Interaction between water and fluorine-doped silicon oxide films deposited by plasma-enhanced chemical vapor deposition

Abstract

The interaction between water and fluorine-doped silicon oxide (SiOF) films has been studied using Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The effects of the interaction on the relative dielectric constant of films were also studied using capacitance–voltage measurements. It was found that SiOF films with high fluorine concentration have three absorption bands attributable to Si–Fn stretching vibration, however, the SiOF films have only one absorption band after humidification. The residual band is assumed to be attributable to silicon monofluoride [Si(O–)3F] sites and the disappearing bands are attributable to silicon difluoride [Si(O–)2F2] sites. Si(O–)2F2 sites are hydrided during humidification and generate Si–OH bonds and HF in the film. In addition, Si(O–)2F2 sites increase the water absorbed in film. The relative dielectric constant of SiOF films capped by silicon nitride decreased steadily with increased fluorine concentration, from 4.5 (SiO2) to less than 2.8 [11.5 at. % (F)], however, that of uncapped SiOF films saturated the decrease at about 3.6 in films having 7.6 at. % (F) or more. This saturation is caused by the increase of Si(O–)2F2 sites in film because the ratio of Si(O–)2F2 sites to total fluorine bonding sites increases markedly at a fluorine concentration above 7.6 at. % (F). Si(O–)2F2 sites increase Si–OH bonds and water absorbed in film, and both, in turn, increase the film dielectric constant.