Overlay budget analysis for the 100 nm device generation

In order to improve overlay capabilities for future exposure tools, it is n ecessary to understand the contributions from various sources. The most imp ortant contributions come from well-known sources like mask pattern placeme nt accuracy, alignment system accuracy and from exposure tool stage perform ance. As the allowances for overlay budget decrease, and improvements in ma sk fabrication and stage performance are made, a number of previously less significant contributions need to be considered. These contributions includ e resolution, optical interference, focusing accuracy of the alignment syst em, and wafer processing deviations. These contributions are characterized in detail in this paper. The investigation was focused on a proven optical alignment system (ALX(TM)) and overlay contribution as they apply to x-ray and optical lithography. Special emphasis was made on contributions from wa fer processing (resist coating and metallization).