Dust removal method for granular polycrystalline silicon

Abstract

The invention relates to a dedusting method of granular polycrystalline silicon, the granular polycrystalline silicon is treated by adopting a microwave radiation heating mode, in the microwave heating process, due to the difference of micro-nano silicon powder and large-particle-size particles in microwave absorption, micro silicon powder is more easily melted and adhered to the surfaces of the large particles, so that the scattering of the micro silicon powder is effectively reduced, and the dedusting effect of the granular polycrystalline silicon is improved. According to the method, the granular polycrystalline silicon is heated in a vacuum or inert atmosphere through a tubular microwave oven, the temperature can be adjusted to 600-1200 DEG C, and the treatment effect is optimized by controlling the power and the heating rate. Compared with a traditional heat conduction heating mode, the microwave heating technology provided by the invention not only can quickly reduce micro silicon powder in the granular polycrystalline silicon and obviously reduce the turbidity value to be below 5NTU, but also has the advantages of low energy consumption and high efficiency, and the treatment cost is greatly reduced. According to the dust removal method for the granular polycrystalline silicon, an efficient and environment-friendly dust removal solution is provided for the polycrystalline silicon industry.

Description

Technical Field

[0001] The present invention relates to the technical field of polysilicon dust removal, and in particular to a method for removing dust from granular polysilicon. Background Art

[0002] High-purity polysilicon is an important raw material in the modern photovoltaic and semiconductor industries, and is widely used in the manufacture of solar cells and integrated circuits. However, in the production process of polysilicon, especially when using the fluidized bed method (CVD method) to produce granular polysilicon, a large amount of micro-silicon powder is often produced. These micro-silicon powders adhere to the surface of granular silicon to form a large number of micro-nano particles. Due to the large specific surface area of ​​these micro-silicon powders, they are very easy to fly under high temperature conditions and enter the subsequent production links, bringing a series of technical problems.

[0003] At present, the methods for producing granular polysilicon mainly include the modified Siemens method and the fluidized bed method. The fluidized bed method has become a widely used method in the industry because of its simple equipment structure, low investment and high production efficiency. However, the fluidized bed method also has some disadvantages that cannot be ignored, especially in the quality control of granular polysilicon. During the production process of the fluidized bed method, although the granular silicon generated is relatively large, it still inevitably carries a certain proportion of microsilicon powder by-products, which usually accounts for 5% to 15% of the total product. Microsilicon powder not only affects the purity of granular silicon, but also easily causes dust problems in the silicon melt. These microsilicon powders not only increase the loss of silicon raw materials in the production process, but also lead to high turbidity of granular silicon in the vertical single crystal, which significantly increases the broken edge rate of the single crystal rod, affecting the downstream use effect.

[0004] Turbidity value is an important indicator to measure the content of microsilicon powder in granular silicon, which is directly related to the use effect of granular silicon. The turbidity value of granular silicon is usually expressed in NTU (turbidity unit). The higher the turbidity value, the more microsilicon powder is suspended in the granular silicon. According to the existing technology, the turbidity value of granular silicon produced by fluidized bed method is about 120NTU, which is much higher than some application standards with higher requirements, resulting in a higher edge breaking rate in the single crystal production process. Therefore, reducing the amount of microsilicon powder in granular polysilicon and reducing the turbidity value have become key technical problems to improve the quality of granular silicon products and meet higher requirements.

[0005] At present, there are relatively limited technical solutions for the removal or reduction of microsilicon powder in granular polysilicon. Although traditional physical methods such as electrostatic dust removal and screening can reduce the microsilicon powder in granular silicon to a certain extent, due to their limited treatment effect and the inability to solve the problem of microsilicon powder adhering to and adsorbing on the surface of granular silicon, they have not been able to effectively reduce the turbidity value of granular silicon. In addition, the existing heat treatment methods mainly rely on traditional heating technologies, such as heat conduction heating in a heating furnace. Although this heating method can treat granular polysilicon to a certain extent, it has low efficiency and high energy consumption, and it is easy to cause oxidation of the surface of granular silicon during the treatment process, further affecting the quality of granular silicon; existing dust removal methods, such as physical screening and electrostatic dust removal, can reduce some silicon powder, but due to the small particle size and large specific surface area of ​​microsilicon powder, conventional methods cannot effectively remove microsilicon powder, resulting in granular polysilicon still having high turbidity values ​​and dust problems during use, affecting downstream applications, especially the production quality of single crystal rods.

