JP6260603B2 - Silicon carbide single crystal substrate, silicon carbide epitaxial substrate, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a silicon carbide single crystal substrate, a silicon carbide epitaxial substrate, and a method for manufacturing the same, and more specifically, a silicon carbide single crystal substrate having a major surface with a maximum diameter of 100 mm or more, a silicon carbide epitaxial substrate, and a method for manufacturing the same. It is about.

  2. Description of the Related Art In recent years, silicon carbide has been increasingly used as a material for semiconductor devices in order to enable higher breakdown voltages, lower losses, and use in high-temperature environments for semiconductor devices such as MOSFETs (Metal Oxide Field Effect Transistors). It is being Silicon carbide is a wide band gap semiconductor having a larger band gap than silicon that has been widely used as a material for forming semiconductor devices. Therefore, by adopting silicon carbide as a material constituting the semiconductor device, it is possible to achieve a high breakdown voltage and a low on-resistance of the semiconductor device. In addition, a semiconductor device that employs silicon carbide as a material has an advantage that a decrease in characteristics when used in a high temperature environment is small as compared with a semiconductor device that employs silicon as a material.

  A silicon carbide substrate used for manufacturing a semiconductor device is formed, for example, by slicing a silicon carbide ingot formed by a sublimation method. Japanese Patent Laying-Open No. 2009-105127 (Patent Document 1) describes a method for manufacturing a silicon carbide wafer. According to the silicon carbide wafer manufacturing method, the surface of the workpiece sliced and cut from the SiC ingot is ground and polished, so that the surface of the workpiece is smoothed into a mirror surface. After smoothing the surface of the workpiece, the back surface of the workpiece is ground.

JP 2009-105127 A

  However, in the silicon carbide substrate manufactured by the method described in Japanese Patent Application Laid-Open No. 2009-105127, the silicon carbide substrate may not be stably held by the vacuum chuck when performing the device process.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a silicon carbide single crystal substrate, a silicon carbide epitaxial substrate, and a method of manufacturing the same, which can reduce vacuum adsorption defects. is there.

  A silicon carbide single crystal substrate according to the present invention includes a first main surface and a second main surface opposite to the first main surface. The maximum diameter of the first main surface is 100 mm or more. The first main surface includes a first central region excluding a region within 3 mm from the outer periphery. When the first central region is divided into first square regions each having a side of 250 μm, the arithmetic mean roughness (Sa) of the first square region is less than 0.2 nm in any of the first square regions. And the oxygen concentration in the first square region is not less than 5 atom% and less than 20 atom%.

  The method for manufacturing a silicon carbide single crystal substrate according to the present invention includes the following steps. By slicing the silicon carbide single crystal, a silicon carbide substrate including a first main surface and a second main surface opposite to the first main surface is prepared. The layer including the work-affected layer formed on the first main surface side of the silicon carbide substrate is removed. After removing the work-affected layer, the first main surface includes a first central region excluding a region within 3 mm from the outer periphery. The oxygen concentration in the first central region is measured. The maximum diameter of the first main surface is 100 mm or more. In the step of removing the layer including the work-affected layer, the layer including the work-affected layer is removed by 1.5 μm or more. In the case where the first central region is divided into first square regions each having a side of 250 μm, the oxygen concentration is 5 atomic percent or more and less than 20 atomic percent in any of the first square regions.

  According to the present invention, it is possible to provide a silicon carbide single crystal substrate, a silicon carbide epitaxial substrate, and a method for manufacturing them, which can reduce vacuum adsorption defects.

It is a cross-sectional schematic diagram which shows schematically the structure of the silicon carbide single crystal substrate 1 which concerns on Embodiment 1 of this invention. 1 is a schematic plan view schematically showing the structure of back surface 1b of silicon carbide single crystal substrate 1 according to Embodiment 1 of the present invention. 1 is a schematic plan view schematically showing a structure of surface 1a of silicon carbide single crystal substrate 1 according to Embodiment 1 of the present invention. It is a cross-sectional schematic diagram which shows roughly the structure of the silicon carbide epitaxial substrate 3 which concerns on Embodiment 2 of this invention. It is a flowchart which shows schematically the manufacturing method of the silicon carbide single crystal substrate 1 which concerns on Embodiment 3 of this invention. It is a cross-sectional schematic diagram which shows schematically the 1st process of the manufacturing method of the silicon carbide single crystal substrate 1 which concerns on Embodiment 3 of this invention. It is a cross-sectional schematic diagram which shows schematically the 2nd process of the manufacturing method of the silicon carbide single crystal substrate 1 which concerns on Embodiment 3 of this invention. FIG. 10 is a schematic cross sectional view schematically showing a third step of the method for manufacturing silicon carbide single crystal substrate 1 according to Embodiment 3 of the present invention. FIG. 11 is a schematic plan view schematically showing a third step of the method for manufacturing silicon carbide single crystal substrate 1 according to Embodiment 3 of the present invention. It is a cross-sectional schematic diagram which shows schematically the manufacturing method of the silicon carbide single crystal substrate 1 which concerns on Embodiment 4 of this invention. It is a cross-sectional schematic diagram for demonstrating the definition of TTV (Total Thickness Variation). It is a figure which shows the relationship between the oxygen concentration of the back surface 1b of the silicon carbide single crystal substrate 1, and the variation | change_quantity of TTV. It is a figure which shows the relationship between the oxygen concentration of the back surface 1b of the silicon carbide single crystal substrate 1, and the arithmetic mean roughness (Sa) of the back surface 1b of the silicon carbide single crystal substrate 1 after epitaxial layer formation. It is a figure which shows the relationship between the arithmetic mean roughness (Sa) of the back surface 1b of the silicon carbide single crystal substrate 1 before epitaxial layer formation, and the variation | change_quantity of TTV. The relation between the arithmetic average roughness (Sa) of the back surface 1b of the silicon carbide single crystal substrate 1 before the formation of the epitaxial layer and the arithmetic average roughness (Sa) of the back surface 1b of the silicon carbide single crystal substrate 1 after the formation of the epitaxial layer. FIG.

[Description of Embodiment of Present Invention]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. In the present specification, the individual orientation is indicated by [], the collective orientation is indicated by <>, the individual plane is indicated by (), and the aggregate plane is indicated by {}. As for the negative index, “−” (bar) is attached on the number in crystallography, but in this specification, a negative sign is attached before the number.

  As a result of intensive studies on the cause of the vacuum suction failure of the substrate, the inventors have obtained the following knowledge and found the present invention.

