Manufacturing method for silicon carbide substrates

Abstract

This invention provides a method for manufacturing silicon carbide substrates with high cleanliness. [Solution] A method for manufacturing a silicon carbide substrate, comprising the steps of: chemically mechanically polishing a silicon carbide substrate using a polishing solution containing permanganate; sequentially washing the chemically mechanically polished silicon carbide substrate with sulfuric acid peroxide, ammonia peroxide, hydrochloric acid peroxide, and hydrofluoric acid; and drying the washed silicon carbide substrate using a spin dryer, wherein in the step of washing the chemically mechanically polished silicon carbide substrate with sulfuric acid peroxide, the silicon carbide substrate is washed while ultrasonic waves are irradiated onto the sulfuric acid peroxide; and in the step of drying using a spin dryer, with the lid of the spin dryer open, air is passed from the opening of the spin dryer toward the exhaust port, and then the silicon carbide substrate is placed inside the spin dryer to dry the silicon carbide substrate.

Description

Technical Field

[0001] This disclosure relates to a silicon carbide substrate. This application claims priority based on Japanese Patent Application No. 2019-093882, filed on May 17, 2019. All the descriptions contained in the Japanese patent application are incorporated herein by reference.

Background Art

[0002] WO 2016 / 063632 (Patent Document 1) describes a method for cleaning a silicon carbide substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The silicon carbide substrate according to this disclosure has a main surface. The maximum diameter is 150 mm or more. On the main surface, the total area of regions where the concentration of each of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc is less than 5×10 , [Figure 4] , [Figure 3] , [Figure 2] , 2 , [Figure 1] , [Figure 5] ,

[0005] , , , , , 10 , , , atoms / cm<00000​​​​​​​​​​​​​​​​​​​​Figure 5 is a schematic cross-sectional view showing the first step of the method for manufacturing a silicon carbide substrate according to this embodiment. [Figure 6] Figure 6 is a schematic cross-sectional view showing the second step of the silicon carbide substrate manufacturing method according to this embodiment. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] The purpose of this disclosure is to provide a silicon carbide substrate with high cleanliness. [Effects of this disclosure] According to this disclosure, a silicon carbide substrate with a high degree of cleanliness can be provided. [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be listed and described.

[0007] (1) The silicon carbide substrate 100 according to this disclosure has a main surface 1. The maximum diameter is 150 mm or more. On the main surface 1, the concentrations of each of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc are 5 × 10 10 atoms / cm 2 The total area of ​​the region that is less than [a certain value] is 95% or more of the area of ​​main surface 1.

[0008] (2) In the case of the silicon carbide substrate 100 described in (1) above, the total area may be 98% or more of the area of ​​the main surface 1.

[0009] (3) In the case of the silicon carbide substrate 100 according to (1) or (2) above, sulfur may be present on the main surface 1. 10 atoms / cm 2 The area exceeding the above may be 1% or more of the area of ​​the main surface 1.

[0010] (4) According to the silicon carbide substrate 100 described in (3) above, the sulfur concentration is 5 × 10 10 atoms / cm 2 The area exceeding the above may be 50% or more of the area of ​​the main surface 1.

[0011] (5) According to the silicon carbide substrate 100 according to any one of (1) to (4) above, chlorine may be present on the main surface 1. The region where the chlorine concentration is 5×10 10 atoms / cm 2 or more may be 1% or more of the area of the main surface 1.

[0012] (6) According to the silicon carbide substrate 100 according to (5) above, the region where the chlorine concentration is 5×10 10 atoms / cm 2 or more may be 50% or more of the area of the main surface 1.

[0013] (7) According to the silicon carbide substrate 100 according to any one of (1) to (6) above, on the main surface 1, the region where the aluminum concentration is 1×10 12 atoms / cm 2 or more may be less than 1% of the area of the main surface 1.

[0014] (8) According to the silicon carbide substrate 100 according to any one of (1) to (7) above, on the main surface 1, the region where the potassium concentration is 1×10 12 atoms / cm 2 or more may be less than 1% of the area of the main surface 1.

[0015] (9) According to the silicon carbide substrate 100 according to any one of (1) to (8) above, on the main surface 1, the region where the calcium concentration is 1×10 12 atoms / cm 2 or more may be less than 1% of the area of the main surface 1. [Details of Embodiments of the Present Disclosure] Hereinafter, embodiments of the present disclosure will be described based on the drawings. 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 exponents, in crystallography, a "-" (bar) is placed above the number, but in this specification, a negative sign is placed before the number.

[0016] <Silicon Carbide Substrate Composition> First, the configuration of the silicon carbide substrate 100 according to this embodiment will be described. Figure 1 is a schematic plan view showing the configuration of the silicon carbide substrate 100 according to this embodiment. Figure 2 is a schematic cross-sectional view along line II-II in Figure 1.

