Protection method for wafer laser cutting and wafer laser cutting method

Abstract

The application discloses a wafer laser cutting protection method and a wafer laser cutting method, and forms a protection layer on a wafer to be cut, comprising the steps that a modified water-based protection slurry is coated on the wafer to be cut to form a water-based coating layer, the water-based coating layer is heated in a first temperature range to perform solidification and flow leveling, physical entanglement and phase separation occur between the modified polyvinyl alcohol and etherified cellulose in the water-based coating layer, so that a micrometer-level porous skeleton structure is formed in the water-based coating layer; the water-based coating layer with the porous skeleton structure is heated in a second temperature range to perform cross-linking reinforcement, the molecular chains of the etherified cellulose are cross-linked into an ether bond cross-linking structure through hydroxyl groups, so that the water-based coating layer forms a modified water-based protection layer. Compared with the prior art, the modified water-based protection layer with the porous skeleton structure is formed on the wafer, can effectively absorb the fragments generated in wafer cutting, prevents wafer damage, and is convenient to clean after cutting.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to protection during laser cutting of wafers. Background Technology

[0002] In laser cutting processes within semiconductor packaging, wafer protective coatings must simultaneously meet the core requirements of high light shielding, adhesion of dicing debris, patterning accuracy, and process compatibility. Existing technologies generally suffer from the following limitations: On the one hand, when using resin materials as the protective layer for laser cutting, the inherently low thermal conductivity of resin materials (the thermal conductivity of polyamide resin is generally between 0.3 W / mK and 0.5 W / mK) causes significant heat accumulation in the chip edge area during the cutting process, leading to carbonization defects. Furthermore, cleaning after cutting is difficult, and there is a risk of residual adhesive remaining. On the other hand, chipping often occurs during cutting, and these fragments can easily damage the wafer.

[0003] Therefore, there is an urgent need for a protective method and a wafer laser cutting method that can solve the above problems during wafer laser cutting. Summary of the Invention

[0004] The purpose of this invention is to provide a protective method and a wafer laser cutting method during wafer laser cutting. When cutting a wafer, a modified water-based protective layer with a porous skeleton structure is formed on the wafer, which can effectively absorb the fragments generated during cutting, prevent wafer damage, and facilitate cleaning after cutting.

[0005] To achieve the above objectives, the present invention provides a protective method for wafer laser dicing, used to form a dicing protective layer on the wafer to be diced, comprising the steps of: coating the wafer to be diced with a modified water-based protective slurry to form a water-based coating, wherein the modified water-based protective slurry comprises modified polyvinyl alcohol and etherified cellulose mixed together with a slurry substrate; heating the water-based coating within a first temperature range for curing and leveling, causing physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose to form a micron-scale porous framework structure; heating the water-based coating forming the porous framework structure within a second temperature range for cross-linking reinforcement, causing the molecular chains of the etherified cellulose to form ether bonds through hydroxyl groups to form a cross-linked structure, thereby forming a modified water-based protective layer, wherein the temperature in the second temperature range is higher than the temperature in the first temperature range, and the dicing protective layer comprises the modified water-based protective layer.

[0006] Preferably, the first temperature range is 60–85°C, which allows for extensive physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose, while preventing premature drying of the water-based coating surface due to excessive temperature, thus avoiding hindering internal moisture drainage, and also preventing the porous framework structure from collapsing due to excessive moisture loss. More preferably, the first temperature range is 80±5°C, which can rapidly and stably produce a porous framework structure.

[0007] Preferably, the second temperature range is 110–130°C, which allows for the formation of effective ether cross-linking structures between the molecular chains of etherified cellulose. More preferably, the second temperature range is 120°C ± 5°C, which allows for the rapid formation of ether cross-linking structures between the molecular chains of etherified cellulose.

[0008] Preferably, heating the water-based coating within a first temperature range for curing and leveling specifically involves placing the wafer coated with the water-based coating on a hot plate within the first temperature range for a first duration for curing and leveling.

[0009] Specifically, heating the water-based coating, which forms a porous framework structure, within a second temperature range for cross-linking enhancement involves placing the wafer coated with the water-based coating on a hot plate within the second temperature range for a second duration to enhance cross-linking. Alternatively, other methods can be used to heat and dry the water-based coating, such as oven heating or infrared heating.

