Wafer processing method

Abstract

The present invention provides a method for processing a wafer, comprising: detecting the curvature of the wafer, wherein the wafer has a first surface and a second surface relative to the first surface, wherein the first surface is a concave surface and the second surface is a convex surface; sequentially performing a mid-grinding process on the first surface and the second surface to obtain a mid-grinded first surface and a mid-grinded second surface; sequentially performing a fine grinding process on the mid-grinded first surface and the mid-grinded second surface to obtain a finely ground first surface and a finely ground second surface.

Description

Technical Field

[0001] The invention relates to a wafer, and in particular to a wafer processing method. Background Art

[0002] In the semiconductor industry, before forming an epitaxial layer or other film layer on a wafer, the surface of the wafer needs to be ground to adjust the thickness of the wafer and make the surface of the wafer flatter. However, in the existing grinding process, after grinding the wafer, the surface of the wafer will be damaged, and the residual stress generated by these damages will increase the bow of the wafer. If the front and back sides of the wafer are ground multiple times, the wafer is prone to fatigue failure due to repeated changes in the bow. Summary of the invention

[0003] The invention provides a wafer processing method, which can improve the problem of fatigue damage of the wafer after processing.

[0004] At least one embodiment of the present invention provides a method for processing a wafer, comprising: detecting the curvature of the wafer, wherein the wafer has a first surface and a second surface opposite to the first surface, wherein the first surface is a concave surface, and the second surface is a convex surface; sequentially performing a medium grinding process on the first surface and the second surface to obtain a medium-ground first surface and a medium-ground second surface, wherein the medium grinding process comprises: grinding the first surface and the second surface with a first grinding wheel, wherein the grit number of the first grinding wheel is #12000 to #15000, and the rotation speed of the first grinding wheel is 3500rpm to 4000rpm; after the medium grinding process, sequentially performing a fine grinding process on the medium-ground first surface and the medium-ground second surface to obtain a fine-ground first surface and a fine-ground second surface, wherein the fine grinding process comprises: grinding the medium-ground first surface and the medium-ground second surface with a second grinding wheel, wherein the grit number of the second grinding wheel is #27000 to #30000, and the rotation speed of the second grinding wheel is 2033rpm to 2133rpm.

[0005] At least one embodiment of the present invention provides a method for processing a wafer, comprising: detecting the curvature of the wafer, wherein the wafer has a first surface and a second surface opposite to the first surface, wherein the first surface is a concave surface, and the second surface is a convex surface; sequentially performing a medium grinding process on the first surface and the second surface to obtain a medium ground first surface and a medium ground second surface, wherein the medium grinding process comprises: grinding the first surface and the second surface with a first grinding wheel, wherein the particle size number of the first grinding wheel is #12000 to #15000, and the rotation speed of the first grinding wheel is 3500rpm to 4000rpm; after the medium grinding process, sequentially performing a fine grinding process on the medium ground first surface and the medium ground second surface, wherein the fine grinding process comprises: The wafer is fixed on a work platform, wherein the second surface that has been mid-grinded faces the work platform; the first surface that has been mid-grinded is ground with a second grinding wheel to obtain a first surface that has been finely ground, wherein the grit number of the second grinding wheel is greater than the grit number of the first grinding wheel, and the rotation speed of the second grinding wheel is 2033 rpm to 2133 rpm, and the rotation speed of the work platform is 149 rpm to 199 rpm; the wafer is turned over and the wafer is re-fixed on the work platform, wherein the first surface that has been finely ground faces the work platform; and the second surface that has been mid-grinded is ground with a second grinding wheel to obtain a second surface that has been finely ground, wherein the rotation speed of the work platform is 149 rpm to 199 rpm, and the rotation speed of the work platform is not a factor of the rotation speed of the second grinding wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1A to FIG. 1I is a cross-sectional schematic diagram of a wafer processing method according to an embodiment of the present invention;

[0007] Figure 2A is a flow chart of a wafer processing method according to an embodiment of the present invention;

[0008] Figure 2B is a cross-sectional schematic diagram of a wafer according to an embodiment of the present invention;

[0009] Figure 2C is a cross-sectional schematic diagram of a wafer according to an embodiment of the present invention;

[0010] Figure 3 is a curvature line graph of wafer processing methods according to some embodiments of the present invention and some comparative examples;

[0011] Figure 4 It is a curvature line graph of wafer processing methods according to some embodiments of the present invention and some comparative examples.

