TTL ALIGNMENT FOR EXCIMER-LASER ALIGNER - REAL-TIME SMART WITH CORRECTING LATERAL CHROMATIC ABERRATION

This paper presents a real-time SMART (separated mark TTL alignment) technique for optical lithography systems. The new TTL alignment optical system corrects lateral chromatic aberration which has made reticle-to-wafer real-time alignment (during exposure) at all mark positions impossible. The optical method for correcting lateral chromatic aberration is described. This correcting method was applied to a KrF excimer laser optical lithography aligner to demonstrate the principle of this alignment method. The simulation results of the alignment beam positions were similar to the experimental results. The alignment signal intensity at each alignment mark position was sufficient to allow the use of the positioning signal for a detector; an overlay accuracy of +/-0.05 mu m(3 sigma) was achieved.