[0010] More preferably, the water-based coating is cured and leveled for a first duration within a first temperature range, resulting in an evaporation rate greater than 95%. The water-based coating, forming a porous framework structure, is then subjected to crosslinking reinforcement for a second duration within a second temperature range, resulting in a crosslinking degree of ether bonds between the molecular chains of the etherified cellulose greater than or equal to 60%. The second duration is shorter than the first duration. This significantly shorter crosslinking reinforcement duration not only ensures that the water-based coating has dried sufficiently after curing and leveling to form a structurally stable modified water-based protective layer with a stable porous framework structure, but also results in an extremely short crosslinking reinforcement time. This not only rapidly improves the thermal stability of the porous framework structure but also effectively prevents prolonged high-temperature damage to the modified water-based protective layer.

[0011] Specifically, the first duration is 5–12 minutes. More specifically, the first duration is 10 ± 2 minutes to ensure sufficient physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose, thereby creating a sufficiently dense porous framework structure in the water-based coating. Specifically, the second duration is 60 ± 10 seconds.

[0012] Preferably, the pore size in the porous framework structure is 1μm-5μm.

[0013] Preferably, the protection method during wafer laser dicing further includes the steps of: forming a light-shielding layer on the modified water-based protective layer using a light-shielding protective material, curing the light-shielding layer, and forming a through opening in the light-shielding layer at a position corresponding to the wafer dicing kerf, so that the light-shielding layer is divided into several light-shielding portions by the dicing kerf, and the dicing protection layer includes the light-shielding layer. Forming independent light-shielding layers on the modified water-based protective layer provides a targeted light-shielding effect for the dicing protection layer, preventing laser damage to the wafer.

[0014] More preferably, the width of the opening is greater than the width of the dicing track, and a buffer zone is formed between the opening and the dicing track in the width direction of the opening. Specifically, in the width direction of the opening, the distance between the edge of the light-shielding portion and the dicing track is greater than or equal to 5 μm and less than or equal to 10 μm. The buffer zone can enhance the wafer's resistance to thermal stress cracking during wafer dicing.

[0015] Specifically, the light-shielding protective material uses polyimide prepolymer as a matrix and is also mixed with light-shielding fillers. Curing the light-shielding layer specifically includes heating the cutting protective layer in an inert environment within a third temperature range, thereby activating the polyimide prepolymer and embedding it into the porous framework structure of the modified water-based protective layer to form a mechanically interlocking structure. The temperature in the third temperature range is higher than the temperature in the second temperature range. This solution effectively improves the adhesion between the light-shielding layer and the modified water-based protective layer, preventing the light-shielding layer from detaching and extending its service life. Furthermore, the gradual increase in temperature within the first, second, and third temperature ranges allows the modified water-based protective layer to undergo step-by-step curing, effectively eliminating interlayer thermal expansion mismatch between the modified water-based protective layer and the wafer's surface to be cut, significantly reducing the risk of peeling compared to traditional single-stage curing methods.

[0016] More preferably, heating the light-shielding layer in a third temperature range under an inert environment specifically includes: heating the light-shielding layer for a fourth duration in a fourth temperature range for primary curing; and heating the light-shielding layer for a fifth duration in a fifth temperature range for secondary curing. The third temperature range includes both the fourth and fifth temperature ranges, where the temperature in the fourth temperature range is lower than the temperature in the fifth temperature range, and the fourth duration is longer than the fifth duration. This method gradually heats and cures the light-shielding layer, improving its adhesion. Alternatively, the light-shielding layer can be cured only once.

[0017] Specifically, the fourth temperature range is 140–160°C, the fourth duration is 15–25 min, the fifth temperature range is 170–190°C, and the fifth duration is 3–7 min.

[0018] More preferably, a light-shielding protective material is printed onto the modified water-based protective layer using screen printing technology to form a light-shielding layer. This results in higher opening precision for the light-shielding layer. Of course, other methods can also be used to form the light-shielding layer, not limited to screen printing, such as metal deposition etching, coating, and other processes.

[0019] More preferably, the light-shielding filler used in the light-shielding protective material is nano-carbon black, and the nano-carbon black content in the light-shielding protective material is 5.5 wt%, with a particle size of 30 nm. This solution enables the light-shielding layer to effectively absorb laser light, improving its light-shielding performance. The light-shielding filler is not limited to nano-carbon black; it can also be amorphous silicon or other light-absorbing materials, or other reflective materials. The light-shielding protective material is not limited to pastes; it can also be inks, metals, etc.

[0020] More preferably, before forming a light-shielding layer on the modified water-based protective layer, the surface of the modified water-based protective layer is subjected to plasma surface treatment, which effectively improves the interlayer bonding force between the modified water-based protective layer and the light-shielding layer, and significantly improves the peel resistance of the light-shielding layer.

