SiC substrate manufacturing method

Abstract

To provide a method of manufacturing an SiC baseboard which can shorten a manufacturing lead time for an SiC baseboard and can reduce manufacturing costs.SOLUTION: After grinding a surface side on which an Si surface is exposed and grinding a rear surface side so that an arithmetic average height Sa of a rear surface on which a C-face is exposed is 1 nm or less, only the surface side is ground without grinding the rear surface side. When the rear surface side is ground in this manner, warpage of an SiC baseboard can be suppressed without further grinding the rear surface side of the SiC baseboard. Accordingly, a manufacturing lead time for an SiC baseboard for use in manufacturing of a power device and the like can be shortened, and also manufacturing costs can be reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a SiC substrate. [Background technology]

[0002] Power devices such as inverters and converters are required to have a large current capacity and a high breakdown voltage. To meet these requirements, power devices are often manufactured using silicon carbide (SiC) substrates. Such SiC substrates are generally manufactured from SiC ingots.

[0003] For example, a SiC substrate is cut from a SiC ingot using a wire saw or the like so that the Si face is exposed on the front surface and the C face is exposed on the back surface. The Si face is a face terminated with Si and is expressed as the (0001) face using Miller indices. The C face is a face terminated with C and is expressed as the (000-1) face using Miller indices.

[0004] Furthermore, in a SiC substrate, epitaxial growth of a SiC thin film is easier on the Si face than on the C face, so when manufacturing a power device using this SiC substrate, the power device is generally formed on the surface side where the Si face is exposed.

[0005] However, when a SiC substrate is cut from a SiC ingot, its front and back surfaces tend to become rough (large irregularities tend to form on the front and back surfaces). Furthermore, a rough surface makes it difficult to epitaxially grow a SiC thin film on the surface. Therefore, when manufacturing a power device using a SiC substrate, the surface of the SiC substrate needs to be flattened (mirror-finished).

[0006] Furthermore, if only the front surface of the SiC substrate is planarized, the SiC substrate may warp significantly due to the difference in roughness between the front surface and the back surface. Therefore, SiC substrates used in the manufacture of power devices are manufactured by grinding both the front and back surfaces to reduce the roughness on both surfaces, and then polishing both the front and back surfaces to planarize both surfaces (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-105697 Summary of the Invention [Problem to be solved by the invention]

[0008] When power devices are formed only on the front side of a SiC substrate, where the Si face is exposed, planarizing the back side, where the C face of the SiC substrate is exposed, does not directly affect the performance of the power devices. On the other hand, polishing both the front side and the back side of a SiC substrate increases the manufacturing lead time of the SiC substrate and also increases the manufacturing cost.

[0009] In view of this, an object of the present invention is to provide a method for manufacturing a SiC substrate that can shorten the manufacturing lead time for the SiC substrate and reduce the manufacturing cost. [Means for solving the problem]

[0010] According to the present invention, there is provided a method for manufacturing a SiC substrate, comprising: a separating step of separating an SiC substrate from an SiC ingot so as to expose an Si face on the front surface and a C face on the back surface; a grinding step of grinding both the front surface side and the back surface side of the SiC substrate after the separating step; and a polishing step of polishing only the front surface side of the SiC substrate without polishing the back surface side of the SiC substrate after the grinding step, wherein the grinding step includes a first grinding step of grinding the front surface side of the SiC substrate and a second grinding step of grinding the back surface side of the SiC substrate, and in the second grinding step, the back surface side of the SiC substrate is ground so that the arithmetic mean height Sa of the back surface is 1 nm or less. The grinding of the back surface of the SiC substrate is completed by the second grinding step. A method for manufacturing a SiC substrate is provided.

[0011] Preferably, the average particle size of the abrasive grains contained in the grinding stone used in the second grinding step is 0.3 μm or less. [Effects of the Invention]

[0012] In the present invention, the front surface side where the Si plane is exposed is ground, and the back surface side is ground so that the arithmetic mean height Sa of the back surface where the C plane is exposed is 1 nm or less, and then only the front surface side is polished without polishing the back surface side. When the back surface side is ground in this manner, warping of the SiC substrate can be suppressed without further polishing the back surface side of the SiC substrate. Therefore, in the present invention, it is possible to shorten the manufacturing lead time and reduce manufacturing costs for SiC substrates used in the manufacture of power devices, etc. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flowchart schematically showing an example of a method for manufacturing a SiC substrate. [Figure 2] FIG. 2 is a perspective view schematically illustrating an example of a SiC substrate separated from a SiC ingot. [Figure 3] FIG. 3 is a perspective view schematically illustrating an example of a processing device. [Figure 4]FIG. 4(A) is a side view that schematically shows how the front surface side of the SiC substrate is ground, and FIG. 4(B) is a side view that schematically shows how the back surface side of the SiC substrate is ground. [Figure 5] FIG. 5 is a partial cross-sectional side view that schematically shows how the front surface side of the SiC substrate is polished. DETAILED DESCRIPTION OF THE INVENTION

[0014] Embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow chart schematically showing an example of a method for manufacturing a SiC substrate. In this method, first, a SiC substrate is separated from a SiC ingot so as to expose the Si face on the front surface and the C face on the back surface (separation step: S1). Fig. 2 is a perspective view schematically showing an example of a SiC substrate separated from a SiC ingot.

