Silicon material cleaning method

Abstract

The invention discloses a silicon material cleaning method. The silicon material cleaning method comprises the following steps: providing a silicon material to be treated; placing the to-be-treated silicon material in a low-carbon alcohol aqueous solution for alcohol washing treatment to obtain an alcohol-washed silicon material; then carrying out acid pickling treatment on the alcohol-washed silicon material by adopting an organic strong acid solution to obtain an acid-washed silicon material; carrying out water washing treatment and drying treatment on the acid-washed silicon material to obtain a clean silicon material; wherein the organic strong acid in the organic strong acid solution comprises any one of trichloromethanesulfonic acid and benzene methanesulfonic acid. According to the method provided by the invention, the organic strong acid in the organic strong acid solution can react with most impurities such as metal impurities, organic matters and surface oxides on the surface of the to-be-treated silicon material, and the product is extremely easy to dissolve in the solvent, so that the product can be separated from the silicon material in time; and in the reaction process, a large amount of toxic and harmful gas cannot be generated. In addition, the acidity of the selected organic strong acid is high, a good impurity removal effect can be achieved through a small amount of organic acid, and the material washing cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon material cleaning, and in particular to a method for cleaning silicon material. Background Art

[0002] As the photovoltaic industry gradually develops in the direction of high quality and low cost, silicon rod crystal pulling has transitioned from batch and multiple loading and pulling to uninterrupted continuous pulling. Since continuous crystal pulling requires high-quality granular polysilicon raw materials, the requirements for the material washing process before crystal pulling are becoming more and more stringent.

[0003] In the production process of electronic-grade polysilicon, the silicon rods produced by gas phase reduction need to be crushed. During the transportation and crushing process, various impurities will increase on the surface of the silicon blocks. The increased impurities will reduce the purity of the silicon material, resulting in a decrease in the yield of downstream products and an increase in costs. During the transportation and crushing of silicon materials, the increased impurities are mainly metal impurities, in addition to a small amount of organic matter, oxides and other impurities.

[0004] The existing material washing process uses a mixed acid system of pure water and highly concentrated nitric acid and hydrofluoric acid to etch polysilicon, and then bags it after cleaning and drying for the next step of feeding. However, although this method has a rapid impurity removal process, it has the following disadvantages: due to the chemical reaction between the strong acid and the surface of the silicon material, the surface layer is continuously corroded and peeled off. The violent reaction and fast chemical corrosion rate make the corrosion process difficult to accurately control and the process stability is poor, resulting in poor stability of silicon material cleaning quality; due to the reaction of strong acid with silicon material to generate nitrogen oxides or concentrated nitric acid volatilizes and decomposes into brown-yellow nitrogen oxides, a large amount of yellow smoke will be generated during the corrosion process, which is very harmful to the human body and the environment; and the cleaning process generates a large amount of wastewater and waste gas, which need to be treated by dedicated facilities to meet environmental protection requirements before they can be discharged, which undoubtedly makes production conditions more stringent and increases production costs. Summary of the invention

[0005] The purpose of the present invention is to provide a cleaning method in order to overcome the defects of the above-mentioned prior art.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] The present invention provides a method for cleaning silicon material, comprising the following steps:

[0008] Providing silicon materials to be processed;

[0009] placing the silicon material to be treated in a low-carbon alcohol aqueous solution for alcohol washing to obtain an alcohol-washed silicon material;

[0010] Then, the alcohol-washed silicon material is pickled with an organic strong acid solution to obtain the pickled silicon material;

[0011] The acid-washed silicon material is then washed with water and dried to obtain clean silicon material;

[0012] Wherein: the organic strong acid in the organic strong acid solution includes any one of trichloromethanesulfonic acid and benzenesulfonic acid.

[0013] In some embodiments of the present invention, the strong organic acid solution is obtained by dissolving trichloromethanesulfonic acid or toluenesulfonic acid in a mixed solvent of an organic solvent and pure water, wherein the organic solvent is a low-carbon alcohol.

[0014] In some embodiments of the present invention, the low-carbon alcohol includes one or more of ethanol, n-propanol and isopropanol, preferably ethanol.

