Reliable process integrating pretreatment, cleaning and storage for improving appearance yield of LTO (Low Temperature Oxidation) film

Abstract

The invention relates to the technical field of silicon wafer processing, in particular to a pretreatment cleaning and storage integrated reliable process for improving LTO film appearance yield, which comprises the following steps: loading a silicon wafer to be subjected to SC-1 cleaning into a wafer box, preparing two SC-1 cleaning solutions from NH4OH, H2O2 and ultrapure water according to a volume ratio, carrying out sectional cleaning on the silicon wafer by using the SC-1 cleaning solutions, and drying the cleaned silicon wafer to obtain the LTO film. The method comprises the following steps: transferring a wafer box to an ultrapure water tank for ultra-rinsing, immersing the wafer box into an HF tank for cleaning, transferring the wafer box to the ultrapure water tank again for ultra-rinsing, spin-drying the wafer box, placing the spin-dried wafer box in a Class10-grade clean storage shed for standing, then taking out a silicon wafer from the storage shed for depositing an LTO film, taking out the silicon wafer after the deposition film forming process is completed, and testing the film thickness. And inspecting the appearance, identifying the defects of uneven film color, particles, scratches and the like, and counting the primary yield of the appearance.

Description

Technical Field

[0001] This invention relates to the field of silicon wafer processing technology, and more specifically to a reliable process that integrates pretreatment cleaning and storage to improve the appearance yield of LTO films. Background Technology

[0002] When performing APCVD chemical vapor deposition of LTO thin films on silicon wafers, the film color varies depending on the film thickness. If particles adhere to the silicon wafer, the film color at defective locations is abnormally noticeable, resulting in a low first-pass yield of the LTO film appearance. The ratio of NH4OH to H2O2 in existing processes is insufficient to fully meet the surface cleanliness requirements of high-end semiconductor devices in actual production. Furthermore, cleaned silicon wafers are susceptible to environmental particle contamination during transport and storage. Therefore, there is an urgent need to find a reliable process that integrates pretreatment cleaning and storage to improve the LTO film appearance yield.

[0003] Silicon wafer surface particles are an unavoidable "invisible killer" in semiconductor manufacturing. Their harm extends throughout the entire process from wafer fabrication and chip design to manufacturing and packaging. Particle contamination on the silicon wafer surface poses a serious threat to semiconductor manufacturing, directly affecting device performance and yield. Therefore, strict cleanroom management, process optimization (such as SC-1 cleaning), and online detection (such as laser scattering particle monitoring) can minimize particle contamination and ensure chip performance and yield.

[0004] The common pretreatment cleaning process for silicon wafers is SC-1 cleaning, which is the first step in the RCA standard cleaning process. It is mainly used to remove organic contaminants and particles from the surface of the silicon wafer. The SC-1 cleaning solution is a mixture of ammonia, hydrogen peroxide, and water. Under the oxidation of H2O2, the silicon wafer surface generates SiO2 (approximately 6nm, which is hydrophilic). This SiO2 is then corroded by NH4OH to generate ((NH4)2SiO3). Immediately after corrosion, oxidation occurs again. This process of oxidation and corrosion is repeated, so the particles attached to the silicon wafer surface also fall into the cleaning solution along with the corrosion layer. This efficient cleaning of the silicon wafer surface provides a clean substrate for subsequent processes.

[0005] As shown in the reaction equation based on the mechanism of action, theoretically, the ratio of NH4OH to H2O2 added should be 1:1. However, in actual production, the first-pass yield of LTO film processed according to this ratio cannot fully meet the requirements of subsequent processes. Furthermore, for a certain product's export appearance standard, abnormal film color caused by particles constitutes a defective product, requiring rework, which increases costs and presents a significant disadvantage. Therefore, it is necessary to improve the first-pass yield of LTO film appearance by improving silicon wafer pretreatment cleaning and storage. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a reliable process that integrates pretreatment, cleaning, and storage to improve the appearance yield of LTO membranes.

