阅读说明：本技术 碳化硅衬底 (Silicon carbide substrate ) 是由 冲田恭子 本家翼 于 2020-04-01 设计创作，主要内容包括：本公开内容所涉及的碳化硅衬底具有主面。所述碳化硅衬底的最大直径为150mm以上。在主面中,钠、铝、钾、钙、钛、铁、铜和锌各自的浓度小于5×10～(10)原子/cm～(2)的区域的总面积为主面的面积的95％以上。(The silicon carbide substrate according to the present disclosure has a main surface. The maximum diameter of the silicon carbide substrate is 150mm or more. The concentration of each of sodium, aluminum, potassium, calcium, titanium, iron, copper and zinc in the main face is less than 5X 10 10 Atom/cm 2 The total area of the regions (a) is 95% or more of the area of the main surface.)

1. A silicon carbide substrate, wherein the silicon carbide substrate has a main surface,

the maximum diameter of the silicon carbide substrate is 150mm or more, and

in the main face, the respective concentrations of sodium, aluminium, potassium, calcium, titanium, iron, copper and zinc are less than 5 x 10¹⁰Atom/cm²The total area of the regions (a) is 95% or more of the area of the main surface.

2. The silicon carbide substrate according to claim 1, wherein the total area is 98% or more of the area of the main surface.

3. The silicon carbide substrate according to claim 1 or claim 2, wherein sulfur is present in the major face, and

the concentration of sulfur is 5 x 10¹⁰Atom/cm²The above region is 1% or more of the area of the main surface.

4. The silicon carbide substrate according to claim 3, wherein the concentration of sulfur is 5 x 10¹⁰Atom/cm²The above region is 50% or more of the area of the main surface.

5. The silicon carbide substrate according to any one of claim 1 to claim 4,

chlorine is present in the main face, and

the concentration of the chlorine is 5 x 10¹⁰Atom/cm²The above region is 1% or more of the area of the main surface.

6. The silicon carbide substrate according to claim 5, wherein the chlorine concentration is 5 x 10¹⁰Atom/cm²The above region is 50% or more of the area of the main surface.

7. The silicon carbide substrate according to any one of claims 1 to 6, wherein the concentration of aluminum in the main surface is 1 x 10¹²Atom/cm²The above region is less than 1% of the area of the main surface.

8. The silicon carbide substrate according to any one of claims 1 to 7, wherein the concentration of potassium in the main surface is 1 x 10¹²Atom/cm²The above region is less than 1% of the area of the main surface.

9. The right of claim 1The silicon carbide substrate according to claim 8, wherein the concentration of calcium in the main surface is 1 x 10¹²Atom/cm²The above region is less than 1% of the area of the main surface.

Technical Field

The present disclosure relates to silicon carbide substrates. The present application claims priority based on japanese patent application No. 2019-093882, which was filed on 5/17/2019. The entire contents of the disclosures in the japanese patent applications are incorporated herein by reference.

Background

WO2016/063632 (patent document 1) describes a method for cleaning a silicon carbide substrate.

Documents of the prior art

Patent document

Patent document 1: WO2016/063632

Disclosure of Invention

The silicon carbide substrate according to the present disclosure has a main surface. The maximum diameter of the silicon carbide substrate is 150mm or more. The concentration of each of sodium, aluminum, potassium, calcium, titanium, iron, copper and zinc in the main face is less than 5X 10¹⁰Atom/cm²The total area of the regions (a) is 95% or more of the area of the main surface.

Drawings

Fig. 1 is a schematic plan view showing the structure of a silicon carbide substrate according to the present embodiment.

FIG. 2 is a schematic sectional view taken along line II-II of FIG. 1.

FIG. 3 is a schematic plan view showing a measurement region of a metal impurity.

Fig. 4 is a flowchart schematically showing a method for manufacturing a silicon carbide substrate according to the present embodiment.

Fig. 5 is a schematic cross-sectional view showing a first step of the method for producing a silicon carbide substrate according to the present embodiment.

Fig. 6 is a schematic cross-sectional view showing a second step of the method for producing a silicon carbide substrate according to the present embodiment.

Detailed Description

[ problem to be solved by the present disclosure ]

An object of the present disclosure is to provide a silicon carbide substrate having high cleanliness.

[ Effect of the present disclosure ]

According to the present disclosure, a silicon carbide substrate with high cleanliness can be provided.

[ description of embodiments of the present disclosure ]

First, embodiments of the present disclosure will be described.

