Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges

Abstract

Hydrogenated carbon nitride films were deposited by reactive dc magnetron sputtering in mixed ${\mathrm{Ar/N}}_2/{\mathrm{H}}_2$ discharges at temperatures of 100 and 350 °C. The total pressure was kept constant at 0.33 Pa and the gas mixtures were varied in order to study the effect of the hydrogen on the resulting film structure and properties. Chemical sputtering effects taking place during deposition were found to be an important factor for the growth and structural evolution. When ${\mathrm{H}}_2$ is mixed into the discharge gas, the growth rate decreases considerably and the films become denser due to desorption of volatile species, like hydrocarbons, ${\mathrm{NH}}_3$ and HCN. For a ${\mathrm{H}}_2$ fraction above 15%, no net film growth takes place. The hydrogen concentration incorporated into the films was highest (up to $\text{∼33}$ at. %) for low growth temperatures and low nitrogen concentrations. Furthermore, the results indicate that substantial amount of hydrogen are bonded to nitrogen. The incorporation of hydrogen in the structure interrupts the relatively long basal planes in graphite-like structures, and some regions transform into an amorphous structure. Nanoindentation measurements of the film showed decreased elasticity, as well as decreased hardness when incorporating hydrogen. However, fullerene-like films grown at 350 °C in ${\mathrm{N}}_2/{\mathrm{H}}_2$ discharges exhibit high elasticity for ${\mathrm{H}}_2$ partial pressures as high as ${\text{∼10}}^{\text{−3}}$ Pa due to low H incorporation into these films.