Feeding method for recycling broken silicon wafers and method for preparing monocrystalline silicon

Abstract

The invention belongs to the field of photovoltaic materials, and particularly provides a feeding method for cyclic utilization of broken silicon wafers and a method for preparing monocrystalline silicon, the feeding method for cyclic utilization of broken silicon wafers comprises the following steps: heating a single crystal furnace by using heaters, the power of a first heater being less than or equal to 80kw, and the power of a second heater being less than or equal to 60kw; silicon materials are added into the crucible through the cylindrical feeder, the silicon materials comprise a top-layer blocky silicon material, a bottom-layer blocky silicon material and a middle-layer mixed silicon material clamped between the top-layer blocky silicon material and the bottom-layer blocky silicon material, and the middle-layer mixed silicon material comprises a blocky silicon material layer and a broken silicon wafer layer; and after all the silicon materials enter the crucible, the power of the first heater is greater than or equal to 90kw, and the power of the second heater is greater than or equal to 70kw. According to the feeding method, the broken silicon wafers can be smoothly fed into the crucible, the recycling rate of the broken silicon wafers can be increased, the drawing process of monocrystalline silicon is not influenced, and the raw material cost can be effectively reduced.

Description

Technical Field

[0001] This application belongs to the technical field of photovoltaic materials. Specifically, it relates to a feeding method for recycling broken silicon wafers and a method for preparing single-crystalline silicon. Background Art

[0002] Under the background of the current development of the photovoltaic industry, it is inevitable to produce broken silicon wafers during the production of slicing and batteries. Especially the broken silicon wafers produced at the battery end, after a series of chemical processes such as doping and diffusion, the proper treatment of broken silicon wafers has become one of the more difficult problems in the industry. If the generated broken silicon wafers can be processed and returned to the crystal pulling end for recycling, it will be of great significance. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, the present invention proposes a feeding method for recycling broken silicon wafers and a method for preparing single-crystalline silicon that can effectively improve the problem of material jamming during the feeding process of broken silicon wafers.

[0004] The first aspect of the present application provides a feeding method for recycling broken silicon wafers. According to an embodiment of the present application, the feeding method for recycling broken silicon wafers includes: heating a single crystal furnace using heaters, where the heaters include a first heater and a second heater, the first heater is located on the inner sidewall of the single crystal furnace, the second heater is located at the bottom of the single crystal furnace, the power of the first heater is set to be less than or equal to 80 kw, and the power of the second heater is set to be less than or equal to 60 kw; adding silicon materials into a crucible inside the single crystal furnace through a cylindrical feeder, where the silicon materials in the cylindrical feeder include: top-layer massive silicon materials, bottom-layer massive silicon materials, and an intermediate-layer mixed silicon material sandwiched between the top-layer massive silicon materials and the bottom-layer massive silicon materials, and the intermediate-layer mixed silicon material includes a massive silicon material layer and a broken silicon wafer layer; after all the silicon materials in the cylindrical feeder enter the crucible, setting the power of the first heater to be greater than or equal to 90 kw and setting the power of the second heater to be greater than or equal to 70 kw. In this feeding method, in a "sandwich" laminated manner, that is, the intermediate-layer mixed silicon material containing a broken silicon wafer layer is sandwiched between the top-layer massive silicon materials and the bottom-layer massive silicon materials. On the one hand, the bottom-layer massive silicon materials can absorb part of the heat and delay the softening of the broken silicon wafers; on the other hand, the top-layer massive silicon materials can push the intermediate-layer mixed silicon material into the crucible, and during the process of the top-layer massive silicon materials and the massive silicon material layer in the intermediate-layer mixed silicon material entering the crucible under the action of gravity, part of the broken silicon wafers stuck to the inner wall of the feeder can be brought into the crucible, so as to ensure that the broken silicon wafers are smoothly put into the crucible, which is more conducive to improving the recycling rate of broken silicon wafers, not only has no impact on the single crystal silicon pulling process, but also can effectively reduce the raw material cost. In addition, before feeding, heating the single crystal furnace can increase the temperature inside the single crystal furnace, avoid the silicon liquid in the crucible from crystallizing and damaging the quartz crucible due to too fast heat loss after feeding, and at the same time, setting the power value of the first heater to be less than or equal to 80 kw and the power value of the second heater to be less than or equal to 60 kw can prevent the temperature inside the single crystal furnace from being too high when the silicon materials are added to the crucible, causing the broken silicon wafers in the cylindrical feeder to soften and resulting in material jamming; and, after all the silicon materials enter the crucible, then increasing the power values of the first heater and the second heater can prevent the problem of material jamming caused by the softening of the broken silicon wafers in the cylindrical feeder compared with increasing the power values before the silicon materials are added to the crucible. At the same time, the feeding method of the present application does not require pre-mixing of broken silicon wafers and massive silicon materials, and when problems occur in the single crystal silicon pulling process and trace back to the silicon material raw materials, the massive silicon materials and broken silicon wafers can be directly processed correspondingly without separating the broken silicon wafers and massive silicon materials again, and the operation is simpler.

[0005] According to an embodiment of the present application, the number of cylinders of silicon material added into the crucible through the cylindrical feeder is n cylinders, where: the total mass of the broken silicon wafers contained in the n cylinders of silicon material accounts for 20% to 40% of the total mass of the n cylinders of silicon material; in 1 cylinder of silicon material, the mass of the broken silicon wafers accounts for 0% to 60% of the total mass of the 1 cylinder of silicon material; n is an integer from 2 to 6.

