Superconformal Copper Deposition in Through Silicon Vias by Suppression-Breakdown
Daniel Josell, Thomas P. Moffat
The evolution of superconformal Cu electrodeposition in high aspect ratio through silicon vias (TSVs) is examined as a function of polymer suppressor concentration, applied potential and hydrodynamics. Electroanalytical measurements in a CuSO4-H2SO4-Cl electrolyte are used to explore and quantify the effect of such parameters on the metal deposition process. Hysteretic voltammetry due to suppressor breakdown reveals an S-shaped negative differential resistance that lead to non-linear spatial-temporal patterning during metal deposition. For given hydrodynamic conditions, cyclic voltammetry reveals the potential regime over which positive-feedback gives rise to the superconformal feature filling dynamic. Significantly, the breakdown of suppression is primarily related to polymer concentrations in the electrolyte while its reformation is dependent on polymer transport to the interface. Morphological evolution during the early stages of TSV filling reveals two distinct growth front geometries. For dilute polymer concentrations, the initial bifurcation into passive-active surfaces occurs on the side walls of the TSVs followed by bottom-up fill. The depth of the initial sidewall bifurcation within the via increases with polymer concentration. For higher polymer concentrations, i.e. ≥ 25 mol/L, active metal deposition is rapidly confined to the bottom surface of the via followed by sustained bottom-up filling. Localized deposition results from coupling between suppression breakdown and surface topography and, once activated, deposition is sustained on the moving planar surface segments.
Journal of the Electrochemical Society
copper, electrodeposition, superfill, TSV, through silicon via, superconformal