Pulsed Laser Induced Melt and Phase Transformation of Ni Silicide Layers on Si Substrate

Abstract

Thermally grown Ni₂ Si and NiSi₂ layers on <111> Si substrates were irradiated by 40 ns Nd laser pulses in the energy density range 0.3–2.0 J/cm². The samples were analyzed by time-resolved reflectivity, 2.0 MeV He⁺ Rutherford backscattering in combination with channeling and by transmission electron microscopy. In the NiSi₂/Si system the melt starts at the free surface (1280 K) and propagates towards the inside. Dissolution of substrate silicon atoms occurs when the silicon temperature reaches the liquidus temperature (1400 K). In the Ni₂Si/Si samples the melt starts instead at the interface when it reaches the eutectic temperature (1250 K). The subsequent propagation towards the surface is limited by the mass transport of silicon atoms to maintain a composition near that of the eutectic. In some cases the surface may melt also at the congruent melting temperature (1570 K), giving rise after solidification to a quite complex structure. The different behaviour of the two silicides/silicon systems is explained in terms of phase diagram.