STRUCTURE AND CHEMICAL-COMPOSITION OF FLUORINATED SIO2-FILMS DEPOSITED USING SIF4 O-2 PLASMAS/

Attenuated total reflection Fourier transform infrared spectroscopy an d spectroscopic ellipsometry were employed for chemical and structural analysis of fluorinated SiO2 deposited in SiF4 and O-2 plasmas. Isoto pic substitution of O-16(2) with O-18(2) in the feed gas mixture was u sed to determine whether F is bonded to Si or O atoms in the film. Iso topic substitution experiments revealed that infrared active SiO-F str etching mode in SiO2 matrix appears at 1372 cm(-1) but only when the S iF4-to-O-2 ratio of the feed gas mixture is reduced below 0.1. The SiO F species in fluorinated SiO2 result from insertion of O into SiF bond s, which have been already incorporated into the film. Deposition expe riments using O-16(2) and O-18(2) also helped identify silicon mono-an d di-fluorides (O3SiF and O2SiF2), which were most abundant in fluorin ated SiO2. The stretching mode of O3Si-F appears at 950 cm(-1), wherea s the antisymmetric and symmetric stretching modes of O2Si-F-2 appear at 990 cm(-1) and 920 cm(-1), respectively. The concentration of silic on fluorides increase monotonically with increasing SiF4-to-O-2 ratio. The increase in silicon fluoride concentration causes the Si-O-Si pho non peaks to blueshift and narrow by relaxing the Si-O-Si bond angle a nd by decreasing the film density. Narrowing of the SiO2 phonon at 108 0 cm(-1) is due to SiOSi bond angle relaxation and not due to a more h omogenous and ordered fluorinated SiO2 structure than unfluorinated Si O2 as suggested in previous reports. This bond angle relaxation and de nsity reduction are accompanied by a decrease in the refractive index. Although the low refractive index signals low dielectric constant, th e chemical susceptibility of SiF to O-2 and H2O limits the maximum all owable silicon fluoride concentration in SiOF films to approximately 1 1 at.%. (C) 1997 American Vacuum Society. [S0734-2101(97)01906-4].