HARDNESS AND YOUNGS MODULUS OF AMORPHOUS A-SIC THIN-FILMS DETERMINED BY NANOINDENTATION AND BULGE TESTS

Due to its interesting mechanical properties, silicon carbide is an ex cellent material for many applications. In this paper, we report on th e mechanical properties of amorphous hydrogenated or hydrogen-free sil icon carbide thin films deposited by using different deposition techni ques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a-S ixC1-x:H PECVD, a-SiC LAD, and a-SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoin dentation and bulge techniques, respectively. Hardness (H), Young's mo dulus (E), and Poisson's ratio (v) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a-SixC1-x:H PECVD films, both hardness and Young's modulus are dependent on the fi lm composition. The nearly stoichiometric a-SiC:H films present higher H and E values than the Si-rich a-SixC1-x:H films. For hydrogen-free a-SiC films, the hardness and Young's modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a-SiC films present both hardness and Young's modulus values higher by about 50% than those of hydrogenated a-SiC:H PECVD films. By using the FTIR absorption spectr oscopy, we estimated the Si-C bond densities (N-SiC) from the Si-C str etching absorption band (centered around 780 cm(-1)), and were thus ab le to correlate the observed mechanical behavior of a-SiC films to the ir microstructure. We indeed point out a constant-plus-linear variatio n of the hardness and Young's modulus upon the Si-C bond density, over the N-SiC investigated range [(4-18) X 10(22) bond.cm(-3)], regardles s of the film composition or the deposition technique.