Partially Coherent Imaging in Two Dimensions and the Theoretical Limits of Projection Printing in Microfabrication

Optical projection printing is quantitatively studied, using the diffracted image of two bars of equal width and space and an aspect ratio of three. Hopkins' four-dimensional integral for partially coherent imaging is used for the numerical analysis. Diffraction-limited lenses with a circular pupil are used. Constant intensity profiles in an absorptionless photoresist and nonreflective substrate are evaluated. Then the tolerances of defocus and intensity are derived using a linewidth tolerance of ±2.5 percent of the mask linewidth which varies from 0.5, 0.75, 1, 1.5, 2, to 2.5 µm. The illuminations used have σ = 0, 0.5, 0.7, 0.78, 1, 1.3, and infinity. Copyright © 1980 by The Institute of Electrical and Electronics Engineers, Inc.