WO2010118692A1

WO2010118692A1 - Method and device for metallurgical purification using liquid dross filter and method for purifying polysilicon

Info

Publication number: WO2010118692A1
Application number: PCT/CN2010/071794
Authority: WO
Inventors: 郑智雄; 张伟娜; 马殿军
Original assignee: 南安市三晶阳光电力有限公司
Priority date: 2009-04-17
Filing date: 2010-04-15
Publication date: 2010-10-21

Abstract

Disclosed are a method and a device for metallurgical purification using a liquid dross filter, the method comprises adding a given amount of metal or alloy with melting point lower than that of metal to be purified and density higher than that of metal to be purified during the directional solidification process for metallurgically purifying metals, wherein the metal or alloy with melting point lower than that of metal to be purified and density higher than that of metal to be purified forms a liquid dross filter during the cooling of ingots, a variety of impurities in the metal to be purified are filtered onto the surface of ingots along with the dross filter from bottom to top; the device comprises a vacuum oven body, a graphite crucible disposed within the oven body, a heat insulation cage disposed around the graphite crucible, a heater provided between the graphite crucible and the heat insulation cage, and a cooling system which aerates at fixed points and is located on the bottom. Also disclosed is a method for metallurgically purifying polysilicon using the liquid dross filter.

Description

Method and device for metallurgical purification by liquid filter and purification method of polysilicon

Technical field

The invention relates to a method and a device for metallurgical purification, in particular to a method and a device for metallurgical purification using a liquid filter and a method for purifying polycrystalline silicon.

Background technique

At present, there are various methods for metal purification in metallurgy. For example, in the refining of polycrystalline silicon, it is generally believed that the use of inexpensive industrial silicon to prepare solar grade polycrystalline silicon is one of the most effective ways to reduce costs. In order to reduce manufacturing costs, the use of low-purity silicon materials to manufacture solar cells has been a goal pursued. The preparation of polycrystalline silicon by physical method mainly refers to the preparation of high-purity polycrystalline silicon materials by means of metallurgical smelting using advanced smelting and manufacturing equipment. The melting methods mainly include vacuum melting method, plasma beam melting method, electron beam melting method, etc., and assist in directional solidification, Various refining processes and means such as regional remelting, surface slagging, atmosphere control, etc. to prepare high-purity polycrystalline silicon. The purity goal of manufacturing polycrystalline silicon by physical method is solar grade. It has the advantages of low investment, low energy consumption and no pollution to the environment to meet the needs of the rapid development of photovoltaic industry.

Since the advent of the theory of physical silicon purification of silicon materials, various methods have been discussed for the method of purifying silicon materials by physical methods, including Japanese electron beams, ion beam decontamination, high temperature smelting and impurity removal. Constantly reducing costs and improving purification quality have always been the goal of physical purification of silicon materials.

In the physical method, the combination of high-temperature smelting and directional solidification is the most significant, with less pollution and low cost, which is suitable for large-scale industrial production. However, the purity of polycrystalline silicon after directional solidification is generally 4-5N (99.99%-99.999%wt), which cannot meet the needs of the solar industry, mainly because the conventional purification device cannot accurately control the temperature in the interior of the crucible. The difference in temperature is large, making the grain size of the cast polycrystalline silicon unstable, and it cannot be used for purification of polycrystalline silicon by filtration.

Summary of the invention

One of the objects of the present invention is to overcome the deficiencies of the prior art and to provide a device for metallurgical purification using a liquid filter that can more accurately control the temperature throughout the crucible and the temperature difference between the crucibles is small.

It is still another object of the present invention to provide a method for metallurgical purification using a liquid screen that can obtain high purity metals.

It is still another object of the present invention to provide a method for purifying polycrystalline silicon using a liquid screen which can purify 4-5N silicon to the solar level.

