No abstract

The atomic layer deposition of copper metal thin films was achieved using a three precursor sequence entailing Cu(OCHMeCH2NMe2)2, formic acid, and hydrazine. A constant growth rate of 0.47−0.50 Å/cycle was observed at growth temperatures between 100 and 170 °C. The resulting films are high purity and have low resistivities.

Molybdenum trioxide films have been deposited using thermal atomic layer deposition techniques with bis(tert-butylimido)bis(dimethylamido)molybdenum. Films were deposited at temperatures from 100 to 300 °C using ozone as the oxidant for the process. The Mo precursor was evaluated for thermal stability and volatility using thermogravimetric analysis and static vapor pressure measurements. Film properties were evaluated with ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and secondary electron microscopy. The growth rate per cycle was determined to extend from 0.3 to 2.4 Å/cycle with <4% nonuniformity (1-sigma) with-in-wafer across a 150 mm wafer for the investigated temperature range.

Tertbutylallylcobalttricarbonyl (tBu-AllylCo­(CO)3) is shown to have strong substrate selectivity during atomic layer deposition of metallic cobalt. The interaction of tBu-AllylCo­(CO)3 with SiO2 surfaces, where hydroxyl groups would normally provide more active reaction sites for nucleation during typical ALD processes, is thermodynamically disfavored, resulting in no chemical reaction on the surface at a deposition temperature of 140 °C. On the other hand, the precursor reacts strongly with H-terminated Si surfaces (H/Si), depositing ∼1 ML of cobalt after the first pulse by forming Si–Co metallic bonds. This remarkable substrate selectivity of tBu-AllylCo­(CO)3 is due to an ALD nucleation reaction process paralleling a catalytic hydrogenation, which requires a coreactant that acts as a hydrogen donor rather than a source of bare protons. The chemical specificity demonstrated in this work suggests a new paradigm for developing selective ALD precursors. Namely, selectivity can be achieved by tailoring the ligands in the coordination sphere to obtain structural analogues to reaction intermediates for catalytic transformations that exhibit the desired chemical discrimination.

Treatment of MCl 2 (M = Cr, Mn, Fe, Co, Ni) with 2 equiv of lithium metal and 1,4-di-tertbutyl-1,3-diazadiene ( tBu2 DAD) in tetrahydrofuran at ambient temperature afforded Cr( tBu2 DAD) 2 (38%), Mn( tBu2 DAD) 2 (81%), Fe( tBu2 DAD) 2 (47%), Co( tBu2 DAD) 2 (36%), and Ni( tBu2 DAD) 2 (41%). Crystal structure determinations revealed monomeric complexes that adopt tetrahedral coordination environments and were consistent with tBu2 DAD radical anion ligands. To evaluate the viability of M( tBu2 DAD) 2 (M = Cr, Mn, Fe, Co, Ni) as potential film growth precursors, thermogravimetric analyses, preparative sublimations, and solid-state decomposition studies were performed. Mn( tBu2 DAD) 2 is the most thermally robust among the series, with a solid-state decomposition temperature of 325 °C, a sublimation temperature of 120 °C/0.05 Torr, and a nonvolatile residue of 4.3% in a preparative sublimation. Thermogravimetric traces of all complexes show weight loss regimes from 150 to 225 °C with final percent residues at 500 °C ranging from 1.5 to 3.6%. Thermolysis studies reveal that all complexes except Mn( tBu2 DAD) 2 decompose into their respective crystalline metal powders under an inert atmosphere. Mn( tBu2 DAD) 2 may afford amorphous manganese metal upon thermolysis.