Method for manufacturing silicon carbide epitaxial substrates and silicon carbide semiconductor devices

Abstract

This invention provides a silicon carbide epitaxial substrate and a method for manufacturing a silicon carbide semiconductor device that can accurately measure carrier concentration. [Solution] The silicon carbide epitaxial substrate according to this disclosure comprises a silicon carbide substrate and a silicon carbide epitaxial layer. The silicon carbide epitaxial layer is formed on the silicon carbide substrate. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.7 or greater.

Description

[Technical Field]

[0001] This disclosure relates to a silicon carbide epitaxial substrate and a method for manufacturing a silicon carbide semiconductor device. [Background technology]

[0002] Japanese Patent Publication No. 2022-095160 (Patent Document 1) describes a method for calculating the carrier concentration of a silicon carbide epitaxial substrate. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-095160 [Overview of the project] [Problems that the invention aims to solve]

[0004] The object of this disclosure is to provide a silicon carbide epitaxial substrate and a method for manufacturing a silicon carbide semiconductor device that can accurately measure carrier concentration. [Means for solving the problem]

[0005] The silicon carbide epitaxial substrate according to this disclosure comprises a silicon carbide substrate and a silicon carbide epitaxial layer. The silicon carbide epitaxial layer is formed on the silicon carbide substrate. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.7 or greater. [Effects of the Invention]

[0006] According to this disclosure, it is possible to provide a silicon carbide epitaxial substrate capable of accurately measuring carrier concentration and a method for manufacturing a silicon carbide semiconductor device. [Brief Description of the Drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a silicon carbide epitaxial substrate according to the present embodiment. [Figure 2] FIG. 2 is a partial cross-sectional schematic view showing a state of measuring an X-ray photoelectron spectroscopy spectrum of a silicon carbide epitaxial layer. [Figure 3] FIG. 3 is a schematic view showing an X-ray photoelectron spectroscopy spectrum of a silicon carbide epitaxial layer in the present embodiment. [Figure 4] FIG. 4 is a schematic view showing a spectrum with waveform separation. [Figure 5] FIG. 5 is a cross-sectional schematic view showing a process of forming a silicon carbide epitaxial layer on a silicon carbide substrate. [Figure 6] FIG. 6 is a flowchart schematically showing a manufacturing method of a silicon carbide semiconductor device according to the present embodiment. [Figure 7] FIG. 7 is a cross-sectional schematic view showing a process of forming a body region. [Figure 8] FIG. 8 is a cross-sectional schematic view showing a process of forming a source region. [Figure 9] FIG. 9 is a cross-sectional schematic view showing a process of forming a trench on a third main surface of a silicon carbide epitaxial layer. [Figure 10] FIG. 10 is a cross-sectional schematic view showing a process of forming a gate insulating film. [Figure 11] FIG. 11 is a cross-sectional schematic view showing a process of forming a gate electrode and an interlayer insulating film. [Figure 12] FIG. 12 is a cross-sectional schematic view showing the configuration of a silicon carbide semiconductor device according to the present embodiment. [Figure 13] FIG. 13 is a schematic view showing the configuration of a non-contact carrier concentration measuring device. [Embodiments for Carrying Out the Invention]

[0008] [Summary of Embodiments of the Present Disclosure] First, an overview of the embodiments of this disclosure will be provided. In the crystallographic descriptions herein, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. While negative crystallographic exponents are usually indicated by placing a "-" (bar) above the number, in this specification, negative crystallographic exponents are indicated by placing a negative sign before the number.

[0009] (1) The silicon carbide epitaxial substrate according to this disclosure comprises a silicon carbide substrate and a silicon carbide epitaxial layer. The silicon carbide epitaxial layer is formed on the silicon carbide substrate. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.7 or greater.

[0010] (2) In the case of the silicon carbide epitaxial substrate described in (1) above, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 1.5 or greater.

[0011] (3) In the case of the silicon carbide epitaxial substrate described in (1) above, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 2.5 or greater.

[0012] (4) The silicon carbide epitaxial substrate according to this disclosure comprises a silicon carbide substrate and a silicon carbide epitaxial layer. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.7 or greater.

[0013] (5) In the case of a silicon carbide epitaxial substrate according to any of the above (4), when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from SiO2 may be 1 or more.

[0014] (6) In the case of a silicon carbide epitaxial substrate according to any of the above (4), when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 1.7 or greater.

[0015] (7) The silicon carbide epitaxial substrate according to this disclosure comprises a silicon carbide substrate and a silicon carbide epitaxial layer. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.5 or greater.

