A nonwoven polishing pad having a density gradient in the inner and outer rings, and a method of making and use thereof

Abstract

The present application provides a kind of non-woven polishing pad with density gradient of inner and outer ring and its preparation method, non-woven substrate includes circular with radius R;When impregnated by coating polyurethane resin solution, non-woven substrate is fixed on rotating platform in horizontal original position rotating state, is discharged from top to bottom by a material pipe set above rotating platform in two positions, with the rotation of rotating platform, liquid diffuses to outer ring, so that two coatings are completed;After two coatings, immerse in DMF aqueous solution to solidify;When impregnated for the first time, material pipe is fixed above the first position of polishing pad, the distance between first position and the center of circular non-woven substrate is R1, and R1=0.4R~0.6R;When impregnated for the second time, material pipe is fixed above the second position of polishing pad.The polishing pad processes 2000pcs silicon substrate at a stable rate, and the absolute value of difference between middle and edge is within 60nm.

Description

Technical Field

[0001] This invention relates to the field of semiconductor polishing pad technology, and in particular to a nonwoven polishing pad with a density gradient between its inner and outer rings, its preparation method, and its applications. Background Technology

[0002] In the semiconductor manufacturing field, silicon wafers serve as the basic substrate material, and global planarization of their surface is a crucial step in realizing multilayer integrated circuit structures. Chemical mechanical polishing (CMP) is currently the mainstream technology for achieving global planarization.

[0003] However, existing technologies still have many shortcomings. One particularly prominent problem is the unevenness of polishing across different areas of the silicon wafer surface. Specifically, the material removal rate at the wafer edges is significantly lower than in the center (i.e., the "edge effect"), resulting in the overall wafer surface flatness failing to meet requirements. The main reason for this uneven removal rate between the inner and outer rings is:

[0004] 1) Uneven contact stress distribution between the polishing pad and the silicon wafer: During polishing, due to the rigid structure and rotational motion of the silicon wafer, the contact between the central area and the polishing pad is tighter and more stable, while the edge area tends to "warp," resulting in a decrease in the actual contact stress in this area and a corresponding decrease in material removal rate. 2) Differences in polishing slurry flow and renewal kinetics: Polishing slurry is usually supplied from the center or side of the polishing pad. Under centrifugal force, the polishing slurry is rapidly thrown towards the periphery of the silicon wafer, resulting in a short residence time in the central area and insufficient chemical reaction. In the edge area, although the flow volume is sufficient, the slurry film thickness and pressure are unstable, and byproducts tend to accumulate there, all of which affect the stability and consistency of the removal rate in this area. 3) Characteristics of the polishing pad: The hardness, elasticity, and surface texture of the polishing pad all affect the polishing effect. Different polishing pads will affect the pressure distribution and polishing slurry retention capacity, thus affecting the removal rate. For example, a harder polishing pad may exacerbate pressure differences, while a softer polishing pad may help to evenly distribute pressure, but may cause excessive deformation at the outer edge, leading to an excessively high removal rate.

[0005] To address the aforementioned issues, both academia and industry have implemented various improvement measures. For instance, uneven pressure between the inner and outer rings can be addressed by modifying the polishing head of the polishing machine to achieve zoned pressure application. However, the process window for this approach is relatively small, and slight changes in other factors necessitate readjusting the pressure parameters. Regarding the distribution of polishing slurry flow, some polishing pad manufacturers process asymmetrical grooves on the surface of the pad to balance the distribution of the slurry between the inner and outer rings. However, this also has limitations; the grooves leave corresponding patterns on the silicon wafer surface, which are difficult to remove. Currently, the mainstream material used in the industry is still the ungrooved pad. To address the issue of polishing pad characteristics that prevent the production of products with high flatness, patent CN101600540B utilizes ultrafine fibers to prepare nonwoven fabric. The ultrafine fibers form fiber clusters in the thickness direction, giving the nonwoven fabric a certain rigidity. After impregnation, curing, and post-treatment processes, a polishing pad that is less prone to scratches and possesses excellent flatness is produced. However, this approach is relatively complex, and the difference between the inner and outer rings becomes increasingly pronounced as the polishing pad is used over time. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a nonwoven polishing pad with a density gradient between the inner and outer rings, its preparation method and application, in order to solve the problem that the difference between the inner and outer rings becomes more and more obvious as the polishing pad is used for a longer period of time.

