Advanced mask aligner lithography (AMALITH)

Abstract

Mask aligners were the dominating lithography tool for the first 20 years of semiconductor industry. In the 1980s industry changed over to projection lithography. However, mask aligners were never sorted out and still today hundreds of new mask aligners are sold each year. This continuing success of mask aligner lithography is due to two basic trends in lithography: (a) Costs for leading-edge lithography tools double approximately every 4.4 years; and (b) the number of lithography steps per wafer was increasing from a few litho layers to more than 35 layers now. This explains why mask aligners, a very cost-effective solution for uncritical litho layers, are still widely used today. In over 50 years of semiconductor industry the mask aligner system has changed tremendously. However, only little effort was undertaken to improve the shadow printing process itself. We now present a new illumination system for mask aligners, the MO Exposure Optics (MOEO), which is based on two microlens-type Köhler integrators located in Fourier-conjugated planes. The optics stabilizes the illumination against misalignment of the lamp-to-ellipsoid position. It provides improved light uniformity, telecentric illumination and allows freely shaping the angular spectrum of the illumination light by spatial filtering. It significantly improves the CD uniformity, the yield in production and opens the door to a new era of Advanced Mask Aligner Lithography (AMALITH), where customized illumination, optical proximity correction (OPC), Talbot-lithography, phase shift masks (AAPSM) and source mask optimization (SMO) are introduced to mask aligner lithography.