SiOCH low-k thin films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using trimethylsilane (3MS)-oxygen mixtures at different substrate temperature from 200 to 400 degreesC, while the other conditions were fixed. The effect of substrate temperature on the mechanical, optical and electrical properties of the SiOCH thin films was investigated using nanoindentation, ellipsometry, Fourier transform infrared (FTIR) spectroscopy and C-V measurement techniques. It was found that the deposition rate decreased more than 67% as the temperature increased from 200 to 400 degreesC. The SiOCH films prepared at lower temperature showed lower dielectric constant and refractive index, but the mechanical properties became poorer because the hardness and Young's modulus decrease largely with the deposition temperature. FTIR spectra revealed that more -CH and -CH3 groups were introduced into the SiO2 network of the films at lower deposition temperature. The -CH and -CH3 groups and cage structure of Si-O bonds in the films were thought to be responsible for lowering the dielectric constant, refractive index, hardness and Young's modulus. Trade-off among the mechanical and electrical properties of such low-k SiOCH films was observed for films deposited at different deposition temperature. (C) 2004 Elsevier B.V. All rights reserved.