[0007] To achieve the above and other related objectives, the present invention is implemented by including the following technical solutions.

[0008] The first aspect of the present invention provides a method for preparing a nonwoven polishing pad with an inner and outer ring exhibiting a density gradient, wherein the nonwoven base fabric includes a circle with a radius of R;

[0009] When the polyurethane resin solution is applied for impregnation, the non-woven base fabric is fixed on the rotating platform and rotates horizontally in situ. The material is fed from top to bottom at two positions through a feeding pipe located above the rotating platform. As the rotating platform rotates, the liquid spreads to the outer circle, thus completing two coatings. After the two coatings are completed, the fabric is immersed in DMF aqueous solution for solidification.

[0010] During the first coating and impregnation, the feed tube is fixed above the first position of the polishing pad, and the distance from the first position to the center of the circular nonwoven fabric base is R1. And R1 = 0.4R ~ 0.6R;

[0011] During the second coating and impregnation process, the feed tube is fixed above the second position of the polishing pad, and the distance from the second position to the center of the circular nonwoven fabric base is R2. And R2=0 R ~0.2R.

[0012] Preferably, R1 = 0.45 R ~ 0.55 R. More preferably, R1 = 0.5 R.

[0013] Preferably, R2 = 0 R ~ 0.1R. More preferably, R2 = 0 R, in which case the second position is located above the center of the circle.

[0014] In this application, R1 and R2 refer to the distance from the corresponding point on the nonwoven fabric base to the center of the nonwoven fabric base where the center of the feeding end of the feeding tube is located.

[0015] Preferably, the flow rate of the discharge tube is 100~2000 ml / min. For example, it can be 100 ml / min, 150 ml / min, 200 ml / min, 250 ml / min, 300 ml / min, 350 ml / min, 400 ml / min, 450 ml / min, 500 ml / min, 550 ml / min, 600 ml / min, 650 ml / min, 700 ml / min, 750 ml / min, 800 ml / min, 850 ml / min, 900 ml / min, 950 ml / min, 1000 ml / min, 1100 ml / min, 1200 ml / min, 1300 ml / min, 1400 ml / min, 1500 ml / min, 1600 ml / min, 1700 ml / min, 1800 ml / min, 1900 ml / min, or 2000 ml / min.

[0016] Preferably, the diameter of the feeding tube is 7-15cm. For example, it can be 7cm, 8cm, 9cm, 10cm, 11cm, 12cm, 13cm, 14cm, or 15cm. If the diameter is too large, the overall control precision will decrease, which is not conducive to forming a non-woven polishing pad with a density gradient between the inner and outer rings. If the diameter is too small, the fluid impact force will be too large, making it prone to splashing and not conducive to forming a smooth coating.

[0017] Preferably, the distance between the discharge end of the feeding tube and the nonwoven base fabric is 10~20cm. For example, it can be 10cm, 11cm, 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm or 20cm.

[0018] Preferably, when coating or impregnating, the rotation speed of the rotating platform is 20-50 rpm, such as 20 rpm, 25 rpm, 30 rpm, 35 rpm, 40 rpm, 45 rpm, or 50 rpm. Excessive rotation speed generates significant centrifugal force, which is detrimental to controlling resin distribution and makes it more likely to be distributed at the edges. Insufficient rotation speed generates too little centrifugal force, which is also detrimental to resin diffusion, resulting in a concentration of resin in the discharge area.

[0019] Preferably, during the first coating or impregnation, the material is applied for a coating time of 80-100 seconds, such as 85 seconds, 90 seconds, or 95 seconds.

[0020] Preferably, when applying the second coating for impregnation, the coating time is 25-35 seconds, such as 25 seconds, 26 seconds, 27 seconds, 28 seconds, 29 seconds, 30 seconds, 31 seconds, 32 seconds, 33 seconds, 34 seconds, or 35 seconds.

