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

Abstract

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.

Design and fabrication of resonant grating laser mirrors for single mode emission in microchip lasers

“…This design is considered with an approximation of avoiding the conformal coverage of gratings by the multilayer stack [5]. This hypothesis states that, during the conformal deposition of the thin film above the periodic structures, the conformality can be greatly reduced and can be eliminated when the thickness of the deposited film is at least equal to half of the grating linewidth [6,7].…”

High Aspect Ratio Tilted Gratings Through Local Electric Field Modulation in Plasma Etching

“…4-inch N-type 〈1 0 0〉 Si double side polished wafers were used for the preparation of sample chips, and the wafers are 250 μm thick. We normally use low resistivity wafers (0.001-0.01 Ω cm) for the convenience of following the trench filling process [9]. First, the wafer was coated with a 50 nm layer of Cr, which works as hard mask during the DRIE process.…”

“…Diffractive X-ray optics are periodic microstructures, whose aspect ratio grows as a function of the X-ray energy because of the weak interaction of X-rays with matter. For example, in grating based X-ray interferometry (XGI) for medical diagnostics at 20 keV X-ray energy [6], the gratings with pitch size in the range of 1-5 µm are made of Si trenches, filled with Au for height higher than 30 µm [7][8][9], while Au thickness higher than 100 µm [10] are necessary for X-ray dark-field chest radiography, where tube acceleration voltage peak is typically higher than 60 kV [11]. Limited by the available optics fabrication techniques, X-ray imaging systems suffer from the misalignment between the X-ray source emission and the diffractive microstructures.…”

A Study on the Dynamic Forming Mechanism Development of the Negative Poisson’s Ratio Elastomer Molds—Plate to Plate (P2P) Forming Process

“…Moreover, the micro/nano-structural substrates of different sizes and shapes [ 7 , 8 ] prepared by different processing methods (top-down, bottom-up) have high SERS enhancement factors and can be used for medical detection. At present, microstructural components, such as micro-nano gratings [ 9 , 10 , 11 , 12 , 13 , 14 ], polarizers, and lenses, can be completed by technologies such as nano-imprint, exposure, and development [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. However, there is a problem of material selection if etching is used for microstructure fabrication.…”