Abnormal rework method for wafer backside thinning

Abstract

The abnormal reworking method for wafer back thinning provided by the present invention is used for reworking abnormal wafers whose back thinning is not completed. The abnormal reworking method comprises: providing a support sheet with the same radial size as the abnormal wafer; transferring the support sheet to the alignment workbench with the back side facing upward; detecting the center of the back side of the support sheet and pausing the wafer back thinning machine; forming a water film on the back side of the support sheet; placing the abnormal wafer with the front side facing downward on the back side of the support sheet, and making the edges of the abnormal wafer and the support sheet overlap, and the water film bonds the abnormal wafer to the support sheet; starting the wafer back thinning machine, and the conveying robot grabs the abnormal wafer and the support sheet from the back side of the abnormal wafer, and after lifting to a set height, pausing the wafer back thinning machine; peeling the support sheet from the front side of the abnormal wafer; starting the wafer back thinning machine again, and transferring the abnormal wafer to the corresponding grinding workbench. In this way, the abnormal wafer can be reworked, which helps to improve the yield of the product.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to an abnormal reworking method for wafer backside thinning. Background Art

[0002] With the development of semiconductor technology, integrated circuit technology has begun to study 5nm or even 3nm. As the feature size decreases, the number of transistors per unit area of ​​integrated circuits doubles, and the functions of integrated circuits become more powerful. When discussing how to reduce the thermal resistance of devices in integrated circuits and do a good job of heat dissipation and cooling of devices, the wafer backside thinning process was proposed.

[0003] A commonly used wafer back thinning process is the Taiko process. When the Taiko process is used to grind the back of the wafer, the edge portion of the wafer periphery is retained, and only the inner circle (i.e., the central area of ​​the back of the wafer) is ground and thinned. Currently, in the Taiko process, the wafer is coarsely ground and finely ground by two grinding wheels, Z1 and Z2. However, during the thinning process, due to alarms or failures of the wafer back thinning machine, there is a problem that the wafer cannot be transferred to the Z2 grinding wheel for fine grinding after being coarsely ground by the Z1 grinding wheel. In this case, abnormal wafers will be scrapped. How to rework abnormal wafers that have not completed back thinning needs to be solved urgently. Summary of the invention

[0004] The invention provides an abnormal rework method for wafer backside thinning, which can be used to rework abnormal wafers whose backside thinning has not been completed, thereby helping to improve product yield.

[0005] In order to achieve the above-mentioned object, the present invention provides an abnormal rework method for wafer backside thinning, which is used to rework an abnormal wafer whose backside thinning has not been completed. The abnormal rework method comprises:

[0006] Providing a support sheet, wherein the radial dimensions of the support sheet and the abnormal wafer are the same;

[0007] The support sheet is transferred to an alignment workbench of a wafer back thinning machine, and the support sheet is placed on the alignment workbench with the back side facing upwards;

[0008] The wafer back thinning machine detects the center of the back side of the support sheet, and after obtaining the position of the center, the wafer back thinning machine is paused;

[0009] forming a water film on the back side of the support sheet;

[0010] Placing the abnormal wafer with its front side facing downward on the back side of the support sheet, and making the edges of the abnormal wafer and the support sheet overlap, so that the water film bonds the abnormal wafer to the support sheet;

[0011] The wafer back thinning machine is started, and a conveying robot grabs the abnormal wafer and the supporting sheet from the back side of the abnormal wafer, and after the conveying robot is lifted to a set height, the wafer back thinning machine is paused;

[0012] peeling the support sheet off the front side of the abnormal wafer;

[0013] The wafer backside thinning machine is started again, and the abnormal wafer is transferred to a corresponding grinding workbench to continue the backside thinning process for the abnormal wafer.

[0014] Optionally, the method for forming a water film on the back side of the support sheet includes: soaking a dust-free cloth with water; and squeezing the dust-free cloth so that a portion of water on the dust-free cloth drips onto the back side of the support sheet to form the water film.

