Effect of Chloride Concentration on Copper Deposition in Through Silicon Vias.

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.