Structural, mechanical and tribological characterizations of a-C : H : Si films prepared by a hybrid PECVD and sputtering technique

Abstract

a-C : H : Si films were prepared under different CH4/Ar ratios by a hybrid radio frequency plasma-enhanced chemical vapour deposition (RFPECVD) and unbalanced magnetron sputtering technique. Characterizations showed that the CH4/Ar ratio affected not only the content but also the chemical state of the doped Si, thus further affecting the microstructures, mechanical and tribological performances of the a-C : H : Si films. Generally, when the CH4/Ar ratio was low (⩽4/2), the Si-doping content dropped with increased CH4 percentage, accompanied by a decreased sp3(C–Si+C–C)/sp2(C=C), increased ID/IG ratio and up-shift of the G peak position, as can be seen from the Raman spectra, while at a higher CH4 percentage (e.g. CH4/Ar = 5/2), the prepared a-C : H : Si films exhibited a series of aberrant properties due to the incorporation of abundant H and the high oxidization of the doped Si. Another unique characteristic of our films was the presence of numerous Si–Si bonds at high Si content, which was not observed in the a-C : H : Si films produced by the decomposition of Si-containing gaseous precursors. Moreover, although Si incorporation improved such properties of the DLC films as adhesion strength, internal stress and tribological moisture sensitivity, its effectiveness in enhancing the mechanical and tribological performances were governed not by the Si-doping content or sp3-C fraction but by the film continuity or adhesion (minimized interlinking destruction by the Si–H, C–H, Si–O–Si bonds) and sp2(C=C) fraction (based on the film continuity).