**EUV Lithography and Resolution Enhancement Techniques**

350 Recent Advances in Nanofabrication Techniques and Applications

Cheng, G. & Hu, C. (2011). X-ray Zernike apodized photon sieves for phase-contrast

Cheng, G., Hu, C., Xu P. & Xing, T. (2010). Zernike apodized photon sieves for high-

Cheng, G., Xing, T., Yang, Y. & Ma, J. (2008). Resolution enhancement of photon sieve based

Cheng, G., Xing, T., Lin, W., Zhou, J., Qiu, C., Liao, Z., Yang, Y., Hong, L. & Ma, J. (2007).

Cheng, G., Xing, T., Lin, W., Zhou, J., Qiu, C., Liao, Z. & Ma, J. (2006). Design and fabrication

Fang, N., Lee, H., Sun, C. & Zhang, X. (2005). Sub-diffraction-limited optical imaging with a

Kipp, L., Skibowski, M., Johnson, R. L., Berndt, R., Adelung, R., Harm, S. & Seemann, R.

R. Menon, D. Gil, G. Barbastathis, and Smith, H. (2005). Photon-sieve lithography. *J. Opt.* 

Yang, Y., Fu, Y., Yao, H., Hu, S., Zhou, S., Yan, W., Chen, W., Cheng, G. & Li, Z. (2009).

Yang, Y., Hu, S., Yao, H., Cheng, G., Zhang, C. & Yan, W. (2007). Nanolithography in the

51736, ISBN 978-0-8194-6636-5, San Jose, CA, USA, Feb. 27-Mar. 01, 2007 Cheng, G., Xing, T., Yang, Y. & Ma, J. (2007). Experimental characterization of optical

resolution phase-contrast x-ray microscopy. *Opt. Lett.,* Vol.35, No.21, pp. 3610-3612,

on apodization. *Proc. SPIE,* Vol.6832, pp.83229-83229, ISBN 978-0-8194-7007-2,

Photon sieve array x-ray maskless nanolithography. *Proc. SPIE*, Vol.6517, pp.51736-

properties of photon sieve. *Proc. SPIE,* Vol.6724, pp.D7240-D7240, ISBN 978-0-8194-

of low-numerical-aperture amplitude-photon sieve. *Chinese Journal of Sensors and* 

(2001) Sharper images by focusing soft X-rays with photon sieves. *Nature,* Vol.414,

Beam Splitter Achieved by Using Metallic Structure with Nanoslits. *J. Comput.* 

Evanescent Near Field by Using Nano-filmed Noble Metal Layers. *Proc. SPIE,* Vol.6724, pp.A7241-A7241, ISBN 978-0-8194-6881-9, Chengdu, China, Jul. 08-12,

microscopy. *Acta Phys. Sin.* Vol.60, No.8, ISSN 1000-3290

ISSN 0146-9592

2007

Beijing, China, Nov. 12-14, 2007

6881-9, Chengdu, China, Jul. 08-12, 2007

No.6860, pp. 184-188, ISSN 0028-0836

*Actuators*, Vol.19, No.5, pp.2344-2347, ISSN 1004-1699

*Soc. Am. A,* Vol.22, No.2, pp.342-345, ISSN 1084-7529

*Theor. Nanosci.*, Vol.6, No.5, pp.1030-1033, ISSN 1546-1955

silver superlens. *Science*, Vol.308, No.5721, ISSN 0036-8075

**18** 

Sho Amano *University of Hyogo* 

*Japan* 

**Laser-Plasma Extreme Ultraviolet Source** 

**Incorporating a Cryogenic Xe Target** 

*Laboratory of Advanced Science and Technology for Industry (LASTI)* 

Optical lithography is a core technique used in the industrial mass production of semiconductor memory chips. To increase the memory size per chip, shorter wavelength light is required for the light source. ArF excimer laser light (193 nm) is used at present and extreme ultraviolet (EUV) light (13.5 nm) is proposed in next-generation optical lithography. There is currently worldwide research and development for lithography using EUV light (Bakshi, 2005). EUV lithography (EUVL) was first demonstrated by Kinoshita et al. in 1984 at NTT, Japan (Kinoshita et al., 1989). He joined our laboratory in 1995 and has since been actively developing EUVL technology using our synchrotron facility NewSUBARU. Today,

To use EUVL in industry, however, a small and strong light source instead of a synchrotron is required. Our group began developing laser-produced plasma (LPP) sources for EUVL in the mid-1990s (Amano et al., 1997). LPP radiation from high-density, high-temperature plasma, which is achieved by illuminating a target with high-peak-power laser irradiation, constitutes an attractive, high-brightness point source for producing radiation from EUV

Light at a wavelength of 13.5 nm with 2% bandwidth is required for the EUV light source, which is limited by the reflectivity of Mo/Si mirrors in a projection lithography system. Xe and Sn are known well as plasma targets with strong emission around 13.5 nm. Xe was mainly studied initially because of the *debris problem*, in which debris emitted from plasma with EUV light damages mirrors near the plasma, quickly degrading their reflectivity. This problem was of particular concern in the case of a metal target such as Sn because the metal would deposit and remain on the mirrors. On the other hand, Xe is an inert gas and does not deposit on mirrors, and thus has been studied as a deposition-free target. Because of this advantage, researchers initially studied Xe. To provide a continuous supply of Xe at the laser focal point, several possible approaches have been investigated: employing a Xe gas puff target (Fiedrowicz et al., 1999), Xe cluster jet (Kubiak et al., 1996), Xe liquid jet (Anderson et al., 2004; Hansson et al., 2004), Xe capillary jet (Inoue et al., 2007), stream of liquid Xe droplets (Soumagne et al., 2005), and solid Xe pellets (Kubiak et al., 1995). Here, there are solid and liquid states, and their cryogenic Xe targets were expected to provide higher laser-to-EUV power conversion efficiency (CE) owing to their higher density compared with the gas state. In addition, a smaller gas load to be evacuated by the exhaust

EUVL is one of the major themes studied at our laboratory.

**1. Introduction** 

light to x-rays.

pump system was expected.
