Method for fully driving silicon and efficiently dissolving polycrystalline silicon

Abstract

The invention provides a method for fully and efficiently dissolving polycrystalline silicon, which comprises the following steps: A) crushing, digesting and cleaning, washing and drying polycrystalline silicon to obtain pretreated polycrystalline silicon; carrying out digestion cleaning on the pretreated polycrystalline silicon by using a first digestion solution; b) mixing the pretreated polycrystalline silicon with a second digestion solution, and heating for digestion; c) continuously heating and digesting the solution until the solution is nearly dry, adding hydrofluoric acid to drive silicon, continuously heating the solution until the solution is nearly dry, and adding nitric acid to drive acid; and D) adding nitric acid, continuously heating the solution until the solution is nearly dry, and adding dilute nitric acid for rinsing to complete the dissolution of the polycrystalline silicon. The method disclosed by the invention is simple to operate, high in dissolving efficiency and suitable for large-scale industrial production; according to the invention, complete dissolution of polycrystalline silicon can be realized, and the accuracy of a test result is ensured. According to the method disclosed by the invention, sufficient dissolution and removal of silicon can be ensured, the on-machine requirement of ICP MS (Inductively Coupled Plasma Mass Spectrometer) is met, and the equipment loss is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material analysis and detection, and particularly relates to a method for efficiently dissolving polysilicon with sufficient silicon removal. Background Art

[0002] As a typical representative of the third-generation wide-bandgap semiconductor materials, silicon carbide has significant advantages in key parameters such as bandgap width, breakdown electric field, thermal conductivity, electron saturation rate, and radiation resistance, meeting the stringent requirements of modern industries for high-power, high-voltage, and high-frequency application scenarios. During the manufacturing process of silicon carbide chips, metal impurities in the substrate can rapidly diffuse in the chips through diffusion or electromigration, directly affecting their performance and lifespan. Among them, polysilicon is the most critical raw material for silicon carbide synthesis. It first synthesizes silicon carbide particles with carbon powder, and then sublimes and decomposes under high temperature and high pressure, and crystallizes on the surface of the seed crystal to grow into a silicon carbide ingot. During the process, metal impurities in polysilicon will also be directly doped into the silicon carbide crystal along with the main components of carbon and silicon, causing great losses to the yield of subsequent device chips. Therefore, it is very important to ensure the accuracy and timeliness of monitoring the metal content of raw material polysilicon particles during the industrial production of silicon carbide.

[0003] Currently, for the determination of various metal impurity elements in polysilicon particles, the acid dissolution method is usually used for treatment, and then ICP-MS is used for analyzing the metal impurity content. However, this method has the following problems: ① The dissolution time is long. When dissolving 1 g of polysilicon sample with a 1:3 ratio of hydrofluoric acid to nitric acid, it takes up to 3.75 h, which is not applicable in the high-paced industrial production. The efficiency is low and it cannot meet the requirements of online monitoring of product quality by upstream material preparation parties and the timeliness requirements of incoming material inspection by downstream users, and the labor cost is too high; ② The dissolution is incomplete. Even after repeated digestion, there are still residues, resulting in a deviation between the test result and the true value; ③ Most of the silicon in the dissolved solution using the above method will volatilize, but there is still up to 2000 ppm of silicon residue in the solution, that is, the silicon removal is not sufficient, which is much higher than the requirement of the silicon content in the ICP-MS upper machine solution (usually it is recommended that the silicon content < 10 ppm). This will cause silicon to remain on the instrument cone, and even after rinsing, it cannot be removed. In the long run, it will shorten its service life. More importantly, it will affect the accuracy of the test results of samples with low-concentration silicon element detection requirements; ④ The initial reaction is intense, immediately generating a large amount of harmful gases such as nitrogen oxides (NOx), posing a certain threat to the health of on-site operators.

[0004] Therefore, developing a method that can efficiently and completely dissolve polysilicon with sufficient silicon removal, thereby improving the detection efficiency, reducing the labor cost, ensuring the accuracy of the test results, reducing equipment loss, and reducing safety risks, and better meeting the requirements of fast-paced industrialization, has important industrial application value. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for dissolving polysilicon with sufficient silicon removal and high efficiency. The method in the present invention has high dissolution efficiency for polysilicon, complete dissolution, sufficient silicon removal and good safety.