[0007] The technical solution of this invention is: a reliable process integrating pretreatment, washing, and storage to improve the appearance yield of LTO membranes, comprising the following steps: Step 1: Load the silicon wafers to be cleaned by SC-1 into the wafer cassette; Step 2: Prepare two SC-1 cleaning solutions by mixing NH4OH, H2O2, and ultrapure water in volume ratios of 1:2:45 to 1:2.5:44.5 and 1:1.5:45.5 to 1:2:45, respectively. The concentration of the first solution should be higher than that of the second solution. After stirring evenly, let stand for 5-8 minutes for later use. Step 3: SC-1 segmented cleaning: ① Place the tablet box in the cleaning machine and first immerse it in the first type of SC-1 cleaning solution prepared in step 2 for cleaning; ② Immerse the tablet box in the second type of SC-1 cleaning solution prepared in step 2 for cleaning. Step 4: Transfer the tablet cassette after SC-1 cleaning to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 5: Immerse the tablet cassette in the HF bath for 5-7 minutes; Step 6: Transfer the tablet cassette to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 7: Place the rinsed tablets in a spin dryer for spin drying, while simultaneously introducing nitrogen gas to assist in the drying process; Step 8: Place the wafer cassette containing the silicon wafers after spin drying into a Class 10 clean storage shed. The storage shed is purged with nitrogen and equipped with a particulate filter. The temperature inside the shed is controlled at 23±2℃. Let it stand for 10-15 minutes to allow for subsequent LTO film deposition. Step 9: The Q-Time for film deposition in the storage shed is 3-5 hours. After that, the silicon wafer is taken out of the storage shed and deposited in an atmospheric pressure tray transfer reactor to deposit an LTO film. Chemical vapor deposition is performed at a film deposition temperature of 450±10℃. Step 10: After the deposition process is complete, shut off the gas supply and remove the silicon wafer after it has cooled down. Step 11: After unloading the silicon wafer, use F50 to test the film thickness and view the film thickness map; at the same time, use Optima to check the appearance, identify defects such as uneven film color, particles, scratches, etc., and calculate the first-pass yield of appearance.

[0008] Preferably, in the first step, the spacing between silicon wafers in the wafer cassette is controlled to be 2-3mm to avoid mutual friction between the silicon wafer surfaces.

[0009] Preferably, in the third step, sub-step ① controls the cleaning temperature to 40-65℃ and the cleaning time to 8-12 minutes, during which ultrasonic oscillation at 20-30 kHz is used.

[0010] Preferably, in the third step, sub-step ② controls the cleaning temperature to 40-65℃ and the cleaning time to 5-7 minutes, during which ultrasonic oscillation at 20-30 kHz is used.

[0011] Preferably, in step seven, the spin-drying speed is controlled at 600-700 r / min and the spin-drying time is 3-5 min.

[0012] The beneficial effects of this invention are: ① This invention controls the ratio of NH4OH to H2O2 addition at 1:1.5-1:2.5, and uses segmented cleaning. The first cleaning is performed at a higher concentration (1:2~1:2.5), and the second cleaning is performed at a lower concentration (1:1.5~1:2). This results in silicon wafers with high surface cleanliness, avoiding the disadvantages of excessively high concentrations causing corrosion pits and insufficient oxidation stripping due to excessively low concentrations. ② Storing the cleaned silicon wafers in a high-cleanliness storage shed reduces the risk of particulate contamination from the environment. Furthermore, fixing the storage shed and the Q-Time for film formation at 3-5 hours ensures consistent silicon wafer surface conditions, laying the foundation for subsequent deposition processes. ③ The process requires no additional complex equipment; it can be achieved simply through parameter optimization and process standardization. It is easy to operate, cost-effective, and can be quickly applied to existing semiconductor silicon wafer production lines. These three points enable the production of LTO films with high first-pass yield. The process of this invention is simple and can effectively reduce particles in the pretreatment washing and storage processes, which has an important impact on the yield of subsequent processing and the performance of the final product. It can effectively improve the membrane appearance yield and reduce the rework cost of defective products. Detailed Implementation

[0013] To enable those skilled in the art to more clearly understand the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments.

[0014] Step 1: Place the silicon wafers to be cleaned by SC-1 into the wafer cassette. The spacing between the silicon wafers in the wafer cassette should be controlled at 2-3mm to avoid mutual friction between the silicon wafer surfaces. Step 2: Prepare two SC-1 cleaning solutions by mixing NH4OH, H2O2, and ultrapure water in volume ratios of 1:2:45 to 1:2.5:44.5 (NH4OH:H2O2:ultrapure water) and 1:1.5:45.5 to 1:2:45 (NH4OH:H2O2:ultrapure water). Stir well and let stand for 5-8 minutes before use. Step 3: SC-1 segmented cleaning. ① Place the wafer cassette (hereinafter referred to as wafer cassette) containing the silicon wafers into the cleaning machine. First, immerse the wafer cassette in the first type of SC-1 cleaning solution prepared in Step 2 (the ratio of the solution is shown in Table 1). Control the cleaning temperature at 40-65℃ and the cleaning time at 8-12 minutes, during which ultrasonic oscillation at 20-30 kHz is used. ② Immerse the wafer cassette in the second type of SC-1 cleaning solution prepared in Step 2 (the ratio of the solution is shown in Table 1). Control the cleaning temperature at 40-65℃ and the cleaning time at 5-7 minutes, during which ultrasonic oscillation at 20-30 kHz is used. Table 1. Comparison of the chemical solution ratio in this embodiment with that of the existing SC-1 cleaning machine. Step 4: Transfer the tablet cassette after SC-1 cleaning to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 5: Immerse the tablet cassette in the HF bath for 5-7 minutes; Step 6: Transfer the tablet cassette to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 7: Place the rinsed tablets into a spin dryer, control the spin speed to 600-700 r / min, and the spin time to 3-5 min, while simultaneously introducing nitrogen gas to assist drying. Step 8: Place the spun-dry film cassette in a Class 10 clean storage shed. The storage shed is filled with nitrogen and equipped with a particulate filter. The temperature inside the shed is controlled at 23±2℃. Let it stand for 10-15 minutes to allow for subsequent LTO membrane deposition. Step 9: The Q-Time for film deposition in the storage shed is 3-5 hours. After that, the silicon wafer is taken out from the storage shed and deposited in an atmospheric pressure tray transfer reactor (APCVD). The chemical vapor deposition is carried out at a film deposition temperature of 450±10℃. Step 10: After the deposition process is complete, shut off the gas supply and remove the silicon wafer after it has cooled down. Step 11: After unloading the silicon wafer, use F50 to test the film thickness and view the film thickness map; at the same time, use Optima to check the appearance, identify defects such as uneven film color, particles, scratches, etc., and calculate the first-pass yield of appearance, see Table 2.

