Study of 5-Alkynylpyrimidines as Cobalt Superfilling Inhibitors

Electrodeposition technology is the key core technology for achieving micro/nanoscale interconnection in high-end chip manufacturing. Recently, cobalt interconnect structures have been the ideal choice for constructing electronic pathways in process nodes below 14 nm due to the fact that cobalt has a smaller electron mean free path compared to copper; thus, studying the electroplating filling behavior of cobalt in micronano scale space has become a hot topic in the field of chip manufacturing. In this article, an electroplating solution containing a new 5-alkynylpyrimidine (5-EP) as an inhibitor is designed for electrochemical tests, including cyclic voltammetry and linear sweep voltammetry. The results indicate that the 5-EP significantly inhibits cobalt electrodeposition. The change in the nucleation mode of cobalt in an electroplating solution with the inhibitor (5-EP) was revealed by chronoamperometry, where cobalt atoms nucleate in a three-dimensional continuous manner instead of three-dimensional instantaneous nucleation. In situ enhanced Raman spectroscopy is used to further analyze the adsorption of the inhibitor (5-EP) molecules on the cobalt surface during the electroplating process from a spectroscopic perspective. The energy gap value of the additive molecule obtained through quantum chemical calculations is △E = ELUMO – EHOMO = 3.302 eV, indicating that the additive molecule has high reactivity and higher adsorption strength at the metal interface. The calculated electrostatic potential (ESP) values of the molecule range from a minimum of −47.29 kJ/mol to a maximum of 70.89 kJ/mol. Lower ESP values imply higher electron density. Molecular dynamics simulations calculate the adsorption energy of the additive molecule (5-EP) on Co(100) to be −133.96 kcal/mol, indicating that the 5-EP molecule has good adsorption capability. Electroplating experiments reveal that the addition of 6 ppm 5-EP to the plating solution enables defect-free filling of blind holes. Finally, it is also revealed by characterization tests (scanning electron microscopy/atomic force microscopy/X-ray diffraction) that the inhibitor (5-EP) effectively reduces the surface roughness of the cobalt coating and, meantime, promotes the preferential growth of cobalt along the 100 and 110 crystal planes.