Ruthenium (Ru) is rapidly emerging as a critical material for next-generation Back-End-of-Line (BEOL) interconnects in advanced semiconductor manufacturing. As copper (Cu) interconnects scale down, traditional diffusion barriers (like TaN) take up too much volume, increasing resistance. Ru serves as a direct, thin, and reliable alternative, enabling continued scaling below 5nm nodes. Key Applications of Ru in Next-Generation BEOL Barrierless Conductor/Liner Material:
Direct-to-Dielectric Contact: Ru can be deposited directly on dielectric materials (e.g., via Atomic Layer Deposition – ALD) and acts as its own diffusion barrier. This eliminates the need for separate, high-resistance TaN/Ta barriers.
Lower Electromigration: Ru has a high melting point and good adhesion to both Cu and dielectrics, enhancing electromigration resistance compared to traditional liners, which is critical for electromigration reliability in narrow, high-current density lines.
Reduced Resistance: Using Ru as a liner or a partial seed layer allows for thinner barrier thicknesses (under 2 nm), leaving more room for the conductive material itself, thus lowering overall resistivity. Area-Selective ALD (AS-ALD) Barriers:
Via Optimization: Instead of blanket deposition, ALD allows Ru to be deposited selectively at the bottom of trenches or vias.
“Bottomless” Barriers: Selective deposition enables “bottomless” barriers, where the barrier is only on the sidewalls (preventing sidewall diffusion) but not on the bottom surface, which reduces via contact resistance and improves reliability. Semi-Damascene Integrated Schemes:
Air Gaps and Patterning: In semi-damascene approaches, Ru is used as the conductor/barrier layer, allowing the fabrication of air gaps between metal lines.
Reduced Capacitance ©: This reduces the RC delay (resistance × capacitance) because air has a lower dielectric constant than solid ILDs, which is crucial for high-speed performance, especially when using high-aspect-ratio metal lines. Multilayered Hybrid Barriers:
Ru/MgO/Ta Stacks: Research shows that ultra-thin tri-layer structures, such as Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm), can act as effective barriers, with Ru providing superior structural stability at high temperatures. Benefits Over Traditional Materials
Conformality: ALD Ru offers excellent conformity, which is superior to PVD (Physical Vapor Deposition) techniques used for traditional TaN/Ta, allowing for uniform coatings in high-aspect-ratio trenches.
Scaling: As interconnects become smaller, the resistance of the barrier layer becomes more dominant. Ru’s ability to act as a combined barrier and liner helps manage this resistance bottleneck.
If you can tell me the specific node (e.g., 5nm, 3nm) or device type (e.g., DRAM, Logic) you’re interested in, I can provide more targeted details on current integration challenges.
Area-selective ALD of diffusion barriers for via optimization