Indium phosphide substrate and method for manufacturing indium phosphide substrate

Abstract

The ratio of the integrated intensity of indium in oxide form to the integrated intensity of indium in indium phosphide form is defined as the first integrated intensity ratio. The ratio of the integrated intensity of indium in metallic indium to the integrated intensity of indium indium phosphide form is defined as the second integrated intensity ratio. The ratio of the integrated intensity of phosphorus in oxide form to the integrated intensity of phosphorus in indium phosphide form is defined as the third integrated intensity ratio. The ratio of the integrated intensity of indium to the integrated intensity of phosphorus is defined as the fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 or higher and 3.20 or lower. The second integrated intensity ratio is 0.05 or higher and 0.30 or lower. The third integrated intensity ratio is 2.90 or higher and 11.00 or lower. The fourth integrated intensity ratio is 1.15 or higher and 2.00 or lower.

Description

Technical Field

[0001] This invention relates to indium phosphide substrates and methods for manufacturing indium phosphide substrates. Background Technology

[0002] Japanese Patent Application Publication No. 62-252140 (Patent Document 1) discloses a cleaning method for cleaning mirror-polished InP wafers by cleaning a mixture containing phosphoric acid or hydrogen fluoride.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 62-252140. Summary of the Invention

[0006] The indium phosphide substrate of this invention is an indium phosphide substrate having a main surface. X-ray photoelectron spectroscopy (XPS) is used to capture photoelectrons released to the outside of the indium phosphide substrate by irradiating the center of the main surface with X-rays at an incident energy of 200 eV and a take-off angle of 45°. The intensity spectra of the detection intensity of indium's 4d electrons and phosphorus's 2p electrons are then determined. The ratio of the integrated intensity of indium in oxide form to the integrated intensity of indium in indium phosphide form is defined as a first integrated intensity ratio. The ratio of the integrated intensity of indium in metallic indium form to the integrated intensity of indium in indium phosphide form is defined as a second integrated intensity ratio. The ratio of the integrated intensity of phosphorus in oxide form to the integrated intensity of phosphorus in indium phosphide form is defined as a third integrated intensity ratio. The ratio of the integrated intensity of indium to the integrated intensity of phosphorus is defined as a fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 or higher and 3.20 or lower. The second integral intensity ratio is 0.05 or higher and 0.30 or lower. The third integral intensity ratio is 2.90 or higher and 11.00 or lower. The fourth integral intensity ratio is 1.15 or higher and 2.00 or lower. Attached Figure Description

[0007] Figure 1 This is a planar schematic diagram illustrating the structure of the indium phosphide substrate of this embodiment.

[0008] Figure 2 For along Figure 1 A schematic diagram of the cross section of line II-II.

[0009] Figure 3 To show Figure 2 A magnified cross-sectional view of region III.

[0010] Figure 4This is a schematic diagram illustrating the structure of the analytical system used in X-ray photoelectron spectroscopy.

[0011] Figure 5 This is a schematic diagram showing the In4d spectrum of the indium phosphide substrate of this embodiment.

[0012] Figure 6 This is a schematic diagram showing the P2p pattern of the indium phosphide substrate of this embodiment.

[0013] Figure 7 A flowchart is provided to schematically illustrate the method for manufacturing the indium phosphide substrate according to this embodiment.

[0014] Figure 8 This is an enlarged cross-sectional schematic diagram illustrating the process of immersing an indium phosphide single crystal substrate in an acidic solution.

[0015] Figure 9 This is an enlarged cross-sectional schematic diagram illustrating the process of immersing an indium phosphide single crystal substrate in ozone water.

[0016] Figure 10 This is an enlarged cross-sectional schematic diagram showing the surface state of an indium phosphide substrate in the presence of excessive phosphorus.

[0017] Figure 11 An enlarged cross-sectional schematic diagram to illustrate the state of metaphosphoric acid collapse.

[0018] Figure 12 This is an enlarged cross-sectional schematic diagram showing the state in which indium oxide is formed on an indium phosphide single crystal substrate.

[0019] Figure 13 A graph showing the first integral intensity ratio of the indium phosphide substrates and the yield of the epitaxial substrates for samples 1 to 11.

[0020] Figure 14 A graph showing the second integral intensity ratio of the indium phosphide substrates and the yield of the epitaxial substrates for samples 1 to 11.

[0021] Figure 15 A graph showing the third integral intensity ratio of the indium phosphide substrates and the yield of the epitaxial substrates for samples 1 to 11.

[0022] Figure 16 A graph showing the fourth integral intensity ratio of the indium phosphide substrates and the yield of the epitaxial substrates for samples 1 to 11. Detailed Implementation

[0023] [The problem this invention aims to solve]

[0024] The purpose of this invention is to provide an indium phosphide substrate and a method for manufacturing an indium phosphide substrate that can improve the yield of epitaxial substrates.

[0025] [Effects of the Invention]

[0026] According to the present invention, an indium phosphide substrate and a method for manufacturing an indium phosphide substrate are provided that can improve the yield of epitaxial substrates.

[0027] [Summary of Implementation Methods]

[0028] First, an outline of the embodiments of the present invention (hereinafter also referred to as this embodiment) will be described.

[0029] (1) The indium phosphide substrate of the present invention is an indium phosphide substrate having a main surface. X-ray photoelectron spectroscopy is used to capture photoelectrons released to the outside of the indium phosphide substrate by irradiating the center of the main surface with X-rays at an incident energy of 200 eV and an emission angle of 45°, thereby determining the detection intensity spectrum of indium's 4d electrons and the detection intensity spectrum of phosphorus's 2p electrons. The ratio of the integrated intensity of indium in oxide form to the integrated intensity of indium in indium phosphide form is defined as a first integrated intensity ratio. The ratio of the integrated intensity of indium in metallic indium form to the integrated intensity of indium in indium phosphide form is defined as a second integrated intensity ratio. The ratio of the integrated intensity of phosphorus in oxide form to the integrated intensity of phosphorus in indium phosphide form is defined as a third integrated intensity ratio. The ratio of the integrated intensity of indium to the integrated intensity of phosphorus is defined as a fourth integrated intensity ratio. The first integrated intensity ratio is 1.10 or higher and 3.20 or lower. The second integrated intensity ratio is 0.05 or higher and 0.30 or lower. The third integral intensity ratio is 2.90 or higher and 11.00 or lower. The fourth integral intensity ratio is 1.15 or higher and 2.00 or lower.

[0030] In this way, the indium phosphide substrate according to this embodiment suppresses the excessive or insufficient amounts of indium oxide, metallic indium, and phosphorus oxide in the surface layer. As a result, the yield of the epitaxial substrate can be improved.

[0031] (2) The method for manufacturing the indium phosphide substrate of the present invention includes the following steps: Immersing an indium phosphide single crystal substrate in an acidic solution. After immersing the indium phosphide single crystal substrate in the acidic solution, rinsing the indium phosphide single crystal substrate with ultrapure water. After rinsing the indium phosphide single crystal substrate with ultrapure water, immersing the indium phosphide single crystal substrate in ozone water. After immersing the indium phosphide single crystal substrate in ozone water, rinsing the indium phosphide single crystal substrate with ultrapure water. The hydrogen ion index of the acidic solution is 2.0 or higher and 4.0 or lower, and the ozone concentration in the ozone water is 3 ppm or higher and 30 ppm or lower; or, the hydrogen ion index of the acidic solution is 1.0 or higher and 5.0 or lower, and the ozone concentration in the ozone water is 10 ppm or higher and 30 ppm or lower. This improves the yield of the epitaxial substrate.

