Indium phosphide substrate and semiconductor epitaxial wafer

Abstract

The indium phosphide substrate has a (relative intensity of fragment ions composed of only H, C, N, O, and F) / (relative intensity of fragment ions including one or more of In and P and one or more of C, N, O, and F) of from 0.6 to 0.9 for all identifiable positive ion fragment ions having a mass-to-charge ratio m / z≤350, obtained by ToF-SIMS analysis, on the substrate surface.

Description

Indium phosphide substrates and semiconductor epitaxial wafers

[0001] The present invention relates to indium phosphide substrates and semiconductor epitaxial wafers.

[0002] Indium phosphide (InP), also known as indium phosphide, is a III-V group compound semiconductor material composed of indium (In) of group III and phosphorus (P) of group V. Its semiconductor properties include a band gap of 1.35 eV and an electron mobility of approximately 5400 cm / V·s, with higher electron mobility under high electric fields than other common semiconductor materials such as silicon and gallium arsenide. Furthermore, its stable crystal structure at room temperature and pressure is a cubic zinc blende structure, and its lattice constant is characterized by a larger value than that of compound semiconductors such as gallium arsenide (GaAs) and gallium phosphide (GaP).

[0003] Single-crystallized InP is used in high-speed electronic devices, taking advantage of its larger electron mobility compared to silicon and the like. Furthermore, its larger lattice constant compared to gallium arsenide (GaAs) and gallium phosphide (GaP) can reduce the lattice mismatch rate during heteroepitaxial growth of ternary alloy crystals such as InGaAs and quaternary alloy crystals such as InGaAsP. Therefore, InP single crystals are used as substrates for various optical communication devices, such as semiconductor lasers, optical modulators, optical amplifiers, optical waveguides, light-emitting diodes, and photodetectors, which are formed by stacking these alloy compounds, as well as for optical integrated circuits that combine these devices.

[0004] A new single-crystal thin film may be grown epitaxially on an InP substrate using, for example, molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) (see Patent Document 1). In this case, the InP substrate is generally subjected to heat treatment (thermal cleaning) in an epitaxial furnace before epitaxial growth in order to remove impurities from the surface of the InP substrate.

[0005] JP 2015-008318 A

[0006] If thermal cleaning is insufficient, organic substances and oxides remain on the surface of the InP substrate, preventing proper epitaxial growth, or organic substances and oxides remain as impurities at the interface between the epitaxial crystal layer formed by epitaxial growth and the indium phosphide substrate, resulting in deterioration of device characteristics.

[0007] During thermal cleaning in MOCVD, PH3 (phosphine) gas is generally introduced to prevent the decomposition of P on the surface due to heat, but in MBE, PH3 gas cannot be introduced due to the need to grow in a vacuum, which makes thermal cleaning insufficient. Furthermore, even with MOCVD, in order to obtain a clean surface, it is necessary to raise the temperature during thermal cleaning and take a long time, which is economically disadvantageous.

[0008] Therefore, an object of the embodiments of the present invention is to provide an indium phosphide substrate and a semiconductor epitaxial wafer that can effectively remove impurities from the substrate surface without performing excessive thermal cleaning.

