Effects of wafer emissivity on rapid thermal processing temperature measurement

Lightpipe radiation thermometers (LPRTs) are widely used to measure wafer temperatures in rapid thermal processing (RTP) tools. Using blackbody-calibrated LPRTs to infer the wafer temperature, it is necessary to build a model to predict the effective emissivity accounting for the wafer and chamber radiative properties as well as geometrical features of the chamber. The uncertainty associated with model-corrected temperatures can be investigated using test wafers instrumented with thin-film thermocouples (TFTCs) on which the LPRT target spot has been coated with films of different emissivity. A model of the wafer-chamber arrangement was used to investigate the effects of Pt (ε_s=0.25) and Au (ε_s=0.05) spots on the temperature distribution of the test wafers with the emissivity of 0.65 and 0.84. The effects of the shield reflectivity and the cool lightpipe (LP) tip on the wafer temperature were evaluated. A radiance analysis method was developed and a comparison of model-based predictions with experimental observations was made on a 200 mm wafer in the NIST RTP test bed. The temperature rises caused by the low-emissivity spot were predicted and the cooling effect of the LP tip was determined. The results of the study are important for developing the model-corrected temperature measurement and uncertainty estimates using LPRT in semiconductor thermal processes.