Indium phosphide substrate and method for producing the same

Abstract

The ratio of the integral intensity of elemental indium present as an oxide to the integral intensity of elemental indium present as indium phosphide is a first integral intensity ratio. The ratio of the integral intensity of elemental indium present as metallic indium to the integral intensity of elemental indium present as indium phosphide is a second integral intensity ratio. The ratio of the integral intensity of elemental phosphorus present as an oxide to the integral intensity of elemental phosphorus present as indium phosphide is a third integral intensity ratio. The ratio of the integral intensity of elemental indium to the integral intensity of elemental phosphorus is a fourth integral intensity ratio. The first integral intensity ratio is 1.10 or more and 3.20 or less. The second integral intensity ratio is 0.05 or more and 0.30 or less. The third integral intensity ratio is 2.90 or more and 11.00 or less. The fourth integral intensity ratio is 1.15 or more and 2.00 or less.

Description

[Technical field]

[0001] The present disclosure relates to indium phosphide substrates and methods for making indium phosphide substrates. [Background technology]

[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 liquid containing phosphoric acid or hydrogen fluoride. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 62-252140 Summary of the Invention

[0004] The indium phosphide substrate according to the present disclosure is an indium phosphide substrate having a main surface. By X-ray photoelectron spectroscopy, in which X-rays are irradiated to 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°, photoelectrons emitted to the outside of the indium phosphide substrate are captured, and a spectrum of the detection intensity of the 4d electrons of indium and a spectrum of the detection intensity of the 2p electrons of phosphorus are obtained. The ratio of the integrated intensity of the indium element present as an oxide to the integrated intensity of the indium element present as indium phosphide is defined as a first integrated intensity ratio. The ratio of the integrated intensity of the indium element present as metallic indium to the integrated intensity of the indium element present as indium phosphide is defined as a second integrated intensity ratio. The ratio of the integrated intensity of the phosphorus element present as an oxide to the integrated intensity of the phosphorus element present as indium phosphide is defined as a third integrated intensity ratio. The ratio of the integrated intensity of the indium element present as an oxide to the integrated intensity of the 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. The fourth integrated intensity ratio is 1.15 or more and 2.00 or less. [Brief description of the drawings]

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

[0006] [Problem that this disclosure aims to solve] An object of the present disclosure is to provide an indium phosphide substrate capable of improving the yield of epitaxial substrates and a method for manufacturing the indium phosphide substrate.

[0007] [Effects of this disclosure] According to the present disclosure, it is possible to provide an indium phosphide substrate capable of improving the yield of epitaxial substrates and a method for manufacturing an indium phosphide substrate.

[0008] [Outline of the embodiment] First, an overview of an 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. By X-ray photoelectron spectroscopy, in which X-rays are irradiated to 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°, photoelectrons emitted to the outside of the indium phosphide substrate are captured, and a spectrum of the detection intensity of the 4d electrons of indium and a spectrum of the detection intensity of the 2p electrons of phosphorus are obtained. The ratio of the integrated intensity of the indium element present as an oxide to the integrated intensity of the indium element present as indium phosphide is defined as a first integrated intensity ratio. The ratio of the integrated intensity of the indium element present as metallic indium to the integrated intensity of the indium element present as indium phosphide is defined as a second integrated intensity ratio. The ratio of the integrated intensity of the phosphorus element present as an oxide to the integrated intensity of the phosphorus element present as indium phosphide is defined as a third integrated intensity ratio. The ratio of the integrated intensity of the indium element present as an oxide to the integrated intensity of the 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. The fourth integrated intensity ratio is 1.15 or more and 2.00 or less.

[0010] In this way, the indium phosphide substrate according to the present embodiment prevents the amounts of indium oxide, metallic indium, and phosphorus oxide in the surface layer from becoming excessively large or small, thereby improving the yield of epitaxial substrates.

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

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

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

[0014] (5) According to 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 the ozone water may be 10 seconds or more and 5 minutes or less. This makes it possible to effectively improve the yield of epitaxial substrates.

