Method for cleaning quartz crucible

Abstract

The invention relates to the technical field of quartz crucible production, in particular to a quartz crucible cleaning method which comprises the following steps: S1, washing: washing a quartz crucible by using ultrapure water according to a first preset water pressure; s2, alkali cleaning: soaking the quartz crucible in an alkaline cleaning solution at a first preset temperature; s3, pickling: at a second preset temperature, carrying out chemical reaction on an acidic cleaning solution and the quartz crucible; s4, high-pressure water washing: washing the quartz crucible by using ultrapure water according to a second preset water pressure; s5, drying: drying the quartz crucible according to a third preset temperature; wherein the second preset temperature is 20-45 DEG C, and the acidic cleaning solution is formed by mixing HF with the concentration of 10%-30% and H2SO4 or HNO3 with the concentration of 1%-10%, so that the etching speed is adjusted by adjusting the temperature and the HF concentration in the pickling step, impurities on the inner surface of the quartz crucible are removed within reasonable time, and the smoothness of the inner surface of the quartz crucible meets the standard.

Description

Technical Field

[0001] The invention relates to the technical field of quartz crucible production, in particular to a quartz crucible cleaning method. Background Art

[0002] With the rapid development of electronic information technology, people's demand for electronic products has gradually increased, and the requirements are becoming higher and higher, thus promoting the high-quality development of the semiconductor industry; single crystal silicon is an important material for making semiconductor devices, among which the purity of single crystal silicon is one of the most important factors affecting the quality of semiconductor products, and quartz crucible is the main component in the production of single crystal silicon, and the cleanliness of its inner surface is an important factor affecting the purity of single crystal silicon rods.

[0003] At present, the raw materials used in the production of quartz crucibles are usually quartz sand, including natural quartz sand and synthetic quartz sand. Although the purity of quartz sand is high enough, there are still gas-liquid inclusions in the production process of quartz crucibles, and the arc melting method currently used also has the risk of introducing impurities into the quartz crucible. In addition, in the subsequent sandblasting, cutting, testing and other processes, the inner surface of the quartz crucible may also be contaminated with organic matter such as oil stains.

[0004] Therefore, in order to improve the cleanliness of the inner surface of the quartz crucible, the inner surface of the quartz crucible needs to be cleaned. The existing methods for cleaning the inner surface of the quartz crucible include chemical cleaning and physical cleaning. Among them, the main processes of chemical cleaning are pickling, rinsing and drying. The most important process in chemical cleaning is pickling, which uses highly corrosive acid to react chemically with the crucible to etch and peel off impurities on the inner surface of the crucible. In this process, the etching rate needs to be controlled. If the etching rate is too fast, defects such as pits and scratches will appear on the inner surface of the quartz crucible, affecting the smoothness of the inner surface of the quartz crucible; if the etching rate is too slow, the production efficiency of the quartz crucible will be reduced, and the impurities on the inner surface of the quartz crucible cannot be removed within a reasonable time. Summary of the invention

[0005] In view of this, it is necessary to provide a quartz crucible cleaning method that can control the etching rate during the pickling process to remove impurities on the inner surface of the quartz crucible within a reasonable time and make the smoothness of the inner surface of the quartz crucible meet the standard, thereby ensuring that the quality of the inner surface of the quartz crucible meets the standard.

