A wax-removing cleaning process for semiconductor silicon polishing wafers

Abstract

The present invention discloses a wax-removing cleaning process for semiconductor silicon polishing wafers. The process comprises the following steps: (1) After the silicon wafer is polished with wax, it is transferred to diluted hydrogen peroxide within 180 seconds and soaked for 2-10 minutes. Then, when the silicon wafer is removed from the ceramic plate, the silicon wafer is always kept in hydrogen peroxide or its surface is kept wet by spraying hydrogen peroxide; (2) Within 60 minutes after the completion of the previous step, 2 SC1, 2 hydrogen peroxides and 2 ultrapure waters are used to perform wax-removing cleaning on the silicon wafer, and the cleaning process is: SC1-ultrapure water-hydrogen peroxide-SC1-ultrapure water-hydrogen peroxide. The cleaning time of SC1 is 2-10 minutes, and the cleaning time of hydrogen peroxide is 0.5-10 minutes; (3) Before pre-cleaning, the silicon wafer is transferred to hydrogen peroxide for storage, and at the same time, the silicon wafer is pre-cleaned within 120 minutes, dried from wet to dry, and then finally cleaned. The present invention can greatly reduce the influence of contamination and corrosion on the surface of the silicon wafer, and thus obtain a silicon polishing wafer with a surface of ultra-high cleanliness.

Description

Technical Field

[0001] The present invention relates to a wax-removing cleaning process for semiconductor silicon polishing wafers, which is used to prepare wafers with ultra-high surface cleanliness and belongs to the technical field of semiconductor materials. Background Art

[0002] With the development of semiconductor technology, the performance requirements of integrated circuit products are getting higher and higher, the physical line width is getting narrower and narrower, and at the same time, the surface cleanliness requirements for silicon substrate polishing wafers are getting higher and higher. Improving the surface particle quality of wafers through various technical means has become a key process in wafer processing.

[0003] Currently, the mainstream single-sided chemical mechanical polishing method (CMP) for silicon substrate materials internationally all adopts the method of wax-pasted polishing. Wax polishing can well control the geometric parameters of wafers, but at the same time, there is also the problem that organic wax is likely to remain on the wafer surface and cause particle contamination. If the wax removal and cleaning are not thorough, and the organic wax adheres to the wafer surface, after the wafer changes from a wet state to a dry state, the adhesion force of the wax is further enhanced, and it is very difficult to remove the residual contamination through the final cleaning, which will further affect the surface particle quality of the wafer, especially for small-sized particles of 65nm - 120nm.

[0004] Currently, the industry generally uses the method of alkaline wax remover cleaning for wax removal. This cleaning method can only ensure a good level for particles larger than 120nm. The wax removal and cleaning method is simple, but there are also risks of incomplete wax removal and over-corrosion, especially for smaller-sized 65nm LPD (Light Point Defect) and LPDN (Light Point Defect Non-cleanable). Therefore, wax removal and cleaning need to ensure thorough wax removal while preventing over-corrosion of the surface. Summary of the Invention

[0005] The purpose of the present invention is to provide a wax-removing cleaning process for semiconductor silicon polishing wafers, which can solve the problems of incomplete wax removal and cleaning, easy contamination and corrosion, and can obtain wafers with an ultra-high cleanliness surface.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A wax-removing cleaning process for semiconductor silicon polishing wafers includes the following steps:

[0008] (1) After the wax polishing of the wafer is completed, it is transferred to diluted hydrogen peroxide within 180 seconds and soaked for 2 - 10 minutes. The volume ratio of this diluted hydrogen peroxide is H2O2∶H2O = 1∶30 - 1∶500;

[0009] (2) Within 60 minutes after the completion of step (1), dewaxing and cleaning of the silicon wafer is carried out. For dewaxing and cleaning, 2 portions of Solution 1 (SC1), 2 portions of hydrogen peroxide, and 2 portions of ultrapure water are used. The process of dewaxing and cleaning is as follows:

[0010] (a) Solution 1 cleaning (SC1), using ultrasonic cleaning, with a cleaning time of 2 - 10 minutes. The volume ratio of Solution 1 is NH4OH∶H2O2∶H2O = 1∶2∶5 - 1∶2∶100, and the temperature is 30 - 80°C;