[0017] As shown in Figures 1 and 2, the silicon carbide substrate 100 according to this embodiment mainly has a first main surface 1, a second main surface 2, and a chamfered portion 6. The second main surface 2 is on the opposite side from the first main surface 1. The chamfered portion 6 is continuous with each of the first main surface 1 and the second main surface 2. Each of the first main surface 1 and the second main surface 2 is a flat surface. The first main surface 1 is the surface on which an epitaxial layer (not shown) is formed. The silicon carbide substrate 100 is made of, for example, a polytype 4H hexagonal silicon carbide single crystal. The silicon carbide substrate 100 contains n-type impurities such as nitrogen.

[0018] The first principal surface 1 is, for example, the {0001} plane or a plane angled 8° or less off-center from the {0001} plane. Specifically, the first principal surface 1 is, for example, the (0001) plane or a plane angled 8° or less off-center from the (0001) plane. The first principal surface 1 may also be, for example, the (000-1) plane or a plane angled 8° or less off-center from the (000-1) plane. If the first principal surface 1 is the (0001) plane, then the second principal surface 2 is the (000-1) plane.

[0019] As shown in Figure 2, the chamfered portion 6 has a first curved region 3, an outer peripheral end 5, and a second curved region 4. The first curved region 3 is connected to the first main surface 1. The first curved region 3 is located outside the first main surface 1. The second curved region 4 is connected to the second main surface 2. The second curved region 4 is located outside the second main surface 2. As shown in Figure 2, in a cross section perpendicular to the first main surface 1, each of the first curved region 3 and the second curved region 4 is arc-shaped. Each of the first curved region 3 and the second curved region 4 is curved so as to protrude outward.

[0020] The outer peripheral end 5 is the outermost portion in the radial direction parallel to the first main surface 1. The outer peripheral end 5 is connected to the first curved region 3 and the second curved region 4, respectively. In the radial direction, the first curved region 3 is located between the first main surface 1 and the outer peripheral end 5. Similarly, in the radial direction, the second curved region 4 is located between the second main surface 2 and the outer peripheral end 5.

[0021] As shown in Figure 1, the outer peripheral end 5 has an orientation flat portion 7 and an arc-shaped portion 8. The arc-shaped portion 8 is connected to the orientation flat portion 7. The orientation flat portion 7 extends along a first direction 101. Both the first direction 101 and the second direction 102 are parallel to the first main surface 1. The second direction 102 is perpendicular to the first direction 101. The first direction 101 is, for example, the <11-20> direction. The second direction 102 is, for example, the <1-100> direction.

[0022] If the first principal surface 1 is inclined with respect to the {0001} plane, the first direction 101 may be, for example, the direction obtained by projecting the <11-20> direction onto the first principal surface 1. If the first principal surface 1 is inclined with respect to the {0001} plane, the second direction 102 may be, for example, the direction obtained by projecting the <1-100> direction onto the first principal surface 1.

[0023] As shown in Figure 1, the maximum diameter (first width W1) of the silicon carbide substrate 100 is 150 mm or more. When viewed in a direction perpendicular to the first main surface 1, the maximum diameter of the silicon carbide substrate 100 may be calculated as the diameter of the circle including the arc-shaped portion 8. The first width W1 may be 200 mm or more, or 250 mm or more. There is no particular upper limit to the first width W1, but it may be, for example, 300 mm or less.

[0024] As shown in Figure 1, when viewed in a direction perpendicular to the first main surface 1, the width of the chamfered portion 6 (second width W2) is, for example, 2 mm or more and 3 mm or less. From another point of view, when viewed in a direction perpendicular to the first main surface 1, the distance from the boundary between the first main surface 1 and the chamfered portion 6 to the outer peripheral end 5 is, for example, 2 mm or more and 3 mm or less.

[0025] Next, we will explain the concentration of metal impurities on the first main surface 1. According to the silicon carbide substrate 100 of this embodiment, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) on the first main surface 1 are 5 × 10⁻¹⁰ 10 atoms / cm 2 The total area of ​​regions less than 5 × 10⁻¹⁰ may be 95% or more of the area of ​​the first main surface 1. From another perspective, in the first main surface 1, the concentrations of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are 5 × 10⁻¹⁰. 10 atoms / cm 2 The total area of ​​the region exceeding the above limit may be less than 5% of the area of ​​main surface 1. In other words, the concentration of metal impurities is low in 95% or more of the region of the first main surface 1.

