Showing papers on "Focused ion beam published in 1995"

Applications of focused ion beams in microelectronics production, design and development

Abstract: Focused ion beam (FIB) systems using gallium liquid metal ion sources can remove material with a lateral resolution below 50 nm and can produce metal deposition at a similar resolution with ion beam-enhanced chemical vapour deposition. These capabilities have resulted in many valuable applications for the microelectronics industry. Circuit modifications are possible because existing connections can be severed and reconnected to different locations. Testing of circuitry can be enhanced by isolation of specific circuits, removal of overlayers and by creation of probe pads where desired. Grain sizes can be determined from secondary electron images by the delineation of individual grains due to orientation-dependent channeling of the ion beam. Secondary ion mass spectrometry analyses of small areas can provide ion images, elemental identification of small areas and endpoint detection with depth profiles. Scanning electron microscopy and transmission electron microscopy sections are prepared routinely using the FIB. These FIB-prepared sections are notable because specific features, such as defects, can be exposed and a range of materials including silicon, indium phosphide, gallium arsenide and even metal layers can be cut without distortion. Transmission electron micrographs of superior quality have been obtained with a large area of very uniform thickness that permits identification of features such as areas under stress.

Method for making specimen and apparatus thereof

Abstract: A method for making a specimen for use in observation through a transparent electron microscope, includes a step of milling part of the specimen into a thin film part, which can be observed through a transparent electron microscope, by scanning and irradiating a focused ion beam onto the specimen, a step of observing a mark for detection of a position provided on the specimen as a secondary charged particle image by scanning and irradiating a charged particle beam onto the specimen without irradiating the charged particle beam onto the portion to be milled into the thin film part during the milling, and a step of compensating for positional drift of the focused ion beam during milling in accordance with a result of the observation. The method is carried out by an apparatus which includes irradiation area control means for controlling an irradiation area of the focused ion beam onto the specimen so that a surface of the specimen to be milled into the thin film part is not included in the secondary charged particle image when the secondary charged particle image of the surface, on which the mark for detecting the milling position of the specimen is formed, is displayed by the secondary charged particle image during milling part of the specimen, and compensation means for compensating the positional drift of the focused ion beam during milling in accordance with the mark for detecting the milling position.

H2O enhanced focused ion beam micromachining

Abstract: The use of H2O vapor as a chemical adjunct for focused ion beam micromachining has been investigated. The presence of H2O vapor during micromachining with a 25 keV Ga+ beam increases the removal rate of carbon‐containing materials such as polyimide, PMMA, and other resists by a factor of 20 (relative to physical sputtering), and that of diamond by a factor of 10. In addition, H2O causes a decrease in the removal rate of some other materials (e.g., Si and Al) by as much as a factor of 10, effectively increasing the selectivity of polymers over these other materials by as much as a factor of 200. The dependence of the removal rate on H2O pressure at the sample, pixel dwell time, pixel size, pattern frame time (corresponding to pattern size), and current density has been investigated utilizing PMMA. PMMA removal rates were calculated by measuring the depth of rectangular pits micromachined into PMMA films under the various experimental conditions. In addition to investigating the effect of H2O on material re...

Study of chemically assisted ion beam etching of GaN using HCl gas

Abstract: The use of an Ar ion beam and hydrogen chloride gas in the chemically assisted ion beam etching of GaN grown by metalorganic chemical vapor deposition is reported. Etch rates were investigated as a function of ion beam energy and substrate temperature. Hydrogen chloride gas was found to produce higher etch rates at lower ion beam energies (300 eV) and lower rates at higher energies (600 eV) in comparison to Cl2. Highly anisotropic etch profiles are demonstrated that indicate that the process may be suitable for the fabrication of laser facets and mirrors. Changes in surface stoichiometry resulting from the etching process were also investigated using Auger electron spectroscopy.

Submicron microbeam apparatus using a single-ended accelerator with very high voltage stability

Abstract: The JAERI light-ion microbeam apparatus for high-resolution ion beam analysis was constructed and installed on a beam line of 3 MV single-ended electrostatic accelerator with a high voltage stability of ± 1 × 10−5. In a performance test of the apparatus, the spot size of 0.4 × 0.4 μm2 in FWHM has been achieved so far by using 2 MeV helium ion beam with a target beam current of 77 pA. The light-ion microbeam apparatus and the accelerator system and the beam size measurement using 2 MeV helium ions is described. The ion beam optical design for submicron microbeam is also discussed.

