A protective film for ultra-thin lithium tantalate wafer and a film removal method

Abstract

A protective film and film removal method for an ultra-thin lithium tantalate wafer includes the following steps: ultrasonically cleaning the lithium tantalate wafer with an alkaline cleaning solution; drying the lithium tantalate wafer in a spin dryer; evenly applying the protective film to the front surface of the lithium tantalate wafer and curing it; sandblasting the lithium tantalate wafer; and placing the lithium tantalate wafer in a stripper solution and ultrasonically cleaning it under heating to remove the film, ultimately producing a lithium tantalate wafer with no residual adhesive on the surface. Through process improvements, the present invention effectively solves the problem of residual adhesive remaining on the wafer surface after film removal in traditional processes, while also improving production efficiency, reducing production costs, and ensuring production yield.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and in particular to a protective film for an ultra-thin lithium tantalate wafer and a film stripping method. Background Art

[0002] Lithium tantalate (LiTaO3, LT) exhibits excellent piezoelectric, acousto-optic, ferroelectric, and pyroelectric properties, making it an essential functional material in surface acoustic wave (SAW) devices, optical communications, lasers, and optoelectronics. Polished LT wafers are widely used in the manufacture of electronic communications devices such as resonators, filters, and transducers. Its excellent electromechanical coupling and temperature coefficient make it particularly well-suited for the manufacture of high-frequency SAW devices, which are used in many high-end communications applications, including mobile phones, walkie-talkies, satellite communications, and aerospace.

[0003] Laminating and sandblasting are common processes in lithium tantalate production. Sandblasting typically involves using high-pressure air to convert mortar dust into a fluid, which is then sprayed through specialized pipes and nozzles onto the wafer surface. During the production of lithium tantalate wafers, the back of the wafer must be sandblasted. This requires protective measures on the front of the wafer to prevent mortar from accidentally spraying onto the front, which could affect sandblasting yield. This process is often supplemented by laminating. The wafer protective film used in existing processes is typically made of PVC. This film is applied to the front of the wafer using a laminating machine and then manually removed after sandblasting is complete. However, this process can easily leave residual adhesive on the wafer surface due to incomplete curing of the tape and weak adhesive cohesion, necessitating rework and cleaning, which increases the complexity of the cleaning process. Traditional PVC film application requires a certain amount of pressure, coupled with a blade to remove excess film from the wafer edge. This can easily lead to scratches, chipping, and breakage of ultra-thin lithium tantalate wafers during processing. The existing chip protective film and demolding process have high processing costs, complex processes, and it is difficult to ensure the chip yield. There is an urgent need for a protective film and demolding method for ultra-thin lithium tantalate chips to reduce processing costs, optimize processing technology, and improve processing yield.

[0004] Patent publication number CN113023021A discloses a film-tearing device and a film-tearing control method. The device features a pressure-sensing unit and a control unit. The pressure-sensing unit detects the pressure exerted by the tearing roller on the screen during the tearing process in real time, allowing for timely intervention in the tearing process (e.g., stopping the tearing roller, sounding an alarm, etc.), preventing undesirable film breakage and thereby improving product yield during the tearing process. While this method ensures product yield, it cannot avoid the problem of residual adhesive remaining on the wafer surface after film tearing, requiring wafers with residual adhesive to be reworked and cleaned.

[0005] Therefore, the prior art lacks a lithium tantalate wafer protective film and a demolding technology that can remove the residual adhesive without any residue, has a high product yield, and has a low processing cost. Summary of the Invention

[0006] The present invention provides a protective film and a film removal method for an ultra-thin lithium tantalate wafer to address the defects of the prior art. The method has a stable processing process and solves the problems of residual adhesive left on the wafer surface when the film is peeled off in the traditional film lamination process and the wafer is damaged during the film lamination and peeling process. The obtained wafer surface has high cleanliness, high processing yield, and reduced processing costs.

[0007] The technical solution adopted by the present invention to solve the problem is: a protective film for an ultra-thin lithium tantalate wafer and a method for removing the film, the wafer protective film and the method for removing the film comprising the following steps:

[0008] a) Place the lithium tantalate wafer in an alkaline cleaning solution at 45-55°C and ultrasonically clean it for 10-25 minutes to clean the particle and organic contamination on the wafer surface. Then rinse the wafer in a pure water tank to remove the residual cleaning solution on the wafer surface.

