A protective liquid for the entire wafer thinning and cutting process, and its preparation method and application

Abstract

The present invention relates to a protective liquid for the entire process of wafer thinning and cutting, and a preparation method and application thereof. The protective liquid comprises: a curing agent, a water-soluble resin and deionized water; the mass ratio of the curing agent, the water-soluble resin and the deionized water is 5-10:10-50:40-100. The curing agent has a special structure, which can comprehensively improve the adhesion, water resistance and pencil hardness of the resin, thereby ensuring that the film layer is always firmly attached to the chip surface during multiple processes from wafer thinning to wafer cutting, and can resist chip damage caused by debris splashing and fixtures. The protective liquid containing the curing agent can be applied to the wafer surface from the beginning of the wafer thinning process until the end of the blade cutting. The protective liquid covers more processes and provides more comprehensive protection for the wafer.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor manufacturing technology, and in particular relates to a protective liquid used in the entire process of wafer thinning and cutting, and a preparation method and application thereof. Background Art

[0002] The basic chip packaging process includes wafer thinning, wafer lamination, wafer dicing, chip pasting, and wire bonding. Wafer thinning involves grinding the back of the wafer with a diamond grinding wheel. Before thinning, a film is applied to the chip device layer to prevent damage to the circuit. The wafer is thinned to the desired thickness through three steps: rough grinding, fine grinding, and polishing. There are two main issues commonly encountered during wafer thinning: warping due to mechanical stress, and thermal damage caused by the generation of large amounts of heat during the grinding process, which can be caused by inadequate heat dissipation.

[0003] The most common method for cutting ultra-thin chips is with diamond cutting blades. Diamond abrasives continuously shed and dig up the cutting surface to separate the chips. However, silicon is a brittle material with high hardness and a low melting point. Diamond abrasives introduce significant stress when cutting silicon wafers. The most common problem is edge chipping, including metal layer edge chipping and back cracking. Furthermore, when cutting ultra-thin wafers, particles are generated at the cut surface. These particles can easily be lifted and fall onto the ultra-thin wafer. Furthermore, during the transfer process, many particles from the environment can also land on the surface of the ultra-thin wafer. Many high-end ultra-thin wafers are highly sensitive to particles, significantly reducing their yield. Furthermore, water is sprayed onto the blade and the ultra-thin wafer during the cutting process to cool them. The high-speed rotation of the blade generates a powerful stream of water containing cutting debris, which splashes onto the surface of the ultra-thin wafer, causing scratches and reducing the wafer yield.

[0004] Throughout the entire ultra-thin wafer thinning and dicing process, it is crucial to prevent environmental and dicing particles from falling onto the wafer surface, debris from dicing from scratching the wafer surface, and warping or edge collapse from grinding and dicing, which can reduce the yield of ultra-thin wafers. Therefore, there is an urgent need to develop a protective liquid and method for the entire ultra-thin wafer thinning and dicing process to protect the delicate structures on the wafer surface from damage. Summary of the Invention

[0005] The technical problem solved by the present invention is: how to prevent the environment and particles generated by cutting from falling onto the surface of the ultra-thin wafer, debris generated during cutting from scratching the surface of the ultra-thin wafer, warping or edge collapse caused by grinding and cutting, and other problems during the entire process from wafer thinning to wafer cutting of ultra-thin wafers with a thickness of no more than 100 microns.

[0006] In view of the technical problems existing in the prior art, the present invention designs a protective liquid for the entire process of wafer thinning and cutting, as well as its preparation method and application, to protect ultra-thin wafers from the grinding stage to the end of cutting, thereby preventing damage to the delicate structures on the surface of the ultra-thin wafers and improving the pass rate of ultra-thin wafers.

[0007] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "consisting of..." etc. and similar meanings.

[0008] In order to solve the above-mentioned technical problems, the present invention adopts the following solutions:

[0009] [The first technical solution]

[0010] In a first aspect, a technical solution of the present invention is to provide a method for preparing a curing agent, comprising the following steps:

[0011] Step 1: Add polyethylene glycol-polylysine and an amino silane coupling agent into a reactor at 100-120° C. under nitrogen protection, and stir for 2-4 hours to obtain product A;

[0012] Step 2: Add triol and diisocyanate to the reactor, raise the temperature to 60-80°C, react for 3-4 hours under nitrogen protection, add product A obtained in step 1, maintain the temperature at 60-80°C and continue the reaction for 1-2 hours to obtain product B;

[0013] Step 3: Add an imidazole compound to product B and react at 80-100°C for 2-3 hours to obtain a curing agent.

