Mechanism of Bismuth Stimulated Bottom-up Gold Feature Filling
Daniel Josell, Trevor Braun, Thomas P. Moffat
The mechanism that underlies 〖Bi〗^(3+)-stimulated extreme bottom-up Au filling of trenches and vias in slightly alkaline 〖Na〗_3 Au(〖SO〗_3 )_2+〖Na〗_2 〖SO〗_3 electrolytes is explored. The remarkable void-free feature filling and self-passivation behavior arise from a combination of four factors. Firstly, Bi adsorption leads to an increase in the Au deposition rate with a non-linear acceleration of the Au deposition with Bi coverage occurring around a critical coverage. Secondly, the rates of 〖Bi〗^(3+) adsorption and Au deposition are dependent on potential and electrolyte composition in a non-trivial manner such that gradients of Au(〖SO〗_3 )_2^(3-) and SO_3^(2-) derived from reduction of the Au(〖SO〗_3 )_2^(3-) during deposition accentuate deposition farther from the feature opening. Thirdly, the interplay between the above factors and surface area reduction at the bottom of filling features leads to strengthening and stabilization of localized active deposition at the bottoms of high aspect ratio recessed features. Finally, as bottom-up feature filling nears completion, weakening of the concentration gradients, decreased contribution of area change to Bi enrichment along with sustained desorption kinetics lead to the steady state Bi coverage on the growth front falling below the critical value, attenuating the highly localized filling dynamic such that bottom-up growth eventually terminates as the front approaches the feature openings. Experimentally, the impact of the electrolyte components 〖Na〗_3 Au(〖SO〗_3 )_2, 〖Na〗_2 〖SO〗_3 and 〖Bi〗^(3+) and the potential-dependent kinetic factors on the rate of Au electrodeposition are quantified. The derived parameters are applied within the surfactant conservation Curvature Enhanced Accelerator Coverage model to simulate the filling of high aspect ratio trenches. Good agreement is observed with key aspects of experimental bottom-up Au filling including the incubation period of conformal deposition, followed by the transition to localized bottom-up growth, sustained bottom-up filling and finally self-passivation of filling as the growth front nears the field.
, Braun, T.
and Moffat, T.
Mechanism of Bismuth Stimulated Bottom-up Gold Feature Filling, Journal of the Electrochemical Society, [online], https://doi.org/10.1149/1945-7111/acaccc, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935865
(Accessed March 29, 2023)