[0006] The present invention provides a quartz crucible cleaning method, comprising the following steps: S1, water washing: using ultrapure water to wash the quartz crucible at a first predetermined water pressure to remove washable foreign matter adhering to the surface of the quartz crucible; S2, alkaline cleaning: soaking the quartz crucible with an alkaline cleaning solution at a first predetermined temperature to remove organic pollutants attached to the surface of the quartz crucible; S3, pickling: using an acidic cleaning liquid to chemically react with the quartz crucible at a second predetermined temperature to etch and peel off impurities on the surface of the quartz crucible; S4, high-pressure water washing: using ultrapure water to wash the quartz crucible at a second predetermined water pressure to remove residual acidic cleaning solution and reaction products of the acidic cleaning solution and the quartz crucible; S5, drying: drying the quartz crucible at a third predetermined temperature to quickly remove moisture on the surface of the quartz crucible to prevent water stains from forming on the surface of the quartz crucible; The second predetermined temperature in step S3 is 20°C-45°C, and the acid cleaning solution is a mixture of HF with a concentration of 10%-30% and H2SO4 or HNO3 with a concentration of 1%-10%. The etching speed of the quartz crucible is adjusted by controlling the temperature during pickling and the concentration of HF. H2SO4 or HNO3 is used to react with alkaline earth metal impurities on the surface of the quartz crucible to reduce the generation of insoluble substances.

[0007] Preferably, in step S3, the second predetermined temperature is 25° C., and the acid cleaning solution is a mixture of HF with a concentration of 25% and H2SO4 or HNO3 with a concentration of 10%.

[0008] Preferably, the first predetermined water pressure in step S1 is 0.2-1.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

[0009] Preferably, the first predetermined temperature in step S2 is 60° C.-90° C.; the alkaline cleaning solution is a mixed solution of NaOH and a surfactant, wherein the content of NaOH is 1%-5%, and the content of the surfactant is 0.5%-3%.

[0010] Preferably, the surfactant is a cationic surfactant.

[0011] Preferably, the second predetermined water pressure in step S4 is 0.5-2.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

[0012] Preferably, the third predetermined temperature in step S5 is 80°C-200°C.

[0013] The present invention has the following beneficial effects: 1. The etching rate during pickling is adjusted by adjusting the temperature during pickling and the concentration of HF in the acid cleaning solution; specifically, as the temperature increases and the HF concentration increases, the etching rate during pickling increases, and vice versa, the etching rate during pickling decreases. By maintaining the temperature at 20°C-45°C and the HF concentration at 10%-30%, the etching rate during pickling can be maintained within an appropriate range to ensure that impurities on the inner surface of the quartz crucible are removed within a reasonable time, and the smoothness of the inner surface of the quartz crucible meets the standard, thereby ensuring that the quality of the inner surface of the quartz crucible meets the standard; 2. Add H2SO4 or HNO3 to the acid cleaning solution to provide H + , inhibiting the ionization of HF and increasing the effective etching substances HF and HF2 in the acid cleaning solution - concentration; at the same time, H2SO4 or HNO3 reacts chemically with alkaline earth metal impurities on the surface of the quartz crucible, such as Ca, Mg and Al, to generate soluble metal salts, such as CaSO4, MgSO4, Ca (NO3) 2 and Mg (NO3) 2, etc., to reduce the insoluble metal salts generated by hydrofluoric acid and alkaline earth metal impurities, such as CaF2, MgF2 and AlF3, etc., thereby improving the cleanliness of the inner surface of the quartz crucible; 3. Since the organic pollutants attached to the surface of the quartz crucible do not react with the acidic cleaning solution, after the quartz crucible is pickled, the area with the organic pollutants attached is etched at a different depth from other areas, forming stains. By alkali washing the quartz crucible before pickling, the organic pollutants attached to the surface of the quartz crucible can be removed to prevent the formation of stains. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of the quartz crucible cleaning method of the present application.

[0015] Figure 2 It is a graph showing the experimental results of sample 1 in Example 1 of the present application.

[0016] Figure 3 This is a graph showing the experimental results of Sample 2 in Example 1 of the present application.

[0017] Figure 4 It is a graph showing the experimental results of sample 3 in Example 1 of the present application.

