Series polishing process of laser delaminated silicon carbide thinned wafer

Abstract

The application provides a series polishing process of laser delamination silicon carbide thinning wafer, and the series polishing process comprises the following steps: sequentially polishing laser delamination silicon carbide thinning wafer i times to obtain a required polished wafer; the roughness of the wafer obtained by the i-th polishing treatment is higher than that of the i+1-th polishing treatment, the hardness of the polishing pad required by the i-th polishing treatment is higher than that of the i+1-th polishing treatment, and the pH of the polishing liquid required by the i-th polishing treatment is smaller than that of the i+1-th polishing treatment; wherein i is a natural number and traverses from 1 to n, and n is a natural number and is not less than 2. The silicon carbide thinning wafer is obtained by laser-induced fracture delamination and thinning in sequence. The problems of high surface roughness, poor uniformity, scratch residue and low processing efficiency of the polished wafer are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polishing process, in particular to a series polishing process of laser stripping silicon carbide wafer. BACKGROUND

[0002] As the third generation of semiconductor materials, silicon carbide has broad application scenarios in the fields of aerospace, new energy vehicles, consumer electronics, etc. Compared with existing silicon-based semiconductor devices, silicon carbide semiconductor devices can not only be used in more severe environments, but also can realize efficient and high-frequency processing of information.

[0003] The surface quality of the silicon carbide substrate has a great influence on the performance of the silicon carbide-based device, but due to the high hardness and high stability of silicon carbide, the current silicon carbide polishing method is relatively low in efficiency, which hinders the wide use of silicon carbide-based devices. The current polishing method of silicon carbide wafer mainly combines mechanical polishing and chemical mechanical polishing.

[0004] Among them, mechanical polishing mainly uses diamond powder as abrasive, which has high material removal rate, but will cause surface and subsurface damage, and is generally used as a pre-process of chemical mechanical polishing. The traditional chemical mechanical polishing method is to place four parallel polishing heads, each of which places multiple wafers for polishing. This method is prone to cause problems such as high concentration of metal ions on the surface of the polished silicon carbide wafer and poor hydrophilic effect. SUMMARY

[0005] The present application provides a series polishing process of laser stripping silicon carbide wafer, which comprises the following steps:

[0006] The present application provides a series polishing process of laser stripping silicon carbide wafer, which comprises the following steps:

[0007] The silicon carbide wafer is first coarsely polished to obtain a first polished wafer, the first coarsely polished wafer is then medium-polished to obtain a second polished wafer, and the second polished wafer is finally finely polished to obtain a third polished wafer.

[0008] The laser stripping silicon carbide wafer is sequentially polished i times to obtain the required polished wafer; the roughness of the wafer obtained by the i-th polishing process is higher than that of the i+1-th polishing process, the hardness of the polishing pad required by the i-th polishing process is higher than that of the i+1-th polishing process, and the pH of the polishing liquid required by the i-th polishing process is smaller than that of the i+1-th polishing process; wherein i is a natural number and traverses from 1 to n, n is a natural number and is not less than 2.

[0009] The silicon carbide wafer is sequentially obtained by laser-induced cleavage stripping and thinning.

[0010] Another aspect of the present application provides a polishing wafer, the surface roughness of the silicon carbide polishing wafer is not higher than 0.1nm; preferably, the surface roughness of the polishing wafer is not higher than 0.08nm. The polishing wafer is obtained by laser cleavage, thinning, and serial polishing.

[0011] Compared with the prior art, the beneficial effects of the present application include at least one of the following:

[0012] (1) The present application reduces the wafer by single wafer and single side polishing process for not less than 2 times. It is beneficial to solve the problems of high surface roughness, poor uniformity, scratch residue, low processing efficiency and other problems, and is beneficial to further form a very low damage silicon carbide substrate.