[0015] In some embodiments of the present invention, the alcohol washing treatment is performed under ultrasonic conditions, and the liquid-to-solid ratio of the alcohol washing treatment is 100-400 mL: 1 kg;

[0016] Preferably, the mass concentration of the low-carbon alcohol aqueous solution is 40%-60%;

[0017] Preferably, the temperature of the alcohol washing treatment is room temperature, and the ultrasonic time is 10-30 min.

[0018] In some embodiments of the present invention, the temperature of the pickling solution is ≤10°C;

[0019] Preferably, the pickling treatment includes a first pickling treatment and a second pickling treatment, wherein the first pickling treatment is to add trichloromethanesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises; the second pickling treatment is to add toluenesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises to obtain pickled silicon material, wherein the mass ratio of trichloromethanesulfonic acid to toluenesulfonic acid is 2:3-1:1.

[0020] In some embodiments of the present invention, the liquid-to-solid ratio of the first pickling stage is 40-100 mL: 1 kg, and the time is 2-3 h; the liquid-to-solid ratio of the second pickling stage is 60-100 mL: 1 kg, and the time is 2-3 h;

[0021] Preferably, after the second stage of pickling is completed, ultrasonication is performed for 30-60 minutes.

[0022] In some embodiments of the present invention, the resistivity of pure water used in the water washing treatment is ≥18MΩ·cm;

[0023] Preferably, the liquid-to-solid ratio of the water washing treatment is 100-400 mL: 1 kg;

[0024] Preferably, the temperature of the water washing treatment is room temperature, and the washing cycle is 3-5 times.

[0025] In some embodiments of the present invention, the acid washing treatment further includes an alkali washing treatment, and the alkali solution used in the alkali washing treatment is a NaOH solution with a mass concentration of 5%-15%;

[0026] Preferably, the liquid-to-solid ratio of the alkali washing treatment is 100-200 ml: 1 kg;

[0027] Preferably, the alkali washing treatment is carried out at a temperature of 65-80°C and for a time of 30-40 minutes.

[0028] In some embodiments of the present invention, the drying treatment comprises: vacuum drying the washed silicon material obtained by the water washing treatment at a temperature of 100-150° C. and a vacuum degree of ≤-0.95 kPa.

[0029] In some embodiments of the present invention, the further step includes: crushing and bagging the clean silicon material to obtain feed silicon, and then pulling the feed silicon.

[0030] The present invention has the following beneficial effects:

[0031] The present invention provides a method for cleaning silicon material, comprising the following steps: providing silicon material to be treated; placing the silicon material to be treated in a low-carbon alcohol aqueous solution for alcohol washing to obtain alcohol-washed silicon material; then using an organic strong acid solution to acid-wash the alcohol-washed silicon material to obtain acid-washed silicon material; then washing the acid-washed silicon material with water and drying it to obtain clean silicon material; wherein the organic strong acid in the organic strong acid solution includes any one of trichloromethanesulfonic acid and benzenesulfonic acid. The above-mentioned cleaning method can effectively remove impurities such as metal impurities, surface oxides and organic matter in silicon materials, that is, the organic strong acid in the organic strong acid solution can react and transform the metal impurities on the surface of the silicon material into salt and hydrogen, oxidize the carbon, hydrogen, oxygen and other organic impurities into CO2 and H2O, and transform the surface oxide impurities into silicic acid. The entire cleaning and impurity removal process is precisely controllable, and most of the impurities on the surface of the silicon material can be quickly and effectively removed, thereby improving the safety and stability of the material washing process; the organic strong acid has good stability and will not volatilize to produce toxic and harmful gases, and no toxic and harmful gases and a large amount of wastewater will be produced during the cleaning reaction, thereby improving the environmental friendliness of the material washing process; in addition, the organic strong acid has strong acidity, and a small amount of organic acid can achieve the impurity removal effect, thereby reducing the cost of material washing. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0033] Figure 1The present invention is a flow chart of the method for cleaning silicon material provided in the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0035] A method for cleaning silicon material provided by an embodiment of the present invention is described in detail below.

