Advanced Lithographic Techniques Research Articles

Super-High-Frequency SAW Resonators on AlN/Diamond

This letter describes the procedure to manufacture high-performance surface acoustic wave (SAW) resonators on AlN/diamond heterostructures working at frequencies beyond 10 GHz. In the design of SAW devices on AlN/diamond systems, the thickness of the piezoelectric layer is a key parameter. The influence of the film thickness on the SAW device response has been studied. Optimized thin films combined with advanced e-beam lithographic techniques have allowed the fabrication of one-port SAW resonators with finger width and pitch of 200 nm operating in the 10-14 GHz range with up to 36 dB out-of-band rejection.

Unidirectional Liquid Crystal Pretilt Generation on Asymmetric Nanoscaled Groove Pattern Driven by Atomic Force Microscopic Tip

We demonstrate uniformly and unidirectionally distributed pretilt characteristics of a liquid crystal cell fabricated via a substrate with a scan-directional slant nanosized surface groove pattern driven through an atomic force microscopic (AFM) tip that is continuously modulating the contact force in the scanning line direction. The resultant electro-optic characteristics of the liquid crystal (LC) cell made by our advanced AFM lithography technique show that it generates a unidirectional pretilt that guarantees wider LC applications.

Generating Nanostructures with Multiphoton Absorption Polymerization using Optical Trap Assisted Nanopatterning

The need to generate sub 100 nm features is of interest for a variety of applications including optics, optoelectronics, and plasmonics. To address this requirement, several advanced optical lithography techniques have been developed based on either multiphoton absorption polymerization or near-field effects. In this paper, we combine strengths from multiphoton absorption and near field using optical trap assisted nanopatterning (OTAN). A Gaussian beam is used to position a microsphere in a polymer precursor fluid near a substrate. An ultrafast laser is focused by that microsphere to induce multiphoton polymerization in the near field, leading additive direct-write nanoscale processing.

Near‐Bulk Conductivity of Gold Nanowires as Nanoscale Interconnects and the Role of Atomically Smooth Interface

The electronics industry has consistently decreased the dimensions of structural components and they are now well into the nanoscale range. Naturally, a significant portion of the chip is composed of interconnects. Besides, the engineering problems associated with short wavelength lithography to achieve smaller components, the performance of increasing number of interconnections has become one of the biggest limiting factors in device performance. [1,2] The power loss, signal degradation, interconnection delays, and other performance limitations related to interconnects should be minimized. The importance of such a task can be seen from the perspective of power dissipation by computation elements. The energy dissipation density in electronic chips approaches that in nuclear reactors. [3,4] Therefore, the decrease of the resistivity of metal interconnects is one of the key challenges in the design of nanoscale electronic circuits. Intense studies on methods of preparation of interconnects by advanced lithographic techniques including e-beam lithography lead to the preparation of Au, Pd, Pt, and Cu nanowires (NWs) with resistivities much greater than the bulk metal value (see Supporting Information). [5‐11] The reason for the drastic increase in resistivity for NWs is that charge carriers experience grain boundaries reflections and surface scattering. The smaller the diameter of the conductor, the greater this effect becomes. Even NWs with diameters much above the nanometer scale can exhibit resistivities as high as two orders of magnitude greater that the bulk. [12]

Spread Spectrum Orthogonal Frequency Coded SAW Tags and Sensors Using Harmonic Operation

This paper presents a preliminary investigation of orthogonal frequency coding (OFC) surface acoustic wave tags and sensors at a 500- and 900-MHz operational frequency range using conventional contact lithography techniques. The higher frequency devices are achieved using second harmonic operation; eliminating the need for advanced lithography techniques. The objective of this effort is to increase the technology readiness level of wideband OFC tags at higher frequencies. Measured device results are presented and compared with coupling of modes model predictions to demonstrate performance. The fundamental and harmonic device response is compared for devices designed for operation in the 900-MHz frequency band. The experimental correlation against an ideal matched filter is also presented.

