Fine Pattern Fabrication by the Molded Mask Method (Nanoimprint Lithography) in the 1970s

Abstract

Nanoimprint lithography has recently been attracting the attention of many researchers in the field of nanofabrication technology. Although the study of nanoimprint lithography was initiated by Chou et al. around 1995, a fine-pattern fabrication technology, whose concept is similar to nanoimprint lithography, had been proposed and studied at NTT Laboratories in Japan as early as in the 1970s. The technology was based on the combination of the molding of plastic film on a substrate and dry etching of the molded film and substrate surface. It is considered that most of the basic concepts in current nanoimprint lithography were included in this early study. Some demonstration experiments using diffraction gratings, microsized test patterns, LSI patterns and microlenses were carried out to verify the feasibility of the technology at that time. The key point of the technology to fabricate fine patterns accurately was the fluidity of the plastic film. It was called the ''Molded Mask Method'' and this paper introduces the study on the molded mask method of those days.

The Molded Mask Method: The Origin of Nanoimprint Lithography

“…We conducted feasibility studies in the 1970s on the molded mask method and demonstrated its technical features and applicability as a novel technology for fabricating devices and components [4,[11][12][13][14][15][16]. One decade after the invention of the molded mask method, Napoli and Russell filed their patent in the United States and another decade later the studies by S. Y. Chou and C. G. Willson were reported.…”

“…Therefore, we can trace the origin of nanoimprint lithography back to the molded mask method invented in the 1970s. Figure 1 shows the basic concept behind the molded mask method and shows that it is essentially the same as present-day nanoimprint lithography [4,[11][12][13][14][15][16].…”

“…We conducted various experiments in the 1970s to examine the feasibility of the molded mask method [4,[11][12][13][14][15][16].…”

“…The technology was developed as a novel method to replicate fine patterns and threedimensional structures, and was named the "molded mask method" [4]. Studies on the molded mask method were conducted about one decade before the patent by L. S. Napoli was filed and about two decades before publication of the reports by S. Y. Chou and C. G. Willson.…”

Next-generation lithography – an outlook on EUV projection and nanoimprint

“…Nanoimprint lithography (NIL) was invented and demonstrated in the 1970s by Susumu Fujimori at NTT in Japan, but it was not until 1995 when Stephen Chou and coworkers at the University of Minnesota (later at Princeton University) published their first results that NIL started to gain broader attention, by demonstrating 10-nm-imprint capabilities at a time when 50 nm was considered as the resolution limit of projection lithography (see Figure 2) [7,8]. At that time, X-ray proximity lithography (using 1.3-nm wavelength) was seen as an alternative to DUV projection, using 248-nm light from KrF-excimer lasers.…”