Annealing technique of cast polycrystalline silicon

Abstract

The invention relates to an annealing technique of cast polycrystalline silicon, which uses a polycrystalline silicon ingot casting furnace, wherein the polycrystalline silicon ingot casting furnace comprises a heat insulation cage and a heat insulation base plate arranged below the heat insulation cage, a crucible is arranged in the heat insulation cage, and the external surface of the bottom of the crucible is provided with a graphite base plate. After the polycrystalline silicon growth step in the crucible, the height of the heat insulation cage or heat insulation base plate is lowered or enhanced to adjust the distance between the heat insulation cage and heat insulation base plate, so that the temperature in the crucible drops at the rate of 0.5-5 DEG C / minute, and the crucible bottom temperature fluctuation does not exceed 50 DEG C; and when the difference between the temperature in the crucible and the temperature of the crucible bottom is within 50 DEG C, the annealing is completed. The crucible bottom temperature is the temperature below the crucible bottom graphite protecting sheet. The technique reduces the back diffusion of impurities, greatly enhances the yield of the silicon bulk, and saves the energy consumption.

Description

technical field [0001] The invention relates to an annealing process of cast polycrystalline silicon. Background technique [0002] In the solar photovoltaic field, crystalline silicon accounts for more than 90% of the entire solar photovoltaic field due to its raw material source and preparation cost advantages. In the preparation process of crystalline silicon, polysilicon ingot technology plays a dominant role. The polysilicon ingot and silicon wafer manufacturing process technology is to use a large heat exchange ingot furnace, apply directional solidification technology, control the input and output of heat, and grow polysilicon ingots under a lower temperature gradient. The usual ingot process flow is: heating , melting, crystal growth, annealing and cooling. In order to obtain excellent silicon ingots, a suitable crystal growth process is required, but the annealing process after the crystal growth is completed is also very important. [0003] During the silicon cr...

AI Technical Summary

Problems solved by technology

This technology has great damage to the furnace body and is not practical for mass production

At the same time, there is no obvious contribution to improving product quality, and there is no obvious advantage in cost control

Images