Manufacturing method for SiC polycrystalline substrate

Abstract

To provide a SiC polycrystalline substrate which can smoothen a Sic polycrystalline substrate surface roughness (arithmetic average height Sa value regulated by ISO 25178) to 0.3 nm order.SOLUTION: A SiC polycrystalline substrate manufacturing method has a double side wrapping process, a grinding process, and a polishing process. The polishing process comprises: a first process in which slurry containing diamond abrasive grains with an average grain diameter of 0.2 μm to 0.5 μm is dropped onto a resin pad with a Shore D hardness of 80 HSD or more, and mechanical polishing is performed until a surface roughness (Sa value) measured by a fringe scan method becomes 0.3 nm order (0.3nm≤Sa<0.4nm); and a second process in which chemical polishing is performed by a resin or a cloth pad using a colloidal silica aqueous polishing liquid adjusted to pH 7 to 8, and a processing time is seto a time for maintaining the surface roughness (Sa value) formed in the first process.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a manufacturing method for a SiC polycrystalline substrate, which includes a double-sided lapping step of roughly polishing both sides of a SiC polycrystalline substrate, a grinding step of surface grinding the SiC polycrystalline substrate, and a polishing step of smoothing one side of the SiC polycrystalline substrate, and in particular to an improvement to the manufacturing method capable of smoothing the surface roughness of a SiC polycrystalline substrate (surface roughness indicated by the arithmetic mean height Sa value defined in ISO 25178) to the order of 0.3 nm (0.3 nm≦Sa<0.4 nm). [Background technology]

[0002] Silicon carbide (SiC) has a band gap three times larger than silicon (Si) (4H-SiC: 3.8 eV, 6H-SiC: 3.1 eV, silicon: 1.1 eV) and a high thermal conductivity (5 W / cm K, silicon: 1.5 W / cm K). In recent years, SiC single crystals have begun to be used as a substrate material for power devices. For example, compared to conventional Si power devices, SiC power devices have achieved a withstand voltage 5 to 10 times larger and an operating temperature several hundred degrees higher. Furthermore, they can reduce the power loss of the element to about one-tenth, so they have been put to practical use in inverters for railway vehicles, etc.

[0003] SiC single crystals as substrate materials are usually produced by a gas phase method called sublimation recrystallization method (modified Lely process) (see, for example, Non-Patent Document 1), and are processed to the desired diameter and thickness.

[0004] The modified Lely process is a method for growing bulk SiC single crystals by heating and subliming solid SiC raw material (usually powder) at high temperatures (over 2,400°C). The sublimated Si atoms and carbon atoms are transported by diffusion through an inert gas atmosphere as vapor at 2,400°C, and become supersaturated on a seed crystal placed at a lower temperature than the raw material, causing it to recrystallize.

[0005] However, because the process temperature in this modified Lely process is very high at over 2,400°C, it is extremely difficult to control the temperature and convection during crystal growth, and to control crystal defects, and the SiC single crystal substrates produced by this method have numerous crystal defects called micropipes and other crystal defects (stacking faults, etc.), making it extremely difficult to manufacture high-quality SiC single crystal substrates that can withstand electronic device use with a high yield. As a result, high-quality SiC single crystal substrates with few crystal defects that can be used for electronic devices are very expensive, and devices using such SiC single crystal substrates are also expensive, which has hindered the widespread use of SiC single crystal substrates.

[0006] In view of this, in recent years, a method has been proposed for producing a SiC substrate in which a SiC single crystal thin plate layer is formed on a SiC polycrystalline substrate by preparing a SiC single crystal substrate and a SiC polycrystalline substrate, performing a step of bonding the SiC single crystal substrate and the SiC polycrystalline substrate together, and then performing a step of thinning the SiC single crystal substrate (see, for example, Non-Patent Document 2).

