High Temperature Materials for Thin-Film Thermocouples on Silicon Wagers

摘要

We are developing an instrumented calibration wafer for radiometric temperature measurements in rapid thermal processing (RTP) tools for semiconductor processing. The instrumented wafers has sputter deposited thin-film thermocouples to minimize the thermal disturbance of the wafer by the sensors. The NIST calibration wafer also employs platinum-palladium wire thermocouples to achieve a combined standard uncertainty of 0.4 deg C in temperature measurement of the thin-film thermocouple junction at 900 deg C. The high temperatures of the wafer has required the development of new thin-film material systems. We report the results of our testing and characterization of sputtered platinum, palladium, rhodium, and iridium thin films using titanium bond coats on thermally oxidized silicon wafers. Depth profiling with secondary ion mass spectrometry was used to determine the diffusion profiles from the metal film to the silicon after heat treatments as high as 1000 degrees C. Electron microscopy and optical microscopy were used to follow reactions and the deterioration of the thermoelectric films. In addition, performance tests up to 1000 degrees C in the NIST RTP test bed were used to determine the stability of the material systems.