[0015] 2 is separated from a cylindrical SiC ingot so that the Si face is exposed on its front surface 11a and the C face is exposed on its back surface 11b. This separation step (S1) is performed by cutting the SiC substrate 11 from the SiC ingot using a wire saw such as a diamond wire saw.

[0016] Alternatively, the separation step (S1) may be performed by peeling off the SiC substrate 11 from the SiC ingot using a laser beam having a wavelength (e.g., 1064 nm) that transmits through SiC. In this case, first, the laser beam is irradiated onto the SiC ingot with the focal point of the laser beam positioned at a predetermined depth (a depth corresponding to the thickness of the SiC substrate 11 to be peeled off) from the surface of the SiC ingot.

[0017] This forms a peeling layer inside the SiC ingot. Then, an external force is applied to this SiC ingot. As a result, the SiC ingot separates from the peeling layer, which serves as a separation starting point. That is, the SiC substrate 11 is separated from the SiC ingot.

[0018] Next, after both the front surface 11a side and the back surface 11b side of the SiC substrate 11 are ground (grinding step: S2), only the front surface 11a side of the SiC substrate 11 is polished without polishing the back surface 11b side (polishing step: S3). Figure 3 is a perspective view schematically showing an example of a processing apparatus capable of grinding and polishing the SiC substrate 11.

[0019] Note that the X-axis direction (front-back direction) and the Y-axis direction (left-right direction) shown in FIG. 3 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction (vertical direction) perpendicular to the X-axis and Y-axis directions.

[0020] 3 includes a base 4 that supports each component. An opening 4a is formed in the front upper surface of the base 4, and a transfer mechanism 6 that transfers a SiC substrate while holding it by suction is provided within this opening 4a. Furthermore, the transfer mechanism 6 can also turn the SiC substrate 11 upside down while holding it.

[0021] Moreover, cassette tables 8a and 8b are provided in front of the opening 4a. Cassettes 10a and 10b, each capable of accommodating a plurality of SiC substrates 11, are placed on the cassette tables 8a and 8b. Moreover, a position adjustment mechanism 12 for adjusting the position of the SiC substrate 11 is provided diagonally behind the opening 4a.

[0022] The position adjustment mechanism 12 includes, for example, a table 12a configured to support the central portion of the SiC substrate 11, and a plurality of pins 12b configured to be able to move toward and away from the table 12a in an area outside the table 12a. For example, the SiC substrate 11 carried out from the cassette 10a by the transport mechanism 6 is carried onto the table 12a.

[0023] Then, in the position adjustment mechanism 12, the position of the SiC substrate 11 loaded onto the table 12a is adjusted. Specifically, by moving the plurality of pins 12b closer to the table 12a until they come into contact with the side surfaces of the SiC substrate 11 loaded onto the table 12a, the center position of the SiC substrate 11 is adjusted to a predetermined position in a plane parallel to the X-axis direction and the Y-axis direction (XY plane).

[0024] Further, a transfer mechanism 14 is provided near the position adjustment mechanism 12, which turns and transfers the SiC substrate 11 while holding it by suction. This transfer mechanism 14 has a suction pad that can suck the upper surface side of the SiC substrate 11, and transfers the SiC substrate 11, the position of which has been adjusted by the position adjustment mechanism 12, backward. Further, a disk-shaped turntable 16 is provided behind the transfer mechanism 14.

[0025] The turntable 16 is connected to a rotary drive source (not shown) such as a motor, and rotates around a rotation axis that passes through the center of the turntable 16 and is parallel to the Z-axis direction. In addition, on the upper surface of the turntable 16, multiple (for example, four) chuck tables 18 are provided at approximately equal intervals along the circumferential direction of the turntable 16.

[0026] Then, the transfer mechanism 14 transfers the SiC substrate 11 from the table 12a of the position adjustment mechanism 12 to the chuck table 18 arranged at a transfer-in / transfer-out position near the transfer mechanism 14. The turntable 16 rotates, for example, in the direction of the arrow shown in Fig. 3, and moves each chuck table 18 to the transfer-in / transfer-out position, the rough grinding position, the finish grinding position, and the polishing position in this order.

[0027] Furthermore, the chuck table 18 is connected to a suction source (not shown) such as a vacuum pump, and can hold the SiC substrate 11 placed on the upper surface of the chuck table 18 by applying a suction force to the SiC substrate 11. The chuck table 18 is also connected to a rotation drive source (not shown) such as a motor, and can be rotated by the power of this rotation drive source around a rotation axis that passes through the center of the chuck table 18 and is parallel to the Z-axis direction.

