Tetramethylsilane (TMS) diluted highly with hydrogen is used for depositing a-SiC:H thin films at room temperature under varying degrees of ion bombardment in a 13.56 MHz RF powered, asymmetrical plasma reactor. An impedance analysis is used to estimate the ion energy and flux at the substrate while an optical emission spectrometer (OES) and a quadrupole mass spectrometer (MS) are used to estimate the concentrations of the chemical species in the plasma phase. The measured physicochemical reactor parameters are related to the growth rate using Langmuir-Hinshelwood and Eley-Rideal models. Based on Fourier transform infrared spectroscopy data of the deposited films, the impedance analysis of the reactor, and the on-line measurement data obtained with OES and MS, the growth mechanisms of the film under energetic ion bombardment conditions (low chamber pressure and high power) are suggested.