[0012] Description of Reference Numerals

[0013] 10: chip;

[0014] 100: working platform;

[0015] S1: first surface (concave);

[0016] S1': the second surface ground during the warp;

[0017] S1”: first surface after fine grinding;

[0018] S2: second side (convex);

[0019] S2': the second surface of the warp mill;

[0020] S2”: the second side after fine grinding;

[0021] 200: grinding head;

[0022] 210: first grinding wheel;

[0023] 210a: second grinding wheel. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals are used in the drawings and the description to refer to the same or like parts.

[0025] FIG. 1A to FIG. 1I It is a cross-sectional schematic diagram of a wafer processing method according to an embodiment of the present invention.

[0026] Please refer to Figure 1A The wafer 10 has a first surface S1 and a second surface S2 opposite to the first surface S1. The material of the wafer 10 includes, for example, silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), indium antimonide (InSb), gallium nitride (GaN), silicon carbide (SiC) or zinc selenide (ZnSe).

[0027] In this embodiment, the method for manufacturing the wafer 10 includes first forming an ingot, and then slicing the ingot to obtain the wafer 10. The ingot is manufactured in a high temperature environment, for example. In some instances, the ingot may have residual stress due to the temperature difference at different positions during the manufacturing process. These residual stresses may cause the wafer 10 obtained after slicing the ingot to bend.

[0028] In this embodiment, after the wafer 10 is obtained by slicing the wafer, the curvature (Bow) of the wafer 10 is detected. After the wafer 10 is detected, it is found that the first surface S1 is a concave surface, and the second surface S2 is a convex surface. In some embodiments, the wafer 10 is a silicon carbide wafer, the first surface S1 is a silicon surface, and the second surface S2 is a carbon surface, but the present invention is not limited thereto. In other embodiments, the second surface S2 is a silicon surface, and the first surface S1 is a carbon surface.

[0029] Please refer to Figures 1B to 1E , the first surface S1 and the second surface S2 are subjected to intermediate grinding process in sequence to obtain the intermediate ground first surface S1' and the intermediate ground second surface S2'. The intermediate grinding process includes grinding the first surface S1 and the second surface S2 with a first grinding wheel 210. The particle size number of the first grinding wheel 210 is #12000 to #15000 (the corresponding abrasive particle size is 140 microns to 130 microns), and the rotation speed of the first grinding wheel 210 is 3500rpm to 4000rpm. In the present embodiment, when performing the intermediate grinding process, the feed amount applied by the first grinding wheel 210 to the wafer 10 is 0.15 microns to 0.17 microns.

[0030] Please refer to Figure 1B as well as Figure 1C First, the wafer 10 is placed on the working platform 100 , wherein the second surface S2 faces the working platform 100 and the first surface S1 faces away from the working platform 100 .

[0031] The first surface S1 is ground by the first grinding wheel 210. For example, the grinding head 200 drives the first grinding wheel 210 to rotate and applies a force toward the first surface S1 to the first grinding wheel 210, thereby grinding the first surface S1 to obtain a ground first surface S1'.

[0032] In this embodiment, both the first grinding wheel 210 and the working platform 100 rotate. For example, the first grinding wheel 210 rotates in a clockwise or counterclockwise direction at a speed of 3500 rpm to 4000 rpm. The working platform 100 rotates in a clockwise or counterclockwise direction at a speed of 200 rpm to 250 rpm.

[0033] In the present embodiment, the rotation speed of the first grinding wheel 210 is 3500 rpm to 4000 rpm, and the rotation speed of the first grinding wheel 210 is related to the force (pressure) applied by the first grinding wheel 210 to the wafer 10. The smaller the pressure applied by the first grinding wheel 210 to the wafer 10, the faster the rotation speed of the first grinding wheel 210. If too much pressure is applied to the surface of the wafer 10, the rotation speed of the first grinding wheel 210 is too slow, and the curvature of the wafer 10 after grinding changes greatly, making the wafer 10 more susceptible to fatigue damage. If too little pressure is applied to the surface of the wafer 10, the rotation speed of the first grinding wheel 210 is too fast, the total thickness variation (TTV) of the wafer 10 is insufficient, making the surface of the wafer 10 not flat (the surface roughness (Ra) is too large).

