Method for fabricating semiconductor device including nitrided gate insulator

A method of fabricating a semiconductor device, the method comprising:

• forming an interface layer on a substrate;
• forming a first gate insulating layer having a first dielectric constant on the interface layer, and
• forming a second gate insulating layer having a second dielectric constant smaller than the first dielectric constant and including silicon (Si) on the first gate insulating layer;
• annealing the substrate;
• nitriding the first and second gate insulating layers after annealing the substrate, in an atmosphere comprising a nitride gas;
• forming a work function control layer on the nitrided gate insulating layers;
• and
• forming a metal gate electrode on the work function control layer.

A method of fabricating a semiconductor device, the method comprising:

• providing a substrate;
• forming a first interface layer on the substrate in a first region;
• forming a second interface layer, having a width different from that of the first interface layer, on the substrate in the second region;
• forming a first gate insulator doped with silicon (Si) on the first interface layer;
• forming a second gate insulator doped with silicon (Si) on the second interface layer;
• annealing the substrate;
• nitriding the first gate insulator so that the first gate insulator has a first nitrogen concentration and nitriding the second gate insulator so that the second gate insulator has a second nitrogen concentration different from the first nitrogen concentration, after the annealing of the substrate;
• forming a work function control layer on the first and second gate insulators after nitriding the first and second gate insulators;
• and
• forming a metal gate electrode on the work function control layer.