[0018] Figure 5 It is a graph showing the experimental results of sample 4 in Example 1 of the present application. DETAILED DESCRIPTION

[0019] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0020] Please refer to Figure 1The present invention provides a quartz crucible cleaning method, comprising the following steps: S1, water washing: using ultrapure water to wash the quartz crucible at a first predetermined water pressure to remove washable foreign matter adhering to the surface of the quartz crucible; S2, alkaline cleaning: soaking the quartz crucible in an alkaline cleaning solution at a first predetermined temperature to remove organic pollutants attached to the surface of the quartz crucible, such as fingerprints and equipment oil stains; S3, pickling: using an acidic cleaning liquid to chemically react with the quartz crucible at a second predetermined temperature to etch and peel off impurities on the surface of the quartz crucible; S4, high-pressure water washing: using ultrapure water to wash the quartz crucible at a second predetermined water pressure to remove residual acidic cleaning solution and reaction products of the acidic cleaning solution and the quartz crucible; S5, drying: drying the quartz crucible at a third predetermined temperature to quickly remove moisture on the surface of the quartz crucible to prevent water stains from forming on the surface of the quartz crucible; The second predetermined temperature in step S3 is 20°C-45°C, and the acid cleaning solution is a mixture of HF with a concentration of 10%-30% and H2SO4 or HNO3 with a concentration of 1%-10%. The etching speed of the quartz crucible is adjusted by controlling the temperature during pickling and the concentration of HF. H2SO4 or HNO3 is used to react with alkaline earth metal impurities on the surface of the quartz crucible to reduce the generation of insoluble substances.

[0021] Furthermore, in step S3, the second predetermined temperature is 25° C., and the acid cleaning solution is a mixture of HF with a concentration of 25% and H2SO4 or HNO3 with a concentration of 10%. Under this parameter, the etching effect of the acid cleaning solution is optimal.

[0022] The acid cleaning solution has the following beneficial effects: 1. The etching rate during pickling is adjusted by adjusting the temperature during pickling and the concentration of HF in the acid cleaning solution; specifically, as the temperature increases and the HF concentration increases, the etching rate during pickling increases, and vice versa, the etching rate during pickling decreases. By maintaining the pickling temperature at 20°C-45°C and the HF concentration in the acid cleaning solution at 10%-30%, the etching rate during pickling can be maintained within an appropriate range to ensure that impurities on the inner surface of the quartz crucible are removed within a reasonable time, and the smoothness of the inner surface of the quartz crucible meets the standard, thereby ensuring that the quality of the inner surface of the quartz crucible meets the production standard; 2. Add H2SO4 or HNO3 to the acid cleaning solution to provide H+, inhibit the ionization of HF, and increase the effective etching substances HF and HF2 in the acid cleaning solution. -concentration; at the same time, H2SO4 or HNO3 reacts chemically with alkaline earth metal impurities on the surface of the quartz crucible, such as Ca, Mg and Al, to generate soluble metal salts, such as CaSO4, MgSO4, Ca (NO3) 2 and Mg (NO3) 2, etc., to reduce the insoluble metal salts generated by hydrofluoric acid and alkaline earth metal impurities, such as CaF2, MgF2 and AlF3, etc., thereby improving the cleanliness of the inner surface of the quartz crucible; 3. Since the reaction between HF and quartz crucible is a secondary reaction, the concentration of HF has a significant effect on the reaction rate. If the concentration of HF is lower than 10%, the reaction rate between HF and quartz crucible is low, resulting in reduced pickling efficiency; if the concentration of HF is higher than 30%, the reaction rate between HF and quartz crucible is too fast, resulting in a large roughness on the inner surface of the quartz crucible. The inner surface of the quartz crucible with a large roughness is easy to become a crystallization nucleus, thereby causing the crucible to lose clarity, which is not conducive to long-term crystal pulling; 4. If the concentration of H2SO4 or HNO3 is lower than 1%, the formation of insoluble matter cannot be reduced, resulting in a decrease in the purity of the quartz crucible; at the same time, it is unable to provide sufficient H+ for the reaction of the HF quartz crucible, resulting in a decrease in the reaction rate of HF and the quartz crucible; if the concentration of H2SO4 or HNO3 is higher than 10%, since H2SO4 or HNO3 does not react chemically with the quartz crucible, excessively high concentrations of H2SO4 or HNO3 will lead to a waste of raw materials and an increase in the amount of waste acid that needs to be treated, increasing the cost of the enterprise; 5. If the temperature during pickling is lower than 20°C, the reaction rate between the acid cleaning solution and the quartz crucible will be slow, resulting in a slow pickling speed and reduced production efficiency of the quartz crucible. If the temperature of the acid cleaning solution is higher than 45°C, the reaction rate between the acid cleaning solution and the quartz crucible will be too fast, resulting in a larger roughness of the inner surface of the quartz crucible. The larger inner surface roughness will make the quartz crucible easy to lose transparency, thereby affecting the service life of the quartz crucible. At the same time, HF is a strong acid with high volatility and toxicity. Excessive temperature will increase the volatility of HF, affecting the safe production in the workshop and reducing the utilization rate of HF.

