CN101787563B - Method and device for removing impurities phosphorus and boron in polysilicon by induction and electron beam melting - Google Patents

Abstract

The invention relates to a method and a device for removing impurity phosphorus and boron in polycrystalline silicon by induction and electron beam melting, wherein the method comprises the following steps: removing impurity phosphorus in silicon by using an electron beam melting mode to obtain low-phosphorus polycrystalline silicon, melting the low-phosphorus polycrystalline silicon by using an induction coil, and removing impurity boron in the polycrystalline silicon by using an evaporation mode to obtain the low-phosphorus low-boron polycrystalline silicon. The method removes impurities of phosphorus and boron in the polycrystalline silicon by using electron beams and an induction heating mode, has large yield, realizes continuous smelting, has good phosphorus and boron impurity removing effect and high removing efficiency, effectively applies the characteristic of high heating temperature of an induction coil, is simple and easy to operate, integrates the double effects of removing phosphorus and boron, has stable purification effect, and is suitable for large-scale industrial production.

Description

Method and device for removing impurities phosphorus and boron in polysilicon by induction and electron beam melting

technical field

The invention relates to the technical field of purifying polysilicon by physical metallurgy technology, in particular to a method and device for removing impurity boron and phosphorus in polysilicon by using induction heating and electron beam smelting technology.

Background technique

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

(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) 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. .

(3) Silane method: It is a process of producing silane (SiH4) with fluorosilicic acid (H2SiF6), sodium, aluminum, and hydrogen as the main raw materials, and then producing polysilicon by 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.

(4) Fluidized bed method: a process for producing polysilicon with SiCl4 (or SiF4) 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.

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.

Existing metallurgical methods to remove impurity boron in polysilicon mainly include plasma beam, hydrometallurgy and slagging methods, and their commonality is that the impurity boron in silicon is converted into other substances or removed in other forms. Among them, boron removal by plasma beam is to make boron in silicon react with oxygen ions to form boron oxide. Since boron oxide has a high vapor pressure, it escapes from the surface of molten silicon in gaseous form to remove boron; hydrometallurgy uses pickling The method is to convert boron into other compounds, which can be dissolved in water to achieve the effect of removal; the slagging method is to add a slag-forming agent, which has a strong binding ability with boron in silicon, forming an insoluble silicon The substance of the melt floats above the silicon liquid to achieve the purpose of removing boron.

On the other hand, applying induction heating in metallurgical smelting to melt materials is a common method in this field, such as the invention patent with application number 200810011631.8, which uses induction heating and electron beams to utilize the relatively high vapor pressure of impurity phosphorus in polysilicon Large, so that impurity phosphorus forms steam and escapes from the silicon surface to achieve the purpose of removal, and the remaining silicon substrate achieves the effect of purification; but this patent cannot use induction heating to remove boron.

Furthermore, the technologies for removing phosphorus and boron in the existing metallurgical methods are two independent technologies that are not related to each other. There are mainly electron beam smelting and vacuum induction smelting for phosphorus removal, among which the best effect is the electron beam smelting technology. Boron removal methods include plasma beam smelting, slagging and pickling, among which plasma beam technology is the best.

However, since the removal of phosphorus and boron are two independent links, taking electron beam and plasma beam as examples, both need to melt and smelt silicon separately to obtain the target product, which not only overlaps the process, increases the cost, but also causes a lot of problems Heat is lost and wasted, and the cost of the other two types of equipment is relatively high, which increases the cost of equipment use and increases the difficulty of technology promotion.

Contents of the invention

In view of the existing problems in the prior art, the present invention aims to disclose a method and device for removing impurity phosphorus and boron in polysilicon by induction and electron beam melting, that is, using electron beam melting technology to reduce the content of impurity element phosphorus in polysilicon to less than 0.00008%; and then apply induction heating melting technology to reduce the content of boron, an impurity element in polysilicon, to less than 0.00003%, and then meet the requirements for the use of silicon materials for solar cells.

