Preparation method of silicon seed crystal for fluidized bed method

Abstract

The invention belongs to the technical field of preparation of crystalline silicon, and particularly relates to a preparation method of a silicon seed crystal for a fluidized bed method. The preparation method of the silicon seed crystal for the fluidized bed method comprises the following steps that polycrystalline silicon particles obtained after polycrystalline silicon is crushed are soaked in acid liquor, non-oxidizing gas is introduced into the bottom of the acid liquor to enable the polycrystalline silicon particles to be overturned and rubbed, solid-liquid separation, washing and drying are conducted, and the silicon seed crystal is obtained, and the acid liquor comprises hydrofluoric acid. Crushed polycrystalline silicon particles are mostly in irregular shapes with edges and corners, the edges and corners of the polycrystalline silicon particles are large in specific surface area and can be etched into fluffy etching layers more easily by hydrofluoric acid, the fluffy layers fall off under the action of friction after non-oxidizing gas is introduced, the edges and corners of the particles are rapidly cut off under the combined action of etching and friction, and therefore the service life of the particles is prolonged. The preparation method disclosed by the invention is simple and easy to implement and low in cost, new impurities are not introduced, surface oxidation is avoided, special equipment or high temperature is not needed, and the energy consumption is reduced to a great extent.

Description

Technical Field

[0001] The invention relates to the technical field of crystalline silicon preparation, and in particular to a method for preparing silicon seed crystals by a fluidized bed process. Background Art

[0002] Silicon seed crystal is one of the necessary raw materials for preparing polysilicon by silane fluidized bed method. The main principle of silane fluidized bed process is to react silane or trichlorosilane with silicon seed crystal in the environment of hydrogen carrier. In the production process, trichlorosilane (SiHCl3) is firstly produced by cold hydrogenation reaction, and then trichlorosilane is subjected to disproportionation reaction to generate silane gas (SiH4). Then, with hydrogen (H2) as carrier, silane or trichlorosilane is injected into the reactor from the bottom of the fluidized bed furnace and rises to the heating zone (about 500-700℃), while silicon seed crystal is injected from the top of the reactor or placed in the reactor in advance. The gas flow rate injected from the bottom is sufficient to boil the seed crystal, so the suspended seed crystal particles continue to grow epitaxially, and when the silicon particles grow to a sufficient weight, they will settle to the bottom of the reactor, and the by-products of the reaction are discharged from the bottom pipeline of the reactor. Therefore. The morphology of silicon seed crystals has an important influence on the stability of the fluidized bed process: the higher the proportion of irregular granular silicon seed crystals, that is, low-sphericity granular silicon seed crystals in the fluidized bed, the lower the corresponding minimum fluidizing velocity. Too low a minimum fluidizing velocity is not conducive to the stable operation of the fluidized bed, which will lead to increased boiling degree of the fluidized bed, increase bed porosity, and make silicon dust more likely to be generated. However, silicon has a high hardness, and it is not easy to make it into a spherical or quasi-spherical shape.

[0003] At present, the commonly used preparation methods of silicon seed crystals include grinding, crushing, melting, etc. Taking the crushing method as an example, in the process of polycrystalline silicon rod crushing, there is a high probability of introducing foreign impurities and oxidation of the surface of broken particles. It is also easy to produce silicon dust, resulting in material loss; low-purity granular silicon seed crystals are the main factor that reduces the purity of the product granular silicon. The melting method is to heat and melt the polycrystalline silicon, and disperse it into droplets through a dispersion device. The droplets will form a nearly spherical shape under the action of surface tension, and naturally become spherical silicon seed crystal particles after solidification. This method must be heated to above 1400°C, with high energy consumption and high equipment requirements. Summary of the invention

[0004] The invention provides a method for preparing silicon seed crystals by fluidized bed method, which solves the problems that impurities are easily introduced into the crushing method, the surface is easily oxidized, and the melting method has high energy consumption.

[0005] In order to solve the above technical problems, the technical solution of the method for preparing silicon seed crystals by fluidized bed method of the present invention is as follows: A method for preparing silicon seed crystals for fluidized bed process comprises the following steps: immersing polycrystalline silicon particles obtained after polycrystalline silicon is crushed in acid solution, introducing non-oxidizing gas into the bottom of the acid solution to make the polycrystalline silicon particles tumble and rub, and obtaining silicon seed crystals by solid-liquid separation, washing and drying, wherein the acid solution comprises hydrofluoric acid.

