Optimized Control For Yield Using Scanner Controls In Overlay, Focus and Critical Dimension

摘要

Current control systems of lithographic apparatus (scanner) focus on controlling overlay, CD, and focus using measured values, and then trying to minimize those values in a root mean square sense under constraints determined by the scanner. Minimizing the overlay, focus, or CD error comes at a price - it heavily weights extreme deviations from zero overlay/ed/focus, focusing on minizing those large errors. At the same time, if many dies have small hut non-zero overlay error, it will try to improve these many small contribution. However yield of the process is not directly improved using this strategy. Overlay/Focus/CD control are all methods of achieving that yield. The current goal functions do not directly aim for this, and we propose to fix this.