CN101545135B - Method for preparing and purifying solar grade silicon crystal - Google Patents
Method for preparing and purifying solar grade silicon crystal Download PDFInfo
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- CN101545135B CN101545135B CN2009100983702A CN200910098370A CN101545135B CN 101545135 B CN101545135 B CN 101545135B CN 2009100983702 A CN2009100983702 A CN 2009100983702A CN 200910098370 A CN200910098370 A CN 200910098370A CN 101545135 B CN101545135 B CN 101545135B
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Abstract
The invention discloses a method for preparing and purifying a solar grade silicon crystal, which is characterized in that: the purification and the preparation process of the silicon crystal are performed in a crystal lifting furnace (equipment for growing crystal by using a Czochralski method), and a crucible processed by using a graphite material is used as a container to be directly contacted with a silicon raw material (and melt obtained after the melting of the silicon raw material). The operation process of the method comprises the following steps: (1) heating the graphite crucible to melt the silicon raw material in the graphite crucible, and evaporating impurities under conditions of a silicon melt temperature of 1,500 to 2,000 DEG C and a silicon melt surface vacuum degree of 0 to 500 Pa; (2) controlling the temperature of the silicon melt to be 1,410 to 1,500 DEG C, and preparing the silicon crystal by seed-crystal induction; (3) when the silicon melt in the graphite crucible is to be used up, heating the crucible to 1,600 to 1,850 DEG C, controlling the silicon melt surface vacuum degree to be 0 to 5 Pa, and evaporating the residual impurities in the silicon melt; (4) reducing the temperature and keeping the temperature in the graphite crucible above 800 DEG , and adding the next batch of silicon raw material into the graphite crucible; and (5) repeating the operations in steps (1) to (4) for continuous production. The silicon crystal produced by the method has low oxygen content, improves the photoinduced attenuation property of solar cells made of boron doped silicon crystal and realizes continuous production.
Description
Technical field
The present invention relates to the silicon crystal material preparation field, relate in particular to the method that a kind of Czochralski of employing method is purified and prepared solar-grade silicon crystals.
Background technology
Czochralski method (being called for short the CZ method) is a kind of widely used method of silicon crystal growth.The equipment of crystal lifting furnace (Crystal Puller) for adopting C Z method to carry out crystal growth.Silicon crystal is semicon industry and the photovoltaic industry material of normal use.
The CZ method is normally placed inner crucible (quartz crucible) in the crucible (generally being the plumbago crucible of three lobes or pintongs graphite flake being combined formation) outside, melted silicon induces down by seed crystal to grow columned silicon crystal in inner crucible (quartz crucible).Above process is finished in the crystal lifting furnace.
A kind of crucible that is used for growing silicon crystal is for example disclosed in the Chinese invention patent 200410061587.3, and a kind of method of utilizing this crucible to come growing silicon crystal by the Czochralski method, the inner crucible that wherein is used for CZ method growing silicon crystal also adopts quartz crucible.
The preparation method of a kind of monocrystalline silicon draw machines with thermal field charcoal/charcoal crucible disclosed in Chinese invention patent application 200610043186.4, when also mentioning the silicon crystal growth in this method, be to place quartz crucible in the crucible (charcoal/charcoal crucible) outside, silicon melt places quartz crucible to carry out crystalline processing.
The main component of quartz crucible is a silicon-dioxide, and at high temperature the partial oxygen atom can dissociate out from quartz, enters into silicon crystal.Therefore, have higher oxygen concn by quartz crucible as the crystal that the C Z method of container grows.For the silicon crystal that needs utmost point low oxygen content under some use occasion, for example,, reduce the negative impact that photo attenuation is brought in order to improve life-span as boron-doping photovoltaic silicon materials, the oxygen level in the silicon crystal need minimize.In this case, avoid using quartz crucible to solve the high problem of CZ method silicon crystal oxygen level from root.But do not use quartz crucible directly to use plumbago crucible then can cause other problem.Topmost difficulty is that volumetric expansion caused damage to plumbago crucible when silicon solidified.When silicon cooled off with graphite, the difference of both thermal expansivity also can cause damage to graphite.
