Wafer double-side grinding device and method using profiled grinding wheel

Abstract

The application provides a wafer double-side grinding device and method using a special-shaped grinding wheel. The device comprises: a carrier ring for loading and positioning a wafer; a driving assembly connected with the carrier ring for driving the carrier ring to rotate; a first static pressure plate arranged on one side of the carrier ring, the first static pressure plate being provided with air holes and water holes, the air holes being used for adsorbing and fixing the wafer when the wafer is positioned on the carrier ring; a second static pressure plate arranged on the other side of the carrier ring, the second static pressure plate also being provided with air holes and water holes, the air holes and water holes on the first static pressure plate and the second static pressure plate being used for spraying water and air on the wafer at the same time when the wafer is ground; and two elliptical grinding wheels symmetrically arranged on two sides of the wafer, the two elliptical grinding wheels being used for rotating in different directions to grind the wafer, wherein the minor axis of the elliptical grinding wheel passes through the center of the wafer, and the major axis of the elliptical grinding wheel covers the end face of the wafer. The device can disperse periodic stress and solve the problem of concentric ring lines.

Description

Technical Field

[0001] This invention relates to the field of wafer grinding, and in particular to a wafer double-sided grinding apparatus and method using irregularly shaped grinding wheels. Background Technology

[0002] Double-sided grinding (DDG) process relies on pairs of diamond grinding wheels to simultaneously grind and thin both sides of the wafer. It can remove the cutting damage layer on both sides at one time and simultaneously adjust the thickness on both sides of the wafer. It has the advantages of high processing efficiency, simultaneous removal on both sides, and controllable cost, and has now become an indispensable core process in silicon wafer manufacturing.

[0003] Existing DDG equipment generally adopts a circular, equal-diameter concentric grinding wheel structure. The geometric centers of the two grinding wheels are completely coincident with the rotation center of the equipment spindle, and the outer diameter of the grinding wheels is the same. The wafer is placed in a planetary gear carrier and simultaneously completes its rotation and revolution under the drive of the central gear and internal gear ring. The high-speed rotation of the concentric circular grinding wheels completes the removal of material on both sides. Although this traditional concentric, equal-diameter grinding wheel structure can achieve basic double-sided grinding and thinning, it has revealed several inherent defects that are difficult to avoid during long-term mass production.

[0004] The periodic overlap of grinding paths easily leads to concentric ring marks (C Mark) defects on the wafer surface. Because the grinding wheel and spindle are perfectly concentric, the grinding path of any diamond abrasive grain on the wheel is a concentric circle centered on the wafer's center. All the grinding paths of the abrasive grains continuously overlap in the same radial annular region of the wafer, causing periodic concentration of radial cutting stress and forming visible concentric ring marks on the wafer surface. These ring defects cause excessive deviations in the wafer's nanoscale topography, and subsequent chemical mechanical polishing (CMP) processes cannot completely eliminate the mark, directly leading to focus shift and poor pattern transfer during photolithography, significantly reducing chip yield. Summary of the Invention

[0005] In view of the shortcomings of the above-mentioned related technologies, the purpose of this invention is to provide a wafer double-sided grinding device and method using irregularly shaped grinding wheels to solve the problem of concentric ring patterns in the related technologies.

[0006] To achieve the above and other related objectives, the present invention provides a wafer double-sided grinding apparatus employing a shaped grinding wheel, comprising:

[0007] Carrier rings are used to load and position wafers;

[0008] A drive component, connected to the carrier ring, is used to drive the carrier ring to rotate;

[0009] A first static pressure plate is disposed on one side of the carrier ring. The first static pressure plate is provided with air holes and water holes. The air holes can be used for adsorption and fixation when the wafer is positioned on the carrier ring.

[0010] The second static pressure plate is located on the other side of the carrier ring. The second static pressure plate is also provided with air holes and water holes. The air holes and water holes on the first static pressure plate and the second static pressure plate can be used to spray water and blow air onto the wafer at the same time during the grinding of the wafer.

[0011] Two elliptical grinding wheels are symmetrically arranged on both sides of the wafer. The two elliptical grinding wheels are used to rotate in opposite directions to grind the wafer. The minor axis of the elliptical grinding wheel passes through the center of the wafer, and the major axis of the elliptical grinding wheel covers the end face of the wafer.

