METHOD FOR MANUFACTURING TRANSISTOR

摘要

PURPOSE: A method for fabricating a transistor is provided to improve the operating feature of a semiconductor device by controlling the refresh time. CONSTITUTION: A first insulating film(32) is formed on a semiconductor substrate(31). A trench(33) is formed by selectively etching the semiconductor substrate(31) and the first insulating film(32). A second insulating film side wall is formed in an inner wall of the trench(33). Ions are implanted so as to control a threshold voltage by using the first insulating film(32) and the second insulating film side wall as a mask. Then, the first insulating film(32) and the second insulating film side wall are removed. A gate insulating film(36) is formed on the semiconductor substrate(31). A gate(37) is formed in the trench(33). A source/drain(38) area is formed on the surface of the semiconductor substrate(31).