[0032] (3) In the method for manufacturing the indium phosphide substrate according to (2) above, the acidic solution may contain any one of organic acid, hydrochloric acid or hydrofluoric acid.

[0033] (4) According to the manufacturing method of indium phosphide substrate according to (2) or (3) above, in the process of immersing the indium phosphide single crystal substrate in an acidic solution, the temperature of the acidic solution can be room temperature. The immersion time of the indium phosphide single crystal substrate in the acidic solution can be more than 10 seconds and less than 5 minutes. As a result, the yield of epitaxial substrates can be effectively improved.

[0034] (5) According to any one of the manufacturing methods of indium phosphide substrates in (2) to (4) above, in the process of immersing the indium phosphide single crystal substrate in ozone water, the temperature of the ozone water can be room temperature. The immersion time of the indium phosphide single crystal substrate in ozone water can be more than 10 seconds and less than 5 minutes. As a result, the yield of epitaxial substrates can be effectively improved.

[0035] [Details of the implementation method]

[0036] The following is a detailed description of embodiments of the present invention based on the accompanying drawings. Furthermore, in the following drawings, identical or equivalent parts are labeled with the same reference numerals, and their descriptions will not be repeated. In the crystallographic descriptions in this specification, [] represents a single crystal direction, <> represents a family of crystal directions, () represents a single crystal plane, and {} represents a family of crystal planes. Furthermore, regarding negative indices, in crystallography, a "-" (horizontal bar) is usually placed above the number, but in this specification, a negative sign is placed before the number.

[0037] <Indium Phosphide Substrate>

[0038] First, the structure of the indium phosphide substrate 100 (hereinafter also referred to as InP substrate 100) of this embodiment will be explained. Figure 1 This is a planar schematic diagram showing the structure of the InP substrate 100 in this embodiment. Figure 2 For along Figure 1 A schematic cross-sectional view of line II-II. (See attached diagram.) Figure 1 and Figure 2 As shown, the InP substrate 100 has a first main surface 1, a second main surface 2, and an outer peripheral surface 9.

[0039] 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 top 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 the first direction 101 and the second direction 102.

[0040] The first primary surface 1 is, for example, the {100} plane of a single crystal indium phosphide constituting the InP substrate 100. The first direction 101 and the second direction 102 are, for example, <011> Direction. The second direction 102 is perpendicular to the first direction 101.

[0041] like Figure 2 As shown, the second main surface 2 is opposite to the first main surface 1. The direction from the second main surface 2 toward the first main surface 1 is designated as the third direction 103. The third direction 103 is the growth direction of the indium phosphide single crystal during the fabrication of the InP substrate 100. For example, the third direction 103 is... <100> Orientation. The outer peripheral surface 9 is connected to the first main surface 1 and the second main surface 2, respectively. The edge line between the first main surface 1 and the outer peripheral surface 9 is defined as the outer edge 8. In the following, the first main surface 1 and the second main surface 2 are also referred to as main surfaces.

[0042] like Figure 1 As shown, 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.

[0043] At least one of a notch, a positioning flat edge, or an indicator flat edge may be provided on the outer peripheral surface 9. When at least one of a notch, a positioning flat edge, or an indicator flat edge is provided on the outer peripheral surface 9, the center of the circle including the arc along the part of the arc-shaped outer peripheral surface 9 is set as center O when viewed from above.

[0044] The InP substrate 100 may contain any one of sulfur (S), iron (Fe), or tin (Sn) as an impurity. The InP substrate 100 may also be free of impurities. In other words, the InP substrate 100 may also be undoped.

[0045] Figure 3 To show Figure 2 An enlarged cross-sectional view of region III. (See diagram below.) Figure 3As shown, the InP substrate 100 has an indium phosphide single crystal substrate 10 (hereinafter also referred to as InP single crystal substrate 10), a first surface layer 11 and a second surface layer 12.

[0046] 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. When viewed from above, the third main surface 3 is, for example, circular. The fourth main surface 4 is opposite to the third main surface 3. The third main surface 3 is located in a third direction 103 relative to the fourth main surface 4.

[0047] The first surface layer 11 is located 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 comprises 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, less than 2 nm.

[0048] The second surface layer 12 is located on the fourth main surface 4. From another viewpoint, the InP single-crystal substrate 10 is located 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 comprises 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, less than 2 nm. Hereinafter, the first surface layer 11 and the second surface layer 12 are also simply referred to as surface layers.

[0049] X-ray photoelectron spectroscopy

[0050] Next, the method for analyzing the surface state of the InP substrate 100 using X-ray photoelectron spectroscopy (XPS) will be described.

[0051] <Analysis System>

[0052] Figure 4 This is a schematic diagram illustrating the structure of the analytical system used in X-ray photoelectron spectroscopy. (Example:) Figure 4 As shown, the analysis system 200 mainly includes an X-ray generating device 20, a vacuum container 30, and an electron spectrometer 40.

[0053] X-ray generating device 20 generates X-rays. X-rays are also called radiation. X-ray generating device 20 can generate X-rays with energies of 50 eV or more and 2000 eV or less. For example, the X-ray generating device 20 can use the beamline "BL17" at the Kyushu Synchrotron Light Research Center in Saga Prefecture.

[0054] like Figure 4As shown, the X-ray generating device 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.

[0055] The first slit 22 is positioned relative to the X-ray source 21 in the direction of arrow A. 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.

[0056] The grating 23 is positioned relative to the first slit 22 in the direction of arrow A. The grating 23 is a beam splitter. The grating 23 monochromates the X-rays. The line density at the center of the grating 23 is, for example, 400 l / mm.

[0057] The second slit 24 is positioned relative to the grating 23 in the direction of arrow A. From another viewpoint, the grating 23 is positioned 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 restricts the diffusion of monochromatic X-rays. The slit width of the second slit 24 is, for example, 30 μm.

[0058] Vacuum container 30 is connected to X-ray generating device 20. Vacuum container 30 is positioned relative to X-ray generating device 20 in the direction of arrow A. Vacuum container 30 is the portion where InP substrate 100 is disposed.

[0059] An electron spectrometer 40 is connected to a vacuum container 30. The electron spectrometer 40 is connected to an X-ray generating device 20 via the vacuum container 30. The electron spectrometer 40 has a hemispherical analyzer (not shown) and a detector (not shown). The hemispherical analyzer disperses photoelectrons. The detector counts the number of photoelectrons at each kinetic energy level. For example, a high-resolution XPS analyzer "R3000" manufactured by Scienta Omicron can be used as the electron spectrometer 40.

[0060] The internal spaces of the X-ray generating device 20, the vacuum container 30, and the electron spectrometer 40 are maintained at an ultra-high vacuum. Specifically, the pressure inside the internal spaces of the X-ray generating device 20, the vacuum container 30, and the electron spectrometer 40 is, for example, 4 × 10⁻⁶. - 7 Pa.

[0061] <Analytical Methods>

[0062] Next, the method for analyzing the surface state of the InP substrate 100 using the analysis system 200 will be explained.

[0063] First, an InP substrate 100 is placed inside a vacuum container 30. X-rays are irradiated onto the InP substrate 100 from an X-ray generating device 20. Specifically, an X-ray source 21 uses a magnetic field generated by a deflecting electromagnet (not shown) within a circular accelerator (not shown) to bend the travel direction of high-energy electrons. As a result, X-rays are radiated along the tangent to the travel direction of the high-energy electrons. The X-ray source 21 outputs these X-rays along arrow A.