[0012] Optionally, the minor axis of the elliptical grinding wheel is equal to half the radius of the wafer, and the major axis of the elliptical grinding wheel is equal to the minor axis of the elliptical grinding wheel plus the radius of the wafer.

[0013] Optionally, the drive assembly includes a drive member, a drive gear, and a gear ring. The gear ring is disposed on one side of the carrier ring, the drive gear is connected to the drive member, and the drive gear meshes with the gear ring.

[0014] Optionally, a carrier ring plate is provided on the inner side of the carrier ring, the carrier ring plate is used to fix the wafer, and a limiting member is provided on the carrier ring, the limiting member is used to position the wafer.

[0015] A method for double-sided wafer polishing using the above-mentioned wafer double-sided polishing apparatus with irregularly shaped grinding wheels, the method comprising: clamping the wafer in a carrier ring and placing the wafer between two symmetrically arranged elliptical grinding wheels;

[0016] A drive assembly is used to drive the carrier ring to rotate, so that the wafer rotates at a predetermined speed.

[0017] Two elliptical grinding wheels are driven to rotate at a predetermined speed, wherein the speed of the elliptical grinding wheels is greater than the speed of the wafer, the two elliptical grinding wheels rotate in opposite directions, the minor axis of the elliptical grinding wheels passes through the center of the wafer, and the major axis of the elliptical grinding wheels covers the end face of the wafer.

[0018] Simultaneously, water and air are sprayed onto the wafer through the water holes and air holes on the first and second static pressure plates.

[0019] The wafer is coarsely ground by driving two elliptical grinding wheels at a predetermined feed rate.

[0020] After rough grinding, reduce the feed speed of the two elliptical grinding wheels to perform intermediate grinding on the wafer;

[0021] After intermediate grinding is completed, the feed speed of the two elliptical grinding wheels is further reduced to perform fine grinding on the wafer;

[0022] After fine grinding, the wafer is smoothed while keeping the rotation speed of the two elliptical grinding wheels constant, and then the two elliptical grinding wheels are retracted synchronously.

[0023] Optionally, the rotational speed of the two elliptical grinding wheels is 3000-6000 rpm.

[0024] Optionally, the intermediate grinding steps are as follows: intermediate grinding first stage: the rotation speed remains unchanged, and the feed speed is reduced to a predetermined speed; intermediate grinding second stage: when the amount removed reaches a preset value, the feed speed is reduced again to perform intermediate grinding on the wafer.

[0025] Optionally, the feed rate for the coarse grinding is 200-350 μm / min, the feed rate for the first stage of the intermediate grinding is 80-100 μm / min, the feed rate for the second stage of the intermediate grinding is 60-80 μm / min, and the feed rate for the fine grinding is 30-40 μm / min.

[0026] Optionally, the finishing step is as follows: the two elliptical grinding wheels stop feeding, the elliptical grinding wheels maintain a constant rotation speed and remain idle, and the wafer continues to rotate for 5 seconds.

[0027] Optionally, before using the elliptical grinding wheel, the end faces of the elliptical grinding wheels are first dressed, and after dressing, the flatness of the two elliptical grinding wheels is ≤0.5μm.

[0028] As described above, the wafer double-sided grinding apparatus and method using irregularly shaped grinding wheels of the present invention have the following beneficial effects: by using the above-mentioned apparatus, the wafer and the elliptical grinding wheel rotate at different speeds, continuously generating non-repeating non-periodic trajectories, avoiding the superposition of periodic stress. Since the non-periodic disordered trajectory disperses the periodic stress, the problem of poor nano-morphology at the center and edge of the wafer is fundamentally solved. Attached Figure Description

[0029] Figure 1 The image shown is a front view of the double-sided grinding device in an embodiment of the present invention.

[0030] Figure 2 The image shown is a side view of the double-sided grinding device in an embodiment of the present invention.

[0031] Figure 3 The diagram shows the dimensions of the elliptical grinding wheel and the wafer in an embodiment of the present invention.

[0032] Figure 4 The diagram shown is a schematic representation of each grinding stage in an embodiment of the present invention.

[0033] Figure 5 The diagram shows the trajectory of an elliptical grinding wheel in an embodiment of the present invention.

[0034] Figure 6 The diagram shown is a schematic representation of an elliptical grinding wheel in an embodiment of the present invention.

