Conformal growth of low friction HfB_xC_y hard coatings

Thin films of HfB_xC_y are deposited in a cold wall CVD apparatus using Hf(BH₄)₄ precursor and 3,3-dimethyl-1-butene, (CH₃)₃CCH=CH₂, as a controllable source of carbon, at substrate temperatures of 250-600°C. As-deposited films grown at 250°C are highly conformal (e.g., in a very deep trench, the step coverage is above 90% at a depth/width of 30:1), exhibit dense microstructure, and appear amorphous in X-ray diffraction. Increasing the carbon content from 5 to 21 at.% decreases the hardness from 21 to 9 GPa and the reduced modulus from 207 to 114 GPa. Films grown at 600°C with carbon contents of 28 and 35 at.% exhibit enhanced hardness of 25 and 23 GPa, and reduced modulus of 211 and 202 GPa, respectively. Annealing the 300°C grown films at 700°C affords a nanocrystalline structure with improved mechanical properties. For films with the highest and lowest carbon contents, respectively: the coefficient of sliding friction is in the range of 0.05-0.08 and the H/E and H³/E² ratios range from 0.08-0.11 and 0.15-0.40. These values indicate that C-containing films should exhibit improved wear performance in tribological applications.