[0006] The present invention provides a method for dissolving polysilicon with sufficient silicon removal and high efficiency, comprising the following steps:

[0007] A) Crushing, digesting and cleaning, washing with water and drying polysilicon to obtain pretreated polysilicon;

[0008] Using a first digestion solution to digest and clean the pretreated polysilicon, the first digestion solution comprising nitric acid and hydrofluoric acid with a volume ratio of (2.5 - 3.5):1;

[0009] B) Mixing the pretreated polysilicon with a second digestion solution and heating for digestion;

[0010] The second digestion solution comprises nitric acid and hydrofluoric acid with a volume ratio of 1:(14 - 16);

[0011] The volume concentration of nitric acid in steps A) and B) is 70 - 75%, and the volume concentration of hydrofluoric acid is 45 - 50%;

[0012] C) After completing the digestion in step B), continue to heat the digestion solution until it is nearly dry, add hydrofluoric acid for silicon removal, continue to heat the solution until it is nearly dry, and add nitric acid for acid removal;

[0013] D) After adding nitric acid, continue to heat the solution until it is nearly dry, add dilute nitric acid for rinsing to complete the dissolution of polysilicon.

[0014] Preferably, in step A), the particle size of the crushed polysilicon is 1 - 3 mm.

[0015] Preferably, in step A), the temperature of the digestion and cleaning is 20 - 25 °C, and the time of the digestion and cleaning in step A) is 5 - 8 min.

[0016] Preferably, the temperature of the drying in step A) is 140 - 160 °C.

[0017] Preferably, the mass ratio of the pretreated polysilicon to the volume of the second digestion solution is (0.8 - 1.2) g:(30 - 35) mL.

[0018] Preferably, in step B), the pretreated polysilicon is wetted with water, mixed with the second digestion solution, reacted in a covered container for 3 - 10 min, and then heated for digestion.

[0019] Preferably, the digestion temperature in step B) is 170 - 190°C, and the digestion time in step B) is 20 - 25 min.

[0020] Preferably, the volume concentration of hydrofluoric acid added in step C) is 45 - 50%, and the ratio of the volume of hydrofluoric acid to the mass of pretreated polysilicon is (14 - 16) mL : (0.8 - 1.2) g.

[0021] Preferably, the volume concentration of nitric acid added in step C) is 70 - 75%, and the ratio of the volume of nitric acid to the mass of pretreated polysilicon is (14 - 16) mL : (0.8 - 1.2) g.

[0022] Preferably, in steps C) and D), the solution is heated to near dryness at a temperature of 170 - 190°C.

[0023] The present invention provides a method for dissolving polysilicon with sufficient and efficient silicon removal, comprising the following steps: A) crushing, digestion cleaning, water washing and drying polysilicon to obtain pretreated polysilicon; using a first digestion solution to carry out digestion cleaning on the pretreated polysilicon, the first digestion solution comprising nitric acid and hydrofluoric acid with a volume ratio of (2.5 - 3.5) : 1; B) mixing the pretreated polysilicon with a second digestion solution and heating for digestion; the second digestion solution comprising nitric acid and hydrofluoric acid with a volume ratio of 1 : (14 - 16); the concentrations of nitric acid in steps A) and B) are 70 - 75%, and the concentration of hydrofluoric acid is 45 - 50%; C) after completing the digestion in step B), continue to heat the digestion solution to near dryness, add hydrofluoric acid for silicon removal, continue to heat the solution to near dryness, and add nitric acid for acid removal; D) continue to heat the solution to near dryness after adding nitric acid, add dilute nitric acid for rinsing to complete the dissolution of polysilicon.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) High efficiency: The method of the present invention is simple to operate and has a high dissolution efficiency, being suitable for large-scale industrial production.

[0026] (2) Complete dissolution: By optimizing the ratio of the digestion solution and the digestion conditions, the present invention can achieve complete dissolution of polysilicon, ensuring the accuracy of the test results.

