AERIAL IMAGE STUDIES OF AN ADVANCED DEEP-UV EXPOSURE SYSTEM

A method to measure directly the aerial image of arbitrary patterns, i maged by a stepper optics in a very thin layer of photoresist, is pres ented. Using this technique we characterised the optical properties of an advanced Deep UV stepper. Measured and simulated aerial images dif fer significantly, which can be attributed to imperfections of the pro jection optics. The major goal of this study was to find out the aeria l image related limitations of lithographic process windows for patter ns with 0.35 mu m and 0.25 mu m ground rule. Experimental data for sev eral types of illumination (conventional and oblique illumination tech niques) were obtained., and the aerial image induced offsets between t he widths of isolated and grouped lines studied.