Due to polycrystallization, the emissivity of amorphous silicon is known to vary during annealing at temperatures above 500°C. This transition from α-Si to poly-Si usually occurs during the ramp and the beginning of steady stages of the rapid thermal process. However, the majority of current temperature control methods in RTP neglect time-dependent change of emissivity, and the temperature profile of process calibration is different from that of real annealing process. Various kinds of wafers with in-situ doped amorphous Si are investigated using emissivity-independent temperature control. Some process parameters and material parameters, such as ramp rate and doping level, are explored to study their influences on emissivity change, and consequently on electrical and optical parameters.

Current trends of silicon integrated circuit manufacturing demand better temperature control in various thermal processing steps. Rapid thermal processing (RTP) has become a key technique because its single wafer process can accommodate the reduced thermal budget requirements arising from shrinking the dimensions of devices and the trend to larger wafers. However, temperature control by conventional infrared pyrometry, which is highly dependent on wafer back side conditions, is insufficiently accurate for upcoming technologies. Lucent Technologies Inc., formerly known as AT&T Microelectronics and AT&T Bell Laboratories, has developed a powerful real-time pyrometry technique using the A/C ripple signal from heating lamps for in-situ temperature measurement. Temperature and electrical data from device wafers have been passively collected by ripple pyrometers in three RTP systems and analyzed. In this paper we report the statistical analysis of ripple temperature and electrical data from device wafers for a typical implant anneal process temperature range of 900 to 1000 °C.

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.