Polishing pad for fine polishing process of silicon wafer as well as preparation method and application of polishing pad

Abstract

The invention provides a polishing pad for a silicon wafer fine polishing process as well as a preparation method and application of the polishing pad. The polishing pad comprises a porous polyurethane skin layer and an elastic impregnation layer, the elastic impregnated layer is a non-woven fabric impregnated and cured with polyurethane; the porous polyurethane skin layer is formed on the elastic impregnated layer by adopting polyurethane slurry through wet film forming and has a pore structure extending from the surface to the elastic impregnated layer, the pore diameter of an opening in the surface of the skin layer is 40-80 [mu] m, the side wall of the pore is provided with a microporous channel for a polishing solution to pass through, and the size of the microporous channel is 0.1-10 [mu] m. According to the product, the storage amount of the polishing solution is increased in the silicon wafer fine polishing process, so that the pressure distribution is more uniform in the polishing process, the polishing solution distribution efficiency is improved, and scratches are avoided while the polishing rate is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor polishing pad, in particular to a polishing pad for silicon wafer fine polishing process and a preparation method and use thereof. BACKGROUND

[0002] In the existing silicon wafer fine polishing process, the material of the polishing pad is unevenly distributed, which is manifested in unreasonable pore structure, irregular size and position of the pore diameter. The unreasonable pore structure includes non-ideal porosity, pore shape and connectivity; the irregular size of the pore diameter includes large difference in the pore diameter of different regions of the polishing pad; and the irregular position of the pore diameter includes non-uniform distribution of the pore diameter, which may be in the form of aggregation or sparseness.

[0003] The main reason is that the film coating process of the existing product is not perfect, usually without treatment on the surface of the impregnated substrate, resulting in thick dense layer (distance from the bottom of the micro-pore to the surface of the substrate) and less number of micro-pores, and thin micro-pore layer; and there are certain problems in the formula, resulting in no smaller level of pores between the micro-pores, which is not conducive to the mutual flow of the polishing liquid, resulting in uneven pressure distribution in the polishing process, affecting the slurry distribution efficiency, and finally leading to scratches after polishing. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a polishing pad for silicon wafer fine polishing process and a preparation method and use thereof, for solving the problem of uneven pressure distribution caused by the lack of intercommunication channels on the surface of the polishing pad in the prior art, poor slurry distribution efficiency, and thus polishing scratches.

[0005] To achieve the above-mentioned purposes and other related purposes, the present application is realized by the following technical scheme.

[0006] The present application provides a polishing pad for silicon wafer fine polishing process, which comprises a porous polyurethane skin layer and an elastic impregnated layer; the elastic impregnated layer is a non-woven fabric impregnated and solidified with polyurethane; the porous polyurethane skin layer is formed on the elastic impregnated layer by wet film forming with polyurethane slurry, and has a pore structure extending from the surface to the elastic impregnated layer, the opening diameter at the surface of the skin layer is 40-80 μm, and the micro-pore channel for the polishing liquid to pass through is provided on the side wall of the pore, the size of the micro-pore channel is 0.1-10 μm.

[0007] Preferably, the pore structure is in the shape of a water droplet.

[0008] Preferably, the polyurethane is polyester type polyurethane.

[0009] Preferably, the aperture size at the skin surface is 40-80 μm, such as can be 40-70 μm, 40-60 μm, 60-80 μm, 50-80 μm, 70-80 μm, etc., more preferably, the aperture size at the skin surface is 60-80 μm.

[0010] Preferably, the size of the micro-pores is diverse, such as can be 0.1-1 μm, 1-2 μm, 2-3 μm, 3-4 μm, 4-5 μm, 5-6 μm, 6-7 μm, 7-8 μm, 8-9 μm, 0.1-1.5 μm, 0.1-2.5 μm, 0.1-3.5 μm, 0.5-4.5 μm, 0.5-5.5 μm, etc.

[0011] Preferably, the finished thickness of the polishing pad is 1.3-1.6 mm, such as can be 1.3 mm, 1.35 mm, 1.4 mm, 1.45 mm, 1.5 mm, 1.55 mm, or 1.6 mm.

[0012] Preferably, the thickness of the elastic impregnation layer is 0.6-1.0 mm. Such as can be 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm.

[0013] Preferably, the density of the polishing pad is 0.3700-0.3750 g / cm 3 , such as can be 0.3710 g / cm 3 , 0.3720 g / cm 3 , 0.3730 g / cm 3 , 0.3740 g / cm 3 , or 0.3750 g / cm 3 .