Principle of filtration

The use of liquid screen metallurgy method, in the case of purified silicon, refers to the addition of a certain amount of low-melting alloying elements (In, Ga or Sn) during the directional solidification and purification of silicon to form a liquid filter, which is used as a silicon during cooling. The solid crystal is ingot, and various impurities (such as B, P, etc.) in the silicon are filtered from the bottom to the surface of the ingot with the screen. The principle utilized by the method is as follows: 1) the solubility of the impurity in the liquid filter is higher than the solid solubility in the solid silicon, so the impurities dissolved in the filter are moved to the liquid surface along the filter screen during the ingot process; 2) The filter material is made of high-density elements (such as Sn). The impurities that are insoluble in the filter cannot pass through the filter. During the ingot process, it floats on the liquid filter and finally solidifies on the surface of the ingot. (Sn density: 7.28) g/cm ³ ; Si density: 2.33 g/cm ³ ). With this method, 4-5N polysilicon can be effectively purified to more than 6N.

In the process of filter filtration, the thermal field stabilization is a guarantee for the slow migration of the liquid filter balance during the silicon cm ³ crystallization process.

The object of the invention is achieved by the following technical solutions:

A device for metallurgical purification by liquid filter is based on directional solidification and purification of polycrystalline silicon, changing the thermal field, and improving the process route with the movement of the filter, so that it is suitable for metallurgical purification by liquid filter, and is particularly suitable for filtering. Purification of polysilicon for the purpose of purifying 4-5N silicon to solar grade. The utility model comprises: a vacuum furnace body; a quartz crucible disposed in the furnace body; a graphite crucible disposed outside the quartz crucible to accommodate the quartz crucible; and an insulation cage disposed on the periphery of the graphite crucible;

It is characterized by:

A heater located between the graphite crucible and the insulated cage, and a fixed-point inflatable cooling system at the bottom of the vacuum furnace.

The aforementioned heater includes a side heater and a bottom heater.

The aforementioned side heaters and bottom heaters are respectively a plurality of thermocouples that distribute the sides or bottom of the graphite crucible.

The aforementioned fixed point air cooling system includes a plurality of gas tubes with their air outlets facing different regions of the graphite crucible.

The aforementioned quartz crucible is provided with temperature measuring elements for measuring the temperature of different regions of the crucible.

It also includes a control system for controlling the measuring components, the heater and the fixed point air cooling system to maintain the temperature balance of the metal in the vacuum furnace while cooling, and the liquid filter can rise steadily.

A further object of the invention is achieved by the following technical solutions:

A method for metallurgical purification by liquid screen, in which a certain amount of other metal or alloying elements are added as a filter material in a purified metal during directional solidification metallurgical purification, and the melting point of the other metal or alloy elements is lower than The metal is purified and has a density greater than the density of the metal being refined; the low melting point metal or alloy forms a liquid screen during the cooling of the ingot, and the various impurities in the purified metal are filtered from the bottom to the surface of the ingot with the screen.

The aforementioned ratio of purified metal to screen material is 70-85 wt: 15-30 wt.

A further object of the present invention is achieved by the following technical solutions:

A method for purifying polycrystalline silicon by using a liquid filter screen, the steps of which are:

Step 1: 4-5N polysilicon by weight of 70-85, filter material parts by weight of 15-30; placed in a quartz crucible;

Step 2: Vacuum the furnace, charge the inert gas, and stop the diffusion pump to maintain a slight positive pressure (1~1.5 atmospheres) in the furnace;

Step 3: Turn on the control power, the heater starts to heat until the mixture of silicon and filter material is completely melted, according to the ratio, the melting temperature is 1100 ° C -1400 ° C, and the heat preservation is at least 2 h;

Step 4: Turn on the temperature control, so that the silicon in the crucible is gradually cooled and crystallized at 0.2 ° C - 5 ° C / h; after cooling to 900 ° C, the temperature can be rapidly cooled, and the cooling rate is 10-20 ° C / h;

Step 5: After the silicon crystallization process is finished, the temperature is lowered, the silicon ingot is taken out, and the screen material and impurities on the upper surface and the surrounding area are removed.

The screen material used in the present invention must have a melting point lower than the melting point of silicon and a density greater than the density of silicon.

An alloy or a mixture of metals such as Ga or Sn or In metal or any combination of these three metals. Thus, after the filter material and the silicon mixture are dissolved, the filter material can be lowered to the bottom of the solution; as the temperature is lowered, after the silicon crystallizes, the filter material remains liquid, rises due to the continuous crystallization of silicon, and is filtered during the ascending process. Impurities.