[0028] A columnar support structure 20 is provided behind each of the rough grinding position and the finish grinding position (behind the turntable 16). A Z-axis movement mechanism 22 is provided on the front surface (the surface on the turntable 16 side) of the support structure 20. This Z-axis movement mechanism 22 is fixed to the front surface of the support structure 20 and has a pair of guide rails 24 extending along the Z-axis direction.

[0029] A moving plate 26 is connected to the front sides of the pair of guide rails 24 in a manner that allows it to slide along the pair of guide rails 24. A screw shaft 28 extending along the Z-axis direction is disposed between the pair of guide rails 24. A motor 30 for rotating the screw shaft 28 is connected to the upper end of the screw shaft 28.

[0030] A ball screw is formed by providing a nut portion (not shown) that houses balls that roll on the surface of the rotating screw shaft 28 on the surface of the screw shaft 28 where the spiral groove is formed. That is, when the screw shaft 28 rotates, the balls circulate inside the nut portion, and the nut portion moves along the Z-axis direction.

[0031] Furthermore, this nut portion is fixed to the rear surface (back surface) side of the movable plate 26. Therefore, when the screw shaft 28 is rotated by the motor 30, the movable plate 26 moves along the Z-axis direction together with the nut portion. Furthermore, a fixing device 32 is provided on the front surface (front surface) of the movable plate 26.

[0032] The fixture 32 supports a grinding unit 34 for grinding the SiC substrate 11. The grinding unit 34 includes a spindle housing 36 fixed to the fixture 32. A spindle 38 extending along the Z-axis direction is rotatably housed in the spindle housing 36.

[0033] A rotary drive source (not shown), such as a motor, is connected to the upper end of the spindle 38, and the spindle 38 can rotate around a rotation axis that is a straight line parallel to the Z-axis direction by the power of this rotary drive source. The lower end of the spindle 38 is exposed from the bottom surface of the spindle housing 36, and a disk-shaped mount 40 is fixed to this lower end.

[0034] A grinding wheel 42a for rough grinding is attached to the underside of the mount 40 of the grinding unit 34 on the rough grinding position side. This grinding wheel 42a for rough grinding has a disk-shaped wheel base with roughly the same diameter as the mount 40. A plurality of grinding wheels (grinding wheels for rough grinding), each having a rectangular parallelepiped shape, are fixed to the underside of this wheel base.

[0035] Similarly, a grinding wheel 42b for finish grinding is attached to the underside of the mount 40 of the grinding unit 34 on the finish grinding position side. This grinding wheel 42b for finish grinding has a disk-shaped wheel base with roughly the same diameter as the mount 40. A plurality of grinding wheels (finish grinding wheels), each of which has a rectangular parallelepiped shape, are fixed to the underside of this wheel base.

[0036] Each of the rough grinding wheel and the finish grinding wheel includes abrasive grains made of, for example, diamond or cBN (cubic boron nitride) and a bond that holds the abrasive grains in place. The bond may be, for example, a metal bond, a resin bond, or a vitrified bond.

[0037] The average particle size of the abrasive grains contained in the grinding wheel for finish grinding is generally smaller than that of the abrasive grains contained in the grinding wheel for rough grinding. For example, the average particle size of the abrasive grains contained in the grinding wheel for rough grinding is 0.5 μm or more and 30 μm or less, and the average particle size of the abrasive grains contained in the grinding wheel for finish grinding is less than 0.5 μm.

[0038] Furthermore, liquid supply nozzles (not shown) are arranged near the grinding wheels 42a, 42b to supply a liquid (grinding fluid) such as pure water to the processing point when grinding the SiC substrate 11. Alternatively, instead of or in addition to these nozzles, openings for supplying liquid may be provided in the grinding wheels 42a, 42b, and the grinding fluid may be supplied to the processing point through these openings.

[0039] A support structure 44 is provided on the side of the polishing area (on the side of the turntable 16). An X-axis movement mechanism 46 is provided on the side of the support structure 44 facing the turntable 16. The X-axis movement mechanism 46 is fixed to the side of the support structure 44 facing the turntable 16, and has a pair of guide rails 48 extending along the X-axis direction.

[0040] A moving plate 50 is connected to the pair of guide rails 48 on the turntable 16 side thereof in a manner that allows it to slide along the pair of guide rails 48. A screw shaft 52 extending along the X-axis direction is disposed between the pair of guide rails 48. A motor 54 for rotating the screw shaft 52 is connected to the front end of the screw shaft 52.

