Analysis of structural changes in plasma-deposited fluorinated silicon dioxide films caused by fluorine incorporation using ring-statistics based mechanism
V. Pankov et al., Analysis of structural changes in plasma-deposited fluorinated silicon dioxide films caused by fluorine incorporation using ring-statistics based mechanism, J APPL PHYS, 86(1), 1999, pp. 275-280
Fluorinated silicon dioxide (SiOF) films were prepared by remote plasma enh
anced chemical vapor deposition using SiF4, O-2, H-2, and He reaction gases
. Fourier transform infrared spectroscopy studies accompanied by molecular
orbital (MO) modeling were used to explain structural changes in SiOF films
caused by F incorporation. On the basis of the results of MO modeling, it
was shown that F atoms incorporated into the SiOF network only slightly aff
ect the geometry of ring units, the main building blocks of SiOF film netwo
rk, and cannot cause strong changes in the value of the average Si-O-Si ang
le, <theta >. Ring-statistics-based mechanism is proposed to explain the in
crease in <theta > in SiOF films with F content. It is supposed that intera
ction of highly reactive F species from the incoming flux with the growing
SiOF network during deposition process induces the preferential conversion
of the most strained small-order ring units into those of higher order char
acterized by larger <theta >. As a result, the <theta > in SiOF film increa
ses and film structural homogeneity improves with increasing the F content
in the incoming flux. It is assumed that structural changes in SiOF films c
aused by F incorporation are not the abrupt transition from the ring-built
SiOF network to the ring-free chain-like network, but a continuous shift of
the ring distribution function towards the large-size high-order rings whi
ch causes the increase in <theta > within SiOF network, a reduction in the
film density, and an enhancement of the film moisture absorptivity. (C) 199
9 American Institute of Physics. [S0021-8979(99)04613-7].