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(Color online) Schematic of various nanofabrication processes using holographic nanopatterns. (a) The top photoresist (PR) is patterned by laser interference lithography. (b) The intermediate antireflective coating (ARC) layer is patterned by RIE. (c) A metal film (e.g., Cr) is deposited (e.g., by e-beam evaporation). (d) and (e) The metal/PR/ARC trilayer is released from the silicon substrate. (f) Silicon nanopillar structures are fabricated by DRIE, where the metal structures are used as etch mask. (g) The metal/PR/ARC trilayer is transferred on a new silicon substrate. (h) Silicon nanohole structures are fabricated by DRIE, where the trilayer is used as etch mask and then released again for repetitive processes. (i) The metal/PR/ARC trilayer is transferred on a new polydimethylsiloxane (PDMS) substrate and used as deposition mask for a metal (e.g., gold). (j) After the deposition of gold (Au), the trilayer is released again for repetitive processes.
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In this article, the authors report a new lift-off process to obtain nanoporous free-standing trilayer film of metal/photoresist/antireflective coating (ARC) stack and to reuse the thin and flexible membrane as a versatile stencil lithography mask for the dual purposes. For the initial lift-off process of metal nanostructures, nanoperiodic pore pat...
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... advan- tages and potential applications of such an advanced nanofab- rication processes are also discussed in this paper. Figure 1 shows the overall fabrication schemes of the pro- posed lift-off process and the new applications of the free- standing PR membrane to the stencil lithography for both etching and deposition processes. First [ Fig. 1(a)], large-area (wafer-scale) periodic nanopore patterns are created on a PR film by using a laser interference lithography. ...Context 2
... The advan- tages and potential applications of such an advanced nanofab- rication processes are also discussed in this paper. Figure 1 shows the overall fabrication schemes of the pro- posed lift-off process and the new applications of the free- standing PR membrane to the stencil lithography for both etching and deposition processes. First [ Fig. 1(a)], large-area (wafer-scale) periodic nanopore patterns are created on a PR film by using a laser interference lithography. Between the PR film and silicon substrate, an antireflective coating (ARC) is interlayered to minimize the vertical standing wave effects along the sidewall of the registered PR nanostructures. In order to make ...Context 3
... laser interference lithography. Between the PR film and silicon substrate, an antireflective coating (ARC) is interlayered to minimize the vertical standing wave effects along the sidewall of the registered PR nanostructures. In order to make through-holes of the PR/ ARC bilayer, the opened ARC layer is also etched by reactive ion etching (RIE) [ Fig. 1(b)]. Similar to traditional lift-off process, a metal film (e.g., Cr) is deposited through the bilayer pore patterns [ Fig. 1(c)]. However, instead of remov- ing the metal/PR/ARC trilayer after the metal deposition, the trilayer composite film is just released as a free-standing membrane from the silicon substrate by using specially ...Context 4
... minimize the vertical standing wave effects along the sidewall of the registered PR nanostructures. In order to make through-holes of the PR/ ARC bilayer, the opened ARC layer is also etched by reactive ion etching (RIE) [ Fig. 1(b)]. Similar to traditional lift-off process, a metal film (e.g., Cr) is deposited through the bilayer pore patterns [ Fig. 1(c)]. However, instead of remov- ing the metal/PR/ARC trilayer after the metal deposition, the trilayer composite film is just released as a free-standing membrane from the silicon substrate by using specially designed chemical solution (NH 3 /H 2 O 2 /H 2 O) [ Fig. 1(d)]. The chemical only helps the physical release process of the film by ...Context 5
... a metal film (e.g., Cr) is deposited through the bilayer pore patterns [ Fig. 1(c)]. However, instead of remov- ing the metal/PR/ARC trilayer after the metal deposition, the trilayer composite film is just released as a free-standing membrane from the silicon substrate by using specially designed chemical solution (NH 3 /H 2 O 2 /H 2 O) [ Fig. 1(d)]. The chemical only helps the physical release process of the film by generating air bubbles between the ARC layer and silicon substrate with the aid of etching silicon in a slow rate. 13,14 After the complete separation of the trilayer film, we obtain only metal nanostructures on the silicon substrate [ Fig. 1(e)]. Such metal ...Context 6
