CHARACTERIZING THE REMOTE PLASMA POLYMERIZATION OF OCTAFLUOROCYCLOBUTANE INDUCED BY RF-DRIVEN HOLLOW-CATHODE DISCHARGE

Thin films with hydrophobic character are required for many applicatio ns, e.g., as diffusion barrier or as corrosion protection. These prope rties can be realized by plasma polymerization of fluorocarbon monomer s such as C4F8 to produce homogeneous layers of PTFE-like structure. P lasma polymerization requires plasma sources with high deposition rate s even when processing thermally unstable substrates or those that abs orb RF power. Furthermore, excellent film homogeneity is often needed when coating large surface areas. Here we characterize a radio frequen cy (RF) remote process to deposit such films where discharge and proce ssing zone are separated. As primary discharge we use a novel, linear, hollow-cathode RF plasma source. The feasibility for homogeneous larg e-area deposition has already been demonstrated for organosilicon comp ounds (HMDSO). In this paper the remote polymerization of C4F8 is char acterized. Geometric effects are discussed as well as the influence of excitation power and gas flows on the process. Deposition rates of 16 0 nm min(-1) and a homogeneity of +/- 2% over a linear dimension of 25 0 mm are realized. Contact angles of up to 120 degrees correspond to t hose on conventional poly(tetrafluoroethylene) (PTFE). The refractive index of the films was determined to 1.375 +/- 0.025. Fourier transfor m infra-red spectra proved the existence of PTFE-like structures. (C) 1998 Elsevier Science S.A.