8. Nanoimprint Lithography

Nanoimprint lithography is an emerging nanopatterning method, combining nanometer-scale resolution and high throughput. In a top-down approach, a rigid stamp with a surface relief is pressed into a thin film of soft material on a hard substrate. The film is hardened before the stamp is retrieved, and the surface relief is copied into the thin film. A pattern with nano- to micrometer scale features can be replicated in a parallel process, and the stamp may be reused many times. This makes nanoimprint lithography a promising technique for volume manufacturing of nanostructured components. At present, structures with feature sizes down to 5 nm have been realized, and the resolution is limited by the ability to manufacture the stamp relief. For historical reasons, the term nanoimprint lithography (NIL) refers to a hot embossing process, where a thin film of thermoplastic material is softened by heating it, and the embossed film is hardened again when it is cooled down. In ultraviolet (UV)-NIL, a photo-polymerizable resin is used together with a UV-transparent stamp. The resin is liquid at room temperature, allowing easy embossing of the stamp, before the resin is hardened by UV exposure. In this chapter we will give an overview of nanoimprint lithography, with emphasis on NIL. Material aspects of stamps and resists are discussed. Thin-film rheology plays a central role of the understanding of the nanoimprint process, since the resist is patterned by mechanical deformation. We discuss specific applications where imprint methods have significant advantages over other structuring methods. We conclude by discussing the areas where further development in this field is required.