On the mechanism of crystal growth orientation of ion beam assisted deposited thin films

Abstract: The high number of degrees of freedom of the process parameters of ion beam assisted thin film deposition allows the formation of thin films with special features. Among these process parameters are ion energy, ion irradiation intensity, atom condensation rate and ion impact angle. By contrast to plasma deposition methods, these parameters are independent of each other and can be selected over a wide range. By carefully selecting the ratio I A of condensing atoms to impacting ions, the ion energy and the angle of ion incidence, films with a high degree of crystallographic orientation can be formed. To-date several mechanisms for the development of texture are discussed. Among them is the sputter theory which explains the growth of particular planes by sputtering and channeling. In a comparative study, this theory is applied to transition metal nitrides of group 4, 5 and 6 of the periodic system of elements. Based on results of structural measurements, the mechanisms which are involved in texture formation are discussed as a function of the process parameters arrival ratio I A , ion energy and ionic species. It turns out that it is not the ion energy deposited per atom but the momentum transfer per unit volume which correlates with the observed changes in preferred crystal orientation.

Focused ion beam insulator deposition

Abstract: Focused ion beam (FIB) induced deposition of insulating films from TEOS, a SiO2 precursor, is reported. Deposition was typically carried out using a 30 kV beam of Ga+ ions with a range of ion beam currents from 40 to 2000 pA. The deposition rate was measured as a function of beam current density into the scanned area and scan period, with a typical rate of 0.3 μm3/nC being noted. An important application of the FIB is to repair integrated circuits enabling faster debugging and shorter design cycles. With the continuing trend toward devices containing more interconnect layers having narrower tracks and spaces, it is becoming increasingly difficult to access lower metal levels when they are completely covered by wide upper tracks. Localized FIB insulator deposition enables contact to lower level metal without first removing large areas of the upper metal layers which would otherwise be required. In such structures isolation resistances of more than 15 GΩ have been measured between the metal layers, corresponding to resistivities greater than 108 Ω cm, with a breakdown voltage for the material in the range of 20 to greater than 100 V/μm.

Recent advances in vacuum arc ion sources

Abstract: Intense beams of metal ions can be formed from a vacuum arc ion source. Broadbeam extraction is convenient, and the time-averaged ion beam current delivered downstream can readily be in the tens of milliamperes range. The vacuum arc ion source has for these reasons found good application for metallurgical surface modification--it provides relatively simple and inexpensive access to high dose metal ion implantation. Several important source developments have been demonstrated recently, including very broad beam operation, macroparticle removal, charge state enhancement, and formation of gaseous beams. The authors have made a very broad beam source embodiment with beam formation electrodes 50 cm in diameter, producing a beam of width {approximately}35 cm for a nominal beam area of {approximately}1,000 cm{sup 2}, and a pulsed Ti beam current of about 7 A was formed at a mean ion energy of {approximately}100 keV. Separately, they`ve developed high efficiency macroparticle-removing magnetic filters and incorporated such a filter into a vacuum arc ion source so as to form macroparticle-free ion beams. Jointly with researchers at the High Current Electronics Institute at Tomsk, Russia, and the Gesellschaft fuer Schwerionenforschung at Darmstadt, Germany, they`ve developed a compact technique for increasing the charge states of ions produced in the vacuum arc plasma and thus providing a simple means of increasing the ion energy at fixed extractor voltage. Finally, operation with mixed metal and gaseous ion species has been demonstrated. Here, they briefly review the operation of vacuum marc ion sources and the typical beam and implantation parameters that can be obtained, and describe these source advances and their bearing on metal ion implantation applications.

Novel Method for Defect Detection in Al Stripes by Means of Laser Beam Heating and Detection of Changes in Electrical Resistance

Abstract: We have successfully detected defects (voids and Si nodules) in Al stripes using an optical beam induced current (OBIC) system in which defects, even those beneath a metal surface, were detectable as the difference in changes in resistance, produced by laser beam heating, between defective and defect-free areas. Our method, which we refer to as optical beam induced resistance change (OBIRCH), is nondestructive since the temperature increase caused by laser irradiation is on the order of 1° C and the density of the base current applied to the stripes is on the order of 106 A/cm2 or less. The results of scanning ion microscopy (SIM) (conducted after areas identified by OBIRCH as being defective had been successively cross-sectioned with a focused ion beam [FIB]) indicated that the minimum void size detectable by OBIRCH was on the order of 10-3 µ m3, and we are able to show that OBIRCH has many advantages over conventional void detection methods.

