1. The grinding wheel for polishing the silicon carbide substrate is characterized by comprising a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 22-45% of diamond abrasive, 5-40% of epoxy acrylic resin, 20-35% of lignocellulose and 10-20% of nano silicon dioxide.

2. The grinding wheel for polishing a silicon carbide substrate according to claim 1, wherein the diamond abrasive is foamed diamond and has a particle size of 0.5 to 2.0 μm.

3. The grinding wheel for polishing a silicon carbide substrate as recited in claim 1, wherein the lignocellulose has an aspect ratio of 100-200 and a length of 500-800 μm.

4. The grinding wheel for polishing a silicon carbide substrate according to claim 1, wherein the nano silica is monodisperse mesoporous silica.

5. A method for producing a grinding wheel for polishing a silicon carbide substrate according to any one of claims 1 to 4, comprising the steps of:

1) putting lignocellulose into epoxy acrylic resin liquid with solid content of 50-60% in a mass ratio of 4-6:1, uniformly stirring, centrifuging, pouring into a glass container, placing in a 50-70 ℃ oven, and irradiating with ultraviolet light for 1-3h to obtain a spongy cellulose plate;

2) pouring diamond abrasive and nano silicon dioxide into the rest epoxy acrylic resin liquid, uniformly stirring and centrifuging to obtain a resin and abrasive mixed liquid, and filling the resin and abrasive mixed liquid into an injector for later use;

3) placing the cellulose board prepared in the step 1) in a mould of a vacuum press, and completely injecting the resin and abrasive mixed liquid into the cellulose board;

4) putting the product obtained in the step 3) into a drying oven at 50-70 ℃, and irradiating for 4-6h by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product of the polishing grinding wheel into square blocks with side length of 10-30mm by adopting a diamond wire and chamfering R1;

6) and adhering the chamfered square blocks to the composite matrix at intervals of 1-3mm, and performing finish machining to obtain the grinding wheel for polishing.

6. The method of manufacturing a grinding wheel for polishing a silicon carbide substrate according to claim 5, wherein in the step 3), the press pushes the syringe at a pressure of 5 to 20mp and at a speed of 2 to 5 μm/s to push the resin and abrasive mixed liquid into the cellulose plate, and the lower side of the press is evacuated at a speed of 0.7 to 0.8L/s until the resin and abrasive mixed liquid is completely injected into the cellulose plate.

7. The method for producing a grinding wheel for polishing a silicon carbide substrate according to claim 5, wherein in the step 6), the composite matrix is prepared by mixing, by mass, a mixture of (2-4): and (1-3) mixing the polyurethane and lignocellulose.

Background

Silicon Carbide (Silicon Carbide) is a compound formed by C element and Si element, more than 200 Silicon Carbide allotype crystal structures are found at present, wherein 4H type SiC (4H-SiC) with a hexagonal structure has the advantages of high critical breakdown electric field and high electron mobility, and is an excellent semiconductor material for manufacturing high-voltage, high-temperature and radiation-resistant power semiconductor devices. The conductive silicon carbide single crystal substrate material is a base material for manufacturing a silicon carbide semiconductor device. The semi-insulating silicon carbide wafer substrate material has high resistance, can bear higher frequency, and has wide space in the 5G communication and new generation intelligent interconnection and sensing periods. With the market trend of global silicon carbide wafers, two substrate materials are required in 2020, 15 ten thousand wafers in 4 inches and 13 ten thousand wafers in 6 inches. However, the difficulty of growing high-quality and large-size silicon carbide single crystals is high, the silicon carbide is of a layered structure, the silicon carbide is easy to cleave, the processing performance is poor, and step-shaped defects are easily introduced to the surface of the substrate, so that the quality of an epitaxial layer is influenced. The price of the silicon carbide substrate with the same size is dozens of times of that of the sapphire substrate, and the high price limits the large-scale application of the silicon carbide substrate. Since many defects of a semiconductor device are basically directly copied from a substrate, the quality and processing level of the substrate are particularly important for epitaxial production. The method is particularly important for controlling the grinding quality defects of the silicon carbide substrate.

