Atomic Layer Deposition of Conformal Wafer-scale WS₂ Films: a Promising Liner and Barrier Alternative for Back-end-of-Line Applications

The continued scaling of silicon integrated circuits makes it crucial to find substitute materials for both the front-end-of-line (FEOL, transistors) and back-end-of-line (BEOL, interconnects) applications. Currently, approximately 4-nm thickness is required for conventional liners and barriers to be effective. In forthcoming sub-5 nm technology nodes, these would occupy a substantial share of the interconnect cross-section and consequently increase the resistivity of Cu interconnects. Conversely, downscaling the thickness of the liner and barrier layers would result in poor Cu blocking efficiency. Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been recently identified as promising candidates for Cu diffusion barrier and liner applications at the sub-nm scale. However, most 2D TMDs are grown using chemical vapor deposition processes at high temperatures (&gt;800°C), making them incompatible with BEOL applications. Plasma-assisted growth can reduce growth temperatures, but poor conformality and plasma-induced defects remain challenges.<br/>Here, we report a complete thermal (no plasma assistance) atomic layer deposition (ALD) process for the deposition of crystalline WS₂ growth at &lt;450 °C, suitable for BEOL integration. The process yields layer-controlled conformal (&gt;95%) growth of WS₂ on an 8-inch wafer scale. Raman spectroscopy and transmission electron microscopy measurements were used to elucidate the quality and number of layers in WS₂, whereas x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy were used to assess the stoichiometry and compositional uniformity, respectively. We further show that as-grown single and multilayer WS₂ grown <i>via</i> ALD are promising candidates as a liner layer: Cu interconnects with thickness of 10—20 nm show 50% reduction in resistivity when deposited on WS₂ compared to the reference SiO₂/Si substrate. In addition, thermal stress measurements of Cu/WS₂ layers show that WS₂ is a potential diffusion barrier alternative as it effectively blocks the diffusion of Cu into the surrounding dielectric. Our results demonstrate that 2D TMDs grown <i>via </i>thermal ALD are promising building blocks for BEOL applications beyond the 5 nm nodes.