Low-pressure CVD of (Tix,W1-x)Ny from WF6, TiCl4 and NH3

In this work chemical vapour deposited (CVD) coatings of (Tix,W1-x)Ny from TiCl4, WF6, NH3 and Ar were investigated. This coating material has previously been deposited using other vacuum techniques but no publication has so far demonstrated CVD of (Tix,W1-x)Ny. The studied (Tix,W1-x)Ny coatings had a metallic molar ratio (Ti:W) close to 2:1 and 1:1, and were slightly over-stoichiometric with regard to N. The coatings appeared homogeneous and crystallised in a rock salt structure on an α-Al2O3 substrate. The cell parameter varied between 4.16 and 4.23 Å as a function of the deposition conditions, ranging from a pure TiNx to a pure WNx coating. The texture in the normal direction was 〈100〉 for the TiNx and (Tix,W1-x)Ny coatings and 〈111〉 for WNx. Electron backscattered diffraction (EBSD) results showed that a strong correlation to the substrate existed but random in-plane orientation was also present. The microstructure showed columnar grains with well defined facets growing. Adding a mixture of TiCl4 and WF6 to produce (Tix,W1-x)Ny did increase the grain size significantly when compared to the case when only one metal precursor was present. The down-stream thickness profile, using only WF6 and NH3, displayed mass transport control behaviour, with the coating thickness converging to zero within the deposition zone. Using only TiCl4 on the other hand showed a uniform deposition profile, the signs of a surface kinetics controlled process.