[0009] b) placing the lithium tantalate wafer treated in step a) in a spin dryer and drying the wafer at a rotation speed of 300 to 1000 rpm for 3 to 8 minutes to obtain a wafer with a dry surface and no water marks;

[0010] c) placing the lithium tantalate wafer treated in step b) on a screen printing table, uniformly coating the front surface of the lithium tantalate wafer with a wafer protective film by screen printing, and then irradiating the lithium tantalate wafer coated with the protective film under an ultraviolet lamp for 1 to 5 minutes to allow the wafer protective film to cure;

[0011] d) adsorbing the front surface of the lithium tantalate wafer treated in step c) onto a vacuum platform of a sandblasting machine for sandblasting;

[0012] e) The lithium tantalate wafer treated in step d) is placed in a stripping agent cleaning solution at 70-85° C. and ultrasonically immersed for 10-30 minutes for stripping treatment, and then the wafer is placed in a pure water tank for rinsing to remove the stripping agent residue on the wafer surface. Finally, the wafer is dried to obtain a lithium tantalate wafer with no residual glue on the surface.

[0013] In step a), an alkaline cleaning solution is heated and ultrasonically cleaned to remove particle and organic contamination from the wafer surface, thereby preventing poor adhesion of the protective film due to contamination such as particles, grease, etc. on the wafer surface. The cleaning ultrasonic frequency is 40 kHz, and the alkaline cleaning solution is a mixture of an alkaline detergent and pure water in a certain proportion.

[0014] The alkaline cleaning solution in step a) is prepared by mixing pure water and an alkaline cleaning agent in a volume ratio of 3 to 10:1, and the mass fractions of the components constituting the alkaline cleaning agent are 50 to 60% pure water, 5 to 20% inorganic base, 10 to 20% chelating agent, 5 to 15% inorganic auxiliary agent, and 5 to 10% organic base.

[0015] In the above step b), the wafer is dried using a spin dryer to avoid residual water stains on the wafer surface that may affect the adsorption effect of the protective film.

[0016] In step c) above, a protective film is evenly applied to the front surface of the wafer by screen printing. The screen printing screen is set to 100-200 mesh. The wafer protective film is a viscous liquid mixture made of polyester, acrylic acid, a monomer mixture, and an additive. The lithium tantalate wafer coated with the protective film is placed under an ultraviolet lamp to accelerate the curing of the wafer protective film. The liquid protective film is applied by screen printing, thereby avoiding damage to the wafer during the application process.

[0017] The mass ratio of the components of the protective film in step c) is 35-50% polyester, 10-20% monomer mixture, 15-25% acrylic acid, and 15-25% diluent. The illumination of the ultraviolet lamp is 600-2000 mw / cm 2 .

[0018] In the above step d), high-pressure air is used to spray the slurry onto the surface of the wafer through the pipeline and the nozzle. Vacuum adsorption is used to fix the wafer to effectively prevent the wafer from falling off while minimizing the adsorption of mortar particles onto the front of the wafer. The nozzle pressure is 0.20-0.30 MPa, the nozzle reciprocates 4-6 times, and the sandblasting temperature is 70-80°C.

[0019] In step e) above, the lithium tantalate wafer is placed in a stripper cleaning solution for cleaning. The alkaline substances and additives in the stripper react with the polyester and acrylic acid in the protective film at a certain temperature. At the same time, ultrasound will accelerate the removal of the protective film. This method avoids damage to the wafer caused by manual film tearing and avoids residual adhesive left after film tearing.

[0020] In the above step e), the release agent is prepared by mixing pure water, an inorganic base, a surfactant, a co-solvent, and a stripping aid.

[0021] The release agent cleaning solution in step e) is prepared by mixing pure water and the release agent in a volume ratio of 3 to 9:1, and the mass ratio of the components constituting the release agent is 40 to 65% pure water, 5 to 15% sodium hydroxide, 10 to 25% surfactant, 5 to 15% cosolvent, and 3 to 10% stripping agent.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] First, the wafer protective film used in the present invention is a mixture of polyester and acrylic acid. After heating, it reacts with an alkaline cleaning solution and is easily removed by ultrasound, thus solving the problem of residual adhesive left on the wafer surface when the traditional film is removed.

[0024] Secondly, the ultra-thin lithium tantalate wafer protective film proposed by the present invention is a viscous liquid mixture, which is applied by screen printing combined with ultraviolet light. No external pressure or blade cutting of the protective film is required, thus avoiding the fragmentation and edge collapse caused by traditional film laminating machines during the laminating process, and achieving a high processing yield.

[0025] Thirdly, the chemical stripping method adopted by the present invention reduces the manual film tearing process, avoids the chip damage caused by improper film tearing, and improves the processing yield;

[0026] Fourthly, the film sticking and tearing processes adopted by the present invention reduce production costs, while reducing manpower input and labor loss, and improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the processing flow of the present invention.

[0028] Figure 2 Schematic diagram of the relationship between the stripping and cleaning temperature and the stripping effect in Examples 1, 2, and 3 of the present invention.

[0029] Figure 3 Schematic diagram of the relationship between the sodium hydroxide content and the demolding effect in the demolding agents of Examples 2, 4, and 5 of the present invention.

[0030] Figure 4 Schematic diagram comparing the demolding effects of the process of the present invention and the traditional process in Examples 4, 5 and 6 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the following examples, but the scope of protection of the present invention should not be limited thereto.

[0032] Example 1:

[0033] a) Prepare an alkaline cleaning agent according to the following mass fractions: 10% inorganic base, 15% chelating agent, 8% inorganic additive, 7% organic base, and 60% pure water. Mix the mixture in a volume ratio of 5:1 between pure water and alkaline cleaning agent to form an alkaline cleaning solution. Place the lithium tantalate wafer in the alkaline cleaning solution at 50°C and perform ultrasonic cleaning at 40kHz for 20 minutes.

[0034] b) Place the cleaned lithium tantalate wafer into a spin dryer and spin dry it at a speed of 500 rpm for 5 minutes;

[0035] c) Place the lithium tantalate wafer on a screen printing table, evenly apply the liquid protective film to the front of the lithium tantalate wafer to be processed by screen printing, and then place the lithium tantalate wafer coated with the protective film under a UV LED for 3 minutes;

[0036] d) The front side of the lithium tantalate wafer was adsorbed on the vacuum platform of the sandblasting machine for sandblasting. The sandblasting temperature was 72°C, the nozzle pressure was 0.26 MPa, and the nozzle was reciprocated for 6 times.

[0037] e) A release agent was prepared according to the mass fractions of the following ingredients: 45% pure water, 5% sodium hydroxide, 25% surfactant, 15% cosolvent, and 10% stripping aid. The mixture was mixed in a volume ratio of pure water to release agent of 7:1 to form a release agent solution. Lithium tantalate wafers were ultrasonically immersed in the release agent solution at 60°C for 15 minutes. 422 wafers were put into the release agent solution. 14 wafers had residual adhesive on the surface, 3 wafers were scratched, and 0 wafers had edge chipping. The surface residual adhesive rate was 3.32%, the scratch rate was 0.71%, the edge chipping rate was 0.00%, and the yield rate was 95.97%.

[0038] Example 2:

[0039] a) Same as Example 1;

[0040] b) Same as Example 1;

[0041] c) Same as Example 1;

[0042] d) Same as Example 1;

[0043] e) A release agent was prepared according to the mass fractions of the following ingredients: 45% pure water, 5% sodium hydroxide, 25% surfactant, 15% cosolvent, and 10% stripping aid. The mixture was mixed in a volume ratio of pure water to release agent of 7:1 to form a release agent solution. Lithium tantalate wafers were ultrasonically immersed in the release agent solution at 70°C for 15 minutes. 453 wafers were put into the release agent solution. 8 wafers had residual adhesive on the surface, 2 wafers were scratched, and 0 wafers had edge chipping. The surface residual adhesive rate was 1.77%, the scratch rate was 0.44%, the edge chipping rate was 0%, and the yield rate was 97.79%.

