Showing papers on "Focused ion beam published in 2005"

Introduction to focused ion beams : instrumentation, theory, techniques, and practice

Abstract: The Focused Ion Beam Instrument.- Ion - Solid Interactions.- Focused Ion Beam Gases for Deposition and Enhanced Etch.- Three-Dimensional Nanofabrication Using Focused Ion Beams.- Device Edits and Modifications.- The Uses of Dual Beam FIB in Microelectronic Failure Analysis.- High Resolution Live Imaging of FIB Milling Processes for Optimum Accuracy.- FIB for Materials Science Applications - a Review.- Practical Aspects of FIB Tem Specimen Preparation.- FIB Lift-Out Specimen Preparation Techniques.- A FIB Micro-Sampling Technique and a Site Specific TEM Specimen Preparation Method.- Dual-Beam (FIB-SEM) Systems.- Focused Ion Beam Secondary Ion Mass Spectrometry (FIB-SIMS).- Quantitative Three-Dimensional Analysis Using Focused Ion Beam Microscopy.- Application of FIB in Combination with Auger Electron Spectroscopy.

Recent Developments in Nanofabrication Using Focused Ion Beams

Abstract: Focused ion beam (FIB) technology has become increasingly popular in the fabrication of nanoscale structures. In this paper, the recent developments of the FIB technology are examined with emphasis on its ability to fabricate a wide variety of nanostructures. FIB-based nanofabrication involves four major approaches: milling, implantation, ion-induced deposition, and ion-assisted etching of materials; all these approaches are reviewed separately. Following an introduction of the uniqueness and strength of the technology, the ion source and systems used for FIB are presented. The principle and specific techniques underlying each of the four approaches are subsequently studied with emphasis on their abilities of writing structures with nanoscale accuracy. The differences and uniqueness among these techniques are also discussed. Finally, concluding remarks are provided where the strength and weakness of the techniques studied are summarized and the scopes for technological improvement and future research are recommended.

Ion beam lithography and nanofabrication: a review

Abstract: To overcome the diffraction constraints of traditional optical lithography, the next generation lithographies (NGLs) will utilize any one or more of EUV (extreme ultraviolet), X-ray, electron or ion beam technologies to produce sub-100 nm features. Perhaps the most under-developed and under-rated is the utilization of ions for lithographic purposes. All three ion beam techniques, FIB (Focused Ion Beam), Proton Beam Writing (p-beam writing) and Ion Projection Lithography (IPL) have now breached the technologically difficult 100 nm barrier, and are now capable of fabricating structures at the nanoscale. FIB, p-beam writing and IPL have the flexibility and potential to become leading contenders as NGLs. The three ion beam techniques have widely different attributes, and as such have their own strengths, niche areas and application areas. The physical principles underlying ion beam interactions with materials are described, together with a comparison with other lithographic techniques (electron beam writing a...

Measuring fracture toughness of coatings using focused-ion-beam-machined microbeams

Abstract: Measuring the toughness of brittle coatings has always been a difficult task. Coatings are often too thin to easily prepare a freestanding sample of a defined geometry to use standard toughness measuring techniques. Using standard indentation techniques gives results influenced by the effect of the substrate. A new technique for measuring the toughness of coatings is described here. A precracked micro-beam was produced using focused ion beam (FIB) machining, then imaged and loaded to fracture using a nanoindenter.

Size dependence of mechanical properties of gold at the sub-micron scale

Abstract: The results of both experimental studies and molecular dynamics simulations indicate that crystals exhibit strong size effects at the sub-micron scale. In experimental studies, the size effects are usually explained by strain gradients. By contrast, atomistic simulations suggest that the yield strength depends on the size even without strain gradients and scales with the sample size through a power relationship. Here we address these two different approaches to the size dependence of mechanical properties. Results of uniaxial compression experiments on gold single crystals at the sub-micron scale, without significant stress/strain gradients, are presented. The free-standing single-crystal Au cylinders are created by focused ion beam machining and are subsequently compressed using a nanoindenter fitted with a diamond flat punch. Compressive stresses and strains, as well as pillar stiffnesses, are determined from the test data. The experiments show that the flow stresses of these pillars increase significantly with decreasing pillar diameter, reaching several GPa for the smallest pillars. These high strengths appear to be controlled by dislocation starvation, which is unique to small crystals.

