Lithographic projectors with dark-field illumination

A new resolution enhancement technique for photolithography that allows the illumination of each and every feature on a reticle to be customized is de scribed. Customization is important because different feature types, e.g., contact holes, isolated lines, dense gratings, etc., must be illuminated di fferently if the best possible image at the largest depth-of-focus is to be produced. Examples of the imaging performance of a conventional lithograph ic projector retrofitted with dark-field illumination for three feature typ es commonly encountered in semiconductor lithography are presented. (C) 199 9 American Vacuum Society. [S0734-211X(99)07806-3].