Constitution and mechanical properties of sputtered films in the system Si-C-N studied by XRD, AFM, TEM, NI and molecular dynamics simulation


C. Ziebert, S. Ulrich


Forschungszentrum Karlsruhe, Institut für Materialforschung I,  Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany



Thin films of SiC and SiCN have been deposited on Si substrates and cemented carbide inserts by RF magnetron sputtering from a SiC target. At first the substrate temperature and the bias voltage have been varied from 200 C up to 800 C and from 0 to -70 V respectively in pure Ar atmosphere to investigate the influence on the composition, the constitution and the mechanical properties of SiC films. At second the nitrogen content was systematically varied between 0 and 33 vol.% at a substrate temperature of 800 C without bias voltage to investigate its influence on the structure and properties of SiCN films. The films have been characterized by EMPA, XRD and TEM. Hardness, residual stress and critical load of failure in dependence of the film thickness have been investigated by nanoindentation, wafer bending and scratch test. Moreover the small-angle cross-section nanoindentation method (SACS) has been applied for hardness depth-profiling. The topographical changes in dependence of the deposition parameters and the N2 content have been studied by AFM. Even at a substrate temperature of 800 C all films deposited in pure Ar were amorphous due to oxygen contamination. However, even a very small N2 addition of 0.2 vol.% removed the oxygen contamination and enabled the formation of crystalline films. At nitrogen concentration of 0.4.% a two-phase microstructure of phases similar to alpha-SiC and beta-SiC with nanocrystalline grains of 5-10 nm is formed. This nanostructure results in a superhard film with hardness of 45 GPa, however residual stress also rises up from 0.6 to 2.4 GPa and average surface roughness increases from 0.2 to 0.9 nm. At 33% nitrogen the films become amorphous and the hardness of these films decreases drastically to 20 GPa. To get more insight into the phase formation during sputter deposition and to calculate the elastic properties molecular dynamics simulations have been performed with modified Tersoff potentials by using XMD and Materials Explorer software.