The desired silicon material purity of crystal silicon solar energy battery need be more than 6N (99.9999%).Therefore, the silicon materials below the 6N purity often required further to be purified before being made into desired policrystalline silicon of solar energy photovoltaic utilization or silicon single-crystal ingot casting.Usually need under high-temperature vacuum, will carry out after the fusing of silicon raw material owing to purify, and also need before the crystal growth the fusing of silicon raw material, therefore most economical energy-conservation way is, promptly purifies after the fusing of silicon raw material, not with the melted silicon crystallisation by cooling, just carry out the growth of silicon crystal after the purification.But will purify and the scheme finished continuously of crystal growth has the difficulty that is difficult to overcome in the CZ method of traditional employing quartz crucible as container.At first, for volatile impurity is volatilized from the melted silicon liquid level, the purification environment need be less than the vacuum tightness of 500Pa.Yet when vacuum tightness drops to 500Pa when following, quartz crucible when temperature is higher (SiO2) will cause boiling of silicon liquid or silicon liquid level instability with the silicon monoxide (SiO) that melted silicon (Si) reaction generates, and make SiO make the SiO concentration the silicon liquid fall very lowly from the liquid level volatilization fast, thereby cause the reaction of quartz crucible and melted silicon to be accelerated, make the quartz crucible distortion even leak silicon.Secondly, often the temperature than crystal growth is higher for the temperature of silicon materials purification.Though quartz crucible can bear the required temperature of crystal growth (1400～1550 ℃) for a long time, can not under the required high temperature (1550～1850 ℃) of purifying, work long hours.
Summary of the invention
But the invention provides the method that a kind of continuous production, employing CZ method that product purity is high carry out the silicon crystal preparation and purify.
A kind of preparation of solar-grade silicon crystals and method of purification, whole process is carried out in the crystal lifting furnace, and the crucible that adopts graphite material processing is as the container that directly contacts with silicon raw material (and the liquation after the fusing).
Its method comprises the steps:
(1) heating makes the silicon raw material fusing in the plumbago crucible, 1500～2000 ℃ of melted silicon temperature, under melted silicon surface vacuum degree 0～500Pa condition evaporation impurity one hour or more than;
(2) control melted silicon temperature is induced preparation cylindrical silicon crystal by seed crystal between 1410～1500 ℃.
So far promptly can obtain the higher silicon crystal of purity,, must purify once more remaining melted silicon in the reaction later stage plumbago crucible in order to realize serialization production,
(3) along with the continuous generation of silicon crystal, melted silicon reduces gradually in the plumbago crucible, when the remaining quality of the melted silicon in the plumbago crucible is 0.1～3.5KG, is warming up to 1600～1850 ℃, the vacuum degree control on melted silicon surface is evaporated impurity remaining in the melted silicon at 0～5Pa;
(4) cooling but keep that temperature adds next batch silicon raw material more than 800 ℃ in the plumbago crucible in plumbago crucible;
(5) the operation continuous production of repeating step (1)～step (4).
Evaporation impurity in the step (1), what be primarily aimed at is volatile impurity, and volatile impurity contains at least a element in phosphorus, arsenic, boron, the oxygen, and impurity can be with the form volatilization of compound or simple substance.In addition, volatile impurity also comprises metallic impurity such as aluminium, iron, copper, titanium and contains the volatile compound of metallic impurity.Usually need lower vapour pressure in order to reach the impurity volatilization, furnace pressure should remain on the following vacuum tightness of 500Pa.According to the principle that vacuum is purified, the volatilization earlier of element simple substance that vapour pressure is big or compound.And the most of impurity of the steaming pressure ratio of silicon are low.For example, when the temperature of melted silicon during at 1700K, the vapour pressure of silicon only has 0.0689Pa.Therefore, when the steaming pressure ratio silicon of impurity or its compound is higher (＞0.0689Pa), impurity will be evaporated prior to silicon, realize the purification of silicon raw material.The time and the temperature of carrying out the high-temperature vacuum volatilization process should be according to the content and the type decided of impurity in the silicon, and volatilization process should continue more than 1 hour usually, and the melted silicon medial temperature should remain on more than 1500 ℃.Containing under the more situation of metallic impurity, the purification environment should remain on the melted silicon medial temperature more than 1550 ℃, and the vacuum tightness on melted silicon surface is at 0～5Pa.