[0015] Optionally, the edges of the support sheet and the abnormal wafer both have notches, and the notches of the support sheet and the abnormal wafer have the same size; the method of placing the abnormal wafer face down on the back side of the support sheet includes: making the notch of the abnormal wafer overlap with the notch of the support sheet.

[0016] Optionally, the method of peeling the support sheet from the front side of the abnormal wafer includes: pushing the support sheet out of the front side of the abnormal wafer within a plane where the back side of the support sheet is located.

[0017] Optionally, the method for peeling the support sheet from the front side of the abnormal wafer includes: blowing compressed air from the sides of the support sheet and the abnormal wafer, wherein the compressed air blows out at least a portion of the water film from between the support sheet and the abnormal wafer, thereby separating the support sheet and the abnormal wafer.

[0018] Optionally, the process used for thinning the back side of the wafer is a Taiko process, and the Taiko process includes: rough grinding the central area of ​​the back side of the wafer and fine grinding the central area of ​​the back side of the wafer;

[0019] In the Taiko process, a wafer for which backside thinning is not completed due to anomalies is an abnormal wafer.

[0020] Optionally, when the abnormal wafer has completed the rough grinding and has not yet undergone the fine grinding, the method of transferring the abnormal wafer to the corresponding grinding workbench includes: the conveying robot transfers the abnormal wafer to the transfer workbench; the transfer workbench sends the abnormal wafer to the fine grinding workbench.

[0021] Optionally, when the abnormal wafer has not completed the rough grinding, the method of transferring the abnormal wafer to the corresponding grinding workbench includes: the conveying robot transfers the abnormal wafer to the transfer workbench; the transfer workbench sends the abnormal wafer to the rough grinding workbench.

[0022] Optionally, the supporting sheet is a supporting wafer, a glass plate or a resin plate.

[0023] Optionally, the back side of the support sheet is covered with a protective film, and the water film is formed on the protective film.

[0024] In the abnormal rework method for wafer back thinning of the present invention, a support sheet having the same radial size as the abnormal wafer is provided, and then the center of the back of the support sheet is detected (i.e., the back of the support sheet is geometrically aligned), and then the back of the support sheet is bonded to the front of the abnormal wafer using a water film, and the edges of the abnormal wafer and the support sheet are made to coincide, so that the back of the abnormal wafer can be geometrically aligned, and then the support sheet is peeled off from the front of the abnormal wafer, and the back thinning process of the abnormal wafer can continue. That is to say, in the abnormal rework method for wafer back thinning of the present invention, a support sheet is used to replace the abnormal wafer to achieve back geometric alignment, and the abnormal wafer and the support sheet bonded by the water film are easy to separate and will not contaminate the abnormal wafer, so that the rework of the abnormal wafer whose back thinning has not been completed can be achieved, which helps to reduce scrap and improve product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart of thinning the back side of a wafer using the Taiko process.

[0026] Figure 2 A schematic cross-sectional view of an abnormal wafer.

[0027] Figure 3 The figure is a flow chart of an abnormal rework method for wafer backside thinning according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The abnormal rework method for wafer backside thinning proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0029] Figure 1 FIG. 1 is a flow chart of thinning the back side of a wafer using the Taiko process. Figure 1As shown, the normal process of thinning the back side of a wafer using the Taiko process includes: sending the wafer placed in a wafer transfer box (FOUP) into a wafer back thinning machine; the wafer back thinning machine geometrically aligns the back side of the wafer to determine the center of the back side of the wafer; the wafer is sent to a rough grinding workbench, and the first grinding wheel (Z1) performs rough grinding on the central area of ​​the back side of the wafer; the wafer is sent to a fine grinding workbench, and the second grinding wheel (Z2) performs fine grinding on the central area of ​​the back side of the wafer.

