Method for recycling waste silicon materials

Abstract

The present invention belongs to the technical field of single crystal silicon preparation, and specifically discloses a method for recycling waste silicon materials, including: S10, pre-treating the waste silicon materials; S20, pulling the pre-treated waste silicon materials into rod-shaped preparation materials by the direct pulling method; S30, crushing the rod-shaped preparation materials, and screening out silicon materials with a particle size that meets the preset target; S40, mixing the screened silicon materials with conventional silicon materials to prepare single crystal silicon rods. This scheme realizes the recycling of waste silicon materials, which can not only ensure the quality of the drawn single crystal silicon rods, but also save the cost of silicon materials. In the case that the current price of silicon materials is far greater than the processing cost of waste silicon powder materials, this scheme can save the manufacturing cost of single crystal silicon rods, increase corporate profits, and has good practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of single crystal silicon preparation, and in particular relates to a method for recycling waste silicon materials. Background Art

[0002] Solar photovoltaic power generation plays an important role in renewable energy. Photovoltaic energy is considered to be the most important energy in the 21st century, mainly because photovoltaic power generation has incomparable advantages: cleanliness, safety, widespread, long life, maintenance-free, practicality, resource sufficiency and potential economy.

[0003] Monocrystalline silicon has attracted much attention due to its excellent performance. It is the most basic and widely used material for the production of semiconductor devices such as large-scale integrated circuits, and is also an important material for solar cells. Its quality directly affects the quality of semiconductors and solar cell products.

[0004] Among them, single crystal silicon rod is one of the industrialized products of single crystal silicon, which is formed by shaping or pulling in the furnace through zone melting or Czochralski process. At present, the most widely used method in the industry is to use the pulling method to prepare single crystal silicon rod, that is, in the single crystal furnace, the seed crystal is inserted into the molten polysilicon and then pulled to obtain the single crystal silicon rod, which specifically includes the main steps of dismantling the furnace - charging - melting - drawing the neck - releasing the shoulder - turning the shoulder - equalizing the diameter - finishing - stopping the furnace.

[0005] At present, with the promotion of the crystal pulling CCZ (continuous straight pulling) process, the demand for small silicon materials with a particle size of less than 50mm is gradually increasing. Therefore, in the production process, it is necessary to crush the silicon materials with larger particle sizes into small silicon materials that meet the production needs. The crushed silicon materials are divided into two categories with a particle size of 2mm as the boundary. One category is silicon materials with a particle size of less than 50mm and greater than 2mm. This type of silicon material can be directly put into the furnace for use after pretreatment; the other category is silicon materials with a particle size of less than 2mm. This type of silicon material has a large amount of silicon powder, which seriously affects the crystallization of single crystals, so it cannot be directly put into the furnace for use. At present, the treatment method for silicon materials with a particle size of less than 2mm is usually scrapping. In recent years, with the continuous increase in the price of silicon materials, it has directly led to an increase in the cost of single crystal silicon rods and solar cells, resulting in a waste of resources. Therefore, the reuse of waste silicon materials with a particle size of less than 2mm has become an urgent problem to be solved in the industry. Summary of the invention

[0006] The purpose of the present invention is to provide a method for recycling waste silicon materials, so as to purify and reuse waste silicon materials below 2 mm that are scrapped in the prior art, thereby saving the manufacturing cost of single crystal silicon rods and increasing corporate profits.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for recycling waste silicon materials, comprising:

[0009] S10, pre-treating the waste silicon material;

[0010] S20, drawing the pretreated waste silicon material into a rod-shaped preparatory material by a Czochralski method;

[0011] S30, crushing the rod-shaped prepared material to select silicon materials with a particle size that meets a preset target;

[0012] S40, mixing the screened silicon material with conventional silicon material to prepare single crystal silicon rods.

[0013] Optionally, the step S10 includes:

[0014] S11, removing metal impurities by a magnetic separator; and / or

[0015] S12, removing particulate impurities with a particle size of less than 0.5 mm through a sieve.

