Extreme Bottom-Up Superfilling of Through-Silicon-Vias by Damascene Processing: Suppressor Disruption, Positive Feedback and Turing Patterns

Abstract

Extreme bottom-up copper superfilling of through-silicon-vias (TSV) is demonstrated using a CuSO4-H2SO4 electroplating bath containing chloride and a polyether suppressor. Via filling occurs almost exclusively by deposition on the bottom via surface. The differential between the incoming fluxes of hydrated metal cations and larger suppressor molecules is accentuated by the recessed via geometry and accounts for preferential metal deposition initiating and growing from the bottom surface. The bottom-up growth front eventually propagates beyond the via opening and a substantial overburden develops. Feature filling is enhanced in electrolytes with a high [Cu2+]/[H3O+] ratio where global coupling by migration helps sustain the flux of Cu2+ to actively growing surface sections. Bottom-up superfilling relies on positive feedback whereby inhibition provided by adsorption of the polyether additive on the chloride saturated surface is disrupted by the metal deposition reaction. Release of the water of hydration that accompanies reduction of the Cu2+ aquo complex contributes to the sustained disruption of suppressor activity at the growth front. The correlation between TSV superfilling and additive-generated voltammetric hysteresis on planar substrates, which also involves a negative-differential-resistance (S-NDR) coupled with the electrolyte resistance, provides a general framework for understanding and guiding optimization of the bottom-up growth mode in recessed surface features.