In-Line Temperature Monitoring of Rapid Thermal Annealing Processes

Process control for rapid thermal annealing (RTA) steps in silicon integrated circuit manufacturing is highly dependent on the repeatability of wafer annealing temperatures. The heating lamps in RTA ovens are controlled by an infrared pyrometer in a feedback-control loop. Methods currently in production allow some variability in annealing temperature, owing to the variability of wafer backside emissivities and the fixed emissivity value used for each process recipe. To provide an independent in-situ temperature sensor with potentially improved accuracy, an RTA oven equipped with a ripple pyrometer was used for passive data collection. Results obtained over extensive wafer processing indicate that the ripple temperatures have a correlation with electrical tester data and that the ripple pyrometer repeatability is better than 3°C at 1 standard deviation.