US Patent 7560772 Semiconductor integrated circuit device and manufacturing method thereof

After silicon oxide film (9) is formed on the surface of a semiconductor substrate (1), the silicon oxide film (9) in a region in which a gate insulation film having a small effective thickness is formed is removed using diluted HF and after that, high dielectric constant insulation film (10) is formed on the semiconductor substrate (1). Consequently, two kinds of gate insulation films, namely, a gate insulation film (12) comprised of stacked film of high dielectric constant insulation film (10) and silicon oxide film (9) and gate insulation film (11) comprised of the high dielectric constant insulation film (10) are formed on the semiconductor substrate (1).