  Substrate vacuum suction failure may occur due to deformation of the substrate shape. The inventors have noted that the back surface of the substrate is unevenly roughened after the epitaxial layer is formed on the surface of the substrate. One of the causes of uneven roughening of the backside of the substrate is that a partially damaged layer (damaged layer) is formed on the backside of the substrate when slicing the ingot or grinding the substrate. This is considered to be because the work-affected layer undergoes thermal sublimation during the formation of the layer. When the back surface of the substrate is unevenly uneven, stress is generated in the substrate and the substrate is deformed. If the epitaxial layer is formed on the surface of the substrate in a state where the substrate is deformed, the outer peripheral side of the back surface of the substrate is sublimated, and conversely, the epitaxial layer is formed on the outer peripheral side of the back surface of the substrate, thereby further deforming the substrate. Therefore, it is thought that the vacuum suction failure of the substrate occurs. Note that when the maximum diameter of the main surface of the substrate is large (for example, 100 mm or more), the amount of warpage is also large, so that it is likely that defective vacuum suction of the substrate easily occurs.

  Therefore, the inventors perform chemical mechanical polishing on the back surface on which the work-affected layer is formed, and remove the layer including the work-affected layer by 1.5 μm or more, thereby removing the work-affected layer formed on the back surface. It was considered that the back surface of the substrate can be prevented from being roughened when the epitaxial layer is grown, almost completely removed. Further, the inventors pay attention to the fact that the work-affected layer contains a large amount of oxygen, and by measuring the oxygen concentration on the back surface of the substrate, it is possible to evaluate how much the work-affected layer remains on the back surface of the substrate. Thought.

  (1) Silicon carbide single crystal substrate 1 according to the embodiment includes a first main surface 1b and a second main surface 1a opposite to the first main surface 1b. The maximum diameter of the first main surface 1b is 100 mm or more. The first main surface 1b includes a first central region IRb excluding a region ORb within 3 mm from the outer periphery. When the first central region IRb is divided into first square regions 4b each having a side of 250 μm, the arithmetic mean roughness (Sa) of the first square region 4b is 0 in any first square region 4b. The oxygen concentration in the first square region 4b is 5 atomic% or more and less than 20 atomic%.

  According to silicon carbide single crystal substrate 1 according to (1) above, in any first square region 4b, the arithmetic mean roughness (Sa) of first square region 4b is less than 0.2 nm, and The oxygen concentration in the first square region 4b is not less than 5 atom% and less than 20 atom%. Thereby, when growing an epitaxial layer, it can suppress that the 1st main surface 1b of the silicon carbide single crystal substrate 1 becomes rough. As a result, the vacuum adsorption failure of silicon carbide single crystal substrate 1 can be reduced.

  (2) Preferably in silicon carbide single crystal substrate 1 according to (1) above, second main surface 1a includes second central region IRa excluding region ORa within 3 mm from the outer periphery. When the second central region IRa is divided into second square regions 4a each having a side of 250 μm, the arithmetic mean roughness (Sa) of the second square region 4a is 0. Less than 2 nm. Reduction in arithmetic mean roughness (Sa) of both first main surface 1b and second main surface 1a of silicon carbide single crystal substrate 1 reduces warpage of silicon carbide single crystal substrate 1 and TTV. Deterioration can be suppressed.

  (3) Preferably in silicon carbide single crystal substrate 1 according to (1) or (2) above, no mechanical polishing mark is formed on first main surface 1b. Thereby, the roughness of first main surface 1b of silicon carbide single crystal substrate 1 can be further reduced.

  (4) Silicon carbide epitaxial substrate 3 according to the embodiment includes silicon carbide single crystal substrate 1 according to any one of (1) to (3) and silicon carbide epitaxial layer 2. Silicon carbide epitaxial layer 2 is provided on second main surface 1a of silicon carbide single crystal substrate 1. In any first square region 4b, the arithmetic average roughness (Sa) of the first square region 4b is less than 1.5 nm. Thereby, the vacuum suction defect of silicon carbide epitaxial substrate 3 can be reduced. In the case where abnormal growth portions such as particles are present on the back surface 1b of the silicon carbide single crystal substrate 1, “the first square region 4b in any first square region 4b on the back surface 1b of the silicon carbide single crystal substrate 1”. The arithmetic average roughness (Sa) is less than 1.5 nm "means that the arithmetic average roughness (Sa) in any of the first square regions 4b excluding the first square region 4b in which the abnormally grown portion is present. Is less than 1.5 nm. The abnormally grown portion is, for example, a portion whose width along the direction parallel to the back surface 1b is 0.1 μm or more and whose height along the direction perpendicular to the back surface 1b is 1 μm or more. That is.

  (5) The method for manufacturing silicon carbide single crystal substrate 1 according to the embodiment includes the following steps. By slicing the silicon carbide single crystal, silicon carbide substrate 5 including first main surface 1b and second main surface 1a opposite to first main surface 1b is prepared. Layer 6b including work-affected layer 6b1 formed on first main surface 1b side of silicon carbide substrate 5 is removed. After removing the work-affected layer 6b1, the first main surface 1b includes a first central region IRb excluding a region within 3 mm from the outer periphery. The oxygen concentration in the first central region IRb is measured. The maximum diameter of the first main surface 1b is 100 mm or more. In the step of removing the layer 6b including the work-affected layer 6b1, the layer 6b including the work-affected layer 6b1 is removed by 1.5 μm or more. In the case where the first central region IRb is divided into first square regions 4b each having a side of 250 μm, the oxygen concentration is 5 atomic percent or more and less than 20 atomic percent in any of the first square regions 4b. Thereby, when growing an epitaxial layer, it can suppress that the 1st main surface 1b of the silicon carbide single crystal substrate 1 becomes rough. As a result, the vacuum adsorption failure of silicon carbide single crystal substrate 1 can be reduced.

  (6) Preferably in the method for manufacturing silicon carbide single crystal substrate 1 according to (5) above, the arithmetic mean roughness (Sa) of first square region 4b is 0.2 nm in any first square region 4b. Is less than. Reduction in arithmetic mean roughness (Sa) of both first main surface 1b and second main surface 1a of silicon carbide single crystal substrate 1 reduces warpage of silicon carbide single crystal substrate 1 and TTV. Deterioration can be suppressed.

  (7) Preferably, in the method for manufacturing silicon carbide single crystal substrate 1 according to (5) or (6) above, the step of removing layer 6b including work-affected layer 6b1 is performed on the first main surface 1b. A step of performing mechanical mechanical polishing. Thereby, the arithmetic mean roughness (Sa) of the 1st main surface 1b of the silicon carbide single crystal substrate 1 can be reduced effectively.

