Cutting processing method of double-layer silicon filter
By forming a scribe channel on the wafer substrate of the double-layer silicon filter and cutting along the scribe channel, the problem of cracking and damage during the cutting process is solved, and the yield rate is improved.
Patent Information
- Application Number
- CN202411782031.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-05
- Publication Date
- 2025-04-18
AI Technical Summary
In the cutting and processing methods of existing double-layer silicon filters, cracking and damage can easily occur at the wafer cutting, resulting in a decrease in yield.
Cracking and damage affecting device performance is avoided by forming scribe channels for cutting on the upper and lower backs of the double-layer silicon wafer substrate and cutting along the scribe channels during cutting.
It effectively avoids the impact of cracking and damage during cutting process on device performance and improves the yield rate of the double-layer silicon filter.
Smart Images
Figure CN119853637A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of wafer processing, and in particular to a cutting processing method for a double-layer silicon filter. Background Art
[0002] When cutting double-layer silicon filters, there are two processing methods in the prior art: laser cutting and mechanical cutting in coordination, or only mechanical cutting. Among them, the laser cutting and mechanical cutting in coordination method is complicated, inefficient, and has a high production cost. As for the mechanical cutting method alone, it is easy to cause chipping and damage at the cutting point of the wafer during cutting, and the yield rate decreases. Summary of the invention
[0003] 1. Technical issues to be resolved The invention provides a cutting processing method for a double-layer silicon filter, which is used to solve the problem that the existing cutting processing method for the double-layer silicon filter causes cracking and damage at the cutting position due to cutting and slicing, thereby causing a decrease in the yield rate.
[0004] (II) Technical solution The present invention provides a method for processing a double-layer silicon filter, comprising a double-layer silicon wafer substrate preparation step and a device cutting step. The double-layer silicon wafer substrate preparation step includes providing a double-layer silicon wafer substrate, the double-layer silicon wafer substrate includes an upper wafer and a lower wafer, the upper wafer includes an upper back side, an upper silicon substrate and an upper bonding surface, the lower wafer includes a lower back side, a lower silicon substrate and a lower bonding surface, wherein the upper back side, the upper bonding surface, the lower back side and the lower bonding surface are formed by respectively depositing metal on two surfaces of the upper silicon substrate and the lower silicon substrate, the upper back side includes a metal layer formed at a step on the upper back side. a scribe line for cutting, the upper back side step is a portion on the upper back side for cutting to form a step of the double-layer silicon filter, the scribe line is a portion on the upper back side where no metal deposition is performed, the upper bonding surface and the lower bonding surface respectively include a bonding area and a non-bonding area, wherein metal deposition is performed only on the bonding areas of the upper bonding surface and the lower bonding surface, and the double-layer silicon wafer substrate is bonded by the bonding area in the upper bonding surface and the bonding area in the lower bonding surface; The device cutting step includes: cutting the scribe line at the upper back side step, removing part of the upper wafer as step waste, and cutting the edges of the multiple double-layer silicon filters in the double-layer silicon wafer substrate to obtain multiple separated double-layer silicon filters.
[0005] In some embodiments, the upper silicon substrate includes a silicon groove formed at a step of the upper silicon substrate, and the non-bonding area in the upper bonding surface includes a portion corresponding to the silicon groove, wherein the step of the upper silicon substrate is a portion on the upper bonding surface side of the upper silicon substrate corresponding to the upper back side step, and the silicon groove is a groove formed on the upper silicon substrate by etching.
[0006] In some embodiments, the upper back side further includes a scribe line formed at an edge of an upper back side device, wherein the edge of the upper back side device is a portion on the upper back side corresponding to an edge of the plurality of double-layer silicon filters.
[0007] In some embodiments, the upper silicon substrate further includes a silicon groove formed on the upper silicon substrate at a location corresponding to an edge of the upper back device, and the non-bonding area in the upper bonding surface includes a location corresponding to the silicon groove.
[0008] In some embodiments, the depth of the silicon trench is less than 1 / 2 of the upper silicon substrate.
[0009] In some embodiments, the lower back side includes a scribe line formed at an edge of a lower back side device, wherein the edge of the lower back side device is a portion on the lower back side corresponding to an edge of the plurality of double-layer silicon filters.
