Plasma etch fabrication of 60:1 aspect ratio silicon nanogratings with 200 nm pitch

Mukherjee, Pran; Bruccoleri, Alexander R.; Heilmann, Ralf K.; Schattenburg, Mark L.; Kaplan, Alex F.; Guo, L. Jay

doi:10.1116/1.3507427

Cited by 34 publications

(24 citation statements)

References 15 publications

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“…15 Experiments with 4 lm deep etches showed that a clean stop on SiO 2 can be achieved when using a low frequency platen power of 380 kHz. The etch parameters were the same as those presented by Mukherjee et al, 12 except that the etch time was 9 min and the platen power was linearly ramped from 30 to 57 W. This etch stop is critical for patterning CAT gratings since a uniform and completely etched grating will remain after the final removal of the buried SiO 2 (see Fig. 5).…”

Section: Fabrication Methodologymentioning

confidence: 98%

“…The front side is masked with 400 nm of thermal SiO 2 and etched with a rapid-cycle Bosch process in an STS Pegasus tool as demonstrated in past work. 12 This work focused on etching the CAT gratings in bulk silicon for process development. The 200-nm-pitch CAT grating pattern is created via interference lithography (IL) 13 and transferred into the 400-nm-thick thermal SiO 2 layer via a trilayer stack.…”

Section: Fabrication Methodologymentioning

confidence: 99%

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Fabrication of nanoscale, high throughput, high aspect ratio freestanding gratings

Bruccoleri

Mukherjee

Heilmann

et al. 2012

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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A nanofabrication process has been developed for a novel critical-angle transmission grating for astronomical x-ray spectroscopy. The pitch of the gratings is 200 nm and the depth is 4 μm, which exceeds the state-of-the-art in aspect ratio by over a factor of 2 for ultrahigh aspect ratio freestanding nanoscale gratings with open areas on the order of 50% and spanning several square centimeters. They have a broad array of other applications, including neutral mass spectroscopy, ultraviolet filtration, and phase contrast imaging x-ray spectroscopy. The gratings are fabricated as a monolithic structure in silicon via two lithographic and pattern transfer processes, integrated together on a silicon-on-insulator wafer. The grating is patterned via interference lithography and transferred into the 4 μm device layer via a Bosch deep reactive-ion etch (DRIE). The grating channels are then filled without voids by spinning photoresist on them, which wicks into the channels. The sample is then bonded under vacuum via Crystal Bond™ to a carrier wafer, and a honeycomb pattern is etched via DRIE through the handle layer until it stops cleanly on the buried SiO2. The buried SiO2 is etched away, and the sample is separated from the carrier. The resist filling is cleaned from the channels and the grating is critical-point dried to create a freestanding structure. The freestanding gratings can now be mounted to external frames and structurally analyzed and tested for launch and deployment in space.

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Section: Fabrication Methodologymentioning

confidence: 98%

Section: Fabrication Methodologymentioning

confidence: 99%

Fabrication of nanoscale, high throughput, high aspect ratio freestanding gratings

Bruccoleri

Mukherjee

Heilmann

et al. 2012

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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“…The line-edge roughness in the mask is likely due to a combination of the initial patterning of the photoresist and pattern transfer steps into the thermal SiO 2 . 17 The line-edge roughness adds to the roughness caused by the Bosch process and it is likely that reducing the initial mask line-edge roughness via improved lithography and pattern transfer could improve the final sidewall roughness after KOH polishing. Additionally, several other factors were observed and suspected to prevent successful polishing.…”

Section: Analysis Of Failed Polishing Attemptsmentioning

confidence: 99%

“…An improved DRIE process was developed in order to address the bowing of the process developed by Mukherjee et al 17 This new process significantly reduced the bowing of the deep etch and the minimum bar-width was increased to 100 nm. The new process increased the passivation step duration by 50% and decreased the coil power by 25%.…”

Section: Improved Deep Etch For Koh Polishing 4 Lm-deep 200 Nm-pimentioning

confidence: 99%

Potassium hydroxide polishing of nanoscale deep reactive-ion etched ultrahigh aspect ratio gratings

