CN209162251U - A kind of polycrystal silicon ingot pouring device - Google Patents

Abstract

The utility model relates to a kind of polycrystal silicon ingot pouring devices, belong to photovoltaic technology field, it solves the problems, such as that polycrystal silicon ingot crystal dislocation density is big in the prior art.This polycrystal silicon ingot pouring device includes furnace body, heat-insulation cage equipped with liftable movement in furnace body, crucible, crucible guard boards, graphite bottom plate, graphite cover board, top heater and side heater are equipped in heat-insulation cage, graphite bottom plate is placed on heat exchange platform, crucible is placed on graphite bottom plate, heat exchange platform is equipped with auxiliary cooling device, and cooling temperature is adjusted in the auxiliary cooling device.This polycrystal silicon ingot pouring device passes through setting auxiliary cooling device, the heat exchanger effectiveness of adjustable bottom heat exchange platform eliminates the transverse temperature difference of solid liquid interface so that silicon ingot bottom and side temperature gradient are uniform, so that long chip reduces dislocation density to stabilization.

Description

A kind of polycrystal silicon ingot pouring device

Technical field

The utility model belongs to photovoltaic technology field, is related to a kind of pouring device of polycrystal silicon ingot, especially a kind of fritting The device of method casting polycrystal silicon ingot.

Background technique

Solar power generation is the important means of human use's solar energy, and solar battery is then the master for realizing photoelectric conversion Device is wanted, the photoelectric conversion efficiency of solar battery determines the utilization conversion ratio of solar energy source.In recent years, world's solar-electricity The speed of the yield in pond and installed capacity every year all 30% is fast-developing.Currently, the accumulative installed capacity in the whole world is 25.4GW, in advance It counts the installed capacity of the year two thousand twenty whole world and is up to 278GW.

Currently, the type of solar battery is increasing, wherein crystal silicon solar energy battery especially polycrystalline silicon solar Battery will occupy leading position within following one period with lower cost and higher transfer efficiency.But relative to Traditional energy, the cost is relatively high for polycrystalline silicon solar power generation, and market rate is relatively low.From current global situation and entire row From the point of view of the development of industry, improving the transfer efficiency of polysilicon solar cell, reducing the cost of electricity-generating of photovoltaic module is photovoltaic industry Inexorable trend.As how lower cost prepares hot spot of the efficient solar battery as industry research.Except battery Outside technological factor, the excessively high dislocation density of conventional polysilicon silicon wafer is one of the principal element for limiting polycrystal silicon cell transfer efficiency. On the one hand dislocation producing cause in conventional polysilicon silicon wafer is that carbon content is excessively high in silicon ingot, carbon atom is small compared with silicon atom radius, meeting Cause biggish distortion of lattice, generates a large amount of dislocations；It on the other hand is the limitation of traditional directional freeze method, at the beginning of crystal growth Phase, there are biggish dislocation density in crystal, later period dislocation multiplication causes whole spindle position dislocation density excessively high, directly affects the sun The incident photon-to-electron conversion efficiency of energy battery.

For the bad situation of crystal growth primary growth, seed crystal high-efficiency polycrystalline silicon technology can be used, that is, used millimeter Grade silicon material carries out epitaxial growth as nucleating center, and the silicon liquid of melting is guided to carry out when solidifying by nucleating center of high quality silicon material Columnar growth.And in crystal growing process, temperature gradient when directional solidification is also the important ring for determining crystal quality, existing The problem of the type of cooling maximum used in technology is non-uniform temperature at Solid-Liquid Separation, and generating transverse temperature difference leads to crystal The orientation of growth is poor, big so as to cause the dislocation density of polycrystal silicon ingot, affects the incident photon-to-electron conversion efficiency of solar battery.

Utility model content

The purpose of this utility model is the presence of the above problem in view of the prior art, and it is stable to propose a kind of temperature gradient Polycrystal silicon ingot pouring device.

The purpose of this utility model can be realized by the following technical scheme: a kind of polycrystal silicon ingot pouring device, including furnace Body, the interior heat-insulation cage equipped with liftable movement of the furnace body, the heat-insulation cage is interior to be equipped with crucible, crucible guard boards, graphite bottom Plate, graphite cover board, top heater and side heater, the graphite bottom plate are placed on heat exchange platform, the earthenware Crucible is placed on graphite bottom plate, which is characterized in that the heat exchange platform is equipped with auxiliary cooling device, and the auxiliary is cold But cooling temperature is adjusted in device.