[0014] Furthermore, the amino silane coupling agent is any one of (3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane.

[0015] Furthermore, the triol is any one of 1,2,3-propanetriol, 1,2,4-butanetriol, and 1,2,6-hexanetriol.

[0016] Furthermore, the diisocyanate is any one of hexamethylene diisocyanate, 1,3-diisophenyl cyanate, isophorone diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, m-xylyl diisocyanate, and 1,4-butyl diisocyanate.

[0017] Furthermore, the imidazole compound is any one of imidazole, 2-phenylimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-isopropylimidazole.

[0018] Furthermore, the molar ratio of the polyethylene glycol-polylysine to the amino silane coupling agent is 1-1.5:1.

[0019] Furthermore, the molar ratio of the triol to the diisocyanate is 1:3.5-4.

[0020] Furthermore, the molar ratio of the triol to the amino silane coupling agent is 1.72-1:1.

[0021] Furthermore, the molar ratio of the imidazole to the triol is 1-3:1.

[0022] [Second technical solution]

[0023] In the second aspect, a technical solution of the present invention is to provide a protective liquid for the entire process of wafer thinning and cutting, the components of which include a curing agent, a water-soluble resin and deionized water; the mass ratio of the curing agent, water-soluble resin and deionized water is 5-10:10-50:40-100.

[0024] Furthermore, the water-soluble resin is an acrylic resin containing hydroxyl groups, and has a molecular weight of 5,000-20,000.

[0025] Furthermore, the water-soluble resin is one or more of polyhydroxyethyl acrylate, polyhydroxypropyl methacrylate, hydroxyethyl methacrylate-acrylic acid copolymer, methyl methacrylate-hydroxyethyl methacrylate copolymer, butyl acrylate-hydroxyethyl acrylate copolymer, and methyl methacrylate-hydroxyethyl acrylate-acrylic acid copolymer.

[0026] Furthermore, the water-soluble resin is one or more of polyhydroxyethyl acrylate, polyhydroxypropyl methacrylate, hydroxyethyl methacrylate-acrylic acid copolymer, and methyl methacrylate-hydroxyethyl methacrylate copolymer.

[0027] [The third technical solution]

[0028] In a third aspect, a technical solution of the present invention is to provide a method for preparing the protective solution, comprising the following steps:

[0029] Step 1: Weigh the respective mass parts of curing agent, water-soluble resin and deionized water;

[0030] Step 2: Stir the components at room temperature at a speed of 200-500 r / min for 1-5 hours to obtain the protective solution.

[0031] Furthermore, the stirring speed in step 2 is 200-500 r / min, for example, 200 r / min, 300 r / min, 400 r / min, or 500 r / min.

[0032] Furthermore, the stirring time in step 2 is 1-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h.

[0033] [The fourth technical solution]

[0034] In a fourth aspect, a technical solution of the present invention is to provide a use of the protective liquid to protect the precision structure of the chip surface in multiple processes from wafer thinning to chip cutting.

[0035] [Fifth technical solution]

[0036] In a fifth aspect, a technical solution of the present invention is to provide a method for using the protective liquid, comprising the following steps:

[0037] Step 1: Add protective liquid droplets to the wafer surface and rotate at a speed of 500-1500 rpm for 30-60 seconds;

[0038] Step 2: Bake the wafer with the protective liquid spin-coated on its surface at 100-130°C for 5-30 minutes to solidify the film and form a protective layer; the protective layer is formed on the front surface precision structure of the wafer;

[0039] Step 3: Apply tape to one side of the wafer covered with the protective layer, with the tape on the front side of the wafer; grind, polish, and thin the back side of the wafer to the required thickness; and remove the grinding tape.

[0040] Step 4: Apply a blue film on the back of the wafer and cut the wafer;

[0041] Step 5: After screening and rearranging the cut chips, clean the protective layer on the chip surface and remove the protective layer.

[0042] The curing agent of the present invention has unique advantages:

[0043] First, the present invention applies a protective liquid to the wafer surface and heat-cures it before the wafer thinning process. Under heating conditions, the curing agent in the protective liquid releases free isocyanate groups, which further react with the hydroxyl groups in the water-soluble resin to increase the cross-linking density of the system.

[0044] Secondly, the hydrolysis of the siloxane in the curing agent forms Si-O-Si covalent bonds with the silicon substrate, enhancing the adhesion between the film and the wafer. Simultaneously, during the curing process, silicon atoms migrate to the film surface, increasing its hydrophobicity. This increased crosslink density makes the film structure denser, further preventing water molecules from penetrating and improving the film's water resistance.