(1) The silicon carbide substrate 100 according to the present disclosure has a main surface 1. The maximum diameter of the silicon carbide substrate is 150mm or more. In the main face 1, the respective concentrations of sodium, aluminum, potassium, calcium, titanium, iron, copper and zinc are less than 5 × 10¹⁰Atom/cm²The total area of the regions (a) is 95% or more of the area of the main surface 1.

(2) According to the silicon carbide substrate 100 according to the above (1), the total area can be 98% or more of the area of the main surface 1.

(3) According to the silicon carbide substrate 100 according to the above (1) or (2), sulfur may be present in the main surface 1. The concentration of sulfur is 5X 10¹⁰Atom/cm²The above region may be 1% or more of the area of the main surface 1.

(4) According to the silicon carbide substrate 100 of the above (3), the concentration of sulfur is 5X 10¹⁰Atom/cm²The above region may be 50% or more of the area of the main surface 1.

(5) According to the silicon carbide substrate 100 according to any one of the above (1) to (4), chlorine may be present on the main surface 1. The concentration of chlorine is 5X 10¹⁰Atom/cm²The above region may be 1% or more of the area of the main surface 1.

(6) According to the silicon carbide substrate 100 of the above (5), the concentration of chlorine is 5X 10¹⁰Atom/cm²The above region may be 50% or more of the area of the main surface 1.

(7) According to the silicon carbide substrate 100 of any one of the above (1) to (6), the concentration of aluminum in the main surface 1 is 1 × 10¹²Atom/cm²The above region may be less than 1% of the area of the main face 1.

(8) According to the silicon carbide substrate 100 of any one of the above (1) to (7), the concentration of potassium in the main surface 1 is 1 × 10¹²Atom/cm²The above region may be less than 1% of the area of the main face 1.

(9) According to the silicon carbide substrate 100 of any one of the above (1) to (8), the concentration of calcium in the main surface 1 is 1 × 10¹²Atom/cm²The above area may be smaller than the main surface1% of the area of 1.

[ details of embodiments of the present disclosure ]

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding portions are denoted by the same reference numerals, and the description thereof will not be repeated. In the description of the crystallographic aspects in the present specification, the individual orientation is represented by [ ], the collective orientation is represented by < >, the individual plane is represented by () and the collective plane is represented by { }. In addition, negative exponent is a number with a "-" (bar) added to it in crystallography, but in this specification, a negative sign is added before the number.

< formation of silicon carbide substrate >

First, the structure of the silicon carbide substrate 100 according to the present embodiment will be described.

Fig. 1 is a schematic plan view showing the structure of a silicon carbide substrate 100 according to the present embodiment.

Fig. 2 is a schematic sectional view taken along line II-II of fig. 1.

As shown in fig. 1 and 2, the silicon carbide substrate 100 according to the present embodiment mainly includes a first main surface 1, a second main surface 2, and a chamfered portion 6. The second main surface 2 is located on the opposite side of the first main surface 1. The chamfered portion 6 is connected to each of the first main surface 1 and the second main surface 2. The first main surface 1 and the second main surface 2 are each a flat surface. The first main surface 1 is a surface on which an epitaxial layer (not shown) is formed. The silicon carbide substrate 100 is made of, for example, a polycrystalline 4H-type silicon carbide single crystal. The silicon carbide substrate 100 contains n-type impurities such as nitrogen, for example.

The first main surface 1 is, for example, a {0001} plane or a plane deviated from the {0001} plane by 8 ° or less. Specifically, the first main surface 1 is, for example, a (0001) plane or a plane deviated by 8 ° or less from the (0001) plane. The first main surface 1 may be, for example, a (000-1) surface or a surface deviated by 8 ° or less from the (000-1) surface. When the first main surface 1 is a (0001) surface, the second main surface 2 is a (000-1) surface.

As shown in fig. 2, the chamfered portion 6 has a first bent region 3, an outer peripheral end portion 5, and a second bent region 4. The first curved region 3 is connected to the first main surface 1. The first curved region 3 is located outward of the first main surface 1. The second curved region 4 is connected to the second main surface 2. The second bending region 4 is located outside the second main surface 2. As shown in fig. 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 has an arc shape. The first curved region 3 and the second curved region 4 are each curved in a convex manner to the outside.

The outer peripheral end 5 is an outermost portion in a radial direction parallel to the first main surface 1. The outer peripheral end 5 is connected to each of the first bending region 3 and the second bending region 4. In the radial direction, the first bending region 3 is located between the first main surface 1 and the outer peripheral end 5. Likewise, the second bent region 4 is located between the second main surface 2 and the outer peripheral end 5 in the radial direction.

