Thermoplastic polyurethane foaming sheet as well as preparation method and application thereof

Abstract

The invention relates to a thermoplastic polyurethane foaming sheet as well as a preparation method and application thereof, and belongs to the technical field of thermoplastic polyurethane foaming sheets. The preparation method of the sheet provided by the invention comprises the following steps: compounding an isolating layer onto a prepared thermoplastic polyurethane base film, and rolling to obtain a composite coiled material; the composite coiled material is subjected to two-stage dynamic saturation treatment under specific conditions in a CO2 gas environment, and a saturated composite coiled material is obtained; separating an isolating layer in the saturated composite coiled material, and then heating, foaming, rolling, shaping and cutting under specific conditions to obtain the thermoplastic polyurethane foamed sheet. The thermoplastic polyurethane foaming sheet prepared by the method is further used for preparing a polishing pad, the polishing pad has an excellent polishing effect on silicon carbide, polishing scratches on a silicon carbide wafer are few, the removal rate is high, and the service life is long.

Description

Technical Field

[0001] The invention relates to the technical field of thermoplastic polyurethane foam sheets, in particular to a thermoplastic polyurethane foam sheet and a preparation method and application thereof. Background Art

[0002] Chemical mechanical polishing (CMP) technology is a key step in achieving highly flat wafer surfaces in semiconductor manufacturing. It polishes the wafer surface by combining chemical and physical effects. Under a certain pressure and in the presence of polishing liquid, the wafer and the polishing pad move relative to each other. With the organic combination of the mechanical grinding effect of nano-abrasives and the chemical corrosion effect of oxidants, catalysts, etc., the material is peeled off layer by layer to achieve a highly flattened effect. The advantage of CMP technology lies in its comprehensive flattening capability. It can perform global flattening on the entire wafer surface to achieve nano-level surface flatness, meeting the extremely high requirements of modern integrated circuits for wafer surfaces.

[0003] Silicon carbide wafers have attracted much attention in the semiconductor field due to their unique physical properties. They have a wide bandgap, high hardness, high thermal conductivity, and excellent chemical stability. These properties make silicon carbide wafers perform well in high-temperature, high-voltage, and high-frequency applications, and are suitable for manufacturing high-power density switching devices such as power modules for electric vehicles and solar inverters. In addition, silicon carbide wafers are also widely used in the field of optoelectronic devices, including high-speed communications, photodetection, and lasers. Due to their high thermal conductivity and low crystal defect density, they are ideal for preparing high-quality optoelectronic devices.

[0004] Silicon carbide has a high hardness, with a Mohs hardness of 9.2 to 9.6. Its high hardness and brittleness make it easy to cause brittle fracture of the material during the grinding process, leaving a surface broken layer on the surface of the material, and causing more serious surface and sub-surface damage, affecting the processing accuracy. The extremely high hardness and chemical stability lead to low efficiency of traditional CMP polishing, and it takes dozens of hours to remove a small amount of material, which increases the difficulty of grinding and polishing. Cast polyurethane polishing pads have high hardness and rigidity, and are prone to deep surface damage during the polishing process. Although the polishing pad made of damping cloth can reduce scratches through the double-layer structure design, its oxidation resistance is poor and the polishing pad has a short service life.

[0005] Therefore, there is an urgent need to develop a material for preparing a silicon carbide polishing pad with long service life and good polishing quality. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a thermoplastic polyurethane foam sheet and its preparation method and application. The polishing pad prepared with the sheet provided by the present invention has a long service life and has an excellent polishing effect on silicon carbide, with less scratches on the polishing of silicon carbide wafers and a high removal rate.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a method for preparing a thermoplastic polyurethane foam sheet, characterized in that it comprises the following steps:

[0009] (1) Compounding the isolation layer onto the thermoplastic polyurethane base film and rolling it up to obtain a composite coil;

[0010] (2) subjecting the composite coil to a dynamic saturation treatment in a CO2 gas environment to obtain a saturated composite coil;

[0011] The dynamic saturation treatment includes a first stage and a second stage: the saturation conditions of the first stage are: temperature 50-90°C, pressure 10-30MPa, and duration 1-2 hours; the saturation conditions of the second stage are: temperature 20-30°C, pressure 3-6MPa, and duration 2-5 hours;

[0012] (3) separating the isolation layer from the saturated composite coil, then heating for foaming, rolling for shaping, and cutting to obtain the thermoplastic polyurethane foam sheet; the rolling shaping temperature is 45-80°C.

