Letter

Nature 447, 299-302 (17 May 2007) | doi:10.1038/nature05826; Received 18 August 2006; Accepted 30 March 2007

Annealing-induced interfacial toughening using a molecular nanolayer

Darshan D. Gandhi1, Michael Lane3, Yu Zhou2, Amit P. Singh1, Saroj Nayak2, Ulrike Tisch4, Moshe Eizenberg4 & Ganapathiraman Ramanath1

  1. Materials Science & Engineering Department,
  2. Physics Department, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
  3. IBM Microelectronics, T.J. Watson Research Center, Yorktown Heights, New York 10598, USA
  4. Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel

Correspondence to: Ganapathiraman Ramanath1 Correspondence and requests for materials should be addressed to G.R. (Email: ramanath@rpi.edu).

Self-assembled molecular nanolayers (MNLs) composed of short organic chains and terminated with desired functional groups are attractive for modifying surface properties for a variety of applications. For example, organosilane MNLs are used as lubricants1, in nanolithography2, for corrosion protection3 and in the crystallization of biominerals4. Recent work has explored uses of MNLs at thin-film interfaces, both as active components in molecular devices5, and as passive layers, inhibiting interfacial diffusion6, 7, 8, promoting adhesion9, 10 and toughening brittle nanoporous structures11. The relatively low stability of MNLs on surfaces at temperatures above 350–400 °C (refs 12, 13), as a result of desorption14 or degradation, limits the use of surface MNLs in high-temperature applications. Here we harness MNLs at thin-film interfaces at temperatures higher than the MNL desorption temperature to fortify copper–dielectric interfaces relevant to wiring in micro- and nano-electronic devices. Annealing Cu/MNL/SiO2 structures at 400–700 °C results in interfaces that are five times tougher than pristine Cu/SiO2 structures, yielding values exceeding approx20 J m-2. Previously, similarly high toughness values have only been obtained using micrometre-thick interfacial layers15, 16, 17. Electron spectroscopy of fracture surfaces and density functional theory modelling of molecular stretching and fracture show that toughening arises from thermally activated interfacial siloxane bridging that enables the MNL to be strongly linked to both the adjacent layers at the interface, and suppresses MNL desorption. We anticipate that our findings will open up opportunities for molecular-level tailoring of a variety of interfacial properties, at processing temperatures higher than previously envisaged, for applications where microlayers are not a viable option—such as in nanodevices or in thermally resistant molecular-inorganic hybrid devices.

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