Substrate Selectivity of (^tBu-Allyl)Co(CO)₃during Thermal Atomic Layer Deposition of Cobalt

Abstract

Tertbutylallylcobalttricarbonyl ( t Bu-AllylCo(CO) 3 ) is shown to have strong substrate selectivity during atomic layer deposition of metallic cobalt. The interaction of t Bu-AllylCo(CO) 3 with SiO 2 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 t Bu-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.