[0010] In some embodiments, the device cutting step also includes cutting using a double-sided cutting method, and the double-sided cutting includes cutting with a knife along a first direction and cutting with the knife along a second direction, wherein the first direction is from the upper wafer to the lower wafer, and the second direction is from the lower wafer to the upper wafer.
[0011] In some embodiments, the device cutting step further includes cutting the lower wafer for the first time at a depth of 1 / 3 to 1 / 2 of the lower wafer.
[0012] In some embodiments, the double-sided cutting further includes first cutting the lower wafer along the second direction.
[0013] In some embodiments, the step of cutting the device comprises: Adhere the upper back surface to the UV film, and cut along the second direction at the edge of the lower back surface device; The UV film is subjected to debonding treatment, and the back of the lower layer is adhered to the UV film. Cutting is performed along the first direction at the scribe line at the step on the back side of the upper layer, the cutting depth being the thickness of the upper layer wafer, and then removing the step waste; Cutting is performed along the first direction at the edge of the lower step, the cutting depth being the remaining thickness of the lower wafer after the lower wafer is cut for the first time, and the edge of the lower step is the edge of the exposed lower wafer after the step waste is removed; and Cutting is performed along the first direction at the edge of the upper back surface device, and the cutting depth is the thickness of the upper wafer plus the remaining thickness.
[0014] (III) Beneficial effects According to the present invention, a cutting method for a double-layer silicon filter is provided, and a scribe line is formed for cutting so that the cracking damage caused by cutting at the scribe line will not affect the overall performance of the device, thereby improving the yield rate. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 is a three-dimensional diagram of a double-layer silicon filter according to an embodiment of the present invention; Figure 2 is a schematic diagram of the decomposed structure of a double-layer silicon filter according to an embodiment of the present invention; Figure 3 is a schematic structural diagram of a double-layer silicon wafer substrate according to an embodiment of the present invention; Figure 4 is a schematic structural diagram of an upper back surface and a lower back surface of a double-layer silicon wafer substrate according to an embodiment of the present invention; Figure 5 is a schematic structural diagram of an upper bonding surface and a lower bonding surface of a double-layer silicon wafer substrate according to an embodiment of the present invention; Figure 6 is a schematic structural diagram of an upper wafer of a double-layer silicon wafer substrate according to an embodiment of the present invention; Figure 7 This is one of the structural schematic diagrams of a cutting method for a double-layer silicon filter according to an embodiment of the present invention; Figure 8 This is a second structural schematic diagram of a cutting method of a double-layer silicon filter according to an embodiment of the present invention; Fig. 9 This is a third structural schematic diagram of a cutting method of a double-layer silicon filter according to an embodiment of the present invention; Fig.10 This is the fourth structural schematic diagram of the cutting process of a double-layer silicon filter according to an embodiment of the present invention.
[0016] Description of reference numerals: A: upper wafer; B: lower wafer; 2: upper back side; 3: upper silicon substrate; 41: upper bonding surface; 6: lower back side; 5: lower silicon substrate; 42: lower bonding surface; 4: bonding surface; 1: step; 7: scribe line; 21: step on the upper back side; 401: bonding area; 402: non-bonding area; 8: edge; 9: silicon groove; 28: edge of the upper back side device; 68: edge of the lower back side device; F: UV film; 428: edge of the lower bonding surface device. DETAILED DESCRIPTION
[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0018] Figure 1 is a perspective view of a double-layer silicon filter according to an embodiment of the present invention. Figure 2 Schematic diagram of the decomposed structure of a double-layer silicon filter according to an embodiment of the present invention. Figure 3 Schematic diagram of the structure of a double-layer silicon wafer substrate according to an embodiment of the present invention. Figure 4 It is a structural schematic diagram of the upper back side and the lower back side of a double-layer silicon wafer substrate according to an embodiment of the present invention. Figure 5 It is a schematic structural diagram of an upper bonding surface and a lower bonding surface of a double-layer silicon wafer substrate according to an embodiment of the present invention.
[0019] like Figures 1 to 5 , which shows the structure of a double-layer silicon filter manufactured according to the cutting and processing method of the double-layer silicon filter provided by the present invention.