[0009] The above problems are solved by the present invention, which is specified as follows: 1. An indium phosphide substrate in which, for all identifiable positive ion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis of the substrate surface, (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.6 or more and 0.9 or less. 2. An indium phosphide substrate in which, for all identifiable negative ion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis of the substrate surface, (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.6 or more and 0.9 or less. 3. 3. The indium phosphide substrate according to claim 1 or 2, having a diameter of 50 mm or more and 150 mm or less. 4. When an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, a peak hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 5. The indium phosphide substrate according to any one of 1 to 3 above, wherein when an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the silicon sheet concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E11 atoms / cm 2 6. The indium phosphide substrate according to any one of 1 to 4 above, wherein when an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the background level of the D-SIMS analyzer for hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate in D-SIMS analysis is 2E16 cm 3 The background level of the D-SIMS analyzer for carbon concentration was set to 2E15 cm 36. The indium phosphide substrate according to any one of 1 to 5 above, wherein the sheet hydrogen concentration and the sheet carbon concentration are each below the lower detection limit of the D-SIMS analyzer. 7. A semiconductor epitaxial wafer comprising the indium phosphide substrate according to any one of 1 to 6 above, and an epitaxial crystal layer provided on the surface of the indium phosphide substrate. 8. A semiconductor epitaxial wafer comprising the indium phosphide substrate according to any one of 1 to 6 above, and an epitaxial crystal layer provided on the surface of the indium phosphide substrate. 9. The indium phosphide substrate according to any one of 1 to 5 above, wherein the sheet hydrogen concentration and the sheet carbon concentration are each below the lower detection limit of the D-SIMS analyzer. 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 9. The semiconductor epitaxial wafer according to 7 above, comprising an indium phosphide substrate and an epitaxial crystal layer provided on the surface of the indium phosphide substrate, wherein the silicon sheet concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E11 atoms / cm 2 10. A semiconductor epitaxial wafer comprising an indium phosphide substrate and an epitaxial crystal layer provided on a surface of the indium phosphide substrate, wherein the background level of a D-SIMS analyzer for hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 2E16 cm 3 The background level of the D-SIMS analyzer for carbon concentration was set to 2E15 cm 3 11. A semiconductor epitaxial wafer, comprising an indium phosphide substrate and an epitaxial crystal layer provided on the surface of the indium phosphide substrate, wherein the peak hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm. 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 A semiconductor epitaxial wafer is as follows:

[0010] According to the embodiments of the present invention, it is possible to provide an indium phosphide substrate and a semiconductor epitaxial wafer that can effectively remove impurities from the substrate surface without performing excessive thermal cleaning.

[0011] 1 shows the results of D-SIMS analysis of a sample according to Example 1, which was carried out after epitaxial growth. 2 shows the results of D-SIMS analysis of a sample according to Comparative Example 1, which was carried out after epitaxial growth.

[0012] Next, the embodiments for carrying out the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] [Indium Phosphide Substrate] In one aspect, an indium phosphide substrate according to an embodiment of the present invention has a substrate surface in which, for all identifiable positive ion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis, the (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.6 or more and 0.9 or less.

[0014] Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a technique in which a solid sample is irradiated with an ion beam (primary ions) and the ions (secondary ions) emitted from the surface are mass-separated using the difference in their flight times (time of flight is proportional to the square root of their mass). ToF-SIMS analysis can obtain information on elements or molecular species present at a depth of 1 nm or less from the sample surface with extremely high detection sensitivity. In ToF-SIMS analysis of the surface of an indium phosphide substrate, fragment ions are obtained, and in an embodiment of the present invention, for all identifiable positive fragment ions having a mass-to-charge ratio m / z≦350, the ratio of the relative intensity of fragment ions composed only of gaseous components H, C, N, O, and F to the relative intensity of fragment ions containing one or more of In and P, which are the main components of the indium phosphide substrate, and one or more of H, C, N, O, and F, i.e., (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is controlled to be 0.6 or more and 0.9 or less. Since the ratio of relative intensities of fragment ions composed only of the gas components H, C, N, O, and F is 0.6 or more, there are many components on the surface of the indium phosphide substrate that are easily desorbed by thermal cleaning, making it possible to satisfactorily remove impurities from the substrate surface without performing excessive thermal cleaning as in the past. Here, "excessive thermal cleaning" refers, for example, to subjecting the surface of the indium phosphide substrate to heat treatment at 650°C or higher for one hour or more. Furthermore, since the ratio of relative intensities of fragment ions composed only of the gas components H, C, N, O, and F is 0.9 or less, the amount of impurities such as carbon on the surface of the indium phosphide substrate is suppressed, which has the advantage of making them easier to remove by thermal cleaning.

[0015] In the indium phosphide substrate according to the embodiment of the present invention, for all identifiable positive ion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis on the substrate surface, it is preferable that the ratio (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.7 or more and 0.8 or less.

[0016] In another aspect, the indium phosphide substrate according to an embodiment of the present invention has, for all identifiable anion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis on the substrate surface, a ratio of (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) of 0.6 to 0.9.

