CN102408112A - A method and equipment for purifying polysilicon by electron beam melting under a high-purity silicon substrate - Google Patents

Abstract

The invention belongs to the technical field of purifying polycrystalline silicon by using a physical metallurgy technology. A method for purifying polycrystalline silicon by electron beam melting under a high-purity silicon substrate comprises the first step of material preparation and pretreatment; the second step is to form a high-purity silicon substrate: then starting an electron beam to completely melt the high-purity silicon material at 200-500mA, slowly reducing the beam to zero, namely forming a high-purity polycrystalline silicon ingot in a water-cooled crucible, adjusting the electron beam to 150-300mA to melt the high-purity polycrystalline silicon ingot, and forming a layer of high-purity silicon substrate after 2-5 min; thirdly, smelting and purifying: and continuously and slowly dropping the high-phosphorus silicon material into the molten pool, increasing the beam current to 300-700mA, melting the high-phosphorus silicon material to form high-phosphorus silicon liquid, removing impurity phosphorus, flowing into the crucible from the flow guide port to obtain low-phosphorus silicon liquid, and solidifying to obtain the low-phosphorus polysilicon ingot. The method has the advantages of good purification effect, simple process, energy conservation, pollution reduction, suitability for batch production, simple equipment structure, unique concept, simple operation and low cost, and can realize continuous smelting.

Description

A method and equipment for purifying polysilicon by electron beam melting under a high-purity silicon substrate

technical field

The invention belongs to the technical field of purifying polysilicon by physical metallurgical technology, and particularly relates to a method for purifying polysilicon by electron beam smelting under the action of a high-purity silicon substrate and removing impurity phosphorus in polysilicon; in addition, the invention also relates to its equipment.

Background technique

Solar cells can convert solar energy into electrical energy. In today's shortage of conventional energy sources, solar energy has great application value. Solar grade polysilicon material is one of the important raw materials for making solar cells. At present, the preparation of polysilicon materials for solar cells has formed a large-scale production worldwide, and the main technical routes are as follows:

(1) Improved Siemens method: The Siemens method uses hydrochloric acid (or hydrogen, chlorine gas) and metallurgical grade industrial silicon as raw materials to perform hydrogen reduction from trichlorosilane. Now the relatively mature technology in foreign countries is the Siemens method, and it has already formed an industry. The law has been developed to the third generation and is now being improved to the fourth generation. The first-generation Siemens method is non-closed, that is, the by-products of the reaction are hydrogen and trichlorosilane, resulting in a great waste of resources. The widely used third-generation improved Siemens process has achieved complete closed-loop production, hydrogen, trichlorohydrosilane and hydrochloric acid are all recycled, and the scale is more than 1,000 tons per year. However, its comprehensive power consumption is as high as 170kw h/kg, and the production is intermittent, so it is impossible to form a continuous operation in the production of Si.

(2) Silane method: It is a process of preparing silane (SiH ₄ ) with fluosilicic acid (H ₂ SiF ₆ ), sodium, aluminum, and hydrogen as the main raw materials, and then producing polysilicon through thermal decomposition. This method is based on a chemical process, which consumes a lot of energy, and has no obvious advantages compared with the Siemens method.

(3) Fluidized bed method: It is a process for producing polysilicon with SiCl ₄ (or SiF ₄ ) and metallurgical grade silicon as raw materials. The granular polysilicon process is a typical one in the fluidized bed process route. But the technical route of the process is in the debugging stage.

(4) Metallurgical method: use directional solidification and other technological means to remove metal impurities; use plasma beam smelting to remove boron; use electron beam smelting to remove phosphorus and carbon, so as to obtain solar-grade polysilicon with low production costs. This method consumes less energy, and the energy consumption per unit output is less than half of the Siemens method. Now Japan, the United States, Norway and other countries are engaged in the research and development of metallurgical methods. Among them, Japan's JFE technology is the most mature and has been put into industrial production. .

Among the many methods for preparing silicon materials, only the improved Siemens method, silane method, and metallurgical method can be put into industrial production. However, the improved Siemens method and silane method require large equipment investment, high cost, serious pollution, and complicated processes, which are not conducive to the popular application of solar cells. In comparison, the metallurgical method has the characteristics of short production cycle, low pollution, and low cost. The focus of research and development in various countries. Electron beam smelting is one of the important methods for metallurgical purification of polysilicon. It can effectively reduce the impurity phosphorus in polysilicon. However, in the current process of electron beam smelting and purification of polysilicon, water-cooled crucibles are generally used directly for melting crucibles. Direct use of water-cooled crucibles not only causes serious energy losses , high energy consumption, high cost, and easy to cause contamination by foreign impurities, which reduces the purity of polysilicon.

