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Ring-Field Vs Full-Field Projection Systems: An Optical Performance Comparison

Full-field (e.g., steppers) and ring-field (e.g., scanners) systems can be expected to differ in resolution, depth of focus, and exposure latitude as a result of their optical and opto-mechanical designs. In this study we compare the results of performance simulation of two exploratory optical systems, both having the same nominal resolution. Working values of resolution and depth of focus are determined based on the approach of B.J. Lin. The impact of wafer unflatness on the focus budget is assessed by measurement of a batch of six-inch wafers. Various focusing algorithms are simulated, leading to a measure of the reduction in focal tolerance due to wafer unflatness for both ring- and full-field systems.