... (NH 3 /H 2 O 2 /H 2 O) [ Fig. 1(d)]. The chemical only helps the physical release process of the film by generating air bubbles between the ARC layer and silicon substrate with the aid of etching silicon in a slow rate. 13,14 After the complete separation of the trilayer film, we obtain only metal nanostructures on the silicon substrate [ Fig. 1(e)]. Such metal nanostructures (e.g., Cr) can further be used as robust etch mask in the deep reactive ion etching (DRIE) of the silicon, allowing to obtaining high-aspect-ratio silicon nanopillar structures [ Fig. 1(f)]. Meanwhile, the free-standing trilayer membrane can be transferred onto a new silicon substrate, where the flexible ...Context 7
... slow rate. 13,14 After the complete separation of the trilayer film, we obtain only metal nanostructures on the silicon substrate [ Fig. 1(e)]. Such metal nanostructures (e.g., Cr) can further be used as robust etch mask in the deep reactive ion etching (DRIE) of the silicon, allowing to obtaining high-aspect-ratio silicon nanopillar structures [ Fig. 1(f)]. Meanwhile, the free-standing trilayer membrane can be transferred onto a new silicon substrate, where the flexible membrane is directly placed on the new substrate without using any spacers between them [ Fig. 1(g)]. Then, the conformable contact between the trans- ferred membrane and the new substrate can allow new etching ...Context 8
... in the deep reactive ion etching (DRIE) of the silicon, allowing to obtaining high-aspect-ratio silicon nanopillar structures [ Fig. 1(f)]. Meanwhile, the free-standing trilayer membrane can be transferred onto a new silicon substrate, where the flexible membrane is directly placed on the new substrate without using any spacers between them [ Fig. 1(g)]. Then, the conformable contact between the trans- ferred membrane and the new substrate can allow new etching capability, which is not effective in typical stencil lithography using spacers, using the trilayer nanoporous membrane as a new etch mask. Then, it will result in nanohole structures [ Fig. 1(h)], instead of nanopillar ...Context 9
... without using any spacers between them [ Fig. 1(g)]. Then, the conformable contact between the trans- ferred membrane and the new substrate can allow new etching capability, which is not effective in typical stencil lithography using spacers, using the trilayer nanoporous membrane as a new etch mask. Then, it will result in nanohole structures [ Fig. 1(h)], instead of nanopillar structures obtainable from the lift-off process [ Fig. 1(f)]. It suggests that just by perform- ing single holographic nanopatterning, we can obtain both nanopillar-and nanohole-type structures at the same time con- veniently. The trilayer membrane can also be released again from the new silicon substrate by ...Context 10
... between the trans- ferred membrane and the new substrate can allow new etching capability, which is not effective in typical stencil lithography using spacers, using the trilayer nanoporous membrane as a new etch mask. Then, it will result in nanohole structures [ Fig. 1(h)], instead of nanopillar structures obtainable from the lift-off process [ Fig. 1(f)]. It suggests that just by perform- ing single holographic nanopatterning, we can obtain both nanopillar-and nanohole-type structures at the same time con- veniently. The trilayer membrane can also be released again from the new silicon substrate by using the same chemical solution (NH 3 /H 2 O 2 /H 2 O) and reused multiple times. In ...Context 11
... at the same time con- veniently. The trilayer membrane can also be released again from the new silicon substrate by using the same chemical solution (NH 3 /H 2 O 2 /H 2 O) and reused multiple times. In addi- tion to silicon substrates, the thin flexible trilayer membrane can also be transferred to many other substrate materials, such as PDMS [ Fig. 1(i)] where the direct lithography with photo- resist material is not effective as discussed earlier. Then, various nanostructures can also be effectively defined on the PDMS substrate through the nanoporous membrane, e.g., dep- osition of metals [ Fig. 1(j)]. The trilayer can also be released by using the detaching solution (NH 3 /H 2 O 2 ...Context 12
... trilayer membrane can also be transferred to many other substrate materials, such as PDMS [ Fig. 1(i)] where the direct lithography with photo- resist material is not effective as discussed earlier. Then, various nanostructures can also be effectively defined on the PDMS substrate through the nanoporous membrane, e.g., dep- osition of metals [ Fig. 1(j)]. The trilayer can also be released by using the detaching solution (NH 3 /H 2 O 2 /H 2 O) and reused for many ...Context 13