[0013] (2) Compared with the prior art, the serial polishing process of the present application obtains a polishing wafer with a surface roughness of not higher than 0.1nm. BRIEF DESCRIPTION OF DRAWINGS

[0014] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0015] Figure 1 The flow chart of the serial polishing process of the laser cleavage silicon carbide wafer thinning wafer of the present application is shown. DETAILED DESCRIPTION

[0016] In order to more clearly explain the overall concept of the present application, the following will be described in detail with reference to the drawings.

[0017] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, therefore, the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0018] In addition, in the description of the present application, it should be understood that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, therefore, it cannot be understood as a limitation on the present application.

[0019] In the present application, unless specifically defined and limited otherwise, the terms "mounting", "connected", "connection", "fixed", and the like should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection, and can also be communication; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements or interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0020] In the present application, unless specifically defined and limited otherwise, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0021] In an exemplary embodiment of the present application, the serial polishing process of the laser lift-off silicon carbide thinned wafer of the present application comprises the following steps:

[0022] The laser lift-off silicon carbide thinned wafer is sequentially polished i times to obtain the required polished wafer; the roughness of the wafer obtained by the i-th polishing process is higher than that of the i+1-th polishing process, the hardness of the polishing pad required for the i-th polishing process is higher than that of the i+1-th polishing process, and the pH of the polishing liquid required for the i-th polishing process is smaller than that of the i+1-th polishing process; wherein i is a natural number and traverses from 1 to n, n is a natural number and is not less than 2. The particle size of the polishing liquid required for the i-th polishing process is smaller than that of the i+1-th polishing process. In this way, the surface roughness of the polished wafer obtained by serial polishing is smaller. The further prepared substrate product has higher quality.

[0023] Wherein, i can be 2, the laser lift-off silicon carbide thinned wafer is sequentially polished 2 times, the first polishing is rough polishing, and the first wafer is obtained. The first polished wafer is further polished for the second time, and the second polishing is medium polishing to obtain the required polished wafer. The hardness of the polishing pad required for the first polishing is greater than that of the polishing pad required for the second polishing, the pH of the polishing liquid required for the first polishing is less than that of the polishing liquid required for the second polishing, and finally the surface roughness of the wafer obtained by the first polishing is higher than that of the second polishing.

[0024] i can be 3, the laser ablation silicon carbide thinning sheet is sequentially polished for 3 times, and the polishing process is shown in Figure 1 The first polishing is rough polishing, and a first polished wafer is obtained. The first polished wafer is further polished for the second time, and a second polished wafer is obtained. Finally, the second polished wafer is polished for the third time to obtain a desired polished wafer. The polishing pad required for the first polishing process has a hardness greater than that of the polishing pad required for the second polishing process, which has a hardness greater than that of the polishing pad required for the third polishing process. For example, the rough polishing pad can be polyurethane, and the hardness of the polyurethane is 85-95 HA. The polishing liquid can be an acidic alumina polishing liquid, and the particle size of the polishing liquid is 90-130 nm. Preferably, the pH value of the polishing liquid is 3-4, and the particle size of the polishing liquid is 100-120 nm. The medium polishing pad is a non-woven fabric, and the hardness of the non-woven fabric is 70-83 HA. The polishing liquid is a neutral manganese oxide or neutral alumina polishing liquid, and the particle size of the polishing liquid is 65-85 nm. The polishing pad for fine polishing is a damping cloth, and the hardness of the damping cloth is 55-68 HA. The polishing liquid is an alkaline silicon oxide polishing liquid, and the pH value of the polishing liquid is 9-12. The particle size of the polishing liquid is 35-62 nm. The pH value of the polishing liquid required for the first polishing process is less than that of the polishing liquid required for the second polishing process, which is less than that of the polishing liquid required for the third polishing process. The removal rate of the first polishing is 3.5-5.5 μm / h, the removal rate of the second polishing is 1-3 μm / h, and the removal rate of the third polishing is 0.1-0.5 μm / h. The thinning sheet is sequentially processed according to the polishing process, and the surface roughness of the polished wafer gradually decreases. For example, the surface roughness of the polished wafer obtained by rough polishing is not higher than 0.3 nm, the surface roughness of the polished wafer obtained by medium polishing is not higher than 0.2 nm, and the surface roughness of the polished wafer obtained after fine polishing is not higher than 0.1 nm.

