| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Monday Sessions |
| Session TF1-MoM |
| Session: | Precursors and Surface Reactions |
| Presenter: | Bo Chen, University of California, Riverside |
| Authors: | B. Chen, University of California, Riverside Y. Yao, University of California, Riverside Q. Ma, University of California, Riverside F. Zaera, University of California, Riverside Y. Duan, University of Delaware A.V. Teplyakov, University of Delaware J. Coyle, Carleton University S. Barry, Carleton University |
| Correspondent: | Click to Email |
The search for appropriate metallorganic compounds with clean chemistry has long been one of the central issues in atomic layer deposition (ALD) development. Metal amidinates have been shown to be excellent candidates for such purpose owing to their relatively simple synthesis methodology, fair volatility and reactivity, and ease with which they can be modified at the ancillary peripheral moieties. Recent studies of these compounds have suggested that they tend to dimerize, and in some cases even form tetramers, in the solid state. This finding raises important questions regarding the structures of metal amidinates during their vaporization, dosing, and activated adsorption in ALD process. In our study, three families of copper amidinate precursors, copper(I)-N,N'-di-sec-butyl-acetamidinate, copper(I)-N-sec-butyl-2-iminopyrrolidinate, and copper(I)-N-tert-butyl-5,5-dimethyl-2-iminopyrrolidinate, have been investigated to test the role of steric effects in ligand substituents on their surface chemistry over nickel and silicon oxide surfaces. It has been found that, by following specific ligand design strategies such as strengthening inner C–N bonds and preventing β-hydride elimination, it is possible to improve on the thermal stability of these precursors, and consequently on the chemical quality of the deposited films. Liquid-injection field desorption ionization mass spectrometry data proved that the dimeric and tetrameric structures of the copper amidinates in the solid state are retained upon vaporization into the gas phase (the dimers for the first and third compounds, a tetramer for the second), and X-ray photoelectron spectroscopy data pointed to the retention of the dimeric structure on the surfaces. Density-functional theory calculations of the relative energies of formation of the monomers, dimers, and tetramers confirmed the experimental results. The retaining of dimeric and tetrameric structures of metal amidinates upon initial adsorption implies that the dissociation of the dimers into the monomers on solid surfaces, as required in ALD processes, is likely to occur at high temperatures, to induce Cu reduction and ligand decomposition.