Displacement Talbot Lithography Research Articles

P‐107: High‐Resolution Periodic Patterning for Volume Manufacturing on +300mm Size Substrates Using Displacement Talbot Lithography

The photonic device market has a need for low‐cost, high‐resolution periodic patterning that scales with product maturity to large substrate sizes. Eulitha's DTL (Displacement Talbot Lithography) technology was limited to only a single exposure field per substrate on preexisting platforms which can fully pattern 100 and 150mm substrates. The new ‘PhableS' is Eulitha's step‐and‐repeat solution to bring all the advantages of the DTL patterning to larger substrates.The PhableS tool builds on Eulitha's patented displacement Talbot lithography technology to open the way for customers to fully scale to high volume production. This tool retains the strong technical performance; including 60nm half pitch resolution (DUV version), 140x140mm2 single shot exposure field, large depth of focus (hundreds of microns), high throughput (+40wph), non‐contact, mask‐based patterning. Automated wafer and mask handling support industry expected repeatability and defect‐free patterning.

Synthesis of Well-Ordered Functionalized Silicon Microwires Using Displacement Talbot Lithography for Photocatalysis.

Metal-assisted chemical etching (MACE) is a cheap and scalable method that is commonly used to obtain silicon nano- or microwires but lacks spatial control. Herein, we present a synthesis method for producing vertical and highly periodic silicon microwires, using displacement Talbot lithography before wet etching with MACE. The functionalized periodic silicon microwires show 65% higher PEC performance and 2.3 mA/cm2 higher net photocurrent at 0 V compared to functionalized, randomly distributed microwires obtained by conventional MACE at the same potentials.

Angle-Resolved Optical Characterization of a Plasmonic Triangular Array of Elliptical Holes in a Gold Layer

Plasmonic arrays are grating-like structures able to couple an incoming electromagnetic field into either localized or propagating surface plasmonic modes. A triangular array of elliptical holes in a gold layer were realized resorting to displacement Talbot lithography. Scanning electron microscopy was used to evaluate the geometrical features and finite time domain simulations were performed to verify the consistency of the design. The optical response was characterized by angle-resolved reflectance and transmittance measurements. The results demonstrate the good quality and uniformity of the array. Furthermore, the study on the dependence of the optical response on both the hexagonal lattice and the elliptical hole-defined symmetry properties was conducted allowing the distinction of their effects on both the localized and propagating plasmonic modes. The results indicate that the localized component of the plasmonic modes is mainly affected by the elliptical shape, while the propagating part is influenced by the hexagonal lattice symmetry.

Nanofabrication Process Scale-Up via Displacement Talbot Lithography of a Plasmonic Metasurface for Sensing Applications

The selection of an affordable method to fabricate plasmonic metasurfaces needs to guarantee complex control over both tunability and reproducibility of their spectral and morphological properties, making plasmonic metasurfaces suitable for integration into different sensing devices. Displacement Talbot lithography could be a valid solution thanks to the limited fabrication steps required, also providing the highly desired industrial scalability. Fabricated plasmonic metasurfaces are represented by a gold nanohole array on a glass substrate based on a triangular pattern. Scanning electron microscopy measurements have been recorded, showing the consistency of the surface features with the optimized design parameters. Reflectance and transmittance measurements have also been carried out to test the reliability and standardization of the metasurface’s optical response. Furthermore, these plasmonic metasurfaces have also been successfully tested for probing refractive index variations in a microfluidic system, paving the way for their use in sensitive, real-time, label-free, and multiplexing detection of bio-molecular events.

Exploring the surface-enhanced Raman scattering (SERS) activity of gold nanostructures embedded around nanogaps at wafer scale: Simulations and experiments

A unique way of converting free space light into a local electromagnetic field in small spaces is via metallic nanostructuring. In this work fabrication, experimental characterization and simulation of surface-enhanced Raman scattering (SERS) active specimens based on Au nanostructures are discussed. We used displacement Talbot lithography (DTL) to fabricate silicon nano-wedge substrates with Au nanostructures embedded around their apices. After the ion beam etching process, a nanogap is introduced between two Au nanostructures templated over nano-wedges, yielding specimens with SERS characteristics. The Au nanostructures and the nanogaps have symmetric and asymmetric configurations with respect to the wedges. With this nanofabrication method, various wafer-scale specimens were fabricated with highly controllable nanogaps with a size in the order of 6 nm for symmetric gaps and 8 nm for asymmetric gaps. SERS characteristics of these specimens were analyzed experimentally by calculating their analytical enhancement factor (AEF). According to finite-difference time-domain (FDTD) simulations, the Raman enhancement arises at the narrow gap due to plasmonic resonances, yielding a maximum AEF of 6.9 × 106. The results highlight the SERS activity of the nanostructures and ultimately comply with reliable substrates for practical applications.