[0021] Preferably, before coating the wafer to be diced with the modified water-based protective slurry to form a water-based coating, the wafer to be diced is also cleaned, hydrophilic modified, and dried to increase the adhesion of the wafer to the modified water-based protective slurry.

[0022] Preferably, the thickness of the water-based coating is 20±0.5μm.

[0023] Preferably, the slurry substrate comprises deionized water and oxidized starch. The oxidized starch may also be replaced by other materials that produce the slurry.

[0024] The present invention also provides a wafer laser cutting method, comprising: forming a cutting protective layer on the wafer to be cut using the protective method for wafer laser cutting as described above; cutting the wafer along the cutting path using a laser to divide it into several bare cores; and immersing the bare cores in deionized water to dissolve the water-based protective layer in the deionized water.

[0025] Compared with existing technologies, this invention uses a slurry substrate composed of modified polyvinyl alcohol and etherified cellulose as a protective material, which is coated onto a wafer to form a water-based coating. Then, heating within a first temperature range causes physical entanglement and initial phase separation between the modified polyvinyl alcohol and etherified cellulose in the water-based coating. This allows the water-based coating to dry while simultaneously forming a micron-scale porous framework structure. Further heating within a second temperature range causes the molecular chains of the etherified cellulose in the water-based coating to form ether bonds, resulting in a structurally stable modified water-based protective layer. This significantly improves the thermal stability of the porous framework structure in the modified water-based protective layer, preventing the heat generated during dicing from affecting the stability of the porous framework structure. This provides reliable fragmentation protection for the wafer, allowing the porous framework structure to absorb fragments generated during subsequent wafer dicing, preventing damage to the wafer. Furthermore, the modified water-based protective layer has excellent water solubility, making it easy to clean after wafer dicing. Attached Figure Description

[0026] Figure 1 This is a flowchart of the wafer laser cutting method of the present invention.

[0027] Figure 2 This is another flowchart of the wafer laser cutting method of the present invention.

[0028] Figure 3 This is a flowchart of the protection method during wafer laser cutting according to the present invention. Detailed Implementation

[0029] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0030] refer to Figures 1 to 3 The present invention provides a protective method for wafer laser cutting, which is used to form a cutting protective layer on the wafer 10 to be cut, including steps S1 to S3.

[0031] refer to Figures 1 to 3 Step S1: Provide the wafer 10 to be cut.

[0032] In an even better manner, the wafer 10 to be cut is also subjected to surface pretreatment in S1.

[0033] Specifically, the surface pretreatment of the wafer 10 to be cut includes steps S11 to S13.

[0034] S11, ultrasonic cleaning of wafer 10 is performed using a cleaning solution, which effectively removes particles with a diameter greater than 0.3μm from the surface of wafer 10, reducing the residual density to below 0.05 particles / cm².

[0035] S12, hydrophilic modification of the surface of wafer 10 is performed, reducing its contact angle to below 3°, thereby significantly improving the adhesion of the modified water-based protective layer 20.

[0036] S13, perform a drying process on the surface of wafer 10 to ensure that the surface of wafer 10 is completely dry and free of any liquid residue.

[0037] In step S11, the cleaning solution used is SC-1 (mixture ratio of NH4OH:H2O2:H2O=1:1:5), and ultrasonic cleaning is performed at 65°C for 10 minutes. In step S12, the surface is hydrophilically modified by treatment with 300W O2 plasma for 30 seconds. In step S13, after removing residual liquid by nitrogen purging, wafer 10 is baked on an 80°C hot plate for 1 minute to ensure that the surface of wafer 10 is completely dry and free of any liquid residue.

[0038] refer to Figures 1 to 3 Step S2: A modified water-based protective slurry is coated on the wafer 10 to be cut to form a water-based coating 20a.

[0039] Specifically, the modified water-based protective slurry comprises modified polyvinyl alcohol, etherified cellulose, and a slurry base material mixed together. The slurry base material comprises deionized water and oxidized starch.

[0040] Before step S2, a step of preparing a modified water-based protective slurry is included: using deionized water with a resistivity >18 MΩ·cm as the matrix, 12 wt% of modified polyvinyl alcohol (degree of hydrolysis 88%, degree of polymerization 1700), 8 wt% of etherified cellulose (e.g., hydroxyethyl methyl cellulose, viscosity 4000 cP), and 5 wt% of oxidized starch (degree of carboxyl substitution 0.35) are added sequentially. The specific process is as follows: the deionized water is heated to 85±2℃, the modified polyvinyl alcohol is added, and it is ultrasonically vibrated at 40 kHz for 10 minutes to dissolve it; after the solution is cooled to 50℃, the etherified cellulose is added, and the mixture is allowed to stand for defoaming for 10 minutes; finally, the oxidized starch is added and the mixture is vibrated and mixed for 15 minutes to ensure that the final viscosity of the slurry is controlled at 120±10 cP (25℃).