[0006] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing silicon seed crystals for a fluidized bed process in a pioneering manner, wherein the polycrystalline silicon particles obtained by crushing are immersed in an acid solution containing hydrofluoric acid, and the polycrystalline silicon particles obtained by crushing are mostly irregular shapes with edges and corners. When immersed in hydrofluoric acid, the edges and corners of the polycrystalline silicon particles have a larger specific surface area, react with hydrofluoric acid faster, and are etched most severely, forming a fluffy etching layer on the surface of the polycrystalline silicon particles. When a non-oxidizing gas is introduced into the acid solution containing hydrofluoric acid, the fluffy layer falls off under the action of friction, exposing a new silicon crystal surface, which continues to be corroded by hydrofluoric acid. Under the combined action of etching and friction, the edges and corners of the particles are quickly cut off to form spherical particles, that is, silicon seed crystals with a higher sphericity are obtained.

[0007] The method for preparing silicon seed crystals provided by the present invention is simple and easy, low in cost, does not contain fine dust, does not introduce new impurities, does not cause surface oxidation, does not require special equipment or high temperature, and greatly reduces the energy consumption when preparing silicon seed crystals; the obtained quasi-spherical silicon seed crystals are used in the fluidized bed method to prepare polycrystalline silicon, the fluidized bed boiling is highly stable, and the production is easy to control. Compared with the grinding method, the silicon seed crystals prepared by the present invention have higher sphericity, purity, and raw material utilization, less friction between particles, and less wear.

[0008] It is understandable that the closer the shape of silicon particles is to spherical, the smaller the specific surface area, the slower the etching, and the more irregular the particle shape is, the larger the specific surface area is, such as tetrahedron, octahedron, and flake, the faster it is etched. These factors are conducive to particles of all shapes tending to be spherical. In addition, for those particularly fine dust materials, they are completely dissolved after etching; after the fluffy layer falls off, it continues to react with hydrofluoric acid to generate fluorosilicic acid, which is also dissolved in the acid solution.

[0009] In order to further improve the sphericity of the silicon seed crystal, preferably, the time for introducing the non-oxidizing gas is 2 to 12 hours.

[0010] In order to further improve the etching efficiency, preferably, the mass fraction of hydrofluoric acid in the acid solution is 0.1-5%. If the mass fraction of hydrofluoric acid is too small, the production efficiency will be reduced. If the mass fraction is too large, more silicon at non-corners will be etched while etching the corners of the particles, resulting in waste of silicon material. More preferably, the mass fraction of hydrofluoric acid in the acid solution is 0.2-2%. Among them, the hydrofluoric acid solution uses electronic grade hydrofluoric acid solution, and the electronic grade hydrofluoric acid solution is used to reduce the introduction of impurities as much as possible.

[0011] In order to further improve the purity of silicon seed crystals and reduce impurities introduced during the crushing process, preferably, the acid solution includes hydrochloric acid, and the mass fraction of hydrochloric acid in the acid solution is 0.5-1.5%. Hydrochloric acid can better dissolve and remove impurity ions such as calcium, magnesium, iron, nickel, and copper introduced during the crushing process.

[0012] In order to further reduce the impurity content, preferably, the mass fractions of hydrofluoric acid and hydrochloric acid in the acid solution are 1-1.2% and 0.5-1.5%, respectively.

[0013] In order to further spheroidize the polysilicon particles more completely and improve the utilization rate of raw materials, preferably, the mass ratio of the polysilicon particles to the acid solution is 1: (0.5~5).

[0014] In order to further improve the etching efficiency, preferably, the diameter of the polysilicon particles is 0.1-1 mm.

[0015] In order to further improve the utilization rate of raw materials, preferably, an alkali metal salt is introduced into the acid solution after the silicon seed crystal is prepared to react and produce a precipitate, and hydrofluoric acid is added after filtering out the precipitate, and then the polysilicon particles are soaked. The alkali metal salt is selected from one of potassium fluoride, potassium carbonate, and sodium carbonate. In the acid solution after the silicon seed crystal is prepared, fluorosilicic acid is contained due to the etching effect, and the addition of an alkali metal salt can precipitate fluorosilicate. DETAILED DESCRIPTION

[0016] The technical concept of the method for preparing silicon seed crystals by fluidized bed method of the present invention is as follows: The existing technology for preparing silicon seed crystals generally adopts the crushing method and the melting method, but the crushing method is easy to introduce impurities and cause surface oxidation, resulting in low purity of silicon seed crystals; the melting method requires heating to a high temperature, resulting in high energy consumption. The present invention innovatively uses acid etching and friction to corrode and fall off the edges and corners of irregular polycrystalline silicon particles, which is conducive to particles of all shapes tending to be spherical, overcoming the problems of easy introduction of impurities and easy surface oxidation in the crushing method, as well as the high energy consumption of the melting method.