Contents of the invention

The present invention overcomes the above disadvantages and provides a method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate. First, a layer of high-purity silicon substrate is formed inside a water-cooled crucible by electron beam smelting, and then Melting and purifying polysilicon, reducing energy consumption, avoiding crucible pollution, and effectively improving the purity of polysilicon. Another object of the present invention is to provide an equipment for purifying polysilicon by electron beam smelting under a high-purity silicon substrate, which has simple structure, convenient operation and good purification effect.

The technical solution adopted by the present invention to achieve the above object is: a method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate, and the specific process is:

The first step of material preparation and pretreatment: first fill the water-cooled crucible with high-purity silicon material, and after closing the furnace door, vacuum the vacuum chamber to below 0.002Pa;

The second step is to form a high-purity silicon substrate: then turn on the electron beam current of 200-500mA to completely melt the high-purity silicon material, slowly reduce the beam current to zero, that is, form a high-purity polycrystalline silicon ingot in a water-cooled crucible, and adjust the electron beam spot It is located in the center of the water-cooled crucible, and then the electron beam current is turned on at 150-300mA to melt the high-purity polysilicon ingot, and a layer of high-purity silicon substrate is formed after 2-5 minutes;

The third step of smelting and purification: finally turn on the feeding device, and the high-phosphorus silicon material will continuously and slowly fall into the molten pool. At this time, increase the beam current to 300-700mA, and at the same time adjust the position of the electron beam spot so that the right side is smelted in the molten pool , the left side is used to melt the high-phosphorus silicon material that has just fallen into the molten pool. After the high-phosphorus silicon material is melted, a high-phosphorus silicon liquid is formed. After the high-phosphorus silicon liquid is smelted, impurity phosphorus is removed, and then flows into In the crucible, a low-phosphorus silicon liquid is obtained, and after solidification, a low-phosphorus polysilicon ingot is obtained.

The first step of material preparation and pretreatment: use mechanical pumps, Roots pumps and diffusion pumps to evacuate the equipment respectively, and evacuate the vacuum chamber to a high vacuum below 0.002Pa; Add cooling water to keep the temperature at 30-45°C; preheat the electron gun, set the high voltage to 30-32kV, after the high voltage is stable for 5-10 minutes, turn off the high voltage, set the beam current of the electron gun to 100-200mA for preheating, preheat After 10-15 minutes of heat, turn off the electron gun beam.

The high phosphorus silicon material is a broken material or a powder material.

An equipment for purifying polysilicon by electron beam smelting under a high-purity silicon substrate. The equipment consists of a furnace door and a vacuum furnace wall to form a vacuum device. The inner cavity of the vacuum device is a vacuum chamber; The water-cooled crucible is fixedly installed on the water-cooled support rod, the high-purity silicon substrate is placed on the inner wall of the water-cooled crucible, the feeding device is installed on the left side of the top of the vacuum furnace wall, the electron gun is installed on the top of the vacuum furnace wall, and its lower end is facing the water-cooled crucible; water-cooled support The base is fixedly installed on the right side of the bottom of the vacuum furnace wall, the graphite block is fixedly installed on the water-cooled support base, the crucible is installed on the graphite block, and the water-cooled crucible guide port is aligned with the crucible.

A mechanical pump, a Roots pump, a diffusion pump and an air release valve are respectively installed on the wall of the vacuum furnace.

The invention first uses electron beam melting to form a high-purity polysilicon substrate, and then continuously melts high-phosphorus polysilicon material with a small beam under the action of the substrate to quickly remove impurity phosphorus in the polysilicon. The high-purity polysilicon substrate formed in this method isolates the smelted silicon melt from the water-cooled crucible, which has the effect of heat insulation, reduces the heat taken away by the water-cooled crucible, increases the temperature at the bottom of the melt, and accelerates the removal of impurities. The diffusion volatilization removal rate of phosphorus is high, and the high-purity silicon substrate reduces the pollution of impurities on the water-cooled crucible wall to the melting polysilicon, and improves the purity of polysilicon. The method has good purification effect, simple process, energy saving, external pollution reduction, and is suitable for mass production.

The equipment of the present invention has simple structure and unique concept, and the high-purity silicon substrate is obtained by smelting on a water-cooled crucible. The operation is simple, the cost is low, continuous smelting can be realized, the production efficiency is high, and it is suitable for large-scale industrial production.

Description of drawings

Accompanying drawing 1 is a kind of schematic diagram of the equipment structure of electron beam smelting purification polysilicon under high-purity silicon substrate.