[0036] The purpose of silicon material cleaning is to make the silicon material surface clean and free of impurities, so as to ensure the purity of silicon material and avoid pollutants affecting product quality. According to the causes of pollutants, they can be roughly divided into four categories: metal impurities, organic impurities, surface oxide impurities, and particulate impurities. Among them: the impurities added on the surface of silicon material are mainly metal impurities, followed by a small amount of organic impurities, natural oxide layer, particles and other impurities. Metal impurities exist on the surface of silicon material in three surface forms: van der Waals attraction, covalent bond and electron transfer. The metal impurities added on the surface of silicon material include metals such as Na, Mg, Al, K, Ca, Cr, Fe, Co, Ni, Cu, Zn, W, etc.; organic impurities refer to compounds containing carbon, hydrogen and oxygen elements, which come from chemical drugs, lubricants, chemical fiber materials, etc. These organic impurities will be oxidized and decomposed during the heat treatment of silicon material to produce oxides; surface oxide impurities are formed by surface oxidation of silicon material in the natural environment, usually silicon dioxide; particulate impurities are generally silicon powder, silicon nitride powder, dust and fine sand, etc.

[0037] At present, the HF-HNO3 corrosion system is widely used for etching polycrystalline silicon wafers. Studies have shown that the corrosion of silicon materials in HF-HNO3 solution includes two basic processes, namely the initial oxidation reaction and the subsequent dissolution reaction. The chemical equation of the main reaction of silicon corrosion in HF-HNO3 solution is:

[0038] 3Si+4HNO3=3SiO2+4NO+2H2O

[0039] SiO2+6HF=H2SiF6+2H2O

[0040] In the above etching and cleaning methods, it is generally believed that the silicon material first undergoes an oxidation reaction with HNO3 to generate SiO2, and then HF reacts with SiO2 to dissolve and corrode the SiO2 formed on the surface of the silicon block, thereby removing impurities attached to the surface of the silicon block and near its inner surface. However, in the process of using the above HF-HNO3 etching system to remove impurities on the surface of the silicon material to be treated, the following problems still exist:

[0041] (1) The reaction between silicon material and mixed acid is violent and highly exothermic. During the pickling process, silicon material will be consumed to generate H2SiF6, which increases the loss of silicon material and makes the cleaning quality of silicon material unstable.

[0042] (2) When silicon material is put into mixed acid, the reaction is quite violent, producing a large amount of waste gas such as NO. When the HNO3 concentration is very high, the reduction product is not only NO, but also other valence reduction products such as NO, causing the solution to turn yellow, thus affecting the color of the silicon material surface.

[0043] (3) Concentrated HNO3 is unstable and easily volatilizes and decomposes into brown-yellow nitrogen oxides, which are harmful to the environment. HF is also unstable and is a highly volatile toxic gas. The use of the above-mentioned mixed acid system is also accompanied by the dangers of fire and explosion, chemical burns, mechanical accidents, etc. The above-mentioned poor stability of nitric acid and hydrofluoric acid will also increase the amount of cleaning.

[0044] (4) Wastewater and waste gas generated by cleaning must be treated in dedicated facilities before they can be discharged.

[0045] In order to overcome the defects of the above-mentioned prior art, an embodiment of the present invention provides a method for cleaning silicon material, comprising the following steps:

[0046] Providing silicon materials to be processed;

[0047] placing the silicon material to be treated in a low-carbon alcohol aqueous solution for alcohol washing to obtain an alcohol-washed silicon material;

[0048] Then, the alcohol-washed silicon material is pickled with an organic strong acid solution to obtain the pickled silicon material;

[0049] The acid-washed silicon material is then washed with water and dried to obtain clean silicon material;

[0050] Wherein: the organic strong acid in the organic strong acid solution includes any one of trichloromethanesulfonic acid and benzenesulfonic acid.

[0051] The above method for cleaning silicon materials has the following advantages:

[0052] (1) The organic strong acid in the organic strong acid solution includes any one of trichloromethanesulfonic acid and benzenesulfonic acid. The acidity of the above organic strong acid can reach the acidity of inorganic strong acid. When the above organic strong acid solution is used to clean silicon material, the organic strong acid in the organic strong acid solution can react with the metal impurities on the surface of the silicon material to produce metal salts and H2, oxidize the carbon, hydrogen, oxygen and other organic impurities into CO2 and H2O, and convert the surface oxide impurities into silicic acid. In the whole cleaning and impurity removal process, not only no toxic and harmful gases are generated, but also most of the impurities on the surface of the silicon material can be quickly and effectively removed, the loss of silicon material is small, the reaction is easy to control, and the cleaning quality of the silicon material is high.