[0041] A nut portion (not shown) that houses balls that roll on the surface of the rotating screw shaft 52 is provided on the surface of the screw shaft 52 on which the spiral groove is formed, thereby forming a ball screw. That is, when the screw shaft 52 rotates, the balls circulate inside the nut portion, and the nut portion moves along the X-axis direction.

[0042] The nut portion is fixed to the surface (back surface) of the moving plate 50 that faces the support structure 44. Therefore, when the screw shaft 52 is rotated by the motor 54, the moving plate 50 moves along the X-axis direction together with the nut portion. Furthermore, a Z-axis movement mechanism 56 is provided on the surface (front surface) of the moving plate 50 that faces the turntable 16.

[0043] The Z-axis movement mechanism 56 has a pair of guide rails 58 that are fixed to the surface of the moving plate 50 and extend along the Z-axis direction. A moving plate 60 is connected to the pair of guide rails 58 on the turntable 16 side in a manner that allows it to slide along the pair of guide rails 58.

[0044] A screw shaft 62 extending along the Z-axis direction is disposed between the pair of guide rails 58. A motor 64 for rotating the screw shaft 62 is connected to the upper end of the screw shaft 62. A nut portion (not shown) for accommodating balls that roll on the surface of the rotating screw shaft 62 is provided on the surface of the screw shaft 62 on which a spiral groove is formed, thereby constituting a ball screw.

[0045] That is, when the screw shaft 62 rotates, the balls circulate inside the nut portion, causing the nut portion to move along the Z-axis direction. In addition, this nut portion is fixed to the surface (back surface) of the moving plate 60 that faces the moving plate 50. Therefore, when the screw shaft 62 is rotated by the motor 64, the moving plate 60 moves along the Z-axis direction together with the nut portion.

[0046] Furthermore, a fixture 66 is provided on the surface (front surface) of the moving plate 60 facing the turntable 16. This fixture 66 supports a polishing unit 68 for polishing the SiC substrate 11. The polishing unit 68 includes a spindle housing 70 fixed to the fixture 66.

[0047] A spindle 72 extending along the Z-axis direction is rotatably housed in the spindle housing 70. A rotation drive source (not shown) such as a motor is connected to the upper end of the spindle 72, and the spindle 72 rotates by the power of this rotation drive source.

[0048] The lower end of the spindle 72 is exposed from the underside of the spindle housing 70, and a disk-shaped mount 74 is fixed to this lower end. A disk-shaped polishing pad 76 is attached to the underside of the mount 74. The polishing pad 76 has a disk-shaped base with approximately the same diameter as the mount 74.

[0049] A disk-shaped polishing layer having roughly the same diameter as the mount 74 is fixed to the underside of the base. This polishing layer is a fixed abrasive layer with abrasive grains dispersed therein. For example, the polishing layer is manufactured by impregnating a polyester nonwoven fabric with a urethane solution in which abrasive grains with an average grain size of 0.4 μm to 0.6 μm are dispersed, followed by drying.

[0050] The abrasive grains dispersed within the polishing layer are made of materials such as SiC, cBN, diamond, or metal oxide particles. The metal oxide particles are made of silica (SiO2), ceria (CeO2), zirconia (ZrO2), or alumina (Al2O3). The polishing layer is flexible and bends slightly in response to the pressure applied when polishing the SiC substrate 11.

[0051] Furthermore, the radial centers of the spindle 72, the mount 74, the base of the polishing pad 76, and the polishing layer are generally aligned, and a cylindrical through-hole is formed through these centers. This through-hole communicates with a polishing liquid supply source (not shown) that supplies a liquid (polishing liquid) such as pure water to the processing point when polishing the SiC substrate 11.

[0052] The polishing liquid supply source includes a polishing liquid storage tank, a liquid pump, etc. The polishing liquid supply source supplies the polishing liquid to the chuck table 18 positioned at the polishing position through a through-hole formed in the spindle 72, etc. The polishing liquid may or may not contain abrasive grains.

[0053] Further, a transfer mechanism 78 that turns and transfers the SiC substrate 11 while holding it by suction is provided on the side of the transfer mechanism 14. This transfer mechanism 78 has a suction pad that can suck the upper surface side of the SiC substrate 11, and transfers the SiC substrate 11 placed on the chuck table 18 positioned at the load / unload position forward.

[0054] Further, a cleaning mechanism 80 configured to be able to clean the upper surface side of the SiC substrate 11 carried out by the transfer mechanism 78 is disposed in front of the transfer mechanism 78 and behind the opening 4a. The SiC substrate 11 cleaned by this cleaning mechanism 80 is then transferred by the transfer mechanism 6 and housed in, for example, a cassette 10b.

[0055] In the processing device 2, for example, the grinding step (S2) and the polishing step (S3) are performed in the following order: First, while the front surface side of the SiC substrate 11 accommodated in the cassette 10a is being sucked, the transfer mechanism 6 unloads the SiC substrate 11 from the cassette 10a and loads the SiC substrate 11 onto the table 12a of the position adjustment mechanism 12 so that the front surface 11a faces up. Next, the SiC substrate 11 is aligned by bringing a plurality of pins 12b into contact with the SiC substrate 11.