[0016] (8) In the case of a silicon carbide epitaxial substrate according to any of the above (7), when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiOx The ratio of the area of the spectrum derived from SiO₂ to the area of the spectrum derived from Si may be 0.7 or more.

[0017] (9) According to the silicon carbide epitaxial substrate according to (7) above, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the energy of the incident X-ray is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of the spectrum derived from SiO₂ to the area of the spectrum derived from Si may be 1 or more.

[0018] (10) According to the silicon carbide epitaxial substrate according to any one of (1) to (9) above, the diameter of the silicon carbide epitaxial substrate may be 150 mm or more.

[0019] (11) According to the silicon carbide epitaxial substrate according to any one of (1) to (9) above, the diameter of the silicon carbide epitaxial substrate may be 200 mm or more and 203.2 mm or less.

[0020] (12) The method for manufacturing a silicon carbide semiconductor device according to the present disclosure includes a step of preparing a silicon carbide epitaxial substrate according to any one of (1) to (11) above, a step of cleaning the silicon carbide epitaxial substrate, and a step of forming an electrode on the silicon carbide epitaxial layer.

[0021] [Details of Embodiments of the Present Disclosure] Hereinafter, based on the drawings, details of embodiments of the present disclosure will be described. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated. In the crystallographic description in this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. Also, for negative indices, in crystallography, "-" (bar) is attached above the number, but in this specification, a negative sign is attached before the number.

[0022] First, the configuration of the silicon carbide epitaxial substrate 200 according to this embodiment will be described. Figure 1 is a schematic cross-sectional view showing the configuration of the silicon carbide epitaxial substrate 200 according to this embodiment. As shown in Figure 1, the silicon carbide epitaxial substrate 200 according to this embodiment has a silicon carbide substrate 100 and a silicon carbide epitaxial layer 40. The silicon carbide epitaxial layer 40 is provided on the silicon carbide substrate 100.

[0023] The silicon carbide substrate 100 has a first main surface 1 and a second main surface 2. The second main surface 2 is on the opposite side of the first main surface 1. Each of the first main surface 1 and the second main surface 2 is, for example, planar. The silicon carbide substrate 100 is made of, for example, hexagonal silicon carbide. The polytype of the hexagonal silicon carbide is, for example, 4H. The silicon carbide substrate 100 contains n-type impurities such as nitrogen.

[0024] The first principal surface 1 is, for example, the {0001} plane or a plane inclined by an off-angle with respect to the {0001} plane. Specifically, the first principal surface 1 may be the (0001) plane or a plane inclined by an off-angle with respect to the (0001) plane, or the (000-1) plane or a plane inclined by an off-angle with respect to the (000-1) plane. The off-angle may be, for example, 5° or less, or 3° or less. The off-direction may be, for example, the <11-20> direction.

[0025] The diameter of the first main surface 1 may be, for example, 150 mm or more, or 200 mm or more. The diameter of the first main surface 1 may be, for example, 200 mm or more and 203.2 mm or less.

[0026] The silicon carbide epitaxial layer 40 is provided on the first main surface 1 of the silicon carbide substrate 100. The silicon carbide epitaxial layer 40 has a third main surface 3 (front surface). The third main surface 3 constitutes the front surface of the silicon carbide epitaxial substrate 200. The second main surface 2 constitutes the back surface of the silicon carbide epitaxial substrate 200.

[0027] (X-ray photoelectron spectroscopy: XPS) Figure 2 is a schematic cross-sectional view showing the measurement of the X-ray photoelectron spectroscopy spectrum 20 of the silicon carbide epitaxial layer 40. The X-ray photoelectron spectroscopy spectrum 20 is measured, for example, using the Sumitomo Electric beamline BL17 at the Kyushu Synchrotron Radiation Research Center in Saga Prefecture. The Sumitomo Electric beamline BL17 is a soft X-ray beamline. The light source of the Sumitomo Electric beamline BL17 uses a polarizing electromagnet. The white X-rays emitted from the light source are selected into incident X-rays with the required energy by a spectrometer using a diffraction grating. Synchrotron radiation is used as the incident X-rays.

