Deposition of Copper by the H₂-Assisted Reduction of Cu(tmod)₂ in Supercritical Carbon Dioxide:  Kinetics and Reaction Mechanism

The kinetics and reaction mechanism for copper deposition by the hydrogen-assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper(II), [Cu(tmod) 2 ], in supercritical carbon dioxide was studied using a differential cold wall reactor. At substrate temperatures between 220 and 270 °C, the measured film growth rate ranged between 5 and 35 nm/min. The overall apparent activation energy was 51.9 kJ/mol. Film growth rate exhibited zero-order dependence on the precursor at precursor concentrations between 0.02 and 0.5 wt % Cu (tmod) 2 in CO 2 and a zero-order dependence on hydrogen at hydrogen concentrations greater than 0.06 wt % in CO 2 . Zero-order precursor dependence over large concentration ranges promotes exceptional step coverage. At lower concentrations of either reagent a 1 / 2 -order dependence was observed. Film growth rate was negative order with respect to excess quantities of the hydrogenated ligand byproduct, (tmod)H, and film growth could be suppressed completely at (tmod)H concentrations above 1 wt %. With use of the results of the experiments, a heterogeneous reaction mechanism is proposed. Protonation of the adsorbed ligand (tmod) was found to be the rate-determining step. A Langmuir−Hinshelwood rate expression was used to correlate the data with good agreement.