Reactively sputtered ZrN used as an Al/Si diffusion barrier in a Zr contact to silicon

Abstract

An evaluation of the processing of zirconium nitride and the usefulness of this nitride as a diffusion barrier between aluminum and silicon has been carried out. Reactive sputtering from an elemental zirconium target in a mixture of Ar/N2 makes it possible to change the nitrogen content in the deposited film. The composition variation with N2 concentration will be presented. Films have been prepared using rf-diode reactive sputtering. The as-deposited film resistivity dependence on bias voltage has also been studied. Zirconium deposited on silicon forms a silicide at 550–600 °C. We have found by Rutherford backscattering spectroscopy analysis that during this silicide formation on arsenic implanted silicon substrates, the arsenic is piled up at the silicon/silicide interface. This effect favors the formation of a low resistance Ohmic contact. Since the barrier height between the silicide and silicon is expected to be 0.55 eV we want to point out that this contact may be useful for both n- and p-type regions. It is confirmed by the RBS analysis that the zirconium nitride prevents Al/Si interreactions up to 550–600 °C. Evaluation of the following process that needs only one single pump down to form a complete contact metallization system will be presented: zirconium is sputtered on top of the silicon. Nitrogen is then mixed to the argon and zirconium nitride is formed by reactive sputtering on top of the zirconium layer. Finally, aluminum is deposited on top of the zirconium nitride. This multilayer structure is then annealed to form the silicide and simultaneously cure induced radiation damages from previous processing steps. The RBS analysis shows no interaction between the aluminum and the silicon after a heat treatment in 600 °C for 30 min.