[0013] The present invention provides a method for preparing a thermoplastic polyurethane foam sheet, the main strategy of which is:

[0014] First, the thermoplastic polyurethane base film is rewound online to obtain a composite coil. The composite process in this step is that the isolation layer and the thermoplastic polyurethane base film are in direct physical contact, without any other medium in between. In the subsequent dynamic saturation treatment, the isolation layer can avoid direct contact with the base film, accelerate the dissolution and diffusion of high-pressure gas in the base film, and improve the uniformity of gas dissolution in the base film, which is beneficial to the subsequent heating and foaming and improves the comprehensive performance of the sheet. If the strategy of not adopting a composite isolation layer is adopted, the performance of the sheet will be significantly deteriorated.

[0015] Secondly, the traditional temperature-raising foaming method usually adopts the strategy of room temperature saturation and high temperature foaming. The gas diffusion rate at room temperature is slow, resulting in a long time for the gas to reach dissolution equilibrium in the sample, and the foaming sample preparation efficiency is low. The present invention adopts a two-stage, specific dynamic saturation treatment under a CO2 high-pressure gas environment: under the specific saturation conditions of the first stage, nanoscale microcavities can be formed in the thermoplastic polyurethane of the composite coil, while releasing the internal stress generated by the molecular chain when it is rolled and bent, which is conducive to the uniform growth of the pores in the foaming stage; under the specific saturation conditions of the second stage, the nanoscale microcavities act as gas diffusion channels, which can significantly reduce the dissolution and diffusion of the gas in the thermoplastic polyurethane, greatly shortening the time required for the high-pressure gas to reach dissolution equilibrium.

[0016] The thermoplastic polyurethane foam sheet prepared by the dynamic saturation treatment under the specific CO2 high-pressure gas environment of the present invention has high hardness, good flatness, and moderate pore diameter. After being further prepared into a polishing pad, it has an excellent polishing effect on silicon carbide. If the saturation treatment conditions are not suitable, the sheet performance deteriorates, and the polishing effect of the polishing pad on silicon carbide also significantly deteriorates; if the gas environment used is not suitable, a good silicon carbide polishing effect cannot be achieved.

[0017] The saturated composite coil is separated from the isolation layer online and then heated for foaming. After the thermoplastic polyurethane base film is heated for foaming, wrinkles and bends will occur on both sides of the coil due to the boundary effect, which will reduce the flatness of the sample. Therefore, it is further rolled and shaped to improve the overall uniformity of the foamed sheet after cutting. Appropriate temperature conditions need to be controlled during rolling shaping. Too high a temperature will cause the pores to deform, while too low a temperature will not effectively improve the overall uniformity of the foamed sheet.

[0018] The thermoplastic polyurethane foam sheet prepared by the preparation strategy provided by the present invention can be used to prepare a polishing pad, which has a long service life, a good polishing effect on silicon carbide, a high polishing removal rate, few polishing scratches and a low depth, and can achieve extremely low silicon wafer surface roughness after polishing, which can well solve the problems of low polishing efficiency, easy to cause deep damage, and short material service life in the prior art.

[0019] Preferably, in step (1), the preparation method of the thermoplastic polyurethane base film is:

[0020] The thermoplastic polyurethane is prepared by melt extrusion and casting process, and the Shore hardness of the thermoplastic polyurethane is 50-80D.

[0021] The molecular chain of thermoplastic polyurethane can be divided into soft segments and hard segments. The ratio of soft and hard segments affects the hardness of the polymer. The higher the hard segment content, the higher the hardness of the thermoplastic polyurethane and the stronger the rigidity of the molecular chain. During the physical foaming process, the dissolution and diffusion of gas in high-hardness thermoplastic polyurethane slow down, and the difficulty of cell growth also increases. Optimizing the hardness of thermoplastic polyurethane can better control the physical properties of the foamed sheet and the final product.