[0044] Example 3:

[0045] a) Same as Example 1;

[0046] b) Same as Example 1;

[0047] c) Same as Example 1;

[0048] d) Same as Example 1;

[0049] e) A release agent was prepared according to the mass fractions of the following ingredients: 45% pure water, 5% sodium hydroxide, 25% surfactant, 15% cosolvent, and 10% stripping aid. The mixture was mixed in a volume ratio of pure water to release agent of 7:1 to form a release agent solution. Lithium tantalate wafers were ultrasonically immersed in the release agent solution at 80°C for 15 minutes. 401 wafers were put into the release agent solution. 7 wafers had residual adhesive on the surface, 2 wafers had scratches, and 0 wafers had edge chipping. The surface residual adhesive rate was 1.75%, the scratch rate was 0.50%, the edge chipping rate was 0.00%, and the yield rate was 97.76%.

[0050] Comparing Examples 1, 2, and 3, as shown in Table 1, the stripping and cleaning effect is affected by the cleaning temperature. When the temperature is too low, the stripping effect is poor. At the same time, due to the pyroelectric properties of the lithium tantalate wafer itself, the cleaning temperature cannot be too high.

[0051] Table 1 Wafer cleaning residual adhesive rate and scratch rate of Examples 1, 2, and 3

[0052] Test items Example 1 Example 2 Example 3 Residual glue rate 3.32% 1.77% 1.75% Scratch rate 0.71% 0.44% 0.50%

[0053] Example 4:

[0054] a) Same as Example 1;

[0055] b) Same as Example 1;

[0056] c) Same as Example 1;

[0057] d) Same as Example 1;

[0058] e) A release agent was prepared according to the mass fractions of the following ingredients: 57% pure water, 8% sodium hydroxide, 20% surfactant, 10% cosolvent, and 5% stripping aid. The mixture was mixed in a volume ratio of 7:1 between pure water and release agent to form a release agent solution. Lithium tantalate wafers were ultrasonically immersed in the release agent solution at 70°C for 15 minutes. 460 wafers were put into the solution, and 1 wafer had residual adhesive on the surface, 0 wafers had scratches, and 0 wafers had edge chipping. The surface residual adhesive rate was 0.22%, the scratch rate was 0.00%, the edge chipping rate was 0.00%, and the yield rate was 99.78%.

[0059] Example 5:

[0060] a) Same as Example 1;

[0061] b) Same as Example 1;

[0062] c) Same as Example 1;

[0063] d) Same as Example 1;

[0064] e) A release agent was prepared according to the mass fraction of the following ingredients: 50% pure water, 15% sodium hydroxide, 20% surfactant, 10% cosolvent, and 5% stripping aid. The mixture was mixed in a volume ratio of pure water to release agent of 7:1 to form a release agent solution. Lithium tantalate wafers were ultrasonically immersed in the release agent solution at 70°C for 15 minutes. 445 wafers were put into the release agent solution. 1 wafer had residual adhesive on the surface, 0 wafers had scratches, and 0 wafers had edge chipping. The surface residual adhesive rate was 0.22%, the scratch rate was 0.00%, the edge chipping rate was 0.00%, and the yield rate was 99.78%.

[0065] Comparing Examples 2, 4, and 5, as shown in Table 2, the demolding and cleaning effect is affected by the concentration of sodium hydroxide in the demolding agent. When the concentration is low, the demolding effect is poor, and when the concentration is 8%, the demolding and cleaning effect is good. Continuing to increase the sodium hydroxide concentration has little effect on the demolding effect.

[0066] Table 2 Wafer cleaning residual adhesive rate and scratch rate of Examples 2, 4, and 5

[0067] Test items Example 2 Example 4 Example 5 Residual glue rate 1.77% 0.22% 0.22% Scratch rate 0.44% 0.00% 0.00%

[0068] Example 6:

[0069] a) Same as Example 1;

[0070] b) Same as Example 1;

[0071] c) Use a film laminating machine to attach a traditional PVC protective film to the lithium tantalate wafer. During laminating, the film tension is controlled at 0.18 MPa, the blade cutting temperature is 70°C, and the cutting speed is 2000 pps to obtain a lithium tantalate wafer with the film attached to the front side.

[0072] d) The front side of the lithium tantalate wafer was adsorbed on the vacuum platform of the sandblasting machine for sandblasting. The sandblasting temperature was 72°C, the nozzle pressure was 0.26 MPa, and the nozzle was reciprocated for 6 times.