[0006] According to an embodiment of the present application, the intermediate layer mixed silicon material includes 2 to 4 broken silicon wafer layers and 2 to 4 massive silicon material layers, and the broken silicon wafer layers and the massive silicon material layers are arranged alternately.

[0007] According to an embodiment of the present application, among the 2 to 4 broken silicon wafer layers, there are a first broken silicon wafer layer and a second broken silicon wafer layer. The first broken silicon wafer layer is closer to the bottom massive silicon material than the second broken silicon wafer layer. Among them, the mass of the first broken silicon wafer layer is greater than the mass of the second broken silicon wafer layer; when feeding materials, the bottom massive silicon material enters the crucible earlier than the top massive silicon material.

[0008] According to an embodiment of the present application, the mass ratio of the massive silicon material layer to the broken silicon wafer layer is 1 to 3:1.

[0009] According to an embodiment of the present application, the mass of the top massive silicon material is greater than or equal to 20 kg.

[0010] According to an embodiment of the present application, the mass of the bottom massive silicon material is greater than or equal to 20 kg.

[0011] According to an embodiment of the present application, when adding each cylinder of the silicon material, the solid-liquid ratio in the crucible is 18% to 22%.

[0012] According to an embodiment of the present application, in the order of addition from front to back, the n cylinders of silicon material are defined as the 1st cylinder of silicon material, the 2nd cylinder of silicon material,..., the nth cylinder of silicon material; after adding the (i - 1)th cylinder of silicon material, when the solid-liquid ratio in the crucible is 25% to 35%, the power of the first heater is set to be less than or equal to 80 kw, and the power of the second heater is set to be less than or equal to 60 kw; when the solid-liquid ratio in the crucible is 18% to 22%, add the ith cylinder of silicon material. After the ith cylinder of silicon material completely enters the crucible, set the power of the first heater to be greater than or equal to 90 kw, and set the power of the second heater to be greater than or equal to 70 kw, where i is an integer from 2 to n.

[0013] According to an embodiment of the present application, after adding the n-tube silicon material, slag adhesion treatment is further included, and the slag adhesion treatment includes: when the linear diameter of the unmelted solid material floating on the molten silicon surface in the crucible of the single crystal furnace is between 70 mm and 150 mm; inserting the seed crystal into the molten silicon surface, after the seed crystal adheres to the unmelted solid material, pulling the seed crystal up and down repeatedly 3 to 5 times, and then pulling the seed crystal and the unmelted solid material out of the molten silicon surface and staying at a position 100 mm to 150 mm away from the molten silicon surface for 15 min to 20 min, and then taking out the seed crystal and the unmelted solid material.

[0014] According to an embodiment of the present application, the seed crystal has fine crystals.

[0015] According to an embodiment of the present application, the pulling speed of the seed crystal is 250 mm / h to 350 mm / h.

[0016] According to an embodiment of the present application, after taking out the seed crystal and the unmelted solid material, it further includes: adjusting the position of the crucible to 0 mm to -100 mm and the furnace pressure to 2 Torr to 4 Torr, so that the molten silicon in the crucible of the single crystal furnace boils to remove impurities.

[0017] In a second aspect of the present application, a method for preparing single crystal silicon is provided. According to an embodiment of the present application, the method includes: adding silicon material into the crucible of the single crystal furnace by using the feeding method described above; performing single crystal silicon drawing.

[0018] According to an embodiment of the present application, when performing single crystal silicon drawing, if solid floating impurities appear on the molten silicon surface in the crucible of the single crystal furnace, the single crystal silicon being drawn is broken, and slag adhesion treatment is performed. After there are no solid floating impurities on the molten silicon surface, single crystal silicon drawing is restarted. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of a feeder filled with silicon material according to an embodiment of the present application.

[0020] Figure 2 is a schematic structural diagram of a feeder filled with silicon material according to another embodiment of the present application.

[0021] Figure 3 is a photo of a feeder filled with silicon material according to an embodiment of the present application.

[0022] Figure 4 is a photo of the molten silicon surface in the crucible after impurity removal in the furnace according to an embodiment of the present application. Detailed Description

[0023] Embodiments of the present invention will be described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0024] This application is made based on the inventor's discovery and recognition of the following facts and problems: In the photovoltaic industry, it is inevitable to produce broken silicon wafers during the production process of slicing and batteries. Especially for the broken silicon wafers generated at the battery end, if the broken silicon wafers can be reasonably recycled, the cost can be reduced and the economic benefits can be improved. Currently, the broken silicon wafers can be put into a single crystal furnace for recycling as raw materials for pulling single crystal silicon. However, due to the relatively thin thickness of the broken silicon wafers, during the process of adding them into the crucible of the single crystal furnace, because the temperature in the single crystal furnace is relatively high, the broken silicon wafers are more likely to be softened by heat, and thus stick to the inner wall of the feeder, causing material jamming and affecting the feeding efficiency. Based on this, the inventor of this application has found that by using a quartz feeder for feeding operations in the form of a "sandwich" stack, the problem of material jamming caused by the softening of silicon fragments during the feeding process can be effectively improved.

