Polishing pad material and preparation method and application thereof

Abstract

The invention discloses a polishing pad material and a preparation method and application thereof, and relates to the technical field of chemical mechanical polishing. The prepared polishing pad material has a more uniform foam structure and has hardness and density more suitable for CMP treatment of silicon carbide, the prepared polishing pad is adopted for CMP treatment of a silicon carbide wafer, the traditional rough polishing and fine polishing processes can be integrated into one step, efficiency is greatly improved, the silicon surface removal rate can reach 2 micrometers / h or above, and the polishing pad material is suitable for CMP treatment of silicon carbide. The removal rate of the carbon surface can reach more than 6 [mu] m / h, meanwhile, the polishing effect is similar, the average scratch depth of the silicon surface is within 510 pm, the average scratch depth of the carbon surface is within 720 pm, and the overall surface roughness of silicon carbide is below 0.1 nm.

Description

Technical Field

[0001] The invention relates to the technical field of chemical mechanical polishing, and in particular to a polishing pad material and a preparation method and application thereof. Background Art

[0002] As a third-generation semiconductor material, silicon carbide has the characteristics of high thermal conductivity, high breakdown field strength, and high electron saturation velocity. These characteristics make silicon carbide devices have significant application advantages in fields with requirements such as high temperature resistance, high voltage resistance, and low energy loss. As power semiconductors, silicon carbide devices can replace traditional silicon-based devices and are widely used in electric vehicles, industrial control, new energy and other fields. As RF devices, silicon carbide devices can achieve higher operating frequencies and higher power densities, and are widely used in 5G communications, satellite communications and other fields.

[0003] However, due to the high hardness, high wear resistance and high chemical inertness of silicon carbide, the MRR (material removal rate) is relatively low, about 3μm / h, during the processing of silicon carbide by CMP (chemical mechanical polishing). In addition, how to control parameters to achieve a stable polishing process during the CMP treatment of silicon carbide has always been a technical difficulty. Simple mechanical polishing will produce scratches, while chemical polishing may cause uneven corrosion, so it is necessary to combine the mechanical action of the polishing pad and the chemical action of the polishing liquid to achieve the ideal polishing effect.

[0004] At present, the existing CMP treatment of silicon carbide often uses a hard pad made of cast polyurethane for rough polishing, and then uses a damping cloth polishing pad for fine polishing to achieve the flatness of the silicon carbide surface. However, the polishing process using this process is inefficient and time-consuming. At the same time, the cast polyurethane used in the rough polishing has a cross-linked molecular chain structure. Although it can maintain structural stability during the polishing process, its excessive hardness can easily cause scratches on the wafer surface; and the polyurethane resin in the damping cloth during fine polishing often uses low-hardness polyurethane as a raw material. The linear molecular chain structure of polyurethane is easily degraded under the action of strong oxidants and in a high-speed and high-temperature polishing environment, and has a short service life. Therefore, in order to improve the polishing efficiency of silicon carbide, it is urgent to provide a polishing pad material that can replace the existing process, integrate rough polishing and fine polishing into one step, and have a good polishing effect. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a method for preparing a polishing pad material. First, a polyurethane base film of a specific hardness is isothermally annealed online at a specific temperature, and then the temperature is increased to foam it, so as to obtain a polyurethane foam material that is more suitable for polishing silicon carbide. The use of this material to polish silicon carbide can replace the existing process, integrate rough polishing and fine polishing into one step, and have an excellent polishing effect.

[0006] Another object of the present invention is to provide a polishing pad material.

[0007] Another object of the present invention is to provide a polishing pad.

[0008] Another object of the present invention is to provide an application of a polishing pad.

[0009] Another object of the present invention is to provide a method for polishing silicon carbide.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a polishing pad material comprises the following steps:

[0012] S1. The polyurethane base film is subjected to online isothermal annealing to obtain an annealed base film; the online isothermal annealing temperature is Tf-50 to Tf-20; the polyurethane is a thermoplastic polyurethane having a hardness of Shore D50 to 75 and a Tf of 180 to 210°C;

[0013] S2. Immerse the annealed base film obtained in step S1 in a supercritical fluid, heat it up for foaming, and obtain a polishing pad material; the temperature for heating and foaming is Tf-100 to Tf-40.

