Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device comprising the steps of:

• (a) preparing a semiconductor substrate having an upper surface and a lower surface;
• (b) after the step (a), forming a first insulating film extending from an upper surface of the semiconductor substrate to an inside of the semiconductor substrate;
• (c) after the step (b), forming a second insulating film having a thickness thinner than the first insulating film on the first insulating film;
• (d) after the step (c), forming a first conductive film on the second insulating film;
• (e) after the step (d), forming an interlayer insulating film on the upper surface of the semiconductor substrate so as to cover the first conductive film;
• (f) after the step (e), forming a first contact hole in the interlayer insulating film, the first conductive film, the second insulating film and the first insulating film so that a bottom portion of the first contact hole is located in the first insulating film,
• (g) after the step (f), subjecting the interlayer insulating film, the second insulating film and the first insulating film to an isotropic etching treatment, and
• (h) after the step (g), embedding a first plug in the first contact hole,
• wherein a side surface of the interlayer insulating film is separated from a side surface of the first conductive film so that a part of an upper surface of the first conductive film is exposed from the interlayer insulating film in the first contact hole by the isotropic etching treatment in the step (g),
• wherein a side surface of the first insulating film and a side surface of the second insulating film in the first contact hole are separated from the side surface of the first conductive film so that a part of a lower surface of the first conductive film is exposed from the first and second insulating films by the isotropic etching treatment in the step (g), and
• wherein a first distance from the lower surface of the first conductive film to the bottom portion of the first contact hole is longer than a second distance from the side surface of the first conductive film to the side surface of the interlayer insulating film.