| 摘要 |
PURPOSE: A method for fabricating a semiconductor device is provided to improve reliability of the device by using a stepped gate insulating layer. CONSTITUTION: In the method, a sacrificial oxide layer is formed on a semiconductor substrate and covered with a resist pattern defining a portion narrower than a gate region. Next, impurity ions such as nitrogen are implanted into the substrate through the resist pattern to form an ion-implanted region for reducing the oxidation of the substrate. The resist pattern and the sacrificial oxide layer are then removed, and the substrate is oxidized with heat to form the stepped gate insulating layer(14). Since the ion-implanted region suppresses the oxidation of the substrate, the stepped gate insulating layer(14) has a thin portion above the ion-implanted region. After that, a polysilicon layer(15a), a refractory metal layer(WSix)(16) and a cap insulating layer(17) are sequentially formed and selectively patterned to form a gate, which has a central portion disposed above the thin portion of the stepped gate insulating layer(14) and an edge portion disposed above a thick portion. Next, a sidewall spacer(18) and a source/drain region(19) are formed.
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