[0027] (3) Sufficient silicon removal: By adding an excessive amount of hydrofluoric acid to dissolve the silicon matrix for silicon removal, and then adding an appropriate amount of nitric acid for acid removal, it further ensures the sufficient dissolution and silicon removal of silicon, meets the requirements for ICP MS analysis, and reduces equipment wear.

[0028] (4) Safety: The surface of the sample is wetted with ultrapure water, which slows down the violent reaction between the polysilicon sample and the digestion solution, preventing acid splashing and immediate overflow of nitrogen oxides, ensuring the personal safety of the operator and meeting the requirements of safe production. Detailed implementation method

[0029] The present invention provides a method for dissolving polysilicon with sufficient and efficient silicon removal, comprising the following steps:

[0030] A) Crush, digest and clean, wash with water and dry the polysilicon to obtain pretreated polysilicon;

[0031] Use a first digestion solution to digest and clean the pretreated polysilicon, and the first digestion solution comprises nitric acid and hydrofluoric acid with a volume ratio of (2.5 - 3.5):1;

[0032] B) Mix the pretreated polysilicon with a second digestion solution and heat for digestion;

[0033] The second digestion solution comprises nitric acid and hydrofluoric acid with a volume ratio of 1:(14 - 16);

[0034] The volume concentration of nitric acid in step A) and step B) is 70 - 75%, and the volume concentration of hydrofluoric acid is 45 - 50%;

[0035] C) After completing the digestion in step B), continue to heat the digestion solution until it is nearly dry, add hydrofluoric acid for silicon removal, continue to heat the solution until it is nearly dry, and add nitric acid for acid removal;

[0036] D) After adding nitric acid, continue to heat the solution until it is nearly dry, add dilute nitric acid for rinsing to complete the dissolution of polysilicon.

[0037] In the present invention, the polysilicon is a raw material for preparing silicon carbide crystals. Preferably, the polysilicon is first crushed to obtain polysilicon particles with a particle size of 1 - 3 mm, then the obtained polysilicon particles are wetted with ultrapure water and mixed with the first digestion solution for digestion and cleaning. After stripping all the surface layers of the polysilicon, it is washed with ultrapure water, and then the washed polysilicon particles are dried to constant weight to obtain pretreated polysilicon.

[0038] In the present invention, the first digestion solution comprises nitric acid and hydrofluoric acid, and the volume ratio of nitric acid to hydrofluoric acid is preferably (2.5 - 3.5):1, more preferably 3:1, such as 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, preferably a range value with any of the above values as the upper or lower limit; the volume concentration of nitric acid is preferably 70 - 75%, more preferably 71 - 74%, and the volume concentration of hydrofluoric acid is preferably 45 - 50%, more preferably 46 - 49%.

[0039] In the present invention, the temperature of the digestion and cleaning is preferably 20 - 25°C, more preferably 22 ± 2°C, and the time of the digestion and cleaning is preferably 5 - 8 min.

[0040] In the present invention, the drying is preferably drying by baking, and the temperature of the drying is preferably 140 - 160°C, more preferably 145 - 155°C, and most preferably 150 - 155°C.

[0041] After obtaining the pretreated polysilicon, in the present invention, the pretreated polysilicon is placed in a clean covered container such as a covered PFA crucible, wetted with ultrapure water, then a second digestion solution is added, and after covering and reacting for 5 - 6 min, heating is carried out for digestion to completely dissolve the pretreated polysilicon.

[0042] In the present invention, the second digestion solution comprises nitric acid and hydrofluoric acid, and the volume ratio of nitric acid to hydrofluoric acid is preferably 1:(14 - 16), more preferably 1:15; the volume concentration of nitric acid is preferably 70 - 75%, more preferably 71 - 74%, and the volume concentration of hydrofluoric acid is preferably 45 - 50%, more preferably 46 - 49%. The mass ratio of the pretreated polysilicon to the volume of the second digestion solution is preferably (0.8 - 1.2) g:(30 - 35) mL, more preferably (0.9 - 1.2) g:32 mL, such as 0.9 g:32 mL, 0.95 g:32 mL, 0.9774 g:32 mL, 1.0 g:32 mL, 1.0490 g:32 mL, 1.1 g:32 mL, 1.15 g:32 mL, 1.1971 g:32 mL, 1.2 g:32 mL, preferably a range value with any of the above values as the upper or lower limit.

