Numerical study on stress control of silicon ingot for photovoltaic applications

When continuous silicon ingot casting is performed using directional solidification-a metallurgical refining method for producing high-purity silicon ingots-the thermal stress and microstructure inside the ingots must be monitored for ensuring the desired yield and purity. This study determined the temperature gradient and thermal stress during silicon ingot casting by applying various controlled parameters to the process simulation. Our results indicate that the temperature gradient influences the thermal stress generated during casting; reducing the temperature gradient can help reduce the thermal stress. The ingot exhibited the lowest thermal stress at an electron beam (E-beam) power of 6 kW, an ingot growth rate of 0.02 mm/min, and a molten silicon level of -10 mm. Quasi-single crystalline silicon ingot was produced via crystal growth simulation under thermal stress-minimizing conditions with single-crystalline seed. The quasi-single crystalline silicon ingot maintained the [001] grain orientation and the purity increased from 2N to 7N6.