[0014] The preparation method of the polishing pad material provided by the present invention first performs online isothermal annealing on polyurethane to obtain a polyurethane base film with a more uniform hard segment distribution, and then heats up for foaming to obtain a polyurethane polishing pad material with suitable pore size, uniform size and distribution, and moderate hardness. When the obtained material is used to polish silicon carbide, rough polishing and fine polishing can be integrated into one step, and the polishing effect is excellent. It should be noted that the raw material used in the preparation method provided by the present invention is thermoplastic polyurethane elastomer. Other types of polyurethane elastomers such as MPU (mixed polyurethane elastomer) and CPU (cast polyurethane elastomer) have undergone cross-linking reactions themselves and cannot produce a pore structure through physical foaming.

[0015] The method provided by the present invention first performs online isothermal annealing in step S1, which can improve the pore distribution and size uniformity of the polyurethane polishing pad material. The molecular chain of polyurethane can be divided into soft segments and hard segments, and the two different structures will form different microphases based on thermodynamic incompatibility. Among them, the microphase formed by the aggregation of the hard segment phase is the hard segment domain, which can act as the nucleation site of the pores in the physical foaming process. However, for polyurethane that has not been treated in any way, the hard segment domain usually has uneven size and spatial distribution, which will cause the pores to aggregate, distribute and size unevenly in the polyurethane foaming process. In this regard, the present invention first pre-treats the polyurethane before foaming in step S1, and by performing online isothermal annealing on the polyurethane (the real-time temperature deviation during the annealing process does not exceed 3°C), the size and spatial distribution uniformity of the hard segment domain can be improved, so that the hard segment domain tends to form more pore nuclei during the foaming process, rather than expanding the pores around the existing pores, thereby improving the nucleation efficiency of the polyurethane in the heating foaming stage in step S2, and the uniformity of the pore distribution and size of the obtained polyurethane foam sheet, thereby improving the polishing effect. The annealing temperature in the annealing step has an important influence on the uniformity of the pores. If the temperature of the online isothermal annealing in step S1 is too low, the activity of the molecular chain will be limited, the homogenization degree of the hard segment domain will be limited, and it will be difficult to achieve the effect of homogenizing the pores in the subsequent foaming stage; if the annealing temperature is too high, the modulus of the polyurethane base film will be too low, which will cause difficulties in pulling the base film on the one hand, and easily induce the growth of large-sized spherulites on the other hand, reducing the uniformity of the pores. Therefore, the temperature of online isothermal annealing should be limited to Tf-50~Tf-20, that is, the annealing temperature should be 50~20℃ lower than the flow point.

[0016] The preparation method provided by the present invention also defines the hardness and flow point Tf (viscous-flow temperature, i.e., the viscous flow temperature, the temperature at which the polyurethane molecules change from a highly elastic state to a viscous flow state) of the polyurethane raw material itself. This is because only when the flow point of the polyurethane raw material is 180-210°C and the hardness is Shore D50-75, the hardness of the obtained polyurethane polishing pad material can be suitable for polishing silicon carbide. The flow point of polyurethane is closely related to the molecular weight, degree of branching, etc. of the polyurethane, while the hardness is related to the hard segment content in the microstructure of the polyurethane. If the flow point is too high or too low, it means that the length or degree of branching of the molecular chain is not appropriate; if the hardness is too high or too low, it means that the hard segment content in the microstructure of the polyurethane is not appropriate. When the method provided by the present invention is used to process polyurethane raw materials with inappropriate hardness or flow point, the pore size and distribution of the obtained polyurethane foam sheet are also inappropriate, resulting in it being unsuitable for polishing silicon carbide. It is speculated that this is because the hard segment content and the length of the molecular chain will affect the foaming process.

