Kinetic analysis and steric-hindrance effects in thermal atomic layer deposition of high-purity cobalt films with dicobalt hexacarbonyl tert-butylacetylene as the precursor

Thermal atomic layer deposition of cobalt (Co) using dicobalt hexacarbonyl tert-butylacetylene (CCTBA) and H2 was investigated for application as an interconnect material in ultra-large-scale integrated circuits. In this study, H2 reduction conditions were optimized to obtain Co thin films with high purity and low resistivity. The effects of H2 partial pressure and supply time on the chemical composition and resistivity were systematically analyzed. The growth per cycle (GPC) was evaluated by varying the CCTBA supply time, and self-limiting behavior was observed. The saturated GPC was 0.018 nm/cycle, which is lower than previously reported values due to a carbon impurity reduction. This corresponds to approximately 0.088 monolayers, attributed to the steric hindrance effect (SHE) of CCTBA adsorption. The SHE was analyzed by combining density functional theory-calculated adsorption structures with random sequential adsorption simulations, and the results showed good agreement with the experimental values. The adsorption probability of CCTBA at 100 °C was estimated to be 1.3 × 10−4. Conformal film growth was achieved on trench structures with an aspect ratio of 9.7. The carbon impurity concentration decreased with increasing H2 supply, reaching a composition of 99% Co and 1% C under an H2 pressure of 555 Pa and a supply time of 20 s. The probability of the surface reduction reaction of adsorbed CCTBA was estimated to be 5.3 × 10−9 at 100 °C. Resistivity was examined in relation to the film thickness, and a Co film with a bulk-like resistivity of 10 μΩ cm was successfully obtained.