Abstract
In optical lithography, the projection optics is known as the high accurate exposure tool for 3-dimensional device patterning such as MEMS (Micro Electro Mechanical Systems). Required optical performances of the projection optics are resolution capability of pattern density and depth of focus (DOF) on step-heights. Generally, larger numerical aperture (NA) of projection optics is quite effective on higher resolution, but loses DOF on the contrary. The capability of micro-lens-array (MLA) patterning has the resolution limit around 20-30μm in Sag (lens height) by the conventional high NA projection lens. Therefore, projection optics with lower NA and deeper DOF is required for the MLA patterning with 100μm Sags for various applications. This paper reports the effectivity of the combination of the newly developed projection lens with adjustable NA of 0.06-0.22 and a photo-mask with quasi-continuous intensity distribution by a density control of scattered square micro-dot-patterns. By experiments, this method has been proved to realize the MLA patterning with 100μm Sags with errors less than surface roughness of 2μm RMS and Sag shape deviation of 5μm.
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