A cobalt layer deposition study: Dicobaltatetrahedranes as convenient MOCVD precursor systems

Low melting or liquid cobalt(0) MOCVD precursors of type [Co 2(CO)6(2-RCCR')] (R = H, R' = (CH 3)3Si, nC4H9, nC5H11, nC6H 13, nC7H15; R = nC 3H7, R' = (CH3)3Si, CH3; R = R' = C2H5, (CH3)3Si) have been prepared by the reaction of the appropriate alkynes with Co2(CO) 8. Variation of the substituents at the C,C triple bond allowed the study of their influence on the thermal behaviour and vapour pressure. These measurements showed that the cobalt(0) precursors are suitable for application within the MOCVD (Metal-Organic Chemical Vapour Deposition) process. Decomposing deposition of the cobalt precursors was realized in a home-built vertical cold-wall CVD reactor under mild conditions without any addition of co-reactants. The obtained dense and conformal cobalt layers have been characterized by SEM, EDX and XPS measurements. Depending on the precursor applied, pure cobalt films (96.7% Co) or mixtures of cobalt, carbon and cobalt oxide with varying composition with layer thicknesses of 35-90 nm were formed.