Nanometer-scale voids in PECVD silicon-oxide films probed by variable-energy positron lifetime spectroscopy: A comparison with infrared spectroscopy

Variable-energy positron lifetime spectroscopy was conducted for plasma-dep osited thin films of hexamethyldisiloxane (HMDSiO), prepared from pure HMDS iO at different discharge powers and monomer pressures, and from HMDSiO/oxy gen mixtures at different oxygen pressures. The lifetime of ortho-positroni um (o-Ps) in films deposited from pure HMDSiO increased with the increasing ratio (I-SiO/l(SiCH)) of integrated absorbance of the Si-O-Si band to that of the Si-(CH3)(y) (y = 2, 3) band determined by infrared (IR) absorption spectroscopy. The increase in the o-Ps lifetime, indicative of the enlargem ent of nanometer-scale voids in the film, suggests that the weak interactio n between Si-(CH3), groups and other segments may lead to flexible regions and larger voids. A film deposited from a HMDSiO/ O-2 mixture had a less st able structure, and no correlation was observed between o-Ps lifetime and I -SiO/l(SiCH) for films deposited from HMDSiO/O-2 mixtures. (C) 2001 Elsevie r Science Ltd. All rights reserved.