Low-temperature wafer-scale growth of ultrathin tungsten disulfide for bifunctional interconnect barriers and liners

In the future, the miniaturization of integrated circuits will require copper wires to be scaled down in the back-end-of-line (BEOL) process. This will, in turn, require a scaling down of the barrier and liner coatings that prevent copper diffusion and ensure metal adhesion to the dielectric. Here we show that thin (<1 nm) and conformal tungsten disulfide (WS2) layers can be grown on the wafer-scale using thermal atomic layer deposition without plasma at BEOL-compatible temperatures (350 °C) and can function as both barriers and liners for interconnects. We show that the WS2 can reduce the resistivity of 10-nm-thick copper films by more than six orders of magnitude compared with a reference system (without the WS2 layer) due to the improved wettability of copper. Monolayer WS2 can prevent copper diffusion into silicon dioxide (SiO2) under thermal stress, and it is projected to improve wire lifetimes under electrical stress. Density functional theory calculations also highlight the potential of multilayer WS2 films as diffusion barriers due to misaligned grain boundaries. Thin and conformal tungsten disulfide (WS2) layers, which are grown at the wafer scale using thermal atomic layer deposition at back-end-of-line compatible temperatures, can function as both barriers and liners for interconnects.