[0028] The incident X-rays are irradiated onto the third main surface 3 of the silicon carbide epitaxial layer 40. As shown in Figure 2, the angle between the incident direction 21 of the incident X-rays and the third main surface 3 is the incident angle θ1 of the incident X-rays. Photoelectrons 23 are emitted from near the third main surface 3 of the silicon carbide epitaxial layer 40. The photoelectrons 23 are detected by a detector (not shown). The angle between the photoelectron extraction direction 22 of the photoelectron extraction 23 and the third main surface 3 is the photoelectron extraction angle θ2. The measurement depth D is, for example, 0.5 nm to 2 nm.

[0029] In this embodiment, the energy of the incident X-rays when measuring the X-ray photoelectron spectroscopy spectrum 20 of the silicon carbide epitaxial layer 40 is 200 eV. The incident X-rays are incident on the third principal surface 3 at an incident angle θ1. The photoelectrons 23 are emitted in a direction approximately perpendicular to the direction of incidence of the incident X-rays. That is, the value obtained by adding the photoelectron extraction angle θ2 to the incident angle θ1 of the incident X-rays is, for example, 90°. When the incident angle θ1 of the incident X-rays is, for example, 60°, the photoelectron extraction angle θ2 is 30°. When the incident angle θ1 of the incident X-rays is, for example, 45°, the photoelectron extraction angle θ2 is 45°. When the incident angle θ1 of the incident X-rays is, for example, 5°, the photoelectron extraction angle θ2 is 85°.

[0030] Figure 3 is a schematic diagram showing the X-ray photoelectron spectroscopy spectrum 20 of the silicon carbide epitaxial layer 40 in this embodiment. In Figure 3, the horizontal axis represents the binding energy (unit: eV), and the vertical axis represents the photoelectron intensity (unit: kcounts). X-ray photoelectron spectroscopy spectra are often analyzed after background processing. Background subtraction methods used in X-ray photoelectron spectroscopy spectra include the Shirley method. For example, the photoelectron intensity in the binding energy range of 96 eV to 98 eV may be considered substantially zero.

[0031] Figure 4 is a schematic diagram showing the waveform-separated spectrum. The X-ray photoelectron spectroscopy spectrum 20 of the silicon carbide epitaxial layer 40 is waveform-separated into three spectra: the first spectrum 41, the second spectrum 42, and the third spectrum 43, after being fitted using spectral analysis software. The spectral analysis software is, for example, MultiPak® manufactured by ULVAC-FI, Inc.

[0032] As shown in Figure 4, the first spectrum 41 is a spectrum originating from SiO2. The binding energy (first energy E1) corresponding to the peak of the first spectrum 41 is, for example, around 103.7 eV. The area of ​​the region between the first spectrum 41 and the horizontal axis is considered to be the area of ​​the first spectrum 41.

[0033] As shown in Figure 4, the second spectrum 42 is SiO x This spectrum originates from [source]. The binding energy (second energy E2) corresponding to the peak of the second spectrum 42 is, for example, around 102.8 eV. X is, for example, a value between 1 and 1.5. The area of ​​the region between the second spectrum 42 and the horizontal axis is considered to be the area of ​​the second spectrum 42.

[0034] As shown in Figure 4, the third spectrum 43 is a spectrum originating from SiC. Spectra originating from SiC are related to the bond between Si and C (carbon). The binding energy (third energy E3) corresponding to the peak of the third spectrum 43 is, for example, around 100.9 eV. The area between the third spectrum 43 and the horizontal axis is considered to be the area of ​​the third spectrum 43.

[0035] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from (1) may be 0.7 or greater, 1.0 or greater, 1.5 or greater, 2.0 or greater, or 2.5 or greater.

[0036] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from () may be 3.0 or less, 2.8 or less, or 2.7 or less.

[0037] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from ( ) may be 0.7 or greater, 0.85 or greater, 1 or greater, 1.3 or greater, or 1.7 or greater.

[0038] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from ( ) may be 2.1 or less, 1.9 or less, or 1.8 or less.

[0039] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from () may be 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.85 or greater, or 1 or greater.

[0040] In this embodiment, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial substrate 200 is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from ( ) may be 1.4 or less, 1.2 or less, or 1.1 or less.

[0041] (Method for manufacturing silicon carbide epitaxial substrates) Next, a method for manufacturing the silicon carbide epitaxial substrate 200 according to this embodiment will be described.

[0042] First, a process is carried out to prepare the silicon carbide substrate. First, an ingot composed of polytype 4H silicon carbide single crystals is formed, for example, by sublimation. After the ingot is shaped, it is sliced ​​using a multi-wire saw device. This cuts out the silicon carbide substrate 100 from the ingot.

