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0983-LL05-05

Direct Focused Ion Beam Drilling of Nanopores Nick Patterson1,2, V. Carter Hodges1, Michael J. Vasile1, David P. Adams1, Zhu Chen3, and C. Jeff Brinker1,3 1 Sandia National Laboratories, Albuquerque, NM, 87185 2 New Mexico Institute of Mining and Technology, Socorro, NM, 87801 3 University of New Mexico, Albuquerque, NM, 87106 ABSTRACT Focused 30keV gallium ion beam, single-pixel drilling combined with backside particle detection is used to fabricate pores having exit diameters as small as ~11 nm in 200 nm-thick silicon nitride membranes. The backside channelplate detector response obtained about the onset of breakthrough is interpreted by plan-view transmission electron microscopy investigations of hole morphology. Immediately prior to breakthrough, there is a rise in detector signal as the local membrane thickness is reduced. This likely occurs as a result of ion transmission and, possibly, forward sputtering. At the dose required for breakthrough a maximum detector signal is obtained thus providing a potential method for end point detection. The focused ion drilling technique avoids broad area beam exposure methods that are often used to reduce hole diameter to nanometer dimension. In addition, the current approach overcomes difficulties in determining a required dose for breakthrough such as those that arise from an inhomogeneous membrane thickness, redeposition, or ion channeling.

INTRODUCTION Nanometer-scale pores are of interest for molecular electronics, for sensing of DNA[1-4], viruses, and metal ions[5], and as apertures in various beam-defining optical applications[6-8]. Toward this end, recent work demonstrates how focused ion beam (FIB)[1-8] techniques and other methods [9,10] can be used to define extremely small diameter holes in membranes or in coatings placed at the end of a fiber or a tip. In most studies to date involving ion beam patterning of membranes, nanometer-scale pores are defined by first creating a large through-hole. This may be accomplished by sputtering, etching or ablation. Subsequently, material is added to the eroded volumes so to partially close the holes. In exemplary work, Li et al.[1] first showed that a broad area beam of ions can close down a pre-existing hole in a thin membrane. This intriguing result (referred to as sculpting) led to creation of holes as small as 1.8 nm[1] when employing a backside single ion detector[11]. Recent work by Mitsui [12] shows that ion-stimulated transport is responsible for the accretion of matter about the periphery of a hole when using a broad area ion beam. Since the original work by Li, hole closure (and creation of nanoholes) has been demonstrated using a variety of other methods. A reduced hole diameter has been accomplished using a scanned focused beam of gallium ions[13], a beam of high energy electrons[13,14], stimulated chemical vapor deposition [7,15] and atomic layer deposition[16]. Despite much progress, additional research and development is required. Potentially new fabrication methods are needed, because it is unc