Showing papers on "Focused ion beam published in 1999"

Submicron stacked-junction fabrication from Bi2Sr2CaCu2O8+δ whiskers by focused-ion-beam etching

Abstract: We fabricated submicron-sized intrinsic Josephson junctions by the focused-ion-beam (FIB) etching method The principal result was a reduction of the in-plane junction area to 03 μm2 by direct FIB etching with no degradation in the critical transition temperature (Tc) In the current (I)–voltage (V) characteristics of these stacks, the gap structure and the normal state resistance are clearly observed together with a reduction of the Joule heating and disappearance of the branch structure The Coulomb staircase structure was found in the I–V curves of submicron junctions as a result of their small effective capacitance of fF order

Scaling of ferroelectric and piezoelectric properties in Pt/SrBi2Ta2O9/Pt thin films

Abstract: Scaling of the ferroelectric and piezoelectric properties in Pt/SrBi2Ta2O9/Pt thin films was studied. Focused ion beam milling was used to fabricate submicron devices (1×1, 0.5×0.5, 0.25×0.25, 0.09×0.09, and 0.07×0.07 μm2) and scanning force microscopy was used to examine their piezoelectric response. It was found that capacitors as small as 0.09×0.09 μm2 exhibit good piezoelectric/ferroelectric properties and that submicron (0.25×0.25 μm2) capacitors show resistance to bipolar fatigue with up to at least 109 cycles. The results were compared with similar capacitor structures milled in the Pb1.0(Nb0.04Zr0.28Ti0.68)O3 system where structures as small as 0.07×0.07 μm2 were analyzed.

Side-wall damage in a transmission electron microscopy specimen of crystalline si prepared by focused ion beam etching

Abstract: In focused ion beam (FIB) fabrication of cross-sectional transmission electron microscopy (X-TEM) specimens, highly accelerated ion beams sometimes cause serious damage. The damage can be induced in both the specimen surface and the side walls. We used the X-TEM technique to investigate the sidewall damage in crystalline Si. The damaged layer was found to be about 20 nm thick in the case of 30-keV-FIB etching. We evaluated several techniques for reducing the damage, such as gas-assisted etching (GAE) with iodine, low-energy FIB etching, and cleaning by broad argon ion milling or by wet etching. The damage depth was 19 nm for GAE and 10 nm for 10 keV FIB etching, and was reduced to 7 nm by 3 keV argon ion milling with a beam current of 20 μA and a tilt angle between the beam and the specimen of 4°. Wet etching using a mixture of nitric and hydrofluoric acid removed most of the damaged layer. The effect of the damaged layer on TEM observation was also investigated, and it was shown that removal of the damag...

Reconstruction of three-dimensional chemistry and geometry using focused ion beam microscopy

Abstract: A technique to reconstruct high resolution three-dimensional structural images and chemical maps using focused ion beam microscopy is presented. A focused ion beam microscope is used to collect secondary electron images and secondary ion mass spectroscopy elemental maps as a function of depth. These images and elemental maps are then used to reconstruct volume image and chemical maps with 20 nm lateral and depth resolutions. Methods to improve lateral resolution and to reduce uncertainties due to differential sputtering are also discussed.

Depth control of focused ion-beam milling from a numerical model of the sputter process

Abstract: A mathematical model of focused ion-beam milling is used to generate dwell times for the vector scanned pixel address scheme of a focused ion-beam deflection system. The model incorporates the absolute sputter yield of the solid as a function of the angle of incidence, and the relationship between the ion-beam current distribution and the pixel size of the deflection pattern. The object of this work is to be able to call for an arbitrary geometric shape to be ion milled and then have the numerical model compute the pixel dwell times for the deflection system such that the final cavity is sputtered. Experimental verification of the procedure was accomplished with parabolic troughs, hemispherical troughs, and cosine troughs. The term “trough” means a plane of symmetry in the ion-milled cavity. These same geometric shapes were also ion milled using a rotational axis of symmetry, yielding sinusoidal ring patterns, parabolic dishes, and hemispherical dishes. The absolute maximum depth for each of the cavities ...

3D intrinsic Josephson junctions using c-axis thin films and single crystals

Abstract: We report successful fabrication of 3D intrinsic Josephson junctions (IJJs) using c-axis YBCO thin films of 800 nm thickness and Bi-2212 single-crystal whiskers. The stacks of IJJs were prepared by a lateral focused ion beam etching method. The width depending on the required junction size and the full depth of film thickness were patterned in a micro area from the normal direction etching. By tilting the sample stage up to 90°, two grooves of the bridge were etched from the lateral direction in accordance with the required junction size. The junctions did not show any degradation of critical current density (Jc) down to an in-plane area of 0.5 µm2.