[0007] According to this manufacturing method of SiC substrate, the thickness of the SiC single crystal substrate can be reduced to several times or several hundred times less than that of the conventional method, so the cost of the SiC substrate can be significantly reduced compared to the conventional method in which the entire substrate is made of expensive and high-quality SiC single crystal. In addition, since it is possible to form elements such as power devices on a high-quality SiC single crystal layer with few crystal defects, it is possible to significantly improve device performance and manufacturing yield.

[0008] In the process of bonding such a SiC single crystal substrate and a SiC polycrystalline substrate, the SiC polycrystalline substrate is required to be dense and highly pure, and to have a high surface smoothness with a surface roughness (arithmetic mean height Sa value defined in ISO 25178) of the order of about 0.3 nm. For this reason, a chemical vapor deposition method (hereinafter sometimes referred to as a CVD method) is used to manufacture the SiC polycrystalline substrate, and a method for manufacturing a SiC polycrystalline substrate using the CVD method is described in Patent Documents 1 and 2.

[0009] Non-Patent Document 3 describes a manufacturing method for a SiC single crystal substrate, which can smooth the surface roughness (Sa value) of the SiC single crystal substrate to about 0.1 nm order (0.1 nm≦Sa<0.2 nm). That is, this manufacturing method for SiC single crystal substrates comprises a double-sided lapping process in which both sides of the SiC single crystal substrate are roughly polished using B4C abrasive grains with a grain size of 40 μm, a rough grinding process in which the SiC single crystal substrate is surface-ground using a grinding wheel having diamond abrasive grains of No. 4000 (ISO 8486 designation), a precision grinding process in which the SiC single crystal substrate is surface-ground using a grinding wheel having diamond abrasive grains of No. 8000 (ISO 8486 designation), and a chemical mechanical polishing (CMP) process in which one side of the ground SiC single crystal substrate is smoothed using catalytic reaction type colloidal silica, and it is said that this method can produce a SiC single crystal substrate with a highly flat and smooth surface [surface roughness (Sa value) of the order of 0.1 nm]. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 8-026714 [Patent Document 2] Japanese Patent Application Publication No. 8-188408 [Non-patent literature]

[0011] [Non-Patent Document 1] Yu.M.Tairov and VFTsvetkov: J.of Cryst.Growth 43(1978)209 [Non-Patent Document 2] Journal of the Japan Society for Precision Engineering, 2017, Vol. 83, No. 9, pp. 833-836 [Non-Patent Document 3] DENSO Technical Review, Vol. 20 2015, p. 222-228. Summary of the Invention [Problem to be solved by the invention]

[0012] However, when the method of Non-Patent Document 3 described above, which can smooth the surface roughness (Sa value) of a SiC single crystal substrate to the order of 0.1 nm (0.1 nm≦Sa<0.2 nm), is applied to a manufacturing method of a SiC polycrystalline substrate, there is a problem that the surface roughness (Sa value) of the SiC polycrystalline substrate cannot be smoothed to the order of 0.3 nm (0.3 nm≦Sa<0.4 nm) for the following reasons.

[0013] First, even if dense and high-purity polycrystalline SiC is manufactured by the CVD method described in Patent Documents 1 and 2, the growth orientation of the polycrystalline grains is not constant. Furthermore, silicon carbide (SiC) is a compound composed of two elements, silicon (Si) atoms and carbon (C) atoms, which have significantly different atomic radii, and it is known that carbon is more easily oxidized than silicon. Therefore, during the chemical mechanical polishing (CMP) process for smoothing the SiC polycrystalline substrate, the chemical etching rate of each polycrystalline grain is slightly different, resulting in differences in the processing rate for each polycrystalline grain, and as a result, minute irregularities (grain boundary steps) are generated along the grain boundaries of the polycrystalline grains.

[0014] For the above reasons, even if the method of Non-Patent Document 3 is applied to a manufacturing method of a SiC polycrystalline substrate, it is not possible to smooth the surface roughness (Sa value) of the entire SiC polycrystalline substrate to the order of 0.3 nm, and there is a problem that it is costly to smooth the surface roughness (Sa value) to the order of 0.3 nm by repeated polishing.