  (8) Preferably, in the method for manufacturing silicon carbide single crystal substrate 1 according to (7) above, the step of performing chemical mechanical polishing on first main surface 1b is performed at the first polishing rate at the first chemical And a step of performing a second chemical mechanical polishing at a second polishing rate slower than the first polishing rate after the step of performing a mechanical mechanical polishing and the step of performing the first chemical mechanical polishing. When the polishing rate is high, the silicon carbide single crystal substrate 1 can be polished in a shorter time than when the polishing rate is low, but it is difficult to sufficiently reduce the arithmetic average roughness (Sa) after polishing. is there. Therefore, first, a large portion of the work-affected layer is removed in a short time at the first polishing rate, which is a relatively fast polishing rate, and then the silicon carbide single crystal substrate at a second polishing rate that is slower than the first polishing rate. By polishing one first main surface 1b, it is possible to reduce the final arithmetic average roughness (Sa) of the first main surface 1b while shortening the entire polishing time.

  (9) Preferably in the method for manufacturing silicon carbide single crystal substrate 1 according to any of (5) to (8) above, second main surface 1a has a second center excluding a region within 3 mm from the outer periphery. The region IRa is included. When the second central region IRa is divided into second square regions 4a each having a side of 250 μm, the arithmetic mean roughness (Sa) of the second square region 4a is 0. Less than 2 nm. Reduction in arithmetic mean roughness (Sa) of both first main surface 1b and second main surface 1a of silicon carbide single crystal substrate 1 reduces warpage of silicon carbide single crystal substrate 1 and TTV. Deterioration can be suppressed.

  (10) In the method for manufacturing silicon carbide single crystal substrate 1 according to any of (5) to (9) above, preferably, no mechanical polishing mark is formed on first main surface 1b. Thereby, the roughness of first main surface 1b of silicon carbide single crystal substrate 1 can be further reduced.

(11) In the method for manufacturing a silicon carbide epitaxial substrate according to the embodiment, silicon carbide single crystal substrate 1 is prepared by the method for manufacturing silicon carbide single crystal substrate 1 according to any of (5) to (10) above. . Silicon carbide epitaxial layer 2 is formed on second main surface 1a of silicon carbide single crystal substrate 1. After the step of forming silicon carbide epitaxial layer 2, the arithmetic mean roughness (Sa) of first square region 4b is less than 1.5 nm in any first square region 4b. Thereby, the vacuum suction defect of silicon carbide epitaxial substrate 3 can be reduced. In the case where abnormal growth portions such as particles are present on the back surface 1b of the silicon carbide single crystal substrate 1, “the first square region 4b in any first square region 4b on the back surface 1b of the silicon carbide single crystal substrate 1”. The arithmetic average roughness (Sa) is less than 1.5 nm "means that the arithmetic average roughness (Sa) in any of the first square regions 4b excluding the first square region 4b in which the abnormally grown portion is present. Is less than 1.5 nm.
[Details of the embodiment of the present invention]
(Embodiment 1)
First, the structure of the silicon carbide silicon carbide substrate according to the first embodiment of the present invention will be described with reference to FIGS.

  Referring to FIGS. 1 and 2, silicon carbide single crystal substrate 1 according to the first embodiment has a first main surface 1b (back surface 1b) and a second main surface opposite to first main surface 1b. Surface 1a (surface 1a). Surface 1 a is a surface on which an epitaxial layer is to be formed in a semiconductor manufacturing process using silicon carbide single crystal substrate 1. The back surface 1b is a surface on which a back electrode is to be formed, for example, in the case of a vertical semiconductor device. Silicon carbide single crystal substrate 1 is made of a material containing, for example, polytype 4H hexagonal silicon carbide.

  Surface 1a of silicon carbide single crystal substrate 1 may be a {0001} plane or a plane off by about 10 ° or less from the {0001} plane. Specifically, surface 1a of silicon carbide single crystal substrate 1 may be a (0001) plane or a (000-1) plane, or a plane off by about 10 ° or less from (0001) plane or (000− 1) The surface may be off by about 10 ° or less from the surface.

  Maximum diameter D of each of back surface 1b and front surface 1a of silicon carbide single crystal substrate 1 is 100 mm or more, and preferably 150 mm or more. The back surface 1b is composed of a first outer peripheral region ORb within 3 mm from the outer periphery 1b1 toward the center Ob of the back surface 1b, and a first central region IRb surrounded by the first outer peripheral region ORb. In other words, the back surface 1b includes a first outer peripheral region ORb within 3 mm from the outer periphery 1b1 and a first central region IRb excluding the first outer peripheral region ORb within 3 mm from the outer periphery 1b1. The center Ob of the back surface 1b is the center of the circle when the back surface 1b is a circle. When back surface 1b is not a circle, the intersection of back surface 1b with a straight line passing through center of gravity G of silicon carbide single crystal substrate 1 and parallel to the normal of back surface 1b is defined as center Ob of back surface 1b.

  Referring to FIG. 2, a case is assumed in which first central region IRb of back surface 1b is divided into virtual first square regions 4b each having a side of 250 μm. The first central region IRb has good arithmetic average roughness in all regions and exhibits a low oxygen concentration. Specifically, in any first square region 4b, the arithmetic mean roughness (Sa) of the first square region 4b is less than 0.2 nm, and the oxygen concentration in the first square region 4b is 5 At least% and less than 20 atom%. Preferably, in any first square region 4b, the arithmetic mean roughness (Sa) of the first square region 4b is less than 0.15 nm, more preferably less than 0.1 nm. Preferably, in any first square region 4b, the oxygen concentration in the first square region 4b is 5 atomic percent or more and less than 15 atomic percent, and more preferably 5 atomic percent or more and less than 10 atomic percent. The arithmetic average roughness (Sa) is a parameter obtained by extending the two-dimensional arithmetic average roughness (Ra) to three dimensions, and is defined by the following equation.

  The arithmetic average roughness (Sa) can be measured by, for example, a white interference microscope (BW-D507 manufactured by Nikon Corporation). The measurement area of the arithmetic average roughness (Sa) by the white interference microscope is, for example, a square area with a side of 250 μm. The oxygen concentration can be measured by ESCA (Electron Spectroscopy for Chemical Analysis).

