Techniques and Applications for Non-Planar Lithography
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Techniques and Applications for Non-Planar Lithography John A. Rogers Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, U.S.A. ABSTRACT Certain classes of three dimensional nanostructures can be fabricated by contact printing patterns onto curved or non-flat surfaces. This paper reviews some of our work that demonstrates this approach by using microcontact printing to form a range of three dimensional structures with feature sizes as small as 1-2 microns and it demonstrates their use in a variety of functional devices. We also describe a nanotransfer printing technique with operational characteristics that are similar to those of microcontact printing but which enables nanometer resolution. High resolution replica molding techniques provide a method for producing copies of some of these printed structures. INTRODUCTION General techniques for fabricating complex, three dimensional nanostructures are important to the future of nanoscience and technology. Historically, research and development in the area of micro/nanofabrication has been driven mainly by the needs of the microelectronics industry. The spectacularly successful techniques that have emerged from those efforts – photolithography, electron beam lithography, etc. – are extremely well suited to the tasks for which they were principally designed: forming structures of radiation sensitive materials (e.g. photoresists or electron beam resists) on ultraflat glass or semiconductor surfaces. Significant challenges exist in adapting these methods for three dimensional structures since the limited depth of focus restricts their use to patterning on flat surfaces. As a result, complex objects formed with these techniques must be generated using layer-by-layer strategies that can be slow and difficult to implement. Some of the oldest and conceptually simplest forms of lithography – embossing, molding, stamping, writing, etc. – are now being re-examined for their potential to serve as the basis for nanofabrication techniques that are capable of producing complex three dimensional shapes [1]. Considerable progress has been made in the last few years, mainly by combining these approaches or variants of them with new materials, chemistries and processing techniques. This paper summarizes some of our past efforts to develop and apply to curved surfaces high resolution printing methods, in which a ‘stamp’ forms a pattern of ‘ink’ on a surface that it contacts. It briefly describes the techniques and presents some examples of their use in building functional three dimensional micro and nanostructures. It also shows that molding approaches which incorporate flexible, elastomeric molds can be used to replicate certain structures of this type.
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EXPERIMENT Figure 1 schematically illustrates approaches for building high resolution stamps and molds as pattern transfer elements. In this example, photolithography patterns a thin layer of resist on a silicon wafer. Stamps and molds are generated from this structure in one of two ways: by casting against
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