For the improvement of ArF photoresist removal performance, the effect of acetic acid (HAc) and isopropyl alcohol (IPA) in an ozonated water cleaning system was investigated by combining experimental and simulation results. The ArF photoresist removal rate increased by 6.8 times with an increase in HAc concentration in ozonated water vapor. With a higher ozone concentration, a lower hydroxyl radical (OH center dot) concentration, and no reaction between photoresist by HAc observed, it is concluded that the improvement of the ArF photoresist removal rate with the addition of HAc results from a higher aqueous ozone concentration due to extended lifetime and a higher solubility of ozone due to the OH center dot scavenging effect. The increase in IPA concentration in ozonated water vapor also improved the ArF photoresist removal rate by 12 times. Simulation results show that OH center dot concentration was much lower than pure ozonated water, presumably due to a slower OH center dot formation rate. ArF photoresist was removed at a relatively high speed in the vapor of IPA and water mixture even in the absence of aqueous ozone. Therefore, it is concluded that the improved photoresist removal rate with an IPA addition in ozonated water mainly results from the direct oxidation of photoresist by IPA itself. (C) 2008 The Electrochemical Society.