[0025] In view of this, a first aspect of this application provides a feeding method for recycling broken silicon wafers. According to the embodiments of this application, the feeding method for recycling broken silicon wafers includes: heating a single crystal furnace by using heaters, the heaters including a first heater and a second heater, the first heater being located on the inner side wall of the single crystal furnace, the second heater being located at the bottom of the single crystal furnace, the power of the first heater being set to be less than or equal to 80 kw, and the power of the second heater being set to be less than or equal to 60 kw; adding silicon materials into the crucible in the single crystal furnace through a cylindrical feeder, wherein, with reference to Figure 1 , the silicon materials in the cylindrical feeder include: a top layer of massive silicon materials 30, a bottom layer of massive silicon materials 10, and an intermediate layer of mixed silicon materials 20 sandwiched between the top layer of massive silicon materials 30 and the bottom layer of massive silicon materials 10, the intermediate layer of mixed silicon materials 20 including a layer of massive silicon materials 22 and a layer of broken silicon wafers 21; after all the silicon materials in the cylindrical feeder enter the crucible, setting the power of the first heater to be greater than or equal to 90 kw and setting the power of the second heater to be greater than or equal to 70 kw.

[0026] In this feeding method, in the form of a "sandwich" laminate, that is, the intermediate layer of mixed silicon materials containing fragmented silicon wafers is clamped between the top-layer massive silicon materials and the bottom-layer massive silicon materials. On the one hand, the bottom-layer massive silicon materials can absorb a part of the heat and delay the softening of the fragmented silicon wafers; on the other hand, the top-layer massive silicon materials can push the intermediate layer of mixed silicon materials into the crucible, and during the process that the massive silicon material layers in the top-layer massive silicon materials and the intermediate layer of mixed silicon materials enter the crucible under the action of gravity, some fragmented silicon wafers adhered to the inner wall of the feeder can be brought into the crucible, so as to ensure that the fragmented silicon wafers are smoothly put into the crucible, which is more conducive to improving the recycling rate of the fragmented silicon wafers. It not only has no impact on the single-crystal silicon drawing process, but also can effectively reduce the raw material cost.

[0027] In addition, before feeding, heating the single-crystal furnace can increase the temperature inside the single-crystal furnace, avoid the crystallization damage of the quartz crucible caused by too rapid heat loss after feeding, and at the same time, make the power value of the first heater less than or equal to 80 kw and the power value of the second heater less than or equal to 60 kw, which can prevent the temperature inside the single-crystal furnace from being too high when the silicon materials are added to the crucible, causing the fragmented silicon wafers in the cylindrical feeder to soften and resulting in material jamming; and after all the silicon materials enter the crucible, then increasing the power values of the first heater and the second heater can prevent the problem of material jamming caused by the softening of the fragmented silicon wafers in the cylindrical feeder compared with increasing the power values before the silicon materials are added to the crucible.

[0028] At the same time, the feeding method of the present application does not require pre-mixing the fragmented silicon wafers and the massive silicon materials. And when the single-crystal silicon drawing process has problems and traces back to the silicon material raw materials, the massive silicon materials and the fragmented silicon wafers can be directly processed correspondingly without separating the fragmented silicon wafers and the massive silicon materials again, and the operation is simpler.

[0029] In this article, the fragmented silicon wafers refer to the fragmented silicon wafers generated during the production and processing processes (such as slicing, etc.) of silicon wafers and batteries. The thickness of the fragmented silicon wafers is generally in the micron range, such as 100 microns to 500 microns, etc., and the radial dimension is generally from a few millimeters to dozens of millimeters. The massive silicon materials refer to the silicon raw materials with certain shapes and sizes after a series of purification and other process treatments. Usually, they are obtained from raw materials containing silicon elements (such as metallurgical-grade silicon, etc.) through processes such as refining. Their purity is relatively high, and they are the key starting materials for producing single-crystal silicon. The shapes of the massive silicon materials are diverse and can be irregular blocks. The size of the massive silicon materials is generally between 5 mm and 50 mm.

[0030] It can be understood that in this feeding method, the amount of silicon materials to be added can be selected according to the amount of remaining silicon materials in the crucible of the single-crystal furnace. If less silicon materials need to be added, only the silicon materials in one feeder can be added. If more silicon materials need to be added, that is, filling one feeder with silicon materials cannot meet the feeding requirement, then the silicon materials in multiple feeders can be added sequentially.

[0031] According to an embodiment of the present application, the number of cylinders of silicon material added into the crucible through the cylindrical feeder is n cylinders, where n is an integer from 2 to 6, and n can specifically be 2, 3, 4, 5, 6, etc. Thus, most usage scenarios can be satisfied, and the usage range is wider. Also, the specific addition amount of broken silicon wafers in the silicon material can be adjusted according to actual needs, as long as at least one feeder's silicon material contains broken silicon wafers.

[0032] According to an embodiment of the present application, the total mass of the broken silicon wafers contained in the n cylinders of silicon material accounts for 20% - 40% of the total mass of the n cylinders of silicon material (specifically such as 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc.). Within the above mass ratio range, broken silicon wafers can be effectively recycled, greatly reducing the raw material cost, and at the same time, it will not affect the pulling process of single crystal silicon.

[0033] According to an embodiment of the present application, in one cylinder of silicon material, the mass of the broken silicon wafers accounts for 0% - 60% of the total mass of the one cylinder of silicon material (specifically it can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.). Specifically, when n cylinders of silicon material need to be added, not every cylinder of silicon material needs to contain broken silicon wafers, that is, one cylinder of silicon material can be all blocky silicon material; when the feeder contains broken silicon wafers, the mass ratio of the broken silicon wafers in one cylinder of silicon material does not exceed 60% at most. Thus, broken silicon wafers can be effectively recycled, greatly reducing the raw material cost, and at the same time, it will not affect the pulling process of single crystal silicon.

