A comparison of liquid and gas phase surface preparation of III–V compound semiconductors for atomic layer deposition F.L. Lie a , W. Rachmady b , A.J. Muscat a, * a Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA b Components Research, Intel Corporation, Hillsboro, OR 97124, USA article info Article history: Received 29 April 2008 Accepted 3 July 2008 Available online 16 July 2008 Keywords: Surface preparation Liquid phase Gas phase HF Water InAs InSb Native oxide removal Atomic layer deposition Al 2 O 3 High-k abstract Native oxide removal and surface termination of InAs(1 0 0) and InSb(1 0 0) using liquid and gas phase HF chemistries were studied using X-ray photoelectron spectroscopy. Aqueous HF etching removed the native oxides on InAs and produced elemental As, which reoxidized when exposed to air. On InSb the native oxides were not completely removed due to F-termination, which passivated the surface. Gas phase HF etching of InSb native oxide completely removed Sb 2 O 5 producing a stoichiometric semicon- ductor surface terminated by F atoms on primarily In surface sites. On InAs gas phase HF completely removed As 2 O 3 producing two surface stoichiometries. For the majority of HF to water molar ratios stud- ied, a stoichiometric bulk metal and an As-rich overlayer were produced. For a lean HF composition, an As-rich bulk metal and In-rich overlayer were produced. Deposition of Al 2 O 3 by atomic layer deposition (ALD) at 170 °C directly onto F-terminated InSb produced a chemically sharp Al 2 O 3 /InSb interface. ALD of Al 2 O 3 on an In-rich overlayer on InAs resulted in an interfacial layer containing As-oxide. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Significantly higher electron mobilities compared to silicon make III–V compound semiconductors the materials of choice for high speed, low power devices [1]. The poor quality of thermal oxide layers grown on these surfaces, however, has limited the use of III–V materials in microelectronics. Recent advances in depositing high-k films on silicon using atomic layer deposition (ALD) could expand the use of III–V materials in high volume man- ufacturing. ALD offers precise control of film thickness, low pro- cessing temperatures, and excellent conformality on high aspect ratio structures [2–4]. ALD relies on self-terminating chemisorp- tion of a reactant on a surface producing up to a monolayer cover- age [5]. Techniques must be developed to form low defect interfaces by chemically saturating the atoms on a III–V surface with covalent bonds to a high-k film deposited by ALD. Surface preparation prior to ALD to remove native oxides and to passivate or activate III–V atoms ensures that the best possible interfaces will be made and improves reliability. Surface treatment affected the composition and the thickness of interfacial layers and the ultimate quality of gate stacks on III–V surfaces, such as GaAs [6,7]. There are several reported etching techniques to remove na- tive oxides from InAs and InSb [8–12]. Chemical etching using liquid mixtures of HCl and isopropanol removed oxides from InAs and InSb generating elemental group V atoms and InCl x species on these surfaces, which were subsequently thermally desorbed in ultrahigh vacuum [8,9]. Due to the relatively high thermal stability of In 2 O 3 , thermal treatment of In-based III–V substrates faces pref- erential loss of the group V species causing In droplets to form on the surface [10,11]. The formation of In droplets depends on the heating rate, the annealing temperature, and the applied As over pressure [11]. Recently the removal of native oxides from a InSb(1 0 0) surface was demonstrated without surface roughening by annealing at 250 °C under a molecular hydrogen flux [12]. The aim of this study was to investigate and compare native oxide removal and termination of InSb and InAs(1 0 0) surfaces using gas phase HF etching prior to ALD. Gas phase surface prepa- ration could be attractive to develop environmentally sustainable processes that reduce the consumption of etchants and ultra pure water. Diffusivities of chemical species in gases are typically three orders of magnitude greater than in liquids, providing minimal resistance and rapid transport of reactants or etching prod- ucts to/from a sample surface. Gas phase etching also enables greater control of surface termination, which could facilitate the 0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.07.004 * Corresponding author. Tel.: +1 520 626 6580; fax: +1 520 626 5397. E-mail address: muscat@erc.arizona.edu (A.J. Muscat). URL: http://muscat.chee.arizona.edu/ (A.J. Muscat). Microelectronic Engineering 86 (2009) 122–127 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee