Fabrication and formation of Ta/Pt-Si ohmic contacts applied to high-temperature Through Silicon Vias (TSVs)

Platinum/tantalum/silicon ohmic contacts were designed, fabricated and characterized to withstand high-temperature post-processing: the ohmic behavior was maintained after 1 h annealing, at temperatures up to 850 °C in an oxidizing environment. A LPCVD silicon nitride layer was added to passivate the contacts from oxidation and concentrated wet hydrofluoric acid (HF 49%) process steps; the later being widely used for the release of free-standing MEMS structures. The linear Transfer Length Method (TLM) was implemented to infer the specific contact resistance at the metal-silicon interface. The Pt/Ta/Si contacts were studied as part of the fabrication process of high-temperature Through Silicon Vias (TSVs). The fabricated KOH-TSVs are dedicated to a “via first” 3D-integration of a delicate RF-MEMS device. They are also of interest for harsh-environment silicon-based MEMS applications: one-week operation test at high-temperature, up to 450 °C, showed a high electrical resistance stability.