WO2012139362A1

WO2012139362A1 - Polysilicon ingot casting furnace and polysilicon ingot casting method

Info

Publication number: WO2012139362A1
Application number: PCT/CN2011/080602
Authority: WO
Inventors: 史珺; 宗卫峰; 水川; 佟晨; 程素玲
Original assignee: 上海普罗新能源有限公司
Priority date: 2011-04-11
Filing date: 2011-10-10
Publication date: 2012-10-18
Also published as: CN102732959A

Abstract

Disclosed is a polysilicon ingot casting furnace. A furnace body comprises an upper furnace cover (1), a furnace stack (2) and a furnace bottom (3). The furnace bottom (3) and the furnace stack (2) are connected in a hydraulic manner. A heat insulator is cubic, and the heat insulator comprises an upper heat insulator (8) and a lower heat insulator (4). A graphite platform (6) is located in the heat insulator, and four crucibles are placed on the graphite platform (6). An upper heater (9) and a lower heater (5) are both located in the heat insulator. The upper heater (9) is located under the top surface of the upper heat insulator (8). The lower heater (5) is located under the graphite platform (6). The upper heater (9) and the upper heat insulator (8) are fixed together and fixed on the furnace stack (2). The lower heater (5) and the lower heat insulator (4) are fixed together and are capable of being separated from the upper heat insulator (8) and moving downwards. Further disclosed is a polysilicon ingot casting method. The present invention can improve the throughput of a single ingot casting furnace exponentially while ensuring desired quality, can increase the utilization of existing devices while saving the investment cost of the devices, and can save energy, water and gas.

Description

Polycrystalline silicon ingot furnace and polycrystalline silicon ingot casting method

Technical Field

The invention relates to the field of solar polycrystalline silicon ingots, in particular to a polycrystalline silicon ingot furnace, and to a polycrystalline silicon ingot casting method.

Background Art

Polycrystalline silicon ingot technology was developed from around 2004. When people discovered that the polycrystalline silicon ingots could be sliced and made into solar cells, the polycrystalline silicon ingot furnace was started. Compared with single crystal furnaces, polycrystalline silicon ingot furnaces are characterized by low cost, large output, and easy handling. Since 2007, the global production of polycrystalline silicon photovoltaic cells has surpassed that of monocrystalline silicon. By 2010, the proportion of polycrystalline silicon has risen to more than 70%.

The existing polycrystalline silicon ingot furnace adopts electric resistance or induction heating to melt the polycrystalline silicon with a good ratio, and then adopts a method of solidifying from the bottom and gradually solidifying upward crystal growth to obtain a polycrystalline silicon ingot. Since 2004, the output of the existing polycrystalline silicon ingot furnace has ranged from 120 kg to 170 kg, 250 kg, 450 kg to 660 kg. Due to the larger single furnace output of the existing polycrystalline silicon ingot furnace, the higher the production efficiency and the lower the unit energy consumption, therefore, many manufacturers hope to develop a higher yield polycrystalline silicon ingot furnace.

At present, the existing polysilicon ingot furnace that can be seen on the market has a maximum capacity of 660 kg, which is a single silicon ingot. Some companies have tried 800 kilograms, but they have been stranded for various reasons. The main reason is that if the weight of a single silicon ingot is too large, the size must be correspondingly increased. In the long crystal phase of the ingot, the bottom of the ingot is cooled first, and the top is cooled, so that the crystal can grow slowly from the bottom to the top. The cooling is carried out by the bottom silicon crystal carrying the heat to the bottom. However, if the size of the silicon ingot is too large, since the thermal conductivity of the silicon crystal is not good, the temperature difference between the bottom and the top will be too large to generate stress, and in addition, the crystal is too long to cause deformation during crystal growth, and, moreover, What is important is that too large silicon ingots bring difficulties to the manufacture of tantalum and the processing of silicon ingots and the opening of silicon ingots. Not only do new types of ancillary equipment are required, but also the cost of such accessories and the like. A big challenge. Therefore, the method of increasing the single silicon ingot not only has little contribution to the improvement of the single furnace output, but also has already faced a bottleneck.

