Bottom-Up Gold Filling of High Aspect Ratio Trenches

Abstract

Bottom-up superconformal Au filling of trenches as tall as seventeen micrometers, with aspect ratios of 26, is demonstrated. Deposition is conducted in a near-neutral Na3Au(SO3)2 electrolyte containing a micromolar concentration of Bi3+, known to accelerate the Au deposition and provide void-free, bottom-up filling of smaller trenches. Electroanalytical and X-ray photoelectron spectroscopy (XPS) measurements show that a Bi surface species is responsible for the accelerated Au deposition. The adsorbed Bi 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 trigonal pyramidal features in its absence to the growth of smooth epitaxial deposits once the fractional coverage of Bi reaches 0.15 ± 0.02 (1σ). A non-linear dependence of Au deposition rate on Bi coverage gives rise to extended incubation prior to the onset of bottom-up feature filling. For higher transport conditions, shearing of the interface limits Bi coverage to a value of approximately 0.05 or less, which correlates with a small leakage or passive current for Au deposition. The unusual correlation of Bi coverage with hydrodynamics is consistent with the inception and localization of deposition to the most recessed, and thereby quiescent, bottom surface of the patterned trench arrays.