Abstract:
Plasma polymerization of hexamethyldisiloxane (PPHMDSO) was used to deposit SiOxCyHz
thin films on silicon and polyimide substrates, using low-frequency plasma and microwave
plasma discharge at low pressure. The effects of plasma chamber pressure, oxygen rate in
Ar/O2 mixture, treatment time and post-treatment on the films characteristics were studied.
The thickness, surface properties and chemical structure of the deposited thin films were
analyzed using profilo-meter measurements, scanning electron microscopy (SEM), static
contact angle and infrared spectroscopy (FTIR and FTIR-ATR). At low frequencies and for
certain deposition parameters, nano-powders of different concentrations and sizes were
observed on the deposited thin films surface. The FTIR analysis revealed that the chemical
formula of the deposited layers is close to SiOxCyHz one, with more organic character when
chamber pressure and/or deposition time were increased. Water contact angle measurements
show that the increase in the deposition pressure and deposition time leads to the growth on
the polyimide and silicon substrates of thin layers with super-hydrophobic surface due to the
increase in the concentration of the nano-powders on the treated surfaces. Plasmas created in
HMDSO vapours using a microwave frequency plasma in ECR reactor leads to the deposition
of similar PPHMDSO thin layer on polyimide and silicon surfaces. A post-treatment of these
coating layers using a microwave plasma created in Ar/O2 mixtures shows that the increase of
oxygen rate in this mixture and the increase in the post-treatment time induces a significant
decrease of the contact angle because of a decrease in the layers roughness (revealed by AFM
characterization) and mainly, because of a more surface oxidation of the thin layers (revealed
by FTIR analyzes).