As shown in FIG. 1-3, the filtering method of the silicon material of the present invention is to add a certain amount of low melting point alloying elements (In, Ga or Sn) during the direction solidification and purification of silicon, so that impurities form a sieve, and silicon acts as a cooling process. The solid crystal is ingot, and various impurities (such as B, P, etc.) in the silicon are filtered from the bottom to the surface of the ingot with the screen. The principle utilized by the method is as follows: 1) the solubility of the impurity in the liquid filter is higher than the solid solubility in the solid silicon, so the impurities dissolved in the filter are moved to the liquid surface along the filter screen during the ingot process; 2) The filter material is made of high-density elements. The impurities that are insoluble in the filter cannot pass through the filter. During the ingot process, it floats on the liquid filter and finally solidifies on the surface of the ingot. The Sn density is 7.28g/cm ^{3 .} ;Si density: 2.33 g/cm ³ ).

As can be seen from the above description of the present invention, the present invention provides a method for metallurgical purification using a liquid screen, which is particularly suitable for purifying polycrystalline silicon. The present invention uses a filter material to filter impurities in silicon, which can effectively reduce silicon. The content of impurities, especially the impurity content of B, can be reduced from the original 2-4 ppmwt to 0.5-1 ppmwt. 4-5N silicon can be purified to the solar grade. The apparatus of the present invention employs a control system to control the measurement elements, heaters, and fixed point aerated cooling systems to maintain temperature balance throughout the crucible during crystallization of the silicon. Thermal field stabilization is a guarantee for the slow migration of the liquid screen balance during the crystallization of silicon. Compared with the original polycrystalline silicon ingot technology, the invention effectively improves the uniform distribution of resistivity, and the grain size of the cast polycrystalline silicon is more stable.

DRAWINGS

Figure 1 is a schematic diagram of the principle of purifying silicon material by filtration method - high temperature melting state.

Figure 2 is a schematic diagram of the principle of purifying silicon material by filtration method - polycrystalline silicon growth stage.

Figure 3 is a schematic diagram of the principle of purification of silicon material by filtration - the stage of growth completion.

Figure 4 is a schematic view showing the structure of the apparatus of the present invention.

Figure 5 is a schematic block diagram of the apparatus of the present invention.

Among them: In Figure 1-3, A is liquid silicon, B is solid silicon, C is liquid filter, and D is liquid filter mixed with liquid silicon.

detailed description

Figure 1 to Figure 3 illustrate the principle of filtration using pure silicon as an example. As shown in Fig. 1, the polycrystalline silicon is melted at a high temperature; as shown in Fig. 2, the growth phase of the polycrystalline silicon, the Gibbs free energy of the polycrystalline silicon crystal is high, and the silicon crystallization crystallizes through the filter. The melting point of silicon is 1414 ° C, and the melting point of tin is 232 ° C. Tin will move slowly upward from the bottom with the crystalline silicon.

Figure 3 shows the growth completion stage: when the silicon ingot is completed, the liquid screen still appears in liquid form and above the ingot. Finally, it is cooled and solidified and cut off. Impurities that are less dense and insoluble in the screen cannot pass through the screen, and the impurities that dissolve in the screen above the screen are inside the screen. Therefore, the removed filter is no longer used.

An embodiment of the apparatus for metallurgical purification using a liquid screen, as shown in FIG. 4 and FIG. 5, comprises: a vacuum furnace body 10 having a quartz crucible 1 disposed in the furnace body; The graphite crucible 2 of the quartz crucible 1; the thermal insulation cage 4 disposed on the periphery of the graphite crucible, including a side heat insulating cage 41 and a bottom heat insulating cage 42; a heater 3 between the graphite crucible 2 and the heat insulating cage 4 A side heater 31 and a bottom heater 32 are included for heating the graphite crucible 2 from the side and the bottom, respectively, thereby heating the material in the quartz crucible 1. The side heater 31 and the bottom heater 32 are respectively composed of a plurality of thermoelectric wires 33 distributed in different regions of the side surface and the bottom surface.