[0011] (b) Ultrapure water cleaning, with spraying and rapid drainage carried out 1 - 3 times;

[0012] (c) Hydrogen peroxide cleaning, with a volume ratio of H2O2∶H2O = 1∶30 - 1∶500, and a cleaning time of 0.5 - 10 minutes;

[0013] (d) Solution 1 cleaning (SC1), using megasonic cleaning, with a cleaning time of 2 - 10 minutes. The volume ratio of Solution 1 is NH4OH∶H2O2∶H2O = 1∶2∶5 - 1∶2∶100, and the temperature is 30 - 80°C;

[0014] (e) Ultrapure water cleaning, with spraying and rapid drainage carried out 1 - 3 times;

[0015] (f) Hydrogen peroxide cleaning, with a volume ratio of H2O2∶H2O = 1∶30 - 1∶500, and a cleaning time of 0.5 - 10 minutes;

[0016] (3) After the dewaxing and cleaning is completed, before the pre - cleaning starts, the silicon wafer is stored in diluted hydrogen peroxide. The volume ratio of this diluted hydrogen peroxide is H2O2∶H2O = 1∶30 - 1∶500. At the same time, the pre - cleaning of the silicon wafer is carried out within 120 minutes to change the silicon wafer from wet to dry, and then the final cleaning is carried out.

[0017] The dewaxing and cleaning process of the present invention is applicable to 5 - 8 - inch silicon polished wafers.

[0018] Preferably, in the step (1), after the silicon wafer is polished with wax, it is transferred to diluted hydrogen peroxide solution within less than 10 seconds and soaked for 5 minutes, and then the silicon wafer is removed from the ceramic plate, so that the silicon wafer is always kept in the hydrogen peroxide solution or the surface is kept wet by spraying hydrogen peroxide solution. The purpose of this step is that after polishing, the silicon wafer quickly enters the dilute hydrogen peroxide solution, and the main function is to quickly form strong hydrophilicity on the surface of the silicon wafer, and then quickly dilute the residual polishing solution on the surface to avoid further corrosion of the silicon wafer surface; when taking the wafer, keeping the silicon wafer in the dilute hydrogen peroxide solution all the time or spraying hydrogen peroxide solution is mainly to maintain the strong hydrophilicity of the silicon wafer surface and prevent the wax molecules or particulate molecules in water from forming strong adsorption on the silicon wafer surface and being difficult to be cleaned and removed. The volume ratio of the diluted hydrogen peroxide solution into which the silicon wafer enters is preferably 1:200, and the volume ratio of the diluted hydrogen peroxide solution used for spraying is preferably 1:500.

[0019] In the step (2), dewaxing and cleaning are carried out within 60 minutes after polishing. The main reason is that the longer the silicon wafer is soaked in water, the stronger the adsorption force of the surface wax molecules or other contaminants is. Therefore, it is preferably within 30 minutes after the step (1) to carry out dewaxing and cleaning on the silicon wafer. Dewaxing and cleaning are carried out using 2 SC1 solutions (SC1), 2 hydrogen peroxide solutions and 2 ultrapure water rinses. The main function of ammonia water in the 2 SC1 solutions is to react with wax to form soluble substances and remove the surface wax. The function of hydrogen peroxide in the SC1 solution is on the one hand to reduce the corrosion effect of ammonia water by oxidizing the surface of the silicon wafer, and on the other hand to carry out oxidation reaction with organic wax to make it easier to be removed; the reason for the 2 hydrogen peroxide rinses is that after the silicon wafer is cleaned with the SC1 solution, the surface hydrophilicity is reduced. Therefore, the main function is to fully oxidize the surface of the silicon wafer. The first hydrogen peroxide rinse protects the surface from being over-corroded, and the second hydrogen peroxide rinse enhances the surface hydrophilicity to prevent the formation of strong particle adsorption. The cleaning temperatures of the 2 SC1 solutions are preferably 70 °C respectively, the cleaning time is preferably 5 minutes, and the volume ratios are preferably NH4OH:H2O2:H2O = 1:2:30 and NH4OH:H2O2:H2O = 1:2:60 respectively. The first SC1 is cleaned by ultrasonic cleaning, and the main purpose is to remove particles with a particle size larger than 120 nm on the surface. The ultrasonic intensity is 300 ± 50 W, and the frequency is 30 - 130 kHz; preferably, the ultrasonic intensity is set to 300 W and the frequency is 130 kHz. The second SC1 is cleaned by megasonic cleaning, and the main purpose is to remove particles with a particle size less than 120 nm on the surface. The megasonic intensity is 1000 ± 200 W, and the frequency is 0.75 - 1 MHz; preferably, the megasonic intensity is set to 1000 W and the frequency is 1 MHz. After the SC1 cleaning, 1 ultrapure water tank is set for spraying and rapid drainage. After the silicon wafer enters the pure water tank, the spraying is always on, and the water is drained immediately after the silicon wafer is immersed in pure water. The rapid drainage time is less than 5 seconds. The rapid drainage time is preferably less than 2 seconds and is carried out continuously 3 times.

