Direct-write Electron-beam Lithography Research Articles

(Invited) Chiral Metamaterials for Polarized Photoluminescence

Metasurfaces offer compact routes to spatial and polarization control of luminescence from nearby emitters, enabling applications ranging from document security to stereoscopic displays to sensing.Most of the time, light-emitters are distributed evenly across the surface. This talk will discuss an alternate approach, where we use direct-write electron beam lithography to pattern semiconductor nanocrystals into targeted shapes and locations, creating a highly tailored metasurface. We use a combination of nanoscale fabrication, Fourier-space photoluminescence measurements, and computational methods to study the circularly polarized photoluminescence from these designer structures.We will discuss the influence of patterning on the resulting optical properties, including the effects of spatial averaging and dipole orientation. We will then show an optimization strategy to produce highly polarized light at chosen angles of outcoupling. The final part of the talk will discuss adding layers of complexity, including the chirality of the underlying pattern, and creating light-emitting solids from intrinsically chiral semiconductor nanocrystals.

Quasi-TPPs/Fano resonance systems based on an MDM waveguide structure and its sensing application.

In this paper, quasi-Tamm plasmon polaritons (TPPs)/Fano resonance systems based on metal-dielectric-metal (MDM) waveguides are proposed. TPPs are surface electromagnetic modes formed at the interface between a metal and a one-dimensional dielectric photonic crystal (PhC). A metal plasmonic Bragg reflector (PBR) in a MDM waveguide is equivalent to a dielectric PhC, which is realized by periodic MDM waveguide width modulation and leads to the photonic bandgap. By introducing a thin Ag baffle and a PBR in MDM waveguide core, the quasi-TPPs are excited at the interface between the Ag baffle and the PBR, when the phase-matching condition is met. The proposed structure can be fabricated with focused ion beam or electron beam direct-writing lithography, avoiding complex fabrication procedures of manufacturing dielectric PhC by filling the MDM waveguide core with different dielectric materials. Furthermore, an MDM waveguide side-coupled resonator system is constructed to generate Fano resonance by placing a PBR on the side of the MDM waveguide and an Ag baffle in the waveguide core. The Fano resonance originates from the interference between a broad continuum state provided by the Ag baffle and a discrete state provided by quasi-TPPs. The sensing performance of the Fano resonance system is investigated. In this design, the open PBR structure replaces the traditional closed resonant cavity, which makes it more convenient to contact with analytes. The numerical simulations demonstrate that a high sensitivity of 1500nm/RIU and figure of merit value of 4.08×105 are achieved.

(Invited, Digital Presentation) Circularly Polarized Photoluminescence from Nanostructured Arrays of Light Emitters

Metasurfaces offer compact routes to spatial and polarization control of luminescence from nearby emitters. The most common integration strategy is to coat a patterned metamaterial or metasurface with a film of light emitting material. For example, structures such as arrays of Au nanorods coated with achiral light emitters exhibit circularly polarized photoluminescence at specific outcoupled angles. However, the degree of circular polarization in these systems is limited to relatively low values, and does not coincide with the angles with high photoluminescence intensity.This talk will discuss an alternative strategy, where the light emitters are patterned instead. We show that this structure offers several advantages: rather than averaging over the contributions of emitters in many different locations, this system exhibits highly directional photoluminescence with high degrees of circular polarization. Most importantly, the photoluminescence intensity is high at the same angles where the degree of circular polarization is high.These patterned light-emitting nanostructures are formed using direct-write electron beam lithography on semiconductor nanocrystals. This versatile method is capable of forming structures with aspect ratios greater than 2 and feature sizes as small as 30 nm, photoluminescence is retained after patterning, and the system is robust to multiple patterning steps.

Nanoscale flexible organic thin-film transistors.

Direct-write electron-beam lithography has been used to fabricate low-voltage p-channel and n-channel organic thin-film transistors with channel lengths as small as 200 nm and gate-to-contact overlaps as small as 100 nm on glass and on flexible transparent polymeric substrates. The p-channel transistors have on/off current ratios as large as 4 × 109 and subthreshold swings as small as 70 mV/decade, and the n-channel transistors have on/off ratios up to 108 and subthreshold swings as low as 80 mV/decade. These are the largest on/off current ratios reported to date for nanoscale organic transistors. Inverters based on two p-channel transistors with a channel length of 200 nm and gate-to-contact overlaps of 100 nm display characteristic switching-delay time constants between 80 and 40 ns at supply voltages between 1 and 2 V, corresponding to a supply voltage-normalized frequency of about 6 MHz/V. This is the highest voltage-normalized dynamic performance reported to date for organic transistors fabricated by maskless lithography.