[0006] Therefore, developing a new type of high-efficiency, low-energy treatment method that can effectively remove microsilicon powder in granular silicon and reduce the turbidity value of granular silicon without damaging the performance of granular silicon has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for dust removal of granular polysilicon to solve the problems of high content of microsilicon powder in granular polysilicon, excessive turbidity value and low dust removal efficiency existing in the conventional methods in the prior art.

[0008] In order to solve the above technical problems, the present invention provides a method for removing dust from granular polycrystalline silicon, comprising the following steps:

[0009] S1: preparing granular polycrystalline silicon and loading it into a reaction vessel, heating the granular polycrystalline silicon by microwave radiation, and maintaining an inert atmosphere or vacuum state in the reactor during the heating process;

[0010] S2: After the granular polysilicon is heated to 600-1200° C., a continuous heat preservation treatment is performed. After the heat preservation is completed, the granular polysilicon is cooled, and the microsilicon powder is removed, thereby reducing the turbidity value of the granular polysilicon.

[0011] Compared with the prior art, the dust removal method of granular polysilicon in the present application has the following advantages: Efficient removal of microsilicon powder: The dust removal method of granular polysilicon in the present invention uses microwave radiation heating to make the microsilicon powder attached to the surface of the granular polysilicon quickly melt during the heating process and adhere to the surface of larger particles to form a whole. Compared with the traditional heat conduction heating method, microwave heating directly acts on the inside of the material through electromagnetic waves, the heating is more uniform, and the removal efficiency of microsilicon powder is significantly improved; reduce turbidity value: the microwave heating method of the present invention can effectively reduce the microsilicon powder in granular polysilicon, and reduce the turbidity value of granular polysilicon to below 5NTU. This technical effect can directly improve the application effect of granular polysilicon in downstream production, especially in the production of single crystal rods, effectively reducing the broken edge rate and dislocation defects; energy saving and high efficiency: compared with traditional heating methods, microwave heating has higher heating efficiency and energy efficiency, can quickly increase the temperature of granular polysilicon and heat it evenly, shorten the processing time, and reduce the overall energy consumption and processing cost; avoid oxidation: during the heating process, the method of the present invention maintains an inert atmosphere or a vacuum state to effectively avoid oxidation of the surface of granular polysilicon, ensuring that its subsequent use performance is not affected. In the prior art, the microsilicon powder content of granular polysilicon is high, and the turbidity value is too large, which affects its application in the production of single crystal rods and leads to a high broken edge rate and dislocation defects. Existing methods cannot effectively remove microsilicon powder, especially micro-nano silicon powder, which leads to dust and silicon raw material loss. The dust removal method of granular polysilicon of the present invention uses microwave heating technology and different absorption characteristics of microwaves to materials to melt the microsilicon powder and adhere to the surface of the particles, thereby achieving effective removal of microsilicon powder, significantly reducing the turbidity value of granular polysilicon, and solving the problems of dust and excessive turbidity in the prior art.

[0012] In a possible implementation, in step S1, the reaction vessel is a crucible, and the device used for microwave radiation heating is a tubular microwave oven.

[0013] Compared with the prior art, by adopting the above-mentioned technical scheme, the efficiency of microwave heating is further improved by using a crucible, and the microsilicon powder in the granular polysilicon can be efficiently melted and adhered to the surface of the particles, reducing the scattering and dusting problems of the microsilicon powder, which significantly reduces the turbidity value of the granular polysilicon and ensures the high purity of the product and good subsequent use performance; by combining a tubular microwave oven and a crucible, the inside of the material can be heated directly by microwave radiation without relying on an external heat source, which not only heats quickly, but also heats the granular polysilicon more evenly, effectively avoiding overheating or uneven heating; compared with the conventional heating method adopted in the prior art, the present invention can effectively reduce the amount of microsilicon powder, improve the quality of granular polysilicon, and significantly improve production efficiency and economic benefits.

[0014] In a possible implementation, in the step S1, the particle size of the granular polysilicon is 1-3 mm.

[0015] Compared with the existing technology, the above technical solution is used to control the particle size of granular polysilicon within 1-3mm, which is an optimized choice. This particle size range ensures that the specific surface area of ​​the particles is moderate, which can not only fully absorb microwave radiation energy, but also maintain good heating uniformity; compared with particles that are too large or too small, particles in this particle size range can achieve the best heating effect during microwave heating.

