Additives for Superconformal Gold Feature Filling

Abstract

An overview of the effect of additives on Au electrodeposition from Na3Au(SO3)2 based electrolytes is presented with an emphasis on filling of fully metallized recessed surface features such as trenches and vias. The impact of heavy metal additives Tl+, Pb2+, and Bi3+ is reviewed and accompanied by a brief survey of the effects of Sb3+, Te4+, SeCN−, 3-mercapto-1-propanesulfonic acid (MPS) and polyethyleneimine (PEI) additions. The addition of Tl+, Pb2+, Bi3+ or Sb3+ accelerates the kinetics of Au(SO3)2 3− reduction to Au, as manifest in hysteretic voltammetry and rising chronoamperometric transients, and yields bright specular deposits. Gold deposition with Pb2+ addition exhibits superconformal filling in sub-micrometer trenches while Bi3+ addition induces a more extreme bottom-up filling, but Tl+ and Sb3+ additions yield essentially conformal deposition for the conditions examined. Modest acceleration and hysteresis observed with Te4+ addition reflect roughening due to limited nucleation, 3D growth and delayed coalescence, rather than catalysis, and are associated with conformal feature filling. Unlike the other additives, SeCN−, MPS and PEI inhibit the deposition kinetics. Breakdown of suppression during deposition in micrometer size trenches is biased toward recessed surfaces where the flux of suppressor is constrained, yielding localized deposition and superconformal filling.

Mechanism of Bismuth Stimulated Bottom-up Gold Feature Filling

“…An additional change has been made to the electrolyte conductivity κ, which has been increased from 10 S•m −1 to 20 S•m −1 to reduce the resistive losses that could restrict active area and localize deposition toward the bottoms of recessed features as in suppressor-containing electrolytes. [34][35][36][37][38][39] Deposition contours colored according to the predicted Bi coverage capture the evolution of filling from 0 s to 21000 s in 3000 s increments. The contours from 12000 s to 21000 s in the lower half of the trench are shown separately, colored according to the metal deposition rate.…”

“…However, for those examples, feature filling is associated with depletion of the suppressor away from feature openings due to its consumption within the deposit. [34][35][36][37][38][39] More importantly, the growth front and resulting microstructure in the Au systems [37][38][39] tend to resemble those of additive-free deposition, which are distinctly inferior to the smooth compact deposits provided by + Bi 3 additions. Four distinctive and important characteristics of void-free filling in the + Bi 3 -containing electrolyte are: 1) an "incubation period" of conformal deposition, 2) subsequent activation of deposition localized to the bottom surface of features, 3) continuing bottom-up deposition that yields void-free filling and 4) self-passivation of the active growth front at a distance from the feature opening defined by operating conditions.…”

Survey of P-Block Metal Additives for Superconformal Cu Deposition in an Alkaline Electrolyte

“…This includes several reports of superconformal filling of submicrometer size features. [29][30][31][32][33][34][35] Likewise, Bi 3+ as well as Pb 2+ and Tl + , for that matter, are all well-known accelerators of Au deposition 36 in sulfite (and cyanide) electrolytes that have been shown to yield superconformal feature filling, 37,38 with Pb 2+ additions being more effective for trench filling and Tl + additions generating bright surfaces. In moderately acidic complexing Cu electrolytes, Pb 2+ has been reported to yield indications of superconformal feature filling, 39 albeit as a modest suppressor.…”