This study examined the effects of phase separation by postdeposition annealing (PDA) on the microstructures and electrical properties of atomic layer deposited (ALD) Hf-silicate films with various Si contents. The changes in the leakage current density after PDA at 1000 degrees C were affected mainly by the phase separation of the films and crystallization of HfO2. The percolation of a crystallized HfO2 phase in the Hf-silicate film is believed to cause the high leakage. The flatband voltage shifted toward the ideal value with increasing amounts of the phase-separated SiO2 top layer as a result of the increased PDA temperature. (c) 2008 The Electrochemical Society.