Abstract
The high numerical aperture (NA) lenses which are required to produce today's geometries place stringent demands on focus quality. When high NA is coupled with wide image fields, high quality field-by-field leveling is also required. This paper reports focus and leveling performance of a g-line system with 0.55 NA and 20 mm field. Its performance in the areas of focus repeatability and global and field-by-field leveling are reviewed both in terms of image quality and throughput achieved. Factors affecting the useable depth of focus (DOF) at 0.6 micrometers feature sizes, including thin film stack, resist type, resist thickness and field flatness will be discussed. Finally, two models describing the dependance of DOF with linewidth are compared with actual data from several aligners, including this one. It will be shown that a model depending only on exposure wavelength accurately fits the experimental data.
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