  Referring to FIGS. 1 and 3, surface 1a of silicon carbide single crystal substrate 1 is divided into second outer peripheral region ORa within 3 mm from outer periphery 1a1 toward center Oa of surface 1a, and second outer peripheral region ORa. It is comprised by the enclosed 2nd center area | region IRa. In other words, the surface 1a includes a second outer peripheral region ORa within 3 mm from the outer periphery 1a1 and a second central region IRa excluding the second outer peripheral region ORa within 3 mm from the outer periphery 1a1. The center Oa of the surface 1a is the center of the circle when the surface 1a is a circle. When surface 1a is not a circle, the intersection of surface 1a with a straight line passing through center of gravity G of silicon carbide single crystal substrate 1 and parallel to the normal of surface 1a is defined as center Oa of surface 1a. Preferably, no mechanical polishing mark is formed on the back surface 1b.

  Referring to FIG. 3, a case is assumed where second central region IRa of surface 1a is divided into virtual second square region 4a having a side of 250 μm. Preferably, the second central region IRa has a good arithmetic mean roughness in all regions and exhibits a low oxygen concentration. Specifically, in any second square region 4a, the arithmetic mean roughness (Sa) of the second square region 4a is preferably less than 0.2 nm. The oxygen concentration in the second square region 4a is preferably 5 atomic percent or more and less than 20 atomic percent. Preferably, in any second square region 4a, the arithmetic mean roughness (Sa) of the second square region 4a is less than 0.15 nm, more preferably less than 0.1 nm. Preferably, in any second square region 4a, the oxygen concentration in the second square region 4a is 5 atomic percent or more and less than 15 atomic percent, more preferably 5 atomic percent or more and less than 10 atomic percent.

Next, the function and effect of silicon carbide single crystal substrate 1 according to the first embodiment will be described.
According to silicon carbide single crystal substrate 1 according to the first embodiment, arithmetic mean roughness (Sa) of first square region 4b is less than 0.2 nm in any first square region 4b, and The oxygen concentration in the first square region 4b is not less than 5 atom% and less than 20 atom%. Thereby, it is possible to prevent the back surface 1b of the silicon carbide single crystal substrate 1 from being rough when growing the epitaxial layer. As a result, the vacuum adsorption failure of silicon carbide single crystal substrate 1 can be reduced.

  According to silicon carbide single crystal substrate 1 according to the first embodiment, surface 1a includes second central region IRa excluding region ORa within 3 mm from the outer periphery. When the second central region IRa is divided into second square regions 4a each having a side of 250 μm, the arithmetic mean roughness (Sa) of the second square region 4a is 0. Less than 2 nm. By reducing the arithmetic mean roughness (Sa) of both back surface 1b and front surface 1a of silicon carbide single crystal substrate 1, it is possible to suppress the deterioration of warpage and TTV of silicon carbide single crystal substrate 1.

  Furthermore, according to silicon carbide single crystal substrate 1 according to the first embodiment, no mechanical polishing mark is formed on back surface 1b. Thereby, the roughness of back surface 1b of silicon carbide single crystal substrate 1 can be further reduced.

(Embodiment 2)
Next, the structure of the silicon carbide epitaxial substrate according to the second embodiment of the present invention will be described.

  Referring to FIG. 4, silicon carbide epitaxial substrate 3 according to the second embodiment includes silicon carbide single crystal substrate 1 described in the first embodiment and carbonized carbon provided on surface 1 a of silicon carbide single crystal substrate 1. The silicon epitaxial layer 2 is mainly included. Silicon carbide epitaxial layer 2 includes an impurity such as nitrogen and has n type. The impurity concentration of silicon carbide epitaxial layer 2 may be lower than the impurity concentration of silicon carbide single crystal substrate 1. Silicon carbide epitaxial layer 2 has a thickness of, for example, 10 μm.

  When silicon carbide epitaxial layer 2 is formed on surface 1a of silicon carbide single crystal substrate 1, the arithmetic average roughness (Sa) of back surface 1b of silicon carbide single crystal substrate 1 increases. Referring again to FIG. 2, in any first square region 4 b on back surface 1 b of silicon carbide single crystal substrate 1 in a state where silicon carbide epitaxial layer 2 is formed on surface 1 a of silicon carbide single crystal substrate 1. The arithmetic mean roughness (Sa) of the first square region 4b is less than 1.5 nm. Preferably, in any first square region 4b, the arithmetic mean roughness (Sa) of the first square region 4b is less than 1.0 nm, more preferably less than 0.5 nm. When an abnormally grown portion such as particles is present on the back surface 1b of the silicon carbide single crystal substrate 1, the arithmetic mean roughness (Sa) of the first square region 4b is the first square region including the abnormally grown portion. Measured except for 4b.

  According to silicon carbide epitaxial substrate 3 according to the second embodiment, silicon carbide single crystal substrate 1 according to the first embodiment and silicon carbide epitaxial layer 2 are provided. Silicon carbide epitaxial layer 2 is provided on second main surface 1a of silicon carbide single crystal substrate 1. In any first square region 4b, the arithmetic average roughness (Sa) of the first square region 4b is less than 1.5 nm. Thereby, the vacuum suction defect of silicon carbide epitaxial substrate 3 can be reduced.

(Embodiment 3)
Next, a method for manufacturing silicon carbide single crystal substrate 1 according to Embodiment 3 of the present invention will be described.

  First, an ingot made of a silicon carbide single crystal is manufactured by, for example, a sublimation recrystallization method. Specifically, for example, a seed crystal made of a silicon carbide single crystal and a raw material powder made of silicon carbide polycrystal are inserted into a crucible (not shown) made of graphite, for example. Next, the crucible in which the raw material powder is arranged is heated to sublimate the raw material powder to generate a sublimation gas, and the sublimation gas is recrystallized on the seed crystal. During the sublimation of silicon carbide, recrystallization proceeds while impurities such as nitrogen are introduced into the crucible. When the silicon carbide single crystal having a desired size is grown on the seed crystal, heating of the crucible is stopped. A silicon carbide single crystal is taken out from the crucible.

  Next, an ingot forming step (S10: FIG. 5) is performed. Referring to FIG. 6, the silicon carbide single crystal taken out from the crucible is processed into an ingot 10 having a cylindrical shape, for example. By growing hexagonal silicon carbide in the <0001> direction, crystal growth can be advanced while suppressing generation of defects. Therefore, it is preferable to produce the ingot 10 whose longitudinal direction x is the <0001> direction.