[0014] Preferably, the compression rate of the polishing pad is 25.00-27.00%, such as can be 25.00%, 25.05%, 25.10%, 25.15%, 25.20%, 25.25%, 25.30%, 25.35%, 25.40%, 25.45%, 25.50%, 25.55%, 25.60%, 25.65%, 25.70%, 25.75%, 25.80%, 25.85%, 25.90%, 25.95%, 26.00%, 26.05%, 26.10%, 26.15%, 26.20%, 26.25%, 26.30%, 26.35%, 26.40%, 26.45%, 26.50%, 26.55%, 26.60%, 26.65%, 26.70%, 26.75%, 26.80%, 26.85%, 26.90%, 26.95%, 27.00%.

[0015] Preferably, the compressibility of the polishing pad is 73-77%, such as 73%, 74%, 75%, 76% or 77%.

[0016] Preferably, the polishing pad has a Shore hardness of 50-52 Shore A. More preferably, the polishing pad has a Shore hardness of 51 Shore A.

[0017] Preferably, the basis weight of the nonwoven fabric used as the base fabric is 120-135 g / m². 2 For example, it can be 120 g / m³. 2 121 g / m 2 122 g / m 2 123 g / m 2 124 g / m 2 125 g / m 2 126 g / m 2 127 g / m 2 128 g / m 2 129 g / m 2 130g / m 2 131g / m 2 132 g / m 2 133 g / m 2 134 g / m 2 Or 135 g / m 2 The nonwoven fabric described in this application may be made of polyester (such as PET), polypropylene, polyamide (nylon, PA), viscose fiber, polyethylene (PE), etc.

[0018] Preferably, in the elastic impregnation layer, the impregnation polyurethane solution includes 10-100 parts by weight of impregnation polyurethane, 30-50 parts by weight of DMF and 0.2-0.8 parts by weight of color paste; wherein the impregnation polyurethane is a polyester-type polyurethane with a viscosity of 80,000-120,000 cps at 25°C and a solid content of 29-31 wt%.

[0019] The weight percentage of the impregnating polyurethane in the impregnation polyurethane solution can be selected according to actual conditions, as long as it is a polyester-type polyurethane and can be mixed and formulated to suit the impregnation of nonwoven fabrics. For example, in the above technical solution, it can be 80 parts by weight, 90 parts by weight, 70 parts by weight, 95 parts by weight, etc. Specifically, the DMF can be 35 parts by weight, 40 parts by weight, 45 parts by weight, etc.; specifically, the color paste can be 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, or 0.8 parts by weight. More preferably, the impregnating polyurethane has a viscosity of 80,000 cps, 85,000 cps, 90,000 cps, 95,000 cps, 100,000 cps, 105,000 cps, 110,000 cps, 115,000 cps, or 120,000 cps at 25°C. More preferably, the solid content is 29 wt%, 30 wt%, or 31 wt%.

[0020] More preferably, based on the total mass of the color paste, the color paste comprises: 55-65 wt% DMF, 4-8 wt% polyethylene glycol, 0.001-2 wt% bactericide, 0.5-10 wt% wetting and dispersing agent, 2-40 wt% carbon black, and 0.001-3 wt% defoamer. More preferably, the bactericide is iodopropynyl butylcarbamate (IPBC). More preferably, the wetting and dispersing agent is Dispersago®-9720. More preferably, the carbon black has a specific surface area of ​​160-180 m². 2 / g, more specifically, the carbon black is Cabot carbon black C5X865. More preferably, the defoamer is VOK®-DF 7015. Specifically, in the color paste, DMF can be 55wt%, 58wt%, 60wt%, 62wt%, or 65wt%; the amount of polyethylene glycol can be 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%; the amount of bactericide can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, or 2wt%; the amount of wetting and dispersing agent can be 0.5wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 5.5wt%, or 6wt%; carbon black is used to provide black pigment, and it needs to be easy to disperse, with an amount of 1wt%, 1.5wt%, 2wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, or 17wt%; and the amount of defoamer can be 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 3wt%.

[0021] More preferably, impregnation is performed by two opposing rollers, with the gap between the rollers being less than the thickness of the nonwoven fabric, such as slightly less than the thickness of the nonwoven fabric. For example, if the nonwoven fabric is 1 mm thick, the roller gap is 0.9 mm.

[0022] Preferably, after impregnation, the material is further solidified in a DMF aqueous solution; and then washed and dried to obtain the elastic impregnated layer. More preferably, the concentration of the DMF aqueous solution used for solidification after impregnation is 15~25wt%. For example, it can be 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, or 25wt%.

[0023] Preferably, the wet film formation includes the following steps:

[0024] 1) The elastic impregnated layer is first wetted with a DMF aqueous solution;

[0025] 2) The surface is ironed using an ironing wheel until the moisture content of the elastic impregnated layer is 25-30 wt%;

[0026] 3) Apply polyurethane slurry onto the elastic impregnation layer;

[0027] 4) It solidifies upon entering the DMF aqueous solution;

[0028] 5) Wash with water and dry.