[0017] In an embodiment of the present invention, for all identifiable anion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis on the substrate surface, the ratio of relative intensities of fragment ions composed only of gaseous components H, C, N, O, and F is 0.6 or more. Therefore, there are many components on the surface of the indium phosphide substrate that are easily desorbed by thermal cleaning, and it is possible to effectively remove impurities from the substrate surface without performing excessive thermal cleaning as in the past. In addition, the main components In and P are increased, and the amount of impurities is correspondingly reduced. Furthermore, since the ratio of relative intensities of fragment ions composed only of the gaseous components H, C, N, O, and F is 0.9 or less, the amount of impurities such as carbon is suppressed on the surface of the indium phosphide substrate, which has the advantage of making them easier to remove by thermal cleaning.

[0018] In the indium phosphide substrate according to the embodiment of the present invention, for all identifiable anion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis on the substrate surface, it is preferable that the ratio (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.7 or more and 0.8 or less.

[0019] In the embodiment of the present invention, ToF-SIMS analysis can be performed as follows. For example, a TOF-SIMS 4S manufactured by ION-TOF is used to analyze one point at the center of the substrate. The analysis conditions are as follows: Bi3 + A measurement area of ​​500 μm x 500 μm is measured using a neutralization gun. Two measurement modes, positive ions and negative ions, are used, and all identifiable ion peaks with a mass-to-charge ratio m / z≦350 are extracted. In ToF-SIMS analysis, the secondary ion intensity varies depending on the analysis conditions, so in order to correct for variations due to the conditions of the instrument, the intensity of each ion is calculated using the following formula: + And the anion is 31P - The relative intensity is calculated by dividing the ion intensity by the ion intensity of the sample.

[0020] The indium phosphide substrate according to the embodiment of the present invention may have a diameter of 50 mm or more and 150 mm or less. Also, the indium phosphide substrate according to the embodiment of the present invention may have a diameter of 50 mm or more and 100 mm or less, or 50 mm or more and 76.2 mm or less.

[0021] The indium phosphide substrate according to the embodiment of the present invention may contain a dopant. The dopant may be one or more selected from S, Zn, Fe, and Sn. The dopant concentration of the indium phosphide substrate is not limited, and may be 1×10 16 ~1 x 10 19 cm -3 may be.

[0022] The indium phosphide substrate according to the embodiment of the present invention, which will be described in detail later, has a structure in which, when an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the peak concentration of hydrogen at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 According to this configuration, the peak concentration of hydrogen, which is a typical constituent element of organic matter, at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer and the indium phosphide substrate is preferably 3E16 atoms / cm or less. 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 Since the temperature is controlled as follows, impurities on the substrate surface are effectively removed, and a semiconductor epitaxial wafer can be obtained in which impurities at the interface between the substrate and the epitaxial crystal layer are reduced.

[0023] The indium phosphide substrate according to the embodiment of the present invention, which will be described in detail later, has a silicon sheet concentration of 3E11 atoms / cm at the interface between the epitaxial crystal layer and the indium phosphide substrate when an epitaxial crystal layer is provided on the surface of the indium phosphide substrate. 2 According to this configuration, the sheet concentration of silicon, which is a typical constituent element of organic matter, at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer and the indium phosphide substrate is preferably 3E11 atoms / cm or less. 2 Since the temperature is controlled as follows, impurities on the substrate surface are effectively removed, and a semiconductor epitaxial wafer can be obtained in which impurities at the interface between the substrate and the epitaxial crystal layer are reduced.

[0024] The indium phosphide substrate according to the embodiment of the present invention, which will be described in detail later, has an epitaxial crystal layer formed on the surface of the indium phosphide substrate, and the hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is measured by a D-SIMS analyzer to have a background level of 2E16 cm 3 The background level of the D-SIMS analyzer for carbon concentration was set to 2E15 cm 3 When the sheet concentration of hydrogen and the sheet concentration of carbon are each preferably below the lower limit of detection of the D-SIMS analyzer, the phrase "the sheet concentration of hydrogen and the sheet concentration of carbon are each below the lower limit of detection of the D-SIMS analyzer" means that no hydrogen concentration peak or carbon concentration peak is present, and the sheet concentrations cannot be calculated. According to this configuration, the hydrogen concentration and the carbon concentration are each controlled to be below the lower limit of detection of the D-SIMS analyzer at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer and the indium phosphide substrate, so that impurities on the substrate surface are successfully removed, and a semiconductor epitaxial wafer can be obtained in which impurities at the interface between the substrate and the epitaxial crystal layer have been reduced.

