1. NiSi Formation in Electrochemically-Etched Silicon Nanowires W. Xu* ,1 , Vadim Palshin 2 , J.C. Flake** ,1 1 Gordon and Mary Cain Department of Chemical Engineering 2 Center for Advanced Microstructure and Devices Louisiana State University, Baton Rouge LOUISIANA STATE UNIVERSITY
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4. Integration of Electroless SiNWs: Fabrication of SiNWs via electroless etching SiNWs deposition on lithographically patterned electrodes Thermal annealing to form self-aligned NiSi contacts Electrical measurement Advantages over conventional approach: Low cost compared to VLS L arge scale fabrication R elative simple silicidation process Low process temperatu re Enables FET / nanowire sensor fabrication. Characterization Separation of SiNWs from parent substrate LOUISIANA STATE UNIVERSITY
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7. Cross-section SEM imagines of fabricated SiNWs on substrate SEM imagines of sep a rated SiNWs deposited On substrate Large quantity of SiNWs deposited on substrate To p view SEM imagines of fabricated SiNWs on substrate S iNWs on substrates Se perated SiNWs LOUISIANA STATE UNIVERSITY
8. E lectrical measurement SEM images of Inter-digited electrodes （ IDE ） SEM image of one single SiNW across electrode The fabricated SiNWs were deposited on IDE electroplated with nickel, and annealed at 450°C in reducing atmosphere. Cross-section sketch of SiNWs across the electrodes LOUISIANA STATE UNIVERSITY
9. Electrical measurement Based on the estimation that there are 612 SiNWs across the IDE( by SEM analysis) and the average diameter of nanowire is 150 nm. The corresponding resistivity: Same order of magnitude of silicon for annealed nanowires suggests the lateral NiSi formation is occurred at the end of nanowires and the nanowires is not fully silicized. LOUISIANA STATE UNIVERSITY Bu lk resistance Bare IDE IDE after SiNW deposition IDE after anneal Resistance >1·10 9 Ω （ＯＣ） 4·10 6 Ω 2·10 3 Ω NiSi Silicon IDE after anneal Resistivity 10μΩ∙cm 1-5 Ω∙cm ～ 0.35 Ω∙cm
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14. Directly Functionalize (Si-C, no intermediate oxide) of silicon nanowire surface as a possible solution to passivate the surface and avoid oxidation. For example anodic electrografting of SiNW surfaces with alkyl Grignards (or cathodic electrografting with alkynes) Passivation of Si surface Absorption infrared spectra. [a] ethyl hydrosilylated; [b] ethyl electrografted; [c] methyl hydrosilylated; [d] methyl electrografted. AFM images of passivated silicon surfaces. [A] ethyl anodic electrografting; [B] ethyl hydrosilylation; [C] methyl anodic electrografting; [D] methyl hydrosilylation. Anodic electrografting Thermal hydrosilylation Oxides (XPS) LOUISIANA STATE UNIVERSITY
15. LOUISIANA STATE UNIVERSITY Functionalization of Nanowires ATR FTIR spectra showing neat hexynoic acid top and surfacebound hexynoic acid electrografted to a silicon nanowire surface. FTIR spectra showing BSA top and immobilized BSA onto a silicon nanowire substrate. Z. R. Scheibal et al, Electrochemical and Solid-State Letters, 11 (8) 2008
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17. Acknowledgements: Sponsors: ATMI, Louisiana Board of Regents D. Cao Materials Characterization center, LSU S. S. Vegunta and J. N. Ngunjiri, Department of Chemical Engineering, LSU Thank you for your attention ! LOUISIANA STATE UNIVERSITY
![O utline ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Silicon nanowire sensor Fernando Patolsky, Gengfeng Zheng & Charles M Lieber, NATURE PROTOCOLS VOL.1 NO.4 2006 Silicon nanowire solar cell B. Tian, et al. Nano Lett. Vol.449, NO.18 2007 LOUISIANA STATE UNIVERSITY](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)