Amorphous diamond-like carbon films (DLC) with various silicon, oxygen and nitrogen content were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The films were prepared from the mixture of methane and hexamethyldisiloxane (HMDSO) in r.f. capacitively coupled discharges (13.56 MHz). The reactive plasma was investigated by optical emission spectroscopy and capacitive coupled planar probe. A combination of RBS, ERDA, FTIR and XPS methods was used to study the films' chemical composition and structure. The mechanical properties were studied using a depth sensing indentation technique. The films were mainly composed of C-C, C-H and C-Si bonds. The optimum deposition conditions for the preparation of DLC films, with enhanced thermo-mechanical stability, were determined.