JP2010080471A - Polishing method of sic single crystal substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method of an SiC single crystal substrate by which the presence of an affected layer can be grasped in a CMP (chemical mechanical polishing) process and the continuation and finish of the CMP process can be easily determined. <P>SOLUTION: The polishing method of the SiC single crystal substrate includes: a mechanical polishing process for mechanically polishing a monitor substrate which has a first region having a first impurity concentration and a second region having a second impurity concentration greater than the first impurity concentration, and is formed of a SiC single crystal, and the SiC single crystal substrate having an impurity concentration equal to the first impurity concentration; the CMP process for CMP-processing the monitor substrate and the SiC single crystal substrate after the mechanical polishing process; a step measurement process for measuring a step between the first region and the second region of the monitor substrate after the CMP process; and a polishing finish determination process for determining polishing finish when the measured step is within a predetermined range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor substrate, and more particularly to a CMP technique for a SiC single crystal substrate.

  The manufacturing process of a semiconductor substrate includes a slicing step for forming a crystal-grown ingot material into a substrate, a polishing step for adjusting the substrate shape and surface roughness. The polishing is composed of a plurality of steps, and finally, a CMP (Chemical Mechanical Polishing) step for removing the work-affected layer formed up to the previous step is performed to make the state of the outermost surface of the substrate uniform.

Conventionally, whether or not the work-affected layer has been removed can be determined by a method of directly observing a groove formed on the surface of a measurement object using a separately prepared work-affected layer measurement sample (see, for example, Patent Document 1) or processing. Etching was performed after completion, and was confirmed by the change rate of the etching rate, the increase rate of the etch pits, or the change amount of the half width of the X-ray rocking curve (see, for example, Patent Document 2, Patent Document 3 and Patent Document 4) .)
JP 2001-296118 A (page 7, FIG. 6) JP-A-10-112485 (first page, FIG. 1) Japanese Patent No. 2894154 (page 4, FIG. 1) Japanese Patent Laid-Open No. 5-288540 (page 2)

  However, in the conventional method, since the thickness of the work-affected layer cannot be measured during the CMP process, an appropriate CMP processing amount cannot be known during the processing. For this reason, if the polishing amount in the CMP process is insufficient, the work-affected layer remains, and conversely, if the polishing amount is too large, the substrate shape polished in the previous process is destroyed.

  An object of the present invention is to solve the above-described conventional problems, and to provide a method for grasping the presence or absence of a work-affected layer and detecting an appropriate polishing end point in a CMP process of a SiC single crystal substrate.

  In order to solve the above-described conventional problems, a method for polishing a SiC single crystal substrate according to the present invention has a first region having a first impurity concentration and a second impurity concentration higher than the first impurity concentration. A mechanical polishing step of mechanically polishing a monitor substrate made of an SiC single crystal having a second region and an SiC single crystal substrate having the same impurity concentration as the first impurity concentration, and the mechanical polishing step A CMP process for performing CMP processing on both the monitor substrate and the SiC single crystal substrate; a step measurement process for measuring a step between the first region and the second region of the monitor substrate that has undergone the CMP step; A polishing end determination step of determining that polishing is ended if the measured level difference is within a predetermined range.

  According to the method for polishing a SiC single crystal substrate of the present invention, it is possible to know the presence or absence of a work-affected layer on a substrate very easily by measuring a step formed on a monitor substrate even during CMP. it can.

  In addition, the step can be removed by a normal mechanical polishing process and can be reused. Furthermore, if an ingot end portion that cannot be used as a SiC single crystal substrate is used because of a lack of a predetermined thickness, it can be used without reducing the number of substrates.

  An example of the method for polishing a SiC single crystal substrate of the present invention will be described in detail with reference to the drawings. In addition, the level | step difference in this specification says the value measured by the optical interference type surface roughness measuring apparatus.