[0043] Next, a step is carried out to form a silicon carbide epitaxial layer on the silicon carbide substrate. Specifically, a mixed gas containing silane, propane, ammonia, and hydrogen is introduced into a film deposition apparatus (not shown), and the mixed gas is thermally decomposed on the silicon carbide substrate 100. As a result, a silicon carbide epitaxial layer 40 is formed on the silicon carbide substrate 100.

[0044] Figure 5 is a schematic cross-sectional view showing the process of forming a silicon carbide epitaxial layer on a silicon carbide substrate. As shown in Figure 5, the silicon carbide epitaxial layer 40 may have a buffer layer 51 and a drift layer 52. The buffer layer 51 is formed on the silicon carbide substrate 100 on the first main surface 1. The drift layer 52 is formed on the buffer layer 51. Each of the buffer layer 51 and the drift layer 52 contains n-type impurities, such as nitrogen. The concentration of n-type impurities in the buffer layer 51 may be higher than the concentration of n-type impurities in the drift layer 52.

[0045] Next, ultraviolet light is irradiated onto the third main surface 3 of the silicon carbide epitaxial layer 40. The wavelength of the ultraviolet light is, for example, 365 nm. The intensity of the ultraviolet light is, for example, 300 mW / cm². 2 The ultraviolet light is irradiated onto the third main surface 3 for, for example, 1 minute or more. The ultraviolet light may be irradiated onto the third main surface 3 for, for example, 5 minutes or more, 10 minutes or more, or 30 minutes or more. As a result, the silicon carbide epitaxial substrate 200 according to this embodiment is formed.

[0046] (Manufacturing method for silicon carbide semiconductor devices) Next, a method for manufacturing the silicon carbide semiconductor device 300 according to this embodiment will be described. Figure 6 is a schematic flowchart showing the method for manufacturing the silicon carbide semiconductor device 300 according to this embodiment. As shown in Figure 6, the method for manufacturing the silicon carbide semiconductor device 300 according to this embodiment mainly comprises the steps of preparing a silicon carbide epitaxial substrate (S1), cleaning the silicon carbide epitaxial substrate (S2), and forming electrodes on the silicon carbide epitaxial layer (S3).

[0047] First, a step (S1) is performed to prepare the silicon carbide epitaxial substrate. In the step (S1) to prepare the silicon carbide epitaxial substrate, first, the silicon carbide epitaxial substrate 200 according to this embodiment is prepared (see Figure 5). Next, a step is performed to measure the carrier concentration of the silicon carbide epitaxial layer 40 using a non-contact carrier concentration meter, which will be described later. Note that the step of measuring the carrier concentration of the silicon carbide epitaxial layer 40 may be omitted.

[0048] Next, a cleaning process (S2) for the silicon carbide epitaxial substrate is performed. Specifically, a first cleaning process, a second cleaning process, and a third cleaning process are performed sequentially. In the first cleaning process, the silicon carbide epitaxial substrate 200 is cleaned using sulfuric acid and hydrogen peroxide to remove organic matter. Next, in the second cleaning process, the silicon carbide epitaxial substrate 200 is cleaned using ammonia and hydrogen peroxide to remove particles and organic matter. Next, in the third cleaning process, the silicon carbide epitaxial substrate 200 is cleaned using hydrochloric acid and hydrogen peroxide to remove metallic impurities. Each of the first, second, and third cleaning processes is performed for, for example, 1 to 10 minutes.

[0049] In the step of cleaning the silicon carbide epitaxial substrate (S2), a thin silicon oxide film formed on the third main surface 3 of the silicon carbide epitaxial layer 40 may be removed by ultraviolet irradiation. The silicon carbide epitaxial layer 40 may be cleaned with, for example, hydrofluoric acid.

[0050] Next, the silicon carbide epitaxial substrate 200 is subjected to the following processing. First, ion implantation is performed on the silicon carbide epitaxial substrate 200.

[0051] Figure 7 is a schematic cross-sectional view showing the process of forming the body region. In the process of forming the body region, p-type impurities, such as aluminum, are ion-implanted into the third main surface 3 of the silicon carbide epitaxial layer 40. This forms a body region 113 having a p-type conductivity. The portion where the body region 113 was not formed becomes the drift layer 52 and the buffer layer 51. The thickness of the body region 113 is, for example, 0.9 μm. The silicon carbide epitaxial layer 40 includes the buffer layer 51, the drift layer 52, and the body region 113.

