Bottom-up Gold Filling of High Aspect Ratio Trenches
Stephen J. Ambrozik, Thomas P. Moffat, Daniel Josell, Chen Zhang, Houxian Miao
This work demonstrates bottom-up superconformal Au filling of trenches as tall as seventeen micrometers. Deposition is conducted in a near-neutral Na3Au(SO3)2 + Na2SO3 electrolyte containing a micromolar concentration of Bi3+, known to accelerate the Au deposition and recently shown to provide void-free, bottom-up filling of smaller trenches. Electroanalytical and XPS measurements show that a Bi surface species is responsible for the accelerated Au deposition. The adsorbed Bi also has a profound effect on the morphological evolution of the surface at the concentration and potentials of interests, transitioning from the growth of isolated (111) oriented pyramidal features in its absence to the growth of smooth epitaxial deposits once the fractional coverage of Bi reaches 0.18 ± 0.03 (1). Non-linear dependence on Bi coverage is reflected in an extended incubation period prior to the onset of bottom-up feature filling. For higher transport conditions, shearing of the interface apparently limits the Bi coverage so that a value of approximately 0.05 or less is observed, which correlates with a small leakage or passive current for Au deposition. The unusual correlation of Bi coverage with hydrodynamics is consistent with the observed inception and localization of deposition to the most recessed, and thereby quiescent, bottom surface of the patterned trench arrays.