(Embodiment 1)
In this example, a 4H-n type 3-inch SiC single crystal substrate having an off angle of 4 ° is taken as an example, and a method for detecting the polishing end point will be described. Here, the off-angle indicates an angle from the <0001> plane (on-axis plane) of the SiC single crystal to the <11-20> direction. The allowable off-angle variation is approximately ± 0.5 °.

  FIG. 1 shows a monitor substrate 1 used in this embodiment. The monitor substrate 1 is a SiC single crystal substrate 2 having the same polytype, off-angle, and impurities as the SiC single crystal substrate 2 that detects the polishing end point. As shown in FIG. 1, the monitor substrate 1 partially has a layer B having a different impurity concentration. The impurity concentration in the region other than this layer B is the same as that of the SiC single crystal substrate 2 for detecting the polishing end point. The impurity concentration of B is higher than other portions.

  The layer B having a different impurity concentration is polished in the same manner as other portions in a mechanical polishing process using a metal surface plate and diamond abrasive grains. However, in the CMP process performed using the polishing pad and colloidal silica, the portion of the layer B having a different impurity concentration is polished faster than the other portions, so that a step is generated at the boundary with the layer B. This is probably because the layer B in which more impurities are mixed tends to be unstable both mechanically and chemically compared to a portion having a low impurity concentration, and thus such a step is likely to occur.

  The purpose of CMP is to remove the work-affected layer that occurs in the mechanical polishing process. However, if CMP is performed excessively, the shape of the substrate corrected in the mechanical polishing process is deteriorated. Therefore, it is necessary to correct the shape of the substrate again in the mechanical polishing process. However, the removal state of the work-affected layer is extremely difficult to measure.

  Therefore, in the present invention, the SiC single crystal substrate 2 having the same polytype, off-angle, and impurities as the monitor substrate 1 shown in FIG. And performing the mechanical polishing process and the CMP process under the same conditions at the same time. By making use of the fact that the change in thickness and substrate shape of the work-affected layer formed between the monitor substrate 1 and the SiC single crystal substrate 2 is substantially the same, a predetermined difference in level on the monitor substrate 1 is obtained in advance. If the range is determined, the polishing end point of the SiC single crystal substrate 2 can be easily detected. Further, even if the CMP process is performed excessively, if the monitor substrate 1 is returned to the mechanical polishing process and mechanical polishing is performed again, the step formed in the CMP process is eliminated, so that it can be used again in the CMP process.

  The minimum processing amount on the monitor substrate 1 showing an appropriate CMP processing amount can be obtained from the amount of change in the half width of the X-ray rocking curve. The half width of the X-ray rocking curve is a technique used to measure the crystal quality of a single crystal. If this value is low, the crystallinity is good, and conversely if this value is high, the crystallinity is bad. The full width at half maximum of the X-ray rocking curve is a larger value when the crystallinity is poor, that is, when a work-affected layer remains on the monitor substrate 1 as compared with the case where it is not. However, when there is no work-affected layer, the value becomes lower, and after that, even if CMP is performed, it does not change. Therefore, the step at the first point where the half width of the X-ray rocking curve no longer changes is the minimum state in which the work-affected layer has disappeared, and is the minimum processing amount in an appropriate CMP process. On the other hand, the maximum processing amount of the appropriate CMP process for the monitor substrate 1 can be set based on the deterioration of the substrate shape.

  A method for manufacturing the monitor substrate 1 will be described below. In this embodiment, nitrogen is used as an impurity, but other impurities such as phosphorus and arsenic may be used for n-type, and boron and aluminum may be used for p-type.

  FIG. 2 is a schematic view of the SiC single crystal ingot growth apparatus used in this example. Using this, the monitor substrate 1 can be manufactured. The silicon carbide raw material 4 is housed in the crucible 3, and the seed crystal 6 fixed to the seed crystal support portion of the lid 5 is arranged so as to face the silicon carbide raw material 4. The seed crystal support is a cylinder with a diameter of 75 mm, and the diameter of the seed crystal 6 is 75 mm, the same as the seed crystal support. Since the SiC single crystal ingot gradually increases from the diameter of the seed crystal 6, a 3 inch diameter can be taken out from the SiC single crystal ingot.