[0015] [Details of the embodiment] Hereinafter, the details of the embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic description of this specification, an individual orientation is indicated by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. In addition, 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 schematic diagram showing the configuration of the InP substrate 100 according to this embodiment. Fig. 2 is a cross-sectional schematic diagram taken 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 straight 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 an InP substrate 100. Each of the first direction 101 and the second direction 102 is, for example, <011> The second direction 102 is a direction perpendicular to the first direction 101.

[0019] 2, the second main surface 2 is opposite to the first main surface 1. The direction from the second main surface 2 to the first main surface 1 is defined 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, <100> The outer peripheral surface 9 is continuous with each of the first main surface 1 and the second main surface 2. The ridge line between the first main surface 1 and the outer peripheral surface 9 is defined 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 first main surface 1 has a diameter W1 of, for example, 75 mm or more and 300 mm or less. The diameter W1 is the maximum 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 of a circle including an arc along the portion of the outer peripheral surface 9 that is arc-shaped in plan view is set to be the center O.

[0022] The InP substrate 100 may contain, for example, any of sulfur (S), iron (Fe), and 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 is, for example, circular. The fourth main surface 4 is opposite the third main surface 3. The third main surface 3 is 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 are also 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> 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 vessel 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. As the X-ray generating facility 20, for example, the beamline "BL17" in the Kyushu Synchrotron Light Research Center in Saga Prefecture can be used.

[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 along the direction of an arrow A.

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

[0032] The grating 23 is disposed in the direction of the 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 the arrow A relative to the grating 23. From another point of view, 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 equipment 20. The vacuum vessel 30 is disposed in the direction of the arrow A relative to the X-ray generating equipment 20. The vacuum vessel 30 is a portion in which the InP substrate 100 is disposed.

[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 into different wavelengths. 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 equipment 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 equipment 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 vessel 30. X-rays are irradiated from an X-ray generating facility 20 towards 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). This causes radiation (X-rays) to be 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 part 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 to 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, X-rays of 200 eV are irradiated from the X-ray generating facility 20 .

[0042] The angle (incident angle θ1) between the traveling direction of the X-rays irradiated from the X-ray generating equipment 20 to the InP substrate 100 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. Therefore, only some of the photoelectrons generated in the InP substrate 100 escape into the vacuum while retaining the energy at the time of generation, and are captured by the electron spectrometer 40.

[0044] The angle (take-off angle θ2) 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 activated is 1 / 3 of the brightness of the X-rays emitted from the X-ray source 21 immediately after the X-ray source 21 is activated. The Au4f photoelectron intensity is measured at regular intervals using a standard sample made of gold (Au). Based on the measured Au4f photoelectron intensity, the decay ratio of the Au4f photoelectron intensity is calculated. The X-ray dose is corrected based on the calculated decay ratio.

[0046] <Areas of analysis> Photoelectrons that can escape from the surface of the InP substrate 100 are generated in a region up to a depth equivalent to about 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 is also referred to as the measurement depth.

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

[0048] (Calculation method of integrated intensity ratio) Next, a method for calculating the integrated intensity ratio on the first main surface 1 of the InP substrate 100 based on the kinetic energy distribution of photoelectrons measured in the above-mentioned XPS will be described.

[0049] <In4dスペクトルおよびP2pスペクトル> The kinetic energy E of the photoelectrons emitted from the InP substrate 100 is calculated by multiplying the energy hν of the irradiated X-rays by the binding energy E of the photoelectrons in the InP substrate 100. B and the work function φ, this is expressed by the following Equation 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 the 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 that represents the detection intensity of photoelectrons emitted from the 4d orbital of the In element contained in indium oxide, InP, and metallic indium, respectively. The term "P2p spectrum" refers to a spectrum that represents the detection intensity of photoelectrons emitted from the 2p orbital of the P element contained in phosphate and InP, respectively.

