Cleaning method for electronic-grade polycrystalline silicon core

Abstract

The invention relates to a cleaning method for an electronic-grade polycrystalline silicon core, and belongs to the technical field of electronic-grade polycrystalline silicon core production. The invention provides a method for cleaning a silicon core, which not only can remove impurities such as fine particles, metal pollution, grease and other organic matters on the surface of the silicon core, but also can greatly improve the problems of oxidation yellowing, blackening, acid spots, excessive gold content, excessive carbon content, degreaser and acid liquor residue and the like on the surface of the silicon core after cleaning. Therefore, in the growth process of the polycrystalline silicon rod, the product quality and the yield are further improved, and the energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic-grade polysilicon core production and relates to a cleaning method for electronic-grade polysilicon cores. Background Art

[0002] At present, electronic-grade rod-shaped polysilicon produced by the modified Siemens method is the mainstream raw material for the preparation of electronic components in China. Integrated circuits have more stringent quality requirements for electronic-grade (semiconductor-grade) polysilicon. The entire production process requires raw material purification, polysilicon reduction preparation, product post-processing and other processes. Therefore, in the microelectronics manufacturing industry, the silicon core is a key component, and its purity directly affects the performance of the microcircuit.

[0003] Square silicon cores are generated by longitudinal cutting of single crystal round rods by a cutting machine, and are mainly used as heat carriers for producing native polysilicon by vapor deposition. In the process of producing polysilicon, the silicon core is used as a carrier for the deposition of polysilicon materials in the reduction furnace, and the cleanliness of its surface will directly affect the quality of the final product polysilicon. However, after a series of processes such as head and tail removal, wire cutting, degumming, and cone grinding to meet the specifications, the silicon core may be contaminated by silicon mud dust, organic matter, metal elements, etc. Therefore, in order not to affect subsequent use, it is very necessary to clean the silicon core. The existing silicon core cleaning processes mainly include water washing, mixed acid pickling, rinsing, ultrasonic cleaning, drying and other processes, or manual wiping and then going through the above steps, or using alkali degreasing and other methods to clean the silicon core, but these methods and processes all have certain disadvantages. Such as poor cleaning effect, contamination of the silicon core during manual wiping, metal ion contamination in the alkali solution, degreasing agent and acid residues. Summary of the invention

[0004] The object of the present invention is to provide a method for cleaning electronic-grade polycrystalline silicon cores, which has the characteristics of having a good and stable cleaning effect on the silicon core and being beneficial to improving the apparent quality after cleaning.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for cleaning electronic grade polysilicon cores, the method comprises the following specific steps:

[0007] S1: The first cleaning area

[0008] The silicon core is firstly plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning.

[0009] S2: The second cleaning area

[0010] After the first part of the cleaning is completed, the silicon core is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid, and the second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. After the pickling is completed, it is washed once with high-purity water to complete the second part of the cleaning;

[0011] S3: The third cleaning area

[0012] After the second cleaning, the silicon core is pickled again with a hydrofluoric acid solution. After the pickling is completed, it is washed twice with high-purity water to complete the third cleaning;

[0013] S4: The fourth cleaning area

[0014] The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning;

[0015] S5: Drying and cooling

[0016] The silicon core that has completed the fourth part of cleaning is dried with Class 100 clean air or high-purity nitrogen at 60-80°C. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

[0017] Furthermore, the entire cleaning area is in a negative pressure state compared to the external environment, and the pressure difference is ≥5Pa.

[0018] Furthermore, air curtains are provided between the areas for cleaning the first part and the second part, the areas for cleaning the second part and the third part, and the areas for cleaning the third part and the fourth part.

[0019] Furthermore, the resistivity of high-purity water during the cleaning process is greater than 17.5 MΩ·cm.

[0020] Furthermore, the ozone content of the ozone solution in S1 is 2.5 mg / L.

[0021] Furthermore, the acid solution used for the first mixed acid pickling in S2 is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a mass concentration of 37wt%, wherein the volume ratio of the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution is 1:(2~9):(0.5~2).

[0022] Furthermore, the acid solution used for the second mixed acid pickling in S2 is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water, wherein the volume ratio of the hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:(1-6):(20-70).

[0023] Furthermore, the hydrofluoric acid solution in S3 is prepared by using 49 wt % hydrofluoric acid and high-purity water in a volume ratio of 1:(8-12), and the cleaning time is 1-5 min.

[0024] Furthermore, the purity of the high-purity nitrogen in S5 is 99.9999%.