  In silicon carbide single crystal growth using the sublimation recrystallization method, the silicon carbide raw material 4 must be sublimated, but the sublimation of silicon carbide requires a high temperature of 2000 ° C. or higher. At a high temperature of 2000 ° C. or higher, the radiant heat is lost in proportion to the fourth power of the temperature, so the crucible 3 and the lid 5 need to be covered with the heat insulating material 7. The crucible 3 and the lid 5 covered with the heat insulating material 7 are placed in a quartz reaction tube 8. The reaction tube 8 has a double tube structure, and is cooled by flowing cooling water 9 during crystal growth. A gas inlet 10 is provided at the upper part of the reaction tube 8, and a gas outlet 11 is provided at the lower part.

  Thereafter, the inside of the reaction tube 8 is replaced with an inert gas. Argon (Ar) is suitable as the inert gas in terms of cost, purity, and the like. In this inert gas replacement, the inside of the reaction tube 8 is first evacuated to a high vacuum from the gas exhaust port 20 and then filled with an inert gas from the gas inlet 10 to normal pressure. Here, nitrogen gas is flowed to introduce impurities into the SiC single crystal ingot. Argon gas is introduced at a flow rate of 30 sccm and nitrogen gas is introduced at a flow rate of 20 sccm.

  Thereafter, the crucible 3 and the lid 5 are heated at a high frequency by causing a high frequency current to flow through the coil 12 spirally wound around the reaction tube 8 to raise the temperature. When raising the temperature, the inside of the reaction tube 8 needs to be kept at a pressure of about several tens of kPa. This is to prevent sublimation of the silicon carbide raw material 4 at low temperatures (below the desired crystal growth temperature) and prevent crystal growth from starting.

  Temperature control at the time of heating is performed by a radiation thermometer 14 through a temperature measuring window 13 made of quartz provided in the upper and lower portions of the reaction tube 8 and a temperature measuring hole provided in the upper and lower portions of the heat insulating material 7. The temperature at the lower part of the crucible 3 and the upper part of the lid 5 is measured, feedback is applied to a high-frequency power source (not shown), and the high-frequency current flowing through the coil 12 is controlled. Thus, after raising the temperature to a desired temperature, the pressure is gradually reduced to start crystal growth. In this example, the temperature at the bottom of the crucible 4 is 2250 ° C., the temperature at the center of the top of the crucible 4 is 2200 ° C., the pressure inside the reaction tube 8 is 0.133 kPa, and crystal growth is performed for 35 hours.

  Thereafter, in order to form a layer having a high nitrogen concentration, the nitrogen gas flow rate is changed to 70 sccm and held for 3 minutes, after which the nitrogen gas flow rate is returned to 20 sccm and crystal growth is performed for 5 hours. At the end of crystal growth, contrary to the start of growth, the pressure inside the reaction tube 8 is increased to 80 kPa over 1 hour to stop the sublimation of the raw material from the silicon carbide raw material 4 and then slowly cooled to room temperature. To do.

  The SiC single crystal ingot including the portion to be the monitor substrate 1 manufactured under the above conditions is sliced to obtain the monitor substrate 1 and the normal SiC single crystal substrate 2. Each substrate is polished after being sliced. The SiC single crystal ingot produced by the SiC single crystal growth method is partially in a state having a high nitrogen concentration layer. When this SiC single crystal ingot is sliced with a cutting device such as a wire saw with an inclination of 4 ° (off angle of 4 °), a part of the sliced SiC single crystal substrate 2 has a nitrogen concentration as shown in FIG. Thus, the monitor substrate 1 has a different area.

  Note that most SiC single crystal substrates 2 that do not have regions with different nitrogen concentrations can be used as ordinary substrates. Further, in the above-described method for producing a SiC single crystal ingot, the portion where the flow rate of nitrogen gas is changed is not at the end of the growth of the SiC single crystal ingot as in this embodiment, but may be at the beginning of the growth. Since most of the subsequent SiC single crystal substrate 2 becomes the monitor substrate 1, it is better not to perform unless the monitor substrate 1 is desired in large quantities.

