Pulsed plasma enhanced and hot filament chemical vapor deposition of fluorocarbon films

Fluorocarbon films from pulsed plasma enhanced chemical vapor deposition (P PECVD) and hot filament chemical vapor deposition (HFCVD) show a greater ra nge in composition and structure compared to films from conventional CVD pr ocesses. Films were deposited using hexafluoropropylene oxide (HFPO), 1,1,2 ,2-tetrafluoroethane (HFC-134) and difluoromethane (HFC-32) as the feed gas es. Film characterization was performed through high resolution solid-state F-19 and C-13 nuclear magnetic resonance (NMR) techniques. Increasing puls e off-time during HFPO PPECVD resulted in films with more linear CF2 charac ter and reduced the amount of cross-linking/branching, attributed to CF2 ch ain propagation dominating during the off-time. HFC PPECVD films contained significantly less fluorine and more of carbon unsaturation, attributed to plasma hydrogen scavenging of fluorine to form hydrogen fluoride. Switching from PPECVD to HFCVD with HFPO as the feed gas resulted in films resemblin g bulk poly(tetrafluoroethylene) (PTFE), as a result of clean thermal break down of HFPO to form polymerizing CF2 radicals. Isothermal annealing of PPE CVD films revealed two different thermal decomposition pathways: one which involved CF3 loss in more cross-linked films, and one which involved oligom er desorption/chain unzipping in films with a substantial linear CF2 chain component. (C) 2000 Elsevier Science S.A. All rights reserved.