Copper silicide nanocrystals on hydrogen-terminated Si(001) A.R. Laracuente ⁎, L.A. Baker 1,2 , L.J. Whitman 3 Chemistry Division, Naval Research Laboratory, Washington, DC 20375–5342, USA abstract article info Article history: Received 30 September 2011 Accepted 9 December 2013 Available online 23 December 2013 Keywords: Scanning tunneling microscopy Copper Silicon Hydrogen Silicides Surface defects In this paper we describe the surface characterization of Cu deposited onto nominally-flat and roughened hydrogen-terminated Si(001) surfaces in ultra-high vacuum using scanning tunneling microscopy. Cu forms Cu 3 Si 3D-islands with markedly different geometries depending on the surface roughness of the underlying H-terminated silicon surface. Anisotropic islands oriented perpendicular to the dimer-rows are observed on the nominally-flat H-terminated surface, while mostly isotropic islands are observed on the rough-engineered H-terminated surface. These results could have implications with respect to both surface-templated growth of nanostructures and Cu-based microelectronics. Published by Elsevier B.V. 1. Introduction Due to the ubiquity of copper and silicon in modern electronics, the advancement of our understanding of the interactions between Cu and Si, particularly Si(001), is of great importance. We have previously described a scanning tunneling microscopy (STM) study of the deposi- tion of Cu on Si(001) and the effects that hydrogen termination has on the surface structure post-Cu deposition.[1] In these previous studies, we observed that exposing the Cu/Si(001) interface to atomic H pro- duced a “rough” island + vacancy structure, as compared to “pristine” H-terminated Si(001). In this paper, we examine the deposition of Cu on H-terminated Si(001) surfaces and investigate the role of surface defects on island growth morphology. These results have potential im- plications with respect to both surface-templated growth of nanostruc- tures and Cu-based microelectronics. Modern integrated circuits utilize Cu-based interconnects.[2] Cross- contamination of Cu into other device features, however, can prove det- rimental to overall device performance.[3,4] To combat Cu contamina- tion in semiconductor devices, interconnect trenches are lined with a Cu diffusion barrier typically made of tantalum or titanium nitride.[5,6] An ultimate diffusion barrier would consist of simply a single atomic layer capable of preventing penetration into the bulk. Hydrogen is a ju- dicious choice for model studies of such an atomic diffusion barrier be- cause it saturates the dangling bonds present on the clean Si(001) surface, thus lowering the surface reactivity. In addition, H-terminated Si(001) is relatively well-understood, moderately stable, and is easily prepared.[7] The interaction of H-terminated Si(001) surfaces with metals has previously been reported.[8] Studies have also demonstrated that H can be selectively desorbed from the surface using an STM tip to create a template to pattern the deposited metal. In these studies, reactive metals (Al,[9] Co,[10] Fe[11]) were found to segregate to the H- desorbed, clean Si(001) regions. Previous theoretical treatments of Ni, which is highly reactive towards Si, suggest that on the H-terminated Si(001) surface, diffusion into the bulk can be blocked.[12,13] These studies also proposed that on room temperature surfaces Ni is further confined to diffusion paths along the dimer rows. All three results strongly suggest that H might be an effective barrier against Cu diffusion. When diffusion of adsorbed species into bulk Si is prevented or sig- nificantly diminished, absorbed species have no choice but to diffuse laterally on the surface. These surface diffusing species typically nucle- ate to form islands whose shape is determined by the type of interac- tions present between the diffusing species and the substrate, and between the diffusing species themselves. Surface defects and surface roughness are likely to have notable effects on the overall growth mor- phology. Because H-termination significantly decreases the surface re- activity towards adsorbed species, we are interested in understanding how subsequent metal growth might be affected by the presence of islands and vacancies purposely created on the Si surface. To examine this issue we have deposited additional Cu on top of the pristine H:Si and compared the morphology to that observed when deposited on top of rough, H:(Cu/Si) surfaces. In this way Cu serves as a probe for testing the qualities of H as a Cu diffusion barrier on H-terminated Si and for studying the effects that surface roughness has on subsequent Cu deposition. Surface Science 624 (2014) 52–57 ⁎ Corresponding author. E-mail address: laracuente@nrl.navy.mil (A.R. Laracuente). 1 Present address: Department of Chemistry, Indiana University, Bloomington, IN 47405, USA. 2 NRC Postdoctoral Research Associate at NRL. 3 Present address: Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA. 0039-6028/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.susc.2013.12.006 Contents lists available at ScienceDirect Surface Science journal homepage: www.elsevier.com/locate/susc