[0043] The present application optimizes the oxidation - complexation kinetics and thermodynamics to achieve an optimal balance among the digestion rate, acid utilization rate and safety of the second digestion solution, realizing efficient and thorough silicon digestion. The second digestion solution in the present invention not only can shorten the reaction time with the polysilicon sample, but also has the following functions:

[0044] ① Synergistic effect of oxidation and complexation: For polysilicon samples, HF in the second digestion solution is in excess, while HNO3 is in relatively small amount. The excess HF (1:15) ensures that the sample is completely complexed and dissolved, and a small amount of HNO3 (1 part) is sufficient to provide the acidic environment required for oxidation.

[0045] ② Reaction rate and complete digestion: Since HF will directly react with silicon to generate H2SiF6 and hydrogen gas (H2): Si + 6HF → H2SiF6 + 2H2↑, but this reaction is relatively slow and requires HNO3 to accelerate the oxidation step. The ratio of 1:15 ensures that HF is always in excess, avoiding stagnation during the reaction.

[0046] ③ Reduction of nitrogen oxide generation: Excess HF can inhibit the excessive decomposition of HNO3 (producing toxic NO2), and at the same time reduce the solution viscosity and promote the uniformity of the reaction.

[0047] ④ Avoidance of silicon residue: Too low a ratio (such as 1:5) may lead to incomplete dissolution of SiO2, forming insoluble substances that wrap silicon particles; too high a ratio (such as 1:20) wastes HF and increases corrosion. The ratio of 1:15 ensures that HF is always in excess, making the digestion process continuously efficient.

[0048] ⑤ After the sample is completely digested, add the same volume of hydrofluoric acid. For polysilicon samples, adding excess hydrofluoric acid consumes silicon ions, which is essential for subsequent complete removal of silicon.

[0049] In the present invention, the temperature of the digestion is preferably 170 - 190 °C, more preferably 175 - 185 °C, such as 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, and is preferably a range value with any of the above values as the upper or lower limit; the time of the digestion is preferably 20 - 25 min. The present invention preferably adds the second digestion solution in multiple portions.

[0050] After the digestion is completed, the present invention removes the container lid, continues heating to evaporate the solution to near dryness, and then adds hydrofluoric acid, maintaining the heating temperature to further promote the complete dissolution of silicon and the removal of silicon.

[0051] In the present invention, the volume concentration of the hydrofluoric acid is preferably 45-50%, more preferably 46-49%. The ratio of the volume of the hydrofluoric acid to the mass of the pretreated polysilicon is (14-16) mL: (0.8-1.2) g, more preferably 15 mL: (0.8-1.2) g, such as 15 mL: 0.8 g, 15 mL: 0.85 g, 15 mL: 0.9 g, 15 mL: 0.95 g, 15 mL: 0.9774 g, 15 mL: 1.0 g, 15 mL: 1.0490 g, 15 mL: 1.05 g, 15 mL: 1.1 g, 15 mL: 1.15 g, 15 mL: 1.1971 g, 15 mL: 1.2 g, and is preferably a range value with any of the above values as the upper or lower limit.

[0052] After the solution to which hydrofluoric acid is to be added is evaporated to near dryness, nitric acid is added, and the heating temperature is maintained for acid removal. At this time, using a low-boiling acid to remove a high-boiling acid will be more thorough.

[0053] In the present invention, the volume concentration of the nitric acid is preferably 70-75%, more preferably 71-74%. The ratio of the volume of the nitric acid to the mass of the pretreated polysilicon is preferably (14-16) mL: (0.8-1.2) g, more preferably 15 mL: (0.8-1.2) g, such as 15 mL: 0.8 g, 15 mL: 0.85 g, 15 mL: 0.9 g, 15 mL: 0.95 g, 15 mL: 0.9774 g, 15 mL: 1.0 g, 15 mL: 1.0490 g, 15 mL: 1.05 g, 15 mL: 1.1 g, 15 mL: 1.15 g, 15 mL: 1.1971 g, 15 mL: 1.2 g, and is preferably a range value with any of the above values as the upper or lower limit.

