A method for rapidly polishing diamond wafers

Abstract

The present invention discloses a method for rapidly polishing diamond wafers. Specifically, a self-dressing freeze-dried gel grinding wheel is used to polish the diamond wafer on a grinding and polishing machine, achieving rapid polishing of the diamond wafer. The present invention sequentially vacuum-dries and freeze-dries the gel to obtain a freeze-dried gel block for the self-dressing gel grinding wheel. This block is then combined with a substrate to obtain the self-dressing freeze-dried gel grinding wheel. This method is the first to use a freeze-dried gel block as a polishing tool, achieving the advantages of lower roughness and higher yield compared to existing methods for grinding diamond wafers.

Description

Technical Field

[0001] The invention belongs to grinding and polishing technology, and in particular relates to a method for quickly grinding and polishing a diamond wafer. Background Art

[0002] Diamond wafers, as a representative material for third-generation semiconductors, possess numerous excellent characteristics, including ultra-high thermal conductivity and an ultra-wide bandgap, and are considered the "star material" of third-generation semiconductors. However, due to the inherently high hardness and brittleness of diamond wafers, the difficulty in processing them limits their rapid development, and wafer processing technology has become one of the bottlenecks restricting their development. Grinding and polishing is a crucial step in the diamond wafer processing process and a necessary step in existing wafer processing. However, due to the difficult processing of diamond wafer materials, the efficiency of existing traditional grinding wheels for wafer processing is extremely low, becoming a bottleneck restricting their rapid industrialization. Therefore, it is necessary to develop new grinding wheels that can grind diamond wafers with high efficiency and low roughness. Summary of the Invention

[0003] For diamond processing, the present invention designs a method for rapidly grinding and polishing diamond wafers based on a novel self-dressing freeze-dried gel grinding wheel. Different from existing processing methods, the present invention achieves high-quality grinding effects in a significantly shorter time.

[0004] The present invention adopts the following technical solutions:

[0005] A method for rapidly grinding and polishing diamond wafers includes the following steps: using a self-dressing freeze-dried gel grinding wheel on a grinding and polishing machine to grind and polish the diamond wafer, thereby completing the rapid grinding and polishing of the diamond wafer. When machining a workpiece using the self-dressing freeze-dried gel grinding wheel, only water is required, without the need for other reagents. This method can achieve a nanometer-level roughness effect with a high material removal rate. The surface roughness of the polished diamond wafer obtained is less than 1 nm, or even 0.5 nm, achieving a rough polishing effect.

[0006] The preparation method of the self-dressing freeze-dried gel grinding wheel of the present invention comprises the following steps: adding mixture 2 to mixture 1, then adding mixture 3, and stirring to obtain a mixed solution; pouring the mixed solution into a mold and immersing the mold in a calcium salt solution to obtain a gel; then subjecting the gel to vacuum drying and freeze drying in sequence to obtain a freeze-dried gel block for the self-dressing gel grinding wheel; and combining the freeze-dried gel block for the self-dressing gel grinding wheel with a matrix to obtain the self-dressing freeze-dried gel grinding wheel.

[0007] In the present invention, sodium alginate, carboxymethyl chitosan, and water are mixed to obtain mixture 1; aramid powder is mixed with water to obtain mixture 2; and glass fiber powder and diamond abrasive are mixed with water to obtain mixture 3. Preferably, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive, and water in the mixture is (15-25):(3-8):(80-110):(180-230):(50-100):1200, preferably (15-25):(3-8):(90-105):(190-210):(70-90):1200. The diamond abrasive is a W10-W63 diamond abrasive, and the remaining raw materials are conventional raw materials in the field of gel abrasive tools.

[0008] In the present invention, the stirring speed is 800-1500 rpm, and the time is 1-15 hours; preferably, the stirring speed is 900-1200 rpm, and the time is 2-10 hours.

[0009] In the present invention, the calcium salt solution is a calcium chloride aqueous solution; the immersion time in the calcium salt solution is 100 to 150 minutes; and the calcium salt concentration in the calcium salt solution is 0.1 to 1 wt%.

