Process for Forming a Transition Zone Terminated Superconformal Filling

Patent Description

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).