Polishing pad for silicon wafer final polishing process and method of making and use thereof

Abstract

The application provides a polishing pad for a silicon wafer fine polishing process, a preparation method and use thereof. 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 formation using polyurethane slurry, and has a pore structure extending from the surface to the elastic impregnated layer. The aperture diameter of the opening at the skin layer surface is 40-80 microns, and the side wall of the opening has a micropore channel for the polishing liquid to pass through. The size of the micropore channel is 0.1-10 microns. The product increases the storage amount of the polishing liquid in the silicon wafer fine polishing process, makes the pressure distribution more uniform in the polishing process, improves the polishing liquid distribution efficiency, ensures the polishing rate, and does not produce scratches.

Description

Technical Field

[0001] This invention relates to the field of semiconductor polishing pad technology, and in particular to a polishing pad for the fine polishing process of silicon wafers, its preparation method, and its uses. Background Technology

[0002] In existing silicon wafer polishing processes, the material distribution of the polishing pad is uneven, manifested as an unreasonable pore structure and irregular pore size and location. Unreasonable pore structure includes poor porosity, pore shape, and connectivity; irregular pore size includes large differences in pore diameter across different areas of the polishing pad; and irregular pore location includes non-uniform pore distribution, which may be clustered or sparse.

[0003] The main reason is that the coating process of existing products is not perfect. Usually, the surface of the impregnated substrate is not treated, resulting in a thicker dense layer (the distance from the bottom of the micropore to the surface of the substrate) and a smaller number of micropores, resulting in a thinner micropore layer. In addition, there are some problems with the formula, which results in the absence of smaller pores between micropores, which is not conducive to the mutual flow of polishing fluid. This leads to uneven pressure distribution during the polishing process, affects the slurry distribution efficiency, and ultimately makes it easy to produce scratches after polishing. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a polishing pad for the fine polishing process of silicon wafers, its preparation method and application, to solve the problem of uneven pressure distribution and poor slurry distribution efficiency caused by the lack of interconnected channels on the surface of the polishing pad in the prior art, which leads to polishing scratches.

[0005] To achieve the above and other related objectives, the present invention is implemented by including the following technical solutions.

[0006] This invention provides a polishing pad for a silicon wafer polishing process. The polishing pad includes a porous polyurethane skin and an elastic impregnation layer. The elastic impregnation layer is a nonwoven fabric impregnated and cured with polyurethane. The porous polyurethane skin is formed on the elastic impregnation layer by wet film formation of polyurethane slurry, and has a pore structure extending from the surface to the elastic impregnation layer. The pore diameter at the surface of the skin is 40~80μm, and the sidewalls of the pores have micropore channels for the passage of polishing fluid. The size of the micropore channels is 0.1~10μm.

[0007] Preferably, the pore structure is teardrop-shaped.

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

[0009] Preferably, the pore size at the surface of the skin is 40~80μm, such as 40~70μm, 40~60μm, 60~80μm, 50~80μm, 70~80μm, etc. More preferably, the pore size at the surface of the skin is 60~80μm.

[0010] Preferably, the size of the micropore channel is diverse, such as 0.1~1μm, 1~2μm, 2~3μm, 3~4μm, 4~5μm, 5~6μm, 6~7μm, 7~8μm, 8~9μm, 0.1~1.5μm, 0.1~2.5μm, 0.1~3.5μm, 0.5~4.5μm, 0.5~5.5μm, etc.

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

[0012] Preferably, the thickness of the elastic impregnation layer is 0.6~1.0 mm. For example, it 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 / cm³. 3 For example, it can be 0.3710 g / cm³ 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 ratio of the polishing pad is 25.00% to 27.00%, such as 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... 0.90%, 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) DMF concentration in the coagulation tank (%) Moisture content (%) of substrate surface before coating Semi-finished product thickness (mm) <![CDATA[Density (g / cm 3 ).]]> Compression rate (%) Compression rebound 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 is substandard) -- -- -- -- 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 lifespan (h) Removal rate (nm / min) Are there any scratches? Ra, nm Haze, ppm Remark Example 1 Lightly mixed 51 78 none 0.19 0.014 qualified Example 2 Lightly mixed 52 77 none 0.17 0.011 qualified Example 3 Lightly mixed 50 80 none 0.18 0.013 qualified Comparative Example 1 Lightly mixed 5 75 (first 2 hours) none -- -- The polishing is satisfactory for the first 2 hours, but the polishing rate drops significantly after 2 hours, resulting in insufficient polishing life. Comparative Example 2 Lightly mixed -- -- -- -- -- The thickness deviation was too large, and the product was deemed unqualified during processing; no polishing test was performed. Comparative Example 3 Lightly mixed -- 30 have 0.64 0.065 During the test, the removal rate was severely insufficient. Comparative Example 4 Lightly mixed 5 110 have 0.28 0.030 During the test, the surface showed severe wear after 5 hours, indicating insufficient lifespan. Comparative Example 5 Lightly mixed -- 45 none 0.47 0.055 Remove deficiencies during testing Comparative Example 6 -- -- -- -- -- -- After solidification, the coating showed insufficient adhesion to the substrate, and further processing and testing were not conducted.