[0052] Next, a process for forming the source region is carried out. Figure 8 is a schematic cross-sectional view showing the process for forming the source region. Specifically, n-type impurities, such as phosphorus, are ion-implanted into the body region 113. This forms a source region 114 having an n-type conductivity. The thickness of the source region 114 is, for example, 0.4 μm. The concentration of n-type impurities in the source region 114 is higher than the concentration of p-type impurities in the body region 113.

[0053] Next, a contact region 118 is formed by ion implantation of p-type impurities, such as aluminum, into the source region 114. The contact region 118 penetrates the source region 114 and the body region 113 and is formed to be in contact with the drift layer 52. The concentration of p-type impurities in the contact region 118 is higher than the concentration of n-type impurities in the source region 114.

[0054] Next, activation annealing is performed to activate the ion-implanted impurities. The activation annealing temperature is, for example, between 1500°C and 1900°C. The activation annealing time is, for example, about 30 minutes. The activation annealing atmosphere is, for example, an argon atmosphere.

[0055] Next, a step is performed to form trenches on the third main surface 3 of the silicon carbide epitaxial layer 40. Figure 9 is a schematic cross-sectional view showing the step of forming trenches on the third main surface 3 of the silicon carbide epitaxial layer 40. A mask 117 having an opening is formed on the third main surface 3, which consists of a source region 114 and a contact region 118. Using the mask 117, the source region 114, the body region 113, and a part of the drift layer 52 are removed by etching. As an etching method, for example, inductively coupled plasma reactive ion etching can be used. Specifically, for example, inductively coupled plasma reactive ion etching using SF6 or a mixed gas of SF6 and O2 as the reaction gas is used. By etching, recesses are formed on the third main surface 3.

[0056] Next, thermal etching is performed in the recesses. Thermal etching can be performed by heating in an atmosphere containing a reactive gas having at least one type of halogen atom, with the mask 117 formed on the third main surface 3. For example, a mixed gas of chlorine gas and oxygen gas is used as the reaction gas, and thermal etching is performed at a heat treatment temperature of, for example, 700°C to 1000°C. In addition to the chlorine gas and oxygen gas mentioned above, the reaction gas may also contain a carrier gas. Examples of carrier gases that can be used include nitrogen gas, argon gas, or helium gas.

[0057] As shown in Figure 9, a trench 56 is formed on the third main surface 3 by thermal etching. The trench 56 is defined by a side wall surface 53 and a bottom wall surface 54. The side wall surface 53 consists of a source region 114, a body region 113, and a drift layer 52. The bottom wall surface 54 consists of the drift layer 52. Next, the mask 117 is removed from the third main surface 3.

[0058] Next, a process for forming a gate insulating film is carried out. Figure 10 is a schematic cross-sectional view showing the process for forming the gate insulating film. Specifically, a silicon carbide epitaxial substrate 200, on which trenches 56 are formed on the third main surface 3, is heated in an oxygen-containing atmosphere at a temperature of, for example, 1300°C to 1400°C. This forms a gate insulating film 115 that is in contact with the drift layer 52 at the bottom wall surface 54, in contact with the drift layer 52, the body region 113, and the source region 114 at the side wall surface 53, and in contact with the source region 114 and the contact region 118 at the third main surface 3.

[0059] Next, the process of forming the gate electrode is carried out. Figure 11 is a schematic cross-sectional view showing the process of forming the gate electrode and the interlayer insulating film. The gate electrode 127 is formed inside the trench 56 so as to be in contact with the gate insulating film 115. The gate electrode 127 is positioned inside the trench 56 and is formed on the gate insulating film 115 so as to face the side wall surface 53 and the bottom wall surface 54 of the trench 56, respectively. The gate electrode 127 is formed, for example, by the LPCVD (Low Pressure Chemical Vapor Deposition) method.

[0060] Next, an interlayer insulating film 126 is formed. The interlayer insulating film 126 is formed to cover the gate electrode 127 and to be in contact with the gate insulating film 115. The interlayer insulating film 126 is formed, for example, by chemical vapor deposition. The interlayer insulating film 126 is made of a material containing, for example, silicon dioxide. Next, parts of the interlayer insulating film 126 and the gate insulating film 115 are etched so that openings are formed on the source region 114 and the contact region 118. This exposes the contact region 118 and the source region 114 from the gate insulating film 115.

[0061] A step (S3) is performed to form an electrode on the silicon carbide epitaxial layer. Specifically, a step of forming a source electrode is then performed. The source electrode 116 is formed so as to be in contact with the source region 114 and the contact region 118, respectively (see Figure 12). The source electrode 116 is formed, for example, by a sputtering method. The source electrode 116 is composed of a material including, for example, Ti (titanium), Al (aluminum), and Si (silicon).

