Optical projection system design for photoresist exposure.

In the exposure of microcircuits, it is attractive to replace contact printing with projection printing to avoid direct contact between the silicon wafer and glass master. Since etched photoresists do not exhibit a gray scale, the conventional criteria of projection printing do not apply. In order to establish adequate criteria for projection printing onto photoresists, the imaging properties of diffraction-limited optics and the recording characteristics of photoresists are examined. A criterion based on edge uncertainty of lines is proposed. Other aspects of projection systems are briefly considered.