High Resolution Electron Beam Lithography Research Articles

Chemical patterns of octadecyltrimethoxysilane monolayers for the selective deposition of nanoparticles on silicon substrate

The use of nano-objects to make the active part of reproducible nanodevices requires their controlled assembling on specific areas of substrates. In this work, we propose to use van der Waals interactions to assemble selectively gold particles covered by alkyl-thiol ligands on hydrophobic OctadecylTriMethoxySilane (OTMS) patterns defined on SiO 2/Si substrates by a process combining nano-imprint lithography (NIL) or high resolution electron beam lithography (HREBL) and atmospheric chemical vapor deposition (CVD) of silane. A study by atomic force microscopy (AFM) reveals that homogeneous patterns of OTMS self-assembled monolayers, extending on several square millimeters, have been made. These OTMS patterns, with a lateral dimension ranging from 2 μm down to 50 nm, can be located at a precise place of a nanodevice, for example, between nanoelectrodes. Preliminary results of selective nanoparticle deposition on these chemical patterns are presented.

Fabrication of force sensors based on two-dimensional photonic crystal technology

We propose the simulation and the fabrication of a photonic crystal (PhC) strain-sensitive structure, showing that the optical properties of photonic crystals can be used to realize sensing devices characterized by a high degree of compactness and good resolution. The force/pressure optical sensor has been realized by designing a bulk GaAs/AlGaAs photonic crystal microcavity operating in the wavelength range 1300–1400 nm. The simulations show that the resonant wavelength of the mode localized in the microcavity shifts its spectral position following a linear behaviour when a pressure ranging between 0.25 Gpa and 5 GPa is applied, thus allowing the possibility to achieve pressure resolution of 5.82 nm/GPa. High-resolution electron beam lithography technique followed by inductively coupled plasma process were used to transfer the designed geometry on the sample.

Fogging effect correction method in high-resolution electron beam lithography

We report on a fogging effect correction (FEC) method to be used in high-resolution e-beam lithography (EBL). In the new version of the previously presented PROX-In software tool, originally developed to determine the numerical proximity parameters for the proximity effect correction (PEC), was now implemented also the possibility of correcting large-range pattern distortion effects in connection with the modified PROXECCO TM tool from PDF Solutions. This allows a complex exposure optimization by dose modulation of long-range fogging and/or loading effects with the standard PEC method using the same corrector. The presented approach is fast and effective, does not use any special additional technology steps and uses only standard high-resolution measuring techniques. The reviewed method was successfully implemented into mask production at different absorber stacks. It is also used for the determination of FEC input parameters and complex exposure optimization in e-beam direct write and step and flash imprint lithography (SFIL) template manufacturing with sub-50 nm resolution capability.

Spin accumulation in ferromagnetic/nonmagnetic devices

ABSTRACTWe have fabricated ferromagnetic/nonmagnetic (FM/NM) metal heterojunctions for the detection of the spin accumulation effect in different nonmagnetic metals. The polycrystalline heterojunctions are prepared by high resolution electron beam lithography (HR-EBL) and a special oblique evaporation technique. The ferromagnetic (FM) and the nonmagnetic (NM) metal are evaporated on top of each other in a single evaporation process to achieve a clean interface between the two metals. The spin accumulation effect is detected in nonmagnetic copper (Cu) and aluminum (Al), from which we determine the polarization of the interface between the ferromagnetic and nonmagnetic metal.

High-resolution electron beam lithography for the fabrication of high-density dielectric metamaterials

Electron beam lithography has been applied to the fabrication of nanoscale two-dimensional chiral structures with various designs. A fabrication process for planar chiral structures in a thin silicon nitride layer using electron beam lithography and dry etching is presented. A top conductive coating is applied during electron-beam exposure to prevent the occurrence of charging effects caused by the non-conductive silica substrate. Different doses are chosen during the lithography process depending on the complexities and densities of different chiral designs. A very well defined transmission diffraction pattern from arrays of Peano-Gosper fractals is obtained. The optical activity of these dielectric metamaterials shows great potential in their applications of optoelectronic devices and communications.