Technical Problem

The technical problem to be solved by the present invention is to provide a polycrystalline silicon ingot furnace which can double the output of a single ingot furnace and ensure good quality without changing the niobium and silicon ingot access and the opening device for the ingot. Therefore, the utilization rate of the existing equipment can be improved and the investment cost of the equipment can be saved, energy saving, water saving, and solar saving can be saved, and the cost can be saved. To this end, the present invention also provides a polycrystalline silicon ingot casting method using the polycrystalline silicon ingot furnace.

Technical Solution

In order to solve the above technical problems, the polycrystalline silicon ingot furnace provided by the present invention comprises: a furnace body and a heat insulator in the furnace body, a graphite platform, four crucibles, an upper heating body and a lower heating body. The furnace body includes an upper furnace cover, a furnace body and a furnace bottom, and the furnace bottom and the furnace body are hydraulically connected, and the furnace bottom can be separated or closed from the furnace body. The heat insulating body is cuboidal, and the heat insulating body comprises an upper heat insulating body and a lower heat insulating body. The graphite platform is located in the heat insulator and surrounded by the heat insulator, and the four crucibles are placed on the graphite platform. The upper heating body and the lower heating body are both located in the heat retaining body, and the upper heating body is located below the top surface of the upper heat insulating body of the top of the crucible, and the lower heating body is located at the graphite Below the platform, the upper heating body and the upper heat retaining body are fixed together and fixed to the furnace body, and the lower heating body and the lower heat insulating body are fixed together and can be separated from the upper heat insulating body together Move Downward.

A further improvement is that the four crucibles are placed on the graphite platform in a field shape.

A further improvement is that the sides of the four turns are 720 mm to 1200 mm, respectively.

A further improvement is that the four crucibles are standard gauges or special gauges for solar grade polycrystalline silicon ingots.

A further improvement is that the upper heating body completely covers the four turns, and the outer edge of the upper heating body is larger than the outer edge of the four turns by 5% to 30%, and the four turns are The outer side surface and the heat retaining body are spaced apart by a distance, and a portion of the upper heating body outside the outer edge of the four turns is used to heat the sides of the four turns.

A further improvement is that a shield is placed around each of the turns.

A further improvement is that the upper heating body is composed of two heating circuits, which can work simultaneously and can also be hot backups to each other.

A further improvement is that the lower heat retaining body is connected to the lifting and lowering mechanism, and the lower heat insulating body is lowered by the lifting and lowering mechanism.

In order to solve the above technical problem, the polycrystalline silicon ingot method provided by the present invention comprises the following steps:

Step 1. Lowering and opening the bottom of the furnace with a hydraulic device and loading the silicon material into the four crucibles,

Step 2: Raise the bottom of the furnace to close it and start vacuuming.

Step 3: When the degree of vacuum of the furnace body reaches 1 Pa, the upper heating body and the lower heating body are powered, and the heating of the silicon material is started and the silicon material is completely melted.

Step 4, performing a crystal growth process, comprising the steps of: gradually reducing the power of the lower heating body to gradually lower the temperature of the bottom of the crucible, and when the bottom temperature of the crucible is lower than the melting point of the silicon material Crystallization starts and polysilicon is formed; when the power of the lower heating body drops to zero, the lower heat insulator and the lower heater are lowered together, so that the polysilicon continues to grow upward.

Step 5: lifting the lower heat insulator and the lower heat body, annealing the polysilicon, and then cooling the polysilicon.

Step 6. When the temperature of the polycrystalline silicon ingot formed by the polysilicon is lowered to 300 ° C or lower, the bottom of the furnace is lowered and the polycrystalline silicon ingot is taken out.

Advantageous Effects

The beneficial effects of the invention are:

1 The polycrystalline silicon ingot furnace of the invention has four crucibles, and can realize four furnaces for producing four polycrystalline silicon ingots, thereby multiplying the output of the single ingot furnace.

2 The design of the edge of the upper heating body of the polycrystalline silicon ingot furnace of the present invention is larger than the size of the edge of the four crucibles, so that the upper heating body can be heated at the upper portion to realize the four crucibles. The side heating can form a gradient gradually decreasing from the top to the bottom on the sides of the four turns during the growth of the polysilicon, so that the isothermal surface in each of the crucibles can be horizontal, and the heat dissipation on the outer side of the crucible can be solved. The problem of the level of the isothermal surface is not high. A good isothermal surface can ultimately improve the quality of the polycrystalline silicon ingot. At the same time, the polycrystalline silicon ingot furnace of the present invention does not need to increase the size of each polycrystalline silicon ingot to increase the yield of the polycrystalline silicon ingot, and can avoid the horizontal temperature field of the crucible caused by the large-sized polycrystalline silicon ingot being difficult to maintain, and the vertical temperature difference It will be very large and the resulting crystal growth quality will be deteriorated, so that good columnar crystals can be formed and the quality of the product can be improved.

