TWI621165B - Processing method of sapphire substrate - Google Patents

Abstract

An object of the present invention is to provide a sapphire substrate having a small amount of waste when cut out from a sapphire crystal rod and capable of forming a front surface and a back surface of a sapphire substrate with an A surface having good compatibility with a light emitting layer formed of a gallium nitride compound semiconductor. A guaranteed processing method for sapphire substrates. The solution is a method for processing a sapphire substrate cut from a sapphire crystal rod and grinding the sapphire substrate on the front and back sides of the sapphire substrate. The processing method includes a holding step, holding the object to be processed, and The side surface is held on a rotatable chuck table; and a grinding step of rotating the chuck table holding the sapphire substrate, while rotating the grinding wheel configured as a ring-shaped grinding wheel while contacting the grinding ocher with another sapphire substrate The side surface is polished, and in the polishing step, a slurry mixed with diamond abrasive grains is supplied as a polishing liquid to a polishing portion formed by polishing vermiculite.

Description

Processing method of sapphire substrate Field of invention

The present invention relates to a sapphire substrate. More specifically, it is a method for processing a sapphire substrate cut from a sapphire crystal rod and forming a front surface and a back surface with an A surface, and polishing the sapphire substrate.

Background of the invention

In the manufacturing step of the optical device, a light-emitting layer made of a gallium nitride-based compound semiconductor is formed on a sapphire substrate surface area, and is formed in a plurality of regions divided by a plurality of scribe lines forming a grid. Optical devices such as light emitting diodes and laser diodes constitute optical device wafers. Then, the optical device wafer is cut along the dicing path to divide the area where the optical device is formed to manufacture individual optical devices.

Sapphire is formed into a crystal structure having a crystal plane called A-plane, C-plane, and R-plane, and a sapphire substrate with the A-plane, C-plane, and R-plane as the front and back surfaces is formed by cutting out a sapphire ingot. That is to say, the sapphire crystal rod has a truncated cone shape similar to a cylinder, and the bottom surface and the top surface of the truncated cone shape are A surface, the surface orthogonal to the A surface is the C surface, and it is inclined relative to the C surface. The surface is the R surface; when the core material is cut out from the top surface to the bottom surface, a sapphire substrate with the A surface as the front and the back can be formed, and the frustoconical body The sapphire substrate with the C surface as the front and the back can be formed when the cut sheet is cut out in a direction parallel to the A side. When the core material is cut out from the direction orthogonal to the R plane, the R can be formed. The front and back are made of sapphire substrates. Because the crystal structures of the A, C, and R planes are different, the ideal method is to appropriately select a sapphire substrate that can correspond to the crystal structure of the light-emitting layer of the laminated layer.

Although an optical device wafer is manufactured by forming a light-emitting layer on a surface area of a sapphire substrate, the sapphire substrate cut before the light-emitting layer is laminated is also polished with a polishing device to planarize the front and back surfaces (see, for example, Patent Document 1). ).

Prior art literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 2007-38357

Summary of invention

In view of the fact that the above-mentioned C-plane of sapphire can pass through the polishing device, the substrate of the optical device wafer usually uses a sapphire substrate with the C-plane as the front and back.

However, as the sapphire substrate with the C surface as the front and back, the sapphire crystal rod in the shape of a truncated cone is cut out from the side in a direction parallel to the A surface as described above, so there are sapphire crystal rods The problem of excessive waste and poor productivity.

On the other hand, the A side is made into a front and back sapphire substrate. As described above, the frustum-shaped sapphire crystal rod is dug out from the top surface to the bottom surface and cut into thin slices. Therefore, the sapphire crystal rod has less waste and emits light at the same time as a gallium nitride-based compound semiconductor. The layer has the advantage of good compatibility. However, when the A surface is polished with a polishing device, gouges are generated and there is a problem that the surface accuracy cannot be ensured.

The present invention has been made in view of the above-mentioned facts, and its main technical problem is to provide an A that has less waste when cutting out a sapphire crystal rod and has good compatibility with a light-emitting layer formed of a gallium nitride-based compound semiconductor. The surface accuracy of the sapphire substrate on the front and back sides can be obtained to ensure the processing method of the sapphire substrate.