[0064] The X-rays emitted from X-ray source 21 are of high brightness. Specifically, the number of photons emitted from X-ray source 21 per second is, for example, 10. 9 Photons / second. X-rays emitted from X-ray source 21 are parallelized using a parallelizing mirror (not shown). A portion of the parallelized X-rays passes through a first slit 22. The X-rays passing through the first slit 22 are monochromated by a grating 23. The diffusion of the monochromated X-rays is confined by a second slit 24.

[0065] The energy of the X-rays irradiated from the X-ray generating device 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 grating density 23.

[0066] For example, when the slit width of the first slit 22 and the second slit 24 is 30 μm and the scribe line density at the center of the grating 23 is 400 l / mm, 200 eV of X-rays are irradiated from the X-ray generating device 20.

[0067] The angle (incident angle θ1) between the direction of travel of the X-rays irradiating the InP substrate 100 from the X-ray generating device 20 and the first main surface 1 of the InP substrate 100 is not particularly limited, for example, it is set to 5°. By irradiating the InP substrate 100 with X-rays, photoelectrons are released from the InP substrate 100.

[0068] A portion of the photoelectrons released from the InP substrate 100 lose energy due to inelastic scattering. Therefore, only a portion of the photoelectrons generated in the InP substrate 100 escape into the vacuum while retaining the energy at which they were generated, and are captured by the electron spectrometer 40.

[0069] The angle (escape angle θ2) between the direction of travel B of the photoelectrons arriving at 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.

[0070] In addition, the brightness (intensity) of the X-rays emitted from the X-ray source 21 decays with time. For example, the brightness of the X-rays emitted from the X-ray source 21 11 hours after the start of the X-ray source 21 is 1 / 3 of the brightness of the X-rays emitted from the X-ray source 21 just after the start. The Au4f photoelectron intensity is measured at regular intervals using a standard specimen made of gold (Au). Based on the measured Au4f photoelectron intensity, the decay ratio of the Au4f photoelectron intensity is obtained. Based on the obtained decay ratio, the X-ray exposure is corrected.

[0071] <Analysis object region>

[0072] The photoelectrons that can escape from the surface of the InP substrate 100 are generated in a region up to about 3 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 object. Hereinafter, this depth is also referred to as the measurement depth.

[0073] Based on the parameters of the 4d electrons of the indium (In) element in InP, indium oxide, and metallic indium, the parameters of the 2p electrons of the phosphorus (P) element in InP and phosphorus oxide, and the X-ray incident energy, the measurement depth can be calculated. For example, when the X-ray incident energy is 200 eV and the escape 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.

[0074] (Calculation method of integral intensity ratio)

[0075] Next, based on the kinetic energy distribution of the photoelectrons measured in the above XPS, a method for calculating the integral intensity ratio in the first main surface 1 of the InP substrate 100 will be described.

[0076] <In4d spectrum and P2p spectrum>

[0077] The kinetic energy E of the photoelectrons released from the InP substrate 100 is expressed by the following mathematical formula 1 using the energy hν of the irradiated X-rays, the binding energy E B of the photoelectrons in the InP substrate 100, and the work function φ.

[0078]

[0079] Using the above mathematical formula 1, based on the kinetic energy distribution of the photoelectrons released from the InP substrate 100, a spectrum showing the binding energy distribution of the photoelectrons is calculated. Specifically, by performing a narrow scan over a specified binding energy range, an In4d spectrum and a P2p spectrum are obtained.

[0080] In this specification, the "In4d spectrum" is defined as a spectrum representing the detection intensity of photoelectrons emitted from the 4d orbitals of the In element contained in indium oxide, InP, and metallic indium. The "P2p spectrum" is defined as a spectrum representing the detection intensity of photoelectrons emitted from the 2p orbitals of the P element contained in phosphorus oxide and InP.

[0081] The In4d spectrum can be obtained by narrow scanning within the range of binding energies above 14 eV and below 24 eV. Similarly, the P2p spectrum can be obtained by narrow scanning within the range of binding energies above 127 eV and below 137 eV. By performing narrow scanning, the measurement accuracy of both the In4d and P2p spectra can be improved.

[0082] In narrow scans, it is possible to use an energy interval of 0.05 eV, a cumulative time of 100 ms for each energy value, and a cumulative count of 2 to 5 times. The energy resolution E / ΔE is 3480.

[0083] <Background Correction>

[0084] Background correction was performed on the obtained In4d and P2p spectra using the Shirley method (Reference: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, No. 6, pp. 243-247). Therefore, the background-corrected In4d spectra were calculated based on the difference between the In4d spectra obtained through narrow scanning and the background. Similarly, the background-corrected P2p spectra were calculated based on the difference between the P2p spectra obtained through narrow scanning and the background.

[0085] <Cyclic Offset Correction>

[0086] When performing the aforementioned X-ray photoelectron spectroscopy on an InP crystal, charge shifts may occur. In this case, the In4d and P2p spectra may each shift to the higher energy side by a maximum of approximately 1 eV. Therefore, charge shift correction is performed by fixing the peak positions of the In4d and P2p spectra.

[0087] Specifically, the peak positions of the detection intensities of In elements present in oxide form (In-O), In elements present in InP form (In-P), and In elements present in metallic form (In-In) contained in the In4d spectrum are fixed. More specifically, the confinement energy of the detection intensity peak of In-O is set to 17.9 eV. The confinement energy of the detection intensity peak of In-P is set to approximately 17.0 eV or higher and 17.5 eV or lower. The confinement energy of the detection intensity peak of In-In is set to approximately 16.0 eV or higher and 16.5 eV or lower. Furthermore, the detection intensity peaks of In-P and In-In are influenced by the InP single-crystal substrate 10 (reference). Figure 3 The influence of this is therefore difficult to fix into a single value. Thus, as described above, the peak positions of the detection intensities of In-P and In-In each have a width of 0.5 eV.

[0088] Similarly, the peak positions of the detection intensities of P elements in oxide form (PO) and P elements in InP form (P-In) contained in the P2p spectrum were fixed. Specifically, the confinement energy of the detection intensity peak of PO was set to 132.82 eV. The confinement energy of the detection intensity peak of P-In was set to approximately 128.2 eV or higher and 128.7 eV or lower. Furthermore, similar to In-P and In-In, the detection intensity peak of P-In was affected by the InP single-crystal substrate 10 (reference). Figure 3 The influence of P-In is such that it is difficult to fix it to a single value. Therefore, as mentioned above, the peak position of the detection intensity of P-In has a width of 0.5 eV.

[0089] Based on the above method, the corrected In4d spectrum LI and the corrected P2p spectrum LP were obtained respectively. Figure 5 This is a schematic diagram showing the In4d pattern L1 of the InP substrate 100 of this embodiment. Figure 6 This is a schematic diagram showing the P2p pattern LP of the InP substrate 100 in this embodiment. Figure 5 and Figure 6 In each of these graphs, the horizontal axis represents the binding energy, and the vertical axis represents the detection intensity of the photoelectrons. Figure 5 The figure shows the detection intensity in the range of binding energy above 14 eV and below 24 eV. Figure 6 The figure shows the detection intensity in the range of binding energy above 127 eV and below 137 eV. Figure 5 In the data, each spectrum was normalized to a value of 1, representing the photoelectron intensity at the maximum peak of the In4d spectrum LI. Figure 6 In the P2p spectrum, each spectrum was normalized to 1 with the photoelectron intensity at the maximum peak of LP.