[0045] Thirdly, the introduction of rigid structures such as aromatic groups and isocyanate groups in the curing agent also improves the pencil hardness of the film.

[0046] Fourthly, the amino groups in the curing agent and the hydroxyl groups in the water-soluble resin form a hydrogen bond network, which can guide the reactants to approach, reduce the transition state energy, and accelerate the curing reaction process, so that the curing agent and the water-soluble resin can fully react in a short time.

[0047] Therefore, the curing agent with a special structure comprehensively improves the adhesion, water resistance and pencil hardness of the water-soluble resin, thereby ensuring that the film layer is always firmly attached to the wafer surface during multiple processes from wafer thinning to wafer cutting, and can resist wafer damage caused by debris splashing.

[0048] The present invention provides a protective liquid for the entire wafer thinning and cutting process, and a preparation method and application thereof, which have the following beneficial effects:

[0049] 1. The protective liquid of the present invention is applied to the wafer surface from the beginning of the wafer thinning process until the end of cutting. The protective liquid covers more processes and provides more comprehensive protection for the wafer.

[0050] 2. The protective liquid coating of the present invention exhibits excellent adhesion, water resistance, and hardness. During the baking process, the isocyanate groups in the curing agent are released and react with the hydroxyl groups in the water-soluble resin, increasing the degree of cross-linking of the water-soluble resin. Furthermore, the aromatic, carbamate, and siloxane groups introduced by the curing agent impart higher water resistance, hardness, and adhesion to the film. This ensures that the coating adheres firmly to the wafer surface during the grinding and cutting processes, protecting the delicate structures on the wafer from contamination or damage.

[0051] 3. The protective solution of the present invention has excellent storage stability. Because the isocyanate groups are blocked with imidazole compounds, they are not released until heated to the deblocking temperature. At room temperature, there are no free isocyanate groups in the protective solution and they do not react with water, allowing for stable storage.

[0052] Therefore, the protective liquid and the protective method of the present invention have very good application prospects and large-scale industrial promotion potential in the field of ultra-thin wafer processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 : is the infrared spectrum of curing agent 1;

[0054] Figure 2 : A micrograph of the electrode after soaking and cleaning in Comparative Example 2, magnified 1870 times;

[0055] Figure 3 : A micrograph of the electrode after immersion and cleaning in Example 1, magnified 1870 times;

[0056] Figure 4 : A photo of the film state after the water resistance test of Comparative Example 1;

[0057] Figure 5 : A photograph of the film layer after the water resistance test of Example 1;

[0058] Figure 6 : This is a photo of comparative example 4 after adhesion test;

[0059] Figure 7 : This is a photo of the adhesion test of Example 1. DETAILED DESCRIPTION

[0060] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0061] Preparation method of curing agent 1-curing agent 8:

[0062] Step 1: Add the polymer and amino silane coupling agent into the reactor at 120°C under nitrogen protection and stir for 3 hours to obtain product A;

[0063] Step 2: Add triol and diisocyanate to the reactor, heat to 80°C, react under nitrogen protection for 4 hours, add product A obtained in step 1, maintain the temperature at 80°C and continue to react for 2 hours to obtain product B;

[0064] Step 3: Add an imidazole compound to product B and react at 100° C. for 3 hours to obtain a curing agent.

[0065] Table 1: Curing Agent 1-Curing Agent 8

[0066]

[0067] Preparation methods of protective liquid embodiments and comparative examples of the present invention:

[0068] Step 1: Weigh the respective mass parts of curing agent, water-soluble resin and deionized water;

[0069] Step 2: Add the various components into a mixing container equipped with a stirrer, and stir at a speed of 400 r / min for 2 hours at room temperature to obtain the protective solution.

[0070] Table 2: Examples 1 to 9 of protective solutions

[0071]

[0072] Table 3: Comparative Examples 1 to 5 of Protective Liquid

[0073]

[0074] Table 4: Test data of Examples 1 to 9 and Comparative Examples 1 to 5

[0075]

[0076] About performance testing and description:

[0077] Method of use of the protective liquid embodiment and comparative example of the present invention:

[0078] Step 1: Add 50ml of protective solution to the wafer surface and use a spin coater to rotate at 1000r / min for 60s;

[0079] Step 2: The wafer with the protective liquid spin-coated on its surface is transferred to a forced air drying oven and baked at 120°C for 10 minutes to solidify the film and form a protective layer; the protective layer is formed on the precision structure on the front side of the wafer;

[0080] Step 3: Apply tape to one side of the wafer covered with the protective layer, with the tape on the front side of the wafer; grind, polish, and thin the back side of the wafer to the required thickness; and remove the grinding tape.

