Structural and mechanism study on enhanced thermal stability of hydrogenated diamond-like carbon films doped with Si/O

Abstract

a-C:H and a-C:H:Si:O films with two different Si/O co-doping contents had been deposited using a PECVD system by the mixture of C2H2 and HMDSO gas. The structure evolution of as-deposited and annealed films had been characterized by the Raman spectroscopy, XPS and FTIR. A progressive increase of sp2 carbon sites and a reduction of sp3 with the increase of the annealing temperature were expected. However, the Si/O co-doping was found to be able to reduce the graphitization degree of the annealed films. After annealing at 400 °C, the decrease rate of sp3 fraction of a-C:H film was 14.2%, while the a-C:H:Si:O (0.93 at.% Si) film was 8.16% and the a-C:H:Si:O (3.62 at.% Si) film was 6.8%. To understand the mechanism on the improved thermal stability by Si/O co-doping, the structure and residual stress of the a-C:H and a-C:H:Si:O films were analyzed. The results revealed that silicon atoms were incorporated into the carbon network by substituting carbon atoms of the films, which had also been characterized contributed to produce the CSi sp3 bonds stabilized by the oxygen. Residual stress characterization also demonstrated that, the residual stress of the a-C:H:Si:O films was greatly reduced compared with that of the a-C:H films. Therefore, the fraction of the highly strained CC sp3 bonds, which were more likely to break at elevated temperature, was reduced in the a-C:H:Si:O films. This kind of structure evolution endowed the a-C:H:Si:O films higher hardness and adhesion at high temperature.