A support
electrode (2) and a counter
electrode (16) constituting
parallel plate electrodes are disposed in a process vessel (1). A substrate (W) with an organic material film formed thereon is supported by the support
electrode (2). A high-frequency power of a frequency of 40 MHz or above for generating the
plasma is applied to the support electrode (2), so that a high-frequency
electric field is formed between the support electrode (2) and the counter electrode (16). A process gas is supplied into the process vessel (1) to generate
plasma of the process gas by the high-frequency
electric field. The organic material film on the substrate (W) is etched with the
plasma, with an organic material film serving as a
mask. The process gas includes an
ionization accelerating gas, such as Ar, that is ionized from a
ground state or metastable state with an
ionization energy of 10 eV or below and has a maximum
ionization cross-section of 2×1016 cm2 or above.