Ultra-high aspect ratio high-resolution nanofabrication for hard X-ray diffractive optics

Chang, Chi-Hsuan; Sakdinawat, Anne

doi:10.1038/ncomms5243

Cited by 173 publications

(170 citation statements)

References 31 publications

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“…Other potentially undesirable results include the lateral etching of the nanocatalyst ( Figure 1C, Scheme 3) or lack of etching altogether ( Figure 1C, Scheme 4). AuNPs are understood to catalyze etching preferentially in the <100> direction but can also deviate from this path because of the nonhomogenous injection of holes from other surrounding catalysts 50 and their own facets 47 or to dislodgement by the hydrogen gas produced during etching.…”

Section: Resultsmentioning

confidence: 99%

Catalyst Self-Assembly for Scalable Patterning of Sub 10 nm Ultrahigh Aspect Ratio Nanopores in Silicon

Smith

Patil

Ferralis

et al. 2016

ACS Appl. Mater. Interfaces

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Nanoporous silicon (NPSi) has received significant attention for its potential to contribute to a large number of applications, but has not yet been extensively implemented because of the inability of current state-of-the-art nanofabrication techniques to achieve sufficiently small pore size, high aspect ratio, and process scalability. In this work we describe the fabrication of NPSi via a modified metal-assisted chemical etching (MACE) process in which silica-shell gold nanoparticle (SiO 2 −AuNP) monolayers self-assemble from solution onto a silicon substrate. Exposure to the MACE etchant solution results in the rapid consumption of the SiO 2 spacer shell, leaving well-spaced arrays of bare AuNPs on the substrate surface. Particles then begin to catalyze the etching of nanopore arrays without interruption, resulting in the formation of highly anisotropic individual pores. The excellent directionality of pore formation is thought to be promoted by the homogeneous interparticle spacing of the gold core nanocatalysts, which allow for even hole injection and subsequent etching along preferred crystallographic orientations. Electron microscopy and image analysis confirm the ability of the developed technique to produce micrometer-scale arrays of sub 10 nm nanopores with narrow size distributions and aspect ratios of over 100:1. By introducing a scalable process for obtaining high aspect ratio pores in a novel size regime, this work opens the door to implementation of NPSi in numerous devices and applications.

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Section: Resultsmentioning

confidence: 99%

Catalyst Self-Assembly for Scalable Patterning of Sub 10 nm Ultrahigh Aspect Ratio Nanopores in Silicon

Smith

Patil

Ferralis

et al. 2016

ACS Appl. Mater. Interfaces

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“…With the presence of h + , Si underneath the metal catalysts is etched by HF. MaCE for fabrication of HAR nanostructures on Si, such as nanowires, [9][10][11][12][13][14][15][16] nanogratings 17 and nanopores, 18 have been extensively studied. Recently, capability of MaCE in fabricating uniform micrometer-scale HAR structures was demonstrated.…”

mentioning

confidence: 99%

Charge Transport in Uniform Metal-Assisted Chemical Etching for 3D High-Aspect-Ratio Micro- and Nanofabrication on Silicon

Zhao

Wong

2015

ECS J. Solid State Sci. Technol.

