Surface and Interface Processes during Atomic Layer Deposition of Copper on Silicon Oxide

by Roy G. Gordon, Min Dai, Jinhee Kwon
Citation
Title:
Surface and Interface Processes during Atomic Layer Deposition of Copper on Silicon Oxide
Author:
Roy G. Gordon, Min Dai, Jinhee Kwon
Year: 
2010
Publication: 
Volume: 
26
Issue: 
6
Start Page: 
3911
End Page: 
3917
Publisher: 
Language: 
English
URL: 
Select license: 
Select License
DOI: 
10.1021/la903212c
PMID: 
ISSN: 
Abstract:

The initial surface chemistry and growth mechanisms of the atomic layer deposition (ALD) of metallic copper on SiO2 surfaces are investigated using an amidinate precursor (copper(I) di-sec-butylacetamidinate, [Cu(sBu-amd)]2) and molecular hydrogen. Using in situ Fourier transform infrared spectroscopy together with calculations based on density functional theory, we show that the initial surface reaction of [Cu(sBu-amd)]2 with hydroxylated SiO2 takes place by displacement of one of the sec-butylacetamidinate ligands at a surface −OH site, thus forming a Si−O−Cu−(sBu-amd) surface species, evident by the stretching vibrations of Si−O−Cu and the chelating −NCN− bonds. Molecular hydrogen exposure during a subsequent pulse dissociates most of the sec-butylacetamidinate ligands bound to surface Cu, which releases free amidine vapor, leaving Cu atoms free to agglomerate on the surface and thus opening more reactive sites for the next [Cu(sBu-amd)]2 pulse. Copper agglomeration is evident in the IR absorbance spectra through the partial recovery of the intensity of SiO2 optical phonon modes upon H2 reduction, which was lost after the reaction of [Cu(sBu-amd)]2 with the initial SiO2 surface. The thermally activated ligand rearrangement from a bridging to a monodentate structure occurs above 220 °C through hydrogenation of the ligand by surface hydroxyl groups after exposure to a [Cu(sBu-amd)]2 pulse. As Cu particles grow with further ALD cycles, the activation temperature is lowered to 185 °C, and hydrogenation of the ligand takes place after H2 pulses, catalyzed by Cu particles on the surface. The surface ligand rearranged into a monodentate structure can be removed during subsequent Cu precursor or H2 pulses. Finally, we postulate that the attachment of dissociated ligands to the SiO2 surface during the [Cu(sBu-amd)]2 pulse can be responsible for carbon contamination at the surface during the initial cycles of growth, where the SiO2 surface is not yet completely covered by copper metal.

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