High temperature materials for thin-film thermocouples on silicon wafers

We have developed an instrumented calibration wafer for radiometric tempera ture measurements in rapid thermal processing (RTP) tools for semiconductor processing. The instrumented wafers have sputter deposited thin-film therm ocouples to minimize the thermal disturbance of the wafer by the sensors. T he National Institute of Standards and Technology (NIST) calibration wafer also employs platinum-palladium wire thermocouples to achieve a combined st andard uncertainty of 0.4 degreesC in the temperature measurement of the th in-film thermocouple junction at 900 degreesC. The high temperatures of the wafer has required the development of new thin-film material systems. We h ave reported the results of our testing and characterization of sputtered p latinum, palladium, rhodium, and iridium thin films using titanium bond coa ts on thermally oxidized silicon wafers. Depth profiling with secondary ion mass spectrometry was used to determine the diffusion profiles from the me tal film to the silicon after heat treatments as high as 1000 degreesC. Ele ctron microscopy and optical microscopy were used to follow the reactions a nd the deterioration of the thermoelectric films. In addition, performance tests up to 1000 degreesC in the NIST RTP test bed were used to determine t he stability of the material systems. Failure mechanisms and limitations of the thin-him thermocouple materials have been discussed with data on hyste resis and drift in thermometry performance. The results of our evaluations indicated that Rh/Ir thin-film thermocouples have the best properties for w afer temperatures above 900 degreesC. (C) 2000 Elsevier Science S.A. All ri ghts reserved.