High aspect ratio arrays of Si nano-pillars using displacement Talbot lithography and gas-MacEtch

Structuring Si in arrays of vertical high aspect ratio pillars, ranging from nanoscale to macroscale feature dimensions, is essential for producing functional interfaces for many applications. Arrays of silicon 3D nanostructures are needed to realize photonic and phononic crystals, waveguides, metalenses, X-ray wavefront sensors, detectors. In particular, arrays of Si nanopillars are used as bio-interfaces in neural activity recording, cell culture, microfluidics, sensing and on-chip manipulation. Here, we demonstrate a strategy for realizing arrays of protruding sharp Si nanopillars, using displacement Talbot lithography combined with metal-assisted chemical etching (MacEtch) in gas phase. Such combination enables reliable and low cost pathway for fabrication of ordered nanopillars arrays on large scale. With the double exposure of a linear grating mask in orthogonal orientations and the lift-off technique, we realized a catalyst pattern of holes in a Pt thin film with a period of 1 μm and hole diameter in the range of 100–250 nm. MacEtch in gas phase by using vapor HF and oxygen from air allows to etch arrays of protruding Si nanopillars 200 nm-thick and aspect ratio in the range of 200 (pillar height/width) with an etching rate up to 1 μm/min. Gas-MacEtch has the advantage of no capillary stiction, no ion beam damage of the Si substrate, nanometric resolution and high fidelity of pattern transfer. In combination with controlled uniformity of feature size on large area, spatial frequency doubling and high resolution of Talbot lithography, the proposed method is an easy-to-scale-up processing that can support the fabrication of Si pillars arrays for many valuable applications both at micro and nano-scale.

Self-Aligned Crystallographic Multiplication of Nanoscale Silicon Wedges for High-Density Fabrication of 3D Nanodevices.

High-density arrays of silicon wedges bound by {111} planes on silicon (100) wafers have been created by combining convex corner lithography on a silicon dioxide hard mask with anisotropic, crystallographic etching in a repetitive, self-aligned multiplication procedure. A mean pitch of around 30 nm has been achieved, based on an initial pitch of ∼120 nm obtained through displacement Talbot lithography. The typical resolution of the convex corner lithography was reduced to the sub-10 nm range by employing an 8 nm silicon dioxide mask layer (measured on the {111} planes). Nanogaps of 6 nm and freestanding silicon dioxide flaps as thin as 1-2 nm can be obtained when etching the silicon at the exposed apices of the wedges. To enable the repetitive procedure, it was necessary to protect the concave corners between the wedges through "concave" corner lithography. The produced high-density arrays of wedges offer a promising template for the fabrication of large arrays of nanodevices in various domains with relevant details in the sub-10 nm range.

High Aspect Ratio Arrays of Si Nano-Pillars Using Displacement Talbot Lithography and Gas-Macetch

High Aspect Ratio Arrays of Si Nano-Pillars Using Displacement Talbot Lithography and Gas-Macetch

Ultra‐thin GaAs solar cells with nanophotonic metal‐dielectric diffraction gratings fabricated with displacement Talbot lithography

AbstractUltra‐thin photovoltaics enable lightweight flexible form factors, suitable for emerging terrestrial applications such as electric vehicle integration. These devices also exhibit intrinsic radiation tolerance and increased specific power and so are uniquely enabling for space power applications, offering longer missions in hostile environments and reduced launch costs. In this work, a GaAs solar cell with an 80‐nm absorber is developed with short circuit current exceeding the single pass limit. Integrated light management is employed to compensate for increased photon transmission inherent to ultra‐thin absorbers, and efficiency enhancement of 68% over a planar on‐wafer equivalent is demonstrated. This is achieved using a wafer‐scale technique, displacement Talbot lithography, to fabricate a rear surface nanophotonic grating. Optical simulations definitively confirm Fabry‐Perot and waveguide mode contributions to the observed increase in absorption and also demonstrate a pathway to short circuit current of 26 mA/cm2, well in excess of the double pass limit.