[0016] During microwave heating, electromagnetic energy is converted into thermal energy due to the polarization of molecules inside the material, and the absorption capacity of microwave heating depends on the dielectric properties and loss factor of the material; generally, particles with smaller particle sizes show better microwave absorption capacity, which may be because smaller particles have a larger specific surface area and can provide more interfaces for absorbing microwave energy, thereby improving the overall absorption efficiency. In other words, particle size has an important influence on the microwave absorption performance of the material. In view of the above reasons, in granular polysilicon products, the particle size of the main particles is about 1-3mm, and the silicon powder adsorbed on the surface of the particles is only micro-nano-level, which leads to a large difference in the absorption capacity of the main particles and micro-nano-level silicon powder to microwaves during microwave heating, so that under the same microwave heating conditions, the heating rate is also different; that is, under the same microwave heating conditions, micro-nano-level silicon powder is easier to reach a molten state than millimeter-level silicon particles. After the micro-nano-level silicon powder is melted, it is easy to firmly adhere to the surface of particles with larger particle sizes and form an integral body with silicon particles with larger particle sizes, thereby effectively reducing the turbidity of silicon particles and reducing the dust problem when granular polysilicon products are used in direct-pull single crystals.

[0017] In a possible implementation, in step S1, the power of the microwave radiation heating is 200-4000W, and the heating rate is 10-200°C / min.

[0018] Compared with the prior art, the above technical solution can be used to uniformly heat granular polysilicon in a relatively short time by adjusting microwave heating within a power range of 200-4000W and controlling the heating rate to 10-200℃ / min. Microwave heating polarizes the molecules inside the material through electromagnetic waves, thereby converting electromagnetic energy into thermal energy. During microwave radiation heating, power and heating rate directly affect the heating rate and uniformity of the material. Microwave treatment allows microsilicon powder to melt rapidly and firmly adhere to the surface of larger particles; this not only reduces the dust of microsilicon powder and the turbidity value of granular polysilicon, but also effectively improves production efficiency and avoids the problem of particle surface oxidation or failure to fully remove microsilicon powder due to uneven temperature in traditional heating methods.

[0019] In a possible implementation, in step S1, during the heating process, the inert atmosphere is one or both of nitrogen and argon, and the gas flow rate is 50-100 mL / min.

[0020] Compared with the prior art, the above technical solution can effectively avoid surface oxidation of granular polysilicon during heating and provide a stable reaction environment, thereby improving the dust removal effect and maintaining the high purity of granular polysilicon. In the conventional heating process, especially in a high temperature environment, the surface of granular polysilicon easily reacts with oxygen in the air, resulting in the formation of oxides, which not only affects the quality of the particles, but may also cause problems in subsequent processing. The use of an inert atmosphere such as nitrogen and argon can help avoid this oxidation phenomenon and ensure that the surface of the granular polysilicon remains pure.

[0021] In a possible implementation, in step S2, the insulation time is 10 to 100 minutes.

[0022] Compared with the prior art, the above technical scheme can optimize the melting and adhesion process of microsilicon powder in granular polycrystalline silicon, ensure that the microsilicon powder is completely combined with larger granular polycrystalline silicon, thereby effectively reducing the turbidity value of granular polycrystalline silicon; in the method of the present invention, the selection of holding time is crucial to the heating process. Too short holding time may cause the microsilicon powder to fail to completely melt and adhere to the surface of the particles, while too long holding time may cause energy waste; therefore, by reasonably setting the holding time to 10 to 100 minutes, it can ensure that the microsilicon powder is completely removed and combined with the particles, while avoiding unnecessary energy waste.

[0023] In a possible implementation, in step S2, the granular polysilicon is cooled by natural cooling along with the furnace.

[0024] Compared with the prior art, the above technical solution can avoid thermal stress and surface cracks caused by sudden temperature drop during the cooling process, and ensure the structural stability of the granular polysilicon during the cooling process; compared with traditional cooling methods, such as rapid cooling or forced cooling, cracks or stress concentration may occur on the surface of the particles, thereby affecting the quality of the particles and subsequent performance; and the present invention further selects the method of natural cooling with the furnace, which can gradually cool down the granular polysilicon over a longer period of time, thereby avoiding the generation of thermal stress and maintaining the integrity and quality of the particles.

[0025] In a possible implementation, in the step S2, after the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 5 NTU, and no surface oxidation occurs.

