EXAFS investigation of laser nitridation and laser carburization of silicon

Abstract

The effects of laser irradiation in controlled atmospheres (methane and nitrogen) on the structural properties of single crystalline silicon have been studied by extended x-ray absorption fine structure (EXAFS). The incorporation of carbon in the silicon matrix leads to the formation of polycrystalline cubic SiC (beta-SiC) with a good degree of crystallinity. The carbide phase is mixed with non-reacted silicon and its relative fraction, estimated from the fine structure oscillations, shows a monotonic increase with the number of laser shots. The irradiation in nitrogen atmosphere produces highly disordered or amorphous silicon nitride layers with thicknesses of the order of a few tens of nanometers. The fraction of Si3N4 relative to non-reacted silicon reaches the value of 40-50% after a few laser shots and a negligible dependence on the number of pulses has been observed.