[0073] e) The lithium tantalate wafers after sandblasting were ultrasonically immersed in pure water at 40°C for 30 minutes, and then the protective film on the surface of the wafers was manually torn off slowly along the edge. 396 wafers were put in, 21 of which had residual adhesive on the surface, 6 were scratched, and 1 had chipped edges. The surface residual adhesive rate was 5.30%, the scratch rate was 1.52%, the chipped edge rate was 0.25%, and the yield rate was 92.93%.

[0074] Comparing Examples 4, 5, and 6, as shown in Table 3, the adhesive residue rate and scratch rate of the protective film applying and stripping method adopted by the present invention are significantly lower than those of the traditional protective film applying and stripping method.

[0075] Table 3 Wafer cleaning residual adhesive rate and scratch rate of Examples 4, 5, and 6

[0076] Test items Example 4 Example 5 Example 6 Residual glue rate 0.22% 0.22% 5.30% Scratch rate 0.00% 0.00% 1.52%

[0077] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A protective film and a film removal method for an ultra-thin lithium tantalate wafer, characterized in that: The following specific steps are included: a) Place the lithium tantalate wafer in an alkaline cleaning solution at 45-55°C and ultrasonically clean it for 10-25 minutes to clean the particle and organic contamination on the wafer surface. Then rinse the wafer in a pure water tank to remove the residual cleaning solution on the wafer surface. b) placing the lithium tantalate wafer treated in step a) in a spin dryer and drying the wafer at a rotation speed of 300 to 1000 rpm for 3 to 8 minutes to obtain a wafer with a dry surface and no water marks; c) placing the lithium tantalate wafer treated in step b) on a screen printing table, and evenly coating the front surface of the lithium tantalate wafer by screen printing a thick liquid wafer protective film having a mass ratio of polyester of 35-50%, monomer mixture of 10-20%, acrylic acid of 15-25%, and diluent of 15-25%. The screen printing screen is 100-200 mesh. The lithium tantalate wafer coated with the protective film is then placed under an ultraviolet lamp for 1-5 minutes to allow the wafer protective film to solidify. The ultraviolet lamp illumination is 600-2000 mw / cm 2 ; d) adsorbing the front surface of the lithium tantalate wafer treated in step c) onto a vacuum platform of a sandblasting machine for sandblasting at a temperature of 70 to 80° C.; e) The lithium tantalate wafer treated in step d) is placed in a stripping agent cleaning solution at 70-85° C. and ultrasonically immersed for 10-30 minutes for stripping treatment, and then the wafer is placed in a pure water tank for rinsing to remove the stripping agent residue on the wafer surface. Finally, the wafer is dried to obtain a lithium tantalate wafer with no residual glue on the surface.

2. The protective film and film removal method for an ultra-thin lithium tantalate wafer according to claim 1, characterized in that: In step a), the alkaline cleaning solution is prepared by mixing pure water and an alkaline cleaning agent in a volume ratio of 3 to 10:1, wherein the mass fractions of the components constituting the alkaline cleaning agent are 50 to 60% pure water, 5 to 20% inorganic base, 10 to 20% chelating agent, 5 to 15% inorganic auxiliary agent, and 5 to 10% organic base.

3. The protective film and film removal method for an ultra-thin lithium tantalate wafer according to claim 1, characterized in that: In the step d), high-pressure air is used to spray the mortar pipeline and the nozzle onto the surface of the wafer. The nozzle pressure is 0.20-0.30 MPa, and the nozzle reciprocates 4-6 times.

4. The protective film and film removal method for an ultra-thin lithium tantalate wafer according to claim 1, characterized in that: In the step e), the lithium tantalate wafer is placed in a stripper cleaning solution for cleaning. The stripper is formed by mixing pure water, an inorganic base, a surfactant, a cosolvent, and a stripping aid. The stripper cleaning solution is formed by mixing pure water and the stripper in a volume ratio of 3 to 9:

1. The mass ratio of the components constituting the stripper is 40 to 65% pure water, 5 to 15% sodium hydroxide, 10 to 25% surfactant, 5 to 15% cosolvent, and 3 to 10% stripping aid.

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