Wafer thinning methods

Abstract

This invention relates to the field of semiconductor manufacturing technology, and more particularly to a wafer thinning method. The wafer thinning method includes the following steps: S1: halving the front side of the wafer; S2: applying a protective film to the front side of the wafer, the thickness of which is greater than or equal to 215 μm; S3: loading the wafer onto the grinding station of a thinning machine, where the thinning machine grinds the back side of the wafer, and the spindle speed of the thinning machine is 3500 rpm to 4500 rpm. The DBG process is used to thin ultra-thin wafers. By applying a protective film with a thickness greater than or equal to 215 μm to the front side of the halved wafer, the support effect on the wafer is improved, reducing stress release and wafer warping during the thinning process. By increasing the spindle speed of the thinning machine, the grinding force during the thinning process is increased, improving grinding efficiency, further reducing local stress, avoiding defects such as wafer breakage and fragmentation, and improving the product yield of the wafer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a wafer thinning method. Background Technology

[0002] Traditional wafer grinding and dicing processes involve sequentially applying a protective film to the front of the wafer, grinding the back of the wafer, applying another protective film to the back of the wafer, removing the protective film from the front of the wafer, and finally dicing the entire wafer. In traditional wafer grinding and dicing processes, grinding the back of the wafer to below 120µm can easily lead to problems such as cracking on the back of the wafer and its edges, and warping of the wafer after the protective film is removed.

[0003] To address these issues, a dicing before grinding (DBG) process is employed. DBG sequentially performs half-dicing on the front side of the wafer, applying a film to the front side, grinding the back side, applying another film to the back side, and peeling off the film from the front side. Half-dicing refers to cutting a certain depth on the front side of the wafer, but not completely severing it. Releasing wafer stress after half-dicing improves the problem of breakage during grinding caused by wafer stress, making it particularly suitable for processing ultra-thin wafers (thickness less than 100μm).

[0004] With the development of wafer technology, wafer circuit design is becoming increasingly complex, and the step difference between the central and edge regions of the wafer is widening. As storage capacity and the number of packaging layers increase, the required wafer thickness is also decreasing. Existing DBG processes are prone to quality defects such as breakage and fragmentation during the thinning process of ultra-thin wafers with a thickness of less than 50μm, reducing wafer yield. Summary of the Invention

[0005] The purpose of this invention is to provide a wafer thinning method to avoid quality defects such as breakage and fragmentation during the DBG process for thinning ultra-thin wafers, thereby improving the product yield of wafers.

[0006] To achieve this objective, the technical solution adopted by the present invention is as follows:

[0007] The wafer thinning method includes the following steps:

[0008] S1: Half-cut the front side of the wafer;

[0009] S2: A protective film is applied to the front side of the wafer, the thickness of which is greater than or equal to 215 μm;

[0010] S3: The wafer is fed to the grinding station of the thinning machine, the thinning machine grinds the back side of the wafer, and the spindle speed of the thinning machine is 3500rpm~4500rpm.

[0011] As an optional solution, in step S2, the protective film includes a polyolefin film and an adhesive film, wherein the polyolefin film covers and adheres to the front side of the wafer through the adhesive film.

[0012] As an optional feature, the polyolefin film has a film thickness greater than or equal to 200 μm, and the adhesive film has a film thickness greater than or equal to 15 μm.

[0013] As an optional solution, in step S3, the thinning machine sequentially performs rough grinding and fine grinding on the back side of the wafer; in the rough grinding, the spindle speed of the thinning machine is 3500rpm to 4000rpm; in the fine grinding, the spindle speed of the thinning machine is 4000rpm to 4500rpm.

[0014] As an optional option, the thinning amount of the fine grinding process accounts for 20% to 25% of the total thinning amount.

[0015] As an optional option, in the fine grinding process, the thinning machine uses 2000# to 4000# diamond grinding wheels to grind the back side of the wafer, and the axial feed speed is set to three speed ranges: 0.3um / s, 0.15um / s and 0.1um / s.

[0016] As an optional solution, in the rough grinding process, the thinning machine uses 320# to 600# diamond grinding wheels to grind the back side of the wafer, and the axial feed speed is set to three speed ranges: 3um / s, 2um / s and 1.5um / s.

[0017] As an optional solution, in step S3, before grinding the wafer, the thinning machine fixes the wafer at the grinding station.

