Titanium hydride formation in Ti/Pt/Au-gated InP HEMTs

Ti/Pt metal layers are an integral part of the gate stack of many GaAs PHEMTs and InP HEMTs. These devices are known to be affected by H/sub 2/ exposure. In this study, Auger Electron Spectroscopy (AES) measurements of Ti/Pt bilayers are correlated with electrical measurements of InP HEMTs fabricated with Ti/Pt/Au gates. The FET measurements show that H/sub 2/ exposure shifts the device threshold voltage through the piezoelectric effect. AES reveals the formation of titanium hydride (TiH/sub x/) in Ti/Pt bilayers after identical H/sub 2/ exposures. These results indicate that the volume expansion associated with TiH/sub x/ formation causes compressive stress in Ti/Pt/Au gates, leading to the piezoelectric effect. After a subsequent recovery anneal in N/sub 2/, the FET measurements show that V/sub T/ recovers. AES measurements confirm that the TiH/sub x/ in hydrogenated Ti/Pt bilayers also decreases after further annealing in N/sub 2/.