Atomic Layer Deposition of WS₂ on Low-k Dielectric Substrates for Back-End-Of-Line Integration

The progressive miniaturization of silicon integrated circuits necessitates the exploration of alternative materials for both the front-end-of-line (FEOL, transistors) and back-end-of-line (BEOL, interconnects) circuitry. Currently, the efficacy of traditional liners and barriers (e.g., Ta/TaN) requires an approximate thickness of 30-40 Å. In forthcoming sub-5 nm nodes, these components will occupy a significant portion of the interconnect cross-section, leading to a substantial increase in the resistivity of Cu interconnects. Conversely, the reduction in thickness of liner and barrier layers would result in a decrease in Cu blocking efficiency. Two-dimensional (2D) transition metal dichalcogenides (TMDs) were recently demonstrated as promising candidates for bifunctional ultra-thin liner and diffusion barrier materials in the sub-nanometer-scales. However, the majority of 2D TMDs are synthesized <i>via</i> chemical vapor deposition processes at elevated temperatures (&gt;800°C). This makes it difficult to use them in BEOL integration, where the temperature limit is 450°C. While plasma-assisted growth offers the potential to mitigate the high-temperature requirement, it also implies poor conformality in deposition, and the emergence of plasma-induced defects in the TMDs as limitations.<br/>Here, we present a thermal atomic layer deposition (ALD) approach that does not require plasma assistance to grow crystalline WS₂ at temperatures below 400°C, on dielectric materials, including low- k and SiO₂ substrates. This growth approach does not alter the stoichiometry of the low- k material and retains its k value, making it a suitable method for BEOL integration. The process results in layer-controlled, conformal (&gt;95%) wafer-scale growth of WS₂ on 200 mm dielectric substrates. Furthermore, the single-layer WS₂ helps reduce Cu resistivity &gt;70% compared to the reference low- k and SiO₂/Si substrates. Thermal and electrical stress tests on the monolayer WS₂ film reveal a high blocking efficiency against both types of stress. This low- k -compatible ALD-grown monolayer WS₂ not only addresses the downscaling challenge but also serves as an efficient bifunctional (liner and barrier) layer grown using a directly industry-compatible process.