Siloxane Copolymers for Nanoimprint Lithography**

Nanoimprint lithography (NIL) is a fabrication technology that offers high-throughput, ultrahigh resolution patterning at great cost savings compared to most competing next-generation radiative lithography methods. As a result of its rapid development in the past decade and its potential for sub-100 nm lithography, NIL has been listed by MIT’s Technology Review as one of ten emerging technologies that are likely to change the world, and the International Technology Roadmap for Semiconductors also recently announced the inclusion of NIL onto their roadmap as a candidate technology to begin in production in 2013. Two of the most critical steps in NIL are mold release and pattern transfer by dry etching. In this process, patterned relief features are physically molded into a thin layer of polymer resist on the substrate workpiece. Figure 1 illustrates the thermal nanoimprint process, in which the mold and substrate are pressed together with sufficient force and temperature to cause the resist to conform to the patterns. The temperature is reduced back down below the resist’s glass-transition temperature (Tg) and the two pieces are separated, leaving the patterned resist on the substrate. The large contact area between the mold and the resist gives rise to good adhesion forces. Ideal mold release should maintain resist shape integrity, and complete mold-resist separation, while the resist remains attached to the substrate. Furthermore, in order for the patterned resist structures to facilitate further lithography, the polymer must possess some chemical-etch selectivity so that it may serve as a masking layer. Up until now, researchers have commonly used commercial thermal plastic materials, such as poly(methyl methacrylate) (PMMA) and polystyrene (PS) as NIL resists. However, these materials are not at all optimized for the special requirements of the NIL process. Selection of a polymer system for use as the NIL resist should consider critical aspects of correct pattern replication, modest imprint temperature and pressure, proper mold release, and etch selectivity.