Effect of blocking and tunnel oxide layers on the charge trapping properties of MIS capacitors with ALD HfO2/Al2O3 nanolaminated films

Abstract

Electrical and charge trapping properties of HfO2/Al2O3 nanolaminated stacks incorporated in three types of metal-insulator-silicon capacitor structures (without blocking and tunnel oxide layers; with 20 nm Al2O3 as blocking oxide and ∼3 nm Al2O3 or thermal SiO2 as tunnel layer) were investigated. HfO2/Al2O3 stacks exhibit a positive initial oxide charge, and adding of the 3 nm Al2O3 tunnel layer to the capacitor doubles the amount of the positive charge and the density. Using SiO2 as a tunnel layer resulted in a negative initial oxide charge which is interpreted by the effect of dipole formation at the Al2O3/SiO2 interface. Tunnel SiO2 provides lowest density of the interface states at silicon and leakage currents. The insertion of blocking and tunnel oxide layers to the capacitors significantly widens the memory windows; capacitors with a SiO2 tunnel oxide demonstrate largest memory windows.