Process method for improving surface roughness of 12-inch silicon wafer before polishing

Abstract

The invention discloses a process method for improving the surface roughness of a 12-inch silicon wafer before polishing, and the method comprises the following steps: (1) putting the 12-inch silicon wafer after double-sided grinding into a wafer box, and then putting the wafer box into a water tank containing a citric acid aqueous solution for soaking for 30-180 minutes; (2) sequentially putting the soaked silicon wafer into an active agent tank, a cleaning agent tank and a No.2 liquid tank for soaking or cleaning; a solvent in the active agent tank is composed of water, KOH, a cleaning agent and an active agent according to the ratio of (75-85): (1.5-2.5): (0.5-1.5): (2-4), a solvent in the cleaning agent tank is composed of water, KOH, a cleaning agent and an active agent according to the ratio of (75-85): (1.5-2.5): (2-4): (0.25-0.75), and the second liquid is composed of hydrochloric acid, hydrogen peroxide and pure water according to the ratio of (0.5-1.5): (0.5-1.5): (55-65); and (3) carrying out multi-section gradient accurate grinding thinning processing on the cleaned silicon wafer by using an accurate grinding machine. According to the method, the surface roughness of the 12-inch silicon wafer before polishing is improved by improving the cleaning process and the fine grinding process, and the integrated circuit process line width of the 12-inch polished wafer can be further optimized.

Description

Technical Field

[0001] This invention relates to a process method for improving the surface roughness of a 12-inch silicon wafer before polishing, belonging to the field of semiconductor materials technology. Background Technology

[0002] With the continuous development of technology, the application scenarios of smart devices are becoming increasingly diverse, leading to increasingly stringent requirements for the 12-inch polished wafers needed to manufacture integrated circuits. Grinding 12-inch silicon wafers is the final purely mechanical process before polishing, its main function being to ensure that the surface quality and thickness consistency of the product before polishing reach the micron level. While the thickness consistency of 12-inch silicon wafers can generally be achieved through machine hardware during grinding, its surface quality can only be optimized through process optimization.

[0003] In the 90 / 64nm era of integrated circuits, the grinding process for 12-inch silicon wafers involved double-sided grinding followed by single-sided grinding. With the advent of the 28nm era, due to the increased demands on 12-inch silicon wafers, the grinding process changed to double-sided grinding + etching + single-sided grinding. This process change in the 28nm era not only resolved the dimple and surface particle issues of 12-inch silicon wafers but also reduced the surface roughness from tens or even hundreds of nanometers to around ten nanometers. However, with the increasing application of 14nm technology, the surface roughness of 12-inch silicon wafers manufactured using the original process can no longer fully meet the parameter requirements of the 14nm era. Summary of the Invention

[0004] The purpose of this invention is to provide a process method to improve the surface roughness of 12-inch silicon wafers before polishing, thereby further improving the surface quality of silicon wafers and meeting the parameter requirements of the 14-nanometer era.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A process method for improving the surface roughness of a 12-inch silicon wafer before polishing includes the following steps: (1) Place the double-sided ground 12-inch silicon wafer into the wafer cassette, and then immerse the wafer cassette in a water bath containing citric acid solution for 30~180 min; (2) After soaking, the silicon wafers are placed in the activator tank, the cleaning agent tank, and the No. 2 liquid tank in sequence for soaking or cleaning; the components of the solvent in the activator tank are: water, KOH, cleaning agent and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(0.5-1.5):(2-4); the components of the solvent in the cleaning agent tank are: water, KOH, cleaning agent and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(2-4):(0.25-0.75); the components of the No. 2 liquid are: hydrochloric acid, hydrogen peroxide and pure water, and the mass ratio between the components is: hydrochloric acid:hydrogen peroxide:pure water = (0.5-1.5):(0.5-1.5):(55-65); (3) The cleaned silicon wafers are subjected to multi-stage gradient fine grinding and thinning using a fine grinding machine.

[0006] Preferably, in step (1), the mass percentage concentration of the citric acid aqueous solution is 1~5%.

[0007] Preferably, in step (1), the temperature of the citric acid aqueous solution is 20-25°C.

[0008] Preferably, in step (2), the surfactant is a high-purity 3F surfactant, and the main component of the cleaning agent is potassium hydroxide.

[0009] Preferably, in step (2), the temperature in the surfactant tank is controlled at 60-80℃ and the soaking time is 250-300s; the temperature in the cleaning agent tank is controlled at 60-80℃ and the soaking time is 250-300s; the temperature in the No. 2 liquid tank is controlled at 60-80℃ and the cleaning time is 280-300s.

[0010] Preferably, in step (3), the spindle speed of the fine grinding is 1400-2100 rpm, the silicon wafer speed is 80-210 rpm, and the spindle feed rate is 0.1-0.5 μm / s.

[0011] Preferably, in step (3), the first stage is semi-finish grinding, and the process parameters are: spindle speed of 1700~2100 rpm, silicon wafer speed of 140~210 rpm, and feed rate of 0.3~0.5 μm / s; the second stage is finish grinding, and the process parameters are: spindle speed of 1700~2100 rpm, silicon wafer speed of 140~210 rpm, and feed rate of 0.15~0.20 μm / s.

[0012] The beneficial effects of this invention are: This invention improves the surface roughness of 12-inch silicon wafers before polishing by modifying the cleaning process and the fine grinding process. On the one hand, the improved cleaning process after double-sided grinding uses lemon water immersion, surfactant immersion, cleaning agent cleaning, and No. 2 liquid cleaning to thoroughly clean the silicon wafer surface without introducing new impurities and defects. On the other hand, the improved fine grinding process uses multi-stage gradient grinding (i.e., a semi-fine grinding + fine grinding integrated method) to improve the surface roughness of the product.

[0013] The process method of this invention can manufacture 12-inch silicon wafers with surface roughness down to the nanometer level, which is beneficial for further optimizing the integrated circuit process linewidth of 12-inch polished wafers. Attached Figure Description

[0014] Figure 1 The average surface roughness Ra of silicon wafers obtained by the conventional method and the process method of the present invention is compared.

[0015] Figure 2 The average surface roughness Rq of silicon wafers obtained by the conventional method and the process method of the present invention is compared.

[0016] Figure 3 The average surface roughness Rz of silicon wafers obtained by the conventional method and the process method of the present invention is compared. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features and advantages of the present invention, the following description, in conjunction with the accompanying drawings and embodiments, further illustrates the present invention.

[0018] The process method for improving the surface roughness of a 12-inch silicon wafer before polishing provided by this invention includes the following steps: (1) Place the double-sided polished 12-inch silicon wafer into the wafer cassette, and then immerse the wafer cassette in a water bath containing citric acid aqueous solution for 30-180 minutes. The temperature of the citric acid aqueous solution is 20-25℃. (2) After soaking, the silicon wafers are placed in the activator tank, the cleaning agent tank, and the No. 2 liquid tank in sequence for soaking or cleaning. The solvent in the activator tank consists of water, KOH, cleaning agent, and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(0.5-1.5):(2-4). The temperature in the activator tank is controlled at 60-80℃, and the soaking time is 250-300s. The solvent in the cleaning agent tank consists of water, KOH, cleaning agent, and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(2-4):(0.25-0.75). The temperature inside the cleaning agent tank is controlled at 60-80℃, and the soaking time is 250-300s; the composition of solution No. 2 is: hydrochloric acid, hydrogen peroxide and pure water, and the mass ratio between the components is: hydrochloric acid: hydrogen peroxide: pure water = (0.5-1.5):(0.5-1.5):(55-65). The temperature inside the solution No. 2 tank is controlled at 60-80℃, and the cleaning time is 280-300s. (3) The cleaned silicon wafers are subjected to multi-stage gradient fine grinding and thinning using a fine grinding machine.

[0019] Conventional processes use etching for cleaning. While etching removes dust from the silicon wafer surface, it also peels off a layer, introducing new defects. In the process of this invention, the silicon wafer surface is cleaned sequentially using lemon water immersion, surfactant immersion, cleaning agent, and solution No. 2, without introducing new impurities or defects.

[0020] This invention improves the fine grinding process by employing multi-stage gradient grinding (i.e., a semi-fine grinding + fine grinding integrated approach) to improve product surface roughness. Semi-fine grinding first removes the large damaged layer from the product surface, followed by fine grinding to significantly improve surface roughness. During fine grinding, the spindle speed is controlled at 1400-2100 rpm, the wafer speed at 80-210 rpm, and the spindle feed rate at 0.1-0.5 μm / s. As a preferred embodiment of this invention, a two-stage gradient grinding process is used. The first stage is semi-fine grinding, with process parameters of: spindle speed 1700-2100 rpm, wafer speed 140-210 rpm, and feed rate 0.3-0.5 μm / s; the second stage is fine grinding, with process parameters of: spindle speed 1700-2100 rpm, wafer speed 140-210 rpm, and feed rate 0.15-0.20 μm / s. In semi-finish grinding, controlling appropriate process parameters and adjusting the ratio between spindle speed, wafer speed, and feed rate to a suitable range, especially controlling the feed rate, can remove as much of the large damage layer on the product surface as possible. In finish grinding, further reducing the feed rate to a suitable range can further reduce the surface roughness of the product. When adjusting the ratio between spindle speed, wafer speed, and feed rate, the surface roughness initially improves gradually with increasing wafer speed and spindle speed, reaching a relatively stable level. However, as the wafer speed and spindle speed continue to increase, the surface roughness begins to deteriorate.

[0021] Example The 40 double-sided polished silicon wafers were divided into two groups of 20 wafers each.

[0022] The first group was treated using traditional methods. The specific process was as follows: KOH was used for etching and cleaning, and single-sided grinding was performed. The etching and cleaning process was as follows: the silicon wafers were immersed in soda ash, solution No. 1, and solution No. 2 in sequence. The soda ash ratio was 45% KOH, the temperature was 70℃, and the immersion time was 300s. The solution No. 1 ratio was (ammonia:hydrogen peroxide:pure water = 1:1:18), the temperature was 70℃, and the immersion time was 280-360s. The solution No. 2 ratio was (hydrofluoric acid:hydrochloric acid:hydrogen peroxide:pure water = 0.5:3:3:60), the temperature was 70℃, and the immersion time was 300s.

[0023] The etched and cleaned silicon wafers are then subjected to fine grinding. The fine grinding process parameters are: spindle speed 1400 rpm, silicon wafer speed 210 rpm, and feed rate 0.3 μm / s.

[0024] After the product is finely ground, white light interference is used to test the surface roughness. The surface roughness test rule is to test 9 points per piece, with 1 point at the center of the silicon wafer, 4 points at half the radius, and 4 points at the outermost edge. The test focusing range is 80 mm × 80 mm.

[0025] The second group of 20 silicon wafers was processed using the method of this invention. The specific process is as follows: First, they were soaked in citric acid (citric acid: pure water = 1:100) at 25°C for 30 minutes. Then, they were directly placed in an activator bath (water:KOH:cleaning agent:activator = 80:2:1:3) at 60-80°C for 250-300 seconds. Next, they were pre-cleaned in a cleaning agent bath (water:KOH:cleaning agent:activator = 80:2:3:0.5) at 60°C for 250-300 seconds. Finally, they were placed in solution No. 2 for final cleaning (acid:hydrogen peroxide:pure water = 1:1:60) at 60°C for 290 seconds. The surfactant used above is high-purity 3F surfactant produced by Jiangsu Jingjiu Microelectronics Materials Co., Ltd., with production batch number 250946; the cleaning agent is ANIMS-101 cleaning agent produced by Jinan Dexi Technology Co., Ltd., with production batch number 2508191005.

[0026] The cleaned silicon wafers are then subjected to multi-stage grinding. The first stage is semi-finish grinding, with the following process parameters: spindle speed 1800 rpm, silicon wafer speed 185 rpm, and feed rate 0.3 μm / s. The second stage is finish grinding, with the following process parameters: spindle speed 1800 rpm, silicon wafer speed 185 rpm, and feed rate 0.17 μm / s.