[0017] The method for preparing silicon seed crystals for fluidized bed process provided by the present invention comprises the following steps: mechanically crushing polycrystalline silicon to obtain polycrystalline silicon particles with a diameter of 0.1-1 mm, immersing the polycrystalline silicon particles in acid solution, introducing non-oxidizing gas at the bottom of the acid solution for 2-12 hours to cause the polycrystalline silicon particles to tumble and rub, and performing solid-liquid separation, washing, and drying to obtain silicon seed crystals, wherein the acid solution comprises hydrofluoric acid with a mass fraction of 0.1-5%, and the mass ratio of the polycrystalline silicon particles to the acid solution is 1:(0.5-5).

[0018] It is understandable that the acid solution may be a single hydrofluoric acid solution or a mixed acid solution formed by hydrofluoric acid and hydrochloric acid.

[0019] In a specific implementation, the mass ratio of polysilicon particles to acid liquid is 1:(0.5~3).

[0020] In a specific implementation manner, the non-oxidizing gas may be nitrogen, argon, hydrogen or other gases, or other gases that can prevent oxidation of the surface of silicon particles.

[0021] In a specific embodiment, the polycrystalline silicon is a polycrystalline silicon rod or block.

[0022] In a specific embodiment, the washing is carried out with water.

[0023] The present invention is further described in detail below with reference to specific embodiments.

[0024] 1. Specific embodiments of the method for preparing silicon seed crystals by fluidized bed method provided by the present invention Example 1 The preparation method of silicon seed crystal for fluidized bed process of this embodiment is as follows: The polysilicon rods are mechanically crushed to obtain polysilicon particles with a diameter of 0.1~1mm. 100g of the polysilicon particles are transferred to a closed container, and 150g of a hydrofluoric acid solution with a mass fraction of 2% is added to soak the polysilicon particles. At the same time, nitrogen is blown into the bottom of the closed container to make the polysilicon particles tumble and rub up and down. The nitrogen blowing is continued for 2h, the liquid is filtered out, and then washed with ultrapure water and dried to obtain 75g of spherical silicon seed crystals with a diameter of 0.03-1.0mm.

[0025] Example 2 The preparation method of silicon seed crystal for fluidized bed process of this embodiment is as follows: The polysilicon rods are mechanically crushed to obtain polysilicon particles with a diameter of 0.1~1mm. 100g of the polysilicon particles are transferred to a closed container, and 50g of a hydrofluoric acid solution with a mass fraction of 1.5% is added to soak the polysilicon particles. At the same time, argon gas is blown into the bottom of the closed container to make the polysilicon particles tumble and rub up and down. The blowing of argon gas is continued for 6 hours, the liquid is filtered out, and then washed with ultrapure water and dried to obtain 72g of spherical silicon seed crystals with a diameter of 0.03-1.0mm.

[0026] Example 3 The preparation method of silicon seed crystal for fluidized bed process of this embodiment is as follows: The polysilicon rods are mechanically crushed to obtain polysilicon particles with a diameter of 0.1~1mm. 100g of the polysilicon particles are transferred to a closed container, and 300g of a hydrofluoric acid solution with a mass fraction of 0.2% is added to soak the polysilicon particles. At the same time, hydrogen is blown into the bottom of the closed container to make the polysilicon particles tumble and rub up and down. The hydrogen blowing is continued for 12h, the liquid is filtered out, and then washed with ultrapure water and dried to obtain 76g of spherical silicon seed crystals with a diameter of 0.03-1.0mm.

[0027] Example 4 The preparation method of silicon seed crystal for fluidized bed process of this embodiment is as follows: The polysilicon rods are mechanically crushed to obtain polysilicon particles with a diameter of 0.1~1mm. 100g of polysilicon particles are transferred to a closed container, and 200g of mixed acid solution is added to soak the polysilicon particles. The mass fraction of hydrofluoric acid in the mixed acid solution is 1%, and the mass fraction of hydrochloric acid is 0.5%. At the same time, nitrogen gas is blown into the bottom of the closed container to make the polysilicon particles tumble and rub up and down. The blowing of nitrogen gas is continued for 8 hours, the liquid is filtered out, and then washed with ultrapure water and dried to obtain 74g of spherical silicon seed crystals with a diameter of 0.03-1.0mm.

[0028] Example 5 The preparation method of silicon seed crystal for fluidized bed process of this embodiment is as follows: The polysilicon rods are mechanically crushed to obtain polysilicon particles with a diameter of 0.1~1mm. 100g of polysilicon particles are transferred to a closed container, and 200g of mixed acid solution is added to soak the polysilicon particles. The mass fraction of hydrofluoric acid in the mixed acid solution is 1.2%, and the mass fraction of hydrochloric acid is 1.5%. At the same time, nitrogen is blown into the bottom of the closed container to make the polysilicon particles tumble and rub up and down. The blowing of nitrogen is continued for 3h, the liquid is filtered out, and then washed with ultrapure water and dried to obtain 75g of spherical silicon seed crystals with a diameter of 0.03-1.0mm.

