Residual strain distribution in casting ingot of multi-crystalline silicon

By using a scanning infrared polariscope (SIRP), the residual strain distribution has been characterized in specially-prepared vertical slices of rectangular blocks cut from two conventional casting ingots in production scale. All the blocks clearly revealed local strain increase in the shapes of straight-pillar and long-pyramid but its distribution was significantly different from block to block. The averaged vertical profiles exhibited common W-shape in the center blocks, while it was more distorted in the peripheral blocks, which may reflect casting process condition such as thermal stress applied to the whole ingot.