Hot Carrier Degradation in Deep Sub-Micron Nitride Spacer Lightly Doped Drain N-Channel Metal-Oxide-Semiconductor Transistors

Spacer bottom oxide in the nitride spacer lightly doped drain (LDD) device, which is used to prevent huge interfacial states between the nitride and silicon interface, plays an important role in the hot carrier test. Because of the stress due to atomic size mismatch between the nitride spacer and silicon, trap-assisted hot electron tunneling is more significant in a nitride spacer LDD device than in the oxide spacer counterpart. A thicker bottom oxide can eliminate this effect. However, the optimal thickness of the nitride spacer bottom oxide should be varied for different poly-silicon gate structures. The hot carrier stress in a nitride spacer LDD device causes multi-stage degradation under I_sub,max stress. It is dominated by electron trapping at the early stage, interfacial state (N_it) creation at the second stage, and self-limiting hot carrier degradation at the final stage. The degradation for I_g,max stress in nitride spacer LDD devices is mostly caused by electrons trapped in the nitride/oxide interface.