MO Exposure Optics: Pushing Limits of Shadow Printing Lithography in Mask Aligners

Mask aligners were the dominating litho tool for the first 20 years of semiconductor industry, until industry changed over to projection litho in the 1980s. However, mask aligner lithography was never sorted out. Still today, some hundreds of new aligners are sold every year. Mask aligners have evolved much since then, however, the shadow printing mechanism and the related illumination system has not changed much over 30 years. We now present a new illumination system for mask aligners, the MO Exposure Optics®, which is based on two microlens-type Köhler integrators located in Fourier-conjugated planes. The optics stabilized the illumination against misalignment of the lamp position in ellipsoid. It also provides improved light uniformity, telecentric illumination and allows to freely adjust the angular spectrum of the illumination light by spatial filtering. It significantly improves CD uniformity and yield in production and opens the door to a new era of Advanced Mask Aligner Lithography (AMALITH), providing customized illumination, optical proximity correction (OPC), Talbot-lithography, phase shift masks (AAPSM) and source mask optimization (SMO) in mask aligners.