Issue 14, 2015

Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions

Abstract

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.

Graphical abstract: Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions

Supplementary files

Article information

Article type
Paper
Submitted
07 Feb 2015
Accepted
26 Feb 2015
First published
11 Mar 2015

Nanoscale, 2015,7, 6311-6318

Author version available

Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions

M. Shirazi and S. D. Elliott, Nanoscale, 2015, 7, 6311 DOI: 10.1039/C5NR00900F

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