3 The polycrystalline silicon ingot furnace of the present invention does not need to change the bismuth and silicon ingot access and the opening device for the ingot, that is, the polycrystalline silicon ingot furnace of the invention can be compatible with the equipment on the existing production line, thereby saving investment cost, and Can improve production efficiency.

4 The four enamels of the present invention are placed in a field and have a certain space in the middle for placing the slabs, the ratio of the insulating cage area to the rated output or the insulation of the silicon material. The specific surface area is significantly lower than that of the existing single ingot; in addition, the design of the upper heating body of the present invention can omit the side heating body, so that the furnace type of the present invention can have significant energy saving effect, and the present invention can also be used Water and solar terms can save costs.

Description of Drawings

1 is a schematic cross-sectional view showing a polycrystalline silicon ingot furnace according to an embodiment of the present invention;

2 is a top crystal photograph of a polycrystalline silicon ingot produced by a polycrystalline silicon ingot method according to an embodiment of the present invention;

3 is a longitudinal cross-sectional photograph of a polycrystalline silicon ingot produced by a polycrystalline silicon ingot method according to an embodiment of the present invention;

4 is a top crystal photograph of a polycrystalline silicon ingot produced by the method of polycrystalline silicon ingot according to the second embodiment of the present invention;

Figure 5 is a longitudinal cross-sectional photograph of a polycrystalline silicon ingot produced by the method of polycrystalline silicon ingot according to the second embodiment of the present invention;

6 is a top crystal photograph of a polycrystalline silicon ingot produced by the method of three polycrystalline silicon ingots according to an embodiment of the present invention;

Figure 7 is a longitudinal cross-sectional photograph of a polycrystalline silicon ingot produced by the third polycrystalline silicon ingot method of the embodiment of the present invention.

Best Mode

Mode for Invention

As shown in FIG. 1, it is a schematic cross-sectional view of a polycrystalline silicon ingot furnace according to an embodiment of the present invention.

The polycrystalline silicon ingot furnace of the embodiment of the invention comprises: a furnace body and a heat insulator in the furnace body, a graphite platform 6, four crucibles 7, an upper heating body 9 and a lower heating body 5.

The furnace body comprises an upper furnace cover 1, a furnace body 2 and a furnace bottom 3, and the furnace bottom 3 and the furnace body 2 are hydraulically connected, and the furnace bottom 3 and the furnace body can be passed by the hydraulic device 2 Separate or closed, used to load and unload silicon or polycrystalline silicon ingots. The furnace body shell is made of a stainless steel water-cooled furnace shell. The upper furnace cover 1 functions to fix the upper heating body 9, connect the heating water cable, install the top temperature measuring device, and connect the ventilation pipe. The furnace body 2 is fixed with a side insulator, that is, an insulator constituting the heat insulator, and is also connected to a vacuum pipeline. The furnace body 2 is supported on the ground by four brackets, the upper furnace cover 1 is directly placed on the furnace body 2 and sealed by a flange; the furnace bottom 3 is suspended by a hydraulic system On the furnace body 2, when the hydraulically controlled furnace bottom is lifted and sealed, the vacuum sealing is also performed through the flange. The hearth 3 and the furnace body 2 adopt a hydraulic suspension mechanism, and the hydraulic mechanism can control the furnace bottom 3 to stop at any height within the stroke. The furnace bottom 3 is provided with a plurality of temperature measuring points, which can measure the temperature of each raft and different positions, so that the bottom temperature condition in the furnace can be clearly displayed on the display and provided to Control System.

The heat insulating body is cuboidal, and the heat insulating body includes an upper heat insulating body 8 and a lower heat insulating body 4. The graphite platform 6 is located in the heat insulator and surrounded by the heat insulator, and the four turns 7 are placed on the graphite platform 6. The size of the crucible may be a standard polycrystalline silicon ingot such as 450 kg, 500 kg, 660 kg or 800 kg, and the sides of the four crucibles are respectively 720 mm to 1200 mm.

