PURPOSE: To prevent damage of a photoresist material at the time of photodevelopment by placing the photoresist film formed on a silicon substrate in the atmosphere of a halide gas and projecting patternwise ultraviolet laser beams on this substrate to develop the photoresist as well as to etch the surface of the substrate.

CONSTITUTION: The pattern is formed on the silicon substrate by forming the thin photoresist film on the silicon substrate oxidized by heat, placing it in a reactor having a window, introducing the halide gas, such as NF3, CCl2F2, CCl4, SF6, or CF4, very stable in normal temperature into the reactor to convert the atmosphere into the gas, projecting patternwise ultraviolet beams through the window on the photoresist to develop it by excitation of the gas and the substrate, as well as to etch the surface of the substrate, thus permitting damage of the photoresist film to be prevented at the time of photoetching, and development of the photoresist and etching to be executed in one step.