[0025] [Method for Manufacturing Indium Phosphide Substrate] In a method for manufacturing an indium phosphide substrate according to an embodiment of the present invention, first, an indium phosphide single crystal ingot is prepared, then the indium phosphide single crystal ingot is ground into a cylindrical shape, and the ground indium phosphide single crystal ingot is cut into a substrate using a wire saw or the like.

[0026] Next, in order to remove the process-affected layer generated in the cutting process using the wire saw, the substrate after cutting is immersed in a mixed solution of an aqueous solution of phosphoric acid and hydrogen peroxide, etc., to etch the surface.

[0027] Next, the outer periphery of the substrate is chamfered to a diameter of 50 mm to 150 mm, etc. After chamfering, at least one surface, preferably both surfaces, of the substrate are polished (lapping).

[0028] Next, the polished substrate is immersed in a mixed solution of phosphoric acid solution, hydrogen peroxide solution, and ultrapure water for surface etching. Next, the surface of the substrate is polished with an abrasive for mirror polishing to a mirror finish, and then washed to produce an indium phosphide (single crystal) substrate.

[0029] Here, when an indium phosphide substrate is polished and cleaned by a known method, the surface energy is very high immediately after polishing and cleaning, and the substrate is in an active state, so it easily bonds with organic matter in the air. The organic matter thus formed forms bonds with In and P, and therefore tends to be difficult to remove during heat treatment (thermal cleaning). In contrast, in an embodiment of the present invention, an indium phosphide substrate having an organic film attached thereto that is easily removed during thermal cleaning can be obtained by the following manufacturing method.

[0030] First, the cleaned indium phosphide substrate is placed in a commercially available PP (polypropylene) container and heated for 3 to 5 hours at 80 to 100° C. Examples of commercially available PP containers include the following: PP manufactured by Japan Entegris: ・2-inch individual container: H22-20-JV-SET or H22-20-JP-SET ・3-inch individual container: H22-30-JP-SET ・4-inch individual container: H22-40-JP-SET ・PP cassette storage container: E97-102-61C02 PP manufactured by ePAK, P / N: ・2-inch individual container: eWB0021-ASSY-1 ・3-inch individual container: eWB0572-ASSY-1 ・4-inch individual container: eWB0573-ASSY-1 When the PP container itself is heated alone at 80°C for 30 minutes and the outgassing is analyzed by GC-MS, it has been found that approximately 800 ng of outgassing occurs per 1 gram of container. Therefore, as described above, by storing the indium phosphide substrate in a PP container and heating it at 80 to 100°C for 3 to 5 hours, a sufficient amount of degassing is present near the surface of the indium phosphide substrate, and the organic film originally formed on the substrate surface is replaced with organic matter derived from the degassing. This organic matter is easily decomposed when thermal cleaning is performed, making it easy to obtain a surface with few surface impurities during epitaxial growth even with a short heat treatment time. In this way, because impurities on the substrate surface are easily decomposed by thermal cleaning before epitaxial growth, the film quality of the epitaxially grown film can be improved, and improved device characteristics can be expected.

[0031] [Semiconductor Epitaxial Wafer] By epitaxially growing a semiconductor thin film on the surface of an indium phosphide substrate according to an embodiment of the present invention using a known method, an epitaxial crystal layer can be formed, thereby producing a semiconductor epitaxial wafer. As an example of the epitaxial growth, a HEMT (High Electron Mobility Transistor) structure can be formed by epitaxially growing an InAlAs buffer layer, an InGaAs channel layer, an InAlAs spacer layer, and an InP electron supply layer on the surface of the indium phosphide substrate. When producing a semiconductor epitaxial wafer having such a HEMT structure, a mirror-finished indium phosphide substrate is typically etched with an etching solution such as sulfuric acid / hydrogen peroxide to remove impurities such as silicon (Si) adhering to the substrate surface. After this etching process, the back surface of the indium phosphide substrate is supported by contacting it with a susceptor, and an epitaxial film is formed on the surface of the indium phosphide substrate by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD).