The nitrogen concentration in the SiC single crystal ingot produced by the above SiC single crystal growth method is approximately 5 × 10 ¹⁸ or more and less than 1 × 10 ¹⁹ when the flow rate of nitrogen gas is 20 sccm, and the nitrogen concentration is 70 sccm. Is approximately 2 × 10 ¹⁹ or more and less than 5 × 10 ¹⁹ . When this SiC single crystal ingot is sliced into the SiC single crystal substrate 2, it has a nitrogen concentration of 5 × 10 ¹⁸ or more and less than 1 × 10 ¹⁹ . In the case of the monitor substrate 1, a layer having a nitrogen concentration of 2 × 10 ¹⁹ or more and less than 5 × 10 ¹⁹ is placed in a portion having a nitrogen concentration of 5 × 10 ¹⁸ or more and less than 1 × 10 ¹⁹ .

  FIG. 3 is a flowchart showing an outline of the process of the method for polishing a SiC single crystal substrate in the present embodiment. The flowchart comprises a) a mechanical polishing step (one or more steps using a metal surface plate and diamond as polishing grains), b) a CMP step, and c) a step measurement step.

  In the steps a) and b), the monitor substrate 1 made of the SiC single crystal and the normal SiC single crystal substrate 2 are simultaneously processed under the same conditions. b) In the CMP process, the monitor substrate 1 is formed with the region having the different nitrogen concentration (the layer B shown in FIG. 1) on the substrate as described above. Form. In step c), the step on the monitor substrate 1 is measured, and the presence or absence of an appropriate CMP processing amount is determined based on the measurement result. (Polishing end determination step) If the amount of processing by CMP is appropriate, the step becomes a predetermined range, and the CMP step ends. If the processing amount by CMP is insufficient, that is, if the work-affected layer remains, the step becomes shallow and b) the CMP process is performed again.

  On the other hand, if the amount of processing by CMP is excessive, the shapes of the monitor substrate 1 and the SiC single crystal substrate 2 are deteriorated. Therefore, the substrate shape must be flattened by returning to a) mechanical polishing step. By returning the monitor substrate 1 to a) the mechanical polishing step and b) the step formed in the CMP step disappears, the same processing can be performed again, and the monitor substrate 1 can be reused. Here, since the polishing rate in the b) CMP step is lowered due to deterioration of the polishing pad or the like, it is not possible to know the presence or absence of a work-affected layer simply by time alone.

  a) The mechanical polishing process is a process in which the monitor substrate 1 and the normal SiC single crystal substrate 2 are simultaneously subjected to rough polishing and precision polishing using a metal surface plate and diamond abrasive grains under the same conditions. The purpose is to flatten the crystal substrate 2.

  FIG. 4A is a schematic diagram of a polishing apparatus for performing a) mechanical polishing process used in this example. 4B is an enlarged view of the polishing block 3 in FIG. 4A, and FIG. 4C is a perspective view showing members constituting the polishing block 3 in FIG. 4B. The polishing block 3 has a structure in which a weight 5 for applying pressure is placed on the work guide 4 as shown in FIG. 4B. The monitor substrate 1 or the SiC single crystal substrate 2 is as shown in FIG. 4C. Attached to the lower surface of the jig 6 and stored in the work guide 4.

  In FIG. 4C, the monitor substrate 1 and the SiC single crystal substrate 2 are attached to the attaching jig 6 one by one, but a plurality of the same size may be attached simultaneously. The monitor substrate 1 and the SiC single crystal substrate 2 may be attached to the attachment jig 6 with a heat-soluble adhesive. The polishing block 3 assembled in this manner is supported by the arm 8 by rotating the polishing surface plate 7, and the monitor substrate 1 or the SiC single crystal substrate 2, the attaching jig 6, the weight 5, and the work guide 4 are provided. The monitor substrate 1 or the SiC single crystal substrate 2 is polished by rotating on the polishing platen 7.

