The effects of structure, composition, and chemical bonding on the mechanical properties of Si-aC:H thin films

The objective of this study was to correlate mechanical properties with the structure and chemistry of silicon-incorporated amorphous hydrocarbon (Si-aC:H) films deposited by reactive sputtering. Hardness and elastic modulus were measured via microindentation, and intrinsic compressive stress was determined from radius-of-curvature measurements using surface mapping microscopy. Film chemistry was investigated with X-ray photoelectron spectroscopy, electron energy-loss spectroscopy, Raman spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy. Conventional- and high-resolution transmission electron microscopy revealed that the Si-aC:H phase is amorphous and TiC exists at the Si-aC:H/Ti phase boundary. Mechanical properties such as hardness, modulus, and intrinsic stress decreased with increasing Si and H content in the films, for Si/C⩾0.04. Measurements show that this is most likely due to a decrease in CC sp3 bonds, accompanied by an increase in CSi and CH bonds. In addition, the Si-aC:H film with Si/C=0.04 is fundamentally different from the other Si-aC:H films with higher Si and H contents. It is concluded that a film with diamond-like carbon characteristics can be deposited using a low tetramethyl silane (TMS) flow rate, such that Si/C=0.04 in the film. However, films deposited with higher TMS flow rates (such that Si/C⩾0.06 in the films) are more characteristic of amorphous hydrogenated silicon carbide.