[0034] According to an embodiment of the present application, there is no particular limitation on the specific operation method of sequentially adding n feeders of silicon material into the crucible of the single crystal furnace. As an example, the silicon material can be added to the feeder, and then the feeder is used to add it into the crucible of the single crystal furnace. Specifically, for example, the feeder filled with silicon material is placed above the crucible in the single crystal furnace through a lifting assembly, the discharge port of the feeder is opened, and the silicon material is output from the feeder under the action of gravity and put into the crucible. If multiple cylinders of silicon material need to be added, the above operation can be repeated to sequentially add multiple cylinders of silicon material.

[0035] According to an embodiment of the present application, referring to Figure 1 , the intermediate layer mixed silicon material 20 includes 2 - 4 broken silicon wafer layers 21 and 2 - 4 blocky silicon material layers 22, and the broken silicon wafer layers 21 and the blocky silicon material layers 22 are arranged alternately. Thus, by arranging the blocky silicon material layer and the broken silicon wafer layer alternately, the problem of softening and jamming of broken silicon wafers can be further improved, ensuring that the broken silicon wafers are smoothly put into the crucible, reducing the impact on the single crystal furnace and the growth of the single crystal silicon rod during the feeding of broken silicon wafers, and improving the utilization rate of broken silicon wafers.

[0036] According to an embodiment of the present application, referring toFigure 2 , among the 2 to 4 fragmented silicon wafer layers 21, it includes a first fragmented silicon wafer layer 212 and a second fragmented silicon wafer layer 211. The first fragmented silicon wafer layer 212 is closer to the bottom massive silicon material 10 than the second fragmented silicon wafer layer 211. Among them, the mass of the first fragmented silicon wafer layer 212 is greater than the mass of the second fragmented silicon wafer layer 211; when feeding materials, the bottom massive silicon material 10 enters the crucible earlier than the top massive silicon material 30. Thus, when adding materials, the first fragmented silicon wafer layer preferentially enters the crucible under the action of gravity, with a fast feeding speed, and the situation where the fragmented silicon wafers are heated and softened can be further improved, thereby effectively improving the problem of material jamming.

[0037] According to the embodiments of the present application, the mass ratio of the massive silicon material layer to the fragmented silicon wafer layer is 1 to 3:1, specifically it can be 1:1, 2:1, 3:1, etc. As an example, the mass ratio of the massive silicon material layer to the fragmented silicon wafer layer can be 2:1. Within the above ratio range, the massive silicon material layer and the fragmented silicon wafers can cooperate better to improve the problem of softening and jamming of the fragmented silicon wafers. If the ratio of the two is too high, the feeding amount of the fragmented silicon wafers is small, which is not conducive to the recycling of the fragmented silicon wafers. If the ratio of the two is too low, the improvement effect on the problem of softening and jamming of the fragmented silicon wafers is relatively not obvious.

[0038] According to the embodiments of the present application, the mass of the top massive silicon material is greater than or equal to 20 kg, specifically it can be 20 kg, 25 kg, 30 kg, 35 kg, 40 kg, 45 kg, 50 kg, 55 kg, 60 kg, etc. Thus, within the above mass range of the top massive silicon material, a greater gravitational force can be given to the intermediate layer of mixed silicon material, and then the intermediate layer of mixed silicon material can enter the crucible faster, thereby more effectively improving the problem of softening and jamming of the fragmented silicon wafers.

[0039] According to the embodiments of the present application, the mass of the bottom massive silicon material is greater than or equal to 20 kg, specifically it can be 20 kg, 25 kg, 30 kg, 35 kg, 40 kg, 45 kg, 50 kg, 55 kg, 60 kg, etc. Thus, the bottom massive silicon material can better isolate the radiation of the heat in the single crystal furnace to the fragmented silicon wafer layer, thereby better improving the problem of softening and jamming of the fragmented silicon wafers.

[0040] According to the embodiments of the present application, the capacity of the feeder is 120 kg to 130 kg, specifically it can be 120 kg, 121 kg, 122 kg, 123 kg, 124 kg, 125 kg, 126 kg, 127 kg, 128 kg, 129 kg, 130 kg, etc.

[0041] In some embodiments, the capacity of the feeder can be 120 kg to 130 kg, and the mass of the top layer of massive silicon materials, the bottom layer of massive silicon materials, the layer of massive silicon materials, and the layer of broken silicon wafers are each independently 10 kg to 30 kg. As an example, the capacity of the feeder can be 120 kg to 130 kg, the mass of the top layer of massive silicon materials, the bottom layer of massive silicon materials, and the layer of broken silicon wafers are all 20 kg, and the mass of the layer of massive silicon materials is 10 kg. Thus, the effect of improving the problem of softening and jamming of broken silicon wafers is better, and the utilization rate of broken silicon wafers is higher.

[0042] According to an embodiment of the present application, in order to avoid rapid heat loss in the crucible during the feeding process and avoid crystallization of the molten silicon in the crucible, which may damage the crucible, it can be controlled by controlling the feeding timing and adjusting the parameters of the single crystal furnace, so that the added silicon material melts quickly and avoid crystallization of the molten silicon.

