Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two reactants. ALD processes have been successfully demonstrated for many compounds but for very few pure metals. Copper has replaced aluminium in electronic interconnect because of its good conductivity and superior resistance to electro-migration.  However, even with ALD, it has so far proved impossible to deposit a continuous layer of copper at 1-2 nm thickness because of the high tendency of copper to agglomerate.Lee et al.1 proposed the use of an organometallic reducing reagent ZnEt2 for copper ALD (equation 1), in contrast to previous reducing agents such as H2, alcohols and H-plasma. Transmetallation is proposed as the reaction mechanism for deposition. But competing reactions result in Zn impurities. Vidjayacoumar2,3et al. tested two other organometallic reagents AlMe3 and BEt3 for copper deposition but found them to be unreactive. Cu(dmap)2 +  Et2Zn � Cu0? +   Zn(dmap)2  +  C4H10?.................(1)        In our study we map out the pathway for transmetallation and competing reactions using quantum chemical calculations of both a gas phase4 and surface model. We compute a variety of different precursor ligands that differ in electronegativity of the ligating atoms, conjugation and steric hindrance, in order to determine the optimum precursor for transmetallation ALD.         To address the problems with metal alkyl co-reagents, we propose alternative reducing agents.  We also find 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 2).  We propose this as a novel route to the ALD of copper.MCp2 + CuL2� Cu0 + MCp2L2?  �(2)Using Vanadocene as the metallocene and Cu(acac)2 as the precursor source, experimental it is seen that the reaction is possible in the solution phase. A polar solvent methanol was needed for the reaction to take place. However, a surface deposition of Cu on Ru substrate was not seen.Acknowledgement:  Thanks to Science Foundation Ireland for funding the project under the 'ALDesign' project, 09.IN1.I2628. JW, LK and MP thanks the support of Science Foundation Ireland (SFI) under the FORME Strategic Research Cluster Award number 07/SRC/I1172 is gratefully acknowledged.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.

Organometallic reagents ZnEt<sub>2</sub> and metallocene to be used for the reduction of copper for its atomic layer deposition: A study through DFT

248th National Meeting (2014)

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Organometallic reagents ZnEt2 and metallocene to be used for the reduction of copper for its atomic layer deposition: A study through DFT

Organometallic reagents ZnEt₂ and metallocene to be used for the reduction of copper for its atomic layer deposition: A study through DFT