Emissivity correcting pyrometer for temperature measurement in low pressure chemical vapor deposition

Rapid thermal processing (RTP) low pressure chemical vapor deposition (LPCVD) requires accurate wafer temperature measurement to control film deposition during processing. The temperature sensor discussed detects a portion of the target radiance as a DC signal. The remainder of the target radiance is chopped, reflected back onto the target, and recollected by the sensor as an AC signal. Two versions of the sensor were developed. Unit 1 separates the pyrometer (DC) and chopper reflector components. Unit 2 combines both components into a single unit. The DC signal is calibrated to target radiance using a blackbody source. The ratio of AC to DC signals is related to target spectral emissivity via a second calibration using a prepared surface of known emissivity. After calibration, both units are evaluated against oxidizing steel surfaces. Unit 1 successfully tracks relative changes in oxidizing steel emissivity. Unit 2 suffers from internal reflections of the modulated AC signal which dominate those reflected off the target, preventing an evaluation of its sensitivity to alignment