[0081] Step 4: Apply a blue film on the back of the wafer and cut the wafer;

[0082] Step 5: After screening and rearranging the cut chips, clean the protective layer on the chip surface and remove the protective layer.

[0083] Performance 1 The test method for aluminum electrode corrosion is:

[0084] The chip was immersed in the protective solution for 6 h in a static Class 100 clean room. The chip was then taken out and the chip surface was rinsed with ultrapure water for 2 min and dried with nitrogen. The corrosion of the electrode was observed under a dark field microscope at a magnification of 1870 times.

[0085] Performance 2 Water resistance test method is:

[0086] Spin-coat the protective liquid on the Dummy sheet and solidify it, soak it in water, take it out after 24 hours and spin-dry it, and observe the state of the film layer. If the protective film on the Dummy sheet does not fall off, it indicates that its water resistance meets the requirements.

[0087] Performance 3 pencil hardness test method is:

[0088] The protective liquid was spin-coated on the dummy sheet and cured. The hardness of the paint film was measured using a portable pencil hardness tester (Zhonghua brand high-grade drawing pencil) according to GB / T 6739-2006. The hardness from soft to hard is: 9B-8B-7B-6B-5B-4B-3B-2B-1B-HB-FH-1H-2H-3H-4H-5H-6H-7H-8H-9H.

[0089] Performance 4 Adhesion test method is:

[0090] The protective liquid was spin-coated onto a dummy sheet and cured, and adhesion was tested using the cross-grid method. Adhesion grade criteria are as follows: 0B: Large flakes of coating peeled off at the edges and intersections of the scribe line, with the total peeled area exceeding 65%; 1B: Large flakes of coating peeled off at the edges and intersections of the scribe line, with the total peeled area between 35-65%; 2B: Large flakes of coating peeled off at the edges and intersections of the scribe line, with the total peeled area between 15-35%; 3B: Small flakes of coating peeled off at the edges and intersections of the scribe line, with the total peeled area between 5-15%; 4B: Small flakes of coating peeled off at the intersections of the scribe line, with the total peeled area less than 5%; 5B: The scribe line edge is smooth, with no coating peeling at the edges or intersections.

[0091] Performance 5 Storage stability test method is:

[0092] Store the protective solution at 25°C. Observe its appearance and condition every two weeks and test its viscosity. If the appearance, condition, and viscosity of the protective solution remain unchanged, it is considered storage-stable. The maximum storage time for the protective solution is then determined. The time it takes for the protective solution to gel is also recorded. If the curing agent releases isocyanate groups, the protective solution will gel. If the appearance and viscosity of the protective solution remain unchanged, it indicates that there are no free isocyanate groups.

[0093] Analysis of the test results:

[0094] Based on Table 4, it can be seen that the protective liquid of the embodiment of the present invention significantly improves water resistance, adhesion, pencil hardness and storage time compared with the protective liquid of the comparative example, and reduces corrosion of the aluminum electrode.

[0095] The protective liquid in Comparative Example 1 does not contain a curing agent but only contains a water-based resin. The adhesion and water resistance on the substrate are very poor, and the absence of a rigid group also results in a low pencil hardness of the film layer.

[0096] The curing agent of Comparative Example 2 is Product B. The silane coupling agent in Product B can enhance the adhesion between the resin and the substrate, but the improvement is small.

[0097] The curing agent in Comparative Example 3 is Product A, i.e., an unblocked isocyanate curing agent. Although the film performance is significantly improved, the protective liquid contains free isocyanate groups, which react with water and resin. The protective liquid cannot be stored stably and quickly gels after being placed for one day, making it unusable subsequently.

[0098] The curing agent in Comparative Example 4 is toluene diisocyanate, which can increase the crosslinking density of the resin, but compared with the isocyanate curing agent containing a silane coupling agent in the embodiment, the improvement in the adhesion between the film layer and the substrate is smaller.

[0099] The curing agent of Comparative Example 5 is curing agent 8, which does not contain free amino groups and cannot guide the reactants to accelerate the curing reaction process. Therefore, the resin and curing agent cannot fully react in a short time. Therefore, the film performance is slightly improved, but still worse than the embodiment.