[0026] Preferably, on the first main surface 1, the concentrations of each of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc are 5 × 10⁻⁶. 10 atoms / cm 2 The total area of ​​the region that is less than 5 × 10⁻¹⁰ may be 98% or more of the area of ​​main surface 1, or 98.5% or more. From another point of view, in the first main surface 1, the concentrations of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are 5 × 10⁻¹⁰. 10 atoms / cm 2 The total area of ​​the region described above may be less than 2% or less than 1.5% of the area of ​​main surface 1.

[0027] Sulfur may be present on the first main surface 1. The concentration of sulfur (S) is 5 × 10⁻⁶. 10 atoms / cm 2 The region exceeding this limit may be 1% or more of the area of ​​the first main surface 1. The sulfur concentration is 5 × 10⁻⁶. 10 atoms / cm2 The region that is above 25% or more, 50% or more, or 60% or more of the area of ​​the first main surface 1. The sulfur concentration is 5 × 10 10 atoms / cm 2 The lower limit of the region that is greater than or equal to the above limit is not particularly limited, but may be, for example, 75% or less of the area of ​​the first main surface 1.

[0028] The concentration of sulfur (S) is 1 × 10 12 atoms / cm 2 The region exceeding this limit may be 1% or more of the area of ​​the first main surface 1. The sulfur concentration is 1 × 10⁻⁶. 12 atoms / cm 2 The region that is above 25% or more, 50% or more, or 60% or more of the area of ​​the first main surface 1. The sulfur concentration is 1 × 10 12 atoms / cm 2 The lower limit of the region that is greater than or equal to the above limit is not particularly limited, but may be, for example, 75% or less of the area of ​​the first main surface 1.

[0029] Chlorine may be present on the first main surface 1. The concentration of chlorine (Cl) is 5 × 10⁻⁶. 10 atoms / cm 2 The region exceeding this limit may be 1% or more of the area of ​​the first main surface 1. The chlorine concentration is 5 × 10⁻⁶. 10 atoms / cm 2 The area exceeding the above may be 25% or more of the area of ​​the first main surface 1, 50% or more of the area of ​​the first main surface 1, or 60% or more of the area of ​​the first main surface 1. The chlorine concentration is 5 × 10 10 atoms / cm 2 The lower limit of the region that is greater than or equal to the above limit is not particularly limited, but may be, for example, 75% or less of the area of ​​the first main surface 1.

[0030] The concentration of chlorine (Cl) is 1 × 10 12 atoms / cm 2 The region exceeding this limit may be 1% or more of the area of ​​the first main surface 1. The chlorine concentration is 1 × 10⁻⁶. 12 atoms / cm 2The area exceeding the above may be 25% or more of the area of ​​the first main surface 1, 50% or more of the area of ​​the first main surface 1, or 60% or more of the area of ​​the first main surface 1. 12 atoms / cm 2 The lower limit of the region that is greater than or equal to the above limit is not particularly limited, but may be, for example, 75% or less of the area of ​​the first main surface 1.

[0031] In the first main surface 1, the aluminum concentration is 1 × 10⁻⁶ 12 atoms / cm 2 The area exceeding this limit may be less than 1% of the area of ​​the first main surface 1. In the first main surface 1, the aluminum concentration is 1 × 10⁻⁶. 12 atoms / cm 2 The region above this level is not required.

[0032] In the first main surface 1, the potassium concentration is 1 × 10⁻⁶ 12 atoms / cm 2 The region exceeding this limit may be less than 1% of the area of ​​the first main surface 1. In the first main surface 1, the potassium concentration is 1 × 10⁻⁶. 12 atoms / cm 2 The region above this level is not required.

[0033] In the first main surface 1, the calcium concentration is 1 × 10⁻⁶ 12 atoms / cm 2 The region exceeding this limit may be less than 1% of the area of ​​the first main surface 1. In the first main surface 1, the calcium concentration is 1 × 10⁻⁶. 12 atoms / cm 2 The region above this level is not required.

[0034] Next, we will explain the method for measuring the concentration of metal impurities on the first main surface 1. The concentration of metal impurities can be measured using a total internal reflection X-ray fluorescence analyzer. For example, the TXRF-3760 manufactured by Rigaku Corporation can be used as the analyzer. This analyzer has multiple excitation X-ray sources and can measure elements from light elements such as Na to heavy elements such as U using the optimal excitation X-ray for the element being measured. Specifically, for Na, Al, and Mg, W-Ma (1.78 keV) excitation X-rays are used. For elements with atomic numbers greater than K up to U (especially K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cl, and S), W-Lb (9.67 keV) excitation X-rays are used.

[0035] The X-ray power is, for example, 35kV-255mA. The incident direction is 39°. The incident angle for W-Ma is 0.500°. The measurement time for W-Ma is 10 seconds / point. The incident angle for W-Lb is 0.100°. The measurement time for W-Lb is 10 seconds / point. The analyzer also has an XY drive stage, which can measure the in-plane distribution of the element being measured. For example, the first main surface 1 can be divided into 101 equally-area regions, and the concentration of the element being measured can be measured at these 101 locations. The concentration of metal impurities refers to the number of atoms per unit area.

