Investigation of volumetric radiation effects in lightpipe thermometry

A major obstacle to the widespread implementation of rapid thermal processing (RTP) is the challenge of wafer temperature measurement. Frequently, lightpipe radiation thermometers (LPRT) are used to measure wafer temperatures in RTP reactors. While the lightpipe distorts the wafer temperature profile less than temperature measurement techniques which require physical contact, the presence of the lightpipe influences the wafer temperature profile. This paper presents the results of a theoretical study exploring that influence. Radiation transfer in the LPRT is modeled with varying levels of rigor, ranging from a volumetrically non-participating treatment to a full (gray) solution of the radiative transfer equation. The results of the study clearly indicate the need to model the lightpipe as a volumetrically participating, semitransparent medium and further, underline the need for knowledge of accurate radiative properties of the lightpipe material