Interaction between water and fluorine-doped silicon oxide film deposited by PECVD

The interaction between water and fluorine-doped silicon oxide (SiOF) films has been studied focusing on the relation between the fluorine bonding configuration in the film and film hygroscopicity. SiOF films with a high fluorine concentration have three IR absorption bands between 985 cm^-1 and 920 cm^-1. These bands are assumed to be attributable to silicon monofluoride and silicon difluoride sites. It was found that silicon difluoride sites interact with H₂O more easily than silicon monofluoride sites. Silicon difluoride sites are hydrided during humidification. The hygroscopicity of SiOF film with a high fluorine concentration is assumed to be due to an increase in the silicon difluoride sites in the film, because the ratio of silicon difluoride sites to total fluorine bonding sites increases markedly above a certain fluorine concentration. Plasma-enhanced chemical vapor deposition of SiOF film with excess helium dilution in the reactant gas was also studied to reduce the hygroscopicity of SiOF film. It was found that helium dilution decreases the number of silicon difluoride sites, and simultaneously increases the number of silicon monofluoride sites. Film having a high fluorine concentration deposited with helium dilution exhibited lower hygroscopicity and a lower relative dielectric constant than the film deposited without He. It is essential to reduce the silicon difluoride sites in SiOF film to obtain highly reliable film