The bottom of the vacuum furnace body 10 is provided with a stainless steel shield 6 and a fixed point inflation cooling system 5 is disposed. The system includes a ventilation main pipe 51. The ventilation main pipe 51 is connected to a plurality of ventilation pipes 52, and the front ends of the plurality of inflation pipes 52 pass through the stainless steel. The guard plate 6 and the bottom plate of the heat insulating cage 4, the air outlets of the air tube 52 respectively face different regions of the graphite crucible 2. Ventilation ducts 52 of the air outlets of different zones are controlled by valves 53 respectively.

The measuring element 7 is mounted around the graphite crucible 2.

The control system 8 is used to connect and control the measuring element 7, the heater 3 and the fixed point air cooling system 5.

An embodiment of the method for metallurgical purification of a liquid screen using the present invention:

Example 1

Taking the purified polysilicon as an example, when the device of the present invention is used, the 4-5N polycrystalline silicon is placed in the quartz crucible 1 while the filter material Sn is placed, and after vacuum pumping to 10-3 Pa, the control power is turned on, and the heater starts to heat. Until the silicon and filter material mixture is completely melted. Fill with argon, stop the diffusion pump to maintain a slight positive pressure inside the furnace, and keep it for 2-3 hours. Then turn on the temperature control and let it cool down gradually. In order to ensure a stable temperature, the slower part of the temperature drop will be cooled by partial argon gas through each valve. The temperature difference around the bottom of the crucible is maintained at about 0.2-0.5 ° C by means of aeration cooling. After the crystallization process is completed, the ingot is taken out and the upper surface and the periphery are removed.

Example 2

The steps and methods are the same as those in Embodiment 1, except that the metal purified in the present embodiment is Ge, and the material as the mesh material is Ga.

Example 3

The steps and methods are the same as those in the first embodiment except that the metal purified in the present embodiment is Ge, and the filter material is In.

Example 3

The procedure and method are the same as those in Embodiment 1, except that the metal purified in the present embodiment is Ge, and the material as the screen material is Sn.

Embodiments of the method for purifying polycrystalline silicon using a liquid filter screen of the present invention:

Example 5

Put 400 kg of 4-5N polysilicon into the quartz crucible, and put 60 kg of Sn and Ga as the filter material, of which Sn 55kg, Ga 5kg, after vacuum pumping to 10-3Pa, argon gas is charged, the diffusion pump is stopped to maintain a slight positive pressure in the furnace, the control power is turned on, and the heater starts to heat until the 1380 °C silicon and filter material mixture is completely melted and kept for 2 hours. Then, the temperature control is turned on to gradually cool the material in the crucible, and the cooling rate is 0.2 ° C / h. During this process, silicon begins to crystallize and the filter material moves up slowly. The process needs to maintain the temperature balance inside the crucible. The temperature difference between the same horizontal plane in the crucible is kept at 0.2 °C-0.5 °C. The thermal field is stable. A guarantee of slow upward movement. After the temperature is cooled to 900 °C, the temperature can be quickly lowered, and the cooling rate is 10 °C / h. After the crystallization process is finished, it is cooled, the ingot is taken out, the upper surface and the periphery are cut off, and the ingot is sliced. Test results: the B content in 4-5N polysilicon was reduced from 2-4 ppmwt to 0.5-1 ppmwt, and the remaining impurities were also effectively reduced, and 4-5N polysilicon was purified to above 6N.

Example 6

Put 160kg of 4-5N polysilicon into the quartz crucible, and put 40kg of Sn and Ga as the filter material, of which Sn 39kg, Ga 1kg, vacuum pumped to 10-3Pa, filled with argon gas, stop the diffusion pump to maintain a slight positive pressure in the furnace, open the control power, the heater starts to heat until the 1400 °C silicon and filter material mixture is completely melted, kept for 3h. Then turn on the temperature control to gradually cool the material in the crucible, and the cooling rate is 1 °C / h. During this process, the silicon begins to crystallize and the filter material moves up slowly. The process needs to maintain the temperature balance inside the crucible. The temperature difference between the same horizontal plane in the crucible is kept at 0.2 °C-0.5 °C. The thermal field is stable. The guarantee that the net balance moves up slowly. After the temperature is cooled to 900 °C, the temperature can be quickly lowered, and the cooling rate is 15 °C / h. After the crystallization process is finished, cooling, the ingot is taken out, the upper surface and the surrounding area are cut off, and the ingot is sliced. The test result: the B content in the 4-5N polycrystalline silicon is reduced from the original 2-4 ppmwt to 0.5-1 ppmwt, and the remaining impurities are also effectively reduced. 4-5N polysilicon is purified to above 6N.