[0053] (2) Based on (1), it can be seen that no toxic or harmful gases are generated during the silicon material cleaning process, the cleaning solution does not change color, and will not affect the color of the silicon material surface.

[0054] (3) Trichloromethanesulfonic acid and toluenesulfonic acid are stable in nature, not easy to volatilize and decompose, and can effectively overcome the defects of the HF-HNO3 corrosion system, such as the unstable concentration of organic strong acid solution and the large acid consumption caused by the instability of HF and HNO3.

[0055] (4) The cleaning method provided in the embodiment of the present invention is used to clean the silicon material to be treated. The gases generated are mainly H2 and CO2, and no toxic or harmful gases are generated. The waste water generated during the cleaning process mainly comes from the low-carbon alcohol aqueous solution used in the alcohol washing step. Since the pure water used in the water washing step is recycled after treatment, the water washing step does not generate waste water. It can be seen that the entire cleaning method does not generate toxic or harmful gases, generates less waste water, and is more environmentally friendly.

[0056] In addition, the silicon material cleaning method provided by the present invention also has the following advantages:

[0057] (1) The low-carbon alcohol in the low-carbon alcohol aqueous solution used includes one or more of ethanol, n-propanol and isopropanol. The low-carbon alcohol aqueous solution is advantageous as a dissolving and reaction system because: the selected organic strong acid is easily soluble in the low-carbon alcohol, and the organic strong acid also has good water solubility, and the organic strong acid can be separated from the surface of the silicon material in time by washing with water. The organic strong acid solution is not easy to remain on the surface of the silicon material, thereby reducing the probability of "acid spots" appearing on the surface of the silicon material. In addition, the metal salts, silicic acid, etc. produced by the reaction are easily soluble in water and can be easily removed by washing with water, thereby improving the cleanliness of the surface of the silicon material.

[0058] (2) Since the HF-HNO3 corrosion system achieves the purpose of cleaning and removing surface impurities by corroding and dissolving the surface layer of the silicon material, the concentration of HF and HNO3 in the HF-HNO3 corrosion system, the corrosion temperature and time are crucial to the dissolution and corrosion depth of the surface layer of the silicon material. If the corrosion of the silicon material surface is not obvious, the cleaning effect of the silicon material will be affected. If the corrosion of the silicon material surface is too much, it will not only easily deepen the erosion degree of the silicon material surface and increase the loss of polysilicon, but also easily form spots on the silicon material surface. When the organic strong acid solution provided by the embodiment of the present invention is used to clean the silicon material, the organic strong acid can directly react with the metal impurities on the surface of the silicon material to generate corresponding salts, without the need for the process of oxidation followed by dissolution as in the previous HF-HNO3 corrosion system, and the cleaning controllability is good.

[0059] (3) Strong organic acids have the characteristics of small dosage and strong acidity. A good impurity removal effect can be achieved with a small amount of strong organic acid, thus reducing the cost of washing materials.

[0060] As can be seen from the above, the cleaning method of silicon material provided by the embodiment of the present invention includes: firstly subjecting the silicon material to be treated to an alcohol washing treatment, wherein the low-carbon alcohol aqueous solution can dissolve some impurities on the surface of the silicon material to be treated, especially organic impurities and particulate impurities, thereby removing some organic impurities and particulate impurities, and then performing an acid washing treatment, wherein the organic strong acid in the organic strong acid solution can react with most of the metal impurities, organic impurities and natural oxidation impurities, and the reaction product is separated from the surface of the silicon material and enters the mixed solvent, thereby achieving impurity removal of the silicon material, and then subjecting the acid washed silicon material to a water washing treatment to remove the acid and other impurities remaining on the surface of the silicon material, and finally performing a drying treatment to remove the moisture in the silicon material to obtain a clean silicon material.

[0061] In some optional embodiments, the strong organic acid solution is obtained by dissolving trichloromethanesulfonic acid or toluenesulfonic acid in a mixed solvent of an organic solvent and pure water, wherein the organic solvent is a low-carbon alcohol.

[0062] In some optional embodiments, the low-carbon alcohol includes one or more of ethanol, n-propanol and isopropanol, preferably ethanol; the resistivity of pure water in the low-carbon alcohol aqueous solution is ≥18 MΩ·cm.