Disclosure of Invention

The invention aims to prepare a grinding wheel for polishing a silicon carbide substrate, the grinding wheel is a soft polishing material and has a porous structure, has strong chip capacity and self-sharpening property, can continuously feed and keep sharpness, can replace the grinding effect of a CMP (chemical mechanical polishing) process by using an end face grinding technology, and can efficiently remove grinding marks or defects and the like generated by a coarse grinding process compared with the CMP process, thereby solving the problems of long grinding period and low efficiency, low precision of grinding workpieces, high surface quality defective rate of the workpieces, great environmental pollution caused by liquid grinding materials and the like of the silicon carbide crystal CMP.

In order to achieve the purpose, the invention adopts the following technical scheme:

the grinding wheel for polishing the silicon carbide substrate comprises a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 22-45% of diamond abrasive, 5-40% of epoxy acrylic resin, 20-35% of lignocellulose and 10-20% of nano silicon dioxide.

Further, the diamond abrasive is preferably foam diamond, and the particle size is 0.5-2.0 μm. The surface of the foam diamond is provided with a certain pit, so that the abrasive and the resin adhesive have better holding force and are easier to micro-break to form a new cutting edge.

Further preferably, the length-diameter ratio of the lignocellulose is between 100 and 200, and the length is 500 and 800 μm. Lignocellulose is an indispensable component in a formula, and the lignocellulose has a fiber structure with capillary action and can quickly transmit liquid in a system to an interface and a surface to form a three-dimensional network structure; the two kinds of lignocellulose have good brittleness, can be brittle-broken to form a new cutting edge during grinding, have good sharpness and can obtain better grinding quality.

Further, the nano silicon dioxide is monodisperse mesoporous dioxide. On one hand, the mesoporous structure is used as an auxiliary material for polishing, on the other hand, the mesoporous structure is beneficial to filling of an adhesive, and the interface bonding effect is improved while the dispersion uniformity is ensured.

The invention also provides a preparation method of the grinding wheel for polishing the silicon carbide substrate, which comprises the following steps:

1) putting lignocellulose into epoxy acrylic resin liquid with the solid content of 50-60% in a mass ratio of 4-6:1, uniformly stirring, centrifuging (for removing bubbles), then pouring into a glass container, placing into an oven at 50-70 ℃, and irradiating for 1-3h by using ultraviolet light to obtain a spongy cellulose plate penetrating through a porous three-dimensional net structure, wherein the pore size is 80-200mm, and the pore size is 75-85%;

2) pouring diamond abrasive and nano silicon dioxide into the rest epoxy acrylic resin liquid, uniformly stirring and centrifuging to obtain a resin and abrasive mixed liquid, and filling the resin and abrasive mixed liquid into an injector for later use;

3) placing the cellulose board prepared in the step 1) in a mould of a vacuum press, and completely injecting the resin and abrasive mixed liquid into the cellulose board;

4) putting the product obtained in the step 3) into a drying oven at 50-70 ℃, and irradiating for 4-6h by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product of the polishing grinding wheel into square blocks with side length of 10-30mm by adopting a diamond wire and chamfering R1 to ensure that the grinding contact is circular arc linear contact and avoid the influence of corner fragments generated by point contact on the surface quality of a workpiece;

6) and adhering the chamfered square blocks to the composite matrix at intervals of 1-3mm, and performing finish machining to obtain the grinding wheel for polishing.

The grinding wheel for polishing prepared by the invention is of a three-dimensional reticular porous structure, the pore size is 40-150 mu m, and the porosity is 45-55%.

Specifically, in the step 3), the press pushes the injector at the pressure of 5-20mp and the speed of 2-5 μm/s, so that the resin and abrasive mixed liquid is pushed into the cellulose plate, and the vacuum is drawn from the lower side of the press at the speed of 0.7-0.8L/s until the resin and abrasive mixed liquid is completely injected into the cellulose plate.

Further, in the step 6), the composite matrix is prepared by mixing the following components in percentage by mass (2-4): and (1-3) mixing the polyurethane and lignocellulose. The resin fiber porous matrix can play a role in buffering and damping besides ensuring good adhesion.