[0090] Peak separation

[0091] Next, the In4d spectrum LI and the P2p spectrum LP are each separated into multiple Gaussian functions. In this specification, this operation is also referred to as "peak separation".

[0092] Specifically, assume that the corrected In4d spectrum LI is represented by the sum of multiple Gaussian functions. The In4d spectrum LI is then expressed as three mathematical expressions (expression 2, expression 3, and expression 4). Expressions 2, 3, and 4 correspond to the In-O spectrum, the In-P spectrum, and the In-In spectrum, respectively.

[0093] [Mathematical Expression 1]

[0094]

[0095] [Mathematical Expression 2]

[0096]

[0097] [Mathematical Expression 3]

[0098]

[0099] Furthermore, the In4d spectrum splits into two sub-peaks due to the influence of spin (In4d). 3 / 2 and In4d 5 / 2 (Peak splitting). In4d 3 / 2 The strength and In4d 5 / 2 The ratio of their intensities (strength ratio) is 2:3. In4d 3 / 2 The binding energy is greater than In4d 5 / 2 The binding energy is small. In4d 3 / 2 The binding energy and In4d 5 / 2 The absolute value of the difference in binding energy (energy difference) is set to 0.90 eV here. Therefore, the In-O spectrum (Equation 2), the In-P spectrum (Equation 3), and the In-In spectrum (Equation 4) each correspond to In4d. 3 / 2 and In4d 5 / 2 The sum of two Gaussian functions is used to represent it. Additionally, in the In-O spectrum, due to the blunting of the peaks, it appears as if no peak splitting has occurred, but similarly to In-P or In-In, it is approximated using two sub-peaks.

[0100] In equations 2, 3, and 4 above, Y1, Y2, and Y3 each represent photoelectron intensity. The units for Y1, Y2, and Y3 are dimensionless. X represents the binding energy. The unit for X is eV. a1, a2, a3, b1, b2, b3, c1, c2, and c3 are each variables. The units for a1, a2, and a3 are dimensionless. The units for b1, b2, b3, c1, c2, and c3 are eV.

[0101] The square of the difference between the measured value of In4d spectrum LI after correction and the sum of Y1, Y2, and Y3 ([measured value - (Y1 + Y2 + Y3)]) is calculated as follows: 2 The variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) are optimized in the way that the minimum value is achieved. In addition, the binding energy values ​​of the detection intensity peaks of In-O, In-P, and In-In mentioned above are substituted into b1, b2, and b3 respectively.

[0102] The values ​​or ranges of each variable (a1, a2, a3, b1, b2, b3, c1, c2, c3) are as follows.

[0103] a1, a2, and a3 are real numbers greater than or equal to 0.

[0104] b1 = 19.9 eV

[0105] 17.0eV≤b2≤17.5eV

[0106] 16.0eV≤b3≤16.5eV

[0107] 0.3eV≤c1≤1.05eV

[0108] 0.3eV≤c²≤1.05eV

[0109] 0.3eV≤c3≤1.05eV

[0110] As described above, by peak separation, the spectra of In-O, In-P, and In-In can be obtained in the range of binding energies above 14 eV and below 24 eV. Figure 5 In the diagram, In-O spectrum L1 shows the obtained In-O spectrum. In-P spectrum L2 shows the obtained In-P spectrum. In-In spectrum L3 shows the obtained In-In spectrum.

[0111] Similarly, assume that the corrected P2p spectrum LP described above is represented by the sum of multiple Gaussian functions. The P2p spectrum LP is then expressed as two mathematical expressions (Formula 5 and Formula 6). Formula 5 and Formula 6 correspond to the spectra of PO and P-In, respectively.

[0112] [Mathematical Expression 4]

[0113]

[0114] [Mathematical Expression 5]

[0115]

[0116] Furthermore, similar to the In4d spectrum, the P2p spectrum splits into two sub-peaks (P2p) due to the influence of spin. 1 / 2 and P2p 3 / 2 (Peak splitting). P2p 1 / 2 The strength and P2p 3 / 2 The ratio of their intensities (strength ratio) is 1:2. (P2p) 1 / 2 The binding energy is greater than that of P2p 3 / 2 The binding energy is small. P2p 1 / 2 The binding energy of P2p 3 / 2 The absolute value of the difference in binding energy (energy difference) is set to 0.85 eV here. Therefore, the spectrum of PO (Equation 5) and the spectrum of P-In (Equation 6) are respectively derived from the P2p... 1 / 2 and P2p 3 / 2 The sum of two Gaussian functions is used to represent it. Additionally, in the spectrum of PO, due to the peak blunting, it appears that no peak splitting has occurred, but similarly to P-In, it is approximated using two sub-peaks.

[0117] In equations 5 and 6 above, Y4 and Y5 each represent photoelectron intensity. The units for Y4 and Y5 are dimensionless. X represents the binding energy. The unit for X is eV. a4, a5, b4, b5, c4, and c5 are each variables. The units for a4 and a5 are dimensionless. The units for b4, b5, c4, and c5 are eV.

[0118] The square of the difference between the measured value of LP in the corrected P2p spectrum and the sum of Y4 and Y5 is calculated as ([measured value - (Y4 + Y5)]). 2 The variables (a4, a5, b4, b5, c4, c5) are optimized in the way that minimizes the value of each variable. In addition, the binding energy values ​​of the detection intensity peaks of PO and P-In mentioned above are substituted into b4 and b5 respectively.

[0119] The values ​​or ranges of each variable (a4, a5, b4, b5, c4, c5) are as follows.

[0120] a4 and a5 are real numbers greater than or equal to 0.

[0121] b4 = 132.82 eV

[0122] 128.2 eV ≤ b5 ≤ 128.7 eV

[0123] 0.3eV≤c⁴≤1.05eV

[0124] 0.3eV≤c5≤1.05eV

[0125] As described above, by peak separation, the spectra of PO and P-In can be obtained in the range of binding energies above 127 eV and below 137 eV. Figure 6 In the diagram, PO spectrum L4 shows the obtained PO spectrum. P-In spectrum L5 shows the obtained P-In spectrum.

[0126] Furthermore, to determine the peak intensities of Y1 to Y5 mentioned above, the following corrections were performed. The probability of generating photoelectrons through X-ray irradiation is called the photoionization efficiency (η). η varies depending on the element, orbital, and incident X-ray energy. The unit of η is dimensionless. Corrections were performed by dividing the measured detection intensities of the In4d spectrum LI and the P2p spectrum LP by η. This allows for comparison of the respective amounts of In and P elements present in the InP substrate 100.

[0127] The values ​​for η can be obtained from the data published on the following website. Specifically, the photoionization efficiency (η) of In4d with an incident X-ray energy of 200 eV is set to 0.68. The photoionization efficiency (η) of P2p with an incident X-ray energy of 200 eV is set to 3.49.

[0128] (Website) https: / / vuo.elettra.eu / services / elements / WebElements.html (Additionally, the references used for the data are 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).)