[0023] Furthermore, the first predetermined water pressure in step S1 is 0.2-1.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

[0024] Furthermore, the first predetermined temperature in step S2 is 60° C.-90° C.; the alkaline cleaning solution is a mixed solution of NaOH and a surfactant, wherein the content of NaOH is 1%-5%, and the content of the surfactant is 0.5%-3%.

[0025] Furthermore, the surfactant is an iso-cationic surfactant, for example, dodecyldimethylbenzyl ammonium chloride.

[0026] Using this alkaline cleaning solution for alkaline cleaning has the following beneficial effects: 1. NaOH reacts chemically with the organic pollutants on the surface of the quartz crucible, converting them into substances with higher solubility; the role of the surfactant is to increase the solubility of organic pollutants on the surface of the quartz crucible and promote the degradation of organic pollutants; thereby improving the cleaning effect of the alkaline cleaning solution on organic pollutants; 2. Improve the solubility of surfactants by controlling the temperature. Within this temperature range, the solubility of surfactants is relatively high. Too high or too low temperature will cause the solubility of surfactants to be greatly reduced, thus affecting the promotion effect on organic pollutants; 3. Since the surface of the quartz crucible will be contaminated with organic pollutants during the production process, and the acidic cleaning solution does not react with the organic pollutants, when the acidic cleaning solution chemically reacts with the quartz crucible, the etching depth of the area covered by the organic pollutants and other areas is different, and eventually stains will be formed on the inner surface of the quartz crucible that are difficult to remove by subsequent processes such as water washing, resulting in reduced cleanliness of the inner surface of the quartz crucible; the present invention can effectively remove organic pollutants contaminated on the surface of the quartz crucible by adding an alkaline washing process before the acid washing process, so as to prevent the formation of stains and thus improve the cleanliness of the inner surface of the quartz crucible.

[0027] Furthermore, the second predetermined water pressure in step S4 is 0.5-2.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

[0028] Furthermore, the predetermined temperature in step S5 is 80°C-200°C.

[0029] Example 1: Experiment on the influence of various parameters of alkaline cleaning solution on printing stains In this embodiment, four 5*5cm samples were taken from the same quartz crucible for experiment, and the other processing steps remained unchanged. During the alkaline washing step, the four samples were immersed in alkaline cleaning solutions with different temperatures and compositions for 1 hour, the mass of the alkaline cleaning solution used was 400g, and the immersion container was a tetrafluoroethylene cup. The experimental conditions and experimental results are shown in the following table: Table 1

[0030] By comparing the parameters of the four experiments and the stains on the sample surface, it can be seen that NaOH and surfactant are indispensable, and the temperature must be controlled within an appropriate range, otherwise obvious stains will be left on the surface of the quartz crucible after pickling.

