SUBSTRATE BIAS EFFECT ON THE TRIBOLOGICAL PROPERTIES OF A-SI1-XCX-H FILMS

a-Si1-xCx:H films were synthesized by r.f. plasma-assisted chemical va pour deposition at deposition temperatures < 200 degrees C from methan e-silane gas mixtures. By adjusting the r.f. power, the bias voltage V -b was varied between -300 and -500 V. The film composition was measur ed by electron probe microanalysis. The wear resistance (ball-on-disk test) determined for films deposited at the two selected bias voltages was correlated with their mechanical properties (depth-sensing indent ation technique) and internal compressive stresses (bending beam metho d). The performance of the a-Si1-xCx:H films was compared with that of reference a-C:H films prepared under similar conditions. The mechanic al properties (hardness and Young's modulus) and internal compressive stresses for films deposited at -300 V are consistently higher than fo r films deposited at -500 V. The better mechanical properties result i n an improved wear resistance under humid nitrogen (50% relative humid ity) conditions. In a humid air test environment, however, the improve ment is negligible, most probably because of a tribochemical wear mech anism due to the presence of oxygen. The same tendencies are observed for the pure a-C:H films, which show on average a much higher wear res istance.