During long brilliant, for the variation for realizing longitudinal temperature gradient, after heat-insulation cage rises, due to bottom silicon ingot no longer into Row heating, therefore bottom silicon ingot and peripheral temperature reduce, since the temperature of silicon ingot two sides is nature decline, bottom temp is also certainly So decline, in the initial stage, silicon ingot side and distance from bottom solid liquid interface are equidistant, therefore the interface of solid-liquid intersection is in cross Temperature is identical on direction, and long crystalline substance process is smooth, but with the rising of silicon ingot solid liquid interface, bottom heat exchange and side heat exchange Efficiency will be significantly different, because more and more remoter with solid liquid interface at the heat exchange of bottom, and the side of solid liquid interface and sidewall of crucible Distance is constant always, and the side of solid liquid interface and middle portion temperature imbalance lead to transverse temperature difference occur in order to prevent, influences long crystalline substance Direction needs the raising with solid liquid interface, steps up the heat exchanger effectiveness of silicon ingot bottom, equal to reach solid liquid interface temperature Weighing apparatus, there is no the purposes of transverse temperature difference.Using auxiliary cooling device, cooling efficiency is adjusted, is continuously improved during long brilliant The heat exchanger effectiveness of bottom, so that bottom is consistent with the temperature gradient of side.

In above-mentioned polycrystal silicon ingot pouring device, the auxiliary cooling device includes being set to heat exchange mesa base Cooling line, the external argon gas of the cooling line, the inlet end of the cooling line is equipped with frequency-changeable compressor.Utilize change Frequency compressor improves gas flow to change cooling velocity and guarantees the transverse temperature difference that solid-liquid is practised physiognomy according to different temperatures demand It is as small as possible.

This polycrystal silicon ingot casting device further includes argon inlet pipe, and the argon inlet pipe passes through furnace body, heat-insulation cage, and Connect with the cooling line on heat exchange platform, the external escape pipe in the outlet side of the cooling line, the escape pipe around It is protruded into crucible above to heat-insulation cage and across top heater and graphite cover board, the air-flow that the escape pipe sprays is directed at earthenware Melt above crucible.

The effect of argon inlet pipe is to provide cooling for cooling line, simultaneously as argon gas is laggard by cooling line Sufficient heat exchange is gone, therefore the argon gas sprayed from escape pipe is high temperature argon, so that argon gas is directly injected into the silicon of melting The temperature decrease that not will lead to silicon liquid on liquid is conducive to maintain the temperature gradient of silicon liquid unaffected, in addition, the mesh of injection argon gas Be the impurity that suspends in silicon liquid is carried out it is evenly dispersed so that the silicon ingot ingredient after solidify is uniform, crystal phase structure after long crystalline substance Stablize, dislocation density is small, effectively promotes polycrystal silicon ingot quality.

Alternatively, in above-mentioned polycrystal silicon ingot pouring device, the auxiliary cooling device includes setting Cooling water channel in heat exchange platform, the cooling water channel are circular layout in heat exchange mesa base, the cooling water Road is equipped with flow control valve.Argon inlet pipe passes through furnace body, heat-insulation cage, top heater and graphite cover board and is directly protruding into crucible It is interior.

In above-mentioned polycrystal silicon ingot pouring device, the crucible bottom is laid with one layer of silicon particle, and silicon particle layer forms tool There is the supporting structure of countless holes.

In above-mentioned polycrystal silicon ingot pouring device, the silicon particle is that the high temperature resistant silicon of surface coating silicon nitride layer is broken Material.Original silicon fusing point in silicon particle is 1420 ± 2 °, and traditional half process of smelting uses merely silicon particle to lay crucible bottom, is being cast Because affected by many factors in ingot stove heating, fusion process, once seed crystal has melted, seed crystal forming core cannot be played the role of.And work as When silicon particle surface is covered with silicon nitride powder, it will play the role of protecting silicon particle, so as not to fusing, to protect well Keep seed crystal here.Silicon nitride chemical formula Si₃N₄, white powder crystal, 1900 DEG C of fusing point, silicon nitride pole high temperature resistant will not melt after heated At melt body, can just be decomposed until 1900 DEG C.Therefore it only needs to keep without repeatedly souning out solid liquid interface in silicon material melting process Certain time between 1420~1900 DEG C, melting to wear without having to worry about silicon particle influences its function as forming core.

