Stress reduction in a-C:H coatings through the addition of nitrogen to the feed gas

Intrinsic stress in amorphous hydrogenated carbon (a-C:H) coatings was reduced through addition of 10–20 sccm N2 to the feed gas. The compressive stresses observed in this study were in the range −0.91 to −1.6 GPa. Approximately 2–3 at.% nitrogen was incorporated into the coatings as determined using elastic recoil detection (ERD). Raman spectroscopy shows that the G peak of samples made with nitrogen is shifted to higher wave numbers, and that there is a more pronounced 'shoulder' at the D peak position. It is hypothesized that nitrogen addition to the feed gas at a flow rate of 20 sccm enhances the formation of aromatic rings associated with the D peak. The stress reduction noted for nitrogen addition at 10 sccm was contributed to a reduction in the mean coordination number of the network. Positron beam analysis (PBA) was used to show that in a high temperature deposition the interface of the nitrogen-containing coating has more open space. This phenomenon can contribute to a reduction of the compressive stress by reducing the interfacial stress. Annealing tests were performed to monitor this open volume using Raman and PBA analysis.