[0029] Preferably, wet film formation can be carried out in a wet processing workshop, typically a constant temperature (20~30℃) and constant humidity (20~45%) workshop. Specifically, when using a wet production line, rollers can be used to support and guide the strip-shaped elastic impregnated layer for the wet film formation process.

[0030] In step 1), the elastic impregnation layer is further squeezed by rollers (such as rubber rollers) to promote the wetting of the elastic impregnation layer by the DMF aqueous solution.

[0031] Preferably, in step 1), the concentration of the DMF aqueous solution is 12-20 wt%. For example, it can be 12 wt%, 13 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%.

[0032] It should be noted that the ironing process in step 2) is essential. This involves using ironing wheels at a specific temperature to achieve the desired surface moisture content. Generally, the number of ironing wheels, their temperature, and the application time can be set according to the specific production process. Preferably, the surface temperature of the ironing wheels is 85~100℃, such as 85℃, 88℃, 90℃, 92℃, 95℃, 98℃, 100℃, etc. More preferably, the surface temperature of the ironing wheels is 90~95℃. Preferably, the moisture content of the elastic impregnated layer surface after ironing is 25%~30% (obtained using a humidity meter). This is not arbitrarily set. If the surface moisture content is too high, the pores inside the porous polyurethane skin will be too large, the product density will be low, the compression rebound will increase, and ultimately the product will not be wear-resistant. For example, the surface moisture content after ironing may be 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, or 30wt%.

[0033] The coating in step 3) can be performed in a thin film coating machine. Preferably, the coating thickness is 1.8~2.1mm, such as 1.8mm, 1.9mm, 2.0mm or 2.1mm. This coating thickness can be controlled by the coating gap on the thin film coating machine. To achieve the need for precise control, a coating machine with a tolerance of ±0.1mm can be selected.

[0034] Preferably, the polyurethane slurry in step 3) comprises: 50-300 parts by weight of polyurethane, 10-70 parts by weight of DMF, 0.2-1 parts by weight of nonionic surfactant, 0.05-0.5 parts by weight of wetting agent, 0.5-5.0 parts by weight of color paste, and 0.001-1 parts by weight of leveling agent. Specifically, the amount of polyurethane in the polyurethane slurry can be 80 parts by weight, 90 parts by weight, 100 parts by weight, 110 parts by weight, 120 parts by weight, 130 parts by weight, 140 parts by weight, 150 parts by weight, 160 parts by weight, 170 parts by weight, 180 parts by weight, etc.; specifically, the DMF can be 20 parts by weight, 30 parts by weight, 40 parts by weight, 50 parts by weight, or 60 parts by weight; specifically, the nonionic surfactant is 0.2 parts by weight, 0.3 parts by weight, etc. The amounts are 0.4 parts by weight, 0.5 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, or 1 part by weight; specifically, the color paste is 0.5 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, or 5 parts by weight; specifically, the leveling agent is 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, or 1 part by weight.

[0035] More preferably, the nonionic surfactant is Span 80. More preferably, the wetting agent is OT-75. More preferably, the leveling agent is BY33. More preferably, based on the total mass of the color paste, the color paste comprises: 55~65wt% DMF, 4~8wt% polyethylene glycol, 0.001~2wt% bactericide, 0.5~10wt% wetting and dispersing agent, 2~40wt% carbon black, and 0.001~3wt% defoamer. Specifically, in the color paste, DMF can be 55wt%, 58wt%, 60wt%, 62wt%, or 65wt%; the amount of polyethylene glycol can be 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%; the amount of bactericide can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, or 2wt%; the amount of wetting and dispersing agent can be 0.5wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 5.5wt%, or 6wt%; carbon black is used to provide black pigment, and it needs to be easy to disperse, with an amount of 1wt%, 1.5wt%, 2wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, or 17wt%; and the amount of defoamer can be 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 3wt%. More preferably, the bactericide is iodopropynyl butylcarbamate. More preferably, the wetting and dispersing agent is Dispersago®-9720. More preferably, the carbon black has a specific surface area of ​​160~180m². 2 / g; More specifically, the carbon black is Cabot carbon black C5X865. More preferably, the defoamer is VOK®-DF 7015.

[0036] In step 4), the further introduction of the DMF aqueous solution is to create a porous structure on the surface. If the concentration of DMF at this point is too high, it will lead to a higher density of the final polishing pad, a reduction in the number of internal micropores, a decrease in the liquid storage capacity of the polishing pad, and a decrease in the material removal rate of the product. Preferably, in step 4), the concentration of the DMF aqueous solution is 15~25wt%, such as 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, or 25wt%.

