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A Volatile Dialane Complex from Ring-Expansion of an N-Heterocyclic Carbene and its Use in Atomic Layer Deposition of Aluminum Metal Films

preprint
submitted on 15.11.2018 and posted on 15.11.2018 by Kyle Blakeney, Philip Martin, Charles Winter
Treatment of the stable N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazolin-2-ylidene with two equivalents of AlH3(NMe3) afforded the structurally unusual ring expanded dialane complex 1 in 72% yield after sublimation. Complex 1 has a distorted norbornane-like C3N2Al2 core with two pseudo-tetrahedral Al dihydride sites. Treatment of 1 with Cp2TiCl2 as a model for metal thin film precursors produced the hydride-bridged Ti(III)-Al heterobimetallic complex 2 in 45% crystalline yield. Complex 1 shows good volatility and thermal stability, subliming at 90-100 °C and 50 mTorr and decomposing in the solid state at ~200 °C. The vapor pressure of 1 is 0.75 Torr at 120 °C. These physical properties are promising for a potential atomic layer deposition (ALD) precursor. Aluminum metal films were deposited by thermal ALD using AlCl3 and 1 as precursors with a growth rate of ~3.5 Å/cycle after 100 cycles within an ALD window between 120-140 °C. The films are crystalline aluminum metal by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis showed aluminum metal with 7.0 at.% C, 3.6 at.% N, and 0.9 at.% Cl impurities. The aluminum metal films had an electrically discontinuous morphology. Conductive aluminum metal films have been deposited under similar conditions using a different aluminum hydride reducing co-reactant, which highlights the impact that small precursor differences can have on film characteristics.

Funding

BASF Corporation, US National Science Foundation

History

Email Address of Submitting Author

blakeney@chem.wayne.edu

Institution

Wayne State University

Country

United States

ORCID For Submitting Author

0000-0002-0375-0056

Declaration of Conflict of Interest

No conflict of interest

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