[0016] Optionally, the step S20 includes:

[0017] S21, filling the waste silicon material into a single crystal furnace;

[0018] S22, heating and melting the waste silicon material into silicon melt;

[0019] S23, preheating the seed crystal, and after the silicon melt reaches the seeding temperature, immersing the seed crystal in the silicon melt for seeding growth to form a thin neck;

[0020] S24, after the seeding growth is completed, shoulder release and shoulder rotation are performed, and then equal diameter growth is performed;

[0021] S25, after the equal diameter growth is completed, the tail is cut off and the rod-shaped prepared material is taken out.

[0022] Optionally, the step S20 further includes:

[0023] S26, adding the waste silicon material into the single crystal furnace through a feeding device, and then repeating steps S22 to S25.

[0024] Optionally, step S26 includes:

[0025] The feeding device is placed at the throat of the single crystal furnace to preheat the waste silicon material in the feeding device, and then the height of the feeding device is lowered and the feeding device is opened to feed the waste silicon material into the single crystal furnace, wherein the preheating time is 10-20 minutes and the preheating temperature is 300-500°C.

[0026] Optionally, during the seeding growth process in step S23, the pulling speed of the seed crystal is adjusted to control the diameter of the narrow neck to 5-7 mm, and the length of the narrow neck is controlled to be greater than 50 mm, and the narrow neck has an edge line; and / or

[0027] In the shoulder release process in step S24, the pulling speed of the seed crystal is gradually controlled to 0.6-0.8 mm / min, and the cone height formed by the shoulder release is controlled to be greater than or equal to 40 mm; and / or

[0028] During the isodiametric growth process in step S25, the pulling speed of the seed crystal is less than or equal to 1.0 mm / min.

[0029] Optionally, after each step S25, a vacuum test is performed on the single crystal furnace.

[0030] Optionally, the waste silicon material refers to silicon material with a particle size less than 2 mm, and the silicon material with a particle size meeting a preset target is silicon material with a particle size of 2-50 mm.

[0031] Optionally, after each step S25, wait for 1-2 hours before opening the furnace to take out the rod-shaped prepared material, and the auxiliary chamber lifting speed when opening the furnace is 30 mm / min.

[0032] Optionally, a water-free guide tube is provided in the single crystal furnace.

[0033] Beneficial effects of this scheme: This scheme condenses the waste silicon powder into rod-shaped preparatory materials through the direct pulling method, and then crushes the rod-shaped preparatory materials to screen out silicon materials with particle sizes that meet the specifications so as to be directly put into the furnace for use when pulling single crystal silicon rods, thereby realizing the reuse of waste silicon materials and greatly saving silicon material costs. In addition, this scheme mixes the prepared silicon materials with conventional silicon materials to form silicon materials that can be put into the furnace again to ensure the success rate of pulling single crystal silicon rods and the quality of single crystal silicon rods. At present, the price of silicon materials is far greater than the reprocessing cost of waste silicon materials. This scheme can effectively save the manufacturing cost of single crystal silicon rods and increase corporate profits, and has good practicality. DETAILED DESCRIPTION

[0034] In the following description and the appended claims, waste silicon material refers to fine silicon material with a particle size of less than 2 mm. Since this type of silicon material contains a lot of silicon powder, it will seriously affect the crystallization of single crystals during the single crystal silicon pulling process. Therefore, it cannot be directly put into the furnace for use and is scrapped, and is therefore called waste silicon material.

[0035] A single crystal furnace refers to a device that uses a graphite heater to melt polycrystalline materials such as polysilicon in an inert gas (mainly nitrogen and helium) environment and grows them into non-dislocated single crystal silicon rods using the Czochralski method.

[0036] The seed crystal refers to the seed crystal used to grow a single crystal silicon rod by the Czochralski method. The seed crystal has the same crystal orientation as the single crystal silicon to be grown and is smaller in size than the single crystal silicon.

[0037] Equal diameter means that during the growth of single crystal silicon, the variation range of its outer diameter is within the error range (for example, no more than 2 mm).

[0038] The thermal field refers to the thermal system in the single crystal furnace, which is used to melt polycrystalline materials such as polycrystalline silicon in the graphite crucible.

[0039] In the existing RCZ (multiple feeding) process, before pulling crystals, the silicon material with a larger particle size needs to be crushed into small pieces of silicon material that meet production needs (particle size between 2mm and 50mm), and the existing silicon material crushing equipment can usually control the upper limit of the silicon material particle size but cannot control the lower limit of the silicon material, so it can ensure that the particle size of the silicon material after crushing is less than 50mm, but cannot ensure that its particle size is greater than or equal to 2mm. In this embodiment, the crushed silicon material is divided into two categories based on the particle size of 2mm. One category is silicon material with a particle size less than 50mm and greater than or equal to 2mm. This type of silicon material can be directly put into the furnace for use after pretreatment; the other category is silicon material with a particle size less than 2mm. This type of silicon material has a large amount of silicon powder, which seriously affects the crystallization of single crystals, so it cannot be directly put into the furnace for use. At present, the treatment method for silicon material with a particle size less than 2mm is usually scrapping. With the recent continuous increase in the price of silicon material, it will lead to an increase in the cost of silicon material, waste resources, and bring unnecessary impacts to crystal pulling. In view of the above problems, this embodiment provides a method for recycling waste silicon materials, which can convert waste silicon materials into silicon materials that can be reused in the furnace through the Czochralski method, thereby saving silicon material costs. The specific scheme is as follows:

[0040] A method for recycling waste silicon materials comprises the following steps:

[0041] S10, pre-treating the waste silicon material;

[0042] S20, drawing the treated waste silicon material into a rod-shaped prepared material by a direct pulling method;

[0043] S30, crushing the rod-shaped prepared material to select silicon materials with a particle size that meets the preset target;

[0044] S40, mixing the screened silicon material with conventional silicon material to prepare a single crystal silicon rod.

[0045] Based on the above scheme, this method reuses the waste silicon materials with a particle size less than 2mm that have been scrapped in the prior art. At a time when the current silicon material price is far greater than the processing cost of waste silicon powder, this scheme can save the manufacturing cost of single crystal silicon rods and increase corporate profits, and has good practicality.

[0046] Each step of the method for recycling waste silicon materials of the present invention is described in more detail below.

[0047] In some embodiments, step S10 includes:

[0048] S11, removing metal impurities by a magnetic separator; and / or

[0049] S12, removing particulate impurities with a particle size of less than 0.5 mm through a sieve.

[0050] In this embodiment, the waste silicon material contains impurities and the impurities are mainly metal particles, graphite powder particles and other tiny particles. These impurities will seriously affect the forming of the rod-shaped preparatory material, reduce the drawing success rate, and also cause the drawn rod-shaped preparatory material to be easily broken, causing damage to the crucible device in the single crystal furnace, and increasing the difficulty of operations such as taking and discharging materials. In addition, the silicon material containing impurities will also affect the subsequent drawing of single crystal silicon rods and fail to achieve the expected effect. Therefore, various impurities need to be removed before drawing the rod-shaped preparatory material.

[0051] Specifically, the particle size of tiny particles such as graphite powder contained in waste silicon materials is usually below 0.5mm. To remove these tiny particles, screening machines with corresponding particle size specifications are mainly used for screening. They can well remove tiny particle impurities below 0.5mm, and while screening out impurity particles below 0.5mm, they can also remove a small amount of silicon powder with a particle size below 0.5mm, thereby avoiding the difficulty in forming the rod-shaped preparatory material during the drawing process caused by silicon powder with too small a particle size.

[0052] In this step, metal impurities can be directly removed by a magnetic separator.

[0053] In some embodiments, after the waste silicon material is pre-treated for impurity removal and before the rod-shaped pre-material is pulled by the CZ method, the single crystal furnace needs to be pre-treated:

[0054] Specifically, the hot field of the single crystal furnace is first subjected to the first hot field impurity removal treatment by means of grinding, wiping, etc., to remove the dust, volatiles, etc. adhered in the hot field. Then, the hot field after the first impurity removal is installed on the single crystal furnace, and the hot field is heated and calcined at a high temperature (above 400°C) for more than 10 minutes, specifically 500-600°C. In this process, the unstable impurities in the hot field of the single crystal furnace can be decomposed and volatilized, and then the hot field is vacuumed until the furnace pressure in the single crystal furnace is below 10Pa. During the vacuuming process, the gas impurities after decomposition and volatilization in the single crystal furnace are removed to improve the cleanliness in the single crystal furnace, and the leakage rate of the single crystal furnace can be tested to ensure the stability of the single crystal furnace.

[0055] Then, the process proceeds to step S20, in which the treated waste silicon material is pulled into a rod-shaped preparatory material by a direct pulling method.