Low-temperature growth and ion-assisted deposition.

Abstract: Using standard molecular-dynamics methods, we have simulated silicon molecular-beam epitaxy on a (100) substrate, subject to a second beam of low-energy argon atoms. We find that the presence of the ion beam has an important effect on the structure of the deposits formed: good crystalline material forms at significantly lower temperatures, where otherwise a thermal beam yields an amorphous deposit. This is because the ion beam provides local excitations, which allow the deposited atoms to find their proper crystal lattice sites.

Analysis of rolling contact fatigued microstructure using focused ion beam sputtering and transmission electron microscopy observation

Abstract: It is well known that a steel which is subjected to fatigue under severe conditions shows peculiar microstructures that are quite different from those of undeformed one or even one which is subjected to a conventional uniaxially deformation. This is particularly true in the case of a steel used in a ball bearing which is subjected to a rolling contact fatigue under severe conditions. The evolution of such a peculiar microstructure can induce flaking of the steel during rolling contact. Recently, a new technique called a focused ion beam (FIB) to prepare TEM specimens has been developed and applied widely to semiconducting materials. In this study the FIB technique was applied to examine by TEM a peculiar microstructure in a steel evolved during a rolling contact fatigue.

Ion-beam apparatus and method for analyzing and controlling integrated circuits

Abstract: An ion-beam apparatus and method for analyzing and controlling integrated circuits. The ion-beam apparatus comprises a stage for holding one or more integrated circuits (ICs); a source means for producing a focused ion beam; and a beam-directing means for directing the focused ion beam to irradiate a predetermined portion of the IC for sufficient time to provide an ion-beam-generated electrical input signal to a predetermined element of the IC. The apparatus and method have applications to failure analysis and developmental analysis of ICs and permit an alteration, control, or programming of logic states or device parameters within the IC either separate from or in combination with applied electrical stimulus to the IC for analysis thereof. Preferred embodiments of the present invention including a secondary particle detector and an electron floodgun further permit imaging of the IC by secondary ions or electrons, and allow at least a partial removal or erasure of the ion-beam-generated electrical input signal.

Low‐damage specimen preparation technique for transmission electron microscopy using iodine gas‐assisted focused ion beam milling

Abstract: A novel method is presented for the preparation of high‐resolution electron microscopy specimens with gas‐assisted focused ion beam (FIB) milling. An etching rate of InP is enhanced 11–13 times with iodine gas‐assisted FIB milling, compared to conventional FIB milling. Specimens with lower radiation damage can be prepared due to lower ion dose during FIB milling, and show no anomalous contrast which comes from the artifacts during FIB milling. Damaged layer introduced during FIB milling was also investigated.

Image-to-image registration focused ion beam system

Abstract: An image-to-image registration system employs interactive computer graphic systems to align and register a number of image representations of a particular device from a variety of sources including, for example, optical microscopic images, computer aided design representations, etc., to an image obtained by a focused ion beam system. The registration enables accurate alignment of the images to the FIB image so that subsurface features which may not be detectable via the FIB image may be located and used to guide operation of the FIB system for milling or conductor/insulator deposition or the like. Counting of aluminum grains is enhanced by use of the invention to register images of a sample taken at several different tilt angles. The registered images are combined to give a more accurate representation of grain boundaries, enabling a more accurate grain count.

Focused-Ion-Beam Digging of Biological Specimens

Abstract: The focused ion beam (FIB) technique has been applied for digging damageable biological specimens of human hair and the housefly eye. Sharp cross-sections have been formed for these specimens and their cross-sectional structures have been observed in scanning ion microscope (SIM) images. The applicability of FIB has been confirmed for these biological specimens.

Semiconductor device having diffusion regions formed with an ion beam absorber pattern

Abstract: In implantation of ions into a wafer, in the manufacture of a semiconductor device, a desired ion beam absorber pattern having locally different thicknesses is previously formed on a major surface of the wafer. The ion beam absorber pattern absorbs an ion beam to be implanted and is formed of a thin film material with its absorbency varying depending on its thickness. Ions are implanted once on the major surface of the wafer through this ion beam absorber pattern to form desired different impurity profiles in depth of desired regions on the major surface of the wafer.

