High Resolution Electron Beam Lithography Research Articles

NbN superconducting nanonetwork fabricated using porous silicon templates and high-resolution electron beam lithography

Superconducting NbN nanonetworks with a very small number of interconnected nanowires, with diameter of the order of 4 nm, are fabricated combining a bottom-up (use of porous silicon nanotemplates) with a top-down technique (high-resolution electron beam lithography). The method is easy to control and allows the fabrication of devices, on a robust support, with electrical properties close to a one-dimensional superconductor that can be used fruitfully for novel applications.

Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas.

Understanding plasmon-mediated electron emission and energy transfer on the nanometer length scale is critical to controlling light-matter interactions at nanoscale dimensions. In a high-resolution lithographic material, electron emission and energy transfer lead to chemical transformations. In this work, we employ such chemical transformations in two different high-resolution electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and hydrogen silsesquioxane (HSQ), to map local electron emission and energy transfer with nanometer resolution from plasmonic nanoantennas excited by femtosecond laser pulses. We observe exposure of the electron-beam resists (both PMMA and HSQ) in regions on the surface of nanoantennas where the local field is significantly enhanced. Exposure in these regions is consistent with previously reported optical-field-controlled electron emission from plasmonic hotspots as well as earlier work on low-electron-energy scanning probe lithography. For HSQ, in addition to exposure in hotspots, we observe resist exposure at the centers of rod-shaped nanoantennas in addition to exposure in plasmonic hotspots. Optical field enhancement is minimized at the center of nanorods suggesting that exposure in these regions involves a different mechanism to that in plasmonic hotspots. Our simulations suggest that exposure at the center of nanorods results from the emission of hot electrons produced via plasmon decay in the nanorods. Overall, the results presented in this work provide a means to map both optical-field-controlled electron emission and hot-electron transfer from nanoparticles via chemical transformations produced locally in lithographic materials.

Ultrahigh-Q optomechanical crystal cavities fabricated in a CMOS foundry

Photonic crystals use periodic structures to create frequency regions where the optical wave propagation is forbidden, which allows the creation and integration of complex optical functionalities in small footprint devices. Such strategy has also been successfully applied to confine mechanical waves and to explore their interaction with light in the so-called optomechanical cavities. Because of their challenging design, these cavities are traditionally fabricated using dedicated high-resolution electron-beam lithography tools that are inherently slow, limiting this solution to small-scale or research applications. Here we show how to overcome this problem by using a deep-UV photolithography process to fabricate optomechanical crystals in a commercial CMOS foundry. We show that a careful design of the photonic crystals can withstand the limitations of the photolithography process, producing cavities with measured intrinsic optical quality factors as high as Qi = (1.21 ± 0.02) × 106. Optomechanical crystals are also created using phononic crystals to tightly confine the GHz sound waves within the optical cavity, resulting in a measured vacuum optomechanical coupling rate of g0 = 2π × (91 ± 4) kHz. Efficient sideband cooling and amplification are also demonstrated since these cavities are in the resolved sideband regime. Further improvements in the design and fabrication process suggest that commercial foundry-based optomechanical cavities could be used for quantum ground-state cooling.

Fabrication of CdMgTe/Cd(Mn)Te nanostructures with the application of high-resolution electron-beam lithography

Abstract In this work we report on fabrication of quantum wires and quantum point contacts from the modulation doped CdMgTe/Cd(Mn)Te structures, with the application of a high-resolution electron-beam lithography . We emphasize on methods which were not yet utilized for these substrate materials. In particular, we describe the so-called shallow-etching approach, which allows for the fabrication of quantum constrictions of a physical width down to 100 nm, which are characterized by the smoother confining potential as compared to the deep-etched devices. For that purpose, a single-line exposure mode of electron-beam lithography has been used. We demonstrate also, how to combine the etching of separating grooves with the thermal evaporation of metal side-gates into a single post-processing stage of a quantum point contact fabrication. This article is an expanded version of the scientific reports presented at the International Conference on Semiconductor Nanostructures for Optoelectronics and Biosensors 2016 ICSeNOB2016, May 22–25, 2016, Rzeszow, Poland.

Test of mode-division multiplexing and demultiplexing in free-space with diffractive transformation optics.