[0129] <Integral Intensity Ratio>

[0130] exist Figure 5In the diagram, the area of ​​the region enclosed by the L1 and horizontal axis of the In-O spectrum is defined as the integrated intensity of In-O. The integrated intensity of In-O corresponds to the number of photoelectrons released from the 4d orbitals of In-O. Alternatively, the integrated intensity of In-O corresponds to the amount of indium oxide present in the region being analyzed by XPS.

[0131] exist Figure 5 In the XPS analysis, the area of ​​the region enclosed by the L2 and horizontal axes of the In-P spectrum is defined as the integrated intensity of In-P. The integrated intensity of In-P corresponds to the number of photoelectrons released from the 4d orbitals of In-P. Alternatively, the integrated intensity of In-P corresponds to the amount of indium phosphide present in the region being analyzed by XPS.

[0132] exist Figure 5 In the diagram, the area enclosed by the L3 region and the horizontal axis of the In-In spectrum is defined as the integrated intensity of In-In. The integrated intensity of In-In corresponds to the number of photoelectrons released from the 4d orbitals of In-In. Alternatively, the integrated intensity of In-In corresponds to the amount of metallic indium present in the region being analyzed by XPS.

[0133] exist Figure 5 In the XPS analysis, the area of ​​the region enclosed by the In4d spectrum LI and the horizontal axis is defined as the integrated intensity of indium. The integrated intensity of indium corresponds to the number of photoelectrons released from the 4d orbitals of indium. Alternatively, the integrated intensity of indium corresponds to the amount of indium present in the region being analyzed by XPS.

[0134] exist Figure 6 In the XPS analysis, the area enclosed by the L4 region of the PO spectrum and the horizontal axis is defined as the integrated intensity of PO. The integrated intensity of PO corresponds to the number of photoelectrons released from the 2p orbitals of PO. Alternatively, the integrated intensity of PO corresponds to the amount of phosphorus oxides present in the region being analyzed by XPS.

[0135] exist Figure 6 In the XPS analysis, the area of ​​the region enclosed by the L5 axis and the horizontal axis is defined as the integrated intensity of P-In. The integrated intensity of P-In corresponds to the number of photoelectrons released from the 2p orbitals of P-In. Alternatively, the integrated intensity of P-In corresponds to the amount of indium phosphide present in the region being analyzed by XPS.

[0136] exist Figure 6In the XPS analysis, the area of ​​the region enclosed by the LP and the horizontal axis of the P2p spectrum is defined as the integrated intensity of phosphorus. The integrated intensity of phosphorus corresponds to the number of photoelectrons released from the 2p orbitals of phosphorus. Alternatively, the integrated intensity of phosphorus corresponds to the amount of phosphorus present in the region being analyzed by XPS.

[0137] 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-described XPS analysis is performed on the first main surface 1 of the InP substrate 100 of this embodiment, the first integrated intensity ratio is 1.10 or higher and 3.20 or lower. For example, the first integrated intensity ratio can be 1.30 or higher or 1.50 or higher. For example, the first integrated intensity ratio can be 3.00 or lower or 2.50 or lower.

[0138] The ratio of the integrated intensity of In-In to the integrated intensity of In-P is defined as the second integrated intensity ratio. In other words, the second integrated intensity ratio is the value obtained by dividing the integrated intensity of In-In 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 of this embodiment, the second integrated intensity ratio is 0.05 or higher and 0.30 or lower. For example, the second integrated intensity ratio can be 0.10 or higher, or 0.15 or higher. For example, the second integrated intensity ratio can be 0.25 or lower, or 0.20 or lower.

[0139] The ratio of the integrated intensity of PO to the integrated intensity of P-In is defined as the third integrated intensity ratio. In other words, the third integrated intensity ratio is the value obtained by dividing the integrated intensity of PO 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 of this embodiment, the third integrated intensity ratio is 2.90 or higher and 11.00 or lower. For example, the third integrated intensity ratio can be 3.00 or higher, or 5.50 or higher. For example, the third integrated intensity ratio can be 10.00 or lower, or 6.00 or lower.

[0140] The ratio of the integrated intensity of indium to the integrated intensity of phosphorus is defined as the 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 of this embodiment, the fourth integrated intensity ratio is 1.15 or higher and 2.00 or lower. For example, the fourth integrated intensity ratio can be 1.30 or higher, or 1.50 or higher. For example, the fourth integrated intensity ratio can be 1.80 or lower, or 1.60 or lower.

[0141] Furthermore, when the above-described XPS analysis is performed on the second main surface 2 of the InP substrate 100 of this embodiment, the numerical ranges of the first integral intensity ratio, the second integral intensity ratio, the third integral intensity ratio, and the fourth integral intensity ratio can be the same as the numerical ranges described above.

[0142] <Indium Phosphide Substrate Manufacturing Method>

[0143] Next, the manufacturing method of the InP substrate 100 of this embodiment will be described. Figure 7 A flowchart is provided to schematically illustrate the manufacturing method of the InP substrate 100 according to this embodiment. (For example...) Figure 7 As shown, the manufacturing method of the InP substrate 100 in this embodiment mainly includes: a step of preparing an indium phosphide single crystal substrate (S10), a step of immersing the indium phosphide single crystal substrate in an acidic solution (S20), a first cleaning step (S30), a step of immersing the indium phosphide single crystal substrate in ozone water (S40), and a second cleaning step (S50).

[0144] First, the process of preparing an indium phosphide single crystal substrate (S10) is performed. An InP single crystal substrate 10 is prepared. Specifically, an indium phosphide single crystal is manufactured, for example, using a vertical crystal boat method. The indium phosphide single crystal is sliced ​​using, for example, a wire saw to form the InP single crystal substrate 10.

[0145] For example, the InP single crystal substrate 10 is polished on the third main surface 3 and the fourth main surface 4, respectively. Specifically, the InP single crystal substrate 10 is polished so that its surface becomes mirror-like. To remove polishing agents or the like adhering to the polished InP single crystal substrate 10, the InP single crystal substrate 10 is cleaned, for example, with hydrofluoric acid. The InP single crystal substrate 10 is then cleaned by boiling, for example, with IPA (Isopropyl Alcohol). The surface of the InP single crystal substrate 10 is then dried. The above-described InP single crystal substrate 10 is prepared through the above steps (see reference). Figure 3 ).

[0146] Next, the process of immersing the indium phosphide single crystal substrate in an acidic solution is carried out (S20). Figure 8 This is an enlarged cross-sectional schematic diagram illustrating the process (S20) of immersing an indium phosphide single-crystal substrate in an acidic solution. Figure 8 As shown, 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.

[0147] The acidic 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 index of the acidic solution 81 is 1.0 or higher and 5.0 or lower. The hydrogen ion index of the acidic solution 81 can, for example, be 1.8 or higher or 2.5 or higher. The hydrogen ion index of the acidic solution 81 can, for example, be 4.7 or lower or 3.5 or lower.

[0148] The temperature of the acidic solution 81 is, for example, room temperature (e.g., 25°C). The time for which the InP single crystal substrate 10 is immersed in the acidic solution 81 (first time) is, for example, 10 seconds or more and 300 seconds (5 minutes) or less. The first time can be, for example, 60 seconds or more or 120 seconds or more. The first time can be, for example, 240 seconds or less or 180 seconds or less.

[0149] A rotor (not shown) can also be placed inside the acidic solution 81. The acidic solution 81 can also be stirred by rotating the rotor inside the acidic solution 81 using magnetic force. This can promote the reaction between the acidic solution 81 and the InP single crystal substrate 10.