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Recently, metal-assisted chemical etching (MaCE) has been proposed as a promising method for micro-and nanostructures fabrication on silicon (Si) with high aspect ratio, high geometric uniformity and low cost. In MaCE, electron holes (h + ) are injected into Si through catalytic reduction of H 2 O 2 on metal catalyst thin film patterns. Si beneath the metal is etched through a redox reaction where h + are involved. This work investigated a fundamental electrochemical process during MaCE: the transport of h + , and revealed its unique correlation with the 3D profile of the etching results. It is discovered that under the uniform etching condition, etching occurs both in the Si beneath the catalysts as well as on the sidewall of the etched space. On N-type Si, the sidewall etching is intrinsically depressed, and highly vertical HAR structures are formed; on P-type Si and undoped Si, the sidewall tapering becomes significant as the pattern number and density increase. The variation of the 3D profile can be explained by the CT during etching using a Schottky junction model, which show dependence on the intrinsic properties of the Si. CT involved in the two etching process can further be correlated by diffusion or drift of h + , which explains the influence of catalysts geometry. Fabrication of micro-and nanostructures on silicon (Si) is a key step in manufacturing of modern electronic and optoelectronic devices. Especially, the high-aspect-ratio (HAR) structures, of which the vertical dimension is much larger than the lateral dimension, enable orders-of-magnitude higher integration density and superior system performance compared to that of traditional planar structures by utilizing the space inside Si. HAR structures, such as deep trenches and deep holes, have been widely used in advanced Si-based devices. For example, deep trenches are the core structures in the microelectromechanical systems; 1 deep holes serve as the interconnect routes in the emerging 3D integration technology in microelectronic packaging. 2Most of these HAR structures are fabricated by selective removal of certain volume of Si from the bulk Si substrate, which is generally referred to as the etching of Si. Until now, the major applicable Si etching method for HAR structures fabrication is the deep reactive ion etching (DRIE). 3,4 In DRIE, Si is put in a gas chamber and etched by plasma. Although DRIE is able to fabricate a wide range of HAR structures, it is suffered from high cost. On the other hand, metal-assisted chemical etching (MaCE), a novel low-cost wet chemical etching method, has attracted attention from both academia and industry.

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“…However, at the same time, a high efficiency hard X-ray FZP would need to have a very high t, measured in microns, resulting in aspect ratios, Ar=t/Δr, of hundreds. This kind of aspect ratio is very difficult to achieve by using the standard lithographic methods and requires novel fabrication routes [14,24].…”

Section: Introductionmentioning

confidence: 99%

Overview of the multilayer-Fresnel zone plate and the kinoform lens development at MPI for intelligent systems

et al. 2015

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The ultimate goal of our research is to develop novel fabrication methods for high efficiency and high resolution X-ray optics. To this end, we have been pursuing the fabrication of several innovative diffractive/refractive optics designs. One such optic is the multilayer type Fresnel zone plate (ML-FZP). Our fabrication process relies on the atomic layer deposition (ALD) of two materials on a smooth glass fiber followed by a focused ion beam (FIB) based slicing and polishing. The ALD process allows much smaller outermost zone widths than the standard electron beam lithography based FZPs, meaning FZPs with potentially higher resolutions. Moreover, by depositing the multilayer on a cm long glass-fiber FZPs with very high optical thicknesses can be fabricated that can efficiently focus harder X-rays as well. A 21 nm half-pitch resolution was achieved using the ML-FZPs. Another optic we have been working on is the kinoform lens, which is a refractive/diffractive optic with a 100 % theoretical focusing efficiency. Their fabrication is usually realized by using approximate models which limit their success. Recently the fabrication of real kinoform lenses has been successfully realized in our lab via gray-scale direct-write ion beam lithography without any approximations. The lenses have been tested in the soft X-ray range achieving up to ~90 % of the calculated efficiency which indicates outstanding replication of the designed profile. Here we give an overview of our research and discuss the future challenges and opportunities for these optics.

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Ultra-high aspect ratio high-resolution nanofabrication for hard X-ray diffractive optics

Cited by 173 publications

References 31 publications

Catalyst Self-Assembly for Scalable Patterning of Sub 10 nm Ultrahigh Aspect Ratio Nanopores in Silicon

Catalyst Self-Assembly for Scalable Patterning of Sub 10 nm Ultrahigh Aspect Ratio Nanopores in Silicon

Charge Transport in Uniform Metal-Assisted Chemical Etching for 3D High-Aspect-Ratio Micro- and Nanofabrication on Silicon

Overview of the multilayer-Fresnel zone plate and the kinoform lens development at MPI for intelligent systems

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