Dynamics of the hydrodynamical growth of columns on silicon exposed to ArF excimer-laser irradiation

We present new results about the development of the whiskerlike structures that grow on silicon single crystals exposed in air to ArF excimer-laser irradiation. Small depressions appear on the surface after 100-200 laser pulses. With the next pulses, the size of these depressions increases, without change in depth, and new depressions are formed. At the end of this step the non-depressed regions are constricted and form a reticular network with a mesh size of some mu m. With more pulses the material of the network tends to desert the branches and accumulate in the nodes, and discrete hillocks result. The hillocks progressively change their shape until tall columns are formed. Independent of this process, small protuberances appear on flat areas of the irradiated spot, initially in regions far from the center of the spot. These protuberances evolve to mushroom-type shapes, which remain much shorter than the columns.