[0010] In the present invention, during vacuum drying, the vacuum degree is 500-1000 Pa, the time is 1-2 hours, and the temperature is 40-60°C. During freeze drying, the vacuum degree is 1-50 Pa, the temperature is reduced to -80--60°C over 5-7 hours, and then maintained for 20-30 hours. Preferably, during freeze drying, the vacuum degree is 1-5 Pa, the temperature is reduced to -75--65°C over 5.5-6.5 hours, and then maintained for 21-27 hours. Before freeze drying, the vacuum-dried gel is frozen at -30--10°C for 3-5 hours and then freeze dried.

[0011] In the present invention, the grinding and polishing machine is an existing product. This method, without changing the existing grinding and polishing process, requires only the replacement of the grinding wheel. This method can achieve nanometer-level roughness without the need for abrasives or other reagents, requiring only water, thus achieving the level of rough polishing. During grinding and polishing, the rotational speed ranges from 1200 / 200 rpm to 2000 / 500 rpm, with a processing time of 20 to 50 minutes. Preferably, the rotational speed ranges from 1300 / 250 rpm to 1800 / 400 rpm, with a processing time of 25 to 40 minutes. The rotational speed of 1200 / 200 rpm refers to the rotational speed of the two discs in the grinding and polishing machine, which is common sense. The polishing target of the present invention is a diamond wafer. Before grinding and polishing, its surface roughness ranges from 80 to 150 nm. After processing using the method of the present invention, a surface roughness of less than 0.5 nm can be achieved.

[0012] The prior art adopts a heat-curing method to obtain a gel with mechanical strength for processing wafers. It has good flexibility and avoids the use of external abrasives. However, its dimensional stability is poor and the grinding effect needs to be improved. Due to the use of sol-gel means and drying technology, the grinding wheel prepared by the present invention has a certain flexibility. At the same time, during the freeze-drying process, the water molecules inside directly sublimate to produce holes. At the same time, due to the addition of supporting materials such as glass fiber and aramid, the agglomerate has a certain strength and will not deform during the processing. Through self-dressing, the abrasive particles inside can be continuously exposed to achieve high grinding and polishing efficiency. At the same time, since the agglomerate has a certain flexibility, it will not produce a hard collision with the diamond wafer during the processing, which greatly reduces the breakage rate of the diamond wafer and improves the production yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a diagram showing the effect of the self-dressing freeze-dried gel grinding wheel of the present invention after processing a diamond wafer;

[0014] Figure 2 This is a roughness effect diagram after processing a diamond wafer using the self-dressing freeze-dried gel grinding wheel of the present invention. DETAILED DESCRIPTION

[0015] The raw materials used in this invention are all existing products in the field and meet the general requirements of existing gel materials. The fiber powder has a particle size of 100 to 800 mesh. The invention's innovation lies in the selection of different existing raw materials, the design of a new formula, and the combination of freeze-drying technology to produce a hard gel block that can be used in diamond wafer grinding and polishing, achieving excellent processing results. The surface roughness is evaluated using a three-dimensional roughness indicator, and the instrument used is an AFM Nanoview atomic force microscope from Suzhou Feishiman Co., Ltd. The specific testing methods are conventional.

[0016] Example 1

[0017] 20 g of sodium alginate, 5 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 800 rpm for 2 h at room temperature to prepare a mixture 1;

[0018] In another beaker, 500 g of water and 100 g of aramid powder were added and stirred at 60° C. and 550 rpm for 60 min to prepare mixture 2.

[0019] In another beaker, add 500 g of water, 200 g of glass fiber powder, and 80 g of diamond abrasive (W30), and stir at 550 rpm for 30 min at room temperature to prepare mixture 3;

[0020] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0021] At room temperature, mixture 2 was added to mixture 1, and stirred at 1000 rpm for 2 h. Then, mixture 3 was added and stirred at 1000 rpm for 8 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 120 min and taken out to obtain a gel.

[0022] The gel was placed in a vacuum drying oven and vacuum-dried at 50°C for 1.5 hours, with a vacuum of 800 Pa. After removal, it was frozen at -18°C for 4 hours, then freeze-dried for 6 hours, cooled to -70°C, and then freeze-dried at -70°C for 24 hours. This yielded a freeze-dried gel block, which was used for self-dressing gel grinding wheels, maintaining a vacuum of 2 Pa. Unlike flexible polishing pads disclosed in the prior art, the freeze-dried gel block of the present invention does not contain water, whereas existing flexible polishing pads must contain water for use. However, hydrogel flexible polishing pads are not suitable for high-speed processing of diamond wafers.

