CN103073000B - Method for removing boron through plasma auxiliary slagging - Google Patents

Method for removing boron through plasma auxiliary slagging Download PDF

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CN103073000B
CN103073000B CN201310046435.5A CN201310046435A CN103073000B CN 103073000 B CN103073000 B CN 103073000B CN 201310046435 A CN201310046435 A CN 201310046435A CN 103073000 B CN103073000 B CN 103073000B
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silicon
silicon liquid
boron
oxygen
slag
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CN103073000A (en
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杨凤炳
龚炳生
李伟生
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Fujian Shanghang Xingheng silicon products Co.,Ltd.
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FUJIAN XING ZHAOYANG SILICON MATERIALS Co Ltd
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Abstract

The invention relates to a method for removing boron through plasma auxiliary slagging. The method comprises the following steps of heating a silicon block in a medium-frequency induction furnace graphite crucible, and dissolving the silicon block into silicon liquid; adding a slagging agent into the silicon liquid, continuously heating the silicon liquid until the slagging agent is completely melted, and keeping the temperature of the silicon liquid, wherein the slagging agent consists of Na2CO3, K2CO3 and SiO2; preheating a graphite rod with a vent, after the graphite rod is fully preheated, inserting a ventilating rod into the silicon liquid, and introducing oxygen; meanwhile, starting a high-pressure plasma generator, ionizing the oxygen in an oxygen passage into oxygen ions at the room temperature, and filling the oxygen ions into the silicon liquid through the graphite rod; and filling the silicon liquid into a temperature-keeping furnace to be solidified, and after a silicon ingot is cooled, removing slag blocks on the surface of the silicon ingot. By the method, the slag amount can be effectively reduced, silicon loss caused when silicon is wrapped in slag is reduced, the cost for purifying polycrystalline silicon is reduced, the content of boron in refined low-boron polycrystalline silicon obtained after purification is relatively low, and the boron-removing effect is good.

