Bottom-up Au Filling of Trenches in Curved Wafers

Published

March 4, 2024

Author(s)

Daniel Josell, Thomas P. Moffat, Thomas Gnaupel-Herold, David Raciti, Martin Stauber, Yu Q, Liyang Chen, M Rawlik, Marco Stampanoni, Lucia Romano

Abstract

A 〖Bi〗^(3+)-stimulated Au electrodeposition process in slightly alkaline 〖Na〗_3 Au(〖SO〗_3 )_2+〖Na〗_2 〖SO〗_3 electrolytes has been previously demonstrated for void-free extreme bottom-up filling of trenches with aspect ratios (height/width) exceeding 60 in gratings that are key to advanced X-ray imaging technologies. Effective use of the full area of the gratings, patterned here across 100 mm Si wafers, with conventional X-ray sources requires the gratings have a finite radius of curvature to improve alignment of the high aspect ratio Au-filled trenches with divergent X-rays. This work demonstrates bottom-up Au filling in gratings of aspect ratio 40 that are attached to curved holders with concave radius of 30 cm and 20 cm. The Au-filled gratings retain substantial curvature after they are released, but they can also be re-bent after release or used while still mounted on a suitably designed holder. Contactless mapping of curvature and elastic strain over the surfaces of un-patterned Si wafers mounted on curved holders capture the actual curvature and strains imposed using different attachment geometries. Analogous maps of Au-filled gratings after their release from the curved holders capture the residual (intrinsic) curvature of the gratings and associated elastic strains in the underlying Si. The intrinsic curvatures are consistent with requirements for improved function in X-ray imaging. The associated strains are substantially below those that would be induced in gratings that were Au filled while planar and then bent to an equal radius. The fabricated gratings enable improved uniformity across the field of view in an X-ray phase contrast imaging system due to their intrinsic curved state.

Citation

Journal of the Electrochemical Society

Pub Type

Journals

Download Paper

https://doi.org/10.1149/1945-7111/ad2958

Local Download

Keywords

Gratings, imaging, phase contrast imaging, gold, superfill

Citation

Josell, D. , Moffat, T. , Gnaupel-Herold, T. , Raciti, D. , Stauber, M. , Q, Y. , Chen, L. , Rawlik, M. , Stampanoni, M. and Romano, L. (2024), Bottom-up Au Filling of Trenches in Curved Wafers, Journal of the Electrochemical Society, [online], https://doi.org/10.1149/1945-7111/ad2958, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957307 (Accessed October 10, 2025)