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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. References [1]International Technology Roadmap for Semiconductors—Interconnect, available at http://www.itrs.net/Links/2013ITRS/Home2013.htm. [2]Awano, et al., “Carbon Nanotubes for VLSI: Interconnect and Transistor Applications”, IEEE Proc., Vol. 98, No. 12, December 2010 [3]Whilhite, et al., “Metal–nanocarbon contacts”, Semicond. Sci. Technol., Vol. 29, 2014 [4]Christianzen, et al., “Via-depletion Electromigration In Copper Interconnects”, IEEE Trans. On Device And Materials Reliability, Vol. 6, No. 2, June 2006 [5]S. Vollebregt, et al., “Carbon nanotube vertical interconnects fabricated at temperatures as low as 350 C”, Carbon 71, 249 (2014). [6] A.P. Graham, et al., “How do carbon nanotubes fit into the semiconductor roadmap?”, Appl. Phys. A, Vol. 80, pp. 1141, 2005. [7]J. Dijon, et al., “Ultra-high density Carbon Nanotubes on Al-Cu for advanced Vias”, IEDM 2010.