[0015] The present invention has been made with attention to these problems, and an object of the present invention is to provide a method for manufacturing a SiC single crystal substrate that can smooth the surface roughness (Sa value) of the entire SiC polycrystalline substrate to the order of 0.3 nm. [Means for solving the problem]

[0016] The present inventors have carried out the following technical studies in order to solve the above problems.

[0017] First, silicon carbide (SiC) is a material that is said to be the third hardest material after diamond and boron carbide, and the bond between silicon atoms and carbon atoms is extremely strong, but some of the bonds are broken on the crystal surface. Therefore, when catalytic reaction type colloidal silica is applied to a SiC polycrystalline substrate and chemical mechanical polishing (CMP) described in Non-Patent Document 3 is performed, the carbon atoms whose bonds are broken are preferentially chemically bonded with oxygen atoms and vaporized and desorbed. It is considered that the reaction in which the remaining silicon atoms are dissolved in the colloidal silica and desorbed occurs repeatedly on the surface of the SiC polycrystal. Therefore, if silicon atoms and carbon atoms, which have different processes of desorption from the SiC polycrystal, can be desorbed at similar speeds, it is considered that the above-mentioned minute irregularities (grain boundary steps) are unlikely to occur even if the growth orientation of the polycrystalline grains is different.

[0018] However, even with various measures, the rate at which silicon atoms are desorbed cannot keep up with the rate at which carbon atoms are desorbed. For this reason, it is necessary to minimize the processing time of chemical mechanical polishing (CMP) and to suppress the occurrence of grain boundary steps due to differences in polishing speed.

[0019] It was found that a good method to reduce the processing time of chemical mechanical polishing (CMP) is to add a mechanical polishing process before the chemical mechanical polishing (CMP) process, smooth the surface roughness (Sa value) of the SiC polycrystalline substrate to about 0.3 nm order by this mechanical polishing, and then perform chemical mechanical polishing (CMP) under appropriate polishing conditions. However, it was confirmed that if the Shore D hardness of the resin pad used in mechanical polishing is less than 80HSD, the surface roughness (Sa value) of the SiC polycrystalline substrate cannot be processed to 0.5 nm or less by mechanical polishing, and it was found that in order to smooth the above surface roughness (Sa value) to about 0.3 nm order, it is necessary to use a resin pad with a Shore D hardness of 80HSD or more and a diamond slurry containing diamond abrasive grains with an average particle size of 0.2μm to 0.5μm.

[0020] Based on the above findings, the inventor dropped a diamond slurry containing diamond abrasive grains with an average particle size of 0.2 μm to 0.5 μm onto a resin pad with a Shore D hardness of 80 HSD or more, performed mechanical polishing until the surface roughness (Sa value) measured by the fringe scan method was about 0.3 nm order, and further performed chemical mechanical polishing (CMP) using a resin or cloth pad with a colloidal silica aqueous polishing liquid adjusted to pH 7 to 8 for a short period of time [treatment time during which the surface roughness (Sa value) of about 0.3 nm order formed by mechanical polishing is maintained], and discovered that the surface roughness of the SiC polycrystalline substrate (surface roughness indicated by the arithmetic mean height Sa value specified in ISO 25178) was smoothed to about 0.3 nm order (0.3 nm≦Sa<0.4 nm). The present invention was completed based on such technical findings.

[0021] That is, the first invention according to the present invention is: A method for manufacturing a SiC polycrystalline substrate, comprising: a double-sided lapping step of roughly polishing both sides of a SiC polycrystalline substrate obtained by slicing SiC polycrystalline; a grinding step of surface-grinding the lapped SiC polycrystalline substrate; and a polishing step of smoothing one side of the ground SiC polycrystalline substrate, The polishing step is A first polishing process involves dropping a diamond slurry containing diamond abrasive grains with an average particle size of 0.2 μm to 0.5 μm onto a resin pad with a Shore D hardness of 80 HSD or more, and mechanically polishing the surface until the surface roughness (arithmetic mean height Sa value specified in ISO 25178) measured by the fringe scan method is on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm); a second polishing step in which chemical mechanical polishing is performed with a resin or cloth pad using a colloidal silica aqueous polishing liquid adjusted to pH 7 to 8, and the processing time is set to a time for maintaining the surface roughness (Sa value) formed in the first polishing step; The present invention is characterized in that it is composed of:

[0022] The second aspect of the present invention is In the method for producing a SiC polycrystalline substrate according to the first aspect of the present invention, In the second polishing step, the upper limit of the time for maintaining the surface roughness (Sa value) is 30 minutes; The third invention is In the method for producing a SiC polycrystalline substrate according to the first aspect of the present invention, The method is characterized in that in the first polishing step, the dropping speed of the diamond slurry is 8 mL / min or more.

[0023] Next, the fourth aspect of the present invention is In the method for producing a SiC polycrystalline substrate according to any one of the first to third aspects of the present invention, The double-sided lapping process is characterized by the use of B4C abrasive grains of 100 to 300 (ISO 8486 designation), The fifth invention is In the method for producing a SiC polycrystalline substrate according to any one of the first to fourth aspects of the present invention, The grinding process is characterized in that it is a precision grinding process using a grinding wheel having diamond abrasive grains of 6000 to 8000 (ISO 8486), The sixth invention is, In the method for producing a SiC polycrystalline substrate according to any one of the first to fourth aspects of the present invention, The grinding process is characterized by being comprised of a rough grinding process using a grinding wheel having diamond abrasive grains of No. 600 to No. 2000 (ISO 8486 designation) and a precision grinding process using a grinding wheel having diamond abrasive grains of No. 6000 to No. 8000 (ISO 8486 designation). Effect of the Invention

[0024] According to the method for producing a SiC polycrystalline substrate of the present invention, In the first polishing process prior to chemical mechanical polishing, mechanical polishing is performed until the surface roughness (Sa value) measured by the fringe scan method is on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm), which reduces the processing time of the chemical mechanical polishing in the second polishing process.

[0025] This suppresses the occurrence of grain boundary differences caused by differences in processing speed (polishing speed) between individual polycrystalline grains, and has the effect of smoothing the surface roughness (Sa value) of the entire SiC polycrystalline substrate to the order of 0.3 nm. [Brief description of the drawings]

[0026] [Figure 1] This is a graph showing the relationship between the average particle size (μm) of diamond abrasive grains in mechanical polishing, in which a diamond slurry containing diamond abrasive grains is dropped onto a resin pad with a Shore D hardness of 80HSD, and the surface roughness Sa (nm) of the entire SiC polycrystalline substrate (periphery, center, and intermediate parts of the substrate) after chemical mechanical polishing. [Diagram 2] This is a graph showing the relationship between the average particle size (μm) of diamond abrasive grains in mechanical polishing in which a resin pad with a Shore D hardness of less than 80HSD (Shore D hardness of 75HSD) is used to drop a diamond slurry containing diamond abrasive grains and polish the substrate, and the surface roughness Sa (nm) of a SiC polycrystalline substrate after mechanical polishing. [Diagram 3] 3(A) and (B) are explanatory diagrams of the configuration of a wrapping device used in the double-sided wrapping process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present invention will be described in detail.

[0028] The method for producing a SiC polycrystalline substrate according to the present invention includes the steps of: A method for manufacturing a SiC polycrystalline substrate, comprising: a double-sided lapping step of roughly polishing both sides of a SiC polycrystalline substrate obtained by slicing SiC polycrystalline; a grinding step of surface-grinding the lapped SiC polycrystalline substrate; and a polishing step of smoothing one side of the ground SiC polycrystalline substrate, The polishing step is A first polishing process involves dropping a diamond slurry containing diamond abrasive grains with an average particle size of 0.2 μm to 0.5 μm onto a resin pad with a Shore D hardness of 80 HSD or more, and mechanically polishing the surface until the surface roughness (arithmetic mean height Sa value specified in ISO 25178) measured by the fringe scan method is on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm); a second polishing step in which chemical mechanical polishing is performed with a resin or cloth pad using a colloidal silica aqueous polishing liquid adjusted to pH 7 to 8, and the processing time is set to a time for maintaining the surface roughness (Sa value) formed in the first polishing step; The present invention is characterized in that it is composed of the above.

