Electron Beam Lithography Technique Research Articles

Fabrication of high-resolution nanostructures of complex geometry by the single-spot nanolithography method.

The paper presents a method for the high-resolution production of polymer nanopatterns with controllable geometrical parameters by means of a single-spot electron-beam lithography technique. The essence of the method entails the overexposure of a positive-tone resist, spin-coated onto a substrate where nanoscale spots are exposed to an electron beam with a dose greater than 0.1 pC per dot. A single-spot enables the fabrication of a nanoring, while a chain of spots placed at distance of 5–30 nm from each other allows the production of a polymer pattern of complex geometry of sub-10 nm resolution. We demonstrate that in addition to the naturally oxidized silicon substrates, gold-coated substrates can also successfully be used for the single-spot nanopattering technique. An explanation of the results related to the resist overexposure was demonstrated using Monte Carlo simulations. Our nanofabrication method significantly accelerates (up to 10 times) the fabrication rate as compared to conventional lithography on positive-tone resist. This technique can be potentially employed in the electronics industry for the production of nanoprinted lithography molds, etching masks, nanoelectronics, nanophotonics, NEMS and MEMS devices.

Fabrication of FePt and CoPt Magnetic Nanodot Arrays by Electrodeposition Process

Fabrication of Co-Pt and Fe-Pt ferromagnetic nanodot arrays for the application of ultra-high density bit patterned media (BPM) by electrochemical processes was described. In order to form patterned substrates for nanodot arrays with the density higher than 1 Tbit/inch2, electron beam lithography technique was employed. Nanopatterns with 25 nm and 18 nm pitch, which correspond to 1 and 2 Tbit/inch2 were successfully formed by optimizing the condition of the lithography process, and Co-Pt and Fe-Pt with relatively high coercivity of 4.8 kOe and 10.3 kOe were formed by electrodeposition. By utilizing the nanopatterned substrates, Co-Pt and Fe-Pt nanodot arrays with 25 nm and 35 nm pitch were uniformly formed. These results demonstrate capability of the electrochemical processes for fabricating magnetic nanodot arrays with Tbit-level density.

Influence of random zone positioning errors on the resolving power of Fresnel zone plates.

Fresnel zone plates produced by electron beam lithography and planar etching techniques provide a resolving power of about 10 nm. An alternative zone plate fabrication approach is based on alternately coating a micro-wire with two different materials. With this process, very thin zone layers with very high aspect ratios can be deposited. However, depending on the fabrication method, random zone positioning errors may introduce strong aberrations. We simulate the effect of positioning errors using different random fluctuations and study their influence on zone plate resolution. We find that random errors significantly decrease the contrast transfer of X-ray microscopes. Additionally, we derive an upper bound for the mean acceptable variance of the deposition rate.

New polyoxometalates containing hybrid polymers and their potential for nano-patterning.

Two new polyoxometalate (POM)-based hybrid monomers (Bu4 N)5 (H)[P2 V3 W15 O59 {(OCH2 )3 CNHCO(CH3 )CCH2 }] (2) and (S(CH3 )2 C6 H4 OCOC(CH3 )=CH2 )6 [PV 2Mo10 O40 ] (5) were developed by grafting polymerizable organic units covalently or electrostatically onto Wells-Dawson and Keggin-type clusters and were characterized by analytical and spectroscopic techniques including ESI-MS and/or single-crystal X-ray diffraction analyses. Radical initiated polymerization of 2 and 5 with organic monomers (methacryloyloxy)phenyldimethylsulfonium triflate (MAPDST) and/or methylmethacrylate (MMA) yielded a new series of POM/polymer hybrids that were characterized by (1) H, (31) P NMR and IR spectroscopic techniques, gel-permeation chromatography as well as thermal analyses. Preliminary tests were conducted on these POM/polymer hybrids to evaluate their properties as photoresists using electron beam (E-beam)/extreme ultraviolet (EUV) lithographic techniques. It was observed that the POM/polymer hybrid of 2 with MAPDST exhibited improved sensitivity under EUV lithographic conditions in comparison to the MAPDST homopolymer resist possibly due to the efficient photon harvesting by the POM clusters from the EUV source.