[0026] Compared with the prior art, the above technical scheme can effectively reduce the microsilicon powder in granular polysilicon, significantly reduce the turbidity value, and avoid the problem of surface oxidation of silicon particles during high-temperature heating; although the dust removal method in the prior art can remove part of the microsilicon powder, due to the failure to effectively control the oxidizing environment during the heating process, oxidation reactions often occur on the surface of the granular polysilicon, which not only affects the quality of the particles, but also leads to a decrease in performance during subsequent use; the method of the present invention can effectively avoid the occurrence of oxidation reactions by adopting an inert atmosphere or a vacuum heating environment, thereby ensuring the purity and performance of the particles, and has the advantages of significantly improving production efficiency and reducing costs, while improving the performance of granular polysilicon in high-precision applications such as single crystal rod production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a comparison diagram of granular silicon before and after treatment, wherein the left figure is a schematic diagram of granular silicon before treatment, and the right figure is a schematic diagram of granular silicon after treatment;

[0028] Figure 2 Surface microscopic morphology of the granular polysilicon in Example 1 of the present invention before and after being treated by the removal method, wherein the left figure is a schematic diagram of the granular silicon before treatment, and the right figure is a schematic diagram of the granular silicon after treatment. DETAILED DESCRIPTION

[0029] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0030] The present invention provides a method for removing dust from granular polycrystalline silicon, comprising the following steps:

[0031] S1: preparing granular polycrystalline silicon and loading it into a reaction vessel, heating the granular polycrystalline silicon by microwave radiation, and maintaining an inert atmosphere or vacuum state in the reactor during the heating process;

[0032] S2: After the granular polysilicon is heated to 600-1200° C., a continuous heat preservation treatment is performed. After the heat preservation is completed, the granular polysilicon is cooled, and the microsilicon powder is removed, thereby reducing the turbidity value of the granular polysilicon.

[0033] As a preferred solution, in step S1, the reaction vessel is a crucible, and the device used for microwave radiation heating is a tubular microwave oven.

[0034] As a preferred solution, in step S1, the particle size of the granular polysilicon is 1-3 mm.

[0035] As a preferred solution, in step S1, the power of the microwave radiation heating is 200-4000W, and the heating rate is 10-200°C / min.

[0036] As a preferred solution, in step S1, during the heating process, the inert atmosphere is one or both of nitrogen and argon, and the gas flow rate is 50-100 mL / min.

[0037] As a preferred solution, in step S2, the insulation time is 10 to 100 minutes.

[0038] As a preferred solution, in step S2, the granular polysilicon is cooled by natural cooling along with the furnace.

[0039] As a preferred solution, in the step S2, after the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 5NTU, and surface oxidation does not occur.

[0040] The following provides an embodiment combined with specific data to describe the technical solution of the above modification of the present invention:

[0041] Embodiment 1:

[0042] Embodiment 1 provides a method for removing dust from granular polycrystalline silicon, comprising the following steps:

[0043] S1: Prepare granular polycrystalline silicon with a particle size of 2 mm and put it into a crucible, and heat the granular polycrystalline silicon by microwave radiation by adding it into a tubular microwave oven. The power of the microwave radiation heating is 2000 W, and the heating rate is 100°C / min. During the heating process, an inert atmosphere is maintained in the reactor, and the inert atmosphere is a mixture of nitrogen and argon, and the gas flow rate is 75 mL / min;

[0044] S2: After the granular polysilicon is heated to 900°C, it is continuously kept warm for 55 minutes. After the end of the heat preservation, the granular polysilicon is naturally cooled along with the furnace, thus completing the removal of the microsilicon powder and reducing the turbidity value of the granular polysilicon. After the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 3NTU, and no surface oxidation occurs.

[0045] Embodiment 2:

[0046] Embodiment 2 provides a method for removing dust from granular polycrystalline silicon, comprising the following steps:

[0047] S1: preparing granular polycrystalline silicon with a particle size of 1 mm and loading it into a crucible, and heating the granular polycrystalline silicon by microwave radiation in a tubular microwave oven, wherein the power of the microwave radiation heating is 200 W, the heating rate is 10° C. / min, and the vacuum state in the reactor is maintained during the heating process;

[0048] S2: After the granular polysilicon is heated to 600°C, it is continuously kept warm for 10 minutes. After the insulation is completed, the granular polysilicon is naturally cooled along with the furnace, thus completing the removal of the microsilicon powder and reducing the turbidity value of the granular polysilicon. After the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 5NTU, and no surface oxidation occurs.