Spatial periodicities inside the Talbot effect: understanding, control and applications for lithography.

Displacement Talbot Lithography (DTL) is a simple patterning technique for creating periodic sub-micron features on wafer areas up to 200 mm diameter for applications in, for example, plasmonic, photonic crystals, and metamaterials. It exploits the diffraction and interference generally avoided in classical lithography. The Talbot effect, on which DTL is based, is the periodic spatial repetition of a periodic mask illuminated by coherent light. The modelling of this phenomenon is essential to fully understand and predict the interference pattern obtained; for mask periods greater than twice the wavelength, new spatial periodicities are generally introduced that are smaller than the Talbot length. This study reports simulations of multiple 1D masks to explain the influence of these smaller spatial periodicities on the Talbot effect. By changing the mask configuration, one can tailor the spatial periodicity contributions and thus, control the feature size, uniformity, and contrast for Talbot-effect-based lithography.

Optimization of displacement Talbot lithography for fabrication of uniform high aspect ratio gratings

Displacement Talbot lithography can rapidly pattern periodic nanostructures with high depth of focus over large area. Imperfections in the phase mask profile and the stage movement inaccuracies during the exposure cause linewidth variation in every second line of binary gratings. While this beating is barely visible in patterned photoresist, it leads to substantial depth variation when transferred into high aspect ratio silicon structures, because of micro-loading in deep reactive ion etching. A proper scan range compensated the defect, and a beating-free grating with pitch size of 1 μm and aspect ratio of 54:1 is demonstrated.

High-birefringence waveguide Bragg gratings fabricated in a silica-on-silicon platform with displacement Talbot lithography

High-birefringence waveguide Bragg gratings for the C-band are fabricated in the Silica-on-Silicon platform with Displacement Talbot Lithography (DTL). Transmission and reflection spectrums of the Bragg wavelength splitting were measured and calculated. The birefringence here is up to 7.919×10−4 to 1.670×10−3, much higher than existing devices via other platforms. We illustrate the principle and advantage of DTL though theoretical analysis and numerical simulation. The birefringence of waveguide Bragg gratings here are customized with their device configuration (i.e., waveguide width and grating etched depth), enabling an effective method to construct scalable Silica-on-Silicon devices for highly linear-polarized external-cavity semiconductor lasers.

Wafer-scale nanofabrication of sub-100 nm arrays by deep-UV displacement Talbot lithography

In this manuscript, we demonstrate the potential of replacing the standard bottom anti-reflective coating (BARC) with a polymethylglutarimide (PMGI) layer for wafer-scale nanofabrication by means of deep-UV displacement talbot lithography (DTL). PMGI is functioning as a developable non-UV sensitive bottom anti-reflective coating (DBARC). After introducing the fabrication process using a standard BARC-based coating and the novel PMGI-based one, the DTL nanopatterning capabilities for both coatings are compared by means of the fabrication of etched nanoholes in a dielectric layer and metal nanodots made by lift-off. Improvement of DTL capabilities are attributed to a reduction of process complexity by avoiding the use of O2 plasma etching of the BARC layer. We show the capacity of this approach to produce nanoholes or nanodots with diameters ranging from 95 to 200 nm at a wafer-scale using only one mask and a proper exposing dose. The minimum diameter of the nanoholes is reduced from 118 to 95 nm when using the PMGI-based coating instead of the BARC-based one. The possibilities opened by the PMGI-based coating are illustrated by the successful fabrication of an array of nanoholes with sub-100 nm diameter for GaAs nanowire growth on a 2″ GaAs wafer, a 2″ nanoimprint lithography (NIL) master stamp, and an array of Au nanodots made by lift-off on a 4″ silica wafer. Therefore, DTL possess the potential for wafer-scale manufacturing of nano-engineered materials.

Large-Scale Fabrication of Optically Active Plasmonic Arrays via Displacement Talbot Lithography

Periodic nanoapertures fabricated in thin metal films exhibit a range of interesting properties in the presence of electromagnetic waves including phenomena such as extraordinary optical transmission (EOT). Fundamentally, these effects are mediated by plasmons and have been shown to have a vast range of applications, including, colour filtering, chemical sensing, and as components in solar cells. In the majority of cases, the high spatial resolution required for precise fabrication of these structures is limited to direct writing techniques such as Focused Ion Beam (FIB) and Electron beam lithography (EBL), which only cover relatively small, micron-sized, areas. In this article, we describe and demonstrate the fabrication of plasmonically active devices in the visible range using Displacement Talbot Lithography (DTL). This method allows nanometre-resolution photolithography to be performed over very large areas (whole wafers) without any significant degradation in quality. We present experimental results for a range of different structures including periodic, aperiodic and hexagonal configurations in silver films.

