Showing papers on "Focused ion beam published in 1998"

High definition aperture probes for near-field optical microscopy fabricated by focused ion beam milling

Abstract: We have improved the optical characteristics of aluminum-coated fiber probes used in near-field scanning optical microscopy by milling with a focused ion beam. This treatment produces a flat-end face free of aluminum grains, containing a well- defined circularly-symmetric aperture with controllable diameter down to 20 nm. The polarization behavior of the tips is circularly symmetric with a polarization ratio exceeding 1:100. The improved imaging characteristics are demonstrated by measuring single molecule fluorescence. Count rates increase more than o­ne order of magnitude over unmodified probes, and the molecule images map a spatial electric field distribution of the aperture in agreement with calculations. (C) 1998 American Institute of Physics.

Preliminary evaluation of an SF5+ polyatomic primary ion beam for analysis of organic thin films by secondary ion mass spectrometry †

Abstract: Organic vapor deposited thin films of pure biomolecules, polymer films and biomolecules dispersed in gelatin and biological tissue have been analyzed in a magnetic sector secondary ion mass spectrometer using an SF5+ primary ion beam at keV impact energies. In comparison to Ar+ bombardment under identical conditions, bombardment with SF5+ gives a 10 to 50 fold enhancement in the secondary ion yields for characteristic molecular ions. The SF5+ primary ion beam can be focussed to a small spot allowing molecular ion images to be obtained at micrometer spatial resolution with enhanced sensitivity. More importantly, the decay in molecular ion signal as a function of primary ion dose commonly observed in SIMS using monoatomic primary ions is either eliminated or greatly reduced, allowing molecular depth profiles to be obtained of organic thin films. By continuing to sample intact molecules as sputtering proceeds into the sample, the total number of detected characteristic secondary ions is increased by as much as a factor of approximately 700 for SF5+ bombardment as compared to Ar+ bombardment under identical analytical conditions. This effect is thought to be a result of the high erosion rate and the low penetration depth inherent in the use of a polyatomic primary projectile.

Applications of the FIB lift-out technique for TEM specimen preparation.

Abstract: A site-specific technique for cross-section transmission electron microscopy specimen preparation of difficult materials is presented. A focused ion beam was used to slice an electron transparent membrane from a specific area of interest within a bulk sample. Micromanipulation lift-out procedures were then used to transport the electron-transparent specimen to a carbon-coated copper grid for subsequent TEM analysis. The FIB (focused ion beam) lift-out technique is a fast method for the preparation of site-specific TEM specimens. The versatility of this technique is demonstrated by presenting cross-sectioned TEM specimens from several types of materials systems, including a multi-layered integrated circuit on a Si substrate, a galvanized steel, a polycrystalline SiC ceramic fiber, and a ZnSe optical ceramic. These specimens have both complex surface geometry and interfaces with complex chemistry. FIB milling was performed sequentially through different layers of cross-sectioned materials so that preferential sputtering was not a factor in preparing TEM specimens. The FIB lift-out method for TEM analysis is a useful technique for the study of complex materials systems for TEM analysis.

Increasing throughput of a near-field optical fiber probe over 1000 times by the use of a triple-tapered structure

Abstract: We fabricated a new probe with extremely high throughput introducing a triple-tapered structure to reduce the loss in a tapered core, to focus the light, and to excite effectively the HE11 mode. A focused ion beam and selective chemical etching were used for fabrication. Over a 1000-fold increase in the throughput of the triple-tapered probe with the aperture diameter D<100 nm was realized in comparison with the conventional single-tapered probe. Furthermore, due to the third taper with a small cone angle, the localized optical near field on the triple-tapered apertured probe with D=60 nm has been confirmed.

A new type of electrostatic ion trap for storage of fast ion beams

Abstract: A new technique for trapping of fast (keV) ion beams is presented. The trap, which is electrostatic, works on a principle similar to that of optical resonators. The main advantages of the trap are the possibility to trap fast beams without need of deceleration, the well-defined beam direction, the easy access to the trapped beam by various probes, and the simple requirement in terms of external beam injection. Results of preliminary experiments related to the radiative cooling of molecular ions are also reported.

Preparation of transmission electron microscope samples

Abstract: A sectional transmission electron microscope (TEM) specimen and a method of forming the same is provided. The specimen includes two separate electron transparent regions, namely a first electron transparent segment for analyzing a specific feature and a second electron transparent segment for analyzing bulk features. The first electron transparent segment is formed using a focused ion beam (FIB) technique, while the second electron transparent segment is formed by a wedge forming technique. The latter step is carried out by protecting the first segment with an adhesive filler and a covering glass layer, polishing a surface of the specimen at an angle to an opposite surface, while simultaneously exposing the previously formed first segment, and removing the filler and glass layer.

Light Emitting Micropatterns of Porous Si Created at Surface Defects

Abstract: We report a principle that allows one to write visible light emitting silicon patterns of arbitrary shape down to the submicrometer scale. We demonstrate that porous Si growth can electrochemically be initiated preferentially at surface defects created in an $n$-type Si substrate by ${\mathrm{Si}}^{++}$ focused ion beam bombardment. For $n$-type material in the dark, the electrochemical pore formation potential (Schottky barrier breakdown voltage) is significantly lower at the implanted locations than for an unimplanted surface. This difference in the threshold voltages is exploited to achieve the selectivity of the pore formation process.

Transmission Electron Microscope Specimen Preparation of Zn Powders Using the Focused Ion Beam Lift-Out Technique

Abstract: Particles of Zn powder have been studied to show that high-quality scanning electron microscope (SEM) and transmission electron microscope (TEM) specimens can be rapidly produced from a site-specific region on a chosen particle by the focused ion beam (FIB) lift-out technique. A TEM specimen approximately 20-µm long by 5-µm wide was milled to electron transparency, extracted from the bulk particle, and micromanipulated onto a carbon coated copper mesh TEM grid. Using the FIB lift-out method, we were able to prepare a site-specific TEM specimen from a difficult material in under 3 hours. The TEM analysis of the lift-out specimen revealed a large amount of thin area free from characteristic signs of damage that may be observed as a result of conventional argon ion milling. The overall microstructure of the specimen prepared by the FIB lift-out method was consistent with samples prepared by conventional metallographic methods. A grain size of ∼10 to 20 µm was observed in all specimens by both TEM and SEM analysis. Light optical microscopy revealed the presence of internal voids in ∼10 to 20 pct of all particles. The SEM analysis showed the voids to extend over ∼70 pct of the particle volume in some cases.

Historical review of electron beam ion sources (invited)

Abstract: Thirty years have passed since the modern concept of the production of highly charged ions in dense electron beams was first proposed, and less since the first electron beam ion source (EBIS) was built and tested. Milestones from the EBIS history, and future prospects are described in view of today’s needs in the production and use of highly charged ions. Various versions of EBIS, such as the classic EBIS, the electron beam ion trap—EBIT, the cross-over EBIS (T)-XEBIS/T and others were constructed, studied, and used in different laboratories. The ion-by-ion and “evaporative” cooling techniques are used to increase the time of ion confinement in an electron beam, ion charge states and ion yield. An alternative way to increase the ion yield is an increase of the electron beam current. The different concept of an ion source based on EBIS which uses multiple reflection of primary electrons and formation of a so-called electron string state is studied as well. Stability of electron-ion systems and nonexcitatio...

Formation of visible light emitting porous GaAs micropatterns

Abstract: Pore growth on n-type GaAs (100) can be initiated in 1 M HCl solution by electrochemical polarization of the material anodic to a critical potential value—the pore formation potential (PFP). At surface defects, however, the PFP is significantly lower (shifted cathodically). Focused ion beam, implantation of Si++ was used to create defined patterns in the substrate. At these implant sites, the growth of porous GaAs was selectively achieved by polarization below the overall PFP. From the porous GaAs patterns visible photoluminescence at green-yellow wavelengths can be observed. This technique, thus, allows the production of light emitting porous GaAs micropatterns of arbitrary shape by a direct writing process.

Chemically and geometrically enhanced focused ion beam micromachining

Abstract: Improvements in focused ion beam (FIB) material removal rates utilizing geometric and chemical enhancement were investigated. Geometrical optimization of FIB micromachining of Permalloy and diamond was investigated to determine the magnitude of material removal rate gains that could be attained by increasing the angle of the ion beam with respect to the sample surface normal. The combination of geometrical optimization with chemical enhancement (C2Cl4 for Permalloy and H2O and XeF2 for diamond) was then investigated to determine whether additional gains in material removal rate could be attained. FIB sharpening of a diamond nanoindenter tip is also presented as a practical example of diamond micromachining with H2O as the removal rate enhancing species.