[0021] Preferably, during coagulation, the concentration of the DMF aqueous solution is 17-22 wt%, such as 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, or 22 wt%. In the coagulation bath containing the DMF aqueous solution, the DMF solvent in the resin migrates into the water through the displacement between water and the DMF solvent, causing the resin to coagulate and regenerate on the nonwoven fibers. The concentration of the DMF solution affects the coagulation rate.

[0022] The remaining small amount of DMF is then removed by washing with water, and after drying, a semi-finished non-woven polishing pad is obtained. Further, both sides of the semi-finished non-woven polishing pad are sanded. Preferably, the thickness of the final product is controlled at 1.1~1.5mm, such as 1.3mm. Double-sided adhesive is applied to one side, and the final polishing pad is obtained.

[0023] Preferably, the nonwoven fabric in this application is selected from one of polypropylene, polyester, nylon, viscose fiber, acrylic fiber, polyethylene fiber, chlorofiber, polyester, and polyamide. More preferably, it is polyester. More preferably, its forming process is needle-punched staple fiber, and the fiber fineness is 1~10D (e.g., 1D, 2D, 3D, 4D, 5D, 6D, 7D, 8D, 9D, 10D). Preferably, the basis weight of the nonwoven fabric is 200~300 g / cm³. 2 (e.g., 200 g / cm) 2 210 g / cm 2 220 g / cm 2 230 g / cm 2 240 g / cm 2 250 g / cm 2 260 g / cm 2 270g / cm 2 280 g / cm 2290 g / cm 2 300 g / cm 2 Preferably, the thickness of the nonwoven fabric is 1~3mm.

[0024] Preferably, the polyurethane resin solution has a solid content of 18-22 wt% and a viscosity of 500-2500 cps at 25°C, such as 500 cps, 600 cps, 700 cps, 800 cps, 900 cps, 1000 cps, 1100 cps, 1200 cps, 1300 cps, 1400 cps, 1500 cps, 1600 cps, 1700 cps, 1800 cps, 1900 cps, 2000 cps, 2100 cps, 2200 cps, 2300 cps, 2400 cps, or 2500 cps. More preferably, the polyurethane resin solution has a solid content of 18 wt%, 19 wt%, 20 wt%, 21 wt%, or 22 wt%. This can be obtained by mixing a raw polyurethane solution with DMF. More preferably, the solid content of the raw polyurethane resin solution is 25-35 wt%, and the viscosity at 25°C is 10,000-30,000 cps; for example, the solid content of the raw polyurethane resin solution is 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, or 35 wt%, and the viscosity at 25°C is 10,000-30,000 cps, such as 10,000 cps. The polyurethane resin solution contains 11,000 cps, 12,000 cps, 13,000 cps, 14,000 cps, 15,000 cps, 16,000 cps, 17,000 cps, 18,000 cps, 19,000 cps, 20,000 cps, 23,000 cps, 24,000 cps, 25,000 cps, 26,000 cps, 27,000 cps, 28,000 cps, 29,000 cps, and 30,000 cps. The polyol component in the raw polyurethane resin solution includes, but is not limited to, polyester polyols, polyether polyols, and polycarbonate polyols, preferably polyester polyols. The isocyanate component includes, but is not limited to, one or more of TDI (toluene diisocyanate), MDI (diphenylmethane diisocyanate), HDI (hexamethyl diisocyanate), and IPDI (isophorone diisocyanate), preferably MDI. Preferably, the 100% modulus range of the raw polyurethane resin is 10-30 MPa, and more preferably 20-26 MPa. In one specific embodiment, the raw polyurethane resin solution was purchased from Asahikawa Chemical.

[0025] A second aspect of the present invention also discloses a nonwoven polishing pad formed using any of the preparation methods described above.

[0026] Preferably, the thickness of the nonwoven polishing pad is 1.1~1.5mm, such as 1.1mm, 1.2mm, 1.3mm, 1.4mm or 1.5mm.

[0027] The third invention also discloses the use of the nonwoven polishing pad as described above in the CMP process to improve the uneven removal rate of the inner and outer rings.

