Al_2O_3/HfO_2 Multilayer High-k Dielectric Stacks for Charge Trapping Flash Memories

摘要

Dielectric and electrical properties of Al_2O_3/HfO_2 multilayer stacks depositedrnby atomic layer deposition (ALD) in dependence on the thickness of Al_2O_3rnand HfO_2 layers and the post-deposition annealing (PDA) in different ambientrn(O_2, N2, air) are investigated in terms of their application as trapping layersrnin emerging charge-trapping non-volatile flash memories. Differentiation isrnmade between different processes giving rise to hysteresis effects: trappingrnof electrons and holes under positive and negative gate bias, respectively (asrnuseful processes which define the memory window), and the generation ofrnpositive charge under high electric field stress (which degrades the stacksrnand results in permanent damage and ultimately in breakdown). Dependencernof these processes on HfO_2 and Al_2O_3 thickness as well as annealingrnambient is analyzed. It is established that electrically active defects andrntrapping phenomena are most strongly affected by the annealing ambient.rnOxygen annealing is favorable in terms of charge storage ability as itrnincreases electron trapping and improves the electric field stress stability ofrnAl_2O_3/HfO_2 multilayer stacks.