The future of focused electron beam-induced processing

A perspective is sketched for the field of focused electron beam-induced processing (FEBIP). The FEBIP lithography technique is compared to the very successful resist-based electron beam lithography (EBL) technique. The advantages of FEBIP over EBL are identified, the main advantage being its high spatial resolution. This will enable FEBIP to become an important lithography technique for the fabrication of devices with critical dimension in the range between 1 and 20 nm and serve as a complementary technique to EBL. It will be discussed what needs to be done to achieve this and what the potential applications are.

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.

High-In-content InGaAs quantum point contacts fabricated using focused ion beam system equipped with N2 gas field ion source

Quantum point contacts (QPCs) in high-In-content InGaAs modulation-doped heterostructures fabricated using a focused ion beam (FIB) system equipped with a N2 gas field ion source (GFIS) are demonstrated. The minimum physical size of the fabricated QPCs in this study is ∼30 nm, which is smaller than the typical physical size of QPCs (>50 nm) obtained by electron beam lithography and etching techniques. In addition, the fabricated QPCs are characterized electrically at low temperatures with magnetic fields. Since some of them show conductance quantization behaviors, the results indicate that the GFIS-FIB process is promising for quantum device fabrication.

Manipulating the Profile of Nanostars

Using electron-beam lithography and ion milling techniques, we fabricate nanostar biosensors with different shapes and various designs to show tunable plasmon resonances. We also demonstrate further profile control over the outlines of nanostars and both under-and over-etched particles are achieved and compared. Moreover, the tunability of such plasmon-based sensors can find extensive and important applications in spectroscopy and enhanced biosensing.

Surface-enhanced Raman scattering of crystal violets from periodic array of gold nanocylinders

The periodic arrays of gold nanocylinder with 121 nm in diameter, 6.3 nm in gap, and 34 nm in thickness are fabricated on glass by electron-beam lithography and lift-off techniques. Some crystal violet molecules are coated on the array by using the dipping and drawing method. In addition, the surface-enhanced Raman scattering (SERS) spectra of these samples with and without gold nanocylinder arrays are characterized specifically. The largest enhancement factor is obtained when the excitation wavelength corresponds to the peak wavelength of localized surface plasmon resonance (LSPR). The density functional theory and the finite-difference time-domain method are used for the calculations of the extinction spectrum of the arrays and Raman spectra of the crystal violet, respectively. These results unambiguously demonstrate that the periodic arrays of gold nanocylinder have good and effective surface-enhanced properties for Raman scattering of crystal violets, and they also show that the excitation wavelength corresponding to the peak one of the LSPR is one of the major reasons causing SERS.

Fabrication of nanoscale Bi Hall sensors by lift-off techniques for applications in scanning probe microscopy

Bismuth Hall effect sensors with active sizes in the range of 0.1–2 μm have been fabricated by electron beam lithography and lift-off techniques for applications in scanning Hall probe microscopy. The Hall coefficients, offset resistances and minimum detectable fields of the sensors have been systematically characterised as a function of device size. The minimum detectable field of 100 nm probes at 300 K and dc currents of 5 μA was found to be Bmin = 0.9 mT Hz−0.5 with scope for up to a factor of ten reduction by using higher Hall probe currents. This is significantly lower than in similar samples fabricated by focused ion beam (FIB) milling of continuous Bi films, suggesting that the elimination of FIB damage and Ga+ ion incorporation through the use of lift-off techniques leads to superior figures of merit. A number of ways in which the room temperature performance of our sensors could be further improved are discussed.

Optical sensor based on a single CdS nanobelt.

In this paper, an optical sensor based on a cadmium sulfide (CdS) nanobelt has been developed. The CdS nanobelt was synthesized by the vapor phase transportation (VPT) method. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) results revealed that the nanobelt had a hexagonal wurtzite structure of CdS and presented good crystal quality. A single nanobelt Schottky contact optical sensor was fabricated by the electron beam lithography (EBL) technique, and the device current-voltage results showed back-to-back Schottky diode characteristics. The photosensitivity, dark current and the decay time of the sensor were 4 × 104, 31 ms and 0.2 pA, respectively. The high photosensitivity and the short decay time were because of the exponential dependence of photocurrent on the number of the surface charges and the configuration of the back to back Schottky junctions.