[0150] like Figure 8 As shown, the In atoms on the third main surface 3 react with the H atoms in the acidic solution 81. + Ionic reaction. As a result, In atoms ionize. The ionized In atoms dissolve into the acidic solution 81. Therefore, P atoms become excess on the third main surface 3. Phosphorus oxide 71 is formed on the third main surface 3 by the reaction of P atoms with, for example, water molecules in the acidic solution 81.

[0151] After the initial exposure, the InP single crystal substrate 10 was removed from the acidic solution 81. Phosphorus oxide 71 was formed on the third main surface 3 through the reaction of P atoms with oxygen in the atmosphere.

[0152] Next, the first cleaning step (S30) is performed. Ultrapure water (not shown) is prepared. The dissolved oxygen concentration of the ultrapure water is, for example, below 100 ppb. The InP single crystal substrate 10 is cleaned using the ultrapure water. This removes the acidic solution 81 adhering to the InP single crystal substrate 10.

[0153] Next, the process of immersing the indium phosphide single crystal substrate in ozone water is carried out (S40). Figure 9 This is an enlarged cross-sectional schematic diagram illustrating the process (S40) of immersing an indium phosphide single-crystal substrate in ozone water. Figure 9 As shown, 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.

[0154] The ozone concentration in ozone water 82 is between 3 ppm and 30 ppm. For example, the ozone concentration in ozone water 82 can be above 5 ppm, above 8 ppm, or above 10 ppm. For example, the ozone concentration in ozone water 82 can be below 25 ppm, below 20 ppm, below 18 ppm, or below 15 ppm.

[0155] In the method for manufacturing the InP substrate 100 according to this embodiment, the hydrogen ion index of the acidic solution 81 and the ozone concentration in the ozone water each satisfy either condition 1 or condition 2 below. (Condition 1) The hydrogen ion index of the acidic solution 81 is 2.0 or higher and 4.0 or lower, and the ozone concentration in the ozone water 82 is 3 ppm or higher and 30 ppm or lower. (Condition 2) The hydrogen ion index of the acidic solution 81 is 1.0 or higher and 5.0 or lower, and the ozone concentration in the ozone water 82 is 10 ppm or higher and 30 ppm or lower.

[0156] The temperature of the ozone water 82 is, for example, room temperature (e.g., 25°C). The immersion time of the InP single crystal substrate 10 in the ozone water 82 (second time) is, for example, more than 10 seconds and less than 300 seconds (5 minutes). The second time can be, for example, more than 60 seconds or more, or more than 120 seconds. The second time can be, for example, less than 240 seconds or less, or less than 180 seconds.

[0157] like Figure 9 As shown, P atoms existing in the form of indium phosphide and P atoms existing in the form of oxide react with hydroxyl radicals (OH) in 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 excess. Consequently, In atoms 73 migrate on the third main surface 3. Indium oxide 72 is formed by the oxidation of a portion of the In atoms 73. Tiny indium droplets 74 are formed by the aggregation of multiple In atoms 73. Hereinafter, indium droplets 74 are also referred to as metallic indium 74.

[0158] After a second time interval, 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 In atoms 73 with oxygen in the atmosphere.

[0159] Next, a second cleaning step (S50) is performed. Ultrapure water (not shown) with 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. This removes the ozone water 82 adhering to the InP single-crystal substrate 10.

[0160] Through the above processes, phosphorus oxide 71, indium oxide 72, and indium droplets 74 are formed on the third main surface 3. For ease of explanation, in Figure 8 and Figure 9 In the diagram, phosphorus oxide 71, indium oxide 72, and indium droplet 74 are each illustrated as independent objects. In reality, phosphorus oxide 71, indium oxide 72, and indium droplet 74 constitute the first surface layer 11 on the third main surface 3 (see reference). Figure 3 ).

[0161] Similarly, phosphorus oxide 71, indium oxide 72, and indium droplets 74 are formed on the fourth main surface 4. Phosphorus oxide 71, indium oxide 72, and indium droplets 74 constitute a second surface layer 12 on the fourth main surface 4 (see reference). Figure 3 The InP substrate 100 of this embodiment is manufactured through the above processes.

[0162] Next, the effects of the indium phosphide substrate and the method for manufacturing the indium phosphide substrate in this embodiment will be explained.

[0163] When manufacturing epitaxial substrates using InP substrate 100, the yield of the epitaxial substrate is lower than expected. Specifically, there is an increase in haze on the surface of the epitaxial substrate. Haze is the value of the amount of scattered light divided by the amount of incident light when light is irradiated onto the surface of the object under test. Furthermore, there is an increase in the number of LPDs (Light Point Defects) in the epitaxial substrate. LPDs are surface defects detected by measuring the scattered light generated when light is irradiated onto the surface of the epitaxial substrate.

[0164] Haze and the amount of LPD (Liquidity-to-Depth) are each used as indicators to evaluate the surface condition of epitaxial substrates. Excessive haze degrades the characteristics of semiconductor devices fabricated using epitaxial substrates. Similarly, excessive LPD degrades the characteristics of semiconductor devices fabricated using epitaxial substrates.

[0165] In exploring solutions to improve the surface condition of epitaxial substrates, the inventors focused on the composition of the InP substrate 100 near the main surface. For example, due to cleaning of the InP substrate 100, oxides sometimes form on its surface. In conventional XPS equipment, because the incident X-ray energy is high (e.g., around 2 keV), only average information about a region approximately 9 nm from the substrate surface can be measured. Therefore, in conventional XPS equipment, it is impossible to extract information only from the region very close to the surface. Consequently, in conventional XPS equipment, when a very thin layer composed of oxides or the like exists on the main surface of the InP substrate 100, it is impossible to quantitatively analyze this layer with high precision.

[0166] The inventors devised a method to perform XPS analysis on a region very close to the host surface by using X-ray incident energy of 200 eV and photoelectron escape angle θ2 of 45°. By performing XPS under these conditions, information about a region approximately 1.5 nm below the host surface could be extracted. Based on this information, the inventors obtained the following insights.

[0167] The inventors discovered that the presence of indium (In-O, In-P, and In-In) and phosphorus (PO and P-In) in the surface layer of the InP substrate 100 affects the haze and LPD of the epitaxial substrate.

[0168] Figure 10 This is an enlarged cross-sectional schematic diagram showing the surface state of the InP substrate 100 when there is an excessive amount of phosphorus (PO, P-In). In the case of excessive PO, the first surface layer 11 contains excessive phosphorus oxides. Figure 10 As shown, under these conditions, phosphorus oxides react with moisture in the atmosphere. This forms metaphosphoric acid portion 75. Metaphosphoric acid portion 75 is composed of metaphosphoric acid ((HPO3)2). n )constitute.

[0169] Figure 11 This is an enlarged cross-sectional schematic diagram showing the state of collapse of the metaphosphoric acid section 75. (See attached image.) Figure 11 As shown, the metaphosphoric acid portion 75 is formed by covering the first surface layer 11 with the metaphosphoric acid portion 75. The physical strength of the metaphosphoric acid portion 75 is relatively low. Therefore, when the InP substrate 100 is transported into the interior of the epitaxial growth furnace, the metaphosphoric acid portion 75 sometimes collapses. Due to the collapse of the metaphosphoric acid portion 75, tiny bumps 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.

[0170] Figure 12 This is an enlarged schematic diagram showing the state in which indium oxide 72 is formed on the InP single crystal substrate 10. (See diagram below.) Figure 12 As shown, a portion of the exposed InP single-crystal substrate 10 reacts with moisture and oxygen in the atmosphere, thereby forming indium oxide 72.