[0035] Component designation explanation

[0036] 1. Carrier ring; 2. First static pressure plate; 3. Second static pressure plate; 4. Elliptical grinding wheel; 5. Wafer; 6. Limiting component; 7. Driving component; 8. Driving gear; 9. Gear ring. Detailed Implementation

[0037] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0039] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for the device in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The phrase “between” as used herein includes both endpoint values.

[0040] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0041] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0042] like Figures 1 to 5As shown, this embodiment provides a wafer double-sided grinding apparatus using irregularly shaped grinding wheels. The apparatus includes a carrier ring 1, a drive assembly, a first static pressure plate 2, a second static pressure plate 3, and two elliptical grinding wheels 4. It should be noted that the carrier ring 1, drive assembly, first static pressure plate 2, second static pressure plate 3, and two elliptical grinding wheels 4 are structures found in vertical double-sided grinding and thinning machines. Their arrangement on vertical double-sided grinding and thinning machines is mature technology and will not be detailed here. This embodiment mainly describes the arrangement and operation process of the carrier ring 1, drive assembly, first static pressure plate 2, second static pressure plate 3, and two elliptical grinding wheels 4.

[0043] The carrier ring 1 is a structure for clamping the wafer 5. A carrier ring plate is provided on the inner side of the carrier ring 1, which surrounds the periphery of the wafer 5 and fixes the wafer 5 in place. The carrier ring 1 also has a limiting member 6, which can be understood as a protrusion on the carrier ring 1 that bulges towards the wafer 5. The edge of the wafer 5 has a groove that engages with the limiting member 6. When the wafer 5 is clamped onto the carrier ring 1, the limiting member 6 engages with the groove on the wafer 5 to limit its position.

[0044] The drive assembly includes a drive component 7, a drive gear 8, and a gear ring 9. The drive component 7 is mounted on a vertical double-sided grinding and thinning machine. The drive gear 8 is connected to the drive component 7. The gear ring 9 is located on one side of the carrier ring 1, and the drive gear 8 and the gear ring 9 mesh. When the drive component 7 drives the drive gear 8 to rotate, the drive gear 8 drives the carrier ring 1 to rotate through the gear ring 9, thereby causing the wafer 5 to rotate at a predetermined speed.

[0045] The first static pressure plate 2 and the second static pressure plate 3 are respectively disposed on both sides of the carrier ring 1. Both the first static pressure plate 2 and the second static pressure plate 3 are provided with air holes and water holes. The air holes can be connected to the pneumatic system for inhaling or blowing air, while the water holes can be connected to the water system for spraying water.

[0046] After wafer 5 is clamped onto carrier ring 1, the first static pressure plate 2 approaches wafer 5 and the vents on the first static pressure plate 2 begin to draw in air, thus adsorbing and fixing wafer 5. Then, the second static pressure plate 3 moves toward wafer 5 to a set position to clamp wafer 5 with the first static pressure plate 2. When grinding of wafer 5 begins, the first static pressure plate 2 and the second static pressure plate 3 release wafer 5, and the vents on the first static pressure plate 2 begin to blow air, and the vents on the second static pressure plate 3 also begin to blow air. By blowing air on both sides of wafer 5, its position can be ensured to be in the middle of the two static pressure plates. At the same time, the water holes on the two static pressure plates begin to spray water, which lubricates wafer 5 and prevents scratches on wafer 5.

[0047] A grinding spindle is located on each side of the carrier ring 1. The two grinding spindles are equipped with fixed elliptical grinding wheels 4, and are kept collinear to ensure grinding accuracy. After the two elliptical grinding wheels 4 are installed on their respective grinding spindles, they remain symmetrical. When grinding the wafer 5 begins, the two elliptical grinding wheels 4 rotate simultaneously in opposite directions. Simultaneously, the drive assembly drives the wafer 5 to rotate. Then, the two elliptical grinding wheels 4 move according to a set feed rate, sequentially completing rough grinding, medium grinding, fine grinding, and finishing of the wafer 5. It should be noted that the rotational speed of the elliptical grinding wheels 4 is greater than the rotational speed of the wafer 5.

