Exploring the Limits of Bottom-Up Gold Filling to Fabricate Diffraction Gratings

Abstract

Gold deposition on rotating disk electrodes, Bi 3+ adsorption on planar Au films and superconformal Au filling of trenches up to 45 μm deep are examined in Bi 3+ -containing Na 3 Au(SO 3 ) 2 electrolytes with pH between 9.5 and 11.5. Higher pH is found to increase the potential-dependent rate of Bi 3+ 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 Na 3 Au(SO 3 ) 2 , on bottom-up filling is examined in trenches up to ≈ 210 μm deep with aspect ratio of depth/width ≈ 30. The microstructures of void-free, bottom-up filled trench arrays used as X-ray diffraction gratings are 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.

Towards the Fabrication of High-Aspect-Ratio Silicon Gratings by Deep Reactive Ion Etching

“…The actual filling of the Si gratings with Au is out of the scope of this paper. However, a few experimental data from the literature for the Au absorption gratings with periods of 1.2 μm [ 49 ], 3 μm [ 50 ], 5.25 μm [ 50 ], 6 μm [ 51 ] and 14 μm [ 52 ] are presented in Figure 7 b as a benchmark. Figure 7 represents the state of the art of grating fabrication using Si DRIE technology and the prospects for future application.…”

“…The empty symbols and horizontal blue lines in ( a ) represent experimental data on Si etched grating reported in this work. The solid dots in ( b ) correspond to Si DRIE gratings filled with Au reported elsewhere (1.2 μm [ 49 ], 3 μm [ 50 ], 5.25 μm [ 50 ], 6 μm [ 51 ], 14 μm [ 52 ]). The projection of the horizontal blue lines from plot ( a ) to plot ( b ) indicates that higher energy coverage can be obtained if the Si gratings produced in this work are filled with Au.…”

High‐Aspect‐Ratio Grating Microfabrication by Platinum‐Assisted Chemical Etching and Gold Electroplating

“…With respect to other approaches of the damascene process, [36] the seed growth from the bottom [37,38] does not need any additional step of conformal metallization [39] and allows to create a compact Au filling [40] independently of aspect ratio. [41] The Pt catalyst was designed to have a full interconnected pattern that can be used as metallization for seed growth of Au by electroplating (Figure 1h). The Si trenches were oxidized in air so that they became electrically isolated, [38] thus promoting the growth of Au from the bottom of the trench.…”

“…With respect to other approaches of the damascene process, [ 36 ] the seed growth from the bottom [ 37,38 ] does not need any additional step of conformal metallization [ 39 ] and allows to create a compact Au filling [ 40 ] independently of aspect ratio. [ 41 ]…”

Microfabrication of X-ray Optics by Metal Assisted Chemical Etching: A Review

“…In the case of Si based technology, the Si etched structure can affect the quality of the Au electroplating filling, some distortions [22] or voiding inside the template, resulting in less X-ray diffraction efficiency. Atomic layer deposition of metallic coating has been implemented to create a metallization layer for Au electroplating with conventional damascene approaches [94,95] and Au bottom up superfilling processes [96]. MacEtch offers the possibility to benefit of the original catalyst layer as a seed for the Au electroplating filling.…”