[0056] In this embodiment, the Czochralski method in step S20 is divided into the following main stages:

[0057] S21, filling the waste silicon material into a single crystal furnace.

[0058] This embodiment mainly adopts a one-furnace-multiple-rods process. In this process, when the first rod is drawn, the waste silicon material can be directly placed in the crucible during the furnace loading process.

[0059] S22, heating and melting the waste silicon material into silicon melt.

[0060] Specifically, the pretreated waste silicon material is introduced into the graphite crucible of the single crystal furnace, and then the single crystal furnace system is controlled to heat and melt the waste silicon material in the graphite crucible, so that the waste silicon material forms a liquid silicon melt.

[0061] S23, preheating the seed crystal, and after the silicon melt reaches the seeding temperature, immersing the seed crystal in the silicon melt for seeding growth to form a thin neck.

[0062] The seed crystal preheating includes: switching the system to automatic mode, so that the system temperature gradually rises in a step-by-step manner, specifically, preheating the seed crystal for the first time for 30 minutes at the upper part of the guide tube, then lowering the seed crystal to the middle part of the guide tube for the second preheating for 10 minutes, then lowering the seed crystal to the lower edge of the guide tube for the third preheating for 10 minutes, and finally lowering the seed crystal to a position near the liquid surface for the fourth preheating for 10 minutes, thus completing the step-by-step preheating of the seed crystal. The temperature of the first preheating, the temperature of the second preheating, the temperature of the third preheating and the temperature of the fourth preheating rise in a step-by-step manner.

[0063] After the seed crystal is preheated, the seed crystal is brought into contact with the silicon melt for temperature testing. When the temperature is appropriate, the seed crystal is lowered into the silicon melt for contact before seeding. The characteristic of the silicon melt reaching the seeding temperature is that after the seed crystal and the silicon melt come into contact, an aperture gradually appears around the seed crystal, and finally the aperture becomes round.

[0064] In this step, the seed crystal is preheated by gradually increasing step-by-step temperature, so that the temperature of the seed crystal increases layer by layer. Sufficient preheating can not only prevent the seed crystal from being broken by rapid heating, but also ensure that the temperature reaches the standard when it contacts with the silicon melt, and the preheating effect is good.

[0065] The seeding growth includes: immersing the seed crystal into the silicon melt after the silicon melt reaches the seeding temperature, and after the four edges of the seed crystal begin to grow, controlling the seeding pulling speed, and starting to pull the seed crystal upward to perform a thin neck operation after a given pulling speed, and adjusting the pulling speed during the seeding process to control the diameter of the thin neck between 5-9mm, and finally controlling the length of the thin neck to be greater than 50mm, and ensuring that the thin neck has edges and the edges are continuous during the seeding process, so that the silicon atoms in the obtained rod-shaped preparation are arranged relatively orderly, thereby improving the success rate of pulling.

[0066] In the above-mentioned seeding growth step, the diameter of the thin neck is 2-3 mm larger than the diameter of the thin neck of the conventionally pulled single crystal silicon rod, so as to increase the strength of the thin neck and ensure that the thin neck is not easy to break; and, the length of the thin neck in this embodiment is about one half of the length of the thin neck of the conventionally pulled single crystal silicon rod, so as to reduce the risk of breakage of the rod-shaped preparatory material during the seeding process.

[0067] S24, after the seeding growth is completed, shoulder release and shoulder rotation are performed, and then equal diameter growth is entered.

[0068] Among them, after entering the shoulder release step, the pulling speed of the seed crystal is gradually controlled to 0.6-0.8mm / min, the seed crystal is slowly pulled up, and the cone height formed by the shoulder release is controlled to be greater than or equal to 40mm. In order to prevent the fracture accident during the shoulder release process, the crucible is given a certain speed to lift the graphite crucible upward during the shoulder release, and the distance between the lower end of the rod-shaped preparation material and the silicon melt liquid surface is controlled to be maintained between 20-30mm until the shoulder plate is formed. If the shoulder release fails, the thin neck part and the shoulder plate part are placed in the silicon melt and the system is controlled to heat up for remelting, and the seeding growth is resumed after the temperature rises.

