A silicon nitride film is formed on a substrate so as to cover semiconductor devices. After having formed more than one layer of conducting members and interlayer dielectric portion, such as silicon oxide interlayer films on the silicon nitride film, an opening is formed in said interlayer dielectric portion so as to reach the silicon nitride film. The substrate with thus defined opening is etched in an etching solution containing hydrogen fluoride acid therein to remove away the silicon oxide interlayer portion. As the silicon oxide interlayer portion is etched in the solution, this forms electrical interconnection that are not surrounded with any oxides. As the silicon nitride film works as an etching stopper layer in this etching above, the semiconductor devices are protected against the etching process.