[0022] Preferably, the extrusion temperature is 190-210°C.

[0023] Preferably, in the step (1), the thermoplastic polyurethane base film is preheated before being composited.

[0024] Hot air is used for preheating before lamination in order to reduce the internal force generated by the base film during winding and to improve the overall stability of the formed composite coil.

[0025] Preferably, the isolation layer is a porous mesh with a mesh size of 8-200.

[0026] As a preferred solution of the present invention, the porous mesh is made of thermoplastic or thermosetting plastic.

[0027] Preferably, in step (2), the saturation temperature of the first stage is 70-80°C, the pressure is 15-22 MPa, and the duration is 2 hours; the saturation temperature of the second stage is 25-30°C, the pressure is 4-5 MPa, and the duration is 4 hours.

[0028] Under the above-mentioned preferred dynamic saturation treatment conditions, the obtained thermoplastic polyurethane foam sheet is used for the preparation of polishing pads, which can achieve a higher quality polishing effect on silicon carbide, with an average scratch depth of less than 250pm, a removal rate greater than 7.5μm / h, and the surface roughness of the silicon carbide wafer after polishing is less than 0.05nm.

[0029] Preferably, the foaming temperature is 100-160°C.

[0030] More preferably, the foaming temperature is 110-150°C.

[0031] As a preferred embodiment of the present invention, the foaming temperature is 130-140°C.

[0032] In the method of the present invention, it is necessary to control the appropriate temperature for heating and foaming: on the one hand, high temperature can soften the polymer and reduce the matrix modulus of the polymer; on the other hand, high temperature causes the solubility of the gas in the polymer to decrease, and the dissolved gas gathers in the nanoscale microcavity and diffuses into the air at the same time, driving the growth of the bubbles.

[0033] Preferably, the roller pressing pressure is 2-8 kPa.

[0034] Appropriate pressure conditions need to be controlled during roller forming. Too high pressure will cause the bubbles to deform, while too low pressure will not effectively improve the overall uniformity of the foamed sheet.

[0035] In a second aspect, the present invention provides a thermoplastic polyurethane foam sheet prepared by the above-mentioned method for preparing a thermoplastic polyurethane foam sheet.

[0036] Preferably, the properties of the prepared thermoplastic polyurethane foam sheet are as follows: Shore hardness is 35-65D, the average diameter of the pores is 5-30 μm, and the density is 0.6-1.05 g / cm 3 , the cortex thickness is 0.1-0.6mm.

[0037] The thermoplastic polyurethane foam sheet prepared by the above-mentioned thermoplastic polyurethane foam sheet preparation method has high hardness, suitable pore diameter, density and skin thickness, excellent performance, and is conducive to further application in the preparation of polishing pads.

[0038] In a third aspect, the present invention provides a polishing pad, which is prepared by splitting, cutting, slotting, and back-adhesion of the thermoplastic polyurethane foam sheet as claimed in claim 8. The slots are concentric circular grooves.

[0039] In a fourth aspect, the present invention provides a method for polishing silicon carbide, comprising the following steps:

[0040] Silicon carbide is polished using the polishing pad and silicon carbide polishing liquid as claimed in claim 9 until the polishing of the silicon carbide is completed; the compression rate of the polishing pad is 1-6%.

[0041] As a preferred solution of the present invention, the compression rate of the polishing pad is 2-5%, and the rotation speed of the polishing lower plate is 50-60 rpm.