[0041] For step S2, a modified water-based protective slurry is coated onto the wafer 10 to be diced to form a water-based coating 20a, wherein the coating thickness ranges from 10 to 40 μm. A coating thickness > 10 μm ensures that the porous framework structure can effectively capture debris, while a coating thickness < 40 μm avoids cracking problems caused by the difference in drying rates between the inner and outer layers during the curing of the water-based coating 20a. A coating thickness of 20 ± 0.5 μm is preferred.

[0042] Specifically, after the slurry is prepared, it is immediately spin-coated on a spin coater at an acceleration of 3000 rpm / s²: the first stage maintains 800 rpm for 3 seconds to achieve uniform slurry spreading; the second stage rapidly increases to 2500 rpm for 30 seconds to accurately determine the film thickness, ultimately forming a uniform coating with a thickness of 20±0.5 μm as water-based coating 20a. In this embodiment, spin coating is used to coat the modified water-based protective slurry on wafer 10. Alternatively, spray coating can be used instead of spin coating.

[0043] refer to Figures 1 to 3 In step S3, the water-based coating 20a is heated and cured, causing physical entanglement and preliminary phase separation between the modified polyvinyl alcohol and etherified cellulose in the water-based coating 20a. This allows the water-based coating 20a to dry while forming a micron-sized porous framework structure 21 within it. Furthermore, the molecular chains of etherified cellulose in the water-based coating 20a undergo ether crosslinking through residual hydroxyl groups to form an ether crosslinking structure. This results in the formation of a modified water-based protective layer 20 in the water-based coating 20a. The cutting protective layer includes the modified water-based protective layer 20.

[0044] refer to Figure 3 Step S3 includes S31 to S32.

[0045] S31, the water-based coating 20a is heated within a first temperature range to cure and level, causing physical entanglement and preliminary phase separation between the modified polyvinyl alcohol and etherified cellulose in the water-based coating 20a, thereby forming a micron-scale porous framework structure 21 in the water-based coating 20a.

[0046] The first temperature range is defined as the temperature range within which physical entanglement and phase separation occur between the modified polyvinyl alcohol and etherified cellulose, without causing the surface of the water-based coating 20a to dry too quickly. In this embodiment, the first temperature range is 60-85°C, allowing for significant physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose. Preferably, the first temperature range is 80±5°C, enabling the porous framework structure 21 to be generated stably and rapidly.

[0047] The pore size of the porous framework structure 21 is 1μm-5μm. In this embodiment, step S31 promotes rapid evaporation of moisture in the water-based coating 20a, with an evaporation rate greater than 95%.

[0048] In this embodiment, the water-based coating 20a is placed on a hot plate within the first temperature range for a first duration to cure and level. Alternatively, other methods can be used to heat and dry the water-based coating 20a, such as oven heating or infrared heating.

[0049] The selection of the first duration is related to factors such as the heating method, heating temperature, thickness of the water-based coating 20a, and water content. When selecting the first duration, it is necessary to consider not only the time required for physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose, but also to ensure that the evaporation rate in the water-based coating 20a is greater than 95%. In this embodiment, the first duration is 5–12 minutes. A first duration of 10 ± 2 minutes is preferred, and 10 to 12 minutes is even better, to ensure sufficient physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose, resulting in a sufficient porous framework structure 21 in the water-based coating 20a, and an evaporation rate greater than 95% in the water-based coating 20a.

[0050] S32, the water-based coating 20a, which forms the porous framework structure 21, is heated within a second temperature range to strengthen its cross-linking properties. This causes the molecular chains of the etherified cellulose in the water-based coating 20a to form ether bonds through hydroxyl groups, thereby creating a modified water-based protective layer 20. The ether bond cross-linking structure between the molecular chains of the etherified cellulose significantly improves the thermal stability of the porous framework structure 21 in the modified water-based protective layer 20, preventing the heat generated during cutting from affecting the stability of the porous framework structure 21 and providing reliable fragmentation protection for the wafer 10.