[0030] During the process of backside thinning of wafers using the Taiko process, wafers that have not been completely ground (i.e., backside thinning has not been completed) may be forced to stop grinding due to alarms or failures of the wafer backside thinning machine, resulting in abnormal wafers. Figure 2 Figure 1 is a cross-sectional diagram of an abnormal wafer. Figure 2 As shown, a protruding Taiko ring 101 is formed on the back of the abnormal wafer 100 , and the back of the abnormal wafer 100 will no longer be a flat surface. Thus, the back of the abnormal wafer 100 cannot be accurately geometrically aligned, and thus the abnormal wafer 100 cannot be reworked.

[0031] In order to rework an abnormal wafer whose back side thinning has not been completed, this embodiment provides an abnormal rework method for wafer back side thinning. The abnormal rework method is used to rework an abnormal wafer whose back side thinning has not been completed.

[0032] The process used for thinning the back side of the wafer may be a Taiko process. The Taiko process may include: rough grinding the central area of ​​the back side of the wafer and fine grinding the central area of ​​the back side of the wafer. In the Taiko process, a wafer that has not completed back side thinning due to an abnormality is an abnormal wafer. The back side of the abnormal wafer is uneven, and it is not easy to achieve geometric centering of the back side. However, it is not limited to this, and the abnormal wafer may also be produced by abnormal cessation of other grinding processes.

[0033] Figure 3 FIG. 1 is a flow chart of an abnormal rework method for wafer backside thinning according to an embodiment of the present invention. Figure 3 As shown, the abnormal rework method includes:

[0034] S1, providing a support sheet, wherein the radial dimensions of the support sheet and the abnormal wafer are the same;

[0035] S2, transferring the support sheet to an alignment workbench of a wafer back thinning machine, and placing the support sheet on the alignment workbench with the back side facing upward;

[0036] S3, the wafer back thinning machine detects the center of the back side of the support sheet, and after obtaining the position of the center, pauses the wafer back thinning machine;

[0037] S4, forming a water film on the back side of the support sheet;

[0038] S5, placing the abnormal wafer with its front side facing downward on the back side of the support sheet, and making the edges of the abnormal wafer and the support sheet overlap, and the water film bonds the abnormal wafer to the support sheet;

[0039] S6, starting the wafer back thinning machine, and the conveying robot grabs the abnormal wafer and the supporting sheet from the back side of the abnormal wafer, and after the conveying robot is lifted to a set height, pausing the wafer back thinning machine;

[0040] S7, peeling the support sheet off the front side of the abnormal wafer;

[0041] S8, restarting the wafer backside thinning machine, transferring the abnormal wafer to a corresponding grinding workbench, and continuing to perform backside thinning on the abnormal wafer.

[0042] Specifically, in this embodiment, the support sheet can be a support wafer, a glass plate or a resin plate, etc., and the radial dimension of the support sheet is the same as the radial dimension of the abnormal wafer, so that the support sheet can be used to replace the abnormal wafer to achieve back geometric alignment. The back side of the support sheet is a flat surface, so that the back side of the support sheet can be geometrically aligned later. The edges of the support sheet and the abnormal wafer can both have a notch, and the notch size of the support sheet and the abnormal wafer is the same. In order to enhance the rigidity of the support sheet, the thickness of the support sheet can be greater than the thickness of the abnormal wafer.

[0043] In this embodiment, the reworking of the abnormal wafer by using the wafer back thinning machine can be controlled by a reworking program set in the wafer back thinning machine. However, it is not limited thereto, and the wafer back thinning machine can be manually controlled to rework the abnormal wafer.

[0044] In this embodiment, in step S2, the method of transferring the support sheet to the alignment workbench of the wafer back thinning machine may include: placing the support sheet in an empty wafer transfer box; clicking to run the rework program in the wafer back thinning machine, transferring the support sheet from the wafer transfer box to the alignment workbench, and placing the support sheet on the alignment workbench with the back side facing up.

[0045] Execute step S3, the back thinning machine detects the center of the back of the support sheet (that is, the back thinning machine performs geometric centering on the back of the support sheet), and after obtaining the position of the center of the back of the support sheet, the back thinning machine is paused. It should be noted that, in one embodiment, after the back thinning machine starts to detect the center of the back of the support sheet, as long as the pause button is pressed, the back thinning machine will stop running after detecting the position of the center of the back of the support sheet.

[0046] Execute step S4 to form a water film on the back side of the support sheet. In this embodiment, the method for forming a water film on the back side of the support sheet may include: soaking the dust-free cloth with water; opening a baffle of the crystal back thinning machine, extending the dust-free cloth to the top of the back side of the support sheet, squeezing the dust-free cloth so that part of the water on the dust-free cloth drips on the back side of the support sheet to form the water film. In order to improve the adhesion of the water film, the water dripped from the dust-free cloth can be evenly distributed on the back side of the support sheet. However, it is not limited to this, and a dropper can be used to evenly drip water on the back side of the support sheet to form a water film.

[0047] Step S5 is executed to place the abnormal wafer face-down on the back side of the support sheet, and the edges of the abnormal wafer and the support sheet are overlapped, and the water film bonds the abnormal wafer to the support sheet. It should be noted that the water film has surface tension, and when the front side of the abnormal wafer is placed on the water film, the surface tension of the water film causes the abnormal wafer to bond to the support sheet.

[0048] In order to improve the centering accuracy of the abnormal wafer, in this embodiment, the method of placing the abnormal wafer face down on the back side of the support sheet may further include: making the notch of the abnormal wafer overlap with the notch of the support sheet.

[0049] In order to enhance the bonding force between the abnormal wafer and the support sheet, in this embodiment, after the abnormal wafer is placed on the support sheet, the abnormal wafer may be pressed downward to reduce the gap between the abnormal wafer and the support sheet.

[0050] In this embodiment, a pattern or device may be formed on the front side of the abnormal wafer. In order to prevent particles on the back side of the support sheet from damaging the abnormal wafer, a protective film may be formed on the back side of the support sheet, the protective film covers the back side of the support sheet, and the water film may be formed on the protective film. The protective film may be a photoresist film. However, it is not limited thereto, and the thickness and material of the protective film may be selected as required.

[0051] Execute step S6, start the wafer back thinning machine, and the conveying robot (of the wafer back thinning machine) grabs the abnormal wafer and the support sheet from the back of the abnormal wafer. After the conveying robot is raised to a set height, the wafer back thinning machine is paused. It should be noted that, in one embodiment, when the conveying robot starts to move to grab the abnormal wafer and the support sheet, as long as the pause button is pressed, the conveying robot will grab the abnormal wafer and the support sheet and stop before moving to the transfer workbench.

[0052] In this embodiment, the conveying robot can grab the abnormal wafer and the supporting sheet by vacuum adsorbing the back side of the abnormal wafer. After grabbing, in order to facilitate the subsequent peeling of the supporting sheet from the front side of the abnormal wafer, the conveying robot raises the abnormal wafer and the supporting sheet to a set height. It should be noted that the set height should not be too high to avoid the supporting sheet from falling from a height and breaking when separating from the abnormal wafer; the set height should not be too low to facilitate the separation of the supporting sheet and the abnormal wafer.

[0053] Execute step S7 to peel the support sheet from the front side of the abnormal wafer. In this embodiment, the method for peeling the support sheet from the front side of the abnormal wafer may include: after the conveying robot stops moving, opening a baffle of the wafer back thinning machine, pushing the support sheet out of the front side of the abnormal wafer in the plane where the back side of the support sheet is located, or in other words, pulling the support sheet out of the front side of the abnormal wafer from the horizontal direction.

[0054] It should be noted that, since the abnormal wafer is relatively thin, if the support sheet and the abnormal wafer are pried apart from the vertical direction, the abnormal wafer is easily broken under the action of the water film tension, and thus the abnormal wafer and the support sheet are separated from the horizontal direction in this embodiment. In addition, since the abnormal wafer is relatively thin and there is a Taiko ring on the back of the abnormal wafer, the adsorption of the back of the abnormal wafer by the conveying robot is not very firm (i.e., the vacuum of the abnormal wafer by the conveying robot is not complete), so when separating the support sheet and the abnormal wafer, it is necessary to separate slowly and not to move the abnormal wafer, so as to avoid the abnormal wafer falling due to the conveying robot failing to adsorb the abnormal wafer.