Fabrication and characterization of silicon nanowires with triangular cross section

Fabrication processes for silicon nanowires with triangular cross section are presented. Processes based on high resolution electron beam lithography and anisotropic etching have been developed on silicon on insulator substrates. As shown by numerical simulations, the triangular shape of the wire allows strong reduction of the dimensions by successive oxidation steps. Moreover, it is easy to define a gate on top of the wire that wraps the device and, with the back gate silicon substrate, allows the biasing of the structure on all sides. The conduction through the wire, as a function of the gate bias and for different temperatures, is reported and discussed.

Specialized Electron Beam Nanolithography for EUV and X-Ray Diffractive Optics

Diffraction of electromagnetic radiation remains a viable method for manipulation and focusing of extreme ultraviolet and X-ray wavelengths where the optical properties preclude significant phase shift without attenuation. As the wavelength becomes smaller, the characteristic dimensions needed for effective utilization of diffraction proportionally shrink, placing significant demands on the half-pitch of the diffractive structure. State-of-the-art nanofabrication technology is then required. Additionally, line placement over the entire grating, zone plate lens, or other diffractive element requires an accuracy on the order of a small fraction of a linewidth over the entire structure. This places a heavy burden on the alignment and calibration of the pattern-generating tool. In the case of zone plate lenses, smooth curved geometric elements are required. Specialized techniques for electron beam lithography have been developed to meet these demands, which diverge from the technology used to meet the challenges encountered in mask making and electronic circuit research. The techniques are in four areas: on axis calibration, beam placement, subpixel image processing for overlay, and smooth generation of arc shapes. Using the ensemble of these specialized techniques, high-resolution electron beam lithography nanofabrication has been used to successfully make diffractive structures with linewidths approaching 10 nm and near diffraction limited optical performance.

Synthesis and characterization of calixarene derivatives as resist materials for electron-beam lithography

This article describes the electron-beam resist properties of a class of calixarene derivatives for high-resolution electron-beam lithography. The derivatives, which are based on a calix[4]resorcinarene framework, are unique in that the bridging carbon is functionalized with a long chain (C11) alkyl group. Our studies reveal that the electron-beam sensitivity of the calix[4]resorcinarenes is markedly lower than a standard calix[6]arene material, consistent with the increase in sensitivity that is observed with the number of monomers for these systems. Comparison of the sensitivity of the calix[4]resorcinarenes with four member calix[4]arenes from the literature reveals very similar values, indicating that chemical modification at the bridging carbon has no appreciable effect on sensitivity. The minimum linewidth resolution of the calix[4]resorcinarenes under our experimental conditions was found to be approximately 50nm at a threshold line dose of 65nC∕cm. Our results also demonstrate the ability to chemically modify calixarene compounds at the bridging carbon position while maintaining electron-beam sensitivity. These findings are intended to open avenues for more extensive modification schemes in developing resist materials for high-resolution electron-beam lithography.

Low-field magnetoresistance in a nanopatterned manganite track

We report on the definition of tracks with ∼50-nm wide nanoconstrictions in a manganite epitaxial film, by high-resolution electron beam lithography and ion beam etching. Magnetotransport measurements at low temperature indicate a linear high-field magnetoresistance, with symmetric resistance jumps (1–3%) visible in the 500 Oe range. We discuss the origin of this effect in terms of domain-wall scattering in manganites.

Patterning of sub-10-nm Ge islands on Si(100) by directed self-assembly

A process is reported for creating arbitrary patterns of sub-10-nm Ge islands on a Si(100) substrate by directed self-assembly. Carbon-based templates are created on Si substrates by electron-beam-induced deposition using high-resolution electron beam lithography. Ozone etching, followed by annealing in ultra-high vacuum, yields small (<4nm) SiC nucleation sites for subsequently deposited Ge. Quantitative analysis of atomic force microscope images reveals templated Ge islands with mean diameter d∼8nm, averaging 2000±500 atoms per island, with controlled spacings as small as 35 nm, and 2 nm absolute positional accuracy. The Ge∕Si nanostructures reported here may find use in end-of-scaling classical computing and single-electron devices and spin-based quantum computing architectures.