[0042] Silicon carbide is chemically inert, and its high hardness and brittleness make it easy to cause brittle fracture of the surface material during the polishing process, thereby causing scratches on the wafer surface. By selecting a silicon carbide polishing liquid, the silicon carbide surface can be oxidized to play a role in chemical corrosion. Under the combined effect of the polishing pad prepared from the specific thermoplastic polyurethane foam sheet of the present invention and the nano-abrasive, high-quality polishing of the silicon carbide wafer can be achieved: after the silicon carbide is polished, the silicon carbide surface roughness (Ra) can be achieved to be less than 0.1nm, the average scratch depth is less than 300pm, and the polishing removal rate is higher than 6.0μm / h. By controlling the basic properties of the raw material sheet prepared by the polishing pad and the polishing process, it can be ensured that the polished silicon carbide wafer has a high-quality polished surface.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The present invention significantly accelerates the dissolution of CO2 in the composite coil by adopting the strategy of online composite isolation layer. By further regulating the conditions of dynamic saturation, temperature rise foaming, and roller pressing shaping, a high-hardness thermoplastic polyurethane foam sheet with good flatness, suitable porous structure, and controllable physical properties can be prepared.

[0045] (2) The present invention further provides a polishing pad made of a thermoplastic polyurethane foam sheet obtained by a specific preparation method. The polishing pad, combined with a specific polishing process, can make the surface roughness (Ra) of the silicon carbide wafer lower than 0.1nm, the removal rate greater than 6μm / h, and the scratch depth lower than 300pm, thereby ensuring that the polished silicon carbide wafer has a high-quality polishing surface, thereby solving the problems of low polishing efficiency, easy to cause deep damage, and short material service life of silicon wafers in the prior art. DETAILED DESCRIPTION

[0046] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific examples. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0047] The following basic descriptions are given for the materials used in the following embodiments and comparative examples, but they are not limited to these materials:

[0048] Thermoplastic polyurethane: Lubrizol ESTANE 58144, Shore hardness 65D;

[0049] Polishing liquid: COPOL-431, Bolinerun;

[0050] Isolation layer: commercially available 100 mesh nylon mesh.

[0051] Example 1

[0052] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention, the preparation method of the thermoplastic polyurethane foam sheet in this embodiment is:

[0053] (1) drying a thermoplastic polyurethane having a Shore hardness of 65D, and then preparing a thermoplastic polyurethane base film through a melt extrusion and casting process; wherein the temperature of the extruder is set to 190-210° C.; online laminating a 100-mesh nylon mesh as an isolation layer to the thermoplastic polyurethane base film, and rolling it up to obtain a composite coil;

[0054] (2) placing the above composite coil in a high-pressure CO2 gas environment for dynamic saturation treatment, which is divided into two stages: the saturation conditions of the first stage are temperature 80°C, pressure 18 MPa, and duration 2 hours; the saturation conditions of the second stage are temperature 28°C, pressure 5 MPa, and duration 4 hours, to obtain a saturated composite coil;

[0055] (3) The saturated composite coil is subjected to online separation of the isolation layer by a traction device, and then heated for foaming at a temperature of 140° C. and a foaming time of 10 min; then rolled for shaping at a pressure of 6 kPa and a temperature of 50° C.; and finally cut online to obtain the thermoplastic polyurethane foam sheet.

[0056] The preparation method of the polishing pad described in this embodiment is:

[0057] The thermoplastic polyurethane foam sheet prepared above is subjected to splitting, cutting, grooving (concentric circular grooves), and back gluing to obtain the polishing pad.

[0058] Example 2

[0059] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention, the difference between this embodiment and embodiment 1 is only that, in the method for preparing the thermoplastic polyurethane foam sheet, the saturated pressure in the first stage in step (2) is 26 MPa.

[0060] Example 3

[0061] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention, the difference between this embodiment and embodiment 1 is only that, in the preparation method of the thermoplastic polyurethane foam sheet, the saturated pressure of the second stage in step (2) is 3 MPa.

[0062] Example 4

[0063] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention is different from Embodiment 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the temperature of the rolling and shaping in step (3) is 75°C.

[0064] Example 5

[0065] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention is different from Embodiment 1 only in that, in the method for preparing the thermoplastic polyurethane foam sheet, the foaming temperature in step (3) is 120°C.

[0066] Example 6

[0067] An embodiment of the thermoplastic polyurethane foam sheet and polishing pad of the present invention is different from Embodiment 1 only in that, in the method for preparing the thermoplastic polyurethane foam sheet, the foaming temperature in step (3) is 150°C.