Description

The method of the auxiliary slagging boron removal of a kind of plasma
Technical field
The present invention relates to a kind of polycrystalline silicon purifying technical field, particularly relate to the novel method of the auxiliary slagging boron removal of a kind of plasma.
Background technology
Energy dilemma and traditional energy have become the main restricting factor of society and the national economic development to the pollution of environment.For maintaining Sustainable development, all actively readjusting the energy structure in countries in the world, greatly develops renewable energy source, and polysilicon solar cell becomes the focus of global concern.The technique that employing improved Siemens is prepared high purity polycrystalline silicon is comparatively complicated, and cost of investment is high, and with it, preparing solar cell will increase battery price greatly.And metallurgy method purifying polycrystalline silicon technique is relatively simple, with low cost, and relatively little to polluting of environment, become the main development direction of solar-grade polysilicon.
Polycrystalline silicon purifying is mainly removed impurity element wherein, as Al, Fe, C, P, B etc., and the non-metallic elements such as P, B are difficult for removing, boron particularly, because the segregation coefficient of boron in silicon is 0.8, close to 1, and saturation steam forces down, and by traditional directional freeze or vacuum melting, removed and cannot be reached requirement.And the content of boron impurity has a great impact the performance of solar cell, require boron content not higher than 0.3ppm, therefore explore the study hotspot that various effective low-cost boron removal methods are polycrystalline silicon purifyings.Mainly by techniques such as air blowing, slag making, plasma body, directional freezes, remove the boron impurity in silicon at present.
Patent CN102452651A discloses the technique that a kind of wet oxygen plasma body is removed boron impurity in silicon, by radio-frequency (RF) plasma reactor, form oxygen containing wet oxygen plasma flame, silicon liquid surface is purged, although present method is feasible, can effectively reduce the content of boron from industrial silicon, but in industrial application, still there is following problem: first, the removal effect of boron is the difficult purity requirement that reaches solar-grade polysilicon still.Secondly, high-temperature plasma flame temperature is high, and silicon loss is large, and apparatus expensive, is not suitable for industrial scale operation.
US Patent No. 5788945 discloses a kind of method that helps slag agent by continuous adding in silicon liquid, and helping slag agent composition is 60%CaO and 40%SiO2, and boron drops to 1ppmw from 40ppmw.This method that helps slag agent that adds continuously, owing to wrapping up in slag, silicon is more, causes silicon loss large, and in slagging process, helps the consumption of slag agent relatively too high, causes cost to increase, and silicon also can produce certain metallic pollution simultaneously.
Patent CN102320610A discloses the refining of a kind of high frequency electromagnetically induced, repeatedly the polysilicon of slag making takes off boron method of purification in batches, slag former is that Na2CO3 and SiO2 mix according to weight ratio 1:1, adopt the refining of this high frequency electromagnetically induced, repeatedly the polysilicon of slag making takes off boron method of purification in batches, although can make the content of boron be reduced to below 0.1ppm, meet the high purity requirement of solar-grade polysilicon, but not fine owing to removing effect of boron in slagging process, slag former consumption is relatively too high, cause cost to increase, and more owing to wrapping up in silicon in slag, cause silicon loss large.
Summary of the invention
The object of the present invention is to provide the novel method that a kind of technique is simple, cost is low, the high pressure plasma of applicable Industry Promotion is assisted slagging boron removal, the method first adopts intermediate frequency furnace induction heating industrial silicon in plumbago crucible, then in silicon liquid, add slag former, fusing reaction, and adopt graphite rod to lead to oxygen stirring in silicon liquid; Open ion generator, partial oxidation is ionized into oxonium ion and is directly injected into and in silicon liquid, carries out refining.The mode combining by plasma and slag making, significantly reduces the content of boron in silicon, after cooling, removes the refining low boron polysilicon after silicon silicon ingot surface clinker can be purified.The inventive method has solved that slag former consumption is high, the problem of high-temperature plasma apparatus expensive, has reduced cost, is convenient to industrialization and uses.
In order to realize object of the present invention, the following technical scheme of special employing:
A method for the auxiliary slagging boron removal of high pressure plasma, comprises the following steps:
(1) silico briquette is packed in medium-frequency induction furnace plumbago crucible and heated, and be fused into silicon liquid;
(2) in silicon liquid, drop into slag former, continue heating slag former is melted completely, and keep silicon liquid temp; Described slag former is by Na 2cO 3, K 2cO 3with SiO 2form;
(3) by the graphite rod preheating with vent channel, after preheating fully, venting pin is inserted in silicon liquid, start logical oxygen;
(4) open high-pressure ion producer simultaneously, at room temperature the oxygen in oxygen channel be ionized into oxonium ion and pass through in graphite rod Implanted Silicon liquid;
(5) the silicon liquid obtaining in step (4) is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, the refining low boron polysilicon after being purified.
It is the boron in silicon to be become to lower boiling boron compound gas overflow that high-temperature plasma removes boron, and slagging boron removal is boron to be oxidized to boron oxide enter slag system and remove.The method of the auxiliary slagging boron removal of high pressure plasma provided by the invention, first adopting cryogenic high pressure plasma method that partial oxidation is ionized into oxonium ion is directly injected in silicon liquid, increased the concentration of oxonium ion in silicon liquid, can effectively reduce the quantity of slag, reduce the silicon loss causing because wrap up in silicon in slag, and the selected high pressure plasma generator apparatus of present method is simple, cost is low, easily use, the technological operation of employing is simple, selected Na 2cO 3～K 2cO 3～SiO 2the agent of two alkalimetal oxide slag, can effectively be oxidized to boron oxide boron and enter slag system, pollutes few.In addition, the method for the auxiliary slagging boron removal of high pressure plasma provided by the invention, in the refining low boron polysilicon after being purified, the content of boron, lower than 0.3ppmw, except effect of boron is good, is conducive to extensive Industry Promotion.
In described step (1), adopt intermediate frequency induction heating device by silico briquette heat fused, the temperature of silicon liquid is 1500～1800 ℃.
In described step (2), by mass percentage, Na 2cO 3be 25%～35%, K 2cO 3be 25%～35%, SiO 2be 30 ~ 50%.
The present invention is except the two alkalimetal oxide slag agent of boron employing Na2CO3～K2CO3～SiO2, when Na2CO3 is 25%～35%, K 2cO 3be 25%～35%, SiO 2while being 30 ~ 70%, the agent of two alkalimetal oxide slag is best by the effect of boron oxidation, can effectively remove the boron in industrial silicon, and few with respect to other boron removal method pollution, is conducive to extensive Industry Promotion.
Preferably, in described step (2), by mass percentage, Na 2cO 3be 30%～35%, K 2cO 3be 30%～35%, SiO 2be 30%～40%.
