In situ calibration of lightpipe radiometers for rapid thermal processing between 300°C to 700°C

Many rapid thermal processing (RTP) tools are currently monitored and controlled with lightpipe radiometers (LPRTs), which have been limited to measuring temperatures above 500degC because of the low signal level below 500degC. New commercial LPRTs couple the optical detector directly to the lightpipe, eliminating the signal loss from optical cables. These cable-less light pipe radiometers (CLRTs) are capable of measuring temperature below 300degC. We present the results of calibrating a CLRT against our NIST thin-film thermocouple (TFTC) calibration wafer from 315degC to 700degC in our NIST RTP test bed. Below 550degC, light leakage from the heating lamps of the RTP tool introduced a significant error in the LPRT readings. By measuring the transient response of the CLRTs following rapid energizing of the heating lamps, we were able to differentiate between the radiance of the wafer and ambient chamber light. This allowed us to subtract the ambient chamber light from total measured radiation