Patent ID: 8415750

Claim:
A semiconductor device, comprising: a semiconductor substrate; an element isolation insulating film embedded in the vicinity of a front surface of the semiconductor substrate; a transistor formed adjacent to the element isolation insulating film; a through plug penetrating the semiconductor substrate from a back surface to the front surface so as to penetrate through the element isolation insulating film, and having a multi-stage structure comprising an upper stage portion and a lower stage portion, the upper stage portion having a region surrounded by the element isolation insulating film in the semiconductor substrate, the lower stage portion, wherein the element isolation insulating film is formed a top surface of the lower stage portion and directly contact with the upper stage portion having a diameter larger than that of the upper stage portion; and a contact plug formed directly on the element isolation insulating film and connected to an end portion of the through plug on the front surface side of the semiconductor substrate for connecting a conductive member formed above the front surface side of the semiconductor substrate to the through plug, wherein the upper stage portion and the lower stage portion are both formed in the semiconductor substrate.