... the deposition of metal (Cr) layer on a silicon sub- strate [ Fig. 1(c)], a 50-70 nm thick Cr layer was deposited by using e-beam evaporation (PVD 75, Kurt Lesker, Inc.). The deposition rate was controlled to be less than 0.2 nm/s. During deposition, the pressure of the chamber was main- tained below 10 À5 mTorr to ensure uniform deposition. The same e-beam evaporation process was also applied for the ...Context 14
... Inc.). The deposition rate was controlled to be less than 0.2 nm/s. During deposition, the pressure of the chamber was main- tained below 10 À5 mTorr to ensure uniform deposition. The same e-beam evaporation process was also applied for the deposition of a metal (Au) layer on the new PDMS substrate through the Cr/PR/ARC trilayer transferred [ Fig. 1(i)]. The aspect ratio of the gold nanopillar structures on the PDMS substrate [ Fig. 1(j)] was controlled by changing the deposi- tion time. In this experiment, two different thicknesses of the gold layers, 200 nm and 500 nm, were ...Context 15
... the pressure of the chamber was main- tained below 10 À5 mTorr to ensure uniform deposition. The same e-beam evaporation process was also applied for the deposition of a metal (Au) layer on the new PDMS substrate through the Cr/PR/ARC trilayer transferred [ Fig. 1(i)]. The aspect ratio of the gold nanopillar structures on the PDMS substrate [ Fig. 1(j)] was controlled by changing the deposi- tion time. In this experiment, two different thicknesses of the gold layers, 200 nm and 500 nm, were ...Context 16
... the release of the metal/PR/ARC trilayer film as a free-standing membrane from the substrate [ Fig. 1(d)], cus- tomized solution of NH 3 /H 2 O 2 /H 2 O mixture was prepared and the sample was directly immersed into the solution. The ratio of each chemical was characterized to make sure the bottom ARC layer could be separated from the silicon wafer effectively without fracturing. 13,14 The lift-off process was largely affected by the ...Context 17
... the transfer of the free-standing membrane onto a new substrate [Figs. 1(g) and 1(i)], a new substrate (silicon or PDMS in this experiment) was also immersed into the solution to be placed underneath the trilayer film. Then, the solution was gradually drained out from the container until the trilayer membrane became contacted and spread out on the new substrate. In order to facilitate conformable and good bonding ...Context 18
... and spread out on the new substrate. In order to facilitate conformable and good bonding between the transferred trilayer membrane and the new substrates, the sample was degassed in vacuum for several hours. The same release and transfer methods were applied to the trilayer membranes even after the DRIE etching on the new silicon substrate [ Fig. 1(h)] or the metal deposition on the new PDMS substrate [ Fig. ...Context 19
... conformable and good bonding between the transferred trilayer membrane and the new substrates, the sample was degassed in vacuum for several hours. The same release and transfer methods were applied to the trilayer membranes even after the DRIE etching on the new silicon substrate [ Fig. 1(h)] or the metal deposition on the new PDMS substrate [ Fig. ...Context 20
... compared to the Bosch process that normally results in scalloping sidewall profiles. 19 Due to the very high etch selectivity of the silicon material to metal (e.g., Cr), the degradation or the thinning of the trilayer membrane was not significant. Figures 2(a)-2(c) show the experimental results corre- sponding to the schematics illustrated in Figs. 1(a)-1(c), respectively. Figure 2(a) shows the square array (935 nm in periodicity) of nanopore patterns (pore size of $500 nm) of the negative PR layer (1.5 lm thick) created by using laser interference lithography. Although not shown here, the pore size can be regulated by adjusting the exposure conditions in the lithographic process. 15 ...Context 21
... ARC interlayer. The size of the Cr nanostructures deposited on the bottom surface was $600 nm in diameter, which was slightly smaller than the pore size of the PR/ARC membrane ($650 nm in diameter). Figure 3 shows the Cr/PR/ARC trilayer released from the specially designed wet solution (NH 3 /H 2 O 2 /H 2 O), corre- sponding to the schematic of Fig. 1(d). NH 3 in the solution was designed to slowly etch the silicon and separate the ARC layer from the substrate. 14 In the meantime, H 2 O 2 generates gas bubbles not only in the bulk solution but also at the inter- face between the ARC layer and the silicon substrate. The gas bubbles help to separate and lift up the trilayer membrane from ...Context 22