[0025] Furthermore, the drying time in S5 is 1000 to 1200 seconds.

[0026] The silicon core is made by cutting the silicon rod through the silicon core cutting machine. During the cutting process, the surface of the silicon core is always attached with fine particles such as silicon powder, dust, and fine sand, and there is very serious metal pollution during diamond wire cutting. If these particles and metals remain on the surface of the silicon core, not only will too much degreasing agent or acid solution be consumed in the subsequent degreasing and pickling process, but also the cleaning effect of the silicon block will be affected. Macroscopically, the silicon core has a regular surface structure. The present invention uses a plasma to clean the surface of the silicon core. The first part of the cleaning area performs 1 plasma cleaning, 1 ultrasonic water washing, 1 ozone degreasing, and 2 flushing on the silicon core. The plasma cleaning is to bombard the surface of the silicon core with plasma generated by an atmospheric plasma cleaning machine to achieve the purpose of removing pollution on the surface of the silicon core. In the present invention, ozone solution is used for degreasing. Ozone has extremely strong oxidizing properties and can oxidize most organic matter, thereby removing organic matter to reduce the influence of C content on polysilicon. The post-degreasing flushing is mainly to remove the degreasing agent remaining on the surface of polysilicon.

[0027] The second cleaning area performs two mixed acid pickling and one water washing on the silicon core. The solution of the first mixed acid cleaning is a mixture of high-concentration nitric acid, hydrofluoric acid and hydrochloric acid. Nitric acid can dissolve most metals and react with polysilicon to generate SiO2 to form an oxide layer, while hydrofluoric acid can dissolve SiO2 and remove impurities in the oxide layer. Adding hydrochloric acid to the mixed solution of hydrofluoric acid and nitric acid can further increase the active oxygen in the solution, thereby improving the oxidizability of the entire solution and reacting more violently with metals. Through the above reaction, the surface of polysilicon can be etched to remove metal impurities and oxide layers. The solution of the second mixed acid cleaning is a mixed solution of nitric acid and hydrofluoric acid with a lower concentration. The low solubility of the second mixed acid cleaning solution in this part is to improve the surface morphology of the silicon core and further remove metal impurities.

[0028] The third cleaning area performs HF acid cleaning once and water washing twice on the silicon core. The HF cleaning solution is a mixture of hydrofluoric acid and high-purity water, so that the oxide layer on the surface of the silicon core falls off, improving the surface morphology of the silicon core and removing metal impurities in the oxide layer.

[0029] The fourth cleaning area performs at least 2 megasonic cleanings and 1 rinse on the silicon core. The huge pressure generated by the cavitation effect caused by megasonic cleaning bombards the surface of the silicon core, destroying its surface tension so that the acid remaining on the surface of the silicon core can be fully removed. After each megasonic cleaning, the next megasonic cleaning device is switched to cut off the water to blow away the particles on the surface of the silicon core and shorten the time of the subsequent drying step.

[0030] In the present invention, wind curtains are arranged between the areas of the first and second cleaning parts, the second and third cleaning parts, and the third and fourth cleaning parts to prevent ozone, nitrogen oxides and hydrofluoric acid gases from leaking and affecting each other, and to prevent the gases from affecting subsequent processes.

[0031] The cleaning process of the present invention is all carried out in a Class 100 area, and there are no exposed metal parts in the area. The flower basket and the trough body in contact with the silicon core are all made of ultra-high purity non-metallic materials. The structure of the flower basket is hexagonal, and each trough body can rotate the flower basket through a motion mechanism, thereby driving the silicon core to move.

[0032] Beneficial effects of the present invention:

[0033] The present invention provides a silicon core cleaning method, which can not only remove fine particles, metal pollution, organic impurities such as grease, etc. on the surface of the silicon core, but also greatly improve the problems of oxidation yellowing, blackening, acid spots, excessive gold content, excessive carbon content, degreasing agent and acid residue on the surface of the silicon core after cleaning. Thereby, the product quality and yield rate are further improved during the growth process of polysilicon rods, and energy consumption is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0035] Figure 1 A flow chart of a cleaning method for cleaning electronic grade polycrystalline silicon cores of the present invention;

[0036] Figure 2 The first part of the cleaning method of the present invention is a flow chart of the cleaning area;

[0037] Figure 3 The cleaning area flow chart of the second part of the cleaning method of the present invention;

[0038] Figure 4 The cleaning method of the present invention is a flow chart of the cleaning area in the third part;

[0039] Figure 5 The fourth part of the cleaning method of the present invention is a flow chart of the cleaning area;

[0040] Figure 6 Flow chart of drying and cooling of the cleaning method of the present invention. DETAILED DESCRIPTION

[0041] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0042] Example 1

[0043] In the present invention, all cleaning areas are in a negative pressure state relative to the external environment, and the pressure difference is ≥5Pa; air curtains are provided between each cleaning area; the resistivity of high-purity water during the cleaning process is greater than 17.5MΩ·cm;

[0044] S1: The first cleaning area

[0045] The silicon core is first plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The ozone content of the ozone solution is 2.5 mg / L. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning.

