The Rayleigh criteria for minimum resolution and acceptable depth of focus (DOF) in the case of finite excimer laser bandwidth with a chromatic lens design were re-evaluated both by experiment and by simulation. As a result of chromatic lens design combined with a narrow spectral bandwidth (BW) excimer laser, both resolution and DOF are not only determined by source wavelength and the numerical aperture (NA) of the lens, as predicted by Rayleigh criteria, but also by the laser spectral BW. To fully understand the role of laser spectral BW in chromatic projection printing, the resolution as a function of lens NA, laser spectral BW, and defocus were studied through simulation. The relations between resolution and its corresponding DOF for different laser spectral BW and NA were also obtained. The results were compared to that obtained by Rayleigh criteria. Unlike the single wavelength case, resolution at larger NA is basically limited by the spectral BW of the laser rather than NA of the lens system. The DOF is limited by both laser spectral BW and lens NA. The optimum NA for a given BW for different defocus cases were predicted. The effect of chromatic focus spread due to finite laser spectral BW was compared to the case of single wavelength with small amount defocus. Intel’s rigorous bulk image model has been used for process window simulations1. In the experiment, the effect of finite laser spectral BW to the pattern resolution and DOF were studied for the case of 0.42 NA chromatic lens with finite laser spectral full width at half maximum (FWHM) of 2 pm, 3 pm, 4 pm and 5 pm, respectively. The experimental results were compared to the simulation results.

Date Published: 1 June 1992
PDF: 12 pages
Proc. SPIE 1674, Optical/Laser Microlithography V, (1 June 1992); doi: 10.1117/12.130330

Published in SPIE Proceedings Vol. 1674:
Optical/Laser Microlithography V
John D. Cuthbert, Editor(s)