In order to solve the above-mentioned main technical problems, the method for processing a sapphire substrate provided by the present invention is a method for processing a sapphire substrate cut from a sapphire ingot and grinding the sapphire substrate with front and back sides formed on the A side. The processing method includes a holding step of holding the object to be processed and holding one side of the sapphire substrate on a rotatable chuck table; and a polishing step of rotating the chuck table holding the sapphire substrate while one side Rotate the grinding vermiculite into a ring-shaped grinding wheel while contacting the grinding vermiculite with the other side of the sapphire substrate to grind the other side of the sapphire substrate; in this grinding step, the diamond mixed with diamond is ground. The granular slurry is supplied as a polishing liquid to a polishing portion formed by polishing vermiculite.

The above-mentioned grinding vermiculite is a diamond abrasive grain with a particle size of 1 to 2 μm. It is composed by mixing in a binder, and the above-mentioned polishing liquid is a slurry prepared by mixing pure diamond abrasive particles with a particle diameter of 3 to 9 μm into pure water.

In the method for processing a sapphire substrate according to the present invention, a chuck table holding one side of the sapphire substrate having front and back surfaces formed by the A side is rotated, and at the same time, the grinding wheel arranged to form a ring-shaped grinding wheel is rotated. The grinding step in which the grinding vermiculite is brought into contact with the other side of the sapphire substrate to grind the other side of the sapphire substrate is a grinding process in which a slurry mixed with diamond abrasive grains is supplied as a polishing liquid to the grinding vermiculite. Therefore, the sapphire substrate can be multiplied by the grinding effect of grinding vermiculite and the polishing effect of grinding the vermiculite formed by supplying a slurry obtained by mixing diamond abrasive particles into pure water. The A surface, that is, the surface to be polished, can obtain good surface accuracy without scratching.

2‧‧‧ device case

21‧‧‧Main Department

22‧‧‧ upright wall

221‧‧‧rail

23a, 23b, 5a, 71a

24‧‧‧ Workpiece placement area

25‧‧‧grinding area

3‧‧‧mobile base

31‧‧‧foot

311‧‧‧Guided trench

32‧‧‧ support

4‧‧‧ shaft unit

40‧‧‧Grinding fluid supply mechanism

41‧‧‧Shaft housing

42‧‧‧rotating spindle

421‧‧‧Grinding liquid supply channel

422‧‧‧ with access

43‧‧‧Servo motor

44‧‧‧ Grinding wheel mount

441‧‧‧bolt insertion hole

5‧‧‧ grinding wheel

51‧‧‧ Grinding wheel base

511‧‧‧female screw hole

52‧‧‧ ground vermiculite

55‧‧‧Connecting bolt

6‧‧‧ grinding feed mechanism

61‧‧‧Male Screw

62, 63‧‧‧bearing components

64‧‧‧Pulse motor

7‧‧‧ chuck table mechanism

71‧‧‧Chuck table

72‧‧‧ cover member

73, 74‧‧‧ Telescopic tube mechanism

10‧‧‧ sapphire substrate

10a‧‧‧front

10b‧‧‧ back

11‧‧‧ Substrate

FIG. 1 is a perspective view of a polishing apparatus for implementing a method of polishing a sapphire substrate according to the present invention; FIG. 2 is a perspective view of the polishing wheel mounting base constituting a polishing mechanism mounted on the polishing apparatus shown in FIG. 1; 3 is a perspective view of a grinding wheel mounted on the grinding wheel mounting base shown in FIG. 2; FIG. 4 is a cross-sectional view of a state where the grinding wheel shown in FIG. 3 is mounted on the grinding wheel mounting base shown in FIG. Figure 5 is a perspective view of a sapphire substrate subjected to the grinding process of the sapphire substrate grinding method of the present invention; FIG. 6 is a perspective view showing a state in which a substrate is stuck on the back of the sapphire substrate shown in FIG. 5; FIG. 7 is a schematic view showing a grinding step performed by the grinding device shown in FIG. 1; It is a schematic diagram of the surface roughness measurement area of the sapphire substrate polished by the sapphire substrate polishing method of the present invention.

Forms used to implement the invention

Hereinafter, referring to the drawings, a preferred embodiment of a method for processing a sapphire substrate according to the present invention will be described in further detail.