Application of parametric resonance amplification in a single-crystal silicon micro-oscillator based mass sensor

Abstract: A mass sensing concept based on parametric resonance amplification is proposed and experimentally investigated using a non-interdigitated comb-finger driven micro-oscillator. Mass change can be detected by measuring frequency shift at the boundary of the first order parametric resonance ‘tongue’. Both platinum deposition using focused ion beam (FIB) and water vapor desorption and absorption are used to change the mass of a prototype sensor. Due to the sharp transition in amplitude caused by parametric resonance, the sensitivity is 1–2 order of magnitude higher than the same oscillator working at Simple Harmonic Resonance (SHR) mode in air. Picogram (10 −12 g) level mass change can be easily detected in the sensor with mass about 30 ng and resonance frequency less than 100 kHz. Damping effects and noise processes on sensor dynamics and sensing performance are also investigated and damping has no significant effect on sensor noise floor and sensitivity. Higher sensitivity is expected when the oscillator design is optimized and dimensions are scaled.

Quest for high brightness, monochromatic noble gas ion sources

Abstract: Focused ion beam (FIB) machines are key tools for state-of-the art sample preparation in electron microscopy, for characterization and repair in material sciences, for the semiconductor industry and for nanotechnology in general. Liquid-metal ion sources (LMIS) are widely used in FIB machines because they meet the minimum ion source requirements such as source brightness and reliability. However, in FIB machines, noble gas ion sources are favorable for sputtering, beam-induced etching and deposition, because the implanted ions do not change the electrical behavior of the substrate significantly. There are several efforts by various researchers to develop noble gas ion sources that can be used in FIB machines instead of LMIS. The gas ion sources could not meet the minimum ion source requirements. Therefore, LMIS are still a popular choice among FIB machine users. This review article takes a critical look at the reported efforts in the literature to develop noble gas ion sources for FIB machines.

Fabrication of planar photonic crystals in a chalcogenide glass using a focused ion beam.

Abstract: Free-standing “AMTIR-1” (Ge33As12Se55) chalcogenide glass films have been patterned using a focused ion beam (FIB) to create two-dimensional photonic crystal membranes. The triangular lattices were selected for a photonic bandgap relevant to fiber telecommunications. Optical measurements of transmission spectra as a function of incident angle showed clear signs of Fano resonances, indicating that the structures had strongly modified guided modes.

Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires.

Abstract: The current-bias (I-V) characteristics at various temperatures, T, of focused-ion-beam (FIB)-deposited Pt contacts on GaN nanowires evolves from low-resistance ohmic (linear I-V) to rectifying as the diameter increases, and both exhibit strongly nonmetallic T-dependence. The small-diameter (66 nm) T-dependent resistance is explained by two-dimensional variable range hopping with a small characteristic energy, ensuring low resistance at 300 K. For large diameters (184 nm), back-to-back Schottky barriers explain the nonlinear I-V at all T values and permit an estimate of doping concentration from the bias-dependent barrier height. Both behaviors can be understood by accounting for the role of FIB-induced amorphization of GaN underneath the contact, as confirmed by cross-sectional transmission electron microscopy.

FIB Lift-Out Specimen Preparation Techniques

Abstract: In this chapter, we review methods and applications of the FIB lift-out specimen preparation technique. A historical overview of the development of the technique is given. The ex-situ and in-situ lift-out techniques are described. Examples, advantages, and disadvantages of each of the techniques are presented.

New insight into the solid electrolyte interphase with use of a focused ion beam.

Abstract: The formation and evolution of the solid electrolyte interphase (SEI) film on the surface of natural graphite spheres in the electrolyte of 1 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1) were investigated with use of focused ion beam (FIB) technology. Secondary electron FIB images clearly show the surface and cross-section morphology of the SEI film. The composition variation along the surface and cross section of the SEI film was also explored by the elemental line scan analysis (ELSA). The initial SEI film with an apparent thickness range of similar to 450 to similar to 980 nm is rough in morphology and nonuniform in composition, and contains small splits. After certain electrochemical cycles, the thickened SEI film displays microscale holes and obvious cracks on the surface, and the content of organic compounds increases. In addition, the concept of "internal SEI film" is first proposed based on the characterization of the cross section of the natural graphite spheres with the aid of FIB. Finally, the capacity fading mechanisms of the natural graphite spheres corresponding to different electrochemical stages are discussed.