[0171] As described above, the main surface of the InP substrate 100 can be considered to be in a non-uniform state. Since an epitaxial layer is formed on this non-uniform main surface, unevenness is created on the surface of the epitaxial layer. This results in an increase in the haze of the epitaxial substrate and an increase in the number of LPDs (Laminated Diodes).

[0172] In the surface layer of the InP substrate 100, when the amounts of indium (In-O, In-P, and In-In) and phosphorus (PO and P-In) are appropriate, the surface layer can be removed by heating the InP substrate 100 in a hydrogen atmosphere during epitaxial growth. However, when the amount of indium (In-O, In-P, and In-In) is excessive, the surface layer becomes too thick. In this case, heating the InP substrate 100 in a hydrogen atmosphere sometimes fails to remove the surface layer sufficiently. Consequently, the surface layer hinders epitaxial growth. As a result, the haze of the epitaxial substrate increases and the number of LPDs (Liquid Impedance Depositions) increases.

[0173] According to the InP substrate 100 of this embodiment, when the above-described XPS analysis is performed on the first main surface 1 of the InP substrate 100, the first integrated intensity ratio is 1.10 or higher and 3.20 or lower. The second integrated intensity ratio is 0.05 or higher and 0.30 or lower. The third integrated intensity ratio is 2.90 or higher and 11.00 or lower. The fourth integrated intensity ratio is 1.15 or higher and 2.00 or lower. Thus, according to the InP substrate 100 of this embodiment, excessive amounts of indium oxide 72 and metallic indium 74 in the first surface layer 11 can be suppressed. Therefore, excessive thickness of the first surface layer 11 due to excessive indium content can be suppressed. Consequently, 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, the obstruction of epitaxial growth due to the first surface layer 11 can be suppressed. As a result, the yield of the epitaxial substrate can be improved.

[0174] Furthermore, according to the InP substrate 100 of this embodiment, excessive phosphorus oxide 71 in the first surface layer 11 can be suppressed. Therefore, the formation of metaphosphoric acid portions 75 due to the reaction of phosphorus oxide 71 with atmospheric moisture can be suppressed in the first surface layer 11. Therefore, the collapse of the first surface layer 11 due to impacts or other factors applied to the InP substrate 100 during handling can be suppressed. Therefore, when an epitaxial layer is grown on the first main surface 1, the increase in haze and the increase in the number of LPDs on the epitaxial substrate can be suppressed. As a result, the yield of the epitaxial substrate can be improved.

[0175] To grow an epitaxial film on the first main surface 1 of the InP substrate 100, the InP substrate 100 needs to be heated inside the epitaxial growth furnace to decompose the raw material gases on the first main surface 1, allowing the decomposed raw material gases to react and deposit. However, in the first surface layer 11, if the indium oxide 72, metallic indium 74, and phosphorus oxide 71 are each insufficient, the phosphorus constituting the InP substrate 100 will detach with heating, and the first main surface 1 will become rough. In this case, a good epitaxial film cannot be grown.

[0176] According to the InP substrate 100 of this embodiment, it is possible to prevent the indium oxide 72, indium metal 74, and phosphorus oxide 71 from becoming too scarce in the first surface layer 11. Therefore, by ensuring that indium oxide 72, indium metal 74, and phosphorus oxide 71 are present in appropriate amounts, the yield of the epitaxial substrate can be improved.

[0177] In exploring methods to improve the yield of epitaxial substrates, the inventors conceived of immersing indium phosphide single-crystal substrates in acidic solutions and ozone water, respectively. Further research revealed that by optimizing the hydrogen ion index of the acidic solution and the ozone concentration in the ozone water, it was possible to suppress the excessive or insufficient levels of indium oxide 72, metallic indium 74, and phosphorus oxide 71 in the first surface layer 11 of the InP substrate 100.

[0178] The method for manufacturing the InP substrate 100 in this embodiment includes a step of immersing an indium phosphide single crystal substrate in an acidic solution (S20) and a step of immersing the indium phosphide single crystal substrate in ozone water (S40). The hydrogen ion index of the acidic solution 81 is 2.0 or higher and 4.0 or lower, and the ozone concentration in the ozone water 82 is 3 ppm or higher and 30 ppm or lower; or, the hydrogen ion index of the acidic solution 81 is 1.0 or higher and 5.0 or lower, and the ozone concentration in the ozone water 82 is 10 ppm or higher and 30 ppm or lower.

[0179] Therefore, it can be considered that the chemical reactions caused by immersing the InP single crystal substrate 10 in the acidic solution 81 and the chemical reactions caused by immersing the InP single crystal substrate 10 in the ozone water 82 can each be suppressed from becoming excessive. Thus, in the first surface layer 11 of the InP substrate 100, it is possible to suppress the excessive or insufficient production of indium oxide 72, metallic indium 74, and phosphorus oxide 71. Therefore, the yield of the epitaxial substrate can be improved as described above.

[0180] According to the manufacturing method of the InP substrate 100 in this embodiment, the InP single crystal substrate 10 is immersed in the acidic solution 81 for a period of 10 seconds or more and 300 seconds (5 minutes) or less. Therefore, it can be considered that excessive chemical reactions caused by immersing the InP single crystal substrate 10 in the acidic solution 81 can be suppressed. Thus, it is possible to effectively suppress the excessive or insufficient production of indium oxide 72, metallic indium 74, and phosphorus oxide 71. Therefore, the yield of the epitaxial substrate can be improved as described above.

[0181] According to the manufacturing method of the InP substrate 100 in this embodiment, the InP single crystal substrate 10 is immersed in ozone water 82 for a period of 10 seconds or more and 300 seconds (5 minutes) or less. Therefore, it can be considered that excessive chemical reactions caused by immersing the InP single crystal substrate 10 in ozone water 82 can be suppressed. Thus, it is possible to effectively suppress the excessive or insufficient production of indium oxide 72, metallic indium 74, and phosphorus oxide 71. Therefore, the yield of the epitaxial substrate can be improved as described above.

[0182] Example

[0183] (Sample preparation)

[0184] First, InP substrates 100 of samples 1 to 11 were prepared. InP substrates 100 of samples 1 to 7 are comparative examples. Samples 8 to 11 are exemplary samples. InP substrates 100 of samples 1 to 11 were manufactured according to the manufacturing method of InP substrate 100 described above. Specifically, InP substrates 100 were manufactured using the conditions shown in Table 1 below.

[0185] [Table 1]

[0186]

[0187] Table 1 shows the manufacturing conditions of the InP substrate 100 for samples 1 to 11. In sample 1, the process of immersing the indium phosphide single crystal substrate in ozone water (S40) and the second cleaning process (S50) were not performed. In sample 2, the process of immersing the indium phosphide single crystal substrate in an acidic solution (S20) and the first cleaning process (S30) were not performed. In samples 3 to 11, all processes of the above-described manufacturing method for the InP substrate 100 were performed.

[0188] In samples 1, 5, 10, and 11, acidic solution 81 contains hydrochloric acid, adjusted to a hydrogen ion index of 3. In samples 3, 4, and 9, acidic solutions contain hydrofluoric acid, adjusted to a hydrogen ion index of 1. In samples 6, 7, and 8, acidic solutions contain citric acid, adjusted to a hydrogen ion index of 5.

