Efforts have been made in recent years to develop nanoimprint lithography (NIL) as a viable technology for creating sub-100 nm patterns. In NIL nanometer-scale features of a stamp are embossed into a thin polymer layer heated above its glass transition temperature (Tg). Polymer and stamp are cooled to a temperature below Tg of the polymer, and the stamp is detached. Imprinted structures with 10 nm resolutions have been achieved this way. Most of the research for examining this new technology was performed with poly (methyl methacrylate) (PMMA).
Task of micro resist technology GmbH within the EC-funded project CHANIL was to develop polymers dedicated for NIL.
Imprint temperatures of 80-100 K above the Tg , i.e., 160-200 °C, are necessary to produce a sufficiently low polymer viscosity, when PMMA or other thermoplastic polymers are used. High imprint temperature can cause thermal stress and degradation in the polymer film and increases process time. It is detrimental to some substrates and potential applications and is very exacting to the imprinting equipment. In addition, plasma etch resistance, which is necessary for use of the imprinted patterns as an etch mask, is unsatisfactory for PMMA.
Alternatives to PMMA were proposed to respond to these demands. Thermoplastic polymers for NIL with good thermal and high dry etch stability were developed [H. Schulz, H.-C. Scheer, T. Hoffmann, C.M. Sotomayor Torres, K. Pfeiffer, G. Bleidiessel, G. Gruetzner, Ch. Cardinaud, F. Gaboriau, M.-C. Peignon, J. Ahopelto, B. Heidari, J. Vac. Sci. Technol. B 18 (2000) 1861-1865]. The suitability of a plasma-etch resistant e-beam resist for NIL was also checked [C. Gourgon, C. Perret, G. Micouin, Microelectron. Eng. 61-62 (2002) 385-392].
High thermal stability of thermoplastic polymers like PMMA is inherently related to high Tg , and implicitly requires high imprint temperature. This led to the idea to use special precursors of cross-linked polymers for eliminating this requirement. Prepolymer solutions can be processed in the same way as thermoplastic polymer solutions. Imprinting temperatures below 100 °C can be applied, since the pre-polymers have low molecular weights and low Tg. The structures have to be stabilized by a cross-linking reaction during or after imprinting. We have developed two cross-linked polymer systems; thermally cross-linked polymers mr-I 9000 (micro resist technology GmbH) and photochemically cross-linked polymers mr-L 6000 (micro resist technology GmbH).
Information on the type of the cross-linking polymerization and its impact on the behaviour of polymers during the imprint process is necessary for specifying appropriate processing conditions. When thermally cross-linked polymers are used, process time and temperature depend on the polymerization rate. Photochemically cross-linked polymers offer the possibility of short imprint time and low process temperature. Tg of the polymer governs temperature. Low Tg enables short heating and cooling cycles. The imprinted films are thermally and mechanically stable after cross-linking. That is why the patterns can be used not only as an etch mask, but also for permanent applications. For demonstrating their stability these materials have been used as stamps for nanoimprinting themselves.
The scientific results were presented at the international conferences MNE 2000, 2001 and 2002, SPIE 2001 and 2003, NNT 2002 and trade shows Semicon Europa 2001, 2002 and 2003 in Munich, Productronica 2001 in Munich and are public.
The polymers for NIL provided by micro resist technology GmbH are presented on the website of the company and have been an integral part of the company's marketing. Micro resist technology GmbH has gained a good reputation as a material supplier in the international community of nanoimprint lithography based on these activities and intends to continue the development in this field.