[0069] After shoulder release is completed, the shoulder rotation operation begins, and depending on the shoulder release speed, the shoulder rotation operation is directly performed when the target diameter of the rod preparation material is about 10mm away, and the seed crystal pulling speed is increased to 1.8-2.2mm / min to make the shoulder approximately a right angle.

[0070] After the shoulder is turned, it enters the equal-diameter growth stage, making the single crystal furnace system enter the automatic control mode, and controlling the equal-diameter pulling speed to be less than or equal to 1.0mm / min. Compared with the pulling speed of about 1.5mm / min during the conventional pulling of single crystal rods, this step reduces the pulling speed. First, it is to avoid the rod-shaped preparation from being broken due to excessive pulling speed, and second, it is to reduce the moving speed of the rod-shaped preparation in the guide tube. When the cooling rate is not as good as that of the water-cooled guide tube, reducing the pulling speed of the rod-shaped preparation can make it fully cooled, thereby improving the drawing success rate of the rod-shaped preparation.

[0071] S25. After the equal diameter growth is completed, the tail is cut off and the rod-shaped preparation material is taken out.

[0072] At the end of the equal diameter growth, when the diameter and length of the rod-shaped preparation material reach the predetermined value, the system exits the automatic growth control, stops the crucible lifting, and directly lifts and breaks the rod-shaped preparation material. The graphite crucible is controlled to drop 10mm to separate the rod-shaped preparation material from the liquid surface of the silicon melt, and the pulling speed is set to 2mm / min to lift and break the rod-shaped preparation material upward. Then, turn off the heating power supply, restore the various crystal pulling parameters to the initial state, and proceed to the next step after the cooling time is reached.

[0073] Among them, taking out the rod-shaped preparatory material specifically includes: the first step: setting the pulling speed to 4mm / min, and the time lasts for 30 minutes; the second step: setting the pulling speed to 6mm / min, and the time lasts for 60 minutes; the third step: lifting the rod-shaped preparatory material into the auxiliary chamber furnace, opening the argon channel, slowly covering the flap, allowing argon to be filled into the auxiliary chamber until the relative pressure in the auxiliary chamber reaches -0.5Mpa, then closing the argon, maintaining the negative pressure state for 30 minutes, and then filling the argon to normal pressure to take out the rod-shaped preparatory material.

[0074] In some embodiments, step S20 further includes:

[0075] S26, adding the waste silicon material into the single crystal furnace through a feeding device, and then repeating steps S22 to S25.

[0076] After a single drawing of the rod-shaped preparation material is completed, the discarded silicon material is fed back into the single crystal furnace, and the above steps S22-S25 are repeated until the drawing of the rod-shaped preparation material is completed, thereby achieving the drawing of multiple rods in one furnace.

[0077] In this step, the waste silicon material is mainly introduced into the crucible of the single crystal furnace through feeding devices such as quartz tubes and quartz boats.

[0078] In some embodiments, step S26 also includes: placing the feeding device at the throat of the single crystal furnace to preheat the waste silicon material in the feeding device, and then lowering the height of the feeding device and opening the feeding device to feed the waste silicon material into the single crystal furnace.

[0079] The preheating time is 10-20 min, for example, 10 min, 12 min, 14 min, 16 min, 20 min, etc., and the preheating temperature is 300-500° C., for example, 300° C., 350° C., 400° C., 450° C., 500° C., etc. In this embodiment, the preferred preheating time is 15 min, and the preheating temperature is 400° C.

[0080] On the one hand, the preheating operation is to prevent the silicon material from adhering to the feeding device during the feeding process, so that the waste silicon material can slide more smoothly into the single crystal furnace to improve efficiency; on the other hand, preheating the feeding device can increase the initial temperature of the feeding device, reduce the temperature difference between the feeding device and the single crystal furnace, and avoid the quartz tube, quartz boat and other feeding devices from being cracked and broken due to rapid heat when installed in the single crystal furnace, thereby ensuring the reliability and safety of production.

[0081] It should be understood that in some other embodiments, the preheating of the feeding device and the waste silicon material can also be preheated outside the single crystal furnace, and the preheating form is not limited.

[0082] In some embodiments, after each step S25 is completed, the vacuum of the single crystal furnace needs to be tested. If the leakage rate is less than 0.67Pa / min and the limit vacuum is less than 10Pa, the next rod-shaped preparatory material pulling work can be carried out. Otherwise, the furnace is dismantled and the single crystal furnace is reinstalled to ensure the safety and success rate of the next rod-shaped preparatory material pulling.

