| 摘要 |
LOCOS layers for defining NMOSFET and PMOSFET forming regions Rn and Rp are formed, and then a protective oxide layer is formed. A first resist layer, opened above the region Rn, is then formed on the protective oxide layer. By using the first resist layer as a mask, ion implantation is performed twice to form a threshold control layer and a P- layer functioning as a punch-through stopper or the like. By using the first resist layer as a mask, the substrate is etched to remove a portion of the protective oxide layer. Then, the first resist layer is removed. These processes are also performed on the region Rp. Then, a gate oxide layer is formed. Thus, it is possible to prevent a foreign impurity, introduced during the ion implantation, from diffusing the surrounding regions when the resist layers are removed. As a result, the properties of the gate oxide layer can be improved.
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