A polishing method for a high-flatness substrate

Abstract

The invention discloses a polishing method for a high-flatness substrate, wherein a ceramic disc is provided at the bottom of a polishing head, a polishing disc is provided below the ceramic disc, a polishing pad is provided on the polishing disc, a substrate is adsorbed or pasted on the bottom of the ceramic disc, during polishing, the polishing head moves downward to press the substrate on the polishing pad, and a portion of the edge of the substrate exceeds the polishing pad, under the condition that the pressure is 500-800N, the polishing head and the polishing disc rotate at 30-60 rpm, polishing for 25-33 minutes, wherein the polishing head and the polishing disc have the same rotation direction. The present invention controls the contact range of the center and edge of the substrate adsorbed on the ceramic disc on the polishing head and the polishing cloth by controlling the relative position of the polishing head and the polishing cloth, realizes that the removal rate per unit time of each position on the substrate surface tends to be consistent, realizes that the total removal amount of each position on the substrate surface is the same, and finally obtains a substrate surface with high flatness and no damage to the substrate; further combined with a two-step polishing liquid, the comprehensive performance of the substrate is improved.

Description

Technical Field

[0001] The invention relates to a polishing method for a high-flatness substrate, belonging to the technical field of substrate or wafer polishing. Background Art

[0002] With the development of chip technology, the market for various types of semiconductor substrate wafers is expanding, and the quality requirements for substrates or wafers are getting higher and higher. One of the most important parameters is TTV (total thickness variation); the TTV of the substrate affects the heat conduction and MO source attachment during the epitaxial stage, determines the quality of the epitaxial structure, and affects the final performance of the chip. Therefore, substrate manufacturers and epitaxial manufacturers are very concerned about the TTV parameter. In the traditional substrate manufacturing field, the substrate TTV is generally processed to within 5um through mechanical processing technology such as grinding or thinning, and then the substrate surface is processed through CMP polishing technology to achieve global flatness and damage-free substrate surface.

[0003] However, the traditional CMP polishing technology is limited by its polishing model. When the substrate is ground on the polishing cloth, the linear speed of the edge and center of the substrate on the polishing cloth is different. This difference will be more obvious on large-sized substrates, resulting in a large difference in the removal amount of the edge and center of the substrate during the CMP polishing process. As a result, the edge removal rate of the outer ring of the ceramic disk is faster than that of the center of the wafer and the inner ring of the ceramic disk, which affects the TTV of the finished product after CMP polishing. Generally, the processing process of the substrate includes slicing, chamfering, grinding, etching, thinning, polishing, cleaning and other steps. After thinning, CMP polishing technology is used, and the TTV after polishing will be significantly increased compared to before polishing, especially for single-sided polishing, with an increase rate of more than 110%.

[0004] Germanium crystals have a wide range of applications in the field of semiconductor devices. For example, they can be used in the manufacture of high-speed transistors. In the RF front-end modules of 5G communication base stations, they can efficiently process high-frequency signals and reduce delays. They can also be used to manufacture integrated circuits, which can provide good electrical performance, make components tightly connected, reduce signal loss, and meet the requirements of high-performance chips for high-speed computing and low power consumption. They can also be used in the manufacture of infrared detectors and lenses for military thermal imagers and civilian non-contact temperature detection instruments, with good infrared transmittance. They can also be used to manufacture special wavelength LEDs, improve internal quantum efficiency, and have potential applications in special lighting occasions such as plant growth lamps. They can also be used to manufacture high-efficiency multi-junction solar cells, form heterojunctions with other materials, effectively absorb sunlight in different bands, and have advantages in space solar cells. However, no matter what the purpose is, surface quality is an extremely important factor affecting the performance of the device. Surface microcracks, scratches, flatness and other defects will greatly reduce the performance of the device, or even cause it to fail.

[0005] To this end, the present invention overcomes or alleviates the problem of significant increase in TTV caused by CMP polishing through a special polishing method. Summary of the invention

[0006] The present invention provides a polishing method for a high-flatness substrate. The present invention can solve the problem of different removal rates at various points during the polishing process of various positions of a substrate caused by inconsistent linear speeds between the edge and the center of the substrate during CPM polishing, thereby improving the TTV of the substrate after polishing.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0008] A polishing method for a high-flatness substrate, wherein a ceramic disc is provided at the bottom of a polishing head, a polishing disc is provided below the ceramic disc, a polishing pad is provided on the polishing disc, and the substrate is adsorbed or adhered (such as through a wax layer) to the bottom of the ceramic disc. During polishing, the polishing head moves downward to press the substrate onto the polishing pad, and part of the edge of the substrate exceeds the polishing pad. Under the conditions of a pressure of 500 to 700 N and a rotation speed of the polishing head and the polishing disc of 30 to 60 rpm, polishing is performed for 25 to 33 minutes, wherein the polishing head and the polishing disc rotate in the same direction.

