Decomposition of metal alkylamides, alkyls, and halides at reducible oxide surfaces: mechanism of 'clean-up' during atomic layer deposition of dielectrics onto III-V substrates

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Klejna, Sylwia
Elliott, Simon D.
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American Chemical Society
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The pairing of high-k dielectric materials with high electron mobility semiconductors for transistors is facilitated when atomic layer deposition (ALD) is used to deposit the dielectric film. An interfacial cleaning mechanism (‘clean-up’) that results in consumption of semiconductor native oxides and in practically sharp dielectric/semiconductor interfaces has been observed during ALD of Al2O3, HfO2, TiO2, and Ta2O5 with various degrees of success. We undertake a comprehensive study using density functional theory (DFT) to explain differences in the performance of various classes of precursor chemicals in removing native oxide from III-V substrates. The study covers the metals Ta(V), Ti(IV), Zr(IV), Hf(IV), Al(III), Mg(II) combined with methyl, amide, and chloride ligands. Of these, we show that clean-up is most effective when depositing MgO. Clean-up with metal alkylamides has a similar mechanism to clean-up with metal methyls insofar as oxygen is scavenged by the metal. The difference in operation of alkylamide and methyl ligands lies in the affinity of the ligand to the substrate. Alkylamide is shown to be prone to decomposition rather than the migration of the entire ligand evinced by methyl. We investigate the multistep chemical processes associated with decomposition of alkylamide. These processes can also occur during later cycles of high-k ALD and give a chemical vapor deposition (CVD) component to the ALD process. These transformations lead to formation of clean-up products such as aziridine, ethene, N-methyl methyleneimine, hydrogen cyanide, and methane. Some - but not all - of the reactions lead to reduction of surface As2O3 (i.e., clean-up). These results explain the experimentally observed accumulation of metallic arsenic and arsenic suboxide at the interface. Such understanding can help achieve control of oxide-semiconductor interfaces through the appropriate choice of chemical precursor.
Arsenic , Chemical vapor deposition , Chlorine compounds , Deposition , Dielectric films , Ethylene , Hafnium oxides , Ligands , Metal halides , Tantalum oxides , Chemical precursors , Chemical vapor depositions , CVD , Dielectric/semiconductor interface , High electron mobility , High-k dielectric materials , Hydrogen Cyanide , Oxide-semiconductor interfaces , ALD , Atomic layer deposition
KLEJNA, S. & ELLIOTT, S. D. 2014. Decomposition of Metal Alkylamides, Alkyls, and Halides at Reducible Oxide Surfaces: Mechanism of ‘Clean-up’ During Atomic Layer Deposition of Dielectrics onto III–V Substrates. Chemistry of Materials, 26, 2427-2437.
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© 2014 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see