[0029] (1) Shore D hardness of the resin pad used in the first polishing process (1-1) Figure 2 is a graph showing the relationship between the average particle size (μm) of diamond abrasive grains contained in a diamond slurry and the surface roughness Sa (nm) of a SiC polycrystalline substrate after mechanical polishing using a "urethane resin pad with a Shore D hardness of 75 HSD" with a Shore D hardness of less than 80 HSD.

[0030] When the average grain size of the diamond abrasive grains exceeds 1 μm, it is confirmed that the surface roughness Sa (nm) of the SiC polycrystalline substrate after mechanical polishing decreases as the average grain size of the diamond abrasive grains decreases, as shown in Figure 2.

[0031] However, when the average grain size of the diamond abrasive grains becomes 1 μm or less, the surface roughness Sa (nm) of the SiC polycrystalline substrate after mechanical polishing increases as the average grain size of the diamond abrasive grains decreases, as shown in Figure 2, and it is confirmed that the surface roughness Sa (nm) of the SiC polycrystalline substrate cannot be reduced to 0.5 nm or less. The reason for this is presumed to be that when the average grain size of the diamond abrasive grains contained in the diamond slurry becomes smaller, the machinability decreases and it becomes prone to a brittle fracture mode, destroying the single crystal grains of the SiC polycrystalline substrate, or part of the single crystal grains falls off, causing pit-like defects, and increasing the surface roughness Sa (nm).

[0032] (1-2) On the other hand, in mechanical polishing using a resin pad with a Shore D hardness of 80 HSD or more, it is believed that cutting performance can be maintained even if the average particle size of the diamond abrasive grains contained in the diamond slurry is 0.5 μm or less.

[0033] Furthermore, when the average particle size of the diamond abrasive grains is set to 0.2 μm to 0.5 μm, it is possible to smooth the surface roughness Sa (nm) of the SiC polycrystalline substrate to about 0.3 nm order (0.3 nm≦Sa<0.4 nm), and when the dropping speed of the diamond slurry onto the resin pad is set to 8 mL / min or more, it is possible to smooth the surface roughness Sa (nm) of the SiC polycrystalline substrate to about 0.3 nm order (0.3 nm≦Sa<0.4 nm).

[0034] (2) Chemical mechanical polishing in the second polishing process and processing time The chemical mechanical polishing in the second polishing step is a process for removing process-affected layers and linear scratches generated in the grinding step, mechanical polishing step, etc., without worsening the surface roughness Sa (nm) of the SiC polycrystalline substrate formed in the first polishing step, which is on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm), and for maintaining the surface roughness Sa (nm) of the SiC polycrystalline substrate on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm). Chemical mechanical polishing is performed with a resin or cloth pad using a colloidal silica aqueous polishing liquid adjusted to a pH of 7 to 8, and the processing time is set to a time for which the surface roughness Sa (nm) on the order of 0.3 nm is maintained (upper limit 30 minutes).

[0035] (3) Double-sided lapping and grinding processes (3-1) The double-sided lapping process is a process in which a lapping device as shown in Figs. 3(A) and (B) is used to roughly polish both sides of a SiC polycrystalline substrate by placing the SiC polycrystalline substrate between an upper platen and a lower platen and supplying a polishing solution containing boron carbide (B4C) abrasive grains of No. 100 to No. 300 (ISO 8486 designation) between the upper platen and the lower platen.

[0036] (3-2) Grinding process The grinding process is a processing step for surface grinding the lapped SiC polycrystalline substrate, and is composed of a rough grinding process using a grinding wheel having diamond abrasive grains of No. 600 to No. 2000 (ISO 8486 designation) and a precision grinding process using a grinding wheel having diamond abrasive grains of No. 6000 to No. 8000 (ISO 8486 designation), and the rough grinding process may be omitted if necessary. EXAMPLES

[0037] Examples of the present invention will be specifically described below with reference to comparative examples.

