The cooperative ALD mechanism explaining the self-limiting nature of ALD!
Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions
Mahdi Shirazia and Simon D. Elliott
Nanoscale, 2015,7, 6311-6318
DOI: 10.1039/C5NR00900F
Mahdi Shirazia and Simon D. Elliott
Nanoscale, 2015,7, 6311-6318
DOI: 10.1039/C5NR00900F
Atomic layer deposition (ALD) is a technique for producing conformal
layers of nanometre-scale thickness, used commercially in non-planar
electronics and increasingly in other high-tech industries. ALD depends
on self-limiting surface chemistry but the mechanistic reasons for this
are not understood in detail. Here we demonstrate, by first-principle
calculations of growth of HfO2 from Hf(N(CH3)2)4–H2O and HfCl4–H2O and growth of Al2O3 from Al(CH3)3–H2O,
that, for all these precursors, co-adsorption plays an important role
in ALD. By this we mean that previously-inert adsorbed fragments can
become reactive once sufficient numbers of molecules adsorb in their
neighbourhood during either precursor pulse. Through the calculated
activation energies, this ‘cooperative’ mechanism is shown to have a
profound influence on proton transfer and ligand desorption, which are
crucial steps in the ALD cycle. Depletion of reactive species and
increasing coordination cause these reactions to self-limit during one
precursor pulse, but to be re-activated via the cooperative effect in the next pulse. This explains the self-limiting nature of ALD.
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