Growth and Integration of High-Density CNT for BEOL Interconnects
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1079-N06-01
Growth and Integration of High-Density CNT for BEOL Interconnects Ainhoa Romo Negreira1,2, Daire J. Cott1,2, Anne S. Verhulst1,2, Santiago Esconjauregui1,2, Nicolo' Chiodarelli1,2, Johan Ek Weis1, Caroline M. Whelan1, Guido Groeseneken1,2, Marc Heyns1,3, Stefan De Gendt1,4, and Philippe M. Vereecken1 1 IMEC, Kapeldreef 75, Leuven, B-3001, Belgium 2 Department of Electrical Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 1, Leuven, B-3001, Belgium 3 Metallurgy and Materials Engineering Department, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44 bus 2450, Leuven, B-3001, Belgium 4 Chemistry Department, Katholieke Universiteit Leuven, Celestijnenlaan 200f- bus 2404, Leuven, B-3001, Belgium ABSTRACT The integration of high-density CNT bundles as via interconnects in a CNT/Cu-hybrid BEOL stack is evaluated. CNT via-conduits may greatly improve heat dissipation and as such lower interconnect resistance and improve electromigration resistance. Each carbon shell of the nanotube contributes to electrical and thermal conduction and densities as high as 5x1013 shells per cm2 are estimated necessary. CNT growth processes on BEOL compatible metals are presented with tube densities up to 1012cm-2 and shell densities approaching 1013 cm-2 on blanket substrates. Selective growth of CNT bundles with carbon shell densities around 1012cm-2 is demonstrated with high yield. Ohmic behavior of TiN/CNT/Ti contacts is shown with a CNT via resistivity of 1.2 mΩ cm. INTRODUCTION Carbon nanotubes (CNT) are one-dimensional hollow nanostructures with extreme aspect ratios and exceptional mechanical, thermal and electrical properties [1]. One could picture a CNT by rolled-up sheets of graphene: a single graphene layer forms a single-walled (SW-), a double-layer forms a double-walled (DW), and multiple layers form a multi-walled (MW) tube. A single CNT can be as narrow as 0.4nm for the smallest SW-CNT and several hundred nanometer in diameter for MW-CNT [2]. Electrical conductance of ideal metallic CNT is ballistic and thus independent of length in contrast to metal conductors such as copper where conductance is determined by electron scattering. In addition, CNT can carry extreme current densities up to 109 A/cm2 compared to about 106-107 A/cm2 for (capped) interconnect lines. Maybe even more important for interconnect applications is the high thermal conductivity which is expected to be 5 to 10 times higher than copper. In this paper, the possibility to replace copper via interconnects in the BEOL stack by bundles of densely-packed CNT will be presented. A CNT bundle can be considered a series of conducting shells in parallel and its resistance is determined by the total number of shells in the bundle. For example, a bundle of 0
two SW-CNT and two DW-CNT has a total of four CNT (N=4) and six shells ( ∑ nsCNT = 6 ), N
with nsCNT the number of shells in a particular CNT. For CNT with not too large diameter
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