Ramsey Stevens

Bottom-up approach for carbon nanotube interconnects

We report a bottom-up approach to integrate multiwalled carbon nanotubes (MWNTs) into multilevel interconnects in silicon integrated-circuit manufacturing. MWNTs are grown vertically from patterned catalyst spots using plasma-enhanced chemical vapor deposition. We demonstrate the capability to grow aligned structures ranging from a single tube to forest-like arrays at desired locations. SiO2 is deposited to encapsulate each nanotube and the substrate, followed by a mechanical polishing process for planarization. MWNTs retain their integrity and demonstrate electrical properties consistent with their original structure.

Multilayered metal catalysts for controlling the density of single-walled carbon nanotube growth

Abstract Ion beam sputtering has been used for the sequential deposition of metal multilayers on various substrates to control the density of single-walled carbon nanotubes (SWNTs) synthesized by chemical vapor deposition. Underlayers (10–20 nm) of Al and Ir were found to activate the substrates for SWNT growth with Fe as active catalyst. Adding Mo as co-catalyst gives increased production of SWNTs and the density can be controlled by varying the thickness of the different metal layers. High-resolution transmission electron microscopy and Raman scattering are used to characterize the SWNTs.

Electronic properties of multiwalled carbon nanotubes in an embedded vertical array

We demonstrate integration of carbon nanotubes into large scale vertically aligned electrode arrays, by filling the as-grown samples with conformal SiO2 using chemical vapor deposition. Subsequent mechanical polishing yields a flat surface with only the very ends of the nanotube array exposed. The electronic properties of individual carbon nanotubes in the array are measured using current-sensing atomic force microscopy. These vertical nanotube arrays are suitable for fabricating various electronic devices and sensors.

Carbon nanotube tip probes : stability and lateral resolution in scanning probe microscopy and application to surface science in semiconductors

In this paper we present results on the stability and lateral resolution capability of carbon nanotube?(CNT) scanning probes as applied to atomic force microscopy?(AFM). Surface topography images of ultra-thin films (2-5?nm thickness) obtained with AFM are used to illustrate the lateral resolution capability of single-walled carbon nanotube probes. Images of metal films prepared by ion beam sputtering exhibit grain sizes ranging from greater than 10?nm to as small as ~2?nm for gold and iridium respectively. In addition, the imaging stability and lifetime of multi-walled carbon nanotube scanning probes are studied on a relatively hard surface of silicon nitride (Si3N4). AFM images of the Si3N4 surface collected after more than 15?h of continuous scanning show no detectable degradation in lateral resolution. These results indicate the general feasibility of CNT tips and scanning probe microscopy for examining nanometre-scale surface features of deposited metals as well as non-conductive thin films. AFM coupled with CNT tips offers a simple and nondestructive technique for probing a variety of surfaces, and has immense potential as a surface characterization tool in integrated circuit manufacture.

Improved fabrication approach for carbon nanotube probe devices

An improved process is developed for simple and efficient fabrication of carbon nanotube probe devices. This process requires only two steps to make nanotube probes. First a nanotube cartridge is created using chemical vapor deposition, then the nanotubes are transferred from the cartridge to a device using an electric field. Multiwall nanotube probes are made into different device geometries in this approach. Their applications are illustrated by atomic force microscopy imaging of the surface of a terrestrial rock granule selected to simulate the morphology and consistency of a grain of Mars dust and nanolithography on a silicon substrate.

Carbon nanotube scanning probe for profiling of deep-ultraviolet and 193 nm photoresist patterns

The continual scaling down of complementary metal–oxide semiconductor feature size to 100 nm and below necessitates a characterization technique to resolve high-aspect-ratio features in the nanoscale regime. We report the use of atomic force microscopy coupled with high-aspect-ratio multiwalled carbon nanotube (MWCNT) scanning probe tip for the purpose of imaging surface profile of photoresists. MWCNT tips of 5–10 nm in diameter and about a micron long are used. Their exceptional mechanical strength and ability to buckle reversibly enable resolution of steep, deep nanoscale features. Images of photoresist patterns generated by 257 nm interference lithography as well as 193 nm lithography are presented to demonstrate MWCNT scanning probe tips for applications in metrology.

Vertically aligned carbon nanotube heterojunctions

The bottom-up fabrication and electrical properties of end-to-end contacted multiwalled carbon nanotube (MWCNT) heterojunctions are reported. The vertically aligned MWCNT heterojunction arrays are formed via successive plasma-enhanced chemical vapor deposition processing to achieve the layered junction architecture. Electron microscopy and current-sensing atomic force microscopy are used to reveal the physical nature of the junctions. Symmetric, nonlinear I–V curves of the as-fabricated junctions indicate that a tunnel barrier is formed between the end-to-end contacted MWCNTs. Repeated high bias I–V scans of many devices connected in parallel fuses the heterojunctions, as manifested by a shift to linear I–V characteristics.The bottom-up fabrication and electrical properties of end-to-end contacted multiwalled carbon nanotube (MWCNT) heterojunctions are reported. The vertically aligned MWCNT heterojunction arrays are formed via successive plasma-enhanced chemical vapor deposition processing to achieve the layered junction architecture. Electron microscopy and current-sensing atomic force microscopy are used to reveal the physical nature of the junctions. Symmetric, nonlinear I–V curves of the as-fabricated junctions indicate that a tunnel barrier is formed between the end-to-end contacted MWCNTs. Repeated high bias I–V scans of many devices connected in parallel fuses the heterojunctions, as manifested by a shift to linear I–V characteristics.

Nanomanipulation and fabrication by ion beam molding

Nanoscale manipulation is a basic ability needed to realize many of the nanotechnology applications. We demonstrate an ion bean molding technique to shape the configuration of nanostructures. As an example, the native curvature of a carbon nanotube in an atomic force microscope tip and its undesirable angle with respect to the surface are removed by this technique to render the nanotube straight. The straightened nanotube is effectively used in a semiconductor profilometry application. The ion beam molding technique is also shown to be effective in creating a desirable net shape of nanotubes. As mechanical deformation determines electrical and other properties of nanotubes, such manipulation may be of use in nanodevice fabrication.