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0921-T05-04

Nanofabrication of Vertically Aligned Carbon Nanofibers for Contact Characterization Yusuke Ominami1, Quoc Ngo1,2, Makoto Suzuki1, Kevin Mcilwrath3, Konrad Jarausch3, Alan M Cassell2, Jun Li2, and Cary Y Yang1 1 Center for Nanostructures, Santa Clara University, 500 El Camino Real, Santa Clara, CA, 95053 2 Center for Nanotechnology, NASA Ames Research Center, Moffett Field, CA, 94035 3 Hitachi High Technologies America, Pleasanton, CA, 94588 ABSTRACT Recent studies in nanostructural characterization for on-chip interconnect applications using carbon nanofibers (CNFs) are presented. In this paper, we propose a novel technique, for the purpose of characterizing interfacial structures of vertically aligned CNFs for cross-sectional imaging with scanning transmission electron microscopy (STEM). In this technique, vertically aligned CNFs are selectively grown, by plasma-enhanced chemical vapor deposition (PECVD), on a substrate comprising a narrow strip (width ~100nm) fabricated by focused ion beam (FIB). Using high-resolution STEM, we show that CNFs with diameters ranging from 10 -100 nm exhibit very similar graphitic layer morphologies at the base contact interface.

INTRODUCTION The superior properties of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have given rise to an abundance of studies of potential applications. Nanoelectronic devices fabricated using these carbon-based nanostructures have been introduced for both transistor and interconnect applications [1,2]. For future integrated devices, a bottom-up approach for electrical interconnects using vertically aligned CNFs grown by plasma-enhanced chemical vapor deposition (PECVD) has been proposed [3,4]. For interconnect applications, the resistance of carbon nanostructures must be minimized. Because of its strong correlation with electrical transport properties, the detailed interface structure between CNFs and the substrate must be understood. In order to characterize interface structure of CNFs on substrates, scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) have been extensively used [5, 6]. Focused ion beam (FIB) systems using Ga+ ions or ion beam milling using Ar+ ions have been widely employed as tools for TEM sample preparation. If the CNF diameter is 80-100nm, conventional ion beam milling can be used to prepare a thin foil to be examined by TEM. However, if the CNF diameter is 50nm or less, conventional ion beam milling cannot be simply applied due to the following reasons. First, TEM images are constructed by a convolution of transmitted electrons through both CNFs and the protection material over the CNFs. Secondly, the ion beam may damage the intrinsic CNF structure in the process of making a thin foil of 100nm or less because ions can scatter laterally into the thin foil [7]. These issues have been making the interface characterization of small-diameter CNFs exceedingly difficult. To overcome such difficulties, we introduce a bottom-up sample preparation for CNFs through a nanofabrication