The escalating cost for next generation lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990’s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1999, Colburn et al. [Proc. SPIE 379 (1999)] discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as step and flash imprint lithography. The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. This article traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.

Until now, acrylates have been the monomers of choice for use for step and flash imprint lithography ͑SFIL͒ etch barrier formulations, in part because of the commercial availability of silicon-containing acrylates ͑necessary for etch resistance͒, together with their low viscosities and capability for rapid photopolymerization. However, despite many desirable properties, the polymerization of acrylates via radical chain propagation causes some potential issues in the SFIL process as a result of the inhibition of these processes by oxygen. Vinyl ethers are prime candidates to replace acrylates. Their curing proceeds by a cationic mechanism, which is insensitive to oxygen and very rapid, while the vinyl ether group contribution to viscosity is significantly lower than that of an acrylate, silicon-containing vinyl ethers are not widely commercially available, and so were synthesized for this study. As expected, formulations based on these vinyl ethers were lower viscosity and faster curing than the acrylate etch barrier formulations presently employed, while the tensile strength of cured vinyl ether formulations were found to be higher than their acrylate counterparts. In spite of about twice higher template separation force compared with acrylates, the tensile strength of vinyl ether etch barrier formulations is about five times higher than that of acrylate formulations. Therefore, these vinyl ether-based formulations were used to pattern down to 50 nm features using the SFIL process.

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Recent work onStep and Flash Imprint Lithography (SFIL) has been focused on process and materials fundamentals and demonstration of resolution capability. Etch transfer processes have been developed that are capable of transferring imprinted images though 150 nm of residual etch barrier, yielding sub 50 nm lines with aspect ratios greater than 8:1. A model has been developed for the photoinitiated, free radical curing of the acrylate etch barrier materials that have been used in the SFIL process. This model includes the effects of oxygen transport on the kinetics of the reaction and yields a deeper understanding of the importance of oxygen inhibition, and the resulting impact of that process on throughput and defect generation. This understanding has motivated investigation of etch barrier materials such as vinyl ethers that are cured by a cationic mechanism, which does not exhibit these same effects. Initial work on statistical defect analysis has is reported and it does not reveal pathological trends.

The escalating cost for Next Generation Lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1 999, Willson and Sreenivasan discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as Step and Flash Imprint Lithography (5-FIL). The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. This paper traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.