[0017] On the basis of uniform pores and moderate hardness, if the size of the pores is not appropriate, the polyurethane foam sheet will also be unsuitable for polishing silicon carbide. In this regard, the inventors of the present application have found through a large number of experimental studies that the pore size can be controlled by controlling the temperature of the foaming in step S2. The temperature of the foaming will affect the foaming rate. Similar to the nucleation of crystals, although annealing can increase the number of nucleation sites of the pores, too low a temperature during foaming will lead to too slow a nucleation rate and the pores are prone to being too large; too high a foaming temperature will lead to too fast foaming and too small a pore size. The inventors of the present application have found through a large number of experimental studies that when the temperature of the foaming in step S2 is Tf-100 to Tf-40, the resulting pore structure has a pore size that is more suitable for polishing silicon carbide.

[0018] In summary, the polishing effect of the polishing pad material of the present invention on silicon carbide is determined by the hardness of the raw material itself, the size of the pores and the distribution uniformity.

[0019] In a specific embodiment of the present invention, the method for preparing the polyurethane base film in step S1 comprises the following steps: extruding and casting polyurethane particles. More specifically, the film thickness formed by the casting can be a conventional thickness in the art, for example, 1 to 3 mm. It should be noted that the online isothermal annealing described in the present invention refers to the isothermal annealing process being carried out simultaneously with the casting process of the polyurethane base film on the same production line.

[0020] More specifically, the extrusion is performed using a twin-screw extruder, and the temperature of the twin-screw extrusion can be a conventional temperature in the art, such as Tf+10°C.

[0021] More specifically, the step of drying the polyurethane particles before extrusion is also included. More specifically, the drying can be performed at any temperature higher than room temperature, such as 80°C.

[0022] In a specific embodiment of the present invention, after the foaming in step S2, a rolling shaping step is further included, and the pressure of the rolling shaping can be a conventional pressure in the art, such as 6 kPa.

[0023] Preferably, the hardness of the polyurethane is Shore D65-72.

[0024] Optimizing the hardness of polyurethane is helpful to further control the density, hardness, pore size and other properties of subsequent products.

[0025] Preferably, the temperature of the isothermal annealing in step S1 is Tf-40 to Tf-25.

[0026] Preferably, the temperature of the heating and foaming in step S2 is Tf-90 to Tf-60.

[0027] More preferably, the supercritical fluid in step S2 is CO2.

[0028] More preferably, the amount of the supercritical fluid dissolved in the polyurethane-based film after the immersion in step S2 is 2.0-8.0%.

[0029] The solubility of the high-pressure fluid in the polyurethane base film will affect its foaming effect. By optimizing the dissolution amount of the high-pressure fluid, the properties of the product such as the pore size and density can be further controlled. It should be noted that the dissolution amount of the above-mentioned supercritical fluid is 2.0-8.0%, which means that the mass of the dissolved supercritical fluid accounts for 2-8wt% of the total mass of the fluid + base film.

[0030] More preferably, the amount of the supercritical fluid dissolved in the polyurethane-based film after the immersion in step S2 is 4.0-6.0%.

[0031] Preferably, the time of the online isothermal annealing in step S1 is 5 to 15 minutes.

[0032] The duration of online isothermal annealing is also one of the parameters that affect the relevant physical properties of the polyurethane foam sheet. If the time is too short, the annealing effect is not obvious; if the time is too long, the production efficiency is reduced. Considering the annealing effect and production efficiency, the preferred duration of the isothermal annealing in the present invention is 5 to 15 minutes.

[0033] Preferably, the online isothermal annealing in step S1 further includes a step of forming a composite isolation layer.

[0034] In a specific embodiment of the present invention, after the isolation layer is compounded in step S1, step S2 further includes a step of removing the isolation layer after the impregnation.

[0035] The annealed polyurethane base film will have direct physical contact when it is rolled up, which is not conducive to the dissolution and diffusion of the supercritical fluid foaming agent in the base film in the subsequent saturation stage, and reduces the dissolution uniformity of the foaming agent in the base film. Through the online composite isolation layer, a diffusion channel for the high-pressure fluid can be constructed, which can significantly shorten the time for the high-pressure fluid to reach dissolution equilibrium.

[0036] More specifically, the isolation layer is a mesh cloth with holes.

[0037] Since the isolation layer is only used for isolation during foaming and needs to be removed later, the isolation layer selected in the present invention can be any mesh cloth with holes obtained through commercial channels, for example, it can be a polyvinyl chloride mesh cloth with holes.