Method for device editing

Abstract: A method for making connections to conductors buried under dielectrics layers using a focused ion beam and an etch-assisting gas is described. The method uses a halogenated hydrocarbon, such as 2, 2, 2-trifluoroacetamide, to enhance etching of the dielectric while attenuating etching of the conductor once expose. The method thereby allows a via to be milled to contact the conductor without substantial etching and degrading the conductor.

Hybrid Monte Carlo -Particle-in-Cell Simulation of an Ion Thruster Plume

Abstract: A numerical code is described that simulates the plumes of ion thrusters and Hall current thrusters. In the present study, computed e owe eld results are compared with existing experimental measurements for the UK-10 ion thruster. The experimental measurements consist of ion e ux, ion density, and e oating potential data. The numerical code combines the direct simulation Monte Carlo method for modeling collisions with the particle-incell method for modeling plasma dynamics. Xenon neutrals and ions are modeled directly. Electrons are described by the Boltzmann relation. The effect of a e nite back pressure experienced in laboratory experiments is included. Agreement between simulation and experiment issatisfactory. The simulation results are found to bevery sensitive to input conditions assumed at the thruster exit plane. In particular, there is uncertainty in specifying the effects of the curvature of the dished grids of the UK-10 thruster on the ion exit velocity proe le. The sensitivity of the simulations to certain model parameters is also examined. These include the cross section for charge-exchange reactions, the mechanics of charge-exchange reactions, and the electron temperature. The beam ions are found to be only moderately dependent on these variations, whereas the charge-exchange ions are sensitive to them.

High aspect ratio all diamond tips formed by focused ion beam for conducting atomic force microscopy

Abstract: Conductive (boron doped) all diamond tips are best suited for use as electrical probes for scanning probe experiments due to their hardness, chemical inertness, and resistivity against wear. In order to overcome the problems of image distortion induced by the tip shape the aspect ratio of the diamond tips was increased to about 7:1 by focused ion beam milling, maintaining a tip radius of typically 30 nm at the apex. The application of these sharpened tips to conducting atomic force microscopy for local electrical characterization of thin metal–oxide–semiconductor dielectrics is demonstrated. Excess current flow was detected at the transition region between the gate oxide and the bordering field oxide due to oxide thinning introduced by the local oxidation of silicon process.

Micromachining using focused high energy ion beams: Deep Ion Beam Lithography

Abstract: The combination of deep X-ray lithography with electroforming and micromoulding (i.e., LIGA) has been shown to offer high potential for the production of high aspect-ratio microstructures. The LIGA technique, employing synchrotron light and a suitable X-ray mask, allows production of 3D microstructures in PMMA with aspect ratios around 100. Here we demonstrate that the novel technique of Deep Ion Beam Lithography (DIBL), a direct process utilizing a focused beam of MeV ions scanned in a predetermined pattern over a suitable resist material, can produce three dimensional microstructures with sub-micrometer feature sizes. Microstructures extending up to 100 μm from the substrate with aspect ratios approaching 100 can be produced. Multiple exposures at different ion energies allow production of multilayer structures in single resist layers of SU-8, a newly developed, chemically accelerated, negative tone, near UV, photoresist.

Focused ion beam system

Abstract: A focused ion beam (FIB) system produces a final beam spot size down to 0.1 μm or less and an ion beam output current on the order of microamps. The FIB system increases ion source brightness by properly configuring the first (plasma) and second (extraction) electrodes. The first electrode is configured to have a high aperture diameter to electrode thickness aspect ratio. Additional accelerator and focusing electrodes are used to produce the final beam. As few as five electrodes can be used, providing a very compact FIB system with a length down to only 20 mm. Multibeamlet arrangements with a single ion source can be produced to increase throughput. The FIB system can be used for nanolithography and doping applications for fabrication of semiconductor devices with minimum feature sizes of 0.1 μm or less.

Focused ion beam micromilling of GaN and related substrate materials (sapphire, SiC, and Si)

Abstract: Micromilling of GaN films has been obtained using a Ga+ focused ion beam (FIB). The GaN micromilling has been investigated over a range of energies (15–70 keV), incident angles (0°–30°), and number of scans (10–50). At normal incidence, increasing the Ga+ energy up to 50 keV increases the milling rate, while higher energies produce the same (or a slightly decreased) milling rate. Increasing the angle of incidence increases the milling rate at all energies. The highest GaN milling rate of 0.6 μm3/nA s (corresponding to an average yield of 6.6 atoms/ion) has been obtained at 50 keV, 30° incidence, and 50 scans. The milling rate of current substrate materials (sapphire, Si and SiC) for GaN thin film growth is shown to be 2–5 times lower. The sputtering yield is found to vary inversely with the strength of the chemical bond in the materials investigated. Distributed Bragg reflection air/GaN gratings for short cavity lasers were fabricated to show the capability of FIB micromilling to produce optoelectronic de...