[0048] The elliptical grinding wheel in this embodiment is cup-shaped (e.g., ...). Figure 6 The elliptical grinding wheel 4 has a raised edge. During grinding, to disperse the periodic stress of the grinding wheel, the minor axis *a* of the elliptical grinding wheel 4 is equal to half the radius *r* of the wafer 5, and the major axis *b* of the elliptical grinding wheel 4 is equal to the minor axis *a* plus the radius *r* of the wafer 5. Here, both the major and minor axes of the ellipse refer to the size of the raised edge. Since the minor axis *a* of the elliptical grinding wheel 4 is equal to half the radius *r*, the morphology of the central region can be precisely controlled, suppressing the problem of poor central protrusion. The major axis *b* of the elliptical grinding wheel 4 is equal to *a* + *r*, thus the major axis fully covers the radial area of ​​the wafer 5, uniformly removing edge material and improving edge collapse anomalies. The major and minor axes of the elliptical grinding wheel 4 can fully cover the entire area of ​​the wafer 5, achieving no missed or over-grinding issues.

[0049] This embodiment also discloses a method for using the above-described apparatus, the specific steps of which include:

[0050] To avoid affecting the flatness of wafer 5, the grinding wheel spindles are calibrated before clamping wafer 5 to ensure that they are collinear. For example, the coaxiality error of the two spindles is controlled to be ≤0.5μm to make the two elliptical grinding wheels 4 symmetrical, thereby ensuring the symmetry of double-sided grinding.

[0051] To ensure the grinding accuracy of the elliptical grinding wheel 4, the elliptical grinding wheel 4 needs to be dressed before use. First, dress the end faces of the two elliptical grinding wheels 4 separately, with a dressing amount of 2.5mm. After dressing, the flatness of the two elliptical grinding wheels 4 is ≤0.5μm.

[0052] Once the above preparations are completed, install the two elliptical grinding wheels 4 onto the corresponding grinding wheel spindles.

[0053] The wafer 5 is clamped. In this embodiment, the wafer 5 to be processed is first placed in the center of the carrier ring, and the limiting member 6 provided on the carrier ring 1 is inserted into the preset groove on the edge of the wafer 5. The circumferential rotation and radial movement of the wafer 5 relative to the carrier ring 1 are restricted by the insertion and engagement, thereby completing the initial centering of the wafer 5.

[0054] Then drive the first static pressure plate 2 to approach the wafer 5 along the wafer 5 axis, open the negative pressure passage with multiple pores arranged in the first static pressure plate 2, and form a uniform negative pressure adsorption force on the surface of the wafer 5 through the pores, so that the wafer 5 is stably attached to the end face of the first static pressure plate 2, thereby completing the pre-fixation of one side of the wafer 5.

[0055] The second static pressure plate 3 is driven to approach the wafer 5 along the axial direction of the wafer 5. The first static pressure plate 2 and the second static pressure plate 3 clamp the wafer 5 from both sides. After the clamping force reaches the preset value, the pressure is maintained to complete the final clamping and fixing of the wafer 5.

[0056] Two elliptical grinding wheels 4 are driven to rotate at a predetermined speed, wherein the rotational speed of the elliptical grinding wheels 4 is greater than that of the wafer 5. In this embodiment, the rotational speed of the elliptical grinding wheels 4 is 3000-6000 rpm, and the rotational speed of the wafer 5 is 25-35 rpm. Simultaneously, the two elliptical grinding wheels 4 rotate in opposite directions; one elliptical grinding wheel 4 rotates clockwise, and the other rotates counterclockwise. Although the two elliptical grinding wheels 4 rotate in different directions, their minor axes pass through the center of the wafer 5, and their major axes cover the end face of the wafer 5. For example, if the rotational speed of the elliptical grinding wheels 4 is 3000 rpm, and the wafer 5 rotates at a low speed of 30 rpm, the differential rotation of the wafer 5 and the elliptical grinding wheels 4 can continuously generate non-repeating, non-periodic trajectories, avoiding the superposition of periodic stresses.

[0057] When preparing to grind wafer 5, the first static pressure plate 2 and the second static pressure plate 3 release wafer 5 and simultaneously spray water and blow air from both sides of wafer 5. At this time, wafer 5 is in a fluid pad composed of water and air. Specifically, the first static pressure plate 2 and the second static pressure plate 3 move synchronously in opposite directions along the horizontal axis to form a uniform gap between the two sides of wafer 5 and the end faces of the static pressure plates; during the movement, the displacement synchronization error is maintained at ≤2μm to avoid uneven gaps that could cause wafer 5 to be squeezed and shifted from one side.