[0028] As described above, the nonwoven polishing pad with density gradient between its inner and outer rings, its preparation method, and its uses, according to the present invention, have the following beneficial effects:

[0029] In this application, polyurethane resin is coated onto the surface of nonwoven fabric by rotational diffusion penetration, and the resin content in each area is controlled by two coatings. By combining the control of the polyurethane resin slurry and rotation speed, the final polishing pad can maintain a stable processing rate of 2000pcs silicon substrates, and the absolute value of the removal amount difference between the middle and the edge is within 60nm. Attached Figure Description

[0030] Figure 1 The diagram shows a comparison of the initial densities of Examples 1-4, Comparative Examples 1-3, and commercially available products of the present invention.

[0031] Figure 2 The diagram shows a comparison of the compression ratios of Embodiments 1-4, Comparative Examples 1-3, and commercially available products of the present invention.

[0032] Figure 3 The diagram shows a comparison of the air permeability of Examples 1-4, Comparative Examples 1-3, and commercially available products of the present invention.

[0033] Figure 4 The T shown represents Examples 1-4 and Comparative Examples 1-3 of the present invention, as well as commercially available products. D Comparison diagram.

[0034] Figure 5 The T shown represents Examples 1-4 and Comparative Examples 1-3 of the present invention, as well as commercially available products. A Comparison diagram.

[0035] Figure 6 The diagram shows the structure of the polishing pad at positions 1 to 5 in this invention. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does 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. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, 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 for limiting the order of the method steps or limiting 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.

[0039] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0040] The nonwoven polishing pad claimed in this application has a density gradient between its inner and outer rings. It is obtained by feeding material at two locations, spreading it outwards based on centrifugal force of rotation, and then solidifying, washing with water and drying.

[0041] In one specific embodiment, the preparation method of the nonwoven polishing pad in this application includes the following steps, which are further illustrated below.

[0042] For the polyurethane resin solution, any polyurethane solution used to prepare polishing pads is acceptable, provided that its solid content or viscosity at 25°C meets the requirements for polyurethane solutions used in polishing pads. More specifically, the solid content of the polyurethane resin solution is 18-22 wt%. It can be obtained by mixing the raw polyurethane solution and DMF. More preferably, the solid content of the raw polyurethane resin solution is 25-35 wt%, and the viscosity at 25°C is 10,000-30,000 cps. The polyol component in the raw polyurethane resin solution includes, but is not limited to, polyester polyols, polyether polyols, and polycarbonate polyols, preferably polyester polyols. The isocyanate component includes, but is not limited to, one or more of TDI (toluene diisocyanate), MDI (diphenylmethane diisocyanate), HDI (hexamethyl diisocyanate), and IPDI (isophorone diisocyanate), preferably MDI. Preferably, the 100% modulus range of the raw polyurethane resin is 10-30 MPa, more preferably 20-26 MPa. In one specific embodiment, the raw polyurethane resin solution was purchased from Asahikawa Chemical. The polyurethane resin solutions used in the following embodiments of this application are all from Asahikawa Chemical.

[0043] Specifically, before actual coating, the non-woven fabric base is dried and then cut into a circle, such as an 820mm circle. After being cut into a circle, the surface is coated twice to cure and form the polishing pad.

[0044] Specifically, such as Figure 6 As shown, the positions of the two material feeding operations are different in this application. During the first coating and impregnation, the feeding tube is fixed above the first position of the polishing pad, and the distance from the first position to the center of the circular nonwoven fabric base is R1. And R1 = 0.4 R ~ 0.6 R, preferably, R1 = 0.45 R ~ 0.55 R, more preferably, R1 = 0.5 R (e.g. Figure 6 (Near the position shown in circle 3); during the second coating and impregnation, the feed tube is fixed above the second position of the polishing pad, and the distance from the second position to the center of the circular nonwoven fabric base is R2. Furthermore, R2 = 0 R ~ 0.2R, which is essentially close to the center of the nonwoven fabric; more preferably, R2 = 0 R, in which case the second position is located above the center.

[0045] Example 1

[0046] Asahikawa Chemical Polyurethane (preparing polyurethane resin solutions of polyester polyol and MDI system) was used. The organic solvent DMF was added and the mixture was stirred and dispersed at high speed for 30 minutes to form solution A, which was placed in a slurry tank. The final solid content was controlled at 20%wt and the viscosity at 25℃ was 1500cps.

