A method of forming an etching pattern with high resolution and high precision by preventing reaction products from being formed at the interface between an organic antireflection film and a photosensitive material film and by decreasing residuals of the etched film after etching. Formed on a semiconductor substrate (10) are a film (11) of an etching objective made of polysilicon, an organic antireflection film (12), and a photosensitive material film (13) made of a chemical amplification resist material containing (a) an onium salt compound and (b) at least either a sulfone compound or a sulfonate. The photosensitive material film (13) is exposed to light through a mask (14) and developed to form a patterned photosensitive material film (13b). Thereafter, preferably the antireflection film is dry-etched with an SO2-O2 mixture gas, and the etched film is dry-etched to form a pattern of the etched film.