[0027] After multi-stage grinding, the surface roughness of the product is tested using white light interference. The surface roughness test rule is to test 9 points per piece, with 1 point at the center of the silicon wafer, 4 points at half the radius, and 4 points at the outermost edge. The test focusing range is 80 mm × 80 mm.

[0028] Test results showed that 20 pieces (pieces 1-20) processed using traditional methods, such as Figure 1 The mean value of the surface roughness Ra (arithmetic mean deviation) is 2.79 nm; Figure 2 The average surface roughness Rq (root mean square roughness) is 3.49 nm; Figure 3 The average surface roughness Rz (average peak-to-valley height) is 24.26 nm. See Table 1 for data comparison details. Twenty grinding discs (discs 21-40) processed using the method of this invention, such as... Figure 1 The average surface roughness Ra is 1.88 nm; Figure 2 The average surface roughness Rq is 2.34 nm; such as Figure 3 The average surface roughness Rz is 19.23 nm. See Table 1 for data comparison details.

[0029] As shown in the figure, compared with traditional processing methods, the processing method of this invention reduces the average surface roughness Ra of silicon wafers before polishing by 32.62% and the standard deviation by 54.17%; the average surface roughness Rq by 32.95% and the standard deviation by 55.17%; and the average surface roughness Rz by 20.73% and the standard deviation by 90.72%. It is evident that products processed using the method of this invention not only show significant improvements in surface roughness but also substantial improvements in product stability and consistency.

[0030] Table 1

Claims

1. A process method for improving the surface roughness of a 12-inch silicon wafer before polishing, characterized in that, Includes the following steps: (1) Place the double-sided ground 12-inch silicon wafer into the wafer cassette, and then immerse the wafer cassette in a water bath containing citric acid solution for 30~180 min; (2) After soaking, the silicon wafers are placed in the activator tank, the cleaning agent tank, and the No. 2 liquid tank in sequence for soaking or cleaning; the components of the solvent in the activator tank are: water, KOH, cleaning agent and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(0.5-1.5):(2-4); the components of the solvent in the cleaning agent tank are: water, KOH, cleaning agent and activator, and the mass ratio between the components is: water:KOH:cleaning agent:activator = (75-85):(1.5-2.5):(2-4):(0.25-0.75); the components of the No. 2 liquid are: hydrochloric acid, hydrogen peroxide and pure water, and the mass ratio between the components is: hydrochloric acid:hydrogen peroxide:pure water = (0.5-1.5):(0.5-1.5):(55-65); (3) The cleaned silicon wafers are subjected to multi-stage gradient fine grinding and thinning using a fine grinding machine.

2. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 1, characterized in that: In step (1), the mass percentage concentration of the citric acid aqueous solution is 1-5%.

3. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 1, characterized in that: In step (1), the temperature of the citric acid aqueous solution is 20-25℃.

4. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 1, characterized in that: In step (2), the surfactant is a high-purity 3F surfactant, and the main component of the cleaning agent is potassium hydroxide.

5. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 1, characterized in that: In step (2), the temperature in the surfactant tank is controlled at 60-80℃ and the soaking time is 250-300s; the temperature in the cleaning agent tank is controlled at 60-80℃ and the soaking time is 250-300s; the temperature in the No. 2 liquid tank is controlled at 60-80℃ and the cleaning time is 280-300s.

6. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 1, characterized in that: In step (3), the spindle speed of the fine grinding is 1400-2100 rpm, the silicon wafer speed is 80-210 rpm, and the spindle feed rate is 0.1-0.5 μm / s.

7. The process method for improving the surface roughness of a 12-inch silicon wafer before polishing according to claim 6, characterized in that: In step (3), the first stage is semi-finish grinding, and the process parameters are: spindle speed of 1700~2100rpm, silicon wafer speed of 140~210rpm, and feed rate of 0.3~0.5μm / s; the second stage is semi-finish grinding, and the process parameters are: spindle speed of 1700~2100rpm, silicon wafer speed of 140~210rpm, and feed rate of 0.15~0.20μm / s.

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