  Next, a silicon carbide substrate forming step (S20: FIG. 5) is performed. Specifically, a plurality of silicon carbide substrates are manufactured by cutting ingot 10 obtained in the step (S10). Specifically, referring to FIG. 7, first, a columnar (cylindrical) ingot 10 produced is arranged such that a part of its side surface is supported by a support base 20. Next, while the wire 9 travels in the direction along the diameter direction of the ingot 10 (left and right direction in FIG. 7), the ingot 10 approaches the wire 9 along the cutting direction α that is perpendicular to the travel direction. The wire 9 and the ingot 10 come into contact. As the ingot 10 continues to travel along the cutting direction α, the ingot 10 is cut. As described above, by slicing silicon carbide single crystal ingot 10, silicon carbide including back surface 5b (first main surface 5b) and front surface 5a (second main surface 1a) opposite to back surface 5b is obtained. A substrate 5 (FIG. 8) is prepared. The maximum diameter of each of front surface 5a and back surface 5b of silicon carbide substrate 5 is 100 mm or more.

  Next, a rough polishing step (S30: FIG. 5) is performed. Specifically, each of the back surface 5b and the front surface 5a of the silicon carbide substrate 5 is subjected to grinding, polishing, and the like, and the cut surfaces (that is, the front surface 5a and the back surface 5b) formed in the step (S20). ) Is reduced. In the grinding process, a diamond grindstone is used as a tool, the silicon carbide substrate 5 and the grindstone are rotated to face each other, and a part of the substrate surface is removed by cutting at a constant speed. Thereby, the unevenness of surface 5a and back surface 5b is removed and planarized, and the thickness of silicon carbide substrate 5 is adjusted. In polishing, diamond or the like is used as abrasive grains. As the surface plate, a metal surface plate such as iron, copper, tin, or a tin alloy, a composite surface plate of metal and resin, or an abrasive cloth can be used. By using a hard metal surface plate, the rate can be improved. By using a soft surface plate, the surface roughness can be reduced.

  Referring to FIG. 9, after slicing silicon carbide single crystal ingot 10 in the step (S20), or grinding step for each of surface 5a and back surface 5b of silicon carbide substrate 5 in step (S30), and After the polishing process is performed, work-affected layers 6a1 and 6a2 are formed on front surface 5a and back surface 5b of silicon carbide substrate 5, respectively.

  Next, a chemical mechanical polishing step (S40: FIG. 5) is performed. Specifically, by performing chemical mechanical polishing (CMP) on the back surface 1b of the silicon carbide substrate 5, the layer 6b including the work-affected layer 6b1 is removed. More specifically, the back surface 5b of the silicon carbide substrate 5 is oxidized with an oxidizing agent, and the back surface 5b is mechanically polished using abrasive grains. The CMP abrasive grains are preferably a material softer than silicon carbide in order to reduce the surface roughness and the work-affected layer. For example, colloidal silica or fumed silica is used as CMP abrasive grains. Preferably, an oxidizing agent is added to the CMP polishing liquid. For example, hydrogen peroxide water or the like is used as the oxidizing agent. Similarly, CMP is performed also on surface 5 a of silicon carbide substrate 5. Thereby, each of the layer 6b including the work-affected layer 6b1 formed on the back surface 1b side of the silicon carbide substrate 5 and the layer 6a including the work-affected layer 6a1 formed on the front surface 1a side are removed.

  Although the amount of polishing of the substrate by chemical mechanical polishing is usually about 1 μm, it is difficult to completely remove the work-affected layer 6b1 formed on the back surface 5b side of the silicon carbide substrate 5 with a polishing amount of about 1 μm. It is. Therefore, in the present embodiment, the layer 6 b including the work-affected layer 6 b 1 is removed by 1.5 μm or more on the back surface 1 b side of the silicon carbide substrate 5. Preferably, in the step of removing the layer 6b including the work-affected layer 6b1, the layer 6b including the work-affected layer 6b1 is removed by 2 μm or more, more preferably 3 μm or more. Similarly, the layer 6a including the work-affected layer 6a1 formed on the surface 5a side of the silicon carbide substrate 5 is removed by 1.5 μm or more. Preferably, the removal amount of the layer 6a including the work-affected layer 6a1 formed on the front surface 5a side of the silicon carbide substrate 5 is such that the removal of the layer 6b including the work-affected layer 6b1 formed on the back surface 5b side of the silicon carbide substrate 5 is performed. It is almost the same as the amount. Thereby, since the difference in stress between front surface 5a and back surface 5b of silicon carbide substrate 5 can be reduced, warpage of silicon carbide substrate 5 can be reduced.

  Preferably, the step of performing chemical mechanical polishing on back surface 5b of silicon carbide substrate 5 includes a step of performing first chemical mechanical polishing at a first polishing rate and a step of performing first chemical mechanical polishing. And performing a second chemical mechanical polishing at a second polishing rate that is slower than the first polishing rate. For example, the first chemical mechanical polishing step is first performed on the back surface 5b of the silicon carbide substrate 5 using a relatively large abrasive grain, so that most of the work-affected layer 6b1 is made at a relatively high polishing rate. Removed. Next, a second chemical mechanical polishing step is performed on back surface 5b of silicon carbide substrate 5 using abrasive grains smaller than the abrasive grains used in the first chemical mechanical polishing step. The work-affected layers 6a1 and 6b1 may be removed by a method other than chemical mechanical polishing. The work-affected layers 6a1 and 6b1 may be removed by dry etching, for example.

  Referring to FIG. 2 again, back surface 1b of silicon carbide substrate 5 after work-affected layer 6b1 is removed includes a first central region IRb excluding first outer peripheral region ORb within 3 mm from the outer periphery. Preferably, when the first central region IRb is divided into first square regions 4b each having a side of 250 μm, the arithmetic mean roughness (Sa) of the first square region 4b in any of the first square regions 4b. Is less than 0.2 nm. Preferably, after the work-affected layer 6b1 is removed, no mechanical polishing mark is formed on the back surface 1b of the silicon carbide substrate 5.

  Referring to FIG. 3 again, surface 1a of silicon carbide substrate 5 after work-affected layer 6a1 is removed includes second central region IRa excluding second outer peripheral region ORa within 3 mm from the outer periphery. Preferably, when the second central region IRa is divided into second square regions 4a each having a side of 250 μm, the arithmetic mean roughness (Sa) of the second square region 4a in any second square region 4a. Is less than 0.2 nm. Preferably, the difference between the arithmetic mean roughness (Sa) of the first square region 4b and the arithmetic mean roughness (Sa) of the second square region 4a is less than 0.15 nm, more preferably 0. It is less than 1 nm.