Interactions of Serum Derived Proteins with Sub‐Micrometer Structured Surfaces

AbstractThis work presents the development and optimization of two fabrication methods that combine plasma polymerization and electron beam lithography techniques for producing chemical patterns at the sub‐micro scale. The first method uses sacrificial resist as mask to produce the functionalization of the bioadhesive areas and the second method consists in the direct EBL writing of adhesive regions on a non‐adhesive plasma deposited PEO‐like film. The produced patterned surfaces exhibit high binding capacity as tested by Surface Plasmon Resonance Imaging with Human Serum Albumin. Furthermore, we show that adsorption on the structured surfaces is similar to that observed on a flat surface with a direct proportionality to the active area. This work shows the efficiency and suitability of the developed chemical patterning techniques and their high potential applicability for the study of protein surface interactions and miniaturized biosensing device development.

Electroless deposition of metal nanoparticle clusters: Effect of pattern distance

Electroless plating is a deposition technique in which metal ions are reduced as atoms on specific patterned sites of a silicon surface to form metal nanoparticles (NPs) aggregates with the desired characteristics. Those NPs, in turn, can be used as constituents of surface enhanced Raman spectroscopy substrates, which are devices where the electromagnetic field and effects thereof are giantly amplified. Here, the electroless formation of nanostructures was studied as a function of the geometry of the substrate. High resolution, electron beam lithography techniques were used to obtain nonperiodic arrays of circular patterns, in which the spacing of patterns was varied over a significant range. In depositing silver atoms in those circuits, the authors found that the characteristics of the aggregates vary with the pattern distance. When the patterns are in close proximity, the interference of different groups of adjacent aggregates cannot be disregarded and the overall growth is reduced. Differently from this, when the patterns are sufficiently distant, the formation of metal clusters of NPs is independent on the spacing of the patterns. For the particular subset of parameters used here, this critical correlation distance is about three times the pattern diameter. These findings were explained within the framework of a diffusion limited aggregation model, which is a simulation method that can decipher the formation of nanoaggregates at an atomic level. In the discussion, the authors showed how this concept can be used to fabricate ordered arrays of silver nanospheres, where the size of those spheres may be regulated on varying the pattern distance, for applications in biosensing and single molecule detection.

Single Crystalline CuO Nanowire for Resistive Random Access Memory Application

For the development of high density memory arrays of resistive random access memory (RRAM), nanowires provide the potential to reduce the device size to overcome the limitation of conventional lithography. In this work, copper oxide nanowires were synthesized and served as the building block for 1-D RRAM nanodevice. The phase of Copper oxide was identified to be CuO by selected area electron diffraction (SAED) patterns and energy dispersive spectrometer (EDS). We fabricated the Au/CuO-nanowire/Au RRAM nanodevice by electron-beam lithography techniques. From I-V measurement, the forming voltage and RESET voltage were 0.64 V and 5.2 V, respectively. This low forming voltage and ultra-high reset voltage may result from stacking fault in the core of CuO nanowires. From scanning electron microscope (SEM) image ,the as-formed protrusion near the anode and reduction near the cathode after several electrical measurements indicated that the diffusion of oxygen vacancies generating the conducting filament from cathode, result in the change of nanowire morphology. The result will be beneficial to understand the switching properties of nonvolatile memory device at nanoscale.

At low costs: Study on optical propagation losses of silicon waveguides fabricated by electron beam lithography

In this work a novel electron beam lithographic exposure technique suitable for the fabrication of low-loss nanophotonic waveguide structures based on silicon-on-insulator substrate material is presented. This technique utilizes a multi pass exposure approach; hence each feature of the waveguide structures is not only exposed once as in conventional electron beam lithography (EBL) but multiple times. The benefit of this technique lies in a significant reduction of the optical propagation losses (OPLs) of fabricated waveguides. For a multi pass exposure with four exposure passes a reduction of OPLs by more than 1.5dB/cm has been achieved compared to a fabrication based on conventional EBL techniques. At the same time, despite being based on a multi pass approach, the multi pass exposure technique comes at surprisingly low costs in terms of additional exposure time, as the total exposure time including all overhead is only increased by less than 20%.