[0009] During the CMP polishing process of the substrate, the present invention controls the contact range between the substrate and the polishing cloth and controls the pressure during the CMP polishing process, so that the average removal rate per unit time at the edge and center of the substrate tends to be consistent, and the total removal amount at each position on the substrate surface is the same, and finally a highly flat substrate surface without damage to the substrate is obtained.

[0010] This invention is applicable to wax polishing of various semiconductor materials (such as germanium, gallium arsenide, indium phosphide, sapphire, silicon carbide, gallium nitride, etc.), especially the CMP polishing improvement of large-size substrates of the above materials is more obvious.

[0011] For different use occasions, the CMP polishing requirements are different, some require single-sided polishing, and some require double-sided polishing. The present application is particularly suitable for single-sided polishing, which can effectively overcome or alleviate the TTV increase problem caused by polishing.

[0012] In order to improve the flatness of the obtained substrate surface, the maximum distance from the edge of the substrate beyond the polishing pad to the edge of the polishing pad is 19.6% to 40% of the substrate diameter, and more preferably 39.2% to 40%.

[0013] When used for polishing germanium substrates, polishing is carried out in two steps. The first step of polishing uses a first polishing solution containing sodium bicarbonate, silicon dioxide polishing solution and hydrogen peroxide, and the second step uses a second polishing solution containing lauryl alcohol phosphate, polydimethylsiloxane and polyvinyl pyrrolidone.

[0014] The first step of polishing is used to remove the damaged layer, and the second step is used to clean and remove the residue of the first step of polishing, while also achieving film-forming and enhancement effects during polishing.

[0015] In order to further improve the polishing effect, in the second polishing liquid, the polydimethylsiloxane is polyether-modified polydimethylsiloxane.

[0016] In order to further enhance the polishing enhancement effect, the second polishing liquid also contains disproportionated rosin acid potassium soap.

[0017] As one of the specific preferred implementation schemes, the second polishing liquid contains 1-3% lauryl phosphate, 0.3-0.8% polyether-modified polydimethylsiloxane, 0.5-1.0% polyvinyl pyrrolidone, 2-3% disproportionate potassium rosin soap and the balance water.

[0018] The second polishing liquid promotes dispersion uniformity with the coordinated cooperation of various components. While grinding, it has the effects of decontamination, film formation, and enhancement. While ensuring the polishing quality, it also improves the mechanical properties of the germanium substrate.

[0019] % in this application are all mass percentages unless otherwise specified.

[0020] In order to ensure the polishing effect, in the first polishing liquid, the particle size of the silicon dioxide polishing liquid is 80-110 nm; the mass concentration of the hydrogen peroxide is 30.0-32.0%.

[0021] The first polishing liquid contains 1-3% sodium bicarbonate, 3-5% silicon dioxide polishing liquid, 2-4% hydrogen peroxide and the balance water.

[0022] In order to further improve the polishing effect, in the first step of polishing, the flow rate of the first polishing liquid is 500-600 ml / min, and the polishing time is 15-30 min; in the second step of polishing, the flow rate of the second polishing liquid is 800-900 ml / min, and the polishing time is 2-5 min.

[0023] The technologies not mentioned in the present invention are all referred to the prior art.

[0024] The polishing method of the high-flatness substrate of the present invention controls the contact range between the center and edge of the substrate on the ceramic disk adsorbed on the polishing head and the polishing cloth by controlling the relative position of the polishing head and the polishing cloth, so as to achieve the same removal rate per unit time at each position on the substrate surface, and achieve the same total removal amount at each position on the substrate surface, and finally obtain a highly flat and damage-free substrate surface; further combined with the two-step polishing liquid, while effectively removing the damaged layer, the influence of the residual liquid is avoided, and the film formation is enhanced, thereby improving the comprehensive performance of the substrate. For substrates of different sizes, the final finished substrate TTV is more than 4um lower than that of the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of TTV (total thickness variation);

[0026] Figure 2 Schematic diagram of polishing of a high-flatness substrate of the present invention;

[0027] In the figure, 1 is a polishing pad, 2 is a polishing head, 3 is a substrate, and d is a maximum distance from an edge of the substrate extending beyond the polishing pad to an edge of the polishing pad. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0029] In each example, unless otherwise specified, the operation was performed at room temperature (20-25°C).

