Low-temperature deposition of epitaxial transition metal carbide films and superlattices using C60 as carbon source

Abstract: The transition metal carbides are chemical compounds with a unique set of propertiesused in many thin film applications. In this work, thin films of group 4-5 transitionmetal carbides and superlattices were deposited at low temperatures by simultaneousevaporation of C60 using either metal e-beam evaporation or d.c. magnetron sputtering.The co-evaporation process was used to deposit films with Ti, V, Nb and Co. It wasfound that Co was unable to induce a decomposition of C60 and form a carbide, whileTi, V and Nb could form nanocrystalline films at 100°C. At higher temperatures, 250-500°C it was possible to deposit epitaxial carbide films and superlattices. The TiC filmsshowed the best quality, followed by VC and NbC. This was explained by differences inmisfit and the tendency to form free surface carbon. The latter factor is important for theloss of epitaxy and made it difficult to deposit carbon-rich films. Studies of strain-relaxation in TiC films showed that the main glide system is {111}<110>, which isdifferent from TiN, due to the more covalent carbide bonding.A new hybrid sputtering process was used to deposit films of TiC and VC. The processyielded films with higher qualities and reduced the temperature for epitaxy to 100°C forTiC on MgO(OO1). Possible explanations for this low-temperature growth is discussed.The process was also used to deposit TiC/VC superlattices in the temperature range200-800°C. The results showed an extensive intermixing and a degradation of thesuperlattice at 800°C, which was explained by diffusion. Thin superlattices with a highquality could be deposited at 400°C, but a loss of epitaxy was observed for thickerfilms.Finally, initial studies of mechanical and electrical properties of epitaxial films andsuperlattices have also been carried out. The hardness and modulus of elasticity weremeasured by nanoindentation for TiC, VC and TiC/VC superlattices. No hardeningeffects similar to those found for some metal nitride systems could be observed.Epitaxial TiC films on 4H-Sic were found to exhibit favorable properties as Ohmiccontact materials, suggesting a potential use in high-temperature microelectronics.