[0032] In the semiconductor epitaxial wafer according to the embodiment of the present invention, the peak concentration of hydrogen at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 Preferably, it is:

[0033] Hydrogen (H), carbon (C), and silicon (Si) are typical constituent elements of organic matter that adhere to the surface of an indium phosphide substrate. If organic matter adheres to the surface of an indium phosphide substrate, it may be impossible to remove it without extensive thermal cleaning. In contrast, in the semiconductor epitaxial wafer according to the embodiment of the present invention, the peak concentration of hydrogen, which is a typical constituent element of organic matter, is 3E16 atoms / cm at the interface between the epitaxial crystal layer and the indium phosphide substrate. 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 By controlling the temperature as described below, impurities on the substrate surface can be effectively removed, and a semiconductor epitaxial wafer can be obtained in which impurities at the interface between the substrate and the epitaxial crystal layer can be reduced.

[0034] In the semiconductor epitaxial wafer according to the embodiment of the present invention, the peak concentration of hydrogen at the interface between the epitaxial crystal layer and the indium phosphide substrate is 2E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 2E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 7E16 atoms / cm 3 More preferably, it is:

[0035] The peak hydrogen concentration, peak carbon concentration, peak silicon concentration, and sheet concentration of each element at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer according to the embodiment of the present invention and the indium phosphide substrate can be measured as follows: That is, analysis is performed by D-SIMS (Dynamic SIMS) using an analyzer such as a CAMECA SIMS IMS-4f manufactured by Ametec Co., Ltd. (primary ion source: Cs +, acceleration voltage: 14.5 keV, etc.), and the hydrogen peak, carbon peak, and silicon peak at the interface between the epitaxial crystal layer and the indium phosphide substrate are integrated with the horizontal axis representing the analysis depth and the vertical axis representing the element concentration, to calculate the sheet concentration of each element. Regarding the above-mentioned "interface between the epitaxial crystal layer and the indium phosphide substrate," if the indium phosphide substrate contains a dopant, the dopant species can be measured, and the boundary between the region containing the dopant and the region not containing the dopant can be identified as the interface. In the examples and comparative examples described below, a Si peak is observed, and the position of the Si peak can be identified as the interface between the epitaxial crystal layer and the indium phosphide substrate. In the above-mentioned SIMS analysis, the interface between the epitaxial crystal layer and the InP substrate is at a depth corresponding to the surface of the InP substrate, but if each element is present at a higher concentration than the concentration in the epitaxial crystal layer and the bulk concentration of the substrate, a peak will appear. The maximum value of this peak is taken as the peak concentration (peak concentration of hydrogen, peak concentration of carbon, and peak concentration of silicon at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer and the indium phosphide substrate). In SIMS analysis, the peak concentration is the maximum value (peak concentration: unit cm) of hydrogen, carbon, and silicon detected at the interface between the epitaxial film and the substrate by repeating a process of digging a certain amount in the depth direction at a predetermined sputtering rate with primary ions and analyzing the concentration of various elements there, and analyzing the elements to be measured in the depth direction from the surface of the epitaxial film to the substrate. -3 ) The peak concentration may be lower than the actual value due to the roughness caused by sputtering, which may broaden the peak shape. Therefore, it can be more accurately confirmed as the integrated concentration (sheet concentration) of hydrogen, carbon, and silicon detected near the interface. The integrated concentration of hydrogen, carbon, and silicon detected near the interface is calculated as the concentration per unit area (cm2) of the part corresponding to the interface. 2 ) refers to the number of hydrogen, carbon, and silicon atoms present near the interface.

[0036] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0037] (Example 1, Comparative Example 1) In Example 1, an indium phosphide (single crystal) substrate with an organic substance applied to the surface was prepared. In Comparative Example 1, an indium phosphide (single crystal) substrate was prepared which was polished and cleaned by a known method and then sealed with nitrogen within one hour. Next, each indium phosphide substrate was introduced into a metal organic vapor phase epitaxy apparatus (HR-3246 manufactured by Nippon Sanso Co., Ltd.) and the temperature was raised to the growth temperature (650°C). Immediately after the temperature was raised, PH3 gas and trimethylindium vapor were introduced to grow an InP film to a thickness of approximately 200 nm. No particular thermal cleaning time was provided, and growth began immediately after the temperature was raised to the growth temperature. The wafer after epitaxial growth was analyzed by D-SIMS (Dynamic SIMS) using a CAMECA SIMS IMS-4f analyzer (D-SIMS analyzer) manufactured by Ametec Co., Ltd. (primary ion source: Cs + D-SIMS analysis was performed using a D-SIMS (acceleration voltage: 14.5 keV) to calculate the sheet concentration of each element. The hydrogen peak, carbon peak, and silicon peak at the interface between the epitaxial crystal layer and the indium phosphide substrate were integrated over the peak position range (for example, in the case of silicon in Figure 1, depth positions of 0.175 μm to 0.275 μm) with the horizontal axis representing the analysis depth and the vertical axis representing the element concentration. The sheet concentrations are shown in Table 1. The results of the D-SIMS analysis performed after the epitaxial growth are shown in Figure 1 (Example 1) and Figure 2 (Comparative Example 1). Note that, because no peak profile appears near the interface, the sheet concentrations of the hydrogen and carbon components in Figure 1 cannot be calculated as the integrated concentration in the depth direction of the peak profile, and are therefore below the detection limit.