The four crucibles 7 are placed in a field shape with a certain space in the middle for placing the crucible guards. Due to the geometry of 4 ingots corresponding to the arrangement of the four crucibles 7, the ratio of the area of the insulating cage to the rated output or the specific surface area of the insulator used for the silicon material is significantly lower than that of the single ingot. Therefore, the furnace has a remarkable energy saving effect, and the unit energy consumption is reduced by about 20% compared to the single furnace type. At the same time, the argon consumption is reduced by about 60% relative to the single furnace type. The size of the graphite platform 6 has a certain margin and may be slightly larger or slightly smaller.

The upper heating body 9 and the lower heating body 5 are both located in the heat retaining body, and the upper heating body 8 is located below the top surface of the upper heat insulating body 8 at the top of the crucible 7, and the lower heating The body 5 is located below the graphite platform 6, the upper heating body 9 and the upper heat retaining body 8 are fixed together and fixed on the furnace body 2, and the lower heating body 5 and the lower heat insulating body 4 are fixed. Together and together with the upper insulation 8 and moving downwards. The lower heat retaining body 4 is connected to the lifting and lowering mechanism, and is lowered by the lifting and lowering mechanism. During the ingot casting process, the lower heat retaining body 4 is lowered, and the graphite platform 6 is not lowered; when the loading and unloading are performed, the lower heat insulating body 4 and the graphite platform 6 (with four crucibles 7) are lowered together. .

The upper heating body 9 completely covers the four crucibles 7, and the outer edge of the upper heating body 9 has a size larger than the outer edge of the four crucibles 7 by 5% to 30%. The side surface and the heat insulator are spaced apart by a distance, and a portion of the upper heating body 9 outside the outer edge of the four turns 7 is used to heat the sides of the four turns. The growth quality of polycrystalline silicon used in solar photovoltaic cells has a strong relationship with the final cell efficiency. If you want to get good battery quality, you need a larger grain size and the crystal column growth direction is as vertical as possible. For this reason, it is required that the isothermal surface inside the crucible 7 is as horizontal as possible during crystal growth. Since the invention adopts up-and-down heating and no side heating, when the crystal grows, it is easy to cause the outer sides of the four crucibles to be supercooled, and the periphery of the crucible is first cooled, so that the crystal grows from the outside to the inside. Therefore, the outer diameter of the upper heating body 9 is increased in size, and the outer side surface of the crucible 7 is kept at a certain distance from the heat insulating body, so that the outer side surface of the crucible 7 can be always used by the upper heating body 9. Heating is taking place. Moreover, since the upper heating body 9 has a large heating to the upper portion and a lower temperature at the bottom portion, a lower temperature gradient is formed on the side surface to ensure the level of the isothermal surface inside the four crucibles 7. The unique design of the upper heating body 9 not only can provide heat to the silicon material, but also maintains the top temperature when the silicon is fused and directional solidification, and can also maintain a high temperature lower than the side of the crucible during directional solidification. The gradient keeps the solid-liquid interface in the crucible horizontal and ensures the quality of the crystal growth. This design not only improves the crystal growth quality, but also saves energy by eliminating the side heating body.

The upper heating body 9 is composed of two heating circuits, and the two circuits can work at the same time or can be hot backup each other. When one heating circuit fails to work normally, another heating circuit can ensure the melting and crystal growth of the silicon material. The completion. Since the top heating can not be interrupted during ingot casting, this design greatly improves the reliability of the equipment operation and reduces the accident rate. Both sets of graphite heating bodies are connected to the external transformer through the inner and outer water cables. This design ensures that the silicon material is melted at the fastest rate when the silicon material melts, ensuring maximum energy savings and maximum yield.

The lower heating body 5 works simultaneously with the upper heating body 9 when the silicon is melted, so that the silicon can be melted with the highest efficiency, which not only saves energy but also shortens the working time. When the directional solidification is started, the power of the lower heating body 5 can be gradually reduced according to the program. When the power is reduced to zero, the lower thermal insulation of the bottom begins to descend, and the bottom begins to dissipate heat, and the lowering speed of the lower thermal insulation body can be according to the bottom temperature curve. Control, to ensure that the temperature of the bottom of the ingot is lowered according to the set curve, and the silicon ingot is allowed to grow at a set rate.

