Atomic Mechanism of Arsenic Monolayer Doping on oxide-free Silicon(111)
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Atomic Mechanism of Arsenic Monolayer Doping on oxide-free Silicon(111)
Roberto C. Longo,1 Eric C. Mattson,1 Abraham Vega,1 Wilfredo Cabrera,1 Kyeongjae Cho,1 Yves Chabal,1 and Peter Thissen2 1
Department of Materials Science and Engineering, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, USA 2
Karlsruher Institut für Technologie (KIT), Institut für Funktionelle Grenzflächen (IFG), Hermann-vonHelmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
Abstract The reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ~600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ~1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.
Introduction Density scaling and subsequent device dimension reduction continue to drive significant advances in the materials processing and architecture of advanced electronic devices [1]. As gate lengths approach the sub-10 nm regime, junction doping has become an increasing concern due to its importance in controlling short channel effects [2]. Source/drain junction depths must be extremely shallow and abrupt, typically around 1/3 of gate length [3]. Moreover, the transition to non-planar architectures requires innovative methods to reliably dope the semiconductor material with fine control and reproducibility [4]. Unfortunately, the conventional techniques for junction doping, such as ion implantation and anneal [5-7], or plasma doping [8-10], cannot produce uniform and abrupt junctions shallower than 10 nm in depth, due to fundamental broadening of dopant distribution, random dopant fluctuations and ion-induced damage. Recently, monolayer doping (MLD) has emerged as a facile approach and a promising technique for creating ultra-shallow junctions [11-13]. MLD comprises several steps: functionalization of the semiconductor surface with a p- or n-dopant-containing molecule and thermal diffusion of the dopant into the surface. The self-limiting nature of self-assembled monolayers (SAMs) of MLD provides uniform coverage of a specific quantity of dopant containing molecules. Then, subsequent
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