Focused ion-beam fabrication of fiber probes with well-defined apertures for use in near-field scanning optical microscopy

Abstract: We present a focused ion-beam (FIB) fabrication method for very clean and well-defined subwavelength fiber probes with metallic apertures of a desired diameter for use in near-field scanning optical microscopy. Such probes exhibit improved features compared to probes coated with metal by the conventional angled evaporation technique. Examples of FIB fabricated fiber probes are shown and images of a test sample are presented using one of the probes in a near-field microscope.

Development of an Ion and Electron Dual Focused Beam Apparatus for Three-Dimensional Microanalysis

Abstract: We are developing a novel three-dimensional (3D) microanalysis method by means of successive cross-sectional Auger mapping. In this method, a 3D elemental map will be obtained by repetition of the cross-sectioning of a sample using a gallium focused ion beam (Ga FIB) and Auger mapping of the cross section using an electron beam (EB). On the basis of this concept, an ion and electron dual focused beam apparatus was developed by combining a Ga FIB and a mass spectrometer with a scanning Auger microprobe. In this paper, we describe the concept and instrumentation of the dual focused beam apparatus. Two types of preliminary experiments; i) successive cross-sectioning of a microparticle (6.8 µm) and ii) successive cross-sectional sample current imaging of a bonding wire of an IC, demonstrated the capability to create flat analytical surfaces favorable for the 3D analysis with arbitrary shape and heterogeneity.

Nanometer-scale arrangement of human serum albumin by adsorption on defect arrays created with a finely focused ion beam

Abstract: Well-ordered arrays of pits were prepared on gallium arsenide and silicon wafers using a finely focused ion beam (FFIB). The defect pits on gallium arsenide, examined with tapping mode scanning force microscopy (TM-SFM), had a rim diameter of 60 nm and we

Apparatus for surface modification of polymer, metal and ceramic materials using ion beam

Abstract: An apparatus for surface modification of a polymer, metal and ceramic material using an ion beam (IB) is disclosed, which is capable of supplying and controlling a voltage (220) applied to a material to be surface-modified so that an ion beam (IB) energy irradiated to the material is controlled, differentiating the degree of the vacuum of a reaction gas in a portion of a vacuum chamber in which the ion beam is irradiated from that in a portion in which the ion beam is generated, and also being applicable for both-side irradiating processing and continuous processing.

Mathematical modeling of focused ion beam microfabrication

Abstract: A mathematical model for sputtering a shape or cavity with an arbitrary cross-sectional profile has been developed for focused ion beam milling. The ion beam is assumed to have a Gaussian intensity distribution and a submicron width. The model solves for ion beam dwell times on a pixel grid which yields the desired feature depth as a function of the pixel (x,y) coordinate. The solution is unique and accounts for the ion beam flux contribution at any point from all other pixels in the address matrix. A semiempirical sputter yield treatment allows for a very wide range of ion beam/solid combinations and for yield variations with ion energy and angle of incidence. Solutions have been obtained for parabolic surfaces of revolution, a parabolic trench (with a plane of symmetry) and a hemispherical pit. Either a square or a circular pixel matrix was used for the parabolic shapes. Correspondence between the predictions of the model and experimental 20 keV Ga+ sputtering of a parabolic cross-section trench in Si(1...

Focused ion-beam patterning of nanoscale ferroelectric capacitors

Abstract: A 50 kV Ga+ focused ion beam was applied for milling submicron Pt-(La0.5Sr0.5)CoO3–Pb(NbxZryTiz)O3–(La0.5Sr0.5)CoO3–Pt-based ferroelectric capacitor heterostructures prepared by pulsed laser and sol-gel deposition techniques. The milling yields were found to be 0.22±0.02 μm3/nC for Pb(NbxZryTiz)O3, 0.3.4±0.01 μm3/nC for (La0.5Sr0.5)CoO3, and 0.34±0.06 μm3/nC for Pt layers. The influence of the ion beam current and its scan strategy, as well as depth of milling, on the quality of fabricated structures was studied. The minimum sizes down to 0.017 μm2 for the top electrode, and 0.04 μm2 for the capacitor structures milled to the bottom electrode were achieved without an additional sacrificial layer. A scanning probe microscopy technique was employed to test the properties of the milled capacitor structures.