[0023] The freeze-dried gel blocks are bonded to an existing stainless steel substrate using conventional grinding wheel adhesive (such as epoxy AB glue). Multiple freeze-dried gel blocks are then fixed within the tooth grooves of the stainless steel substrate, forming a self-dressing freeze-dried gel grinding wheel. Unlike traditional ceramic-bonded or resin-bonded grinding wheels, this grinding wheel utilizes biosol-gel technology to disperse the abrasive in a sol. Through gelation and freeze-drying, the resulting agglomerates are formed into flexible and porous grinding wheel blocks. These blocks are then fixed to the stainless steel substrate in the desired shape, ultimately creating a grinding and polishing wheel.

[0024] The self-dressing freeze-dried gel grinding wheel was used to grind and polish a 2-inch diamond wafer (Sa is 100nm) on a Tokyo precision grinder HEG300, with a rotation speed of 1500 / 300rpm and a processing time of 30min. The surface roughness Sa of the wafer after processing was 0.396nm and Sq was 1.029nm. The results are shown in Figure 1 and Figure 2 The thickness of the wafer before and after grinding and polishing was measured using a thickness gauge to calculate the material removal rate, which was 6.13 nm / min.

[0025] In comparison, the surface roughness of the 2-inch diamond wafer processed by the grinding and polishing method used in existing industrial production is greater than 10nm, and the processing time of existing production exceeds 5 hours; the self-dressing freeze-dried gel grinding wheel of the present invention is used to process the same workpiece, and the processing efficiency and processing quality are significantly better than the existing industrial production level.

[0026] Comparative Example 1

[0027] The vacuum drying in Example 1 was omitted, and the rest remained unchanged to obtain a freeze-dried gel block. According to the method in Example 1, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 4.89 nm.

[0028] Comparative Example 2

[0029] The freezing and freeze-drying of Example 1 were omitted (i.e., only vacuum drying was performed), and the rest remained unchanged to obtain a flexible gel block. According to the method of Example 1, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. However, the processing could not be performed, and cracks appeared in the flexible gel block within a few tens of seconds after the machine was turned on.

[0030] Comparative Example 3

[0031] The glass fiber powder in Example 1 was replaced with carbon fiber powder, and the rest remained unchanged to obtain a freeze-dried gel block. According to the method of Example 1, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 3.32 nm.

[0032] The aramid powder in Example 1 was omitted, and the rest remained unchanged to obtain a freeze-dried gel block. According to the method of Example 1, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 6.28 nm.

[0033] Example 2

[0034] 17 g of sodium alginate, 7 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 600 rpm for 2 h at room temperature to prepare a mixture 1;

[0035] In another beaker, 500 g of water and 95 g of aramid powder were added and stirred at 60° C. and 650 rpm for 70 min to prepare mixture 2.

[0036] In another beaker, add 500 g of water, 200 g of glass fiber powder, and 82 g of diamond abrasive (W40), and stir at 500 rpm for 30 min at room temperature to prepare mixture 3;

[0037] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0038] At room temperature, mixture 2 was added to mixture 1, and stirred at 1200 rpm for 2 h. Then, mixture 3 was added and stirred at 1000 rpm for 7 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 110 min and taken out to obtain a gel.

[0039] The gel was placed in a vacuum drying oven and vacuum dried at 50°C for 80 minutes with a vacuum degree of 600Pa. After being taken out, it was frozen at -18°C for 4 hours, then freeze-dried, and then dropped to -70°C for 6 hours. It was then freeze-dried at -70°C for 25 hours to obtain freeze-dried gel blocks, which were used for self-dressing gel grinding wheels. The vacuum degree was maintained at 2Pa.

[0040] Example 3

[0041] 22 g of sodium alginate, 6 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 700 rpm for 1.5 h at room temperature to prepare a mixture 1;

[0042] In another beaker, 500 g of water and 105 g of aramid powder were added and stirred at 60° C. and 600 rpm for 60 min to prepare mixture 2.

