Revealing the Origins of Thermally Induced Anomaly in 18 nm Pitch Ruthenium Nanointerconnects on 300 mm Wafers

With copper (Cu) interconnect scaling approaching critical limits, ruthenium (Ru) has emerged as a promising candidate for next-generation nanointerconnects. This work investigates the impact of thermal budget on Ru nanointerconnects with 18-22 nm metal pitch on 300 mm industry-grade wafers through post-etch annealing. The experiments reveal a 10% drop in the line resistance along with an anomalous cylinderization of Ru sidewalls, which triggers multipoint line shorts across wafers as observed by transmission electron microscopy (TEM), thereby lowering yield. To reveal its origin, AStar TEM (automated crystal orientation and phase mapping) guided atomistic investigation is performed based on density functional theory (DFT), machine learned forcefield molecular dynamics (MLFF-MD), and GPU accelerated DFT-lattice kinetic Monte Carlo code. DFT-climbing image nudge elastic band (CINEB) and MLFF-MD simulations demonstrate that Ru nanointerconnect grain edges trigger intersurface self-diffusion from the out-of-plane Ru(0002) surface to sidewall surfaces (Ru(1100)T1 and Ru(1120)). Despite bulk Ru's low atomic self-diffusion coefficient (∼1.83 × 10⁻⁴³ m² s⁻¹ at 420 °C), the atomic arrangements of Ru(1100)T1 and Ru(1120) sidewall surfaces dramatically enhance atomic (5.23 × 10⁻¹⁷ m² s⁻¹ at 420 °C) and adatom (3.92 × 10⁻¹³ m² s⁻¹ at 420 °C) self-diffusion coefficients, respectively. Over time, Ru atoms self-diffuse and accumulate on sidewall surfaces, causing cylinderization, consistent with experimental observations. This work identifies a previously unrecognized manufacturing and reliability challenge in Ru nanointerconnects and reveals its atomistic origins, providing insights of direct relevance to industry for transition from Cu to Ru in future ultrascaled nanointerconnects at Angstrom technology nodes.