Example 7

Put 170kg of 4-5N polysilicon into the quartz crucible, and put 30kg of filter material, of which Sn 28kg, In2kg, after vacuum pumping to 10-3Pa, it is filled with helium gas, the diffusion pump is stopped to maintain the micro-positive pressure in the furnace, the control power is turned on, the heater starts to heat up, and the silicon and filter material mixture is completely melted at 1400 °C. 2.5h. Then the temperature control is turned on to gradually cool the material in the crucible, and the cooling rate is 5 ° C / h. During this process, the silicon begins to crystallize and the filter material moves up slowly. The process needs to maintain the temperature balance inside the crucible. The temperature difference between the same horizontal plane in the crucible is kept at 0.2 °C-0.5 °C. The thermal field is stable. The guarantee that the net balance moves up slowly. After the temperature is cooled to 900 °C, the temperature can be quickly lowered, and the cooling rate is 20 °C / h. After the crystallization process is finished, it is cooled, the ingot is taken out, and the upper surface and the surrounding area are cut off. The test result: the B content in the 4-5N polysilicon is reduced from the original 2-4 ppmwt to 0.5-1 ppmwt, and the remaining impurities are also effectively reduced, 4-5N. The polysilicon is purified to above 6N.

Example 8

Put 150 kg of 4-5N polysilicon into the quartz crucible and put 50kg of filter material, of which Sn 45kg, Ga 3kg, In2kg, after vacuum pumping to 10-3Pa, it is filled with helium gas, the diffusion pump is stopped to maintain the micro-positive pressure in the furnace, the control power is turned on, and the heater starts to heat until the silicon and filter material mixture is completely melted at 1400 °C. 2.5h. Then the temperature control is turned on to gradually cool the material in the crucible, and the cooling rate is 5 ° C / h. During this process, the silicon begins to crystallize and the filter material moves up slowly. The process needs to maintain the temperature balance inside the crucible. The temperature difference between the same horizontal plane in the crucible is kept at 0.2 °C-0.5 °C. The thermal field is stable. The guarantee that the net balance moves up slowly. After the temperature is cooled to 900 °C, the temperature can be quickly lowered, and the cooling rate is 18 °C / h. After the crystallization process is finished, it is cooled, the ingot is taken out, and the upper surface and the surrounding area are cut off. The test result: the B content in the 4-5N polysilicon is reduced from the original 2-4 ppmwt to 0.5-1 ppmwt, and the remaining impurities are also effectively reduced, 4-5N. The polysilicon is purified to above 6N.

The above is only a specific embodiment of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modification of the present invention by this concept should be an infringement of the scope of protection of the present invention.

Industrial applicability

The device of the invention has reasonable design and convenient use, and the process method of the invention can effectively improve the purification purity of polycrystalline silicon to above 6N, achieve solar energy level, and has good industrial applicability.

Claims

A device for metallurgical purification using a liquid filter, comprising: a vacuum furnace body (10); a graphite crucible (2) disposed in the furnace body; a quartz crucible (1) disposed in the graphite crucible (2), disposed in the graphite坩埚 (2) Peripheral insulation cage (4); characterized in that it also includes:

a heater (3) located between the graphite crucible (2) and the insulating cage (4), and

