Predictive Ratio Control of Multizone Thermal Processing System in Lithography

Abstract: Baking of semiconductor substrate is common and critical to photoresist processing in the lithography sequence. Temperature uniformity control is an important issue in photoresist processing with stringent specifications and has a significant impact on the linewidth or critical dimension (CD). In this work, we present the development of a ratio control strategy for controlling temperature uniformity of a silicon wafer substrate. Traditional approach in ratio control does not consider interaction among the different input, our approach takes into consideration the interaction between the different heating zone of the novel multizone thermal system developed by us. The resultant model-based GPC PID controller is designed and tested on the multizone thermal system. Simulation results shows that spatial temperature uniformity can be controlled to within 1C and 0.1C during transient and steady-state operating condition respectively.