Wafer thinning method

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to a wafer thinning method. The wafer thinning method comprises the following steps of S1, performing half cutting on the front surface of a wafer; s2, pasting a protective film on the front surface of the wafer, wherein the thickness of the protective film is greater than or equal to 215 microns; and S3, the wafer is fed to a grinding station of a thinning machine, the back face of the wafer is ground through the thinning machine, and the rotating speed of a main shaft of the thinning machine ranges from 3500 rpm to 4500 rpm. According to the invention, the DBG technology is adopted to thin the ultrathin wafer, and the protection film with the thickness greater than or equal to 215 [mu] m is attached to the front surface of the semi-cut wafer, so that the supporting effect on the wafer is improved, and the problems of stress release and wafer warping in the thinning process of the wafer are reduced. By increasing the rotating speed of the main shaft of the thinning machine, the grinding force in the thinning process is increased, the grinding efficiency is improved, the local stress is further reduced, the defects such as broken wafers and broken wafers are avoided, and the product yield of the wafers is improved.

Description

Technical Field

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

[0002] The traditional wafer grinding and dicing process sequentially involves front-side wafer filming, back-side wafer grinding, back-side wafer filming, front-side wafer film removal, and finally wafer dicing. In traditional wafer grinding and dicing, back-side wafer grinding to less than 120µm can easily lead to cracking of the back and edges of the wafer, as well as wafer warping after the front protective film is removed.

[0003] To address these issues, the Dicing Before Grinding (DBG) process is used. The DBG process sequentially involves half-cutting the front side of the wafer, laminating the front side of the wafer, grinding the back side of the wafer, laminating the back side of the wafer, and finally tearing off the front side of the wafer. Half-cutting involves cutting a certain depth on the front side of the wafer without completely severing it. This releases stress on the wafer, thereby reducing cracking caused by stress during grinding. This process is particularly suitable for processing ultra-thin wafers (thickness less than 100μm).

[0004] With the advancement of wafer technology, wafer circuit designs are becoming increasingly complex, and the step difference between the center and edge areas of the wafer is growing. As storage capacity increases and the number of packaging layers increases, wafer thickness is also required to be thinner. The existing DBG process is prone to quality defects such as breakage and fragmentation during the thinning process of ultra-thin wafers less than 50μm thick, reducing the wafer's product yield. Summary of the Invention

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

[0006] To achieve this object, the technical solution adopted in the present invention is:

[0007] A wafer thinning method comprises the following steps:

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

[0009] S2: applying a protective film to the front surface of the wafer, wherein the thickness of the protective film is greater than or equal to 215 μm;

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

[0011] As an optional solution, in step S2, the protective film includes a polyolefin film and an adhesive film, and the polyolefin film is covered with and adhered to the front surface of the wafer by the adhesive film.

[0012] As an optional solution, the thickness of the polyolefin film is greater than or equal to 200 μm, and the thickness of the adhesive film is greater than or equal to 15 μm.

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

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

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

[0016] As an optional solution, in the rough grinding process, the thinning machine uses a 320# to 600# diamond grinding wheel to grind the back of the wafer, and the axial feed speed is set to three speed sections of 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 to the grinding station.

[0018] As an optional solution, in step S3, after grinding the wafer, 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 the present invention are:

[0021] The wafer thinning method proposed in the present invention adopts the DBG process to thin the ultra-thin wafer, and covers the front side of the half-cut wafer with a protective film, the thickness of the protective film is greater than or equal to 215μm, so that the protective film has sufficient thickness to improve the support effect on the wafer, effectively reduce the stress release and wafer warping problems of the wafer during the thinning process, and at the same time increase the spindle speed of the thinning machine to 3500rpm~4500rpm, increase the grinding force during the wafer thinning process, thereby improving the grinding efficiency and further reducing the local stress of the wafer, so that the wafer thinning method can realize thinning processing of ultra-thin wafers with a thickness of less than 50μm, avoid the occurrence of quality defects such as breakage and fragmentation of the wafer during the thinning process, and improve the product yield of the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] Figure 2 This is a front view of a wafer coated with a protective film provided by an embodiment of the present invention;

[0024] Figure 3 This is a main flow chart of the wafer thinning method provided by an embodiment of the present invention.

[0025] The names and numbers of the components in the figure are as follows:

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

[0027] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved more clearly, the technical solutions of the present invention are further described below with reference to the accompanying drawings and through specific embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the drawings only show portions relevant to the present invention, not all of them.

[0028] In the description of the present invention, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0029] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0030] In the description of this embodiment, terms such as "upper," "lower," "right," and "left" are used to refer to positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate description and simplify operation, and are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes 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 through specific implementation methods.