[0020] Preferably, in step (2), the hydrogen peroxide is diluted hydrogen peroxide with a volume ratio of H2O2:H2O = 1:100, the cleaning time is 3 minutes, and the replacement frequency of hydrogen peroxide is not less than 1 time per 1000 wafers.

[0021] Preferably, in step (3), the volume ratio of the diluted hydrogen peroxide is preferably H2O2:H2O = 1:500. Preferably, the silicon wafer is pre-cleaned within 30 minutes after the dewaxing is completed to change the silicon wafer from a wet state to a dry state.

[0022] In steps (1)-(3), the purity of ammonia water and hydrogen peroxide is of UPS level or above, the mass percentage of ammonia water is 28%-30%, the mass percentage of hydrogen peroxide is 30-32%, and the resistivity of ultrapure water is greater than 18 MΩ·cm.

[0023] The advantages of the present invention are as follows:

[0024] By adding surface treatment methods before and after dewaxing cleaning, it is possible to avoid excessive corrosion of the surface by the polishing liquid and strong adsorption contamination before and after cleaning. At the same time, in the dewaxing cleaning process, on the one hand, the removal effect of wax is improved, and on the other hand, the surface is protected from excessive corrosion and secondary contamination. After dewaxing, a silicon wafer surface without wax contamination and easy to clean is obtained, and the LPD and LPDN levels with particle sizes of 65 nm - 120 nm are significantly improved. Moreover, the implementation process is simple, and the types of chemical liquids used in subsequent pre-cleaning and final cleaning are the same, which can meet the high requirements of current integrated circuits for ultra-high surface cleanliness. Description of the Drawings

[0025] Figure 1 It is a box plot of the surface particles (LPD + LPDN quantity) of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Embodiments

[0026] The following further describes the present invention in conjunction with the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and do not mean to limit the protection scope of the present invention.

[0027] The dewaxing cleaning process of a semiconductor silicon polishing wafer provided by the present invention includes: using a Nachi SPM-23 polishing machine to polish the silicon wafer, and the polishing process parameters and auxiliary materials are the parameters and auxiliary materials commonly used in the industry. After polishing, dilute hydrogen peroxide is used to pre-treat the surface of the silicon wafer before dewaxing cleaning. Two SC1 solutions, two hydrogen peroxides, and two ultrapure waters are used for dewaxing cleaning. After dewaxing is completed, dilute hydrogen peroxide is used again for preservation. Finally, the silicon wafer is pre-cleaned and finally cleaned. The pre-cleaning and final cleaning adopt the RCA cleaning method (SC1 solution and SC2 solution cleaning). After cleaning is completed, an SP2 is used to test the surface particles of the silicon polishing wafer.

