Post treatments by annealing or supercritical carbon dioxide (SCCO2) exposure of plasma-enhanced chemical vapor deposited hydrogenated amorphous silicon carbide (a-SiC:H) films are reported to reduce the dielectric constant up to 2.1. The a-SiC:H films were prepared using diethylsilane diluted in methane. The deposition precursors and conditions were chosen to fabricate a thermally unstable a-SiC:H film with a high concentration of CHn (n = 1, 2, 3) functional groups. The Fourier transform infra-red spectroscopy measurements of as-deposited films show aSiC:H networks and presence of a-C:H moieties throughout the film. The films were then annealed in vacuum up to 450 degrees C to remove thermally unstable CHn as well as other species. After annealing, the dielectric constant of the films decreased from 4.2 up to 2.1 due to the decrease in film density. The reduction suggests the presence of molecular voids/pores. Annealing produced a stable film with thickness decreasing by a maximum of 6% only. SCCO2 treatment was also explored and found to be more effective in the extraction of CHn and other species at 200 degrees C. (c) 2005 Elsevier B.V. All rights reserved.