Session:

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 (>800°C), making them incompatible with BEOL applications. Plasma-assisted growth can reduce growth temperatures, but poor conformality and plasma-induced defects remain challenges.
Here, we report a complete thermal (no plasma assistance) atomic layer deposition (ALD) process for the deposition of crystalline WS₂ growth at <450 °C, suitable for BEOL integration. The process yields layer-controlled conformal (>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 via 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 via thermal ALD are promising building blocks for BEOL applications beyond the 5 nm nodes.

Co-Author(s): Tan Hao (NUS Singapore), Hippolyte Astier (NUS Singapore), Soumyadeep Sinha (NUS Singapore), Chandan Das (Applied Materials, Inc.), John Sudijono (Applied Materials, Inc.), Silvija Gradečak (NUS Singapore)

Muhammed Juvaid Mangattuchali

NUS Singapore

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