In above-mentioned polycrystal silicon ingot pouring device, the crucible bottom and side are coated with silicon nitride coating.Crucible The setting of silicon nitride layer on inner wall, the impurity that crucible internal walls can be effectively prevented enters in crystal, and prevents polycrystal silicon ingot Viscous pot phenomenon, to improve the quality of polycrystal silicon ingot and reduce the operation difficulty of casting ingot process.

In above-mentioned polycrystal silicon ingot pouring device, the furnace body is equipped with vacuum orifice, on the crucible guard boards Equipped with exhaust outlet.

The another object of the utility model is to provide a kind of polycrystal silicon ingot casting method that crystal dislocation density is small: including Following steps: 1), charging before, high temperature resistant silicon particle be uniformly layered on to the crucible bottom of spraying silicon nitride；

2) it, charges；Silicon material is loaded in crucible, and then furnace body is vacuumized；

3), heat: open top part heater and side heater adjust heat-insulation cage height during melting silicon materials, allow Thermal field forms biggish temperature gradient, upper heat and lower cold, to guarantee that silicon material orients fusing from top to bottom；During melting silicon materials Crucible bottom remains i.e. 1420 DEG C of < of supercooling, and high temperature resistant silicon particle is made to be attached to crucible bottom always；

4) after, silicon material has all melted, crucible bottom high temperature resistant silicon particle retains 0.1~1.5cm thickness, covers entire crucible Bottom surface and highly uniform；Argon inlet pipe is opened, argon gas enters cooling pipe by argon inlet pipe, on the one hand flat to heat exchange Platform is cooled down, it is on the other hand heated after melt upper surface of the argon gas into crucible spray gas, then slowly promoted every Hot cage reduces the temperature of silicon melt, forms certain degree of supercooling, and silicon melt starts on the basis of the silicon particle of endless running down It is long brilliant to start forming core；

5), into after growing brilliant process, high temperature resistant silicon particle plays the role of good forming core, and melted silicon erects on the basis of forming core It is straight long brilliant, until heat-insulation cage is promoted to all silicon melts and crystallizes completion；

6), after the completion of whole melt crystallizations, annealed and cooling obtains polycrystal silicon ingot.

Silicon particle place mat in crucible bottom be it is disorderly arranged, particle layer forms a supporting structure, which has Countless holes, in the melting silicon materials stage, the silicon melt that melting silicon materials are formed will be filled in hole, in the initial forming core stage, Under supercooled state, multiple equally distributed forming core sources are formed in silicon particle level, so that it is good to obtain polycrystal silicon ingot Initial forming core, and then grow the crystal with advantage crystal orientation.Specifically, control temperature makes in silicon melt and unfused silicon The silicon melt that material is formed by the silicon melt of solid liquid interface and is filled in hole first reaches supercooled state, and preferential forming core crystallizes, Subsequent silicon melt circle is mobile away from the direction of crucible bottom, silicon melt crystallization and freezing.The initial forming core of polycrystal silicon ingot obtains Good control, to grow beneficial to the prevailing crystal of crystal orientation, therefore can prevent a large amount of proliferation of dislocation, obtain height Quality polycrystal silicon ingot.

In above-mentioned step 4), with the promotion of heat-insulation cage, compressor horsepower gradually mentions the frequency-changeable compressor Height, so that argon gas flows fast flow velocity and is gradually increased, cooling line heat exchanger effectiveness is gradually increased.

Compared with prior art, this polycrystal silicon ingot pouring device is handed over by setting auxiliary cooling device, adjustable bottom heat The heat exchanger effectiveness of platform is changed, so that silicon ingot bottom and side temperature gradient are uniform, eliminates the transverse temperature difference of solid liquid interface, So that long chip reduces dislocation density to stabilization, in addition, crucible bottom is laid with high temperature resistant silicon particle, shape is on the one hand played At the preferable forming core effect of crystal phase, on the other hand since silicon particle is coated with high-temperature-resistant layer, can preventing silicon particle, all melting is led It causes texture chaotic again, can play the role of fixing forming core well, guaranteeing temperature of thermal field gradient stabilization, primary crystalline In the case that quality is high, crystal growth is good after polycrystal silicon ingot directional solidification, and crystal dislocation density is low, is applied to solar battery On can effectively improve incident photon-to-electron conversion efficiency.