[0046] S2: The second cleaning area

[0047] After the first part of the cleaning is completed, the silicon core is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid. The acid solution used in the first mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a volume ratio of 37wt%, wherein the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution are 1:4.5:0.8. The second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. The acid solution used in the second mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water. The volume ratio of the above hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:2:30. After the pickling is completed, high-purity water is used for washing once to complete the second part of the cleaning;

[0048] S3: The third cleaning area

[0049] The silicon core after the second cleaning is again pickled with a hydrofluoric acid solution. The hydrofluoric acid solution is prepared by mixing 49wt% hydrofluoric acid and high-purity water in a volume ratio of 1:8. The cleaning time is 3 minutes. After the pickling is completed, the silicon core is washed twice with high-purity water to complete the third cleaning.

[0050] S4: The fourth cleaning area

[0051] The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning;

[0052] S5: Drying and cooling

[0053] The silicon core that has completed the fourth part of cleaning is dried with 70°C Class 100 clean air for 1200 seconds. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

[0054] Example 2

[0055] In the present invention, all cleaning areas are in a negative pressure state relative to the external environment, and the pressure difference is ≥5Pa; air curtains are provided between each cleaning area; the resistivity of high-purity water during the cleaning process is greater than 17.5MΩ·cm;

[0056] S1: The first cleaning area

[0057] The silicon core is first plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The ozone content of the ozone solution is 2.5 mg / L. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning.

[0058] S2: The second cleaning area

[0059] After the first part of the cleaning is completed, the silicon core is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid. The acid solution used in the first mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a volume ratio of 37wt%, wherein the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution are 1:5:1. The second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. The acid solution used in the second mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water. The volume ratio of the above hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:3:40. After the pickling is completed, high-purity water is used for washing once to complete the second part of the cleaning;

[0060] S3: The third cleaning area

[0061] The silicon core after the second cleaning is again pickled with a hydrofluoric acid solution, wherein the hydrofluoric acid solution is prepared by mixing 49wt% hydrofluoric acid and high-purity water in a volume ratio of 1:10, and the cleaning time is 5 minutes. After the pickling is completed, the silicon core is washed twice with high-purity water to complete the third cleaning;

[0062] S4: The fourth cleaning area

[0063] The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning;

[0064] S5: Drying and cooling

[0065] The silicon core that has completed the fourth part of cleaning is dried with 60°C Class 100 clean air for 1000 seconds. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

[0066] Example 3

[0067] In the present invention, all cleaning areas are in a negative pressure state relative to the external environment, and the pressure difference is ≥5Pa; air curtains are provided between each cleaning area; the resistivity of high-purity water during the cleaning process is greater than 17.5MΩ·cm;

[0068] S1: The first cleaning area

[0069] The silicon core is first plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The ozone content of the ozone solution is 2.5 mg / L. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning.

[0070] S2: The second cleaning area

[0071] After the first part of the cleaning is completed, the silicon core is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid. The acid solution used in the first mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a volume ratio of 37wt%, wherein the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution are 1:9:2. The second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. The acid solution used in the second mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water. The volume ratio of the above hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:6:70. After the pickling is completed, high-purity water is used for washing once to complete the second part of the cleaning;

[0072] S3: The third cleaning area

[0073] The silicon core after the second cleaning is again pickled with a hydrofluoric acid solution. The hydrofluoric acid solution is prepared by 49wt% hydrofluoric acid and high-purity water in a volume ratio of 1:12. The cleaning time is 5 minutes. After the pickling is completed, high-purity water is used for two water washings to complete the third cleaning.

