Ruthenium Interconnect
Ruthenium (Ru) Interconnect — an emerging metal for the narrowest chip wires that promises superior performance at sub-10nm widths due to its short electron mean free path and ability to work without barrier liners.
Why Ruthenium?
- Short mean free path: ~6.7nm (vs Cu: ~39nm, Co: ~11.8nm)
- Shorter MFP → less resistivity increase from surface/grain boundary scattering at small dimensions
- No barrier needed: Ru doesn't diffuse through dielectrics → skip the TaN/Ta liner
- No seed layer needed: Can be deposited directly by CVD/ALD
- Barrier-free + seed-free → more metal in the same cross-section → lower actual resistance
Resistivity Crossover
| Wire Width | Cu + Barrier | Co | Ru |
|---|---|---|---|
| 20nm | ~4 μΩ·cm | ~8 μΩ·cm | ~10 μΩ·cm |
| 10nm | ~10 μΩ·cm | ~10 μΩ·cm | ~10 μΩ·cm |
| 7nm | ~15+ μΩ·cm | ~12 μΩ·cm | ~10 μΩ·cm |
- At ~10nm width: Ru becomes competitive with Cu
- Below 10nm: Ru wins due to minimal resistivity increase
Challenges
- Bulk Ru resistivity (7.1 μΩ·cm) is higher than Cu (1.7 μΩ·cm) — only wins at very small dimensions
- Deposition methods (CVD/ALD) need further optimization for void-free fill
- CMP of Ru is more difficult than Cu
- Limited production experience compared to 25+ years of Cu process maturity
Ruthenium represents the future of the finest metal layers — it's the leading candidate for sub-3nm node interconnects where copper simply can't perform.