[0056] Next, with the front surface 11a of the aligned SiC substrate 11 being sucked, the transfer mechanism 14 unloads the SiC substrate 11 from the table 12a and loads it onto the chuck table 18, which is placed at the load / unload position, with the front surface 11a facing up. Next, the chuck table 18 onto which the SiC substrate 11 has been loaded holds the back surface (lower surface) 11b of the SiC substrate 11 by suction. Next, as shown in FIG. 4(A), the front surface 11a of the SiC substrate 11 is ground.

[0057] Specifically, first, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 is positioned at the rough grinding position. Next, while both the chuck table 18 and the spindle 38 of the grinding unit 34 on the rough grinding position side are rotated, the Z-axis movement mechanism 22 lowers the grinding unit 34 on the rough grinding position side so that the grinding stone of the grinding wheel 42a comes into contact with the front surface (upper surface) 11a of the SiC substrate 11.

[0058] This results in rough grinding of the surface 11a of the SiC substrate 11. At this time, a grinding fluid is supplied to the contact interface (processing point) between the grinding stone of the grinding wheel 42a and the surface 11a of the SiC substrate 11. At this time, the rotation speeds of the chuck table 18 and the spindle 38 are, for example, 1000 rpm or more and 5000 rpm or less. At this time, the lowering speed of the grinding unit 34 when the grinding stone of the grinding wheel 42a and the surface 11a of the SiC substrate 11 are in contact with each other is, for example, 1 μm / sec or more and 10 μm / sec or less.

[0059] Next, the Z-axis movement mechanism 22 raises the grinding unit 34 on the rough grinding position side so that the grinding stone of the grinding wheel 42a is spaced apart from the surface (upper surface) 11a of the SiC substrate 11. Next, the rotations of both the chuck table 18 and the spindle 38 of the grinding unit 34 on the rough grinding position side are stopped. Next, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 is positioned at the finish grinding position.

[0060] Next, while rotating both the chuck table 18 and the spindle 38 of the grinding unit 34 on the finish grinding position side, the Z-axis moving mechanism 22 lowers the grinding unit 34 on the finish grinding position side so that the grinding stone of the grinding wheel 42b comes into contact with the surface (upper surface) 11a of the SiC substrate 11.

[0061] This finish-grinds the surface 11a of the SiC substrate 11. At this time, a grinding fluid is supplied to the contact interface (processing point) between the grinding stone of the grinding wheel 42b and the surface 11a of the SiC substrate 11. At this time, the rotation speeds of the chuck table 18 and the spindle 38 are, for example, 1000 rpm or more and 5000 rpm or less. The lowering speed of the grinding unit 34 when the grinding stone of the grinding wheel 42b and the surface 11a of the SiC substrate 11 are in contact with each other is, for example, less than 1 μm / sec.

[0062] Next, the Z-axis movement mechanism 22 raises the grinding unit 34 on the finish grinding position side so that the grinding stone of the grinding wheel 42b is spaced apart from the surface (upper surface) 11a of the SiC substrate 11. Next, the rotations of both the chuck table 18 and the spindle 38 of the grinding unit 34 on the finish grinding position side are stopped. This completes the grinding of the surface 11a side of the SiC substrate 11 (first grinding step).

[0063] Next, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 passes through the polishing position and is positioned at the load / unload position. Next, the chuck table 18 positioned at the load / unload position stops suctioning the back surface (lower surface) 11b of the SiC substrate 11.

[0064] Next, while the front surface (upper surface) 11a of the SiC substrate 11 placed on the chuck table 18 is being sucked, the transfer mechanism 78 unloads the SiC substrate 11 from the chuck table 18 and loads it into the cleaning mechanism 80 with the front surface facing up. Next, the cleaning mechanism 80 cleans the front surface 11a of the SiC substrate 11.

[0065] Next, with the back surface 11b side of SiC substrate 11 being sucked, transfer mechanism 6 unloads SiC substrate 11 from cleaning mechanism 80 and loads it onto table 12a of position adjustment mechanism 12 with back surface 11b facing up. Next, multiple pins 12b are brought into contact with SiC substrate 11, thereby aligning SiC substrate 11.

[0066] Next, with the back surface 11b of the aligned SiC substrate 11 being sucked, the transfer mechanism 14 unloads the SiC substrate 11 from the table 12a and loads it onto the chuck table 18 arranged at the load / unload position with the back surface 11b facing up. Next, the chuck table 18 onto which the SiC substrate 11 has been loaded holds the front surface (lower surface) 11a of the SiC substrate 11 by suction. Next, as shown in FIG. 4(B), the back surface 11b of the SiC substrate 11 is ground.

