Conformal growth of low friction HfBxCy hard coatings

•CVD of highly conformal hard coatings of hafnium borocarbide, HfBxCy.•Deposition temperature as low at 250 °C using non-halogenated precursor and olefinic carbon source•Films have low coefficient of unlubricated sliding friction and high wear resistance.•Mechanical properties reported across the compositional range 5–35 at.% carbon

Thin films of HfBxCy are deposited in a cold wall CVD apparatus using Hf(BH4)4 precursor and 3,3-dimethyl-1-butene, (CH3)3CCHCH2, 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.