Development of Induced Crystallization as a Pattern Transfer Mechanism for Nanofabrication
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Development of Induced Crystallization as a Pattern Transfer Mechanism for Nanofabrication T. Chraska1, M.J. Cabral2, S. Mesarovic1, D.M. Longo1, E.A. Stach3, J.C. Bean2, and R. Hull1 1 Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 2 Department of Electrical Engineering, University of Virginia, Charlottesville, VA 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA ABSTRACT A novel pattern transfer technique, based upon direct contact between nanofabricated printheads and amorphous films/substrates is being developed. Transfer of features from printhead to substrate is via an induced crystallization mechanism, with a goal of controlling crystal nucleation at dimensions comparable to the printhead features. To realize such a printing mechanism, appropriate mediums/materials that can be crystallized through contact with the printhead elements must be identified. From a range of candidate materials we focus on Ge and Indium Tin Oxide (ITO) films grown by molecular beam epitaxy or sputtering. The crystallization may be induced directly by heating (thermally), pressure (mechanically), or electrical conduction through the contact points. Crystallization of many amorphous materials is known to be self sustaining (so called “explosive crystallization”), raising the need to identify mechanisms for abruptly stopping crystallization if feature dimensions are to be constrained. A set of amorphous or nanocrystalline samples have been studied during crystallization by a heated printhead fabricated with a Focused Ion Beam (FIB). A simplified continuum model suggests the feasibility of achieving lateral confinement of the induced crystallization. In order to characterize fully the transitional and final substrate states, real-time observation of nanoscale crystallization in the transmission electron microscope (TEM) is in progress. A special TEM goniometer is being developed which incorporates a piezoelectrically driven tip and a heating capability to enable observation of tip-substrate contact at elevated temperatures that should give invaluable insight into crystallization mechanisms. INTRODUCTION The requirement of a highly planar substrate for standard optical lithographic methods presents a severe limitation in using such methods, for example, in transferring patterns onto curved surfaces. This limitation, along with other issues, such as the challenges and costs associated with shrinking feature sizes in optical lithography, is leading to a growing interest in novel methods1,2 for pattern transfers. The work presented in this paper is a component of a larger “Nanoprinting" project3 at the University of Virginia with the following broad goal: the ability to transfer patterns with features as small as 100 nm onto a wide range of surfaces including those with constant or varying radius of curvature and over relatively large areas (up to 1 cm2 in a single printing). All pattern transfer mechanisms proposed in this project are achieved by dir
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