Cross section investigations of compositions and sub-structures of tips obtained by focused electron beam induced deposition

Abstract: The spatial evolution of compositions and sub-structures inside focused-electron-beam-deposited tips from dicobalt-octacarbonyl Co2(CO)8 precursor at 25 keV and varying beam current (20 pA - 3 A) is extensively studied for the first time by means of energy dispersive X-ray spectroscopy, transmission electron microscopy, back-scattered electron imaging, and ion-induced secondary electron imaging. Transverse and longitudinal tip cross sections and lamellae were prepared by focused ion beam milling. Two sub-structure types can be distinguished: a nano-composite sub-structure is grown during the initial deposition stage (small-aspect-ratio tips). It consists of cobalt nano-crystals embedded in a carbonaceous matrix. A second distinct cobalt-grain-rich sub-structure develops in high-aspect ratio tips. Both sub-structures vary in appearance and composition with increasing beam current: the initial nano-composite sub-structure increases in cobalt content and nano-crystal size, and the cobalt-grain sub-structure develops polycrystal-, texture-, whisker-, or platelet-like habits. The directed precursor flux from a micro-tube prevents a radial symmetry of the sub-structures with respect to the impinging focused electron beam, at medium to high beam current. Homogeneous nano-composite high-resolution tips with small diameter and length were obtained at low beam current. Observations suggest an additional contribution to pure electron induced precursor molecule decomposition. The influence of electron beam heating and related chemical reactions is discussed.

Observations of nanoindents via cross-sectional transmission electron microscopy: a survey of deformation mechanisms

Abstract: Examination of cross-sections of nanoindents with the transmission electron microscope has recently become feasible owing to the development of focused ion beam milling of site-specific electron transparent foils. Here, we discuss the development of this technique for the examination of nanoindents and survey the deformation behaviour in a range of single crystal materials with differing resistances to dislocation flow. The principal deformation modes we discuss, in addition to dislocation flow, are phase transformation (silicon and germanium), twinning (gallium arsenide and germanium at 400 8C), lattice rotations (spinel), shear (spinel), lattice rotations (copper) and lattice rotations and densification (TiN/NbN multilayers). The magnitude of the lattice rotation, about the normal to the foil, was measured at different positions under the indents. Indents in a partially recrystallized metallic glass Mg66Ni20Nd14 were also examined. In this case a low-density porous region was formed at the indent tip and evidence of shear bands was also found. Further understanding of indentation deformation will be possible with threedimensional characterization coupled with modelling which takes account of the variety of competing deformation mechanisms that can occur in addition to dislocation glide. Mapping the lattice rotations will be a particularly useful way to evaluate models of the deformation process.

Laser accelerated ions and electron transport in ultra-intense laser matter interaction

Abstract: Since their discovery, laser accelerated ion beams have been the subject of great interest. The ion beam peak power and beam emittance is unmatched by any conventionally accelerated ion beam. Due to the unique quality, a wealth of applications has been proposed, and the first experiments confirmed their prospects. Laser ion acceleration is strongly linked to the generation and transport of hot electrons by the interaction of ultra-intense laser light with matter. Comparing ion acceleration experiments at laser systems with different beam parameters and using targets of varying thickness, material and temperature, some insight on the underlying physics can be obtained. The paper will present experimental results obtained at different laser systems, first beam quality measurement on laser accelerated heavy ions, and ion beam source size measurements at different laser parameters. Using structured targets, we compare information obtained from micro patterned ion beams about the accelerating electron sheath, and the influence of magnetic fields on the electron transport inside conducting targets.

Focused Ion Beam Nanopatterning for Optoelectronic Device Fabrication

Abstract: Recent photonic device structures, including distributed Bragg reflectors (DBRs), one-dimensional (1-D) or two-dimensional (2-D) photonic crystals, and surface plasmon devices, often require nanoscale lithography techniques for their device fabrication. Focused ion beam (FIB) etching has been used as a nanolithographic tool for the creation of these nanostructures. We report the use of FIB etching as a lithographic tool that enables sub-100-nm resolution. The FIB patterning of nanoscale holes on an epitaxially grown GaAs layer is characterized. To eliminate redeposition of sputtered materials during FIB patterning, we have developed a process using a dielectric mask and subsequent dry etching. This approach creates patterns with vertical and smooth sidewalls. A thin titanium layer can be deposited on the dielectric layer to avoid surface charging effects during the FIB process. This FIB nanopatterning technique can be applied to fabricate optoelectronic devices, and we show examples of 1-D gratings in optical fibers for sensing applications, photonic crystal vertical cavity lasers, and photonic crystal defect lasers.

