Forming a transition zone terminated superconformal filling in a recess includes: providing an electrodeposition composition including: a metal electrolyte including a plurality of metal ions, solvent, and suppressor; providing the article including: a field surface and the recess that includes a distal position and a proximate position; exposing the recess to the electrodeposition composition; potentiodynamically controlling an electric potential of the recess with a potential wave form; bifurcating the recess into an active metal deposition region and a passive region; forming a transition zone; decreasing the electric potential of the recess by the potential wave form; progressively moving the transition zone closer to the field surface and away from the distal position; and reducing the metal ions and depositing the metal in the active metal deposition region and not in the passive region to form the transition zone terminated superconformal filling in the recess of the substrate.
This invention is an electrodeposition process that permits nickel filling of features such as pinholes in metal tubing. The process uses a deposition rate suppressing additive (“suppressor” that yields “critical behavior” such that deposition occurs at more negative potentials (“active”) but does not occur at more positive deposition potentials (“passivated”); the “critical potential” at which the transition from passivated to active deposition occurs is more negative at higher suppressor concentrations. Equivalently, active deposition occurs where the suppressor concentration is below a “critical concentration” and passivated where the concentration is above the critical concentration; the critical concentration is higher at more negative values of deposition potential. Thus, for appropriately selected deposition potential (i.e., in a limited range of values positive of the critical value for the suppressor concentration in the bulk electrolyte) naturally occurring decrease of suppressor concentration down features yield deposition only in the bottom region of the feature where the suppressor concentration is below the critical value. By systematically changing the deposition potential from values sufficiently positive of the critical potential for the bulk electrolyte to more negative values approach the critical potential for the bulk electrolyte (e.g., by stepping it or sweeping it), the location of the transition from active deposition (lower in the feature) to passivated deposition (higher in the feature) is progressively moved up the feature. For appropriate initial potential and potential history, the feature can be filled entirely, without void or seam formation.
The two figures below show the Ni deposition in cross-sectioned annular TSVs. The first image shows deposition at fixed potentials and suppressor concentrations. Deposition is seen to be localized to only a lower region of the filling features, the transition from passivated to active deposition being higher in the feature for lower suppressor concentration and more negative potential. The second image shows bottom-up filling achieved by systematically stepping the potential from initial potentials that are more positive of the critical potential to potentials that are less positive of the critical potential for the suppressor concentration in the bulk electrolyte (a-c as well as d-e).
Additional development will enable extension to geometries where the pinhole or crack to be filled is remotely located as in tubes or pipers. Such processes would enable remote repair of steam boilers, including in nuclear reactors.