Surface Modification of Silicon Nano Mechanical Structures by Carbon Ion Implantation for Post-fabrication Transformatio
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Surface Modification of Silicon Nano Mechanical Structures by Carbon Ion Implantation for Post-fabrication Transformation to Silicon Carbide Kumar R. Virwani1, Dinesh K. Sood2, Robert G. Elliman3 and Ajay P. Malshe4 1 Department of Microelectronics Photonics, University of Arkansas, 4 Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701, U.S.A. 2 School of Electrical and Computer Engineering, RMIT University, 124 La Trobe Street, Melbourne 3000, Australia 3 Department of Electronic Materials Engineering, Australian National University, Canberra, ACT 0200, Australia. ABSTRACT Internal stresses can cause de-lamination and fracture of coatings and structures and it is well known that ion-implantation can be used to control such behavior through modification of the stress. Here, however, we show that the unique ability of implantation to create controlled stresses in materials by altering both the chemical composition and mechanical properties, combined with an increase in the bending strength of materials, can used to create novel vertical nanostructures. Silicon cantilevers (beams), 193nm thick, 200nm wide and 3µm long, were implanted with carbon ions to create a buried SiCx layers. The internal stresses generated by implantation caused the beams to bend at angles ranging from 10 degrees to greater than 90 degrees, leading to unique vertical nanostructures. This method can be used to create 3-D nano electromechanical systems (NEMS). INTRODUCTION Ion implantation is used very widely in the electronic industry to dope and modify electronic properties of materials [1] and has also been used extensively for the surface treatment of metals and ceramics to enhance their mechanical properties [2]. However, the use of ion implantation to improve the mechanical properties of nanoscale structures is a relatively new development. We have previously [3] shown that the mechanical properties of nanoscale silicon structures can be predictably modified using self ion implantation. It is also known that high fluence carbon implantation into silicon can be used to form stoichiometric silicon carbide [4, 5]. As a mechanical material, silicon carbide has better properties than pure silicon for use at high temperatures [6]. The Young’s modulus of amorphous silicon carbide is higher than the Young’s modulus of crystalline silicon along the direction [6]. The goal of this research was to extend our earlier study of self-implanted structures to explore the effect of high fluence carbon implantation into single crystal nanoscale silicon structures (cantilever beams). EXPERIMENTAL Silicon-on-insulator (SOI) wafers (single crystal [100] orientation) with top silicon thickness of 193nm and an oxide thickness of 400nm were used in a lift-off configuration to fabricate the nanostructures [3, 7]. The SOI wafers were cleaned and coated with a polymethylmethacrylate (PMMA) layer followed by a methaacrylic acid (MAA) layer. Electron beam lithography was
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used to define beams structures i
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