[0051] In step S32, the degree of crosslinking of the molecular chains of etherified cellulose through ether bonds formed by hydroxyl groups is greater than or equal to 60%. This ether bond crosslinking structure can significantly improve the thermal stability of the porous framework structure 21, increasing its decomposition temperature from approximately 180°C in the uncrosslinked state to above 240°C, thereby endowing the wafer 10 with reliable fragmentation protection capabilities. The hydroxyl groups include residual hydroxyl groups in the etherified cellulose, which are natural hydroxyl groups that have not been completely replaced in the etherified cellulose.

[0052] The second temperature range refers to the temperature at which the molecular chains of etherified cellulose can rapidly form ether bonds through hydroxyl groups to create a cross-linking reaction. In this embodiment, the second temperature range is 110-130℃, which allows for the formation of an effective ether bond cross-linking structure between the molecular chains of etherified cellulose. A second temperature range of 120℃±5℃ is preferred, as this allows for a rapid improvement in the ether bond cross-linking structure between the molecular chains of etherified cellulose.

[0053] Specifically, in step S32, heating the water-based coating 20a that forms the porous skeleton structure 21 within a second temperature range to perform cross-linking reinforcement specifically involves placing the water-based coating 20a on a hot plate within the second temperature range for a second duration to perform cross-linking reinforcement, wherein the second duration is shorter than the first duration.

[0054] The second duration can be determined by the dryness, thickness, and cross-linking strengthening temperature of the water-based coating 20a after curing and adsorption. It is necessary to ensure that the degree of cross-linking of the etherified cellulose molecular chains through hydroxyl groups to form ether bonds reaches a preset ratio (e.g., 60%) without damaging the water-based coating 20a. In this embodiment, the second duration is 60 seconds ± 10 seconds.

[0055] Preferably, the protection method during wafer laser cutting also includes steps S4 to S5.

[0056] refer to Figures 1 to 3 In step S4, a light-shielding layer 30 is formed on the modified water-based protective layer 20 using a light-shielding protective material. The light-shielding layer 30 has a through opening 32 at a position corresponding to the dicing channel 11 of the wafer 10, so that the light-shielding layer 30 is divided into several light-shielding portions 31 by the dicing channel 11. The cutting protective layer includes the light-shielding layer 30.

[0057] In this process, a light-shielding protective material is attached to the modified water-based protective layer 20 to form a light-shielding layer 30. The light-shielding protective material uses polyimide prepolymer as a matrix and also contains light-shielding fillers. Specifically, the light-shielding protective material uses 85 wt% polyimide prepolymer as a matrix, adds 5.5 wt% nano-carbon black as a light-shielding filler, and supplements with 0.5 wt% BYK-163 dispersant to ensure uniform dispersion.

[0058] In this embodiment, the particle size of the nano-carbon black is 30 nm, resulting in a light-shielding rate of over 99.6 ± 0.1% for the light-shielding layer 30. Of course, the type, content, and particle size of the light-shielding filler are not limited to the above values. The light-shielding filler can also be amorphous silicon nanoparticles or other light-absorbing materials, or other reflective materials.

[0059] refer to Figure 2 The width of the opening 32 is greater than the width of the cutting channel 11, and a buffer zone 321 is formed between the opening 32 and the cutting channel 11 in the width direction of the opening 32. Specifically, in the width direction of the opening 32, the distance L1 between the edge of the light-shielding portion 31 and the cutting channel 11 is greater than or equal to 5 μm and less than or equal to 10 μm, such that the width of the buffer zone 321 is greater than or equal to 5 μm, thereby enhancing the ability to resist thermal stress cracks.

[0060] In this embodiment, a light-shielding protective material is printed on the modified water-based protective layer 20 using screen printing to form a light-shielding layer 30. A nylon screen is used as the printing template. The pattern on the template has openings 32 at positions corresponding to the dicing tracks 11 on the wafer 10, slightly larger than the width of the dicing tracks 11. For example, in this embodiment, openings 32 within the range of 50μm ± 5μm are selected. The width of these openings 32 is 10μm larger than the width of the dicing tracks 11. After aligning and printing the light-shielding layer 30, the distance between the light-shielding layer 30 and the dicing tracks 11 in the width direction of the openings 21 is greater than or equal to 5μm. Alternatively, the light-shielding layer 30 can also be formed by injection molding, not just screen printing.

[0061] In this embodiment, before printing the light-shielding layer 30, an infrared vision positioning system with a wavelength of 950nm is used to perform high-precision alignment of the printing mold and the wafer 10 to ensure that the positional error between the dicing track 11 of the wafer 10 and the opening 32 of the printing template is strictly controlled within ±4μm.

