| 摘要 |
PURPOSE: To form gate insulating film of different film thickness without lowering element isolation. CONSTITUTION: A formation method of the gate insulating film forming the gate insulating films of the different film thickness on a semiconductor substrate 1 is provided with a process of forming a thick gate insulating film 9 and a thin gate insulating film 10, and then forming a polysilicon film 11 on the gate insulating films 9 and 10; and a process of forming a silicon nitride film 14 on the prescribed region of the polysilicon film 11, then selectively oxidizing the polysilicon film 11 with the silicon nitride film 14 as a mask, and forming an element isolation film 15A and the gate insulating film 15B.
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