Effects of surface treatments using O3 and NH3 on electrical properties and chemical structures of high-k HfO2 dielectric films on strained Si1−xGex∕Si substrates

Abstract

This study examined the chemical interactions between an atomic-layer-deposited (ALD) HfO2 film and strained epitaxial Si1−xGex∕Si (x=0.1,0.2,0.3) substrates during film deposition and postdeposition annealing (PDA), as well as their influence on the electrical properties. The influences of various predeposition surface treatments under O3 (POT) and NH3 (PNT) were also investigated in order to improve the understanding of the chemical and structural changes in thin film systems. Particular focus was made on the migration behavior of Si and Ge in the interface between a HfO2 film and Si1−xGex substrate, which critically affects the capacitance equivalent thickness (CET). The interdiffusion of the substrate elements during ALD and PDA could be controlled by POT and PNT. PNT was effective in reducing the diffusion of both Si and Ge during the ALD and PDA, whereas POT reduced only Si diffusion. The surface treatments reduced the changes in the CET after PDA without any significant increase in the leakage current density. The migration of the substrate elements was traced by secondary ion mass spectroscopy, auger electron spectroscopy, high-resolution transmission microscopy and x-ray photoelectron spectroscopy.