Abstract
A new optical stepper, NSR-1505G6E, has been developed and it will be one of most promising exposure apparatuses for half-micron lithography in next era. g-line is used as an exposure wavelength, and 5X-type projection lens has 15 mm by 15 mm field size. Its N.A. (numerical aperture) is 0.54, maximum value among 5X-type g-line projection lenses ever announced. First, capability of high N.A. is demonstrated by a theoretical approach. Conventional optical theory says that resolution power is proportional to λ/N.A., but multi-reflection within photoresist is not taken into consideration. To investigate resolution power based upon resist patterns, one of most powerful approaches is the vector model developed by M. Yeungl in 1988. A similar simulator has been developed and has been used to confirm that a high N.A. lens has high resolution power even with multi-reflection effect within photoresist. Secondly, performance of projection lens is shown on experimental data basis. Advantages and disadvantages of projection lens are discussed in comparison with an i-line lens with same resolution power. Investigation on N.A. is also made, comparing resist patterns exposed by some lenses with various N.A. values. Finally, total system, including such new functions as chip-leveling and auto-focus, is described.
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