Exploring the Limits of Bottom-Up Gold Filling to Fabricate Diffraction Gratings
Daniel Josell, Stephen J. Ambrozik, Maureen E. Williams, A E. Hollowell, Christian Arrington, Shinichiro Muramoto, Thomas P. Moffat
Gold deposition on rotating disk electrodes, Bi3+ adsorption on planar Au films and superconformal Au filling of trenches up to 45 m deep are examined in Bi+3-containing Na3Au(SO3)2 electrolytes with pH between 9.5 and 11.5. Higher pH is found to increase the potential-dependent rate of Bi adsorption on planar Au surfaces, shortening the incubation period that precedes active Au deposition on planar surfaces and bottom-up filling in patterned features. Decreased contact angles between the Au seeded sidewalls and bottom-up growth front also suggest improved wetting. The bottom-up filling dynamic in trenches is, however, lost at pH 11.5. The impact of Au concentration, 80 mmol/L versus 160 mmol/L Na3Au(SO3)2, on bottom-up filling is examined in trenches up ≈ 210 m deep with aspect ratio of depth/width ≈ 30. The microstructure of void-free, bottom-up filled structures characterized by scanning electron microscopy (SEM) and Electron BackScatter Diffraction (EBSD), revealing marked spatial variation of the grain size and orientation within the filled features.