Mechanically Hard SiCx:H Films in Amorphous Phase

Amorphous hydrogenated silicon carbide (a-SiCx:H) films were deposited onto Si substrates by using the decomposition reaction of tetramethylsilane with the microwave discharged products of Ar. The contamination of H2O molecules was avoided by passing the starting materials through a desiccant (P2O5). A negative bias voltage (�VRF = 0-100 V) was applied to the substrate by using an external radio-frequency source to induce Ar-ion bombardment of the film surface. The pressure of Ar was 0.1 Torr. Film thickness was 1-5 �m under the deposition time of 30 min. Hardness of films under the condition of �VRF = 0 V was �1 GPa. Under the condition of �VRF = 100 V, the hardness was 42�27 GPa; the maximum hardness was 69 GPa. The observed hardness was comparable to or even higher than the hardness of SiC in crystal phase (20-24 GPa). According to the XPS measurements, the x value was 1.06-1.73. The IR intensities of the hydrogen termination structures were prominent under the low �VRF conditions, whereas they reduced at higher �VRF. The Raman spectra showed significant fluorescence signal at low �VRF with negligibly weak scattering signal. At higher �VRF, the fluorescence signal was reduced, and the G (graphitic) band appeared. From the above measurements, �VRF induces a structural change from one-dimensional to twoor three-dimensional structures following hydrogen-removal from the film surface.