Image Placement Differences Between 1:1 Projection Aligners And 10:1 Reduction Wafer Steppers

The characteristic image placement errors of both 1:1 projection aligners and 10:1 reduction wafer steppers are studied with reference to the overlay difference between them. Analytical models have been developed in recent years which allow the user of these sophisticated aligners to mathematically identify the many components of pattern-to-pattern registration errors. Using these models and experimental data, it is shown how the mixing of the two types of exposure tool can be done successfully. For the fabrication of present generation devices, it is possible to mix steppers using global alignment capability with 1:1 projection aligners. A realistic production overlay budget is developed for 10:1 steppers, 1:1 projection aligners, and for a process which mixes the two.