The resin polishing grinding wheel prepared by the invention adopts a special forming mode combining a vacuum high-pressure impregnation method and photocuring, solves the problem of abrasive aggregation of a powder resin hot pressing method, has good dispersion uniformity of the abrasive in a grinding wheel system, has good polishing quality for a silicon carbide lining, avoids grinding abnormity such as grinding scratches and fragments, and has good polishing quality for the silicon carbide lining. Meanwhile, the three-dimensional mesh through hole structure formed by the lignocellulose is beneficial to cooling and chip containing, a new grinding working layer can be formed by brittle fracture and peeling of grinding, and the grinding wheel removing capacity is strong; the hardness of the lignocellulose is low, and the lignocellulose can be combined with a porous structure during grinding to play roles in absorbing grinding impact force and damping; the grinding effect of a CMP (chemical mechanical polishing) process can be replaced, and the problems of grinding marks or defects and the like generated by a rough grinding process can be efficiently removed compared with the CMP process. The silicon carbide substrate polishing grinding wheel prepared by the invention can replace a CMP (chemical mechanical polishing) process, obtain better efficiency and surface quality, and simultaneously solve the problems of dependence on a single process and pollution of free abrasives in chain segments in the silicon carbide processing industry. The resin polishing grinding wheel provided by the invention can be used as a consolidation grinding tool to replace the traditional CMP polishing process, and can solve the polishing process of the silicon carbide substrate. The surface quality of the silicon carbide substrate slice is improved, and the gap between the domestic silicon carbide substrate slice processing industrialization development and abroad is reduced.

Compared with the prior art, the invention has the following beneficial effects:

the grinding wheel for polishing the silicon carbide substrate is mainly used for polishing the silicon carbide substrate, is a soft polishing material, has a porous structure, has strong chip capacity and self-sharpening property, can continuously feed and keep sharpness, can replace the grinding effect of a CMP (chemical mechanical polishing) process by using an end face grinding technology, and can efficiently remove grinding marks or defects and the like generated by a coarse grinding process compared with the CMP process, thereby solving the problems of long grinding period and low efficiency, low precision of grinding workpieces, high surface quality defective rate of the workpieces, great environmental pollution generated by liquid grinding materials and the like of the silicon carbide crystal CMP.

Drawings

FIG. 1 is a structural view of an abrasive layer having a three-dimensional network porous structure in the grinding wheel for polishing according to the present invention.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following examples, but the scope of the present invention is not limited thereto.

In the following examples, the raw materials used were all common commercial products. The diamond abrasive material is foam diamond with the granularity of 0.5-2.0 μm; the length-diameter ratio of the lignocellulose is between 100 and 200, the length is 500 and 800 mu m, and the lignocellulose is a common commercial product. The nano-silica is monodisperse mesoporous silica which is purchased from Nanjing Xiancheng nano material science and technology Limited company, the grain diameter is 300nm, and the product has the product number of 103024.

Example 1

The grinding wheel for polishing the silicon carbide substrate sheet comprises a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 22% of diamond abrasive, 30% of epoxy acrylic resin, 28% of lignocellulose and 20% of nano silicon dioxide.

The preparation method of the grinding wheel for polishing the silicon carbide substrate slice specifically comprises the following steps:

1) adding lignocellulose into epoxy acrylic resin liquid with the solid content of 55% according to the mass ratio of 5:1, uniformly stirring, and centrifuging for 20min at 1500rpm of a centrifuge. And then poured into a glass container having a predetermined volume 3 times the volume of the lignocellulose. Transversely placing a glass container, and placing the glass container in a 60 ℃ oven to irradiate for 2 hours by adopting ultraviolet light to obtain a spongy cellulose plate which penetrates through a porous three-dimensional net structure, wherein the pore size is 80-200mm, and the pores are 75-85%;

2) and (3) pouring the diamond abrasive and the nano silicon dioxide into the residual epoxy acrylic resin liquid, and stirring and mixing. And (3) obtaining a resin and abrasive mixed solution by adopting a vibration centrifuge mode (uniformly mixing and removing air bubbles) at 2000rpm for 2 h. Filling the mixed solution of the resin and the grinding material into an injector for later use;

3) putting the cellulose plate prepared in the step 1) into a mould in a vacuum press, then pushing a syringe by the press at the pressure of 10mp and the speed of 3 mu m/s, pushing the mixed liquid of the resin and the grinding material prepared in the step 2) into the cellulose plate, and drawing vacuum at the speed of 0.71L/s on the lower side of the press until the mixed liquid of the resin and the grinding material is completely injected into the cellulose plate;

4) putting the product obtained in the step 3) into a drying oven at 60 ℃, and irradiating for 4 hours by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product into square blocks with the side length of 20mm by adopting a diamond wire and chamfering R1 to ensure that the grinding contact is circular arc linear contact and avoid the influence of broken corner pieces generated by point contact on the surface quality of a workpiece; this is a routine skill in the art and is not described in detail;

6) and adhering the chamfered square blocks to a self-made circular composite matrix at intervals of 2mm, and performing conventional fine machining to obtain the grinding wheel for polishing. The composite matrix is prepared from the following components in percentage by mass: 1 and lignocellulose.

The grinding wheel abrasive layer for polishing prepared by the invention is of a three-dimensional reticular porous structure (shown in figure 1), the pore size is 40-150 mu m, and the porosity is 45-55%.

In the CMP polishing process, the removal rate of the silicon carbide substrate material is very low and is less than 0.2 mu m/h by using the grinding liquid which takes titanium dioxide and cerium oxide as raw materials for polishing. The polishing of four inches of silicon carbide takes 10 hours, and has low efficiency and high cost.

The grinding wheel for polishing prepared in example 1 was subjected to a thinning test of a silicon carbide substrate sheet. Experimental items: four inches of silicon carbide substrate slices are ground on an Okamoto VG502 thinning machine, the grinding allowance is 10 mu m, the rotating speed of a grinding wheel is 3500rpm, the feeding speed is 0.05 mu m/s, the material removal rate reaches 90 mu m/h, the single-chip processing time is 400s, the grinding surface roughness Ra =1.8nm, the CMP polishing quality is achieved, and the efficiency is improved by a plurality of times compared with CMP.

Example 2

The grinding wheel for polishing the silicon carbide substrate sheet comprises a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 30% of diamond abrasive, 40% of epoxy acrylic resin, 20% of lignocellulose and 10% of nano silicon dioxide.

The preparation method of the grinding wheel for polishing the silicon carbide substrate slice specifically comprises the following steps:

1) adding lignocellulose into epoxy acrylic resin liquid with the solid content of 55% according to the mass ratio of 5:1, stirring and mixing, and centrifuging for 20min at 1500rpm of a centrifuge. And then poured into a glass container having a predetermined volume 3 times the volume of the lignocellulose. Transversely placing a glass container in a 60 ℃ oven, and then irradiating for 2 hours by adopting ultraviolet light to obtain a spongy cellulose plate which penetrates through a porous three-dimensional net structure, wherein the pore size is 80-200mm, and the pores are 75-85%;

2) and (3) pouring the diamond abrasive and the nano silicon dioxide into the residual epoxy acrylic resin liquid, and stirring and mixing. And (3) obtaining a mixed solution of the resin and the grinding material by adopting a vibration centrifuge at 2000rpm for 2 h. Filling the mixed solution of the resin and the grinding material into an injector for later use;

3) putting the cellulose plate prepared in the step 1) into a mould in a vacuum press, then pushing a syringe by the press at the pressure of 10mp and the speed of 3 mu m/s, pushing the mixed liquid of the resin and the grinding material prepared in the step 2) into the cellulose plate, and drawing vacuum at the speed of 0.71L/s on the lower side of the press until the mixed liquid of the resin and the grinding material is completely injected into the cellulose plate;

4) putting the product obtained in the step 3) into a drying oven at 60 ℃, and irradiating for 4 hours by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product into square blocks with the side length of 20mm by adopting a diamond wire and chamfering R1 to ensure that the grinding contact is circular arc linear contact and avoid the influence of broken corner pieces generated by point contact on the surface quality of a workpiece;

6) and adhering the chamfered square blocks to a self-made circular composite matrix at intervals of 2mm, and performing finish machining to obtain the grinding wheel for polishing. The composite matrix is prepared from the following components in percentage by mass: 1 and lignocellulose.

The grinding wheel abrasive layer for polishing prepared by the invention is of a three-dimensional reticular porous structure, the pore size is 40-150 mu m, and the porosity is 45-55%.

The grinding wheel for polishing prepared in example 2 was subjected to a thinning test of a silicon carbide substrate sheet. Experimental items: four-inch silicon carbide substrate slices are ground on an Okamoto VG502 thinning machine, the grinding allowance is 10 mu m, the rotating speed of a grinding wheel is 2800rpm, the feeding speed is 0.06 mu m/s, the material removal rate reaches 108 mu m/h, the single-chip processing time is 333.3s, the grinding surface roughness Ra =2.0nm, the CMP polishing quality is achieved, and the efficiency is improved by multiple times compared with CMP.

Example 3

The grinding wheel for polishing the silicon carbide substrate sheet comprises a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 45% of diamond abrasive, 25% of epoxy acrylic resin, 20% of lignocellulose and 10% of nano silicon dioxide.

The preparation method of the grinding wheel for polishing the silicon carbide substrate slice specifically comprises the following steps:

1) adding lignocellulose into epoxy acrylic resin liquid with the solid content of 55% according to the mass ratio of 5:1, stirring and mixing, and centrifuging for 20min at 1500rpm by adopting a centrifuge. And then poured into a glass container having a predetermined volume 3 times the volume of the lignocellulose. Transversely placing a glass container in a 60 ℃ oven, and then irradiating for 2 hours by adopting ultraviolet light to obtain a spongy cellulose plate which penetrates through a porous three-dimensional net structure, wherein the pore size is 80-200mm, and the pores are 75-85%;

2) and (3) pouring the diamond abrasive and the nano silicon dioxide into the residual epoxy acrylic resin liquid, and stirring and mixing. And (3) obtaining a mixed solution of the resin and the grinding material by adopting a vibration centrifuge at 2000rpm for 2 h. Filling the mixed solution of the resin and the grinding material into an injector for later use;

3) putting the cellulose plate prepared in the step 1) into a mould in a vacuum press, then pushing a syringe by the press at the pressure of 10mp and the speed of 3 mu m/s, pushing the mixed liquid of the resin and the grinding material prepared in the step 2) into the cellulose plate, and drawing vacuum at the speed of 0.71L/s on the lower side of the press until the mixed liquid of the resin and the grinding material is completely injected into the cellulose plate;

4) putting the product obtained in the step 3) into a drying oven at 60 ℃, and irradiating for 4 hours by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product into square blocks with the side length of 20mm by adopting a diamond wire and chamfering R1 to ensure that the grinding contact is circular arc linear contact and avoid the influence of broken corner pieces generated by point contact on the surface quality of a workpiece;

6) and adhering the chamfered square blocks to a self-made circular composite matrix at intervals of 2mm, and performing finish machining to obtain the polishing grinding wheel. The composite matrix is prepared from the following components in percentage by mass: 1 and lignocellulose.

The grinding wheel abrasive layer for polishing prepared by the invention is of a three-dimensional reticular porous structure, the pore size is 40-150 mu m, and the porosity is 45-55%.

The grinding wheel for polishing prepared in example 3 was subjected to a thinning test of a silicon carbide substrate sheet. Experimental items: four-inch silicon carbide substrate slices are ground on an Okamoto VG502 thinning machine, the grinding allowance is 8 mu m, the rotating speed of a grinding wheel is 3000rpm, the feeding speed is 0.05 mu m/s, the material removal rate reaches 90 mu m/h, the single-chip processing time is 320s, the grinding surface roughness Ra =1.8nm, the CMP polishing quality is achieved, and the efficiency is improved by multiple times compared with CMP.