[0189] In samples 3, 6, and 10, the immersion time in the acidic solution was 300 seconds. In samples 1, 7, 9, and 11, the immersion time in the acidic solution was 60 seconds. In samples 4, 5, and 8, the immersion time in the acidic solution was 10 seconds.

[0190] In samples 3, 5, and 7, the ozone concentration in ozonated water 82 was adjusted to 100 ppm. In samples 2, 8, 9, and 10, the ozone concentration in ozonated water 82 was adjusted to 20 ppm. In samples 4, 6, and 11, the ozone concentration in ozonated water 82 was adjusted to 5 ppm.

[0191] 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.

[0192] (Evaluation Method)

[0193] The XPS analysis described above was performed on the first main surface 1 of the InP substrate 100 of 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 measured using the analytical method described above.

[0194] The yield of epitaxial substrates fabricated using InP substrates 100 (samples 1 to 11) was determined. Specifically, multiple InP substrates 100 (samples 1 to 11) were prepared. An epitaxial layer was formed on the first main surface 1 of the InP substrate 100 using metal-organic vapor phase epitaxy (MOVPE).

[0195] Haze and the number of LPDs were measured on the surface of the epitaxial substrate. The areal density of LPDs was determined by dividing the measured number of LPDs by the area of ​​the measurement region. For both haze and LPD measurement, a Surfscan 6220 inspection device manufactured by KLA-Tencor was used. An argon-ion laser was used as the light source. The output power of the light source was set to 30 mW. The wavelength of the light source was set to 488 nm.

[0196] In haze measurement, the minimum value of the ratio of scattered light to incident light is set to 0.0049 ppm. In other words, the lower limit for haze measurement is set to 0.0049 ppm.

[0197] In determining the number of LPDs, the minimum size of the LPDs included in the measurement results is 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 are defined as LPDs. In determining the number of LPDs, the measurement interval is set to 10 μm (Throughput; Low). Both haze measurement and LPD quantity measurement are performed on a region of the epitaxial substrate surface excluding areas within 3 mm of the outer edge of the epitaxial substrate surface (Edge Exclusion). The outer edge of the epitaxial substrate surface is the ridge line between the outer peripheral surface 9 and the epitaxial substrate surface.

[0198] Products with a haze of less than 7 ppm and an LPD areal density of 5 particles / cm³ 2 The following epitaxial substrates are considered acceptable. The yield of epitaxial substrates is calculated by dividing the number of acceptable epitaxial substrates by the total number of epitaxial substrates manufactured.

[0199] (Evaluation Results)

[0200] [Table 2]

[0201]

[0202] Table 2 shows the integrated intensity ratio and epitaxial substrate yield of InP substrate 100 for samples 1 to 11.

[0203] In the samples (samples 8 to 11) of the embodiments, the first integrated intensity ratio is 1.15 or higher and 3.10 or lower. The second integrated intensity ratio is 0.06 or higher and 0.28 or lower. The third integrated intensity ratio is 3.00 or higher and 10.50 or lower. The fourth integrated intensity ratio is 1.18 or higher and 1.99 or lower.

[0204] Figure 13 , Figure 14 , Figure 15 as well as Figure 16 The yield of epitaxial substrates fabricated using InP substrates 100 (samples 1 to 11) is shown in Table 2. Figures 13 to 16 As shown, in samples (samples 8 to 11) with a first integral intensity ratio of 1.10 or higher and 3.20 or lower, a second integral intensity ratio of 0.05 or higher and 0.30 or lower, a third integral intensity ratio of 2.90 or higher and 11.00 or lower, and a fourth integral intensity ratio of 1.15 or higher and 2.00 or lower, the yield of the epitaxial substrate is 90% or higher.

[0205] As described above, it has been confirmed that, compared with the manufacturing method of the InP substrate 100 and the InP substrate 100 of the comparative example, the manufacturing method of the InP substrate 100 and the InP substrate 100 according to the embodiment can improve the yield of the epitaxial substrate.

[0206] It should be considered that the embodiments and examples disclosed herein are exemplary in all respects and not restrictive. The scope of the invention is not shown by the foregoing description but by the claims, and is intended to include all modifications of the same meaning and scope as the claims.

[0207] Explanation of reference numerals in the attached figures

[0208] 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 device; 21: X-ray source; 22: First slit; 23: Grating; 24: Second slit; 30: Vacuum container; 40: Electron spectrometer; 71: Phosphorus oxide; 72: Indium oxide; 73: Indium atom; 74: Metallic indium (indium droplet); 75: Metaphosphoric acid section; 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: PO spectrum; L5: P-In spectrum; LI: In4d spectrum; LP: P2p spectrum; O: Center; W1: Diameter; θ1: Incident angle; θ2: Escape angle.

Claims

1. An indium phosphide substrate having a main surface, X-ray photoelectron spectroscopy (XPS) was used to capture photoelectrons released to the outside of the indium phosphide substrate by irradiating the center of the main surface with X-rays at an incident energy of 200 eV and an emission angle of 45°. The detection intensity spectra of indium's 4d electrons and phosphorus's 2p electrons were then determined. The ratio of the integrated intensity of indium in oxide form to the integrated intensity of indium in indium phosphide form is defined as the first integrated intensity ratio. The ratio of the integrated intensity of indium in its metallic form to that of indium in its indium phosphide form is defined as the second integrated intensity ratio. The ratio of the integrated intensity of phosphorus in oxide form to the integrated intensity of phosphorus in indium phosphide form is defined as the third integrated intensity ratio. When the ratio of the integral intensity of indium to the integral intensity of phosphorus is set as the fourth integral intensity ratio, The first integral intensity ratio is greater than or equal to 1.10 and less than or equal to 3.

20. The second integral intensity ratio is greater than 0.05 and less than 0.

30. The third integral intensity ratio is above 2.90 and below 11.

00. The fourth integral intensity ratio is above 1.15 and below 2.

00.

2. A method for manufacturing an indium phosphide substrate, comprising: The process of immersing an indium phosphide single crystal substrate in an acidic solution; After immersing the indium phosphide single crystal substrate in the acidic solution, the indium phosphide single crystal substrate is then cleaned with ultrapure water. The process of immersing the indium phosphide single crystal substrate in ozone water after the step of cleaning the indium phosphide single crystal substrate with the ultrapure water. as well as Following the process of immersing the indium phosphide single crystal substrate in the ozone water, the indium phosphide single crystal substrate is then rinsed with ultrapure water. The acidic solution has a hydrogen ion index of 2.0 or higher and 4.0 or lower, and the ozone concentration in the ozone water is 3 ppm or higher and 30 ppm or lower; or the acidic solution has a hydrogen ion index of 1.0 or higher and 5.0 or lower, and the ozone concentration in the ozone water is 10 ppm or higher and 30 ppm or lower.

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

4. The method for manufacturing an indium phosphide substrate according to claim 2 or claim 3, wherein, In the process of immersing the indium phosphide single crystal substrate in the acidic solution The acidic solution was at room temperature. The indium phosphide single crystal substrate is immersed in the acidic solution for a time of more than 10 seconds and less than 5 minutes.

5. The method for manufacturing an indium phosphide substrate according to any one of claims 2 to 4, wherein, In the process of immersing the indium phosphide single crystal substrate in the ozone water, The temperature of the ozone water is room temperature. The indium phosphide single crystal substrate is immersed in the ozone water for a period of more than 10 seconds and less than 5 minutes.

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