A simple explanation on the crystallization kinetics of a CW laser crystallization of amorphous silicon

We have studied a CW laser crystallization (CLC) of various-shaped a-Si patterns on glass with changing scanning speed and laser power. The crystallized region inside the patterns showed 3 distinct regions, which is distinguished by their grain size; fine grains of several tens of nanometers near the edge of the pattern, very large grains over a few micrometers at the center of the pattern, so called Sequential Lateral Crystallization region and large grains about a micrometer or less between SLC and fine grain regions. This phenomenon is due to the formation of 2-D temperature gradient inside the pattern. One is the temperature gradient between the edge and center; the temperature of outer region is lower than that of inner region during or right after a CW laser scanning. The other is the temperature gradient along the scan direction; the temperature of starting region of a CW laser scanned area is lower than that of ending region. The former contributes mainly to make molten silicon area inside a pattern, and the latter induces lateral growth along the scan direction to make long grains in SLC region.