Nanoimprint lithography

Abstract

Nanoimprint lithography (NILnanoimprint lithography (NIL)lithographynanoimprint (NIL)) is an emerging high-resolution parallel patterning method, mainly aimed towards fields in which electron-beam 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 in a material by mechanical contact and three-dimensional 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 high-volume manufacturing of nanostructured components. At present, structures with feature sizes smaller than 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 (UVultraviolet (UV)) NIL, a photopolymerizable resin is used together with a UV-transparent stamp. In both processes thin-film 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. Specific applications are presented, where imprint methods have significant advantages over other structuring methods. We conclude by discussing the areas where further development in this field is required.