TTL Alignment for Excimer Laser Aligner

Real-Time SMART with Correcting Lateral Chromatic Aberration

Abstract

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 impossible reticle-to-wafer real-time alignment (during exposure) at all mark positions. The optical method of 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 alignment beam positions were similar to the experimental results. At each alignment mark position, the alignment signal level was sufficient to allow detection as a positioning signal, an overlay accuracy of ± 0.05 μm (3σ) was achieved.