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

Published

September 1, 2003

Author(s)

Kenneth G. Kreider, D H. Chen, D P. DeWitt, William A. Kimes, Benjamin K. Tsai

Abstract

Lightpipe radiation thermometers (LPRTs) are the preferred temperature monitoring sensor 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 light pipe 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 measured LPRT outputs from a position flush with the reflecting plate to within 2 mm of the stationary wafer under steady-state conditions with wafer-to-cold plate separation distances of 6 mm, 10 mm and 12.5 mm. Depressions in the wafer temperature up to 25 C were observed. A finite-element radiation model of the wafer-chamber-lightpipe was developed to predict the temperature depression as a function of proximity distance and separation distance. The experimental results were compared with those from a model that accounts for lightpipe geometry and radiative properties, wafer emissivity and chamber cold plate reflectivity.

Proceedings Title

Characterization and Metrology for ULSI Technology, International Conference | | Characterization and Metrology for ULSI Technology: 2003 International Conference on Characterization and Metrology for ULSI Technology | AIP

Volume

683

Conference Dates

March 24-28, 2003

Conference Title

AIP Conference Proceedings

Pub Type

Conferences

Keywords

lightpipe radiometer, rapid thermal processing, temperature calibration, temperature measurement, thin-film thermocouples

Citation

Kreider, K. , Chen, D. , DeWitt, D. , Kimes, W. and Tsai, B. (2003), Effects of Lightpipe Proximity on Si Wafer Temperature in Rapid Thermal Processing Tools, Characterization and Metrology for ULSI Technology, International Conference | | Characterization and Metrology for ULSI Technology: 2003 International Conference on Characterization and Metrology for ULSI Technology | AIP (Accessed December 8, 2024)