Nanostructuring of gold electrodes for immunosensing applications

Abstract: The fundamental characteristic of nanotechnology is the fabrication of structures with molecular dimensions. In connection with a novel immunosensor, a specifically tailored molecular environment is required which combines immobilized biochemical recognition with electrochemistry. These demands are fulfilled by the creation of nanometer‐size electrodes in a thin film (∼30 nm) of gold consisting of openings commensurate with the size of the biomolecule (∼10 nm). We report on three complementary and advanced fabrication techniques used to produce closely packed distributions of these features: direct focused ion beam milling, lift‐off using polystyrene latex nanospheres as a masking material, and resist exposure by individual ionization tracks produced during high energy heavy ion (∼0.1 MeV/amu) irradiation. The latter two processes are stochastic in nature and exploit the fact that no precise arrangement of the openings is necessary for this application. Fabrication results were analyzed by scanning electron and scanning force microscopy. The three methods are compared with respect to opening size, definition, and packing density and process throughput and control. While nanosphere lift‐off represents a relatively simple and reproducible structuring technique, heavy ion irradiation has the potential for achieving the smallest openings (∼15 nm). Ultimately, the choice of nanostructuring method is dictated by the electrode’s performance in the sensor.

Quantum well structure with self-aligned gate and method of making the same

Abstract: Quantum well structures are fabricated by use of a process employing a Focused Ion Beam (FIB) scanning in the surface of a semiconductor substrate. The quantum well structures thus fabricated include Resonant Tunneling Transistors (RRTs) and one dimensional quantum wire devices, fabricated in conventional Metal Semiconductor Field Effect Transistors (MESFETs) or in High Electron Mobility Transistors (HEMTs). The RRT comprises a pair of implant barriers in the semiconductor substrate, whereby charge carriers are capable of tunneling through the implant barriers into the quantum well during the state of resonance. The one dimensional quantum wire device comprises a multiplicity of implant barriers disposed in the semiconductor substrate substantially parallel to the travelling direction of the charge carriers. The intersection of the implant barriers and the two dimensional gas (2DEG) inside the HEMT enclose truly one dimensional quantum wells which enable electrons to travel therethrough with high mobility. In addition, the potentials of the quantum wells or quantum wires are controlled by a self-aligned gate, such as a T-gate.

The origin of defects in SiO2 thermally grown on Czochralski silicon substrates

Abstract: We have observed the origin of defects in SiO2 thermally grown on Czochralski silicon substrates. Samples were prepared by copper decoration to locate oxide defects, focused ion beam etching to mark them, and subsequent silicon‐substrate thinning for transmission electron microscope observation. Polyhedron structures with sizes ranging from 150 to 300 nm are found in the underlying silicon‐substrate surface layer just under the oxide defects. Two polyhedron structures superimposed on each other are also observed. It is believed that these structures are related to the presence of oxygen precipitates. Oxide defects are thought to arise due to oxide thinning induced at the edge of the silicon‐substrate surface adjacent to the octahedron structures.

A wire probe as an ion source for an electron beam ion trap

Abstract: A thin wire probe inserted near the electron beam in an electron beam ion trap provides a source of ions for the trap. The wire can be plated with a small amount of source material permitting the use of rare or expensive materials. Here we present results on tests with probes of various materials to demonstrate the success of the technique. In one case a sample of approximately 100 ng of 233U was plated on a platinum wire tip and used to continuously fill the trap for 10 days.

YBa/sub 2/Cu/sub 3/O/sub 7/ nano-bridge junctions and dc SQUIDs made by focused ion beam milling

Abstract: YBa/sub 2/Cu/sub 3/O/sub 7/ nano-bridges with widths ranging from 200 to 800 nm were made using Focused Ion Beam milling. The I-V characteristics of the narrowest nano-bridges show, under microwave irradiation, pronounced Shapiro steps up to the transition temperature. An inductively shunted single layer SQUID, using these nano-bridges, has been realised by a combination of Focused Ion Beam milling and selective epitaxial growth. Flux to voltage modulation up to 82 K was observed, with a maximum modulation depth of 3.7 /spl mu/V at 78 K. >

Review of focused ion beam implantation mixing for the fabrication of GaAs‐based optoelectronic devices

Abstract: The fabrication of GaAs‐based optoelectronic components by the technique of focused ion beam (FIB) implantation mixing is reviewed. The basic mechanisms and practice of the FIB‐induced mixing process of GaAs/AlGaAs multiple quantum well and superlattice structures are discussed. The use of the FIB mixing technique for the fabrication of optoelectronic devices (such as channel waveguides and distributed Bragg reflection distributed feedback lasers) by the single‐step, maskless/resistless FIB implantation process is described and their characteristics are reviewed.

