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Structural and electrical characterization of carbon nanotube interconnects by combined transmission electron microscopy and scanning spreading resistance microscopy Thomas Hantschel1, Xiaoxing Ke2, Nicolo’ Chiodarelli1,3, Andreas Schulze1,4, Hugo Bender1, Pierre Eyben1, Sara Bals2, Wilfried Vandervorst1, 4 1 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium. 2 EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium 3 Department of Electrical Engineering, and 4Instituut voor Kern- en Stralingsfysica, K. U. Leuven, B-3001 Leuven, Belgium. ABSTRACT The use of carbon nanotubes (CNT) as interconnects in future integrated circuits (IC) is being considered as a replacement for copper. As this research needs also innovative metrology solutions, we have developed a combined approach for the plane-view analysis of CNT integrated in contact holes where transmission electron microscopy (TEM) enables the quantitative measurement of density and structure of the CNT and where scanning spreading resistance microscopy (SSRM) is used to electrically map the distribution of the CNT. This paper explains the used methodologies in detail and presents results from 300 nm diameter contact holes filled with CNT of 8-12 nm in diameter and a density of about 2 x 1011 cm-2. INTRODUCTION Carbon nanotubes (CNT) are intensively being investigated as a replacement for copper in advanced interconnect structures. Early work demonstrated CNT with 50-100 nm in diameter integrated in 2 µm wide contact holes [1]. Recently, a CNT density of 2 x 1011 cm-2 was shown for 300 nm diameter contact holes [2]. The highest CNT density demonstrated so far is 2.5 x 1012 cm-2 for 1 µm diameter contact holes [3]. The physical and electrical characterization of such structures is extremely challenging but essential for providing feedback for further process optimization. Transmission electron microscopy (TEM) provides high spatial resolution for studying the physical CNT structure in detail. For this, a thin vertical slice of the contact hole is prepared by focused ion beam (FIB) and is then inspected by TEM [4]. This cross-sectional inspection is well suited for contact holes with a low density of CNT but a high density leads to superposition effects in projection preventing the investigation of the shell structure. A pick-andplace approach has been developed whereby individual CNT and CNT bundles are removed from the contact and put onto a TEM grid [5]. TEM tomography of CNT in contact holes has been demonstrated as well but is limited in the attainable resolution [6]. A TEM method for analyzing high densities of CNT in contact holes is therefore wanted. Furthermore, the assessment of the electrical properties of such CNT is so far only indirectly possible by probing with a large top metal contact. An electrical method is hence needed which can electrically map CNT in contact holes. Scanning spreading resistance microscopy (SSRM) looks suited for this task. It is routinely used for two-dimensional (2D) carrier profiling of transistor structures with n