[0063] In some optional embodiments, the alcohol washing treatment is performed under ultrasonic conditions, and the liquid-to-solid ratio of the alcohol washing treatment is 100-400 mL: 1 kg;

[0064] Preferably, the mass concentration of the low-carbon alcohol aqueous solution is 40%-60%;

[0065] Preferably, the temperature of the alcohol washing treatment is room temperature, and the ultrasonic time is 10-30 min.

[0066] The alcohol washing treatment is carried out under ultrasonic conditions. The silicon material to be treated is pre-added into the low-carbon alcohol aqueous solution. The low-carbon alcohol aqueous solution can dissolve some impurities on the surface of the silicon material to be treated, especially organic impurities and particulate impurities. Secondly, the silicon material to be treated is pre-added into the low-carbon alcohol aqueous solution, which is also conducive to the attachment of the low-carbon alcohol aqueous solution to the surface of the silicon material to be treated. When the organic strong acid solution is used for pickling treatment later, the organic strong acid is easily soluble in the low-carbon alcohol aqueous solution, and can quickly react with the impurities on the surface of the silicon material to be treated, thereby improving the treatment efficiency. Thirdly, the organic strong acid is easily soluble in the low-carbon alcohol, and also has good water solubility and can be separated from the silicon material to be treated in time, reducing the residence time of the organic strong acid in the organic strong acid solution on the surface of the silicon material to be treated, thereby reducing the probability of "acid spots" and "spots" on the surface of the silicon material to be treated. It is worth noting that the resistivity of the pure water in the low-carbon alcohol aqueous solution here is ≥18MΩ·cm. When the resistivity of the pure water is ≥18MΩ·cm, there are almost no impurity ions in the pure water, which can ensure that the silicon material to be treated does not introduce new impurities during the alcohol washing process.

[0067] In some optional embodiments, the temperature of the pickling solution is ≤10°C;

[0068] Preferably, the pickling treatment includes a first pickling treatment and a second pickling treatment, wherein the first pickling treatment is to add trichloromethanesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises; the second pickling treatment is to add toluenesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises to obtain pickled silicon material, wherein the mass ratio of trichloromethanesulfonic acid to toluenesulfonic acid is 2:3-1:1.

[0069] In some optional embodiments, the liquid-to-solid ratio of the first pickling stage is 40-100 mL: 1 kg, and the time is 2-3 h; the liquid-to-solid ratio of the second pickling stage is 60-100 mL: 1 kg, and the time is 2-3 h;

[0070] Preferably, after the second stage of pickling is completed, ultrasonication is performed for 30-60 minutes.

[0071] The pickling treatment is carried out under ultrasonic conditions, and at the beginning of the pickling, the temperature of the mixed solution after the alcohol washing treatment needs to be reduced to below 10°C. This is because the organic strong acid in the organic strong acid solution will release a lot of heat during the dissolution and reaction process, resulting in a rapid increase in the temperature of the mixed solution after the addition of the organic strong acid, which increases the danger. High temperature will also accelerate the corrosion process of the organic strong acid, making the impurity removal process difficult to control. Therefore, it is necessary to reduce the temperature to less than 10°C at the beginning of the reaction. In the actual cleaning process, in order to make the cleaning reaction safer and more controllable, trichloromethanesulfonic acid or benzenesulfonic acid is added to the low-carbon alcohol aqueous solution, and stirred until the temperature of the solution no longer rises, indicating that the added trichloromethanesulfonic acid or benzenesulfonic acid is dissolved and the reaction is completed, and then trichloromethanesulfonic acid or benzenesulfonic acid is added, and stirred until the temperature of the solution no longer rises, indicating that the added trichloromethanesulfonic acid or benzenesulfonic acid is dissolved and the reaction is completed, and then the ultrasound is turned on. During the entire pickling process, not only can the impurities on the surface of the silicon material be effectively removed, but the reaction is also controllable, reducing the corrosion of the silicon material.

[0072] In some optional embodiments, the resistivity of pure water used in the water washing treatment is ≥18 MΩ·cm;

[0073] Preferably, the liquid-to-solid ratio of the water washing treatment is 100-400 mL: 1 kg;

[0074] Preferably, the temperature of the water washing treatment is room temperature, and the washing cycle is 3-5 times.

