Abstract
We show that, contrary to the prevailing trend in photolithography, increasing the spatial coherence of illumination does not necessarily improve the performance of phase masks in enhancing resolution and focal depth. Simulations and experiments show that for large (aperiodic) phase masks, the optimal coherence diameter is determined by the minimum resolvable feature size, not the size of the mask. This is due to a trade-off between the destructive interference of adjacent features under coherent illumination and the larger effective aperture of incoherent illumination.
© 1996 Optical Society of America
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