Show that after deliberation after the silicon raw material melted, plumbago crucible can play fully as the effect of depositing the melted silicon container in plumbago crucible, but following reaction still at high temperature takes place with silicon in graphite:
Si+C→SiC
But in the required high-temperature temperature of purifying was 1500～2000 ℃ scope, the reaction of silicon and graphite was slower, and the resultant SiC that reacts will cover the plumbago crucible inwall with solid-state form, stoped the further reaction of silicon and graphite to a certain extent.Purification needs the following higher vacuum tightness of 500Pa.For the time that makes purification shorter, optimum vacuum tightness should be below 5Pa.The main component carbon (C) of plumbago crucible, and very low vapour pressure is still arranged under high temperature and condition of high vacuum degree with the reactant carbonization silicon (SiC) of silicon, make and to have that more impurity or its compound of high-vapor-pressure are easy to reach the purpose of purifying from the liquid level volatilization than carbon, silicon and silicon carbide.For example the oxygen element that photo attenuation is had a significant impact will volatilize from liquid level with the form of SiO.
Through after the purification of above process, still keep impurity in the melted silicon with higher vapor pressure, this class impurity is generally the metallic impurity that minority carrier life time is had a significant impact, for example Fe, Al, Ca, Ti, Cu etc.The segregation coefficient of this class impurity is all smaller, crystal growing process that can be by subsequently with impurity enriched in crystalline afterbody and pot bottom material, thereby make the crystal head have higher purity.
After steam removing volatile impurity through step (1), slightly cooling, control melted silicon temperature is induced the preparation silicon crystal by seed crystal between 1410 (silicon fusing points)～1500 ℃.
In the step (3), when melted silicon will exhaust in the plumbago crucible, promptly in the final stage of crystal growth, because the circular arc-shaped bottom portion of crucible makes melted silicon be difficult to be grown into crystal fully and lifts out liquid level, but be rich in impurity in the remaining melted silicon (the cooling back forms pot bottom material), if continue to stay the problem that can bring two aspects in the plumbago crucible: at first, because silicon is different with the thermal expansivity of graphite, pot bottom material might cause plumbago crucible to crack when cooling.Secondly, in a single day the remaining melted silicon that foreign matter content is a lot of solidifies in the plumbago crucible bottom, then is difficult to by machinery or chemical method pot bottom material and plumbago crucible be separated.This makes plumbago crucible when reinforced production once more, the part of raw materials the when pot bottom material that is rich in impurity will have to produce as next time, the effect and the quality of silicon feedstock purification and crystal growth when having influenced next production.
At the problems referred to above, the present invention proposes operating procedure targetedly.At first, should be as much as possible melted silicon (will form pot bottom material after the cooling) quality of remnants be dropped to below the 3.5KG.By improving operative technique, optimal selection is that the melted silicon quality with remnants drops to below the 1.5KG.Secondly, can be by improving heater power, the temperature of the melted silicon of remnants to be brought up to more than 1600 ℃, vacuum tightness drops to below the 5Pa, scorches and can be able to further volatilization with being difficult to evaporable impurity originally by high temperature.At last, for fear of when cooling silicon different with the thermal expansivity of graphite and cause plumbago crucible to crack, adopt repeatedly reinforced method, make plumbago crucible realize repeatedly using, the work-ing life of prolongation plumbago crucible without cooling.