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

When the first main surface 1 is inclined with respect to the {0001} plane, the first direction 101 may be, for example, a direction in which a < 11-20 > direction is projected onto the first main surface 1. In the case where the first main surface 1 is inclined with respect to the {0001} plane, the second direction 102 may be, for example, a direction in which a < 1-100 > direction is projected onto the first main surface 1.

As shown in fig. 1, the maximum diameter (first width W1) of the silicon carbide substrate 100 is 150mm or more. The maximum diameter of the silicon carbide substrate 100 can be calculated as the diameter of a circle including the arc-shaped portion 8 when viewed in a direction perpendicular to the first main surface 1. The first width W1 may be 200mm or more, or 250mm or more. The upper limit of the first width W1 is not particularly limited, and may be 300mm or less, for example.

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

Next, the concentration of the metal impurity in the first main surface 1 will be described.

According to the silicon carbide substrate 100 of the present embodiment, the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) in the first main surface 1 are less than 5 × 10¹⁰Atom/cm²The total area of the regions (a) may be 95% or more of the area of the first main surface 1. From another viewpoint, in the first main surface 1, each concentration of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) is 5 × 10¹⁰Atom/cm²The total area of the above regions may be less than 5% of the area of the main face 1. That is, the concentration of the metal impurity is low in the region of 95% or more of the first main surface 1.

Preferably, in the first main face 1, the concentration of each of sodium, aluminium, potassium, calcium, titanium, iron, copper and zinc is less than 5 × 10¹⁰Atom/cm²The total area of the regions (2) may be 98% or more, or 98.5% or more of the area of the main surface 1. From another viewpoint, in the first main surface 1, each concentration of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) is 5 × 10¹⁰Atom/cm²The total area of the above regions may be less than 2% or less than 1.5% of the area of the main surface 1.

Sulfur may be present in the first main face 1. The concentration of sulfur (S) was 5X 10¹⁰Atom/cm²The above region may be 1% or more of the area of the first main surface 1. The concentration of sulfur is 5X 10¹⁰Atom/cm²The region above may be 25% or more, 50% or more, or 60% or more of the area of the first main surface 1. To sulfur concentration of 5X 10¹⁰Atom/cm²The lower limit of the above region is not particularly limited, and may be, for example, 75% or less of the area of the first main surface 1.

The concentration of sulfur (S) was 1X 10¹²Atom/cm²Above thatThe area may be 1% or more of the area of the first main surface 1. The concentration of sulfur is 1X 10¹²Atom/cm²The region above may be 25% or more, 50% or more, or 60% or more of the area of the first main surface 1. To sulfur concentration of 1X 10¹²Atom/cm²The lower limit of the above region is not particularly limited, and may be, for example, 75% or less of the area of the first main surface 1.

Chlorine may be present in the first main face 1. The concentration of chlorine (Cl) was 5X 10¹⁰Atom/cm²The above region may be 1% or more of the area of the first main surface 1. The concentration of chlorine is 5X 10¹⁰Atom/cm²The above region 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 concentration of p-chlorine is 5 x 10¹⁰Atom/cm²The lower limit of the above region is not particularly limited, and may be, for example, 75% or less of the area of the first main surface 1.

The concentration of chlorine (Cl) was 1X 10¹²Atom/cm²The above region may be 1% or more of the area of the first main surface 1. The concentration of chlorine is 1X 10¹²Atom/cm²The above region 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 concentration of p-chlorine is 1 x 10¹²Atom/cm²The lower limit of the above region is not particularly limited, and may be, for example, 75% or less of the area of the first main surface 1.

In the first main face 1, the concentration of aluminum is 1 × 10¹²Atom/cm²The above region may be less than 1% of the area of the first main face 1. In the first main face 1, the concentration of aluminum is 1 × 10¹²Atom/cm²The above area may be absent.

In the first main face 1, the concentration of potassium is 1 × 10¹²Atom/cm²The above region may be less than 1% of the area of the first main face 1. In the first main face 1, the concentration of potassium is 1 × 10¹²Atom/cm²The above area may be absent.

In the first main face 1, the concentration of calcium is 1 × 10¹²Atom/cm²The above region may be less than 1% of the area of the first main face 1. In the first main face 1, the concentration of calcium is 1 × 10¹²Atom/cm²The above area may be absent.

