Partial crystallization of silicon by high intensity laser irradiation

Commercial single crystal silicon wafers and amorphous silicon films piled on single crystal silicon wafers were irradiated with a femtosecond pulsed laser and a nanosecond pulsed laser at irradiation intensities between 10(17) W/cm(2) and 10(9) W/cm(2). In the single crystal silicon substrate, the irradiated area was changed to polycrystalline silicon and the piled silicon around the irradiated area has spindly column structures constructed of polycrystalline and amorphous silicon. In particular, in the case of the higher irradiation intensity of 10(16) W/cm(2), the irradiated area was oriented to the same crystal direction as the substrate. In the case of the lower irradiation intensity of 108 W/cm(2), only amorphous silicon was observed around the irradiated area, even when the target was single crystal silicon. In contrast, only amorphous silicon particles were found to be piled on the amorphous silicon film, irrespective of the intensity and pulse duration. Three-dimensional thermal diffusion equation for the piled particles on the substrate was solved by using the finite difference methods. The results of our heat-flow simulation of the piled particles almost agree with the experimental results. (C) 2009 Elsevier B. V. All rights reserved.