Etching is performed on an insulating layer 23 and a conductive layer 32 with a photoresist 41 as the mask, to form an opening 51 in the conductive layer 32. After removing the photoresist 41, another insulating layer 24 is formed all over, which is etched back so as to expose a surface of a conductive layer 31, to thereby cover the inner wall of the opening 51. Then etching is performed on the conductive layer 31 with the latter insulating layer 24 as the mask, so as to form another opening 52 in the conductive layer 31. Then still another insulating layer 25 is formed all over, which is then etched back so as to expose a surface of the conductive layer 32, to thereby fill the opening 52 with the last formed insulating layer 25.