[0062] In this embodiment, a 350-mesh nylon screen (40μm wire diameter, 25N / cm tension) is used for printing the light-shielding layer 30 on the modified water-based protective layer 20. A squeegee with a hardness of 70 Shore A is used at a 60° angle and a pressure of 0.30±0.02MPa. The printing speed is consistently set at 10mm / s (with a repeatability accuracy of ±1μm). During the printing process, the film thickness is monitored online in real time using a laser thickness gauge, and the process is adjusted accordingly to ensure that the resulting paste film thickness accurately reaches the target value of 10±0.8μm. The squeegee angle is not limited to 60 degrees; other angles, such as 75°, can be used. The printing speed is preferably controlled below 12mm / s.

[0063] In contrast, a 280-mesh screen printing plate (accuracy ±8μm) can be used as the printing template, and the squeegee speed can be increased to 20mm / s during printing. Of course, the specific parameters during printing are not limited to the examples above. The control parameters during printing are related to factors such as the thickness of the light-shielding layer 30, the viscosity of the light-shielding protective material used for printing, and the required control accuracy.

[0064] refer to Figures 1 to 3 Step S5, cure the light-shielding layer 30.

[0065] Preferably, step S5 includes: heating the cutting protective layer in an inert environment within a third temperature range, thereby activating the polyimide prepolymer and embedding it into the porous skeleton structure 21 of the modified water-based protective layer 20 to form a mechanical interlocking structure 33, and then curing the light-shielding layer 30 and reheating and curing the modified water-based protective layer 20, wherein the temperature in the third temperature range is greater than the temperature in the second temperature range.

[0066] In step S5, the heating can be achieved by hot plate heating, drying oven heating, hot air heating, infrared heating, etc.

[0067] The inert environment requires that the oxygen content be strictly controlled to <10ppm. High-purity nitrogen (N2) with a purity >99.999% is preferred as the protective gas. Using high-purity nitrogen ensures extremely low oxygen content while also offering excellent process economy, safety, and wide applicability. Of course, the inert gas is not limited to nitrogen; high-purity argon (Ar) or helium (He) can also be used.

[0068] Specifically, step S5 includes S51 and S52.

[0069] Step S51 involves heating the light-shielding layer 30 for a fourth duration within a fourth temperature range to perform a first curing of the light-shielding layer 30 and to initially activate the polyimide prepolymer. This fourth duration heating within the fourth temperature range is applied to the entire wafer-on-wafer dicing protective layer; therefore, this step also performs a second curing treatment on the modified water-based protective layer 20.

[0070] In step S52, the light-shielding layer 30 is heated for a fifth duration within a fifth temperature range to perform secondary curing of the light-shielding layer 30, effectively activating the polyimide prepolymer and embedding it into the porous framework structure 21 to form a mechanically interlocking structure 33. This fifth duration of heating within the fifth temperature range is applied to the entire wafer-level dicing protective layer; therefore, this step also performs a second curing treatment on the modified water-based protective layer 20. At the fifth temperature range, the polyimide segments are effectively activated and embedded within the pre-formed porous framework structure 21 of the lower modified water-based protective layer 20, thereby constructing a robust mechanical interlocking mechanism at the interface between the modified water-based protective layer 20 and the light-shielding layer 30, significantly enhancing the interlayer bonding strength. Alternatively, step S51 can be omitted in step S5, and only step S52 can be used for heating and curing; in this case, the duration of step S52 needs to be extended.

[0071] The third temperature range includes a fourth temperature range and a fifth temperature range. The temperature in the fourth temperature range is lower than the temperature in the fifth temperature range, and the fourth duration is longer than the fifth duration.

[0072] In this embodiment, the fourth temperature range is 140-160℃, and the fourth duration is 15-25 minutes. Preferably, the fourth temperature range is 150℃±5℃. The fifth temperature range is 170-190℃, and the fifth duration is 3-7 minutes. Preferably, the fifth temperature range is 180℃±5℃.

[0073] Preferably, step S3a is included between steps S3 and S4, where the surface of the modified water-based protective layer 20 is subjected to plasma surface treatment, effectively improving the interlayer bonding force between the modified water-based protective layer 20 and the light-shielding layer 30, and significantly improving the peel strength of the light-shielding layer 30. Specifically, argon gas with a power of 50W and a flow rate of 10sccm is used for 60s plasma surface treatment, which increases the peel strength between the light-shielding layer 30 and the modified water-based protective layer 20 by more than 40%.

