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.