[0020] like Figure 2 As shown, the double-layer silicon filter can be divided into five layers, including: upper back surface 2, upper silicon substrate 3, bonding surface 4, lower silicon substrate 5, and lower back surface 6. The upper back surface 2 and the lower back surface 6 are both grounded metal layers, and the bonding surface 4 is a metal layer. Figure 1 As shown, when a single double-layer silicon filter is placed horizontally, a pair of opposite sides thereof have steps 1 .
[0021] In the manufacturing process of double-layer silicon filter, it is necessary to cut the double-layer silicon wafer substrate as the raw material. The double-layer silicon wafer substrate is formed by using two silicon wafers as the upper and lower layers of substrate materials, depositing metal on the surface, and then stacking the two wafers by bonding. When manufacturing double-layer silicon filter, the double-layer silicon wafer substrate is divided into device sizes by cutting, thereby forming a large number of double-layer silicon filter devices, whose morphology is as follows: Figure 1In the process of cutting the double-layer silicon filter, due to the presence of steps, the upper wafer needs to be cut from the step to remove part of the upper wafer as step waste and retain the lower wafer, and then the double-layer silicon wafer substrate is divided into single double-layer silicon filter devices along the edge of the double-layer silicon filter. In the prior art, when cutting the double-layer silicon wafer substrate, it is easy to cause chipping and damage at the cutting position of the wafer, such as Figure 2 As shown, when chipping damage occurs on the upper layer back side 2 or the lower layer back side 6, the appearance of the device is easily damaged. When chipping damage occurs on the bonding surface 4, the performance of the device is easily damaged.
[0022] The invention provides a cutting method for a double-layer silicon filter. The method comprises a double-layer silicon wafer substrate preparation step and a device cutting step.
[0023] The double-layer silicon wafer substrate preparation step includes providing a double-layer silicon wafer substrate as follows: like Figure 3 As shown, the double-layer silicon wafer substrate includes an upper wafer A and a lower wafer B, the upper wafer A includes an upper back surface 2, an upper silicon substrate 3 and an upper bonding surface 41, and the lower wafer B includes a lower back surface 6, a lower silicon substrate 5 and a lower bonding surface 42, wherein the upper back surface 2, the upper bonding surface 41, the lower back surface 6 and the lower bonding surface 42 are formed by respectively depositing metal on the two surfaces of the upper silicon substrate 3 and the lower silicon substrate 5, and the upper bonding surface 41 and the lower bonding surface 42 are bonded to form the bonding surface 4 in the double-layer silicon filter (refer to Figure 2 ).
[0024] In addition, if Figure 4 As shown, the upper back side 2 includes a scribe line 7 for cutting formed at the upper back side step 21. The upper back side step 21 is a portion on the upper back side 2 for cutting to form a step of a double-layer silicon filter. The scribe line 7 is a portion on the upper back side 2 where no metal deposition is performed. That is, when metal deposition is performed on the upper wafer A to form the upper back side 2, a distance for cutting the step is reserved without metal deposition, that is, the scribe line 7 is reserved. Therefore, when cutting is performed at the scribe line 7, even if cracks occur, it will not affect the metal portion of the upper back side, and thus will not affect the appearance performance of the double-layer silicon filter.
[0025] like Figure 5 As shown, the upper bonding surface 41 and the lower bonding surface 42 respectively include a bonding area 401 and a non-bonding area 402, wherein metal deposition is performed only in the bonding area 401 of the upper bonding surface 41 and the lower bonding surface 42, and no metal deposition is performed in the non-bonding area. The double-layer silicon wafer substrate is formed by bonding the bonding area 401 in the upper bonding surface 41 and the bonding area 401 in the lower bonding surface 42.
[0026] The device cutting step in the double-layer silicon filter cutting processing method of the present invention includes: cutting the scribe line 7 at the step 21 on the upper back side, removing part of the upper wafer as step waste, and cutting the edges 8 of the multiple double-layer silicon filters in the double-layer silicon wafer substrate to obtain multiple separated double-layer silicon filters. The edges 8 of the multiple double-layer silicon filters refer to the edge of the lower wafer on the side where the step is formed in the double-layer silicon filter, and the edges of the upper wafer and the lower wafer on the side where the step is not formed.