[0074] refer to Figure 1 and Figure 2 The present invention also discloses a wafer laser cutting method, comprising: forming a cutting protection layer on a wafer 10 to be cut according to the protective method for wafer laser cutting as described above; S6, cutting the wafer 10 along the cutting path 11 using a laser to divide it into a plurality of bare cores 10a; S7, immersing the bare cores 10a with the cutting protection layer attached in deionized water, so that the modified water-based protective layer 20 in the cutting protection layer dissolves in the deionized water, and the cutting protection layer is completely detached from the bare core 10a.

[0075] Step S7 includes immersing the bare core 10a in deionized water at 60°C for 30 minutes to fully dissolve the modified water-based protective layer 20 and release the encapsulated fragments. Finally, the surface of the bare core 10a is rigorously inspected using dark-field optical scanning technology to confirm that the residual fragment density is less than 0.03 particles / mm², thus meeting the process cleanliness requirements.

[0076] Compared with existing technologies, this invention employs a cutting protective layer (including a modified water-based protective layer 20 and a light-shielding layer 30) to provide three layers of protection during laser cutting of the wafer 10 (fragment protection of the modified water-based protective layer 20, optical protection of the light-shielding layer 30, and thermal absorption protection of the water-based protective layer 20), preventing damage to the wafer 10 during laser cutting. This invention has the following advantages over existing technologies: 1. Effective control of cutting fragments: The cutting protection layer includes a modified water-based protection layer 20 with a porous skeleton structure 21, and the porous skeleton structure 21 is strengthened by high-temperature cross-linking to form rigid pore walls (modulus 1.2 GPa), which significantly improves the fragment adsorption force.

[0077] 2. A special light-shielding layer 30 is formed on the modified water-based protective layer 20, which has strong light-shielding performance. The light-shielding layer 30 and the modified water-based protective layer 20 are mechanically interlocked through a mechanical interlocking structure 33, which makes the structure stable. The adhesion between the light-shielding layer 30 and the modified water-based protective layer 20 is >8 MPa, ensuring that the light-shielding layer 30 is attached to the modified water-based protective layer 20. It can effectively shield light on the wafer 10, which significantly improves the optical protection performance and prevents laser damage to the non-cutting area of ​​the wafer 10 during laser cutting.

[0078] 3. In the width direction of the opening 32, a buffer zone 321 is formed between the light-shielding part 31 of the light-shielding layer 30 and the cutting channel 11, which effectively suppresses the extension of thermal stress cracks generated during cutting.

[0079] 4. Based on the endothermic decomposition mechanism of the modified water-based protective layer 20, the decomposition temperature of the modified water-based protective layer 20 is effectively increased through cross-linking enhancement in the second temperature range, completely avoiding the risk of carbonization. Under the laser cutting peak temperature of 220℃, the modified water-based protective layer 20 can still controllably decompose and absorb heat energy, making the cutting protective layer have good thermal stability.

[0080] 5. The modified water-based protective layer 20 is cured by stepwise heating in the first temperature range, the second temperature range, and the third temperature range, which effectively eliminates the interlayer thermal expansion mismatch, improves the adhesion between the modified water-based protective layer 20 and the wafer 10, and effectively reduces the risk of peeling compared with the traditional single curing solution.

[0081] 6. The cutting protective layer is finally cured in the third temperature range under an inert gas environment, ensuring the service life of the cutting protective layer.

[0082] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the scope of the present invention are still within the scope of the present invention.

Claims

1. A protective method for wafer laser cutting, used to form a cutting protective layer on the wafer to be cut, characterized in that: Including the following steps: A modified water-based protective slurry is coated onto a wafer to be diced to form a water-based coating, the modified water-based protective slurry comprising modified polyvinyl alcohol and etherified cellulose mixed together with a slurry substrate; The water-based coating is heated within a first temperature range to cure and level it, causing physical entanglement and phase separation between the modified polyvinyl alcohol and etherified cellulose to form a micron-scale porous framework structure. The water-based coating forming a porous framework structure is heated in a second temperature range to enhance cross-linking, so that the molecular chains of the etherified cellulose form an ether bond cross-linking structure through hydroxyl groups, thereby forming a modified water-based protective layer. The temperature in the second temperature range is greater than the temperature in the first temperature range, and the cutting protective layer includes the modified water-based protective layer.

2. The protective method during wafer laser cutting as described in claim 1, characterized in that: The diameter of the pores in the porous skeleton structure is 1 to 5 μm.

3. The protective method during wafer laser cutting as described in claim 1, characterized in that: The first temperature range is 60–85°C, and the second temperature range is 110–130°C.

4. The protective method during wafer laser cutting as described in claim 1, characterized in that, Specifically, heating the water-based coating within a first temperature range for curing and leveling involves: The wafer coated with the water-based coating is placed on a hot plate in the first temperature range for a first duration to cure and level.