[0051] By narrow scanning the range of binding energy from 14 eV to 24 eV, an In4d spectrum can be obtained. Similarly, by narrow scanning the range of binding energy from 127 eV to 137 eV, a P2p spectrum can be obtained. By narrow scanning, the measurement accuracy of each of the In4d spectrum and the P2p spectrum can be improved.

[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 count of 2 to 5. The energy resolution E / ΔE is 3480.

[0053] <Background correction> The obtained In4d spectrum and P2p spectrum are subjected to background correction by using the Shirley method (Reference: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, Vol. 56, No. 6, 2013, p. 243-247). As a result, the In4d spectrum after background correction is calculated based on the difference between the In4d spectrum obtained by the narrow scan and the background. Similarly, the P2p spectrum after background correction 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 charging 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 charging 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 metal 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 be 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 be 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 one 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 intensity of each of the P element present as an oxide (P-O) and the 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 set to 132.82 eV. The binding energy at the peak of the detection intensity of P-In is set 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 one value. Therefore, as described above, the peak position of the detection intensity of P-In is set to have a width of 0.5 eV.

[0057] As a result, the corrected In4d spectrum LI and the 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 FIG. 5 and FIG. 6, the horizontal axis indicates the binding energy. The vertical axis indicates the detection intensity of the photoelectrons. In FIG. 5, the detection intensity in the range where the binding energy is 14 eV or more and 24 eV or less is shown. In FIG. 6, the detection intensity in the range where the binding energy is 127 eV or more and 137 eV or less is shown. In FIG. 5, each spectrum is normalized with the value of the photoelectron intensity at the maximum peak of the In4d spectrum LI as 1. In FIG. 6, each spectrum is normalized with the value of the photoelectron intensity at the maximum peak of the P2p spectrum LP as 1.

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

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

[0060]

number

[0061]

number

[0062]

number

[0063] The spectrum of In4d has two subpeaks (In4d 3 / 2 and In4d 5 / 2 ) (peak splitting). In4d 3 / 2 Intensity and In4d 5 / 2 The intensity ratio of In4d is 2:3. 3 / 2 The binding energy in In4d 5 / 2 It is smaller than the binding energy in In4d 3 / 2 Binding energy in In4d 5 / 2 Here, the absolute value of the difference (energy difference) between the binding energy at In4d and that at In4d is 0.90 eV. Therefore, the In-O spectrum (Formula 2), the In-P spectrum (Formula 3), and the In-In spectrum (Formula 4) are each 3 / 2 and In4d 5 / 2 It is expressed as the sum of two Gaussian functions corresponding to each of the above. In the In-O spectrum, the peak does not appear to be split because the peak is blunted, but it is approximately expressed using two subpeaks, just like In-P and In-In.

[0064] In the above formulas 2, 3, and 4, Y1, Y2, and Y3 each represent a 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 each are variables. The units of a1, a2, and a3 each are dimensionless. The units of b1, b2, b3, c1, c2, and c3 each 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)] 2Each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) is optimized so that the above-mentioned binding energy values ​​at the peaks of the detected intensities of In-O, In-P, and In-In are substituted for b1, b2, and b3, respectively.

[0066] The values ​​or ranges of the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) are as follows: a1, a2, and a3 are real numbers greater than or equal to 0. b1=19.9eV 17.0 eV ≤ b2 ≤ 17.5 eV 16.0eV≦b3≦16.5eV 0.3eV≦c1≦1.05eV 0.3eV≦c2≦1.05eV 0.3eV≦c3≦1.05eV As described above, by peak separation, it is possible to obtain the spectra of In-O, In-P, and In-In in the binding energy range of 14 eV to 24 eV. In Fig. 5, the In-O spectrum L1 shows the obtained spectrum of In-O. The In-P spectrum L2 shows the obtained spectrum of In-P. The In-In spectrum L3 shows the obtained spectrum of In-In.

