INTRODUCTORY INVITED PAPER : Failure mechanisms due to metallurgical interactions in commercially available AlGaAs/GaAs and AlGaAs/InGaAs HEMTs

Failure mechanisms due to metallurgical interactions have been investigated in commercially available AlGaAs/GaAs HEMTs and AlGaAs/InGaAs pseudomorphic HEMTs (PM-HEMTs) by means of accelerated tests at high temperature, with and without applied bias. In-depth Auger Electron Spectroscopy (AES), Transmission Electron Microscopy (TEM) on device cross-sections and back-etching have been adopted as failure analysis techniques. Main reliability problems have been detected in Schottky gate and ohmic contacts due to thermally activated metal–metal and metal–semiconductor interdiffusion. After thermal storage, Al/Ti gate contacts show a decrease of barrier height with an activation energy Ea=1.3 eV, while the Al/Ni Schottky contacts shows an increase of barrier height with Ea=1.8 eV. An increase of source and drain parasitic resistance has been detected in devices of two suppliers with Ea=1.5–1.6 eV. For both Schottky and ohmic degradation phenomena, the observed failure modes and mechanisms are not affected by the properties of the substrate structure, i.e. we did not observe, as far as metallurgical interactions were concerned, any difference between AlGaAs/GaAs and AlGaAs/InGaAs HEMTs. As a general result, our data show that recently manufactured HEMTs and PM-HEMTs can attain excellent levels of metallurgical stability even during very high temperature accelerated stress. Best results are obtained by device adopting refractory gates and improved ohmic contact schemes.