  At this time, polishing is performed by dropping the polishing agent 9 periodically onto the polishing surface plate 7. In this embodiment, a) Diamond having a particle diameter of 1 μm is used as the abrasive 9 in the final step of the mechanical polishing step, and a tin surface plate is used as the polishing surface plate 7. At this time, the pressure applied to the monitor substrate 1 and the SiC single crystal substrate 2 by the weight 5 is about 100 g / cm 2 in terms of surface pressure, and the rotation speed of the polishing surface plate 7 is about 40 rpm. b) The CMP process is a process in which the monitor substrate 1 made of SiC single crystal and the normal SiC single crystal substrate 2 are simultaneously subjected to CMP using colloidal silica abrasive grains under the same conditions. The purpose is to remove the work-affected layer.

  FIG. 5A is a schematic view of a polishing apparatus for performing the b) CMP step used in this example. 4A is similar to the polishing apparatus for performing the mechanical polishing step, but differs in that the polishing pad 10 is pasted on the polishing surface plate 7 and the polishing agent 9 is colloidal silica. The polishing pad 10 is preferably a nonwoven fabric soaked with urethane. Further, a packing film 11 is inserted between the monitor substrate 1 and the SiC single crystal substrate 2 and the attaching jig 6 to fix each substrate without using a heat-soluble adhesive. At this time, the pressure applied to the monitor substrate 1 and the SiC single crystal substrate 2 by the weight 5 is about 500 g / cm 2 in terms of surface pressure, and the rotation speed of the polishing surface plate 7 is about 40 rpm. Further, in this embodiment, Suba400 manufactured by Nitta Haas Co., Ltd. was used as the polishing pad, and Compol 80 manufactured by Fujimi Incorporated Co. was used as the colloidal silica.

  c) In the step measurement step, the step formed on the monitor substrate 1 (in the vicinity of the layer B shown in FIG. 1) is measured with an optical interference type surface roughness measuring device. In the present Example, it measured using NewView5032 made from Zygo. The presence or absence of a work-affected layer is determined by this step measurement.

  The relationship between the presence / absence of the work-affected layer and the step differs depending on the concentration difference between the two nitrogen concentration regions of the monitor substrate 1. In addition, since the process differs slightly depending on the off-angles of the monitor substrate 1 and the SiC single crystal substrate 2, a) and b) each process must be processed with the monitor substrate 1 and the SiC single crystal substrate 2 having the same off-angle and nitrogen concentration. I must. Also, the size of the substrate to be processed must be the same.

  In order to determine the presence or absence of a work-affected layer by measuring the level difference, the relationship between the half width of the level difference of the monitor substrate 1 and the X-ray rocking curve after both steps a) and b) is measured in advance. b) When the polishing time in the CMP process is increased, the step becomes deeper. However, when this step becomes a certain depth or more, the half width of the X-ray rocking curve does not change. This step depth is a point where a work-affected layer does not exist. That is, the first step depth at which the half width of the X-ray rocking curve no longer changes is the point at which the work-affected layer has disappeared, and this is the minimum value of the step setting value described above.

  Next, how to determine the upper limit value of the step set value will be described. Since this upper limit value is affected by the current value of the value (SORI or TTV) indicating the shape allowed for SiC single crystal substrate 2 and the target value, it is better that the upper limit value is closer to the minimum value of the step set value. This is because b) SORI and TTV deteriorate as the time of the CMP process becomes longer.

  The monitor substrate 1 can be reused by returning to the a) mechanical polishing step, and the relationship between the presence or absence of the work-affected layer and the step is the same as long as the monitor substrate 1 has the same nitrogen concentration and off angle.