[0030] 1. In each case, a germanium substrate was used as an experimental sample and polished using the following chemical solution ratios.

[0031] 1. Configuration of the first polishing liquid:

[0032] 1.1. Medicines:

[0033] Sodium bicarbonate, purity 99%;

[0034] Silica polishing liquid, model OP-S, brand Yunbo, particle size 80-110nm;

[0035] Hydrogen peroxide, mass concentration 30%;

[0036] 1.2. Preparation method of drug solution:

[0037] 1) Pour 100L of deionized water into the dispensing container;

[0038] 2) Use an electronic scale to weigh 1100g of high-purity sodium bicarbonate and pour it into deionized water, stirring until it is completely dissolved;

[0039] 3) After the liquid is stirred evenly, add 4000ml of polishing liquid and stir evenly;

[0040] 4) Add 4000g hydrogen peroxide and stir evenly;

[0041] The liquid medicine is filtered through a filter element with a pore size of 1um and then flows into the polishing pad of the polishing equipment in two ways.

[0042] 2. Configuration of the second polishing liquid:

[0043] 2.1. Medicines:

[0044] Lauryl phosphate, purity 99%, purchased from Nanxing Chemical (Jiangsu) Co., Ltd.;

[0045] Polyether-modified polydimethylsiloxane, model: KP-140, brand: Lanabai; purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.;

[0046] Polyvinylpyrrolidone Luvitec K30, CAS No. 9003-39-8, brand: BASF;

[0047] Disproportionated rosin acid potassium soap, model LLB-253; brand: Lana White, premium grade;

[0048] 2.2. Preparation method of drug solution:

[0049] 1) Pour 100L of deionized water into the dispensing container;

[0050] 2) Using an electronic scale, weigh 1000 g of lauryl alcohol phosphate, 800 g of polyvinyl pyrrolidone Luvitec K30, and 2500 g of potassium rosin soap, pour them into deionized water, and stir until they are completely dissolved;

[0051] 3) After the liquid medicine is stirred evenly, 500 g of polyether-modified polydimethylsiloxane is added and stirred evenly;

[0052] The liquid medicine is filtered through a filter element with a pore size of 1um and then flows into the polishing pad of the polishing equipment in two ways.

[0053] When each liquid medicine is exhausted or about to be exhausted, continue to configure it according to the above method.

[0054] 2. Experiments conducted using the special polishing process of the present invention.

[0055] The following examples are single-sided polishing. A ceramic disc is provided at the bottom of the polishing head, a polishing disc is provided below the ceramic disc, a polishing pad is provided on the polishing disc, and the substrate is adsorbed on the bottom of the ceramic disc. During polishing, the polishing head moves downward to press the substrate onto the polishing pad. The polishing head and the polishing disc rotate in the same direction. The 2-inch and 3-inch machines use the Chuangji 36B equipment, with a ceramic disc diameter of 360 mm and a polishing pad diameter of 914 mm; the 4-inch and 6-inch machines use the Chuangji 50B equipment, with a ceramic disc diameter of 485 mm and a polishing pad diameter of 1280 mm; the polishing pad is the Japanese Chiyoda 5166-NS.

[0056] The distance of the substrate extending beyond the polishing pad mentioned in each example refers to the maximum distance from the edge of the substrate extending beyond the polishing pad to the edge of the polishing pad.

[0057] Experimental groups 1-8 and comparative groups 1-4 were polished continuously with the first polishing liquid, and the flow rate of the first polishing liquid was 600 ml / min. Experimental groups 9-12 were polished in two steps, with the first polishing liquid being used in the first step at a flow rate of 600 ml / min, and the second polishing liquid being used in the second step at a flow rate of 900 ml / min.

[0058] Experimental Group 1

[0059] Take 14 2-inch germanium wafers, and measure the TTV of 1um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 10mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 30 minutes, put it into a cleaning tank for spray cleaning for 1 minute, and spin dry. The final product TTV is ≤1.2um.

[0060] Experimental Group 2

[0061] Take 7 3-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 15mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 30 minutes, put it into a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤2.4um.

[0062] Experimental Group 3

[0063] Take 9 4-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 20mm beyond the polishing pad, the pressure is 700N, the speed of the polishing head and the fixed plate is 30 rpm, the first polishing liquid is used, the flow rate is 600ml / min, polishing is carried out for 33 minutes, and the wafer is placed in a cleaning tank for spray cleaning for 1 minute. The final product TTV is ≤2.5um.

