Materials for Micro and Nano Systems - Carbon Nanotube Growth for I.C. Interconnects

Carbon Nanotube Growth for I.C. Interconnects

G.D. Nessim, Y. Wang, A.J. Hart, D. Acquaviva, J. Oh, J.S. Kim, C. Morgan, N. Abate, M. Seita, C.V. Thompson
Sponsorship: SRC/FCRP IFC, Intel

As integrated circuit technology is developed at dimensions below 32 nm, carbon nanotubes (CNTs) represent an ideal replacement for copper interconnects as they can carry higher current densities, do not need liners, and do not suffer from electromigration. However, fabrication issues such as growing the desired type of CNTs, using CMOS-compatible processes (e.g., ideally at temperature below 400°C) and making electrical contacts and interconnections, remain major technical challenges. For electrical applications, it is important to grow CNTs on conductive substrate [1, 2]. Using appropriate catalyst/substrate metallic thin films, we have grown verticallyaligned, crystalline CNTs using thermal chemical vapor deposition at 475°C (Figure 1). Preliminary electrical measurements show ohmic contact of the CNTs with the metallic substrate.

We have also grown CNTs on conductive substrates into an insulating alumina scaffold with regularly spaced pores (Figure 2). The insulating scaffold is fabricated using interference lithography and anodization of aluminum. This structure simulates an array of nanometer-scale vias filled with CNTs. In order to have CNTs with uniform height (length) and to make electrical contact with all the walls in the multi-wall tubes, we ion-milled the tops after CNT growth. The electrical properties of these CNTs can be collectively characterized through deposition of a conducting overlayer on all the CNTs or individually characterized using an AFM on uncapped CNTs. We plan to characterize electrical properties as a function CNT diameter and length and as a function of contact metallurgy.

Figure 1: Carpet of vertically-aligned CNTs on conductive substrate grown at 475°C (scale bar 500 nm). The catalyst/underlayer system is Fe/Ta. The HRTEM image on the inset shows the crystalline nature of the CNTs (scale bar 5 nm).

Figure 2: The CNTs grown into alumina scaffold with pores regularly spaced. The CNTs are flush with the top surface after ion milling. The inset shows the CNTs prior to ion milling.

References

[1] H.T. Ng, B. Chen, J.E. Koehne, A.M. Cassell, J. Li, J. Han, and M. Meyyappan, “Growth of carbon nanotubes: A combinatorial method to study the effects of catalysts and
underlayers,” Journal of Physical Chemistry B, vol. 107, no. 33, pp. 8484-8489, 2003.
[2] S. Talapatra, S. Kar, S.K. Pal, R. Vajtai, L. Ci, P. Victor, M.M. Shaijumon, S. Kaur, O. Nalamasu, and P.M. Ajayan, “Direct growth of aligned carbon nanotubes on bulk metals,”
Nature Nanotechnology, vol. 1, no. 2, pp. 112-116, 2006.