[0043] According to an embodiment of the present application, when adding each cylinder of the silicon materials, the solid-liquid ratio in the crucible is 18% to 22% (specifically, such as 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, etc.). In other words, after only a little of the previous cylinder of silicon materials to be added remains unmelted, the next cylinder of silicon materials is added. Thus, on the one hand, it can prevent the molten silicon from crystallizing due to rapid heat loss in the crucible caused by adding silicon materials, and on the other hand, it can prevent sputtering of the molten silicon in the crucible during the feeding process.

[0044] In this article, the solid-liquid ratio in the crucible refers to the ratio of the area of solid silicon materials to the total area of the molten silicon liquid surface in the crucible. The proportion of the molten liquid in the furnace refers to the ratio of the area of the liquid (i.e., the area where there is no unmelted solid material) to the total area of the molten silicon liquid surface in the crucible. Specifically, it can be obtained by taking a photo of the molten silicon liquid surface and then measuring and calculating through the photo.

[0045] According to an embodiment of the present application, in the order of addition from front to back, the n cylinders of silicon materials are defined as the first cylinder of silicon materials, the second cylinder of silicon materials,..., the nth cylinder of silicon materials; after adding the (i - 1)th cylinder of silicon materials, when the solid-liquid ratio in the crucible is 25% to 35% (specifically, such as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc.), the power of the first heater is set to be less than or equal to 80 kw, and the power of the second heater is set to be less than or equal to 60 kw; when the solid-liquid ratio in the crucible is 18% to 22%, the ith cylinder of silicon materials is added, and after the ith cylinder of silicon materials completely enters the crucible, the power of the first heater is set to be greater than or equal to 90 kw, and the power of the second heater is set to be greater than or equal to 70 kw, where i is an integer from 2 to n. Thus, it can further prevent the molten silicon from crystallizing due to rapid heat loss in the crucible caused by adding silicon materials.

[0046] According to an embodiment of the present application, after adding the n-cylinder silicon material, slag sticking treatment is further included. The slag sticking treatment includes: when the linear diameter of the unmelted solid material floating on the molten silicon surface in the crucible of the single crystal furnace is between 70 mm and 150 mm; inserting the seed crystal into the molten silicon surface, after the seed crystal adheres to the unmelted solid material, lifting the seed crystal repeatedly 3 to 5 times, and then lifting the seed crystal and the unmelted solid material out of the molten silicon surface and staying at a position 100 mm to 150 mm away from the molten silicon surface for 15 min to 20 min, and then taking out the seed crystal and the unmelted solid material. Thus, part of the unmelted solid material is retained, impurities can enrich towards the unmelted solid material and adhere to the unmelted solid material, and by repeatedly lifting the seed crystal, the unmelted solid material can be removed from the crucible after adhering to the seed crystal, thereby improving the purity of the molten silicon in the crucible and not affecting the single crystal silicon drawing process. And staying the seed crystal and the unmelted solid material for a certain time before taking them out can largely avoid the low-temperature explosion of the unmelted solid material caused by the rapid decrease in temperature.

[0047] According to an embodiment of the present application, the surface of the seed crystal is provided with fine crystals. Thus, the unmelted solid material is more likely to adhere to the fine crystals, which is more conducive to removing the unmelted solid material from the crucible. As an example, a used seed crystal can be adopted, which has more fine crystals on its surface, and the effect of adhering to the unmelted solid material is better, and adopting the used seed crystal is more conducive to cost reduction.

[0048] According to an embodiment of the present application, the lifting speed of the seed crystal is 250 mm / h to 350 mm / h, specifically such as 250 mm / h, 260 mm / h, 270 mm / h, 280 mm / h, 290 mm / h, 300 mm / h, 310 mm / h, 320 mm / h, 330 mm / h, 340 mm / h, 350 mm / h, etc. Within this range of lifting speed, it is further conducive to the adhesion of the seed crystal to the unmelted solid material and the removal of the unmelted solid material from the crucible. If the lifting speed is too fast, the unmelted solid material is likely to burst.

[0049] According to an embodiment of the present application, after taking out the seed crystal and the unmelted solid material, the feeding method further includes: adjusting the position of the crucible to 0 mm to -100 mm and the furnace pressure to 2 Torr to 4 Torr to make the molten silicon in the crucible of the single crystal furnace boil to remove impurities. Thus, the impurities inside the molten silicon can be fully volatilized (such as discharging impurities such as B and Ga), further improving the purity of the molten silicon; at the same time, within the above range of furnace pressure, it is easier for the molten silicon to boil, and within the above range of crucible position, it can prevent the boiling molten silicon from splashing onto the heater and damaging the equipment.

[0050] According to the embodiment of the present application, after the crucible is subjected to slag sticking and boiling to remove impurities, there are no floating impurities visible to the naked eye on the surface of the molten silicon in the crucible (the surface of the molten silicon in the crucible is visible to the naked eye). Figure 4 ).