FIG. 1 is a perspective view of a polishing apparatus for implementing a method for processing a sapphire substrate according to the present invention. The polishing apparatus 1 shown in FIG. 1 has an apparatus casing, which is generally designated by reference numeral 2. The device casing 2 has a main portion 21 having a rectangular parallelepiped shape that extends slenderly, and an upright wall 22 provided at the rear end portion (upper right end in FIG. 1) of the main portion 21 and extending upward. A pair of guide rails 221 and 221 extending in the vertical direction are provided on the front surface of the upright wall 22. The pair of guide rails 221, 221 is provided with a slidable moving base 3. The moving base 3 is provided with a pair of leg portions 31 and 31 extending in the up-and-down direction on both sides of the rear surface, and a guide is slidably fitted to the pair of guide rails 221 and 221 on the pair of leg portions 31 and 31. Ditch 311, 311. On the front surface of the mobile base 3 slidably mounted on the pair of guide rails 221 and 221 provided on the upright wall 22 in this manner, the support portion 32 is provided to protrude forward. A rotating shaft unit 4 serving as a polishing mechanism is attached to the support portion 32.

The rotating shaft unit 4 has a cylindrical rotating shaft mounted on the support portion 32 A housing 41, a rotating main shaft 42 configured to be rotatable on the rotating shaft housing 41, and a servo motor 43 as a driving source for rotationally driving the rotating main shaft 42. The rotating main shaft 42 supported so as to be rotatable on the rotating shaft case 41 is configured to protrude one end portion (lower end portion in FIG. 1) from the lower end of the rotating shaft case 41, and at the end (in FIG. 1) The lower end) is provided with a grinding wheel mount 44. A polishing wheel 5 is mounted on the lower surface of the polishing wheel mounting base 44.

The above-mentioned grinding wheel mount 44 and grinding wheel 5 will be described with reference to FIGS. 2 to 4.

FIG. 2 is a perspective view of the grinding wheel mounting base 44 provided at the lower end of the rotating main shaft 42, and FIG. 3 is a perspective view of the grinding wheel 5 installed at the lower surface of the grinding wheel mounting base 44. The illustrated grinding wheel 5 is mounted to a sectional view of the lower surface of the grinding wheel mount 44 shown in FIG. 2. The grinding wheel mounting base 44 shown in FIGS. 2 and 4 is formed in a circular shape and is integrally provided at the lower end of the rotating main shaft 42. As shown in FIG. 2, the grinding wheel mounting base 44 is formed with four bolt insertion holes 441 spaced at predetermined intervals along the circumferential direction. In addition, as shown in FIG. 4, a plurality of (eight in the illustrated embodiment) a plurality of connecting passages are formed in the grinding wheel mount 44 and communicate with the grinding liquid supply passage 421 formed on the axis of the rotating main shaft 42. 422, as shown in FIGS. 2 and 4, the connecting channels 422 form openings on the lower surface. It is to be noted that the polishing liquid supply channel 421 formed on the axis of the rotating main shaft 42 is connected to the polishing liquid supply mechanism 40 as shown in FIG. 1. This polishing liquid supply mechanism 40 is a polishing liquid formed by supplying a slurry in which diamond abrasive grains are mixed with pure water.

The grinding wheel 5 mounted on the grinding wheel mount 44 configured as described above will be described with reference to FIGS. 3 and 4.

The grinding wheel 5 shown in FIGS. 3 and 4 includes a ring-shaped grinding wheel base 51 and a plurality of grinding vermiculite 52 mounted on a grinding stone installation portion on the outer peripheral portion of the lower surface of the grinding wheel base 51. Made up. The grinding wheel base 51 is provided with four female screw holes 511 formed from the upper surface at positions corresponding to a plurality of bolt insertion holes 441 formed in the grinding wheel mounting base 44. In addition, the polished vermiculite 52 is constituted by kneading diamond abrasive grains having a particle size of 1 to 2 μm in a binder, kneading, molding into a predetermined shape, and firing.

When the grinding wheel 5 configured as described above is mounted on the grinding wheel mounting base 44, as shown in FIG. 4, the upper surface of the grinding wheel base 51 of the grinding wheel 5 abuts the grinding wheel mounting base. 44 is inserted into the lower surface of the grinding wheel mounting base 44 through a plurality of bolt insertion holes 441 (see FIG. 2), and is connected to the plurality of female screw holes 511 provided on the grinding wheel base 51. As shown in FIG. 3, the grinding wheel 5 can be mounted on the lower surface of the grinding wheel mounting seat 44. In the polishing portion formed by the grinding vermiculite 52 of the grinding wheel 5 mounted on the lower surface of the grinding wheel mounting base 44 in this manner, the grinding liquid supply mechanism 40 is operated to pass through the grinding liquid provided on the rotating main shaft 42. The supply channel 421 and the plurality of communication channels 422 formed in the polishing wheel mounting base 44 are supplied with a polishing liquid made of a slurry obtained by mixing diamond abrasive grains with pure water.