... process. It further shows that the thin trilayer membrane is mechanically flexible so that no cracks or fracture is shown on the surface even being bent or rolled. Figure 4(a) shows the Cr nanodot patterns ($600 nm in diameter) retained on the silicon substrate after the separation of the Cr/PR/ARC trilayer, corresponding to the schematic of Fig. 1(e). It shows that the release process using the wet chemical does not delaminate or deform the Cr layer depos- ited on the silicon substrate. Such a well-defined metal layer is useful as a robust etch mask layer, especially in plasma- based dry etching such as DRIE. Figure 4(b) shows the result of DRIE of the silicon substrate by using ...Context 23
... not delaminate or deform the Cr layer depos- ited on the silicon substrate. Such a well-defined metal layer is useful as a robust etch mask layer, especially in plasma- based dry etching such as DRIE. Figure 4(b) shows the result of DRIE of the silicon substrate by using the thin Cr layer ($70 nm) as etch mask, corresponding to the schematic of Fig. 1(f). It shows the silicon nanopillar structures of $1 lm tall. On top of the silicon structures, a thin Cr cap layer is still observable, which indicates the high etch selectivity of the metal layer against the silicon material. Figure 5(a) shows the free-standing Cr/PR/ARC trilayer membrane after being released and then transferred onto a ...Context 24
... $1 lm tall. On top of the silicon structures, a thin Cr cap layer is still observable, which indicates the high etch selectivity of the metal layer against the silicon material. Figure 5(a) shows the free-standing Cr/PR/ARC trilayer membrane after being released and then transferred onto a new silicon substrate, corresponding to the schematic of Fig. 1(g). It shows uniform contact of the transferred membrane onto the new silicon substrate with no fracture or wrinkles. In order to obtain the conformable contact, it was found that the degassing step was critical after physically transferring the free-standing membrane onto the new substrate. Such degassing process helps to remove the gas ...Context 25
... of the PR nanostructures, which resulted in the larger pore dimension in the lower region of the film that directly con- tacted with the silicon substrate. Despite the slight deviation of the fabricated pore sizes compared to that of the stencil membrane, it shows that silicon nanohole structures are uni- formly fabricated, as illustrated in Fig. 1(h). It demonstrates that by using one same stencil, we can obtain both nanopillar patterns [ Fig. 4(b)] and nanohole patterns [ Fig. 5(b)]. It was enabled by the novel reuse of the holographic nanopatterns as a free-standing membrane for both the lift-off and the stencil lithography applications. Although stencil lithography has been ...Context 26
... damage. When used more times, it was observed that the flexibility of the trilayer mem- brane was degraded, often resulting in the fracture of the membrane into pieces in the release/transfer process. Figure 6 shows the free-standing Cr/PR/ARC trilayer membrane (3 cm  3 cm) transferred onto a PDMS substrate, corresponding to the schematic of Fig. 1(i). Figure 6(a) reveals that the transferred trilayer membrane of a large area does not show significant delamination and cracks even when the PDMS substrate is bent or twisted. It demonstrates another advantage of the use of flexible stencil, compared to hard and rigid stencils that were typically used in conven- tional stencil ...Context 27
... trilayer mem- brane and the PDMS substrate. It was also made possible by applying the degassing process of the sample in vacuum, which helps to remove any entrapped gas at the interface. Figure 7 shows the deposition result of a gold layer through the transferred trilayer membrane on the PDMS substrate, corresponding to the schematics of Fig. 1(j). The trilayer membrane was released again from the PDMS sub- strate after the deposition of the gold film by using the same chemical method (NH 3 /H 2 O 2 /H 2 O) used for the silicon sub- strate. In comparison to the release from the silicon substrate, the time required for the release of the trilayer membrane from the PDMS substrate ...Similar publications
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Citations
... In recent years, the use of high-aspect-ratio micro/nanostructures in biochemical applications has sparked a growing interest. 11,12 These structures provide more binding sites for molecules and offer morphological features that promote effective interactions with surface probes during biochemical reactions. 13,14 As an example, zinc oxide (ZnO) nanorods were integrated as the working electrode in an electrochemical biosensor. ...
