here the conductive tube 170 is separated from the lower wire 120 having the lower insulating layer 130 in between the contact plug 160 and the conductive tube 160 may be made of any one of tungsten w copper cu aluminum al and other similar materials but not limited to those mentioned materials the upper insulating layer 180 formed over the middle insulating layer 150 may be made of any one of an oxide film nitride film usg psg bpsg teos and other similar materials but not limited to those mentioned materials the upper wire 190 may be formed over the upper insulating layer 180 and may be connected to the contact plug 160 thus the upper wire 190 and the lower wire 120 may be electrically connected through the contact plug 160 in addition the upper wire 190 and the conductive tube 170 may be separated by the upper insulating layer 180 that is the lower part of the conductive tube 170 may be separated from the lower wire 120 by the lower insulating layer 130 and the upper part of the conductive tube 170 may be separated from the upper wire 190 by the upper insulating layer 180 therefore the length of the conductive tube 170 may be shorter than that of the contact plug 160 the thickness of the lower insulating layer 130 and the upper insulating layer 180 may be less than that of the middle insulating layer 150 in the.