FAILURE MECHANISMS DUE TO METALLURGICAL INTERACTIONS IN COMMERCIALLY AVAILABLE ALGAAS GAAS AND ALGAAS/INGAAS HEMTS/

Failure mechanisms due to metallurgical interactions have been investi gated in commercially available AlGaAs/GaAs HEMTs and AlGaAs/InGaAs ps eudomorphic HEMTs (PM-HEMTs) by means of accelerated tests at high tem perature, with and without applied bias. In-depth Auger Electron Spect roscopy (AES), Transmission Electron Microscopy (TEM) on device cross- sections and back-etching have been adopted as failure analysis techni ques. Main reliability problems have been detected in Schottky gate an d ohmic contacts due to thermally activated metal-metal and metal-semi conductor interdiffusion. After thermal storage, Al/Ti gale contacts s how a decrease of barrier height with an activation energy E-a=1.3 eV, while the Al/Ni Schottky contacts shows an increase of barrier height with E-a=1.8 eV. An increase of source and drain parasitic resistance has been detected in devices of two suppliers with E-a=1.5-1.6 eV. Fo r both Schottky and ohmic degradation phenomena, the observed failure modes and mechanisms are not affected by the properties of the substra te structure, i.e. we did not observe, as far as metallurgical interac tions were concerned, any difference between AlGaAs/GaAs and AlGaAs/In GaAs HEMTs. As a general result, our data show that recently manufactu red HEMTs and PM-HEMTs can attain excellent levels of metallurgical st ability even during very high temperature accelerated stress. Best res ults are obtained by device adopting refractory gates and improved ohm ic contact schemes. (C) 1998 Published by Elsevier Science Ltd. All ri ghts reserved.