[0067] Similarly, it is assumed that the P2p spectrum LP after the above correction is expressed as a sum of multiple Gaussian functions. The P2p spectrum LP is expressed by separating it into the following two formulas (Formula 5 and Formula 6). Formula 5 and Formula 6 correspond to the spectra of PO and P-In, respectively.

[0068]

number

[0069]

number

[0070] As with the In4d spectrum, the P2p spectrum has two subpeaks (P2p 1 / 2 and P2P 3 / 2 ) (peak splitting). 1 / 2 Strength and P2p 3 / 2 The intensity ratio of P2p is 1:2. 1 / 2 The binding energy at P2p 3 / 2 It is smaller than the binding energy at P2p 1 / 2 Binding energy at and P2p 3 / 2 The absolute value of the difference in binding energy between the PO spectrum (Equation 5) and the P-In spectrum (Equation 6) is taken to be 0.85 eV. 1 / 2 and P2P 3 / 2 It is expressed by the sum of two Gaussian functions corresponding to each of the above. In the PO spectrum, the peak does not appear to be split because the peak is blunted, but it is approximately expressed by using two subpeaks, just like P-In.

[0071] In the above formulas 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 each represent variables. The units of a4 and a5 each are dimensionless. The units of b4, b5, c4, and c5 each represent 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 θ = ...

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

[0074] In order to determine the peak intensities Y1 to Y5 described above, the following correction is made. The probability that photoelectrons are generated by X-ray irradiation is called the photoionization efficiency (η). η varies depending on the element, orbital, and incident energy of the X-ray. 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 measurement 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 posted on the following website is used for the value of η. Specifically, the photoionization efficiency (η) of In4d when the incident X-ray energy is 200 eV is taken to be 0.68. The photoionization efficiency (η) of P2p when the incident X-ray energy is 200 eV is taken to be 3.49.

[0076] (Website) https: / / vuo.elettra.eu / services / elements / WebElements.html (The data is based on 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).) <Integrated intensity ratio> In Fig. 5, the area of ​​the region surrounded by the In-O spectrum L1 and the horizontal axis is 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 analyzed by XPS.

[0077] In Fig. 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 to be analyzed by XPS.

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

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

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

[0081] In Fig. 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 to be analyzed by XPS.

[0082] In Fig. 6, the area 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 the 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-mentioned 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 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-mentioned 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 PO to the integrated intensity of P-In is set as a third integrated intensity ratio. In other words, the third integrated intensity ratio is a value obtained by dividing the integrated intensity of PO by the integrated intensity of P-In. When the above-mentioned 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 the indium element to the integrated intensity of the phosphorus element is set as a fourth integrated intensity ratio. In other words, the fourth integrated intensity ratio is a value obtained by dividing the integrated intensity of the indium element by the integrated intensity of the phosphorus element. When the above-mentioned 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 in 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 numerical ranges described above.

[0088] <Method of 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 diagram that outlines 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 performed. An InP single crystal substrate 10 is prepared. Specifically, for example, an indium phosphide single crystal is manufactured using a vertical boat method or the like. For example, the indium phosphide single crystal is sliced ​​using a wire saw or the like 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 surface. 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 manner, 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 performed. Fig. 8 is an enlarged cross-sectional schematic diagram 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 acid solution 81 contains, for example, any one 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 acid solution 81 is 1.0 or more and 5.0 or less. The hydrogen ion exponent of the acid solution 81 may be, for example, 1.8 or more, or 2.5 or more. The hydrogen ion exponent of the acid solution 81 may be, for example, 4.7 or less, or 3.5 or less.

[0093] The temperature of the acid solution 81 is, for example, room temperature (for example, 25° C.). The time (first time) for immersing the InP single crystal substrate 10 in the acid 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 acid solution 81. The acid solution 81 may be stirred by rotating the rotor in the acid solution 81 using magnetic force. This can promote the reaction between the acid solution 81 and the InP single crystal substrate 10.

