A very thin layer (~ 2nm) of metallic Cu is needed by the semiconductor industry to be used as a seed layer for the electrodeposition of Cu. An ideal technique to deposit it will be Atomic Layer Deposition (ALD), if continuous films can be produced at low temperatures. Several innovative precursors have been proposed for Cu ALD. Cu(I) compounds were proposed in this context by Lee et al1. and Coyle et al.2. In our previous work3we have found that Cu(I) compounds are formed as an intermediate at the surface even when Cu(II) compounds are the initial precursor. This gives a reason for investigating Cu(I) compounds as precursors for ALD of the metal.In our work, we explore through Density Functional Theory (DFT) whether various Cu(I) carbene complexes can be suitable ALD precursors (Figure 1). A carbene contains a neutral carbon atom with a valence of two, leaving two unshared valence electrons. As a ligand, the carbene is neutral. We have studied N-heterocyclic carbenes (represented as NHC henceforth) that conjugate with Cu in order to form complexes of the type (NHC)CuX, where X = various anions such as OEt, N(SiMe3)24. The Cu carbene precursors that we have studied vary in terms of conjugation and steric hindrance in the carbene moiety and in terms of identity of the anion.We propose some dual functional complexes that may act both as a reducing agent and as a Cu source5. In , we show a CuH complex, which can donate the H- to another Cu precursor CuL2(L=another ligand), forming neutral by-products (LH and NHC) and metallic Cu(0) as in the equation:2(NHC)CuH + CuL2 --> 3Cu(0) + 2L-H + 2NHC?We compute that such a reaction is thermodynamically possible (e.g. ?E = -22 kJ/mol for L=dmap) because the Cu-H bond is weaker than that of Cu-C (from the carbene). For most other neutral ligands like PPh3, BEt3 etc. the order of bond strengths is reversed and the hydride would not be released. We also find that substitution in the carbene by electronegative groups further reduces the Cu-H bond strength, e.g. by 30 kJ/mol for sulphide substitution. This further facilitates the donation of H-to the surface.(NHC)CuN(SiMe3)2 compounds have recently been proposed as prospective copper precursors6. However, we find that these types of compounds have high steric hindrance around the Cu centre that prevents chemisorption to the surface. We suggest that these compounds need to dissociate into fragments before being chemisorbed. Computing the fragmentation energies, we see that the Cu-N(SiMe3)2 bond strength is twice that of the Cu-carbene bond. We conclude that the Cu-carbene bond will break first and allow the Cu-N(SiMe3)2fragment to chemisorb, as the first step in deposition of metallic Cu.References:  (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) Coyle, J. P.; Johnson, P. A.; DiLabio, G. A.; Barry, S. T.; Mu�ller, J. Inorganic Chemistry 2010  , 49, 2844.(3) Dey, G.; Elliott, S. D. The Journal of Physical Chemistry A 2012  , 116, 8893.(4) Coyle, J. P.; Kurek, A.; Pallister, P. J.; Sirianni, E. R.; Yap, G. P. A.; Barry, S. T. Chemical Communications 2012  , 48, 10440.(5) Dey, G.; Elliott, S. Theor Chem Acc 2013  , 133, 1.(6) 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.

Density functional theory study of new Cu(I)carbene compounds as prospective precursors for Cu ALD

248th National Meeting (2014)

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