Observation of strong contrast from doping variations in transmission electron microscopy of InP‐based semiconductor laser diodes

Abstract: We report strong transmission electron microscope (TEM) contrast between p‐, i‐, and n‐doped InP layers in semiconductor laser diodes. For doping concentrations ∼1018 cm−3, contrast levels on the order 30% are observed between p‐ and n‐type layers. A critical feature of these experiments is that the samples imaged in the TEM are relatively perfect, plane‐parallel sided membranes fabricated with a focused ion beam. This technique offers the ability to detect and map doping variations with nm‐scale resolution, simultaneously with the other compositional and defect information inherent to TEM.

Contrast formation in focused ion beam images of polycrystalline aluminum

Abstract: Focused ion beam secondary electron images of polycrystalline aluminum films are valuable in revealing the grain structure of the films with great clarity on a scale of <50 nm. The contrast mechanism for focused ion beam images in crystalline materials was identified ten years ago as due to crystalline channeling of the ion beam. To our knowledge there has been no report which quantifies this mechanism either with respect to the magnitude of the intensity changes or their angular dependence. The ‘‘critical angles’’ of the angular dependence are expected to depend on the source of the secondary electrons, which may be different than the channeled angular dependence of backscattering or sputtering, for example, because of the difference in the distance of approach between the ion and a target atom at which the physical mechanism of interest takes place. The experiment described here quantifies the change in intensity and angular width in the case of channeled 30 keV Ga ions in aluminum thin films. This has ...

Method of fabricating a semiconductor device using quantum dots or wires

Abstract: An undoped GaAs layer is epitaxially grown on a substrate in a crystal growth device. An undoped Alx Ga1-x As layer is then epitaxially grown to form an undoped hetero-junction structure. After this, a sample is transferred to a focused ion beam (FIB) apparatus. A dopant ion beam is focused and implanted into the Alx Ga1-x As layer in a dot-like or wire-like pattern so that it does not extend to the undoped GaAs layer or channel layer, and a zero- or one-dimensional carrier gas 8 is generated in the channel layer. The invention allows maskless ion implantation, and makes the fabrication process much easier because quantum wires and dots are drawn, patterned or formed directly by ion implantation. In addition, no etching process is required, so quantum wires and quantum dots can be fabricated precisely. Furthermore, since there is no influence of the impurity scattering and damage by ion implantation in the channel where electrons and holes are transported, high mobility is obtained and a high-speed device can be fabricated. The invention overcomes the problem of crystal damage in prior processes that required chemical etching and ion implantation.

Insulator deposition using focused ion beam

Abstract: Methods are provided for depositing insulator material at a pre-defined area of an integrated circuit (IC) by: placing an IC in a vacuum chamber; applying to a localized surface region of the integrated circuit at which insulator material is to be deposited a first gas containing molecules of a dissociable compound comprising atoms of silicon and oxygen and a second gas containing molecules of a compound which reacts with metal ions; generating a focused ion beam having metal ions of sufficient energy to dissociate molecules of the first gas; and directing the focused ion beam at the localized surface region to dissociate at least some of the molecules of the first gas and to thereby deposit on at least a portion of the localized surface region a material containing atoms of silicon and oxygen. The dissociable compound comprises atoms of carbon and hydrogen, such as di-t-butoxydiacetoxy-silane. The compound which reacts with metal ions may be carbon tetrabromide or ammonium carbonate.

Effect of ion beam energy on the synthesis of oriented aluminium nitride thin films

Abstract: Polycrystalline aluminium nitride (A1N) thin films were synthesized by evaporation of aluminium and simultaneous irradiation with nitrogen ions, ion-beam assisted deposition, and the effect of the ion beam energy on the film microstructure was studied. The substrate was single-crystal Si(100), and the substrate temperature was varied from room temperature to 573 K. The kinetic energy of the nitrogen ion beam was varied from 0.05 keV to 0.5 keV. The structure of the A1N thin films was examined by X-ray diffraction (XRD). From the XRD patterns, it is found that (1) the (00•2) plane of hexagonal A1N grows preferentially with an ion beam energy of 0.05 keV (the c -axis oriented structure) independently of the substrate temperature, (2) the intensity of the lines (10•0) and (10•1) becomes stronger with increasing ion beam energy, and (3) the full width at half maximum of the (00•2) diffraction line tends to narrow with decreasing ion beam energy and increasing substrate temperature. The present results show that the ion beam energy plays an important role in the degree of preferred orientation of A1N films and c -axis oriented films can be synthesized at room temperature by controlling the ion beam energy.