Effect of beam limiting aperture and collector potential on multi-element focused ion beams

A compact microwave driven plasma based multi-element focused ion beam system has been developed. In the present work, the effect of reduced beam limiter (BL) aperture on the focused ion beam parameters, such as current and spot size, and a method of controlling beam energy independently by introducing a biased collector at focal point (FP) are investigated. It is found that the location of FP does not change due to the reduction of BL aperture. The location of FP and beam size are found to be weakly dependent on the collector potential in the range from -8 kV to -18 kV.     

Applications of focused ion beams

A finely focused ion beam system is described. Beams of Ga, In, and Au ions emitted from a liquid metal ion source are routinely focused to spot diameters of ∼0.1 to 3.0 μm at a current density of ∼0.5 A/cm² and a beam energy of 20 keV. Focused beams with energies of 1 to 30 keV have also been produced. Three applications are discussed: (1) scanning ion microscopy, (2) mask repair, and (3) ion beam lithography. Scanning ion images illustrating topographic and chemical contrast are presented. The repair of opaque and clear defects in optical masks, and opaque defects in X-ray masks is shown.Defects are imaged with the ion beam and removed by sputter erosion. Edge reconstruction of 0.5 μm features is demonstrated. Most repairs take less than 10 s/μm². The advantages and limitations of ion beams for lithography are discussed.     

Conventional and back-side focused ion beam milling for off-axis electron holography of electrostatic potentials in transistors

Off-axis electron holography is used to characterize a linear array of transistors, which was prepared for examination in cross-sectional geometry in the transmission electron microscope (TEM) using focused ion beam (FIB) milling from the substrate side of the semiconductor device. The measured electrostatic potential is compared with results obtained from TEM specimens prepared using the more conventional 'trench' FIB geometry. The use of carbon coating to remove specimen charging effects, which result in electrostatic fringing fields outside 'trench' specimens, is demonstrated. Such fringing fields are not observed after milling from the substrate side of the device. Analysis of the measured holographic phase images suggests that the electrically inactive layer on the surface of each FIB-milled specimen typically has a thickness of 100 nm.     

A subnanosecond pulsed ion source for micrometer focused ion beams

A new, compact design of an ion source delivers nanosecond pulsed ion beams with low emittance, which can be focused to micrometer size. By using a high-power, 25 fs laser pulse focused into a gas region of 10(-6) mbar, ions at very low temperatures are produced in the small laser focal volume of 5 mum diameter by 20 mum length through multiphoton ionization. These ions are created in a cold environment, not in a hot plasma, and, since the ionization process itself does not significantly heat them, have as a result essentially room temperature. The generated ion pulse, up to several thousand ions per pulse, is extracted from the source volume with ion optical elements that have been carefully designed by simulation calculations. Externally triggered, its subnanosecond duration and even smaller time jitter allow it to be superimposed with other pulsed particle or laser beams. It therefore can be combined with any type of collision experiment where the size and the time structure of the projectile beam crucially affect the achievable experimental resolution.     

Off-axis electron holography of electrostatic potentials in unbiased and reverse biased focused ion beam milled semiconductor devices

Off‐axis electron holography in the transmission electron microscope (TEM) is used to measure two‐dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p–n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed.     

Laser and focused ion beam combined machining for micro dies

We have developed a laser and focused ion beam (FIB) compound process for press mold dies of a micro lens array (MLA) and a micro needle array (MNA) in a glassy carbon (GC). The press mold die of the MLA was roughly fabricated by UV-YAG laser. After this process, we finished this surface by scanning FIB. As a result, higher accuracy and good roughness of surface profile can be realized. An optical glass is used to confirm the shape of lens. Moreover, we fabricated 6 × 6 through-holes in the GC by the spiral drilling in addition to the focus position movement of the UV laser for press mold die of the MNA. After the FIB process, we were able to make the needle die of surface and hole wall roughness less than 0.9 μm. A silicon rubber is used to confirm the shape of the holes.     

Focal-plane imaging of crossed beams in nonlinear optics experiments

An application of focal-plane imaging that can be used as a real time diagnostic of beam crossing in various optical techniques is reported. We discuss two specific versions and demonstrate the capability of maximizing system performance with an example in a combined dual-pump coherent anti-Stokes Raman scattering-interferometric Rayleigh scattering experiment (CARS-IRS). We find that this imaging diagnostic significantly reduces beam alignment time and loss of CARS-IRS signals due to inadvertent misalignments.     