  Next, an oxygen concentration measurement step (S50: FIG. 5) is performed. Specifically, the oxygen concentration at five measurement locations on the back surface 5b of the silicon carbide substrate 5 is measured by ESCA. The oxygen concentration is measured at any four locations in the annular region excluding the region near the center of the back surface 5b of the silicon carbide substrate 5 and the first central region IRb from the center to a distance half the radius. It is a place. The four arbitrary positions are preferably, for example, a position near 0 °, a position near 90 °, a position near 180 °, and a position near 270 ° when viewed from the normal direction of the back surface 5b.

  As described above, the work-affected layer 6b1 contains more oxygen than the region other than the work-affected layer 6b1 in the silicon carbide substrate 5. Therefore, the amount of the work-affected layer 6b1 remaining on the back surface 5b of the silicon carbide substrate 5 can be estimated by measuring the oxygen concentration on the back surface 5b of the silicon carbide substrate 5. As a result of the oxygen concentration measurement, when it is found that the work-affected layer 6b1 remains more than the reference value, additional CMP may be performed on the back surface 5b of the silicon carbide substrate 5. When the first central region IRb after the step of removing the work-affected layer 6b1 is divided into first square regions 4b each having a side of 250 μm, the oxygen concentration is 5 atomic% or more in any of the first square regions 4b. Less than 20 atomic percent. Even when the work-affected layer 6b1 is completely removed, a natural oxide film is formed on the back surface 5b of the silicon carbide substrate 5, so the oxygen concentration on the back surface is considered not to be less than 5 atomic%.

  Next, a step of cleaning silicon carbide substrate 5 with hydrofluoric acid is performed. Specifically, for example, by immersing silicon carbide substrate 5 in a 10% hydrofluoric acid solution, the silicon dioxide film formed on each of front surface 5a and back surface 5b of silicon carbide substrate 5 is removed. Thus, silicon carbide single crystal substrate 1 described in the first embodiment is completed.

  Next, functions and effects of the method for manufacturing silicon carbide single crystal substrate 1 according to Embodiment 3 will be described.

  According to the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment, in the step of removing layer 6b including work-affected layer 6b1, layer 6b including work-affected layer 6b1 is removed by 1.5 μm or more. In the case where the first central region IRb is divided into first square regions 4b each having a side of 250 μm, the oxygen concentration is 5 atomic percent or more and less than 20 atomic percent in any of the first square regions 4b. Thereby, it is possible to prevent the back surface 1b of the silicon carbide single crystal substrate 1 from being rough when growing the epitaxial layer. As a result, the vacuum adsorption failure of silicon carbide single crystal substrate 1 can be reduced.

  In addition, according to the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment, the arithmetic mean roughness (Sa) of first square region 4b is less than 0.2 nm in any first square region 4b. is there. By reducing the arithmetic mean roughness (Sa) of both back surface 1b and front surface 1a of silicon carbide single crystal substrate 1, it is possible to suppress the deterioration of warpage and TTV of silicon carbide single crystal substrate 1.

  Furthermore, according to the method for manufacturing silicon carbide single crystal substrate 1 according to Embodiment 3, the step of removing layer 6b including work-affected layer 6b1 includes a step of performing chemical mechanical polishing on back surface 1b. Thereby, the arithmetic average roughness (Sa) of back surface 1b of silicon carbide single crystal substrate 1 can be effectively reduced.

  Furthermore, according to the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment, the step of performing chemical mechanical polishing on first main surface 1b includes the first chemical machine at the first polishing rate. After the step of performing the polishing and the step of performing the first chemical mechanical polishing, the method includes the step of performing the second chemical mechanical polishing at a second polishing rate slower than the first polishing rate. When the polishing rate is high, the silicon carbide single crystal substrate 1 can be polished in a shorter time than when the polishing rate is low, but it is difficult to sufficiently reduce the arithmetic average roughness (Sa) after polishing. is there. Therefore, first, a large portion of the work-affected layer is removed in a short time at the first polishing rate, which is a relatively fast polishing rate, and then the silicon carbide single crystal substrate at a second polishing rate that is slower than the first polishing rate. By polishing the back surface 1b of 1, the arithmetic average roughness (Sa) of the final back surface 1b can be reduced while shortening the entire polishing time.

  Furthermore, according to the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment, surface 1a includes second central region IRa excluding a region within 3 mm from the outer periphery. When the second central region IRa is divided into second square regions 4a each having a side of 250 μm, the arithmetic mean roughness (Sa) of the second square region 4a is 0. Less than 2 nm. By reducing the arithmetic mean roughness (Sa) of both back surface 1b and front surface 1a of silicon carbide single crystal substrate 1, it is possible to suppress the deterioration of warpage and TTV of silicon carbide single crystal substrate 1.

  Furthermore, according to the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment, no mechanical polishing mark is formed on back surface 1b. Thereby, the roughness of back surface 1b of silicon carbide single crystal substrate 1 can be further reduced.

(Embodiment 4)
Next, a method for manufacturing silicon carbide epitaxial substrate 3 will be described.

  First, silicon carbide single crystal substrate 1 is prepared by the method described in the third embodiment. Next, referring to FIG. 10, silicon carbide single crystal substrate 1 is arranged in a recess formed in susceptor 30. Silicon carbide single crystal substrate 1 is arranged such that back surface 1b of silicon carbide single crystal substrate 1 is in contact with the bottom of the recess of susceptor 30, and surface 1a of silicon carbide single crystal substrate 1 is exposed from the side of susceptor 30. Be placed. Silicon carbide single crystal substrate 1 is arranged on susceptor 30 such that the side surface of silicon carbide single crystal substrate 1 faces the side of a recess formed in susceptor 30.

Next, silicon carbide epitaxial layer 2 is formed on surface 1 a of silicon carbide single crystal substrate 1. For example, a carrier gas containing hydrogen (H ₂ ) and a source gas containing monosilane (SiH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), etc. are on surface 1 a of silicon carbide single crystal substrate 1. Introduced against. Silicon carbide epitaxial layer 2 is formed, for example, under conditions where the growth temperature is 1500 ° C. or higher and 1700 ° C. or lower and the pressure is 6 × 10 ³ Pa or higher and 14 × 10 ³ Pa or lower. The dopant concentration in silicon carbide epitaxial layer 2 is, for example, about 5.0 × 10 ¹⁵ cm ⁻³ . Silicon carbide epitaxial layer 2 has a thickness of, for example, about 10 μm.