Detailed description of the invention

Fig. 1 is the structural schematic diagram of this polycrystal silicon ingot pouring device；

Fig. 2 is the structural schematic diagram of heat exchange platform in this polycrystal silicon ingot pouring device.

In figure, 1, furnace body；11, vacuum orifice；2, heat-insulation cage；3, crucible；4, crucible guard boards；41, exhaust outlet；5, graphite bottom Plate；51, graphite cover board；6, top heater；61, side heater；7, heat exchange platform；71, cooling line；8, argon inlet Pipe；81, escape pipe；9, silicon particle.

Specific embodiment

It is specific embodiment of the utility model and in conjunction with attached drawing below, the technical solution of the utility model is made further Description, but the utility model is not limited to these examples.

As shown in Figs. 1-2, this polycrystal silicon ingot pouring device, including furnace body 1, the interior liftable that is equipped with of the furnace body 1 move Heat-insulation cage 2, crucible 3, crucible guard boards 4, graphite bottom plate 5, graphite cover board 51, top heater 6 are equipped in the heat-insulation cage 2 With side heater 61, the graphite bottom plate 5 is placed on heat exchange platform 7, and the crucible 3 is placed on graphite bottom plate 5 On, the heat exchange platform 7 is equipped with auxiliary cooling device, and cooling temperature is adjusted in the auxiliary cooling device.It is described Auxiliary cooling device include the cooling line 71 for being set to 7 bottom of heat exchange platform, the external argon gas of cooling line 71, The inlet end of the cooling line 71 is equipped with frequency-changeable compressor.The argon inlet pipe 8 passes through furnace body 1, heat-insulation cage 2, and It is connect with the cooling line 71 on heat exchange platform 7, the external escape pipe 81 in the outlet side of the cooling line 71, described goes out Tracheae 81 is around to 2 top of heat-insulation cage and protrudes into crucible 3 across top heater 6 and graphite cover board 51, the escape pipe 81 The melt of 3 top of air-flow alignment crucible of ejection.

During long brilliant, for the variation for realizing longitudinal temperature gradient, after heat-insulation cage 2 rises, no longer due to bottom silicon ingot It is heated, therefore bottom silicon ingot and peripheral temperature reduce, since the temperature of silicon ingot two sides is nature decline, bottom temp is also Naturally decline, in the initial stage, silicon ingot side and distance from bottom solid liquid interface are equidistant, therefore the interface of solid-liquid intersection exists Temperature is identical in transverse direction, and long crystalline substance process is smooth, but as the rising of silicon ingot solid liquid interface, bottom heat exchange and side heat are handed over Changing efficiency will be significantly different, because more and more remoter with solid liquid interface at the heat exchange of bottom, and the side of solid liquid interface and 3 wall of crucible Distance it is constant always, the side of solid liquid interface and middle portion temperature imbalance lead to transverse temperature difference occur in order to prevent, influence to grow Chip is to needing the raising with solid liquid interface, step up the heat exchanger effectiveness of silicon ingot bottom, to reach solid liquid interface temperature Equilibrium, there is no the purposes of transverse temperature difference.Using auxiliary cooling device, cooling efficiency is adjusted, is constantly mentioned during long brilliant The heat exchanger effectiveness of high bottom, so that bottom is consistent with the temperature gradient of side.Using frequency-changeable compressor according to different temperatures need It asks, improves gas flow, to change cooling velocity, the transverse temperature difference for guaranteeing that solid-liquid is practised physiognomy is as small as possible.Argon inlet pipe 8 Effect is to provide cooling for cooling line 71, simultaneously as argon gas has carried out sufficient heat exchange after cooling line 71, Therefore the argon gas sprayed from escape pipe 81 is high temperature argon, so that argon gas, which is directly injected into the silicon liquid of melting, not will lead to silicon liquid Temperature decrease, be conducive to maintain silicon liquid temperature gradient it is unaffected, in addition, injection argon gas purpose be in silicon liquid hang Floating impurity progress is evenly dispersed, so that the silicon ingot ingredient after solidifying is uniform, crystal phase structure is stablized after long crystalline substance, and dislocation density is small, Effectively promote polycrystal silicon ingot quality.

