Approach of fine resist filling technologies forUV-NIL at AIST
Sung-Won Youn, Kenta Suzuki, Hiroshi Hiroshima
Research Center for Ubiquitous MEMS and Micro Engineering (UMEMSME),
National Institute of Advanced Industrial Science and Technology (AIST)
1-2-1, Namiki, Tsukuba, Ibaraki 305-8564, JAPANE-mail: youn.sung-won@aist.go.jp

There has been increasing demand for a low-cost nanofabrication technique such as
ultraviolet nanoimprint lithography (UV-NIL) for high-volume production of large-scale
integrated circuits, optical and bio device components. To accomplish this, we have activelypursued research and development on fine resist filling technologies for UV-NIL using spincoated resins. In this talk, I will first review some research activities of AIST on quick andbubble-free UV-NIL, then cover the design and low-cost fabrication of a mold for lithography.
Although bubble-free filling can be accomplished by performing UV-NIL under vacuum,
non-vacuum processes are desirable because of their lower equipment and operating costs.
Bubble defects could be avoided by using a condensable alternative chloroﬂuorocarbon gas,pentaﬂuoropropane (PFP) as an atmosphere gas [1]. A PFP atmosphere not only is beneficial
for quick and bubble-free cavity filling but also offers benefits such as decreasing the viscosityof the UV-curable resin and lowering the demolding forces. PFP occasionally causes large
pattern shrinkage and degrades the pattern quality depending on the monomer chemical
structures included in the UV-curable resins. However, recent research results that we achieved
demonstrated that such degrade can be avoided by mixing with the Helium gas [2] or byutilizing other condensing gas (trans-1,3,3,3-tetraﬂuoropropene, TFP) having a higher vapor
pressure than PFP [3].
The uneven distribution of a mold pattern density may cause a variation in a residual layer
thickness (RLT), and consequently may result in the variation of lateral critical dimensions or
may lose patterns in the subsequent etch transfer process. Therefore, making the residual layer
thin and uniform over the entire imprint region even for the uneven density distribution ofpattern is important for achieving high ﬁdelity in the etching process. As a solution, we havesuggested the use of capacity-equalized (CE) mold, where deeper complementary cavities areadded to the original trench pattern areas to achieve a uniform pattern capacity per unit area.
By using this method, pattern capacity in mold can be equalized without changing the original
pattern layout. To enhance the possibility of industrial use of CE molds, a mold design software
program (stamp topography automated modification program, STAMP), that can be applicable
to real device patterns where shapes are complex and variation in the pattern density is large
has been developed [4].
Additionally, an ultra-high speed electron beam (UHSEB) lithography system is being
developed as a tool for the low-cost fabrication of wafer-level mold through the collaborative
work between AIST and Elionix Inc. The design concepts and capabilities of the UHSEB
prototype (e.g., 100 times higher throughput over conventional point-beam type EB systems)
will be introduced briefly.
Reference:[1] Hiroshima, H.; Nakagawa, M.; Hirai, Y.; Matsui, S.; J. Photopolym. Sci. Technol. 2013 26,(1) 8796.
[2] Youn, S.W.; Suzuki, K.; Wang, Q.; Hiroshima, H.; Jpn. J. Appl. Phys. 2013 52, 06GJ07.
[3] Suzuki, K.; Youn, S.W.; Hiroshima, H.; Jpn. J. Appl. Phys. 2016 109, 143102-1 - 143102-5.
[4] Youn, S.W.; Suzuki, K.; Hiroshima, H.; Jpn. J. Appl. Phys. 2018 57, 06HG03.