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

摘要

Treatment of the stable N-heterocyclic carbene 1,3-di-tertbutylimidazolin-2-ylidene with 2 equiv 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 pseudotetrahedral Al dihydride sites. Treatment of 1 with Cp2TiCl2 as a model for metal thin film precursors produced a hydride-bridged Ti(III)-Al heterobimetallic complex in 45% crystalline yield. Complex 1 shows good volatility and thermal stability, subliming at 90 to 100 degrees C at 0.05 Torr and decomposing in the solid state at similar to 200 degrees C. The vapor pressure of 1 is 0.75 Torr at 120 degrees C. These physical properties are promising for use as an atomic layer deposition (ALD) precursor. Aluminum metal films were deposited by thermal ALD using AlCl3 and 1 as precursors with a growth rate of similar to 3.5 angstrom/cycle after 100 cycles within an ALD window between 120 and 140 degrees C. The films are crystalline aluminum metal by X-ray diffraction and X-ray photoelectron spectroscopy analysis showed aluminum metal with 7.0 atom % C, 3.6 atom % N, and 0.9 atom % 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 coreactant, which highlights the effect that small precursor differences can have on film characteristics.