[0036] Figure 3 is a schematic plan view showing the measurement area for metal impurities. As shown in Figure 3, the first main surface 1 has a center 10, a first virtual circle 21, a second virtual circle 22, a third virtual circle 23, a fourth virtual circle 24, and a fifth virtual circle 25. The distance between the first virtual circle 21 and the second virtual circle 22 is the same as the distance between the second virtual circle 22 and the third virtual circle 23. The distance between the second virtual circle 22 and the third virtual circle 23 is the same as the distance between the third virtual circle 23 and the fourth virtual circle 24. The distance between the third virtual circle 23 and the fourth virtual circle 24 is the same as the distance between the fourth virtual circle 24 and the fifth virtual circle 25.

[0037] In Figure 3, the circles with dots represent the measurement areas S for metal impurities. The size of the measurement area S is 10 mm in diameter. The measurement areas S are provided at equal intervals along a straight line passing through the center 10 of the first main surface 1 and parallel to the first direction 101. The measurement areas S are provided at equal intervals along a straight line passing through the center 10 of the first main surface 1 and parallel to the second direction 102. One measurement area S is provided at the center 10 of the first main surface 1. Eight measurement areas S are provided at equal intervals along the first virtual circle 21. Sixteen measurement areas S are provided at equal intervals along the second virtual circle 22. Twenty measurement areas S are provided at equal intervals along the third virtual circle 23. Twenty-four measurement areas S are provided at equal intervals along the fourth virtual circle 24. Thirty-two measurement areas S are provided at equal intervals along the fifth virtual circle 25. In other words, a total of 101 measurement areas S are provided on the first main surface 1.

[0038] For example, in a measurement region S (first measurement region) including the center 10 of the first main surface 1, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are measured. In the first measurement region, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are 5 × 10⁻¹⁰. 10 atoms / cm 2 The determination is made as to whether it is less than or equal to .

[0039] Next, in the second measurement area adjacent to the first measurement area, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are measured. In the second measurement area, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are 5 × 10⁻¹⁰. 10 atoms / cm 2 The determination is made as to whether it is less than or equal to .

[0040] As described above, in the 101 measurement areas S from the 1st measurement area to the 101st measurement area, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) were 5 × 10⁻¹⁰. 10 atoms / cm 2 It is determined whether the value is less than 5 × 10⁻¹. For example, if the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) in N measurement areas S out of 101 measurement areas S are 5 × 10⁻¹⁰ 10 atoms / cm 2 If the concentration is less than 5 × 10, then the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are 5 × 10. 10 atoms / cm 2 The total area of ​​regions less than 1 is calculated as the area of ​​the first main surface 1 × N / 101.

[0041] In the above explanation, the main surface was described as the first main surface 1, but the main surface may also be the second main surface 2. From another perspective, the concentration of metal impurities on the second main surface 2 may be the same as the concentration of metal impurities on the first main surface 1.

[0042] <Method for manufacturing silicon carbide substrates> Next, a method for manufacturing the silicon carbide substrate 100 according to this embodiment will be described. As shown in Figure 4, the method for manufacturing the silicon carbide substrate 100 according to this embodiment includes a crystal preparation step (S10), a slicing step (S20), a chamfering step (S25), a double-sided mechanical polishing step (S30), a chemical mechanical polishing step (S40), a sulfuric acid hydrochloride washing step (S50), an ammonia hydrochloride washing step (S60), a hydrochloric acid hydrochloride washing step (S70), a hydrofluoric acid washing step (S80), and a drying step (S90).

[0043] First, a crystal preparation process (S10) is carried out. In the crystal preparation process (S10), a silicon carbide ingot is formed, for example, by sublimation. Next, a slicing process (S20) is carried out. In the slicing process (S20), the silicon carbide ingot is cut into multiple silicon carbide substrates 100 by a saw wire. The silicon carbide substrates 100 are made up of, for example, a polytype 4H hexagonal silicon carbide single crystal. As shown in Figure 1, the silicon carbide substrate 100 has a first main surface 1, a second main surface 2, and an outer peripheral end 5. At this point, the chamfered portion 6 has not been formed.

[0044] Next, a chamfering process (S25) is performed. In the chamfering process (S25), a grinding device (not shown) is used. In the chamfering process, for example, a diamond grinding wheel is used. The area near the boundary between the first main surface 1 and the outer peripheral edge 5 of the silicon carbide substrate 100 is pressed against the rotating diamond grinding wheel. Similarly, the area near the boundary between the first main surface 1 and the outer peripheral edge 5 of the silicon carbide substrate 100 is pressed against the rotating diamond grinding wheel. As a result, a chamfered portion 6 is formed on the silicon carbide substrate 100 (see Figure 2). In the chamfering process (S25), grinding marks may be formed on the chamfered portion 6.