Next, a method of measuring the concentration of the metal impurity in the first main surface 1 will be described.

The concentration of the metal impurities can be measured by a total reflection fluorescent X-ray analysis apparatus. As the analyzer, for example, TXRF-3760 manufactured by Nippon chemical Co., Ltd. The analyzer has a plurality of excitation X-ray sources, and can measure elements from light elements Na to heavy elements U by using excitation X-rays which are most suitable for measuring the elements. Specifically, excitation X-rays of W-Ma (1.78keV) can be used for Na, Al and Mg. For elements having an atomic number greater than K up to the U element (particularly K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cl and S), excitation X-rays of W-Lb (9.67keV) can be used.

The X-ray power is, for example, 35kV to 255 mA. The azimuth angle of incidence was 39 °. The incident angle of W-Ma is 0.500 deg.. The measurement time of W-Ma was 10 seconds/point. The incident angle of W-Lb is 0.100 deg.. The measurement time of W-Lb was 10 seconds/point. The analyzer has an XY drive stage, and can measure the in-plane distribution of the measurement element. For example, the first main surface 1 may be divided into regions of 101 equal areas, and the concentration of the measurement element may be measured at the 101. The concentration of the metal impurities means the number of atoms per unit area.

Fig. 3 is a schematic plan view showing a measurement region of a metal impurity. As shown in fig. 3, the first main surface 1 has a center 10, a first imaginary circle 21, a second imaginary circle 22, a third imaginary circle 23, a fourth imaginary circle 24, and a fifth imaginary circle 25. The first imaginary circle 21 is spaced from the second imaginary circle 22 by the same distance as the second imaginary circle 22 is spaced from the third imaginary circle 23. The second imaginary circle 22 is spaced from the third imaginary circle 23 by the same distance as the third imaginary circle 23 is spaced from the fourth imaginary circle 24. The third imaginary circle 23 is spaced from the fourth imaginary circle 24 by the same distance as the fourth imaginary circle 24 is spaced from the fifth imaginary circle 25.

In fig. 3, a circle having a small dot (dot) represents a measurement region S of the metal impurity. The measurement region S has a size of 10mm phi. The measurement regions 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 regions 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. The measurement region S is provided at 1 in the center 10 of the first main surface 1. The measurement region S is provided at 8 positions at equal intervals along the first virtual circle 21. The measurement regions S are provided at 16 positions at equal intervals along the second virtual circle 22. The measurement region S is provided at 20 points at equal intervals along the third virtual circle 23. The measurement region S is provided at 24 positions at equal intervals along the fourth virtual circle 24. The measurement region S is provided at 32 points at equal intervals along the fifth virtual circle 25. That is, the measurement region S is provided with a total of 101 locations on the first main surface 1.

For example, in a measurement region S (measurement region 1) including the center 10 of the first main surface 1, the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) are measured. In the 1 st measurement region, it was judged whether or not the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu) and zinc (Zn) were less than 5X 10¹⁰Atom/cm²。

Next, in the 2 nd measurement region located adjacent to the 1 st measurement region, the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) were measured. In the 2 nd measurement region, it was judged whether or not the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu) and zinc (Zn) were less than 5X 10¹⁰Atom/cm²。

As described above, in the 101 measurement region S from the 1 st measurement region to the 101 th measurement region, it was judged whether or not the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu) and zinc (Zn) were less than 5X 10¹⁰Atom/cm². For example, in the measurement region S at 101, the concentration of each of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), and zinc (Zn) in the measurement region S at N is less than 5X 10¹⁰Atom/cm²In the case of (1), sodium (Na), aluminum (Al), potassium (K), and calcium may be addedThe respective concentrations of (Ca), titanium (Ti), iron (Fe), copper (Cu) and zinc (Zn) are less than 5 × 10¹⁰Atom/cm²The total area of the regions (1) is calculated as the area of the first main surface (1) × N/101.

In the above description, the principal surface is described as the first principal surface 1, but the principal surface may be the second principal surface 2. From another point of view, the concentration of the metal impurity in the second main face 2 may be the same as the concentration of the metal impurity in the first main face 1.

< method for producing silicon carbide substrate >

Next, a method for manufacturing the silicon carbide substrate 100 according to the present embodiment will be described. As shown in fig. 4, the method for manufacturing a silicon carbide substrate 100 according to the present 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-hydrogen peroxide solution cleaning step (S50), an ammonia-hydrogen peroxide solution cleaning step (S60), a hydrochloric acid-hydrogen peroxide solution cleaning step (S70), a hydrofluoric acid cleaning step (S80), and a drying step (S90).

