To obtain a processing method of a thin film by which a fine and high-accuracy wiring layer can be easily formed at a low cost, and the provide a producing method of a semiconductor device by which a highly integrated and high-performances semiconductor device equipped with a fine and high- accuracy wiring layer can be easily produced at a low cost by using the processing method of a thin film above described.

A resist film pattern 4y is formed as a mask and an org. antireflection film 3 is exposed to light beams in such a wavelength region that the resist film pattern 4y has rather low transmittance (light beams including ≤5% light in 248±0.1nm wavelength). Then the exposed part in the org. antireflection film 3 is removed by wet etching to form an org. antireflection film pattern 3y. Then the resist film pattern 4y and the org. antireflection film pattern 3y are used as a mask to remove an exposed part of a thin film.