[0064] Experimental Group 4

[0065] Take 5 6-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 30mm beyond the polishing pad, the pressure is 800N, the speed of the polishing head and the fixed plate is 30 rpm, the first polishing liquid is used, the flow rate is 600ml / min, polishing is carried out for 33 minutes, and the wafer is placed in a cleaning tank for spray cleaning for 1 minute. The final product TTV is ≤2.6um.

[0066] Experimental Group 5

[0067] Take 14 2-inch germanium wafers, and measure the TTV of 1um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 20mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 30 minutes, put it into a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤1.1um.

[0068] Experimental Group 6

[0069] Take 7 3-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 30mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, the first polishing liquid is used, the flow rate is 600ml / min, polishing is carried out for 30 minutes, and the wafer is placed in a cleaning tank for spray cleaning for 1 minute. The final product TTV is ≤2.3um.

[0070] Experimental Group 7

[0071] Nine 4-inch germanium wafers were taken, and the TTV was measured to be 2um before polishing. The special process of the present invention was used for polishing. During polishing, the substrate was made to extend 40mm beyond the polishing pad, the pressure was 700N, the speed of the polishing head and the fixed plate was 30 rpm, the first polishing liquid was used, the flow rate was 600ml / min, polishing was carried out for 33 minutes, and the wafer was placed in a cleaning tank for spray cleaning for 1 minute. The final product TTV was ≤2.4um.

[0072] Experimental Group 8

[0073] Take 5 6-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 60mm beyond the polishing pad, the pressure is 800N, the speed of the polishing head and the fixed plate is 30 rpm, the first polishing liquid is used, the flow rate is 600ml / min, polishing is carried out for 33 minutes, and the wafer is placed in a cleaning tank for spray cleaning for 1 minute. The final product TTV is ≤2.5um.

[0074] Experimental Group 9

[0075] Take 14 2-inch germanium wafers, and measure the TTV of 1um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 20mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, the first step is to use the first polishing liquid, polish for 28 minutes, the flow rate is 600ml / min, the second step is to use the second polishing liquid, polish for 2 minutes, the flow rate is 900ml / min, and then put into the cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤1.1um.

[0076] Experimental Group 10

[0077] Take 7 3-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 30mm beyond the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, the first step is to use the first polishing liquid, polish for 27 minutes, the flow rate is 600ml / min, the second step is to use the second polishing liquid, polish for 3 minutes, the flow rate is 900ml / min, and then put into the cleaning tank for spray cleaning for 1 minute, the final product TTV≤2.3um.

[0078] Experimental Group 11

[0079] Take 9 4-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 40mm beyond the polishing pad, the pressure is 700N, the speed of the polishing head and the fixed plate is 30 rpm, the first step is to use the first polishing liquid, polish for 29 minutes, the flow rate is 600ml / min, the second step is to use the second polishing liquid, polish for 4 minutes, the flow rate is 900ml / min, and then put into the cleaning tank for spray cleaning for 1 minute, the final product TTV≤2.4um.

[0080] Experimental Group 12

[0081] Take 5 6-inch germanium wafers, and measure the TTV of 2um before polishing. Use the special process of the present invention to polish. During polishing, the substrate is made to extend 60mm beyond the polishing pad, the pressure is 800N, the speed of the polishing head and the fixed plate is 30 rpm, the first step uses the first polishing liquid, polishes for 28 minutes, and the flow rate is 600ml / min, the second step uses the second polishing liquid, polishes for 5 minutes, and the flow rate is 900ml / min, and then puts it into a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤2.5um.

[0082] Table 1 Comparison of data of experimental groups 5-12

[0083]

[0084]

[0085] In the table, the strength change rate and wear resistance change rate refer to the strength change rate and wear resistance change rate before and after polishing, respectively. Negative values ​​indicate a decrease, and positive values ​​indicate an increase.

[0086] Comparison group 1

[0087] Take 14 2-inch germanium wafers, and measure the TTV to be 1um before polishing. Use the normal process in the industry to polish. During polishing, the substrate is completely inside the polishing pad, the substrate protrudes 0mm from the polishing pad, the pressure is 500N, the polishing head and the fixed plate rotate at 60 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 30 minutes, put it in a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤5.8um.

