Nanoimprint Lithography and Lithographically Induced Self-Assembly
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Nanoimprint
Lithography and Lithographically Induced SelfAssembly Stephen Y. Chou
other lithographic methods such as “stamping” with self-assembling “ink.”4 Its simple yet unique principle allows NIL to avoid many problems inherent in other lithographic methods and to achieve high resolution and high throughput at a low cost.
Resolution The resolution of NIL is determined by the mechanical strength of the mold and polymer. Using a silicon dioxide mold and poly(methyl methacrylate) (PMMA) resists (with a Tg of 100C), holes 6 nm in diameter and 60 nm deep in PMMA and PMMA pillars 30 nm in diameter and 35 nm tall have been achieved using NIL5 (Figures 2–4). Many experiments have indicated that with a suitable resist and mold, the resolution of NIL can be below 5 nm. In general, small holes are much easier to imprint than small resist pillars, because the pillars can easily tear off during mold separation and are extremely difficult to image—scanning electron microscopy can easily melt a small polymer pillar.
Three-Dimensional Patterning
Introduction Our ability to pattern nanostructures offers a unique path to discovery and innovation in science and technology. When nanostructures are smaller than a fundamental physical length scale, conventional theory may no longer apply, and new phenomena emerge. To fully benefit from the discovery and innovation in nanostructures and commercialize them, low-cost and high-throughput manufacturing is essential. The biggest challenge is that we do not have a mature nanostructure manufacturing technology to realize the needed low cost and high throughput. Nanoimprint lithography and lithographically induced self-assembly are promising low-cost, high-throughput technologies for manufacturing nanostructures. This article will discuss some of the significant developments that have been made in recent years in this area.
The resist can be a thermal plastic,1 a UV-curable or thermal-curable polymer,2,3 or some other deformable material. For a thermal-plastic resist, the resist is heated above its glass-transition temperature (Tg) during imprinting, then cooled below Tg before it is separated from the mold. For a UV- or thermal-curable polymer resist, after the mold is pressed into the resist, the polymer is cured by UV radiation or thermal heating to harden it (by cross-linking) before separation from the mold. NIL is primarily a physical-deformation process and is fundamentally different from
Another feature of NIL is that it is a three-dimensional (3D) patterning technology, in contrast to the 2D patterning of other lithographies. Three-dimensional features are very desirable in some applications, such as microwave transistors and microelectromechanical systems (MEMS). For example, the T gate for microwave transistors has a narrow footprint for high
Nanoimprint Lithography Principle and Process Nanoimprint lithography (NIL) involves two steps: imprinting and pattern-transfer (Figure 1). In the imprinting step, a mold with nanostructures on its surface is used to deform a thin re
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