In the fields of micro and nanolithography, major advancements in resolution have historically been achieved through use of shorter wavelengths of light. Using phase shift mask technology, it has already been demonstrated that 193 nm photolithography can produce sub-100 nm features. Along this path, such improvements come with an ever increasing cost for photolithographic tools. As conventional projection lithography reaches its limits, Next Generation Lithography (NGL) tools may provide a means to further pattern shrinks, but are expected to have price tag that is prohibitive for many companies.

A significant part of the cost of a projection printing tool is tied up in the optics and the light source. Looking ahead, this trend is not expected to change as tool manufacturers first address the challenges of building lenses from calcium fluoride for 157 nm tools, and later deal with the issues of building multilayer reflective optics for Extreme Ultraviolet (13 nm) systems. As a result, several researchers have considered imprint lithography as the means for achieving high resolution while minimizing tool cost. Investigations by this group and others looking into the sub-100 nm regime indicate that final imprinted resolution is limited only by template resolution.

Imprint lithography techniques are essentially micromolding processes in which the topography of a template defines the patterns created on the substrate. Several different approaches are currently being investigated. Whitesides et. al. use a flexible PDMS template that is coated with a thiol solution, and is subsequently transferred to a substrate coated with a thin layer of gold [1]. Nanoimprint Lithography, developed by Chou et. al. uses a solid mold, such as silicon or nickel [2]. The imprint process is accomplished by heating a resist above its glass transition temperature and imparting a relatively large force to transfer the image into the heated resist. Features as small as 10 nm have been imaged using this approach.

Devices that require several lithography steps and precise overlay require an imprinting process capable of addressing registration issues. Step and Flash Imprint Lithography (S-FIL), a technique developed by Willson et al, solves the problem of overlay by using a transparent quartz template [3]. The process employs a template/substrate alignment scheme to set the template parallel to the substrate. A low viscosity liquid etch barrier material is then injected between template and substrate. The gap is closed and ultraviolet light is illuminated through the template, thereby curing the etch barrier. The template is withdrawn leaving a precisely replicated inverse of the pattern on the template. The viscosity of the etch barrier is sufficiently low, so that minimal pressure (~2-4 psi) and no additional heating is necessary to flow the liquid into the stencil. Finally, because the template is transparent, conventional overlay schemes can be used to align patterns. This paper will review the progress made in the development of S-FIL, and will address both the critical issues that remain to be solved and the possible applications for the technology.

1. Y. Xia, G. M. Whitesides, Angew. Chem. Int. 1998, 37, 550-575.
2. S. Y. Chou, P. R. Krauss, P. J. Renstrom, J. Vac. Sci. Technol. B 1996, 14(6), 4129-4133.
3. M. Colburn et al, Proc. SPIE Vol. 3676, 1999, 379-389.