Real-time spatial control of steady-state wafer temperature during thermal processing in microlithography

An in-situ method to control the steady-state wafer temperature uniformity during thermal processing in microlithography is presented. Based on first principle thermal modeling of the thermal system, the temperature of the wafer can be estimated and controlled in real-time by monitoring the bake-plate temperature profile. This is useful as production wafers usually do not have temperature sensors embedded on it, these bake-plates are usually calibrated based on test wafers with embedded sensors. However as processes are subjected to process drifts, disturbances and wafer warpages, real-time correction of the bake-plate temperatures to achieve uniform wafer temperature at steady-state is not possible in current baking systems. Any correction is done based on run-to-run control techniques which depends on the sampling frequency of the wafers. Our approach is real-time and can correct for any variations in the desired steady-state wafer temperature. Experimental results demonstrate the feasibility of the approach.