Bruccoleri

Guan

Mukherjee

et al. 2013

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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A fabrication process has been developed to chemically polish the sidewalls of 200 nm-pitch gratings via potassium hydroxide (KOH) etching following the Bosch deep reactive-ion etching (DRIE) process. Previous KOH polishing experiments focused on micron scale features. This work is the first reported combined DRIE-KOH etching process on the nanoscale for ultrahigh aspect ratio structures with feature sizes 30 times smaller than previously published work. The primary application of the gratings is x-ray spectroscopy and requires polished sidewalls for efficient x-ray reflection. Polishing is also critical for increasing the open area by narrowing the grating bars, which increases the throughput of x-rays. The increased open area is also valuable for other applications such as ultraviolet filtration, neutron spectroscopy and biofiltration. Advanced Bosch processes leave approximately 4 nm, root mean square (RMS), of roughness on the sidewalls. This roughness needs to be reduced to below 1 nm to efficiently reflect soft x-rays with wavelengths between 1 and 5 nm. Furthermore, high aspect ratio DRIE can result in bar width variations of approximately a factor of two from the top to the middle of the channel, commonly referred to as bowing. The polishing procedure presented here removes the roughness to below the resolution of the scanning electron microscope, and was measured via an atomic force microscope to be less than 1 nm RMS. The bowing has also been reduced by at least a factor of 3. The polishing process takes advantage of the anisotropy of KOH silicon etching. Specifically, the {111} silicon planes etch approximately 100 times slower than other crystal planes. This anisotropy allows the grating bars to be etched in 50% by weight KOH at room temperature for up to 60 min. Long etches have several key requirements, including 0.2 degree alignment of the grating with respect to the {111} planes, mask roughness below 40 nm and minimal defects in the silicon. If these requirements are not met, the grating will quickly be destroyed by the etch, which etches the non-{111} planes in excess of 1 μm per hour. The fabrication steps of this work are described in detail including a novel technique to align the 200 nm-pitch interference lithography image grating to the {111} planes of a ⟨110⟩ silicon wafer.

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“…Over the last 2-3 years we developed masks, pattern transfer and etch recipes for the simultaneous vertical etching of CAT gratings and L1 supports, as well as for the L2 support mesh, first on bulk silicon and separate SOI wafers, and then combined on a single SOI wafer. [24][25][26][27] Thus DRIE on the front and back sides of SOI wafers can be used to fabricate large-area, freestanding CAT grating membranes with minimal support structures.…”

Section: Overviewmentioning

confidence: 99%

Fabrication of large-area and low mass critical-angle x-ray transmission gratings

et al. 2014

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Soft x-ray spectroscopy of celestial sources with high resolving power R = E/∆E and large collecting area addresses important science listed in the Astro2010 Decadal Survey New Worlds New Horizons, such as the growth of the large scale structure of the universe and its interaction with active galactic nuclei, the kinematics of galactic outflows, as well as coronal emission from stars and other topics. Numerous studies have shown that a transmission grating spectrometer based on lightweight critical-angle transmission (CAT) gratings can deliver R = 3000-5000 and large collecting area with high efficiency and minimal resource requirements, providing spectroscopic figures of merit at least an order of magnitude better than grating spectrometers on Chandra and XMM-Newton, as well as future calorimeter-based missions. The recently developed CAT gratings combine the advantages of transmission gratings (low mass, relaxed figure and alignment tolerances) and blazed reflection gratings (high broad band diffraction efficiency, utilization of higher diffraction orders). Their working principle based on blazing through reflection off the smooth, ultra-high aspect ratio grating bar sidewalls has previously been demonstrated on small samples with x rays. For larger gratings (area greater than 1 inch square) we developed a fabrication process for grating membranes with a hierarchy of integrated low-obscuration supports. The fabrication involves a combination of advanced lithography and highly anisotropic dry and wet etching techniques. We report on the latest fabrication results of free-standing, large-area CAT gratings with polished sidewalls and preliminary x-ray tests.

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Plasma etch fabrication of 60:1 aspect ratio silicon nanogratings with 200 nm pitch

Cited by 34 publications

References 15 publications

Fabrication of nanoscale, high throughput, high aspect ratio freestanding gratings

Fabrication of nanoscale, high throughput, high aspect ratio freestanding gratings

Potassium hydroxide polishing of nanoscale deep reactive-ion etched ultrahigh aspect ratio gratings

Fabrication of large-area and low mass critical-angle x-ray transmission gratings

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