Abstract

Recent developments in microlithographic lenses have taken advantage of higher resolution and improved depth of focus associated with reduced wavelength. As wavelengths have dropped below 400 nm, commercially available microscope objectives have become inadequate focusing components in several testing setups used to qualify today’s sophisticated reduction lenses. These testing applications require formation of a diffraction-limited aerial spot at numerical apertures up to 0.5. In addition, this performance must be achieved at several narrowband UV wavelengths. Fortunately, the microobjective must operate only over a single spectral line for a given application. This suggests that spherochromatic correction is required but not parfocality. Also, only minimal field coverage is necessary to align the microobjective for single-point aerial image formation.

© 1987 Optical Society of America