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Title: Development of aligned carbon nanotubes for interconnects applications
Authors: Lu, Jingyu.
Keywords: DRNTU::Engineering::Electrical and electronic engineering::Microelectromechanical systems
DRNTU::Engineering::Materials::Nanostructured materials
Issue Date: 2012
Source: Lu, J. (2012). Development of aligned carbon nanotubes for interconnects applications. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: The demand for faster, cheaper, more compact and multifunctional electronic products has been pushing the dimensions of transistors and interconnects towards the physical limit, various problems arise to threaten the reliability of conventional copper interconnects, including the limited current carrying capacity and evident electromigration. The exceptional physical and chemical properties of the carbon nanotube (CNT) make it a promising candidate as the future interconnect material. However, the development of CNT interconnects has long been impeded by the strong CNT-substrate interaction and the poor process compatibility with semiconductor technologies. This thesis reports the development of aligned CNTs for interconnects applications. Vertically aligned and horizontally suspended CNTs were grown with conventional chemical vapor deposition (CVD) method, and a novel nano Czochralski (CZ) mechanism was proposed to explain the catalytic growth of CNTs. In addition, to improve the process compatibility with the semiconductor technologies, the localized growth of CNTs was demonstrated. Horizontally suspended CNTs were grown from selected silicon trench sidewalls. A key process is to deposit the Fe catalyst layer onto these sidewalls by the tilted electron beam evaporation technique, or to pattern the Fe layer onto these sidewalls via a shadow mask placed on top of the trenches. The deflection of CNT bundles was analyzed with a CNT cantilever model, and the horizontal suspension of these CNTs was mainly attributed to the van der Waals attraction between densely packed CNTs. These results will accelerate the development of CNTs as horizontal interconnects. A novel nano CZ model was proposed to describe the catalytic growth of CNTs. The model regards the catalytic growth of a CNT as a CZ process taking place on the nano scale, thus a chiral CNT grows in a screw extrusion manner instead of linear extrusion as generally assumed, and an equation was deduced to predict the chiral index of the CNT. The model was echoed by the experimental evidence of the uneven longitudinal structural quality distribution in CNTs, which was attributed to the dynamic generation-reconstruction-diffusion (GRD) of defects during the CNT growth. The nano CZ mechanism may shed light on the chirality, quality and property control of CNTs, thus facilitating their applications in interconnects. To improve the CNT process compatibility with the semiconductor technologies, the localized growth of CNTs was developed with microheater devices. A physical model for the local heating effect was built, and a governing equation was deduced to approximate the radial temperature profile in an ideal microheater device, and to identify the key parameters affecting the local heating effect. The microheater devices were fabricated with micromachining and microfabrication technologies, and they were used to grow both vertically aligned and horizontally suspended CNTs locally. The length and quality of the resultant CNTs exhibit strong dependence on the local growth temperatures.
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