[0045] Next, a double-sided mechanical polishing process (S30) is performed. Specifically, the silicon carbide substrate 100 is placed between the first and second surface plates such that the first main surface 1 faces the first surface plate (not shown) and the second main surface 2 corresponds to the second surface plate (not shown). Next, a slurry is introduced between the first main surface 1 and the first surface plate and between the second main surface 2 and the second surface plate. The slurry contains, for example, diamond abrasive grains and water. The diameter of the diamond abrasive grains is, for example, 1 μm or more and 3 μm or less. Mechanical polishing is performed on both sides of the silicon carbide substrate 100 by applying a load to the first main surface 1 by the first surface plate and applying a load to the second main surface 2 by the second surface plate.

[0046] Next, a chemical mechanical polishing process (S40) is carried out. Specifically, chemical mechanical polishing is performed on the first main surface 1 of the silicon carbide substrate 100. Colloidal silica is used as the abrasive grain. A polishing solution containing permanganate is used. A polishing cloth is attached to a surface plate. The polishing cloth is, for example, a nonwoven fabric. The processing pressure is, for example, 300 g / cm². 2 The flow rate of the polishing fluid is, for example, 50 cc / min. The rotation speed of the surface plate is, for example, 40 rpm. The processing time is, for example, 2 hours.

[0047] Next, the sulfuric acid hydrogen water cleaning process (S50) is carried out. In the sulfuric acid hydrogen water cleaning process (S50), an ultrasonic cleaning device is used. As shown in Figure 5, the ultrasonic cleaning device 20 mainly consists of an ultrasonic source 19, a first cleaning tank 12, and a second cleaning tank 13. The second cleaning tank 13 is located on top of the first cleaning tank 12. The second cleaning tank 13 is placed over the opening of the first cleaning tank 12. The first cleaning tank 12 is filled with a first cleaning solution 14 (specifically water). The second cleaning tank 13 is filled with a second cleaning solution 15 (specifically sulfuric acid hydrogen water). The silicon carbide substrate 100 is immersed in sulfuric acid hydrogen water. The ultrasonic source 19 is located at the bottom of the second cleaning tank 13. The second cleaning tank 13 is located on top of the ultrasonic source 19.

[0048] In the sulfuric acid hydrogen peroxide cleaning process (S50), the silicon carbide substrate 100 is cleaned while ultrasonic waves are irradiated into the sulfuric acid hydrogen peroxide to enhance the removal effect of metal impurities. The frequency of the ultrasonic waves is, for example, between 450 kHz and 2 MHz. The ultrasonic waves promote chemical reactions, thereby increasing the reactivity of metal impurities to the sulfuric acid hydrogen peroxide. In addition, the cavitation effect caused by ultrasonic irradiation effectively removes manganese-containing sludge that has entered the grinding marks of the chamfered portion 6.

[0049] In the sulfuric acid and hydrogen peroxide washing process (S50), mainly organic matter and metal impurities are removed. Sulfuric acid and hydrogen peroxide is a solution obtained by mixing sulfuric acid, hydrogen peroxide, and ultrapure water. As the sulfuric acid, for example, concentrated sulfuric acid with a mass percentage concentration of 96% can be used. As the hydrogen peroxide, for example, hydrogen peroxide with a mass percentage concentration of 30% can be used. The same applies to the hydrogen peroxide used in subsequent processes.

[0050] The volume ratio of sulfuric acid, hydrogen peroxide, and ultrapure water in the sulfuric acid peroxide solution is, for example, 10(sulfuric acid):1(hydrogen peroxide):1(ultrapure water) to 10(sulfuric acid):3(hydrogen peroxide):1(ultrapure water). In other words, the volume of sulfuric acid is 10 times the volume of ultrapure water. The volume of hydrogen peroxide is between 1 and 3 times the volume of ultrapure water. The immersion time of the silicon carbide substrate 100 is, for example, 5 minutes or more. The temperature of the sulfuric acid peroxide solution is, for example, room temperature.

[0051] Next, an ammonia hydrogen peroxide cleaning process (S60) is carried out. In the ammonia hydrogen peroxide cleaning process (S60), mainly abrasives and dust are removed. The ammonia hydrogen peroxide is a solution obtained by mixing an aqueous ammonia solution, hydrogen peroxide solution, and ultrapure water. As the aqueous ammonia solution, for example, an aqueous ammonia solution with a mass percentage concentration of 28% can be used. In the ammonia hydrogen peroxide cleaning process (S60), the silicon carbide substrate 100 may be cleaned while ultrasonic waves are irradiated into the ammonia hydrogen peroxide.

