Abstract

We have previously reported the development of a laser plasma EUV source, using mass-limited water droplets, based on the 13 nm and 11.6 nm O⁵⁺ lines, for EUV projection lithography [1]. The spectrum from this source is shown in Fig. 1. A vital feature of this approach [2 ,3 ] is the incorporation of a target limited in mass to the minimum number of EUV atomic radiators required. This feature has advantages for EUV lithography and other applications in minimizing the collateral debris and allowing for continuous operation without the need for periodic maintenance of the optics or target material replenishment. Debris effects were quantified by the measurement of the reflectivity of a Mo/Si multilayer mirror, placed 4 cm from the source, for > 10⁵ laser shots, Fig. 2. The < 1 % variation in reflectivity allows us to predict that the system could run for up to 10⁸ shots without any major degradation in performance.

© 1997 Optical Society of America