In the polycrystalline silicon ingot casting method, the upper and lower double temperature zone resistance heating and melting silicon material is adopted, and the thermal field method is a DSS method in which the crucible and the thermal insulation body are relatively fixed, and the bottom cooling method is used to complete the directional solidification of the crystal. The polycrystalline silicon ingot method of the embodiment of the invention comprises the following steps:

Step 1. The hydraulic system is used to lower and open the furnace bottom 3 and the silicon material is loaded into the four crucibles 7, so that the upper thermal insulation body 8 and the lower thermal insulation body 4 are closed.

Step 2: Raise the bottom 3 to close it and start vacuuming.

Step 3: When the degree of vacuum of the furnace body reaches 1 Pa, the upper heating body 9 and the lower heating body 5 are powered, and the upper and lower heating bodies are simultaneously heated at a high power to drive the silicon at a maximum speed. The material is completely melted.

Step 4: performing a crystal growth process, including a sub-step: gradually reducing the power of the lower heating body, so that the temperature of the bottom of the crucible is gradually decreased, and when the temperature of the bottom of the crucible 7 is lower than the melting point of the silicon material, that is, 1410 ° C. At 1414 ° C, the bottom of the crucible 7 begins to crystallize and form polysilicon. When the power of the lower heating body 5 drops to zero, the temperature drop rate at the bottom of the crucible 7 will slow down or even stop falling, at which time crystal growth may be slowed or even stopped; thus, in the embodiment of the present invention When the bottom heating power is reduced to zero, the lower heat retaining body 4 and the lower heating body 5 are lowered together, so that the crucible 7 radiates heat to the periphery of the furnace bottom 3, thereby making the crucible 7 The temperature of the lower heat retaining body 4 is controlled according to the bottom temperature curve, and the temperature of the bottom of the polycrystalline silicon ingot formed by the polycrystalline silicon is lowered according to a set curve, so that the polycrystalline silicon ingot is crystallized at a set rate. Growing. During the calculated time, when the polysilicon is grown to the top of the crucible 7, the power of the upper heating body 9 is gradually reduced.

Step 5: Lifting the lower heat insulator 4 and the lower heating body 5, annealing the polysilicon, and then cooling the polysilicon.

Step 6. When the temperature of the polycrystalline silicon ingot formed by the polycrystalline silicon is lowered to below 300 ° C, the furnace bottom 3 is lowered and the polycrystalline silicon ingot is taken out.

The method of increasing the ingot yield of a single furnace by using a multi-ingot furnace as described in the embodiment of the present invention, rather than adopting a method of simply increasing the size of the ingot, brings many advantages.

First, if the size of a single ingot is too large or too high, not only is the horizontal temperature field inside each crucible difficult to maintain, but the temperature difference in the vertical direction is also large, resulting in deterioration of crystal growth quality. Experiments have shown that when the size of the ingot exceeds 360 mm, it is difficult for the ingot to grow into a good columnar crystal from the bottom to the top, and the columnar crystal is necessary for the polycrystalline silicon wafer.

In addition, the increase in the size of the ingot requires a simultaneous increase in the size of the crucible, and at the same time, the loading of a single crucible and the removal and transportation of the ingot are greatly increased. In addition, the opening and cutting of large-sized silicon ingots will also present special requirements for the corresponding equipment. This will make the procurement of equipment and equipment more difficult and costly.

Therefore, the manner in which the four spindles are described in the present invention completely avoids the above problems. By using the ingot furnace of the invention, the subsequent silicon ingot processing equipment can be completely universal from transportation to opening and cutting, greatly reducing the equipment input of the user and improving the utilization rate of the existing equipment. Because of the standard size and weight of the ingot, the user can fully use the existing ingot opening and slicing of the existing ingots, saving a lot of equipment investment. Silicon ingots can be processed and handled using existing equipment without having to reorder.

