| 摘要 |
A manufacturing method of this invention has an ion-implantation process for threshold voltage adjustment of an MOS transistor, including a process to form a first well of an opposite conductivity type in a substrate of one conductivity type, to form a second well of the opposite conductivity type having higher impurity concentration than that in the first well, under a region where a thin gate insulation film is formed, to form gate insulation films on the first well and the second well, each having a different thickness, to ion-implant first impurities of the one conductivity type into the wells of the opposite conductivity type under the condition that the impurities penetrate the gate insulation films of different thicknesses and to ion-implant second impurities of the one conductivity type into the second well of the opposite conductivity type under the condition that the second impurities penetrate the thin gate insulation film but do not penetrate the thick gate insulation film. Thus the ion-implantation process for the threshold voltage adjustment of a semiconductor device having gate insulation films of different thicknesses can be rationalized with this invention.
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