[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 lifespan (h) Removal rate (nm / min) Are there any scratches? Ra, nm Haze, ppm Remark Example 1 Lightly mixed 51 78 none 0.19 0.014 qualified Example 1 Heavy doping 47 74 none 0.16 0.019 Because the heavier doping results in a harder material than the lighter doping, and the lighter doping results in slightly lower removal efficiency and lifespan, but these still 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 use in the fine polishing process of silicon wafers, characterized in that, The polishing pad comprises a porous polyurethane skin and an elastic impregnation layer; the elastic impregnation layer is a nonwoven fabric impregnated and cured with polyurethane; the porous polyurethane skin is formed on the elastic impregnation layer by wet film formation of polyurethane slurry, and has a pore structure extending from the surface to the elastic impregnation layer, with pore diameters of 40~80μm at the skin surface, and micropore channels for polishing liquid to pass through on the pore sidewalls, the size of the micropore channels being 0.1~10μm; the pore structure is teardrop-shaped; the density of the polishing pad is 0.3700~0.3750g / cm³; the compressibility of the polishing pad is 25.00~27.00%; the compressive elasticity of the polishing pad is 73~77%; and the Shore hardness of the polishing pad is 50~52 Shore A.

2. The polishing pad according to claim 1, characterized in that, The polyurethane is a polyester-type polyurethane; And / or, the finished thickness of the polishing pad is 1.3~1.6mm; And / or, the thickness of the elastic impregnation layer is 0.6~1.0 mm.

3. The polishing pad according to claim 1, characterized in that, The weight of the nonwoven fabric used as the base material is 120-135 g / m². 2 ; And / or, in the elastic impregnation layer, the impregnation polyurethane solution comprises 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%. And / or, the curing is as follows: after impregnation, further solidification is carried out in a DMF aqueous solution; and the layer is washed and dried to obtain the elastic impregnated layer; the concentration of the DMF aqueous solution used for solidification after impregnation is 12~25wt%.

4. The polishing pad according to claim 3, characterized in that: 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.

5. The polishing pad according to claim 4, characterized in that, The bactericide is iodopropynyl n-butylcarbamate; And / or, the wetting and dispersing agent is Dispersago®-9720; And / or, the specific surface area of ​​carbon black is 160~180m². 2 / g; And / or, the defoamer is VOK®-DF 7015.

6. The polishing pad according to claim 1, characterized in that, The wet film formation process includes the following steps: 1) The elastic impregnated layer is first wetted with a DMF aqueous solution; 2) The surface is ironed using an ironing wheel until the moisture content of the elastic impregnated layer is 25-30 wt%; 3) Apply polyurethane slurry onto the elastic impregnation layer; 4) It solidifies upon entering the DMF aqueous solution; 5) Wash with water and dry.

7. The polishing pad according to claim 6, characterized in that, Includes one or more of the following features: In step 1), the elastic impregnation layer is further squeezed by rollers to promote the wetting of the elastic impregnation layer by the 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 roller is 85~100℃; In step 2), the moisture content of the ironed surface of the elastic impregnated layer is 25%~30%; In step 3), the coating thickness is 1.8~2.1mm; The polyurethane slurry in step 3) includes: 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; In step 4), the concentration of the DMF aqueous solution is 15-25 wt%. In step 5), 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%. In step 5), the drying temperature is 90~130℃.

8. The polishing pad according to claim 7, characterized in that, The nonionic surfactant is Span 80; And / or, the wetting agent is OT-75; And / or, the leveling agent is BY33; And / or, 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; And / or, the polyurethane in the coated polyurethane slurry is polyester polyurethane, which has a viscosity of 150,000-200,000 cps at 25°C and a solid content of 34-36%.

9. A method for preparing a polishing pad as described in any one of claims 1 to 8, characterized in that, First, an elastic impregnation layer is formed by impregnating a nonwoven fabric with a polyurethane solution and then curing it. Then, a porous polyurethane skin is formed on the elastic impregnation layer 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 then ironed with a heated roller.

10. The use of a polishing pad as described in any one of claims 1 to 9 in a silicon wafer fine polishing process.

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