Effect of Chloride Concentration on Copper Deposition in Through Silicon Vias

Abstract

Bottom-up Cu deposition in metallized through silicon vias (TSV) depends on a co-adsorbed polyether–Cl− suppressor layer that selectively breaks down within recessed surface features. This work explores Cu deposition when formation of the suppressor blocking layer is limited by the flux of Cl−. This constraint leads to a transition from passive surfaces to active deposition partway down the via sidewall due to coupling between suppressor formation and breakdown as well as surface topography. The impact of Cl− concentration and hydrodynamics on the formation of the suppressor surface phase and its potential-dependent breakdown is examined. The onset of suppression breakdown is related to the local Cl− coverage as determined by the adsorption isotherm or transport limited flux. A two-additive co-adsorption model is presented that correlates the voltammetric potential of suppression breakdown with the depth of the passive-active transition during TSV filling under conditions of transport limited flux and incorporation of Cl−. The utility of potential waveforms to optimize the feature filling process is demonstrated. At higher Cl− concentrations (≥80 μmol/L), sidewall breakdown during Cu deposition occurs near the bottom of the via followed by a shift to bottom-up growth like that seen at higher Cl− concentrations.