Fabrication of submicron BSCCO stacked junctions by focused ion beam (FIB)

Abstract: A method for the fabrication of in-plane submicron size intrinsic Josephson junctions by focused ion beam (FIB) has been developed. The method includes double-sided processing of thin layered single crystals by FIB and has been demonstrated on high quality BSCCO (2212) single crystal whiskers. The stacked junctions with in-plane area down to 0.3 /spl mu/m/sup 2/ have been fabricated without deterioration of superconducting transition temperature T/sub c/ and the superconducting energy gap /spl Delta/.

A new approach to nuclear microscopy: the ion–electron emission microscope

Abstract: A new multidimensional high lateral resolution ion beam analysis technique, ion–electron emission microscopy (IEEM) is described. Using MeV energy ions, IEEM is shown to be capable of ion beam induced charge collection (IBICC) measurements in semiconductors. IEEM should also be capable of microscopically and multidimensionally mapping the surface and bulk composition of solids. As such, IEEM has nearly identical capabilities as traditional nuclear microprobe analysis, with the advantage that the ion beam does not have to be focused. The technique is based on determining the position where an individual ion enters the surface of the sample by projection secondary electron emission microscopy. The x – y origination point of a secondary electron, and hence the impact coordinates of the corresponding incident ion, is recorded with a position sensitive detector connected to a standard photoemission electron microscope (PEEM). These signals are then used to establish coincidence with IBICC, atomic, or nuclear reaction induced ion beam analysis signals simultaneously caused by the incident ion.

Low-energy cluster ion beam modification of surfaces

Abstract: In cluster ion beam processes, multiple collisions during the impact of accelerated cluster ions upon the substrate surfaces produce fundamentally non-linear processes in a low-energy regime. The gas cluster ion beam process has been applied to produce ultra-shallow junctions (less than 7 nm in Si at 2 keV), very high-rate sputtering (more than two orders of magnitude higher than by monomer ions having the same energy), atomic scale smoothing of surfaces (to average roughness less than 0.2 nm) and reactive thin film formation at low substrate temperatures. This paper will review recent requirements for ion beam processing and the status of ion beam equipment development. Several characteristics of the gas-cluster ion beam processing are capable of meeting these recent requirements and will be demonstrated by our recent experimental and molecular dynamics simulation results.

Focused ion-beam specimen preparation for atom probe field-ion microscopy characterization of multilayer film structures

Abstract: Focused ion-beam milling with a sub-10 nm diameter beam of gallium ions has been used to fabricate field-ion specimens from a multilayer film nanostructure containing 100 repetitions of a bilayer deposited directly onto a planar substrate. Successful field-ion specimen preparation has allowed the observation of these layers on the atomic scale by both field-ion imaging and atom probe compositional analysis.

Lateral growth of focused ion beam deposited platinum for stencil mask repair

Abstract: Focused ion beams can repair conventional lithography masks through milling and deposition. Repairs to stencil masks for ion projection lithography present a greater challenge than conventional mask repair, as the standard model of ion induced deposition requires a surface for deposition to take place. In a stencil mask, a bridge must be formed across the open area, anchored to the mask on either side of a slot. Focused ion beam deposition can induce such horizontal growth of material. Ion-induced growth of platinum over slots up to 3 μm wide in a 2.75 μm silicon membrane is demonstrated for an average beam current density of 7 mA/cm2. The primary method used to accomplish this is by scanning the focused ion beam in a rectangular pattern that extends over the slot. Material is built up from the edges, and grows inwards to span the slot and form a bridge. The direction of gas flow is an important consideration. When gas flow is perpendicular to the slot, the downstream side of the bridge will grow much fas...

Direct writing of low tc superconductor-normal metal-superconductor junctions using a focused ion beam

Abstract: Using a focused ion beam, we have produced superconductor-normal metal-superconductor junctions by controllably removing a portion of the top layer of a patterned superconductor-normal metal thin film. The high-quality junctions showed Josephson coupling which scaled qualitatively with barrier properties and temperature as expected. The largest product of a junction’s critical current and the normal state resistance measured is 98 μV at 4.2 K. The method has good reproducibility and could be exploited in a number of superconducting electronics applications.