[0038] [Example 1] (Double-sided wrapping process) A 6-inch diameter SiC polycrystalline substrate (wafer) was placed between the upper and lower plates of the lapping device shown in Figures 3(A) and (B). Double-sided lapping was performed while supplying a polishing solution containing boron carbide (B4C) abrasive grains No. 280 (ISO 8486 designation) between the upper and lower plates, thereby roughly polishing both sides of the SiC polycrystalline substrate to a total of 20 μm.

[0039] (Grinding) Next, a precision grinding process of 10 μm in total was performed on both sides of the SiC polycrystalline substrate using a precision grinder equipped with a diamond wheel having diamond abrasive grains of No. 7000 (ISO 8486 designation).

[0040] (First polishing process: mechanical polishing) Next, diamond abrasive grains with an average particle size of 0.5 μm were dispersed in water at a concentration of 3 wt%, and a diamond slurry containing 0.2 wt% ethylene glycol and triethanolamine as additives was dropped onto the platen at a rate of 10 mL / min. Mechanical polishing was performed with the platen rotating at a speed of 80 rpm, the head rotating at a speed of 64 rpm, both the platen and head rotating in a CCW (counterclockwise) direction, and a pressure of 60 kPa.

[0041] The platen used was made of SUS and had a resin pad with a Shore D hardness of 80 HSD attached thereon.

[0042] As a result, the large linear scratches that had occurred during the grinding process using the precision grinder disappeared after 15 minutes of mechanical polishing, and the surface roughness Sa (nm) of the mechanically polished SiC polycrystalline substrate was measured using the fringe scan method (an optical surface profile roughness measuring device) to be 0.36 nm at the periphery of the SiC polycrystalline substrate, 0.34 nm at the center of the substrate, and 0.36 nm in the area between the center and the periphery.

[0043] (Second polishing process: chemical mechanical polishing) Next, an aqueous polishing solution of colloidal silica (silica weight ratio: 5 wt%) with an average particle size of 70 nm, adjusted to pH 7.7 by adding sodium hydroxide and hydrogen peroxide, was dropped onto the platen at a rate of 100 mL / min, and chemical mechanical polishing (CMP) was performed for 20 minutes at a pressure of 40 kPa with the platen rotating at a speed of 40 rpm, the head rotating at a speed of 32 rpm, and both the platen and head rotating in CCW (counterclockwise).

[0044] The platen used was made of SUS and had a nonwoven abrasive cloth pad attached thereon.

[0045] Next, the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured using the fringe scan method. The results were 0.39 nm at the peripheral portion of the SiC polycrystalline substrate, 0.37 nm at the central portion of the substrate, and 0.38 nm at the intermediate portion between the central portion and the peripheral portion, which were almost the same values ​​over the entire substrate (peripheral, central, and intermediate portions of the substrate). It was confirmed that the surface roughness Sa over the entire substrate was on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm).

[0046] The results are shown in Tables 1 and 2 below.

[0047] [Example 2] The above-mentioned double-sided lapping process (using B4C abrasive grains) and grinding process (using a precision grinder) were carried out under the same conditions as in Example 1, and the first polishing process (mechanical polishing) was carried out under the same conditions as in Example 1, except that the abrasive grains were changed to "diamond abrasive grains with an average grain size of 0.3 μm." The large linear scratches that had occurred during grinding with the precision grinder disappeared after 40 minutes of mechanical polishing.

[0048] Next, a second polishing step (chemical mechanical polishing) was carried out under the same conditions as in Example 1, and the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured by a fringe scan method. The surface roughness Sa (nm) of the SiC polycrystalline substrate was 0.38 nm at the periphery, 0.35 nm at the central portion of the substrate, and 0.37 nm at the intermediate portion between the center and the periphery, confirming that the surface roughness Sa of the entire substrate was on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm).