  Table 1 shows the relationship between the step of the monitor substrate 1 manufactured under the above conditions, the amount of change from the initial value of the half width of the X-ray rocking curve, and the amount of change from the initial value of the substrate shape. The “steps” shown in Table 1, which were measured 20 times under each condition, were measured using a NewView 5032 manufactured by Zygo Co., Ltd. b) The height of the step formed on the monitor substrate 1 in the CMP process. The “amount of change from the initial value of the half-value width of the X-ray rocking curve” shown in Table 1 is as follows: a) The half-value width of the X-ray rocking curve of the monitor substrate 1 after the mechanical polishing step is set as an initial value. B) The amount of change in the half width of the X-ray rocking curve of the monitor substrate 1 corresponding to the “step” generated in the CMP process with respect to the initial value. Next, “amount of change from the initial value of the substrate shape” shown in Table 1 is as follows: a) SORI of the SiC single crystal substrate 2 after completion of the mechanical polishing process is an initial value, and b) CMP process for this initial value. This shows the amount of change in the monitor substrate 1SORI corresponding to the "step" that occurs. SORI is measured with FT-17 manufactured by NIDEK Co., Ltd., and x when the change in SORI exceeds 1000 nm during 20 measurements, △ when less than 500 nm and less than 1000 nm, and when less than 500 nm ○. Since the difference of about 500 nm corresponds to the measurement error of the measuring apparatus, it can be said that the SORI has hardly changed.

In the case of the monitor substrate 1 in which a layer (layer B) having a nitrogen concentration of 2 × 10 ¹⁹ or more and less than 5 × 10 ¹⁹ is provided in a portion having a nitrogen concentration of 5 × 10 ¹⁸ or more and less than 1 × 10 ¹⁹ from the results of Table 1. For this, the set value of the step may be 60 nm or more and 100 nm or less. In other words, “the amount of change from the initial value of the half width of the X-ray rocking curve” in Table 1 changes from the initial value until the level difference of 60 nm, but does not change when the level difference exceeds 60 nm. Therefore, when the level difference is 60 nm (the minimum value of the level difference), it can be determined that the work-affected layer of the monitor substrate 1 has been removed. Further, from the result of “the amount of change from the initial value of the substrate shape”, the maximum value of the set value of the step is 100 nm. Therefore, when the height of the “step” of the monitor substrate 1 is in the range of 60 nm to 100 nm, it may be determined that b) the CMP process is finished. From the result of “amount of change from the initial value of the substrate shape”, if the shape of the SiC single crystal substrate 2 before the b) CMP process is good, the maximum value of the set value of the step can be increased to 200 nm.

  In the present embodiment, a method for detecting the polishing end point of a 4H-n type SiC single crystal substrate having an off angle of 4 ° in a 3 inch size has been described, but other off angles, polytypes, impurities and Although the set value of the step changes even with the impurity concentration, the polishing end point of the SiC single crystal substrate can be detected by the same method.

  As described above, in the present invention, when an SiC single crystal ingot is first grown, a layer having an impurity concentration higher than that of other portions is previously formed in a portion thereof. The layer having a high impurity concentration is processed in the same manner as other portions in normal mechanical polishing, but the processing rate is higher than that in other portions in CMP, and a step is formed on the substrate due to the difference in processing rates. If this step and the half-value width of the X-ray rocking curve are correlated, the presence or absence of a work-affected layer can be obtained from the amount of change in the half-value width of the X-ray rocking curve as disclosed in Patent Document 4. The level difference at the time when the half-value width of no longer changes becomes a place where the work-affected layer is no longer present. Therefore, if the correlation between the aforementioned step and the half width of the X-ray rocking curve is known in advance, the presence or absence of a work-affected layer can be known even during CMP. By using this substrate as a monitor substrate and processing it under the same conditions simultaneously with a SiC single crystal substrate having the same polytype, off-angle, and impurity concentration as the monitor substrate (the same impurity concentration as the portion of the monitor substrate where the impurity concentration is low), Since the presence or absence of a work-affected layer on the SiC single crystal substrate can be easily determined even in the middle, the polishing end point of the SiC single crystal substrate can be detected. Further, even when the processing rate is changed due to a decrease in the processing rate due to deterioration of the polishing pad or other factors, it is possible to easily cope with it.

