Thermal stability of Ti/Mo and Ti/MoN nanostructures for barrier applications in Cu interconnects

This work focuses on the barrier capabilities of sputter deposited Ti/Mo and Ti/MoN nanofilms against diffusion of Cu into Si substrates. The thermal stability of the corresponding bi-layer barrier structures is investigated after annealing Cu/barrier layer/Si samples at different temperatures in N(2) for 5 min. The drastic increase in sheet resistance of Cu and the probing of Cu(3)Si with x-ray diffraction after high temperature annealing indicate the failure of these barrier structures. The formation of Cu(3)Si at the barrier breakdown temperature is also confirmed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Cu diffusion barrier performance analyses show that a Ti(5 nm)/MoN(5 nm) bi-layer nanostructure fails only after annealing at 800 °C; on the other hand, a Ti(5 nm)/Mo(5 nm) barrier stack is found to break down at 700 °C.