[0043] In another beaker, add 500 g of water, 205 g of glass fiber powder, and 78 g of diamond abrasive (W20), and stir at 600 rpm for 45 min at room temperature to prepare mixture 3.

[0044] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0045] At room temperature, mixture 2 was added to mixture 1, and stirred at 1100 rpm for 2 h. Then, mixture 3 was added and stirred at 1100 rpm for 9 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 90 min and taken out to obtain a gel.

[0046] The gel was placed in a vacuum drying oven and vacuum dried at 50°C for 100 minutes with a vacuum degree of 700Pa; after being taken out, it was frozen at -18°C for 5 hours, then freeze-dried, and then dropped to -70°C for 6 hours, and then freeze-dried at -70°C for 23 hours to obtain freeze-dried gel blocks, which were used for self-dressing gel grinding wheels, and the vacuum degree was maintained at 2Pa.

[0047] Example 4

[0048] According to Example 1, Example 2 and Example 3 were made into grinding wheels respectively, and the same grinding and polishing tests were carried out, and the processing roughnesses of 0.755 nm and 0.925 nm were obtained respectively.

[0049] Example 5

[0050] A 2-inch diamond wafer (Sa of 100 nm) was ground and polished using the self-dressing freeze-dried gel grinding wheel of Example 1. The base was a Tokyo precision grinder HEG300, with a rotation speed of 1600 / 250 rpm and a processing time of 30 minutes. The surface roughness Sa of the wafer after processing was 0.418 nm. The thickness change of the wafer before and after grinding and polishing was measured using a thickness gauge, and the material removal rate was calculated to be 6.09 nm / min.

Claims

1. A method for rapidly grinding and polishing a diamond wafer, comprising the following steps: grinding and polishing the diamond wafer on a grinding and polishing machine using a self-dressing freeze-dried gel grinding wheel to complete the rapid grinding and polishing of the diamond wafer, characterized in that: Add mixture 2 to mixture 1, then add mixture 3, and stir to obtain a mixed solution; pour the mixed solution into a mold and immerse it in a calcium salt solution to obtain a gel; then vacuum dry the gel and freeze dry it in sequence to obtain a freeze-dried gel block for a self-dressing gel grinding wheel; combine the freeze-dried gel block for a self-dressing gel grinding wheel with a matrix to obtain a self-dressing freeze-dried gel grinding wheel; mix sodium alginate, carboxymethyl chitosan, and water to obtain mixture 1; mix aramid powder with water to obtain mixture 2; mix glass fiber powder, diamond abrasive, and water to obtain mixture 3; during vacuum drying, the vacuum degree is 500-1000 Pa, the time is 1-2 hours, and the temperature is 40-60°C; during freeze drying, the vacuum degree is 1-50 Pa, dropped to -80~-60℃ in 5~7 hours, and then maintained for 20~30 hours; in the mixed solution, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive and water is (15~25) : (3~8) : (80~110) : (180~230) : (50~100) : 1200.

2. The method for rapidly polishing a diamond wafer according to claim 1, wherein: In the mixed solution, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive and water is (15-25): (3-8): (90-105): (190-210): (70-90): 1200.

3. The method for rapidly polishing a diamond wafer according to claim 1, wherein: The immersion time in the calcium salt solution is 100 to 150 minutes; the calcium salt concentration in the calcium salt solution is 0.1 to 1 wt%.

4. The method for rapidly polishing a diamond wafer according to claim 1, wherein: The stirring speed is 800 to 1500 rpm, and the stirring time is 1 to 15 hours.

5. The method for rapidly polishing a diamond wafer according to claim 1, wherein: The calcium salt solution is a calcium chloride aqueous solution.

6. The method for rapidly polishing a diamond wafer according to claim 1, wherein: During grinding and polishing, the rotation speed is 1200 / 200rpm~2000 / 500rpm, and the processing time is 20~50min.

7. The method for rapidly polishing a diamond wafer according to claim 6, wherein: During grinding and polishing, the rotation speed is 1300 / 250rpm~1800 / 400rpm, and the processing time is 25~40min.

8. A polished diamond wafer prepared by the method for rapid polishing of a diamond wafer according to claim 1.

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