Focused ion-beam implantation induced thermal quantum-well intermixing for monolithic optoelectronic device integration

Abstract: By focused ion beam implantation induced thermal intermixing the bandgap of quantum-well layer structures can be selectively changed. This allows lateral bandgap engineering and gives a new degree of freedom for lateral structuring. The principle technological aspects like the dependence of the bandgap shift on implantation parameters and the spatial resolution are investigated and applied to the fabrication of photonic and optoelectronic devices. Lateral waveguiding in InP-based materials, the possibility of monolithic integration of bandgap shifted waveguide areas into active devices and the improvement of the lateral carrier confinement in ridge waveguide lasers are demonstrated. Due to the high spatial resolution, modulated bandgap gratings could be realized with periods down to 90 mn. These bandgap gratings were used to create gain-coupled distributed-feedback lasers in different material systems with well controlled single-mode emission.

Study of precursor gases for focused ion beam insulator deposition

Abstract: The electrical properties of insulators formed by focused ion beam induced deposition of various siloxane precursor gases have been compared. Leakage current and breakdown field have been measured by forming metal-insulator-metal structures. It was found that the focused ion beam induced deposition of metal on top of the insulator can substantially degrade the quality of the insulator. We found that the resistivity of the insulator material depends on the deposition yield (e.g., the amount of Ga implantation) as well as on the chemical nature of the precursor gas. From the precursor gases studied, the new compound pentamethylcyclopentasiloxane shows the best performance. Compared to the commercially used tetramethylcyclotetrasiloxane compound, an improvement in resistivity by two orders of magnitude (∼8×1011 versus ∼6×109 Ω cm) and a factor of about 1.5 in breakdown field (650 vs 440 V/μm) could be achieved.

GaN Based Laser Diode with Focused Ion Beam Etched Mirrors

Abstract: GaN-based MQWs-SCH laser diodes (LDs) with Fabry‐Perot resonator mirrors fabricated by focused ion beam (FIB) etching were demonstrated for the first time. The diodes show lasing by pulsed current injection at room temperature with a lasing wavelength near 410 nm. FIB etching of the mirrors significantly reduced the threshold current from 1.25 to 0.75 A. In addition we studied the dependence of I-L characteristics on the successive rotation of the etched mirror of a single device and found a strong angular dependence. A similar study of the tilting angle revealed a very weak variation. © 1999 Published by Elsevier Science S.A. All rights reserved.

Focused ion beam technology applied to microstructure fabrication

Abstract: Focused ion beams (FIBs) have found a place in several research thrusts for the manufacture of mini or micro mechanical objects. This article reports the use of FIB in three distinct applications in microfabrication: prototype structures, micron-sized machine tools and microsurgical manipulators, and ion milling of three dimensional features. Examples of each of these applications are given with the FIB component identified as the enabling or critical component in the technology. The possibility of using FIB milling as part of a production method for micron-sized machine tools is discussed, and the mass production consequences of molds fabricated by three dimensional ion beam milling is also considered. The mathematical procedure and programming steps needed to accurately control FIB three dimensional milling are outlined.

Structural and electrical characterisation of semiconductor materials using a nuclear microprobe

Abstract: High-resolution imaging techniques (submicron) have not traditionally been the domain of MeV ions. Instead, this domain is occupied by a vast array of techniques that utilise scanned low-energy ion beams (keV ion microprobe), electrons (transmission or scanning electron microscopy), light (near field microscopy) or all variants of scanning probe microscopies. Techniques that utilise focused X-rays are also developing. Now, with a nuclear microprobe, high-energy ion beams have begun to enter this domain, bringing a range of unique techniques for making images. With a MeV ion beam focused to a probe smaller than 1 μm, conventional techniques like Rutherford (and non-Rutherford) backscattering spectrometry and particle induced X-ray emission may be used to image and analyse the composition and structure of microscopic regions of inhomogeneous specimens. New ion beam analysis techniques have been developed specifically for use with microbeams. These include ion beam induced charge for imaging charge transport characteristics in materials to ion microtomography for making non-destructive 3-D maps of mass density and elemental composition. Another novel technique is ionoluminescence, which may be used to map various electronic properties of the material. Presented here are some examples of these imaging techniques in a wide variety of semiconductor materials including diamond, HgCdTe, polycrystalline silicon and a mineral semiconductor crystal: pyrite. In all these examples, the specimens display structural inhomogeneities on the scale of 10 μm, making it essential to employ a focused beam. Present limitations to taking imaging with focused MeV ions into the nanometre resolution domain are also discussed.

