Measurement and control of silicon wafer temperature and oxide film thickness in rapid thermal processing using in situ ellipsometry

The application of ellipsometry as an in situ sensor for temperature measurement of a silicon wafer in a rapid-thermal processing system was investigated. Ellipsometry is an optical technique which measures the change in polarization of light as it is reflected from a material. The temperature is determined from the known temperature dependence of the refractive index of the material. For experimental analysis, a rapid-thermal processing system equipped with a single-wavelength, automated ellipsometer for in situ optical measurements was constructed, which included a control architecture that provided full automation and system control. A method was developed which enabled simultaneous determination of the wafer temperature and oxide-film thickness from a single ellipsometric measurement, given knowledge of the refractive index of the oxide. A room-temperature calibration procedure was developed which reduced the oxide refractive index sensitivity of this method by an order of magnitude. The resolution of this method then depended on the resolution of the ellipsometer system, followed by limits in accurate knowledge of the refractive index of the oxide, and the amount of microroughness present on the surface. Differences in the measured temperature were observed when the microroughness exceeded 500 A. The substrate doping did not affect the resolution of this method. A mean temperature difference of 11.4...