[0037] In a preferred embodiment, the linear speed of the wet film-forming process is 1~5 m / min. For example, it can be 1 m / min, 2 m / min, 3 m / min, 4 m / min, or 5 m / min.

[0038] In step 5), the washing process requires coordinated roller squeezing to remove as much solvent as possible. A small amount of solvent can be removed during the drying process. Preferably, the washing conditions are: the DMF concentration in the first washing tank is less than 20 wt%, and the DMF concentration in the last three washing tanks is less than 1 wt%. If the concentration in the last three tanks is higher, leaving more DMF, it can cause visible defects on the product surface, such as orange peel, during drying.

[0039] Preferably, in step 5), the drying temperature is 80~160℃.

[0040] Preferably, the post-processing steps include a grinding step, a hot-pressing texture step, and a groove forming step. More preferably, the surface is first ground with 800-grit sandpaper, and then further ground with 600-grit sandpaper until the aperture diameter is 40-80 μm. Even more preferably, a micron-level groove structure is formed on the surface using hot pressing or machining technology, with a groove depth of 200-300 μm. After applying adhesive to the back and cutting, the finished product is obtained.

[0041] Preferably, the polishing pad in this application further includes an adhesive backing layer disposed on the elastic impregnation layer.

[0042] The second aspect of the present invention also discloses a method for preparing a polishing pad as described above, wherein an elastic impregnation layer is first formed by impregnating a nonwoven fabric with a polyurethane solution and then curing it, and then a porous polyurethane skin is formed on the elastic impregnation layer by a wet film forming process; before coating the polyurethane solution, the surface to be coated is also wetted with a DMF aqueous solution and then flattened by a heated roller.

[0043] The third aspect of the present invention also discloses the use of the polishing pad as described above in the fine polishing process of silicon wafers.

[0044] For example, when used for fine polishing of boron-doped silicon wafers, it can include lightly doped silicon wafers (with a low boron content of 10%). 15 -10 17 atoms / cm 3 Furthermore, the resistivity is extremely high (0.01-0.001 Ω·m) and the silicon wafers are heavily doped (high boron content, 10). 19 -10 21 atoms / cm 3 Furthermore, its resistivity is extremely low, <0.001Ω·m.

[0045] The beneficial effects of the polishing pad and its application in this application are as follows:

[0046] By using an elastic impregnated layer as the coating substrate, the product's compressive resilience is increased. Controlling the surface moisture content of the elastic impregnated layer during coating results in a more uniform and neat cross-sectional pore structure in the product's skin (porous polyurethane skin). These features allow for increased storage of polishing slurry during silicon wafer polishing, resulting in more uniform pressure distribution and improved slurry distribution efficiency. This ensures a high polishing rate without causing scratches. When used for silicon wafer polishing, it meets requirements for removal rate and post-polishing surface quality. Attached Figure Description

[0047] Figure 1 The diagram shown is a structural schematic of the polishing pad of the present invention. Figure 1 The reference numerals in the attached figures are explained as follows: 1 is the porous polyurethane skin; 2 is the elastic impregnation layer; and 3 is the adhesive backing layer.

[0048] Figure 2 The image shown is an optical microscope cross-sectional view of a porous polyurethane polishing pad with specific holes in Embodiment 1 of the present invention.

[0049] Figure 3 The image shown is a SEM image of the porous polyurethane skin cross-section pore structure in Embodiment 1 of the present invention.

[0050] Figure 4 The image shown is an optical microscope image of the pores on the surface of the porous polyurethane skin in Embodiment 1 of the present invention.

[0051] Figure 5 The image shown is a polishing effect diagram of the heavily doped wafer using the polishing pad in Example 1 of this application, obtained by atomic force microscopy.

[0052] Figure 6 The image shown is a polishing effect diagram of a lightly doped wafer using the polishing pad in Example 1 of this application, obtained by atomic force microscopy.

[0053] Figure 7 The image shown is a cross-sectional view of the polishing pad under an optical microscope, as shown in Comparative Example 1.

[0054] Figure 8 The image shown is a cross-sectional view of the polishing pad under an optical microscope, as shown in Comparative Example 2.

[0055] Figure 9 The image shown is a cross-sectional view of the polishing pad under an optical microscope, as shown in Comparative Example 3.

[0056] Figure 10 The image shown is a cross-sectional view of the polishing pad under an optical microscope, as shown in Comparative Example 5.

