Scalable Back-End-of-Line Compatible Growth of WS₂ Thin Films via Atomic Layer Deposition

With the continuous scaling of silicon integrated circuits, identifying alternative materials for both the front-end-of-line (transistors) and back-end-of-line (BEOL, interconnects) technology is becoming increasingly important. Forthcoming sub-5 nm technology node requires a 20 nm interconnect half-pitch size, resulting in the conventional barrier and liner materials thicknesses of less than 4 nm. However, the traditional barriers like TaN/Ta occupy a significant portion of the interconnect cross-section, and this down-scaling reduces the Cu ion blocking efficiency. Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been recently explored as promising candidates for Cu diffusion barrier and liner applications. However, most 2D TMDs are grown at elevated temperatures (&gt;800°C) using chemical vapor deposition, making them incompatible with BEOL processes. Plasma-assisted growth can reduce the growth temperature, but poor conformality and plasma-induced defects remain a challenge. Furthermore, some 2D TMDs growth approaches can only deliver micrometer-scale flakes, and BEOL requires films that are uniform over large areas for circuit integration.<br/>We report a BEOL-compatible growth process of crystalline WS₂ thin films (~2 nm) on dielectric substrates <i>via</i> atomic layer deposition. This complete thermal growth technique offers precise thickness control and large-area conformality. We have successfully deposited high-quality WS₂ thin films on 2 cm x 2 cm SiO₂/Si substrates using an approach that is fully scalable to 8-inch wafers. The quality of the WS₂ thin film is confirmed by microscopic (atomic force microscopy and transmission electron microscopy) as well as spectroscopic (Raman spectroscopy, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and energy dispersive x-ray spectroscopy) measurements. Electrical characterization of the WS₂ thin films was used to evaluate their properties for diffusion barrier and liner applications. We will discuss the potential of the thermal ALD growth of 2D TMDs for interconnect scaling beyond the 5 nm node.