[0068] Comparative Example 1

[0069] A thermoplastic polyurethane foam sheet and a polishing pad, wherein the preparation method of the thermoplastic polyurethane foam sheet is:

[0070] (1) drying a thermoplastic polyurethane having a Shore hardness of 65D, and then preparing a thermoplastic polyurethane base film by melt extrusion and casting process; wherein the temperature of the extruder is set to 190-210° C.; and directly winding the base film without compounding the isolation layer to obtain a thermoplastic polyurethane coil;

[0071] (2) placing the coiled material in a high-pressure CO2 gas environment for dynamic saturation treatment, which is divided into two stages: the saturation conditions of the first stage are 80°C, 18MPa, and 2 hours; the saturation conditions of the second stage are 28°C, 5MPa, and 4 hours, to obtain a saturated coiled material;

[0072] (3) The saturated coil is heated and foamed at a temperature of 140° C. and a foaming time of 10 min; then, it is rolled and shaped under a pressure of 6 kPa and a temperature of 50° C.; and finally, it is cut online to obtain a thermoplastic polyurethane foam sheet.

[0073] The preparation method of the polishing pad is the same as that of Example 1.

[0074] Comparative Example 2

[0075] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from Example 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the high-pressure gas environment in step (2) is N2.

[0076] Comparative Example 3

[0077] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from those of Example 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the saturation temperature of the first stage in step (2) is 100°C.

[0078] Comparative Example 4

[0079] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from those of Example 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the saturation pressure in the second stage in step (2) is 2 MPa.

[0080] Comparative Example 5

[0081] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from those of Example 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the temperature of the rolling and shaping in step (3) is 90°C.

[0082] Comparative Example 6

[0083] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from Example 1 only in that, in the preparation method of the thermoplastic polyurethane foam sheet, the conditions of the dynamic saturation treatment in step (2) are: without stages, with a temperature of 80°C, a pressure of 18 MPa, and a duration of 6 hours.

[0084] Comparative Example 7

[0085] A thermoplastic polyurethane foam sheet and a polishing pad, which are different from those in Example 1 only in that, in the method for preparing the thermoplastic polyurethane foam sheet, the conditions for the dynamic saturation treatment in step (2) are: the saturation conditions in the first stage are a temperature of 80°C, a pressure of 18 MPa, and a duration of 2 hours; and the saturation conditions in the second stage are a temperature of 80°C, a pressure of 8 MPa, and a duration of 4 hours.

[0086] Effect Example 1

[0087] In order to explore the performance of the thermoplastic polyurethane foam sheet provided by the present invention, the thermoplastic polyurethane foam sheet in the embodiment and the comparative example was tested as follows:

[0088] Density: Density test is performed using a density balance;

[0089] Hardness: measured using a Shore hardness tester according to ISO 7619-1.

[0090] Average diameter of pores: The cross section of the high-hardness thermoplastic polyurethane foam sheet is photographed by scanning electron microscopy, and the diameters of more than 100 pores are counted and calculated to obtain the average diameter of the high-hardness thermoplastic polyurethane foam sheet;

[0091] Cortical thickness: measured by scanning electron microscopy;

[0092] Flatness: Take an area of ​​1m 2 Thermoplastic polyurethane foam sheet is laid flat on a flat table. The height of the thermoplastic polyurethane foam sheet is measured at 100 different positions with the table as the height reference point. Among them, 10 points are averaged in the length and width directions, totaling 100 height measurement points. The height average value A is obtained through the data of 100 points, and the variance B is calculated. If 20% A>B, the flatness is evaluated as excellent; if 50% A>B>20%A, the flatness is evaluated as good; if B>50%A, the flatness is evaluated as poor.

[0093] The above performance test results of the embodiments and comparative examples are shown in Table 1 below.

