A General Nonlithographic Method for Producing Nanodots by RIE Etching
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A General Nonlithographic Method for Producing Nanodots by RIE Etching Jacob H. Leach, and Hadis Morkoç Electrical and Computer Engineering, Virginia Commonwealth University, 601 West Main St., Richmond, VA, 23284 ABSTRACT In this work, thin layers of poly(methyl methacrylate) (PMMA) on Ni on silicon substrates were etched almost completely away by oxygen RIE, leaving only the topmost portion of the roughness, generating nanodots of PMMA approximately 30-40nm or smaller in size. After sufficiently hard baking the samples to promote PMMA adhesion to the Ni and to increase the robustness of the PMMA, the nanodots were used as a mask to etch the thin Ni films, thus generating Ni nanodots on Si. The Ni nanodots were then used as a reactive ion (RIE) etch mask, thereby generating Si nanopillars. With further understanding of the mechanism of the generation of the roughness of the PMMA, or with the use of other polymeric materials suitable as wet etching masks, nanodots of varying size should be attainable. This method represents a very simple, low cost, scalable, and general technique to produce nanodots of various thin metals on various substrates.
INTRODUCTION The generation and exploitation of OD and 1D nanodots and nanowires is a rapidly growing field with many researchers involved in realizing the vast potential and understanding the rich underlying physics of these new types of systems. There are generally two methods by which these structures are formed: by direct patterning “lithographic” or “top-down” methods (i.e. electron-beam, dip-pen, nanoimprint, focused ion-beam, etc.), or by an indirect “selfassembled” or “bottom-up” technique (molecular beam epitaxy, biologically self-assembled monolayers, colloidal assemblies, etc.). The lithographic methods boast the advantage of having the ability to arbitrarily define the pattern to be generated onto a substrate; however, they are typically more expensive than the self-assembled techniques, particularly as the size of the patterns decrease, and also they may be relatively slow to generate a pattern over a large area. The “bottom-up” or self-assembled techniques are attractive due to their simplicity and eloquence (for nature is certainly a “bottom-up” builder), their versatility to delicate chemical and biological systems, and their reasonable cost. For a recent review on various nanofabrication techniques, see [1]. Self-masking techniques using RIE have been demonstrated previously for the generation of nanostructures for a number of materials [2]. The work described in this paper is in some way similar but instead of generating an etch mask in-situ inside the RIE chamber and etching to generate nanostructures using this mask, this work uses only oxygen plasma and subsequent processing to allow the generation of nanodots, or subsequently, nanostructures etched using the generated nanodots as RIE masks.
It is known that etching of poly(methyl methacrylate) (PMMA) by oxygen RIE can result in rough PMMA surfaces [3]. In an effort to exploit this typica
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