Method for fabricating semiconductor device

A method for fabricating the semiconductor device comprising the steps of:

• selectively introducing a halogen element or a rare gas at a first concentration into a first region of a silicon substrate;
• selectively introducing a halogen element or a rare gas at a second concentration higher than the first concentration into a second region of the silicon substrate different from the first region;
• and
• wet-oxidizing the silicon substrate to thereby form a first silicon oxide film in the first region, a second silicon oxide film thicker than the first silicon oxide film in the second region, and a third silicon oxide film thinner than the first silicon oxide film in a third region of the silicon substrate different from the first region and the second region.

A method for fabricating the semiconductor device comprising the steps of:

• selectively introducing a halogen element or a rare gas into a first region of a silicon substrate;
• selectively introducing nitrogen in a second region of the silicon substrate different from the first region;
• and
• wet-oxidizing the silicon substrate after dry oxidation to thereby form a first silicon oxide film in the first region, a second silicon oxide film thinner than the first silicon oxide film in the second region, and a third silicon oxide film thinner than the first silicon oxide film and thicker than the second silicon oxide film in a third region of the silicon substrate different from the first region and the second region.