[0052] The volume ratio of ammonia solution, hydrogen peroxide solution, and ultrapure water contained in ammonia hydrogen water is between 1 (ammonia solution):1 (hydrogen peroxide solution):5 (ultrapure water) and 1 (ammonia solution):1 (hydrogen peroxide solution):10 (ultrapure water). In other words, the volume of the ammonia solution is between 1 / 10 and 1 / 5 of the volume of the ultrapure water. Also, the volume of the hydrogen peroxide solution is between 1 / 10 and 1 / 5 of the volume of the ultrapure water. The immersion time of the silicon carbide substrate 100 is, for example, 5 minutes or more. The temperature of the sulfuric acid hydrogen water is, for example, room temperature.

[0053] Next, a hydrochloric acid hydrochloride washing step (S70) is performed. In the hydrochloric acid hydrochloride washing step (S70), heavy metals are mainly removed. Hydrochloric acid hydrochloride is a solution obtained by mixing hydrochloric acid, hydrogen peroxide, and ultrapure water. As the hydrochloric acid, for example, concentrated hydrochloric acid with a mass percentage concentration of 98% can be used. In the hydrochloric acid hydrochloride washing step (S70), the silicon carbide substrate 100 may be washed while ultrasonic waves are irradiated into the hydrochloric acid hydrochloride.

[0054] The volume ratio of hydrochloric acid, hydrogen peroxide, and ultrapure water in hydrochloric acid peroxide solution is, for example, 1 (hydrochloric acid):1 (hydrogen peroxide):5 (ultrapure water) to 1 (hydrochloric acid):1 (hydrogen peroxide):10 (ultrapure water). In other words, the volume of hydrochloric acid is between 1 / 10 and 1 / 5 of the volume of ultrapure water. Also, the volume of hydrogen peroxide is between 1 / 10 and 1 / 5 of the volume of ultrapure water. The immersion time of the silicon carbide substrate 100 is, for example, 5 minutes or more. The temperature of the sulfuric acid peroxide solution is, for example, room temperature.

[0055] Next, a hydrofluoric acid cleaning process (S80) is carried out. In the hydrofluoric acid cleaning process (S80), the silicon oxide film is removed by hydrofluoric acid and the surface is terminated with fluorine. The concentration of hydrofluoric acid in the mixture of hydrofluoric acid and ultrapure water is, for example, 10% to 40%. The immersion time of the silicon carbide substrate 100 is, for example, 5 minutes or more. The temperature of the sulfuric acid solution is, for example, room temperature. In the hydrofluoric acid cleaning process (S80), the silicon carbide substrate 100 may be cleaned while the hydrofluoric acid is irradiated with ultrasound.

[0056] Next, a drying process (S90) is carried out. In the drying process (S90), the silicon carbide substrate 100 is dried, for example, using a spin dryer 30. As shown in Figure 6, the spin dryer 30 comprises a main body 31, a lid 32, an opening 34, and an exhaust port 33. The spin dryer 30 is located in a cleanroom equivalent to Class 100. Before introducing the silicon carbide substrate 100 into the spin dryer 30, with the lid 32 of the spin dryer 30 open, air is passed through the opening 34 of the spin dryer 30 towards the exhaust port 33. The volume of the main body 31 is, for example, 127,000 cm³. 3The area of ​​the opening 34 is, for example, 2700 cm². 2 The amount of air that passes through is, for example, 60m 3 That is the case.

[0057] Next, the silicon carbide substrate 100 is placed in the main body 31 of the spin dryer 30, and the lid 32 is closed. The silicon carbide substrate 100 is rotated around a rotation axis that is almost perpendicular to the first main surface 1 under reduced pressure through the exhaust port 33. The rotation speed of the silicon carbide substrate 100 is, for example, 800 rpm. The rotation time is, for example, 300 seconds. This removes the cleaning liquid adhering to the silicon carbide substrate 100 by centrifugal force.

[0058] Next, the effects and advantages of this embodiment will be described. Generally, the cleanliness of the main surface 1 of a silicon carbide substrate 100 is often discussed using the average value of impurity concentrations measured at multiple locations within the main surface 1. However, if impurities are concentrated in a specific location, discussing it using the average value may result in a small value, potentially leading to it being judged as a good product. In reality, if a silicon carbide semiconductor device is manufactured using a silicon carbide substrate 100 with concentrated impurities, there is a risk of leakage current being generated through the impurities.

