Spatially-programmable thermal processing module for 300 mm wafer processing

Abstract

Thermal processing of photoresist are critical steps in the microlithography sequence. The post-expose bake (PEB) steps for current DUV chemically-amplified resists is especially sensitive to temperature variations. Requirements call for temperature to be controlled to within 0.1°C at temperature between 70°C and 150°C. The problem is complicated with increasing wafer size and decreasing feature size. Conventional thermal system, which utilizes single or dual zone heating, is no longer able to meet these stringent requirements. The reason is that the large thermal mass of conventional hot plates prevents rapid movements in substrate temperature to compensate for real-time errors during transients. The implementation of advanced control systems with conventional technology cannot overcome the inherent operating limitation. A spatially-programmable thermal processing module for the baking of 300 mm wafers has been developed. It is comprised of an array of heating zones that allows for the spatial control of temperature nonuniformities during transients and steady-state. The system provides in-situ sensing of the substrate temperature. Real-time closed-loop control of the substrate temperature is thus possible as oppose to conventional open-loop control of the substrate temperature. Experimental results are provided to demonstrate temperature uniformity during steady-state operation. There are several processing and manufacturing advantages associated with this improved thermal processing system, including CD uniformity control, throughput improvement, and CD temperature sensitivity characterization.