An organic anti-reflective coating (ARC) is formed over a surface of a semiconductor substrate, and a resist layer including a photosensitive polymer is formed on the ARC. The photoresistive polymer contains a hydroxy group. The resist layer is then subjected to exposure and development to form a resist pattern. The resist pattern to then silylated to a given depth by exposing a surface of the resist pattern to a vapor phase organic silane mixture of a first organic silane compound having a functional group capable of reacting with the hydroxy group of the photoresistive polymer, and a second organic silane compound having two functional groups capable of reacting with the hydroxy group of the photoresistive polymer Then, the silylated resist pattern is thermally treated, and the organic ARC is an isotropically etched using the thermally treated resist pattern as an etching mask.