Accelerated Bottom-Up Gold Filling of Metallized Trenches

This work extends previously detailed void-free, bottom-up feature filling in a near-neutral Na₃Au(SO₃)₂ + Na₂SO₃ electrolyte containing micromolar concentrations of Bi³⁺. Bottom-up electrodeposition in 17 microm and 45 microm tall trenches with an aspect ratio greater than 10 is demonstrated using potentiostatic, stepped potential and/or stepped current control. Strategies to shorten the incubation period associated with slow deposition on uniformly passivated surfaces, which precedes bottom-up filling at fixed potential, are explored. The first electron backscatter diffraction studies of bottom-up filled Au deposits reveal large grains that span the trench width and often exceed tens of micrometers in length. In contrast, smaller grains are observed near the tops of filled trenches and, under conditions of marginal filling, mid-height within them.