[0018] As an optional solution, in step S3, after the wafer is ground, the thinning machine automatically cleans and unloads the wafer.

[0019] As an optional solution, during the automatic cleaning process, the thinning machine sequentially performs pre-cleaning, chemical cleaning, rinsing and drying on the wafer, and performs surface passivation treatment on the ground wafer.

[0020] The beneficial effects of this invention are as follows:

[0021] The wafer thinning method proposed in this invention uses the DBG process to thin ultrathin wafers. A protective film with a thickness greater than or equal to 215 μm is applied to the front side of the half-cut wafer to ensure sufficient thickness for improved wafer support. This effectively reduces stress release and wafer warping during the thinning process. Simultaneously, the spindle speed of the thinning machine is increased to 3500 rpm–4500 rpm, increasing the grinding force during wafer thinning and thus improving grinding efficiency. This further reduces local stress on the wafer, enabling the wafer thinning method to process ultrathin wafers with a thickness of less than 50 μm. This avoids quality defects such as wafer breakage and fragmentation during the thinning process, improving wafer yield. Attached Figure Description

[0022] Figure 1 This is a front view of a half-cut wafer provided in an embodiment of the present invention;

[0023] Figure 2 This is a front view of a wafer covered with a protective film, as provided in an embodiment of the present invention.

[0024] Figure 3 This is a flowchart of the main process of the wafer thinning method provided in the embodiments of the present invention.

[0025] The component names and labels in the diagram are as follows:

[0026] 1. Wafer; 11. Front side; 12. Back side; 2. Protective film; 21. Polyolefin film; 22. Adhesive film. Detailed Implementation

[0027] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. Furthermore, it should be noted that, for ease of description, only the parts related to the present invention are shown in the accompanying drawings, not all of them.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0030] In the description of this embodiment, the terms "upper," "lower," "right," and "left," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] With the development of wafer technology, wafer circuit design is becoming increasingly complex, and the step difference between the central and edge regions of the wafer is widening. As storage capacity and the number of packaging layers increase, the required wafer thickness is also decreasing. Existing DBG processes are prone to quality defects such as breakage and fragmentation during the thinning process of ultra-thin wafers with a thickness of less than 50μm, reducing wafer yield.

[0033] like Figures 1-3 As shown in the figure, this embodiment proposes a wafer thinning method, which includes the following steps:

[0034] S1: Half-cut the front side 11 of wafer 1.

[0035] S2: A protective film 2 is attached to the front side 11 of wafer 1, and the thickness of the protective film 2 is greater than or equal to 215μm.

[0036] S3: Load wafer 1 into the grinding station of the thinning machine. The thinning machine grinds the back side 12 of wafer 1, and the spindle speed of the thinning machine is 3500rpm~4500rpm.

[0037] The wafer thinning method proposed in this embodiment uses the DBG process to thin the ultrathin wafer 1. A protective film 2 is attached to the front side 11 of the half-cut wafer 1. The thickness of the protective film 2 is greater than or equal to 215μm, which provides sufficient thickness to improve the support effect on the wafer 1. This effectively reduces stress release and warping of the wafer 1 during the thinning process. At the same time, the spindle speed of the thinning machine is increased to 3500rpm~4500rpm, which increases the grinding force during the wafer 1 thinning process, thereby improving the grinding efficiency and further reducing the local stress of the wafer 1. Thus, the wafer thinning method can achieve the thinning process of ultrathin wafers 1 with a thickness of less than 50μm, avoiding quality defects such as breakage and fragmentation of the wafer 1 during the thinning process, and improving the product yield of the wafer 1.

[0038] like Figure 1 As shown, in step S1, the front side 11 of wafer 1 is first half-cut. Since the equipment and process used for half-cutting in DBG process are existing technologies, the half-cutting process will not be described in detail.

[0039] like Figure 2 As shown, in step S2, the protective film 2 includes a polyolefin film 21 and an adhesive film 22. The polyolefin film 21 covers and adheres to the front side 11 of the wafer 1 via the adhesive film 22. The polyolefin film 21 has good mechanical protection properties, providing better cushioning for the wafer 1 and preventing wafer 1 from breaking. Furthermore, the polyolefin film 21 has high cleanliness and low electrostatic adsorption properties, reducing contamination of the wafer 1. In addition, the polyolefin film 21 has low cost. The adhesive film 22 adheres the polyolefin film 21 to the front side 11 of the wafer 1 to provide protection and good support for the wafer 1 during the thinning (i.e., grinding) process, preventing wafer 1 from warping. In step S2, both the polyolefin film 21 and the adhesive film 22 are free from defects or damage, and there are no bubbles or impurities between the polyolefin film 21 and the adhesive film 22, or between the adhesive film 22 and the back side 12 of the wafer 1.