First, a crystal preparation step (S10) is performed. In the crystal preparation step (S10), a silicon carbide ingot is formed by, for example, a sublimation method. Next, a dicing step (S20) is performed. In the slicing step (S20), the silicon carbide ingot is sliced into a plurality of silicon carbide substrates 100 by a saw wire (saw wire). The silicon carbide substrate 100 is made of, for example, a polycrystalline 4H-type silicon carbide single crystal. As shown in fig. 1, a silicon carbide substrate 100 has a first main surface 1, a second main surface 2, and an outer peripheral end portion 5. At this time, the chamfered portion 6 is not formed.

Next, a chamfering step (S25) is performed. In the chamfering step (S25), a grinding apparatus (not shown) is used. In the chamfering step, a diamond grindstone is used, for example. The vicinity of the boundary of the first main surface 1 and the outer peripheral end portion 5 of the silicon carbide substrate 100 is pressed against the rotating diamond grindstone. Similarly, the vicinity of the boundary between the first main surface 1 and the outer peripheral end portion 5 of the silicon carbide substrate 100 is pressed against the rotating diamond grindstone. Thereby, the chamfered portion 6 is formed on the silicon carbide substrate 100 (see fig. 2). In the chamfering step (S25), grinding marks may be formed in the chamfered portion 6.

Subsequently, a double-side mechanical polishing step (S30) is performed. Specifically, the silicon carbide substrate 100 is disposed between a first stage (not shown) and a second stage (not shown) so that the first main surface 1 faces the first stage and the second main surface 2 corresponds to the second stage. Next, the slurry is introduced between the first main surface 1 and the first stage and between the second main surface 2 and the second stage. The slurry contains, for example, diamond abrasive particles and water. The diameter of the diamond abrasive grains is, for example, 1 μm or more and 3 μm or less. The first main surface 1 is subjected to a load by the first platen, and the second main surface 2 is subjected to a load by the second platen, whereby both surfaces of the silicon carbide substrate 100 are mechanically polished.

Next, a chemical mechanical polishing step is performed (S40). Specifically, the first main surface 1 of the silicon carbide substrate 100 is chemically and mechanically polished. As the abrasive grains, for example, colloidal silica is used. A polishing slurry comprising permanganate is used. And a grinding cloth is arranged on the platform. The polishing cloth is, for example, a nonwoven fabric. The working pressure is, for example, 300g/cm². The flow rate of the polishing liquid is, for example, 50 cc/min. The rotation speed of the platform is for example 40 rpm. The processing time is, for example, 2 hours.

Next, a sulfuric acid-hydrogen peroxide solution cleaning step (S50) is performed. In the sulfuric acid-hydrogen peroxide solution cleaning step (S50), an ultrasonic cleaning apparatus is used. As shown in fig. 5, the ultrasonic cleaning apparatus 20 mainly has an ultrasonic wave generation source 19, a first cleaning tank 12, and a second cleaning tank 13. The second cleaning tank 13 is disposed above the first cleaning tank 12. Second cleaning tank 13 is hung on the opening of first cleaning tank 12. The first cleaning tank 12 contains a first cleaning liquid 14 (specifically, water). The second cleaning tank 13 contains a second cleaning liquid 15 (specifically, a sulfuric acid-hydrogen peroxide solution). The silicon carbide substrate 100 is immersed in a sulfuric acid-hydrogen peroxide mixture. The ultrasonic wave generation source 19 is disposed at the bottom of the second cleaning tank 13. The second cleaning tank 13 is disposed above the ultrasonic wave generation source 19.

In the sulfuric acid-hydrogen peroxide solution cleaning step (S50), the silicon carbide substrate 100 is cleaned while the sulfuric acid-hydrogen peroxide solution is irradiated with ultrasonic waves in order to improve the effect of removing metal impurities. The frequency of the ultrasonic wave is, for example, 450kHz or more and 2MHz or less. The chemical reaction is promoted by using ultrasonic waves. Thereby, the reactivity of the metal impurities to the sulfuric acid-hydrogen peroxide mixed liquid is improved. Further, the sludge containing manganese entering the grinding mark of the chamfered portion 6 can be effectively removed by the cavitation effect caused by the ultrasonic wave irradiation.

