Bottom-Up Gold Filling of High Aspect Ratio Trenches

Ambrozik, Stephen; Moffat, Thomas P.; Zhang, C.; Miao, Hongchen; Josell, Daniel

doi:10.1149/2.0891910jes

Cited by 14 publications

(79 citation statements)

References 66 publications

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“…Figure 3 shows some examples of the produced Au gratings with conformal electroplating. It is noteworthy to mention that the Au grating with pitch of 1.2 µm and grating line height of 27 µm (see Figure 3 d) corresponds to an aspect ratio of 45:1, which is almost twice that obtained by bottom-up Au electroplating approaches [ 16 , 22 ] of gratings in this pitch range. Further optimization of Si etching can also enable Au electroplating of gratings with higher aspect ratios.…”

Section: Gratings Fabricationmentioning

confidence: 83%

“…The described process requires fewer fabrication steps and is therefore much simpler compared to our previously reported method based on low resistivity wafers with the insulating mask and bottom-up electroplating [ 16 ]. Most remarkably, filling the Si structures with Au-electroplating does not require any metal seed layers—as reported in other approaches [ 12 , 13 , 14 , 21 , 22 ]—which substantially further simplifies the fabrication process. In particular, ALD is often used for the metal seeding layer in high aspect ratio structures, but it is a slow and expensive process.…”

Section: Gratings Fabricationmentioning

confidence: 90%

“…We also see a high potential to combine the presented method with the bottom-up Au electroplating technique for efficient grating fabrication [ 21 , 22 , 23 ] or with the partial conformal coating method [ 12 ], as the metallization step can be avoided, in order to further simplify the process and reduce the fabrication costs.…”

Section: Discussionmentioning

confidence: 99%

“…Availability of standard lithographic techniques and well-established technologies for silicon microfabrication are additional advantages of this approach, which opens up the route for a cost-efficient production in larger wafer sizes and higher volumes. Several Si-based technologies for the fabrication of metallic X-ray gratings were recently reported: conformal electroplating with partial (also known as spatial frequency doubling technique) [ 12 ] or complete [ 12 , 13 , 14 ] filling; seedless electroplating through a mask [ 15 , 16 ]; metal casting of Bi [ 17 ], as well as of Au [ 18 ] and Pb alloys [ 19 ]; atomic layer deposition (ALD) of Ir [ 20 ]; bottom-up Au electroplating on a metal seed layer [ 21 , 22 , 23 , 24 , 25 ]. Each of the above techniques has its own strengths and weaknesses.…”

Section: Introductionmentioning

confidence: 99%

“…One drawback is that the method needs a conformal metal seeding, which for the highest aspect ratio structures requires a slow and expensive ALD coating. While not yet fundamentally limited by the process itself, an aspect ratio of 26:1 was reported for a pitch size of 1.3 µm [ 22 ]. Conformal Au electroplating or the damascene approach was demonstrated using ALD deposited Pt (pitch 200 nm, gold height 3.2 µm, aspect ratio 32:1) [ 13 ] and Ru (pitch 6 µm, gold height 180 µm, aspect ratio 60:1) [ 14 ] as plating seed layer.…”

Section: Introductionmentioning

confidence: 99%

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Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating

et al. 2021

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We present a method to produce small pitch gratings for X-ray interferometric imaging applications, allowing the phase sensitivity to be increased and/or the length of the laboratory setup to be minimized. The method is based on fabrication of high aspect ratio silicon microstructures using deep reactive ion etching (Bosch technique) of dense grating arrays and followed by conformal electroplating of Au. We demonstrated that low resistivity Si substrates (<0.01 Ohm·cm) enable the metal seeding layer deposition step to be avoided, which is normally required to initiate the electroplating process. Etching conditions were optimized to realize Si recess structures with a slight bottom tapering, which ensured the void-free Au filling of the trenches. Vapor HF was used to remove the native oxide layer from the Si grating surface prior to electroplating in the cyanide-based Au electrolyte. Fabrication of Au gratings with pitch in the range 1.2–3.0 µm was successfully realized. A substantial improved aspect ratio of 45:1 for a pitch size of 1.2 µm was achieved with respect to the prior art on 4-inch wafer-based technology. The fabricated Au gratings were tested with X-ray interferometers in Talbot–Laue configuration with measured visibility of 13% at an X-ray design energy of 26 keV.

