Superconformal Copper Deposition in Through Silicon Vias by Suppression-Breakdown

Abstract

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 leads to non-linear spatial-temporal patterning during metal deposition. For the given hydrodynamic conditions, cyclic voltammetry reveals the potential regime over which positive-feedback gives rise to the superconformal feature filling dynamic. Breakdown of suppression is primarily related to polymer concentrations in the electrolyte while its reformation is dependent on its transport to the interface. Morphological evolution during the early stages of TSV filling reveals two distinct growth front geometries. For dilute polymer concentrations, an 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 μmol/L, active metal deposition is rapidly confined to the bottom surface of the via followed by sustained bottom-up filling.