Electrical instability of sintered Ta films on (vacuum evaporated) polysilicon structures

Abstract

High purity tantalum metal was deposited on finely polished single crystal, polycrystalline silicon substrates and on the thermally grown oxide layers as a combination of Si/SiO 2/poly-Si/Ta, under oil-free ultra-high vacuum conditions, of the order of ∼6.0 × 10 −9 Torr, at a deposition rate of ∼2.0 Å s −1, using an e-beam evaporator. The measured resistivity of the as-deposited tantalum films show relatively high resistivity values to that of the bulk. Thermal annealing of these poly-Si/Ta, under argon (with 10% H 2) ambient, shows the increase in the resistivity values at relatively low temperatures, and it was observed that the film's electrical conductivity ceases in the temperature range of 500–600°C. The oxidation properties of tantalum and the possible formation of TaSi 2 and Ta 2O 5 were analysed for from a reliability point of view.