[0062] Next, alloying annealing is performed. Specifically, the source electrode 116 in contact with the source region 114 and the contact region 118 is held at a temperature of, for example, 900°C to 1100°C for about 5 minutes. This causes at least a portion of the source electrode 116 to silicide. As a result, a source electrode 116 that is ohmic bonded with the source region 114 is formed (see Figure 12). The source electrode 116 may also be ohmic bonded with the contact region 118.

[0063] Next, the source wiring 119 is formed. The source wiring 119 is electrically connected to the source electrode 116. The source wiring 119 is formed to cover the source electrode 116 and the interlayer insulating film 126 (see Figure 12).

[0064] Next, a process for forming the drain electrode is carried out. First, the silicon carbide substrate 100 is polished on the second main surface 2. This reduces the thickness of the silicon carbide substrate 100. Next, the drain electrode 123 is formed. The drain electrode 123 is formed so as to be in contact with the second main surface 2 (see Figure 12). Thus, the silicon carbide semiconductor device 300 according to this embodiment is manufactured.

[0065] Figure 12 is a schematic cross-sectional view showing the configuration of the silicon carbide semiconductor device 300 according to this embodiment. The silicon carbide semiconductor device 300 is, for example, a metal oxide semiconductor transistor (MOSFET: Metal Oxide Semiconductor Field Effect Transistor). The silicon carbide semiconductor device 300 mainly comprises a silicon carbide epitaxial substrate 200, a gate electrode 127, a gate insulating film 115, a source electrode 116, a drain electrode 123, a source wiring 119, and an interlayer insulating film 126. The silicon carbide epitaxial substrate 200 has a buffer layer 51, a drift layer 52, a body region 113, a source region 114, and a contact region 118. The silicon carbide semiconductor device 300 may also be, for example, a Schottky barrier diode.

[0066] Next, a method for measuring the carrier concentration of the silicon carbide epitaxial layer 40 according to this embodiment will be described.

[0067] Figure 13 is a schematic diagram showing the configuration of a non-contact carrier concentration meter. As shown in Figure 13, the non-contact carrier concentration meter 400 mainly comprises a chuck 111, a corona gun 112, and a Kelvin probe 120. The chuck 111 holds the silicon carbide epitaxial substrate 200. The chuck 111 is made of a conductive material. The chuck 111 is, for example, electrically grounded. The chuck 111 has a substrate holding surface 110.

[0068] The corona gun 112 is positioned opposite the substrate holding surface 110 of the chuck 111. The corona gun 112 generates corona charge. The tip of the corona gun 112 is, for example, conical. The corona gun 112 supplies charge to the third main surface 3 of the silicon carbide epitaxial substrate 200. By applying a voltage to the corona gun 112, the air is ionized and charge is generated. This causes a depletion layer to form on the silicon carbide epitaxial substrate 200.

[0069] The Kelvin probe 120 is positioned opposite the substrate holding surface 110 of the chuck 111. The Kelvin probe 120 is positioned spaced apart from the third main surface 3 of the silicon carbide epitaxial substrate 200. In other words, the Kelvin probe 120 is a non-contact probe. The Kelvin probe 120 can measure the potential (surface potential) of the third main surface 3 of the silicon carbide epitaxial substrate 200. The tip of the Kelvin probe 120 is, for example, cylindrical. The diameter of the tip of the Kelvin probe 120 is, for example, 2 mm.

[0070] The non-contact carrier concentration meter supplies charge to the third main surface 3 of the silicon carbide epitaxial substrate 200, then places the Kelvin probe 120 in a non-contact manner with the third main surface 3 of the silicon carbide epitaxial substrate 200, and measures the potential of the third main surface 3 of the silicon carbide epitaxial substrate 200 using the Kelvin probe 120. Based on the charge supplied to the third main surface 3 and the potential of the third main surface 3, the non-contact carrier concentration meter calculates the carrier concentration of the silicon carbide epitaxial layer 40.

[0071] Next, the effects and advantages of the manufacturing method for the silicon carbide epitaxial substrate 200 and the silicon carbide semiconductor device 300 according to this embodiment will be described.

