Patent ID: 8222706

Claim:
A semiconductor device comprising: a silicon substrate; a first conductive type channel region formed in the silicon substrate; a gate insulating film formed over the channel region; a gate electrode formed over the gate insulating film; a first diffusion region that includes a first impurity with a second conductive type and that is formed over the silicon substrate at both sides of the channel region; and a Si mixed crystal layer with the second conductive type that is in contact with the first diffusion region and buried in a trench portion that is formed in the silicon substrate; wherein, the Si mixed crystal layer includes: a first Si mixed crystal layer that includes a second impurity with a first concentration; a second Si mixed crystal layer formed over the first Si mixed crystal layer and that includes the second impurity with a second concentration higher than the first concentration; and a third Si mixed crystal layer formed over the second Si mixed crystal layer and that includes the second impurity with a third concentration lower than the second concentration.