Effect of Gate Dopant Diffusion on Leakage Current in $\hbox {n}^{+}\hbox {Poly-Si}/\hbox {HfO}_{2}$ and Examination of Leakage Paths by Conducting Atomic Force Microscopy

The effect of gate dopant diffusion on leakage current has been investigated in n⁺poly-Si/HfO₂ capacitors. The HfO ₂ films with low gate doping concentration exhibited very low leakage currents, whereas the films with heavy gate doping concentration showed excessive leakage currents. Conducting atomic force microscopy was applied to examine the current images of the HfO₂ films showing excessive leakage currents, and evident leakage paths with annular shape were observed. The leakage paths observed in the HfO₂ films with heavy doping poly-Si gate may be related to the diffusion of the excessive dopant from the n⁺ poly-Si gate into the HfO₂, particularly through the grain boundaries in the films. This may significantly increase the leakage currents in the n ⁺poly-Si/HfO₂ devices