Patent ID: 7199000

Claim:
A method for manufacturing a semiconductor device, said method comprising; providing a substrate which has a semiconductor layer and an insulating layer, wherein the insulating layer is laid on the substrate and the semiconductor layer is laid on the insulating layer; forming a first transistor at the semiconductor layer; forming a second transistor at the semiconductor layer, wherein the second transistor has a gate electrode whose length is longer than a gate length of the first transistor in a channel direction; and doping impurities into the substrate under the insulator layer, using the gate electrodes of the first and second transistors as masks; wherein the impurities are doped from above a surface of the semiconductor layer in an oblique direction against the surface, and from source side and drain side of the first transistor and the second transistor; and wherein the impurities are doped so that a region of the substrate into which the impurities are doped from the source side of the first transistor overlaps a region of the substrate into which the impurities are doped from the drain side of the first transistor.