[0075] It is worth mentioning that during the water washing process, pure water should be discharged into the sewage pool after each washing of the silicon material. The pure water in the sewage pool is then processed by a pure water machine to obtain pure water with a resistivity of ≥18MΩ·cm, so as to soak and wash the silicon material again. This method can ensure the purity of the pure water, so that it can more efficiently clean the residual substances on the surface of the silicon material, which is helpful for the preparation of high-quality feed silicon. When the acid-washed silicon material is transferred to the water washing tank after pickling, keeping the temperature of the two similar is also conducive to reducing the "acid spots" on the surface of the silicon material. In addition, the sewage generated during the water washing process is treated and recycled, so that the water washing step does not generate wastewater, and the process is green and environmentally friendly.

[0076] In some optional embodiments, the acid washing treatment further includes an alkali washing treatment, and the alkali solution used in the alkali washing treatment is a NaOH solution with a mass concentration of 5%-15%;

[0077] Preferably, the liquid-to-solid ratio of the alkali washing treatment is 100ml-200ml:1kg;

[0078] Preferably, the alkali washing treatment is carried out at a temperature of 65-80°C and for a time of 30-40 minutes.

[0079] Alkaline washing with alkali solution can neutralize the residual strong organic acid on the surface of silicon material. At the same time, alkali solution also has a certain corrosiveness, which can accelerate the dissolution of the oxide film on the surface of silicon material, and then remove the stains, oxides and other impurities on the surface. It can be seen that the use of alkali solution for alkali washing also has a polishing effect, which can better remove metals and oxygen in silicon material.

[0080] In some optional embodiments, the drying treatment comprises: vacuum drying the washed silicon material obtained by the water washing treatment at a temperature of 100-150° C. and a vacuum degree of ≤-0.95 kPa.

[0081] The washed silicon material is dried after the water washing treatment, so as to quickly remove the moisture in the silicon material.

[0082] In some optional embodiments, the process further includes: crushing and bagging the clean silicon material to obtain feed silicon to be used for crystal pulling.

[0083] The clean silicon material is crushed and bagged to obtain feed silicon, which can be directly used for subsequent crystal pulling to produce single crystal silicon.

[0084] In some optional embodiments, the cleaning method of silicon material comprises the following steps: putting the silicon material to be treated into an ethanol aqueous solution in an ethanol pool, controlling a suitable solid-liquid ratio, ultrasonic cleaning, then turning on the circulating water to lower the temperature of the mixed solution in the ethanol pool, slowly adding trichloromethanesulfonic acid, stirring until the temperature no longer rises, then adding toluenesulfonic acid, stirring until the temperature no longer rises, closing the circulating water, and turning on the ultrasound again to obtain the acid-washed silicon material;

[0085] The acid-washed silicon material is transferred into a pure water pool for soaking and washing, and a suitable liquid-solid ratio is controlled, and the washing is circulated for multiple times to obtain a water-washed silicon material;

[0086] The washed silicon material is dried in vacuum hot air to obtain clean silicon material.

[0087] After drying, the clean silicon material is put into a crusher for crushing, and then bagged to obtain feed silicon, ready for crystal pulling.

[0088] The present invention will be further described below in conjunction with the embodiments.

[0089] Example 1

[0090] A method for cleaning silicon material, see Figure 1 , including the following steps:

[0091] (1) Alcohol washing treatment: The low-carbon alcohol aqueous solution used in the alcohol washing treatment can dissolve and remove some impurities on the surface of the silicon material, especially organic impurities and particulate impurities: at room temperature, 100 kg of silicon material is put into an ethanol pool, the mass concentration of the ethanol aqueous solution in the ethanol pool is controlled to be 50%, the liquid-solid ratio is 100-400 mL: 1 kg, and ultrasonic washing is performed for 10-30 minutes to obtain alcohol-washed silicon material.

[0092] (2) Pickling treatment: The organic strong acid solution used for pickling treatment can remove most of the metal impurities, surface oxide impurities and residual organic impurities on the surface of the silicon material: open the circulating water to cool the ethanol temperature to below 10°C, slowly add 40 kg of trichloromethanesulfonic acid, stir until the temperature no longer rises, then add 60 kg of benzenesulfonic acid, stir until the temperature no longer rises, close the circulating water, and start ultrasonic washing for 30-60 minutes to obtain the pickled silicon material.

[0093] (3) Water washing treatment: the pure water used in the water washing treatment can wash away the residual substances on the surface of the silicon material: the above-mentioned acid-washed silicon material is transferred to a pure water pool for immersion washing (the resistivity of the pure water in the pure water pool is ≥18MΩ·cm), the liquid-to-solid ratio is 100:1kg, and the washing is circulated for 3-5 times to obtain water-washed silicon material. After 10 batches of materials are treated with ethanol-water solution, a small amount (≥500mL) of anhydrous ethanol, trichloromethanesulfonic acid and benzenesulfonic acid is added. After 5-8 washings, the liquid is re-prepared, and the pure water is put into the sewage pool after each washing, and then subjected to secondary treatment by a pure water machine.

[0094] (4) Drying treatment: Drying treatment can quickly remove moisture from the silicon material: the washed silicon material is dried in a vacuum hot air drying process at a drying temperature of 100-150° C. and a vacuum degree of ≤-0.95 kPa to obtain a clean silicon material.

[0095] (5) Crushing and packaging for crystal pulling: After drying, 100-400 kg of clean silicon material is taken and put into a crusher for crushing. After crushing, the silicon material is bagged to obtain the feed material for crystal pulling.

[0096] Example 2

[0097] A method for cleaning silicon material, see Figure 1 , including the following steps:

[0098] (1) Alcohol washing treatment: The low-carbon alcohol aqueous solution used in the alcohol washing treatment can dissolve and remove some impurities on the surface of the silicon material, especially organic impurities and particulate impurities: at room temperature, 100 kg of silicon material is put into an alcohol washing tank, the mass concentration of the ethanol aqueous solution in the alcohol washing tank is controlled to be 50%, the liquid-solid ratio is 100-400 mL: 1 kg, and ultrasonic washing is performed for 10-30 minutes to obtain alcohol-washed silicon material.

[0099] (2) Pickling treatment: The organic strong acid solution used for pickling treatment can remove most of the metal impurities, surface oxide impurities and residual organic impurities on the surface of the silicon material: open the circulating water to cool the ethanol temperature to below 10°C, slowly add 40 kg of trichloromethanesulfonic acid, stir until the temperature no longer rises, then add 60 kg of benzenesulfonic acid, stir until the temperature no longer rises, close the circulating water, and start ultrasonic washing for 30-60 minutes to obtain the pickled silicon material.

[0100] (3) Alkaline washing treatment: the alkali solution used in the alkali washing treatment can neutralize the organic acid remaining on the surface of the silicon material and remove stains, oxides and other impurities on the surface: the above-mentioned acid-washed silicon material is put into an alkali solution pool (the alkali solution in the alkali solution pool is a NaOH solution with a mass concentration of 10%), with a liquid-to-solid ratio of 100 mL: 1 kg, and the temperature is raised to 80° C., heated and bubbled for 30-45 minutes, and then cooled to room temperature to obtain an alkali-washed silicon material.

[0101] (4) Water washing treatment. The pure water used in the water washing treatment can wash away the residual substances on the surface of the silicon material: the above-mentioned alkali-washed silicon material is transferred to a pure water pool for soaking and washing (the resistivity of the pure water in the pure water pool is ≥18MΩ·cm), the liquid-to-solid ratio is 100-400mL:1kg, and the washing is circulated for 3-5 times to obtain water-washed silicon material. After treating 10 batches of materials with ethanol-water solution, a small amount (≥500mL) of anhydrous ethanol, trichloromethanesulfonic acid and benzenesulfonic acid is added. After 5-8 washings, the liquid is re-prepared. After each washing, the pure water enters the sewage pool and is then treated twice by a pure water machine.

[0102] (5) Drying treatment: Drying treatment can quickly remove moisture from the silicon material: the washed silicon material is dried in vacuum hot air at a drying temperature of 100-150° C. and a vacuum degree of ≤-0.95 kPa to obtain clean silicon material.

[0103] (6) Crushing and packaging for crystal pulling: After drying, 100-400 kg of clean silicon material is taken and put into a crusher for crushing. After crushing, the silicon material is bagged to obtain the feed material for crystal pulling.