[0049] These results are also shown in Tables 1 and 2 below.

[0050] [Example 3] The above-mentioned double-sided lapping process (using B4C abrasive grains) and grinding process (using a precision grinder) were carried out under the same conditions as in Example 1, and the first polishing process (mechanical polishing) was carried out under the same conditions as in Example 1, except that the abrasive grains were changed to "diamond abrasive grains with an average grain size of 0.2 μm." The large linear scratches that had occurred during grinding with the precision grinder disappeared after 90 minutes of mechanical polishing.

[0051] Next, a second polishing step (chemical mechanical polishing) was carried out under the same conditions as in Example 1, and the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured by a fringe scan method. The surface roughness Sa (nm) of the SiC polycrystalline substrate was 0.39 nm at the periphery, 0.38 nm at the center, and 0.38 nm at the intermediate portion between the center and the periphery, confirming that the surface roughness Sa of the entire substrate was on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm).

[0052] These results are also shown in Tables 1 and 2 below.

[0053] [Comparative Example 1] The above-mentioned double-sided lapping process (using B4C abrasive grains) and grinding process (using a precision grinder) were carried out under the same conditions as in Example 1, and the first polishing process (mechanical polishing) was carried out under the same conditions as in Example 1, except that diamond abrasive grains with an average grain size of 0.1 μm were used. The large linear scratches that had occurred during grinding with the precision grinder finally disappeared after 150 minutes of mechanical polishing.

[0054] Next, a second polishing step (chemical mechanical polishing) was carried out under the same conditions as in Example 1, and the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured by a fringe scan method. The results were 0.45 nm at the periphery of the SiC polycrystalline substrate, 0.51 nm at the central portion of the substrate, and 0.48 nm at the intermediate portion between the center and the periphery, confirming that it would be difficult to achieve a surface roughness Sa of the order of 0.3 nm (0.3 nm≦Sa<0.4 nm) for the entire substrate.

[0055] These results are also shown in Tables 1 and 2 below.

[0056] [Comparative Example 2] The above-mentioned double-sided lapping process (using B4C abrasive grains) and grinding process (using a precision grinder) were carried out under the same conditions as in Example 1, and the first polishing process (mechanical polishing) was carried out under the same conditions as in Example 1, except that the abrasive grains were changed to "diamond abrasive grains with an average grain size of 0.8 μm." The large linear scratches that had occurred during grinding with the precision grinder disappeared after 10 minutes of mechanical polishing.

[0057] Next, a second polishing step (chemical mechanical polishing) was carried out under the same conditions as in Example 1, and the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured by a fringe scan method. The results were 0.52 nm at the peripheral portion of the SiC polycrystalline substrate, 0.53 nm at the central portion of the substrate, and 0.49 nm at the intermediate portion between the central portion and the periphery, confirming that it would be difficult to achieve a surface roughness Sa of the order of 0.3 nm (0.3 nm≦Sa<0.4 nm) for the entire substrate.

[0058] These results are also shown in Tables 1 and 2 below.

[0059] [Comparative Example 3] The above-mentioned double-sided lapping process (using B4C abrasive grains) and grinding process (using a precision grinder) were carried out under the same conditions as in Example 1, and the first polishing process (mechanical polishing) was carried out under the same conditions as in Example 1, except that the abrasive grains were changed to "diamond abrasive grains having an average particle size of 1.0 μm."

[0060] As a result, the large linear scratches that had occurred during the grinding process using the precision grinder disappeared after 3 minutes of mechanical polishing, and when the surface roughness Sa (nm) of the mechanically polished SiC polycrystalline substrate was measured using the fringe scan method (an optical surface profile roughness measuring device), it was 0.58 nm at the periphery of the SiC polycrystalline substrate, 0.58 nm at the center of the substrate, and 0.69 nm in the area between the center and the periphery.

