Effects of Lightpipe Proximity on Si Wafer Temperature in Rapid Thermal Processing Tools

Lightpipe radiation thermometers (LPRTs) are used as temperature monitoring sensors in most rapid thermal processing (RTP) tools for semiconductor fabrication. These tools are used for dopant anneal, gate oxide formation, and other high temperature processing. In order to assure uniform wafer temperatures during processing these RTP tools generally have highly reflecting chamber walls to promote a uniform heat flux on the wafer. Therefore, only minimal disturbances in the chamber reflectivity are permitted for the sensors, and the small 2 mm diameter sapphire lightpipe is generally the temperature sensor of choice. This study was undertaken to measure and model the effect of LPRT proximity on the wafer temperature. Our experiments were performed in the NIST RTP test bed using a NIST thin‐film thermocouple (TFTC) calibration wafer. We measured the spectral radiance temperature with the center lightpipe and compared these with the TFTC junctions and with the three LPRTs at the mid‐radius of the wafer. We me...