A Soft Lithographic Approach to the Fabrication of Single Crystalline Silicon Nanostructures with Well-Defined Dimension
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A Soft Lithographic Approach to the Fabrication of Single Crystalline Silicon Nanostructures with Well-Defined Dimensions and Shapes Yadong Yin,1 Byron Gates2 and Younan Xia2* 1 Department of Materials Science and Engineering 2 Department of Chemistry University of Washington, Seattle, WA 98195 (USA) ABSTRACT A procedure was developed for large-scale fabrication of nanometer-sized structures of single crystalline silicon with well-defined dimensions and shapes. Near-field optical lithography was used to define the nanostructures in a thin film of positive-tone photoresist with an elastomeric phase mask. The nanostructures were then transferred into the underlying silicon-on-insulator (SOI) substrate through a reactive ion etching (RIE) process. With this method, we can routinely generate silicon nanostructures ~130 nm in lateral dimension. They can be supported on the surface of a solid substrate as a patterned array, or released into a freestanding form. The lateral dimension of these silicon structures could be further reduced to as small as ~40 nm using stress-limited oxidation at elevated temperatures. The flexibility of this approach was demonstrated by fabricating nanoscale wires, rods, rings, and interconnected triangles of silicon. Using a two-step exposure method, the silicon nanowires can be precisely “cut” into silicon nanorods with specific lengths. INTRODUCTION Considerable interest has been directed toward silicon nanostructures owing to their important [1] applications in fabricating microelectronic, electro-optical, electromechanical, and sensing systems. Some studies have also suggested the use of silicon nanowires as scanning probes in high-aspect-ratio imaging, as nanoelectrodes in electrochemical detection, and as actuators in fabricating [2] nanoelectromechanical systems (NEMS). A useful technique for producing silicon nanostructures uses nanoparticles as the catalyst to direct the growth of silicon through the vapor-liquid-solid (VLS) mechanism.[3] Such a method can produce large quantity of silicon nanostructures, however, in most cases the products are limited to silicon nanowires. It is also hard to control the purity, uniformity and dimensions (especially the longitudinal). On the other hand, some advanced lithographic techniques such as e-beam writing, x-ray lithography, and proximal-probe lithography have been developed to [4] fabricate silicon nanostructures in a more controllable manner. Although these techniques are successful in generating features as small as ~10 nm without the geometric limitation, they are still very expensive and ineffective in practical applications for rapidly producing large quantities of [5] nanostructures. In this paper, we describe a convenient approach to the fabrication of uniform nanostructures of single crystalline silicon with controllable shapes, dimensions, and at relatively large quantities. EXPERIMENTAL DETAILS Poly(dimethylsiloxane) (PDMS) phase masks were fabricated by casting PDMS prepolymer (Sylgard 184, Dow Corning, MI) against a master whose s
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