Carbon Nanotube Interconnects for End-of-Roadmap Semiconductor Technology Nodes

Advances in semiconductor technology due to aggressive downward scaling of on-chip feature sizes have led to rapid rises in resistivity and current density of interconnect conductors. As a result, current interconnect materials, Cu and W, are subject to performance and reliability constraints approaching or exceeding their physical limits. Therefore, alternative materials such as nanocarbons, metal silicides, and Ag nanowires are actively considered as potential replacements to meet such constraints. Among nanocarbons, carbon nanotube (CNT) is among the leading replacement candidate for on-chip interconnect vias due to its high aspect-ratio nanostructure and superior currentcarrying capacity to those of Cu, W, and other potential candidates. However, contact resistance of CNT with metal is a major bottleneck in device functionalization. To meet the challenge posed by contact resistance, several techniques are designed and implemented. First, the via fabrication and CNT growth processes are developed to increase the CNT packing density inside via and to ensure no CNT growth on via sidewalls. CNT vias with cross-sections down to 40 nm 40 nm are fabricated, which have linewidths similar to those used for on-chip interconnects in current integrated circuit manufacturing technology nodes. Then the via top contact is metallized to increase the total CNT area interfacing with the contact metal and to improve the contact quality and reproducibility. Current-voltage characteristics of individual fabricated CNT vias are measured using a nanoprober and contact resistance is extracted with a first-reported contact resistance extraction scheme for 40 nm linewidth. Based on results for 40 nm and 60 nm top-contact metallized CNT vias, we demonstrate that not only are their current-carrying capacities two orders of magnitude higher than their Cu and W counterparts, they are enhanced by reduced via resistance due to contact engineering. While the current-carrying capacities well exceed those projected for end-of-roadmap technology nodes, the via resistances remain a challenge to replace Cu and W, though our results suggest that further innovations in contact engineering could begin to overcome such challenge

Electrical and Structural Analysis of CNT-Metal Contacts in Via Interconnects

Vertically aligned carbon nanotubes grown by plasmaenhanced chemical vapor deposition offer a potentially suitable material for via interconnects in next-generation integrated circuits. Key performance-limiting factors include high contact resistance and low carbon nanotube packing density, which fall short of meeting the requirements delineated in the ITRS roadmap for interconnects. For individual carbon nanotube s, contact resistance is a major performance hurdle since it is the dominant component of carbon nanotube interconnect resistance, even in the case of vertically aligned carbon nanotube arrays. In this study, we correlate the carbon nanotube-metal interface nanostructure to their electrical properties in order to elucidate growth parameters that can lead to high density and low contact resistance and resistivity

Metal-CNT contacts

To realize carbon nanotube (CNT) as on-chip interconnect materials, the contact resistance stemming from the metal-CNT interface must be well understood and minimized. In this study, we compile existing published results and understanding for two metal-CNT contact geometries, sidewall or side contact and end contact, and address their key performance characteristics. Side contacts typically result in contact resistances \u3e 1 kΩ, whereas end contacts, such as that for as-grown vertically aligned CNTs on a metal underlayer, can be substantially lower. The lower contact resistance for the latter is due largely to strong bonding between edge carbon atoms with atoms on the metal surface, while carrier transport across a side-contacted interface via tunneling is generally associated with high contact resistance. Analyses of high-resolution images of interface nanostructures for various metal-CNT structures, along with their measured electrical characteristics, provide the necessary knowledge for continuous improvements of techniques to reduce contact resistance. Such contact engineering approach is described for both side and end-contacted structures

On-Chip Interconnect Conductor Materials for End-of-Roadmap Technology Nodes

A comprehensive review of challenges and potential solutions associated with the impact of downscaling of integrated circuit (IC) feature sizes on on-chip interconnect materials is presented. The adoption of Moore\u27s Law has led to developments and manufacturing of transistors with nanoscale dimensions, faster switching speeds, lower power consumption, and lower costs in recent generations of IC technology nodes. However, shrinking dimensions of wires connecting transistors have resulted in degradations in both performance and reliability, which in turn limit chip speed and lifetime. Therefore, to sustain the continuous downward scaling, alternative interconnect conductor materials to replace copper (Cu) and tungsten (W) must be explored to meet and overcome these challenges

Fabrication and characterization of carbon nanotube interconnect vias for next-generation technology nodes

We report the electrical characteristics of carbon nanotube (CNT) vias of diameters down to 30 nm for potential application as on-chip interconnects. A CNT packing or areal density of 1.2×1011 /cm2 inside a via has been obtained. The measured resistances of the CNT vias are used to project via resistances in sub-30 nm technology nodes

Contact engineering for nanocarbon interconnects

Electron-beam-induced deposited-tungsten (EBID-W) technique is used to fabricate contacts for carbon nanofiber (CNF) horizontal interconnect and carbon nanotube (CNT) vertical vias to improve the contact resistances at the nanocarbon-metal electrodes

Nanocarbon via interconnects

The continuous downward scaling in integrated circuit (IC) technologies has led to rapid shrinking of transistor and interconnect feature sizes. Scaling causes reduction in interconnect linewidth, which leads to surge in resistance due to increased contributions from grain boundary and surface scattering of electrons in the metal lines. Further, current density inside interconnects is also enhanced by the reduced linewidth and is approaching or exceeding the current-carrying capacity of the existing interconnect metals, copper (Cu) and tungsten (W). The resulting failure due to electromigration presents a critical challenge for end-of-roadmap IC technology nodes. Therefore, alternative materials such as nanocarbons and silicides are being investigated as potential replacements for Cu and W as they have superior electrical and mechanical properties in the nanoscale. In this review, the electrical properties of nanocarbons, in particular carbon nanotubes (CNTs), are examined and their performance and reliability in the sub-100 nm regime are assessed. Further, the measured properties are used to project 30 nm CNT via properties, which are compared with those of Cu and W

Electrical properties of carbon nanotube via interconnects for 30 nm linewidth and beyond

The continuous downward scaling in integrated circuit (IC) technologies has led to rapid shrinking of transistor and interconnect feature sizes. While scaling benefits transistors by increasing the switching speed and reducing the power consumption, it has an adverse impact on interconnects by degrading its electrical performance and reliability. Scaling causes reduction in interconnect linewidth, which leads to surge in resistance due to increased contributions from grain boundary and surface scattering of electrons in the metal lines. Further, current density inside interconnects is also enhanced by the reduced linewidth and is approaching or exceeding the current-carrying capacity of the existing interconnect metals, copper (Cu) and tungsten (W). The resulting failure due to electromigration presents a critical challenge for end-of-roadmap IC technology nodes. Therefore, alternative materials such as nanocarbons and silicides are being investigated as potential replacements for Cu and W as they have superior electrical and mechanical properties in the nanoscale. In this review, the electrical properties of nanocarbons, in particular carbon nanotubes (CNTs), are examined and their performance and reliability in the sub-100 nm regime are assessed. Further, the measured properties are used to project 30 nm CNT via properties, which are compared with those of Cu and W

High-frequency behavior of one-dimensional nanocarbons

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are potential materials for the most advanced silicon devices and circuits due to their excellent electrical properties such as high current capacity and tolerance to electromigration. In addition, at high frequencies, these materials exhibit transport behavior which holds promise for applications as on-chip interconnects

RF characteristics of one-dimensional nanocarbons

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are potential materials for the most advanced silicon devices and circuits due to their excellent electrical properties such as high current capacity and tolerance to electromigration. In addition, at high frequencies, these materials exhibit transport behavior which holds promise for applications as on-chip interconnects