In described step (2), the mass ratio of described silico briquette and slag former is 1:0.6～1.
In the present invention, the consumption of slag former is relatively less, has greatly reduced the silicon loss of wrapping up in silicon in slag and causing, and reduced cost for purification, and in the polysilicon after purifying, the content of boron is very low, and refining effect is good.
Preferably, in described step (2), the mass ratio of described silico briquette and slag former is 1:0.8～1.0.
In the present invention, the mass ratio of silico briquette and slag former is 1:0.8～1.0 o'clock, can greatly reduce the boron content in purified silicon, removes effect of boron very good.
In described step (2), keep silicon liquid temp at 1500～1800 ℃.At this temperature, the negative oxygen ion injecting from graphite rod and oxygen can be to greatest extent and boron generation oxidizing reaction, except effect of boron best.
In described step (3), the flow of described oxygen is 5～12L/min, and the ventilatory response time is 25～35min.
In described step (4), the operating voltage of described high pressure plasma producer is 20～30KV, conduction time 1～3h.
Compared with prior art, beneficial effect of the present invention is:
(1) method of the auxiliary slagging boron removal purifying polycrystalline silicon of high pressure plasma provided by the invention, can effectively reduce the quantity of slag, reduces the silicon loss causing because wrap up in silicon in slag, reduces the cost of purifying polycrystalline silicon;
(2) selected Na 2cO 3～K 2cO 3～SiO 2the agent of two alkalimetal oxide slag, can effectively be oxidized to boron oxide boron and enter slag system, pollutes few;
(3) in the refining low boron polysilicon after purification, the content of boron is very low, removes effect of boron good;
(4) boron removal method of the present invention is simple, easy to operate, and selected high-pressure ion generator apparatus is simple, cost is low, is conducive to extensive Industry Promotion.
Accompanying drawing explanation
Fig. 1 is the device schematic diagram of the auxiliary slagging boron removal of high pressure plasma provided by the invention
Wherein: 1～high pressure plasma power supply; 2～oxygen cylinder; 3～high pressure plasma producer; 4～rubber hose; 5～steel pipe; 6～steel bushing; 7～ventilation graphite rod; 8～Medium frequency induction plumbago crucible; 9～coil.
Embodiment
Below in conjunction with embodiment, the present invention is described in more detail; but not thereby limiting the invention; do not departing under the prerequisite of design philosophy of the present invention, the various changes and modifications that those skilled in the art make technical scheme of the present invention, all belong to protection scope of the present invention.
Embodiment 1
Take primary industry silicon 50kg, silico briquette is packed in medium-frequency induction furnace plumbago crucible and heated, and be fused into silicon liquid, keeping temperature is 1500 ℃.
Take composite fluxing medium, composite fluxing medium Na 2cO 3～K 2cO 3～SiO 2be by weight percentage: Na 2cO 3be 25%, K 2cO 3be 25%, SiO 2be 50%, the mass ratio of composite fluxing medium and industrial silicon is 0.6:1, i.e. 30kg.
In silicon liquid, drop into powdery composite fluxing medium, continue heating slag former is melted completely, and keep silicon liquid temp at 1500 ℃.
By the graphite rod preheating with vent channel, after preheating, venting pin is inserted in above-mentioned silicon liquid and starts logical oxygen, the gas flow of described oxygen is 5L/min, the ventilatory response time is 30min.
Open high pressure plasma producer, at room temperature ducted oxygen partial ionization become to oxonium ion and be injected in silicon liquid, described voltage is 20KV, conduction time 1h;
Silicon liquid obtained above is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, the refining low boron polysilicon after being purified, is denoted as A1.
Embodiment 2
(1) take primary industry silicon 50kg, silico briquette is packed in medium-frequency induction furnace plumbago crucible and heated, and be fused into silicon liquid, keeping temperature is 1700 ° of C.
(2) take composite slag agent, by composite slag agent Na 2cO 3～K 2cO 3～SiO 2be by weight percentage: Na 2cO 3be 30%, K 2cO 3be that 30%, SiO2 is 40%, the mass ratio 0.8:1 of composite slag agent and industrial silicon, i.e. 40kg.
(3) in silicon liquid, drop into powdery slag former, continue heating slag former is melted completely, and keep silicon liquid temp at 1700 ° of C.
(4) by the graphite rod preheating with vent channel, after preheating, venting pin is inserted in above-mentioned silicon liquid and starts logical oxygen, the gas flow of described oxygen is 10L/min, the ventilatory response time is 25min.
(5) open high-pressure ion producer, at room temperature ducted oxygen partial ionization become to oxonium ion and be injected in silicon liquid, described voltage is 25KV, conduction time 2h;
(6) silicon liquid obtained above is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, the refining low boron polysilicon after being purified, is denoted as A2.
Embodiment 3
(1) take primary industry silicon 50kg, silicon material is packed in medium-frequency induction furnace plumbago crucible and heated, and be fused into silicon liquid, described by silico briquette heat fused, be to adopt intermediate frequency induction heating device by silico briquette heat fused, Heating temperature is 1800 ℃.
(2) take composite slag agent, by composite slag agent Na 2cO 3～K 2cO 3～SiO 2be by weight percentage: Na 2cO 3be 35%, K 2cO 3be 35%, SiO 2be 30%, the mass ratio 1:1 of composite slag agent and industrial silicon, i.e. 50kg.
(3) in silicon liquid, drop into powdery slag former, continue heating slag former is melted completely, and keep silicon liquid temp at 1800 ℃.
(4) by the graphite rod preheating with vent channel, after preheating, venting pin is inserted in above-mentioned silicon liquid and starts logical institute gas, the gas flow of described oxygen is 12L/min, the ventilatory response time is 35min.
(5) open high-pressure ion producer, at room temperature ducted oxygen partial ionization become to oxonium ion and be injected in silicon liquid, described voltage is 30KV, conduction time 3h;
(6) silicon liquid obtained above is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, the refining low boron polysilicon after being purified, is denoted as A3.
Comparative example 1
With embodiment 1 difference be: embodiment 1 ionic medium generator power is closed and only passed into oxygen, and other parts are with embodiment 1.
Refining low borosilicate after being purified, is denoted as B1.
Comparative example 2
With embodiment 2 differences be: embodiment 2 ionic medium generator powers are closed and only passed into oxygen, and other parts are with embodiment 2.
Refining low borosilicate after being purified, is denoted as B2.
Comparative example 3
With embodiment 3 differences be: embodiment 3 ionic medium generator powers are closed and only passed into oxygen, and other parts are with embodiment 3.
Refining low borosilicate after being purified, is denoted as B3.
Experimental example 1
Boron assay:
By the result of gained in above-described embodiment, get silicon ingot central part, by ICP～MS, measure the content of B in silicon, measuring result is as table 1.
Table 1
? B／ppmw Test set
Raw material 2.1 ICP～MS
Embodiment A
1 0.28 ICP～MS
Embodiment A
2 0.26 ICP～MS
Embodiment A 3 0.23 ICP～MS
Comparative example B1 0.92 ICP～MS
Comparative example B2 0.76 ICP～MS
Comparative example B3 0.62 ICP～MS
As can be seen from Table 1: embodiment has had significantly reduction with respect to the content of the B of comparative example; Illustrate that method of the present invention can effectively remove boron impurity in silicon, be applicable to industrial scale operation.

