Polygate within wafer CD uniformity improvement by the minimization of lens heating effect

Abstract

The lens heating focus correction on stepper is not good enough on the current procedure provided by ASML ® . It can only solve the wafer to wafer CD variation but not within wafer. It caused the CD at a wafer top and bottom is different. This is because there is no correction for lens heating if no special trigger while exposing within one wafer.In small UDOF process like 0.3 µm poly gate, CD is very sensitive to the focus drift. The within wafer lens heating effect causes the focus drift and worsen focus control. Even the lens heating correction factor has been optimized, it still suffers the poor within wafer CD uniformity issue.One tricky method, using of multi-image setting, to trigger the lens heating correction is proposed to improve the within wafer CD uniformity in this report. The poly gate CD uniformity (3 ) on 0.3 µm production were improved from 25nm to 15nm.