The Surface Chemistry of Atomic Layer Depositions of Solid Thin Films

Atomic layer deposition (ALD) is one of the most promising methodologies available for the growth of solid thin films conformally on complex topographies and with atomic-level control on thickness. However, as a chemical process, ALD can lead to the incorporation of impurities and to the growth of poor-quality films. Here we discuss some possible complications associated with the chemistry of ALD, including its ill-defined stoichiometry, the stepwise and extensive surface conversion possible with the ligands of most ALD metalorganic precursors, the need for the reduction or oxidation of the deposited elements, the poor understanding of the role of the coreactants, the dominant activity of specific minority surface sites in starting ALD processes, and the development of complex layered or three-dimensional structures within the deposited films. The resolution of these issues should help with the development of a more systematic approach for the selection of ALD precursors and for the design of ALD processes.