[0038] Preferably, the heating and foaming time in step S2 is 5 to 30 minutes.

[0039] The present invention also protects the polishing pad material prepared by the above preparation method.

[0040] In a specific embodiment of the present invention, the polishing pad material prepared by the present invention has a hardness of Shore D32-55 and a density of 0.60-1.00 g / cm 3 The average diameter of the pores is 12 to 30 μm, and the coefficient of variation of the pore diameter is 5 to 16%.

[0041] It should be noted that the coefficient of variation of the cell diameter refers to the ratio of the standard deviation of the cell diameter to the average value, which can characterize the uniformity of the cell diameter.

[0042] When the obtained polyurethane polishing pad material meets the above indicators, the obtained polishing pad has moderate hardness, appropriate pore size, uniform and reliable structure, high removal rate for both carbon and silicon surfaces of silicon carbide, shallow scratch depth and smoother surface, and can integrate the traditional rough polishing + fine polishing processes into one step, thereby achieving efficient and high-quality polishing of silicon carbide wafers.

[0043] The present invention also protects a polishing pad made of the above polishing pad material.

[0044] In a specific embodiment of the present invention, after obtaining the polishing pad material in step S2 of the method for preparing the polishing pad material, the polishing pad is obtained by cutting, peeling, punching, grooving, attaching a buffer layer and a back glue to the polishing pad online.

[0045] In a specific embodiment of the present invention, the buffer layer includes at least one of soft foamed polyurethane and melamine soft foam.

[0046] Preferably, the buffer layer is soft foamed polyurethane.

[0047] In a specific embodiment of the present invention, the back adhesive includes at least one of an acrylic pressure-sensitive adhesive and a polyurethane adhesive.

[0048] Preferably, the back adhesive is an acrylic pressure-sensitive adhesive.

[0049] The buffer layer and back glue of the above-mentioned material have better compatibility with the polishing pad material of the present invention, which helps to obtain a better silicon carbide polishing effect.

[0050] The present invention also protects the use of the polishing pad in chemical mechanical polishing of semiconductor materials.

[0051] Preferably, the semiconductor material is silicon carbide.

[0052] The present invention also protects a method for polishing silicon carbide, which is performed using the above-mentioned polishing pad, wherein the polishing pressure is 187 to 315 g / cm 2 .

[0053] The hardness of the polyurethane foam material, the average diameter of the pores and the downward pressure during polishing will affect the removal speed of silicon carbide. When the downward pressure is too large during polishing, the material polishing speed is too fast, which will easily cause scratches on the surface of the silicon carbide wafer and reduce the polishing quality.

[0054] In a specific embodiment of the present invention, the polishing rotation speed is 40-60 rpm.

[0055] In a specific embodiment of the present invention, the polishing can be performed using a conventional polishing liquid in the art as a medium.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The polishing pad material provided by the present invention has a more uniform pore structure, and at the same time has a hardness and density that are more suitable for CMP treatment of silicon carbide. Therefore, by using the polishing pad prepared by the present invention to perform CMP on silicon carbide wafers, the traditional rough polishing + fine polishing process can be integrated into one step, which greatly improves the efficiency. At the same time, the polishing effect is similar to that of the traditional process. The silicon surface removal rate can reach more than 2μm / h, and the average scratch depth is within 510pm. The carbon surface removal rate can reach more than 6μm / h, and the average scratch depth is within 720pm. The overall surface roughness of silicon carbide is below 0.1nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a SEM photograph of the polishing pad material obtained in Example 1.

