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.Index Terms-300-mm wafer processing, in situ temperature measurement, lithography, photoresist processing.

The design of an integrated bake/chill module for photoresist processing in microlithography is presented, with emphasis on the spatial and temporal temperature uniformity of the substrate. The system consists of multiple radiant heating zones for heating the substrate, coupled with an array of thermoelectric devices (TEDs) which provide real-time dynamic and spatial control of the substrate temperature. The TEDs also provide active cooling for chilling the substrate to a temperature suitable for subsequent processing steps. The use of lamp for radiative heating also provide fast ramp-up and ramp-down rates during thermal cycling operations. The feasibility of the proposed approach is demonstrate via simulations based on first principle heat transfer modeling. The distributed nature of the design also means that a simple decentralized control scheme can be used to achieve tight spatial and temporal temperature uniformity specifications.

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Critical dimension (CD) is one the most critical variable in the lithography process with the most direct impact on the device speed and performance of integrated circuit. The development rate can have an impact on the CD uniformity from wafer-to-wafer and within-wafer. Conventional approaches to controlling this process include monitoring the end-point of the develop process and adjusting the development time or concentration from wafer-to-wafer or run-to-run. This paper presents an innovative approach to control the development rate in real-time by monitoring the photoresist thickness. Our approach uses an array of spectrometers positioned above a programmable bakeplate to monitor the resist thickness. The develop process and post-development bake process is integrated into one equipment. The resist thickness can be extracted from the spectrometers data using standard optimization algorithms. With these in-situ measurements, the temperature profile of the bakeplate is controlled in real-time by manipulating the heater power distribution using a control algorithm. We have experimentally obtained a repeatable improvement in controlling the end-point of the develop process from wafer-to-wafer and within wafer.