[0034] In this embodiment, after the first surface S1 is ground by the first grinding wheel 210 , the thickness of the wafer 10 is reduced by tens of micrometers (eg, 20 micrometers), but the present invention is not limited thereto. The thickness of the wafer 10 to be reduced after grinding can be changed according to needs.

[0035] Please refer to Figure 1Das well as Figure 1E Then, the wafer 10 is turned over and fixed on the working platform 100 again, wherein the first surface S1 ′ after the grinding faces the working platform 100 and the second surface S2 faces away from the working platform 100 .

[0036] The second surface S2 is ground by the first grinding wheel 210. For example, the grinding head 200 drives the first grinding wheel 210 to rotate and applies a force toward the second surface S2 to the first grinding wheel 210, thereby grinding the second surface S2 to obtain the ground second surface S2'.

[0037] In this embodiment, both the first grinding wheel 210 and the working platform 100 rotate. For example, the first grinding wheel 210 rotates in a clockwise or counterclockwise direction at a speed of 3500 rpm to 4000 rpm. The working platform 100 rotates in a clockwise or counterclockwise direction at a speed of 200 rpm to 250 rpm.

[0038] In this embodiment, after grinding the second surface S2 with the first grinding wheel 210, the thickness of the wafer 10 is reduced by tens of micrometers (eg, 20 micrometers), but the present invention is not limited thereto. The thickness of the wafer 10 to be reduced after grinding can be changed according to needs.

[0039] Please refer to FIG. 1E to FIG. 1I After the intermediate grinding process, the intermediate ground first surface S1' and the intermediate ground second surface S2' are sequentially subjected to a fine grinding process to obtain a finely ground first surface S1" and a finely ground second surface S2". The fine grinding process includes grinding the intermediate ground first surface S1' and the intermediate ground second surface S2' with a second grinding wheel 210a. The particle size number of the second grinding wheel 210a is #27000 to #30000 (the corresponding abrasive particle size is 60 microns to 50 microns), and the rotation speed of the second grinding wheel 210a is 2033 rpm to 2133 rpm. In the present embodiment, when performing the fine grinding process, the feed amount applied by the second grinding wheel 210a to the wafer 10 is 0.1 microns to 0.12 microns.

[0040] In this embodiment, the rotation speed of the second grinding wheel 210a in the fine grinding process is lower than that of the first grinding wheel 210 in the medium grinding process, and the rotation speed of the working platform 100 in the fine grinding process is lower than that of the working platform 100 in the medium grinding process.

[0041] Please refer to Figure 1F and Figure 1G , the wafer 10 is fixed on the working platform 100 . The second surface S2 ′ after the mid-grinding faces the working platform 100 , and the first surface S1 ′ after the mid-grinding faces away from the working platform 100 .

[0042] The second grinding wheel 210a is used to grind the first surface S1' through mid-grinding to obtain a finely ground first surface S1". For example, the grinding head 200 drives the second grinding wheel 210a to rotate, and applies a force toward the first surface S1' through mid-grinding to the second grinding wheel 210a, thereby grinding the first surface S1' through mid-grinding to obtain a finely ground first surface S1".

[0043] In this embodiment, the second grinding wheel 210a and the work platform 100 both rotate. For example, the second grinding wheel 210a rotates in a clockwise or counterclockwise direction, and the rotation speed is 2033rpm to 2133rpm. The work platform 100 rotates in a clockwise or counterclockwise direction, and the rotation speed is 149rpm to 199rpm. In this embodiment, the rotation speed of the second grinding wheel 210a cannot be divided by the rotation speed of the work platform 100, that is, the rotation speed of the work platform 100 is not a factor of the rotation speed of the second grinding wheel 210a, thereby improving the fineness of the wafer 10 after grinding.

[0044] In this embodiment, after the first surface S1' is ground by the second grinding wheel 210a, the thickness of the wafer 10 is reduced by tens of micrometers (eg, 10 micrometers), but the present invention is not limited thereto. The thickness of the wafer 10 to be reduced after grinding can be changed according to needs.

[0045] Please refer to Figure 1H and Fig. 1I , flip the wafer 10 and re-fix the wafer 10 on the work platform 100, wherein the first surface S1" after fine grinding faces the work platform 100, and the second surface S2' after medium grinding faces away from the work platform 100.

[0046] The second grinding wheel 210a is used to grind the second surface S2' through mid-grinding to obtain a finely ground second surface S2". For example, the grinding head 200 drives the second grinding wheel 210a to rotate, and applies a force toward the second surface S2' through mid-grinding to the second grinding wheel 210a, thereby grinding the second surface S2' through mid-grinding to obtain a finely ground second surface S2".

