Ultrathin HfO2 gate stacks with very high permittivity were fabricated by atomic layer deposition (ALD) and a novel two-step post-deposition annealing (PDA) technique. First, a no-cap pre-crystallization anneal degasses residual contaminations in the ALD layer, and second, a Ti-cap anneal enhances the permittivity of HfO2 by generating a cubic crystal phase. The Ti-cap layer simultaneously suppresses growth of interfacial SiO2 during annealing by absorbing residual oxygen released from HfO2. Using these techniques, the dielectric constant of the ALD-HfO2 could be enhanced to 40 for 2.4-4.0 nm HfO2 thickness. (C) 2013 Elsevier Ltd. All rights reserved.