Technical solution of the present invention is realized like this:

A method for removing impurities phosphorus and boron from polysilicon by induction and electron beam melting, comprising:

The step of removing impurity phosphorus in silicon by electron beam smelting to obtain low-phosphorus polysilicon, and then melting the low-phosphorus polysilicon with an induction coil, and removing boron as an impurity in polysilicon by evaporation to obtain low-phosphorus and low-boron polysilicon; Specific steps are as follows:

1) In a high vacuum atmosphere, add polysilicon material into a water-cooled crucible, use electron beam melting to remove phosphorus and continuously obtain liquid low-phosphorus polysilicon;

2) Still in the high vacuum atmosphere, the liquid low-phosphorus polysilicon flows into the crucible surrounded by an induction coil, and the induction coil is used to evaporate and deposit the liquid low-phosphorus polysilicon to obtain low-boron and low-phosphorus polysilicon;

3) Finally, low-boron and low-phosphorus polysilicon is collected;

The phosphorus content of the low-boron and low-phosphorus polysilicon is not more than 0.00008%, and the boron content is not more than 0.00003%.

The high vacuum atmosphere is that the degree of vacuum is below 0.001Pa;

The beam current of the electron beam melting is 500-1000mA;

During the evaporation and deposition of the liquid low-phosphorus polysilicon, the heating temperature of the induction coil reaches 1800° C. to 2000° C., and the deposition carrier rotates at a speed of 2-30 r/min.

A device used in the method for removing impurities phosphorus and boron in polysilicon by induction and electron beam smelting is a sealing device with a cover on one side, and the inside of the sealing device is a vacuum chamber, which is characterized in that:

There is an isolation plate in the vacuum chamber, which is perpendicular to the side cover, and is fixedly connected with the top plate and the bottom plate of the vacuum chamber, and divides the vacuum chamber into two independent chambers on the left and right;

An electron beam smelting device is installed in the left chamber, and an induction evaporation deposition device is installed in the right chamber, and the two are connected through the communication ports opened at corresponding positions on the isolation plate;

The electron beam smelting device includes a water-cooled copper crucible supported by a left water-cooled support rod, an electron gun, and a filling port, a vacuum pump and an air release valve arranged on the left side wall of the left chamber from top to bottom. The height of the water-cooled copper crucible is Corresponding to the communication port, the electron gun is installed on the top plate of the vacuum chamber, directly above the water-cooled crucible;

The induction evaporation deposition device includes a crucible supported by a right water-cooled support rod, a deposition plate, and a vacuum pump arranged on the top plate of the right chamber; an induction coil is set around the periphery of the crucible; the deposition plate corresponds to the front of the crucible above, and is inserted and hung on the top plate of the right chamber through the support rod fixedly connected with it and is threadedly connected with the top plate;

The right side of the water-cooled copper crucible in the left chamber extends into the right chamber through the communication port of the isolation plate, and is located above the crucible in the right chamber and borders it;

The crucible in the right chamber is made of high temperature resistant and conductive material.

The deposition plate is made of materials with low wettability with silicon, such as silicon, ceramics, or magnesium oxide, silicon carbide, and the like.

Compared with the prior art, the present invention has remarkable technical effect:

(1) The present invention adopts the mode of continuous smelting, removes impurity phosphorus with electron beam, and removes boron with larger segregation coefficient with induction smelting method with induction heating, effectively improves the purity of polysilicon, and reaches the level of solar-grade silicon. Requirements for use, its purification effect is good, the technology is stable, the process is simple, it can complete continuous smelting, the production efficiency is high, and it is suitable for mass production;

It integrates electron beam and induction melting technology and completes it continuously on one piece of equipment, so that silicon can achieve the purpose of co-removing phosphorus and boron after only one melting. The characteristics of liquid raw materials greatly improve the heat utilization rate and simplify the technical means.

其中P_B为硼的饱和蒸气压，

为硼在硅中的活度系数。由于硼的饱和蒸汽压很低，在高温下熔炼硅，硅蒸气中含有的硼只有原硅基体中硼含量的百分之一以下，收集蒸发的硅蒸气，达到去除硼的目的。基于此，本发明采用感应熔炼去除硅中硼提纯硅的方法，有效的去除硅中的杂质硼，达到太阳能级硅对硼的要求。如上所述，由于本发明中电子束熔炼与感应熔炼连续进行，感应熔炼步骤中的多晶硅原料为液态硅，从而可以很容易通过感应法制得硅蒸气，大大降低了能量消耗。(2) According to the Langmuir equation

where P _B is the saturated vapor pressure of boron,

is the activity coefficient of boron in silicon. Since the saturated vapor pressure of boron is very low, when silicon is smelted at high temperature, the boron contained in the silicon vapor is only less than one percent of the boron content in the original silicon matrix, and the evaporated silicon vapor is collected to achieve the purpose of removing boron. Based on this, the present invention adopts the method of removing boron in silicon and purifying silicon by induction melting, effectively removes impurity boron in silicon, and meets the boron requirement of solar-grade silicon. As mentioned above, since the electron beam smelting and induction smelting are carried out continuously in the present invention, the polysilicon raw material in the induction smelting step is liquid silicon, so that silicon vapor can be easily produced by induction, which greatly reduces energy consumption.