[0038]

[0039] In the above-described D-SIMS analysis, each element was present at a higher concentration than the concentration in the epitaxial crystal layer and the bulk concentration in the substrate, resulting in the appearance of a peak in each concentration. The maximum value of this peak was taken as the peak concentration (peak hydrogen concentration, peak carbon concentration, and peak silicon concentration at the interface between the epitaxial crystal layer of the semiconductor epitaxial wafer and the indium phosphide substrate). The peak concentrations are shown in Table 2. Here, in Example 1 of FIG. 1 , the hydrogen and carbon components were present in the D-SIMS analyzer at concentrations below the hydrogen and carbon concentrations, which are gaseous components, i.e., background levels, and no peak profile could be identified. However, the substrate surface was determined to be the position at a depth of 0.2 μm from the outermost surface of the epitaxial wafer, which corresponds to the peak position of the Si component, and the peak concentrations of hydrogen and carbon were determined.

[0040]

[0041] To perform a qualitative analysis of the organic matter adhering to the surface, ToF-SIMS analysis was performed. The ToF-SIMS analysis was performed using a TOF-SIMS 4S manufactured by ION-TOF, and analysis was performed at one point in the center of the substrate. The analysis conditions were as follows: Bi3 + A measurement area of ​​500 μm x 500 μm was measured using a neutralization gun. Two measurement modes, positive ion and negative ion, were used, and all identifiable ion peaks with a mass-to-charge ratio m / z ≦ 350 were extracted. In ToF-SIMS analysis, the secondary ion intensity varies depending on the analysis conditions, etc., so in order to correct for variations due to the conditions of the instrument, the intensity of each ion was calculated using the following formula: + And the anion is 31P - The ToF-SIMS analysis was carried out under conditions where the intensity of each peak was not saturated and under conditions where the surface could be considered non-destructive (static conditions).

[0042] In addition, XPS analysis was performed to investigate the amount of surface organic matter and surface oxides when sufficient thermal cleaning time was allowed. The indium phosphide substrate was cut into approximately 10 mm square pieces in air and then introduced into a PHI5000 Versaprobe II scanning X-ray photoelectron spectrometer manufactured by ULVAC-PHI, Inc. The XPS analysis was performed under the following conditions: X-ray source: Al Kα, monochromator 1486.6 eV, 50 W, charge neutralization mechanism (electron neutralization gun, ion beam), analysis area: 1.0 × 0.2 mm 2 The elements focused on C, O, Si, In, and P. However, since Si was below the detection limit, semi-quantitative values ​​were calculated so that the sum of C, O, In, and P equaled 100%. The horizontal axis of the spectrum was corrected by setting the main peak of the In3d5 spectrum to the InP state (444.6 eV). To investigate the oxidation states of In and P, peak separation was performed focusing on the two spectra, P2p and In3d5. The P2p spectrum was calculated using two components, P-In and P-O, while the In3d5 spectrum was calculated using two components, In-P and other states. After measurements at room temperature, a test to investigate the surface condition after thermal cleaning was performed. The main chamber was degassed from an ultimate vacuum of 1e-5 Pa or less at 80°C and 120°C until the vacuum improved, then heated to 400°C, held at 400°C for 30 minutes, and then cooled (naturally cooled). Measurements were then performed again after the sample returned to room temperature. Tables 3 and 4 show the ToF-SIMS analysis results of Example 1 and Comparative Example 1 relating to positive ion fragment ions. Tables 5 and 6 show the ToF-SIMS analysis results of Example 1 and Comparative Example 1 relating to negative ion fragment ions. Table 7 shows the results of the XPS analysis. Note that "%" in Table 7 stands for atomic %.

