Interconnect building blocks taking shape for sub-20-nm node

Zsolt Tokei and Andreas Schulze -December 05, 2012

Patterning schemes, including multiple patterning and extreme-ultraviolet demonstrators using advanced low-k approaches, are important vehicles for exploring impacts on wire-signaling scenarios and interconnect reliability. Imec has demonstrated dual-damascene interconnects using EUV lithography and a dielectric with a k value of 2.3.

At the same time, LELE (litho-etch-litho-etch) and SADP (self-aligned double patterning) schemes were investigated. LELE can be deployed for local interconnects at the 20-nm node by splitting the IC layout for the two patterning steps. Beyond that, SADP is required to eliminate overlay issues, although further patterning steps are necessary for selecting and connecting only the wires functional to the design. Because of their resolution, single- or multiple-patterning EUV wires remain attractive for future nodes.

As dielectric constants are scaled, assessing the intrinsic reliability limits for dielectrics down to a k value of 2.0 becomes imperative. By comparing organosilicate glass films with k values of 2.0, 2.5, 2.8, and 3.0, Imec showed that intrinsically, even films with a k value of 2.0 can meet a 10-year lifetime.

Meanwhile, researchers are exploring the use of CNTs (carbon nanotubes) as an alternative contact material for copper or tungsten at levels where those classical materials cannot meet the required specifications. Imec researchers have characterized CNTs at the wafer level, obtaining full-wafer resistance data, and have been able to improve yields by applying a top contact clean.

This tomogram of multiwall CNTs is reconstructed from 2-D scans by interpolation.
The surrounding oxide (purple) is displayed as semitransparent.

Imec has also presented an innovative metrology for obtaining structural and electrical information on individual CNTs integrated in contact holes simultaneously at the nanoscale. The technique uses a slice-and-view approach based on electrical atomic-force microscopy. Material removal through successive scanning using doped, ultra-sharp full-diamond probes, manufactured in-house, enables Imec researchers to acquire two-dimensional (2-D) resistance maps originating from different depths on CNT-based interconnects. A 3-D representation (tomogram) is obtained by stacking and interpolating the 2-D resistance maps.

In this way, besides structural information, the resistivity as well as the contact resistance between the CNT and the bottom electrode can be quantitatively determined. These are considered important parameters for the final fabrication and integration of CNTs in future integrated circuits.

1. Most of this work was presented at the 2012 International Interconnect Technology Conference.

2. Schulze, Andreas, et al., "Electrical tomography using atomic force microscopy and its application towards carbon nanotube0based interconnects," Nanotechnology 23:30, 2012.

Zsolt Tokei is program director for nanointerconnects at Imec (Eindhoven, Netherlands). He earned a master of science degree in physics in 1994 from Kossuth University (Debrecen, Hungary). In the framework of a co-directed thesis between that university and the University of Aix Marseille III (France), he obtained his PhD in physics and materials science in 1997. Since joining Imec in 1999, he has worked on such interconnect issues as metallization, electrical characterization, interconnect scaling, and dielectric reliability. He has authored or co-authored more than 180 published works in international scientific journals and conference proceedings.

Andreas Schulze received his bachelor and master of science degrees in electrical engineering from Dresden University of Technology (Germany) in 2004 and 2008, respectively. He is working toward a doctoral degree under the supervision of professor Wilfried Vandervorst at Imec and KU Leuven (Belgium), focusing on two- and three-dimensional dopant and conductivity profiling in confined volumes. He has first-authored four peer-reviewed journal and conference published works and has co-authored 20 scientific papers that have appeared in top-tier journals and international conference proceedings.

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