TEMPERATURE AND CONCENTRATION EFFECTS ON OZONE ASHING OF PHOTORESIST

Photoresist removal was studied using single-crystal silicon samples m ounted on a ceramic heater in an UHV compatible chamber. The photoresi st-coated sample was exposed to an ozone-oxygen mixture at atmospheric pressure and at a flow rate of 4 sl/min. Resist removal rate was meas ured using in situ laser interferometry. The removal rate was found to be a linear function of ozone concentration with a slope of 0.82 nm/s /unit mass fraction at a substrate temperature of 200 degrees C. The l inearity is consistent with a simple chemical rate model. Typical phot oresist removal rates at a mass density fraction ozone concentration o f 0.09 ranged from 2.5 to 13 nm/s for substrate temperatures ranging f rom 150 to 300 degrees C, respectively. These rates are comparable wit h those observed by others. Over this temperature range, removal rates follow standard Arrhenius behavior from which an activation energy of 5.2 kcal/mol was determined. This value is similar to the known activ ation energy of 6.0 kcal/mol for the thermal dissociation of ozone lea ding us to conclude that thermal dissociation is the rate limiting ste p in the process. Our result is also significantly lower than reported previously and may be more accurate since the substantial shrinkage o f photoresist with temperature was accounted for in these results. Add itionally, the combination of concentration and temperature informatio n is shown to lead to an effective chemical reaction rate constant for the removal of photoresist with ozone. (C) 1997 American Vacuum Socie ty.