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submitted on 15.11.2018 and posted on 15.11.2018by Kyle Blakeney, Philip Martin, Charles Winter
Treatment of the stable N-heterocyclic carbene (NHC)
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.