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 neutralization method. Rates of removal of photoresist polymers such as polymethyl methacrylate as functions of the hyperthermal translational energy and background neutral pressure are reported. The results demonstrate this low energy neutral source provides controllable fast neutrals for cleaning applications. Ex situ and in situ measurements yield typical removal rates of about 10 Å/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 collisions. These observations are in good agreement with previous Monte Carlo simulations. The removal rate increases linearly with rf power and is nearly constant as the neutral energy is varied by varying the reflector bias. One consequence of neutral directionality in collimated stream applications is the presence of unremoved carbon compounds on the sidewalls as indicated by angle-resolved x-ray photoelectron spectroscopy.