Surface Kinetics of Polyphenylene Oxide Etching in a CF 4 / O 2 / Ar Downstream Microwave Plasma

A downstream microwave plasma etcher with in situ diagnostics has been constructed to elucidate the chemical mechanisms in plasma etching of polyphenylene oxide (PPO). CF 4 /O 2 /Ar reactant gases are used. Stable reaction products are investigated with mass spectrometry while reactive-free radical information is obtained using optical emission spectroscopy. Additionally, the weight loss of PPO is measured to determine average etch rate. A linear correlation between weight loss measurements of PPO laminates and integration of CO and CO 2 formation measured by mass spectrometry suggests that real-time monitoring of polymer etching can be achieved. Etching dynamics are studied with gas compositions of CF 4 varied from 6.6 to 30%. The etch process exhibits a dynamic reduction in rate with CF 4 ≥ 20%. C 1s spectra of X-ray photoelectron spectroscopy show an increase in fluorination of the etched surface with CF 4 %. A kinetic model based on the dynamic change of the number of carbon sites that are fluorinated is proposed.