Assessment of tetra-alkylchromium compounds for low temperature organo-metallic chemical vapour deposition of Cr-based coatings

Chromium carbide films have been deposited by organo-metallic chemical vapour deposition using the tetra-alkylchromium compounds Cr[C(CH3)3]4 and Cr[CH2C(CH3)3]4 under reduced pressure in the temperature ranges 100-150°C and 250-350°C respectively. The blocking of ?-decomposition mechanisms increases the thermal stability of the second precursor, and subsequently increases the deposition temperature range and palliates the reagent depletion in the gas phase. Both the higher thermodynamic stability of Cr[CH2Si(CH3)3]4 and the lower kinetic lability of the ligand CH2SiMe3 result in a significantly higher temperature range of deposition (450-515°C). However, the decomposition of this third precursor is not as clean as expected, even under hydrogen atmosphere, since Si and C are incorporated in the films leading to an original amorphous material containing a mixture of metallic and covalent bonds. Comparison of the results from the different precursors leads to the hypothesis that a cyclometallation mechanism could be a dominant initial step for the removal of CH2C(CH3)3 and CH2Si(CH3)3 ligands.