In the figure, 1. Electron gun, 2. Diversion port, 3. Vent valve, 4. Diffusion pump, 5. Roots pump, 6. Mechanical pump, 7. Vacuum chamber, 8. Furnace door, 9. Crucible, 10 . Low-phosphorus silicon liquid, 11. Graphite block, 12. Water-cooled support base, 13. Vacuum furnace wall, 14. Water-cooled support rod, 15. Water-cooled crucible, 16. High-purity silicon substrate, 17. High-phosphorus silicon liquid, 18 . High phosphorus silicon material, 19. Feeding device.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments and drawings, but the present invention is not limited to specific embodiments.

Example 1

An equipment for purifying polycrystalline silicon by electron beam smelting under a high-purity silicon substrate. The equipment consists of a furnace door 8 and a vacuum furnace wall 13 to form a vacuum device. The inner cavity of the vacuum device is the vacuum chamber 7; the water-cooled support base 12 is fixedly installed on the vacuum furnace wall. On the right side of the bottom, the graphite block 11 is fixedly installed on the water-cooled support base, and the crucible 9 is installed on the graphite block; the water-cooled support rod 14 is fixedly installed on the left side of the bottom of the vacuum furnace wall, and the water-cooled crucible 15 is fixedly installed on the top of the water-cooled support rod 14 Above, the high-purity silicon substrate 16 is placed on the inner wall of the water-cooled crucible, the feeding device 19 is installed on the left side of the top of the vacuum furnace wall, the electron gun 1 is installed on the top of the vacuum furnace wall, and its lower end is facing the water-cooled crucible, mechanical pump 6, Roots pump 5 , Diffusion pump 4 and deflation valve 3 are installed on the vacuum furnace wall 2 respectively.

Example 2

The method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate using the equipment described in Example 1, the specific steps are as follows:

The first step of material preparation and pretreatment: first fill the water-cooled crucible 15 with high-purity silicon materials with a total impurity content of 3 ppmw, and after closing the furnace door 8, use the mechanical pump 6, Roots pump 5 and diffusion pump 4 to pump vacuum for the equipment respectively , the vacuum chamber 7 is evacuated to a high vacuum of 0.0018Pa; cooling water is introduced into the water-cooled support rod 14, the water-cooled copper crucible 15 and the water-cooled support base 12 to maintain the temperature at 40°C; preheat the electron gun 1, and set the high pressure to 30kV, after the high voltage is stable for 5 minutes, turn off the high voltage, set the electron gun 1 beam current to 200mA for preheating, and after 15 minutes of preheating, turn off the electron gun 1 beam current;

The second step is to form a high-purity silicon substrate: then turn on the beam current of the electron beam to 300mA to completely melt the high-purity silicon material, and then slowly reduce the beam current to zero, that is, form a high-purity polycrystalline silicon ingot in a water-cooled crucible, and adjust the beam spot of the electron beam so that It is located in the center of the water-cooled crucible, after which the electron beam current is turned on to 200mA to melt the high-purity polysilicon ingot, and a layer of high-purity silicon substrate 16 is formed after 5 minutes;

The third step of smelting and purification: finally turn on the feeding device, the phosphorus content is 17ppmw high-phosphorus silicon material 18 continuously and slowly falls into the molten pool, at this time increase the beam current to 400mA, and at the same time adjust the position of the electron beam spot so that the right side is in the molten pool Melting in the pool, the left side is used to melt the high-phosphorus silicon material 18 falling and just falling into the molten pool. After the high-phosphorus silicon material is melted, a high-phosphorus silicon liquid is formed. After the high-phosphorus silicon liquid is smelted, impurity phosphorus is removed, and thereafter from The diversion port flows into the crucible to obtain a low-phosphorus silicon liquid, and after solidification, a low-phosphorus polysilicon ingot is obtained.

According to ELAN DRC-II inductively coupled plasma mass spectrometer equipment (ICP-MS), its phosphorus content is lower than 0.4ppmw, which meets the requirements for the use of solar-grade silicon materials.

Example 3

The method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate using the equipment described in Example 1, the specific steps are as follows:

The first step of material preparation and pretreatment: first fill the water-cooled crucible 15 with high-purity silicon materials with a total impurity content of 2 ppmw, and after closing the furnace door 8, use the mechanical pump 6, Roots pump 5 and diffusion pump 4 to pump vacuum for the equipment respectively , pump the vacuum chamber 7 to a high vacuum of 0.0015 Pa; feed cooling water into the water-cooled support rod 14, the water-cooled copper crucible 15 and the water-cooled support base 12 to keep the temperature at 40°C; preheat the electron gun 1 and set the high pressure to 30kV, after the high voltage is stable for 5 minutes, turn off the high voltage, set the electron gun 1 beam current to 100mA for preheating, and after 15 minutes of preheating, turn off the electron gun 1 beam current;

