Etching polyimide with a nonequilibrium atmospheric-pressure plasma jet

An atmospheric-pressure plasma jet has been used to etch polyimide films at 1.0-8.0 +/- 0.2 mu m/min at 760 Torr and between 50 and 250 degrees C. The plasma was produced by flowing helium and oxygen between two concentric el ectrodes, with the inner one coupled to 13.56 MHz rf power and the outer on e grounded. The etch rate increased with the O-2 partial pressure, the rf p ower and the substrate temperature. The apparent activation energy for etch ing was 0.16 eV. Langmuir-probe measurements revealed that the ion densitie s were between 1 x 10(10) and 1 x 10(11) cm(-3), 5 mm from the end of the p owered electrode. Biasing the substrate had no effect on the rate. Ozone, s inglet sigma metastable oxygen (b (1)Sigma(g)(+)), arid singlet delta metas table oxygen (a (1)Delta(g)) were detected in the plasma by emission spectr oscopy. More ozone was produced in the effluent through the recombination o f O atoms with O-2. Based on the production rate. of O-3, the concentration of O atoms 6 mm from the powered electrode was estimated to be similar to 7 x 10(14) cm(-3) at 6.6 Torr O-2 and 200 W power. It is proposed that O at oms are the principal reactive species involved in etching polyimide. (C) 1 999 American Vacuum Society. [S0734-2101(99)01705-4].