Precision fabrication of EUVL programmed defects with helium ion beam patterning

The availability of metrology solutions, one of the critical factors to drive leading-edge semiconductor devices and processes, has been confronted with difficulties in advanced nodes. For developing new metrology solutions, high-quality test structures fabricated at specific sizes are needed. Electron-beam direct-write lithography has been utilized to manufacture such samples. However, it can encounter significant-resolution difficulties and may require complicated process optimization in sub-10-nm nodes. Therefore, we investigate the feasibility and patterning control of metrology test structures fabricated by helium ion beam (HIB) direct milling and HIB direct-write lithography, where HIB has the sub-nm resolution in nature. Results show that features down to 5 nm are resolvable without any resolution enhancement technique by HIB direct milling. For HIB direct-write lithography, features down to International Roadmap for Devices and Systems 1.5-nm node are also resolvable without optimization from the lithography simulation. Furthermore, patterns beyond the 1.5-nm node can be achievable with the help of the proximity effect correction technique. Preliminary results demonstrate that HIB direct milling and HIB direct-write lithography can be a promising alternative for fabricating pit-type programmed defects (PDs) and bump-type PDs, respectively. In conclusion, HIB is suggested to be a potential tool to fabricated test structures for developing advanced metrology solutions in sub-7-nm nodes.

Solution‐Processed High‐Performance ZnO Nano‐FETs Fabricated with Direct‐Write Electron‐Beam‐Lithography‐Based Top‐Down Route

AbstractZinc oxide (ZnO) has been extensively investigated for use in large‐area electronics; in particular, the solution‐processing routes have shown increasing promise towards low‐cost fabrication. However, top‐down fabrication approaches with nanoscale resolution, towards aggressively scaled device platforms, are still underexplored. This study reports a novel approach of direct‐write electron‐beam lithography (DW‐EBL) of solution precursors as negative tone resists, followed by optimal precursor processing to fabricate micron/nano‐field‐effect transistors (FETs). It is demonstrated that the mobility and current density of ZnO FETs can be increased by two orders of magnitude as the precursor pattern width is decreased from 50 µm to 100 nm. These nano‐FET devices exhibit field‐effect mobility exceeding ≈30 cm2 V−1 s−1 and on‐state current densities reaching 10 A m−1, the highest reported so far for direct‐write precursor‐patterned nanoscale ZnO FETs. Using atomic force microscopy and parametric modeling, the origin of such device performance improvement is investigated. The findings emphasize the influence of pre‐decomposition nanoscale precursor patterning on the grain morphology evolution in ZnO and, consequently, open up large‐scale integration, and miniaturization opportunities for solution‐processed, high‐performance nanoscale oxide FETs.

Biosensors based on nanowire field effect transistors with Schottky contacts

A top-down nanofabrication approach was used to obtain silicon nanowires from silicon-on-insulator wafers using direct-write electron beam lithography and plasma-reactive ion etching. Fabricated with designed pattern silicon nanowires are 0.4, 0.8, 2 μm in width and 100 nm in height. The devices can be applied in future medical diagnostic applications as novel biosensors with detection principle based on the changes in electrical characteristics of the silicon nanowires functionalized with thiol-containing molecules.

Nanoscale Patterning of Colloidal Nanocrystal Films for Nanophotonic Applications Using Direct Write Electron Beam Lithography.

The small size of colloidal nanocrystal quantum dots (QDs) leads to a variety of unique optical properties that are well-suited to nanophotonics, including bright, tunable photoluminescence (PL). However, exploring the properties of solid QD assemblies at the nanoscale has proven challenging because of the limitations in the nanoscale QD patterning methods. Generally, the precise placement of QD solids is difficult to achieve, especially for tall structures with multiple QD layers, and when it is achieved the patterns often cannot withstand the further processing steps required for final device construction. Direct electron beam lithography of QDs has emerged as a straightforward patterning process that does not require ligand exchange and results in structures that retain bright PL. Here, we demonstrate that direct patterning QD films on substrates treated with a self-assembled monolayer of octadecyltrichlorosilane allows us to create feature sizes as thin as 30 nm with heights of multiple layers and characterize the pattern resolution, robustness, and placement accuracy. These structures withstand sonication in a variety of solvents, and the structures are placed within 20 nm of their intended location nearly 100% of the time. We further show how this patterning method can be applied to nanophotonics by measuring the complex refractive index of the QD materials to model the absorption and scattering cross sections of QD structures of various sizes and shapes. These simulations reveal that edge effects arising from the finite shape of the QD nanostructure lead to substantial absorption enhancement when compared to an equivalent volume region taken from a continuous QD film. Finally, we explore more complex structures by patterning QD arrays, multilayer QD structures, and QD disks inside plasmonic resonators.