CRISPR technology has gained widespread adoption for pathogen detection due to its exceptional sensitivity and specificity. Although recent studies have investigated the potential of high-aspect-ratio microstructures in enhancing biochemical applications, their application in CRISPR-based detection has been relatively rare. In this study, we developed a FRET-based biosensor in combination with high-aspect-ratio microstructures and Cas12a-mediated trans-cleavage for detecting HPV 16 DNA fragments. Remarkably, our results show that micropillars with higher density exhibit superior molecular binding capabilities, leading to a tenfold increase in detection sensitivity. Furthermore, we investigated the effectiveness of two surface chemical treatment methods for enhancing the developed FRET assay. A simple and effective approach was also developed to mitigate bubble generation in microfluidic devices, a crucial issue in biochemical reactions within such devices. Overall, this work introduces a novel approach using micropillars for CRISPR-based viral detection and provides valuable insights into optimizing biochemical reactions within microfluidic devices.
... To increase the surface roughness, advanced nanopatterning techniques such as black silicon [13], metal-assisted chemical etching [14], and anodization [15] have been explored to realize such bio-inspired and high-aspect-ratio nanostructures. To further increase the surface roughness and achieve multiscale hierarchical micro-and nanostructures, a nanostencil lithography technique has also been employed, capable of patterning uniform and high-aspect-ratio nanostructures selectively on top, bottom, or both top and bottom of pre-patterned microstructures [16][17][18][19][20]. However, the minimum feature size of the nanostructures attainable in such a technique is limited by the resolution of the nanostencil. ...
The manipulation of droplet mobility on a nanotextured surface by oxygen plasma is demonstrated by modulating the modes of hydrophobic coatings and controlling the hierarchy of nanostructures. The spin-coating of polytetrafluoroethylene (PTFE) allows for heterogeneous hydrophobization of the high-aspect-ratio nanostructures and provides the nanostructured surface with "sticky hydrophobicity", whereas the self-assembledmonolayer coating of perfluorodecyltrichlorosilane (FDTS) results in homogeneous hydrophobization and "slippery superhydrophobicity". While the high droplet adhesion (stickiness) on a nanostructured surface with the spin-coating of PTFE is maintained, the droplet contact angle is enhanced by creating hierarchical nanostructures via the combination of oxygen plasma etching with laser interference lithography to achieve "sticky superhydrophobicity". Similarly, the droplet mobility on a slippery nanostructured surface with the self-assembled monolayer coating of FDTS is also enhanced by employing the hierarchical nanostructures to achieve "slippery superhydrophobicity" with modulated slipperiness.
... The plasma etching with longer duration formed the nanostructures with higher aspect ratio. In addition, the isotropic oxygen plasma etching resulted in the increase of pore size of photoresist patterns and transformed the "pore-on-pore" hierarchical nanostructures to "pillaron-pillar" hierarchical nanostructures ( Fig. 5d- [31,69,70]. ...
