Keiichiro Yamanaka

High-power and narrow-band excimer laser with a polarization-coupled resonator

As a light source for deep submicron lithography the authors have developed a long life and high power KrF narrow band excimer laser by installing a polarization coupled resonator into the conventional narrow band excimer laser with intra-cavity etalons. A maximum output power of 1O. 5Yi with a low etalon-load of L5W arid a narrow spectral band-width of 24pm at 200Hz is obtained. The central wavelength is stabilized to within only 5pm and drift is not observed when increasing the repetition rate from 4Hz to 200Hz without a wavelength feedback loop system. Furthermore the etalon-life is expected to be drastically prolonged to over a billion pulses resulting from the reduction of the etalonload to only about 10 of that in a conventional laser. 2.

Resonator using polarization beamsplitter prism for microlithography KrF excimer laser

We discuss a new resonator design for sub-pm bandwidth (FWHM) KrF excimer laser using an etalon, a grating and prisms. This resonator uses a polarization beam splitter prism (PBSP) which has both functions of splitting polarized beam and beam expansion to reduce the resonator length. In our experiments, the output power is improved 29.4% by using PBSP in comparison with the conventional method, while the bandwidth (FWHM) is reduced from less than 0.9 pm to less than 0.6 pm at the same time. A calculation has been done to confirm the output power dependence on the resonator length and the loss of optics. Its result explains our experimental results approximately. We demonstrated that PBSP has a significant effect to improve the output power of the narrow bandwidth KrF excimer laser that would result in the extension of chamber lifetime. Furthermore, this technique will help the development of the band narrowing excimer laser for microlithography.