Mask aligner process enhancement by spatial filtering
Mask Aligners are used in the Semiconductor Industry to transfer structures with moderate resolution requirements onto substrates. With the casting of the shadow a photochemical reactive resist is exposed. As diffraction appears at the mask structures the exposure wavelength and the proximity gap between mask and wafer influence the quality of the image in the resist. As both parameters are very often not changeable for processes there is a big need to find another way to improve the resist image. In this paper a new approach to enhance the exposure result will be presented. MO Exposure Optics, a novel illumination system for Mask Aligners, uses a combination of two microlens Köhler Integrators. MO Exposure Optics decouples the illumination system in a Mask Aligner from the lamp and ensures a uniform angular spectrum over the whole mask plane. Spatial filtering of the illumination light allows to reduce the diffraction effects at the mask structures and to improve the lithographic process in a Mask Aligner.