GATE STRUCTURE AND A METHOD FOR FORMING THE SAME

摘要

A method for forming a gate structure includes the following steps. A substrate is provided. A silicon oxide layer is formed on the substrate. A decoupled plasma-nitridation process is applied to the silicon oxide layer so as to form a silicon oxynitride layer. A first polysilicon layer is formed on the silicon oxynitride layer. A thermal process is applied to the silicon oxynitride layer having the first polysilicon layer. After the thermal process, a second polysilicon layer is formed on the first polysilicon layer. The first polysilicon layer can protect the gate dielectric layer during the thermal process. The nitrogen atoms inside the gate dielectric layer do not lose out of the gate dielectric layer. Thus, the out-gassing phenomenon can be avoided, and a dielectric constant of the gate dielectric layer can not be changed, thereby increasing the reliability of the gate structure.