Mechanism of Cobalt Bottom-Up Filling for Advanced Node Interconnect Metallization

Abstract

A mechanism of cobalt bottom-up trench fill for advanced node interconnect metallization was studied. The mechanism in question employs a single additive which suppresses cobalt plating and directly impacts the plating rate. Hydrogen, generated simultaneously during plating by electrolysis, reacts with the suppressor via hydrogen reduction, and the product of this reaction is a deactivated form of the suppressor. The local plating rate is governed by the relative concentrations of the activated/deactivated forms. Cyclic voltammetry (CV) shows that the suppressor deactivation is impacted by electrochemical potential, suppressor concentration, rotation rate, and pH, all of which may be controlled to generate bottom up fill in interconnects. Such impacts were confirmed on the plating of patterned coupons. This hydrogen reduction-induced deactivation mechanism provides a theoretical explanation for bottom-up plating in a single additive bath, and the factors that may impact the bottom-up filling.

Full Model for the Two-Step Polarization Curves of Hydrogen Evolution, Measured on RDEs in Dilute Acid Solutions

“…Hydrogen evolution gains, however, further importance, as HER is an almost inevitable side reaction of cathodic electrode processes occurring in aqueous environments. For example, in the electroreduction of CO 2 , or the deposition of base metals, − HER often appears as a parasitic reaction.…”

Operando laser scattering: probing the evolution of local pH gradients on complex electrode architectures

“…1c. These differential Co deposition and H 2 evolution are achieved by the action of an inhibitor additive that is selectively adsorbed on the planar areas and upper side walls of the patterned trenches 36,40 . Moreover, an electrochemically inactive but pH-sensitive compound is employed to probe the evolution of local pH gradients across the interface.…”

Thin layer growth on cobalt surface in solutions simulating slurry chemistry for chemical mechanical polishing

“…Copper interconnects must be encapsulated with refractory barrier metals to suppress the diffusion of copper to dielectric insulators. The volumetric resistance, or effective resistivity, of the interconnects therefore increases, 11,12) because the barrier metal layers must have a thickness necessary to eliminate the copper diffusion. For these reasons, cobalt is proposed as an alternative of copper, especially for narrow interconnects or local interconnects, the dimensions of which are small enough to ensure a lower resistivity of cobalt than that of copper.…”