[0047] 2. Wet forming of polishing pads:

[0048] Select 2mm thick material, 260g / cm² 2 The PET short fiber nonwoven fabric with a fiber fineness of 2 denier is pre-treated in an oven at 100°C for 2 hours to remove moisture and then punched into a circle with a diameter of 820 mm.

[0049] First impregnation: Move the slurry pipe to a position 205mm horizontally from the center of the platform, start the platform at 40rpm, then turn on the peristaltic pump at a flow rate of 800ml / min, turn off the peristaltic pump after 90s, and stop the platform rotation.

[0050] Secondary impregnation: Move the slurry tube to the center of the platform, start the platform at 20 rpm, then turn on the peristaltic pump and maintain the flow rate at 800 ml / min. After 30 seconds, turn off the peristaltic pump and stop the platform rotation and adsorption function (the adsorption function is used to provide negative pressure to fix the nonwoven fabric on the rotating platform, and release paper is used between the rotating platform and the nonwoven fabric).

[0051] Then, the impregnated nonwoven fabric is peeled off from the release paper at the bottom, and then immersed in a coagulation bath (a mixed solution of DMF and water, with a DMF concentration of 20%wt). By utilizing the displacement of water and DMF solvent, the DMF solvent in the resin migrates into the water, allowing the resin to coagulate and regenerate on the nonwoven fabric fibers. The remaining small amount of DMF is removed by washing with water, and the product is dried in an oven at 120℃ for 2 hours to obtain a semi-finished nonwoven polishing pad.

[0052] Both sides of the non-woven polishing pad semi-finished product obtained above are sanded with 180-grit sandpaper, and the final product thickness is controlled at 1.3mm (±0.05mm). Then, double-sided adhesive is applied to one side, and the final polishing pad product is obtained.

[0053] Example 2

[0054] The other conditions are the same as in Example 1, except that the rotation speed is 35 rpm for the first coating and 25 rpm for the second coating.

[0055] Example 3

[0056] The other conditions are the same as in Example 2, except that the viscosity of the resin slurry is 500 cps.

[0057] Example 4

[0058] The other conditions are the same as in Example 2, except that the viscosity of the resin slurry is adjusted to 2500 cps.

[0059] Comparative Example 1

[0060] The other conditions are the same as in Example 2, except that the viscosity of the resin slurry is 5000 cps.

[0061] Comparative Example 2

[0062] The other conditions are the same as in Example 1, except that the rotation speed is 60 rpm for the first coating and 10 rpm for the second coating.

[0063] Comparative Example 3

[0064] Everything else is the same as in Example 1, except that: instead of a first coating for impregnation, a second coating is applied directly for impregnation, the rotation speed is 35 rpm, and the processing time is adjusted from 90 s to 120 s.

[0065] Performance tests were conducted on the final products of Examples 1-4 and Comparative Examples 1-3 as described above:

[0066] 1) Sampling: According to... Figure 6 The sampling method shown involves taking five small circles, each 7mm in diameter, from the center to the edge of the polishing pad, and recording them as samples 1 / 2 / 3 / 4 / 5. The silicon wafer has a diameter of 300mm, and during polishing, the center of the wafer approximately falls on... Figure 6 Therefore, when analyzing the physical properties of the polishing pad, we take sample 3 as the center and samples 1 and 5 as the two sides.

[0067] 2) The hardness test standard refers to GB / T 2411-2008 Plastics and hard rubber: Determination of indentation hardness (Shore hardness) using a hardness tester.

[0068] 3) Density test: The apparent core density shall be determined in accordance with GB / T 6343-2009.

[0069] 4) The compression ratio and compressive elasticity of the polishing pad were tested in accordance with GB / T 24442.1-2009 Textiles - Determination of compressive properties - Part 1: Constant method.

[0070] 5) Air permeability test: The equipment used was Shanghai Fanbiao Textile Testing Technology Co., Ltd., model G571, with the following parameters set: test area 38 cm². 2 The test pressure was 1000 Pa.

