Exploring ultrathin tungsten disulfide as a diffusion barrier for copper interconnects: advanced packaging reliability and a first-principles study

The robust diffusion barriers (DB) are crucial due to the significant prevention of copper (Cu) diffusion/migration, which negatively affects interconnect reliability and compatibility in advanced packaging. With a half-pitch size (20 nm and below) a conventional Ta/TaN DB has a thickness limit to shrinkage below 4 nm, addressing the limited Cu conductivity, and inferior barrier properties to block Cu diffusion. Therefore, ultrathin 0.7 nm tungsten disulfide (WS₂) is utilized as a pioneering DB for Cu interconnects to address this issue. Herein, W is primarily sputtered and sulfurized at 400 °C to convert into WS₂, later confirmed by several characterizations. Based on JE, CV, temperature-dependent breakdown, and DFT verification, we conclude that the ultrathin 0.7 nm WS₂ effectively blocks the Cu diffusion in the range of 9.7–10 MV/cm. Notably, the research is strongly supported by reliability tests, including (−200 to 400 °C) temperature-dependent JE at both low (14.8 MV/cm) and high (8 MV/cm) temperatures, Cu electroplating, warpage tests, tape tests, and other relevant evaluations, which are currently of significant interest in packaging. The obtained results show that the WS₂ DB serving both liner/barrier properties is excellent as compared to conventional Ta(liner)/TaN(barrier). The study demonstrates that WS₂ is BEOL-compatible and industry-friendly, facilitating interconnect scaling beyond the current technology node, and we should not be surprised if used in future advanced packaging.