[0059] Upon investigating the cause of the concentration of impurities in specific locations, it was found that during the manufacturing process of the silicon carbide substrate 100, dust suspended in the atmosphere adheres to the main surface 1 of the silicon carbide substrate 100. For example, the chemical mechanical polishing equipment used in the chemical mechanical polishing process (S40) uses stainless steel components (an alloy mainly composed of iron and containing chromium), and therefore, dust containing iron is generated from the chemical mechanical polishing equipment. Thus, the atmosphere during the manufacturing process of the silicon carbide substrate 100 may contain dust containing various types of metal impurities. Dust containing metal impurities is the cause of contamination of the silicon carbide substrate 100.

[0060] In the sulfuric acid hydrogen peroxide cleaning step (S50) of the silicon carbide substrate 100 according to this embodiment, the silicon carbide substrate 100 is cleaned while ultrasonic waves are irradiated into the sulfuric acid hydrogen peroxide. The ultrasonic waves promote chemical reactions. This increases the reactivity of metal impurities to the sulfuric acid hydrogen peroxide. In addition, the cavitation effect caused by ultrasonic irradiation makes it possible to effectively remove metal impurities that are concentrated in certain locations. Therefore, the concentration of metal impurities can be reduced in most areas of the main surface 1. Specifically, on the main surface 1, the concentrations of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc are reduced to 5 × 10⁻⁶. 10 atoms / cm 2 The total area of ​​regions that are less than 1 can be 95% or more of the area of ​​the main surface 1. This results in a silicon carbide substrate 100 with high cleanliness. As a result, when a silicon carbide semiconductor device is fabricated using the silicon carbide substrate 100, it is possible to suppress the deterioration of the electrical properties of the silicon carbide semiconductor device due to metal impurities.

[0061] Furthermore, a spin dryer may be used to dry the silicon carbide substrate 100 after the cleaning process. When the silicon carbide substrate 100 is placed inside the main body 31 of the spin dryer for drying, dust adhering to the inside of the spin dryer, dust generated during the operation of the spin dryer, or dust floating in the atmosphere around the spin dryer may adhere firmly to the silicon carbide substrate 100, which is wet with the cleaning solution used in the cleaning process. This dust contains metallic impurities and can cause contamination of the silicon carbide substrate 100.

[0062] In the drying process (S90) of the silicon carbide substrate 100 according to this embodiment, before the silicon carbide substrate 100 is placed into the spin dryer 30, a certain amount of air is passed through the opening 34 of the spin dryer 30 toward the exhaust port 33 with the lid 32 of the spin dryer 30 open. After that, the silicon carbide substrate 100 is placed inside the spin dryer 30 and the silicon carbide substrate 100 is dried. This makes it possible to suppress the adhesion of dust containing metal impurities to the main surface 1 of the silicon carbide substrate 100. Therefore, the concentration of metal impurities can be reduced in most areas of the main surface 1. Specifically, on the main surface 1, the concentrations of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc are 5 × 10⁻⁶. 10 atoms / cm 2 The total area of ​​regions that are less than 1 can be 95% or more of the area of ​​the main surface 1. This results in a silicon carbide substrate 100 with high cleanliness. As a result, when a silicon carbide semiconductor device is fabricated using the silicon carbide substrate 100, it is possible to suppress the deterioration of the electrical properties of the silicon carbide semiconductor device due to metal impurities. [Examples]

[0063] (Sample preparation) First, two silicon carbide substrates, one for Sample 1 and one for Sample 2, were prepared. The silicon carbide substrate 100 for Sample 1 is a comparative example. The silicon carbide substrate 100 for Sample 2 is an example. The maximum diameter of the silicon carbide substrate 100 was set to 150 mm.

[0064] The silicon carbide substrate 100 for Sample 2 was manufactured by the manufacturing method according to this embodiment. Specifically, in the sulfuric acid hydrogen peroxide washing step (S50), ultrasonic waves were irradiated onto the sulfuric acid hydrogen peroxide. The frequency of the ultrasonic waves was 950 kHz. The volume ratio of sulfuric acid, hydrogen peroxide, and ultrapure water contained in the sulfuric acid hydrogen peroxide was 10 (sulfuric acid): 1 (hydrogen peroxide): 1 (ultrapure water). The immersion time of the silicon carbide substrate 100 was 30 minutes. The temperature of the sulfuric acid hydrogen peroxide was room temperature. Furthermore, in the drying step (S90) of the silicon carbide substrate 100, before putting the silicon carbide substrate 100 into the spin dryer 30, air was passed from the opening 34 of the spin dryer 30 toward the exhaust port 33 with the lid 32 of the spin dryer 30 open. The amount of air passed through was 60 m³. 3 That's what I decided.

[0065] On the other hand, in the manufacturing method of the silicon carbide substrate 100 related to Sample 1, ultrasonic waves were not irradiated onto the sulfuric acid hydrogen water during the sulfuric acid hydrogen water washing step (S50). The amount of air passing through was 15 m 3 The other manufacturing conditions were the same as those for the manufacturing method of the silicon carbide substrate 100 related to Sample 2.