  By forming silicon carbide epitaxial layer 2 on surface 1a of silicon carbide single crystal substrate 1, back surface 1b of silicon carbide single crystal substrate 1 becomes rougher than before silicon carbide epitaxial layer 2 is formed. . After the step of forming silicon carbide epitaxial layer 2, the arithmetic mean roughness (Sa) of first square region 4b is less than 1.5 nm in any first square region 4b. When an abnormally grown portion such as particles is present on the back surface 1b of the silicon carbide single crystal substrate 1, the arithmetic mean roughness (Sa) of the first square region 4b is the first square region including the abnormally grown portion. Measured except for 4b. Thus, silicon carbide epitaxial layer 2 is manufactured.

  According to the method for manufacturing a silicon carbide epitaxial substrate according to the fourth embodiment, silicon carbide single crystal substrate 1 is prepared by the method for manufacturing silicon carbide single crystal substrate 1 according to the third embodiment. Silicon carbide epitaxial layer 2 is formed on surface 1 a of silicon carbide single crystal substrate 1. After the step of forming silicon carbide epitaxial layer 2, the arithmetic mean roughness (Sa) of first square region 4b is less than 1.5 nm in any first square region 4b. Thereby, the vacuum suction defect of silicon carbide epitaxial substrate 3 can be reduced.

1. Sample Preparation First, silicon carbide single crystal substrate 1 according to samples 1 to 6 was produced. Samples 1 to 5 are examples, and sample 6 is a comparative example. Silicon carbide single crystal substrate 1 according to samples 1 to 6 was manufactured by the method described in the third embodiment except for the following points. Six silicon carbide substrates 5 were prepared by slicing a silicon carbide ingot. CMP was performed on the back surface 5 b of each silicon carbide substrate 5. The polishing amount of the back surface 5b of each silicon carbide substrate 5 is 3.2 μm (sample 1), 3 μm (sample 2), 2.6 μm (sample 3), 1.9 μm (sample 4), and 1.6 μm (sample 5). ) And 0.9 μm (Sample 6). For silicon carbide substrates 5 to be samples 1 to 5, silicon carbide substrate 5 was cleaned with hydrofluoric acid after CMP. The silicon carbide substrate 5 serving as the sample 6 was not cleaned with hydrofluoric acid after CMP. Thus, silicon carbide single crystal substrate 1 according to samples 1 to 6 was prepared. Next, silicon carbide epitaxial layer 2 was formed on surface 1 a of silicon carbide single crystal substrate 1 according to Samples 1 to 6.

2. Measurement First, the arithmetic average roughness (Sa) and oxygen concentration of the back surface 1b of the silicon carbide single crystal substrate 1 according to Samples 1 to 6 were measured. Further, the TTV of the silicon carbide single crystal substrate 1 was measured. Referring to FIG. 11, TTV refers to the other side from the reference surface when one main surface (for example, back surface 1b) of silicon carbide single crystal substrate 1 is pressed against flat reference surface 40a of base 40 serving as a reference. This is a value obtained by subtracting the distance to the minimum height from the distance to the maximum height of the main surface (for example, the surface 1a). Next, after silicon carbide epitaxial layer 2 was formed on surface 1a of silicon carbide single crystal substrate 1, arithmetic average roughness of back surface 1b of silicon carbide single crystal substrate 1 and TTV of silicon carbide epitaxial substrate 3 were measured. A value obtained by subtracting the TTV of the silicon carbide single crystal substrate 1 from the TTV of the silicon carbide epitaxial substrate 3 after the formation of the silicon carbide epitaxial layer 2 was defined as the amount of change in TTV. The arithmetic average roughness of the back surface 1b was measured using a white interference microscope (BW-D507 manufactured by Nikon Corporation). TTV was measured using a FlatMaster (registered trademark) manufactured by Tpopel.

  The arithmetic mean roughness (Sa) and oxygen concentration are measured at the center of the first central region IRb excluding the vicinity of the center of the back surface 5b of the silicon carbide substrate 5 and the region within 3 mm from the outer periphery of the back surface 5b. Measured at a total of 5 locations including 4 locations in the annular region excluding the region from the distance to half the radius. The four annular regions are, for example, a position near 0 °, a position near 90 °, a position near 180 °, and a position near 270 ° when viewed from the normal direction of the back surface 5b. The arithmetic average roughness (Sa) and the average value of the oxygen concentration at the five locations were calculated. The measurement area of arithmetic average roughness (Sa) was a square area with a side of 250 μm. Ideally, the arithmetic average roughness (Sa) and the oxygen concentration are measured in all the first square areas 4b, and the arithmetic average of the first square areas 4b is measured in any first square area 4b. Although it is desirable to confirm that the roughness (Sa) is 0.2 nm or less and the oxygen concentration is 5 atomic% or more and less than 20 atomic%, it takes too much time and is not realistic. Therefore, in the present specification, when the maximum arithmetic average roughness (Sa) is 0.2 nm and the maximum oxygen concentration is 5 atomic% or more and less than 20 atomic% as a result of the measurement at the five locations, It is estimated that the arithmetic mean roughness (Sa) in all the first square regions 4b is 0.2 nm and the oxygen concentration is 5 atomic% or more and less than 20 atomic%. The same applies to the arithmetic average roughness (Sa) and the oxygen concentration in the second square region 4a.

  3. result

  Referring to Table 1 and FIGS. 12 to 15, the oxygen atom concentration on back surface 1 b of silicon carbide single crystal substrate 1, the arithmetic mean roughness (Sa) of back surface 1 b of silicon carbide single crystal substrate 1 before formation of epitaxial layer 2. The arithmetic average roughness (Sa) of back surface 1b of silicon carbide single crystal substrate 1 after formation of epitaxial layer 2 and the amount of change in TTV before and after formation of epitaxial layer 2 will be described.

  Referring to FIG. 12, it can be seen that the oxygen atom concentration on back surface 1b of silicon carbide single crystal substrate 1 has a strong correlation with the amount of change in TTV. Specifically, when the oxygen atom concentration on back surface 1b of silicon carbide single crystal substrate 1 increases, the amount of change in TTV increases. That is, if the amount of the work-affected layer 6b1 remaining on the back surface 1b of the silicon carbide single crystal substrate 1 is large, it is considered that the amount of change in TTV increases.

  Referring to FIG. 13, the oxygen atom concentration on back surface 1b of silicon carbide single crystal substrate 1 has a strong correlation with the arithmetic average roughness (Sa) of back surface 1b of silicon carbide single crystal substrate 1 after formation of epitaxial layer 2. I understand that. Specifically, when the oxygen atom concentration on back surface 1b of silicon carbide single crystal substrate 1 increases, the arithmetic average roughness (Sa) of back surface 1b of silicon carbide single crystal substrate 1 after formation of epitaxial layer 2 increases. That is, if the amount of the work-affected layer 6b1 remaining on the back surface 1b of the silicon carbide single crystal substrate 1 is large, the arithmetic average roughness (Sa) of the back surface 1b of the silicon carbide single crystal substrate 1 after the formation of the epitaxial layer 2 is large. It is considered to be.

