Thermal annealing of fluorocarbon films grown by hot filament chemical vapor deposition

Annealing alters the stability, structure, and morphology of fluorocarbon f ilms grown from hot filament chemical vapor deposition (HFCVD) using hexafl uoropropylene oxide (HFPO) precursor. The composition of these films is gre ater than 97% CF2. The as-deposited film in this study contains extraneous hydroxyl (OH) and carbonyl/carboxyl (CO/COO) groups, as revealed by Fourier transform infrared (FTIR) spectroscopy. Such groups al a found to be therm ally labile and lead to two Film decomposition regimes, centered at 150 and 300 degreesC. This: is similar to the two decomposition onsets at 150-250 and 300 degreesC observed in irradiated bull; PTFE, which are attributed to the loss of peroxy radicals and COOH groups, respectively. A postdepositio n 1 h 400 degreesC in situ vacuum anneal reduced the OH and CO/COO groups i n the HFCVD film to below FTIR detection limits. This postanneal film is fo und to be stable up to 400 degreesC with no evidence of structural changes. The surface morphology of the film quenched from the 1 h 400 degreesC in s itu vacuum anneal, as imaged by optical microscopy (OM), resembles that of the as-deposited film, showing no discernible surface features. However, fo r a film quenched from the 1 h 325 degreesC in situ vacuum anneal, signific ant crystalline spherulites of up to similar to1 mm in diameter are observe d through OM. This is attributed to favorable crystallization in the proxim ity of the melting temperature of bulk PTFE. Intensity differences in FTIR absorption peaks in this: film, compared to the other films, also support t he morphological differences seen.