Real-time predictive control of photoresist film thicknessuniformity

摘要

With the trends toward larger wafer size and the linewidth goingnbelow 100 nm, one of the challenges is to control the resist thicknessnand uniformity to a tight tolerance in order to minimize the thin-filmninterference effect on the critical dimension. In this paper, we proposena new approach to improve resist thickness control and uniformitynthrough the softbake process. Using an array of thickness sensors, anmultizone bakeplate, and advanced control strategy, the temperaturendistribution of the bakeplate is manipulated in real time to reducenresist thickness nonuniformity. The bake temperature is also constrainednto prevent the decomposition of a photoactive compound in the resist. Wenhave experimentally obtained a repeatable improvement in resistnthickness uniformity from wafer-to-wafer and across individual wafers.nThickness nonuniformity of less than 10 Å has been obtained. Onnaverage, there is 10 × improvement in the thickness uniformity asncompared to conventional softbake process