Thin plasma polymer films were deposited from several liquid monomers (mainly siloxane-type monomers) in a low-temperature cascade are torch (CAT) reactor. The effects of monomer structures and plasma parameters on internal stress in the films were experimentally studied. By appropriately adjusting these factors, the internal stress in the film was reduced nearly two orders of magnitude from 10(9) to 10(7) dyn/cm(2). It was noted that the polymer films prepared from siloxane-type monomers showed lower internal stress than their hydrocarbon counterpart. Fourier transform-infrared spectroscopy (FTIR) studies indicated that a large amount of Si-O-Si structure from siloxane monomers, which are very flexible bonds, was preserved in the resultant plasma polymers. Ellipsometry results suggested that the internal stress can be qualitatively correlated with the refractive index of the plasma polymer film.