[0054] After the solution to which nitric acid is added is evaporated to near dryness, it is rinsed 3-5 times with dilute nitric acid and can be used for subsequent detection and analysis of the content of metal impurity elements in polysilicon.

[0055] In the present invention, the mass concentration of the dilute nitric acid is preferably 1-10%, more preferably 3-8%, and most preferably 5-6%.

[0056] The method for dissolving polysilicon in the present invention is efficient and the silicon removal is sufficient, which can be used to improve the accuracy of the analysis of the content of metal impurity elements in polysilicon and is applicable to large-scale industrial production.

[0057] In order to further illustrate the present invention, the following takes examples to describe in detail a method for dissolving polysilicon with sufficient silicon removal and high efficiency provided by the present invention, but it should not be construed as a limitation to the protection scope of the present invention.

[0058] Example 1

[0059] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1, strip all the surface layers, and then wash it with ultrapure water; place the washed sample in a crucible and dry it to constant weight at 150 °C on a hot plate.

[0060] (2) Prepare the digestion solution: Mix 1 mL of 71% nitric acid and 15 mL of 49% hydrofluoric acid.

[0061] (3) Weigh 0.9774 g of the pretreated polysilicon particles into a clean PFA crucible, moisten it with ultrapure water, then pour all the digestion solution prepared in (2) into the crucible containing the sample, cover it and react for 5 minutes, then place it on a hot plate and heat at 180 °C. After 20 minutes, add 1 portion (16 mL) of the digestion solution prepared in (2) with the same dosage. After 22 minutes, the polysilicon particles are completely dissolved.

[0062] (4) After dissolution is complete, remove the cover and continue heating at 180 °C.

[0063] (5) Evaporate to nearly dry and then add 15 mL of 49% hydrofluoric acid to drive off silicon.

[0064] (6) Evaporate to nearly dry and then add 15 mL of 71% nitric acid to drive off acid.

[0065] (7) Evaporate to nearly dry and then rinse 3 times with 100 mL of 5% nitric acid.

[0066] (8) The Si content in the solution for machine testing is 12.4 ppb.

[0067] Example 2

[0068] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1, strip all the surface layers, and then wash it with ultrapure water; place the washed sample in a crucible and dry it to constant weight at 150 °C on a hot plate.

[0069] (2) Prepare the digestion solution: Mix 1 mL of 71% nitric acid and 15 mL of 49% hydrofluoric acid.

[0070] (3) Weigh 1.1971 g of the pretreated polysilicon particles into a clean PFA crucible, moisten it with ultrapure water, then pour all the digestion solution prepared in (2) into the crucible containing the sample, cover it and react for 5 minutes, then place it on a hot plate and heat at 180 °C. After 20 minutes, add 1 portion (16 mL) of the digestion solution prepared in (2) with the same dosage. After 24 minutes, the polysilicon particles are completely dissolved.

[0071] (4) After dissolution is complete, remove the cover and continue heating at 180 °C.

[0072] (5) After evaporating to near dryness, add 15 mL of 49% hydrofluoric acid to remove silicon.

[0073] (6) After evaporating to near dryness, add 15 mL of 71% nitric acid to remove acid.

[0074] (7) After evaporating to near dryness, rinse three times with 100 mL of 5% nitric acid.

[0075] (8) The Si content in the solution for machine testing is < 3 ppb.

[0076] Example 3

[0077] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1, wash it with ultrapure water again after stripping all the surface layers; place the washed sample in a crucible and dry it to constant weight at 150 °C on a hot plate.

[0078] (2) Prepare a digestion solution: Mix 1 mL of 71% nitric acid and 15 mL of 49% hydrofluoric acid.

[0079] (3) Weigh 1.0490 g of the pretreated polysilicon particles into a clean PFA crucible, moisten it with ultrapure water, then pour all the digestion solution prepared in (2) into the crucible containing the sample, cover it and react for 5 minutes, then heat it at 180 °C on a hot plate. After 20 minutes, add 1 portion (16 mL) of the digestion solution prepared in (2) with the same dosage. After 23 minutes, the polysilicon particles are completely dissolved.

[0080] (4) After dissolution is complete, remove the cover and continue heating at 180 °C.