[0055] In other embodiments, the method for peeling the support sheet from the front of the abnormal wafer may include: blowing compressed air from the sides of the support sheet and the abnormal wafer, the compressed air at least blowing out a portion of the water film from between the support sheet and the abnormal wafer, thereby separating the support sheet and the abnormal wafer. In this way, manual separation of the abnormal wafer and the support sheet can be avoided, which helps to reduce human errors. It should be noted that the flow rate of the compressed air, the blowing area on the sides of the support sheet and the abnormal wafer, and the angle between the flow direction of the compressed air and the front of the abnormal wafer can be adjusted as needed, but it is necessary to ensure that the compressed air will not blow the abnormal wafer off the conveying robot.

[0056] After the support sheet is peeled off from the front side of the abnormal wafer, step S8 is performed to start the wafer backside thinning machine again and transfer the abnormal wafer to a corresponding grinding workbench to continue the backside thinning process on the abnormal wafer.

[0057] Specifically, when the abnormal wafer has not completed the rough grinding, the conveying robot transfers the abnormal wafer to the transfer workbench; the transfer workbench sends the abnormal wafer to the rough grinding workbench, and the first grinding wheel (Z1) in the crystal back thinning machine grinds the abnormal wafer to the set rough grinding amount; then the abnormal wafer is transferred to the fine grinding workbench, and the second grinding wheel (Z2) of the crystal back thinning machine performs fine grinding on the abnormal wafer to complete the back thinning process of the abnormal wafer. It should be noted that when the abnormal wafer has been partially rough ground and the whole rough grinding has not been completed, before reworking, it is necessary to determine the grinding amount that has been completed on the abnormal wafer, and it is necessary to set the grinding amount of the abnormal wafer by the first grinding wheel in the reworking formula (for example, the grinding amount can be adjusted by adjusting the grinding time), so that the rough grinding amount of the abnormal wafer reaches the set rough grinding amount after the first grinding wheel is reworked.

[0058] When the abnormal wafer has completed the rough grinding and has not yet been fine-ground, the conveying robot transfers the abnormal wafer to the transfer workbench; the transfer workbench sends the abnormal wafer to the fine-grinding workbench, and the second grinding wheel (Z2) in the crystal back thinning machine fine-grinds the abnormal wafer to complete the back thinning process of the abnormal wafer.

[0059] When the abnormal wafer has been partially fine-ground but not fully fine-ground, before rework, it is necessary to determine the grinding amount that has been completed for the abnormal wafer, and to set the grinding amount of the abnormal wafer by the second grinding wheel in the rework formula (for example, the grinding amount can be adjusted by adjusting the grinding time), so that the grinding amount of the abnormal wafer reaches the set grinding amount after rework by the second grinding wheel.

[0060] After the abnormal wafer is reworked, the reworked wafer can be tested to confirm whether the reworked wafer meets the process requirements.

[0061] In the abnormal rework method for thinning the back side of a wafer of the present embodiment, a support sheet having the same radial dimensions as the abnormal wafer is provided, and then the center of the back side of the support sheet (e.g., the center of a circle) is detected, and then the back side of the support sheet is bonded to the front side of the abnormal wafer using a water film, and the edges of the abnormal wafer and the support sheet are made to coincide, so that the back side of the abnormal wafer can be geometrically aligned, and then the support sheet is peeled off from the front side of the abnormal wafer, and then the back side thinning process can be continued on the abnormal wafer. That is to say, in the abnormal rework method for thinning the back side of a wafer of the present embodiment, a support sheet is used to replace the abnormal wafer to achieve back side geometric alignment, and the abnormal wafer and the support sheet bonded by the water film are easy to separate and will not contaminate the abnormal wafer, so that the abnormal wafer whose back side thinning has not been completed can be reworked, which helps to reduce scrap and improve product yield.

