A study of projected optical images for typical IC mask patterns illuminated by partially coherent light

Optical projection printing using partially coherent illumination is simulated for one micrometer and half micrometer objects representative of typical mask patterns such as contact holes, rectangular bars and openings, intersections of perpendicular lines, and adjacent lines of unequal lengths. The image intensity distributions in absorptionless photoresists on nonreflective substrates are plotted as sets of constant intensity contours. For each pattern and illumination, an exposure-defocus (E-D) diagram is generated by evaluating the combined exposure and defocus tolerance yielding linewidths within ±2.5 percent of the mask linewidth. Besides comparing the image and ED margins of different object shapes and sizes, the effects of high versus low degrees of coherence, single versus dual wavelength, as well as long-wavelength high NA versus short-wavelength low NA were studied using the 1-µm rectangular opening.