Size-dependent creep behaviour of plasma-enhanced chemical vapour deposited silicon oxide films

The time-dependent plastic deformation (creep) behaviours of both as-deposited and annealed plasma-enhanced chemical vapour deposited (PECVD) silicon oxide (SiOx) films were probed by nanoindentation load relaxation tests at room temperature. Our experiments found a strong size effect in the creep responses of the as-deposited PECVD SiOx thin films, which was much reduced after rapid thermal annealing. Based on the experimental results, the deformation mechanism is depicted by the 'shear transformation zone' (STZ)-based amorphous plasticity theories. The physical origin of the STZ is elucidated and linked with the shear banding dynamics. It is postulated that the high strain gradient at shallow indentation depths may be responsible for the reduction in the stress exponent n=partial derivative log(strain rate)/partial derivative log(stress), characteristic of a more homogeneous flow behaviour.