[0027] In an optional embodiment, if Figure 4 As shown, the upper back side 2 also includes a dicing lane 7 formed at an edge 28 of the upper back side device, wherein the edge 28 of the upper back side device is a portion on the upper back side 2 corresponding to an edge 8 of a plurality of double-layer silicon filters, i.e., an edge of the upper back side on a side of the double-layer silicon filter where no step is formed.
[0028] Similarly, when cutting is performed at the scribe line 7 at the edge 28 of the upper back device of the upper back 2, even if cracking occurs, it will not affect the metal part of the upper back, and thus will not affect the appearance performance of the double-layer silicon filter.
[0029] In an optional embodiment, if Figure 4 As shown, the lower back side 6 includes a dicing lane 7 formed at the edge 68 of the lower back side device, wherein the edge 68 of the lower back side device is a portion on the lower back side 6 corresponding to the edge 8 of multiple double-layer silicon filters, that is, the edge of the lower back side in the double-layer silicon filter.
[0030] Similarly, when cutting is performed at the scribe line 7 on the back side of the lower layer, even if cracks occur, it will not affect the metal portion on the back side of the lower layer, and thus will not affect the appearance performance of the double-layer silicon filter.
[0031] In an alternative embodiment, Figure 6 is a schematic structural diagram of an upper wafer of a double-layer silicon wafer substrate according to an embodiment of the present invention. Figure 6As shown, the upper silicon substrate 3 includes a silicon groove 9 formed at the step of the upper silicon substrate, and the non-bonding area in the upper bonding surface 41 includes a portion corresponding to the silicon groove 9, wherein the upper silicon substrate step is a portion on the upper bonding surface 41 side of the upper silicon substrate 3 corresponding to the upper back step 21, and the silicon groove 9 is a groove formed on the upper silicon substrate 3 by etching. That is to say, in the preparation step of the double-layer silicon wafer substrate, when the upper bonding surface and the lower bonding surface are bonded, the position of the silicon groove 9 is reserved for the step of the upper silicon substrate, thereby, when the blade performs step cutting from the upper back step 21 of the upper back 2 to the upper bonding surface 41, the cutting depth reaches the silicon groove 9 to complete the cutting of the part of the upper wafer as the step waste, and compared with the situation in the prior art where the cutting depth needs to reach the upper bonding surface 41, the cracking that may be caused by cutting is avoided from occurring on the upper bonding surface 41, thereby avoiding affecting the internal performance of the device.
[0032] In an optional embodiment, the upper silicon substrate 3 further includes a layer 28 (see FIG. 2 ) formed on the upper silicon substrate 3 and at the edge of the upper back device. Figure 4 ) includes a silicon groove corresponding to a portion thereof, and the non-bonding area in the upper bonding surface 41 includes a portion corresponding to the silicon groove.
[0033] Similarly, when the blade cuts the device edge from the upper back device edge 28 of the upper back side 2 toward the upper bonding surface 41, cracks that may be caused by cutting are avoided from occurring on the upper bonding surface 41, thereby avoiding affecting the internal performance of the device.
[0034] In an optional embodiment, the depth of the silicon groove is less than 1 / 2 of the upper silicon substrate. By properly controlling the depth of the silicon groove, it is possible to avoid wafer fragmentation caused by excessive depth.
[0035] In an optional embodiment, the device cutting step further includes cutting by double-sided cutting, wherein the double-sided cutting includes cutting along a first direction and cutting along a second direction, wherein the first direction is from the upper wafer A to the lower wafer B, and the second direction is from the lower wafer B to the upper wafer A. Optionally, the double-sided cutting further includes first cutting the lower wafer B along the second direction. Optionally, the device cutting step further includes cutting the lower wafer B at a depth of 1 / 3 to 1 / 2 of the lower wafer B when the lower wafer B is cut for the first time.
[0036] The silicon groove is not etched on the lower wafer B, but a double-sided cutting method is adopted, which can appropriately reduce the production cost. The lower wafer B is first cut along the second direction, and the cutting depth is between 1 / 3 and 1 / 2 of the lower wafer B. Then, the remaining lower wafer B is cut along the first direction. Compared with cutting the lower wafer B at one time, cutting in two times can reduce the occurrence of chipping.
[0037] In an optional embodiment, the device cutting step in the cutting method of the double-layer silicon filter includes: Figure 7 FIG. 1 is a schematic diagram of a double-layer silicon filter cutting method according to an embodiment of the present invention. After preparing the double-layer silicon wafer substrate, Figure 7 As shown, the upper back surface 2 of the upper wafer A is adhered to the UV film F, and the lower back surface device edge 68 is cut along the second direction, that is, the cutting is started with the blade facing the lower back surface 6. Optionally, the cutting is performed at the scribe line at the lower back surface device edge 68 of the lower back surface 6. Optionally, the cutting is performed at the center of the scribe line. Optionally, the cutting depth is between 1 / 3 and 1 / 2 of the lower wafer B.
[0038] Figure 8 FIG. 2 is a second structural diagram of a cutting method for a double-layer silicon filter according to an embodiment of the present invention. Figure 8 As shown, the UV film F is subjected to debonding treatment, the double-layer silicon wafer substrate is removed, and the lower back surface 6 is adhered to the UV film F.
[0039] like Figure 8 As shown, cutting is performed along the first direction at the step 21 on the upper back side, the cutting depth is the thickness of the upper wafer A, and then the step waste is removed. Optionally, cutting is performed at the scribe line on the upper back side 2. Optionally, cutting is performed at the center of the scribe line. Optionally, the cutting depth is within the silicon groove 9. After the step is cut as a whole, the step waste is removed, and the lower wafer at the step is exposed.
[0040] Fig. 9 FIG3 is a third structural diagram of a cutting method for a double-layer silicon filter according to an embodiment of the present invention. Fig. 9 As shown, cutting is performed along the first direction at the edge 28 of the upper back device, and the cutting depth is the thickness of the upper wafer A plus the remaining thickness when the lower wafer B is cut for the first time. Optionally, cutting is performed at the scribe line at the edge 28 of the upper back device of the upper back 2. Optionally, cutting is performed at the center of the scribe line. Optionally, when cutting the upper wafer A, the cutting depth is within the silicon groove 9.
[0041] Fig.10 FIG4 is a fourth structural diagram of a cutting method of a double-layer silicon filter according to an embodiment of the present invention. Fig.10 As shown, cutting is performed at the edge 428 of the lower step along the first direction, and the cutting depth is the remaining thickness of the lower wafer B after the first cutting of the lower wafer B. The edge 428 of the lower bonding surface device is the edge of the exposed lower wafer B after removing the step waste.
[0042] After cutting, even if all double-layer silicon filter devices are separated, their lower back surfaces are still adhered to the UV film F. The double-layer silicon filter and the UV film are cleaned and air-dried together, and then the film is expanded to make each double-layer silicon filter evenly spread out to the surroundings, thus obtaining a single double-layer silicon filter device.
[0043] Through the above-mentioned cutting process, a double-layer silicon filter can be obtained with less cracking and damage at the edge, better appearance, and even if cracking and damage occur, it will not extend further to the device area and has little impact on the device performance, thereby improving the yield rate of the double-layer silicon filter.
[0044] In addition, in an optional embodiment, the double-layer silicon wafer substrate preparation step in the double-layer silicon filter cutting processing method also includes: etching the upper bonding surface side of the upper silicon substrate at the upper silicon substrate step and the upper back device edge, and the lower bonding surface side of the lower silicon substrate at the lower back device edge to form silicon grooves, and the non-bonding area includes the parts corresponding to these silicon grooves; the device cutting step includes: single-blade scribing along the first direction at the upper back step and removing the step waste, and then single-blade scribing along the second direction at the lower back to separate each double-layer silicon filter. Thus, the cutting process is further simplified, and due to the effect of the silicon groove, it is possible to avoid cracking on the bonding surface due to cutting, thereby avoiding affecting the internal performance of the device, thereby improving the yield rate of the double-layer silicon filter.
[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A cutting method for a double-layer silicon filter, characterized in that: Including double-layer silicon wafer substrate preparation steps and device cutting steps, The double-layer silicon wafer substrate preparation step comprises: providing a double-layer silicon wafer substrate, the double-layer silicon wafer substrate comprising an upper wafer and a lower wafer, the upper wafer comprising an upper back side, an upper silicon substrate and an upper bonding surface, the lower wafer comprising a lower back side, a lower silicon substrate and a lower bonding surface, wherein the upper back side, the upper bonding surface, the lower back side and the lower bonding surface are formed by respectively depositing metal on two surfaces of the upper silicon substrate and the lower silicon substrate, the upper back side comprises a metal layer formed at a step on the upper back side The upper back side step is a portion on the upper back side for cutting to form a step of the double-layer silicon filter, the scribe line is a portion on the upper back side where no metal deposition is performed, the upper bonding surface and the lower bonding surface respectively include a bonding area and a non-bonding area, wherein metal deposition is performed only on the bonding areas of the upper bonding surface and the lower bonding surface, and the double-layer silicon wafer substrate is bonded by the bonding area in the upper bonding surface and the bonding area in the lower bonding surface; The device cutting step includes: cutting the scribe line at the upper back side step, removing part of the upper wafer as step waste, and cutting the edges of the multiple double-layer silicon filters in the double-layer silicon wafer substrate to obtain multiple separated double-layer silicon filters.
2. The cutting method of the double-layer silicon filter according to claim 1, characterized in that: The upper silicon substrate includes a silicon groove formed at a step of the upper silicon substrate, and the non-bonding area in the upper bonding surface includes a portion corresponding to the silicon groove, wherein the step of the upper silicon substrate is a portion on the upper bonding surface side of the upper silicon substrate corresponding to the upper back side step, and the silicon groove is a groove formed on the upper silicon substrate by etching.
3. The cutting method of the double-layer silicon filter according to claim 1 or 2, characterized in that: The upper back side also includes a scribe line formed at an edge of an upper back side device, wherein the edge of the upper back side device is a portion on the upper back side corresponding to edges of the plurality of double-layer silicon filters.
4. The cutting method of the double-layer silicon filter according to claim 3, characterized in that: The upper silicon substrate further comprises a silicon groove formed on the upper silicon substrate at a position corresponding to an edge of the upper back device, and the non-bonding area in the upper bonding surface comprises a position corresponding to the silicon groove.
5. The cutting method of the double-layer silicon filter according to claim 2 or 4, characterized in that: The depth of the silicon trench is less than 1 / 2 of the upper silicon substrate.
6. The cutting method of the double-layer silicon filter according to claim 5, characterized in that: The lower back side includes a scribe line formed at an edge of a lower back side device, wherein the edge of the lower back side device is a portion on the lower back side corresponding to edges of the plurality of double-layer silicon filters.
7. The cutting method of the double-layer silicon filter according to claim 1 or 6, characterized in that: The device cutting step also includes cutting by double-sided cutting, wherein the double-sided cutting includes cutting along a first direction and the knife cutting along a second direction, wherein the first direction is from the upper wafer toward the lower wafer, and the second direction is from the lower wafer toward the upper wafer.
8. The cutting method of the double-layer silicon filter according to claim 7, characterized in that: When the lower wafer is cut for the first time, the cutting depth is 1 / 3 to 1 / 2 of the lower wafer.
9. The cutting method of the double-layer silicon filter according to claim 8, characterized in that: The double-sided cutting further comprises first cutting the lower wafer along the second direction.
10. The cutting method of the double-layer silicon filter according to claim 9, characterized in that: The device cutting step comprises: Adhere the upper back surface to the UV film, and cut along the second direction at the edge of the lower back surface device; The UV film is subjected to debonding treatment, and the back of the lower layer is adhered to the UV film. Cutting is performed along the first direction at the scribe line at the step on the back side of the upper layer, the cutting depth being the thickness of the upper layer wafer, and then removing the step waste; Cutting is performed along the first direction at the edge of the lower step, the cutting depth being the remaining thickness of the lower wafer after the lower wafer is cut for the first time, and the edge of the lower step is the edge of the exposed lower wafer after the step waste is removed; and Cutting is performed along the first direction at the edge of the upper back surface device, and the cutting depth is the thickness of the upper wafer plus the remaining thickness.