In this polycrystal silicon ingot pouring device, 3 bottom of crucible is laid with one layer of silicon particle 9, and 9 layers of silicon particle form with nothing The supporting structure of several holes, the silicon particle 9 are the high temperature resistant silicon particle 9 of surface coating silicon nitride layer.In silicon particle 9 Original silicon fusing point is 1420 ± 2 °, and traditional half process of smelting uses merely silicon particle 9 to lay 3 bottom of crucible, in ingot casting stove heating, is melted Because affected by many factors during change, once seed crystal has melted, seed crystal forming core cannot be played the role of.And work as 9 surface of silicon particle When being covered with silicon nitride powder, it will play the role of protecting silicon particle 9, so as not to fusing, to be effectively maintained seed crystal. Silicon nitride chemical formula Si3N4, white powder crystal, 1900 DEG C of fusing point, silicon nitride pole high temperature resistant will not be melt into melt body after heated, It can just be decomposed until 1900 DEG C.Therefore in silicon material melting process without repeatedly souning out solid liquid interface, only it need to keep 1420~ Certain time between 1900 DEG C, melting to wear without having to worry about silicon particle 9 influences its function as forming core.3 bottom of crucible Portion and side are coated with silicon nitride coating.The setting of silicon nitride layer on 3 inner wall of crucible, can be effectively prevented the miscellaneous of 3 inner wall of crucible Matter enters in crystal, and prevents polycrystal silicon ingot from viscous pot phenomenon occurs, to improve the quality of polycrystal silicon ingot and reduce casting ingot process Operation difficulty.The furnace body 1 is equipped with vacuum orifice 11 and sets on the crucible guard boards 4 for vacuumizing to furnace body 1 There is exhaust outlet 41, for recycling to injection to the argon gas in crucible 3.

The casting method of this polycrystal silicon ingot pouring device: include the following steps:

1) before, charging, high temperature resistant silicon particle 9 is uniformly layered on to 3 bottom of crucible of spraying silicon nitride, thickness 0.5~ 2cm；

2) it, charges；Silicon material is loaded in crucible 3, and then furnace body 1 is vacuumized；

3), heat: it is high to adjust heat-insulation cage 2 during melting silicon materials for open top part heater 6 and side heater 61 Degree, allows thermal field to form biggish temperature gradient, upper heat and lower cold, to guarantee that silicon material orients fusing from top to bottom；In melting silicon materials 3 bottom of crucible remains i.e. 1420 DEG C of < of supercooling in the process, and high temperature resistant silicon particle 9 is made to be attached to 3 bottom of crucible always；

4) after, silicon material has all melted, 3 bottom high temperature resistant silicon particle 9 of crucible retains 0.1~1.5cm thickness, covers entire earthenware 3 bottom surface of crucible and highly uniform；Argon inlet pipe 8 is opened, argon gas enters cooling pipe by argon inlet pipe 8, on the one hand to heat Switching plane 7 is cooled down, and gas is sprayed in melt upper surface of the argon gas after another aspect is heated into crucible 3, then slowly It is slow to promote heat-insulation cage 2, reduce the temperature of silicon melt, it is 10k/min that temperature, which reduces amplitude, forms certain degree of supercooling, and silicon is molten Body starts to start forming core long crystalline substance on the basis of the silicon particle 9 of endless running down；

5), into after growing crystalline substance, high temperature resistant silicon particle 9 plays the role of good forming core, and melted silicon is vertical on the basis of forming core It is long brilliant, until heat-insulation cage 2 is promoted to all silicon melts and crystallizes completion；

6), after the completion of whole melt crystallizations, annealed and cooling obtains polycrystal silicon ingot.

9 place mat of silicon particle is disorderly arranged, particle layer one supporting structure of formation, supporting structure tool in 3 bottom of crucible There is countless holes, in the melting silicon materials stage, the silicon melt that melting silicon materials are formed will be filled in hole, in initial forming core rank Section, under supercooled state, forms multiple equally distributed forming core sources in 9 level of silicon particle, so that it is good to obtain polycrystal silicon ingot Good initial forming core, and then grow the crystal with advantage crystal orientation.Specifically, control temperature make in silicon melt with it is unfused The silicon material silicon melt that is formed by the silicon melt of solid liquid interface and is filled in hole first reach supercooled state, preferential forming core knot Crystalline substance, subsequent silicon melt circle is mobile away from the direction of 3 bottom of crucible, silicon melt crystallization and freezing.The initial forming core of polycrystal silicon ingot It is well controlled, to grow beneficial to the prevailing crystal of crystal orientation, therefore a large amount of proliferation of dislocation can be prevented, obtained To high quality polycrystal silicon ingot.