[0040] It should be noted that the thickness of the polyolefin film 21 is greater than or equal to 200 μm, and the thickness of the adhesive film 22 is greater than or equal to 15 μm. Because the thickness of the polyolefin film 21 is not less than 200 μm, it provides a relatively thick substrate, thus improving support for the wafer 1, especially enhancing edge support for the front side 11 of the wafer 1 and preventing wafer warping. If the thickness of the polyolefin film 21 is too small (less than 200 μm), the support for the wafer 1 will be insufficient, weakening the protection of the wafer 1. Because the thickness of the adhesive film 22 is not less than 15 μm, its adhesive strength is improved, allowing the polyolefin film 21 to be more stably bonded to the front side 11 of the wafer 1, further enhancing the protection of the wafer 1.

[0041] In step S3, before grinding wafer 1, the thinning machine fixes wafer 1 at the grinding station. Fixing wafer 1 prevents it from shifting position during grinding, improving the grinding accuracy and stability of the grinding process. Since the wafer 1 fixing mechanism of the thinning machine is existing technology, the process of fixing wafer 1 at the grinding station will not be described in detail.

[0042] Specifically, in step S3, the thinning machine sequentially performs rough grinding and fine grinding on the back side 12 of wafer 1. During rough grinding, the spindle speed of the thinning machine is 3500 rpm to 4000 rpm. During fine grinding, the spindle speed is 4000 rpm to 4500 rpm. In this embodiment, the spindle speed of the thinning machine during rough grinding can be 3500 rpm, 3600 rpm, 3700 rpm, 3800 rpm, 3900 rpm, or 4000 rpm, etc., and the spindle speed during fine grinding can be 4000 rpm, 4100 rpm, 4200 rpm, 4300 rpm, 4400 rpm, or 4500 rpm, etc. By increasing the spindle speed during fine grinding, not only can processing efficiency be improved, but local stress on wafer 1 can also be reduced, thus improving the grinding quality.

[0043] It should be noted that the thinning amount in fine grinding accounts for 20% to 25% of the total thinning amount. Compared to the existing fine grinding process, which accounts for about 10% of the total thinning amount, increasing the thinning amount in fine grinding to 20% to 25% optimizes the distribution of thinning amounts between fine and rough grinding. This reduces the thinning amount in rough grinding and increases the thinning amount in fine grinding, allowing fine grinding to better remove the damage layer caused by rough grinding on the surface of wafer 1, thus improving the grinding quality of wafer 1.

[0044] In this embodiment, during the fine grinding process, the thinning machine uses 2000# to 4000# diamond grinding wheels to grind the back side 12 of wafer 1, with axial feed speeds set to three ranges: 0.3 μm / s, 0.15 μm / s, and 0.1 μm / s. During the rough grinding process, the thinning machine uses 320# to 600# diamond grinding wheels to grind the back side 12 of wafer 1, with axial feed speeds set to three ranges: 3 μm / s, 2 μm / s, and 1.5 μm / s. Appropriate diamond grinding wheels are selected based on the different requirements of the fine and rough grinding processes to improve the grinding quality. Meanwhile, during the rough grinding process, axial feed rates of 3 μm / s, 2 μm / s, and 1.5 μm / s are selected sequentially to grind the back side 12 of wafer 1 according to different grinding stages; after the rough grinding process is completed, axial feed rates of 0.3 μm / s, 0.15 μm / s, and 0.1 μm / s are selected sequentially to continue grinding the back side 12 of wafer 1 according to different grinding stages of the fine grinding process.

[0045] In this embodiment, the axial feed rate of the existing fine grinding process is set to three speed ranges: 3um / s, 2um / s and 1.5um / s. By reducing the axial feed rate of the fine grinding process, this embodiment facilitates better release of processing stress in wafer 1, greatly reduces the occurrence of surface cracks in wafer 1, and avoids quality defects such as fragments and chips in wafer 1 during the thinning process.