[0074] S4: The fourth cleaning area

[0075] The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning;

[0076] S5: Drying and cooling

[0077] The silicon core that has completed the fourth part of cleaning is dried with high-purity nitrogen gas with a purity of 99.9999%. The drying time is 1200 seconds. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

[0078] Example 4

[0079] In the present invention, all cleaning areas are in a negative pressure state relative to the external environment, and the pressure difference is ≥5Pa; air curtains are provided between each cleaning area; the resistivity of high-purity water during the cleaning process is greater than 17.5MΩ·cm;

[0080] S1: The first cleaning area

[0081] The silicon core is first plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The ozone content of the ozone solution is 2.5 mg / L. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning.

[0082] S2: The second cleaning area

[0083] The silicon core after the first part of the cleaning is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid. The acid solution used in the first mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a volume ratio of 37wt%, wherein the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution are 1:2:0.5. The second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. The acid solution used in the second mixed acid pickling is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water. The volume ratio of the above hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:1:20. After the pickling is completed, high-purity water is used for washing once to complete the second part of the cleaning;

[0084] S3: The third cleaning area

[0085] The silicon core after the second cleaning is again pickled with a hydrofluoric acid solution. The hydrofluoric acid solution is prepared by mixing 49wt% hydrofluoric acid and high-purity water in a volume ratio of 1:12. The cleaning time is 1 minute. After the pickling is completed, the silicon core is washed twice with high-purity water to complete the third cleaning.

[0086] S4: The fourth cleaning area

[0087] The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning;

[0088] S5: Drying and cooling

[0089] The silicon core that has completed the fourth part of cleaning is dried with high-purity nitrogen gas with a purity of 99.9999%. The drying time is 1200 seconds. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

[0090]

[0091] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for cleaning electronic grade polysilicon cores, characterized in that: The specific steps of the method are as follows: S1: The first cleaning area The silicon core is firstly plasma cleaned, and then ultrasonically cleaned with high-purity water. After ultrasonic cleaning, ozone degreasing treatment is performed with ozone solution. The degreased silicon core is then rinsed twice with high-purity water to complete the first part of cleaning. S2: The second cleaning area After the first part of the cleaning is completed, the silicon core is subjected to two mixed acid picklings. The first mixed acid pickling uses a mixed solution of nitric acid, hydrofluoric acid and hydrochloric acid, and the second pickling uses a mixed solution of nitric acid, hydrofluoric acid and high-purity water. After the pickling is completed, it is washed once with high-purity water to complete the second part of the cleaning; S3: The third cleaning area After the second cleaning, the silicon core is pickled again with a hydrofluoric acid solution. After the pickling is completed, it is washed twice with high-purity water to complete the third cleaning; S4: The fourth cleaning area The silicon core that has completed the third part of the cleaning is subjected to two megasonic cleanings, and after each megasonic cleaning, it is switched to the next megasonic cleaning device, and after the megasonic cleaning, it is rinsed once with high-purity water to complete the fourth part of the cleaning; S5: Drying and cooling The silicon core that has completed the fourth part of cleaning is dried with Class 100 clean air or high-purity nitrogen at 60-80°C. After completion, it is cooled to room temperature to complete the cleaning of the silicon core.

2. A method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The entire cleaning area is in a negative pressure state compared to the external environment, and the pressure difference is ≥5Pa.

3. A method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: Air curtains are arranged between the areas for first and second part cleaning, second and third part cleaning, and third and fourth part cleaning.

4. The method for cleaning electronic grade polycrystalline silicon core according to claim 1, characterized in that: The resistivity of the high-purity water during the cleaning process is greater than 17.5 MΩ·cm.

5. The method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The ozone content of the ozone solution in S1 is 2.5 mg / L.

6. A method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The acid solution used for the first mixed acid pickling in S2 is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and a hydrochloric acid solution with a mass concentration of 37wt%, wherein the volume ratio of the hydrofluoric acid solution, the nitric acid solution and the hydrochloric acid solution is 1:(2-9):(0.5-2).

7. A method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The acid solution used in the second mixed acid pickling in S2 is prepared by a hydrofluoric acid solution with a mass concentration of 49%wt, a nitric acid solution with a mass concentration of 70wt% and high-purity water, wherein the volume ratio of the hydrofluoric acid solution, the nitric acid solution and the high-purity water is 1:(1-6):(20-70).

8. The method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The hydrofluoric acid solution in S3 is prepared by using 49 wt % hydrofluoric acid and high-purity water in a volume ratio of 1:(8-12), and the cleaning time is 1-5 min.

9. A method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The purity of the high-purity nitrogen in S5 is 99.9999%.

10. The method for cleaning electronic grade polysilicon core according to claim 1, characterized in that: The drying time in S5 is 1000-1200s.

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