Ta-incorporated HfO2 with an enhanced thermal stability is grown using atomic layer deposition (ALD). 10 nm films with HfO2:Ta2O5 ALD cycle ratios equal to 1:1 and 2:1 remain amorphous up to 900 and 750 degrees C, respectively. The thermal stability of the 1:1 film is higher than both 10 nm HfO2 and Ta2O5; the dielectric constant of the 2:1 film is 21.5, higher than HfO2 deposited at the same conditions. HfO2-HfTaxOy nanolaminates and periodic films composed of repeated [one ALD layer of Ta2O5 + x ALD layers of HfO2] are grown to study the crystallization mechanism. When x>4 periodic structures with Ta-free HfO2 ultrathin layers exist in the periodic films. For both the nanolaminate and the periodic films, crystallization starts from the HfO2 ultrathin layers, and the HfTaxOy layers block the growth of the crystalline phase. The thermal stability of these two kinds of non-homogeneous films is influenced by the Ta concentration in the HfTaxOy layers, thickness of the HfO2 layers, and thickness of the HfTaxOy layers, with different degrees of importance. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3598172] All rights reserved.