Cantilever tip probe arrays for simultaneous SECM and AFM analysis

Abstract: A cantilever transducer system with platinum tip electrodes in sub-micron regime has been fabricated for simultaneous Scanning Electrochemical Microscopy (SECM) and Atomic Force Microscopy (AFM) analysis. Sharpened High Aspect Ratio Silicon (HARS) tips are shaped combining isotropic and anisotropic deep-reactive etch processes and form the body of the transducer. Deposition of a silicon nitride followed by a back etch step allows embedding these silicon tips in a silicon nitride layer so that they protrude through the nitride. This way, embedded silicon tips with a diameter smaller than 600 nm, a radius smaller than 50 nm, and an aspect ratio higher than 20 can be achieved. Subsequently, a platinum layer and an insulator layer are deposited on these tip structures. Introducing a metal masking technology utilizing Focused Ion Beam (FIB) technology, a precise exposure of the buried metal layer can be achieved to form ultra micro-electrodes on top of the tip. Finally, cantilever structures are shaped and released by etching the silicon substrate from the backside. Electrochemical and mechanical characterization show full functionality of the transducer system. Due to the high aspect ratio topography of the tip structure and low spring constant of silicon nitride cantilevers, these probes are particularly suited for high resolution SECM and AFM analysis. Furthermore, this technology allows a production of both linear probe arrays and two-dimensional probe arrays.

TEM-specimen preparation of cell/mineral interfaces by Focused Ion Beam milling

Abstract: Picocyanobacteria were found to play an important role in calcite precipitation in oligotrophic lakes. In this study, investigations on the interface between cyanobacteria and attached biogenic calcite crystals have been performed to gain further insights into the mechanisms of nucleation of these precipitates. Ultramicrotomy, the conventional preparation technique of thin sections for Transmission Electron Microscopy (TEM) investigations, often fails when working on heterogeneous samples containing soft organic material and hard minerals. Thus, in this study the thin sections were prepared using Focused Ion Beam (FIB) milling. This approach is usually applied in material sciences but until recently was not very common in environmental research. Different analytical TEM methods like Electron Spectroscopic Imaging (ESI) and Electron Energy Loss Spectrometry (EELS) were used to test the suitability of FIB-milling for the preparation of organic/inorganic interface specimens. With this approach we were able to analyze both organic and the inorganic phases of the same sample. Elemental maps of the samples were also calculated. By analyzing the structure of the C K -absorption edge, the different bonding forms of the organic carbon cell and the inorganic carbon of the crystal could be clearly distinguished.

Single fundamental mode photonic crystal vertical cavity laser with improved output power

Abstract: The single fundamental mode output power of photonic crystal vertical cavity lasers is improved by varying sizes of oxide apertures and defect lasing apertures. A maximum output power of 3.1 mW in the fundamental mode has been achieved with a new fabrication process that involves only focused ion beam etching to create holes in selectively oxidised VCSELs.

Nanoscale patterning of Zr-Al-Cu-Ni metallic glass thin films deposited by magnetron sputtering.

Abstract: Completely glassy thin films of Zr-Al-Cu-Ni exhibiting a large super-cooled liquid region (deltaTx = 95 K), very smooth surface (Ra = 0.65 nm), and an extremely high value of Vicker's hardness (Hv = 940), as compared to bulk Zr-Al-Cu-Ni metallic glass, were deposited by radiofrequency magnetron sputtering. Nanoscale patterning ability of Zr-Al-Cu-Ni metallic glass thin films was demonstrated by a focused ion beam etching. The capability to write nanometer-scale patterns (line width approximately 12 nm) opens up a variety of possibilities for fabricating nanomolds for imprint lithography, and a wide range of two- or three-dimensional components for future nanoelectromechanical systems.

