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-Al 2 O 3 -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.

In this work, the combined effect of negative tone photolithography and post-metallization annealing (PMA) on the electrical behavior of Al/Al2O3/p-Ge MOS structures are investigated. During photoresist development, the exposed upper part of the Al2O3 film weakens due to the reaction with the developer. Subsequent processes of Al deposition and PMA at 350°C result in alumina thickness reduction. The gate electrode formation seems to involve at least three processes: a) germanium substrate out-diffusion and accumulation at the top of the alumina layer that takes place during the alumina deposition, b) alumina destabilization, and c) germanium diffusion into the deposited Al metal and Al diffusion into the alumina. The overall effect is the reduction of the alumina thickness due to its partial consumption. It is shown that the germanium diffusion depends on the annealing duration, and not on the annealing ambient (inert or forming gas). Although PMA passivates interface traps near the valence band edge, the insulating properties of the stacks are degraded. This degradation appears as a low-level ac loss, attributed to a hopping current that flows through the Al2O3 layer. The results are discussed and compared to recently reported on Pt/Al2O3/p-Ge structures formed and treated under the same conditions.