1. Carbon Nanotube Vias
By: Rhesa Nathanael

2. Outline What are vias? Why carbon nanotubes for vias?
Fabrication sequence.
Characterization results.
Issues with current efforts.
Summary & Conclusion.

3. What Are Vias?
ITRS, 2007
Intel, IEDM 2007

4. Carbon Nanotubes for Vias
Copper:
Resistance ↑ with scaling.
Electromigration.
Carbon Nanotubes:
Ballistic transport.
Very large resistance to electromigration.
R = h/4e2 = 6.45kΩ
Allows current densities > 109 A/cm2

5. CNT Damascene Process Via hole formation
TaN/Ta barrier layer TiN contact layer Co catalyst nanoparticles
Nanotube growth
CVD (C2H2 + Ar at 1kPa, 450ºC)
SOG coating
CMP nanotubes CMP TiN, TaN/Ta
Ti top contact layer Ta barrier layer Cu interconnect

6. Characterization Results
Ballistic transport
Rc = contact resistance = 0.5kΩ
RCNT = nanotube resistance
RQ = quantum resistance
nCNT = number of shells = 7
λCNT = electron mean free path
H = via height
h = Planck’s constant
e = electron charge
CNT density = 3x1011 cm-2
Mean free path = 80nm  32nm Technology Node (2013)

7. Issues with Current Efforts
Most fabrication efforts  MWCNT.
Most characterization efforts  electrical properties.
CNT via resistance within an order of magnitude of Cu via has been demonstrated.
More effort needed on SWCNT & thermal characterization.
Local interconnect
SWCNT vs. Cu
MWCNT

8. Thermal & Self-Heating Issues
Thermal contact resistance + Joule heating at metal CNT contact
Conclusion:
MWCNT thermal properties inferior to Cu & SWCNT

9. Summary & Conclusion Carbon nanotube for vias: Damascene process.
Ballistic transport.
Electromigration resistance.
Damascene process.
Mean free path 80nm  32nm technology node.
Efforts misplaced?
SWCNT vs. MWCNT.
More careful thermal characterization of CNT vias needed.
Replace Cu?
Dense SWCNT bundles.
Good electrical and thermal contact.

10. References
[1] M. Nihei, et al., “Electrical performance of carbon nanotube via interconnects fabricated by novel damascene process,” International Interconnect Technology Conference 2007, pp
[2] H. Li, et al., “Carbon nanotube vias: a reality check,” Inernational Electron Devices Meeting 2007 pp
[3] B. Q. Wei, et al., “Reliability and current carrying capacity of carbon nanotubes,” App. Phys. Lett., vol. 79, no. 8, pp , 2001