[0049] Embodiment 3:

[0050] Embodiment 3 provides a method for removing dust from granular polycrystalline silicon, comprising the following steps:

[0051] S1: Prepare granular polycrystalline silicon with a particle size of 3 mm and put it into a crucible, and heat the granular polycrystalline silicon by microwave radiation by adding it into a tubular microwave oven. The power of the microwave radiation heating is 4000 W, and the heating rate is 200°C / min. During the heating process, an inert atmosphere or a vacuum state is maintained in the reactor. The inert atmosphere is one or both of nitrogen and argon, and the gas flow rate is 100 mL / min.

[0052] S2: After the granular polysilicon is heated to 1200°C, it is continuously kept warm for 100 minutes. After the heat preservation is completed, the granular polysilicon is naturally cooled along with the furnace, thus completing the removal of the microsilicon powder and reducing the turbidity value of the granular polysilicon. After the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 4NTU, and no surface oxidation occurs.

[0053] like Figure 1 As shown, Figure 1 The comparison diagram of the granular polysilicon in Example 1 of the present invention before and after the dust removal of the present invention can be seen from Figure 1 It can be seen that the surface of the granular polycrystalline silicon treated by a granular polycrystalline silicon dust removal method is not oxidized, and the silicon powder is effectively removed;

[0054] like Figure 2 As shown, Figure 2The surface microscopic morphology of the granular polycrystalline silicon in Example 1 of the present invention before and after the treatment by the removal method is shown in the left picture. The picture on the right is before the treatment and the picture on the left is after the treatment. It can be clearly seen that there are more silicon micropowders in the morphology picture before the treatment, while the microsilicon powders melted on the surface of larger silicon particles after the treatment. This is because the small-particle micro-nano silicon powders have melted on the surface of larger-particle-size particles after the treatment of the present invention, which further proves the technical effect of the present invention.

[0055] The above examples further prove that the present invention provides an efficient method for dust removal of granular polysilicon. The principle is to heat the granular polysilicon with microwave radiation to melt the microsilicon powder and firmly adhere to the surface of larger particles, and to treat it in an inert atmosphere or vacuum environment to avoid oxidation. The method effectively solves the problems of excessively high turbidity value of granular polysilicon, incomplete removal of microsilicon powder, and oxidation of particle surface in the prior art, thereby significantly improving the purity of granular polysilicon, reducing turbidity, improving the performance of granular polysilicon in the production process, and having the advantages of energy saving, high efficiency, and economy.

[0056] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0057] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for removing dust from granular polycrystalline silicon, characterized in that: The following steps are involved: S1: preparing granular polycrystalline silicon and loading it into a reaction vessel, heating the granular polycrystalline silicon by microwave radiation, and maintaining an inert atmosphere or vacuum state in the reactor during the heating process; S2: After the granular polysilicon is heated to 600-1200° C., a continuous heat preservation treatment is performed. After the heat preservation is completed, the granular polysilicon is cooled, and the microsilicon powder is removed, thereby reducing the turbidity value of the granular polysilicon.

2. The method for removing dust from granular polycrystalline silicon according to claim 1, characterized in that: In the step S1, the reaction vessel is a crucible, and the device used for the microwave radiation heating is a tubular microwave oven.

3. The method for removing dust from granular polysilicon according to claim 1, characterized in that: In the step S1, the particle size of the granular polysilicon is 1-3 mm.

4. The method for removing dust from granular polycrystalline silicon according to claim 1, characterized in that: In the step S1, the power of the microwave radiation heating is 200-4000W, and the heating rate is 10-200°C / min.

5. The method for removing dust from granular polycrystalline silicon according to claim 1, characterized in that: In the step S1, during the heating process, the inert atmosphere is one or both of nitrogen and argon, and the gas flow rate is 50-100 mL / min.

6. The method for removing dust from granular polysilicon according to claim 1, characterized in that: In the step S2, the insulation time is 10 to 100 minutes.

7. The method for removing dust from granular polysilicon according to claim 1, characterized in that: In the step S2, the granular polysilicon is cooled by natural cooling along with the furnace.

8. The method for removing dust from granular polycrystalline silicon according to claim 1, characterized in that: In the step S2, after the turbidity value of the granular polysilicon is reduced, the turbidity value of the granular polysilicon is less than 5NTU, and no surface oxidation occurs.

Images