[0083] In some embodiments, the method further comprises waiting for 1-2 hours after each step S25 before opening the furnace to take out the rod-shaped prepared material, and the auxiliary chamber lifting speed is 30 mm / min when the furnace is opened.

[0084] After the rod-shaped preparatory material is drawn, wait for 1-2 hours to allow the rod-shaped preparatory material to cool down in the furnace to prevent the rod-shaped preparatory material from encountering cold air from the outside when the furnace is opened right after drawing, thereby causing cracks due to the sudden cooling.

[0085] The single crystal furnace used in the above steps S21-S26 is provided with a water-free flow guide tube, such as a graphite flow guide tube, a carbon fiber flow guide tube, etc.

[0086] At present, conventional single crystal furnaces are all equipped with water-cooled guide tubes. The water-cooled guide tubes quickly cool down the single crystal silicon rods through circulating cooling water whose temperature is much lower than that of the single crystal silicon rods. However, since the rod-shaped preparatory material in this embodiment is drawn from tiny silicon materials with a particle size of less than 2 mm, the silicon atoms inside the drawn rod-shaped preparatory material are arranged in a disorderly manner and are easily broken. Therefore, if the rod-shaped preparatory material is placed in a water-cooled guide tube for cooling during drawing, it is easy to cause it to be rapidly cooled and broken, thereby reducing the success rate of drawing. In view of the above problem, in this embodiment, the guide tube in the single crystal furnace is set as a water-free guide tube, and the initial cooling temperature of the guide tube is increased, which can not only ensure the cooling effect of the rod-shaped preparatory material, but also reduce the temperature difference between the rod-shaped preparatory material and the guide tube, thereby avoiding the rod-shaped preparatory material from being rapidly cooled and broken.

[0087] The direct pulling method shown in the above steps S21-S26 is roughly the same as the method steps for pulling single crystal silicon rods. However, in this embodiment, the diameter and length of the narrow neck and the rod-shaped preparation are adjusted, the pulling speed is reduced, and a waterless guide tube is selected to overcome the defects in the waste silicon material drawing process, which can greatly improve the success rate of drawing the rod-shaped preparation.

[0088] For example, controlling the diameter, length and pulling speed of the rod-shaped preparation is to ensure that during the pulling process, the rod-shaped preparation is prevented from being pulled too fast or too violently or from being of inappropriate size, causing cracks, or even breakage, which may damage the crucible and other facilities in the single crystal furnace.

[0089] After the rod-shaped preparation is drawn, the following steps are performed:

[0090] S30, crushing the rod-shaped prepared material to select silicon materials with a particle size that meets the preset target.

[0091] The rod-shaped pre-material drawn in step S20 has a disordered internal structure and is easily broken, which is far from meeting the requirements of a single crystal silicon rod. Therefore, the rod-shaped pre-material needs to be broken into silicon materials with a particle size that meets the preset target for further processing.

[0092] Specifically, in this embodiment, the rod-shaped prepared material is crushed mainly by crushing equipment. After the crushing is completed, the silicon material is screened by screening equipment such as a vibrating screen to screen out silicon materials with a particle size less than 50 mm and greater than or equal to 2 mm for backup.

[0093] S40, mixing the screened silicon material with conventional silicon material to prepare a single crystal silicon rod.

[0094] The quality of the spare silicon material obtained by crushing in step S30 is still slightly lower than that of the conventional silicon material. If 100% of the spare silicon material is used to prepare single crystal silicon rods, the quality of the single crystal silicon rods will be poor. Therefore, when preparing single crystal silicon rods, the spare silicon material and the conventional silicon material need to be mixed in a certain ratio and then processed and drawn. Among them, the proportion of the spare silicon material is less than 10% to ensure the drawing success rate and quality of the single crystal silicon rods.

[0095] Among them, conventional silicon material refers to silicon material with a particle size between 2-50 mm formed by directly crushing polycrystalline silicon or amorphous silicon.

[0096] In some embodiments, the method for utilizing waste silicon materials further includes step S50: adding the remaining silicon materials whose particle sizes do not meet the preset target (less than 2 mm) after the silicon materials are screened in step S30 back into the waste silicon materials to repeat the above operation.