[0059] Figure 2 This is a SEM photograph of the polishing pad material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0060] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. Among them, the raw material information used in the embodiments and comparative examples is as follows:

[0061] Polyurethane granules-1: TPU, purchased from Lubrizol, brand ETE 70DT3, hardness is Shore D70, flow point Tf is 205℃;

[0062] Polyurethane granules-2: TPU, purchased from Lubrizol, brand ETE 55DT3, hardness is Shore D55, flow point Tf is 190℃;

[0063] Polyurethane particles-3: TPU, purchased from Risheng Chemical, brand BTE85AU, hardness of Shore D35, flow point Tf of 188°C;

[0064] Polyurethane particles-4: TPU, purchased from Meirui New Materials, brand I80D, hardness of Shore D80, flow point Tf of 205°C;

[0065] Polyurethane particles-5: TPU, purchased from Meirui New Materials, brand E155D, hardness of Shore D55, flow point Tf of 177°C;

[0066] Polyurethane granules-6: TPU, purchased from Lubrizol, brand ETE 50DT3, hardness is Shore D50, flow point Tf is 172℃;

[0067] Polyurethane granules-7: TPU, purchased from Covestro, brand 970U, hardness is Shore D70, flow point Tf is 213℃;

[0068] Soft foamed polyurethane: brand CS90, purchased from Saint-Gobain;

[0069] Melamine soft foam: brand HFT-755, purchased from Huafutai;

[0070] Acrylic pressure-sensitive adhesive: brand LOCTITE DURO-TAK 8087, purchased from Henkel;

[0071] Polyurethane adhesive: brand HR-728, purchased from Huirui Adhesive Industry;

[0072] Polishing liquid: COPOL-431, purchased from Boline;

[0073] Polishing machine: CX-CMP910 single-side polishing machine, purchased from Chenxuan Semiconductor Equipment.

[0074] Example 1

[0075] A method for preparing a polishing pad material comprises the following steps:

[0076] S1. The polyurethane particles-1 are dried, twin-screw continuously extruded, and cast to obtain a polyurethane base film, which is isothermally annealed online and composited with a porous mesh online to obtain an annealed base film; the online isothermal annealing temperature is Tf-30 (175°C) and the time is 10 min;

[0077] S2. Immerse the annealed base film obtained in step S1 in supercritical CO2 until the dissolved amount of CO2 is 4.0%, remove the isolation layer, raise the temperature to Tf-70 (135°C) for foaming, and the foaming time is 10 minutes. After foaming, roll pressing and shaping are performed to obtain the polishing pad material.

[0078] Example 2

[0079] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0080] The temperature of the online isothermal annealing in step S1 is Tf-25 (180° C.).

[0081] Example 3

[0082] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0083] The temperature of the online isothermal annealing in step S1 is Tf-40 (175° C.).

[0084] Example 4

[0085] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0086] The temperature of the online isothermal annealing in step S1 is Tf-20 (185° C.).

[0087] Example 5

[0088] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0089] The temperature of the online isothermal annealing in step S1 is Tf-50 (155° C.).

[0090] Example 6

[0091] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0092] The dissolved amount of CO2 in the polyurethane base film in step S2 is 6.0%.

[0093] Example 7

[0094] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0095] The dissolved amount of CO2 in the polyurethane base film in step S2 is 8.0%.

[0096] Example 8

[0097] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0098] The amount of CO2 dissolved in the polyurethane base film in step S2 is 2.0%.

[0099] Example 9

[0100] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0101] The foaming temperature in step S2 is Tf-80 (125° C.).

[0102] Example 10

[0103] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0104] The foaming temperature in step S2 is Tf-60 (145° C.).

[0105] Embodiment 11

[0106] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0107] The foaming temperature in step S2 is Tf-40 (165° C.).

[0108] Example 12

[0109] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0110] The foaming temperature in step S2 is Tf-100 (105° C.).

[0111] Example 13

[0112] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0113] The polyurethane particles-1 in step S1 were replaced with polyurethane particles-2.

[0114] Comparative Example 1

[0115] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0116] In step S1, no online isothermal annealing is performed.

[0117] The polishing pad materials obtained in Example 1 and this comparative example were characterized by SEM. Figures 1-2 As shown in the figure, it can be clearly seen that the polishing pad material obtained in Example 1 of the present invention has a more uniform pore structure.

[0118] Comparative Example 2

[0119] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0120] The temperature of the online isothermal annealing in step S1 is Tf-10.

[0121] Comparative Example 3

[0122] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0123] The temperature of the online isothermal annealing in step S1 is Tf-60.

[0124] Comparative Example 4

[0125] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0126] The polyurethane particles-1 in step S1 were replaced with polyurethane particles-3.

