Cobalt silicide layers on Si. I. Structure and growth

Abstract

Cobalt silicide layers have been grown by electron‐beam vacuum deposition of Co onto Si wafers, and subsequent thermal treatment above 400 °C. The compounds Co₂Si, CoSi, and CoSi₂ were found by x‐ray diffraction. The compounds grow as successive layers with a thickness ratio of about 3:1:0.1, as was found from comparison with powder diagrams. The silicide growth proceeds faster along grain boundaries. After prolonged heating the Co is consumed and the Co₂Si thickness then decreases. Subsequently the Co₂Si is consumed, the CoSi thickness decreases, and a growing CoSi₂ layer is left. No significant preferred orientation was found in the three silicides, except in CoSi₂, which exhibits a preferred 〈100〉 orientation, when grown on 〈100〉 Si for more than 3 h at 550 °C. Both from x‐ray diffraction intensities and from thickness measurements it is shown that the growth of the Co₂Si and CoSi layers, which is initially approximately linear with time, proceeds with a t^1/2 dependence with an activation energy V of 1.75 eV. The growth is then presumably by Si diffusion through the silicide layers.