[0028] Example 1

[0029] To exclude the influence of single-crystal COP defects, the silicon wafers used in the examples were made of 8-inch lightly doped boron COP-free single crystals. Wax polishing was carried out in sequence of rough polishing, rough polishing, medium polishing, and fine polishing. After the fine polishing was completed, the wafers were transferred to a diluted hydrogen peroxide solution with a volume ratio of H2O2:H2O = 1:200 within 10 seconds and soaked for 5 minutes. Then, the wafers were removed from the ceramic plate. During the wafer removal process, a diluted hydrogen peroxide solution with a volume ratio of H2O2:H2O = 1:500 was used to spray the surface of the wafers. After the wafer removal, the wafers were immediately subjected to dewaxing cleaning. The dewaxing cleaning process was SC1 cleaning - ultrapure water cleaning - hydrogen peroxide cleaning - SC1 cleaning - ultrapure water cleaning - hydrogen peroxide cleaning. The temperature of the two SC1 (solution No. 1) cleanings was 70°C, and the cleaning time was 5 minutes. The volume ratios were NH4OH:H2O2:H2O = 1:2:30 and NH4OH:H2O2:H2O = 1:2:60 respectively. The first SC1 used ultrasonic cleaning with an ultrasonic power set at 300W and a frequency of 130kHz. The second SC1 used megasonic cleaning with a megasonic power set at 1000W and a frequency of 1MHz. The two hydrogen peroxide cleanings had a cleaning time of 3 minutes, and the volume ratio was H2O2:H2O = 1:100 for both. The ultrapure water cleaning tank carried out spraying and rapid drainage, and the rapid drainage time was less than 2 seconds, which was continuously carried out 3 times.

[0030] After the dewaxing cleaning was completed, the wafers were transferred to a diluted hydrogen peroxide solution with a volume ratio of H2O2:H2O = 1:500, and then the wafers were pre-cleaned, changed from wet to dry, and finally cleaned. The pre-cleaning and final cleaning used the conventional RCA cleaning method (a combination of solution No. 1 and solution No. 2). The purity of ammonia water and hydrogen peroxide was of UPS level and above. The mass percentage of ammonia water was 28%-30%, the mass percentage of hydrogen peroxide was 30-32%, and the resistivity of ultrapure water was 18.2 MΩ·cm.

[0031] Comparative Examples

[0032] Three dewaxing cleaning processes were arranged as comparative examples. Similar to the examples, the silicon wafers used in the comparative examples were all made of 8-inch lightly doped boron COP-free single crystals, and the purity grades and concentrations of the ammonia water and hydrogen peroxide used were the same as those in the examples.

[0033] Comparative Example 1: The same silicon wafers as those in Example 1 were selected, and the dewaxing cleaning was changed to only use an alkaline dewaxing agent and ultrapure water for dewaxing cleaning. The dewaxing time was the same as that in Example 1, and other process conditions and procedures were the same as those in Example 1.

[0034] Comparative Example 2: The same silicon wafers as those in Example 1 were selected, and the silicon wafer dewaxing cleaning process was changed to SC1 cleaning - ultrapure water cleaning - SC1 cleaning - ultrapure water cleaning. Other process conditions and procedures were the same as those in Example 1.

[0035] Comparative Example 3: The same silicon wafers as those in Example 1 were selected, and wafer sampling and storage were carried out in ultrapure water before and after dewaxing and cleaning. Other process conditions and procedures were the same as those in Example 1.

[0036] The silicon wafers were processed by the method of Example 1 and three comparative example methods. After processing, the number of LPD+LPDN on the surface of 65 nm was tested by SP2.

[0037] Figure 1 It is a box plot of the data comparison of LPD+LPDN of 65 nm tested by SP2 for the batch of Example 1 and the batches of three comparative examples. As can be seen from the above, compared with the dewaxing and cleaning results of the comparative examples, the surface particle results of the polished wafers after dewaxing and cleaning according to the present invention are better. The surface particle quality of the silicon wafers after dewaxing and cleaning according to the present invention is more excellent, and the mean value and numerical distribution of LPD+LPDN of 65 nm are better than those of the comparative examples. The dewaxing and cleaning method of the present invention has the advantages of less surface contamination and corrosion defects of the silicon wafers and easy cleaning of the silicon wafer surface, and can obtain high-quality silicon polished wafers.

