Mechanical properties of a-C:H and a-C:H/SiOx nanocomposite thin films prepared by ion-assisted plasma-enhanced chemical vapor deposition

a-C:H and a-C:H/SiOx nanocomposite thin films were deposited on silicon, aluminum and polyimide substrates at 25 degrees C in an asymmetric 13.56 MHz r.f.-driven plasma reactor under heavy ion bombardment. Fourier transform infrared spectra of the films indicate that the nanocomposite film appears to consist of an atomic scale random network of a-C:H and SiOx. Raman spectroscopy revealed that the sp(2) carbon fraction in the nanocomposite film was reduced compared with the a-C:H film. The intrinsic stress of both films increased with increasing negative bias voltage (-V-dc) at the substrate. However, the nanocomposite films exhibited lower intrinsic stress compared with a-C:H-only films. Especially, a thin SiOx-rich interlayer was very effective in reducing the film stress and enhancing the bonding strength at the interface. The interlayer allowed deposition of thick Alms of up to 5 mu m. Also, the nanocomposite films were stable in 0.1 M NaOH solution and showed good microhardness.