A method of forming an insulating layer on an conductive layer; forming a first mask layer and a second mask layer on the insulating layer; forming a resist layer on the second mask layer; patterning the resist layer; patterning the second mask layer by using the resist layer as a mask; etching the first mask layer halfway through its thickness by using the resist layer and the second mask layer as a mask; removing the resist layer; etching a remaining portion of the first mask layer using the second mask layer as a mask; forming an interconnect groove by etching the insulating layer using the first mask layer as a mask; and forming an electrically conductive material into the interconnect groove, thereby forming an interconnect layer connected to the conductive layer.