In the sulfuric acid-hydrogen peroxide mixed liquid cleaning step (S50), organic matter, metal impurities, and the like are mainly removed. The sulfuric acid-hydrogen peroxide mixed solution is a solution mixed with sulfuric acid, hydrogen peroxide and ultrapure water. As the sulfuric acid, for example, concentrated sulfuric acid having a mass percentage concentration of 96% can be used. As the hydrogen peroxide, for example, hydrogen peroxide having a mass percentage concentration of 30% can be used. The same applies to hydrogen peroxide to be used in the subsequent steps.

The volume ratio of sulfuric acid, hydrogen peroxide, and ultrapure water contained in the sulfuric acid-hydrogen peroxide mixed 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 the hydrogen peroxide is 1 to 3 times 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 peroxide mixture is, for example, room temperature.

Next, an ammonia-hydrogen peroxide liquid mixture cleaning step (S60) is performed. In the ammonia-hydrogen peroxide liquid mixed liquid cleaning step (S60), mainly the polishing agent and dust are removed. The ammonia-hydrogen peroxide mixed solution is a solution mixed with ammonia water solution, hydrogen peroxide and ultrapure water. As the aqueous ammonia solution, for example, an aqueous ammonia solution having a mass percentage concentration of 28% can be used. In the ammonia-hydrogen peroxide solution cleaning step (S60), the silicon carbide substrate 100 may be cleaned while the ammonia-hydrogen peroxide solution is irradiated with ultrasonic waves.

The volume ratio of the ammonia water solution, the hydrogen peroxide and the ultrapure water contained in the ammonia-hydrogen peroxide mixed solution is 1 (ammonia water solution): 1 (hydrogen peroxide): 5 (ultrapure water) to 1 (aqueous ammonia solution): 1 (hydrogen peroxide): 10 (ultrapure water). In other words, the volume of the aqueous ammonia solution is 1/10 times or more and 1/5 times or less the volume of the ultrapure water. The volume of hydrogen peroxide is 1/10 times or more and 1/5 times or less 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-hydrogen peroxide mixture is, for example, room temperature.

Next, a hydrochloric acid-hydrogen peroxide liquid mixture cleaning step (S70) is performed. In the hydrochloric acid-hydrogen peroxide mixed liquid cleaning step (S70), heavy metals are mainly removed. The mixed solution of hydrochloric acid and hydrogen peroxide is a solution mixed with hydrochloric acid, hydrogen peroxide and ultrapure water. As the hydrochloric acid, for example, concentrated hydrochloric acid having a mass percentage concentration of 98% can be used. In the hydrochloric acid-hydrogen peroxide solution cleaning step (S70), the silicon carbide substrate 100 may be cleaned while the hydrochloric acid-hydrogen peroxide solution is irradiated with ultrasonic waves.

The volume ratio of the hydrochloric acid, hydrogen peroxide and ultrapure water contained in the hydrochloric acid-hydrogen peroxide mixed 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 the hydrochloric acid is 1/10 times or more and 1/5 times or less the volume of the ultrapure water. The volume of hydrogen peroxide is 1/10 times or more and 1/5 times or less 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-hydrogen peroxide mixture is, for example, room temperature.

Next, a hydrofluoric acid cleaning step is performed (S80). In the hydrofluoric acid cleaning step (S80), the silicon oxide film is removed by hydrofluoric acid, and the surface is terminated with fluorine. The concentration of hydrofluoric acid in the mixed liquid in which hydrofluoric acid and ultrapure water are mixed is, for example, 10% or more and 40% or less. The immersion time of the silicon carbide substrate 100 is, for example, 5 minutes or more. The temperature of the sulfuric acid-hydrogen peroxide mixture is, for example, room temperature. In the hydrofluoric acid cleaning step (S80), the silicon carbide substrate 100 may be cleaned while hydrofluoric acid is irradiated with ultrasonic waves.

Next, a drying step (S90) is performed. In the drying step (S90), the silicon carbide substrate 100 is dried using, for example, the spin dryer 30. As shown in fig. 6, the rotary dryer 30 includes a main body 31, a cover 32, an opening 34, and an exhaust port 33. The rotary dryer 30 is disposed in a clean room corresponding to class 100. Before the silicon carbide substrate 100 is put into the spin dryer 30, air is passed through the opening 34 of the spin dryer 30 to the exhaust port 33 with the lid 32 of the spin dryer 30 opened. The body 31 has a volume of, for example, 127000cm³. Opening of the containerThe area of the portion 34 is, for example, 2700cm². The throughput of air is, for example, 60m³。

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 rotates around a rotation axis substantially perpendicular to the first main surface 1 in a state where the pressure is reduced by 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. Thereby, the cleaning liquid adhering to the silicon carbide substrate 100 is removed by centrifugal force.