Returning to FIG. 1, the explanation is continued. The polishing device 1 in the illustrated embodiment has the rotating shaft unit 4 in the vertical direction along the pair of guide rails 221 and 221 (the direction perpendicular to the chuck holding surface described later). ) On the grinding feed mechanism 6. The polishing feed mechanism 6 includes a male screw 61 disposed on the front side of the upright wall 22 and extending in the vertical direction. The male screw 61 The bearing members 62 and 63 mounted on the upright wall 22 support the upper end portion and the lower end portion so as to be freely rotatable. The upper bearing member 62 is provided with a pulse motor 64 as a power source for rotationally driving the male screw 61, and an output shaft of the pulse motor 64 is drivingly connected to the male screw 61. A connecting portion (not shown) protruding rearward from a center portion in the width direction of the moving base 3 is also formed on the rear surface of the moving base 3, and a female screw hole (not shown) is formed in the connecting portion, and The male screw 61 is screwed into the female screw hole. In this way, when the pulse motor 64 rotates forward, the mobile base 3 and the shaft unit 4 will descend, that is, forward, and when the pulse motor 64 reverses, the mobile base 3 and the shaft unit 4 will rise, that is, backward.

With reference to FIG. 1, the chuck table mechanism 7 is disposed on the main portion 21 of the device casing 2. The chuck table mechanism 7 includes a chuck table 71 as a workpiece holding mechanism, a cover member 72 covering the periphery of the chuck table 71, and telescopic tube mechanisms 73 and 74 disposed before and after the cover member 72. The chuck table 71 is made rotatable by a rotation driving mechanism (not shown), and is configured to suck and hold a wafer to be processed on an upper surface thereof by operating a suction mechanism (not shown). In addition, the chuck table 71 may be provided with a chuck table moving mechanism (not shown) in the workpiece placement area 24 shown in FIG. 1 and the grinding area facing the grinding wheel 5 constituting the grinding unit 4 described above. Move between 25. The telescopic tube mechanisms 73 and 74 can be made of a suitable material similar to a canvas cloth material. The front end of the telescopic tube mechanism 73 is fixed to the front surface wall of the main portion 21, and the rear end is fixed to the front end surface of the cover member 72. The front end of the telescopic tube mechanism 74 is fixed to the rear end surface of the cover member 72, and the rear end is fixed to the front surface of the vertical wall 22 of the device casing 2. When the chuck table 71 is directed toward the direction shown by the arrow symbol 23a When moving, the telescopic tube mechanism 73 will be stretched and the telescopic tube mechanism 74 will be contracted; when the chuck table 71 is moved in the direction shown by the arrow symbol 23b, the telescopic tube mechanism 73 will be contracted and the telescopic tube mechanism 74 will be stretched.

The polishing apparatus 1 shown in FIGS. 1 to 4 is configured as described above, and is used when performing a final grinding process described later.

FIG. 5 shows a sapphire substrate processed by the processing method of the present invention. The sapphire substrate 10 shown in FIG. 5 is composed of a sapphire substrate in which the front surface 10 a and the back surface 10 b are A-side, and is formed to have a diameter of 150 mm and a thickness of 300 μm. The sapphire substrate 10 formed in this manner is as shown in FIG. 6, and one surface (the back surface 10 b in the illustrated embodiment) is adhered to a substrate 11 formed of a glass plate or the like through wax.

To process the above-mentioned sapphire substrate 10 to a predetermined thickness, first, rough grinding is performed. Although the grinding liquid supply mechanism 40 and the grinding vermiculite 52 of the grinding wheel 5 in the grinding device 1 shown in FIG. 1 to FIG. 4 described above are different, other structures may be substantially the same. The symbols used in the polishing apparatus 1 are used to describe the rough polishing process. When rough polishing is performed, the polishing liquid supply mechanism 40 supplies a polishing liquid made of pure water as before. In addition, the grinding vermiculite 52 of the grinding wheel 5 used is constituted by mixing a diamond abrasive grain having a particle diameter of 10 to 15 μm into a resin binder, kneading, molding into a predetermined shape, and firing.

