0167-9317/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.mee.2005.04.030 Microelectronic Engineering 80 (2005) 416–419 www.elsevier.com/locate/mee Single Hf atoms inside the ultrathin SiO 2 interlayer between a HfO 2 dielectric film and the Si substrate: How do they modify the interface? S. N. Rashkeev 1 , K. van Benthem, S. T. Pantelides 1 , S. J. Pennycook Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6031, U. S. A. 1 also at Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, U. S. A. Tel: 1-865-241-2350 email: rashkesn@ornl.gov Abstract We show that individual Hf atoms may get incorporated into the SiO 2 interlayer which is formed between the HfO 2 dielectric film and the Si substrate during rapid thermal annealing. We report atomically-resolved Z-contrast images of a Si/SiO 2 /HfO 2 structure together with first-principles calculations which demonstrate that single Hf atoms are in fact present in the interlayer. The location of individual Hf atoms within the interlayer oxide is closely related to the structure of the amorphous oxide near the Si/SiO 2 interface. The Hf defects may affect channel mobility and leakage currents in the HfO 2 /Si electronic devices. Keywords: alternative dielectrics; hafnium oxide; leakage current; scanning transmission electron microscopy 1. Introduction The high-k dielectric oxide HfO 2 is one of the materials which may replace the “conventional” gate dielectric, SiO 2 , in microelectronics due to its high dielectric constant, a relatively large bandgap, and a good thermal stability with Si [1]. The formation of silicates is generally thought to be kinetically suppressed [2,3]. Moreover, the rapid thermal annealing process used for the crystallization of the HfO 2 film on the Si substrate also results in a formation of an ultrathin (0.5 - 1 nm) amorphous SiO 2 interlayer which eliminates the interfacial strain and, therefore, ensures a high-quality Si/dielectric interface. However, HfO 2 exhibits reduced channel mobilities and larger leakage currents relative to pure SiO 2 [4]. It is not known which defects are mainly responsible for that. For example, it is unclear if individual Hf atoms that may get incorporated in the SiO 2 interlayer during the annealing step may contribute to leakage currents. In this work, we combine atomically-resolved Z-contrast scanning transmission electron microscopy (STEM) images of the Si/SiO 2 /HfO 2 system and first-principles density-