  According to the method for polishing a SiC single crystal substrate according to the present invention, the polishing end point in CMP processing of the SiC single crystal substrate can be easily detected, and the monitor substrate can be easily reused. It is useful as a polishing method during CMP processing for manufacturing a substrate.

  Further, according to the method for polishing a SiC single crystal substrate according to the present invention, the CMP polishing end point of the single crystal material substrate can be easily detected, and the monitor substrate can be easily reused. Without being limited to the above, it is also useful as a polishing method at the time of CMP processing for the production of other single crystal materials capable of controlling the impurity concentration during crystal growth.

Diagram showing monitor board The figure which shows a SiC single crystal ingot growth device The flowchart which showed the process outline of the grinding | polishing method of the SiC single crystal substrate of this invention The figure which shows the polisher for performing a mechanical polishing process The figure which shows the polish device for performing CMP process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Monitor substrate 2 SiC single crystal substrate 3 Crucible 4 Silicon carbide raw material 5 Lid body 6 Seed crystal 7 Heat insulating material 8 Reaction tube 9 Cooling water 10 Gas inlet 11 Gas exhaust port 12 Coil 13 Temperature measurement window 14 Radiation thermometer 15 Polishing Block 16 Work guide 17 Weight 18 Sticking jig 19 Polishing surface plate 20 Arm 21 Abrasive agent 22 Polishing pad 23 Packing film

Claims (12)

A monitor substrate made of an SiC single crystal having a first region having a first impurity concentration and a second region having a second impurity concentration higher than the first impurity concentration; and the first impurity concentration; A mechanical polishing step of mechanically polishing together a SiC single crystal substrate having the same impurity concentration;
CMP process for CMP processing the monitor substrate and the SiC single crystal substrate that have undergone the mechanical polishing process;
A step measuring step for measuring a step between the first region and the second region of the monitor substrate that has undergone the CMP step;
Polishing end determination step of determining the end of polishing if the measured level difference is within a predetermined range;
A method for polishing a SiC single crystal substrate comprising: 2. The polishing end determination step, wherein the monitor substrate and the SiC single crystal substrate are determined to be returned to the mechanical polishing step again if the measured level difference is larger than a maximum value in the predetermined range. 2. The method for polishing an SiC single crystal substrate according to 1. 2. In the polishing end determination step, it is determined that the monitor substrate and the SiC single crystal substrate are returned to the CMP step again if the measured level difference is smaller than a minimum value in the predetermined range. The method for polishing a SiC single crystal substrate according to claim 1. The method for polishing a SiC single crystal substrate according to claim 1, wherein the monitor substrate is a 4H, n-type SiC single crystal. The SiC single crystal substrate polishing method according to claim 4, wherein an off angle of the monitor substrate is 3.5 ° or more and 4.5 ° or less. The method for polishing an SiC single crystal substrate according to claim 1, wherein the impurity is nitrogen. The method for polishing an SiC single crystal substrate according to claim 6, wherein the nitrogen concentration in the first region is less than 1 × 10 ¹⁹ and the nitrogen concentration in the second region is 2 × 10 ¹⁹ or more. The nitrogen concentration of the first region is less than 5 × 10 ¹⁸ or more 1 × 10 ^19, SiC single of claim 7 nitrogen concentration of the second region is less than 2 × 10 ¹⁹ or more 5 × 10 ¹⁹ A method for polishing a crystal substrate. The method for polishing an SiC single crystal substrate according to claim 2, wherein the maximum value is approximately 200 nm or less. 10. The method for polishing an SiC single crystal substrate according to claim 9, wherein the maximum value is preferably about 100 nm. 4. The method for polishing a SiC single crystal substrate according to claim 3, wherein the minimum value is the step where the half-value width of the X-ray rocking curve of the monitor substrate surface processed in the CMP process does not change. The method for polishing an SiC single crystal substrate according to claim 3, wherein the minimum value is approximately 60 nm.

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