In recent years, plasma-induced self-formation of polymer nanostructures has emerged as a simple, scalable and rapid nanomanufacturing technique to pattern sub-100 nm nanostructures. High-aspect-ratio nanostructures (>20:1) are fabricated on a variety of polymer surfaces such as poly(methylmethacrylate) (PMMA), polystyrene (PS), polydimethylsiloxane (PDMS), and fluorinated ethylene propylene (FEP). Sub-100 nm nanostructures (i.e. diameter ≤ 50 nm) are fabricated in this one-step process without relying on slow and expensive nanolithography techniques. This review starts with discussion of the self-formation mechanisms including surface modulation, random masks, and materials impurities. Emphasis is put on the applications of polymer nanostructures in the fields of hierarchical nanostructures, liquid repellence, adhesion, lab-on-a-chip, surface enhanced Raman scattering (SERS), organic light emitting diode (OLED), and energy harvesting. The unique advantages of this nanomanufacturing technique are illustrated, followed by prospects.
... Previously, we reported on a soft nanostencil lithography technique, where a free-standing nanostencil membrane was employed for the creation of high-aspect-ratio silicon nanostructures [14,15]. We also showed that silicon nanopillars could be patterned on the top surfaces of microstructures by the soft nanostencil lithography, whereas the nanostructures could not be patterned on the bottom surfaces of the microstructures due to the 'blurring' effect [16]. ...
It is challenging to hierarchically pattern high-aspect-ratio nanostructures on microstructures using conventional lithographic techniques, where photoresist film is not able to uniformly cover on the microstructures as the aspect ratio increases. Such non-uniformity causes poor definition of nanopatterns over the microstructures. Nanostencil lithography can provide an alternative means to hierarchically construct nanostructures on microstructures via direct deposition or plasma etching through a free-standing nanoporous membrane. In this work, we demonstrate the hierarchical fabrication of high-aspect-ratio nanostructures on microstructures of silicon using a free-standing nanostencil, which is a nanoporous membrane consisting of metal (Cr), photoresist (PR), and anti-reflective coating (ARC). The nanostencil membrane is used as a deposition mask to define Cr nanodot patterns on the predefined silicon microstructures. Then, deep reactive ion etching (DRIE) is used to hierarchically create nanostructures on the microstructures using the Cr nanodots as an etch mask. With simple modification of the main fabrication processes, high-aspect-ratio nanopillars are selectively defined only on top of the microstructures, on bottom, or on both top and bottom.
... Stencil lithography, on the other hand, can be used to pattern metal structures on the substrate repeatedly. Recently, we have also developed a process to achieve a tri-layer stencil mask comprised of ARC/photoresist/metal and investigated the use of a tri-layer stencil mask for dual applications to create both negative and positive patterns of the stencil mask via lift-off and dry-etching methods, respectively [98]. ...
... As shown in Figure 10a, ARC and photoresist were patterned using laser interference lithography and plasma etching, then a thin Cr layer (20 nm) was coated on the silicon surface [98]. Instead of removing the membrane with acetone or another solvent, the ARC/photoresist/Cr tri-layer was released by using the mixture of H 2 O 2 and NH 3 . ...
... (a) Schematic of dual patterning of both nanopillars and nanoholes on silicon substrates by using tri-layer membrane based stencil lithography technique. Reprinted with permission from[98]. Copyright[2012], American Vacuum Society; (b) image of a tri-layer membrane placed on microhole-patterned silicon substrate. ...
In this paper, we review the current development of stencil lithography for scalable micro- and nanomanufacturing as a resistless and reusable patterning technique. We first introduce the motivation and advantages of stencil lithography for large-area micro- and nanopatterning. Then we review the progress of using rigid membranes such as SiNx and Si as stencil masks as well as stacking layers. We also review the current use of flexible membranes including a compliant SiNx membrane with springs, polyimide film, polydimethylsiloxane (PDMS) layer, and photoresist-based membranes as stencil lithography masks to address problems such as blurring and non-planar surface patterning. Moreover, we discuss the dynamic stencil lithography technique, which significantly improves the patterning throughput and speed by moving the stencil over the target substrate during deposition. Lastly, we discuss the future advancement of stencil lithography for a resistless, reusable, scalable, and programmable nanolithography method.