Claims (7)

1. a method for the auxiliary slagging boron removal of plasma, is characterized in that, comprises the following steps:
(1) silico briquette is packed in medium-frequency induction furnace plumbago crucible and heated, and be fused into silicon liquid;
(2) in silicon liquid, drop into slag former, continue heating slag former is melted completely, and keep silicon liquid temp; Described slag former is by Na 2cO 3, K 2cO 3with SiO 2form; By mass percentage, in described slag former, Na 2cO 3be 25%～35%, K 2cO 3be 25%～35%, SiO 2be 30～50%; The mass ratio of described silico briquette and slag former is 1:0.6～1;
(3) by the graphite rod preheating with vent channel, after preheating fully, venting pin is inserted in silicon liquid, start logical oxygen;
(4) open high pressure plasma producer simultaneously, at room temperature the oxygen in oxygen channel be ionized into oxonium ion and pass through in graphite rod Implanted Silicon liquid;
(5) the silicon liquid obtaining in step (4) is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, the refining low boron polysilicon after being purified.
2. method according to claim 1, is characterized in that, in described step (1), the temperature of silicon liquid is 1500～1800 ℃.
3. method according to claim 1, is characterized in that, in described step (2), by mass percentage, and in described slag former, Na 2cO 3be 30%～35%, K 2cO 3be 30%～35%, SiO 2be 30%～40%.
4. method according to claim 1, is characterized in that, in described step (2), the mass ratio of described silico briquette and slag former is 1:0.8～1.
5. method according to claim 1, is characterized in that, in described step (2), keeps silicon liquid temp at 1500～1800 ℃.
6. method according to claim 1, is characterized in that, in described step (3), the flow of described oxygen is 5～12L/min, and the ventilatory response time is 25～35min.
7. method according to claim 1, is characterized in that, in described step (4), the operating voltage of described high pressure plasma producer is 20～30KV, conduction time 1～3h.
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Address after: No.1-2, fukeng huyangtangbei Road, Sheshan village, Nanyang Town, Shanghang County, Longyan City, Fujian Province 364211

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Patentee before: FUJIAN XING THE ZHAOYANG SILICON MATERIALS Co.,Ltd.