| 摘要 |
After forming a field insulating film 12 on a substrate, sacrificing or gate oxidation films are formed as oxidation films 14 a and 14 b. An ion implantation layer 18 is formed by one or plurality of implantation process of argon (or fluoride) ion in an element hole 12 a using a resist layer 16 as a mask via the oxidation film 14 a. When the oxidation films 14 a and 14 b are used as sacrificing oxidation films, gate oxidation films are formed in the element holes 12 a and 12 b after removing the resist film 16 and the oxidation films 14 a and 14 b. When the oxidation films 14 a and 14 b are used as gate oxidation films, the oxidation films are once thinned by etching and then thickened after removing the resist layer 16. The gate oxidation film 14 a is thicker than the gate oxidation film 14 b by forming the ion implantation layer 18.
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