The second step is to form a high-purity silicon substrate: then turn on the beam current of the electron beam to 400mA to completely melt the high-purity silicon material, and then slowly reduce the beam current to zero, that is, form a high-purity polycrystalline silicon ingot in a water-cooled crucible, and adjust the beam spot of the electron beam so that It is located at the center of the water-cooled crucible, after which the electron beam current is turned on to 300mA to melt the high-purity polysilicon ingot, and a layer of high-purity silicon substrate 16 is formed after 3 minutes;

The third step of smelting and purification: finally turn on the feeding device, and the high-phosphorus silicon material 18 with a phosphorus content of 15ppmw will continuously and slowly fall into the molten pool. Melting in the pool, the left side is used to melt the high-phosphorus silicon material 18 falling and just falling into the molten pool. After the high-phosphorus silicon material is melted, a high-phosphorus silicon liquid is formed. After the high-phosphorus silicon liquid is smelted, impurity phosphorus is removed, and thereafter from The diversion port flows into the crucible to obtain a low-phosphorus silicon liquid, and after solidification, a low-phosphorus polysilicon ingot is obtained.

According to ELAN DRC-II inductively coupled plasma mass spectrometer equipment (ICP-MS), its phosphorus content is lower than 0.3ppmw, which meets the requirements for the use of solar-grade silicon materials.

Claims (5)

1. A method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate, characterized in that: The first step of material preparation and pretreatment: first fill the water-cooled crucible with high-purity silicon material, and after closing the furnace door, vacuum the vacuum chamber to below 0.002Pa; The second step is to form a high-purity silicon substrate: then turn on the electron beam current of 200-500mA to completely melt the high-purity silicon material, slowly reduce the beam current to zero, that is, form a high-purity polycrystalline silicon ingot in a water-cooled crucible, and adjust the electron beam spot It is located in the center of the water-cooled crucible, and then the electron beam current is turned on at 150-300mA to melt the high-purity polysilicon ingot, and a layer of high-purity silicon substrate is formed after 2-5 minutes; The third step of smelting and purification: finally turn on the feeding device, and the high-phosphorus silicon material will continuously and slowly fall into the molten pool. At this time, increase the beam current to 300-700mA, and at the same time adjust the position of the electron beam spot so that the right side is smelted in the molten pool , the left side is used to melt the high-phosphorus silicon material that has just fallen into the molten pool. After the high-phosphorus silicon material is melted, a high-phosphorus silicon liquid is formed. After the high-phosphorus silicon liquid is smelted, impurity phosphorus is removed, and then flows into In the crucible, a low-phosphorus silicon liquid is obtained, and after solidification, a low-phosphorus polysilicon ingot is obtained. 2. The method for purifying polysilicon by electron beam smelting under a kind of high-purity silicon substrate according to claim 1 is characterized in that: the first step of material preparation and pretreatment: respectively adopt mechanical pump, roots pump and diffusion pump to The equipment is vacuumed, and the vacuum chamber is evacuated to a high vacuum below 0.002Pa; cooling water is passed into the water-cooled support rod, water-cooled crucible and water-cooled support base to maintain the temperature at 30-45 ° C; preheat the electron gun, set the high pressure to 30-32kV, after the high voltage is stable for 5-10 minutes, turn off the high voltage, set the beam current of the electron gun to 100-200mA for preheating, and turn off the beam current of the electron gun after preheating for 10-15 minutes. 3. A method for purifying polysilicon by electron beam smelting under a high-purity silicon substrate according to claim 1, wherein the high-phosphorus silicon material is a fragment material or a powder material. 4. An equipment for purifying polysilicon by electron beam smelting under a high-purity silicon substrate, which is characterized in that: the equipment consists of a furnace door (8) and a vacuum furnace wall (13) to form a vacuum device, and the inner cavity of the vacuum device is a vacuum chamber (7 ); the water-cooled support rod (14) is fixedly installed on the left side of the bottom of the vacuum furnace wall, the water-cooled crucible (15) is fixedly installed on the water-cooled support rod, the high-purity silicon substrate (16) is placed on the inner wall of the water-cooled crucible, and the feeding device (19 ) is installed on the left side of the top of the vacuum furnace wall, the electron gun (1) is installed on the top of the vacuum furnace wall, and its lower end is facing the water-cooled crucible; the water-cooling support base (12) is fixedly installed on the right side of the bottom of the vacuum furnace wall, and the graphite block (11) is fixed Installed on the water-cooled support base, the crucible (9) is installed on the graphite block; the guide port of the water-cooled crucible is aligned with the crucible. 5. According to claim 4, the equipment for purifying polysilicon by electron beam smelting under a high-purity silicon substrate is characterized in that: a mechanical pump (6), a Roots pump (5), Diffusion pump (4) and bleed valve (3).