Next, the operation and effects of the present embodiment will be described.

In general, the cleanliness of the main surface 1 of the silicon carbide substrate 100 is often discussed as an average value of impurity concentrations measured at a plurality of positions within the main surface 1. However, when the impurities are concentrated in a specific site, the average value is small, and the product may be determined as a good product. In practice, when a silicon carbide semiconductor device is manufactured using the silicon carbide substrate 100 in which impurities are concentrated, there is a possibility that a leakage current is generated via the impurities.

As a result of research on the cause of impurities adhering to a specific site in a concentrated manner, it was found that the cause is that dust floating in the atmosphere adheres to the main surface 1 of the silicon carbide substrate 100 during the manufacturing process of the silicon carbide substrate 100. For example, since the chemical mechanical polishing apparatus used in the chemical mechanical polishing step (S40) uses a member made of stainless steel (an alloy containing iron as a main component and chromium), iron-containing dust is generated from the chemical mechanical polishing apparatus. As described above, in the atmosphere in the process of manufacturing the silicon carbide substrate 100, there are cases where dust containing a plurality of metal impurities is contained. The dust containing the metal impurities causes contamination of the silicon carbide substrate 100.

In the step of cleaning the silicon carbide substrate 100 with the sulfuric acid-hydrogen peroxide solution mixture (S50), the silicon carbide substrate 100 is cleaned while the sulfuric acid-hydrogen peroxide solution mixture is irradiated with ultrasonic waves. The chemical reaction is promoted by using ultrasonic waves. Thereby, the reactivity of the metal impurities to the sulfuric acid-hydrogen peroxide mixed liquid is improved. In addition, by cavitation produced by ultrasonic irradiationAs a result, the metal impurities concentrated and attached to a specific site can be effectively removed. Therefore, the concentration of the metal impurities can be reduced in most regions of the main surface 1. Specifically, the main surface 1 can be made to have a concentration of each of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc of less than 5 × 10¹⁰Atom/cm²The total area of the regions (a) is 95% or more of the area of the main surface 1. This makes it possible to obtain a silicon carbide substrate 100 having high cleanliness. As a result, when a silicon carbide semiconductor device is manufactured using the silicon carbide substrate 100, deterioration of electrical characteristics of the silicon carbide semiconductor device due to metal impurities can be suppressed.

In addition, a spin dryer may be used to dry the silicon carbide substrate 100 after the cleaning step. When the silicon carbide substrate 100 is placed in the main body 31 of the spin dryer and dried, dust adhering to the inside of the spin dryer, dust generated when the spin dryer is operated, dust floating in the atmosphere around the spin dryer, or the like may firmly adhere to the silicon carbide substrate 100 wetted with the cleaning liquid used in the cleaning step. The dust contains metal impurities, which causes contamination of the silicon carbide substrate 100.

In the step (S90) of drying the silicon carbide substrate 100 according to the present embodiment, before the silicon carbide substrate 100 is loaded into the spin dryer 30, a certain amount or more of air is passed through the opening 34 of the spin dryer 30 to the exhaust port 33 while the lid 32 of the spin dryer 30 is open. Then, the silicon carbide substrate 100 is placed in the spin dryer 30, and the silicon carbide substrate 100 is dried. This can suppress adhesion of dust containing metal impurities to the main surface 1 of the silicon carbide substrate 100. Therefore, the concentration of the metal impurity can be reduced in most of the region of the main surface 1. Specifically, the main surface 1 can be made to have a concentration of each of sodium, aluminum, potassium, calcium, titanium, iron, copper, and zinc of less than 5 × 10¹⁰Atom/cm²The total area of the regions (a) is 95% or more of the area of the main surface 1. This makes it possible to obtain a silicon carbide substrate 100 having high cleanliness. As a result, when a silicon carbide semiconductor device is manufactured using the silicon carbide substrate 100, metal impurities can be suppressed from causingResulting in deterioration of electrical characteristics of the silicon carbide semiconductor device.

Examples

(sample preparation)

First, the silicon carbide substrate 100 of sample 1 and the silicon carbide substrate 100 of sample 2 were prepared. The silicon carbide substrate 100 according to sample 1 is a comparative example. Sample 2 relates to a silicon carbide substrate 100 as an example. The maximum diameter (diameter) of the silicon carbide substrate 100 was set to 150 mm.