CALDER: The Second-Generation Light Detectors

The main aim of the cryogenic wide-area light detectors with excellent resolution project is the development of cryogenic light detectors with large active area (~50 mm × 50 mm) and noise energy resolution smaller than 20-eV RMS. Such detectors will be used to discriminate the background in next generation large-mass bolometric experiments, such as cryogenic underground observatory for rare events. In this paper, we present the fabrication process of the phonon-mediated kinetic inductance detectors (KIDs). In the first part of the project, Al KIDs have been developed. Thin film Al (40 nm) were evaporated on high quality, high resistivity (>10 kΩ·cm) Si(1 0 0) wafers using a high vacuum electron beam evaporator. Detectors were patterned by direct-write Electron Beam Lithography (EBL) using positive tone resist AR-P 669.06. To improve the energy resolution of our detector, superconductors with higher kinetic inductance, such as the substoichiometric titanium nitride (TiNx), were developed. TiNx is deposited with reactive dc magnetron sputtering. Thus, the fabrication process is subtractive and consists of EBL patterning through negative tone resist AR-N 7700 and SF6 etch using a Deep Reactive Ion Etching - Inductively Coupled Plasma. Critical temperature of TiNx samples was measured using the 4-point probe geometry.

On the spatial resolution limit of direct-write electron beam lithography

The mechanism for direct-write electron-beam lithography in insulating resists is introduced in this letter, and it is based on damage by the induced electric field in transmission electron microscope. Under this mechanism, the direct-write EBL is electron dose-rate dependent, and there is a dose-rate threshold, below which the lithographic process does not operate, regardless of the total electron dose. The spatial resolution is determined by the strength of the induced electric field. In theory, the highest spatial resolution should be set by the dimension of the electron beam, and thus the EBL should be able to create nanostructures at the atomic scale. So far, the best resolution obtained was in the direct write of conductive nanochannels in Li4Ti5O12, in which 1.5nm isolated features and a 1.0–1.5nm half-pitch array of nanochannels were achieved.

Impact of parallelism on data volumes for a multibeam mask writer

Single beam mask writer architectures have satisfied mask patterning requirements for decades, but there is now great interest in multibeam mask writers to handle the throughput and resolution demands arising from the needs of sub-10 nm technology nodes. Future mask writers must transmit terabits of information per second and handle petabytes of data. For electron-beam direct write (EBDW) lithography systems parallelism and lossless layout image compression are techniques which have been considered together to approach the data transfer problem. For the multibeam mask architectures proposed by IMS Nanofabrication and NuFlare, the data being transmitted are significantly processed and modified from the initial proximity-corrected layout images, so the data compression problem the authors consider for this application appears to be for a new type of data. Just as the throughput requirements for EBDW lithography systems necessitate the lossless data compression decoders to swiftly reproduce the layout images from their encodings it is likewise interesting to study simple and effective lossless data compression algorithms for multibeam mask writers. The authors will examine how parallelism affects the total beam compressed data for a family of idealized multibeam architectures inspired by the IMS Nanofabrication eMET series.

Top-Down Nanofabrication and Characterization of 20 nm Silicon Nanowires for Biosensing Applications.

A top-down nanofabrication approach is used to develop silicon nanowires from silicon-on-insulator (SOI) wafers and involves direct-write electron beam lithography (EBL), inductively coupled plasma-reactive ion etching (ICP-RIE) and a size reduction process. To achieve nanometer scale size, the crucial factors contributing to the EBL and size reduction processes are highlighted. The resulting silicon nanowires, which are 20 nm in width and 30 nm in height (with a triangular shape) and have a straight structure over the length of 400 μm, are fabricated precisely at the designed location on the device. The device is applied in biomolecule detection based on the changes in drain current (Ids), electrical resistance and conductance of the silicon nanowires upon hybridization to complementary target deoxyribonucleic acid (DNA). In this context, the scaled-down device exhibited superior performances in terms of good specificity and high sensitivity, with a limit of detection (LOD) of 10 fM, enables for efficient label-free, direct and higher-accuracy DNA molecules detection. Thus, this silicon nanowire can be used as an improved transducer and serves as novel biosensor for future biomedical diagnostic applications.

Efficient layout data compression algorithm and its low-complexity, high-performance hardware decoder implementation for multiple electron-beam direct-write systems

A lossless electron-beam layout (EBL) data compression algorithm, LineDiff Entropy v2.0, and its low-complexity, high-performance hardware decoder for multiple electron-beam direct-write lithography systems are proposed. The algorithm compares consecutive data scanlines and encodes the data based on the change/no-change of pixel values and the lengths of pixel sequences. Then, the compaction steps of data omission, merging, and encoding of consecutive long identical scanlines are applied. Unique short codes are assigned to data with high occurrence frequency. The hardware decoder is designed as three circuit blocks that perform entropy decoding, decompaction, and EBL data generation through parallel outputs. The results demonstrate that our algorithm can achieve excellent compression performance and that the hardware decoder can decompress data at very high data rates.

