Interprocess run-to-run feedforward control for wafer patterning

We consider run-to-run feedforward control from lithography to etch in wafer patterning. Under feedforward control, measured deviations in photoresist linewidth are corrected automatically by adjustment of etch bias. Two potential problems with feedforward control are listed: (1) the possibility of feeding measurement noise forward exists and could result in increased final CD variability, and (2) it may be difficult to adjust etch bias without disturbing other important etch characteristics. First, a controller design that addresses concern (1) is considered. Models of the lithography and measurement errors along with minimum mean square error estimation are employed to reduce the chances of acting on erroneous measurements. Building on the first, a second controller is then designed to address concern (2). The controller selects a recipe from a pre-qualified set rather than making arbitrary etch adjustments. It is assumed the recipes in the set provide a means for adjusting etch bias while guaranteeing acceptable results for other characteristics. Both controllers are simulated using industrial data.