**7. References**


Brown G. H. (1971) Photochromism, Willey-Interscience, New York

162 Advances in Unconventional Lithography

efficiency. In particular, the light-induced isomerization of the embedded photochromic molecules in the flat surfaces is exclusively responsible for the reversible changes in their wetting properties. When the surface is microstructured by realizing patterns with the SM technique, these wetting properties are greatly enhanced. Moreover the control of the characteristics of the patterns (eg. the period), makes possible to control the light induced alterations in the wetting properties of the structured surface, demonstrating that they are influenced by both the changes in the surface polarity and the volume changes of the patterned structures. Finally, last but not least, it is demonstrated the possibility of fully manipulate the diffraction efficiency of thin photochromic polymer gratings. It is shown, that the produced gratings change their diffraction efficiency in a reversible way upon UVgreen laser irradiation. This effect, which is verified also by a theoretical diffraction model, is attributed to the reversible dimensional changes of the imprinted structures, and not to the refractive index changes as is the case in the majority of previous work. Such findings open a way for the production of optically switchable gratings based on reversible dimensional changes. Moreover, the ability to control the wettability of surfaces by microstructuring and to tune it by using photochromic molecules opens the way to the

The authors would like to thank Dr. D. Pisignano, and Dr. E. Mele of the Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia Via Barsanti, 73010 Arnesano (LE) and Dr. L. Persano of the National Nanotechnology Laboratory (NNL) of CNR - Istituto di Nanoscienze, via per Arnesano, 73100 Lecce, Italy for the formation of the

Athanassiou A.; Kalyva M.; Lakiotaki K.; Georgiou S. & Fotakis C. (2005). All-optical

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Athanassiou A.; Varda M.; Mele E.; Lygeraki M. I.; Pisignano D.; Farsari M.; Fotakis, C.;

Athanassiou, A.; Sahinidou, D. ; Arima, V.; Georgiou, S.; Cingolani, R. & Fotakis, C. (2006)

Born M. & Wolf E. (1999) Principles of Optics: Electromagnetic theory of propagation, interference and diffraction of light, 7th Edition, Cambridge University Press.

reversible actuation of photochromic-polymer microsystems. *Advanced Materials*,

Cingolani R. & Anastasiadis S. H. (2006) Photocontrolled Variations in the Wetting Capability of Photochromic Polymers Enhanced by Surface Nanostructuring.

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Influence of laser wavelength and pulse duration on the degradation of polymeric films embedding photochromic molecules. *Journal of Photochemistry and Photobiology* 

application of these optimized patterns to various microfluidic devices.

**6. Acknowledgment** 

**7. References** 

patterned structures presented in this work.

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**Part 5** 

**Extreme UV Lithography** 

polymers: Molecular photo-controllable electroosmotic pumps for micro-fluidic devices. (2010) *Sensors and Actuators B*, Vol.148, pp. (569–576)


**Part 5** 

**Extreme UV Lithography** 

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**9** 

*Japan* 

Atsushi Sekiguchi

*Litho Tech Japan Corporation* 

**Approach to EUV Lithography Simulation** 

**1.1 Simulation based on measured development rate measurements** 

EUV lithography is a reduced projection lithography technology based on 13.5 nm wavelength EUV (Extreme Ultraviolet). Development of EUV lithography is currently underway for the mass production of semiconductor devices for 90 nm design rule applications for ArF dry exposures and for 65 to 45 nm design rule applications for ArF immersion exposures [1-2]. EUV lithography is among the most promising next-generation lithography tools for the 32 nm technology node [3]. The evolving consensus is that EUV exposure technologies will be applied to mass production from the year 2011 [4]. Table 1 showed the relationship among technology node, exposure numerical aperture (NA), and process coefficient factor (k1) [5]. Achieving the 32 nm node based on an ArF laser source exposure technology will require the development of an optical system with NA increased to 1.55 and k1 improved to 0.26. In contrast, an exposure technology based on an EUV light source will permit the use of an optical system with 0.25 NA for mass production of the 32 nm node with room to spare. The requirement for the k1 factor is an easy-to-meet value of 0.59. These factors underscore the promise and importance of EUV exposure technologies. However, the development of EUV exposure equipment presents its own set of technology barriers, as does the development of ArF immersion exposure system. A wavelength of 13.5 nm requires a reflecting optical system with a combination of multiple multilayer reflecting mirrors [6], since no lens material can be used in the 13.5 nm wavelength range, if we rule out dioptric lenses. The development of EUV exposure equipment requires further examination of component technologies, including technologies related to light sources, illumination optical systems, projection optical systems, and masks. Although various exposure equipment manufacturers are actively promoting the development of EUV reduced projection exposure equipment [7-8], a resist material for EUV lithography must be developed before the first exposure system can be introduced. We have developed a new virtual lithography evaluation system with lithograph simulation that takes an approach completely different from conventional resist evaluation technologies (direct evaluation method), which require actual patterning to assess resists. The new evaluation system focuses on open-frame exposures using an EUV light source, measurements of development rates at various exposure doses, and lithography simulations based on development rate data. This chapter presents the results of our evaluations of EUV resists using this new

**1. Introduction** 

system.