In above-mentioned step 4), with the promotion of heat-insulation cage 2, compressor horsepower gradually mentions the frequency-changeable compressor Height, so that argon gas flows fast flow velocity and is gradually increased, 71 heat exchanger effectiveness of cooling line is gradually increased.

This polycrystal silicon ingot pouring device passes through setting auxiliary cooling device, the heat exchange of adjustable bottom heat exchange platform 7 Efficiency eliminates the transverse temperature difference of solid liquid interface so that silicon ingot bottom and side temperature gradient are uniform, so that long chip To stabilization, dislocation density is reduced, in addition, 3 bottom of crucible is laid with high temperature resistant silicon particle 9, on the one hand plays that form crystal phase preferable Forming core effect, on the other hand since silicon particle 9 is coated with high-temperature-resistant layer, can preventing silicon particle 9, all melting leads to texture It is chaotic again, it can play the role of fixing forming core well, guarantee temperature of thermal field gradient stabilization, the high feelings of primary crystalline quality Under condition, crystal growth is good after polycrystal silicon ingot directional solidification, and crystal dislocation density is low, can effectively mention applied on solar battery High incident photon-to-electron conversion efficiency.

The specific embodiments described herein are merely examples of the spirit of the present invention.The utility model institute Belonging to those skilled in the art can make various modifications or additions to the described embodiments or using similar Mode substitute, but without departing from the spirit of the present application or beyond the scope of the appended claims.

Claims (8)

1. a kind of polycrystal silicon ingot pouring device, including furnace body, the interior heat-insulation cage equipped with liftable movement of the furnace body is described Crucible, crucible guard boards, graphite bottom plate, graphite cover board, top heater and side heater, the graphite are equipped in heat-insulation cage Bottom plate is placed on heat exchange platform, and the crucible is placed on graphite bottom plate, which is characterized in that the heat exchange platform It is equipped with auxiliary cooling device, cooling temperature is adjusted in the auxiliary cooling device.

2. a kind of polycrystal silicon ingot pouring device according to claim 1, it is characterised in that: the auxiliary cooling device packet Include the cooling line for being set to heat exchange mesa base, the external argon gas of the cooling line, the air inlet of the cooling line End is equipped with frequency-changeable compressor.

3. a kind of polycrystal silicon ingot pouring device according to claim 2, it is characterised in that: this polycrystal silicon ingot casting device is also Including argon inlet pipe, the argon inlet pipe passes through furnace body, heat-insulation cage, and connects with the cooling line on heat exchange platform It connects, the external escape pipe in the outlet side of the cooling line, the escape pipe is around to heat-insulation cage top and passes through top heating Device and graphite cover board protrude into crucible, the melt above air-flow alignment crucible that the escape pipe sprays.

4. a kind of polycrystal silicon ingot pouring device according to claim 1, it is characterised in that: the auxiliary cooling device packet The cooling water channel being set in heat exchange platform is included, the cooling water channel is circular layout in heat exchange mesa base, described Cooling water channel is equipped with flow control valve, and argon inlet pipe passes through furnace body, heat-insulation cage, top heater and graphite cover board and directly stretches Enter in crucible.

5. a kind of polycrystal silicon ingot pouring device described in any claim in -4 according to claim 1, it is characterised in that: described Crucible bottom is laid with one layer of silicon particle, and silicon particle layer forms the supporting structure with countless holes.

6. a kind of polycrystal silicon ingot pouring device according to claim 5, it is characterised in that: the silicon particle is surface painting Cover the high temperature resistant silicon particle of silicon nitride layer.

7. a kind of polycrystal silicon ingot pouring device described in any claim in -4 according to claim 1, it is characterised in that: described Crucible bottom and side be coated with silicon nitride coating.

8. a kind of polycrystal silicon ingot pouring device described in any claim in -4 according to claim 1, it is characterised in that: described Furnace body be equipped with vacuum orifice, the crucible guard boards be equipped with exhaust outlet.