A fixed point air cooling system (5) located at the bottom of the vacuum furnace body (10).
A device for metallurgical purification using a liquid screen according to claim 1, wherein said heater (3) comprises a side heater (31) and a bottom heater (32).
A device for metallurgical purification using a liquid screen according to claim 2, wherein said side heater (31) and bottom heater (32) are respectively distributed on the side or bottom of the graphite crucible (2). Multiple thermocouples (33).
A device for metallurgical purification using a liquid screen according to claim 1, wherein said fixed point air cooling system (5) comprises a plurality of gas tubes (52), each of which (52) The ports are facing different areas of the graphite crucible (2).
A device for metallurgical purification using a liquid filter according to claim 1 or 4, characterized in that: the bottom of the vacuum furnace body (10) is provided with a stainless steel shield (6), and a fixed point air cooling system (5) The front end of the plurality of inflation tubes (52) passes through the stainless steel shield (6) and the heat insulation cage (4) bottom plate, and the air outlets of the inflation tube (52) respectively face different regions of the graphite crucible (2).
A device for metallurgical purification using a liquid screen according to claim 5, wherein said plurality of gas tubes (52) are provided with control control valves (53)
A device for metallurgical purification using a liquid screen according to claim 1, characterized in that the graphite crucible (2) is provided with a temperature measuring element (7).
A method for metallurgical purification using a liquid screen, characterized in that a directional solidification metallurgical purification metal is carried out in a device according to claim 1, during which a certain amount of other metal or alloying elements are added to the purified metal As a screen material, the screen material has a lower melting point than the purified metal and a density greater than the density of the refined metal.
A method for metallurgical purification using a liquid screen according to claim 8, wherein the purification method comprises the steps of: placing the purified metal into a quartz crucible, simultaneously inserting the filter material, and vacuuming. After 10-3Pa, the control power is turned on, the heater starts to heat until the silicon and filter material mixture is completely melted; the argon gas is charged, the diffusion pump is stopped to maintain the micro positive pressure in the furnace, and the temperature is kept for 2-3 hours; To ensure that the temperature is stable, the slower part of the temperature drop will be cooled by partial argon gas through each valve; the temperature difference at the bottom of the crucible is maintained at about 0.2-0.5 °C by means of aeration cooling; the crystallization process ends. After that, the ingot is taken out, and the upper surface and the periphery are cut off.
A method for metallurgical purification using a liquid screen according to claim 8 or 9, wherein the purified metal is polysilicon or Ge, and the filter material is Ga, or Sn, or In.
A method of metallurgical purification using a liquid screen according to claim 10, wherein said purified metal and screen material have a weight ratio of 70-85: 15-30.
A method for purifying polycrystalline silicon by using a liquid filter screen, the steps of which are:

Step 1: 4-5N polysilicon by weight of 70-85, filter material parts by weight of 15-30; placed in a quartz crucible

Step 2: Vacuum the furnace, fill with inert gas, stop the diffusion pump to maintain a slight positive pressure inside the furnace;

Step 3: Turn on the control power, the heater starts to heat until the mixture of silicon and filter material is completely melted, according to the ratio, the melting temperature is 1100 ° C -1400 ° C, and the heat preservation is at least 2 h;

Step 4: Turn on the temperature control, so that the silicon in the crucible is gradually cooled and crystallized at 0.2 ° C - 5 ° C / h; the temperature is cooled to 900 ° C and then rapidly cooled, the cooling rate is 10-20 ° C / h;

Step 5: After the silicon crystallization process is finished, the temperature is lowered, the silicon ingot is taken out, and the screen material and impurities on the upper surface and the surrounding area are removed.
A method of purifying polycrystalline silicon using a liquid filter according to claim 12, wherein said sieve material is a metal element or alloy or a mixture of metals having a melting point lower than a melting point of silicon and a density greater than a density of silicon.
A method of purifying polycrystalline silicon using a liquid filter according to claim 13, wherein said sieve material is Ga or Sn or In, or any combination alloy or metal mixture of the three metals.
A method for purifying polycrystalline silicon by using a liquid filter according to claim 12 or 13, wherein said sieve material has Sn>90% by weight and other elements <10% by weight.
A method for purifying polycrystalline silicon using a liquid filter according to claim 15, wherein the other elements in the sieve material are Ga or In or Ga-In alloy or Ga, In mixture.
A method for purifying polycrystalline silicon using a liquid filter according to claim 12, wherein the inert gas in step 3 is argon or helium.
A method for purifying polycrystalline silicon using a liquid filter according to claim 12, wherein the holding time in the step 3 is 2h-3h.
A method for purifying polycrystalline silicon by using a liquid filter according to claim 12, wherein during the cooling and crystallization of the silicon in step 4, the temperature difference between the same horizontal plane in the crucible is maintained at 0.2 ° C - 0.5 ° C.