| 摘要 |
PURPOSE: A dual gate formation method of a semiconductor device is provided to prevent a damage of a gate oxide by etching a doped and an undoped polysilicon layers using a same etching selectivity. CONSTITUTION: A gate oxide(120) and an undoped polysilicon layer(130) are sequentially formed on a semiconductor substrate(100) defined to an active and a field regions by a field oxide(110). A doped polysilicon layer(145) is formed by implanting dopants into a desired portion of the undoped polysilicon layer(130). The doped and the undoped polysilicon layers are etched by multi-step etching processes using a dual gate mask pattern, thereby forming a dual gate. That is, the polysilicon layers(130,145) are firstly etched by plasma using mixed gases of fluorine contained gas and halogen gas, secondly etched by mixed gases of halogen gas and inert gas using the gate oxide(120) as a stopper, and thirdly over-etched the gate oxide(120) using a high etching selectivity.
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