A surface modification resist process (SMR), in which polysiloxane is formed on the exposed resist surface by chemical vapor deposition, was studied for subquarter micron pattern fabrication. This paper describes the microscopic and macroscopic reaction mechanisms in SMR when methyltriethoxysilane is used as the chemical vapor deposition gas. Hydrolysis and condensation reactions occurring in acid-catalyzed polysiloxane formation were investigated through Fourier transform infrared spectroscopy. It was demonstrated that the hydrolysis is the dominant reaction rather than the condensation, and is dependent on the generated acid catalyst and sorbed water. Polysiloxane layer growth at the near resist surface was observed by Rutherford backscattering spectroscopy and from cross-sectional views of the polysiloxane layer. The polysiloxane layer initially grows in the resist film because of the dominant diffusion of methyltriethoxysilane molecules. Afterward the diffusion is prevented due to the excessive networking of the polysiloxane so that the polysiloxane layer grows on the resist surface. Furthermore, 0.20 mu m pattern fabrication was demonstrated by applying SMR to KrF excimer laser lithography with an alternating phase-shifting mask.