Concrete way is: through step (3) with the melted silicon of remnants through high temperature scorch further remove impurity after, carry out step (4) again, new silicon raw material is put into plumbago crucible by feeder.Reinforced in order to lower the temperature, should regulate heater power before feeding in raw material and make it not be higher than the power of crystalline isodiametric growth.Add the power intensification after reinforced again and change material once more and form new melted silicon, carry out next time purification and crystal growth.
Feeder can adopt the feeder of form of sleeve, will fill the feeder of silicon material by concubine and put into stove, above the crucible silicon material is being poured among the plumbago crucible.Feeder also can adopt the reinforced method in side, is installed in bell top one side, by opening reinforced switch, the silicon raw material is joined among the plumbago crucible from the side.The material that feeder stretches into furnace high-temperature district part can be processed by charcoal carbon composite, graphite or quartz material.
Consider that from safety and cost angle when repeatedly using, temperature should not be cooled to below 800 ℃ without the refrigerative plumbago crucible, optimal selection should maintain the medial temperature of plumbago crucible more than 1200 ℃ all the time.The purification that repeats and the cycle index of crystal growth be by crystal lifting furnace, plumbago crucible, and the situation of rapid wear product such as vacuum pump and thermal field material and deciding can recycle 5～10 times under normal conditions continuously.
The crucible that the inventive method is used is an integral body, rather than the plumbago crucible of using as auxiliary quartz crucible load-bearing in the traditional C Z method of being made up of three lobes or many lobes, and its inside does not need to serve as a contrast a quartz crucible yet.Owing to do not need to use quartz crucible, so oxygen level is very low in the silicon crystal that generates, operating procedure provided by the invention can also be avoided the plumbago crucible cracking simultaneously.Owing to do not need to use quartz crucible, the present invention can carry out purifying under the high temperature to melted silicon before the crystal growth and the remaining melted silicon after the crystal growth, has avoided owing to the crucible distortion of using quartz crucible to cause and the problem of leaking silicon in addition.At last, repeatedly the use of charging technology has reduced the intensification and the cool down of every stove to a great extent, has saved the energy.The used material of crucible is preferably isostatic pressing formed graphite (Isotropic Graphite) material or charcoal charcoal (C-C) composite graphite material in the present invention, can not use the possibility of the little refractory metal of refractory ceramics or the segregation coefficient in silicon materials as crucible material but do not get rid of.
The present invention adopts the whole crucible of graphite and does not adopt the reaction vessel of quartz crucible as the silicon raw material, in conjunction with the processing of pot bottom material and the feeding technique of continuous silicone raw material, can avoid using the problem that plumbago crucible brings causes because of thermal expansion, what overcome also that existing CZ legal system is equipped with silicon crystal contains the oxygen problem.
The boron-doping silicon crystal with lower oxygen content that the inventive method is produced is made into solar cell, and the negative impact that photo attenuation is brought minimizes, and improves the life-span of photovoltaic product.
The inventive method has been removed the quartz crucible in the CZ method from, not only can increase the productivity of silicon crystal, more can reduce the oxygen level in the silicon crystal, improves the quality of silicon crystal.
Description of drawings
Fig. 1 utilizes the CZ method to carry out the prior art reaction unit synoptic diagram that silicon crystal is produced;
Fig. 2 utilizes the inventive method to prepare the reaction unit synoptic diagram of silicon crystal;
Fig. 3 utilizes the inventive method to carry out the synoptic diagram of secondary charging from concubine;
Fig. 4 utilizes the inventive method to carry out the synoptic diagram of secondary charging from the bell side;
Embodiment
Embodiment 1
Referring to Fig. 1, Fig. 1 is the typical longitudinal section of a CZ method crystal lifting furnace.The silicon raw material that is generally used for growing silicon crystal be placed on inner crucible be in the quartz crucible 2 by well heater 3 heating, under the protection of lagging material 8, be fused into melted silicon 4.It is in the plumbago crucible 1 that quartz crucible 2 is placed on outer crucible.And plumbago crucible be placed on can the crucible shaft 7 of lifting on.In the CZ method, the interface of crystal growth is in the centre of melted silicon 4 free surfaces.By suitably designing heating power, and the given suitable crucible shaft 7 and the rotating speed of seed crystal 5, under the lifting of seed crystal 5 by the seed crystal rope 9 that haulage gear drove, induce melted silicon 4 to grow columned crystal 6.