In recent years, mode-division multiplexing (MDM) has been proposed as a promising solution in order to increase the information capacity of optical networks both in free-space and in optical fiber transmission. Here we present the design, fabrication and test of diffractive optical elements for mode-division multiplexing based on optical transformations in the visible range. Diffractive optics have been fabricated by means of 3D high-resolution electron beam lithography on polymethylmethacrylate resist layer spun over a glass substrate. The same optical sequence was exploited both for input-mode multiplexing and for output-mode sorting after free-space propagation. Their high miniaturization level and efficiency make these optical devices ideal for integration into next-generation platforms for mode-division (de)multiplexing in telecom applications.

Compact sorting of optical vortices by means of diffractive transformation optics.

The orbital angular momentum (OAM) of light has recently attracted a growing interest as a new degree of freedom in order to increase the information capacity of today's optical networks, both for free-space and optical fiber transmission. Here we present our work of design, fabrication, and optical characterization of diffractive optical elements for compact OAM mode division demultiplexing based on optical transformations. Samples have been fabricated with 3D high-resolution electron beam lithography on a polymethylmethacrylate resist layer spun over a glass substrate. Their high compactness and efficiency make these optical devices promising for integration into next-generation platforms for OAM modes processing in telecom applications.

High-Energy Surface and Volume Plasmons in Nanopatterned Sub-10 nm Aluminum Nanostructures.

In this work, we use electron energy-loss spectroscopy to map the complete plasmonic spectrum of aluminum nanodisks with diameters ranging from 3 to 120 nm fabricated by high-resolution electron-beam lithography. Our nanopatterning approach allows us to produce localized surface plasmon resonances across a wide spectral range spanning 2-8 eV. Electromagnetic simulations using the finite element method support the existence of dipolar, quadrupolar, and hexapolar surface plasmon modes as well as centrosymmetric breathing modes depending on the location of the electron-beam excitation. In addition, we have developed an approach using nanolithography that is capable of meV control over the energy and attosecond control over the lifetime of volume plasmons in these nanodisks. The precise measurement of volume plasmon lifetime may also provide an opportunity to probe and control the DC electrical conductivity of highly confined metallic nanostructures. Lastly, we show the strong influence of the nanodisk boundary in determining both the energy and lifetime of surface plasmons and volume plasmons locally across individual aluminum nanodisks, and we have compared these observations to similar effects produced by scaling the nanodisk diameter.

Novel germanium surface modification for sub-10 nm patterning with electron beam lithography and hydrogen silsesquioxane resist

Germanium is a promising high-mobility channel material for future nanoelectronic devices. Hydrogen silsesquioxane (HSQ) is a well known high-resolution electron beam lithography (EBL) resist, which is usually developed in aqueous based developers. However, this feature of HSQ causes troubles while patterning Ge surface as it is always shielded with native Ge oxides. GeO2 is a water soluble oxide, and since HSQ resist is developed in aqueous solvents, this oxide interferes with the patterning. After the EBL exposure, GeO2 is washed off during the development, lifting the patterned structures and making the high-resolution patterning impossible. To avoid this issue, it is necessary to either clean and passivate the Ge surface or use buffer layers between the native Ge oxides and the HSQ layer. In this article, a novel technique to clean the Ge surface prior to HSQ deposition, using simple “household” acids like citric acid and acetic acid, is reported. The acids are able to remove the native Ge oxides as well as efficiently passivate the surface. The acid passivation was found to hold the HSQ sturdily to the Ge surface, even during development with the aqueous salty solvent. Using this process, Ge nanowires having widths down to 5 nm were successfully patterned on germanium-on-insulator substrates. To the best of our knowledge, these are the smallest top-down fabricated Ge nanostructures reported till date.