[0057] Figure 11 The image shown is a cross-sectional view of the polishing pad under an optical microscope, as shown in Comparative Example 6. Detailed Implementation

[0058] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0059] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0060] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0061] This application provides a method such as Figure 1 The polishing pad shown comprises a porous polyurethane skin 1 and an elastic impregnation layer 2. The elastic impregnation layer 2 is formed by impregnating a nonwoven fabric with a polyurethane solution and then curing it. The porous polyurethane skin 1 is formed on the elastic impregnation layer using a wet film-forming process. In addition to conventional coating, the wet film-forming process includes pre-wetting and ironing treatments, resulting in a porous structure in the final polyurethane skin. This porous structure has the following characteristics: the pore size at the skin surface is 40-80 μm, extending from the surface to the elastic impregnation layer. Generally, the pores are teardrop-shaped (gradually increasing in size from the skin surface towards the elastic impregnation layer), and the sidewalls of the pores have micropore channels for the polishing liquid to pass through, the size of which is 0.1-10 μm. More preferably, the pore size at the skin surface is 50-80 μm. More preferably, the size of the micropore channels is 0.1-5 μm.

[0062] In specific embodiments, the post-processing steps also include a grinding step, a hot-pressing texture step, and a groove forming step. For example, the surface is first ground with sandpaper (e.g., 700-900 grit, more specifically 800 grit), and then further ground with sandpaper (500-700 grit, such as 600 grit) until the aperture of the opening at the surface is 40-80 μm (e.g., specifically 60-80 μm). More preferably, a micron-level groove structure is formed on the surface using hot pressing or machining technology, with a groove depth of 200-300 μm. After applying adhesive to the back and cutting, the finished product is obtained.

[0063] The polishing pad in this application also includes an adhesive backing layer 3. In a specific embodiment described below, the adhesive backing is specifically 3M 442, but commonly used adhesives from manufacturers such as Sekisui and Tesa can also be used.

[0064] In the actual preparation of the polishing pad in this application, in order to adopt continuous production, the nonwoven fabric is guided (or squeezed) by various guide rollers (or paired extrusion rollers) and impregnated, washed, coated, dried, etc. in the corresponding tank.

[0065] The test methods for each performance parameter in this application are as follows (the product is in the state of having adhesive backing during testing): thickness test refers to GB / T 6672-2001; density test refers to GB / T 1033.1-2008; compression ratio / compression rebound rate test refers to GB / T 6669-2008; hardness test refers to GB / T 2411-2008.

[0066] In the following embodiments of this application, the impregnated polyurethane is a polyester-type polyurethane with a viscosity of 80,000-120,000 cps at 25°C and a solid content of 29-31%. More preferably, the 100% modulus of the impregnated polyurethane is 9-11 MPa, the elongation at break is ≥250%, and the tensile strength is ≥30 MPs.

[0067] In the following embodiments of this application, the polyurethane in the polyurethane coating slurry is a polyester-type polyurethane. Its viscosity at 25°C is 150,000-200,000 cps, and its solid content is 34-36%. More preferably, the 100% modulus of the polyester-type polyurethane in the coating slurry is 11-13 MPa, its elongation at break is ≥250%, and its tensile strength is ≥63 MPa.

[0068] In the following embodiments of this application, the color paste uses the following formulation. Based on the total mass of the color paste, the color paste comprises: 60wt% DMF, 4-8wt% polyethylene glycol, 1wt% bactericide, 2wt% wetting and dispersing agent, 5wt% carbon black, and 1wt% defoamer; wherein the bactericide is iodopropynyl butylcarbamate; the wetting and dispersing agent is Dispersago®-9720; the carbon black is Cabot carbon black C5X865; and the defoamer is VOK®-DF 7015.

[0069] In the following embodiments of this application, the nonwoven fabric used as the base fabric is a polyester material, such as PET nonwoven fabric, and the basis weight of the nonwoven fabric is 125 g / m². 2 The thickness is 1mm.

[0070] Example 1

[0071] This embodiment provides a specific polishing pad and its preparation method.

[0072] This embodiment includes a detailed description of the usage amount of each raw material and its preparation method, including:

[0073] 1) Fabrication of the elastic impregnation layer:

[0074] Take 10 kg of impregnation polyurethane, add 4 kg of DMF and 0.06 kg of color paste, stir at 2000 rpm for 20 min, and prepare the impregnation polyurethane solution under nitrogen protection by vacuuming.

[0075] The nonwoven fabric is immersed in the above-mentioned impregnation polyurethane solution, and then rolled to ensure uniform fabric feeding with a roller gap of 0.9 mm. After solidification, it is immersed in a 15 wt% DMF aqueous solution, washed in a washing tank, and dried in a drying channel to obtain an elastic impregnated layer. Further, the edges can be trimmed to a suitable size before use. The final thickness of the elastic impregnated layer is 0.9 mm.

