HfO2/Al2O3 stacks are grown on Si (100) substrate by atomic layer deposition and then nitridized using ammonia (NH3) annealing in the temperature range of 600-900 degrees C. The effects of NH3 annealing temperature on the structural and physical properties are investigated. HfO2 phase changes from monoclinic to orthorhombic with the annealing treatment. Moreover, the increasing of the grain size and decreasing of the valence band maximum with increasing annealing temperature are demonstrated. In addition, the film annealed at 900 degrees C clearly shows that there exists an amorphous Al2O3 layer between partially crystalline HfO2 layer and the Si substrate. (C) 2012 Elsevier B.V. All rights reserved.