Film Formation in Hexafluoropropylene Plasmas

Abstract

The gas phase dominated plasma polymerization (PP) of hexafluoropropylene (HFP) produces 0.2 to 0.5 μm particles and 1 μm spherical particle agglomerates which are all incorporated into a transparent and highly adhering PPHFP film. An energy ratio plasma parameter, E, related to the plasma energy and strongly dependent on flow rate (or residence time) was derived. The maximum and plateau in deposition were successfully described when polymerization and etching were exponentially related to E. The chemical structure of the amorphous, crosslinked PPHFP consists largely of similar amounts of C*-CF, CF, CF 2 and CF 3 units. Plasma etching was inhibited by fluorine scavenging and HF formation on the addition of hydrogen to the feed. The deposition and coalescence of smaller particles into a smoother and more uniform surface on adding nitrogen reflects the incorporation of nitrogen into the polymer, the increase in the polar component of surface energy and, perhaps, the decrease in dominance of gas phase versus surface polymerization. The low PP(N 2 /HFP) electrical breakdown strength may be attributed to an alternate conduction mechanism in the relatively polar plasma fluoropolymer.Thin fluoropolymer films can have many advantages including a low coefficient of friction, a low surface energy, thermal stability, biocompatibility, and chemical resistance. Unfortunately, the techniques used to deposit thin films of conventional fluoropolymers can involve etchants, solvents and temperatures that limit their applicability. Plasma polymerization is an ambient temperature, solvent-free process that can be used to deposit highly adhering, pinhole-free and crosslinked thin fluoropolymer films from a variety of compounds including those not polymerizable by standard techniques (7-3). These films would have potential applications in the microelectronics, biomedical, membrane, aerospace and automotive fields (4-9).