In a preferred embodiment of the present invention, the polycrystalline silicon ingot furnace has a single furnace output of 1800 kg, and uses four common 450 kg crucibles, the outer diameter of the furnace is 4 meters, and the heating power is 1200 kilowatts. After testing, the polycrystalline silicon ingot furnace of the preferred embodiment of the present invention saves 20% energy, 30% water saving and more than 60% solar energy than a single 450 kg ingot furnace. Table 1 is a comparison table of operating parameters of a polycrystalline silicon ingot furnace and an existing 450 kg furnace type according to a preferred embodiment of the present invention.

Table 1

项目 project	本发明一较佳实施例多晶硅铸锭炉 Polycrystalline silicon ingot furnace according to a preferred embodiment of the present invention	现有450公斤炉型 Existing 450 kg furnace type
单炉产量 Single furnace output	1800 公斤～2000公斤 1800 kg to 2000 kg	450 公斤～500公斤 450 kg to 500 kg
单个硅锭重量 Single ingot weight	450 公斤～500公斤 450 kg to 500 kg	450 公斤～500公斤 450 kg to 500 kg
单炉最大年产硅锭数量 The maximum annual output of silicon ingots in a single furnace	576 锭 576 spindles	144 锭 144 spindles
单炉最大年产量 Maximum annual output of single furnace	288 吨 288 tons	72 吨 72 tons
100MW 硅片所需设备台数 Number of equipment required for 100MW silicon wafer	≤4 ≤4	≤16 ≤16
硅锭成品规格 Silicon ingot finished product specifications	840×840×(≥260)mm 840×840×(≥260)mm	840×840×(≥260)mm 840×840×(≥260)mm
单次加工周期 Single processing cycle	58 小时 58 hours	58 小时 58 hours
装机功率 Installed power	1200KVA 1200KVA	三组加热，单组最大350 KVA Three groups of heating, single group up to 350 KVA
单位电耗* Unit power consumption*	≤8kwh/kg ≤8kwh/kg	≤10kwh/kg ≤10kwh/kg
循环水流量 Circulating water flow	560L /min 560L / min	200L /min 200L / min
气耗 Gas consumption	<80m³ <80m ³	<58m³ <58m ³

* The power consumption values of both furnace types are measured when using ordinary hard felt as insulation layer.

The steps of the polycrystalline silicon ingot method of the embodiment of the present invention are as follows:

Step 1. Four 870 x 870 x 420 mm quartz crucibles 7 were placed on the graphite platform 6 in the polycrystalline silicon ingot of the embodiment of the present invention, and each of the crucibles 7 was charged with 430 kg.

Step 2: The outside of the crucible 7 is surrounded by a graphite shield, and then the furnace bottom 3 is raised. When the furnace bottom 3 and the furnace body 2 are completely close together, vacuuming is started.

Step 3: When the degree of vacuum reaches 1 Pa, the upper and

lower heating bodies

5 and 9 are started to be powered to start heating the molten silicon. After about 6 hours, the silicon material began to melt. Wait another 2 hours, after the silicon material is completely melted, it is kept at a temperature of 1490 ° C for about half an hour, that is, the temperature is lowered.

Step 4: Perform a crystal growth process, including a sub-step: the top temperature of the crucible 7 is lowered from 1460 ° C to 1400 ° C, and the bottom of the crucible 7 is cooled from 1450 ° C to 950 ° C, and the cooling time is about 32 hours. This process is a crystal growth process of a silicon ingot, that is, a polycrystalline silicon ingot. In the above process, the lower heat retaining body 4 needs to be lowered at about 1200 ° C, otherwise the bottom temperature cannot be lowered in time.

Step 5, then the top temperature is lowered to 1350 ° C in 2 hours. At this time, the lower heat retaining body 4 is lifted again to be close to the upper heat insulating body 8 . It was further reduced to 1150 ° C in 3 hours and kept at 1150 ° C for 2 hours. This process is the process of annealing the ingot. After that, cool down to 900 °C in 3 hours, turn off the heating power, and let the silicon ingot automatically cool down. This is the cooling phase.

Step 6. When the temperature in the furnace is lower than 300 ° C, the lower heat retaining body 4 can be lowered, and the silicon ingot and the 坩埚 7 connecting guard plate are taken out from the furnace by a forklift, and placed in a non-ventilated manner. The room is naturally cooled.

After the outer surface of the above silicon ingot produced by the polycrystalline silicon ingot method of the embodiment of the present invention is removed, the photo of the top crystal is as shown in FIG.