[0025] In addition, the polishing time of each time can be measured according to the quality of the polished wafer required and the number of polishing times. For example, if the polishing times are more, the time required for each polishing process is correspondingly reduced for the same quality of the polished wafer. If the polishing times are less, the time required for each polishing process is correspondingly longer.

[0026] The silicon carbide thinning sheet is obtained by sequentially performing laser-induced fracture and thinning.

[0027] The damage layer depth of the wafer obtained by the laser-induced cleavage is not higher than 110 μm, and the surface crack step height of the wafer is not higher than 70 μm. Further, the damage layer depth of the wafer obtained by the laser-induced cleavage is not higher than 90 μm, the surface crack step height of the wafer is not higher than 60 μm, and the size of the wafer is not less than 8 inches. The Bow of the wafer is less than 70 μm, and the Sori is less than 120 μm; further, the Bow of the wafer is less than 40 μm, and the Sori is less than 90 μm.

[0028] The surface roughness of the wafer obtained by the thinning is not higher than 10 nm, and further, the surface roughness of the wafer obtained by the thinning is not higher than 7 nm.

[0029] The surface roughness of the wafer obtained by the polishing is not higher than 0.2 nm; further, the surface roughness of the wafer obtained by the polishing is not higher than 0.1 nm.

[0030] In the present application, Bow refers to the warping degree of the wafer center relative to the reference plane, and Sori refers to the warping degree of the front surface based on the least square method, representing the deviation degree of the whole substrate relative to the median plane.

[0031] The specific operation of the serial polishing process is as follows:

[0032] The rough polishing pad is polyurethane, and the polishing liquid is acidic alumina polishing liquid. The acidic alumina polishing liquid has a pH of 2-5, a concentration of 1-1.5%, a flow rate of 100-200 ml / min, and a pressure of 300-500 g / cm 2 during polishing. The rotation speed during polishing is 40-70 rpm. Preferably, the acidic alumina polishing liquid has a pH of 3-5, a concentration of 1.2-1.4%, a flow rate of 130-170 ml / min, and a pressure of 350-450 g / cm 2 . The rotation speed during polishing is 50-60 rpm.

[0033] The medium polishing pad is non-woven fabric, and the polishing liquid is neutral manganese oxide or neutral alumina polishing liquid. The neutral manganese oxide or neutral alumina polishing liquid has a pH of 6-8, a concentration of 0.5-1%, a flow rate of 150-250 ml / min, and a pressure of 200-400 g / cm 2 . The rotation speed during polishing is 30-60 rpm. Preferably, the neutral manganese oxide or neutral alumina polishing liquid has a pH of 6-8, a concentration of 0.7-0.9%, a flow rate of 180-220 ml / min, and a pressure of 250-350 g / cm 2 . The rotation speed during polishing is 40-50 rpm.

[0034] The fine polishing pad is a damping cloth, and the polishing liquid is an alkaline silica polishing liquid. 2 Preferably, the alkaline silica polishing liquid has a pH of 10-11, a concentration of 0.7-0.9%, a flow rate of 180-220 ml / min, and a pressure of 250-350 g / cm 2 , and a rotation speed of 40-50 rpm.

[0035] The laser delamination silicon carbide wafer can be obtained by laser cracking and vibration delamination, for example, by the steps S01 to S04, wherein,

[0036] S01, detecting a (0001) crystal face of a silicon carbide ingot to obtain crystal face position information;

[0037] S02, calculating an included angle value between the crystal face position information and a first plane, and determining whether the included angle value meets a preset included angle value requirement, wherein the first plane is always perpendicular to a first direction in which a first laser beam is located;

[0038] S03a, if the requirement is met, a first laser beam is started to scan the silicon carbide ingot to form a to-be-delaminated surface containing a plurality of cracks and extending along the first plane; S03b, if the requirement is not met, the angle of the silicon carbide ingot and / or the angle of the first direction are adjusted, and the step S02 is returned until the included angle value meets the preset included angle value requirement;

[0039] S04, applying vibration to the to-be-delaminated surface to obtain a silicon carbide wafer.

[0040] The steps S01 to S04 can also be described in detail as follows:

[0041] S01, detecting a (0001) crystal face of a silicon carbide ingot to obtain crystal face position information.

[0042] Specifically, the crystal face detection can be performed by using the principle of Bragg diffraction, that is, the surface crystal of the silicon carbide is composed of a crystal face family A, B and C, and the interplanar spacing is d. When a laser beam is projected to the silicon carbide crystal at a grazing angle α, the scattering of the lattice on the crystal face A and the scattering of the lattice on the crystal faces B and C interfere with each other. For the same layer of laser scattering lines, when the included angle between the scattering lines and the crystal face is equal to the grazing angle, the lines produce constructive interference in this direction. For the same layer of scattering lines, when the included angle between the scattering lines and the crystal face is equal to the grazing angle, the lines produce constructive interference in this direction. For different layers of scattering lines, when the optical path difference is an integer multiple of the wavelength, the scattering lines of each face strengthen each other to form a great light intensity. By using this principle, the crystal face detection is completed, and the crystal face information is obtained.

[0043] S02, calculate an included angle value between the crystal plane position information and the first plane, and determine whether the included angle value meets a preset included angle value requirement, wherein the first plane is always perpendicular to a first direction in which the first laser beam is located.

[0044] Specifically, the first plane is a plane in which the silicon carbide ingot is located and which is substantially perpendicular to the first laser beam. The first direction is a direction in which the first laser beam is irradiated. The included angle value is an included angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot. The preset included angle value can be a determined value selected in the range of 0-10°, and further, the preset included angle value can be a determined value selected in the range of 0.5-3.5° or 4.5-7°. For example, it can also be 0° or 4°. The preset included angle value requirement can be equal to the preset included angle value, or can be within 10% of the preset included angle value, for example, 4±0.1°.

[0045] S03a, if yes, start the first laser beam to scan the silicon carbide ingot to form a to-be-peeled surface containing a plurality of cracks and extending along the first plane.

[0046] Specifically, if the included angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot is within the preset included angle value range, the first laser beam is started to perform laser scanning on the silicon carbide ingot to form a to-be-peeled surface containing a plurality of cracks and extending along the first plane. The average output power of the first laser beam can be 0.8-3.5 W, the wavelength can be 780-1100 nm, the scanning speed can be 300-700 mm / s, the scanning interval can be 0.1-0.5 mm, the scanning time can be 10-40 min, and the scanning times can be 2-6.

[0047] S03b, if no, adjust the angle of the silicon carbide ingot and / or the angle of the first direction, and return to the S02 step until the included angle value meets the preset included angle value requirement, and then perform the S03a step.

[0048] Specifically, if the included angle between the (0001) crystal plane of the silicon carbide ingot and the first plane of the silicon carbide ingot is not within the preset included angle value range, the angle of the silicon carbide ingot can be adjusted, i.e., the (0001) plane of the silicon carbide ingot is adjusted, or the first direction in which the first laser beam is located can be adjusted. After the adjustment, return to the S02 step to calculate the included angle value and determine whether the preset included angle value is met. If yes, proceed to S03a; if no, continue to adjust the included angle value until the preset included angle value is met.

[0049] S04, apply vibration to the to-be-peeled surface to obtain a silicon carbide peeled sheet.

[0050] Vibration is applied to the surface to be peeled in the step S03a to make the surface to be peeled extend along the crack or break, and a peeled sheet is obtained. The vibration can be achieved by mechanical vibration, ultrasonic method, or the like. For example, for the ultrasonic method, the frequency of the ultrasonic wave can be 100-150 KHZ, the ultrasonic time can be 10-60 seconds, and the emission mode can be continuous wave or pulse wave.

[0051] The thickness of the silicon carbide peeled sheet obtained by the above processing method can be 100-1000 μm. The size is not less than 8 inches, Bow≤60 μm, Sori≤100 μm, the damage layer depth is ≤100 μm, and the maximum value of the surface crack step height is not more than 70% of the damage layer depth.

[0052] In addition, in order to solve the problem that the edge is easy to collapse, the step S03 can be further provided with the following steps based on the above steps S01-S04: in the case that the included angle value meets the requirement of the preset included angle value, the second laser beam is started to scan the silicon carbide ingot around the circumferential direction of the silicon carbide ingot, and the second direction where the second laser beam is located is ensured to be always parallel to the first plane. The cracking direction of the first laser beam is perpendicular to the laser incidence direction, and the cracking direction of the second laser beam is along the laser incidence direction, which is adjusted by spot shaping. This is beneficial to the peeling of the circumferential edge of the silicon carbide ingot, and can further optimize the damage layer depth and the depth of the surface step crack. The second laser head is arranged to be able to be controlled in linkage with the first laser head, and the two laser heads are used to peel the silicon carbide ingot in turn. The first laser head generates the first laser beam to peel the area of the silicon carbide ingot except the circumferential edge, and the second laser head generates the second laser beam to peel the circumferential edge area of the silicon carbide ingot. The focus of the first laser beam and the position of the second laser beam are controlled to ensure that they generate cracks in the same plane. Compared with the peeling result of only the first laser beam, the second laser beam can optimize the damage layer depth and the depth of the surface step crack by at least 10%. The average output power of the second laser beam is 0.3-0.5 times the average output power parameter of the first laser beam, the wavelength is 780-1100 nm, the scanning speed is 0.3-0.5 times the scanning speed parameter of the first laser beam, the scanning interval is 0.1-0.5 mm, the scanning time is 10-40 minutes, and the scanning times are 2-6.

[0053] Then at least a part of one single face of the single peeled sheet is thinned and / or at least a part of the other single face of the single peeled sheet is thinned, so as to obtain a thinned sheet. The thinning includes coarse grinding and fine grinding, and the roughness of the fine grinding is smaller than that of the coarse grinding. The thinned sheet is sequentially subjected to first polishing, second polishing, third polishing, and so on of one single face to obtain a polished sheet.

[0054] The full monolithic single-side serial polishing process adopted by the application lays a foundation for the subsequent processing technology of the laser ablation silicon carbide thinning sheet obtained by low stress processing.

[0055] The specific operation of the serial polishing process of the application is shown in the following examples.

[0056] Example 1

[0057] Step one, rough polishing: the silicon carbide thinning sheet is first rough polished to obtain a first polished wafer, the rough polishing pad adopts polyurethane with a hardness of 90HA. The polishing liquid is an acidic alumina polishing liquid with an average particle size of 120nm, the acidic alumina polishing liquid has a PH of 3 and a concentration of 1.2%, the flow rate is 120ml / min, the rotation speed is 60rpm, the pressure is 600g / cm 2 , and the polishing time is 10min.

[0058] Step two, medium polishing: the first polished wafer is medium polished to obtain a second polished wafer, the medium polishing pad adopts non-woven fabric with a hardness of 82HA. The polishing liquid is a neutral manganese oxide polishing liquid with an average particle size of 80nm, the neutral manganese oxide polishing liquid has a PH of 6.3 and a concentration of 0.6%, the flow rate is 100ml / min, the rotation speed is 50rpm, the pressure is 500g / cm 2 , and the polishing time is 10min.

[0059] Step three, fine polishing: the second polished wafer is fine polished to obtain a silicon carbide polishing sheet, the fine polishing pad adopts damping cloth with a hardness of 67HA. The polishing liquid is an alkaline silicon oxide polishing liquid with an average particle size of 60nm, the alkaline silicon oxide polishing liquid has a PH of 11 and a concentration of 0.6%, the flow rate is 80ml / min, the pressure is 400g / cm 2 , the rotation speed is 40rpm, and the polishing time is 10min.

