Structure and morphology of fluorocarbon films grown by hot filament chemical vapor desposition

Hexafluoropropylene oxide (HFPO) flow rate and filament preconditioning time were found to strongly influence the structure and morphology of fluorocarbon films grown by hot filament chemical vapor deposition (HFCVD). The four films discussed in this work all exhibited the vibrational frequencies of linear CF₂ chains, which are also characteristic of bulk poly(tetrafluoroethylene) (PTFE), as shown through Fourier transform infrared spectroscopy (FTIR). The films also incorporated hydroxyl (OH) and carbonyl/carboxyl (CO/COO) groups to varying degrees. Analogous to the behavior of irradiated PTFE, the OH and CO/COO groups may have formed when unterminated chain end radicals reacted with oxygen and water. The surface morphology of the four films, as revealed through atomic force microscopy (AFM), ranged from spherical nodules to anisotropic rodlike grains. An increased aspect ratio of the grains and lower OH incorporation both correlated with the decreased film deposition rate. The hypothesis that long CF₂ chains with a preferred direction of growth are favored by slow deposition would account for both the anisotropy in morphology and the reduction in OH chain ends. An analysis of the chamber effluent supports the proposed mechanism for thermal decomposition of HFPO during HFCVD.