[0029] 2. Comparison Comparative Example 1 The preparation method of silicon seed crystal for fluidized bed process of this comparative example is as follows: The polysilicon rods were mechanically crushed to obtain polysilicon particles with a diameter of 0.1-1 mm. 100 g of the polysilicon particles were transferred to a grinder and filled with nitrogen. The rotation speed was 600 r / min and the grinder was ground for 8 h. The fine powder was sieved out with a 500-mesh sieve. The mixture was then washed with ultrapure water and dried to obtain 68 g of spherical silicon seed crystals with a diameter of 0.03-1.0 mm.

[0030] 3. Experimental Examples This experimental example tests and analyzes the sphericity, impurity content, and yield of the silicon seed crystals prepared in the examples and comparative examples. The sphericity is tested with reference to the standard GB / T37406-2019. Unlike the standard, the dispersant deionized water in the standard is replaced with a 0.8% mass fraction of sodium carboxymethyl cellulose solution; the impurity content is tested according to the standard GB / T24582-2023 for the metal impurity content on the surface of the silicon seed crystal, and the purity of the silicon seed crystal is calculated based on this; the yield is calculated by the mass percentage of the obtained quasi-spherical silicon seed crystal product and the polysilicon particle raw material, which represents the raw material utilization rate. The average sphericity, metal ion impurity content, silicon seed crystal purity, and yield obtained by the test are shown in Table 1.

[0031] Table 1 Performance test results of silicon seed crystal Average sphericity (%) Metal ion content (ppb) purity Yield (%) Example 1 88 56 Level 7N 75 Example 2 86 44 Level 7N 72 Example 3 84 57 Level 7N 76 Example 4 86 3 Level 8N 74 Example 5 87 4 Level 8N 75 Comparative Example 1 74 232 Level 6N 68 As can be seen from Table 1, the average sphericity of the silicon seed crystals prepared by the preparation method of the silicon seed crystals provided by the present invention reaches more than 84%; the metal ion content is lower than 60 ppb, and can be as low as 3-4 ppb; the purity of the silicon seed crystals can reach 7N level; and the raw material utilization rate can reach more than 72%.

[0032] The average sphericity of silicon seed crystals obtained by the traditional crushing method (Comparative Example 1) is only 74%, which is much lower than that of the present invention; the metal ion impurity content is more than 4 times that of the present invention; the purity of silicon seed crystals is only 6N level; and the raw material utilization rate can only reach 68%. This shows that the silicon seed crystal preparation method of the present invention, compared with the traditional crushing method, can greatly improve the average sphericity of silicon seed crystals, is more conducive to the stable operation of the fluidized bed, and at the same time improves the purity of silicon seed crystals, reduces the impurity content, and can improve the raw material utilization rate and reduce production costs.

[0033] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing silicon seed crystals by fluidized bed method, characterized in that: The method comprises the following steps: immersing the polycrystalline silicon particles obtained after the polycrystalline silicon is crushed in an acid solution, introducing a non-oxidizing gas into the bottom of the acid solution to make the polycrystalline silicon particles tumble and rub, and performing solid-liquid separation, washing and drying to obtain silicon seed crystals, wherein the acid solution comprises hydrofluoric acid.

2. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, characterized in that: The time for introducing non-oxidizing gas is 2~12h.

3. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, characterized in that: The mass fraction of hydrofluoric acid in the acid solution is 0.1-5%.

4. The method for preparing silicon seed crystals by fluidized bed method according to claim 3, characterized in that: The mass fraction of hydrofluoric acid in the acid solution is 0.2-2%.

5. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, characterized in that: The acid solution includes hydrochloric acid, and the mass fraction of hydrochloric acid in the acid solution is 0.5-1.5%.

6. The method for preparing silicon seed crystals by fluidized bed method according to claim 5, characterized in that: The mass fractions of hydrofluoric acid and hydrochloric acid in the acid solution are 1-1.2% and 0.5-1.5% respectively.

7. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, 3, 4, 5 or 6, characterized in that: The mass ratio of polysilicon particles to acid liquid is 1:(0.5~5).

8. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, characterized in that: The diameter of polysilicon particles is 0.1~1mm.

9. The method for preparing silicon seed crystals by fluidized bed method according to claim 1, characterized in that: After the silicon seed crystal is prepared, an alkali metal salt is introduced into the acid solution to react and produce a precipitate. After filtering out the precipitate, hydrofluoric acid is added and continued to be used to soak the polysilicon particles.