Fabrication of suspended metal–dielectric–metal plasmonic nanostructures

Dipole nano-antennas have predominantly been investigated in their lateral orientation with their long axes in plane with a supporting substrate. However, the response of coupled dipole antennas oriented vertically to a supporting substrate has so far been out of experimental reach. Here, we present a self-aligned electron-beam lithography technique for fabricating such antennas consisting of metal nanostructures on both sides of a suspended silicon nitride membrane. This 30 nm thick membrane provides an ultra-smooth metal/dielectric interface and uniformly defines the antenna feed-gap size in an array of antennas. It is also a suitable substrate for probing the nano-antenna response with monochromated electron energy-loss spectroscopy (EELS) in a transmission electron microscope. We provide details of this double-sided patterning process, and show the excitation of hybridized plasmon modes in EELS with electrons directed along, and at an angle to, the antenna axis.

3D Nanostar Dimers with a Sub‐10‐nm Gap for Single‐/Few‐Molecule Surface‐Enhanced Raman Scattering

Plasmonic nanostar-dimers, decoupled from the substrate, have been fabricated by combining electron-beam lithography and reactive-ion etching techniques. The 3D architecture, the sharp tips of the nanostars and the sub-10 nm gap size promote the formation of giant electric-field in highly localized hot-spots. The single/few molecule detection capability of the 3D nanostar-dimers has been demonstrated by Surface-Enhanced Raman Scattering.

Development of a low cost roll-to-roll nanoimprint lithography system for patterning 8-inch wide flexible substrates

Recent developments in flexible electronics, solar cells, displays, bio-chips and wearable technology have featured various micro/nanostructures in system designs. However, fabricating these micro/nanostructures on flexible substrates using existing technology such as photolithography, electron beam lithography (EBL) and other lithography techniques is troublesome, time consuming and costly. An in-house roll-to-roll ultraviolet nanoimprint lithography (R2R-UVNIL) system was designed and fabricated as an alternative low cost and large area patterning tool. It consists of a coating unit, soft-bake unit and imprinting unit which are connected together using a series of rollers. The aim of the integrated soft-bake stage was to minimise the mould sticking issues during the continuous R2R imprinting using solvent-based resist. The assembled R2R-UVNIL system was tested with imprinting process on an untreated commercial polyethylene terephthalate (PET) film as the flexible substrate, solvent-based SU8-2002 photopolymer as the resist and PDMS soft mould as the imprinting mould. The PDMS soft mould was replicated from an EBL patterned silicon master mould. Imprinting speeds of 50 to 150 mm/min have been achieved in this work, with relatively sound replication quality and formability for patterning sub-2 μm microstructures.

Negative Pattern Scheme (NPS) Design for Nanowire Formation Using Scanning Electron Microscope Based Electron Beam Lithography Technique

In this work, we report the used of Negative Pattern Scheme (NPS) by Electron Microscope Based Electron Beam Lithography (EBL) Technique in connection with scanning electron microscope (SEM) for creating extremely fine nanowires. These patterns have been designed using GDSII Editor and directly transferred on the sample coated with ma-N 2400 Series as the negative tone e-beam resist. The NPS designs having line width of approximately 100 nm are successfully fabricated at our lab. The profile of the nanowire can be precisely controlled by this technique. The optical characterization that is applied to check the nanowires structure using SEM and Atomic Force Microscopy (AFM).

Structural Studies on Superconducting Flux Flow Transistors with Nano-Scale Channel Fabricated by Electron Beam Lithography

The superconducting flux flow transistor (SFFT) with three-channel was successfully fabricated by an electron beam lithography and Ar ion milling technique. In our paper the cross sectional analysis and topological views are investigated for the channel width and the channel height by the atomic force microscopy (AFM) image. Our result shows that the SFFT of multi-structure with a nano-channel is effectively fabricated by an electron-beam lithography method. We present a fabrication process of three-channel SFFT using the electron beam lithography. Mechanisms of nano-channel SFFT are studied.