Catalytic behavior of 3-mercapto-1-propane sulfonic acid on Cu electrodeposition and its effect on Cu film properties for CMOS device metallization

The effect of 3-mercapto-1-propane sulfonic acid (MPSA) on acidic copper electrodeposition for complementary metal oxide semiconductor (CMOS) metallization was characterized as an accelerator and brightener. Electrochemical and spectroscopic analyses revealed that MPSA significantly improved the rate-determining step (rds) of copper deposition through the oxidation of the thiol group to disulfide. Likewise, S–Cu bonding was detected in the subsequent adsorption of disulfide on the copper surface, with the thiolate layer responsible for the bright deposits. The surface-only contamination of S after deposition indicated the repetition of adsorption/reductive desorption of MPSA during copper deposition by which the continuous acceleration could be explained. The adsorption of disulfide was much preferred to that of the inhibiting molecules, which enabled the displacement of inhibiting molecule as reported in recent research. Nevertheless, the combined effect of preferred disulfide adsorption with the catalytic improvement of the rds by MPSA is useful in fully explaining the acceleration effect of MPSA. Annealing at 400 °C reduced the resistivity of copper film down to 2.0 μΩ cm.