Example 4

The grinding wheel for polishing the silicon carbide substrate sheet comprises a base body and an abrasive layer, wherein the abrasive layer comprises the following raw materials in percentage by weight: 28% of diamond abrasive, 25% of epoxy acrylic resin, 35% of lignocellulose and 12% of nano silicon dioxide.

The preparation method of the grinding wheel for polishing the silicon carbide substrate slice specifically comprises the following steps:

1) adding lignocellulose into epoxy acrylic resin liquid with the solid content of 55% according to the mass ratio of 5:1, stirring and mixing, and centrifuging for 20min at 1500rpm by adopting a centrifuge. And then poured into a glass container having a predetermined volume 3 times the volume of the lignocellulose. Transversely placing a glass container in a 60 ℃ oven, and then irradiating for 2 hours by adopting ultraviolet light to obtain a spongy cellulose plate which penetrates through a porous three-dimensional net structure, wherein the pore size is 80-200mm, and the pores are 75-85%;

2) and (3) pouring the diamond abrasive and the nano silicon dioxide into the residual epoxy acrylic resin liquid, and stirring and mixing. And (3) obtaining a mixed solution of the resin and the grinding material by adopting a vibration centrifuge at 2000rpm for 2 h. Filling the mixed solution of the resin and the grinding material into an injector for later use;

3) putting the cellulose plate prepared in the step 1) into a mould in a vacuum press, then pushing a syringe by the press at the pressure of 10mp and the speed of 3 mu m/s, pushing the mixed liquid of the resin and the grinding material prepared in the step 2) into the cellulose plate, and drawing vacuum at the speed of 0.71L/s from the lower side of the press until the mixed liquid of the resin and the grinding material is completely injected into the cellulose plate;

4) putting the step 3) into a 60 ℃ oven, and irradiating for 4 hours by adopting ultraviolet light to obtain a semi-finished product of the polishing grinding wheel;

5) cutting the semi-finished product into square blocks with the side length of 20mm by adopting a diamond wire and chamfering R1 to ensure that the grinding contact is circular arc linear contact and avoid the influence of broken corner pieces generated by point contact on the surface quality of a workpiece;

6) and adhering the chamfered square blocks to a self-made circular composite matrix at intervals of 2mm, and performing finish machining to obtain the polishing grinding wheel. The composite matrix is prepared from the following components in percentage by mass: 1 and lignocellulose.

The grinding wheel abrasive layer for polishing prepared by the invention is of a three-dimensional reticular porous structure, the pore size is 40-150 mu m, and the porosity is 45-55%.

The grinding wheel for polishing prepared in example 4 was subjected to a thinning test of a silicon carbide substrate sheet. Experimental items: four-inch silicon carbide substrate slices are ground on an Okamoto VG502 thinning machine, the grinding allowance is 8 mu m, the rotating speed of a grinding wheel is 2500rpm, the feed speed is 0.04 mu m/s, the material removal rate reaches 72 mu m/h, the single-chip processing time is 400s, the grinding surface roughness Ra =1.5nm, the CMP polishing quality is achieved, and the efficiency is improved by multiple times compared with CMP.

Comparative example 1

The grinding wheel layer with a three-dimensional net structure cannot be prepared by replacing the lignocellulose in the example 3 with the glass fiber. When the prepared grinding wheel is used for grinding a workpiece, the grinding wheel cannot work continuously, and the surface of the ground workpiece has a burn phenomenon. The glass fiber has too high strength and good toughness, a new cutting edge cannot be exposed when the glass fiber is broken during grinding, and the grinding capability of the grinding wheel is weak.

Comparative example 2

The grinding wheel was prepared by changing the monodisperse mesoporous silica of example 2 to ordinary silica (20 μm diameter, an ordinary commercially available product). The bonding effect between the filler interface and the adhesive is poor, and the holding force on the abrasive is poor. In grinding, grinding conditions: grinding of 4 inch silicon carbide substrate wafers on an Okamoto VG502 thin reduction machine with a grinding margin of 10 μm, a wheel speed of 2800rpm, a maximum wheel feed rate of only 0.02 μm/s, 30% of the efficiency of example 2, and a grinding surface roughness Ra =10.0nm, gives poor quality grinding surfaces.