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Thermal processing of photoresist are critical steps in the microlithography sequence. The postexpose bake (PEB) steps for current DUV chemically amplified resists is especially sensitive to temperature variations. The problem is complicated with increasing wafer size and decreasing feature size. Conventional thermal systems are 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. An integrated bake/chill module with in situ temperature measurement capability has been developed for the baking of 300-mm silicon wafers. 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 a complete thermal cycle.
Date of Publication: May 2004