[0094] Table 1 Performance test results of thermoplastic polyurethane foam sheets in the examples and comparative examples

[0095]

[0096]

[0097] As shown in Table 1, the preparation method of the thermoplastic polyurethane foam sheet in Examples 1-6 of the present invention can produce a thermoplastic polyurethane foam sheet with a smooth surface, a porous structure, and controllable density and hardness. The performance parameters of the thermoplastic polyurethane foam sheet are as follows: Shore hardness is 35-65D, the average diameter of the foam cells is 5-30μm, and the density is 0.6-1.05g / cm 3 , the cortex thickness is 0.1-0.6mm.

[0098] From the comparison of the embodiment and the comparative example, it can be known that when the isolation layer is not compounded, or N2 is used as a high-pressure gas, or the dynamic saturation treatment and the rolling parameters are not within the scope of the present application, the density, hardness and average pore size of the obtained thermoplastic polyurethane foam sheet may exceed the above range, and the comprehensive performance deteriorates. Among them, the isolation layer is not compounded during the preparation process of the thermoplastic polyurethane foam sheet of comparative example 1, the density of the prepared thermoplastic polyurethane foam sheet is significantly increased, and the pores fail to grow fully, the flatness of the sample is poor, and the performance is significantly deteriorated; Comparative example 2 uses N2 as a high-pressure gas, the density of the thermoplastic polyurethane foam sheet is also increased, the pores fail to grow fully, and the flatness of the sample is poor; the saturation pressure of the second stage in comparative example 4 is reduced to below the limited range, and the flatness of the obtained thermoplastic polyurethane foam sheet deteriorates; the saturation treatment conditions of constant temperature and constant pressure are used in comparative example 6, the pores fail to grow fully, and the average diameter of the pores is low; the dynamic saturation conditions of the second stage are changed in comparative example 7, resulting in low density.

[0099] Effect Example 2

[0100] In order to explore the performance of the polishing pad made of the thermoplastic polyurethane foam sheet provided by the present invention, the polishing pads in the examples and comparative examples were subjected to the following polishing steps:

[0101] COPOL-431 polishing liquid and Revasum 6EZ single-wafer polisher were used to polish silicon carbide wafers, and the polishing pad prepared by the present invention was used to evaluate the polishing effect. During the polishing process, the compression rate of the polishing pad was 2.8%, the lower plate speed was 50 rpm, and the single polishing time was 2 hours. After polishing, the polishing removal rate and average scratch depth of silicon carbide were obtained by testing, and the surface roughness of the wafer after polishing was evaluated. The results are shown in Table 2:

[0102] Table 2 Performance test results of polishing pads in embodiments and comparative examples

[0103]

[0104] From the data in Table 2, it can be seen that the polishing pad prepared by the preparation method of the embodiment of the present invention has excellent polishing efficiency and polishing effect on silicon carbide wafers: during the polishing process, the material removal rate is greater than 6μm / h, the average scratch depth of the silicon carbide wafer after polishing is less than 300pm, and the surface roughness is less than 0.1nm. Among them, the polishing pad further prepared by the thermoplastic polyurethane foam sheet obtained by the preparation strategy in Example 1 has the best comprehensive polishing effect on silicon carbide wafers, with a high removal rate, an average scratch depth of 225pm, and a low surface roughness of the silicon carbide wafer after polishing.

[0105] The polishing pad prepared by the thermoplastic polyurethane prepared by the preparation method in the comparative example may have a certain index better than the polishing pad in the embodiment, but its polishing effect on silicon carbide wafers is significantly worse than that in the embodiment, and the three evaluation indexes (removal rate, scratch depth and roughness after polishing) cannot be met at the same time, making it difficult to meet the polishing requirements of downstream customers for silicon carbide wafers. Among them, when preparing the coil in comparative example 1, the isolation layer is not compounded, and the coiling is directly carried out, which seriously affects the polishing effect of the polishing pad. Although the polishing rate is significantly faster, the average scratch depth is higher, reaching 432pm, and the roughness after polishing under the same conditions is higher than 0.1nm. From Comparative Example 2, it can be seen that changing the gas of the dynamic saturation treatment to N2 also leads to an increase in the average scratch depth, an increase in the roughness after polishing, and a poor polishing effect; in Comparative Examples 3 and 4, the saturation temperature of the first stage is too high and the saturation pressure of the second stage is too low, respectively, and in Comparative Examples 6 and 7, the dynamic saturation treatment process is changed to constant temperature and constant pressure or constant temperature and variable pressure outside the scope of the present invention, respectively. It can be seen that the change of the dynamic saturation process or parameters significantly affects the polishing effect, and it is impossible to take into account the removal rate, the average scratch depth and the roughness after polishing, and the polishing effect is significantly affected. From Comparative Example 5, it can be seen that when the roller shaping temperature for preparing the thermoplastic polyurethane foam sheet is too high, the average scratch depth of the polishing pad polishing will be significantly increased to more than 300 pm, and the roughness after polishing will also be significantly improved.