In the crystal 6 process of growth, the main component of quartz crucible 2 is a silicon-dioxide, and at high temperature the partial oxygen atom can dissociate out from quartz, enters into crystal 6.Therefore, have higher oxygen concn by quartz crucible 2 as the crystal 6 that the CZ method of container grows.In addition, because quartz crucible exists, system does not allow to carry out high temperature and the vacuum tightness vacuum purification operations less than 500Pa.
Referring to Fig. 2, the present invention no longer adopts quartz crucible as inner crucible as the container of depositing the silicon raw material plumbago crucible of integral body.Before silicon crystal growth after the fusing of silicon raw material, vacuum tightness can be dropped to about 1Pa, and the temperature of melted silicon is risen to 1800 ℃ of evaporations of carrying out impurity in the silicon raw material.The evaporative process of impurity is continued heater power suitably to be descended after 3 hours, and the medial temperature that makes melted silicon 4 is about 1450 ℃.Temperature-stable after 1 hour, is carried out the seed crystal seeding, and finally induce melted silicon 4 to grow columned crystal 6.
When melted silicon content in the crucible seldom the time, obtain suitable temperature by the power of regulating well heater 3, can make melted silicon lift out from liquid level to greatest extent, last remaining melted silicon 13 is about 1KG.Because foreign matter content is more in the remaining melted silicon, therefore heighten heater power once more, the temperature of remaining melted silicon 13 is reached about 1800 ℃, and regulate vacuum tightness and about 1Pa, carry out the volatilization of impurity.After the impurity volatilization is finished, as shown in Figure 3, under the prerequisite of not cooling off plumbago crucible (temperature of plumbago crucible remains on more than 1200 ℃), reinforced by feeder 11.The feeder 11 of filling block and granular silicon raw material 12 hangs down by seed crystal rope 9 from concubine 10, above plumbago crucible silicon raw material 12 is discharged.After filling it up with the silicon raw material in the plumbago crucible 1, can improve heater power, the silicon raw material is melted into melted silicon, carry out next time purification and crystal growing process.Because plumbago crucible does not experience the process of cooling of the big temperature difference, the situation that the crucible of having avoided plumbago crucible may cause because of the thermal expansivity of silicon and graphite is different damages.
More than purification and crystal growing process can carry out 5～10 times continuously, compare with traditional method, add gentle refrigerative process owing to reduced, and have shortened the time of a working cycle, therefore working efficiency have been improved greatly.
Adopt the identical technological process of embodiment 1.Difference is, to carry out the side reinforced by being installed in feeder 14 on the bell for reinforced process.As shown in Figure 4.The silicon raw material of depositing in the feeder 14 15 is particulate state, and equivalent diameter is between 0.5mm～15mm.
Claims (6)
1. the preparation of a solar-grade silicon crystals and method of purification is characterized in that, in the crystal lifting furnace, and the container that the crucible conduct and the silicon raw material of employing graphite material directly contacts:
(1) heating makes the silicon raw material fusing in the plumbago crucible, 1500～2000 ℃ of melted silicon temperature, under melted silicon surface vacuum degree 0～500Pa condition evaporation impurity 1 hour or more than;
(2) control melted silicon temperature is induced the preparation silicon crystal by seed crystal between 1410～1500 ℃;
(3) when the remaining quality of the melted silicon in the plumbago crucible is 0.1～3.5KG, be warming up to 1600～1850 ℃, the vacuum degree control on melted silicon surface is evaporated volatile impurity remaining in the melted silicon at 0～5Pa;
(4) cooling but keep that temperature adds next batch silicon raw material more than 800 ℃ in the plumbago crucible in plumbago crucible;
(5) the operation continuous production of repeating step (1)～step (4).
