Development of short pulse and high power CO 2 laser for EUV lithography

Abstract

Laser produced plasma EUV source is the candidate for high quality, 115 W EUV light source for the next generation lithography. Cost effective laser driver is the key requirement for the realization of the concept as a viable scheme. A CO 2 laser driven LPP system with a Xenon droplet target is therefore a promising light source alternative for EUV. We are developing a high power and high repetition rate CO 2 laser system to achieve 10 W intermediate focus EUV power. High conversion efficiency (CE) from the laser energy to EUV in-band energy is the primarily important issue for the concept to be realized. Numerical simulation analysis of a Xenon plasma target shows that a short laser pulse less than 15 ns is necessary to obtain a high CE by a CO 2 laser. This paper describes on the development of a CO 2 laser system with a short pulse length less than 15 ns, an average power of a few kW, and a repetition rate of 100 kHz based on RF-excited, axial flow CO 2 laser modules. Various issues are reported on the laser system design, namely l00W seeder, parasitic oscillation suppression, small signal gain and saturation fluence, and beam quality. Additional approach to increase the amplification efficiency is discussed. Acknowledgement: This work was supported by NEDO.