Surface modification resist (SMR) process, which gives negative-tone image owing to the polysiloxane formation in the exposed resist surface using chemical vapor deposition, was studied for subquarter micron pattern fabrication. SMR was based on the hydrolysis of alkoxysilane and the subsequent condensation reaction in the presence of an acid catalyst and water. This article describes the application of SMR to ArF excimer laser lithography with enhanced water sorption ability. We propose the copolymer of propylideneimino p-styrenesulfonate (PPISS) and methyl methacrylate with enhanced water sorption ability in order to improve the selectivity of the polysiloxane formation. PPISS generates sulfonic acid and acetone which acts as the diffusion promoter of water molecules. It was demonstrated that the hydrolysis reaction was promoted and the polysiloxane was more selectively formed with high sensitivity by using the proposed polymer. The influence of PPISS units ratio for the selectivity of polysiloxane formation and dry etch durability was investigated. Below 0.2 mu m patterns fabrication was demonstrated by optimizing the ratio of the PPISS unit which functioned as the selective generation of acid and acetone.