[0058] Simultaneous activation of the liquid and gas supply pathways: The liquid phase can use room-temperature deionized water, with a total flow rate of 1.5 L / min for a single static pressure plate. The liquid phase forms basic static pressure support in the gap. The gas phase uses clean, dry compressed air. The gas phase forms micro-nano bubbles in the liquid phase to enhance the buffering effect and also serves as the execution medium for attitude control. Blowing air onto wafer 5 ensures its verticality without tilting, while spraying water onto wafer 5 provides lubrication and protection, preventing scratches.

[0059] After the gas and liquid phases fill the gap together, a stable fluid support pad is formed. At this time, wafer 5 is completely separated from the rigid contact with the static pressure plate and is in a suspended free state, completely eliminating the edge stress introduced by mechanical clamping.

[0060] coarse grinding removal stage

[0061] First, the two elliptical grinding wheels 4 are rapidly fed to a preset position at a predetermined feed rate. This preset position refers to the location where the grinding wheels will grind the wafer 5. Then, rough grinding begins. In this embodiment, the feed rate for rough grinding is 200-350 μm / min. During the cutting process, cutting fluid is used to cool and lubricate the wafer 5. The flow rate of the cutting fluid is set to 2 L / min. Rough grinding can quickly remove the deep damaged layer of the slice, thus completing the thickness reduction of the main body.

[0062] For example, during rough grinding, the rotational speed of the elliptical grinding wheel 4 remains unchanged, the rough grinding feed speed is selected as 240 μm / min, the rough grinding object is the original incoming material, and after rough grinding of the original incoming material, the thickness of the wafer 5 is maintained at 910 μm.

[0063] intermediate grinding stage

[0064] Intermediate grinding can be divided into two stages. In the first stage, the rotational speed of the elliptical grinding wheel 4 remains constant, while the feed rate is reduced to a predetermined speed to grind the wafer 5. In this embodiment, the feed rate in the first stage is 80-100 μm / min. In the second stage, after the removal amount reaches a preset value, the rotational speed of the elliptical grinding wheel 4 remains constant, while the feed rate is reduced again to a predetermined speed to grind the wafer 5. In this embodiment, the feed rate in the second stage is 60-80 μm / min. Intermediate grinding can correct the uneven thickness caused by coarse grinding and smooth out surface stress.

[0065] For example, in the first stage of intermediate grinding, the feed speed of the elliptical grinding wheel 4 is reduced to 100 μm / min. Compared to rough grinding, the amount of material removed from wafer 5 is reduced in the first stage of intermediate grinding. At this time, the amount of material removed from one side of wafer 5 is 25 μm, and the total amount of material removed from both sides is 50 μm. After the amount of material removed reaches 50 μm, the second stage of intermediate grinding is carried out, and the feed speed is reduced again to 80 μm / min. The amount of material removed from one side of wafer 5 is 25 μm, and the total amount of material removed from both sides is 50 μm.

[0066] Fine grinding stage

[0067] Once the removal amount reaches the preset value, the grinding process transitions from intermediate grinding to fine grinding. During this stage, the rotational speed of the elliptical grinding wheel 4 remains constant, and the feed speed is then reduced to a predetermined speed, continuing to grind the wafer 5. In this embodiment, the feed speed for fine grinding is 30-40 μm / min. The fine grinding stage improves surface roughness and releases residual stress from rough grinding by slightly correcting thickness deviations.

[0068] For example, after entering the fine grinding stage from the intermediate grinding stage, the feed rate is reduced to 35 μm / min, and the amount of material removed from wafer 5 is reduced again, that is, the amount of material removed from one side is 2.5 μm, and the total amount of material removed from both sides is 5 μm.

[0069] Finishing stage

[0070] After the wafer 5 is finished, the two elliptical grinding wheels 4 stop feeding and maintain a constant rotation speed while idling. The wafer 5 continues to rotate for 5 seconds. The surface burrs are removed by the slight contact between the elliptical grinding wheels 4 and the wafer 5, further reducing the depth of surface damage. Then, the elliptical grinding wheels 4 on both sides retract synchronously.

[0071] The purpose of finishing is to eliminate surface burrs, micro-cutting marks and surface micro-cracks left by fine grinding through the relative micro-cutting action between the grinding wheel and the wafer 5 without causing significant material removal or damaging the flatness and thickness accuracy of the wafer 5. This further reduces the depth of the subsurface damage layer, while homogenizing the surface grinding stress and improving the consistency of the surface nano-morphology, thus providing a better surface foundation for subsequent chemical mechanical polishing, cleaning or bonding processes.

