Development of Parallel Dip Pen Nanolithography Probe Arrays for High Throughput Nanolithography
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Development of Parallel Dip Pen Nanolithography Probe Arrays for High Throughput Nanolithography David A. Bullen1, Xuefeng Wang1, Jun Zou1, Sung-Wook Chung2, Chang Liu1, and Chad A. Mirkin2 1 Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 2 Department of Chemistry, Northwestern University, Chicago, IL ABSTRACT Dip Pen Nanolithography (DPN) is a lithographic technique that allows direct deposition of chemicals, metals, biological macromolecules, and other molecular “inks” with nanometer dimensions and precision. This paper addresses recent developments in the design and demonstration of high-density multiprobe DPN arrays. High-density arrays increase the process throughput over individual atomic force microscope (AFM) probes and are easier to use than arrays of undiced commercial probes. We have demonstrated passive arrays made of silicon (8 probes, 310 µm tip-to-tip spacing) and silicon nitride (32 probes, 100 µm tip-to-tip spacing). We have also demonstrated silicon nitride “active” arrays (10 probes, 100 µm tip-to-tip spacing) that have embedded thermal actuators for individual probe control. An optimization model for these devices, based on a generalized multilayer thermal actuator, is also described. INTRODUCTION Dip Pen Nanolithography (DPN) is a recently introduced [1] method of scanning probe lithography that offers significant advantages over other lithographic processes. In this method, chemicals are adsorbed onto an AFM probe then deposited on a surface by diffusion from the tip while scanning in contact mode. The most common probe is a silicon nitride AFM tip that has been coated by dipping it in a chemical solution or by evaporation from a heated source. DPN has been successfully applied to a wide variety of patterning tasks. It has been used to pattern biological macromolecules such as thiol-modified ssDNA [2], collagen (via direct patterning) [3], and rabbit immunoglobulin G (via selective adsorption onto 16mercaptohexadecanoic acid patterns) [4]. The meniscus that forms between the probe tip and substrate in air has been used as a nanoscale chemical reactor to pattern sol-gel precursors [5], a variety of metals [6,7], and conducting polymers [8]. Surface binding in the these demonstrations ranges from strong covalent bonds, as in the thiol-gold [1] and silane-oxide [9] systems, to weaker electrostatic, van der Waals, hydrophobic, and hydrogen bonds [10]. In some cases, the covalent chemistries have been shown strong enough to act as masks in various substrate etching applications [11,14]. The wide variety of tasks for which DPN has been used is an indicator of its potential for commercialization, but success will require more than just robust chemistry systems. The real power of DPN can only be unlocked with pattern generation capabilities that far exceed those of single probe systems. The first attempt at multiprobe patterning [12] used a 1-D array of undiced commercial probes. Although this method works, the arrays are so wide (~1.5mm per
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