Degradation of Pt-Al2O3-Ge Metal Oxide Semiconductor Structures due to Pt-Al2O3 Induced Reactions

In this work, Pt-alumina-Ge metal oxide semiconductor structures are investigated. An important finding is that the Pt metal layer reacts with the underlying aluminum of the atomic layer deposited amorphous alumina, forming a crystalline Al-Pt alloy between the Pt and the remaining alumina layer. This effect is attributed to the alumina surface destabilization due to the short exposure to photolithography developer. Subsequent annealing at 350 °C in inert gas ambient does not impose significant changes to the stack, while forming gas annealing at the same temperature seems to further promote the Pt-Al reaction. One of the consequences of the Al-Pt alloy formation is the reduction of the alumina layer thickness. In turn, the insulating properties of the Pt-Al2O3-Ge MOS stacks are degraded, manifested by enhanced density of interface traps near the valence band edge and by the observation of dc conduction mechanism in conductance characteristics, observable at low temperatures. The level of this degradation depends on the extent of the Pt-Al reaction, which is enhanced by the hydrogen annealing, yielding structures characterized by high leakage currents. These findings may add additional knowledge to the understanding of the Ge-based MOS metallization processes, as well as to the subsequent post-metallization annealing recipes.