Characterizing the Two-Dimensional Doping Concentration inside Silicon Nanowires Using Scanning Spreading Resistance Mic
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1178-AA05-03
Characterizing the Two-Dimensional Doping Concentration inside Silicon Nanowires Using Scanning Spreading Resistance Microscopy Thomas Hantschel1, Volker Schulz1, Andreas Schulze1,3, Esteban Angeletti1, Firat Guder1, Volker Schmidt2, Stephan Senz2, Pierre Eyben1 and Wilfried Vandervorst1,3 1 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium. 2 Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany. 3 Instituut voor Kern- en Stralingsfysica, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium. ABSTRACT The characterization of doped regions inside silicon nanowire structures poses a challenge which must be overcome if these structures are to be incorporated into future electronic devices. Precise cross-sectioning of the nanowire along its longitudinal axis is required, followed by two-dimensional electrical measurements with nanometer spatial resolution. The authors have developed an approach to cross-section silicon nanowires and to characterize them by scanning spreading resistance microscopy (SSRM). This paper describes a cleaving- and polishing-based cross-sectioning method for silicon nanowires. High resolution SSRM measurements are demonstrated for epitaxially grown and etched silicon nanowires. INTRODUCTION Silicon nanowires are candidates as building blocks for future integrated devices such as tunnel field-effect transistors (TFET)[1]. Various fabrication schemes for silicon nanowires have already been demonstrated [2-5]. The precise control of the nanowire doping, however, is still a big challenge as one has not been able yet to characterize doped regions directly inside nanowires. The characterization requires two-dimensional electrical measurements on the crosssection of the nanowire. The method of choice for characterizing the doped regions of state-ofthe-art silicon devices is scanning spreading resistance microscopy (SSRM) [6,7]. In SSRM, a sharp diamond tip is scanned over the device cross-section measuring the local spreading resistance which is linked to the carrier concentration. A spatial resolution below 1 nm has been demonstrated. The application of SSRM for silicon nanowire analysis is thus highly desired. However, it is common in SSRM to use long transistor test structures in the order of tenths to hundreds of micrometers which facilitates the cross-sectioning, an approach which cannot be applied to silicon nanowires of fixed diameter and confined volume. Therefore, we have developed both a cleaving- and polishing-based procedure for cross-sectioning silicon nanowires and applied these procedures to etched and to epitaxially grown silicon nanowires. Our SSRM measurements illustrate that two-dimensional electrical images of silicon nanowires can be obtained with high spatial resolution. This paper explains the developed approach and applies it to different nanowire samples. EXPERIMENTAL DETAILS The nanowire samples are scribed with a manual scriber tool with optical microscope from Karl Suss of model RA120 and are cleaved afterwards by using glass cutte
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