[0062] The above description is only a description of the preferred embodiment of the present invention, and is not any limitation on the scope of rights of the present invention. Any technical personnel in this field can make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for abnormal reworking of wafer backside thinning, used for reworking abnormal wafers whose backside thinning has not been completed, characterized in that: include: Providing a support sheet, wherein the radial dimensions of the support sheet and the abnormal wafer are the same; The support sheet is transferred to an alignment workbench of a wafer back thinning machine, and the support sheet is placed on the alignment workbench with the back side facing upwards; The wafer back thinning machine detects the center of the back side of the support sheet, and after obtaining the position of the center, the wafer back thinning machine is paused; forming a water film on the back side of the support sheet; Placing the abnormal wafer with its front side facing downward on the back side of the support sheet, and making the edges of the abnormal wafer and the support sheet overlap, so that the water film bonds the abnormal wafer to the support sheet; The wafer back thinning machine is started, and a conveying robot grabs the abnormal wafer and the supporting sheet from the back side of the abnormal wafer, and after the conveying robot is lifted to a set height, the wafer back thinning machine is paused; peeling the support sheet off the front side of the abnormal wafer; The wafer backside thinning machine is started again, and the abnormal wafer is transferred to a corresponding grinding workbench to continue the backside thinning process for the abnormal wafer.

2. The abnormal rework method according to claim 1, characterized in that: The method of forming a water film on the back side of the support sheet comprises: Soak the dust-free cloth with water; The dust-free cloth is squeezed so that the water on the dust-free cloth drips onto the back side of the supporting sheet to form the water film.

3. The abnormal rework method according to claim 1, characterized in that: The edges of the support sheet and the abnormal wafer both have notches, and the notches of the support sheet and the abnormal wafer have the same size; and the method of placing the abnormal wafer face down on the back side of the support sheet comprises: The notch of the abnormal wafer is made to coincide with the notch of the supporting sheet.

4. The abnormal rework method according to claim 1, characterized in that: The method for peeling the support sheet from the front side of the abnormal wafer comprises: The support sheet is pushed out of the front side of the abnormal wafer within the plane where the back side of the support sheet is located.

5. The abnormal rework method according to claim 1, characterized in that: The method for peeling the support sheet from the front side of the abnormal wafer comprises: Compressed air is blown from the sides of the support sheet and the abnormal wafer, and the compressed air blows at least a portion of the water film out from between the support sheet and the abnormal wafer, thereby separating the support sheet and the abnormal wafer.

6. The abnormal rework method according to claim 1, characterized in that: The process used for thinning the back side of the wafer is a Taiko process, which includes: rough grinding the central area of ​​the back side of the wafer and fine grinding the central area of ​​the back side of the wafer; In the Taiko process, a wafer for which backside thinning is not completed due to anomalies is an abnormal wafer.

7. The abnormal rework method according to claim 6, characterized in that: When the abnormal wafer has completed the rough grinding and has not yet been finely ground, the method of transferring the abnormal wafer to a corresponding grinding workbench includes: The conveying robot transfers the abnormal wafer to the transfer workbench; The transfer workbench transfers the abnormal wafer to the fine grinding workbench.

8. The abnormal rework method according to claim 6, characterized in that: When the abnormal wafer has not completed the rough grinding, the method of transferring the abnormal wafer to the corresponding grinding workbench includes: The conveying robot transfers the abnormal wafer to the transfer workbench; The transfer workbench transfers the abnormal wafer to the rough grinding workbench.

9. The abnormal rework method according to any one of claims 1 to 8, characterized in that: The supporting sheet is a supporting wafer, a glass plate or a resin plate.

10. The abnormal rework method according to any one of claims 1 to 8, characterized in that: The back side of the support sheet is covered with a protective film, and the water film is formed on the protective film.

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