PURPOSE: To omit a resist coating process to take a labor hour by a method wherein a treating process using oxygen plasma and an etching process using a buffered hydrofluoric acid liquid are added after an etchback process ends.

CONSTITUTION: A BPSG film 2 and an SOG film 3 are laminated and formed on a lower wiring layer 1 to form into an interlayer insulting film 4. Then, the film 3 is etched back and residual SOG films 3a are respectively deposited on the end parts of the film 2. The films 3a and the film 2 are exposed to an oxygen plasma atmosphere to improve an etching selectivity. Moreover, a buffered hydrofluoric acid treatment is performed to remove the films 3a and after that, an upper wiring layer 6 is formed on the film 2. Accordingly, a resist coating process to take a labor hour can be omitted and a treating time can be shortened.