Damage induced by laser irradiation of NiSi2/Si 〈111〉 structures

Abstract

Thermally grown NiSi2 layers on 〈111〉 Si substrates were irradiated with single pulses of a Q-switched Nd laser. Melting and solidification dynamics, orientation and structure of the irradiated layers were investigated by in situ time-resolved reflectivity, Rutherford backscattering in combination with channeling and scanning electron microscopy. Melt starts from the surface at 0.35 J/cm2. When the energy density is enough to melt the entire layer, the epitaxially solidified NiSi2 is mainly of B-type orientation. The thermally grown or partially melted layers are a mixture of A- and B-type crystals. A substantial decrease in the reflectivity signal has been found in the case of a partial melting of the thermally grown NiSi2 layers several microseconds after the laser pulse. This decrease has been correlated with the exfoliation of surface materials as found by the scanning electron microscopy of the irradiated samples. Slip planes were also observed after solidification either of a partially melted mixture of A and B type or of a B-type NiSi2 silicide. No exfoliation and a much lower density of slip planes were observed after solidification of a completely melted silicide layer. The dynamics of melting and the damage of the irradiated layers are explained in terms of heat-flow calculation and thermomechanical and mismatch stress.