MNOS stack for reliable, low optical loss, Cu based CMOS plasmonic devices

We study the electro optical properties of a Metal-Nitride- Oxide-Silicon (MNOS) stack for a use in CMOS compatible plasmonic active devices. We show that the insertion of an ultrathin stoichiometric Si3N4 layer in a MOS stack lead to an increase in the electrical reliability of a copper gate MNOS capacitance from 50 to 95% thanks to a diffusion barrier effect, while preserving the low optical losses brought by the use of copper as the plasmon supporting metal. An experimental investigation is undertaken at a wafer scale using some CMOS standard processes of the LETI foundry. Optical transmission measurments conducted in a MNOS channel waveguide configuration coupled to standard silicon photonics circuitry confirms the very low optical losses (0.39 dB.μm ^-1), in good agreement with predictions using ellipsometric optical constants of Cu.