Effects of 95% integral vs. FWHM bandwidth specifications on lithographic Imaging

Bandwidth of a laser spectrum is generally specified in terms of the full-width-at-half-maximum. (FWHM) metric. Another bandwidth specification is based on the 95% integral energy (E95%) of the spectrum. While providing a more complete information about the spectral shape, E95% bandwidth is very sensitive to small changes in spectral background intensity. In this work, both bandwidth specifications and their effects on aerial image properties are evaluated using computer simulations. Also, in order to obtain a more comprehensive understanding of illumination spectrum effects on lithographic imaging, aerial image sensitivity to the shift of central wavelength and to the change of spectral background intensity is investigated. Results show that the overall shape of the laser spectrum is critically important, and that the E95% metric is more suitable for bandwidth specification.