[0081] (5) After evaporating to near dryness, add 15 mL of 49% hydrofluoric acid to remove silicon.

[0082] (6) After evaporating to near dryness, add 15 mL of 71% nitric acid to remove acid.

[0083] (6) After evaporating to near dryness, add 5 mL of 71% nitric acid again to remove acid.

[0084] (7) After evaporating to near dryness, rinse three times with 100 mL of 5% nitric acid.

[0085] (8) The Si content in the solution for machine testing is 17.2 ppb.

[0086] Comparative Example 1

[0087] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1. After stripping all the surface layers, wash it again with ultrapure water; place the washed sample in a crucible and dry it to a constant weight at 150 °C on a hot plate.

[0088] (2) Prepare the digestion solution: Mix 71% nitric acid and 49% hydrofluoric acid in a volume ratio of 3:1.

[0089] (3) Weigh 1.0020 g of the pretreated polysilicon particles into a clean PFA crucible, moisten it with ultrapure water, then pour 8 mL of the digestion solution prepared in (2) into the crucible containing the sample. After covering and reacting for 5 minutes, place it on a hot plate and heat at 180 °C. Add 6 mL of nitric acid every 20 minutes. After 210 minutes, the polysilicon particles are dissolved.

[0090] (4) After dissolution is completed, remove the cover and continue heating at 180 °C.

[0091] (5) Evaporate until nearly dry, then rinse 3 times with 100 mL of 5% nitric acid.

[0092] (6) Test the Si content in the solution on the machine, and the Si content > 2000 ppm.

[0093] Comparative Example 2

[0094] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1. After stripping all the surface layers, wash it again with ultrapure water; place the washed sample in a crucible and dry it to a constant weight at 150 °C on a hot plate.

[0095] (2) Prepare the digestion solution: Mix 71% nitric acid and 49% hydrofluoric acid in a volume ratio of 3:1.

[0096] (3) Weigh 1.0365 g of the pretreated polysilicon particles into a clean PFA crucible, moisten it with ultrapure water, then pour 8 mL of the digestion solution prepared in (2) into the crucible containing the sample. After covering and reacting for 5 minutes, place it on a hot plate and heat at 180 °C. Add 6 mL of nitric acid every 20 minutes. After 225 minutes, the polysilicon particles are dissolved.

[0097] (4) After dissolution is completed, remove the cover and continue heating at 180 °C.

[0098] (5) Evaporate until nearly dry, then rinse 3 times with 100 mL of 5% nitric acid.

[0099] (6) Test the Si content in the solution on the machine, and the Si content > 2000 ppm.

[0100] Comparative Example 3

[0101] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1. After stripping all the surface layers, wash it again with ultrapure water; place the washed sample in a crucible and dry it to a constant weight at 150 °C on a hot plate.

[0102] (2) Prepare the digestion solution: Mix 71% nitric acid and 49% hydrofluoric acid in a volume ratio of 1:2.

[0103] (3) Weigh 0.9774 g of the pretreated polysilicon particles into a clean PFA crucible. After moistening it with ultrapure water, pour 9 mL of the digestion solution prepared in (2) into the crucible containing the sample. Cover it and react for 5 minutes, then place it on a hot plate and heat at 180 °C. Add 2 portions (each portion is 3 mL) of the digestion solution every 20 minutes. After 50 minutes, the polysilicon particles are dissolved.

[0104] (4) After dissolution is completed, remove the cover and continue heating at 180 °C.

[0105] (5) Evaporate to nearly dry and then rinse 3 times with 100 mL of 5% nitric acid.

[0106] (6) The Si content in the solution for machine testing is 1742 ppm.

[0107] Comparative Example 4

[0108] (1) Take a polysilicon block and crush it to a particle size of 1 - 3 mm. Weigh 5 g of the crushed sample, moisten it with ultrapure water, digest and clean it in a solution with a volume ratio of nitric acid to hydrofluoric acid of 3:1. After stripping all the surface layers, wash it again with ultrapure water; place the washed sample in a crucible and dry it to a constant weight at 150 °C on a hot plate.

[0109] (2) Prepare the digestion solution: Mix 71% nitric acid and 49% hydrofluoric acid in a volume ratio of 1:2.

[0110] (3) Weigh 1.1971 g of the pretreated polysilicon particles into a clean PFA crucible. After moistening it with ultrapure water, pour 9 mL of the digestion solution prepared in (2) into the crucible containing the sample. Cover it and react for 5 minutes, then place it on a hot plate and heat at 180 °C. Add 2 portions (each portion is 3 mL) of the digestion solution every 20 minutes. After 55 minutes, the polysilicon particles are dissolved.

[0111] (4) After dissolution is completed, remove the cover and continue heating at 180 °C.

[0112] (5) Evaporate to nearly dry and then rinse 3 times with 100 mL of 5% nitric acid.

[0113] (6) The Si content in the solution for machine testing > 2000 ppm.

[0114] The dissolution conditions of polysilicon in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1:

[0115] Table 1 Dissolution conditions of polysilicon in Examples 1 to 3 and Comparative Examples 1 to 4

[0116]

[0117] As can be seen from Table 1, the volume ratio of nitric acid to hydrofluoric acid in the digestion solution formula described in the present invention is 1:15. That is, compared with Comparative Examples 1 to 4, the dissolution time required in Examples 1 to 3 is shorter, and the residual amount of Si in the solution is reduced from ppm to ppb. Comparing Example 1 with Comparative Example 2, the time cost can be saved by 203 minutes for a single sample, and the efficiency is increased by 90.2%; the residual amount of Si in the solution is reduced from >2000 ppm to 12.4 ppb, and the silicon removal rate can be increased by 99.999%.

[0118] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for dissolving polysilicon sufficiently and efficiently to remove silicon, comprising the following steps: A) Crush, digest and clean, wash with water and dry the polysilicon to obtain pretreated polysilicon; Use a first digestion solution to digest and clean the pretreated polysilicon, and the first digestion solution comprises nitric acid and hydrofluoric acid with a volume ratio of (2.5 - 3.5):1; B) Mix the pretreated polysilicon with a second digestion solution and heat for digestion; The second digestion solution comprises nitric acid and hydrofluoric acid with a volume ratio of 1:(14 - 16); In steps A) and B), the volume concentration of nitric acid is 70 - 75%, and the volume concentration of hydrofluoric acid is 45 - 50%; C) After completing the digestion in step B), continue to heat the digestion solution until it is nearly dry, add hydrofluoric acid to remove silicon, continue to heat the solution until it is nearly dry, and add nitric acid to remove acid; D) After adding nitric acid, continue to heat the solution until it is nearly dry, add dilute nitric acid for rinsing to complete the dissolution of polysilicon.

2. The method according to claim 1, characterized in that, In step A), the particle size of the crushed polysilicon is 1 - 3 mm.

3. The method according to claim 1, wherein In step A), the temperature for digestion and cleaning is 20 - 25°C, and the time for digestion and cleaning in step A) is 5 - 8 min.

4. The method according to claim 1, characterized in that, In step A), the drying temperature is 140 - 160°C.

5. The method according to claim 1, characterized in that, The mass ratio of the pretreated polysilicon to the volume of the second digestion solution is (0.8 - 1.2) g:(30 - 35) mL.

6. The method according to claim 1, wherein In step B), wet the pretreated polysilicon with water, mix it with the second digestion solution, react in a covered container for 3 - 10 min, and then carry out heating digestion.

7. The method according to claim 1, characterized in that In step B), the digestion temperature is 170 - 190°C, and the digestion time in step B) is 20 - 25 min.

8. The method according to claim 1, wherein In step C), the volume concentration of the added hydrofluoric acid is 45 - 50%, and the volume ratio of the hydrofluoric acid to the mass of the pretreated polysilicon is (14 - 16) mL:(0.8 - 1.2) g.

9. The method according to claim 1, characterized in that, In step C), the volume concentration of the added nitric acid is 70 - 75%, and the volume ratio of the nitric acid to the mass of the pretreated polysilicon is (14 - 16) mL:(0.8 - 1.2) g.

10. The preparation method according to claim 1, wherein, In steps C) and D), the solution is heated to nearly dry at a temperature of 170 - 190°C.

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