Threshold Voltage Modulation Using $\hbox{N}_{2}^{+}$ Implantation Into Substrate for Ni Fully Silicided Gate/High-$k$ NMOS

The significance of controlling threshold voltage using nitrogen molecule ion (N
₂

⁺
) implantation into a silicon substrate was demonstrated for an n-channel MOS with a nickel fully silicided gate electrode and a high-
k
gate dielectric. We have clarified the idea that a small part of the implanted nitrogen was activated and acted as a counter dope for a channel by secondary ion mass spectrometry analysis, spreading resistance analysis, and inverse modeling analysis of MOS capacitance-voltage characteristics. It was found that N
₂

⁺
implantation had an advantage over N
⁺
implantation for forming a shallow counter-dope layer because the nitrogen-nitrogen pair has large diffusion coefficient, which resulted in a steep profile of nitrogen in a substrate.