[0076] 2) Fabrication of the surface polyurethane skin:

[0077] Add 10KG of polyurethane, 3KG of DMF and 0.3KG of color paste to the tank and stir at 1500rpm for 5min. Then add 0.066KG of Span 80, 0.02KG of OT-75 and 0.004KG of BY33 and stir at 2500rpm for 20min. Remove the foam generated during the stirring process by vacuuming to prepare the polyurethane slurry. All the above operations are carried out under nitrogen protection.

[0078] The elastic impregnated layer is first immersed in a 12wt% DMF aqueous solution and then surface-smoothed using a hot-rolling wheel until the moisture content of the elastic impregnated layer surface is 27-30%. The above polyurethane slurry is then coated onto the elastic impregnated layer to form a film. The coating process is completed on a thin film coating machine (the coating machine requires a coating accuracy of ±0.1mm). The coating gap is 2.0mm. After coating, the film is placed in a 19-23wt% DMF aqueous solution to solidify. Then, it is washed with water (the washing process requires coordinated roller extrusion to ensure that the solvent is washed away) until the DMF concentration in the first washing tank is less than 20wt% and the DMF concentration in the last three washing tanks is less than 1wt%.

[0079] After washing, the product is dried in a 120℃ drying tunnel. Then, the surface is sanded with 800-grit sandpaper until the surface pores are 60-80μm. Next, it is hot-pressed with a hot press roller with a special surface texture. After cutting, a semi-finished product is obtained. The semi-finished product is 1.5mm thick. After applying adhesive backing, the finished product is obtained.

[0080] like Figure 2 The figure shown is a surface morphology image of the longitudinal section of the polishing pad in this application, taken by SEM. It can be seen that its porous polyurethane skin contains neat, almost translucent teardrop-shaped pores. Figure 3As can be seen, there are many tiny pores between the holes, allowing the polishing fluid to flow between them. Figure 4 The surface pore structure of the porous polyurethane skin can be seen.

[0081] Examples 2-3

[0082] Examples 2 and 3 were obtained by adjusting the coating gap (i.e. coating thickness). The specific coating gaps of Examples 2 and 3 are shown in Table 1.

[0083] Comparative Example 1

[0084] The only difference between Comparative Example 1 and Example 1 is that the coating gap is 1.6 mm.

[0085] Comparative Example 2

[0086] The only difference between Comparative Example 2 and Example 1 is that the coating gap is 2.3 mm.

[0087] Comparative Example 3

[0088] The only difference between Comparative Example 3 and Example 3 is that the concentration of DMF aqueous solution in the coagulation tank is lower, at 10~14wt%.

[0089] Comparative Example 4

[0090] The only difference between Comparative Example 4 and Example 3 is that the concentration of DMF aqueous solution in the coagulation tank is higher, at 26~30wt%.

[0091] Comparative Example 5

[0092] The only difference between Comparative Example 5 and Example 1 is that the surface moisture content of the substrate before coating is low, at 22 wt%.

[0093] Comparative Example 6

[0094] The only difference between Comparative Example 6 and Example 1 is that the surface moisture content of the substrate before coating is higher, at 32wt%.

[0095] The performance of the polishing pads specifically formed in Examples 1-3 and Comparative Examples 1-6 is shown in Table 3.

[0096] Table 1

[0097] Coating gap (mm) Coagulation bath DMF concentration (%) Moisture content of substrate surface before coating (%) Semi-finished product thickness (mm) Density (g / cm 3 ) Compression rate (%) Compression resilience rate (%) Hardness Shore A Example 1 2.0 19-23 27-30 1.5 0.3742 26.42 74.26 51 Example 2 2.0 19-23 25-27 1.5 0.3712 26.55 76.70 51 Example 3 2.0 15-18 27-30 1.5 0.3701 26.76 73.12 51 Comparative Example 1 1.6 19-23 27-30 1.25 (Semi-finished product thickness unqualified) -- -- -- -- Comparative Example 2 2.3 19-23 27-30 1.8 -- -- -- -- Comparative Example 3 2.0 10~14 27-30 1.65 0.365 27．09 74.56 51 Comparative Example 4 2.0 26~30 27-30 1.45 0.385 25.55 76.50 51 Comparative Example 5 2.0 19-23 22 1.55 0.372 26.45 76.8 51 Comparative Example 6 2.0 19-23 32 1.65 0.3702 26.95 74.1 51

[0098] The polishing pads from Examples 1-3 and Comparative Examples 1-6 were polished, and the polishing test process was as follows:

[0099] Polishing machine: NTS 36-inch (Korea), pad size: 910mm, test wafer size: 6-inch, polishing pressure: 130g / cm² 2Polishing solution: SIPOL-3802 produced by Quzhou Bolaina Run Institute; flow rate: 750mL / min; dilution ratio: 1:40; upper and lower plate rotation speed: 30rpm; polishing test was conducted under the above conditions.

