The improvement of electric property and reduction of boron penetration in metal–oxide–Si (MOS) capacitors are clearly achieved by the combination of a gate electrode deposited using amorphous Si(a-Si) and a gate oxynitride formed by a two-step N2O nitridation. The charge-to-breakdown performance of MOS capacitors fabricated by this technique is excellent. The hot-electron induced interface traps and flatband voltage shifts are significantly reduced. This reliability improvement can be explained in terms of a mechanism based on an increase in compressive stress (macroscopic strain) in the oxynitride and relaxation of SiO2/Si interfacial strain. Also this improvement can be due to a reduction of hydrogen-related species diffused from the gate electrode, which is achieved by nitrogen pileup at the gate electrode/oxynitride interface. Boron penetration is significantly suppressed by an a-Si gate electrode because of a larger grain size and a longer dopant diffusion path. The boron penetration is also clearly reduced by a gate oxynitride formed using a two-step N2O nitridation. Boron penetration reduction for this oxynitride can be attributed to the nitrogen incorporation into the gate electrode/oxynitride interface. This approach would be useful for the processes of gate electrode and gate dielectric in the deep submicron MOS transistors. © 2001 American Vacuum Society.