[0031] Example 2: Experiment on the effect of HF concentration in acidic cleaning solution on etching rate Seven 5*5cm samples were taken from the same quartz crucible for experiment. The other treatment steps remained unchanged. During the pickling step, the seven samples were immersed in seven groups of acid cleaning solutions with different HF concentrations at a temperature of 27°C. The mass of each group of acid cleaning solutions was 400g, and no H2SO4 or HNO3 was added. The immersion container was a tetrafluoroethylene cup. The experimental results are shown in the following table: Table 2

[0032] Among them, the etching depth of the quartz crucible is measured using a 3D microscope. Since the immersion time is fixed, the etching depth of the quartz crucible can indicate the etching speed of the quartz crucible. The inner surface roughness of the quartz crucible is measured using a roughness meter. The inner surface purity of the quartz crucible is measured using an ICP-MS inductively coupled plasma mass spectrometer, which represents the sum of the contents of nine elements, namely Li, Na, K, Mg, Ca, Al, Fe, Cu and Ni, per unit area.

[0033] By analyzing the experimental data in Table 2, it can be known that with the increase of HF concentration, the etching speed of the quartz crucible increases accordingly. When the HF concentration is <30%, the inner surface roughness of the quartz crucible is ≤0.1um, which meets the production requirements of the quartz crucible. When the HF concentration is >30%, the inner surface roughness of the quartz crucible is >0.1um, which does not meet the production requirements of the quartz crucible; at the same time, when the HF concentration is <10%, the etching speed of the quartz crucible is slow and the impurity content on the inner surface is also high, which does not meet the production requirements. Therefore, maintaining the HF concentration at 10%-30% can meet the production requirements.

[0034] Furthermore, when the HF concentration is 30%, the etching speed of the quartz crucible is relatively fast, the roughness may exceed the standard, and the production window may become narrower. Therefore, the optimal parameter of the HF concentration is 25%.

[0035] Example 3, Experimental study on the effect of H2SO4 or HNO3 concentration in acidic cleaning solution on the impurity content on the inner surface of quartz crucible Five 5*5cm samples were taken from the same quartz crucible for experiment. The other treatment steps remained unchanged. During the pickling step, the five samples were immersed in five groups of acidic cleaning solutions with different concentrations of H2SO4 or HNO3 at a temperature of 27°C. The mass of each group of acidic cleaning solutions was 400g, the concentration of HF was 25%, and the immersion container was a tetrafluoroethylene cup. The experimental results are shown in the following table: Table 3

[0036] Among them, the etching depth of the quartz crucible is measured using a 3D microscope. Since the immersion time is fixed, the etching depth of the quartz crucible can indicate the etching speed of the quartz crucible. The inner surface roughness of the quartz crucible is measured using a roughness meter. The inner surface purity of the quartz crucible is measured using an ICP-MS inductively coupled plasma mass spectrometer, which represents the sum of the contents of nine elements, namely Li, Na, K, Mg, Ca, Al, Fe, Cu and Ni, per unit area.

[0037] Analysis of the data in Table 3 shows that the concentration of H2SO4 or HNO3 has almost no effect on the etching speed and inner surface roughness of the quartz crucible, and mainly affects the impurity content on the inner surface of the quartz crucible. With the increase of the concentration of H2SO4 or HNO3, the impurity content on the inner surface of the quartz crucible also decreases. When the concentration of H2SO4 or HNO3 is 10%, the impurity content on the inner surface reaches the minimum value of 0.2ng / cm 2 ,Since H2SO4 or HNO3 itself does not participate in the etching reaction on the inner surface of the quartz crucible, continuing to increase the concentration of H2SO4 or HNO3 will only cause a waste of raw materials, so the optimal concentration of H2SO4 or HNO3 is 10%.

[0038] Example 4: Experiment on the effect of temperature on etching rate and acid volatilization rate Six 5*5cm samples were taken from the same quartz crucible for experiment. The other treatment steps remained unchanged. During the pickling step, the six samples were immersed in the same acid cleaning solution at different temperatures. The mass of each group of acid was 400g, the concentration of HF was 25%, and the concentration of H2SO4 or HNO3 was 10%. The immersion container was a tetrafluoroethylene cup. The experimental results are shown in the following table: Table 4

[0039] Among them, the etching depth of the quartz crucible is measured using a 3D microscope. Since the immersion time is fixed, the etching depth of the quartz crucible can indicate the etching speed of the quartz crucible. The inner surface roughness of the quartz crucible is measured using a roughness meter. The acid volatilization rate is calculated according to the acid mass loss rate.

[0040] Analysis of the data in Table 4 shows that as the temperature increases, the etching speed of the quartz crucible also increases. When the temperature is <40°C, the roughness of the inner surface of the quartz crucible is ≤0.1um, which meets the production requirements. When the temperature is >40°C, the roughness of the inner surface of the quartz crucible is >0.1um, which does not meet the production requirements. At the same time, since the etching speed of the quartz crucible is slow at 20°C and the acid volatilization rate of the acid cleaning solution is high at 30°C, the pickling temperature is optimal at 25°C.

[0041] In summary, at a temperature of 25°C, when the HF concentration in the acid cleaning solution is 25%, and the concentration of H2SO4 or HNO3 is 10%, the acid cleaning solution has the best cleaning effect on the inner surface of the quartz crucible.

[0042] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A quartz crucible cleaning method, characterized in that The following steps are involved: S1, water washing: using ultrapure water to wash the quartz crucible at a first predetermined water pressure to remove washable foreign matter adhering to the surface of the quartz crucible; S2, alkaline cleaning: soaking the quartz crucible with an alkaline cleaning solution at a first predetermined temperature to remove organic pollutants attached to the surface of the quartz crucible; S3, pickling: using an acidic cleaning liquid to chemically react with the quartz crucible at a second predetermined temperature to etch and peel off impurities on the surface of the quartz crucible; S4, high-pressure water washing: using ultrapure water to wash the quartz crucible at a second predetermined water pressure to remove residual acidic cleaning solution and reaction products of the acidic cleaning solution and the quartz crucible; S5, drying: drying the quartz crucible at a third predetermined temperature to quickly remove moisture on the surface of the quartz crucible to prevent water stains from forming on the surface of the quartz crucible; The second predetermined temperature in step S3 is 20°C-45°C, and the acid cleaning solution is a mixture of HF with a concentration of 10%-30% and H2SO4 or HNO3 with a concentration of 1%-10%. The etching speed of the quartz crucible is adjusted by controlling the temperature during pickling and the concentration of HF. H2SO4 or HNO3 is used to react with alkaline earth metal impurities on the surface of the quartz crucible to reduce the generation of insoluble substances.

2. The quartz crucible cleaning method according to claim 1, characterized in that: In step S3, the second predetermined temperature is 25° C., and the acid cleaning solution is a mixture of HF with a concentration of 25% and H2SO4 or HNO3 with a concentration of 10%.

3. The quartz crucible cleaning method according to claim 1, characterized in that The first predetermined water pressure in step S1 is 0.2-1.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

4. The quartz crucible cleaning method according to claim 1, characterized in that: The first predetermined temperature in step S2 is 60° C.-90° C.; the alkaline cleaning solution is a mixed solution of NaOH and a surfactant, wherein the content of NaOH is 1%-5%, and the content of the surfactant is 0.5%-3%.

5. The quartz crucible cleaning method according to claim 4, characterized in that: The surfactant is a cationic surfactant.

6. The quartz crucible cleaning method according to claim 1, characterized in that: The second predetermined water pressure in step S4 is 0.5-2.0 MPa; the resistivity of ultrapure water is greater than 12 MΩ.cm.

7. The quartz crucible cleaning method according to claim 1, characterized in that: The third predetermined temperature in step S5 is 80°C-200°C.

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