Effects of deposition pressure on structure and hardness of amorphous carbon nitride films synthesized by shielded arc ion plating

Amorphous carbon nitride (a-C:N) films were synthesized by shielded are ion plating (SAIP) at the wide pressure range of 0.01-30 Pa. It is essential to prepare a-C:N films at pressures below 0.1 Pa or apply negative voltages to substrates at pressures below 1 Pa for fabricating hard films. Appropriate N-2(+) ion bombardment increases compressive stresses and promotes formation of fourfold coordinated carbon micro-networks in a-C:N films. N/C ratios of these hard films were < 0.26 and N atoms substituted for C sites in amorphous carbon networks. On the other hand, in order to raise N/C ratios of a-C:N films, it is necessary to prepare the films at as high a pressure as possible. The maximum N/C ratio was 0.51 at 30 Pa with no substrate bias. Even this value is much lower than 1.33 of hypothetical C3N4. CN radicals were remarkably formed in the plasma at higher pressures and related to nitrogen concentrations in a-C:N films. CN radicals were considered to act as precursors of aromatic plain carbon-nitrogen networks, and a-C:N films prepared at higher pressures were very soft. Conclusively, three-dimensional carbon nitride structures with high hardnesses and high nitrogen concentrations have not achieved at the same time by such PVD processes as SAIP. (C) 1998 Elsevier Science S.A. All rights reserved.