[0047] In this embodiment, the second grinding wheel 210a and the work platform 100 both rotate. For example, the second grinding wheel 210a rotates in a clockwise or counterclockwise direction, and the rotation speed is 2033rpm to 2133rpm. The work platform 100 rotates in a clockwise or counterclockwise direction, and the rotation speed is 149rpm to 199rpm. In this embodiment, the rotation speed of the second grinding wheel 210a cannot be divided by the rotation speed of the work platform 100, that is, the rotation speed of the work platform 100 is not a factor of the rotation speed of the second grinding wheel 210a, thereby improving the fineness of the wafer 10 after grinding.

[0048] In this embodiment, after the second grinding wheel 210a grinds the second surface S2' through the medium grinding, the thickness of the wafer 10 is reduced by tens of micrometers (e.g., 10 micrometers), but the present invention is not limited thereto. In this embodiment, the thickness of the wafer 10 removed by the fine grinding process is less than the thickness of the wafer 10 removed by the medium grinding process.

[0049] Based on the above, since the present embodiment starts grinding from the concave surface (first surface S1) first, the change in curvature of the wafer 10 after the grinding process can be reduced, thereby reducing the problem of fatigue damage of the wafer 10 after grinding. In addition, the present embodiment starts grinding the wafer 10 with a medium grinding process, and the medium grinding process causes less processing damage to the surface of the wafer 10 than the coarse grinding process (grit number of the grinding wheel is #12000 to #15000, and the corresponding abrasive particle size is 140 microns to 130 microns), so it can reduce the difference in damage between the first surface S1 and the second surface S2 of the wafer 10 after processing, and further avoid the problem of the wafer 10 bending due to the large difference in the degree of damage between the first surface S1 and the second surface S2.

[0050] Figure 2A The present invention is a flowchart of a wafer processing method according to an embodiment of the present invention. Figure 2B It is a cross-sectional schematic diagram of a chip according to an embodiment of the present invention. Figure 2C It is a cross-sectional schematic diagram of a chip according to an embodiment of the present invention.

[0051] Please refer to Figure 2A , Figure 2B and Figure 2C , detecting the curvature of the wafers 20 and 30. In the present embodiment, the silicon surface SiS of the wafers 20 and 30 faces upward, and the carbon surface CS faces downward.

[0052] If the curvature of the wafer 20 is positive, such as Figure 2B As shown, the silicon surface SiS of the wafer 20 is a convex surface, and the carbon surface CS is a concave surface. The carbon surface CS and the silicon surface SiS are subjected to medium grinding in sequence, and then the carbon surface CS and the silicon surface SiS are subjected to fine grinding in sequence.

[0053] If the curvature of the wafer 30 is negative, such as Figure 2C As shown, the silicon surface SiS of the wafer 30 is a concave surface, and the carbon surface CS is a convex surface. The silicon surface SiS and the carbon surface CS are subjected to intermediate grinding in sequence, and then the silicon surface SiS and the carbon surface CS are subjected to fine grinding in sequence.

[0054] Based on the above, since the present embodiment starts grinding from the concave surface first, the curvature change of the wafers 20 and 30 after the grinding process can be reduced, thereby reducing the problem of fatigue damage of the wafers 20 and 30 after grinding.

[0055] Figure 3It is a curvature line graph of wafer processing methods according to some embodiments of the present invention and some comparative examples. Figure 3 The vertical axis represents the curvature of the wafer (unit: micrometer). Figure 3 The horizontal axis represents different grinding times. For example, the first grinding can refer to Figure 1B and Figure 1C For the second grinding, please refer to Figure 1D and Figure 1E For the first fine grinding, please refer to Figure 1F and Figure 1G For the second fine grinding, please refer to Figure 1H and Fig. 1I Related instructions.

[0056] Please refer to Figure 3 In the first embodiment, before the grinding process, the curvature of the wafer during the test is positive. For example, the wafer of the first embodiment can refer to Figure 2B , the wafer 20 is silicon carbide, and the carbon surface CS is a concave surface and the silicon surface SiS is a convex surface. In the first embodiment, the first intermediate grinding grinds the carbon surface CS, the second intermediate grinding grinds the silicon surface SiS, the first fine grinding grinds the intermediate-grinded carbon surface CS, and the second fine grinding grinds the intermediate-grinded silicon surface SiS.