[0100] The film was removed after every 60 minutes of polishing. The material removal rate was calculated based on the amount of mass reduction. The roughness was observed using an atomic force microscope (model: DIMENSION EDGE System). The film was also observed with the naked eye under a strong light lamp (model: Yamada Optical YP250). Bright lines longer than 2 cm were identified as scratches, and the number of scratches was recorded.

[0101] The test results are shown in Table 2.

[0102] Table 2

[0103] Silicon wafer type Product life (h) Removal rate (nm / min) With or without scratches Ra, nm Haze, ppm Remarks Example 1 Light doping 51 78 No 0.19 0.014 Qualified Example 2 Light doping 52 77 No 0.17 0.011 Qualified Example 3 Light doping 50 80 No 0.18 0.013 Qualified Comparative Example 1 Light doping 5 75 (first 2h) No -- -- First 2h, qualified, polishing rate decreased seriously after 2h, life not enough Comparative Example 2 Light doping -- -- -- -- -- Thickness deviation too large, judged as unqualified during processing, no polishing test Comparative Example 3 Light doping -- 30 Yes 0.64 0.065 During the test, the removal rate was seriously insufficient Comparative Example 4 Light doping 5 110 Yes 0.28 0.030 During the test, the surface was seriously worn after 5h, life not enough Comparative Example 5 Light doping -- 45 No 0.47 0.055 During the test, the removal was insufficient Comparative Example 6 -- -- -- -- -- -- After coagulation, the adhesion between the coating and the substrate was insufficient, no further processing and testing

[0104] As can be seen from Table 2, the polishing pad formed by the technical solution in this application not only has excellent pore structure and performance, but also has a lifespan of at least 50 hours, a removal speed of 60~100 nm / min, no scratches, and Ra less than 0.2 nm and Haze less than 0.02 ppm when actually used for fine polishing of silicon wafers.

[0105] Furthermore, the polishing pad product prepared in Example 1 above is used for polishing tests in this application, mainly to illustrate the difference between heavily doped and lightly doped polishing, as shown in Table 3.

[0106] Table 3

[0107] Product Silicon wafer type Product life (h) Removal rate (nm / min) With or without scratches Ra, nm Haze, ppm Remarks Example 1 Light doping 51 78 No 0.19 0.014 Qualified Example 1 Heavy doping 47 74 No 0.16 0.019 Because heavy doping is harder than light doping, the removal and life are slightly lower than light doping, but it can meet the requirements

[0108] As can be seen from the above embodiments, comparative examples, and effect data:

[0109] 1) If the coating thickness is too thin, it will not be conducive to the influence of micropores. Secondly, if the coating is too thin, it will not be wear-resistant during the polishing test. If the coating is too thick, the coating will not solidify completely and will flow, resulting in the micropores being skewed and the thickness being uneven after final solidification.

[0110] 2) If the DMF concentration in the coagulation bath is too high, the coagulation speed will be slowed down, which is not conducive to the formation of pores. In the end, the volume, number and density of pores in the coating layer will be reduced, thus affecting the polishing effect. Conversely, if the DMF concentration in the coagulation bath is too low, the pores in the coating layer will be too large, which will make it easy to collapse and reduce the wear resistance, ultimately affecting the polishing effect.

[0111] 3) The moisture content of the substrate surface before coating: If the moisture content is too low, water will seep from the bottom of the substrate to the top during solidification, forming two layers of pores. However, the number of pores in the lower layer is relatively small, resulting in a thicker, denser layer. The two layers are completely disconnected, reducing the storage capacity of the polishing slurry and affecting the final polishing effect. If the moisture content is too high, it will cause the coating to have more and larger through-holes. This will make the coating easy to peel off from the substrate, and the pore walls (the area between the pores) will be thin, affecting the wear resistance and lifespan of the product, and ultimately affecting the polishing effect.

[0112] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

Claims

1. A polishing pad for a final polishing process of a silicon wafer, characterized by, The polishing pad comprises a porous polyurethane skin layer and an elastic impregnated layer; the elastic impregnated layer is a non-woven fabric impregnated and solidified with polyurethane; the porous polyurethane skin layer is formed on the elastic impregnated layer by wet film forming with polyurethane slurry, and has a pore structure extending from the surface to the elastic impregnated layer, the pore opening diameter at the skin layer surface is 40-80 μm, and the pore side wall has micro-pore channels for the polishing liquid to pass through, the size of the micro-pore channels is 0.1-10 μm.

