The influence of rf induced bias on the properties of diamond-like carbon films prepared using ECR-CVD

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapor deposition (ECR-CVD) method with radio-frequency (rf) bias is reported. The structural characteristics of the DLC films were characterized using Raman spectroscopy. The effects of the self-generated dc bias resulting from the rf power on the optical gap, Raman spectra, infrared (IR) absorption, and film hardness in depositions carried out at 7 and 15 mTorr process pressures were investigated. Under conditions of 100 W microwave power and for dc bias variation ranging from −10 to −200 V, there is evidence from Raman scattering analysis to show an increase in the DLC-like characteristic in films deposited at low dc bias at both process pressures. The variation of the D and G line peak position and intergrated intensity ratio (I_D/I_G) in the Raman spectra correlates well with the film hardness profile. There does not seem to be a relationship between the variation of the C-H absorption peak intensity in the IR spectra (bonded hydrogen content) and the optical gap, although films with the highest optical gap tend to show a relatively higher C-H absorption peak intensity in the IR spectra. Films deposited at high dc bias showed a reduction in the C-H infrared absorption, suggesting a reduction in the bonded hydrogen content.