9. Nanoimprint Lithography – Patterning of Resists Using Molding

Nanoimprint lithography (NIL) is an emerging high-resolution parallel patterning method, mainly aimed towards fields in which electronbeam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. In a top-down approach, a surface pattern of a stamp is replicated into a material by mechanical contact and threedimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate at the wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. This makes NIL a promising technique for volume manufacture 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 refers to a hot embossing process (thermal NIL). In ultraviolet (UV)-NIL, a photopolymerizable resin is used together with a UV-transparent stamp. In both processes thinfilm squeeze flow and capillary action play a central role in understanding the NIL process. In this chapter we will give an overview of NIL, with emphasis on general principles and concepts rather than specific process issues and state-of-the-art tools and processes. Material aspects of stamps and resists are discussed. We discuss specific applications where imprint methods have significant advantages over 9.1 Emerging Nanopatterning Methods........ 273 9.1.1 Next-Generation Lithography ........ 274 9.1.2 Variants of Nanoimprint Lithography .......... 275