Chemical sputtering of carbon films by low energy N-2(+) ion bombardment

In this paper experimental evidence for the effect of chemical sputtering of a growing carbon film by nitrogen ion bombardment is reported. The investigation was performed in a carbon sputter deposition facility by using N-2(+) tons of 150 eV. At this low energy physical sputter effects can be neglected. For the gas analysis a highly sensitive quadrupole mass analyser was used. The evolution of one or more volatile compounds giving rise to lines with a mass/charge ratio of 26, 27, 43 and 52 was observed during N-2(+) bombardment of a carbon film. Simultaneously him etching was monitored. The etching rate was estimated to be about 0.5 carbon atoms per incident N-2(+) ion. The experimental results suggest that this etching effect is primarily owing to the formation of a CN radical. If this radical is formed at the surface it reacts with hydrogen and water adsorbates to form compounds such as HCN and OHCN. If it is formed in subsurface layers of the carbon film it can recombine with another CN radical forming then a C2N2 molecule.