[0032] With the advancement of wafer technology, wafer circuit designs are becoming increasingly complex, and the step difference between the center and edge areas of the wafer is growing. As storage capacity increases and the number of packaging layers increases, wafer thickness is also required to be thinner. The existing DBG process is prone to quality defects such as breakage and fragmentation during the thinning process of ultra-thin wafers less than 50μm thick, reducing the wafer's product yield.

[0033] like Figures 1 to 3 As shown, this embodiment provides a wafer thinning method, which includes the following steps:

[0034] S1: half-cutting the front side 11 of the wafer 1.

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

[0036] S3: loading the wafer 1 onto the grinding station of the thinning machine, and the thinning machine grinds the back side 12 of the wafer 1, and the spindle speed of the thinning machine is 3500 rpm to 4500 rpm.

[0037] The wafer thinning method proposed in this embodiment uses the DBG process to thin the ultra-thin wafer 1, and 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 215 μm, so that the protective film 2 has sufficient thickness to improve the support effect on the wafer 1, effectively reducing the stress release and warping problems of the wafer 1 during the thinning process. At the same time, the spindle speed of the thinning machine is increased to 3500 rpm~4500 rpm, which increases the grinding force during the thinning process of the wafer 1, thereby improving the grinding efficiency and further reducing the local stress of the wafer 1, so that the wafer thinning method can realize thinning processing of ultra-thin wafers 1 with a thickness of less than 50 μm, 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 the wafer 1 is first half-cut. Since the equipment and process of half-cutting in the DBG process are both 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, and the polyolefin film 21 is covered and bonded to the front side 11 of the wafer 1 through the adhesive film 22. The polyolefin film 21 has good mechanical protection performance, can provide better buffering effect for the wafer 1, and prevent the wafer 1 from breaking. Moreover, the polyolefin film 21 has high cleanliness and low electrostatic adsorption performance, which reduces the contamination of the wafer 1. In addition, the cost of the polyolefin film 21 is low. The adhesive film 22 bonds 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, thereby preventing the wafer 1 from warping. In step S2, the polyolefin film 21 and the adhesive film 22 are both intact or damaged, and there are no bubbles or impurities between the polyolefin film 21 and the adhesive film 22, and between the adhesive film 22 and the back side 12 of the wafer 1.

[0040] It should be noted that the film thickness of the polyolefin film 21 is greater than or equal to 200 μm, and the film thickness of the adhesive film 22 is greater than or equal to 15 μm. Since the film thickness of the polyolefin film 21 is not less than 200 μm, the polyolefin film 21 as a substrate has a relatively large thickness, thereby improving the support for the wafer 1, especially improving the edge support for the front side 11 of the wafer 1, and avoiding warping of the wafer. If the thickness of the polyolefin film 21 is too small (less than 200 μm), the support force for the wafer 1 is too small, which weakens the protection of the wafer 1. Since the film thickness of the adhesive film 22 is not less than 15 μm, the bonding strength of the adhesive film 22 is improved, so that the polyolefin film 21 can be more stably bonded to the front side 11 of the wafer 1, further improving the protection of the wafer 1.

[0041] In step S3, before grinding wafer 1, the thinning machine secures wafer 1 to the grinding station. This securement prevents wafer 1 from shifting during grinding, improving the grinding accuracy and stability of wafer 1. Because the thinning machine's securement mechanism for wafer 1 is conventional, the process of securing wafer 1 to the grinding station will not be described in detail.

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

[0043] It should be noted that the thinning amount of the fine grinding process accounts for 20% to 25% of the total thinning amount. Compared with the existing fine grinding process, where the thinning amount accounts for approximately 10% of the total thinning amount, by increasing the thinning amount of the fine grinding process to 20% to 25%, the distribution of the thinning amount of the fine grinding process and the rough grinding process is optimized, the thinning amount of the rough grinding process is reduced, and the thinning amount of the fine grinding process is increased, so that the fine grinding process can better remove the damaged layer on the surface of the wafer 1 caused by the rough grinding process, which is conducive to improving the grinding quality of the wafer 1.

[0044] In this embodiment, during fine grinding, the thinning machine uses a 2000# to 4000# diamond grinding wheel to grind the back side 12 of the wafer 1, and the axial feed speed is set to three speed sections: 0.3um / s, 0.15um / s, and 0.1um / s. During rough grinding, the thinning machine uses a 320# to 600# diamond grinding wheel to grind the back side 12 of the wafer 1, and the axial feed speed is set to three speed sections: 3um / s, 2um / s, and 1.5um / s. According to the different requirements of fine grinding and rough grinding, the appropriate diamond grinding wheel is selected to improve the grinding quality of fine grinding and rough grinding. At the same time, in the rough grinding process, the axial feed speeds of 3um / s, 2um / s and 1.5um / s are selected in sequence according to different grinding stages to grind the back side 12 of the wafer 1; after the rough grinding process is completed, the axial feed speeds of 0.3um / s, 0.15um / s and 0.1um / s are selected in sequence according to different grinding stages of the fine grinding process to continue grinding the back side 12 of the wafer 1.

[0045] In this embodiment, the existing axial feed speed of the fine grinding process is set to three speed sections of 3um / s, 2um / s and 1.5um / s respectively. This embodiment reduces the axial feed speed of the fine grinding process to facilitate the wafer 1 to better release the processing stress, greatly reduce the occurrence of cracks on the surface of the wafer 1, and avoid the occurrence of quality defects such as breakage and fragments in the wafer 1 during the thinning process.

[0046] In step S3, after grinding wafer 1, the thinning machine automatically cleans and unloads wafer 1, allowing the half-cut wafer 1 to be loaded, positioned, roughly ground, finely ground, cleaned, and unloaded in the thinning machine, thereby improving the processing efficiency of wafer 1. After the thinning machine completes the grinding process of the back side 12 of wafer 1, it must perform an automatic cleaning process to remove grinding debris, grinding fluid, and contaminants remaining on the surface of wafer 1, ensuring that the surface of wafer 1 meets ultra-high cleanliness requirements.

[0047] During the automatic cleaning process, the thinning machine sequentially pre-cleans, chemically cleans, rinses, and dries the wafer 1, and performs surface passivation treatment on the ground wafer 1. Specifically, the pre-cleaning process begins with a high-pressure spray rinse, using deionized water at a pressure of 4MPa to 6MPa to alternately rinse the front 11 and back 12 of the wafer 1, removing more than 80% of loose grinding debris and grinding fluid residue. Ultrasonic cleaning is then assisted, using the cavitation effect of 40kHz to 80kHz ultrasonic waves to remove particles attached to the wafer surface. During the chemical cleaning process, acidic and alkaline treatments are performed separately. Since both acidic and alkaline treatments are existing technologies, the processes of acidic and alkaline treatments will not be described in detail. Finally, residual chemical reagents on the surface of the wafer 1 are removed by rinsing, and the wafer 1 is dried by methods such as spin drying to ensure the cleanliness and dryness of the wafer 1. A passivation film (such as SiO2, Si3N4, or Al2O3) is deposited on the polished wafer surface using a chemical vapor deposition or physical vapor deposition process to repair microcracks or damaged layers generated during wafer thinning and prevent stress concentration in subsequent processes. Because the pre-cleaning, chemical cleaning, rinsing, drying, and passivation processes for wafer 1 are all conventional techniques, the mechanisms and procedures for these processes will not be further described.

[0048] The above embodiments merely illustrate the basic principles and features of the present invention. The present invention is not limited to the above embodiments. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A wafer thinning method, characterized in that: The steps include: S1: half-cutting the front side (11) of the wafer (1); S2: applying a protective film (2) to the front surface (11) of the wafer (1), wherein the thickness of the protective film (2) is greater than or equal to 215 μm; S3: Loading the wafer (1) to 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 3500 rpm to 4500 rpm.

2. The wafer thinning method according to claim 1, wherein: In step S2, the protective film (2) includes a polyolefin film (21) and an adhesive film (22), and the polyolefin film (21) is covered and bonded to the front surface (11) of the wafer (1) through the adhesive film (22).

3. The wafer thinning method according to claim 2, wherein: The film thickness of the polyolefin film (21) is greater than or equal to 200 μm, and the film thickness of the adhesive film (22) is greater than or equal to 15 μm.

4. The wafer thinning method according to claim 1, wherein: In step S3, the thinning machine sequentially performs rough grinding and fine grinding on the back side (12) of the wafer (1); during the rough grinding, the spindle speed of the thinning machine is 3500 rpm to 4000 rpm; during the fine grinding, the spindle speed of the thinning machine is 4000 rpm to 4500 rpm.

5. The wafer thinning method according to claim 4, wherein: The thinning amount of the fine grinding process accounts for 20% to 25% of the total thinning amount.

6. The wafer thinning method according to claim 4, wherein: In the fine grinding process, the thinning machine uses a 2000# to 4000# diamond grinding wheel to grind the back side (12) of the wafer (1), and the axial feed speed is set to three speed sections of 0.3um / s, 0.15um / s and 0.1um / s.

7. The wafer thinning method according to claim 4, wherein: In the rough grinding process, the thinning machine uses a 320# to 600# diamond grinding wheel to grind the back side (12) of the wafer (1), and the axial feed speed is set to three speed sections of 3um / s, 2um / s and 1.5um / s.

8. The wafer thinning method according to any one of claims 1 to 7, characterized in that: In step S3, before grinding the wafer (1), the thinning machine fixes the wafer (1) to the grinding station.

9. The wafer thinning method according to claim 8, characterized in that: In step S3, after grinding the wafer (1), the thinning machine automatically cleans and unloads the wafer (1).

10. The wafer thinning method according to claim 9, wherein: 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).

Images