Towards a novel positive tone resist mr-PosEBR for high resolution electron-beam lithography

Herein, we present the results of a systematic material development study we carried out in order to obtain a new positive tone resist for high resolution electron-beam lithography. Several acrylic copolymer materials with different mass fractions of the comonomers, different molecular weights and similar molecular weight distributions were synthesized and – as resist solutions – evaluated in terms of electron-beam lithography performance. On the one hand, within the ranges investigated, it was shown that the lithographic sensitivity is significantly influenced by the composition rather than by the molecular weight or molecular weight distribution. On the other hand, the etch resistance of the materials remains unaffected by changes of these parameters. The resist material exhibiting the best combination of the desired properties, mr-PosEBR, is 2 times more sensitive than PMMA (495kDa) and performs comparably to the known high resolution resist ZEP520A. For example, a grating pattern with 29nm wide lines with a period of 100nm could be generated in films of mr-PosEBR with an area dose of 100μC/cm2. In terms of resolution, single lines of only 35nm width could be fabricated via metal lift-off using 100kV EBL. Furthermore, the dry etch stability of mr-PosEBR in a reactive-ion etching (RIE) process (etch gases: CF4/SF6) is similar to the one of ZEP520A (etch rates, mr-PosEBR: 190nm/min, ZEP520A: 150nm/min, silicon: 440nm/min). Moreover, high resolution nanopatterns in mr-PosEBR could be smoothly transferred into the underlying Si substrate by a RIE process.

Generating Large Magnetic Field in a High Resolution Electron Beam Lithography

In this talk we will report about first results and measurements achieved with an electron beam lithographic system (EBL, eLINE Plus CAS) containing a unique in situ setup to not only fabricate but also characterize and measure GMR/TMR based devices. The eLINE Plus CAS is additionally equipped with the capability of generating a large lateral magnetic field, which is indispensible in measurement of spintronic devices or materials, besides of its original SEM and EBL functionalities. This unique EBL instrument, thus, could be not only used as a microscope or a lithography system but also as a analytical instrument for in-situ magnetoelectric transport measurements. Figure 1 shows the structure of the magnet in chamber whose pole tips are placed underneath pole piece of SEM column. The maximum lateral field realized at current stage is about 400 Oe as exciting current is elevated as 2.5 A. This large field has already been applied in in-situ measurement GMR or TMR devices. As shown in Figure 2, utilizing the magnet as well as the other two tungsten probers already installed in the chamber, we have measured magnetotransport properties of a TMR device whose TMR ratio is nearly the same as that measured outside chamber. We will further report about the characterization of the homogeneity of the magnetic field and next steps taken in this project.

Design and fabrication of structural color by local surface plasmonic meta-molecules**Project partially supported by the National Natural Science Foundation of China (Grant No. 61205148).

In this paper, we propose a new form of nanostructures with Al film deposited on a patterned dielectric material for generating structural color, which is induced by local surface plasmonic resonant (LSPR) absorption in sub-wavelength-indented hole/ring arrays. Unlike other reported results obtained by using focus ion beam (FIB) to create metallic nanostructures, the nano-sized hole/ring arrays in Al film in this work are replicated by high resolution electron beam lithography (EBL) combined with self-aligned metallization. Clear structural color is observed and systematically studied by numerical simulations as well as optical characterizations. The central color is strongly related to the geometric size, which provides us with good opportunities to dye the colorless Al surface by controlling the hole/ring dimensions (both diameter and radius), and to open up broad applications in display, jewelry decoration, green production of packing papers, security code, and counterfeits prevention.

Изготовление наноустройств на установках электронно-лучевой литографии высокого разрешения

Изготовление наноустройств на установках электронно-лучевой литографии высокого разрешения

High-yield, ultrafast, surface plasmon-enhanced, Au nanorod optical field electron emitter arrays.

Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100-1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation.

Investigation of CSAR 62, a new resist for electron beam lithography

CSAR 62 is a new positive tone electron beam resist designed to have similar performance to ZEP520A in resolution, speed, and etch resistance. In this paper, the authors have used the resist to carry out high resolution electron beam lithography and as a mask for reactive ion etching on dielectrics, gallium arsenide, and silicon substrates coated with a 160 nm film of aluminum. Comparisons have been made between the results obtained using CSAR 62, ZEP520A, and polymethylmethacrylate. The authors conclude that CSAR 62 does demonstrate similar resolution, sensitivity, and etch resistance as ZEP520A but also gives rise to substantial resist residuals after development. These are almost entirely eliminated by using an alternative developer.