Silsesquioxane-based Photopatternable Porous Low-k Dielectric Materials

AbstractThe future resolution requirements for the semiconductor industry demand advanced lithographic techniques, such as immersion and extreme ultraviolet (EUV) technologies, which will increase the cost of microelectronics manufacturing. Currently, low-k dielectric materials, which are used as insulating layers between the copper wiring, are indirectly patterned using a set of sacrificial layers and etch processes. The sacrificial layers include a photoresist polymer that must first be imaged prior to transferring the pattern to the underlying layers, including the dielectric layer. In order to reduce the number of processing steps required for semiconductor manufacturing, we have developed a novel photo-patternable low-k dielectric material that (1) eliminates the need for sacrificial layers and (2) reduces the number of wafer processing steps. Silsesquioxane copolymers that undergo acid-catalyzed crosslinking when exposed to 193nm wavelength were synthesized. In addition to the direct photo-patternability, the patterned structures are suitable as a dielectric material with a dielectric constant as low as 2.4, and an appreciable elastic modulus (E > 4.0 GPa). These photo-patternable low-k materials represent a ‘greener' approach to semiconductor manufacturing which has the ability to reduce cost, waste materials, and energy consumption.

Observation of frequency band gaps in a one-dimensional nanostructured magnonic crystal

We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.

Height-selective etching for regrowth of self-aligned contacts using MBE

Advanced III–V transistors require unprecedented low-resistance contacts in order to simultaneously scale bandwidth, f max and f t with the physical active region [M.J.W. Rodwell, M. Le, B. Brar, in: Proceedings of the IEEE, 96, 2008, p. 748]. Low-resistance contacts have been previously demonstrated using molecular beam epitaxy (MBE), which provides active doping above 4×10 19 cm −3 and permits in-situ metal deposition for the lowest resistances [U. Singisetti, M.A. Wistey, J.D. Zimmerman, B.J. Thibeault, M.J.W. Rodwell, A.C. Gossard, S.R. Bank, Appl. Phys. Lett., submitted]. But MBE is a blanket deposition technique, and applying MBE regrowth to deep-submicron lateral device dimensions is difficult even with advanced lithography techniques. We present a simple method for selectively etching undesired regrowth from the gate or mesa of a III–V MOSFET or laser, resulting in self-aligned source/drain contacts regardless of the device dimensions. This turns MBE into an effectively selective area growth technique.

Characterisation of nano-interdigitated electrodes

Interdigitated electrodes made up of two individually addressable interdigitated comb-like electrode structures have frequently been suggested as ultra sensitive electrochemical biosensors. Since the signal enhancement effects due to cycling of the reduced and oxidized species are strongly dependent on the inter electrode distances, since the nature of the enhancement is due to overlying diffusion layers, interdigitated electrodes with an electrode separation of less then one micrometer are desired for maximum signal amplification. Fabrication of submicron structures can only be made by advanced lithography techniques. By use of electron beam lithography we have fabricated arrays of interdigitated electrodes with an electrode separation distance of 200 nm and an electrode finger width of likewise 200 nm. The entire electrode structure is 100 micrometre times 100 micrometre, and the active electrode area is dictated by the opening in the passivation layer, that is defined by UV lithography. Here we report measurements of redox cycling of ferrocyanide by coupled cyclic voltammograms, where the potential at one of the working electrodes are varied and either an oxidising or reducing potential is applied to the complimentary interdigitated electrode. The measurements show fast conversion and high collection efficiency round 87% as expected for nano-interdigitated electrodes.

Directed Assembly of Cylinder-Forming Block Copolymers into Patterned Structures to Fabricate Arrays of Spherical Domains and Nanoparticles

The first demonstration of the directed assembly of cylindrical microdomains of a block copolymer into nonregular, patterned structures, as well as the subsequent formation of registered 1D arrays of spherical microdomains and nanoparticles, is presented. Directed assembly of pure cylinder-forming polystyrene-block-poly(t-butylacrylate) copolymer, which can undergo a cylinder-to-sphere morphological transition via thermolysis, on lithographically defined linear, circular, or angled chemical nanopatterns resulted in long-range-ordered cylindrical domains that were registered to the underlying nanopattern. Thermolysis of the cylindrical domains yields registered arrays of spherical domains, which are difficult to pattern with advanced lithographic techniques. The spherical domains maintain uniform size in all patterns studied, including 45° corners. In situ synthesis of metal and metal oxide nanoparticles within the spherical microdomains created linear, circular, and angled nanoparticle 1D arrays, register...

