Atomic transport and integrity of Al₂O₃(2.0 nm)/HfO₂(2.5 nm) gate stacks on Si

Abstract

The integrity of Al2 O3 (2.0 nm) Hf O2 (2.5 nm) Si O2 (<1 nm) Si (001) stacks after rapid thermal annealing at temperature up to 1025 °C was investigated. The structures were prepared by atomic layer deposition and atomic transport was accessed by profiling all elements in the system with subnanometric depth resolution, using medium and low energy ion scattering and narrow resonant nuclear reaction profiling. Al migration toward the stack/Si interface, Al loss by desorption from the surface, and Hf transport across the Al2 O3 film layer toward the outermost surface were observed. The loss of oxygen from the stack is also noticeable, most probably caused by compound dissociation and desorption of oxygen containing species. The possible detrimental effects on device electrical properties of the observed presence of Hf at the outermost surface of the dielectric stack and of Al at the dielectric/Si interface are discussed. © 2007 American Institute of Physics.