The process of removing an overcoat (OC) on the tert-butoxycarbonyl (t-BOC) type chemically amplified positive resists has been studied, and it has been found that in the case of removing the OC after postexposure bake (FEB), or at development, the decrease in the dissolution rate at the exposed region results in the formation of the surface insoluble layer and scum. This reduction in the rate became larger with increasing the OC thickness and the t-BOC ratio in the resist, and it was shown by Fourier transform infrared spectra that the t-BOC group disappeared and a small amount of tert-butoxy moiety appeared in the fully exposed region. When the OC layer remained on the resist film during FEB, isobutene generated by the deprotection of t-BOC was prevented from permeating out of the resist film and then recombined with the OH group in the base polymer. Therefore, it was found and verified that by using the acidic OC material which exhibits a high permeability for gases, the resist performance was improved.