[0097] Specifically, after the crushed silicon material is sieving in step S30, some silicon powder material with particle size that does not meet the standard (particle size less than 2 mm) remains. This part of silicon powder material is the same as the initial waste silicon material of this method and needs to be re-condensed before it can be used to prepare single crystal silicon rods.

[0098] In this step, the silicon powder can be remixed with the waste silicon material to be purified, and then steps S10-S40 are repeated until the remaining waste silicon material and the waste silicon material in step S30 are insufficient to support the drawing of the rod-shaped preparatory material.

[0099] After step S50, the method can not only purify and reprocess the original waste silicon material, but also repeatedly process the silicon powder material generated in the steps of the method, thereby improving the utilization rate of the silicon material.

[0100] In this embodiment, waste silicon powder is purified by the Czochralski method to form silicon material with a particle size that meets the specifications, so as to achieve the reuse of waste silicon material and significantly save the cost of silicon material. In addition, the embodiment mixes the prepared silicon material with conventional silicon material to form silicon material that can be reused in the furnace to ensure the success rate of pulling single crystal silicon rods and the quality of single crystal silicon rods. In the case that the current price of silicon material is far greater than the processing cost of waste silicon powder, the embodiment can effectively save the manufacturing cost of single crystal silicon rods and increase corporate profits, which has good practicality.

[0101] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for recycling waste silicon materials, characterized in that: include: S10, pre-treating the waste silicon material; S20, drawing the pretreated waste silicon material into a rod-shaped preparatory material by a Czochralski method; S30, crushing the rod-shaped prepared material to select silicon materials with a particle size that meets a preset target; S40, mixing the screened silicon material with conventional silicon material to prepare a single crystal silicon rod; The conventional silicon material is a silicon material with a particle size between 2 and 50 mm formed by directly crushing polycrystalline silicon or amorphous silicon; the waste silicon material is a silicon material with a particle size less than 2 mm; and the silicon material with a particle size that meets the preset target is a silicon material with a particle size of 2 to 50 mm. The step S10 comprises: S11, removing metal impurities by a magnetic separator; and / or S12, removing particulate impurities with a particle size of less than 0.5 mm through a sieve; The step S20 comprises: S21, filling the waste silicon material into a single crystal furnace; S22, heating and melting the waste silicon material into silicon melt; S23, preheating the seed crystal, and after the silicon melt reaches the seeding temperature, immersing the seed crystal in the silicon melt for seeding growth to form a thin neck; S24, after the seeding growth is completed, shoulder release and shoulder rotation are performed, and then equal diameter growth is performed; S25, after the equal diameter growth is completed, the tail is cut off and the rod-shaped prepared material is taken out; The step S20 further includes: S26, adding the waste silicon material into the single crystal furnace through a feeding device, and then repeating steps S22 to S25; The step S26 further comprises: The feeding device is placed at the throat of the single crystal furnace to preheat the waste silicon material in the feeding device, and then the height of the feeding device is lowered and the feeding device is opened to feed the waste silicon material into the single crystal furnace, wherein the preheating time is 10-20 minutes and the preheating temperature is 300-500°C.

2. The method for recycling waste silicon materials according to claim 1, characterized in that: During the seeding growth process in step S23, the pulling speed of the seed crystal is adjusted to control the diameter of the narrow neck to 5-9 mm, and the length of the narrow neck is controlled to be greater than 50 mm, and the narrow neck has an edge line; and / or In the shoulder release process in step S24, the pulling speed of the seed crystal is gradually controlled to 0.6-0.8 mm / min, and the cone height formed by the shoulder release is controlled to be greater than or equal to 40 mm; and / or During the isodiametric growth process in step S25, the pulling speed of the seed crystal is less than or equal to 1.0 mm / min.

3. The method for recycling waste silicon materials according to claim 1, characterized in that: After each step S25, the single crystal furnace is subjected to vacuum testing.

4. The method for recycling waste silicon materials according to claim 1, characterized in that: After each step S25, wait for 1-2 hours before opening the furnace to take out the rod-shaped prepared material. When opening the furnace, the lifting speed of the auxiliary chamber is 30 mm / min.

5. The method for recycling waste silicon materials according to claim 1, characterized in that: The single crystal furnace is provided with a water-free guide tube.