A polycrystalline silicon ingot casting device and a method for preparing a silicon ingot

Abstract

The application provides a polysilicon ingot casting device and a method for preparing a silicon ingot. The device includes a quartz crucible and several composite guard plates arranged on the outer periphery of the quartz crucible; each of the composite guard plates includes a graphite layer and is arranged on A metal isolation layer on the graphite layer; the metal isolation layer is in contact with the quartz crucible. The polysilicon ingot casting device is provided with a metal isolation layer on the graphite layer, and the metal isolation layer can hinder the dry reaction between the quartz crucible and the graphite to produce carbon compounds, reduce the carbon content in the silicon ingot, and then improve the quality of the silicon ingot. The effective utilization rate; the grade A rate of polysilicon wafers made by slicing silicon ingots is improved, and the disconnection rate is reduced. Experimental results show that: using the polysilicon ingot casting device provided by the application, the carbon content in the silicon wafer is reduced by 1.5-3ppm; the effective utilization rate of the silicon ingot is increased by 1.2-3.5%; at the same time, the disconnection rate of the silicon wafer is reduced by 0.5-2.5%. The grade A rate of silicon wafers increases by 0.5-1.5%.

Description

technical field [0001] The present application relates to the technical field of polysilicon ingot casting, in particular to a polysilicon ingot casting device and a method for preparing a silicon ingot. Background technique [0002] At present, when casting silicon ingots in ingot furnaces in the photovoltaic industry, advanced directional solidification technology is generally used to make directional growth of grains. The key point of this technology is to gradually cool the molten silicon material from the bottom of the crucible upwards to reach the silicon The purpose of directional crystallization of the ingot from the bottom of the crucible to the top of the crucible. [0003] see figure 1 , figure 1 It is a structural schematic diagram of a photovoltaic ingot casting furnace in the prior art. Since the quartz crucible 02 will soften at high temperature, when the crucible is in a softened state, it cannot bear the silicon material inside because it is heated, expand...

AI Technical Summary

Problems solved by technology

[0004] At present, the thermal field environment of polycrystalline ingots is a carbon environment. The graphite shield is directly in contact with the quartz crucible for heat conduction and heat preservation. Under high temperature conditions, the graphite shield will undergo a dry reaction in contact with the quartz crucible to produce carbon-containing compounds, such as carbon dioxide. The generated carbon dioxide will enter the silicon liquid, eventually increasing the carbon content of the silicon ingot, bringing hard spots, shadows and other impurities, affecting the effective utilization of the silicon ingot

The existing technology relies on the gas to take away carbon-containing compounds by increasing the gas flow rate during the polycrystalline ingot casting process, but the effective utilization rate of silicon ingots obtained in this way is still low

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