[0067] Specifically, first, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 is positioned at the rough grinding position. Next, while both the chuck table 18 and the spindle 38 of the grinding unit 34 on the rough grinding position side are rotated, the Z-axis movement mechanism 22 lowers the grinding unit 34 on the rough grinding position side so that the grinding stone of the grinding wheel 42a comes into contact with the back surface (upper surface) 11b of the SiC substrate 11.

[0068] This roughly grinds the back surface 11b of the SiC substrate 11. At this time, a grinding fluid is supplied to the contact interface (processing point) between the grinding stone of the grinding wheel 42a and the back surface 11b of the SiC substrate 11. At this time, the rotation speeds of the chuck table 18 and the spindle 38 are, for example, 1000 rpm or more and 5000 rpm or less. At this time, the lowering speed of the grinding unit 34 when the grinding stone of the grinding wheel 42a and the back surface 11b of the SiC substrate 11 are in contact with each other is, for example, 1 μm / sec or more and 10 μm / sec or less.

[0069] The grinding wheel 42a used here may be the same as or different from the one used for rough grinding the front surface 11a of the SiC substrate 11. That is, the grinding stone used for rough grinding the back surface 11b of the SiC substrate 11 may be the same as or different from the grinding stone used for rough grinding the front surface 11a of the SiC substrate 11.

[0070] Next, the Z-axis movement mechanism 22 raises the grinding unit 34 on the rough grinding position side so that the grinding stone of the grinding wheel 42a is spaced apart from the back surface (upper surface) 11b of the SiC substrate 11. Next, the rotations of both the chuck table 18 and the spindle 38 of the grinding unit 34 on the rough grinding position side are stopped. Next, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 is positioned at the finish grinding position.

[0071] Next, while rotating both the chuck table 18 and the spindle 38 of the grinding unit 34 on the rough grinding position side, the Z-axis moving mechanism 22 lowers the grinding unit 34 on the finish grinding position side so that the grinding stone of the grinding wheel 42b comes into contact with the back surface (upper surface) 11b of the SiC substrate 11.

[0072] This finish-grinds the back surface 11b of the SiC substrate 11. At this time, a grinding fluid is supplied to the contact interface (processing point) between the grinding stone of the grinding wheel 42b and the back surface 11b of the SiC substrate 11. At this time, the rotation speeds of the chuck table 18 and the spindle 38 are, for example, 1000 rpm or more and 5000 rpm or less. The lowering speed of the grinding unit 34 when the grinding stone of the grinding wheel 42b and the back surface 11b of the SiC substrate 11 are in contact with each other is, for example, less than 1 μm / sec.

[0073] The grinding wheel 42b used here may be the same as or different from the one used in finish grinding the front surface 11a of the SiC substrate 11. That is, the grinding stone used in finish grinding the back surface 11b of the SiC substrate 11 may be the same as or different from the grinding stone used in finish grinding the front surface 11a of the SiC substrate 11.

[0074] The back surface 11b of the SiC substrate 11 is ground so that the arithmetic mean height Sa of the back surface after finish grinding is 1 nm or less. The arithmetic mean height Sa is a parameter indicating surface roughness defined by ISO 25178, and is a parameter obtained by extending the arithmetic mean height Ra, which is a parameter indicating line roughness, to a surface.

[0075] Next, the Z-axis movement mechanism 22 raises the grinding unit 34 on the finish grinding position side so that the grinding stone of the grinding wheel 42b is spaced apart from the back surface (upper surface) 11b of the SiC substrate 11. Next, the rotations of both the chuck table 18 and the spindle 38 of the grinding unit 34 on the finish grinding position side are stopped. This completes the grinding of the back surface 11b side of the SiC substrate 11 (second grinding step).

[0076] Next, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 passes through the polishing position and is positioned at the load / unload position. Next, the chuck table 18 positioned at the load / unload position stops suctioning the front surface (lower surface) 11a side of the SiC substrate 11.

[0077] Next, while the back surface (upper surface) 11b of the SiC substrate 11 placed on the chuck table 18 is being sucked, the transfer mechanism 78 unloads the SiC substrate 11 from the chuck table 18 and loads it into the cleaning mechanism 80 with the back surface 11b facing up. Next, the cleaning mechanism 80 cleans the back surface 11b of the SiC substrate 11.

[0078] Next, while the front surface 11a side of the SiC substrate 11 is being sucked, the transfer mechanism 6 carries the SiC substrate 11 out of the cleaning mechanism 80 and carries it onto the table 12a of the position adjustment mechanism 12 so that the front surface 11a faces up. Next, the SiC substrate 11 is aligned by bringing a plurality of pins 12b into contact with the SiC substrate 11.