[0095] As shown in FIG. 8, the In atoms on the third main surface 3 are reacted with H of the acid solution 81. + ions. As a result, the In atoms are ionized. The ionized In atoms dissolve into the acidic solution 81. Therefore, P atoms become excessive on the third main surface 3. The P atoms react with, for example, water molecules in the acidic solution 81, to form phosphorus oxides 71 on the third main surface 3.

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

[0097] Next, a first cleaning step (S30) is performed. 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. As a result, the acid solution 81 adhering to the InP single crystal substrate 10 is removed.

[0098] Next, a step (S40) of immersing the indium phosphide single crystal substrate in ozone water is performed. Fig. 9 is an enlarged cross-sectional schematic diagram 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 the ozone water 82 is 3 ppm or more and 30 ppm or more. The ozone concentration in the ozone water 82 may be, for example, 5 ppm or more, 8 ppm or more, or 10 ppm or more. The ozone concentration in the 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 acid solution 81 and the ozone concentration in the ozone water each satisfy the following condition 1 or 2. (Condition 1) The hydrogen ion exponent of the acid 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 acid 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 (for example, 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. As a result, the P atoms are ionized. The ionized P atoms dissolve into the ozone water 82. Therefore, In atoms become excessive. As a result, the In atoms 73 migrate on the third main surface 3. A part of the In atoms 73 is oxidized to form indium oxide 72. A plurality of In atoms 73 aggregate to form minute indium droplets 74. Hereinafter, the indium droplets 74 are also 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. Indium oxide 72 is formed on the third main surface 3 by the reaction of the In atoms 73 with oxygen in the air.

[0104] Next, a second cleaning step (S50) is performed. 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, in Figures 8 and 9, phosphorus oxide 71, indium oxide 72, and indium droplets 74 are each illustrated as an independent object. In reality, 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 manner, 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 the present embodiment will be described.

[0108] When an epitaxial substrate is manufactured using the InP substrate 100, the yield of the epitaxial substrate may be lower than expected. Specifically, the 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 the object to be measured by the amount of incident light. In addition, the number of LPDs (Light Point Defects) may increase in the epitaxial substrate. LPDs are surface defects that are detected by measuring the scattered light caused by irradiating the surface of the epitaxial substrate with light.

[0109] Each of the haze and the number of LPDs is used as an index for evaluating the surface condition of the epitaxial substrate. If the haze is too high, the characteristics of the semiconductor device manufactured using the epitaxial substrate are deteriorated. If the number of LPDs is too high, the characteristics of the semiconductor device manufactured using the epitaxial substrate are deteriorated.

[0110] The inventors have focused on the configuration of the InP substrate 100 near the main surface while examining ways to improve the surface condition of the epitaxial substrate. For example, an oxide may be formed on the surface of the InP substrate 100 due to cleaning of the InP substrate 100. In a typical XPS apparatus, the energy of the incident X-rays is large (for example, about 2 keV), so only average information of a region about 9 nm deep from the surface of the substrate can be measured. Therefore, in a typical XPS apparatus, it is not possible to extract information only on a region very close to the surface. Therefore, in a typical XPS apparatus, when a very thin layer made of an oxide or the like is present on the main surface of the InP substrate 100, the layer cannot be quantitatively analyzed with high accuracy.

[0111] The inventors have come up with the idea of ​​performing an analysis of 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 on a region up to a depth of about 1.5 nm from the main surface. Based on the information on this region, the inventors have come to the following findings.

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

[0113] FIG. 10 is an enlarged schematic cross-sectional view showing the surface state of an InP substrate 100 when the amount of phosphorus (PO, P-In) present is excessively large. When the amount of PO is excessively large, the first surface layer 11 contains an excessively large 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 composed of metaphosphate ((HPO3) n )

[0114] FIG. 11 is an enlarged schematic cross-sectional view showing a state in which the metaphosphate portion 75 has collapsed. As shown in FIG. 11, the metaphosphate portion 75 is formed so as to cover the first surface layer 11. The metaphosphate portion 75 has a relatively low physical strength. Therefore, the metaphosphate portion 75 may collapse when the InP substrate 100 is carried inside an 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 part of the InP single crystal substrate 10 is exposed from the first surface layer 11.