2. preparation as claimed in claim 1 and method of purification is characterized in that: 1550～1850 ℃ of melted silicon temperature, evaporate impurity under melted silicon surface vacuum degree 0～5Pa condition in the step (1).
3. preparation as claimed in claim 1 and method of purification is characterized in that: the remaining quality of the melted silicon described in the step (3) is 0.1～1.5KG.
4. preparation as claimed in claim 1 and method of purification is characterized in that: described graphite material is isostatic pressing formed graphite material or charcoal charcoal composite graphite material.
5. preparation as claimed in claim 1 and method of purification is characterized in that: described silicon crystal comprises silicon single-crystal and policrystalline silicon.
6. preparation as claimed in claim 1 and method of purification is characterized in that: step (4) is lowered the temperature but is kept the interior temperature of plumbago crucible more than 1200 ℃, adds next batch silicon raw material in plumbago crucible.
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Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101570888B (en) * | 2009-06-11 | 2011-07-20 | 浙江碧晶科技有限公司 | Method capable of removing carbon-containing impurities for preparing solar-grade silicon crystals |
| CN101781791B (en) * | 2010-03-22 | 2012-03-21 | 浙江星宇电子科技有限公司 | Method for removing impurities in single crystal rod straight pulling process |
| CN102168301A (en) * | 2011-06-03 | 2011-08-31 | 常州江南电力环境工程有限公司 | Graphite crucible in czochralski single crystal furnace |
| CN103011567B (en) * | 2012-12-28 | 2015-09-23 | 江苏太平洋石英股份有限公司 | A kind of preparation method of quartz ceramic crucible |
| CN103266347A (en) * | 2013-05-27 | 2013-08-28 | 英利能源（中国）有限公司 | Treatment method for impurities in silicon material |
| KR101472352B1 (en) * | 2013-06-11 | 2014-12-12 | 주식회사 엘지실트론 | Recharge apparatus |
| CN103603039B (en) * | 2013-12-02 | 2015-09-30 | 天津英利新能源有限公司 | A kind of method of purification of polycrystal silicon ingot tankage |
| CN106591938A (en) * | 2016-12-29 | 2017-04-26 | 柳州市圣垒贸易有限公司 | Method for refining high-purity metallic uranium |
| CN110396715A (en) * | 2019-09-04 | 2019-11-01 | 内蒙古中环光伏材料有限公司 | A kind of pulling of crystals repeatedly throws technique again |
| CN111001483B (en) * | 2019-12-31 | 2024-01-02 | 四川永祥多晶硅有限公司 | Polysilicon crushing system |
| CN115305365B (en) * | 2021-05-08 | 2024-05-28 | 有研稀土新材料股份有限公司 | Device and method for purifying rare earth metal by Czochralski method |
| CN115852154B (en) * | 2022-12-06 | 2024-09-10 | 云南国钛金属股份有限公司 | Method and device for removing impurities from sponge titanium rich in chloride ions |
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| JP2005206442A (en) * | 2004-01-26 | 2005-08-04 | Nippon Steel Corp | Silicon purification method |
| CN101362602A (en) * | 2008-09-18 | 2009-02-11 | 扬州市科尔光电子材料有限公司 | Purification processing method for drawing casting ingot cleaved bark slat and head material |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2005206442A (en) * | 2004-01-26 | 2005-08-04 | Nippon Steel Corp | Silicon purification method |
| CN101362602A (en) * | 2008-09-18 | 2009-02-11 | 扬州市科尔光电子材料有限公司 | Purification processing method for drawing casting ingot cleaved bark slat and head material |
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