Reactive ion etching of a 20 nanometers tungsten gate using a SF6∕N2 chemistry and hydrogen silsesquioxane hard mask resist

This article reports on a direct method for patterning a tungsten gate in the decananometric range using high-resolution electron-beam lithography and reactive ion etching (RIE). Electron-beam lithography is based on the use of hydrogen silsesquioxane for its remarkable properties as a negative-tone resist, for its high resistance to dry etching and its capability to deliver extremely straight sidewalls. The transfer of the resist pattern into the tungsten gate stack is ensured by RIE based on a chemistry using sulfur hexafluoride and nitrogen. An optimization of the tungsten etching step is performed by investigating the impact of the RIE power, gas flows, and pressure on both the anisotropy and selectivity with respect to silicon dioxide. Finally, the integration of a p-type metal-oxide-semiconductor field effect transistor with a tungsten gate and platinum silicide Schottky source∕drain was demonstrated and characterized to show that current-voltage characteristics do not exhibit symptoms of plasma-induced damage.

Experimental determination of anisotropy and demagnetizing factors of single Co nanowires by magnetoresistance measurements

We have investigated the low-temperature magnetoresistance (MR) behavior of Co nanowires with varying widths between 40nm and 5.2μm prepared by high-resolution electron-beam lithography. The wires have a thickness of 20nm and are protected from oxidation by a 10nm carbon cap layer. The magnetoresistance—for magnetic fields applied transversal or perpendicular to the wire—is negative and can be attributed to anisotropic magnetoresistance. The MR curves exhibit a strong dependence on the wire width from which the shape anisotropy and the demagnetizing factors can be deduced. The experimental results are in perfect agreement with the theoretical values for the demagnetization tensor of the general ellipsoid. During the magnetization rotation process a minor contribution from domain-wall nucleation and annihilation occurs.

Guiding Molecular Motors with Nano-Imprinted Structures

This work, for the first time, demonstrates that nano-imprinted samples, with 100 nm wide polymer lines, can act as guides for molecular motors consisting of motor proteins actin and myosin. The motor protein function was characterized using fluorescence microscopy and compared to actomyosin motility on non-structured nitrocellulose surfaces. Our results open for further use of the nano-imprint technique in the production of disposable chips for bio-nanotechnological applications and miniaturized biological test systems. We discuss how the nano-imprinted motor protein assay system may be optimized and also how it compares to previously tested assay systems involving low-resolution UV-lithography and low throughput but high-resolution electron beam lithography.

High-Resolution Electron Beam Lithography and DNA Nano-Patterning for Molecular QCA

Electron beam lithography (EBL) patterning of poly(methylmethacrylate) (PMMA) is a versatile tool for defining molecular structures on the sub-10-nm scale. We demonstrate lithographic resolution to about 5 nm using a cold-development technique. Liftoff of sub-10-nm Au nanoparticles and metal lines proves that cold development completely clears the PMMA residue on the exposed areas. Molecular liftoff is performed to pattern DNA rafts with high fidelity at linewidths of about 100 nm. High-resolution EBL and molecular liftoff can be applied to pattern Creutz-Taube molecules on the scale of a few nanometers for quantum-dot cellular automata.

