Use of scatterometric latent image detector in closed loop feedback control of linewldth

The use of a diffraction-based latent image detector during the postexposure 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 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.