The effects on metal oxide semiconductor field effect transistor properties of nitrogen implantation into p⁺ polysilicon gate

We have studied in detail the effects of nitrogen implantation into a p⁺ polysilicon gate on gate oxide properties for the surface p-channel metal oxide semiconductor (PMOS) below 0.25 μm. The nitrided oxide film can be easily formed by the pile-up of nitrogen into the gate oxide film from the polysilicon gate. It was found that boron penetration through the gate oxide film can be effectively suppressed by nitrogen implantation into a p⁺ polysilicon gate because nitrogen in the polysilicon film can suppress boron diffusion, and the nitrided oxide film can also act as a barrier to boron diffusion. Moreover the hot-carrier hardness can be remarkably improved by the nitrided oxide film since interface state generation can be suppressed by the nitrided oxide film. Furthermore the number of electron traps in the gate oxide film can also be reduced by nitrogen implantation.