[0015] Table 2 Comparison of first-pass yield of appearance in this embodiment with existing LTO films. This is merely a preferred embodiment of the present invention. Those skilled in the art will recognize that the present invention can be modified and varied in many ways. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A reliable process integrating pretreatment, washing, and storage to improve the appearance yield of LTO membranes, characterized in that, Includes the following steps: Step 1: Load the silicon wafers to be cleaned by SC-1 into the wafer cassette; Step 2: Prepare two SC-1 cleaning solutions by mixing NH4OH, H2O2, and ultrapure water in volume ratios of 1:2:45 to 1:2.5:44.5 and 1:1.5:45.5 to 1:2:45, respectively. The concentration of the first solution should be higher than that of the second solution. After stirring evenly, let stand for 5-8 minutes for later use. Step 3: SC-1 segmented cleaning: ① Place the tablet box in the cleaning machine and first immerse it in the first type of SC-1 cleaning solution prepared in step 2 for cleaning; ② Immerse the tablet box in the second type of SC-1 cleaning solution prepared in step 2 for cleaning. Step 4: Transfer the tablet cassette after SC-1 cleaning to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 5: Immerse the tablet cassette in the HF bath for 5-7 minutes; Step 6: Transfer the tablet cassette to an ultrapure water bath and ultra-rinse for 5-7 minutes, while simultaneously using bubbling ultrasonic vibration up and down and left and right. Step 7: Place the rinsed tablets in a spin dryer for spin drying, while simultaneously introducing nitrogen gas to assist in the drying process; Step 8: Place the wafer cassette containing the silicon wafers after spin drying into a Class 10 clean storage shed. The storage shed is purged with nitrogen and equipped with a particulate filter. The temperature inside the shed is controlled at 23±2℃. Let it stand for 10-15 minutes to allow for subsequent LTO film deposition. Step 9: The Q-Time for film deposition in the storage shed is 3-5 hours. After that, the silicon wafer is taken out of the storage shed and deposited in an atmospheric pressure tray transfer reactor to deposit an LTO film. Chemical vapor deposition is performed at a film deposition temperature of 450±10℃. Step 10: After the deposition process is complete, shut off the gas supply and remove the silicon wafer after it has cooled down. Step 11: After unloading the silicon wafer, use F50 to test the film thickness and view the film thickness map; at the same time, use Optima to check the appearance, identify defects such as uneven film color, particles, scratches, etc., and calculate the first-pass yield of appearance.

2. The reliable process for improving LTO membrane appearance yield by integrating pretreatment, washing, and storage according to claim 1, characterized in that: In the first step, the spacing between silicon wafers in the wafer cassette is controlled to be 2-3mm to avoid mutual friction between the silicon wafer surfaces.

3. The reliable process for improving LTO membrane appearance yield by integrating pretreatment, washing, and storage according to claim 1, characterized in that: In the third step, sub-step ① controls the cleaning temperature to 40-65℃ and the cleaning time to 8-12 minutes, during which ultrasonic oscillation at 20-30 kHz is used.

4. The reliable process for improving LTO membrane appearance yield by integrating pretreatment, washing, and storage according to claim 1, characterized in that: In the third step, sub-step ② controls the cleaning temperature to 40-65℃ and the cleaning time to 5-7 minutes, during which 20-30 kHz is used.

5. The reliable process for improving LTO membrane appearance yield by integrating pretreatment, washing, and storage according to claim 1, characterized in that: In step seven, control the spin-drying speed to 600-700 r / min and the spin-drying time to 3-5 min.

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