Claims

1. A dewaxing and cleaning process for a semiconductor silicon polishing wafer, comprising the following steps: (1) After the silicon wafer is polished with wax, transfer it to diluted hydrogen peroxide within 180 seconds and soak it for 2-10 minutes. The volume ratio of the diluted hydrogen peroxide is H2O2:H2O=1:30~1:500; (2) Within 60 minutes after step (1) is completed, the silicon wafer is dewaxed and cleaned. The dewax cleaning uses 2 No. 1 liquids (SC1), 2 hydrogen peroxide solutions and 2 ultrapure water. The dewax cleaning process is as follows: (a) Cleaning with liquid 1 (SC1), using ultrasonic cleaning, the cleaning time is 2-10 minutes, the volume ratio of liquid 1 is NH4OH:H2O2:H2O=1:2:5~1:2:100, and the temperature is 30-80℃; (b) Ultrapure water cleaning, spraying and rapid draining 1-3 times; (c) Hydrogen peroxide cleaning, the volume ratio is H2O2:H2O=1:30~1:500, and the cleaning time is 0.5-10 minutes; (d) Cleaning with liquid 1 (SC1), using megasonic cleaning, the cleaning time is 2-10 minutes, the volume ratio of liquid 1 is NH4OH:H2O2:H2O=1:2:5~1:2:100, and the temperature is 30-80℃; (e) Ultrapure water cleaning, spraying and rapid draining 1-3 times; (f) Cleaning with hydrogen peroxide, the volume ratio is H2O2:H2O=1:30~1:500, and the cleaning time is 0.5-10 minutes; (3) After the dewaxing cleaning is completed, before the pre-cleaning begins, the silicon wafer is kept in diluted hydrogen peroxide with a volume ratio of H2O2:H2O=1:30~1:

500. At the same time, the silicon wafer is pre-cleaned within 120 minutes to dry the silicon wafer from wet, and then the final cleaning is carried out.

2. The dewaxing and cleaning process for the polishing sheet according to claim 1, characterized in that: The silicon wafer is a 5-8 inch silicon wafer and is processed using a conventional rough polishing-rough polishing-medium polishing-fine polishing process.

3. The dewaxing and cleaning process for the polishing sheet according to claim 1, characterized in that: In the step (1), the silicon wafer is immersed in diluted hydrogen peroxide during the entire wafer removal process, or the surface of the silicon wafer is sprayed with diluted hydrogen peroxide to keep the surface of the silicon wafer moist at all times.

4. The dewaxing and cleaning process for the polishing sheet according to claim 3, characterized in that: In the step (1), the volume ratio of the diluted hydrogen peroxide used for soaking the silicon wafer is H2O2:H2O=1:200, and the volume ratio of the diluted hydrogen peroxide used for spraying is H2O2:H2O=1:

500.

5. The dewaxing and cleaning process for the polishing sheet according to claim 1, characterized in that: The purity of the ammonia water and hydrogen peroxide used in the step is UPS or above, the mass percentage of ammonia water is 28%-30%, the mass percentage of hydrogen peroxide is 30-32%, and the resistivity of ultrapure water is greater than 18MΩ·cm.

6. The dewaxing and cleaning process for the polishing sheet according to claim 1, characterized in that: The volume ratio of liquid No. 1 in the step (a) is NH4OH:H2O2:H2O=1:2:30, the temperature is 70°C, and the cleaning time is 5 minutes; the volume ratio of liquid No. 1 in the step (d) is NH4OH:H2O2:H2O=1:2:60, the temperature is 70°C, and the cleaning time is 5 minutes; the volume ratio of hydrogen peroxide in the steps (c) and (f) is H2O2:H2O=1:

100.

7. The dewaxing and cleaning process for the polishing sheet according to claim 1, characterized in that: In the step (2), the ultrasonic intensity is 300±50W, and the frequency is 30-130kHZ; the megasonic intensity is 1000±200W, and the frequency is 0.75-1MHZ. After the silicon wafer enters the pure water tank, the spray is always on, and the water is drained immediately after the silicon wafer is immersed in the pure water, and the drainage time is less than 5 seconds.

8. The dewaxing and cleaning process for a polishing sheet according to claim 1, characterized in that: In the step (2), the frequency of replacing the hydrogen peroxide solution is not less than once per 1000 tablets.

9. The dewaxing and cleaning process for a polishing sheet according to claim 1, characterized in that: In step (3), the volume ratio of the diluted hydrogen peroxide is H2O2:H2O=1:500, and the pre-cleaning and the subsequent final cleaning are RCA cleaning conventionally used in the industry. After the dewaxing is completed, the silicon wafer is pre-cleaned within 30 minutes.

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