A review of focused ion beam sputtering

This paper reviews the applications of focused ion beam (FIB) sputtering for micro/nano fabrication. Basic principles of FIB were briefly discussed, and then empirical and fundamental models for sputtering yield, material removal rate, and surface roughness were presented and compared. The empirical models were more useful for application compared to fundamental models. Fabrication of various micro and nano structures was discussed. Trimmed atomic force microscope (AFM) tips were tested in measurement and imaging of high aspect ratio nanopillars where higher accuracy and clarity were observed. Micromilling tool fabricated using FIB sputtering was used to machine microchannels. Slicing and dwell time control approaches on FIB sputtering were presented for the fabrication of three dimensional microcavities. The first approach is preferred for practical applications. The maximum aspect ratio of 13:1 of the microstructures was achieved. The minimum size of the nanopore was in the range of 2–10 μm. Cavities of microgear of 70 μm outside diameter were sputtered with submicrometer accuracy and 2–5 nm average surface roughness. The microcavities were then filled with polymer in a subsequent micromodling process. The replicated microcomponents were inspected with scanning electron microscope where faithful duplication of accuracy and surface texture of the cavity was observed.     

Subcutoff microwave driven plasma ion sources for multielemental focused ion beam systems

A compact microwave driven plasma ion source for focused ion beam applications has been developed. Several gas species have been experimented including argon, krypton, and hydrogen. The plasma, confined by a minimum B multicusp magnetic field, has good radial and axial uniformity. The octupole multicusp configuration shows a superior performance in terms of plasma density (~1.3 x 10(11) cm(-3)) and electron temperature (7-15 eV) at a power density of 5-10 Wcm(2). Ion current densities ranging from a few hundreds to over 1000 mA/cm(2) have been obtained with different plasma electrode apertures. The ion source will be combined with electrostatic Einzel lenses and should be capable of producing multielemental focused ion beams for nanostructuring and implantations. The initial simulation results for the focused beams have been presented.     

Nano-slit probes for near-field optical microscopy fabricated by focused ion beams

The near-field probes described in this paper are based on metallized non-contact atomic force microscope cantilevers made of silicon. For application in high-resolution near-field optical/infrared microscopy, we use aperture probes with the aperture being fabricated by focused ion beams. This technique allows us to create apertures of sub-wavelength dimensions with different geometries. In this paper we present the use of slit-shaped apertures which show a polarization-dependent transmission efficiency and a lateral resolution of < 100 nm at a wavelength of 1064 nm. As a test sample to characterize the near-field probes we investigated gold/palladium structures, deposited on an ultrathin chromium sublayer on a silicon wafer, in constant-height mode.     

Nano-slit probes for near-field optical microscopy fabricated by focused ion beams

The near-field probes described in this paper are based on metallized non-contact atomic force microscope cantilevers made of silicon. For application in high-resolution near-field optical/infrared microscopy, we use aperture probes with the aperture being fabricated by focused ion beams. This technique allows us to create apertures of sub-wavelength dimensions with different geometries. In this paper we present the use of slit-shaped apertures which show a polarization-dependent transmission efficiency and a lateral resolution of < 100 nm at a wavelength of 1064 nm. As a test sample to characterize the near-field probes we investigated gold/palladium structures, deposited on an ultrathin chromium sublayer on a silicon wafer, in constant-height mode.     

Ion optics of RHIC electron beam ion source

RHIC electron beam ion source has been commissioned to operate as a versatile ion source on RHIC injection facility supplying ion species from He to Au for Booster. Except for light gaseous elements RHIC EBIS employs ion injection from several external primary ion sources. With electrostatic optics fast switching from one ion species to another can be done on a pulse to pulse mode. The design of an ion optical structure and the results of simulations for different ion species are presented. In the choice of optical elements special attention was paid to spherical aberrations for high-current space charge dominated ion beams. The combination of a gridded lens and a magnet lens in LEBT provides flexibility of optical control for a wide range of ion species to satisfy acceptance parameters of RFQ. The results of ion transmission measurements are presented.     

Large-scale process optimization for focused ion beam 3-D nanofabrication

With the ever-decreasing size of manufactured objects, fabrication processes driven by charged particle beams, such as focused ion beam (FIB), become important for a wide spectrum of interdisciplinary applications. A designed three-dimensional (3-D) pattern to fabricate may contain millions of pixels, which will require solving an unprecedented large-scale problem for planning. This paper proposes a general framework of planning FIB milling for fabricating 3-D nanostructures, including model formulations to enable FIB for scalable and automated applications and a corresponding optimization model to support the process planning. The implementation of proposed work does not affect the fabrication quality and yet tremendously reduces the required computational time and data storage during planning. The proposed framework of process planning is further illustrated and verified by simulation and milling experiments of submicron features on Si and Si₃N₄. This research offers an accurate and economical solution to the realization from designs to actual micro/nanoscale models and builds a scientific foundation for immediate development of complex, yet more accurate and cost-effective, beam scanning techniques.     

