Patent ID: 8704311

Claim:
A semiconductor device comprising: a first transistor including: a first impurity layer of a first conductivity type formed in a first region of a semiconductor substrate; a first epitaxial semiconductor layer formed above the first impurity layer; a first gate insulating film formed above the first epitaxial semiconductor layer; a first gate electrode formed above the first gate insulating film; and first source/drain regions of a second conductivity type opposite to the first conductivity type formed in the first epitaxial semiconductor layer and the semiconductor substrate in the first region, the first impurity layer being located between the first source/drain regions; and a second transistor including: a second impurity layer of the second conductivity type formed in a second region of the semiconductor substrate; a second epitaxial semiconductor layer formed above the second impurity layer and having a film thickness different from a film thickness of the first epitaxial semiconductor layer; a second gate insulating film formed above the second epitaxial semiconductor layer; a second gate electrode formed above the second gate insulating film; and second source/drain regions of the first conductivity type formed in the second epitaxial semiconductor layer and the semiconductor substrate in the second region, the second impurity layer being located between the second source/drain regions, wherein the film thickness of the first epitaxial semiconductor layer is larger than the film thickness of the second epitaxial semiconductor layer, and a diffusion velocity of an impurity which forms the first impurity layer is higher than a diffusion velocity of an impurity which forms the second impurity layer.