Effects of applied bias voltage on the properties of a-C: H films

The effects of the applied negative bias voltage on the hydrogen content, refractive index, extinction coefficient, internal stress, Vickers microhardness, adhesion and growth rate of a-C : H films deposited from a C₂H₂ + Ar mixture by a d.c.-r.f. plasma-enhanced chemical vapour deposition process have been investigated. The results showed that the properties of a-C : H films strongly depend on the applied bias voltage. In the investigated bias range (-400 to -1000 V), it was found that, apart from the growth rate and extinction coefficient (which were found to increase with increasing bias), all the other properties studied showed a maximum at around -800 to -900 V. Compared with those studies reported previously on self-bias voltage effects, these results indicated a slight difference between the effects of the self-bias voltage and applied bias voltage. The experimental results are discussed.