Vertical semiconductor device comprising a resurf structure
A technology for a vertical semiconductor device having a RESURF structure, which is capable of preventing the drop of the withstand voltage when the adhesion of external electric charges occurs is provided. The vertical semiconductor device disclosed in the present specification has a cell region and a non-cell region disposed outside the cell region. This vertical semiconductor device has a diffusion layer disposed in at least part of the non-cell region. When the vertical semiconductor device is viewed in a plane, the diffusion layer has an impurity surface density higher than that satisfying a RESURF condition at an end part close to the cell region, and an impurity surface density lower than that satisfying the RESURF condition at an end part far from the cell region. When the vertical semiconductor device is viewed in a plane, a region in the diffusion layer that has the impurity surface density higher than that satisfying the RESURF condition has a greater mean gradient of the impurity surface density than a region in the diffusion layer that has the impurity surface density lower than that satisfying the RESURF condition.
1. A vertical semiconductor device, comprising:
a cell region;
a non-cell region disposed outside the cell region; and
a diffusion layer disposed in at least part of the non-cell region,
wherein when the vertical semiconductor device is viewed in a plane passing through the diffusion layer and the cell region, the diffusion layer has an impurity surface density higher than 1×10 12 [cm −2 ], which satisfies a RESURF condition, at an end part close to the cell region, and an impurity surface density lower than 1×10 12 [cm −2 ], which satisfies the RESURF condition, at an end part far from the cell region, and
wherein a substantially linear relation between the impurity surface density and a length of the vertical semiconductor device when viewed in the plane in a region in the diffusion layer that has the impurity surface density higher than that satisfying the RESURF condition has a greater mean gradient of the impurity surface density than a substantially linear relation between the impurity surface density and a length of the vertical semiconductor device when viewed in the plane in a region in the diffusion layer that has the impurity surface density lower that that satisfying a RESURF condition.
2. The vertical semiconductor device according to claim 1 , wherein, in the diffusion layer, a depth directional distribution of a carrier concentration of an end part far from the cell region has its maximum value at a position below a surface of the diffusion layer.
3. The vertical semiconductor device according to claim 1 ,
wherein a polysilicon layer is laminated on an end part of the diffusion layer that is far from the cell region, and
the polysilicon layer has a concentration of impurity of the same conductivity type as the diffusion layer, that is lower than a maximum value of an impurity concentration of the diffusion layer below the polysilicon layer.