[0060] Example 2

[0061] Step one, rough polishing: the silicon carbide thinning sheet is first rough polished to obtain a first polished wafer, the rough polishing pad adopts polyurethane with a hardness of 88HA. The polishing liquid is an acidic alumina polishing liquid with an average particle size of 110nm, the acidic alumina polishing liquid has a PH of 4 and a concentration of 1.3%, the flow rate is 110ml / min, the pressure is 550g / cm 2 , the rotation speed is 55rpm, and the polishing time is 12min.

[0062] Step two, middle polishing: the first polished wafer is polished to get the second polished wafer, the polishing pad is non-woven cloth, the hardness is 76HA, the polishing liquid is neutral alumina polishing liquid, the average size of the polishing liquid particles is 70nm, the PH value of the neutral alumina polishing liquid is 6.9, the concentration is 0.6%, the flow rate is 100ml / min, the pressure is 450g / cm 2 , the rotating speed is 45rpm, and the polishing time is 12min.

[0063] Step three, fine polishing: the second polished wafer is polished to get the silicon carbide polishing wafer, the polishing pad is damping cloth, the hardness is 65HA, the polishing liquid is alkaline silica polishing liquid, the average size of the polishing liquid particles is 50nm, the PH value of the alkaline silica polishing liquid is 11.5, the concentration is 0.8%, the flow rate is 80ml / min, and the pressure is 350g / cm 2 , the rotating speed is 40rpm, and the polishing time is 12min.

[0064] Example 3

[0065] Step one, rough polishing: the silicon carbide thinning wafer is first polished to get the first polished wafer, the polishing pad is polyurethane, the hardness is 85HA, the polishing liquid is acidic alumina polishing liquid, the average size of the polishing liquid particles is 100nm, the PH value of the acidic alumina polishing liquid is 4.5, the concentration is 1.4%, the flow rate is 110ml / min, and the pressure is 500g / cm 2 , the rotating speed is 50rpm, and the polishing time is 15min.

[0066] Step two, middle polishing: the first polished wafer is polished to get the second polished wafer, the polishing pad is non-woven cloth, the hardness is 73HA, the polishing liquid is neutral manganese oxide polishing liquid, the average size of the polishing liquid particles is 70nm, the PH value of the neutral manganese oxide polishing liquid is 7.2, the concentration is 0.8%, the flow rate is 100ml / min, and the pressure is 400g / cm 2 , the rotating speed is 40rpm, and the polishing time is 15min.

[0067] Step three, fine polishing: the second polished wafer is polished to get the silicon carbide polishing wafer, the polishing pad is damping cloth, the hardness is 65HA, the polishing liquid is alkaline silica polishing liquid, the average size of the polishing liquid particles is 40nm, the PH value of the alkaline silica polishing liquid is 11.5, the concentration is 0.9%, the flow rate is 80ml / min, and the pressure is 300g / cm 2 , the rotating speed is 35rpm, and the polishing time is 15min.

[0068] Example 4

[0069] Based on the embodiment 1, the difference lies in that the silicon carbide thinning sheet is only subjected to two steps of rough polishing and fine polishing, the rough polishing polishing time is 20 min, and the fine polishing polishing time is 30 min.

[0070] Comparative example 1

[0071] Based on the embodiment 1, the difference lies in that the silicon carbide thinning sheet is only subjected to two steps of rough polishing and medium polishing, and the rough polishing time is 20 min and the medium polishing time is 20 min.

[0072] Comparative example 2

[0073] Based on the embodiment 1, the difference lies in that the silicon carbide thinning sheet is only subjected to two steps of medium polishing and fine polishing, and the medium polishing time is 30 min and the fine polishing time is 20 min.

[0074] The performance of the silicon carbide polishing sheet prepared in the embodiment 1-4 and the comparative examples 1-2 is shown in Table 1.

