DFT Calculations to Understand Prospective Methods for Atomic Layer Deposition of Copper. Gangotri Dey*, Simon D. ElliottTyndall National Institute, University College Cork, Dyke Parade, Cork, Irelandgangotri.dey@tyndall.ieAtomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many compounds but for very few pure metals. Copper is replacing aluminium in electronic interconnect because of its good conductivity and superior resistance to electro-migration. But a continuous thin layer (~2 nm is needed for seed layers) is very difficult to deposit, even with ALD, because of the tendency of copper to agglomerate into islands.A new ALD process for Cu has been developed by Lee et al.1based on the following transmetallation reaction:Cu(dmap)2 + Et2Zn ---> Cu0 + Zn(dmap)2 + C4H10 .................(1)The applicability of transmetallation ALD has been extended to other ligands and co-reagents2. A solution phase study revealed3 the possible mechanism and reaction intermediates. We are studying theoretically how the transmetallation mechanism works via quantum chemical (DFT) calculations using the TURBOMOLE package. The mechanism in the solution phase2-4 as well as during the surface ALD process1is studied. We examine the intrinsic reactivity of the transmetallation precursors (gas-phase model) and explicitly model how they react with a copper metal surface (cluster model of surface), using both geometry optimisation and molecular dynamics at the DFT level.These studies lead to the design of other innovative copper precursors like copper(I) carbene compounds5,6. These compounds are expected to have dual function both as a copper source and as the reducing agent, as seen in equation (2). This decreases the chances of foreign metal impurities during deposition.2(NHC)CuH + CuL2 --> 3Cu(0) + 2L-H + 2NHC? �(2)Here L = ligand and NHC = N-heterocyclic carbene ligandWe also compute that various transition metal metallocenes have a reduction potential that is suitable for copper deposition. The reduction potential of most of the metallocenes (MCp2+/MCp2) is lower than the reduction potential of copper (Cu+/Cu0). Hence the metal in the metallocene may donate one or more electrons to copper in exchange for ligands (equation 3). We propose this as a novel route to the ALD of copper.MCp2 + CuL2 --> Cu0 + MCp2L2? �(3)A change in the precursor and/or the reducing agent, as we propose, might decrease the reaction temperature required for copper ALD, which is one route towards preventing agglomeration of copper into islands on the surface.Acknowledgement: Thanks to Science Foundation Ireland for funding the 'ALDesign' project, 09.IN1.I2628.Reference: (1) Lee, B. H.; Hwang, J. K.; Nam, J. W.; Lee, S. U.; Kim, J. T.; Koo, S.-M.; Baunemann, A.; Fischer, R. A.; Sung, M. M. Angewandte Chemie International Edition 2009  , 48, 4536.(2) Vidjayacoumar, B.; Emslie, D. J. H.; Clendenning, S. B.; Blackwell, J. M.; Britten, J. F.; Rheingold, A. Chemistry of Materials 2010  , 22, 4844.(3) Vidjayacoumar, B.; Emslie, D. J. H.; Blackwell, J. M.; Clendenning, S. B.; Britten, J. F. Chemistry of Materials 2010  , 22, 4854.(4) Dey, G.; Elliott, S. D. The Journal of Physical Chemistry A 2012  , 116, 8893.(5) Coyle, J. P.; Dey, G.; Sirianni, E. R.; Kemell, M. L.; Yap, G. P. A.; Ritala, M.; Leskel�, M.; Elliott, S. D.; Barry, S. T. Chemistry of Materials 2013  , 25, 1132.(6) Dey, G.; Elliott, S. Theor Chem Acc 2013  , 133, 1.

DFT calculations to understand prospective methods for atomic layer deposition of copper

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.