Selective effect of ion/surface interaction in low frequency PACVD of SIC:H films: Part B. Microstructural study

A capacitively coupled low frequency PACVD device (ν = 50 kHz, DC bias: |Vdc| = 0 to 400 V) is used to deposit hard amorphous silicon carbide films (a-SiC:H), from the decomposition of precursor tetramethylsilane (TMS) diluted in argon. Such a deposition process induces an ion bombardment of the growing films: energetic ions can sputter atoms from the near surface of the coatings, leading to strong alterations in the microstructure of the deposited material. In order to draw the particular influence of ion bombardment on the coatings, partly compensated by growth phenomena, some deposited films are post-treated in pure argon plasma, then submitted to a crossed analysis by RBS, FTIR and XPS techniques. These results are also compared to previous gas phase considerations [A. Soum-Glaude, L. Thomas, E. Tomasella, J.M. Badie, R. Berjoan, Surf. and Coat. Technol. 200 (1–4), (2005) 855]: Optical Emission Spectroscopy (OES) measurements near films surface, and SRIM© 2003 sputtering simulation. The confrontation of gas phase study, simulation and material analysis highlights general trends. First, silicon can be selectively sputtered in regard to carbon in the DC bias domain [150–250 V], as shown by OES observations on Si+ and H emitting species, Si / C ratio given by RBS, Si–C and Si–H absorption bands on FTIR spectra, and Si sputtering yield calculation with SRIM 2003. More precisely, in this DC bias domain, XPS measurements on the C1s core level peak, SRIM sputtering yields, and the observation of C–H and Si–C absorption bands with FTIR technique, show that sp3 carbon environments (C–C + C–H) can be favored in spite of the Si–C and C–Csp2 ones. Beyond the [150–250 V] domain, this phenomenon is no more noticeable, meaning sputtering is no more selective at higher DC bias. This selectivity can be used to improve hardness of the coatings that can reach 30 GPa.