Ultrathin fluoropolymer films were deposited by a plasma-enhanced chemical
vapor deposition process, from mixtures of hexafluoropropylene (C3F6) and o
ctafluoropropane (C3F8) precursors. Different monomer feed compositions res
ult in different rates of deposition. The C3F6 is the primary polymerizing
species and C3F8 acts to reduce the deposition rate. The structure and comp
osition of these films were characterized using Fourier transform infrared
and angle-resolved x-ray photoelectron spectroscopy. The bulk F:C ratio is
1.1 for the homopolymer film (deposited from C3F6 only) and 1.4 for the cop
olymer film (deposited from C3F6 + C3F8 monomer feed). The copolymer film h
as more -CF3 groups and has a more highly branched structure. The surface F
:C ratio is 1.5 for the homopolymer and 1.7 for the copolymer film. The wat
er contact angle increased with film thickness and with addition of C3F8 to
the monomer feed. A mechanism is presented to describe how the addition of
C3F8 modifies the polymerization process, causes a high surface F:C ratio
of the copolymer films, and leads to reduced surface energy. (C) 1999 Ameri
can Vacuum Society. [SO734-2101(99)01301-9].