2. The polishing pad of claim 1, wherein The pore structure is in the shape of water droplets; And / or, the polyurethane is polyester polyurethane; And / or, the finished thickness of the polishing pad is 1.3-1.6 mm; And / or, the thickness of the elastic impregnated layer is 0.6-1.0 mm; And / or, the density of the polishing pad is 0.3700-0.3750 g / cm³; And / or, the compression rate of the polishing pad is 25.00-27.00%; And / or, the compression elastic modulus of the polishing pad is 73-77%; And / or, the Shore A hardness of the polishing pad is 50-52 Shore A.

3. The polishing pad of claim 1, wherein, The nonwoven fabric as the base fabric has a basis weight of 120-135 g / m 2 ; And / or, in the elastic impregnated layer, the polyurethane solution for impregnation comprises 10-100 parts by weight of impregnated polyurethane, 30-50 parts by weight of DMF, and 0.2-0.8 parts by weight of color paste; wherein the impregnated polyurethane is polyester polyurethane, the viscosity at 25°C is 8-12 million cps, and the solid content is 29-31 wt%.

4. The polishing pad of claim 1, wherein: Based on the total mass of the color paste, the color paste comprises 55-65 wt% DMF, 4-8 wt% polyethylene glycol, 0.001-2 wt% bactericide, 0.5-10 wt% wetting dispersant, 2-40 wt% carbon black, and 0.001-3 wt% defoaming agent; After impregnation, further coagulation in DMF aqueous solution; and water washing and drying to obtain the elastic impregnated layer; the concentration of the DMF aqueous solution used for coagulation after impregnation is 12-25 wt%.

5. The polishing pad of claim 1, wherein The bactericide is iodine propargyl n-butyl amine formate; And / or, the wetting dispersant is Dispersago®-9720; and / or the carbon black has a specific surface area of 160 to 180 m 2 / g; And / or, the defoaming agent is VOK®-DF 7015.

6. The polishing pad of claim 1, wherein The wet film forming comprises the following steps: 1) the elastic impregnated layer is first wetted with DMF aqueous solution; 2) surface ironing treatment is performed with an ironing wheel until the water content on the surface of the elastic impregnated layer is 25-30 wt%; 3) polyurethane slurry is coated on the elastic impregnated layer; 4) coagulation in DMF aqueous solution; 5) water washing and drying.

7. The polishing pad of claim 6, wherein, One or more of the following features is included: In step 1), the elastic impregnated layer is further extruded by a roller to promote the wetting of the elastic impregnated layer with DMF aqueous solution; In step 1), the concentration of the DMF aqueous solution is 12-20 wt%; In step 2), the surface temperature of the ironing wheel is 85-100°C; In step 2), the water content on the surface of the elastic impregnated layer after ironing is 25-30%; In step 3), the coating thickness is 1.8-2.1 mm; The polyurethane paste in step 3) comprises 50-300 parts by weight of polyurethane, 10-70 parts by weight of DMF, 0.2-1 part by weight of non-ionic surfactant, 0.05-0.5 part by weight of wetting agent, 0.5-5.0 parts of color paste and 0.001-1 parts of leveling agent; In step 4), the concentration of the DMF aqueous solution is 15-25 wt%; In step 5), the water washing conditions are that the DMF concentration of the first water washing tank is less than 20 wt%, and the DMF concentration of the last three water washing tanks is less than 1 wt%; In step 5), the drying temperature is 90-130℃.

8. The polishing pad of claim 7, wherein, The non-ionic surfactant is Span 80; And / or, the wetting agent is OT-75; And / or, the leveling agent is BY33; And / or, the color paste comprises 55-65 wt% of DMF, 4-8 wt% of polyethylene glycol, 0.001-2 wt% of bactericide, 0.5-10 wt% of wetting dispersant, 2-40 wt% of carbon black and 0.001-3 wt% of defoaming agent, based on the total mass of the color paste; And / or, the polyurethane in the polyurethane paste for coating is polyester polyurethane, the viscosity of which at 25℃ is 1.5-2 million cps, and the solid content is 34-36%.

9. A method of making a polishing pad as claimed in any one of claims 1 to 8, characterised in that, First, a non-woven fabric is impregnated with a polyurethane solution and then cured to form an elastic impregnated layer, and then a porous polyurethane skin layer is formed on the elastic impregnated layer by using a wet film forming process; before coating the polyurethane solution, the surface to be coated is also wetted with a DMF aqueous solution and treated with a heated roller for ironing.

10. Use of the polishing pad according to any one of claims 1-8 for the fine polishing process of silicon wafers.

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