5. The protective method during wafer laser cutting as described in claim 1, characterized in that, The water-based coating, which has formed a porous framework structure, is heated in a second temperature range to undergo cross-linking reinforcement. Specifically: The wafer coated with the water-based coating is placed on a hot plate in the second temperature range for a second duration to perform crosslinking enhancement.

6. The protective method during wafer laser cutting as described in claim 5, characterized in that: The water-based coating is cured and leveled within a first temperature range for a first duration, such that the evaporation rate of the water-based coating is greater than 95%. The water-based coating, which forms a porous framework structure, is subjected to cross-linking reinforcement within a second temperature range for a second duration, such that the degree of cross-linking of ether bonds between the molecular chains of the etherified cellulose is greater than or equal to 60%. The second duration is shorter than the first duration.

7. The protective method during wafer laser cutting as described in claim 5, characterized in that: The first duration is 5 to 12 minutes, and the second duration is 60 seconds ± 10 seconds.

8. The protective method during wafer laser cutting as described in claim 1, characterized in that: The method also includes the steps of: forming a light-shielding layer on the modified water-based protective layer using a light-shielding protective material, curing the light-shielding layer, forming a through opening in the light-shielding layer at a position corresponding to the wafer dicing channel, so that the light-shielding layer is divided into several light-shielding portions, and the dicing protective layer includes the light-shielding layer.

9. The protective method during wafer laser cutting as described in claim 8, characterized in that: The width of the opening is greater than the width of the cutting channel, and a buffer zone is formed between the opening and the cutting channel in the width direction of the opening.

10. The protective method during wafer laser cutting as described in claim 9, characterized in that: In the width direction of the opening, the distance between the edge of the light-shielding part and the cutting channel is greater than or equal to 5 μm and less than or equal to 10 μm.

11. The protective method during wafer laser cutting as described in claim 8, characterized in that: The light-shielding protective material uses polyimide prepolymer as the matrix and also contains light-shielding fillers; Curing the light-shielding layer specifically includes: heating the cutting protective layer in an inert environment within a third temperature range, thereby activating the polyimide prepolymer and embedding it into the porous skeleton structure of the modified water-based protective layer to form a mechanical interlocking structure, wherein the temperature in the third temperature range is greater than the temperature in the second temperature range.

12. The protective method during wafer laser cutting as described in claim 11, characterized in that: Heating the light-shielding layer in a third temperature range under an inert environment specifically includes: The light-shielding layer is heated for a fourth duration within a fourth temperature range to perform a single curing process; The light-shielding layer is heated for a fifth duration within a fifth temperature range to perform secondary curing; The third temperature range includes a fourth temperature range and a fifth temperature range, wherein the temperature in the fourth temperature range is lower than the temperature in the fifth temperature range, and the fourth duration is longer than the fifth duration.

13. The protective method during wafer laser cutting as described in claim 13, characterized in that: The fourth temperature range is 140–160°C, the fourth duration is 15–25 min, the fifth temperature range is 170–190°C, and the fifth duration is 3–7 min.

14. The protective method during wafer laser cutting as described in claim 8, characterized in that: A light-shielding protective material is printed onto the modified water-based protective layer using screen printing technology to form a light-shielding layer.

15. The protective method during wafer laser cutting as described in claim 8, characterized in that: The light-shielding filler used in the light-shielding protective material is nano-carbon black, and the content of nano-carbon black in the light-shielding protective material is 5.5 wt%, and the particle size of the nano-carbon black is 30 nm.

16. The protective method during wafer laser cutting as described in claim 8, characterized in that: Before forming a light-shielding layer on the modified water-based protective layer, the surface of the modified water-based protective layer is subjected to plasma surface treatment.

17. The protective method during wafer laser cutting as described in claim 1, characterized in that: Before coating the wafers to be diced with a modified water-based protective slurry to form a water-based coating, the wafer surfaces to be diced are cleaned, hydrophilic modified, and dried.

18. The protective method during wafer laser cutting as described in claim 1, characterized in that: The thickness of the water-based coating is 20±0.5μm, and the slurry substrate includes deionized water and oxidized starch.

19. A wafer laser cutting method, characterized in that: include: Using the protective method for wafer laser cutting as described in any one of claims 1-18, a cutting protective layer is formed on the wafer to be cut; Lasers are used to cut wafers along the dicing lines to separate several bare cores; The bare crystals are soaked in deionized water to dissolve the water-based protective layer in the deionized water.

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