Structural and mechanical properties of a-C:H and Si doped a-C:H thin films grown by LF-PECVD

Amorphous hydrogenated carbon (a-C:H) and Silicon doped a-C:H (Si-DLC) and a-C:H/Si-DLC multilayered films were deposited by low frequency plasma enhanced chemical vapour deposition (LF PECVD). Influences of plasma power and substrate temperature were first investigated on structural and mechanical properties of a-C:H films elaborated from cyclohexane–hydrogen mixtures. The hybridation ratio, Csp 2/Csp 3, was evaluated by means of Raman spectroscopy and High Resolution Solid-State Nuclear Magnetic Resonance (SSNMR). Stress measurements were realised by the substrate bending method. Nanoindentation and ball on disk tribometer were used in order to determine nanohardness, Young modulus and friction behaviours respectively. Si-DLC films were then elaborated by incorporating tetramethylsilane in the previous gas mixtures. Those layers revealed a significantly reduced stress level comparing to a-C:H films without a dramatic loss of mechanical properties. Finally a-C:H and Si-DLC layers were associated to elaborate a multilayered system which presents mechanical and tribological properties equivalent to an a-C:H monolayer properties while maintaining a lower residual stress level.