[0057] In the second embodiment, before the grinding process, the curvature of the wafer during the test is negative. For example, the wafer of the second embodiment can refer to Figure 2C , the wafer 30 is silicon carbide, and the carbon surface CS is a convex surface and the silicon surface SiS is a concave surface. In the second embodiment, the first intermediate grinding grinds the silicon surface SiS, the second intermediate grinding grinds the carbon surface CS, the first fine grinding grinds the intermediate ground silicon surface SiS, and the second fine grinding grinds the intermediate ground carbon surface CS.

[0058] Figure 4 It is a curvature line graph of wafer processing methods according to some embodiments of the present invention and some comparative examples. Figure 4 The vertical axis represents the curvature of the wafer (unit: micrometer). Figure 4 The horizontal axis represents different grinding times. For example, the first rough grinding and the second rough grinding are respectively grinding the two sides of the wafer with a grinding wheel with a grit number of #6000 to #8000, and the first fine grinding and the second fine grinding are respectively grinding the two sides of the wafer with a grinding wheel with a grit number of #27000 to #30000.

[0059] In Comparative Example 1, before the grinding process, the curvature of the wafer during the test is positive. For example, the wafer of Comparative Example 1 can be referred to Figure 2B, the wafer 20 is silicon carbide, and the carbon surface CS is a concave surface and the silicon surface SiS is a convex surface. In Comparative Example 1, the first rough grinding grinds the carbon surface CS, the second rough grinding grinds the silicon surface SiS, the first fine grinding grinds the roughly ground carbon surface CS, and the second fine grinding grinds the roughly ground silicon surface SiS.

[0060] In the comparative example 2, before the grinding process, the curvature of the wafer during the test is positive. For example, the wafer of the comparative example 2 can refer to Figure 2B , the wafer 20 is silicon carbide, the carbon surface CS is a concave surface and the silicon surface SiS is a convex surface. In Comparative Example 2, the first rough grinding grinds the silicon surface SiS, the second rough grinding grinds the carbon surface CS, the first fine grinding grinds the roughly ground silicon surface SiS, and the second fine grinding grinds the roughly ground carbon surface CS.

[0061] By comparing Example 1, Example 2, Comparative Example 1 and Comparative Example 2, it can be seen that the use of the medium grinding process instead of the rough grinding process in Example 1 and Example 2 can reduce the change in the curvature of the wafer, thereby avoiding the problem of fatigue damage of the wafer. In some embodiments, the change in the curvature of the wafer before and after the medium grinding process is less than 30 microns. In some embodiments, the change in the curvature of the wafer before and after the fine grinding process is less than 15 microns.

[0062] In addition, if both the medium grinding process and the rough grinding process are omitted, that is, the silicon surface SiS and the carbon surface CS are directly processed by the fine grinding process, more fine grinding processes need to be repeated. Specifically, since the amount of removal by the fine grinding process is smaller, when there are the same amount of uneven areas on the wafer 20, more fine grinding processes need to be performed to remove the uneven areas on the wafer 20 compared to the medium grinding process and the rough grinding process. Based on the above, if the wafer 20 is directly processed by the fine grinding process, more silicon surface SiS and carbon surface CS need to be repeatedly processed, resulting in repeated bending of the wafer 20. Therefore, directly processing the wafer 20 by the fine grinding process will not only increase the processing time, but also make the wafer 20 more likely to break due to the increased number of repeated bendings.

Claims

1. A method for processing a wafer, comprising: detecting a curvature of a wafer, wherein the wafer has a concave surface and a convex surface relative to the concave surface; The concave surface is subjected to a first intermediate grinding process to obtain a first intermediate ground surface, wherein the first intermediate grinding process comprises: Grinding the concave surface with a first grinding wheel, wherein the grit number of the first grinding wheel is #12000 to #15000, and the rotation speed of the first grinding wheel in the first grinding process is 3500 rpm to 4000 rpm; After the first intermediate grinding process, the convex surface is subjected to a second intermediate grinding process to obtain a second intermediate ground surface, wherein the second intermediate grinding process comprises: Grinding the convex surface with the first grinding wheel, wherein the rotation speed of the first grinding wheel in the second grinding process is 3500 rpm to 4000 rpm; After the second intermediate grinding process, the intermediate ground first surface and the intermediate ground second surface are sequentially subjected to a fine grinding process to obtain a finely ground first surface and a finely ground second surface, wherein the fine grinding process comprises: The first surface and the second surface of the warp are ground by a second grinding wheel, wherein the grit number of the second grinding wheel is #27000 to #30000, and the rotation speed of the second grinding wheel is 2033 rpm to 2133 rpm.