To perform rough polishing of the sapphire substrate 10, the sapphire substrate 10 to which the substrate 11 is attached as described above is placed on the substrate 11 side in the same rough polishing device as the polishing device 1 shown in FIG. 1 Is positioned on the upper surface of the chuck table 71 of the workpiece placement area 24, that is, the holding surface. and, The sapphire substrate 10 is sucked and held on the chuck table 71 through the substrate 11 by operating a suction mechanism (not shown). In this way, when the sapphire substrate 10 is sucked and held on the chuck table 71 through the base material 11, the chuck table 71 is moved in the direction shown by the arrow symbol 23a by operating a chuck table moving mechanism (not shown). Move and position to the grinding zone 25.

When the chuck table 71 is positioned in the polishing zone 25 in this manner, the chuck table 71 is rotated at a rotation speed of 200 rpm in a predetermined direction as shown in FIG. 7 while the grinding wheel 5 is rotated at a rotation speed of 800 rpm. The pulse motor 64 of the grinding feed mechanism 6 is driven in a forward direction to lower the grinding unit 4 at a speed of 0.1 μm / sec, and the grinding surfaces of the plurality of grinding vermiculite 52 of the grinding wheel 5 are brought into contact with the sapphire substrate held on the chuck table 71. The front surface 10a (upper surface) of 10 is ground and fed by a predetermined amount (100 μm). As a result, the sapphire substrate 10 held on the chuck table 7 can be polished by 100 μm (rough polishing step).

In this rough grinding step, the grinding liquid supply channel 421 formed in the rotating main shaft 42 supplies the grinding liquid made of pure water to the grinding vermiculite 52 of the grinding wheel 5 through the connecting channel 422 formed in the grinding wheel mount 44. The formed abrasive part.

The front surface 10a of the sapphire substrate 10 which has been subjected to the rough polishing process may be subjected to a final polishing process to improve the surface accuracy. This final polishing process is performed using the polishing apparatus 1 shown in FIGS. 1 to 4. In other words, the polishing liquid supply mechanism 40 provides a polishing liquid made of a slurry obtained by mixing diamond abrasive grains with pure water, and the grinding vermiculite 52 of the grinding wheel 5 is obtained by changing the particle diameter of 1 to The 2 μm diamond abrasive particles are mixed in a binder, kneaded, formed into a predetermined shape, and fired to form a structure. In the following, experiments conducted by the inventor of this case Examples will be described.

[Experiment 1]

The sapphire substrate 10 which has been subjected to the rough grinding process as described above is placed on the upper surface of the chuck table 71 positioned on the workpiece placement area 24 of the grinding device 1 shown in FIG. Ie keep on the surface. Then, the sapphire substrate 10 is sucked and held on the chuck table 71 through the base material 11 by operating a suction mechanism (not shown). In this way, when the sapphire substrate 10 has been attracted and held on the chuck table 71 through the substrate 11, the chuck table moving mechanism (not shown) is operated to move the chuck table 71 in the direction shown by the arrow symbol 23a. Positioned to the grinding zone 25.

When this is done and the chuck table 71 is positioned to the grinding zone 25, as shown in FIG. 7, the chuck table 71 is rotated at a rotation speed of 200 rpm in the direction shown by the arrow symbol 71a, and at the same time, it is rotated around the arrow symbol 5a. The grinding wheel 5 is rotated at a rotation speed of 800 rpm in the direction shown, and the pulse motor 64 of the grinding feed mechanism 6 is driven in the forward direction to lower the grinding unit 4 at a speed of 0.1 μm / sec, so that the grinding wheel 5 has a plurality of grinding vermiculites 52 The polished surface contacts the front surface 10a (upper surface) of the sapphire substrate 10 held on the chuck table 71 and performs a grinding feed of a predetermined amount (30 μm). As a result, the sapphire substrate 10 held on the chuck table 71 can be polished away by 30 μm (final polishing step). In this final grinding step, 5 grams of gold having a particle size of about 9 μm can be mixed with 1 liter of pure water through the grinding liquid supply channel 421 formed in the rotating main shaft 42 and the connecting channel 422 in the grinding wheel mount 44. The slurry made of the abrasive particles of the stone is used as a polishing liquid at a rate of 5 liters (5 liters / minute) for 1 minute to the grinding portion formed by the grinding vermiculite 52 of the grinding wheel 5.

