Patent attributes
A semiconductor device includes a semiconductor substrate formed with a trench having a sidewall including a middle point. The trench includes a first part extending from a surface of the semiconductor substrate to the middle point of the trench and having a diameter that is gradually reduced as the first part extends deeper from the surface of the semiconductor substrate to the middle point of the trench. The trench includes a second part that is deeper than the middle point of the sidewall and that has a larger diameter than the middle point of the sidewall. An electrically conductive film is formed in an interior of the trench so as to be located lower than the middle point of the sidewall, the conductive film having a planarized upper surface, and a collar insulating film is formed on the conductive film and the sidewall of the trench so as to extend through the middle point of the sidewall along the sidewall.