[0071] 6) Polishing performance test: Polishing machine (Okamoto): 820mm, polishing pressure: 120g / cm 3 The lower plate rotation speed was 40 rpm, the flow rate was 100 ml / min, the substrate was a 12-inch silicon substrate, and the polishing slurry was Bonainer Run Silicon Carbide Polishing SIPOL-1806; the polishing time was 90 seconds.

[0072] 7) Removal Amount Detection: The thickness of the silicon wafer before and after polishing is scanned and measured using an optical surface measuring instrument (Qianshi) to obtain the average removal amount T of the silicon wafer. A central area removal amount T C The amount of material removed, T, in the edge region (148mm from the center). E The difference in removal amount T between the edge and the center D =T E -T C The units are all in nm.

[0073] Table 1-3, Figure 1-3 The data includes the physical property parameters of eight products.

[0074] Table 1

[0075]

[0076] Table 2

[0077]

[0078] Table 3

[0079]

[0080] From Tables 1 to 3 and Figures 1-3 It can be seen that:

[0081] Using the four embodiments of this application, under controlled slurry viscosity and relatively reasonable primary and secondary immersion speeds, the final product density exhibits a gradient distribution with lower density in the middle and higher density at the edges (see Table 1, Examples 1-4). The density at position 3 is only 0.4 g / cm³, ranging from 0.38 to 0.95 g / cm³, while the densities at positions 1 and 5 are 0.42 to 0.45 g / cm³. The compressibility and permeability show a distribution with higher density in the middle and lower density at the edges (see Tables 2 and 3, Examples 1-4). When polishing with this type of polishing pad, under the same pressure, the deformation of the pad at both ends of the silicon wafer is smaller, resulting in a higher interfacial pressure with the wafer compared to the central region. Even if the polishing slurry supply at the wafer edges is lower than at the center, the final removal rate will not differ significantly and may even be higher.

[0082] In Comparative Example 1, the viscosity of the impregnating resin was too high, resulting in a slower resin diffusion rate to the outer ring during the first impregnation. Consequently, the resin concentration in region 3 was relatively high, leading to a final product density that was high in the middle and low at the edges. In Comparative Example 2, the viscosity was reasonable, but the first impregnation speed was too fast, causing excessive resin diffusion to the outer ring, resulting in insufficient resin in region 3. The second impregnation speed was too slow, causing slow resin diffusion in the inner center of the polishing pad, while region 5 had an excessive amount of resin. The combined effect of these factors resulted in a final product with an excessively low density in the middle and excessively high density at the edges. In Comparative Example 3, the first impregnation was omitted, and the second impregnation was used directly with a higher speed. Therefore, the resin concentration in the inner ring region (region 5) was low, gradually increasing outwards, resulting in a final polishing pad product with a density that increased from the inside out.

[0083] The commercially available Suba800 product uses a traditional wet manufacturing process, and the physical properties of each region remain basically consistent.

[0084] Furthermore, Tables 4, 5 and Figure 4 , 5 This is data on polishing applications. The pcs in the table refers to the number of silicon wafers that can be successfully polished using a certain amount of polishing slurry on the same polishing pad. For example, 200pcs means polishing 200 wafers.

[0085] Table 4

[0086]

[0087] Table 5

[0088]

[0089] From Tables 4 and 5 and Figure 4 and 5 It can be seen that:

[0090] First, comparing the differences in removal amounts between the center and edges of the silicon wafer, the four example products initially showed greater edge removal amounts than center removal amounts due to lower edge compression ratios and higher contact stress between the edges and the silicon wafer during polishing. D The value is positive, but as polishing progresses, silicon oxide particles will deposit inside the polishing pad, causing the density to increase. In the central region of the silicon wafer (No. 3), due to a larger supply of polishing slurry, more particles are deposited, and the density increases faster. The density difference between the central region and the edge will decrease, and may even be greater in the central region. At this point, the interfacial stress between the center and the edge is not significantly different, and the removal amount is more affected by the polishing slurry supply. Therefore, the edge removal is less than the center, T D It is negative. However, over the entire lifespan of the mat, T... D The absolute value is controlled within 60nm.