Fabrication and electrochemical characterization of interdigitated nanoelectrode arrays

Interdigitated nanoelectrode arrays with controlled electrode bandwidth and gap geometries ranging from 30 nm to 1 μm were fabricated on glass substrates by a planar process involving high resolution electron beam lithography and lift-off, and their characteristic electrochemical responses to an aqueous ferrocene derivative solution were examined using fundamental electrochemical techniques. Despite the comparatively large electrode area of electrode arrays containing 10 bands to a single band electrode, quasi-steady-state currents with high current density were obtained at a slow potential sweep rate in cyclic voltammograms of ferrocene derivative since the lateral dimension of the nanoelectrode arrays was considerably less than the scale of the diffusion layer of redox species. Additionally, it was demonstrated that the electrode thickness influenced limiting currents of voltammograms in the case of nanoelectrode arrays. In generation-collection mode experiments, furthermore, a collection efficiency as high as ∼99% was attained by 100 nm wide electrode arrays with a gap dimension of 30 nm.

High performance laser with nanopatterned active layer by selective area epitaxy

Lasers containing a nanopatterned active layer demonstrating excellent threshold characteristics are presented. The nanopatterned active layer is fabricated using high-resolution electron beam lithography and selective-area metal organic chemical vapour deposition crystal growth. Results demonstrating an order of magnitude improvement over previous results are reported.

High resolution electron beam lithography using a chemically amplified calix[4]arene based resist

The calix[4]arene based resist tetrakis(oxiran-2-ylmethoxy)-tetra-tert-butylcalix[4]arene is presented. The well known chemical amplification techniques can be applied to the nonpolymeric class of calixarenes resulting in area doses below 100μC∕cm2 at 30keV beam energy. This is achieved by application of the concept of cationic polymerization to a calix[4]arene derivative bearing four epoxide residues together with a photoacid generating triarylsulfonium salt. The high resolution capabilities of this calixarene based resist remain mainly intact under optimized bake parameters.

Fabrication and performance of 50 nm T-gates for InP high electron mobility transistors

Fifty nanometre gate length T-gates In0.52A10.48As/In0.53Ga0.47As high electron mobility transistors (HEMTs) on a InP substrate were fabricated with high resolution electron-beam (e-beam) lithography using a novel UVIII/LOR/PMMA T-gate resist stack and with a non-selective digital wet etch gate recess technology. The reproducibility of the gate lithography depends on the substrate slope when mounted on the holder of e-beam lithography tool. This mounting effect is almost eliminated by calibrating the tool using a specially fabricated marker on the wafer instead of the holder marker as in usual. Initial devices exhibited a maximum transconductance (gm) of 950 mS/mm and a current cut-off frequency (ft) of 300 GHz.

Nanoelectrode-based devices for electrical biodetection in liquid solution

The fabrication of nanosystems for the electrical detection of biomolecular interactions is reported. Using a planar process on silicon involving high-resolution electron beam lithography and lift-off, we have demonstrated the reliable fabrication of nanoelectrode-based devices with controlled gap dimensions ranging from 100 nm down to 20 nm. These devices were used to achieve the electrical detection of gold colloids. We show that binding events can occur in inter-electrode gaps, leading to a drastic modification of the electrical transport through the nanojunction. Using a similar approach, electrical measurements in solution were performed by developing Poly(dimetylsiloxane) molded microtanks. First experiments involving gold colloids in solution have shown the possibility of detecting individual nanoparticles. The versatility and the very high sensitivity of these devices added to the simplicity of implementation make this approach very attractive for the fabrication of efficient nanobiosensors.

Nanodevices for correlated electrical transport and structural investigation of individual carbon nanotubes

We report a new approach to the correlation of the structural properties and the transport properties of carbon nanotubes. Through an original combination of UV lithography, custom-made photosensitive sol–gel resist and deep reactive ion etching (RIE), we have successfully integrated membrane technology and nanodevice fabrication for the electrical connection of individual carbon nanotubes. After single wall nanotube (SWNT) deposition by molecular combing and contacting using high resolution electron beam lithography, we obtain a device that allows both the investigation of the nanotubes and the contact regions by transmission electron microscopy (TEM) and the measurement of the electronic transport properties of the same individual nano-object. The whole fabrication process is detailed and the demonstration that the micro membranes are suitable for both TEM inspection and nanoelectrode fabrication is given.