Bottom-up Gold Filling of Trenches in Curved Wafers

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 high aspect ratio trenches in gratings that are key to advanced X-ray imaging technologies. Effective use of the full area of the gratings with conventional X-ray sources requires they have a finite radius of curvature to align the high aspect ratio Au-filled trenches with divergent X-rays. With that in mind, this work demonstrates bottom-up Au filling in gratings that are attached to curved holders. Contactless mapping of the Au-filled gratings captures residual curvature that is retained after their release from the curved holders (i.e., intrinsic curvature). X-ray diffraction captures the elastic strains in the Si underlying the Au-filled trenches of the grating. Complementary measurements on the surfaces of unpatterned Si wafers mounted on curved holders capture the actual curvatures and strains imposed in the mounted gratings. Both intrinsically curved and re-bent toward their radius while mounted, the gratings provide high visibility across the entire field of view of an X-ray phase contrast imaging system and have internal strains substantially below those in planar gratings bent to the same radius.