Patent ID: 7005340

Claim:
A method for manufacturing a semiconductor device, comprising the steps of: (a) forming a first mask layer having a first opening section on a semiconductor substrate of a first conductivity type; (b) forming a first dielectric layer having a specified film thickness on an exposed surface of the semiconductor substrate in the first opening section after forming the first mask layer; (c) forming an impurity layer by introducing a first impurity of a second conductivity type by an ion implantation in the semiconductor substrate through the first dielectric layer, using the first mask layer as a mask; (d) conducting a heat treatment to form a first well by re-distributing the first impurity of the impurity layer, and forming a second dielectric layer having a specified film thickness that is thicker than the first dielectric layer on the exposed surface of the semiconductor substrate in the first opening section, thereby forming the first well and the second dielectric layer simultaneously; (e) forming a second mask layer on at least the first mask layer, the second mask layer having a second opening section that is located at a specified position in the first opening section on the first mask layer; and (f) forming a second well within the first well by introducing a second impurity of the first conductivity type by an ion implantation in the semiconductor substrate through the second dielectric layer using the second mask layer as a mask.