Carbon nanotube processing and chemistry for electronic interconnect applications

Abstract

Carbon nanotubes possess many properties that are ideally suited for electronic applications, such as metallic/semiconducting behavior and ballistic transport. Specifically, in light of mounting concerns over the increasing resistivity of the state-of-the-art interconnect material, copper, and the associated rise in interconnect power consumption and delay, carbon nanotubes are seen as a potential candidate for a future interconnect material. However, current integrated circuit manufacturing processes are ill-equipped to deal with discrete nanomaterials such as carbon nanotubes. In this thesis, several methods for the deposition and directed assembly of as-grown carbon nanotubes are examined. A metal/CNT-film structure is proposed as a relatively simple method to incorporate CNTs into an interconnect structure. Resistance comparisons between structures formed from films of Pd and randomly-aligned SWNTs and control Pd structures are highly variable, indicating that Pd/CNT processing techniques need significant refinement. However, comparisons between structures fabricated with films of randomly-aligned SWNTs and Pd control resistors show that randomly-aligned SWNT films are not competitive with pure metal structures, due to the low packing density and alignment inherent to these films. Finally, a covalent chemical CNT functionalization method to improve CNT handling without degradation in electronic conductivity is examined. SWNTs functionalized with this conductance-preserving carbene-CNT reaction, first reported by Lee et al [1], show resistance about an order of magnitude higher than unfunctionalized SWNTs but also an order of magnitude lower than SWNTs functionalized via a more typical covalent chemistry. In addition, evidence for controllable Fermi level shifting is seen for carbene-functionalized SWNTs, with shifts of up to 100 mV observed, and varying depending on the extent of functionalization and type of carbene group used.