Cutting is performed in the longitudinal direction of the silicon ingot, and a photograph of the cross section is shown in FIG. After inspection, the four silicon ingots are more uniform in crystallization, indicating that the temperature field control meets the design requirements.

The resistivity of the silicon ingot was measured, and the obtained value was between 1 Ω·cm and 2.5 Ω·cm, and the minority carrier lifetime was tested, both of which were 2 μsec or more.

The silicon ingot fully meets the standard requirements of solar cells. After the solar cell was fabricated on the silicon wafer, that is, the silicon ingot, the average conversion efficiency was 16.5%.

The steps of the method for ingot casting polycrystalline silicon according to the second embodiment of the present invention are as follows:

Step 1. Put four 870x870x480 quartz crucibles 7 into the ingot furnace described in the embodiment of the present invention, that is, the graphite platform 6 in the polycrystalline silicon ingot furnace, and each of the crucibles 7 is charged with 490 kg. A total of 1960 kg was charged.

Step 3: When the degree of vacuum reaches 1 Pa, the upper and

lower heating bodies

5 and 9 are started to be powered to start heating the molten silicon. After about 5 hours, the silicon material began to melt. After waiting for another 3 hours, the silicon material is completely melted and maintained at a temperature of 1490 ° C for about half an hour, that is, the temperature is lowered.

Step 4: Perform a crystal growth process, including a sub-step: the top temperature is lowered from 1460 ° C to 1400 ° C, and the bottom is cooled from 1450 ° C to 900 ° C, and the cooling time is about 34 hours. This process is a crystal growth process of a silicon ingot. In the above process, the lower heat retaining body 4 needs to be lowered at about 1200 ° C, otherwise the bottom temperature cannot be lowered in time.

Step 5, then the top temperature is cooled to 1350 ° C in 2 hours. At this time, the lower heat retaining body is lifted again to the upper heat retaining body. It was further reduced to 1150 ° C in 3 hours and kept at 1150 ° C for 2 hours. This process is the process of annealing the ingot. After that, cool down to 900 °C in 3 hours, turn off the heating power, and let the silicon ingot automatically cool down. This is the cooling phase.

Step 6. When the temperature in the furnace is lower than 300 °C, the lower insulation body can be lowered, and the silicon ingot and the Qilian shield are taken out from the furnace by a forklift, and placed in a non-ventilated room to be naturally cooled.

After the outer surface of the above silicon ingot produced by the method of the polycrystalline silicon ingot of the second embodiment of the present invention is removed, the photo of the top crystal is as shown in FIG.

The cutting is performed in the longitudinal direction of the silicon ingot, and a photograph of the cross section is shown in Fig. 5. After inspection, the four silicon ingots are more uniform in crystallization, indicating that the temperature field control meets the design requirements.

The resistivity of the silicon ingot was tested to obtain a value between 1.2 Ω·cm and 2.5 Ω·cm, and the minority carrier lifetime was tested, both of which were above 2 microseconds.

The silicon ingot fully meets the standard requirements of solar cells. After the solar cell was fabricated on the silicon wafer, the average conversion efficiency was 16.7%.

The steps of the third polycrystalline silicon ingot method of the embodiment of the present invention are as follows:

Step 1. Four 1020 x 1020 x 480 mm quartz crucibles 7 were placed on the graphite platform 6 in the ingot furnace described in the examples of the present invention, and each of the crucibles 7 was charged with 660 kg, and a total of 2,640 kg was charged.

Step 2: The outside of the crucible 7 is surrounded by a graphite shield, and then the bottom 3 is raised. When the bottom 3 and the shaft 2 are completely closed, vacuuming is started.

Step 3: When the degree of vacuum reaches 1 Pa, the upper and

lower heating bodies

5 and 9 are started to be powered to start heating the molten silicon. After about 7 hours, the silicon material began to melt. After waiting for another 3 hours, the silicon material is completely melted and maintained at a temperature of 1500 for about half an hour, that is, the temperature is lowered.