The silicon carbide substrate 100 relating to sample 2 was manufactured by the manufacturing method according to the present embodiment. Specifically, in the sulfuric acid-hydrogen peroxide solution cleaning step (S50), ultrasonic waves are irradiated to the sulfuric acid-hydrogen peroxide solution. The frequency of the ultrasonic wave was set to 950 kHz. The volume ratio of sulfuric acid, hydrogen peroxide and ultrapure water contained in the sulfuric acid-hydrogen peroxide mixed solution was set to 10 (sulfuric acid): 1 (hydrogen peroxide): 1 (ultrapure water). The immersion time of the silicon carbide substrate 100 was set to 30 minutes. The temperature of the sulfuric acid-hydrogen peroxide mixed liquid is set to room temperature. In the step of drying the silicon carbide substrate 100 (S90), before the silicon carbide substrate 100 is loaded into the spin dryer 30, air is passed through the opening 34 of the spin dryer 30 to the exhaust port 33 while the lid 32 of the spin dryer 30 is open. The air throughput was set to 60m³。

On the other hand, according to the method for producing the silicon carbide substrate 100 of sample 1, in the sulfuric acid-hydrogen peroxide solution cleaning step (S50), the sulfuric acid-hydrogen peroxide solution is not irradiated with ultrasonic waves. The air throughput was set to 15m³. Other manufacturing conditions were the same as those of the method for manufacturing the silicon carbide substrate 100 according to sample 2.

(measurement method)

Next, the concentration of the metal impurities was measured by using TXRF-3760 manufactured by Nippon chemical Co., Ltd. The X-ray power was set to 35kV-255 mA. The incident azimuth angle was set to 39 °. The incident angle of W-Ma was set to 0.500. The measurement time of W-Ma was set to 10 seconds/point. The incident angle of W-Lb was set to 0.100. The measurement time of W-Lb was set to 10 seconds/point. As shown in fig. 3, in a measurement region S at 101 in the first main surface 1 of the silicon carbide substrate 100, the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) are measured. The area ratio of the region in which the concentration of the metal impurity to be measured is equal to or higher than the reference value is calculated by dividing the number of the measurement regions S by the number of all the measurement regions S (total 101).

(measurement results)

[ Table 1]

Table 1 shows the area ratio of the measurement region S in which the respective concentrations of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) are equal to or higher than the reference values. The reference value was set to 1 × 10¹²Atom/cm²And 5X 10¹⁰Atom/cm²。

As shown in table 1, in the silicon carbide substrate 100 relating to sample 1, each concentration of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) was 5 × 10¹⁰Atom/cm²The area ratios of the above measurement regions S were 7%, 1%, 2%, 1%, 10%, 1%, 88%, and 78%, respectively. On the other hand, in the silicon carbide substrate 100 relating to sample 2, each concentration of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) was 5 × 10¹⁰Atom/cm²The area ratios of the measurement regions S above were 0%, 1%, 0%, 68%, and 62%, respectively.

As shown in table 1, in the silicon carbide substrate 100 relating to sample 1, each concentration of sodium (Na), aluminum (Al), potassium (K), calcium (Ca), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), sulfur (S), and chlorine (Cl) was 1 × 10¹²Atom/cm²The area ratios of the measurement regions S above were 0%, 1%, 0%, 88%, and 78%, respectively. On the other hand, in sample 2And the silicon carbide substrate 100, 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 1X 10¹²Atom/cm²The area ratios of the measurement regions S above were 0%, 68%, and 62%, respectively.

As described above, it was confirmed that the silicon carbide substrate 100 of sample 2 can reduce the area ratio of the region in which the metal impurity to be measured is equal to or greater than the reference value, as compared with the silicon carbide substrate 100 of sample 1.

The embodiments and examples disclosed herein are illustrative in all respects, and are not intended to be limiting. The scope of the present invention is defined not by the above description but by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

Description of the symbols

1 main surface (first main surface), 2 second main surface, 3 first bending region, 4 second bending region, 5 outer peripheral end portion, 6 chamfered portion, 7 oriented flat surface portion, 8 arc portion, 10 center, 12 first cleaning tank, 13 second cleaning tank, 14 first cleaning liquid, 15 second cleaning liquid, 19 ultrasonic wave generation 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 rotary dryer, 31 main body portion, 32 cover, 33 exhaust port, 34 opening portion, 100 silicon carbide substrate, 101 first direction, 102 second direction, S measurement region, W1 first width, W2 second width.