Stripping and cleaning of photoresist using low energy neutrals

Experimental studies of a broad-area hyperthermal neutral stream source for photoresist cleaning are reported. Low energy neutrals are generated from a high-density inductively coupled plasma by the surface reflection neutral ization method. Rates of removal of photoresist polymers such as polymethyl methacrylate as functions of the hyperthermal translational energy and bac kground neutral pressure are reported. The results demonstrate this low ene rgy neutral source provides controllable fast neutrals for cleaning applica tions. Ex situ and in situ measurements yield typical removal rates of abou t 10 Angstrom/s without stream collimation. The removal rates at increasing pressures show a trade-off between creating higher density plasma, leading to a greater initial neutral flux and attenuation of neutrals due to colli sions. These observations are in good agreement with previous Monte Carlo s imulations. The removal rate increases linearly with rf power and is nearly constant as the neutral energy is varied by varying the reflector bias. On e consequence of neutral directionality in collimated stream applications i s the presence of unremoved carbon compounds on the sidewalls as indicated by angle-resolved x-ray photoelectron spectroscopy. (C) 1999 American Insti tute of Physics. [S0021-8979(99)07117-0].