Defect analysis in thermal nanoimprint lithography

Hirai, Yoshihiko; Yoshida, Satoshi; Takagi, Nobuyuki

doi:10.1116/1.1629289

Cited by 169 publications

(114 citation statements)

References 9 publications

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“…Replication methods would be the preferred technology for the development of such structures, allowing their mass production. However, the requirements of PNFs with HAR are challenging for standard masters and replication methods [39][40][41] . This is not only because of the HAR needed for achieving low optical losses but also because of the required low residual layers of o 1 μm.…”

Section: High-aspect-ratio Microstructures (Harms)mentioning

confidence: 99%

“…Si moulds were initially prepared for thermal NIL (T-NIL) with thin layers of PMMA, which is the classical process for achieving low residual layers in thermoplastic polymer resists 39,42,49 . However, thermal processes with non-crosslinked materials impose high stress on the material and often result in ripping during demoulding.…”

Section: Nanoimprint Lithographymentioning

confidence: 99%

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High-aspect-ratio nanoimprint process chains

et al. 2017

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Different methods capable of developing complex structures and building elements with high-aspect-ratio nanostructures combined with microstructures, which are of interest in nanophotonics, are presented. As originals for subsequent replication steps, two families of masters were developed: (i) 3.2 μm deep, 180 nm wide trenches were fabricated by silicon cryo-etching and (ii) 9.8 μm high, 350 nm wide ridges were fabricated using 2-photon polymerization direct laser writing. Both emerging technologies enable the vertical smooth sidewalls needed for a successful imprint into thin layers of polymers with aspect ratios exceeding 15. Nanoridges with high aspect ratios of up to 28 and no residual layer were produced in Ormocers using the micromoulding into capillaries (MIMIC) process with subsequent ultraviolet-curing. This work presents and balances the different fabrication routes and the subsequent generation of working tools from masters with inverted tones and the combination of hard and soft materials. This provides these techniques with a proof of concept for their compatibility with high volume manufacturing of complex micro-and nanostructures.Keywords: cryo-etching; direct 6 write laser lithography; high aspect ratio; moulding; nanoimprint lithography; Ormocer; photonic nanofences; 2-photon polymerization INTRODUCTION High-aspect-ratio microstructures (HARMS), that is, structures with a large height/width ratio, have found many applications 1,2 such as X-ray gratings 3 , gas chromatography columns 4 , magnetic coils 5 , X-ray telescopes 6 , micro-gears 7 , micro-capacitors with highaspect-ratio (HAR) cantilevers 8 , and micromechanical and microoptical elements 9,10 . These structures exhibit aspect ratios (ARs) of over 10 and almost vertical sidewalls, making them much more challenging to develop than the structures typically used in planar technology with moderate ARs of 1 to 2. They are therefore characterized by an intermediate state between two-and threedimensional (2D and 3D), that is, a 2D planar design that is extended into the vertical dimension and often called . There are several methods to produce HAR structures on typical planar substrates, most of them relying on the anisotropy of subtractive pattern transfer of a low AR masking layer into an underlying resist or substrate, that is, by using mask based ultraviolet (UV)-photolithography (PL) with an AR up to 5, silicon etching (for example, dry etching) with an AR up to 20, and direct write laser lithography (DWL) and X-ray lithography with ARs 420 (Refs. 12-15). These methods are continually being improved to produce a higher AR and smaller lateral dimensions. Furthermore, they are enlarged by new techniques that are often subsets of etching processes with different advantages and disadvantages. One of those challenges is the suitability for submicron and nanopatterning, that is, structures with lateral sizes much smaller than 1 μm and the possibility to combine micro-with nanostructures in the same material.There are three main approaches: (1)...

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Section: High-aspect-ratio Microstructures (Harms)mentioning

confidence: 99%

Section: Nanoimprint Lithographymentioning

confidence: 99%

High-aspect-ratio nanoimprint process chains

et al. 2017

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“…A vast body of research has focus on mechanical characteristics such as the template release load. The stress mechanism of the resist and template and the reasons for defects were analyzed [2][3][4]. To suppress the release load and eliminate defects, using novel mold with low surface energy materials [5], increased performance of the resist [6], structure modification or novel template release methods have been proposed [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Analysis of Debonding Problem during Demolding Process of Nanoimprinting

Wang

Zhang

et al. 2017

J. Photopol. Sci. Technol.

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Template release process during nanoimprint lithography was investigated, and the detailed steps of this process were described in order to reduce defects caused by demolding process. The debonding problem was discussed by using optimization of model, numerical simulation and theoretical analysis. The rules and mechanism of debonding were obtained by analyzing the relations between the bonding strength and the vertical stresses of the cementing surface linking the residual layer and the substrate in terms of stress balance theory in fracture mechanics. The location and demolding process which is prone to debond were analyzed. It is concluded that the debonding phenomenon took place at the intermediate position during the second demolding stage, when the adhesion force between the resist and the mold was 0.8 times of other interfaces between the mold and the resist. The debonding phenomenon took place at the angular position during the fourth demolding stage, when the adhesion force between the resist and the mold was 1.2 times bigger than the other interfaces between the mold and the resist.

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“…This step is the key feature of this approach; in contrast to conventional nanoimprint lithography whereby fine, high-aspect ratio molds or mold features are the most costly, in sacrificial imprint, they are the least expensive portion of the structure and are designed to be destroyed during processing. This feature is critical for the scalable incorporation of nanostructured surfaces into three-dimensional (3D) multiscale devices; it also avoids the issue of resist fracture that is ubiquitous in thermal nanoimprinting 21 , whereby thermal expansion mismatch leads to gripping of the structures during cooling and subsequent failure by tear-away of either the imprinted material or the mold. Avoiding damage to the resist is particularly problematic in high-aspect ratio structures due to the nature of stress concentration.…”

Section: Introductionmentioning

confidence: 99%

Multiscale patterning of a metallic glass using sacrificial imprint lithography

et al. 2015

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Bulk metallic glasses (BMGs) have been developed as a means to achieve durable multiscale, nanotextured surfaces with desirable properties dictated by topography for a multitude of applications. One barrier to this achievement is the lack of a bridging technique between macroscale thermoplastic forming and nanoimprint lithography, which arises from the difficulty and cost of generating controlled nanostructures on complex geometries using conventional top-down approaches. This difficulty is compounded by the necessary destruction of any resulting reentrant structures during rigid demolding. We have developed a generalized method to overcome this limitation by sacrificial template imprinting using zinc oxide (ZnO) nanostructures. It is established that such structures can be grown inexpensively and quickly with tunable morphologies on a wide variety of substrates out of solution, which we exploit to generate the nanoscale portion of the multiscale pattern through this bottom-up approach. In this way, we achieve metallic structures that simultaneously demonstrate features from the macroscale down to the nanoscale, requiring only the top-down fabrication of macro/microstructured molds. Upon detachment of the formed part from the multiscale molds, the ZnO remains embedded in the surface and can be removed by etching in mild conditions to both regenerate the mold and render the surface of the BMGs nanoporous. The ability to pattern metallic surfaces in a single step on length scales from centimeters down to nanometers is a critical step toward fabricating devices with complex shapes that rely on multiscale topography for their intended functions, such as biomedical and electrochemical applications.

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Defect analysis in thermal nanoimprint lithography

Cited by 169 publications

References 9 publications

High-aspect-ratio nanoimprint process chains

High-aspect-ratio nanoimprint process chains

Analysis of Debonding Problem during Demolding Process of Nanoimprinting

Multiscale patterning of a metallic glass using sacrificial imprint lithography

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