[0051] As a specific example, the following takes the addition of 6 barrels of silicon material as an example to describe the feeding method of the present application in detail, as follows: First, select a quartz feeder with no obvious pits on the inner wall or a brand new feeder to avoid the risk of increased resistance and jamming caused by the crushed silicon wafers squeezing out the material; To load the first barrel of silicon material, tilt the feeder, and lay 10kg~30kg of block silicon material on the bottom, then add 10kg~30kg of broken silicon wafers, straighten the feeder and rotate it to ensure that the silicon material is laid flat in the feeder, and then add 10kg~30kg of block silicon material, filling up 120kg / barrel in sequence, with block silicon material on the top. Refer to the photo of the feeder filled with silicon material. Figure 3 . Clean the silicon powder in the cylinder in time during the loading process to avoid it from being introduced into the furnace; Preparation of the furnace. The remaining silicon material in the furnace is 120kg~150kg. The furnace is preheated for 20min~40min with the main heater (i.e. the first heater) with a power of 80kw and the secondary heater (i.e. the second heater) with a power of 60kw to avoid excessive heat loss after adding materials, which may cause crystallization of molten silicon and damage the quartz crucible. Then, the feeding is started. After the feeder enters the furnace, the feeding operation begins. After all the silicon materials in the feeder enter the crucible, the heat shield is raised to the upper limit, the crucible position is 50mm, the main heater power is set to 100kw, the secondary heater power is set to 90kw, the crucible speed is set to 0rpm, the argon flow rate is set to 80slpm, and the furnace pressure is set to 8Torr. Two people operate and keep a close eye on the furnace and observe the unloading of broken silicon wafers during the unloading process, and adjust the crucible position in a timely manner. After the first tube of silicon material feeding operation is completed, the furnace pressure is set to 5Torr~6Torr, the crucible speed is set to 1rpm~2rpm, and the argon flow rate is set to 100~120slpm; when the solid-liquid ratio in the crucible is 30%, the power of the main heater is set to 80kw and the power of the secondary heater is set to 60kw. When the solid-liquid ratio in the crucible is 20%, prepare to feed again; The second tube of silicon material, the third tube of silicon material, ..., the sixth tube of silicon material can be added in the same manner as the first tube of silicon material; When all the feeding is completed and the molten silicon in the furnace accounts for 80%, the power of the main heater is set to 80 kw, the power of the secondary heater is set to 20 kw, and the position of the thermal shield is set to 100 mm, so that a small amount of unmelted solid material floats on the molten silicon surface, and the linear diameter of the unmelted solid material is controlled within 70 mm to 150 mm. Then, a used seed crystal with fine crystals on its surface is taken, cleaned and placed into the furnace. The fine crystal part slowly adheres to the unmelted solid material. After the fine crystal adheres to the unmelted solid material, the seed crystal is lifted at a speed of 300 mm / h. The manual operation handle is used to soak the adhesion part of the unmelted solid material and the fine crystal multiple times to ensure firm adhesion and that the slag block will not fall off. Moreover, the seed crystal is lifted up and down multiple times to adsorb visible impurities onto the surface of the unmelted solid material. Then, the seed crystal and the unmelted solid material are lifted out of the molten silicon surface and stay at a position 100 mm to 150 mm away from the molten silicon surface for 15 min to 20 min, and then the seed crystal and the unmelted solid material are taken out.

[0052] After the seed crystal and the unmelted solid material are taken out, the power of the main heater is set to 80 kw, the power of the secondary heater is set to 0 kw, the position of the crucible is set to -100 mm, the rotation speed of the crucible is set to 1 rpm, the argon flow rate is set to 70 slpm to 80 slpm, and the furnace pressure is set to 2 Torr to 4 Torr, so that the molten silicon in the furnace boils, and the molten silicon fluctuates violently to fully volatilize the impurities inside the molten silicon (such as discharging impurities such as B and Ga).

[0053] After the impurities are discharged from the furnace and there are no visible floating impurities on the liquid surface, ensuring that it does not affect the normal crystal pulling, shoulder forming and subsequent equal diameter processes, the single crystal silicon rod pulling can continue subsequently.

[0054] It can be understood that the feeding method for recycling broken silicon wafers in the present application can be applied to different feeding devices, such as automated feeding devices, recharged-Cz feeding devices, continuous feeding devices, intelligent feeding devices, external furnace feeding devices, etc. As an example, the feeding method for recycling broken silicon wafers in the present application is used for a recharged-Cz feeding device. After pulling a single silicon rod, this device keeps the crucible at a high temperature by reserving part of the silicon melt, and then silicon materials are added into the crucible to continue pulling the next silicon rod. This device saves the cooling time and the intake and exhaust time, and the quartz crucible can be reused.

[0055] In the second aspect of the present application, a method for preparing single crystal silicon is provided. According to the embodiments of the present application, the method includes: adding silicon materials into the crucible of a single crystal furnace by using the feeding method described above; performing single crystal silicon pulling. This method can effectively recycle broken silicon wafers, reduce the raw material cost, and the performance of the obtained single crystal silicon is better.

[0056] According to an embodiment of the present application, when pulling single-crystal silicon, if solid floating impurities appear on the molten silicon surface in the crucible of the single-crystal furnace, the single-crystal silicon being pulled is lifted and broken, and slag sticking treatment is carried out. After there are no solid floating impurities on the molten silicon surface, the pulling of single-crystal silicon is restarted. Thus, the quality of the prepared single-crystal silicon can be further improved.

[0057] According to an embodiment of the present application, after slag sticking and boiling for impurity removal are completed, single-crystal silicon rod pulling can be carried out. Specifically, there are no special restrictions on the specific steps and parameters of single-crystal silicon rod pulling, and conventional techniques can be referred to. As an example, the parameters of single-crystal silicon rod pulling can satisfy at least one of the following conditions: the crucible rotation speed is 4 rpm to 6 rpm, the furnace pressure is 4 Torr to 6 Torr, and the argon gas flow rate is 110 slpm to 130 slpm.

