Technologies for Realizing Carbon Nano-Tube (CNT) Vias Clarissa Cyrilla Prawoto 26 November 2014

Outline Challenges in via interconnect for next generation ICs Carbon Nano-Tube (CNT) via as one of the solutions Fabrication techniques to realize CNT vias Issues in CNT vias Conclusion

Challenges in Via Interconnect for Next Generation ICs In current technology: Cu and W Down scaling : Via cross-section area ↓ Current density ↑ Electromigration limits current density High aspect ratio is hard to achieve Need sidewall barrier layer → complexity Open circuit Current technology limit

CNT as Future Via Interconnect Material Carbon Nano-Tube (CNT) : Carbon based – rolled graphene Properties: High current carrying capability (10X Cu) → no electromigration Ballistic transport → Low resistance High via aspect ratio graphene Single Wall CNT Multi Wall CNT CNT via metal

CNT Via Fabrication Steps Standard via opening −TiN and Ta Thin film deposition −Nanoparticles deposition by sputtering Nanoparticles: Fe, Co, Ni As catalyst for CNT growth Conductivity α CNT density α -1 nanoparticle thickness −Bottom-up growth −Final structure: Nanoparticles on top of the grown CNT −Growth Temperature = 350 o C – 800 o C −Higher → lower R −Multiwall structure (MWNT) for metallic type

Issues: Resistance To achieve low resistivity comparable to Cu Need high CNT density Reduce catalyst thickness → reduce CNT diameter → increase density Limitation: Density can’t be increased indefinitely

Issues: Metal to CNT Contact High Resistance Interaction between Metal – CNT is not well understood End contact (a) vs Side contact (b) No resistance model yet Hard to measure and characterize

Issues: Compatibility to Silicon Technology Growth temperature of CNT > 400 o C To achieve low resistance growth rate proportional to temperature Need innovative integration techniques

Conclusion CNT could be the next generation via interconnect material Ballistic transport – Low resistance Able to handle high current density High aspect ratio achievable – bottom-up growth Carbon-based electronics Challenges: CNT density limitation – high resistance CNT-Metal contact High temperature process

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