 1 to 11. Specifically, the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, and the fourth integrated intensity ratio were each measured using the above-described analysis method.

[0135] The yield of epitaxial substrates manufactured using the InP substrates 100 according to Samples 1 to 11 was measured. Specifically, a plurality of InP substrates 100 according to each of Samples 1 to 11 were prepared. An epitaxial layer was formed on the first main surface 1 of the InP substrate 100 by metalorganic vapor phase epitaxy (MOVPE).

[0136] The haze and the number of LPDs were measured on the surface of the epitaxial substrate. The surface density of LPDs was calculated by dividing the number of measured LPDs by the area of ​​the measurement region. A Surfscan 6220 inspection device manufactured by KLA-Tencor Corporation was used to measure the haze and the number of LPDs. An argon ion laser was used as the light source. The output of the light source was 30 mW. The wavelength of the light source was 488 nm.

[0137] In the haze measurement, the minimum value of the ratio of the amount of scattered light to the amount of incident light was 0.0049 ppm (Haze From: 0.0049 ppm). In other words, the lower limit of the haze measurement was 0.0049 ppm.

[0138] In measuring the number of LPDs, the minimum size of LPDs to be included in the measurement results was set to 0.19 μm (Threshold: 0.19 μm). In other words, of the detected surface defects, surface defects with a maximum diameter of 0.19 μm or more were identified as LPDs. In measuring the number of LPDs, the measurement pitch was set to 10 μm (Throughput: Low). The haze measurement and the number of LPDs were each measured in a region of the surface of the epitaxial substrate excluding a region within 3 mm from the outer edge of the surface of the epitaxial substrate (edge ​​exclusion). The outer edge of the surface of the epitaxial substrate is the ridge between the outer circumferential surface 9 and the surface of the epitaxial substrate.

[0139] The haze is 7 ppm or less, and the surface density of LPDs is 5 particles / cm ２ The epitaxial substrates that met the following criteria were determined to be non-defective: The yield of the epitaxial substrates was determined by dividing the number of non-defective epitaxial substrates by the total number of epitaxial substrates manufactured.

[0140] (Evaluation results)

[0141]

[0142] Table 2 shows the integrated intensity ratios of the InP substrate 100 and the yields of the epitaxial substrates for Samples 1 to 11.

[0143] In the samples according to the example (Samples 8 to 11), the first integrated intensity ratio was 1.15 or more and 3.10 or less, the second integrated intensity ratio was 0.06 or more and 0.28 or less, the third integrated intensity ratio was 3.00 or more and 10.50 or less, and the fourth integrated intensity ratio was 1.18 or more and 1.99 or less.

[0144] 13, 14, 15, and 16 show the yields of epitaxial substrates manufactured using InP substrates 100 according to Samples 1 to 11. As shown in Table 2 and Figures 13 to 16, the yields of epitaxial substrates were 90% or higher for samples (Samples 8 to 11) in which the first integrated intensity ratio was 1.10 or higher and 3.20 or lower, the second integrated intensity ratio was 0.05 or higher and 0.30 or lower, the third integrated intensity ratio was 2.90 or higher and 11.00 or lower, and the fourth integrated intensity ratio was 1.15 or higher and 2.00 or lower.

[0145] As described above, it has been confirmed that the InP substrate 100 and the method for manufacturing the InP substrate 100 according to the example can improve the yield of epitaxial substrates compared to the InP substrate 100 and the method for manufacturing the InP substrate 100 according to the comparative example.

[0146] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0147] 1 First main surface, 2 Second main surface, 3 Third main surface, 4 Fourth main surface, 8 Outer edge, 9 Outer peripheral surface, 10 Indium phosphide single crystal substrate, 11 First surface layer, 12 Second surface layer, 20 X-ray generating equipment, 21 X-ray source, 22 First slit, 23 Grating, 24 Second slit, 30 Vacuum vessel, 40 Electron spectrometer, 71 Phosphorus oxide, 72 Indium oxide, 73 Indium atom, 74 Metallic indium (indium droplet), 75 Metaphosphate part, 79 Hole, 81 Acidic solution, 82 Ozone water, 100 Indium phosphide substrate, 101 First direction, 102 Second direction, 103 Third direction, 200 Analysis system, A Arrow, B Direction of travel, L1 In-O spectrum, L2 In-P spectrum, L3 In-In spectrum, L4 P-O spectrum, L5 P-In spectrum, LI In4d spectrum, LP P2p spectrum, O center, W1 diameter, θ1 incident angle, θ2 take-off angle.

Claims

1. An indium phosphide substrate having a main surface, wherein photoelectrons emitted to the outside of the indium phosphide substrate are captured by X-ray photoelectron spectroscopy, in which X-rays are irradiated onto the center of the main surface under conditions of an X-ray incident energy of 200 eV and a photoelectron take-off angle of 45°, and a spectrum of the detected intensity of indium 4d electrons and a spectrum of the detected intensity of phosphorus 2p electrons are obtained, and when the ratio of the integrated intensity of indium element present as oxide to the integrated intensity of indium element present as indium phosphide is defined as a first integrated intensity ratio, the ratio of the integrated intensity of indium element present as metallic indium to the integrated intensity of indium element present as indium phosphide is defined as a second integrated intensity ratio, the ratio of the integrated intensity of phosphorus element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a third integrated intensity ratio, and the ratio of the integrated intensity of indium element present as oxide to the integrated intensity of phosphorus element present as indium phosphide is defined as a fourth integrated intensity ratio, an indium phosphide substrate, wherein the first integrated intensity ratio is 1.10 or more and 3.20 or less; the second integrated intensity ratio is 0.05 or more and 0.30 or less; the third integrated intensity ratio is 2.90 or more and 11.00 or less; and the fourth integrated intensity ratio is 1.15 or more and 2.00 or less.

2. A method for manufacturing an indium phosphide substrate, comprising: a step of immersing an indium phosphide single crystal substrate in an acidic solution; a step of cleaning the indium phosphide single crystal substrate with ultrapure water after the step of immersing the indium phosphide single crystal substrate in the acidic solution; a step of immersing the indium phosphide single crystal substrate in ozone water after the step of cleaning the indium phosphide single crystal substrate with ultrapure water after the step of immersing the indium phosphide single crystal substrate in ozone water; and a step of cleaning the indium phosphide single crystal substrate with ultrapure water after the step of immersing the indium phosphide single crystal substrate in ozone water, wherein the hydrogen ion exponent of the acidic solution is 2.0 or more and 4.0 or less, and the ozone concentration in the ozone water is 3 ppm or more and 30 ppm or less, or the hydrogen ion exponent of the acidic solution is 1.0 or more and 5.0 or less, and the ozone concentration in the ozone water is 10 ppm or more and 30 ppm or less.

3. The method for producing an indium phosphide substrate according to claim 2, wherein the acidic solution contains any one of an organic acid, hydrochloric acid, and hydrofluoric acid.

4. The method for manufacturing an indium phosphide substrate according to claim 2 or 3, wherein in the step of immersing the indium phosphide single crystal substrate in the acidic solution, the temperature of the acidic solution is room temperature, and the time for immersing the indium phosphide single crystal substrate in the acidic solution is from 10 seconds to 5 minutes.

5. The method for manufacturing an indium phosphide substrate according to any one of claims 2 to 4, wherein in the step of immersing the indium phosphide single crystal substrate in the ozone water, the temperature of the ozone water is room temperature, and the time for immersing the indium phosphide single crystal substrate in the ozone water is from 10 seconds to 5 minutes.

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