[Experiment 2 (Comparative Example)]

The sapphire substrate 10 which has been subjected to the rough grinding process as described above is held on the upper surface of the chuck table 71, that is, the holding surface, through the substrate 11 in the same manner as in the above-mentioned Experiment 1, and thereafter the same as above (only the polishing liquid is different) ) Carry out final polishing. That is, the chuck table 71 positioned in the grinding zone 25 is rotated at a rotation speed of 200 rpm in a predetermined direction, while the grinding wheel 5 is rotated at a rotation speed of 800 rpm, and the pulse motor 64 of the grinding feed mechanism 6 is driven in a forward direction to use The polishing unit 4 is lowered at a speed of 0.1 μm / second, so that the polishing surfaces of the multiple grinding vermiculite 52 of the polishing wheel 5 contact the front surface 10a (upper surface) of the sapphire substrate 10 held on the chuck table 71 and perform a predetermined amount of 30 μm polishing. Feed. As a result, the sapphire substrate 10 held on the chuck table 71 can be polished away by 30 μm (final polishing step). In this final polishing step, the polishing liquid made of pure water is supplied to the polishing of the polishing wheel 5 through the polishing liquid supply channel 421 formed in the rotating main shaft 42 and the communication channel 422 formed in the polishing wheel mount 44. Grinding section formed by vermiculite 52.

After measuring the surface roughness of the front surface 10a (upper surface) of the sapphire substrate 10 that has undergone the final polishing steps of Experiment 1 and Experiment 2 (Comparative Example) in the areas I, II, III, IV, and V shown in FIG. 8 The following results can be obtained.

It can be known from the above experimental results that, as in Experiment 1, When the slurry mixed with pure water is used as a polishing liquid, the surface roughness of the A side of the sapphire substrate can be clearly seen in comparison with the case of using a polishing liquid made of pure water as in Experiment 2 (Comparative Example). (Ra) decreases sharply to 1/10. This is obtained by adding the grinding effect of grinding vermiculite 52 and the slurry obtained by mixing the diamond grinding grains with pure water to the polishing performed by the grinding portion formed of grinding vermiculite 52. From this, it can be seen that by using a slurry in which diamond abrasive grains are mixed with pure water as a polishing liquid, the surface accuracy of the sapphire substrate with the A side as the front and back can be ensured, so the A side of the sapphire substrate can be used as Used as the build-up layer of the light-emitting layer. In addition, it is known that when the diamond abrasive grains mixed in the slurry supplied to the grinding section formed by grinding the vermiculite 52 to the grinding wheel 5 use a particle diameter of 10 μm or more, grinding scratches easily occur. Therefore, the diamond abrasive grains mixed in the slurry supplied to the grinding section formed by the abrasive vermiculite 52 are set to be larger and easier than the particle diameter (1 to 2 μm) of the diamond abrasive grains constituting the abrasive vermiculite 52. It is preferable that the particle diameter (10 μm) causing the abrasive scratch is smaller than 3 to 9 μm.

By implementing the sapphire substrate processing method of the present invention as described above, the substrate of the optical device wafer can use the sapphire substrate with the A side as the front and back sides, and can be efficiently cut from the sapphire ingot, thereby reducing the sapphire. The unit price of the substrate is used to manufacture optical devices such as LEDs at a low price. In addition, since the A of the sapphire substrate is a good crystal orientation for the growth of the light-emitting layer formed of a gallium nitride-based compound semiconductor, the quality of optical devices such as LEDs can be improved.

Claims (1)

A method for processing a sapphire substrate is a method for processing a sapphire substrate cut from a sapphire ingot and grinding the sapphire substrate with front and back sides formed on the A side, characterized in that the processing method includes a holding step to keep the processed And a grinding step of rotating the chuck table holding the sapphire substrate while rotating the chuck table holding the sapphire substrate and rotating the grinding wheel to arrange the grinding vermiculite into a ring-shaped grinding wheel. Grinding vermiculite contacts the other side of the sapphire substrate to grind the other side of the sapphire substrate; in this grinding step, the slurry mixed with diamond abrasive grains is supplied to the grinding vermiculite as a polishing liquid. The grinding vermiculite is made by mixing diamond diamond abrasive particles with a particle size of 1 to 2 μm into a binder, and the polishing liquid is obtained by mixing diamond diamond abrasive particles with a particle size of 3 to 9 μm into pure water. Made of slurry.