Self-images contrast enhancement for displacement Talbot lithography by means of composite mesoscale amplitude-phase masks

We propose a new design of composite wavelength-scale amplitude-phase diffraction grating as applied to the displacement Talbot lithography. The grating is composed of a conventional metal amplitude binary mask with superposed dielectric phase steps and provides for manyfold optical contrast enhancement of the integrated ‘Talbot carpet’ as opposed to the amplitude and phase masks purely. By means of the finite element calculations, we analyze the spatial field structure in the proposed gratings with different geometric ridge shapes and show that due to Mie-type resonances excitation the semielliptical dielectric steps in the combination with metal amplitude mask demonstrate excellent spatial resolution (∼) and highest optical contrast (∼22 dB) of integrated Talbot self-images.

Displacement Talbot lithography for nano-engineering of III-nitride materials

Nano-engineering III-nitride semiconductors offers a route to further control the optoelectronic properties, enabling novel functionalities and applications. Although a variety of lithography techniques are currently employed to nano-engineer these materials, the scalability and cost of the fabrication process can be an obstacle for large-scale manufacturing. In this paper, we report on the use of a fast, robust and flexible emerging patterning technique called Displacement Talbot lithography (DTL), to successfully nano-engineer III-nitride materials. DTL, along with its novel and unique combination with a lateral planar displacement (D2TL), allow the fabrication of a variety of periodic nanopatterns with a broad range of filling factors such as nanoholes, nanodots, nanorings and nanolines; all these features being achievable from one single mask. To illustrate the enormous possibilities opened by DTL/D2TL, dielectric and metal masks with a number of nanopatterns have been generated, allowing for the selective area growth of InGaN/GaN core-shell nanorods, the top-down plasma etching of III-nitride nanostructures, the top-down sublimation of GaN nanostructures, the hybrid top-down/bottom-up growth of AlN nanorods and GaN nanotubes, and the fabrication of nanopatterned sapphire substrates for AlN growth. Compared with their planar counterparts, these 3D nanostructures enable the reduction or filtering of structural defects and/or the enhancement of the light extraction, therefore improving the efficiency of the final device. These results, achieved on a wafer scale via DTL and upscalable to larger surfaces, have the potential to unlock the manufacturing of nano-engineered III-nitride materials.

AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy

We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing X-ray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 109 cm−2. However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86%).

Waveguide integrated GaN distributed Bragg reflector cavity using low‐cost nanolithography

This work presents the design, fabrication and measurement of gallium nitride (GaN) distributed Bragg reflector cavities integrated with input and output grating couplers. The devices are fabricated using a new, low-cost nanolithography technique: displacement Talbot lithography combined with direct laser writing lithography. The finite-difference time-domain method has been used to design all the components and measured and modelled results show good agreement. Such devices have applications in GaN integrated photonics and biosensing.

"Double" displacement Talbot lithography: fast, wafer-scale, direct-writing of complex periodic nanopatterns.

We describe a new low-cost nanolithographic tool for creating periodic arrays of complex, nano-motifs, across large areas within minutes. Displacement Talbot lithography is combined with lateral nanopositioning to enable large-area patterning with the flexibility of a direct-write system. In this way, we can create different periodic patterns in short timescales using a single mask with no mask degradation. We demonstrate multiple exposures, combined with discrete lateral displacements, and single exposures, with continuous displacements, to achieve image inversion, pitch reduction, and nanogaps between metal nanoparticles. Our approach provides a flexible route to create large-area nanopatterned materials and devices in high volumes.

Top-down fabrication of GaN nano-laser arrays by displacement Talbot lithography and selective area sublimation

We show that a 4 μm thick GaN layer grown by metal-organic vapour phase epitaxy can be transformed into a well-organized array of GaN nanowires (NWs) using displacement Talbot lithography and selective area sublimation. The optical quality of the GaN NWs obtained by this method is attested by their room temperature photoluminescence and the observation of lasing under optical pumping with a minimum excitation power density threshold of 2.4 MW cm−2.