[0075] Table 1 Performance test table

[0076]

[0077] From Table 1, it can be seen from the embodiment 1-4 that the surface roughness of the polishing sheet prepared by the application is not higher than 0.1 nm. The surface roughness of the embodiment 1 is improved by 0.069 μm compared with the comparative example 1, the surface roughness of the embodiment 1 is not much different from the comparative example 2, but part of the scratches are not completely removed, and the efficiency is reduced by 40%. Compared with the embodiment 1, the total polishing time of the embodiment 2 and the embodiment 3 is slightly increased (20% to 50%), but the surface roughness can be further improved on the basis of the embodiment 1, and the corresponding adjustment needs to be made according to the product specifications and production requirements. Therefore, the three-step polishing method of the application can effectively improve the surface roughness quality while improving the removal rate, and solves the industry problem of conflict between efficiency and quality.

[0078] The application is derived from the special fund support of the Taishan industrial leading talent project.

[0079] The above only describes the embodiments of the application and is not used to limit the application. The application can have various changes and modifications for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the scope of claims of the application.

Claims

1. A series polishing process for laser lift-off of thinned silicon carbide wafers, characterized in that, The series polishing process includes the following steps: The silicon carbide thinning wafer is laser-exfoliated and polished i times sequentially to obtain the desired polished wafer; the roughness of the wafer obtained by the i-th polishing process is higher than that of the (i+1)-th polishing process, the hardness of the polishing pad required for the i-th polishing process is greater than that required for the (i+1)-th polishing process, and the pH of the polishing solution required for the i-th polishing process is less than that required for the (i+1)-th polishing process; where i is a natural number that iterates from 1 to n, and n is a natural number that is not less than 2. The silicon carbide thinned sheet is obtained by laser-induced cracking and peeling followed by thinning. The depth of the damaged layer of the strip obtained by laser-induced cracking and ablation is not higher than 110 μm, and the height of the surface crack step of the strip is not higher than 70 μm. The surface roughness of the thinned sheet obtained by the thinning process is no higher than 10 nm. The particle size of the polishing fluid required for the i-th polishing process is greater than the particle size of the polishing fluid required for the (i+1)-th polishing process. The value of i is 3; the laser-exfoliated silicon carbide thinned sheet is polished three times in sequence to obtain the desired polished sheet; the first polishing is a rough polishing to obtain the first polished sheet; the second polishing is a medium polishing process to obtain the second polished sheet; and finally, the third polishing is a fine polishing process to obtain the desired polished sheet. The coarse polishing pad is made of polyurethane, and the polishing liquid is acidic alumina polishing liquid; the medium polishing pad is made of non-woven fabric, and the polishing liquid is neutral manganese oxide or neutral alumina polishing liquid; the fine polishing pad is made of damping cloth, and the polishing liquid is alkaline silicon oxide polishing liquid.

2. The tandem polishing process according to claim 1, characterized in that, The surface roughness of the thinned sheet is no higher than 7 nm.

3. The tandem polishing process according to claim 1, characterized in that, The acidic alumina polishing slurry has a pH of 2-5 and a particle size of 90-130 nm; the neutral manganese oxide polishing slurry or neutral alumina polishing slurry has a pH of 6-8 and a particle size of 65-85 nm; the alkaline silicon oxide polishing slurry has a pH of 9-12 and a particle size of 35-62 nm.

4. The tandem polishing process according to claim 1, characterized in that, The polyurethane has a hardness of 85~95HA, the nonwoven fabric has a hardness of 70~83HA, and the damping fabric has a hardness of 55~68HA.

5. The tandem polishing process according to claim 1, characterized in that, The removal rate of the first polishing is 3.5~5.5μm / h, the removal rate of the second polishing is 1~3μm / h, and the removal rate of the third polishing is 0.1~0.5μm / h.

6. The tandem polishing process according to claim 1, characterized in that, The surface roughness of the polished sheet is no higher than 0.1 nm.

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