High-density Au nanorod optical field-emitter arrays

We demonstrate the design, fabrication, characterization, and operation of high-density arrays of Au nanorod electron emitters, fabricated by high-resolution electron beam lithography, and excited by ultrafast femtosecond near-infrared radiation. Electron emission characteristic of multiphoton absorption has been observed at low laser fluence, as indicated by the power-law scaling of emission current with applied optical power. The onset of space-charge-limited current and strong optical field emission has been investigated so as to determine the mechanism of electron emission at high incident laser fluence. Laser-induced structural damage has been observed at applied optical fields above 5 GV m−1, and energy spectra of emitted electrons have been measured using an electron time-of-flight spectrometer.

Facile electron-beam lithography technique for irregular and fragile substrates

A facile technique is presented which enables high-resolution electron beam lithography on irregularly-shaped, non-planar or fragile substrates such as the edges of a silicon chip, thin and narrow suspended beams and bridges, or small cylindrical wires. The method involves a spin-free dry-transfer of pre-formed uniform-thickness polymethyl methacrylate, followed by conventional electron beam writing, metal deposition, and lift-off. High-resolution patterning is demonstrated for challenging target substrates. The technique should find broad application in micro- and nano-technology research arenas.

Multistep Aztec profiles by grayscale electron beam lithography for angle-resolved microspectrometer applications

In this paper, grayscale electron beam lithography is applied to generate multistep Aztec profiles (MAPs) for angle-resolved spectral applications such as microspectrometers. Monte Carlo simulations taking into consideration the proximity effect are carried out to calculate the spatial dose distributions for desired profiles, using actual dissolution rates measured on the same resist. The MAPs in PMMA resist with step heights from 50 to 200 nm and step widths from 0.1 to 5 μm are achieved by high-resolution electron beam lithography, and high-resolution scanning electron microscopy and atomic force microscopy are used to characterize the quality of the MAPs. Angle-resolved spectra of the reflectance are obtained using a finite-difference time-domain simulator and by experimental measurements. A distinct angle selection of the wavelengths is demonstrated, though the high surface roughness measured on the deeper steps may cause broadening of the spectral peaks. Initial investigations into the origin of the surface roughness are carried out, and further improvements are discussed.

Investigation of the Hydrogen Silsesquioxane (HSQ) Electron Resist as Insulating Material in Phase Change Memory Devices

Phase change random access memory (PCRAM) affords many advantages over conventional solid-state memories due to its nonvolatility, high speed, and scalability. However, high programming current to amorphize the crystalline phase through the melt-quench process of PCRAM, known as the RESET current, poses a critical challenge and has become the most significant obstacle for its widespread commercialization. In this work, an excellent negative tone resist for high resolution electron beam lithography, hydrogen silsesquioxane (HSQ), has been investigated as the insulating material which locally blocks the contact between the bottom electrode and the phase change material in PCRAM devices. Fabrications of the highly scaled HSQ nanopore arrays (as small as 16 nm) are presented. The insulating properties of the HSQ material are studied, especially under e-beam exposure plus thermal curing. Some other critical issues about the thickness adjustment of HSQ films and the influence of the PCRAM electrode on electron scattering in e-beam lithography are discussed. In addition, the HSQ material was successfully integrated into the PCRAM devices, achieving ultra-low RESET current (sub-100 μA), outstanding on/off ratios (~50), and improved endurance at tens of nanometers.

La2−xSrxCuO4 superconductor nanowire devices

La2−xSrxCuO4 nanowire devices have been fabricated and characterized using electrical transport measurements. Nanowires with widths down to 80nm are patterned using high-resolution electron beam lithography. However, the narrowest nanowires show incomplete superconducting transitions with some residual resistance at T=4K. Here, we report on the refinement of the fabrication process to achieve narrower nanowire devices with complete superconducting transitions, opening the path to the study of novel physics arising from dimension-limited superconductivity on the nanoscale.

Realization of ultra-thin HSQ resist layer for high resolution electron beam lithography using liquid splitting process

In this work we report on a novel method to realize ultra-thin hydrogen silsesquioxane (HSQ) resist layers with a resist thickness of 20nm and below. Unlike conventional methods such as dilution of HSQ or spin coating at very high rotation speeds, our method reduces an initial resist layer thickness by means of liquid splitting. An initial HSQ resist layer thickness of 40nm was thinned to 20nm and a successful pattern definition down to a resolution of 15nm was achieved by using a standard electron beam lithography process on the thinned resist layer. Hence, our method allows simple and effective preparation of sub-20nm HSQ resist layers for dense patterns with ultimate resolution.