(3) In the present invention, the operation process of electron beam smelting to remove impurity phosphorus and induction smelting to remove impurity boron all has a gaseous form, and the independence of the atmosphere must be guaranteed; this equipment adopts two independent and mutually connected vacuum chambers. Form, the two chambers are connected through the communication port for the transmission of liquid silicon, and the vacuum systems in the left and right chambers are far away from the communication port, which ensures the independence of the atmosphere and enables the operation to be realized.

Description of drawings

Fig. 1 is the device schematic diagram of the embodiment of the present invention;

Fig. 2 is a view from direction A in Fig. 1 . In the figure,

1. Right mechanical pump, 2. Vacuum drum, 3. Isolation plate, 4. Support rod, 5. Deposition plate, 6. Low boron and low phosphorus polysilicon, 7. Electron gun, 8. Water-cooled copper crucible, 9 Induction coil, 10 .Crucible, 11. Right water-cooled support rod, 12. Low-phosphorus polysilicon, 13. Square connection port, 14. Vacuum cover, 15. Left water-cooled support rod, 16. Vent valve, 17. Left mechanical pump, 18. Left screw Heresys pump, 19. Left diffusion pump, 20. Polysilicon material, 21. Filling port, 22. Right Rhodes pump, 23. Right diffusion pump, 24. Vacuum chamber right chamber, 25. Vacuum chamber left chamber.

Detailed ways

The present invention will be described in detail below in conjunction with accompanying drawing:

First, the polysilicon material 20 containing 0.0005% boron and 0.0007% phosphorus is put into the water-cooled copper crucible 8, the loading amount of the polysilicon material 20 is one-third of the water-cooled copper crucible 8, and the vacuum cover 14 is closed;

Carry out vacuuming: use the left mechanical pump 17, the left Rhodes pump 18, the right mechanical pump 1, and the right Rhodes pump 22 to pump the left and right vacuum chambers 25, 24 to a low vacuum of 1 Pa, and then use the left diffusion pump 19 at the same time and the right diffusion pump 23 pump the left and right vacuum chambers 25, 24 to below the high vacuum of 0.001Pa; It is partially formed; the plane where the isolation plate 3 is located is perpendicular to the vacuum cover 14, the left chamber 25 of the vacuum chamber is an electron beam melting reaction chamber, and the right chamber 24 of the vacuum chamber is an induction melting reaction chamber; the left chamber The right side of the water-cooled copper crucible 8 in the chamber 25 is inserted into the right chamber 24 through the square communication port 13 at the same height on the isolation plate 3, and is positioned above the crucible 10 in the right chamber and overlaps with it;

In the left chamber of the vacuum chamber, cooling water is passed into the water-cooled copper crucible 8 through the left water-cooled support rod 15, so that the temperature of the water-cooled copper crucible is maintained below 50°; After heating for 5-10 minutes, turn off the high voltage; set the beam current of electron gun 7 to 70-200mA, and after the beam is preheated for 5-10 minutes, turn off the beam current of electron gun 7; Bombard the polysilicon material 20 of the water-cooled copper crucible 8, increase the beam flow of the electron gun 7 to 500-1000mA, and continue the bombardment to melt the polysilicon material into low-phosphorus polysilicon 12; continuously drop the polysilicon material 20 into the water-cooled copper crucible 8 through the filling port 21, The low-phosphorus polysilicon 12 overflows and flows into the crucible 10; the periphery of the crucible 10 is covered with an induction coil 9, and a power of 10-25 kW is set to energize the induction coil 9 to keep the low-phosphorus polysilicon 12 flowing into the crucible 10 in a liquid state; When the content of the polysilicon 12 reaches one-third of the crucible 10, increase the power of the induction coil 9 so that the temperature of the low-phosphorus polysilicon 12 reaches 1800°C-2000°C, and the low-phosphorus polysilicon 12 evaporates;

Rotate the support rod 4 of the rising deposition plate 5, so that the deposition plate 5 rotates at a speed of 2-30 revolutions per minute, and deposit and evaporate low-boron and low-phosphorus polysilicon 6 to the deposition plate 5;

Continuously replenish the polysilicon material 20 into the water-cooled copper crucible 8 through the filling port 21 to ensure the continuation of the reaction;

After the deposition is over, first turn off the electron gun 7, stop energizing the induction coil 9 after 5 minutes, and continue vacuuming for 10-20 minutes; then turn off the left diffusion pump 19 and the right diffusion pump 23 in turn, continue vacuuming for 5-10 minutes, and then Further close the left Rhodes pump 18 and the right Rhodes pump 22, the left mechanical pump 17 and the right mechanical pump 1, open the air release valve 16, open the vacuum cover 14, and collect the low-boron and low-phosphorus polysilicon material 6 from the deposition plate 5.

