Effects of negative low self-bias on hydrogenated amorphous carbon films deposited by PECVD technique

Hydrogenated amorphous carbon films (a-C:H) were deposited by plasma enhanced chemical vapour deposition using a planar RF discharge and pure methane gas. The influence of the negative self-bias (varying from 0 to 400 V) on physical properties is investigated. The density of the materials, characterized by X-ray reflectivity, varies from 1.3 to 1.8 g/cm 3 . The lowest density obtained for the grounded (0 V) film is related to the porosity. Curvature measurements reveal high compressive stress (2.6 GPa) for the film deposited with a self-bias close to 100 V. These different behaviours are related with the different structures (polymerlike, diamondlike, graphitelike) depending on the self-bias used during the deposition process. It is also shown that in spite of these different structures, the surface energies calculated from contact angle measurements using different liquids are similar whatever the used self-bias.