Lossless layout image compression algorithms for electron-beam direct-write lithography

Electron-beam direct-write lithography systems must in the future transmit terabits of information per second to be viable for commercial semiconductor manufacturing. Lossless layout image compression algorithms with high decoding throughputs and modest decoding resources are tools to address the data transfer portion of the throughput problem. The earlier lossless layout image compression algorithm Corner2 is designed for binary layout images on raster-scanning systems. The authors propose variations of Corner2 collectively called Corner2-EPC and Paeth-EPC which apply to electron-beam proximity corrected layout images and offer interesting trade-offs between compression ratios and decoding speeds. Most of our algorithms achieve better overall compression performance than portable network graphics, Block C4, and LineDiffEntropy while having low decoding times and resources.

Design of an electron-optical system with a ball-tip emission source through a numerical optimization method for high-throughput electron-beam–direct-write lithography

To improve the throughput of electron-beam–direct-write lithography (EBDWL), we propose a new electron-optical system (EOS) design method with the capability of systematically optimizing EOSs with various types of emission source. A ball-tip emission source initially proposed by another group is further discussed. A numerical optimization method is utilized in the design method to maximize EOS emission current while satisfying constraints including the size of the electron beam spot and the amount of induced electric field on electrodes and insulators inside EOSs. For performance comparison, two EOSs, one with a generic emission source and the other with a ball-tip emission source, are designed using the proposed method. Preliminary results indicate that a sixfold emission current is obtained from the EOS with the ball-tip emission source. Furthermore, patterning fidelity investigations are conducted using the obtained design results. It is shown that the higher emission current from the ball-tip emission source is achieved without compromising patterning quality.

超並列電子線描画装置用アクティブマトリックスナノ結晶シリコン電子源の開発と動作特性評価に関するレビュー

超並列電子線描画装置用アクティブマトリックスナノ結晶シリコン電子源の開発と動作特性評価に関するレビュー

Standard AZ 5214E photoresist in laser interference and EBDW lithographies

In this paper examples of the applicability of the standard AZ 5214E photoresist are shown. The resist is besides its sensitivity to UV radiation sensitive also to e-beam exposure. The arrays of patterns (holes and columns) were exposed in this photoresist by the experimentally produced Laser Interference Lithography method as well as by the Electron-Beam Direct Write Lithography. With both methods comparable results have been achieved with less than half micron spacing of the patterns, obtaining thus dimensions smaller than usually achieved by standard optical photolithography with the AZ 5214E photoresist.

An information theoretic perspective on e-beam direct-write as complementary lithography

The semiconductor industry is pursuing unidirectional and gridded layouts as an approach to enable high-volume manufacturing for advanced technology nodes. Complementary lithography is a two-step scheme for fabricating such layouts where optical lithography produces unidirectional lines at a fixed pitch and electron-beam direct-write (EBDW) lithography cuts those lines. Since low throughput and high data volumes in the patterning of wafers are challenges facing EBDW lithography, the author considers theoretical and practical aspects of lossless data compression for the transfer of cut images.

Far Field Measurements of Phc Led Prepared by E–Beam Lithography

Abstract The paper deals with optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (LED) structure with photonic crystal (2D PhC) patterned on the top of the structure using Electron Beam Direct Write Lithography (EBDWL). Light-current characteristics measured by integrating sphere shows increase of extracted light intensity as 21.1%. Additionally, extracted light intensity was studied by far-field measurements as a complementary method to light-current characteristics. The far-field measurements show increase of extracted light intensity as 31.2%. We suggest this method as more suitable for evaluation of extracted light intensity because it omits emission from edges of the LED and thus light is measured only from the area where PhC is patterned

(Invited) Ballistic Hot Electron Effects in Nanosilicon Dots and Their Photonic Applications

The physical property of nanocrystalline silicon (nc-Si) dots as a confined wide-gap material relates not only to photonics, but also to electronics. As supported experimentally and theoretically, the electronic structure with discrete levels significantly enhances the impact ionization rate, and then internal electron avalanche occurs at the early stage of photo-excitation or injection. The nc-Si diode, on the other hand, acts as a planar cold cathode which emits ballistic hot electrons. In addition to the use in vacuum, the device is available for the operation in solutions. In vacuum active-matrix nc-Si electron emitter array has been developed for massively parallel electron beam direct-write lithography. Another application scheme in solutions provides alternative thin films deposition of Si, Ge, and SiGe, in which the nc-Si emitter supplies highly reducing electrons. Recent advancements of these studies are discussed.