[0088] Comparison group 2

[0089] Take 7 3-inch germanium wafers, and measure the TTV to be 2um before polishing. Use the normal process in the industry to polish. During polishing, the substrate is completely inside the polishing pad, the substrate protrudes 0mm from the polishing pad, the pressure is 500N, the speed of the polishing head and the fixed plate is 60 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 30 minutes, put it in a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤6.6um.

[0090] Comparison group 3

[0091] Take 9 4-inch germanium wafers, and measure the TTV to be 2um before polishing. Use the normal process in the industry to polish. During polishing, the substrate is completely inside the polishing pad, the substrate protrudes 0mm from the polishing pad, the pressure is 700N, the polishing head and the platen rotate at 30 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 33 minutes, put it in a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤7.4um.

[0092] Comparison group 4

[0093] Take 5 6-inch germanium wafers, and measure the TTV to be 2um before polishing. Use the normal process in the industry to polish. During polishing, the substrate is completely in the polishing pad, the substrate protrudes 0mm from the polishing pad, the pressure is 800N, the polishing head and the fixed plate speed are 30 rpm, and the first polishing liquid is used with a flow rate of 600ml / min. Polish for 33 minutes, put it in a cleaning tank for spray cleaning for 1 minute, and the final product TTV is ≤9.8um.

[0094] Table 2 Comparison of experimental groups 1-8 and control groups 1-4

[0095]

[0096] The experimental results show that the present invention is very effective in improving the flatness of the substrate. After multiple experiments, it is concluded that the optimal substrate exceeds the polishing pad by 35-40% of the wafer diameter.

Claims

1. A method for polishing a substrate with high flatness, wherein a ceramic disc is provided at the bottom of a polishing head, a polishing disc is provided below the ceramic disc, a polishing pad is provided on the polishing disc, and the substrate is adsorbed or adhered to the bottom of the ceramic disc, characterized in that: During polishing, the polishing head moves downward to press the substrate against the polishing pad, and part of the edge of the substrate extends beyond the polishing pad. Polishing is performed for 25 to 33 minutes under the conditions of a pressure of 500 to 700 N and a rotation speed of the polishing head and the polishing disk of 30 to 60 rpm, wherein the polishing head and the polishing disk rotate in the same direction.

2. The polishing method for a high-flatness substrate according to claim 1, characterized in that: The maximum distance from the edge of the substrate beyond the polishing pad to the edge of the polishing pad is 19.6% to 40% of the diameter of the substrate.

3. The polishing method for a high-flatness substrate according to claim 2, characterized in that: The maximum distance from the edge of the substrate beyond the polishing pad to the edge of the polishing pad is 39.2% to 40% of the diameter of the substrate.

4. The polishing method for a high-flatness substrate according to any one of claims 1 to 3, characterized in that: The polishing of the germanium substrate is carried out in two steps. The first step of polishing uses a first polishing solution containing sodium bicarbonate, silicon dioxide polishing solution and hydrogen peroxide, and the second step uses a second polishing solution containing lauryl alcohol phosphate, polydimethylsiloxane and polyvinyl pyrrolidone.

5. The polishing method for a high-flatness substrate according to claim 4, characterized in that: In the second polishing liquid, the polydimethylsiloxane is polyether-modified polydimethylsiloxane.

6. The polishing method for a high-flatness substrate according to claim 4, characterized in that: The second polishing liquid also contains disproportionated rosin acid potassium soap.

7. The polishing method for a high-flatness substrate according to claim 4, characterized in that: The second polishing liquid contains 1-3% lauryl alcohol phosphate, 0.3-0.8% polyether-modified polydimethylsiloxane, 0.5-1.0% polyvinyl pyrrolidone, 2-3% disproportionate potassium rosin soap and the balance water, wherein the aforementioned % are mass percentages.

8. The polishing method for a high-flatness substrate according to claim 4, characterized in that: In the first polishing liquid, the particle size of the silicon dioxide polishing liquid is 80-110 nm; the mass concentration of the hydrogen peroxide is 30.0-32.0%.

9. The polishing method for a high-flatness substrate according to claim 4, characterized in that: The first polishing liquid contains 1-3% sodium bicarbonate, 3-5% silicon dioxide polishing liquid, 2-4% hydrogen peroxide and the balance water, wherein the aforementioned % are mass percentages.

10. The polishing method for a high-flatness substrate according to claim 4, characterized in that: In the first step of polishing, the flow rate of the first polishing liquid is 500-600 ml / min, and the polishing time is 15-30 min; in the second step of polishing, the flow rate of the second polishing liquid is 800-900 ml / min, and the polishing time is 2-5 min.

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