Silicon nanostencils with integrated support structures Shawn Fostner a, * , Sarah A. Burke b , Jessica Topple a , Jeffrey M. Mativetsky c , Jean Beerens d , Peter Grutter a a Physics Department, McGill University, 3600 Rue University, Montreal, QC, Canada H3A 2T8 b Department of Physics, University of California at Berkeley, Berkeley, CA 94720-7300, USA c Institut de Science et d’Ingénierie Supramoléculaires (ISIS) CNRS 7006, Université de Strasbourg, 8 Allée Gaspard Monge, 67000 Strasbourg, France d Centre de Recherche en Nanofabrication et Nanocaractérisation, Département de génie électrique et de génie informatique, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1 article info Article history: Received 9 December 2008 Received in revised form 20 July 2009 Accepted 4 September 2009 Available online 9 September 2009 Keywords: Silicon stencil Pattern transfer Tantalum film Nanostructuring Film stress MEMS Stabilization structures Stencil deformation abstract We describe the fabrication of single crystal silicon membranes for stencil mask deposition. The mem- branes are created using standard microfabrication techniques combined with focussed ion beam milling to give structures with openings hundreds of micrometers to 50 nm in size. Deflection of the membrane structures under the deposition of highly stressed metals films is measured for vacuum deposited tanta- lum films, and used to estimate a film stress of 1.3 ± 0.1 GPa. In order to overcome these significant deflections, we have integrated simple stiffening structures into the membranes themselves which both preserve line of sight to the sample as well as provide a sufficiently large bending moment to resist ver- tical deflections which would otherwise cause noticeable feature broadening. Deposition of metallic nanowires on the surface shows good agreement with the calculated and measured deflections of the reinforced structures. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The quest to control the size and functionality of devices at ever smaller scales has been an area of significant research and develop- ment over the past decades. Lithographic processing for device fab- rication and research has made significant progress in recent years in terms of complexity, size of features, and potential materials. However, most techniques are geared towards the bulk processing of semiconductor wafers in ambient environments, and involve wet processing and stringent material restrictions. Stencil masks are an attractive alternative which use a wide range of nanometer to micrometer openings on a thin stencil within close proximity of a surface to mask physical deposition of a wide range of evaporants on arbitrary substrates. As a result, it is possible to deposit on sen- sitive substrates such as alkali halides under ultrahigh vacuum (UHV) conditions. This leads to the possibility of measurements on structures of well defined chemical composition even at an atomic scale. Numerous examples of nanostencils have been pub- lished using silicon nitride membranes [1–6], cantilever based masks [7,8], and silicon on insulator membranes [9]. Stencils have also been demonstrated in dynamic modes, using AFM cantilevers or mask manipulation in-situ to position apertures relative to the sample [4,5,7,8], and static modes [1,2,6,3,9] with a prefabricated stencil which is clamped directly to the sample. The primary limitation of silicon nitride based masks lies in cre- ating as low stress a membrane as possible in order to avoid cata- strophic failure of the mask, either during manufacture or deposition. In addition, there is the added difficulty of ensuring that the mask maintains its shape during deposition as the depos- ited layers can cause deformation of the membrane depending on the stiffness of the mask and the stress in the deposited layer. There have been recent efforts to create stabilizing structures using silicon nitride masks that are either corrugated or supported by large silicon support frames nearby [10–12] in order to maintain feature size and fidelity during the deposition of high thickness and high stress films. The principle limitation of these techniques is the deformation of the thin membrane near the opening as a re- sult of the trade-off between the size of the support structures and the line of sight between the source and substrate. Large support frames, required to resist significant deformation when using thin membranes, need to be further from the openings in order to avoid occluding the beam of evaporated material. An alternative is to use bulk silicon membranes to create the masks, thereby avoiding the problems of inherently stressed mem- branes such as silicon nitride, but requiring careful thinning of the membranes to achieve acceptable thicknesses. We describe here an all silicon stencil with features as small as 50 nm in conjunction 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2009.09.004 * Corresponding author. E-mail address: sfostner@physics.mcgill.ca (S. Fostner). Microelectronic Engineering 87 (2010) 652–657 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee