Properties of CoSi2 formed on (001) Si

Abstract

Properties of CoSi₂ films formed on (001) Si have been investigated for silicide films formed by solid‐state reaction of either evaporated or sputtered Co with (001) Si substrates. It turns out that CoSi₂ films formed from evaporated Co have a systematically higher resistivity than films formed from sputtered Co, which can be attributed to contaminants that were present in the evaporated metal film. Silicide films formed from evaporated Co develop a strong (110) texture, which becomes more pronounced with increasing annealing temperature. Microstructural analyses revealed that this is due to epitaxial growth of (110) CoSi₂ upon (001) Si. This is a surprising phenomenon as the epitaxy of (001) CoSi₂ on (001) Si would be expected in view of the similarity of the crystal structure and the small lattice mismatch of CoSi₂ and Si. The expected epitaxy of (001) CoSi₂ on (001) Si is also present but for a smaller fraction of the silicide grains. The film stress has been analyzed in terms of thermal and intrinsic stress. From the thermal stress contribution, a value of 140 GPa was calculated for the biaxial elastic constant of CoSi₂. Using this value, it was also possible to interpret the intrinsic stress in terms of the density change upon silicide formation. Transmission electron microscopy and x‐ray diffraction revealed that CoSi₂ can not only grow epitaxially on (001) Si in a (001) and a (110) orientation but that there is also epitaxy close to these orientations with tilts of around 10° relative to the substrate normal. Simple geometrical calculations show that there is a good match for both (001) and (110) CoSi₂ on (001) Si and for a slight tilt from these orientations, all in very good agreement with the observations.