Mechanical Characterization of High Aspect Ratio Silicon Nanolines
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1086-U05-07
Mechanical Characterization of High Aspect Ratio Silicon Nanolines Bin Li1, Huai Huang1, Qiu Zhao1, Zhiquan Luo1, Jang-Hi Im1, Paul S Ho1, Min Kyoo Kang2, Rui Huang2, and Michael W Cresswell3 1 Laboratory for Interconnect and Packaging, Microelectronics Research Center, University of Texas, Austin, TX, 78758 2 Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, TX, 78712 3 M&K Single-Crystal Standards, Frederick, MD, 21702 ABSTRACT In this study, we performed nanoindentation experiments on two sets of silicon nanolines (SiNLs) of widths 24 nm and 90 nm, respectively, to investigate the mechanical behavior of silicon structures at tens of nanometer scale. The high height-to-width aspect ratio (∼15) SiNLs were fabricated by an anisotropic wet etching (AWE) method, having straight and nearly atomically flat sidewalls. In the test, buckling instability was observed at a critical load, which was fully recoverable upon unloading. It was found that friction at the contact between the indenter and SiNLs played an important role in the buckling response. Based on a finite element model (FEM), the friction coefficient was estimated to be in a range of 0.02 to 0.05. The strain to failure was estimated to range from 3.8% for 90 nm lines to 7.5% for 24 nm lines.
INTRODUCTION Silicon-based nanostructures are essential building blocks for nanoelectronic devices and nano-electromechanical systems (NEMS). Fabrication and mechanical characterization of silicon nanostructures have attracted particular interest in recent years. For example, Hoffmann et al. reported an average strain to failure of 6% and a fracture strength of 12 GPa [1] for silicon nanowires (SiNWs) with diameters between 90 nm and 200 nm. The measured strength was significantly higher than those for microscale Si beams (4 GPa) [2] and millimeter scale Si beams (∼500 MPa) [3]. Due to delicate requirements on sample handling, transducer resolution, and the interpretation of measurement data, characterization of mechanical properties at the tens of nanometer scale is still of great challenge [4,5]. Owing to the large surface to volume ratio, friction at contact is of fundamental importance for reliability of micro/nano-devices, such as NEMS and hard-disk drives [6,7]. It has been reported that there was a transition of frictional shear strength, decreasing by almost one order of magnitude as the contact radii shrank into the nanoscale range [8]. This indicates a size effect at contact on friction properties. In this paper, we extended the study of mechanical properties of nanostructures to the tens of nanometer range, by conducting nanoindentation tests on two sets of high aspect ratio (∼15) SiNLs. An AWE process was first used to fabricate the SiNLs, having smooth sidewalls and well-defined cross sections. Buckling instability was investigated in the indentation tests, and FEM simulation was used for the extraction of material properties of the SiNLs, e.g., friction coefficient, strain to failure, etc. It was found t
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