The effects of self-generated DC bias on the characteristics of diamond-like carbon films prepared using ECR-CVD

Abstract

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapour 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 a DC bias variation ranging from −10 V to −200 V, there exists evidence from Raman scattering analysis to show an increase in the diamond-like characteristic in films deposited at low DC bias at both process pressures. The variation of the D and G line peak position and integrated intensity ratio (IDID) 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.