2. The wafer processing method according to claim 1, wherein the first grinding process comprises: Fixing the wafer on a working platform, wherein the convex surface faces the working platform; Grinding the concave surface with the first grinding wheel to obtain the first surface ground in the middle, wherein the rotation speed of the working platform is 200 rpm to 250 rpm; The first grinding process comprises: Turning over the wafer, and re-fixing the wafer on the working platform, wherein the first surface that has been ground faces the working platform; as well as The convex surface is ground with the first grinding wheel to obtain the second surface ground in the middle, wherein the rotation speed of the working platform is 200 rpm to 250 rpm.

3. The wafer processing method according to claim 1, wherein the fine grinding process comprises: Fixing the wafer on a working platform, wherein the second surface that has been grinded faces the working platform; Grinding the medium-ground first surface with the second grinding wheel to obtain the finely ground first surface, wherein the rotation speed of the working platform is 149 rpm to 199 rpm; Turning over the wafer and re-fixing the wafer on the working platform, wherein the finely ground first surface faces the working platform; as well as The medium-ground second surface is ground with the second grinding wheel to obtain the fine-ground second surface, wherein the rotation speed of the working platform is 149 rpm to 199 rpm. 4 . The wafer processing method according to claim 3 , wherein the rotation speed of the work platform is not a factor of the rotation speed of the second grinding wheel. 5 . The wafer processing method according to claim 1 , wherein the wafer is a silicon carbide wafer, the concave surface is a silicon surface, and the convex surface is a carbon surface. 6 . The wafer processing method according to claim 1 , wherein the wafer is a silicon carbide wafer, the convex surface is a silicon surface, and the concave surface is a carbon surface. 7 . The wafer processing method according to claim 1 , wherein when performing the first intermediate grinding process and the second intermediate grinding process, the feed amount applied by the first grinding wheel to the wafer is 0.15 μm to 0.17 μm. 8 . The wafer processing method according to claim 1 , wherein when performing the fine grinding process, the feed amount applied by the second grinding wheel to the wafer is 0.1 μm to 0.12 μm. 9 . The wafer processing method according to claim 1 , wherein a change in the curvature of the wafer before and after performing the first intermediate grinding process and the second intermediate grinding process is less than 30 μm.

10. The wafer processing method according to claim 1, wherein a change in the curvature of the wafer before and after the fine grinding process is less than 15 microns.

11. A method for processing a wafer, comprising: detecting a curvature of a wafer, wherein the wafer has a concave surface and a convex surface relative to the concave surface; The concave surface is subjected to a first intermediate grinding process to obtain a first intermediate ground surface, wherein the first intermediate grinding process comprises: Grinding the concave surface with a first grinding wheel, wherein the grit number of the first grinding wheel is #12000 to #15000, and the rotation speed of the first grinding wheel in the first grinding process is 3500 rpm to 4000 rpm; After the first intermediate grinding process, the convex surface is subjected to a second intermediate grinding process to obtain a second intermediate ground surface, wherein the second intermediate grinding process comprises: Grinding the convex surface with the first grinding wheel, wherein the rotation speed of the first grinding wheel in the second grinding process is 3500 rpm to 4000 rpm; After the second intermediate grinding process, the first surface of the intermediate grinding process and the second surface of the intermediate grinding process are sequentially subjected to a fine grinding process, wherein the fine grinding process comprises: Fixing the wafer on a working platform, wherein the second surface that has been grinded faces the working platform; Grinding the medium-ground first surface with a second grinding wheel to obtain a finely ground first surface, wherein the grit number of the second grinding wheel is greater than the grit number of the first grinding wheel, and the rotation speed of the second grinding wheel is 2033 rpm to 2133 rpm, and the rotation speed of the working platform is 149 rpm to 199 rpm; Turning over the wafer and re-fixing the wafer on the working platform, wherein the finely ground first surface faces the working platform; and The medium-ground second surface is ground with the second grinding wheel to obtain a finely ground second surface, wherein the rotation speed of the working platform is 149 rpm to 199 rpm, and the rotation speed of the working platform is not a factor of the rotation speed of the second grinding wheel.

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