Use of scatterometric latent-image detector in closed-loop feedback control of linewidth

The use of a diffraction-based latent image detector during the post-exposure bake (PEB) step for a chemically amplified resist system was investigated and its use in a feedback control strategy was examined. A calibration between intensity of light diffracted from the wafers during PEB and the final post-develop linewidth was determined. Using this relationship, two feedback control strategies were tested. One method altered the PEB time to compensate for unmeasured process disturbances and drive the linewidth to its target. The other method involved altering of the develop time. We found that using the post-exposure bake monitor in a feedback control system can improve wafer-to-wafer and lot-to-lot variability to below that which has been possible through conventional SEM measurements.