Comparative studies of parameters calibration for focused ion beam deposition

This paper describes the interaction between operating parameters of target wafer surface. We use an organometallic (C) precursor gas in the focused ion beam deposition process. Under the beam intensity conditions (30kV), the influences of the on-target beam control parameters, such as dwell time, beam spacing, minimum frame time and scan type, were investigated by the deposition tests. The analysis was carried out with the variation of dimensions and shapes of the single pattern. The operating parameters considered in this research are implemented in the next double-patterning deposition. The test presented how their interaction appeared on the processing results. The analysis configured out the FIB induced deposition of single pattern with the variation of operating parameters. Additionally the result shows that the sequent beam job influenced the double-patterning deposition significantly. On-beam target conditions should be optimized for the target complicated shapes and high aspect-ratios     

Alloy liquid metal ion sources and their application in mass separated focused ion beams

For special purposes like writing ion implantation or ion mixing in the micrometer- or sub-micrometer range different ion species are needed. Therefore alloy liquid metal ion sources (LMISs) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au(73)Ge(27), Au(82)Si(18), Au(77)Ge(14)Si(9), Co(36)Nd(64), Er(69)Ni(31), and Er(70)Fe(22)Ni(5)Cr(3) were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMISs discussed above have been used in the Rossendorf FIB system IMSA especially for writing implantation to fabricate sub-micrometer pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi(2) micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume-loss method. Especially this technique was used for the fabrication of various kinds of micro-tools.     

Deterministic fabrication of nanostructures for plasmonic lens by focused ion beam

Plasmonic lens is a key component in the development of sub-wavelength resolution optical system for bio-imaging and nanolithography applications. In order to develop a deterministic fabrication capability for nanostructures on plasmonic lens by using focused ion beam, this paper presents a highly robust and accurate surface topography model based on level set method. Sputtered atom distribution and angular dependence of sputter yield are calculated by Monte Carlo simulation programs SRIM/TRIM and TRIDYN, respectively. Redeposition effect is included in the physical model and successfully embedded into a topography simulation program by applying the level set method. The proposed model is validated and evaluated in the focused ion beam fabrication experiments. Simulation error of less than 7% is obtained. Two types of nanostructures for plasmonic lens were fabricated using the machining parameters approved by this simulation model. Simulation errors of 7 and 2?nm were found in a nanodots array and a spiral Bragg grating, respectively. The results clearly demonstrate the effectiveness of the modelling approach developed for deterministic fabrication of nanostructures.     

Localized grounding, excavation, and dissection using in-situ probe techniques for focused ion beam and scanning electron microscopy: experiments with rock varnish

While investigating rock varnish, we explored novel uses for an in‐situ micromanipulator, including charge collection, sample manipulation, as well as digging and dissection at the micron level. Dual‐beam focused ion beam microscopes (DB‐FIB or FIBSEM) equipped with micromanipulators have proven to be valuable tools for material science, semiconductor research, and product failure analysis. Researchers in many other disciplines utilize the DB‐FIB and micromanipulator for site‐specific transmission electron microscope (TEM) foil preparation. We have demonstrated additional applications for in‐situ micromanipulators. SCANNING 34: 279–283, 2012. © 2012 Wiley Periodicals, Inc.     

Homogenous and ultra-shallow lithium niobate etching by focused ion beam

Focused ion beam (FIB) milling has been used for fast prototyping of lithium niobate (LiNbO₃, LN) devices with feature size from sub-to hundreds of micrometers. However, a promising and challenging depth range of tens-of-nanometers or below is rarely attended. Moreover, the surface roughness, related closely with device performances, is particularly non-negligible for such an ultra-shallow etching. Here, the surface roughness evolution was studied on ultra-shallow FIB etched LN structures. It was found that the inhomogeneous etching of the metallic film, coated on LN surface to avoid charge accumulation, had a detrimental effect on the LN surface roughness control. By thinning the gold thickness to 7 nm, sub-nanometer surface roughness was reported for etching depth of several nanometers. This work paves the way towards a homogenous and ultra-shallow FIB milling of LN nano-structures.     

The prospects of a subnanometer focused neon ion beam

The success of the helium ion microscope has encouraged extensions of this technology to produce beams of other ion species. A review of the various candidate ion beams and their technical prospects suggest that a neon beam might be the most readily achieved. Such a neon beam would provide a sputtering yield that exceeds helium by an order of magnitude while still offering a theoretical probe size less than 1-nm. This article outlines the motivation for a neon gas field ion source, the expected performance through simulations, and provides an update of our experimental progress.