[0127] Comparative Example 5

[0128] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0129] The polyurethane particles-1 in step S1 were replaced with polyurethane particles-4.

[0130] Comparative Example 6

[0131] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0132] The polyurethane particles-1 in step S1 were replaced with polyurethane particles-5.

[0133] Comparative Example 7

[0134] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0135] The polyurethane particles-1 in step S1 were replaced with polyurethane particles-6.

[0136] Comparative Example 8

[0137] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0138] The foaming temperature in step S2 is Tf-110 (95° C.).

[0139] Comparative Example 9

[0140] A method for preparing a polishing pad material, wherein the method differs from Example 1 only in that:

[0141] The foaming temperature in step S2 is Tf-30 (175° C.).

[0142] Performance Testing

[0143] 1. Performance tests of polishing pad materials

[0144] Next, various indicators of the polishing pad material are tested, and the test method is as follows:

[0145] Density test: Use a density balance to measure the density of the polishing pad material. The sample mass used for the test is 3 to 5 g.

[0146] Flow point test: obtained by using a capillary rheometer, with a heating rate of 3°C / min and a load of 3kg;

[0147] Hardness test: Use Shore hardness tester, according to standard ISO 7619-1;

[0148] Average pore diameter test of the pores: The cross-section of the polishing pad material obtained in the embodiment and the comparative example was photographed by scanning electron microscopy, the diameters of 100 pores were counted and the average diameter of the polishing pad material obtained in the embodiment and the comparative example was calculated;

[0149] The coefficient of variation of cell diameter = standard deviation of cell diameter / average cell diameter*100%.

[0150] The test results are shown in Table 1 below:

[0151] Table 1. Performance test data of polishing pad materials obtained in Examples and Comparative Examples

[0152]

[0153]

[0154] From the experimental data in Table 1, it can be seen that the present invention can prepare a polyurethane foam sheet with controllable density and hardness and uniform pores. The hardness of the sheet is Shore D34-55 and the density is 0.60-1.00 g / cm 3 The average pore diameter is 13 to 29 μm, and the coefficient of variation of the pore diameter within the statistical range is 6 to 18%.

[0155] According to the data of Examples 1 to 5 in Table 1, it can be seen that when the temperature of the online isothermal annealing in step S1 is within the preferred range of Tf-40 to Tf-25 of the present invention (Examples 1 to 3), the obtained polishing pad material has smaller and more uniform pores. According to the data of Examples 1, 6 to 8, it can be seen that in step S2, the polyurethane base film is impregnated with CO2 supercritical fluid, and the dissolved amount of CO2 in the obtained base film is within the range of 2.0 to 8.0%. The uniformity of the pore size in the sheet obtained after foaming first increases and then decreases. Therefore, the preferred dissolved amount of CO2 in the base film of the present invention is 2.0 to 8.0%, and further preferably 4.0 to 6.0% (Examples 1 and 6).

[0156] According to the data of Examples 1, 9 to 12, the performance indicators of the obtained polyurethane foam sheet, such as hardness, density, cell size and coefficient of variation thereof, are higher or lower, respectively.

[0157] According to the data of Comparative Examples 1 to 3, it can be seen that if the online isothermal annealing is not performed in step S1 of the preparation method provided by the present invention, or the temperature of the online isothermal annealing is not appropriate, the cell uniformity of the obtained polishing pad material will be reduced.

[0158] According to the data of Comparative Examples 4 to 7, when the hardness or flow point of the polyurethane raw material selected in step S1 is not within the range required by the present invention, the preparation method provided by the present invention cannot produce a polyurethane foam sheet with uniform pore distribution and size.

[0159] According to Comparative Examples 8 to 9, if the foaming temperature in step S2 is too low (Comparative Example 8), it will lead to insufficient foaming, decreased uniformity of pore size, and excessive hardness and density of the polyurethane sheet; if the foaming temperature in step S2 is too high (Comparative Example 9), the obtained sheet will have too high a foaming degree, too low hardness, and too large pores, which will also make it unsuitable for polishing silicon carbide.

[0160] 2. Polishing effect test

[0161] Next, the polishing effect of the polishing pad material was tested.