[0072] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A wafer double-sided grinding apparatus employing an irregularly shaped grinding wheel, characterized in that, include: Carrier rings are used to load and position wafers; A drive component, connected to the carrier ring, is used to drive the carrier ring to rotate; A first static pressure plate is disposed on one side of the carrier ring. The first static pressure plate is provided with air holes and water holes. The air holes can be used for adsorption and fixation when the wafer is positioned on the carrier ring. The second static pressure plate is located on the other side of the carrier ring. The second static pressure plate is also provided with air holes and water holes. The air holes and water holes on the first static pressure plate and the second static pressure plate can be used to spray water and blow air onto the wafer at the same time during the grinding of the wafer. Two elliptical grinding wheels are symmetrically arranged on both sides of the wafer. The two elliptical grinding wheels are used to rotate in opposite directions to grind the wafer. The minor axis of the elliptical grinding wheel passes through the center of the wafer, and the major axis of the elliptical grinding wheel covers the end face of the wafer.

2. The wafer double-sided grinding apparatus using a shaped grinding wheel according to claim 1, characterized in that, The minor axis of the elliptical grinding wheel is equal to half the radius of the wafer, and the major axis of the elliptical grinding wheel is equal to the minor axis of the elliptical grinding wheel plus the radius of the wafer.

3. The wafer double-sided grinding apparatus using irregularly shaped grinding wheels according to claim 1, characterized in that, The drive assembly includes a drive element, a drive gear, and a gear ring. The gear ring is located on one side of the carrier ring. The drive gear is connected to the drive element and meshes with the gear ring.

4. The wafer double-sided grinding apparatus using a shaped grinding wheel according to claim 1, characterized in that, The carrier ring has a carrier ring plate on its inner side, which is used to fix the wafer. The carrier ring has a limiting member, which is used to position the wafer.

5. A method for double-sided wafer polishing using the wafer double-sided polishing apparatus with irregularly shaped grinding wheels as described in claim 1, characterized in that, The method includes: The wafer is clamped in a carrier ring and placed between two symmetrically arranged elliptical grinding wheels; A drive assembly is used to drive the carrier ring to rotate, so that the wafer rotates at a predetermined speed. Two elliptical grinding wheels are driven to rotate at a predetermined speed, wherein the speed of the elliptical grinding wheels is greater than the speed of the wafer, the two elliptical grinding wheels rotate in opposite directions, the minor axis of the elliptical grinding wheels passes through the center of the wafer, and the major axis of the elliptical grinding wheels covers the end face of the wafer. Simultaneously, water and air are sprayed onto the wafer through the water holes and air holes on the first and second static pressure plates. The wafer is coarsely ground by driving two elliptical grinding wheels at a predetermined feed rate. After rough grinding, reduce the feed speed of the two elliptical grinding wheels to perform intermediate grinding on the wafer; After intermediate grinding is completed, the feed speed of the two elliptical grinding wheels is further reduced to perform fine grinding on the wafer; After fine grinding, the wafer is smoothed while keeping the rotation speed of the two elliptical grinding wheels constant, and then the two elliptical grinding wheels are retracted synchronously.

6. The method according to claim 5, characterized in that: The rotational speed of the two elliptical grinding wheels is 3000-6000 rpm.

7. The method according to claim 5, characterized in that: The intermediate grinding process is as follows: Intermediate grinding stage 1: The rotation speed remains constant while the feed speed is reduced to a predetermined speed; Intermediate grinding stage 2: When the amount removed reaches a preset value, the feed speed is reduced again to perform intermediate grinding on the wafer.

8. The method according to claim 7, characterized in that: The feed rate for the coarse grinding is 200-350 μm / min, the feed rate for the first stage of the intermediate grinding is 80-100 μm / min, the feed rate for the second stage of the intermediate grinding is 60-80 μm / min, and the feed rate for the fine grinding is 30-40 μm / min.

9. The method according to claim 5, characterized in that: The finishing process is as follows: the two elliptical grinding wheels stop feeding, the elliptical grinding wheels maintain a constant rotation speed and remain idle, and the wafer continues to rotate for 5 seconds.

10. The method according to claim 5, characterized in that: Before using the elliptical grinding wheel, the end faces of the elliptical grinding wheels are first dressed. After dressing, the flatness of the two elliptical grinding wheels is ≤0.5μm.

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