Robust Bottom-Up Gold Filling of Deep Trenches and Gratings
Daniel Josell, William Alexander Osborn, Maureen E. Williams
This work extends application of an extreme variant of superconformal Au electrodeposition to deeper device architectures while exploring factors that constrain its function and thereby the robustness of void-free processing. The unconventional bottom-up process is used to fill diffraction gratings with trenches 94 m deep and 305 m deep, with aspect ratios (AR, height/width) of just below 20 and 15, respectively, in near-neutral 0.16 mol∙L−1 Na3Au(SO3)2 + 0.64 mol∙L−1 Na2SO3 electrolyte containing ≈ 50 mol∙L−1 Bi3+ additive. Although the aspect ratios are modest compared to previously demonstrated void-free filling beyond AR = 60, the deepest trenches in this work exceed the dimension of the previous work by 100 m — a nearly 50% increase in depth that can be filled void-free. Processes that substantially accelerate the start of bottom-up deposition demonstrate a linkage between transport and success versus failure in void-free filling. Final profiles are highly uniform across 65 mm square gratings, including those repaired through the use of multiple depositions, because of self-passivation inherent to the process. Imaging of sectioned features by electron microscope as well as electron backscatter diffraction assessment of microstructure confirm the fully dense Au and void-free filling indicated by the electrochemical measurements. Characterization of the difference in X-ray transmission through pairs of aligned and misaligned gratings, summarized in so-called fringe visibilities averaging more than 80% at 50 kV X-ray tube voltage across the deeper gratings and 70% at 40 kV across the shallower gratings, are also consistent with uniformly dense, void-free fill across the gratings.
, Osborn, W.
and Williams, M.
Robust Bottom-Up Gold Filling of Deep Trenches and Gratings, Journal of the Electrochemical Society, [online], https://doi.org/10.1149/1945-7111/ ac5c0b, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934067
(Accessed December 11, 2023)