[0079] Next, with the front surface 11a of the aligned SiC substrate 11 being sucked, the transfer mechanism 14 unloads the SiC substrate 11 from the table 12a and loads it onto the chuck table 18, which is placed at the load / unload position, with the front surface 11a facing up. Next, the chuck table 18 onto which the SiC substrate 11 has been loaded holds the back surface (lower surface) 11b of the SiC substrate 11 by suction. Next, as shown in FIG. 5, the front surface 11a of the SiC substrate 11 is polished.

[0080] Specifically, first, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 passes through the rough grinding position and the finish grinding position and is positioned at the polishing position. Next, while both the chuck table 18 and the spindle 72 of the polishing unit 68 are rotating, the Z-axis movement mechanism 56 lowers the polishing unit 68 so that the polishing layer of the polishing pad 76 comes into contact with the surface (upper surface) 11a of the SiC substrate 11.

[0081] This polishes the surface 11a of the SiC substrate 11. At this time, the polishing liquid 13 is supplied from the polishing liquid supply source to the surface (upper surface) 11a of the SiC substrate 11 via a through-hole 82 that penetrates the spindle 72, the mount 74, and the polishing pad 76.

[0082] At this time, the rotation speed of the chuck table 18 is, for example, 300 rpm or more and 750 rpm or less. Also, the rotation speed of the spindle 72 is, for example, 300 rpm or more and 1000 rpm or less. Also, at this time, the pressure applied to the surface 11a of the SiC substrate 11 is, for example, 200 g / cm. 2 More than 750g / cm 2 The following is the result.

[0083] Next, the Z-axis movement mechanism 56 raises the polishing unit 68 so that the polishing layer of the polishing pad 76 is spaced apart from the surface (upper surface) 11a of the SiC substrate 11. Next, the rotations of both the chuck table 18 and the spindle 72 are stopped. This completes the polishing of the surface 11a side of the SiC substrate 11.

[0084] Next, the turntable 16 rotates so that the chuck table 18 holding the SiC substrate 11 is positioned at the load / unload position. Next, the chuck table 18 positioned at the load / unload position stops suctioning the back surface (lower surface) of the SiC substrate 11.

[0085] Next, while the front surface (upper surface) 11a of the SiC substrate 11 placed on the chuck table 18 is being sucked, the transfer mechanism 78 unloads the SiC substrate 11 from the chuck table 18 and loads it into the cleaning mechanism 80 with the front surface 11a facing up. Next, the cleaning mechanism 80 cleans the front surface 11a of the SiC substrate.

[0086] Next, the transfer mechanism 6 carries the SiC substrate 11 into the cassette 10b while sucking the front or back side of the SiC substrate 11. This completes the grinding step (S2) and the polishing step (S3) in the processing device 2.

[0087] In the above-described method for manufacturing a SiC substrate, the front surface 11a side where the Si surface is exposed is ground, and the back surface 11b side where the C surface is exposed is ground so that the arithmetic mean height Sa of the back surface 11b side is 1 nm or less, and then only the front surface 11a side is polished without polishing the back surface 11b side.

[0088] When the back surface 11b side is ground in this manner, warpage of the SiC substrate 11 can be suppressed without further polishing the back surface 11b side of the SiC substrate 11. Therefore, this method can shorten the manufacturing lead time of the SiC substrate 11 used in the manufacture of power devices and the like, and reduce the manufacturing cost.

[0089] The above-described method is one aspect of the present invention, and the present invention is not limited to the above-described method. For example, in the grinding step (S2) of the above-described method for manufacturing a SiC substrate, the front surface 11a side is ground and then the back surface 11b side is ground, but in the grinding step (S2) of the present invention, the back surface 11b side may be ground and then the front surface 11a side may be ground.

[0090] In this case, after grinding the side of front surface 11a of SiC substrate 11, front surface 11a of SiC substrate 11 can be polished without turning over SiC substrate 11 held on chuck table 18. Therefore, in this case, it is possible to further shorten the manufacturing lead time of SiC substrate 11 used in the manufacture of power devices and the like, and further reduce manufacturing costs.

[0091] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Example]

[0092] An example of a method for manufacturing a SiC substrate according to the present invention will be described below. First, a cylindrical SiC ingot with a diameter of 6 inches was prepared. Next, three SiC substrates were cut from the SiC ingot using a diamond wire saw so that the Si face was exposed on the front surface and the C face was exposed on the back surface, and the thickness was 500 μm to 600 μm. Next, rough grinding and finish grinding were performed on both the front surface and back surface of one of the three SiC substrates under the same conditions.

[0093] Specifically, the rough grinding was performed using a grinding wheel having a grinding stone including a vitrified bond that holds the abrasive grains and diamond grains with an average grain size of 14 μm. Furthermore, during the rough grinding, the rotation speed of both the grinding wheel and the chuck table that holds the SiC substrate was set to 2000 rpm, and the lowering speed of the grinding unit with the grinding stone in contact with the front or back surface of the SiC substrate was set to 3 μm / sec.