[0115] Fig. 12 is an enlarged schematic diagram showing a state in which indium oxide 72 is 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 air, 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 causes an increase in haze and an increase in the number of LPDs in the epitaxial substrate.

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

[0118] According to the InP substrate 100 of this embodiment, when the above-mentioned XPS analysis is performed on the first main surface 1 of the InP substrate 100, 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. Thus, according to the InP substrate 100 of this embodiment, the indium oxide 72 and the metallic indium 74 are prevented from becoming excessively large in the first surface layer 11. Therefore, the first surface layer 11 is prevented from becoming excessively thick due to the excessively large amount of indium element present. As a result, when an epitaxial layer is grown 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] Moreover, according to the InP substrate 100 of this embodiment, the first surface layer 11 is prevented from having an excessive amount of phosphoric acid 71. Therefore, it is possible to prevent the first surface layer 11 from forming a metaphosphate portion 75 due to the reaction of the phosphoric acid 71 with moisture in the air. Therefore, it is possible to prevent the first surface layer 11 from collapsing due to an impact applied to the InP substrate 100 when the InP substrate 100 is carried. Therefore, when an epitaxial layer is grown on the first main surface 1, it is possible to prevent an increase in haze and an increase in the number of LPDs in the epitaxial substrate. As a result, it is possible to improve the yield of the epitaxial substrate.

[0120] In order 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 amount of each of the indium oxide 72, metallic indium 74, and phosphorus oxide 71 in the first surface layer 11 is excessively small, phosphorus constituting the InP substrate 100 is released upon heating, and the first main surface 1 becomes 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 indium oxide 72, the metallic indium 74, and the phosphorus oxide 71 are appropriately present, and thus the yield of the epitaxial substrate can be improved.

[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 both an acidic solution and ozone water. As a result of further intensive studies, 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 acid solution, and a step (S40) of immersing the indium phosphide single crystal substrate in ozone water. The hydrogen ion exponent of the acid 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, or the hydrogen ion exponent of the acid 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.

[0124] This is believed 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 amounts of 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 makes it possible to improve the yield of epitaxial substrates as described above.

[0125] According to the manufacturing method of the InP substrate 100 according to this embodiment, the time for immersing the InP single crystal substrate 10 in the acid solution 81 is 10 seconds or more and 300 seconds (5 minutes) or less. This is believed to prevent the chemical reaction caused by immersing the InP single crystal substrate 10 in the acid solution 81 from proceeding excessively. Therefore, it is possible to effectively prevent each of the indium oxide 72, the metallic indium 74, and the phosphorus oxide 71 from becoming excessively large or small. Therefore, it is possible to improve the yield of the epitaxial substrate as described above.

[0126] According to the manufacturing method of the InP substrate 100 according to this embodiment, the time for immersing the InP single crystal substrate 10 in the ozone water 82 is 10 seconds or more and 300 seconds (5 minutes) or less. This is believed to be able to suppress excessive progress of chemical reactions caused by immersion of the InP single crystal substrate 10 in the ozone water 82. This effectively prevents the indium oxide 72, metallic indium 74, and phosphorus oxide 71 from becoming excessively large or small. This makes it possible to improve the yield of the epitaxial substrate as described above. EXAMPLES

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

[0128] [Table 1]

[0129] Table 1 shows the manufacturing conditions of the InP substrate 100 according to Samples 1 to 11. In Sample 1, the step (S40) of immersing the indium phosphide single crystal substrate in ozone water and the second cleaning step (S50) were not performed. In Sample 2, the step (S20) of immersing the indium phosphide single crystal substrate in an acidic solution and the first cleaning step (S30) were not performed. In Samples 3 to 11, all steps of the above-mentioned manufacturing method of 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] In samples 3, 5, and 7, the ozone concentration in the ozone water 82 was adjusted to 100 ppm. In samples 2, 8, 9, and 10, the ozone concentration in the ozone water 82 was adjusted to 20 ppm. In samples 4, 6, and 11, the ozone concentration in the ozone water 82 was adjusted to 5 ppm.