[0091] Comparative Example 1 initially exhibits a high density in the central region (number 3) and a low density at the edges. Therefore, at the start of polishing, the density at the center is higher than at the edges, T D The value is negative, and the difference increases with usage time, with the absolute value exceeding 60nm when processing 1400Pcs.

[0092] In Comparative Example 2, the density in the central region (No. 3) is too low, so initially, the density at the center of the silicon wafer is much lower than at the edge. D The value is positive and the absolute value exceeds 60nm.

[0093] In Comparative Example 3, the central region (No. 3) is higher than the inner region (No. 5), while the outer region (No. 1) is lower. During silicon wafer polishing rotation, the edge experiences lower stress and lower removal when passing through region No. 1, and higher stress and higher removal when passing through region No. 5. On average, the removal is not significantly different from that of the central region. (T) D It is close to zero, but as usage time decreases, it eventually exceeds 60nm in absolute terms when processing 1400Pcs.

[0094] The performance of the commercially available Suba800 is similar to that of Comparative Example 3.

[0095] Compared to the overall average removal rate, as the pad's usage time increases, the density of each area increases, especially in the central area, where the internal porosity decreases. This results in a reduction in the supply of polishing slurry, leading to a decrease in the overall removal rate. Figure 5 As can be seen, in Comparative Examples 1 and 3, Suba800 has a higher density in the central region (No. 3), so the average removal rate gradually decreases after processing 1000pcs. In contrast, the four examples and Comparative Example 2, which have a lower density in the central region, have better rate stability.

[0096] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0097] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a nonwoven polishing pad with a density gradient between its inner and outer rings, characterized in that, The nonwoven base fabric includes a circle with radius R; When the polyurethane resin solution is applied for impregnation, the non-woven base fabric is fixed on the rotating platform and rotates horizontally in situ. The material is fed from top to bottom at two positions through a feeding pipe located above the rotating platform. As the rotating platform rotates, the liquid spreads to the outer circle, thus completing two coatings. After the two coatings are completed, the fabric is immersed in DMF aqueous solution for solidification. During the first coating and impregnation, the feed tube is fixed above the first position of the polishing pad. The distance between the first position and the center of the circular nonwoven fabric base is R1, and R1 = 0.4R ~ 0.6R. During the second coating and impregnation, the feed tube is fixed above the second position of the polishing pad. The distance between the second position and the center of the circular nonwoven fabric base is R2, and R2 = 0 R ~ 0.2R. When coating by impregnation, the rotation speed of the rotating platform is 20~50 rpm; The solid content of the polyurethane resin solution is 18~22wt%, and the viscosity at 25°C is 500~2500cps; For the first coating by impregnation, the amount of material applied should be sufficient for a coating time of 80-100 seconds. ； When applying the second coating for impregnation, the material should be applied for 25-35 seconds. During solidification, the concentration of the DMF aqueous solution is 17-22 wt%. The nonwoven fabric is selected from one of polypropylene, polyester, nylon, viscose fiber, acrylic fiber, polyethylene fiber, chlorofiber, polyester, and polyamide. The nonwoven fabric has a basis weight of 200~300 g / cm³. 2 The thickness of the nonwoven fabric is 1~3mm; The polyurethane resin solution is obtained by mixing a raw polyurethane solution and DMF; the solid content of the raw polyurethane resin solution is 25~35wt%, and the viscosity at 25°C is 10000~30000cps. The 100% modulus range of the raw polyurethane resin is 10~30 MPa.

2. The preparation method according to claim 1, characterized in that, Includes one or more of the following features: The flow rate of the discharge pipe is 100~2000 ml / min; The diameter of the discharge pipe is 7~15cm; The distance between the discharge end of the feeding pipe and the nonwoven base fabric is 10~20cm.

3. The preparation method according to claim 1, characterized in that, After solidification, the process also includes washing, drying, and polishing.

4. The nonwoven polishing pad formed by the preparation method according to any one of claims 1 to 3.

5. The use of the nonwoven polishing pad according to claim 4 in a CMP process for improving uneven removal rates between inner and outer rings.

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