wall of the contact hole as seen in fig2 b further with the washing solution of the present invention since the etching rate is moderated reduction in thickness of a conductor layer is reduced and consequently occurrence of disconnection of a conductor or incomplete contact between conductors can be suppressed then where washing is performed while the solution is kept at a low temperature of 30 to 60 u00b0 c the etching rate can be further suppressed in this instance if mechanical vibrations such as ultrasonic vibrations are applied then the washing effect can be further improved while suppressing the etching rate low however since the washing capacity drops at a temperature lower than 30 u00b0 c the washing solution is preferably used at a temperature higher than 30 u00b0 c also where an organic acid ammonium salt other than ammonium acetate was used as the organic acid ammonium salt to be added to the apm substantially similar results to that illustrated in fig1 were obtained where the original concentration of nh 4 oh in the apm to which the organic acid ammonium salt is added is low even if the added amount of the organic acid ammonium salt is small the difference in etching rate between a doped.