Thermomechanical stress analysis and measurement in quasi-monolithic integration technology (QMIT)

This paper is dedicated to thermomechanical stress measurement and analysis with a new technology for microwave and millimeter-wave applications called quasi-monolithic integration technology (QMIT). A measurement-based method and a three-dimensional (3-D) finite-element simulator are applied to achieve the thermomechanical stress distribution under different temperatures for the different structures fabricated by QMIT. A closed-loop temperature measurement system consisting of a Pt-100 temperature sensor, a Peltier element, and a digitally controlled current source enables temperature measurements with a resolution of better than 0.1°C. The surface profiles on the silicon substrate around the active devices have been measured using scanning probe microscopy (SPM), surface profiling (DEKTAK) (Veeco Instruments Inc., New York), or white-light interferometry [Tarraf et al. (2004)]. The measured results show very good agreement with the results of theoretical model calculations. The simulation results reveal a much lower induced thermomechanical stress for the enhanced QMIT structure than the earlier concept of QMIT, which results in a better lifetime and reliability for this technology.