Estimated and observed nucleation densities of electrodeposited Cu and Cu-Ag particles at n-Si(001) substrate

Abstract

We have examined the particle density of electrodeposited Cu and Cu-Ag particles from acidic sulfate bath. Based on the potentiostatic transients, the nucleation densities of the deposits were estimated with the Scharifker-Hills model, the Scharifker-Mostany model, the Heerman-Tarallo model, the approach proposed by Sluyters-Rehbach et al., and the model based on the roughness of the planar diffusion field from the one-point correlation function. All the fitted nucleation densities significantly underestimate the particle density observed under SEM. The average grain size suggests that all the nuclei are growing with respect to time. Those behaviors suggest that the coalescence of the diffusion fields occurs much earlier than the full coalescence of the nucleation exclusion zones. Furthermore, we have also attempted to explain the observed nucleation densities with the surface defect density of heavily-doped n-Si(001) substrate and the volume of the electrolyte required for forming the critical nucleus of Cu or Ag. The assumption that the Cu(II) species are immediately consumed at the substrate has been justified, from which a characteristic time is proposed to evaluate the impact of the rate of concentration drop on the mass-transfer behavior of the system.