As detected by ELAN DRC-II inductively coupled plasma mass spectrometer (ICP-MS), the content of boron and phosphorus in the low-boron and low-phosphorus polysilicon 6 is reduced to below 0.00003%, and the content of phosphorus is reduced to below 0.00003%. Requirements for the use of silicon materials.

The invention uses electron beam and induction heating to remove impurity phosphorus and boron in polysilicon, the output is large, continuous smelting is realized, the removal effect of phosphorus and boron impurities is good, the removal efficiency is high, and the characteristics of high heating temperature of induction coil are effectively used, The method is simple and easy, integrates the dual effects of phosphorus removal and boron removal, has a stable purification effect, and is suitable for large-scale industrial production.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (3)

1. the method for foreign matter of phosphor and boron in the polysilicon is removed in induction and electron beam melting, comprising:

Remove the step that foreign matter of phosphor in the silicon obtains low-phosphorous polysilicon with the electron beam melting mode, with ruhmkorff coil low-phosphorous polysilicon is carried out melting again, thereby remove the step that boron impurities in the polysilicon obtains low-phosphorous low boron polysilicon through the mode of evaporation; Its concrete steps are following:

1) under high vacuum atmosphere, in cold-crucible, adds polycrystalline silicon material, with dephosphorization of electron beam melting mode and the lasting low-phosphorous polysilicon that obtains liquid state;

2) then still in high vacuum atmosphere, making liquid low-phosphorous polysilicon flow into outer race has in the crucible of ruhmkorff coil, adopts ruhmkorff coil to make low-phosphorous polysilicon evaporation of said liquid state and deposition obtain the low low-phosphorous polysilicon of boron;

3) will hang down the low-phosphorous polysilicon of boron at last collects;

The phosphorus content of the low-phosphorous polysilicon of said low boron is not more than 0.00008%, and boron-containing quantity is not more than 0.00003%;

Wherein, said high vacuum atmosphere is that vacuum tightness is below 0.001Pa;

The line of said electron beam melting is 500-1000mA;

In the step (2), the Heating temperature of ruhmkorff coil reaches 1800 ℃-2000 ℃, and its deposition carrier is with the speed rotation of 2-30r/min.

2. the device of foreign matter of phosphor and boron in the polysilicon is removed in induction and electron beam melting, is side tightness system with cover, and the inside of said tightness system is Vakuumkammer, it is characterized in that:

In the said Vakuumkammer division board is arranged, perpendicular with said side cover, and be fixedly connected two separate chamber about Vakuumkammer is divided into the top board and the base plate of said Vakuumkammer;

The electron beam melting device is set in the said left chamber, the induction evaporation mode deposition apparatus is set in the right chamber, the connected entrance that both offer through corresponding position on the said division board links;

Said electron beam melting device comprises feeding port, vacuum pump and the purging valve that is reached the left side wall of being located at left chamber from top to bottom by the water jacketed copper crucible of left water-cooled they sup-port, electron beam gun; The height of said water jacketed copper crucible is corresponding with said connected entrance; Said electron beam gun is installed on the top board of Vakuumkammer, be positioned at said cold-crucible directly over;

Said induction evaporation mode deposition apparatus comprises by crucible, the deposition plate of right water-cooled they sup-port and is arranged at the vacuum pump on the top board of right chamber; The outer race of said crucible has ruhmkorff coil; Said deposition plate correspondence hang on crucible directly over, and insert on the top board that is hung on said right chamber and through the support bar that is fixedly connected with it and to be threaded with said top board;

The connected entrance that division board is passed on the right side of the water jacketed copper crucible of left chamber stretches into right chamber, is positioned at the top of right chamber crucible and has a common boundary with it;

Crucible in the said right chamber adopts material high temperature resistant and conduction.

3. the device of foreign matter of phosphor and boron in induction according to claim 2 and the electron beam melting removal polysilicon is characterized in that:

Said deposition plate adopts and the low material of silicon wettability.

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