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

[0134] (Evaluation method) The above-mentioned 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-mentioned analysis method.

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

[0136] The haze and the number of LPDs were measured on the surface of the epitaxial substrate. The surface density of LPDs was measured by dividing the number of LPDs measured by the area of ​​the measured region. In measuring the haze and the number of LPDs, an inspection device, Surfscan6220, manufactured by KLA-Tencor Corporation, was used. The light source was an argon ion laser. The output of the light source was 30 mW. The wavelength of the light source was 488 nm.

[0137] In the measurement of haze, the minimum value of the scattered light amount / incident light amount 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, among 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 and the number of LPDs are each measured in a region of the surface of the epitaxial substrate excluding a region within a distance of 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] Haze is 7 ppm or less and the surface density of LPD 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] [Table 2]

[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 embodiment (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 Figs. 13 to 16, the yields of epitaxial substrates were 90% or more in the samples (Samples 8 to 11) in which the first integrated intensity ratio was 1.10 or more and 3.20 or less, the second integrated intensity ratio was 0.05 or more and 0.30 or less, the third integrated intensity ratio was 2.90 or more and 11.00 or less, and the fourth integrated intensity ratio was 1.15 or more and 2.00 or less.

[0145] As described above, it has been confirmed that the InP substrate 100 and the manufacturing method of the InP substrate 100 according to the embodiment can improve the yield of epitaxial substrates, compared to the InP substrate 100 and the manufacturing method of 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 as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[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 metaphosphoric acid 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 travel direction, L1 In-O spectrum, L2 In-P spectrum, L3 In-In spectrum, L4 PO spectrum, L5 P-In spectrum, LI In4d spectrum, LP P2p spectrum, O center, W1 diameter, θ1 incident angle, θ2 take-off angle.

Claims

1. 1. An indium phosphide substrate having a major surface, capturing photoelectrons emitted to the outside of the indium phosphide substrate 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°; The spectrum of the detected intensity of the indium 4d electrons and the spectrum of the detected intensity of the phosphorus 2p electrons are obtained. a ratio of an integrated intensity of indium element present as an oxide to an integrated intensity of indium element present as indium phosphide is defined as a first integrated intensity ratio; a 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; a 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; When the ratio of the integrated intensity of indium element to the integrated intensity of phosphorus element is defined as a fourth integrated intensity ratio, the first integrated intensity ratio is equal to or greater than 1.10 and equal to or less than 3.20, the second integrated intensity ratio is equal to or greater than 0.05 and equal to or less than 0.30, the third integrated intensity ratio is equal to or greater than 2.90 and equal to or less than 11.00, an indium phosphide substrate, wherein the fourth integrated intensity ratio is equal to or greater than 1.15 and equal to or less than 2.00;

2. Immersing an indium phosphide single crystal substrate in an acidic solution; a step of washing 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; 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 ozone water, a hydrogen ion exponent of the acidic solution is 2.0 or more and 4.0 or less, and an ozone concentration in the ozone water is 3 ppm or more and 30 ppm or less, or a hydrogen ion exponent of the acidic solution is 1.0 or more and 5.0 or less, and an 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. In the step of immersing the indium phosphide single crystal substrate in the acidic solution, the temperature of the acidic solution is room temperature; 4. The method for producing an indium phosphide substrate according to claim 2, wherein the indium phosphide single crystal substrate is immersed in the acidic solution for 10 seconds or more and 5 minutes or less.

5. In the step of immersing the indium phosphide single crystal substrate in the ozone water, The temperature of the ozone water is room temperature, 4. The method for producing an indium phosphide substrate according to claim 2, wherein the indium phosphide single crystal substrate is immersed in the ozone water for 10 seconds or more and 5 minutes or less.

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