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In optical projection lithography of all types, optimum performance depends on the design and precise alignment of the source(s) and optical components that illuminate photomasks, as well as those for the projection lens. In this paper, we illustrate the effects ofabnormalities in the illumination system; these abnormalities include asymmetric nonuniformity of the light source, obscurations, aberrations ofthe illumination optics, and telecentric error."Complex" illumination describes cases wherein all or part ofthe field ofa stepper or scanning tool is illuminated asymmetrically. The interaction of complex illumination at the photomask with defocus or aberrations generates interference effects in the same manner as phase shifting or off-axis illumination, thereby modulating the image and, in many cases, shifting the image from its intended location. We calculate, from scalar coherence theory, quantitative influences on overlay for 0.35 im lithography, and we determine selected tolerances for source uniformity and symmetry as a function of wavelength and coherence parameter. The effects of complex illumination are object-dependent, and we describe the variation with mask poiarity, feature size, and proximity. We will consider the use ofphase masks, the use ofa scanned source and projection lens, and the use ofoff-axis illumination as special cases and describe their interaction with complex illumination in lithography. With the use of simulation software for lithography, we demonstrate the effects of complex illumination within photoresist patterns.We show that, for expected performance of illumination in a well-characterized step and repeat or scanning tool, the effects of complex illumination are seen to be small in comparison to expected alignment tolerances. For selected cases, we demonstrate that abnormalities arising from obstructed or incorrectly positioned components cause significant errors.

An evaluation procedure for advanced I-line photoresists is presented. The evaluation is comprehensive in nature, including manufacturing and quality requirements as well as the usual patterning performance tests. The evaluation is divided into three general categories: Performance, Manufacturability, and Materials. These categories include a total of 23 individual performance tests and 15 evaluation criteria. A scoring method is described which assigns a numerical rating to the resist performance. Weighting constants contained in this procedure can be adjusted to vary the emphasis on particular measures of the photoresist performance.