The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node have shifted engineers' attention from the traditional and proven dielectric SiO2 to materials of higher dielectric constant also known as high-k materials such as hafnium oxide (HfO2) and aluminum oxide (Al2O3). These high-k materials are projected to replace silicon oxide (SiO2). In order to address the complex process integration and reliability issues, it is important to investigate the mechanical properties of these dielectric materials in addition to their electrical properties. In this study, HfO2 and Al2O3 have been fabricated using atomic layer deposition (ALD) on (100) p-type Si wafers. Using nanoindentation and the continuous stiffness method, we report the elastomechanical properties of HfO2 and Al2O3 on Si. ALD HfO2 thin films were measured to have a hardness of 9.5 +/- 2 GPa and a modulus of 220 +/- 40 GPa, whereas the ALD Al2O3 thin films have a hardness of 10.5 +/- 2 GPa and a modulus of 220 +/- 40 GPa. The two materials are also distinguished by very different interface properties. HfO2 forms a hafnium silicate interlayer, which influences its nanoindentation properties close to the interface with the Si substrate, while Al2O3 does not exhibit any interlayer. (C) 2008 The Electrochemical Society.