[0094] The finish grinding was performed using a grinding wheel having a grinding stone including abrasive grains made of diamond with an average grain size of 0.2 μm and a vitrified bond for holding the abrasive grains. Furthermore, in the finish grinding, the rotation speed of both the grinding wheel and the chuck table for holding the SiC substrate was set to 3000 rpm, and the lowering speed of the grinding unit when the grinding stone was in contact with the front surface 11 a or the back surface 11 b of the SiC substrate 11 was set to 0.15 μm / sec. Thus, the SiC substrate of Example 1 was obtained.

[0095] Next, rough grinding and finish grinding were performed on both sides of another of the three SiC substrates under the same conditions as for the SiC substrate of Example 1, except that the average abrasive grain size of the grinding stone of the grinding wheel used for finish grinding was different. Specifically, this finish grinding was performed using a grinding wheel with a grinding stone containing abrasive grains made of 0.3 μm diamond and a vitrified bond that held the abrasive grains. This resulted in the SiC substrate of Example 2.

[0096] Next, rough grinding and finish grinding were performed on both sides of the remaining one of the three SiC substrates under the same conditions as for the SiC substrates of Examples 1 and 2, except that the average abrasive grain size of the abrasive grains contained in the grinding stone of the grinding wheel used for finish grinding was different. Specifically, this finish grinding was performed using a grinding wheel having a grinding stone containing abrasive grains made of 0.5 μm diamond and a vitrified bond that held the abrasive grains. This resulted in a SiC substrate of the comparative example.

[0097] Table 1 below shows the arithmetic mean height Sa of the rear surface after finish grinding was performed on both sides of each of the SiC substrates of Examples 1 and 2 and the comparative example. [Table 1]

[0098] Next, polishing was performed on only the front side of each of the SiC substrates of Examples 1 and 2 and Comparative Example, without polishing on the back side. Specifically, this polishing was performed using a polishing pad including a polishing layer in which abrasive grains made of silica (SiO2) with a particle size of 0.4 μm to 0.6 μm were dispersed in a nonwoven fabric. Furthermore, in this polishing, the rotation speed of the polishing pad was set to 745 rpm, the rotation speed of the chuck table holding the SiC substrate was set to 750 rpm, and the pressure applied to the surface of the SiC substrate was set to 400 g / cm. 2 It was decided.

[0099] Table 2 below shows the amount of warpage of the SiC substrates of Examples 1 and 2 and the comparative example after polishing only the front surface side of each SiC substrate without polishing the rear surface side. [Table 2]

[0100] As shown in Tables 1 and 2, by grinding the front surface side of the SiC substrate where the Si face is exposed and grinding the back surface side so that the arithmetic mean height Sa of the back surface where the C face is exposed is 1 nm or less, it was found that the amount of warpage of the SiC substrate can be reduced even when polishing only the front surface side without polishing the back surface side of the SiC substrate. [Explanation of symbols]

[0101] 11:SiC substrate (11a: front side, 11b: back side) 13: Polishing liquid 2: Processing equipment 4: Base (4a: opening) 6: Transport mechanism 8a, 8b: Cassette table 10a, 10b: cassette 12: Position adjustment mechanism (12a: table, 12b: pin) 14: Transport mechanism 16: Turntable 18: Chuck table 20 :Support structure 22:Z-axis movement mechanism 24: Guide rail 26: Moving plate 28: Screw shaft 30: Motor 32: Fixture 34: Grinding unit 36: Spindle housing 38: Spindle 40: Mount 42a, 42b: Grinding wheels 44:Support structure 46:X-axis movement mechanism 48: Guide rail 50: Moving plate 52: Screw shaft 54: Motor 56:Z-axis movement mechanism 58: Guide rail 60: Moving plate 62: Screw shaft 64: Motor 66: Fixtures 68: Polishing unit 70: Spindle housing 72: Spindle 74: Mount 76: Polishing pad 78:Transport mechanism 80: Cleaning mechanism 82: Through hole

Claims

1. a separation step of separating the SiC substrate from the SiC ingot so as to expose a Si-face on a front surface and a C-face on a back surface; a grinding step of grinding both the front surface side and the back surface side of the SiC substrate after the separation step; a polishing step of polishing only the front surface side of the SiC substrate without polishing the back surface side thereof after the grinding step, The grinding step includes: a first grinding step of grinding the front surface side of the SiC substrate; a second grinding step of grinding the back surface side of the SiC substrate, In the second grinding step, the back surface side of the SiC substrate is ground so that an arithmetic mean height Sa of the back surface is 1 nm or less; The method for manufacturing a SiC substrate, wherein grinding of the back surface side of the SiC substrate is completed by the second grinding step.

2. 2. The method for manufacturing a SiC substrate according to claim 1, wherein an average particle size of abrasive grains contained in the grinding stone used in the second grinding step is 0.3 μm or less.

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