... Bottom-up approaches such as soft lithography [5,6] and self-assembly [7] are relatively inexpensive and offer scalability, but suffer from limited design geometries and lack of control of the shape and position of nanostructures. Hybrid nanofabrication approaches such as nanoimprint lithography [8,9], edge lithography [10,11], and stencil lithography [12,13] are promising in terms of reducing fabrication costs and offering more flexibility in design of nanopattern geometries. Other nanofabrication methods such as laser interference lithography [14][15][16] and maskless etching [17][18][19] are capable of patterning large areas with specific patterns, but are not suitable for patterning arbitrary shapes. ...
Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology.
... The cross-sectional view shows the smooth vertical sidewall profile of the nanopore patterns of the negative photoresist layer, which was made possible by using the ARC interlayer. 35,[38][39][40][41][42][43] During exposure, the incident light hitting the substrate interferes with the light reflected from the substrate. Without ARC, the intensities of reflective and incident light become comparable; this results in a significant standing wave in the vertical direction with a period equal to half of the laser's wavelength. ...
The authors present a high-throughput fabrication technique to create a large-area graphene nanomesh (GNM). A patterned negative photoresist layer was used as an etch mask atop chemical vapor deposition grown graphene on Cu foil. Shielded by the periodic nanopatterned photoresist mask, the graphene layer was selectively etched using O2 plasma, forming a GNM layer. A poly(methyl methacrylate) layer was spun on the GNM atop copper foil, and the GNM was subsequently transferred onto a SiO2/Si substrate by etching away the copper foil. Large-area (5 × 5 cm), periodic (500 and 935 nm in pitch), uniform, and flexible GNMs were successfully fabricated with precisely controlled pore sizes (200–900 nm) and neck widths (down to ∼20 nm) by adjusting the pattern generation of holographic lithography and the O2 plasma etching process parameters. This holographic lithography-based transfer method provides a low-cost manufacturing alternative for large-area, nanoscale-patterned GNMs on an arbitrary substrate.
... The base-level nanostructures of a larger dimension can be prepared by using a lithographic method, such as laser interference lithography. Among various nanolithography techniques, laser interference lithography is one of the most efficient optical lithography techniques to create uniform nanopattern arrays over a large substrate area (wafer-level) with good control of the pattern periodicity [23,24], allowing many new applications in nanofabrication with superior simplicity and convenience [25][26][27][28][29][30][31][32][33][34]. In this optical lithography, vertical standing wave effects due to reflection of the incident light from the substrate surface cause serious scalloping profiles along the sidewalls of the patterned photoresist structures [35]. ...
In this paper, we introduce a simple fabrication technique which can pattern high-aspect-ratio polymer nanowire structures of photoresist films by using a maskless one-step oxygen plasma etching process. When carbon-based photoresist materials on silicon substrates are etched by oxygen plasma in a metallic etching chamber, nanoparticles such as antimony, aluminum, fluorine, silicon or their compound materials are self-generated and densely occupy the photoresist polymer surface. Such self-masking effects result in the formation of high-aspect-ratio vertical nanowire arrays of the polymer in the reactive ion etching mode without the necessity of any artificial etch mask. Nanowires fabricated by this technique have a diameter of less than 50 nm and an aspect ratio greater than 20. When such nanowires are fabricated on lithographically pre-patterned photoresist films, hierarchical and hybrid nanostructures of polymer are also conveniently attained. This simple and high-throughput fabrication technique for polymer nanostructures should pave the way to a wide range of applications such as in sensors, energy storage, optical devices and microfluidics systems.
... Then, a free-standing trilayer membrane consisting of Cr (top), photoresist (middle), and ARC (bottom) is placed on the microstructured silicon substrate [ Fig. 1(b)]. A customized fabrication procedure, reported in detail earlier, 29,30 is employed for the preparation and transfer of the freestanding trilayer membrane. Briefly, the ARC and photoresist materials are spin-coated on a planar silicon substrate, forming a bilayer. ...
