Study on the Structural Stability and Charge Trapping Properties of High-k HfO2 and HFO2/Al2O3/HfO2 Stacks

In this work, high-k dielectric stacks of HfO2 and HfO2/Al2O3/HfO2 (HAH) were deposited on SiO2/Si substrates by atomic layer deposition as charge trapping layers in charge trapping devices. The structural stability and the charge trapping characteristics of such stacks were investigated using Metal-Alumina-Hafnia-Oxide-Silicon (MAHOS) structure. The surface roughness of HfO2 was stable up to 11 nm with the insertion of 0.2 nm thick Al2O3. The effect of the thickness of the HAH stack and the thickness of intermediate Al2O3 on charge trapping characteristics were investigated for MAHOS structure under various gate bias pulse with duration of 100 ms. The threshold voltage shift after programming and erase showed that the memory window was increased with increasing bias on gate. However, the programming window was independent of the thickness of HAH charge trapping layers. When the thickness of Al2O3 insertion increased from 0.2 nm to 1 nm, the erase window was decreased without change in the programming window.