for nanoimprint lithography are overlay, defects, template patterning and template wear. However, recently Kumar et al. have shown that amorphous metals (metallic glasses) can be patterned on sub-100 nm scale, which can significantly reduce the template cost. Overlay The current overlay 3 sigma capability is 10 nm. Overlay has a better chance with step-and-scan approaches as opposed to full-wafer imprint. Defects As with immersion lithography, defect control is expected to improve as the technology matures. Defects from the template with size below the post-imprint process bias can be eliminated. Other defects would require effective template cleaning and/or the use of intermediate polymer stamps. When vacuum is not used during the imprint process, air can get trapped, resulting in bubble defects. This is because the imprint resist layer and the template or stamp features are not perfectly flat. There is an elevated risk when the intermediate or master stamp contains depressions (which are especially easy air traps), or when the imprint resist is dispensed as droplets just before imprinting, rather than pre-spun onto the substrate. Sufficient time must be allowed for the air to escape. These effects are much less critical if flexible stamper materials are used, e.g. PDMS. Another issue is adhesion between stamp and resist. High adhesion (sticking) may delaminate resist, which then stays on stamp. This effect degrades pattern, reduces yield and damages stamp. It can be mitigated by employing an FDTS antistiction layer on a stamp. Template patterning High resolution template patterning can currently be performed by electron beam lithography or focused ion beam patterning; however at the smallest resolution, the throughput is very slow. As a result, optical patterning tools will be more helpful if they have sufficient resolution. Such an approach has been successfully demonstrated by Greener et al. whereby robust templates were rapidly fabricated by optical patterning of a photoresist-coated metal substrate through a photomask. If homogeneous patterns on large areas are required, interference lithography is a very attractive patterning technique. Other patterning techniques (including even double patterning) may also be used. Kumar and Schroers at Yale developed the nanopatterning of amorphous metals which can be used as inexpensive templates for nanoimprinting. Currently, state-of-the-art nanoimprint lithography can be used for patterns down to 20 nm and below. Template wear The use of substantial pressure to not only contact but also penetrate a layer during imprinting accelerates the wear of imprint templates compared to other