Methods of examining a specimen and of preparing a specimen for transmission microscopic examination

Abstract: A method of examining a specimen comprising the steps of providing transmission electron microscope apparatus, mounting a specimen in a vacuum chamber of focused ion beam apparatus, isolating a site of the specimen with the focused ion beam apparatus in the vacuum chamber, and with the site located in the vacuum chamber, examining the site with the transmission electron microscope apparatus.

Implanted gallium-ion concentrations of focused-ion-beam prepared cross sections

Abstract: A gallium (Ga) focused-ion-beam (FIB) has been popularly used to prepare cross-sectional samples for transmission electron microscopes (TEMs) and scanning electron or ion microscopes. However, characteristics of the FIB-prepared cross sections such as ion concentration and radiation damage have been little studied either in theory or in experiment. In the present study, cross sections prepared by 30 keV Ga FIB are modeled using a combination of analytical and Monte Carlo methods to calculate the implanted Ga concentration. It is found that the Si/W layered sample is cross sectioned at grazing angles β≈2.5° and 6° for these layers, respectively. The implanted Ga ions for the cross-sectioned Si and W layers are concentrated very near their surfaces of <10 nm to yield the Ga concentrations CGa of about 4 and 9 at % for these layers, respectively. Although there is some differences in sample materials between the calculations and the experiments, the calculated CGa values for Si and W layers roughly agree with the experimental values for the magneto-optical disk TEM sample. This agreement firmly supports the present modeling of FIB-milled cross sections.

Method and apparatus for ion beam scanning in an ion implanter

Abstract: An ion implanter for implanting ions in a target substrate is arranged to scan the ion beam at the point of extraction of the beam from the ion source. The ion beam extraction assembly includes an electrode construction in which an extraction electrode adjacent the ion source aperture is split into two halves. A differential voltage is applied across the two halves of the extraction electrode to deflect the ion beam being extracted from the ion source electrostatically. The plane of deflection is arranged to coincide with the plane if dispersion of the ions in a mass analyser magnet downstream of the extraction point and the deflected beam of ions of desired mass/charge ratio is still brought to focus at a common mass selection slit at the exit of the analyser magnet.

Microprocessing at the fingertips

Abstract: Microprocessing, or micromachining, is here approached in a broad rather than profound way. Following a short description of its origin in microelectronics is a classification of more recent advances into three-dimensional processing, anisotropy inducing techniques, stencil processing and conventional machining adapted to micromachining. For each process the major advantages and drawbacks are accounted for. Also, a representative result accompanies every presentation. In all, more than 20 processes are dealt with: wet etching, dry etching, Lithographie-Galvanoformung-Abformung (LIGA), grey-tone lithography, spatial forming, stereolithography, laser chemical processing, local electrodeposition, two-photon-absorbed photopolymerization, focused ion beam (FIB), electrochemically and ion-induced anisotropy, nanoparticle lithography, fast atom beam (FAB), dicing, assembling, lathe machining, milling, die forging and electro-discharge machining (MEDM and WEDG).

MoS2 deposited by ion beam assisted deposition: 2H or random layer structure?

Abstract: The structure of MoS 2 films grown by ion beam assisted deposition is investigated using transmission electron microscopy. Films consist of stacks of S–Mo–S planes with a [001] texture; however, three-dimensional crystal symmetry is disrupted by a high density of planar defects. Selected area electron diffraction patterns show ( hk 0) and (00 l ) reflections, features similar to a random layer structure, as well as diffuse (103) reflections. It is suggested that these films do not have a true random layer structure, but rather a two-dimensional structure formed by nonrandom in-plane translations.

Masked ion beam lithography with highly charged ions

Abstract: Masked ion beam lithography using highly charged ions is demonstrated for the first time by producing an array of hundreds of ordered micrometer wide dots using Xe44+ on poly(methylmethacrylate) resist. At low dose, exposure of the resist is incomplete and isolated single-ion impact sites can be seen within the exposed areas. Atomic force microscope images of the single-ion impact sites show craters with a width of 24 nm. At high dose, the exposure is complete and the dot morphology is consistent with limitations from the mask. Scanning electron microscope images indicate that the sidewall slope is steeper than four.