[0058] Embodiments of the present application are described in detail below.

[0059] Example 1 Select a quartz feeder with no obvious pits on the inner wall or a brand-new feeder to avoid the risk of increased resistance during feeding caused by the extrusion of broken silicon wafers, resulting in material jamming; Load the first cylinder of silicon material. Tilt the feeder, lay a bottom layer of 20 kg of block silicon at the bottom, then add 20 kg of broken silicon wafers, straighten the feeder and rotate to ensure that the block silicon is flattened in the feeder, and then add 10 kg of block silicon. Fill it up to 120 kg / cylinder in sequence, and the top layer is 20 kg of block silicon. Clean the silicon powder in the cylinder in time during the loading process to avoid introducing it into the furnace; Prepare the furnace platform. There is 130 kg of remaining silicon material in the furnace, and preheat the furnace for 20 min with the main heater power of 80 kw and the secondary heater power of 60 kw; After preheating, after the feeder enters the furnace, start the feeding operation. After all the silicon material in the feeder enters the crucible, lift the heat shield to the upper limit position, 50 mm from the crucible position, set the main heater power to 100 kw, set the secondary heater power to 90 kw, set the crucible rotation speed to 0 rpm, set the argon gas flow rate to 80 slpm, set the furnace pressure to 8 Torr, and have 2 people operate and closely monitor the furnace interior. Observe the feeding situation of the broken silicon wafers during the feeding process, record the feeding time as 1 minute and 40 seconds, and at the same time facilitate timely adjustment of the crucible position; Set the furnace pressure to 5 Torr, set the crucible rotation speed to 1 rpm, and set the argon gas flow rate to 110 slpm; when the solid-liquid ratio in the crucible is 30%, adjust the main heater power to 80 kw and the secondary heater power to 60 kw. When the solid-liquid ratio in the crucible is 20%, prepare for re-feeding; The second cylinder of silicon material, the third cylinder of silicon material,..., the sixth cylinder of silicon material can be fed according to the first cylinder of silicon material; When all the silicon materials in the 6th cylinder are completely fed and the proportion of the molten liquid in the furnace is 80%, the power of the main heater is set to 80 kw, the power of the secondary heater is set to 20 kw, and the position of the thermal shield is set to 100 mm, so that a small amount of unmelted solid materials float on the molten silicon surface, and the linear diameter of the unmelted solid materials is controlled within 70 mm to 150 mm. Then, a seed crystal used and with fine crystals on the surface is cleaned and placed into the furnace. The fine crystal part slowly adheres to the unmelted solid materials. After the fine crystal adheres to the unmelted solid materials, the seed crystal is lifted at a speed of 300 mm / h. The manual operation handle is used to immerse the adhesion part of the unmelted solid materials and the fine crystal multiple times to ensure firm adhesion and that the slag blocks will not fall off. And the seed crystal is lifted up and down multiple times to adsorb visible impurities onto the surface of the unmelted solid materials. Then, the seed crystal and the unmelted solid materials are lifted out of the molten silicon surface and stay at a position 120 mm away from the molten silicon surface for 15 min, and then the seed crystal and the unmelted solid materials are taken out.

[0060] After the seed crystal and the unmelted solid materials are taken out, the power of the main heater is set to 80 kw, the power of the secondary heater is set to 0 kw, the position of the crucible is set to -100 mm, the rotation speed of the crucible is set to 1 rpm, the argon flow rate is set to 75 slpm, and the furnace pressure is set to 3 Torr, so that the molten silicon in the furnace boils and the molten silicon fluctuates violently to fully volatilize the internal impurities of the molten silicon. Then, the single-crystal silicon pulling process is carried out.

[0061] Example 2 Same as Example 1, the difference is: the first cylinder of silicon materials is loaded. The feeder is tilted, and 20 kg of massive silicon materials are laid at the bottom, and then 30 kg of broken silicon wafers are added. The feeder is righted and rotated to ensure that the massive silicon materials are flattened in the feeder. Then, 10 kg of massive silicon materials, 20 kg of broken silicon wafers, 10 kg of massive silicon materials and 10 kg of broken silicon wafers are added in sequence. The top layer is 20 kg of massive silicon materials, and each cylinder is filled with 120 kg. The feeding time is 1 minute and 20 seconds.

[0062] Comparative Example 1 Same as Example 1, the specific difference is: the massive silicon materials and the broken silicon wafers are mixed evenly and then added to the feeding cylinder. The feeding time is 2 minutes.

[0063] From the above examples and comparative examples, it can be seen that by using the feeding method of the sandwich stack of the present application, the feeding speed is faster, indicating that the broken silicon wafers are less likely to soften and jam the material. At the same time, compared with the method of mixing the massive silicon materials and the broken silicon wafers evenly and then feeding, the feeding method of the present application does not require pre-mixing the broken silicon wafers and the massive silicon materials. And when problems occur in the single-crystal silicon pulling process and trace back to the silicon material raw materials, the massive silicon materials and the broken silicon wafers can be directly processed accordingly without separating the broken silicon wafers and the massive silicon materials again, and the operation is simpler.

