The electrical properties of dielectric stacks of SiO2 and Al2O3 prepared by atomic layer deposition method

Abstract

We produced dielectric stacks composed of ALD SiO2 and ALD Al2O3, such as SiO2/Al2O3, Al2O3/SiO2, and SiO2/Al2O3/SiO2, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO2/Al2O3 shows lowest leakage current for negative bias region below 6.4 V, and Al2O3/SiO2 showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al2O3 and SiO2/Al2O3. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO2 (6.5 nm)/Al2O3 (12.6 nm) is -6.4 V, which agrees well with the experimental observation (-6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO2 layer. (C) 2011 Elsevier B. V. All rights reserved.