Automated electrical measurements of registration errors in step-and-repeat optical lithography systems

An automated electrical measurement technique for evaluating registration errors in step-and-repeat optical lithography systems is discussed, with emphasis on the ability of such equipment to meet the manufacturing requirements of very-large-scale integration (VLSI). Sources of registration error are outlined, and the relative contributions of these errors for a group of wafers stepped on a commercial 10:1 reduction system are reported. The components of registration error obtained from specially designed resistor structures are displayed using computer-drawn vector displacement maps and frequency plots. The data are analyzed using a six-parameter model which determines the extent to which level-to-level translation, rotation, and linear dimensional changes are present. Estimates of and stage-stepping precision are made by determining the residual errors in both the registration data and the data obtained from specially designed control structures.