Position and size of the electron beam in the high-energy electron beam ion trap

Abstract: In the last decade, many spectroscopic studies have been performed using the electron beam ion trap. Often these measurements rely on the electron beam as an effective slit, yet until now, no systematic study of the position and size of the electron beam under various operating conditions has been made. Here, we present a thorough study of the electron beam's position and size (and thus the electron density) as affected by various operating parameters, and give optimal parameter ranges for operating the device as a spectroscopic source. It is shown that the diameter is constant as the energy is varied, which is important for accurate cross-section measurements.

Room-temperature visible and infrared photoluminescence from Pr-implanted GaN films by focused-ion-beam direct write

Abstract: Visible and infrared photoluminescence (PL) have been obtained from Pr-implanted GaN films using focused-ion-beam (FIB) direct write utilizing a Pr–Pt liquid alloy ion source. FIB implantation was performed on GaN films grown by molecular-beam epitaxy (MBE), hydride vapor-phase epitaxy, and metalorganic chemical-vapor deposition. After annealing, strong room-temperature emission was observed in the red (at 650 nm) and in the infrared (at several wavelengths including 0.96, 1.3, and 1.9 μm). Essentially identical PL spectra were obtained in the implanted GaN films as in the in situ Pr-doped GaN films grown by MBE.

Experimental evidence for Coulomb charging effects in submicron Bi-2212 stacks

Abstract: Focused ion beam (FIB) and ion milling techniques are developed for the fabrication of Bi2Sr2CaCu2O8+1d (Bi-2212) stacked junctions with in-plane size L ab ranging from several microns down to the submicron scale without degradation of superconducting transition temperature Tc. It is found that the behavior of submicron junctions (Lab<1 µm) is quite different from that of larger ones. The critical current density is considerably suppressed, the hysteresis and multibranched structure of the current-voltage (I-V) characteristics are eliminated, and a periodic structure of current peaks appears reproducibly on the I-V curves at low temperatures. The period ΔV of the structure is consistent with the Coulomb charging energy of a single pair, ΔV=e/C, where C is the effective capacitance of the stack. It is considered that this behavior originates from the Coulomb blockade of the intrinsic Josephson tunneling in submicron Bi-2212 stacks.

Microstructure modification of silver films deposited by ionized magnetron sputter deposition

Abstract: Silver films have been deposited under controlled ion bombardment by ionized magnetron sputter deposition (IMSD). The technique uses a built-in rf coil to generate an inductively coupled plasma confined close to the substrate. This enables precise control of both the bombarding ion flux (by rf power) and the energy (by substrate bias). By varying the flux and energy of bombarding ions, the film’s structure and properties can be easily modified. Crystallography, grain size, and film texture have been characterized using the x-ray diffraction method, and film stress was measured by a substrate curvature technique. A focused ion beam was used to section the deposited films and to observe the surface morphology and cross-sectional structure. The electrical resistivity ratio (room to liquid nitrogen temperature: R298 K/R77 K) was used to investigate the influence of the film structure on the conductivity. The persistence of bombardment induced film property variation with thickness was studied in terms of the texture variation in bilayers consisting of IMSD and magnetron sputtering deposited films. It is found that the microstructure of deposited films depends predominantly on the ion bombardment during the initial stages of film growth. Using the IMSD technique, the structure and related properties of silver films have been modified by depositing films under precisely controlled ion bombardment.

Transmission Electron Microscope Specimen Preparation of Metal Matrix Composites Using the Focused Ion Beam Miller

Abstract: Transmission electron microscope samples of two types of metal matrix composites were prepared using both traditional thinning methods and the more novel focused ion beam miller. Electropolishing methods were able to produce, very rapidly, thin foils where the matrix was electron transparent, but the ceramic reinforcement particles remained unthinned. Thus, it was not possible in these foils to study either the matrix-reinforcement interface or the microstructure of the reinforcement particles themselves. In contrast, both phases in the composites prepared using the focused ion beam miller thinned uniformly. The interfaces in these materials were clearly visible and the ceramic reinforcement was electron transparent. However, microstructural artifacts associated with ion beam damage were also observed. The extent of these artifacts and methods of minimizing their effect were dependent on both the materials and the milling conditions used.

A microaccelerometer structure fabricated in silicon-on-insulator using a focused ion beam process

Abstract: Focused ion beam processing (FIB) has been employed for the fabrication of a microaccelerometer structure starting with bonded silicon-on-insulator substrates A short FIB processing step involves cutting a narrow gap obliquely in a silicon beam This gap is used for reading out an acceleration The process time is less than 2 min which could be viable for the manufacture of high value sensors SOI material is ideal to fabricate suspended structures with simple processing steps A novel, so-called `tapping mode' readout is studied It is based on a periodic closing of the readout gap and a duty cycle measurement Electron tunnelling readout is proposed for high sensitivity applications