[0104] The following table shows the test results of detecting impurities on the surface of the obtained raw silicon by glow discharge mass spectrometry (GDMS) after the silicon material was washed 5 times by the method provided in Example 1. The 5 washings and the average of the 5 washing data are respectively referred to as Experimental Group 1, Experimental Group 2, Experimental Group 3, Experimental Group 4, Experimental Group 5 and the average of the experimental group data.

[0105]

[0106] It can be seen from the above table that the solution provided by the embodiment of the present invention can effectively remove impurities such as O, C, Ni, Fe, Al, Na, K, Ca, Zn, and Cu on the surface of the silicon material, and the cleaning effect is stable. The cleaning process does not produce toxic and harmful gases and a large amount of waste water, which reduces the requirements for environmental protection and reduces production costs.

[0107] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for cleaning silicon material, characterized in that: The following steps are involved: Providing silicon materials to be processed; placing the silicon material to be treated in a low-carbon alcohol aqueous solution for alcohol washing to obtain an alcohol-washed silicon material; Then, the alcohol-washed silicon material is subjected to an acid-washing treatment using an organic strong acid solution to obtain an acid-washed silicon material; Then the acid-washed silicon material is subjected to water washing and drying to obtain clean silicon material; Wherein: the organic strong acid in the organic strong acid solution includes any one of trichloromethanesulfonic acid and benzenesulfonic acid.

2. The cleaning method according to claim 1, characterized in that: The organic strong acid solution is obtained by dissolving trichloromethanesulfonic acid or benzenesulfonic acid in a mixed solvent of an organic solvent and pure water, wherein the organic solvent is a low-carbon alcohol.

3. The cleaning method according to claim 2, characterized in that: The low-carbon alcohol includes one or more of ethanol, n-propanol and isopropanol, preferably ethanol.

4. The cleaning method according to claim 1, characterized in that: The alcohol washing treatment is carried out under ultrasonic conditions, and the liquid-to-solid ratio of the alcohol washing treatment is 100-400 mL: 1 kg; Preferably, the mass concentration of the low-carbon alcohol aqueous solution is 40%-60%; Preferably, the temperature of the alcohol washing treatment is room temperature, and the ultrasonic time is 10-30 minutes.

5. The cleaning method according to claim 1, characterized in that: The temperature of the pickling solution is ≤10°C; Preferably, the pickling treatment includes a first pickling treatment and a second pickling treatment, wherein the first pickling treatment is to add the trichloromethanesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises; the second pickling treatment is to add the toluenesulfonic acid to the low-carbon alcohol aqueous solution and stir until the temperature no longer rises to obtain the pickled silicon material, wherein: the mass ratio of the trichloromethanesulfonic acid to the toluenesulfonic acid is 2:3-1:

1.

6. The cleaning method according to claim 5, characterized in that: The liquid-to-solid ratio of the first pickling stage is 40-100 mL: 1 kg, and the time is 2-3 hours; the liquid-to-solid ratio of the second pickling stage is 60-100 mL: 1 kg, and the time is 2-3 hours; Preferably, after the second stage of pickling is completed, ultrasonication is performed for 30-60 minutes.

7. The cleaning method according to claim 1, characterized in that: The resistivity of the pure water used in the water washing treatment is ≥18MΩ·cm; Preferably, the liquid-to-solid ratio of the water washing treatment is 100-400 mL: 1 kg; Preferably, the water washing treatment is carried out at room temperature, and the washing cycle is repeated 3-5 times.

8. The cleaning method according to any one of claims 1 to 7, characterized in that: The acid washing treatment further includes an alkali washing treatment, wherein the alkali solution used in the alkali washing treatment is a NaOH solution with a mass concentration of 5%-15%; Preferably, the liquid-to-solid ratio of the alkali washing treatment is 100-200 ml: 1 kg; Preferably, the alkali washing treatment is carried out at a temperature of 65-80°C and for a time of 30-40 minutes.

9. The cleaning method according to any one of claims 1 to 7, characterized in that: The drying treatment comprises: vacuum drying the washed silicon material obtained by the water washing treatment at a temperature of 100-150° C. and a vacuum degree of ≤-0.95 kPa.

10. The cleaning method according to any one of claims 1 to 7, characterized in that: Also includes: The clean silicon material is crushed and bagged to obtain feed silicon, which is then ready for crystal pulling.

Images