Patent ID: 7582932

Claim:
A silicon carbide semiconductor device comprising: a semiconductor substrate including a silicon carbide substrate having a first conductive type or a second conductive type, a first semiconductor layer made of the first conductive type silicon carbide and having an impurity concentration lower than an impurity concentration of the silicon carbide substrate, a second semiconductor layer made of the second conductive type silicon carbide, and a third semiconductor layer made of the first conductive type silicon carbide, which are stacked in this order; a trench disposed in a cell region of the semiconductor substrate and penetrating the second and the third semiconductor layers to reach the first semiconductor layer; a channel layer having the first conductive type and disposed on a sidewall and a bottom of the trench; an oxide film disposed on the channel layer in the trench and including a part for functioning as a gate oxide film; a gate electrode disposed on a surface of the oxide film in the trench; a first electrode electrically connecting to the third semiconductor layer; and a second electrode electrically connecting to the silicon carbide substrate, wherein a position of a boundary between the first semiconductor layer and the second semiconductor layer is disposed lower than an utmost lowest position of the oxide film in the trench, an impurity concentration of the second conductive type impurity in the second semiconductor layer is gradually reduced from a height of a position of the oxide film disposed on the bottom of the trench to the boundary between the first semiconductor layer and the second semiconductor layer, and an impurity concentration of the first conductive type impurity in the channel layer is higher than an impurity concentration of the first conductive type impurity in the first semiconductor layer.