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1018-EE10-07

High-Current Reliability of Carbon Nanofibers for Interconnect Applications Hirohiko Kitsuki1, Makoto Suzuki1, Quoc Ngo1,2, Kristofer Gleasson1, Alan M. Cassell2, Yusuke Ominami1, Christopher R. Moylan3, Jun Li2, and Cary Y. Yang1 1 Center for Nanostructures, Santa Clara University, Santa Clara, CA, 95053 2 Center for Advanced Aerospace Materials and Devices, NASA Ames Research Center, Moffett Field, CA, 94035 3 Department of Electrical Engineering, University of California-Santa Cruz, Santa Cruz, CA, 95064 ABSTRACT We present a high-current reliability study of carbon nanofibers (CNFs) for interconnect applications. In situ scanning transmission electron microscopy (STEM) reveals structural damage to CNFs after current stress. The effect of heat dissipation on the current capacity is also discussed by using different experimental configurations. Long-time reliability tests are performed with a vertical via interconnect structure, showing promising high reliability of CNF interconnects for future electronic devices. INTRODUCTION Carbon nanostructures including carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have recently been investigated as possible materials for integrated circuit interconnects [1,2] because of their chemically stable nature and high electrical and thermal conductivities. While CNTs have been well studied as an interconnect material, recent investigations reveal that lower growth temperature [3] and better directional control [1] have been achieved in CNFs, which are critical for realistic device fabrication processes. Comprehensive studies on current capacity in CNT systems have reported successive graphitic wall breakdown in multi-walled CNTs [4,5]. For CNF systems, we have recently reported high-field transport properties [6], demonstrating high-current reliability of a CNF via structure embedded in an oxide matrix for on-chip interconnects. However, the failure mode of CNFs due to excess current and the accompanying physical mechanisms still remain to be investigated. Since atomic-scale imaging using STEM shows that CNFs consist of cup-shaped graphitic layers stacked along the fiber axis [7], structural damage caused by high current stress is likely different from that of CNTs. In order to extend the application-driven development of carbon-based interconnects, we performed a detailed investigation of the current-carrying capacity and reliability of CNFs. Based on detailed characterization using in situ STEM before, during, and after current-induced breakdown of the device, we propose a model for current-induced breakdown in CNF structures. The role of local Joule heating process in the breakdown is also discussed. In addition, reliability measurements at room and elevated temperatures are performed to demonstrate the robust nature of the CNFs under high-current stress conditions.

EXPERIMENT Figure 1 illustrates our STEM imaging techniques for the current-induced breakdown of CNF. To investigate the detailed failure mechanism, a suspended CNF device structure between two e