Patterning of parallel nanobridge structures by reverse nanostencil lithography using anedge-patterned stencil

We propose a new process for forming parallel nanobridge patterns by nanostencillithography. In this process, a low-stress silicon nitride stencil with parallel nanobridgestructures is fabricated by a new edge patterning technique where those nanobridges areformed simultaneously via sidewall features using the conventional photolithography andanisotropic dry etching process. After forming primary Cr patterns on the oxidized Sisubstrate by depositing Cr through the edge-patterned stencil, those patterns aretransferred onto the underlying Si layer in a reversed manner, leading to the formation ofparallel Cr nanobridge patterns on the Si substrate. Using this process, we havesuccessfully produced 85 nm-wide parallel Cr nanobridge patterns from a stencil with115 nm-wide nanobridge structures that was fabricated by conventional microlithography.As there is no need for advanced lithography techniques in preparing the nanobridgestencil, the combination of the edge patterning and reverse nanostencil process provides acost-effective tool for the massive fabrication of parallel nanobridge arrays at the 100 nmscale.

A Novel Nanofabrication Technique for the Array of Nanogap Electrodes

We demonstrated a sidewall spacer nanofabrication technique for nanogap electrodes fabrication. Nanogap between gold and polycrystalline silicon (ploy-Si) electrodes is defined without using any advanced lithographic techniques. The feature size of nanogap electrodes fabricated using this technique is mainly determined by the thickness of sidewall spacer. The proposed technique showed that reproducible nanogap distances from 10 to 100 nm on the 6 in. wafer were easily obtained. Binding of 15 nm gold nanoparticles across the 10 nm electrodes leading to a drastic change of the electrical conductance has also been demonstrated. Under a bias of 3 V, the conductive current increases from 2 pA to 300 nA after binding of 15 nm gold nanoparticles across the 10-nm electrodes. We believed that this technique can be contributed to the development of high-density nanogap electrodes for applications in biomolecules or nanoparticles detection.

QUANTA, CIPHERS AND COMPUTERS

On the atomic scale, matter obeys the rules of quantum mechanics which are quite different from the classical rules that determine the properties of conventional computers. Today's advanced lithographic techniques can etch logic gates and wires less than a micron across onto the surfaces of silicon chips. Soon they will yield even smaller parts and inevitably reach a point where logic gates are so small that they are made out of only a handful of atoms. So, if computers are to become smaller in the future, new, quantum technology must replace or supplement what we have now. This article provides a grand overview of quantum information theory from the concept of quantum bits (qubits) to entanglement to quantum computation to quantum cryptography.

Nanomachining by Colloidal Lithography

Colloidal lithography is a recently emerging field; the evolution of this simple technique is still in progress. Recent advances in this area have developed a variety of practical routes of colloidal lithography, which have great potential to replace, at least partially, complex and high-cost advanced lithographic techniques. This Review presents the state of the art of colloidal lithography and consists of three main parts, beginning with synthetic routes to monodisperse colloids and their self-assembly with low defect concentrations, which are used as lithographic masks. Then, we will introduce the modification of the colloidal masks using reactive ion etching (RIE), which produces a variety of nanoscopic features and multifaceted particles. Finally, a few prospective applications of colloidal lithography will be discussed.

Mechanotransduction at cell-matrix and cell-cell contacts.

Mechanical forces play an important role in the organization, growth, maturation, and function of living tissues. At the cellular level, many of the biological responses to external forces originate at two types of specialized microscale structures: focal adhesions that link cells to their surrounding extracellular matrix and adherens junctions that link adjacent cells. Transmission of forces from outside the cell through cell-matrix and cell-cell contacts appears to control the maturation or disassembly of these adhesions and initiates intracellular signaling cascades that ultimately alter many cellular behaviors. In response to externally applied forces, cells actively rearrange the organization and contractile activity of the cytoskeleton and redistribute their intracellular forces. Recent studies suggest that the localized concentration of these cytoskeletal tensions at adhesions is also a major mediator of mechanical signaling. This review summarizes the role of mechanical forces in the formation, stabilization, and dissociation of focal adhesions and adherens junctions and outlines how integration of signals from these adhesions over the entire cell body affects how a cell responds to its mechanical environment. This review also describes advanced optical, lithographic, and computational techniques for the study of mechanotransduction.

