At the 2025 IEEE International Interconnect Technology Conference (IITC), imec, a research and innovation hub in nanoelectronics and digital technologies, has presented Ru lines at 16nm pitch with average resistance as low as 656Ω/µm. The 16nm pitch metal lines were fabricated using a semi-damascene integration flow optimized for cost-effective manufacturability, making it an attractive approach for fabricating the first local interconnect metal layer of the A7 and beyond technology nodes.
Ruthenium (Ru) semi-damascene was originally proposed by imec as an attractive module approach to address the increasing resistance-capacitance (RC) delay concerns associated with Cu dual-damascene when metal pitches scale below 20nm. Semi-damascene is a two-level metallization module that starts with the direct etch of the first local interconnect metal layer (M0) and is potentially expandable to multiple layers.
In 2022, imec experimentally demonstrated direct etched low-resistance Ru lines at 18nm metal pitch and expanded the integration scheme towards a two-metal-level module using fully self-aligned vias (FSAVs).
Imec now presents 16nm pitch direct etched Ru lines with a record-low average resistance of 656Ω/µm. Forty percent of the 16nm pitch Ru line structures were shown to meet the resistance target (as predicted based on thin film resistivity), corresponding to 8nm-wide local interconnects. For the 18-22nm pitch range, full-wafer yields of 90% and higher were obtained.
The presented semi-damascene integration flow relies on a modified EUV-based self-aligned double patterning (SADP) approach—referred to as spacer-is-dielectric (SID) SADP—in combination with direct etching of Ru. Three key elements from the integration flow are critical to achieving low resistance values and ensuring cost-effective manufacturability.
The first element is the choice of cheap oxide and nitride-based materials for the hard masks, spacers and gap fill. Second is the implementation of a pattern inversion step in combination with an optimized SiO₂ gap fill. Third was an improved Ru etch step during which the oxidation of the SiN hard mask was minimized to avoid line bridge defectivity.
Seongho Park, nano-interconnect program director at imec, said, “Now that the industry is picking up Ru direct metal etch, imec is looking ahead to future generations and discussing further optimizations to its semi-damascene flow as well as new integration options. In an invited paper, imec shows advances in pillar-based FSAV approaches that are key to expanding the integration towards a two-metal-level scheme.
“In other papers presented at 2025 IITC, besides Ru patterning optimization, strategies to mitigate thermally induced morphology changes are investigated. Looking further ahead, imec experimentally demonstrates an epitaxially grown 25nm thin film of Ru to result in much lower resistive interconnects, approaching for the first time the bulk resistivity of Ru in the thin film regime.”