[0064] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0065] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0066] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A feeding method for recycling broken silicon wafers, characterized in that, Including: Using a heater to heat a single crystal furnace, the heater includes a first heater and a second heater. The first heater is located on the inner side wall of the single crystal furnace, and the second heater is located at the bottom of the single crystal furnace. The power of the first heater is set to be less than or equal to 80 kw, and the power of the second heater is set to be less than or equal to 60 kw; Adding silicon materials into a crucible in the single crystal furnace through a cylindrical feeder. The silicon materials in the cylindrical feeder include: top-layer massive silicon materials, bottom-layer massive silicon materials, and an intermediate-layer mixed silicon material sandwiched between the top-layer massive silicon materials and the bottom-layer massive silicon materials. The intermediate-layer mixed silicon material includes a massive silicon material layer and a broken silicon wafer layer; After all the silicon materials in the cylindrical feeder enter the crucible, set the power of the first heater to be greater than or equal to 90 kw and set the power of the second heater to be greater than or equal to 70 kw.

2. The feeding method for recycling broken silicon wafers according to claim 1, characterized in that, The number of cylinders of silicon materials added into the crucible through the cylindrical feeder is n cylinders, where: The total mass of the broken silicon wafers contained in n cylinders of silicon materials accounts for 20% - 40% of the total mass of n cylinders of silicon materials; in one cylinder of silicon materials, the mass of the broken silicon wafers accounts for 0% - 60% of the total mass of the one cylinder of silicon materials; n is an integer from 2 to 6.

3. The feeding method for recycling broken silicon wafers according to claim 2, characterized in that The intermediate-layer mixed silicon material includes 2 - 4 broken silicon wafer layers and 2 - 4 massive silicon material layers, and the broken silicon wafer layers and the massive silicon material layers are arranged alternately.

4. The feeding method for recycling broken silicon wafers according to claim 3, characterized in that, Among the 2 - 4 broken silicon wafer layers, there are a first broken silicon wafer layer and a second broken silicon wafer layer. The first broken silicon wafer layer is closer to the bottom-layer massive silicon material than the second broken silicon wafer layer. Among them, the mass of the first broken silicon wafer layer is greater than the mass of the second broken silicon wafer layer; when feeding materials, the bottom-layer massive silicon material enters the crucible earlier than the top-layer massive silicon material.

5. The feeding method for recycling broken silicon wafers according to claim 1, characterized in that, The mass ratio of the massive silicon material layer to the broken silicon wafer layer is 1 - 3:

1.

6. The feeding method for recycling broken silicon wafers according to claim 1, characterized in that, The mass of the top-layer massive silicon material is greater than or equal to 20 kg.

7. The feeding method for recycling broken silicon wafers according to claim 1, wherein, The mass of the bottom-layer massive silicon material is greater than or equal to 20 kg.

8. The feeding method for recycling broken silicon wafers according to claim 2, characterized in that, When adding each cylinder of silicon materials, the solid-liquid ratio in the crucible is 18% - 22%.

9. The feeding method for recycling broken silicon wafers according to claim 8, characterized in that, According to the addition order from front to back, define n cylinders of silicon materials as the 1st cylinder of silicon materials, the 2nd cylinder of silicon materials,..., the nth cylinder of silicon materials respectively; After adding the (i - 1)th cylinder of silicon materials, when the solid-liquid ratio in the crucible is 25% - 30%, set the power of the first heater to be less than or equal to 80 kw and set the power of the second heater to be less than or equal to 60 kw; when the solid-liquid ratio in the crucible is 18% - 22%, add the ith cylinder of silicon materials. After all the ith cylinder of silicon materials enters the crucible, set the power of the first heater to be greater than or equal to 90 kw and set the power of the second heater to be greater than or equal to 70 kw, where i is an integer from 2 to n.

10. The feeding method for recycling broken silicon wafers according to claim 2, characterized in that, After adding n cylinders of silicon materials, it also includes slag adhesion treatment, and the slag adhesion treatment includes: When the linear diameter of the unmolten solid materials floating on the molten silicon liquid surface in the crucible of the single crystal furnace is between 70 mm and 150 mm; Insert the seed crystal into the molten silicon surface. After the seed crystal adheres to the unmelted solid material, lift the seed crystal repeatedly 3 to 5 times, and then lift the seed crystal and the unmelted solid material out of the molten silicon surface and stay at a position 100 mm to 150 mm away from the molten silicon surface for 15 min to 20 min, and then take out the seed crystal and the unmelted solid material.

11. The feeding method for recycling broken silicon wafers according to claim 10, characterized in that, The seed crystal has fine crystals.

12. The feeding method for recycling broken silicon wafers according to claim 10, wherein The pulling speed of the seed crystal is 250 mm / h to 350 mm / h.

13. The feeding method for recycling broken silicon wafers according to claim 10, characterized in that, After taking out the seed crystal and the unmelted solid material, it further includes: Adjust the position of the crucible to 0 mm to -100 mm and the furnace pressure to 2 Torr to 4 Torr to make the molten silicon in the crucible of the single crystal furnace boil to remove impurities.

14. A method for preparing monocrystalline silicon, characterized in that, It includes: Adding silicon material into the crucible of the single crystal furnace by using the feeding method according to any one of claims 1 to 13; Carrying out single crystal silicon drawing.

15. The method according to claim 14, wherein When carrying out single crystal silicon drawing, if there are solid floating impurities on the molten silicon surface in the crucible of the single crystal furnace, break the single crystal silicon being drawn and carry out slag sticking treatment. After there are no solid floating impurities on the molten silicon surface, restart single crystal silicon drawing.

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