SiOC(-H) films with low dielectric constant were deposited on p-type Si(100) substrate using ultraviolet (UV)-source assisted plasma-enhanced chemical vapor deposition with a mixture of bis-trimethylsilylmethane (BTMSM: H9C3-Si-CH2-Si-C3H9) and oxygen gases. Fourier transform infrared spectroscopy was used to investigate the bonding configuration and relative carbon content of the SiOC(-H) films. UV illumination of the BTMSM/O-2 plasma was used to control the plasma parameters and deposition properties. The addition of He gas to the mixture of BTMSM and O-2 raised the electron density from 2.5 x 10(9) to 9.8 X 10(9) cm(-3). The lowest dielectric constant was 2.4, and was deposited using a mixture of BTMSM+O-2+He gases with UV illumination. The bonding structure of the SiOC(-H) composite film consists of distinct Si-O-Si and Si-O-C bonds, indicating the existence of caged Si-C bonds, and this enhances the porosity of the film. UV illumination increased the relative content of the ring link mode of the SiOC(-H) films. (c) 2005 Elsevier B.V. All rights reserved.