To reduce the quantity of leak current of a semiconductor device with an STI structure.
A method for manufacturing a semiconductor device includes the stages of separating a 1st element region 1b from other element regions and also separating a 2nd element region 1a from other element regions by forming grooves in a semiconductor substrate 1 and burying insulators; covering a section which is disposed in the 1st element region 1b of the semiconductor substrate 1, and a section 2b which is adjacent to the 1st element region with an antioxidant film (b); forming an oxide film 3a in the 2nd element region 1a by subjecting the semiconductor substrate 1 to heat oxidation; removing the antioxidant film 20b; and forming a 2nd gate oxide film for a 2nd transistor by making the oxide film 3a in the 2nd element region 1a thick, by subjecting the semiconductor substrate 1 to heat oxidation again while forming a 1st gate oxide film for a 1st transistor in the 1st element region 1b.
Fujitsuna Hideyoshi
Osamu Suzawa