[0162] Preparation of polishing pad: The polishing pad material obtained in the embodiment and the comparative example is subjected to online cutting, peeling, punching, grooving, and laminating with a buffer layer and / or back adhesive of different materials to obtain a polishing pad.

[0163] Polishing effect test: Effect examples 1 to 6 are shown.

[0164] Effect example 1.

[0165] The polishing pad materials obtained in the examples and comparative examples were cut, peeled, punched, and grooved online, and a soft foamed polyurethane buffer layer and an acrylic pressure-sensitive adhesive backing were attached to obtain a polishing pad; the polishing pad was installed on a CX-CMP910 single-sided polishing machine, the turntable speed was 50 rpm, and a silicon carbide special polishing liquid COPOL-431 was used. The polishing liquid flow rate was 200 mL / min and the down pressure was 200 g / cm 2 , a 6-inch silicon carbide wafer was polished for 1 hour, and no diamond dressing disk was required during the polishing process. The roughness was measured by Bruker Dimension Icon, and the scratches were measured by atomic force microscopy.

[0166] Effect example 2.

[0167] An existing process for chemical mechanical polishing of silicon carbide includes firstly using cast polyurethane for rough polishing and then using a damping cloth polishing pad for fine polishing, which specifically includes the following steps:

[0168] A 6-inch silicon carbide wafer was polished using a CX-CMP910 single-sided polisher. The turntable speed was 50 rpm, the polishing liquid flow rate was 200 mL / min, and the down pressure was 200 g / cm 2 For rough polishing, non-woven polishing pad JZ-3020 and polishing liquid JZ-8010 were used, and the polishing time was 1 hour; for fine polishing, damping cloth polishing pad SUBA800 and polishing liquid COPOL-136 were used, and the polishing time was 1.5 hours. The roughness after polishing was measured by Bruker Dimension Icon, and the scratches were measured by atomic force microscopy.

[0169] Effect example 3.

[0170] The polishing pad material obtained in Example 1 was cut, peeled, punched, and grooved online, and then attached with an acrylic pressure-sensitive adhesive backing to obtain a polishing pad; the polishing pad was installed on a CX-CMP910 single-sided polishing machine, the turntable speed was 50 rpm, and a silicon carbide special polishing liquid COPOL-431 was used. The polishing liquid flow rate was 200 mL / min and the down pressure was 200 g / cm 2 , a 6-inch silicon carbide wafer was polished for 1 hour, and no diamond dressing disk was required during the polishing process. The roughness was measured by Bruker Dimension Icon, and the scratches were measured by atomic force microscopy.

[0171] Effect example 4.

[0172] The polishing pad material obtained in Example 1 was cut, peeled, punched, and grooved online, and a melamine soft foam buffer layer and an acrylic pressure-sensitive adhesive backing were attached to obtain a polishing pad; the polishing pad was installed on a CX-CMP910 single-sided polishing machine, the turntable speed was 50 rpm, and a silicon carbide special polishing liquid COPOL-431 was used. The polishing liquid flow rate was 200 mL / min and the down pressure was 200 g / cm 2 , a 6-inch silicon carbide wafer was polished for 1 hour, and no diamond dressing disk was required during the polishing process. The roughness was measured by Bruker Dimension Icon, and the scratches were measured by atomic force microscopy.

[0173] Effect example 5.

[0174] The polishing pad material obtained in Example 1 was cut, peeled, punched, and grooved online, and a soft foamed polyurethane buffer layer and a polyurethane adhesive backing were attached to obtain a polishing pad; the polishing pad was installed on a CX-CMP910 single-sided polishing machine, the turntable speed was 50 rpm, and a special silicon carbide polishing liquid COPOL-431 was used. The polishing liquid flow rate was 200 mL / min and the down pressure was 200 g / cm 2, a 6-inch silicon carbide wafer was polished for 1 hour, and no diamond dressing disk was required during the polishing process. The roughness was measured by Bruker Dimension Icon, and the scratches were measured by atomic force microscopy.