[0100] Further comparison is made through the accompanying drawings in the specification:

[0101] from Figure 1 It can be seen that 3336cm -1 The NH stretching vibration peak is at 1727 cm -1 The peak of C=O stretching vibration is located at 1040cm -1 At 2260cm -1 No characteristic peak of -N=C=O group was observed, which proved that the isocyanate was completely reacted. This proves that the blocked curing agent 1 was successfully synthesized. Figure 2 It can be seen that after soaking and cleaning in Comparative Example 2, a bright blue structure appeared on the chip electrode surface under the dark field of a microscope, indicating that the chip electrode surface was severely corroded. Figure 3 It can be seen that after soaking and cleaning in Example 1, there is almost no irregular bright structure on the chip electrode surface under the dark field of the microscope, which indicates that the chip electrode surface is not corroded. Figure 4 It can be seen that after the water resistance test of Comparative Example 1, the film layer completely fell off, indicating that the water resistance of the film layer is poor. Figure 5 It can be seen that after the water resistance test of Example 1, the film layer is intact and has no changes, indicating that the film layer has good water resistance. Figure 6 It can be seen that after the adhesion test of Comparative Example 4, the area of the film layer peeling off after the 3M tape was torn off was more than 5% but less than 15%, and the adhesion level was judged to be 3B. Figure 7 It can be seen that after the adhesion test of Example 1, the film layer is intact after the 3M tape is torn off without any falling off, and the adhesion level is judged to be 5B.

[0102] The present invention has been described above by way of example in conjunction with the embodiments and accompanying drawings. It is obvious that the implementation of the present invention is not limited to the above-mentioned methods. As long as various improvements are made using the method concepts and technical solutions of the present invention, or the concepts and technical solutions of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a curing agent, characterized in that: The steps include: Step 1: Add polyethylene glycol-polylysine and an amino silane coupling agent into a reactor at 100-120° C. under nitrogen protection, and stir for 2-4 hours to obtain product A; Step 2: Add triol and diisocyanate to the reactor, raise the temperature to 60-80°C, react for 3-4 hours under nitrogen protection, add product A obtained in step 1, maintain the temperature at 60-80°C and continue the reaction for 1-2 hours to obtain product B; Step 3: Add an imidazole compound to product B and react at 100°C for 2-3 hours to obtain a curing agent; The amino silane coupling agent is any one of (3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane; The triol is any one of 1,2,3-propanetriol, 1,2,4-butanetriol, and 1,2,6-hexanetriol; The diisocyanate is any one of hexamethylene diisocyanate, 1,3-diisophenyl cyanate, isophorone diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, m-xylyl diisocyanate, and 1,4-butyl diisocyanate; The imidazole compound is any one of imidazole, 2-phenylimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-isopropylimidazole.

2. The method for preparing a curing agent according to claim 1, wherein The molar ratio of the polyethylene glycol-polylysine to the amino silane coupling agent is 1-1.5:1; the molar ratio of the triol to the diisocyanate is 1:3.5-4; and the molar ratio of the imidazole to the triol is 1-3:

1.

3. A protective liquid for the entire wafer thinning and cutting process, characterized in that: Contains the curing agent according to claim 1.

4. The protective liquid according to claim 3, characterized in that The components include a curing agent, a water-soluble resin and deionized water; the mass ratio of the curing agent, the water-soluble resin and the deionized water is 5-10:10-50:40-100.

5. The protective liquid according to claim 4, characterized in that The water-soluble resin is an acrylic resin containing hydroxyl groups and has a molecular weight of 5000-20000.

6. A method for preparing the protective solution according to any one of claims 3 to 5, characterized in that: The following steps are involved: Step 1: Weigh the respective mass parts of curing agent, water-soluble resin and deionized water; Step 2: Stir the components at room temperature at a speed of 200-500 r / min for 1-5 hours to obtain the protective solution.

7. A method for using the protective solution according to any one of claims 3 to 5, characterized in that: The steps include: Step 1: Add protective liquid droplets to the wafer surface and rotate at a speed of 500-1500 rpm for 30-60 seconds; Step 2: Bake the wafer with the protective liquid spin-coated on its surface at 100-130°C for 5-30 minutes to solidify the film and form a protective layer; the protective layer is formed on the front surface of the wafer; Step 3: Apply tape to one side of the wafer covered with the protective layer, with the tape on the front side of the wafer; grind, polish, and thin the back side of the wafer to the required thickness; Remove the abrasive tape; Step 4: Apply a blue film on the back of the wafer and cut the wafer; Step 5: After screening and rearranging the cut chips, clean the protective layer on the chip surface and remove the protective layer.

8. Use of the protective liquid according to any one of claims 3 to 5 for protecting the precise structure of a chip surface in multiple processes from wafer thinning to chip cutting.

Images