Referring to FIG. 14 and Table 1, when the arithmetic average roughness (Sa) before the formation of the epitaxial layer 2 is 0.22 nm (sample 6), the change amount of TTV is 14 μm, which is the most among the six samples. A large value was shown. On the other hand, when the arithmetic average roughness (Sa) before the formation of the epitaxial layer 2 is about 0.08 nm to 0.09 nm (samples 1 to 5), the amount of change in TTV is about 3 μm to 9 μm. .

Referring to FIG. 15 and Table 1, when the arithmetic average roughness (Sa) before the formation of the epitaxial layer 2 is 0.22 nm (sample 6), the arithmetic average roughness (Sa) after the formation of the epitaxial layer 2 is 1. 7 nm, which is the largest value among the six samples. On the other hand, when the arithmetic average roughness (Sa) before the formation of the epitaxial layer 2 is about 0.08 nm to 0.09 nm (samples 1 to 5), the arithmetic average roughness (Sa) after the formation of the epitaxial layer 2 is The thickness was about 0.14 nm to 0.9 nm.

  From the above results, the silicon carbide single crystal substrate 1 (samples 1 to 5) manufactured by cleaning the back surface 5b of the silicon carbide substrate 5 to 1.6 μm or more and cleaning the silicon carbide substrate 5 with hydrofluoric acid was polished. The oxygen atom concentration is smaller than that of the silicon carbide single crystal substrate 1 (sample 6) produced by washing the silicon carbide substrate 5 with hydrofluoric acid, and the arithmetic average roughness (Sa) of the back surface is 0.9 μm. It was confirmed to be small. Further, the arithmetic average roughness (Sa) of back surface 1b of silicon carbide epitaxial substrate 3 according to samples 1 to 5 is smaller than the arithmetic average roughness (Sa) of back surface 1b of silicon carbide epitaxial substrate 3 according to sample 6. confirmed. Furthermore, it was confirmed that the amount of change in TTV according to samples 1 to 5 was smaller than the amount of change in TTV according to sample 6.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Silicon carbide single crystal substrates 1a1, 1b1 Outer peripheries 1a, 5a Surface (second main surface)
1b, 5b Back surface (first main surface)
2 Silicon carbide epitaxial layer 3 Silicon carbide epitaxial substrate 4a Second square region 4b First square region 5 Silicon carbide substrate 6a, 6b Layers 6a1, 6b1 Work-affected layer 9 Wire 10 Ingot 20 Support base 30 Susceptor 40 Base 40a Reference plane G center of gravity IRa second central region IRb first central region ORa second outer peripheral region ORb first outer peripheral region Oa, Ob center x longitudinal direction

Claims (11)

A silicon carbide single crystal substrate comprising a first main surface that is a back surface and a second main surface that is a surface opposite to the first main surface,
The maximum diameter of the first main surface is 150 mm or more;
The first main surface includes a first central region excluding a region within 3 mm from the outer periphery,
In the case where the first central region is divided into first square regions each having a side of 250 μm, the arithmetic mean roughness (Sa) of the first square region is 0. 0 in any of the first square regions. A silicon carbide single crystal substrate which is less than 2 nm and has an oxygen concentration in the first square region of 5 atomic% or more and less than 20 atomic%. The second main surface includes a second central region excluding a region within 3 mm from the outer periphery,
When the second central region is divided into second square regions each having a side of 250 μm, the arithmetic average roughness (Sa) of the second square region is 0.2 nm in any of the second square regions. The silicon carbide single crystal substrate according to claim 1, wherein   The silicon carbide single crystal substrate according to claim 1, wherein no mechanical polishing mark is formed on the first main surface. A silicon carbide single crystal substrate according to any one of claims 1 to 3,
A silicon carbide epitaxial layer provided on the second main surface of the silicon carbide single crystal substrate,
The silicon carbide epitaxial substrate in which the arithmetic mean roughness (Sa) of the first square region is less than 1.5 nm in any of the first square regions. Preparing a silicon carbide substrate including a first main surface that is a back surface and a second main surface that is a surface opposite to the first main surface by slicing a silicon carbide single crystal;
Removing a layer including a work-affected layer formed on the first main surface side of the silicon carbide substrate,
After removing the work-affected layer, the first main surface includes a first central region excluding a region within 3 mm from the outer periphery, and
Measuring the oxygen concentration of the first central region,
The maximum diameter of the first main surface is 150 mm or more;
In the step of removing the layer containing the work-affected layer, the layer containing the work-affected layer is removed by 1.5 μm or more,
In the case where the first central region is divided into first square regions each having a side of 250 μm, the oxygen concentration is 5 atomic% or more and less than 20 atomic percent in any of the first square regions. A method for manufacturing a substrate.   6. The method for manufacturing a silicon carbide single crystal substrate according to claim 5, wherein the arithmetic mean roughness (Sa) of the first square region is less than 0.2 nm in any of the first square regions.   The method for manufacturing a silicon carbide single crystal substrate according to claim 5 or 6, wherein the step of removing the layer including the work-affected layer includes a step of performing chemical mechanical polishing on the first main surface. . The step of performing chemical mechanical polishing on the first main surface includes the step of performing first chemical mechanical polishing at a first polishing rate;
The carbonization according to claim 7, further comprising a step of performing a second chemical mechanical polishing at a second polishing rate slower than the first polishing rate after the step of performing the first chemical mechanical polishing. A method for producing a silicon single crystal substrate. The second main surface includes a second central region excluding a region within 3 mm from the outer periphery,
When the second central region is divided into second square regions each having a side of 250 μm, the arithmetic average roughness (Sa) of the second square region is 0.2 nm in any of the second square regions. The method for producing a silicon carbide single crystal substrate according to any one of claims 5 to 8, which is less than 10.   The method for manufacturing a silicon carbide single crystal substrate according to any one of claims 5 to 9, wherein mechanical polishing marks are not formed on the first main surface. Preparing a silicon carbide single crystal substrate by the method for manufacturing a silicon carbide single crystal substrate according to any one of claims 5 to 10, and
Forming a silicon carbide epitaxial layer on the second main surface of the silicon carbide single crystal substrate,
After the step of forming the silicon carbide epitaxial layer, the arithmetic average roughness (Sa) of the first square region is less than 1.5 nm in any of the first square regions. Method.

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