[0066] (Measurement method) Next, the concentrations of metal impurities were measured using a TXRF-3760 manufactured by Rigaku Corporation. The X-ray power was set to 35kV-255mA. The incident direction was set to 39°. The incident angle for W-Ma was set to 0.500°. The measurement time for W-Ma was 10 seconds / point. The incident angle for W-Lb was set to 0.100°. The measurement time for W-Lb was also 10 seconds / point. As shown in Figure 3, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) were measured in 101 measurement areas S on the first main surface 1 of the silicon carbide substrate 100. The area ratio of the areas where the concentration of the metal impurities to be measured was above the standard value was calculated by dividing the number of measurement areas S where the concentration of the target metal impurities was above the standard value by the total number of measurement areas S (101 in total).

[0067] (Measurement results)

[0068]

Table 1

[0069] Table 1 shows the area ratio of the measurement region S where the concentration of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S) and chlorine (Cl) is not less than the reference value. The reference value is 1×10 12 atoms / cm 2 and 5×10 10 atoms / cm 2 .

[0070] As shown in Table 1, in the silicon carbide substrate 100 according to Sample 1, the area ratios of the measurement region S where the concentration of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S) and chlorine (Cl) is not less than 5×10 10 atoms / cm 2 were 7%, 1%, 2%, 2%, 1%, 10%, 1%, 1%, 88% and 78% respectively. On the other hand, in the silicon carbide substrate 100 according to Sample 2, the area ratios of the measurement region S where the concentration of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S) and chlorine (Cl) is not less than 5×10 10 atoms / cm 2 were 0%, 0%, 1%, 0%, 0%, 0%, 0%, 0%, 68% and 62% respectively.

[0071] As shown in Table 1, in the silicon carbide substrate 100 according to Sample 1, the area ratios of the measurement region S where the concentration of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S) and chlorine (Cl) is not less than 1×10 12 atoms / cm 2The area percentages of the measurement region S were 0%, 1%, 1%, 1%, 0%, 0%, 0%, 0%, 0%, 88%, and 78%, respectively. On the other hand, in the silicon carbide substrate 100 of sample 2, the concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) were 1 × 10⁻⁶. 12 atoms / cm 2 The area percentages of the measurement region S were 0%, 0%, 0%, 0%, 0%, 0%, 0%, 0%, 0%, 68%, and 62%, respectively.

[0072] As described above, it was confirmed that, compared to the silicon carbide substrate 100 of Sample 1, the silicon carbide substrate 100 of Sample 2 can reduce the area proportion of regions where the metal impurities to be measured are above the standard value.

[0073] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope. [Explanation of Symbols]

[0074] 1 Main surface (first main surface), 2 Second main surface, 3 First curved region, 4 Second curved region, 5 Outer edge, 6 Chamfered portion, 7 Orientation flat portion, 8 Arc-shaped portion, 10 Center, 12 First cleaning tank, 13 Second cleaning tank, 14 First cleaning solution, 15 Second cleaning solution, 19 Ultrasonic source, 20 Ultrasonic cleaning device, 21 First virtual circle, 22 Second virtual circle, 23 Third virtual circle, 24 Fourth virtual circle, 25 Fifth virtual circle, 30 Spin dryer, 31 Main body, 32 Lid, 33 Exhaust port, 34 Opening, 100 Silicon carbide substrate, 101 First direction, 102 Second direction, S Measurement area, W1 First width, W2 Second width.

Claims

1. A process of chemically and mechanically polishing a silicon carbide substrate using a polishing solution containing permanganate, A step of sequentially washing the chemically mechanically polished silicon carbide substrate using sulfuric acid hydrochloride, ammonia hydrochloride, hydrochloric acid hydrochloride, and hydrofluoric acid, The process includes drying the washed silicon carbide substrate using a spin dryer, In the step of cleaning the chemically mechanically polished silicon carbide substrate with the sulfuric acid peroxide, the silicon carbide substrate is cleaned while ultrasonic waves are irradiated onto the sulfuric acid peroxide. A method for manufacturing a silicon carbide substrate, comprising the step of drying using the spin dryer, in which, with the lid of the spin dryer open, air is passed from the opening of the spin dryer toward the exhaust port, and then the silicon carbide substrate is placed inside the spin dryer and the silicon carbide substrate is dried.

2. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the frequency of the ultrasonic waves is 450 kHz or more and 2 MHz or less.

3. After the drying process using the spin dryer, the concentrations of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc on the main surface of the silicon carbide substrate are 5 × 10 10 atoms / cm 2 A method for manufacturing a silicon carbide substrate according to claim 1 or claim 2, wherein the total area of ​​the region that is less than 95% or more of the area of ​​the main surface.

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