[0072] When measuring the carrier concentration of a silicon carbide epitaxial substrate using a non-contact carrier concentration meter, it was sometimes impossible to accurately measure the carrier concentration. Specifically, if trap levels exist on the surface of the silicon carbide epitaxial substrate, the charge injected by coronagun 112 is trapped in the trap levels. In this case, a mismatch occurs between the amount of charge injected and the effective amount of charge required for depletion. Specifically, the actual amount of charge injected is greater than the effective amount of charge required for depletion. As a result, the carrier concentration is overestimated.

[0073] The inventors diligently investigated methods for accurately measuring carrier concentration and obtained the following findings. Specifically, by irradiating the surface of a silicon carbide epitaxial substrate with, for example, high-intensity ultraviolet light, SiO x We conceived the idea of ​​forming a silicon oxide film in which the ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from SiO2 is high.

[0074] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other element] is 0.7 or greater. This allows for accurate measurement of the carrier concentration.

[0075] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 1.5 or greater. This allows for more accurate measurement of the carrier concentration.

[0076] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 2.5 or greater. This allows for more accurate measurement of the carrier concentration.

[0077] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 0.7 or greater. This allows for more accurate measurement of the carrier concentration.

[0078] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from SiO2 may be 1 or greater. This allows for more accurate measurement of the carrier concentration.

[0079] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 1.7 or greater. This allows for more accurate measurement of the carrier concentration.

[0080] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 0.5 or greater. This allows for more accurate measurement of the carrier concentration.

[0081] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from [the other component] may be 0.7 or greater. This allows for more accurate measurement of the carrier concentration.

[0082] According to the silicon carbide epitaxial substrate of this disclosure, when the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under conditions where the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO x The ratio of the area of ​​the spectrum derived from SiO2 to the area of ​​the spectrum derived from SiO2 may be 1 or greater. This allows for more accurate measurement of the carrier concentration.

[0083] The method for manufacturing a silicon carbide semiconductor device according to this disclosure includes the steps of preparing the silicon carbide epitaxial substrate described above, cleaning the silicon carbide epitaxial substrate, and forming electrodes on the silicon carbide epitaxial layer. In the step of cleaning the silicon carbide epitaxial substrate, the silicon oxide film formed on the surface of the silicon carbide epitaxial substrate can be removed. This makes it possible to maintain a low contact resistance between the silicon carbide epitaxial layer and the electrodes. [Examples]

[0084] (Sample preparation) Silicon carbide epitaxial substrates 200 for samples 1-3 were prepared. The silicon carbide epitaxial layers of the silicon carbide epitaxial substrates 200 for samples 1 and 2 were irradiated with ultraviolet light. The wavelength of the ultraviolet light irradiated onto the silicon carbide epitaxial substrates 200 for samples 1 and 2 was 365 nm. The intensity of the ultraviolet light was 300 mW / cm². 2The ultraviolet irradiation times for the silicon carbide epitaxial substrate 200 in samples 1 and 2 were set to 1 minute and 30 minutes, respectively. For sample 3, ultraviolet irradiation was not performed on the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate 200.

[0085] (Experimental method) Next, using the BL17 Sumitomo Electric beamline at the Kyushu Synchrotron Radiation Research Center, incident X-rays were irradiated onto the third main surface 3 of the silicon carbide epitaxial layer 40 of the silicon carbide epitaxial substrate 200 for samples 1-3, and the intensity of photoelectrons 23 emitted from the silicon carbide epitaxial layer 40 was measured. The photoelectron extraction angles θ2 were set to 30°, 45°, and 85°. The energy of the incident X-rays was set to 200 eV.

[0086] <Specifications of Sumitomo Electric Beamline BL17> Light source: Polarizing electromagnet Spectrometer: Variable angle diffraction grating spectrometer (400 diffractometers / mm, 1000 diffractometers / mm, 1400 diffractometers / mm, 2200 diffractometers / mm) Energy range: 50-2000 eV Number of photons: >10 9 photons / s@50~1400eV Energy resolution: E / ΔE > 3480 @ 400 eV Beam size: 0.95mm (height) x 0.05mm (width) Neutralizing gun: Not used Detector: Photoelectron analyzer (SCientaomicron, R3000) Slit size: 30 μm (Experimental results)

[0087] [Table 1]

[0088] Table 1 shows the experimental results. In Table 1, the area of ​​the spectrum originating from SiO2 and SiO xThe area of ​​the spectrum originating from and the area of ​​the spectrum originating from Si-C are shown. The area of ​​the spectrum originating from SiO2 and SiO x The area of ​​the spectrum originating from the Si-C orbital and the area of ​​the spectrum originating from Si-C are values ​​where the area of ​​the spectrum originating from the Si 2p orbital is set to 1. Therefore, the units of the areas shown in Table 1 are dimensionless.