Ultra-Thin Resists for Advanced Lithography

The continuous reduction of feature sizes in integrated circuits (IC) is driving the development of advanced lithographic techniques that enable patterning of sub-100-nm features with good fidelity and process margins. Requirements for printing these sub-100-nm features includes tight control of critical dimensions (CD), line edge roughness, and resist profiles. Reduction in exposure wavelengths to 157 nm and extreme ultraviolet (EUV) is pushing the development of new families of resist systems and the use of thin imaging layers that overcome the high absorption by materials of 157-nm and EUV radiation. In addition, thin imaging techniques may provide benefits for low-k1 and high-NA lithography using 193-nm radiation. The use of ultra-thin resists (UTR) introduces new concerns for resist properties including the possibility for increased defectivity and the reduction in etch resistance. In this paper, we describe results of studies using ultra-thin resist integrations to build working devices. These investigations have shown that UTR are not inherently limited by defectivity, and working devices with high yield have been fabricated using UTR integrations on multiple levels.

Quantum interference in a one-dimensional silicon nanowire

We study electronic transport within a lithographically defined silicon nanowire for zero and finite bias. The 10-nm wide and 500-nm long nanowire is fabricated by advanced electron-beam lithographic techniques. Transport experiments reveal clear quantum size effects in the conduction through the wire. Energy quantization within the wire leads to a shift in conduction threshold. Quantum interference effects cause an oscillatory pattern in the conductance. At low source-drain bias, transport is dominated by shallow tunneling barriers. At higher bias, additional nanowire modes are found to contribute to the conductance.

Epitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates.

Parallel processes for patterning densely packed nanometre-scale structures are critical for many diverse areas of nanotechnology. Thin films of diblock copolymers can self-assemble into ordered periodic structures at the molecular scale (approximately 5 to 50 nm), and have been used as templates to fabricate quantum dots, nanowires, magnetic storage media, nanopores and silicon capacitors. Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications. Graphoepitaxy, in-plane electric fields, temperature gradients, and directional solidification have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.

A micro-fluxgate sensor based on the Matteucci effect of amorphous magnetic fibers

Abstract The design, construction and performance of a novel micro-fluxgate sensor is presented in this work. The sensor is based on the large Matteucci effect that is observed in amorphous fibers of typical stoicheiometry Fe77.5Si7.5B15 after proper annealing. The sensor requires a single planar coil to function, which was constructed with conventional printed-circuit techniques along with the sensor signal conditioning circuitry. A new signal extraction technique was applied that is superior to the conventional second-order-harmonic concept, as far as sensitivity and signal-to-noise ratio are concerned. A conventional fiber, with diameter 125 μm and a glass-covered fiber, with core diameter 20 μm and glass-cover thickness 20 μm, were used as magnetic cores in the fluxgate sensor. The amorphous fibers were mounted, subsequently, above a planar coil by soldering each two ends without any further mechanical treatment, like bending or twisting. Current annealing was performed before mounting, for both magnetic core types in order to optimize the inductive response of the fibers. The sensor sensitivity, before amplification, was measured to be 74000 V/T. The low magnetic noise observed allows for a relatively high overall precision, which in the case of glass-covered fiber has been verified to be 60 nT; this figure may easily improve by known signal conditioning techniques. The overall sensor head dimensions are 60 mm ×30 mm. Further scaling down may be achieved by means of advanced lithographic techniques in the case of glass-covered amorphous fibers only, which exhibit significant Matteucci effect in lengths down to 5 mm.

Nanoimprint and micro-contact printing tri-layer processes

Replication of patterns at a nanometer scale is a challenge for both advanced optical lithography and post-optical techniques. Considerable industrial effort has been devoted to the so-called leading-edge optical methods and the next generation lithography techniques. In parallel, a number of low-cost techniques such as nanoimprint and micro-contact printing are being investigated. In these methods, pattern replication is performed in non-conventional ways so that diffraction and scattering problems are no longer relevant. However, several other critical issues have to be studied. This paper describes two tri-layer pattern-transfer techniques, which can be used to improve the process latitude and the process compatibility. Pattern replication and lift-off transfer with feature sizes down to 30 nm and 150 nm have been achieved respectively by nanoimprint and micro-contact printing. As application examples, high-density magnetic dot structures are obtained and studied by measuring magneto-optical Kerr hysteresis loops.