Step 4: Perform a crystal growth process, including a sub-step: when the temperature is lowered to 1460 ° C, the temperature is maintained for 1 hour. Then, the top temperature is lowered from 1460 ° C to 1400 ° C, and the bottom is cooled from the current temperature to 860 ° C, and the cooling time is about 34 hours. This process is a crystal growth process of a silicon ingot. In the above process, the lower heat retaining body 4 needs to be lowered at about 1200 ° C, otherwise the bottom temperature cannot be lowered in time.

Step 5, then the top temperature is lowered to 1350 ° C in 2 hours. At this time, the lower heat retaining body 4 is lifted again to be close to the upper heat insulating body 8 . It was further reduced to 1150 ° C in 3 hours and kept at 1150 ° C for 2 hours. This process is an ingot annealing stage. After that, cool down to 900 °C in 3 hours, turn off the heating power, and let the silicon ingot automatically cool down. This is the silicon ingot cooling stage.

Step 6. When the temperature in the furnace is lower than 300 °C, the lower heat retaining body 4 can be lowered, and the silicon ingot and the 坩埚7 connecting plate are taken out from the furnace by a forklift, and placed in a non-ventilated room to be naturally cooled.

After the outer surface of the above silicon ingot produced by the method of the polycrystalline silicon ingot of the second embodiment of the present invention is removed, the photo of the top crystal is shown in Fig. 6.

The ingot fully meets the standard requirements of solar cells. After the solar cell was fabricated on the silicon wafer, the average conversion efficiency was 16.7%.

The present invention has been described in detail by way of specific examples, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention.

Industrial Applicability

Sequence List Text

Claims

1 a polycrystalline silicon ingot furnace, comprising: a furnace body and a heat retaining body located in the furnace body, a graphite platform, four crucibles, an upper heating body and a lower heating body;

The furnace body includes an upper furnace cover, a furnace body and a furnace bottom, and the furnace bottom and the furnace body are hydraulically connected, and the furnace bottom can be separated or closed from the furnace body;

The heat insulating body is cuboidal, and the heat insulating body comprises an upper heat insulating body and a lower heat insulating body;

The graphite platform is located in the heat insulator and surrounded by the heat insulator, and the four crucibles are placed on the graphite platform;

The upper heating body and the lower heating body are both located in the heat retaining body, and the upper heating body is located below the top surface of the upper heat insulating body of the top of the crucible, and the lower heating body is located at the graphite Below the platform, the upper heating body and the upper heat retaining body are fixed together and fixed to the furnace body, and the lower heating body and the lower heat insulating body are fixed together and can be separated from the upper heat insulating body together Move Downward.

2 The polycrystalline silicon ingot furnace according to claim 1, wherein the four crucibles are placed on the graphite platform in a field shape.

3 The polycrystalline silicon ingot furnace according to claim 1, wherein the four sides have a side length of 720 mm to 1200 mm.

4 The polycrystalline silicon ingot furnace according to claim 1, wherein said upper heating body completely covers said four turns, and said outer heating body has an outer edge size larger than an outer edge size of said four turns %～30%, the outer sides of the four turns are separated from the heat insulating body by a certain distance, and the portion of the upper heating body outside the outer edge of the four turns is used for the four turns The side is heated.

5. A polycrystalline silicon ingot furnace according to claim 1, wherein a shield is placed around each of said weirs.

6 The polycrystalline silicon ingot furnace according to claim 1, wherein the upper heating body is composed of two heating circuits, and the two heating circuits can work simultaneously and can also be hot backups to each other.

7. A method of ingot casting polysilicon, comprising the steps of:

Step 1: using a hydraulic device to lower and open the furnace bottom and loading silicon material into the four crucibles;

Step two, raising the bottom of the furnace to close it, and starting to vacuum;

Step 3: when the degree of vacuum of the furnace body reaches 1 Pa, the upper heating body and the lower heating body are powered, and the heating of the silicon material is started and the silicon material is completely melted;

Step 4, performing a crystal growth process, comprising the steps of: gradually reducing the power of the lower heating body to gradually lower the temperature of the bottom of the crucible, and when the bottom temperature of the crucible is lower than the melting point of the silicon material Starting to crystallize and form polysilicon; when the power of the lower heating body drops to 0, the lower heat insulator and the lower heating body are lowered together, so that the polysilicon continues to grow upward;

Step 5: lifting the lower heat insulator and the lower heating body, annealing the polysilicon, and then cooling the polysilicon;