7 is removed subsequently as shown in fig3 c a lower layer portion 8 of a second insulating layer composed of an silicon oxide film is deposited 300 nm as an interlayer insulating layer a silicon nitride film 9 used as an etching stopper layer is deposited 100 nm and an upper layer portion 10 of the second insulating layer composed of the silicon oxide film is deposited 300 nm as a trench forming insulating layer next as shown in fig3 d a via hole communication hole 11 and dummy patterns portions not included in a wiring portion 12 are formed by a photolithography technology and etching technology using a photoresist 7 u2032 at this time etching is performed in order of the silicon oxide film the upper layer portion 10 of the second insulating film used as the trench forming insulating layer the silicon nitride film 9 used as the etching stopper layer and the silicon oxide layer the lower layer portion 8 of the second insulating film used as the interlayer insulating layer as gases for etching the silicon oxide film c 4 f 8 co o 2 and ar are used on the other hand a magnetron rie reactive ion etching apparatus is generally used for the etching at this time an etching condition is set to c 4 f 8 co o 2 ar 14 50 5 300 sccm pressure.