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] For the indium phosphide substrate according to Example 1, for all identifiable positive and negative ion fragment ions having a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis of the substrate surface, the (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) was in the range of 0.6 to 0.9. Therefore, it can be seen that the indium phosphide substrate according to Example 1 has an organic film on the substrate surface substituted with organic matter derived from degassing, and the organic matter is easily decomposed when thermal cleaning is performed, making it easy to obtain a surface with few surface impurities during epitaxial growth even with a short heat treatment time. For the indium phosphide substrate according to Comparative Example 1, the (relative intensity of fragment ions composed only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) ratio for both the cation fragment ions and the anion fragment ions was outside the range of 0.6 or more and 0.9 or less. For this reason, excessive thermal cleaning may be required to obtain a surface with few surface impurities during epitaxial growth.

[0049] According to one embodiment of the present invention, it is possible to provide an indium phosphide substrate and a semiconductor epitaxial wafer that can effectively remove impurities from the substrate surface without excessive thermal cleaning. Because indium phosphide substrates are used as materials for light-emitting and receiving elements for optical communications, one embodiment of the present invention may contribute to the advancement of optical communications technology. Therefore, one embodiment of the present invention may contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which states, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

Claims

1. An indium phosphide substrate in which, for all identifiable positive ion fragment ions with a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis of the substrate surface, the ratio (relative intensity of fragment ions consisting only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.6 or more and 0.9 or less.

2. An indium phosphide substrate in which, for all identifiable anion fragment ions with a mass-to-charge ratio m / z≦350 obtained by ToF-SIMS analysis of the substrate surface, the ratio (relative intensity of fragment ions consisting only of H, C, N, O, and F) / (relative intensity of fragment ions containing one or more of In and P and one or more of H, C, N, O, and F) is 0.6 or more and 0.9 or less.

3. The indium phosphide substrate according to claim 1 or 2, having a diameter of 50 mm or more and 150 mm or less.

4. When an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the peak concentration of hydrogen at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 3. The indium phosphide substrate according to claim 1 or 2, wherein:

5. When an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the silicon sheet concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E11 atoms / cm 2 3. The indium phosphide substrate according to claim 1 or 2, wherein:

6. When an epitaxial crystal layer is provided on the surface of the indium phosphide substrate, the background level of the D-SIMS analyzer for hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 2E16 cm 3 The background level of the D-SIMS analyzer for carbon concentration was set to 2E15 cm 3 3. The indium phosphide substrate according to claim 1, wherein the sheet concentration of hydrogen and the sheet concentration of carbon are each below the lower detection limit of the D-SIMS analysis device.

7. A semiconductor epitaxial wafer comprising the indium phosphide substrate according to claim 1 or 2 and an epitaxial crystal layer provided on the surface of the indium phosphide substrate.

8. At the interface between the epitaxial crystal layer and the indium phosphide substrate, the peak concentration of hydrogen is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 8. The semiconductor epitaxial wafer of claim 7, wherein:

9. A semiconductor device comprising an indium phosphide substrate and an epitaxial crystal layer formed on the surface of the indium phosphide substrate, wherein the silicon sheet concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E11 atoms / cm 2 A semiconductor epitaxial wafer is as follows:

10. A semiconductor device comprising an indium phosphide substrate and an epitaxial crystal layer formed on the surface of the indium phosphide substrate, wherein the background level of the D-SIMS analyzer for hydrogen concentration at the interface between the epitaxial crystal layer and the indium phosphide substrate is 2E16 cm 3 The background level of the D-SIMS analyzer for carbon concentration was set to 2E15 cm 3 and the sheet concentration of hydrogen and the sheet concentration of carbon are each below the lower detection limit of the D-SIMS analysis device.

11. A semiconductor device comprising an indium phosphide substrate and an epitaxial crystal layer formed on the surface of the indium phosphide substrate, wherein the peak concentration of hydrogen at the interface between the epitaxial crystal layer and the indium phosphide substrate is 3E16 atoms / cm 3 Hereinafter, the peak concentration of carbon is 3E15 atoms / cm 3 Hereinafter, the peak concentration of silicon is 8E16 atoms / cm 3 A semiconductor epitaxial wafer is as follows:

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