[0046] In step S3, after grinding wafer 1, the thinning machine automatically cleans and unloads wafer 1, thus enabling the semi-cut wafer 1 to undergo loading, positioning, rough grinding, fine grinding, cleaning, and unloading processes in the thinning machine, improving the processing efficiency of wafer 1. After completing the grinding process on the back side 12 of wafer 1, the thinning machine needs to remove residual grinding debris, grinding fluid, and contaminants on the surface of wafer 1 through an automatic cleaning process to ensure that the surface of wafer 1 meets the requirements of ultra-high cleanliness.

[0047] During the automated cleaning process, the thinning machine sequentially performs pre-cleaning, chemical cleaning, rinsing, and drying on wafer 1, and then performs surface passivation treatment on the ground wafer 1. Specifically, in the pre-cleaning process, high-pressure spray rinsing is first used, with deionized water at a pressure of 4MPa to 6MPa alternately rinsing the front side 11 and back side 12 of wafer 1 to remove more than 80% of loose grinding debris and grinding fluid residue. Ultrasonic-assisted cleaning is then used, employing the cavitation effect of 40kHz to 80kHz ultrasound to peel off adhering particles from the wafer surface. In the chemical cleaning process, acidic and alkaline treatments are performed respectively. Since both acidic and alkaline treatments are existing technologies, their processes will not be described in detail. Finally, rinsing removes residual chemical reagents from the surface of wafer 1, and wafer 1 is dried using methods such as spin drying to ensure its cleanliness and dryness. A passivation film (such as SiO2, Si3N4, Al2O3) is deposited on the surface of the polished wafer using chemical vapor deposition or physical vapor deposition processes to repair microcracks or damaged layers generated during wafer thinning and to avoid stress concentration in subsequent processes. Since the pre-cleaning, chemical cleaning, rinsing, drying, and passivation processes for wafer 1 are all existing technologies, the mechanisms and procedures used for these processes will not be described in detail.

[0048] The above embodiments merely illustrate the basic principles and characteristics of the present invention. The present invention is not limited to the above embodiments. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wafer thinning method, characterized in that, It enables the thinning process of ultra-thin wafers with a thickness of less than 50 μm, including the following steps: S1: Half-cut the front side (11) of the wafer (1); S2: A protective film (2) is attached to the front side (11) of the wafer (1), and the thickness of the protective film (2) is greater than or equal to 215 μm; S3: The wafer (1) is loaded into the grinding station of the thinning machine, the thinning machine grinds the back side (12) of the wafer (1), and the spindle speed of the thinning machine is 3500rpm~4500rpm; In step S2, the protective film (2) includes a polyolefin film (21) and an adhesive film (22), wherein the polyolefin film (21) is covered and bonded to the front side (11) of the wafer (1) by the adhesive film (22). The thickness of the polyolefin film (21) is greater than or equal to 200 μm, and the thickness of the adhesive film (22) is greater than or equal to 15 μm. In step S3, the thinning machine sequentially performs rough grinding and fine grinding on the back side (12) of the wafer (1); in the rough grinding, the spindle speed of the thinning machine is 3500rpm~4000rpm; in the fine grinding, the spindle speed of the thinning machine is 4000rpm~4500rpm. The thinning amount of the fine grinding process accounts for 20% to 25% of the total thinning amount, so that the fine grinding process can better remove the damage layer caused by the rough grinding process on the surface of the wafer (1).

2. The wafer thinning method according to claim 1, characterized in that, In the fine grinding process, the thinning machine uses 2000# to 4000# diamond grinding wheels to grind the back side (12) of the wafer (1), and the axial feed speed is set to three speed ranges: 0.3um / s, 0.15um / s and 0.1um / s.

3. The wafer thinning method according to claim 1, characterized in that, In the rough grinding process, the thinning machine uses 320# to 600# diamond grinding wheels to grind the back side (12) of the wafer (1), and the axial feed speed is set to three speed ranges: 3um / s, 2um / s and 1.5um / s.

4. The wafer thinning method according to any one of claims 1 to 3, characterized in that, In step S3, before grinding the wafer (1), the thinning machine fixes the wafer (1) at the grinding station.

5. The wafer thinning method according to claim 4, characterized in that, In step S3, after the wafer (1) is ground, the thinning machine automatically cleans and unloads the wafer (1).

6. The wafer thinning method according to claim 5, characterized in that, During the automatic cleaning process, the thinning machine sequentially performs pre-cleaning, chemical cleaning, rinsing and drying on the wafer (1), and performs surface passivation treatment on the ground wafer (1).

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