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Section: Gratings Fabricationmentioning

confidence: 83%

Section: Gratings Fabricationmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating

et al. 2021

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A four‐grating interferometer for x‐ray multi‐contrast imaging

Miao,

Williams,

Josell

2024

Medical Physics

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BackgroundX‐ray multi‐contrast imaging with gratings provides a practical method to detect differential phase and dark‐field contrast images in addition to the x‐ray absorption image traditionally obtained in laboratory or hospital environments. Systems have been developed for preclinical applications in areas including breast imaging, lung imaging, rheumatoid arthritis hand imaging and kidney stone imaging.PurposePrevailing x‐ray interferometers for multi‐contrast imaging include Talbot‐Lau interferometers and universal moiré effect‐based phase‐grating interferometers. Talbot‐Lau interferometers suffer from conflict between high interferometer sensitivity and large field of view (FOV) of the object being imaged. A small period analyzer grating is necessary to simultaneously achieve high sensitivity and large FOV within a compact imaging system but is technically challenging to produce for high x‐ray energies. Phase‐grating interferometers suffer from an intrinsic fringe period ranging from a few micrometers to several hundred micrometers that can hardly be resolved by large area flat panel x‐ray detectors. The purpose of this work is to introduce a four‐grating x‐ray interferometer that simultaneously allows high sensitivity and large FOV, without the need for a small period analyzer grating.MethodsThe four‐grating interferometer consists of a source grating placed downstream of and close to the x‐ray source, a pair of phase gratings separated by a fixed distance placed downstream of the source grating, and an analyzer grating placed upstream of and close to the x‐ray detector. The object to be imaged is placed upstream of and close to the phase‐grating pair. The distance between the source grating and the phase‐grating pair is designed to be far larger than that between the phase‐grating pair and the analyzer grating to promote simultaneously high sensitivity and large FOV. The method was evaluated by constructing a four‐grating interferometer with an 8 µm period source grating, a pair of phase gratings of 2.4 µm period, and an 8 µm period analyzer grating.ResultsThe fringe visibility of the four‐grating interferometer was measured to be ≈24% at 40 kV and ≈18% at 50 kV x‐ray tube operating voltage. A quartz bead of 6 mm diameter was imaged to compare the theoretical and experimental phase contrast signal with good agreement. Kidney stone specimens were imaged to demonstrate the potential of such a system for classification of kidney stones.ConclusionsThe proposed four‐grating interferometer geometry enables a compact x‐ray multi‐contrast imaging system with simultaneously high sensitivity and large FOV. Relaxation of the requirement for a small period analyzer grating makes it particularly suitable for high x‐ray energy applications such as abdomen and chest imaging.

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Extreme Bottom-up Gold Filling of High Aspect Ratio Features

Josell

Moffat

2023

Acc. Chem. Res.

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Conspectus Where copper interconnects fabricated using superconformal electrodeposition processes have enabled dramatic advances in microelectronics over the past quarter century, gold filled gratings fabricated using superconformal Bi3+-mediated bottom-up filling electrodeposition processes promise to enable a new generation of X-ray imaging and microsystem technologies. Indeed, bottom-up Au-filled gratings have demonstrated excellent performance in X-ray phase contrast imaging of biological soft tissue and other low Z element samples even as studies using gratings with inferior Au fill have captured the potential for broader biomedical application. Four years ago, the Bi-stimulated bottom-up Au electrodeposition process was a scientific novelty where gold deposition was localized entirely on the bottoms of metallized trenches 3-μm-deep and 2-μm-wide, an aspect ratio of only 1.5, on centimeter scale fragments of patterned silicon wafers. Today the room-temperature processes routinely yield uniformly void-free filling of metallized trenches 60-μm-deep and 1-μm-wide, an aspect ratio 60, in gratings patterned across 100 mm Si wafers. Four distinctive characteristics of the evolution of void-free filling in the Bi3+-containing electrolyte are seen in experimental Au filling of fully metallized recessed features such as trenches and vias: (1) an “incubation period” of conformal deposition, (2) subsequent Bi-activated deposition localized on the bottom surface of features, (3) sustained bottom-up deposition that yields void-free filling, and (4) self-passivation of the active growth front at a distance from the feature opening defined by operating conditions. A recent model captures and explains all four features. The electrolyte solutions are simple and nontoxic, being near-neutral pH and composed of Na3Au(SO3)2 + Na2SO3 containing micromolar concentrations of Bi3+ additive, the latter generally introduced through electrodissolution from the metal. The influences of additive concentration, metal ion concentration, electrolyte pH, convection, and applied potential have been examined in some depth using both electroanalytical measurements on planar rotating disk electrodes and studies of feature filling, thereby defining and elucidating relatively wide processing windows for defect-free filling. The process control for bottom-up Au filling processes is observed to be quite flexible, with online changes of potential as well as concentration and pH adjustments during the course of filling compatible with processing. Furthermore, monitoring has enabled optimization of the filling evolution, including to shorten the incubation period for accelerated filling and to fill features of ever higher aspect ratio. The results to date indicate that the demonstrated filling of trenches with an aspect ratio of 60 represents a lower bound, a value determined only by the features presently available.

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Bottom-Up Gold Filling of High Aspect Ratio Trenches

Cited by 14 publications

References 66 publications

Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating

Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating

A four‐grating interferometer for x‐ray multi‐contrast imaging

Extreme Bottom-up Gold Filling of High Aspect Ratio Features

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