Suppression of Ge–O and Ge–N bonding at Ge–HfO 2 and Ge–TiO 2 interfaces by deposition onto plasma-nitrided passivated Ge substrates: Integration issues Ge gate stacks into advanced devices S. Lee a , J.P. Long a , G. Lucovsky a, * , J.L. Whitten a , H. Seo a , J. Lu ¨ ning b a Department of Physics, North Carolina State University, Raleigh, NC 27695-8202, USA b Stanford Synchrotron Research Laboratory, Menlo Park, CA 94025, USA Received 9 July 2007 Available online 31 August 2007 Abstract A study of changes in nano-scale morphology of thin films of nano-crystalline transition metal (TM) elemental oxides, HfO 2 and TiO 2 , on plasma-nitrided Ge(1 0 0) substrates, and Si(1 0 0) substrates with ultra-thin (0.8 nm) plasma-nitrided Si suboxide, SiO x , x < 2, or SiON interfacial layers is presented. Near edge X-ray absorption spectroscopy (NEXAS) has been used to determine nano-scale morphology of these films by Jahn-Teller distortion removal of band edge d-state degeneracies. These results identify a new and novel application for NEXAS based on the resonant character of the respective O K 1 and N K 1 edge absorptions. This paper also includes a brief discussion of the integration issues for the introduction of this Ge breakthrough into advanced semiconductor circuits and systems. This includes a comparison of nano-crystalline and non-crystalline dielectrics, as well as issues relative to metal gates. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction A significant problem in the development of field effect transistors on Ge substrates is the formation of defective interfacial transition regions with Ge–O bonds between Ge substrates and gate dielectrics [1]. One solution is to deposit a thin Si layer on the Ge, and then form a passiv- ating/protective SiON interfacial layer; however, this adds to the equivalent oxide thickness [2]. An alternative approach for eliminating interfacial Ge–O bonds is pre- sented. A sacrificial interfacial GeN layer is formed on the Ge substrate, protecting the substrate surface from oxi- dation during film deposition. This layer is removed by a post-deposition anneal in Ar at 800 °C leaving high-k HfO 2 and TiO 2 thin film dielectrics in direct bonding-con- tact with the Ge substrate with no detectable nitride or oxide transition region. This new and novel application for NEXAS relies critically on the resonant character of the X-ray absorption. A second and equally important part of the paper addresses differences in defects in optimized nano- and non-crystalline Hf-based dielectrics, highlighting gate stack interface issues. This includes the interface with a Ge sub- strate, as well as the integration of either dual metal gates or a single mid-gap gate dielectric. 2. Experimental methods and results Nano-crystalline HfO 2 and TiO 2 films of 2–6 nm thick were deposited at 300 °C by a remote plasma-enhanced chemical-vapor-deposition onto remote plasma-nitrided Ge substrates, and compared with HfO 2 and TiO 2 films deposited onto Si substrates with 0.6–0.8 nm thick SiON interfacial layers [1,2]. The combination of resonant atom- specific O K 1 and N K 1 absorptions is an effective way to study buried interfaces, and in particular relationships between bonding in oxide dielectrics, and interfacial transi- tion regions. 0026-2714/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2007.07.068 * Corresponding author. E-mail address: lucovsky@ncsu.edu (G. Lucovsky). www.elsevier.com/locate/microrel Available online at www.sciencedirect.com Microelectronics Reliability 48 (2008) 364–369