[0106] In summary, the present invention provides a thermoplastic polyurethane foam sheet and a preparation method and application thereof. By regulating the preparation process and parameters of the thermoplastic polyurethane foam sheet, the dynamic saturation and foaming effect thereof are optimized, and a high-hardness thermoplastic polyurethane foam sheet with good flatness, a suitable porous structure, and controllable physical properties is obtained. The thermoplastic polyurethane foam sheet is applied in the preparation of a polishing pad, and silicon carbide is polished in combination with a specific polishing process. The surface roughness (Ra) of the silicon carbide wafer can be lower than 0.1nm, the removal rate is greater than 6μm / h, and the scratch depth is lower than 300pm, thereby ensuring that the polished silicon carbide wafer has a high-quality polished surface, solving the problems of low polishing efficiency, easy deep damage, and short material service life of silicon wafers in the prior art, and having high application value.

[0107] 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 thermoplastic polyurethane foam sheet, characterized in that: The following steps are involved: (1) Compounding the isolation layer onto the thermoplastic polyurethane base film and rolling it up to obtain a composite coil; (2) subjecting the composite coil to a dynamic saturation treatment in a CO2 gas environment to obtain a saturated composite coil; The dynamic saturation treatment includes a first stage and a second stage: the saturation conditions of the first stage are: temperature 50-90°C, pressure 10-30MPa, and duration 1-2 hours; the saturation conditions of the second stage are: temperature 20-30°C, pressure 3-6MPa, and duration 2-5 hours; (3) separating the isolation layer from the saturated composite coil, then heating for foaming, rolling for shaping, and cutting to obtain the thermoplastic polyurethane foam sheet; the rolling shaping temperature is 45-80°C.

2. The method for preparing a thermoplastic polyurethane foam sheet according to claim 1, wherein: In the step (1), the preparation method of the thermoplastic polyurethane base film is: The thermoplastic polyurethane is prepared by melt extrusion and casting process, and the Shore hardness of the thermoplastic polyurethane is 50-80D.

3. The method for preparing a thermoplastic polyurethane foam sheet according to claim 2, characterized in that: The extrusion temperature is 190-210°C.

4. The method for preparing a thermoplastic polyurethane foam sheet according to claim 1, wherein: In the step (1), the thermoplastic polyurethane base film is preheated and then composited.

5. The method for preparing a thermoplastic polyurethane foam sheet according to claim 1, wherein: The isolation layer is a porous mesh with mesh size of 8-200.

6. The method for preparing a thermoplastic polyurethane foam sheet according to claim 1, characterized in that: The foaming temperature is 100-160°C.

7. The method for preparing a thermoplastic polyurethane foam sheet according to claim 1, characterized in that: The pressure of the roller pressing is 2-8 kPa.

8. Thermoplastic polyurethane foam sheet prepared by the method for preparing thermoplastic polyurethane foam sheet according to any one of claims 1 to 7.

9. A polishing pad, characterized in that: The polishing pad is prepared by splitting, cutting, grooving and back-adhesion of the thermoplastic polyurethane foam sheet as claimed in claim 8.

10. A method for polishing silicon carbide, characterized in that: The following steps are involved: Silicon carbide is polished using the polishing pad and silicon carbide polishing liquid as claimed in claim 9 until the polishing of the silicon carbide is completed; the compression rate of the polishing pad is 1-6%.

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