Solid State Interaction and Nano-Scale Silicide Formation for Co/Ti Multilayers on Silicon

Abstract

The formation of a 12nm thick, continuous and thermally stable COSi₂ layer was described in our previous work [MRS Proc. 238, 587 (1992)]. Interdiffusion in the Co/Ti-Si multilayer system has been further studied and the initial Ti(O) thickness is shown to be a critical parameter in controlling its effectiveness as a diffusion barrier, and in modulating the Co-Si and Ti-Si compctctive reactions. Three Ti(O) and three Co layers with thickness from ~5nm 20nm were deposited sequentially, with Ti(O) as the first layer, on Si-(100) substrates by dual source thermal evaporation. The morphology of the CoSi_x/Si interface was strongly influenced by Ti(O) thickness from ~5nm to ~10nm, and a 12nm thick uniform CoSi₂ layer with ~28μΩ-cm resistivity was produced as decribed previously. When the initial Ti(O) thickness was increased to ~20nm and the Co thickness set at ~10nm, Co diffusion was suppressed and Ti reacted with Si yielding an ~10nm amorphous TiSi_x layer at 550°C. This amorphous layer transformed to a 15nm thick uniform C-54 TiSi₂ layer after selective removal of upper layers and a 750°C plus 800°C annealing. A flat silicide/Si interface and a ~58μΩ-cm resistivity were obtained. The significance of both thermodynamic and kinetic factors in the compctetive reactions is discussed.