Atomically-resolved imaging by frequency-modulation atomic force microscopy using a quartz length-extension resonator

Abstract: Using a 1MHz length-extension type of quartz resonator as a force sensor for frequency-modulation atomic force microscopy (AFM), atomically resolved images of the Si(111)-(7×7) surface was obtained. Fabrications of a tip attached at the front end of the resonator by focused ion beam, and removal of the native oxide layer on the tip by in-situ field ion microscopy are found effective for achieving the highly-resolved AFM imaging.

Lateral Templating for Guided Self-Organization of Sputter Morphologies†

Abstract: Methods for the fabrication of large areas of nanoscale features with controlled period and intraperiod organization are of interest because of the potential for high-throughput mass production of nanoscale devices. Due to their potential in this regard, much recent attention has been devoted to self-organization processes, in which processing causes the spontaneous emergence of a nanoscale pattern. The short-range order can be quite high but some envisaged applications require long-range order, which is destroyed by uncontrolled topological defects arising spontaneously from the self-organization process. A potentially successful hierarchical fabrication strategy is the fabrication of controlled features at a small, but lithographically tractable, length scale by methods such as conventional mask or optical-standing-wave lithography, in order to guide a self-organization process at the finest length scale. Topographic patterning has been used for templating the local disorder in two-dimensional (2D) self-assembled monolayers and for templating defect organization or elimination in three-dimensional (3D) colloidal crystallization. Topography has also been used to manipulate semiconductor quantum-dot placement, composition, and strain, through its effect on stress, surface energy, and mobility. 3D short-range ordering of grown-in quantum-dot short-period superlattices can result from multilayer growth; nanoscale topographic templating of the first layer could dramatically accelerate the development of order and lead to true long-range order. Lithographically and focused ion beam (FIB)-patterned topographies have recently been used to template quantum-dot growth in linear chains, periodic 2D lattices, and in more complex configurations that are promising for novel nanoelectronic architectures, such as quantum cellular automata. The finest features have been templated by serial writing with a FIB, a prohibitively expensive process for mass production that might be circumvented by using a hierarchical fabrication strategy. Here we report the influence of patterned boundaries on the primary material of complementary metal oxide semiconductor (CMOS) technology, i.e., a Si(001) substrate, in guiding self-organized topographic ripples spontaneously appearing during uniform irradiation with low energy Ar ions. We show that the long-range order of the features can be greatly enhanced by this lateral-templating approach. The emerging pattern can be manipulated by changing the boundary spacing and misorientation with respect to the projected ion-beam direction. We develop a scalar figure of merit, a dimensionless topological defect density, to characterize the degree of order of the pattern. At small boundary separation, greatest order is observed when the separation is near an integer multiple of the spontaneously arising feature size. The defect density is exceedingly low up to a critical misorientation angle, beyond which topological defects develop in proportion to the incremental misorientation. These results suggest the potential utility of lateral templating ion-irradiation-induced topographic patterns for highthroughput fabrication at sublithographic length scales. Sputter patterning is the spontaneous formation of oneand two-dimensional arrays of topographical ripples and dots on the surfaces of solids eroded by a directed ion beam. This phenomenon has been observed for a wide range of ion species, energies, and incident angles on a variety of materials, including glass, semiconductors, metals, and insulators. Spontaneously emerging feature sizes, which are selected by the kinetics and, consequently, are continuously tunable via the operating conditions, have been reported as small as 15 nm. In general, controlling the behavior of such driven systems is important in many areas of science and engineering. The success of lateral templating raises the possibility of controlling the morphology at a fine length scale in mass production. Because ion irradiation is currently used for doping control in the mass production of semiconductor devices, there may be little impediment to its rapid uptake for morphology control. We investigate the control of the self-organized sputter pattern by using lithography to control only the boundaries of the field over which morphological features evolve. The system chosen for study was silicon with argon-ion irradiation under conditions known to create a topographically rippled surface with small ordered domains at a spontaneously arising “natural” wavelength of k= 140 nm. Details are reported in the Experimental section. The morphological development of templated and non-templated regions was compared after exposure under identical conditions. Figure 1a shows an atomic force microscopy (AFM) topograph of a templated substrate after ion bombardment. The initial configuration consists of a series of 200 nm mesas and 200 nm valleys with a periodicity of 400 nm, as shown in the top trace in Figure 1b. Figure 1a and the bottom trace of Figure 1b C O M M U N IC A IO N S