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Pingdingshan Wanhui Graphite Co., Ltd.
Pingdingshan Wanhui Graphite Co., Ltd.

Isostatic Graphite Block Used for Thermal Field Systems in Semiconductor and Photovoltaic Industries in the Manufacture of Crystalline Silicon

In the semiconductor industry, isostatic graphite blocks exhibit good isotropy, excellent thermal conductivity, good resistance to thermal shock, high resistance to bending and compression, and can effectively reduce the internal stress generated by sudden temperature changes, thus extending the lifespan of equipment and appliances. Therefore, they are used in the deep processing of graphite components for silicon crystal growth equipment in the fields of semiconductor and solar photovoltaic power generation. With the rapid development of the photovoltaic industry, the size of the monocrystalline silicon thermal field has grown from 24 inches to 36 inches, and the size of the graphite thermal field components used has increased accordingly, with technical requirements constantly improving, particularly requiring high-purity graphite.

1. Isostatic graphite blocks for heat field systems

In the direct drawing monocrystalline silicon thermal field, the isostatic graphite block components include about 30 types of crucibles, heaters, electrodes, heat insulation shielding plates, seed crystal clamps, rotating crucible base plates, various circular plates, and thermal reflection plates. Among them, 80% of isostatic graphite blocks are used to manufacture crucibles and heaters. In recent years, the diameter requirements for monocrystalline silicon rods have been increasingly higher, with the production of 300mm chips becoming mainstream, and accordingly, the diameter of the monocrystalline furnace heating zone is mostly 800mm. The graphite crucible in the furnace reached a diameter of 860mm to protect the placed quartz crucible, the diameter of the heater was about 960-1000mm, and the diameter of some other components reached a maximum of 1500mm. In the manufacturing process of multi-crystalline silicon wafers for solar cells, the first step is to melt the multi-crystalline silicon fragments into multi-crystalline silicon ingots, and the heater of the ingot casting furnace needs to be made of isostatic graphite blocks.

2. Use of isostatic graphite blocks

1. Monocrystalline pulling furnace thermal field system. The monocrystalline pulling furnace thermal field system is mainly used in the monocrystalline silicon growth and pulling processes in the photovoltaic and semiconductor industries, and is a key equipment for preparing monocrystalline silicon. The photovoltaic silicon monocrystalline manufacturing process evolved from the semiconductor silicon monocrystalline, and the two have the same framework in terms of equipment, process, and thermal field system, with the main difference being the purity of the silicon monocrystal product and the purity requirements for thermal field materials. The purity requirements for semiconductor silicon monocrystals are higher than 99.99%, while for photovoltaic silicon monocrystals, a purity higher than 99.99% is sufficient; regarding the requirements for ash content in thermal field materials, photovoltaic P-type monocrystals require<200ppm, N-type monocrystals require <100ppm, and semiconductor silicon monocrystals require <30ppm.

2. Polycrystalline ingot furnace thermal field system. The polycrystalline ingot furnace thermal field system is a key equipment for polycrystalline ingot casting in the photovoltaic industry, mainly including top plates, heating bodies, cover plates, protective plates and other components.

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