[0061] Next, a second polishing step (chemical mechanical polishing) was carried out under the same conditions as in Example 1, and the surface roughness Sa (nm) of the chemically mechanically polished (CMP) SiC polycrystalline substrate was measured by a fringe scan method. The results were 0.58 nm at the periphery of the SiC polycrystalline substrate, 0.55 nm at the central portion of the substrate, and 0.53 nm at the intermediate portion between the center and the periphery, confirming that it would be difficult to achieve a surface roughness Sa of the order of 0.3 nm (0.3 nm≦Sa<0.4 nm) for the entire substrate.

[0062] These results are also shown in Tables 1 and 2 below.

[0063] [Table 1]

[0064] [Table 2]

[0065] [confirmation] The graph in Figure 1 shows the relationship between the average particle size (μm) of diamond abrasive grains in mechanical polishing, in which a diamond slurry containing diamond abrasive grains is dropped onto a resin pad with a Shore D hardness of 80HSD for polishing, and the surface roughness Sa (nm) of the entire SiC polycrystalline substrate (peripheral, central, and intermediate portions of the substrate) after chemical mechanical polishing. It is confirmed that when the average particle size of diamond abrasive grains contained in the diamond slurry in mechanical polishing using a resin pad with a Shore D hardness of 80HSD is in the range of 0.2μm to 0.5μm (Examples 1 to 3), the surface roughness Sa (nm) of the entire SiC polycrystalline substrate after chemical mechanical polishing can be smoothed to the order of 0.3nm (0.3nm≦Sa<0.4nm). [Industrial Applicability]

[0066] According to the method of the present invention, the surface roughness Sa (nm) of the entire SiC polycrystalline substrate can be smoothed to the order of 0.3 nm (0.3 nm≦Sa<0.4 nm), and therefore has industrial applicability as a manufacturing method for SiC polycrystalline substrates used for SiC substrates.

Claims

1. A method for manufacturing a SiC polycrystalline substrate, comprising: a double-sided lapping step of roughly polishing both sides of a SiC polycrystalline substrate obtained by slicing SiC polycrystalline; a grinding step of surface-grinding the lapped SiC polycrystalline substrate; and a polishing step of smoothing one side of the ground SiC polycrystalline substrate, The polishing step is A first polishing step is a step of dropping a diamond slurry containing diamond abrasive grains having an average grain size of 0.2 μm to 0.5 μm onto a resin pad having a Shore D hardness of 80 HSD or more, and mechanically polishing the pad until the surface roughness (arithmetic mean height Sa value defined in ISO 25178) measured by a fringe scan method is on the order of 0.3 nm (0.3 nm≦Sa<0.4 nm); a second polishing step in which chemical mechanical polishing is performed with a resin or cloth pad using a colloidal silica aqueous polishing liquid adjusted to a pH of 7 to 8, and the treatment time is set to a time for maintaining the surface roughness (Sa value) formed in the first polishing step; A method for producing a SiC polycrystalline substrate, comprising:

2. 2. The method for producing a SiC polycrystalline substrate according to claim 1, wherein in the second polishing step, the upper limit of the time for maintaining the surface roughness (Sa value) is 30 minutes.

3. 2. The method for producing a polycrystalline SiC substrate according to claim 1, wherein in the first polishing step, the diamond slurry is dropped at a rate of 8 mL / min or more.

4. In the above double-sided wrapping process, B of 100 to 300 (ISO 8486 indication) 4 The method for producing a SiC polycrystalline substrate according to any one of claims 1 to 3, characterized in that C abrasive grains are applied.

5. The method for producing a SiC polycrystalline substrate according to any one of claims 1 to 4, characterized in that the grinding step is a precision grinding step using a grinding wheel having diamond abrasive grains of No. 6000 to No. 8000 (ISO 8486 designation).

6. The method for producing a SiC polycrystalline substrate according to any one of claims 1 to 4, characterized in that the grinding process is composed of a rough grinding process using a grinding wheel having diamond abrasive grains of No. 600 to No. 2000 (ISO 8486 designation) and a precision grinding process using a grinding wheel having diamond abrasive grains of No. 6000 to No. 8000 (ISO 8486 designation).

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