Properties of CoSi2 formed on (001) Si

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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.