[0089] Under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle θ2 is 30°, in the third main surface of the silicon carbide epitaxial substrates of samples 1 to 3, SiO x The ratio of the spectral area derived from SiO2 to the spectral area derived from was 1.43, 2.56, and 0.59, respectively.

[0090] Under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle θ2 is 45°, in the third main surface of the silicon carbide epitaxial substrates of samples 1 to 3, SiO x The ratio of the spectral area derived from SiO2 to the spectral area derived from was 0.83, 1.75, and 0.59, respectively.

[0091] Under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle θ2 is 85°, in the third main surface of the silicon carbide epitaxial substrates of samples 1 to 3, SiO x The ratio of the spectral area derived from SiO2 to the spectral area derived from was 0.52, 1.03, and 0.35, respectively.

[0092] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0093] 1. First main surface 2. Second main surface 3. Third Main Surface 20 X-ray photoelectron spectroscopy spectrum 21 Incident direction 22 Removal direction 23 Photoelectrons 40 Silicon carbide epitaxial layer 41 First Spectrum 42 Second Spectrum 43 Third Spectrum 51 Buffer Layer 52 Drift Layers 53 Side wall 54 Bottom wall 56 Trench 100 Silicon carbide substrate 110 Board holding surface 111 Chuck 112 Corona Cancer 113 Body Region 114 Source Area 115 Gate insulating film 116 Source electrodes 117 masks 118 Contact Area 119 Source Wiring 120 Kelvin probe 123 Drain electrode 126 Interlayer insulating film 127 Gate 200 Silicon Carbide Epitaxial Substrates 300 Silicon Carbide Semiconductor Devices 400 Non-contact carrier concentration meter D Measurement depth E1 First Typical E2 Second Energy E3 Third Energy

Claims

1. Silicon carbide substrate and The silicon carbide substrate comprises a silicon carbide epitaxial layer formed on the silicon carbide substrate, When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ A silicon carbide epitaxial substrate in which the ratio of spectral areas originating from is 0.7 or greater.

2. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ The silicon carbide epitaxial substrate according to claim 1, wherein the ratio of spectral areas derived from is 1.5 or more.

3. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 30°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ The silicon carbide epitaxial substrate according to claim 1, wherein the ratio of spectral areas derived from is 2.5 or more.

4. Silicon carbide substrate and The silicon carbide substrate comprises a silicon carbide epitaxial layer formed on the silicon carbide substrate, When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ A silicon carbide epitaxial substrate in which the ratio of spectral areas originating from is 0.7 or greater.

5. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer was measured under the condition that the energy of the incident X-ray was 200 eV and the photoelectron extraction angle was 45°, SiO ｘ The ratio of the area of the spectrum derived from SiO ２ to the area of the spectrum derived from is 1 or more. The silicon carbide epitaxial substrate according to claim 4.

6. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 45°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ The silicon carbide epitaxial substrate according to claim 4, wherein the ratio of spectral areas derived from is 1.7 or more.

7. Silicon carbide substrate and The silicon carbide substrate comprises a silicon carbide epitaxial layer formed on the silicon carbide substrate, When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ A silicon carbide epitaxial substrate in which the ratio of spectral areas originating from is 0.5 or greater.

8. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ The silicon carbide epitaxial substrate according to claim 7, wherein the ratio of spectral areas derived from is 0.7 or more.

9. When the X-ray photoelectron spectroscopy spectrum of the silicon carbide epitaxial layer is measured under the conditions that the incident X-ray energy is 200 eV and the photoelectron extraction angle is 85°, SiO ｘ SiO for the area of ​​the spectrum derived from ２ The silicon carbide epitaxial substrate according to claim 7, wherein the ratio of the area of ​​the spectrum derived from is 1 or more.

10. The silicon carbide epitaxial substrate according to any one of claims 1 to 9, wherein the diameter of the silicon carbide epitaxial substrate is 150 mm or more.

11. The silicon carbide epitaxial substrate according to any one of claims 1 to 9, wherein the diameter of the silicon carbide epitaxial substrate is 200 mm or more and 203.2 mm or less.

12. A step of preparing a silicon carbide epitaxial substrate according to any one of claims 1 to 9, A step of cleaning the silicon carbide epitaxial substrate, A method for manufacturing a silicon carbide semiconductor device, comprising the step of forming an electrode on the silicon carbide epitaxial layer.

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