[0175] The polishing test data is shown in Table 2:

[0176] Table 2. Polishing effect test data

[0177]

[0178]

[0179] According to Table 2, it can be seen from the effect example 1 of the present application that the silicon carbide polishing pad obtained in the embodiment has excellent polishing rate and polishing effect on both the carbon surface and the silicon surface of the 6-inch silicon carbide wafer, and the polishing pad obtained in the comparative example has poor polishing effect on the silicon carbide wafer. At the same time, the polishing effect in the present invention is similar to the existing rough polishing + fine polishing process (effect example 2), but the time consumption is greatly reduced.

[0180] According to the effects of Examples 1 and 6 to 8 in Effect Example 1, it can be seen that the amount of supercritical fluid dissolved in the polyurethane base film after the immersion in step S2 is increased (Example 6), which can improve the polishing effect within a certain range, but further improvement (Example 7) is likely to lead to excessive and uncontrollable foaming, which in turn causes the polishing effect to decrease.

[0181] According to the data of Examples 1 and 9 to 12 in Effect Example 1, it can be seen that when the foaming temperature in step S2 is not within the preferred range of Tf-90 to Tf-60 of the present invention (Examples 11 to 12), the performance indicators such as hardness, density, pore size and coefficient of variation of the obtained polyurethane foam sheet are respectively higher or lower. It is difficult to achieve a higher removal rate, lower surface scratch depth and roughness when polishing silicon carbide using the corresponding polyurethane foam sheet, and the polishing effect is reduced. Therefore, the preferred foaming temperature in step S2 of the present invention is Tf-90 to Tf-60.

[0182] According to the data of the comparative example in Effect Example 1, it can be seen that in the preparation method provided by the present invention, if step S1 does not perform isothermal annealing or the isothermal annealing conditions are inappropriate, the foaming temperature in step S2 is inappropriate, or the hardness and flow point of the polyurethane raw material itself are inappropriate, the polishing effect of the obtained polyurethane foam sheet on silicon carbide will be reduced.

[0183] According to effect examples 1, 3 to 5, when the material of the buffer layer is soft foamed polyurethane and the material of the back adhesive is acrylic pressure-sensitive adhesive, the back adhesive, the buffer layer and the polishing pad material obtained by the present invention have better compatibility, so the obtained polishing pad has a better polishing effect.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a polishing pad material, characterized in that: The steps include: S1. The polyurethane base film is subjected to online isothermal annealing to obtain an annealed base film; the online isothermal annealing temperature is Tf-50 to Tf-20; the polyurethane is a thermoplastic polyurethane having a hardness of Shore D50 to 75 and a Tf of 180 to 210°C; S2. Immerse the annealed base film obtained in step S1 in a supercritical fluid, heat it up for foaming, and obtain a polishing pad material; the temperature for heating and foaming is Tf-100 to Tf-40.

2. The method for preparing the polishing pad material according to claim 1, characterized in that: The hardness of the polyurethane is Shore D65-72.

3. The method for preparing the polishing pad material according to claim 1, characterized in that: The temperature of heating and foaming in step S2 is Tf-90 to Tf-60.

4. The method for preparing the polishing pad material according to claim 1 or 3, characterized in that: Include at least one of the following (c) to (d): (c) The supercritical fluid in step S2 is CO2; (d) The amount of the supercritical fluid dissolved in the polyurethane base film after the immersion in step S2 is 2.0 to 8.0%.

5. The method for preparing the polishing pad material according to claim 1, characterized in that: Include at least one of the following (e) to (g): (e) The time of online isothermal annealing in step S1 is 5 to 15 minutes; (f) after the online isothermal annealing in step S1, the step of online composite isolation layer is also included; (g) The heating and foaming time in step S2 is 5 to 30 minutes.

6. A polishing pad material prepared by the preparation method according to any one of claims 1 to 5.

7. A polishing pad made of the polishing pad material according to claim 6.

8. Use of the polishing pad according to claim 7 in chemical mechanical polishing of semiconductor materials.

9. The use according to claim 8, characterized in that The semiconductor material is silicon carbide.

10. A method for polishing silicon carbide, characterized in that: The polishing pad according to claim 7 is used, and the polishing pressure is 187 to 315 g / cm 2 .

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