... The trilayer film was then released from the supporting substrate in a NH 3 /H 2 O 2 / H 2 O solution (1:1:10 in volume ratio). 29,30 The solution was gradually replaced by de-ionized water in order to rinse and transfer the free-standing membrane in the liquid water. The free-standing trilayer membrane was transferred onto the microstructured silicon substrate to fully cover the surface by immersing the prepatterned silicon substrate underneath the trilayer membrane floating in the water and then draining the liquid. ...
... 1(c) and 1(d)], the sample was etched by using the same cryogenic DRIE process that was previously used in the fabrication of the first-level microstructures. After that, the nanoporous trilayer membrane was released from the silicon substrate by using the same solution of NH 3 /H 2 O 2 /H 2 O. 29,30 For the fabrication of the high-aspect-ratio nanopillar structures on the microstructures [Figs. 1(e)-1(h)], a Cr layer of 30 nm thick was first deposited on the sample by using ebeam evaporation (PVD 75, Kurt J. Lesker Company). ...
Hierarchical nanostructures are typically fabricated with multiple lithography steps on prepatterned micro- or nanostructures. However, such conventional multiple lithography steps result in poor coverage and uniformity, especially when patterning on high-aspect-ratio micro- or nanostructures. In this work, the authors present a new fabrication method which can make hierarchical nanostructures even on high-aspect-ratio prepatterns, using a free-standing trilayer membrane. The nanoporous trilayer composite films, consisting of metal/photoresist/antireflective coating, is created on a planar silicon substrate by using laser interference lithography, reactive ion etching, and e-beam deposition. Then, a customized solution of ammonia (NH3), hydrogen peroxide (H2O2), and water (H2O) is used to release the composite film from the supporting substrate. The free-standing composite membrane is then transferred on a prepatterned silicon substrate. Showing no major defects on the membrane surface, the flexible and soft trilayer membrane allows a good, uniform contact with the top surface of the prepatterns and is utilized as a robust etch mask in the deep reactive ion etching (DRIE) process of silicon to fabricate hierarchical nanopore structures. Since the membrane covers the top surfaces of the prepatterns seamlessly, the nanopore patterns of the membrane are transferred onto the top surfaces with great fidelity during the etching process. The membrane can also be used as a stencil for deposition processes. For example, metal is deposited through the nanoporous membrane by a lift-off process. Then, the transferred metal nanodot patterns are used as an etch mask in the DRIE process to achieve high-aspect-ratio hierarchical nanopillar structures. Compared to conventional methods to fabricate hierarchical nanostructure, the introduced new approach is more reliable and versatile to realize large-area hierarchical nanostructures with a- good uniformity, in both nanopore and nanopillar array by using the same single membrane.
... A variant of this technique uses epoxy to bond the metal layer directly to a glass carrier [13]. Alternatively, the metal plus photoresist pattern can be further transferred into the underlying antireflection layer using RIE and then peeled off the wafer, producing a thin, flexible perforated stencil which may then be placed on another surface or substrate as a mask for etching or deposition [20]. ...
The non-uniform intensity profile of Gaussian-like laser beams used in interference lithography (IL) leads to a non-uniform dose and feature size distribution across the sample. Previously described methods to improve dose uniformity are reviewed. However, here we examine the behavior of the non-uniformity from the viewpoint of photoresist response rather than the IL system configuration. Samples with a fixed intra-sample dose profile were exposed with an increasing average dose. A line/space pattern with a period of 240 nm across an area of 2 × 2 cm(2) was produced using IL on identical samples using a HeCd laser operated at 325 nm and a Lloyd's mirror IL system. A binary model of photoresist response predicts that the absolute range of line widths in nanometers should be significantly reduced as the overall sample dose is increased. We have experimentally verified a reduction in the range of line widths within a given sample from 50 to 16 nm as the overall dose is increased by only 60%. This resulted in a drop in the narrowest line width from 120 to 65 nm. An etch process is demonstrated to increase the line width by generating a wider secondary chrome hard mask from the narrowly patterned primary chrome hard mask. The subsequent fabrication of a silicon nanoimprint mold is used as a demonstration of the technique.
