**10. References**


This chapter briefly reviewed our LPP-EUV source. First, we characterized the source at a wavelength of 13.5 nm with 2% bandwidth as an EUVL source and achieved a maximum CE of 0.9%. When the driving laser power is 110 W at 320 pps, the average power of 1 W is obtained at the wavelength and this is thought to be sufficient for the source to be used in various studies. However, the EUV power required for industrial semiconductor products is more than 100 W at present; our power is two orders of magnitude less. To approach the requirements of an industrial EUV source, the remaining tasks are considered. The majority of Xe plasma debris is fast ions, which can be mitigated using gas and/or a magnetic/electric field relatively easily. The drum system can supply the Xe target for laser pulses with energy up to 1 J at 10 kHz. Therefore, a remaining task is powering up the driving laser. A short pulse laser with average power of the order of 10 kW (i.e., *high average and high peak brightness laser*) must be developed and such a breakthrough is much hoped

Not limiting the wavelength to 13.5 nm with 2% bandwidth and using the broad emission at 5–17 nm, a maximum CE of 30% is achieved. Pumping with laser power of 100 W, high average power of 20 W is already obtained and the source is useful for applications other than industrial EUVL using Mo/Si mirrors. We are now applying our source to microprocessing and/or material surface modification. Our source also emits around the wavelength of 6 nm considered desirable for the next lithography source. In conclusion, our LPP source is a practicable continuous EUV source having possibilities for various

Part of this work was performed under the auspices of MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) under the contract subject "Leading Project

Amano, S., Shimoura, A., Miyamoto, S. & Mochizuki, T. (1997). High-repetition-rate pulse

Amano, S. & Mochizuki, T. (2001). High average and high peak brightness slab laser. *IEEE J.* 

Amano, S., Nagano, A.: Inoue, T., Miyamoto, S. & Mochizuki, T. (2008). EUV light sources

Amano, S., Masuda, K., Shimoura, A., Miyamoto, S. & Mochizuki, T. (2010a).

Nd:YAG slab laser for x-ray source by cryogenic target, *1997 OSA Technical Digest Series, Vol.11, Conference Edition, CLEO97,* p.523, Baltimore, USA, May 18-23, 1997 Amano, S., Shimoura, A., Miyamoto, S. & Mochizuki, T. (1999). Development of a high

repetition rate Nd:YAG slab laser and soft X-ray generation by X-ray cryogenic

by laser-produced plasmas using cryogenic Xe and Li targets. *Rev. Laser. Eng.* 

Characterization of a laser-plasma extreme ultraviolet source using a rotating

**8. Conclusion** 

for.

applications.

**9. Acknowledgment** 

**10. References** 

for EUV lithography source development".

target. *Fusion Eng. and Design* 44, pp.423-426

cryogenic Xe target. *Appl. Phys.B* 101, pp.213-219

*Quantum Electron.* 37(2), pp.296-303

36(11), pp.715-720 (in Japanese)


**19** 

J.P. Allain

*Purdue University United States of America* 

**Collector Mirrors** 

**Irradiation Effects on EUV Nanolithography** 

Exposure of collector mirrors facing the hot, dense pinch plasma in plasma-based EUV light sources to debris (fast ions, neutrals, off-band radiation, droplets) remains one of the highest critical issues of source component lifetime and commercial feasibility of nanolithography at 13.5-nm. Typical radiators used at 13.5-nm include Xe, Li and Sn. Fast particles emerging from the pinch region of the lamp are known to induce serious damage to nearby collector mirrors. Candidate collector configurations include either multi-layer mirrors (MLM) or single-layer mirrors (SLM) used at grazing incidence. Due to the strong absorbance of 13.5 nm light only reflective optics rather than refractive optics can work in addition to the need

This chapter presents an overview of particle-induced damage and elucidates the underlying mechanisms that hinder collector mirror performance at 13.5-nm facing highdensity pinch plasma. Results include recent work in a state-of-the-art in-situ EUV reflectometry system that measures real time relative EUV reflectivity (15-degree incidence and 13.5-nm) variation during exposure to simulated debris sources such as fast ions, thermal atoms, and UV radiation (Allain et al., 2008, 2010). Intense EUV light and off-band radiation is also known to contribute to mirror damage. For example off-band radiation can couple to the mirror and induce heating affecting the mirror's surface properties. In addition, intense EUV light can partially photoionize background gas used for mitigation in the source device. This can lead to local weakly ionized plasma creating a sheath and accelerating charged gas particles to the mirror surface inducing sputtering. In this overview we will also summarize studies of thermal and energetic particle exposure on collector mirrors as a function of temperature simulating the effects induced by intense off-band and EUV radiation found in EUVL sources. Measurements include variation of EUV reflectivity

In this chapter the details from the EUV radiation source to the collector mirror are linked in the context of mirror damage and performance (as illustrated in Figure 1). The first section summarizes EUV radiation sources and their performance requirements for high-volume manufacturing. The section compares differences between conventional discharge plasma produced (DPP) versus laser plasma produced (LPP) EUV light sources and their possible combinations. The section covers the important subject of high-density transient plasmas and their interaction with material components. The different types of EUV radiators, debris

**1. Introduction** 

for ultra-high vaccum conditions for its transport.

with mirror damage and in-situ surface chemistry evolution.

