Low-k films with k of 2.5-2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition (PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and H 2 carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950-1200 cm -1 arising from the Si-O stretching mode of the ring (1065 cm -1) and chain structure (1000 cm -1), respectively; a band at 750-900 cm -1 due to Si-O bending (790 cm -1); Si-CH 3 rocking mode (760 cm -1); a sharp band centered at 1260 cm -1 due to a Si-CH 3 bending mode; and a broadband at 2800-3000 cm -1 due to the CH group. A comparison of the IR spectra of the PECVD film and TVTMCTS liquid reveals that vinyl vibrations (Si-CHCH 2) at 960, 1410, and 3030-3095 cm -1 for CH 2 and at 1598 cm -1 for CC present in the liquid were not detected in the CVD films. Hence CC bonds were broken in the plasma polymerization process. As the pressure and the deposition temperature (T D) increased, the intensity of the Si-O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and T D we can control the structure of the film. There is a good correlation found between the Si-CH 3 and Si-O ring intensities and k values; the increasing Si-CH 3 and Si-O ring is accompanied by decreasing k. The films were thermally stable up to 400°C annealing temperature.