High Focused Ion Beam Research Articles

Fabrication of glass microlenses using focused Xe beam.

Focused ion beam (FIB) systems based on high brightness plasma ion sources are becoming largely diffuse in material and semiconductor research, thanks to the higher current densities and milling rates provided by noble gas ions (e.g., Xe) compared with traditional liquid metal Ga FIBs. In this paper, we demonstrate the feasibility of a rapid, direct milling of microlenses in glass substrates using high current Xe plasma FIB. We present quantitative analyses of roughness and profile of microlenses with diameters up to 230-µm and focal distances between 7 mm and 1.4 mm. We characterized the performance of the lenses by mapping the transmitted intensity through the lenses, by forming an image of a resolution object by scanning the focused spot and collecting the transmitted intensity, and in full-field imaging experiments. The results indicate the applicability of plasma focused ion beam systems for direct writing in glass of high-quality micro-optical elements with diffraction-limited focusing.

Mechanisms of material removal and mass transport in focused ion beam nanopore formation

Despite the widespread use of focused ion beam (FIB) processing as a material removal method for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing, the basic material removal mechanisms of FIB processing are not well understood. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms of material removal and rearrangement and describe the role of explosive boiling in forming nanopores. FIB nanopore fabrication is typically understood to occur via sputter erosion. This can be shown to be the case in low flux systems, where individual ion impacts are sufficiently separated in time that they may be considered as independent events. But our detailed MD simulations show that in high flux FIB processing, above a threshold level at which thermal effects become significant, the primary mechanism of material removal changes to a significantly accelerated, thermally dominated process. Under these conditions, the target is heated by the ion beam faster than heat is conducted away by the material, leading quickly to melting, and then continued heating to nearly the material critical temperature. This leads to explosive boiling of the target material with spontaneous bubble formation and coalescence. Mass is rapidly rearranged at the atomistic scale, and material removal occurs orders of magnitude faster than would occur by simple sputtering. While the phenomenology is demonstrated computationally in silicon, it can be expected to occur at lower beam fluxes in other cases where thermal conduction is suppressed due to material properties, geometry, or ambient thermal conditions.

Challenges and Solutions in Preparation for High Resolution Failure Analysis of Power Electronics

The high-resolution failure analysis of power electronic devices is very challenging, as relatively large features have to be accessed and analyzed with nanometer resolution. Recently new tools have been introduced for fast and efficient sample preparation of stacked devices and complex packages. One of them is the focused ion beam (FIB) technique using a high energy Xenon Plasma-FIB. This paper outlines preparation issues needed to find the physics of failure of large and complex devices as used in power electronics. Different methods like high throughput Plasma FIB preparation to combined Laser-FIB preparation are compared. Additionally an innovative mechanical preparation technique developed for interface defect preparation of power electronic materials will be introduced. Within the paper selected case studies regarding reliability investigations and failure analysis are presented for example on silver sinter layers and bond wire contacts done by high resolution Transmission Electron Microscopy (TEM). In addition, an assessment of the analysis throughput increase, of new extended application ranges and current limitations will be given.

Fabrication of nanopore on pyramid

There have been tremendous interests about the fabrication of metallic nanopore due to the ultrafast genome sequencing biosensor capability. In this report, the fabrication of the nanopore on the Au coated SiO2 pyramid has been examined using various high energy electron beam irradiation and focused ion beam (FIB) milling techniques. The microfabricated Au nano-apertures on pyramid were irradiated with various high energy electron beam and FIB techniques. The formation of the nanopore dependent on the probe current was also examined using electron probe micro-analysis (EPMA). The nanopore on the Au coated SiO2 pyramid is found to be an AuSi mixture. The Au nanopore on the crater type hole was also fabricated using FIB Ga ion beam scanning. The shrinking rate was found to be the fastest compared with those fabricated with the other electron beam techniques.

Evaluating focused ion beam induced damage in soft materials

Focused ion beam (FIB) microscopy uses Ga+ ions to remove material from a sample for a variety of imaging and preparation techniques. While considerable work has examined the effects of FIB exposure on a number of materials, optimized FIB conditions for use with softer polymeric materials are yet to be determined. In this report we use phase contrast AFM to measure local changes in the elastic modulus of polycarbonate surfaces parallel to a sectioning FIB at varying beam energies. We show that polycarbonate surfaces exposed to lower FIB energies appear stiffer than the bulk material whereas surfaces exposed to the higher beam energies of up to 25keV are more representative of the bulk material. Energy dispersive spectroscopy (EDS) indicates that the polymer surfaces become stiffer because of Ga+ implantation from the FIB. Our experimental observations are supported by computer simulations showing an increase in the residual Ga+ concentration near-surface at lower FIB energies. A high energy FIB is therefore shown to be less invasive, producing a surface more representative of the bulk material, than using low energy FIB when sectioning polymers.

Effects of focused ion beam milling on electron backscatter diffraction patterns in strontium titanate and stabilized zirconia

This study investigates the effect of focused ion beam (FIB) current and accelerating voltage on electron backscatter diffraction pattern quality of yttria-stabilized zirconia (YSZ) and Nb-doped strontium titanate (STN) to optimize data quality and acquisition time for 3D-EBSD experiments by FIB serial sectioning. Band contrast and band slope were used to describe the pattern quality. The FIB probe currents investigated ranged from 100 to 5000 pA and the accelerating voltage was either 30 or 5 kV. The results show that 30 kV FIB milling induced a significant reduction of the pattern quality of STN samples compared to a mechanically polished surface but yielded a high pattern quality on YSZ. The difference between STN and YSZ pattern quality is thought to be caused by difference in the degree of ion damage as their backscatter coefficients and ion penetration depths are virtually identical. Reducing the FIB probe current from 5000 to 100 pA improved the pattern quality by 20% for STN but only showed a marginal improvement for YSZ. On STN, a conductive coating can help to improve the pattern quality and 5 kV polishing can lead to a 100% improvement of the pattern quality relatively to 30 kV FIB milling. For 3D-EBSD experiments of a material such as STN, it is recommended to combine a high kV FIB milling and low kV polishing for each slice in order to optimize the data quality and acquisition time.

Ion Beam Irradiation Effects on Resist Materials

6 MeV/u ion beams such as Si14+, Ar18+, Kr36+ and Xe54+ and 30 kV Ga+ focused ion beam (FIB) were irradiated to a chemically amplified deep-UV resist TDUR-P722 (Tokyo Ohka Kogyo) and electron beam (EB) resists ZEP520A and ZEP7000 (ZEON). Clear patterns were obtained on all resists for high energy ion beams, and it was confirmed that resist sensitivities were correlated with the energy deposition. In contrast, high flux FIB irradiation induced crosslinking reactions of resist polymers, and positive-negative inversion took place.

Production of a helium beam in a focused ion beam machine using an electron beam ion trap

Gallium liquid-metal ion sources that have been introduced in the late 1970s have allowed the development of a new class of micro- and nanofabrication tools collectively denominated as focused ion beam (FIB) machines. To investigate the potential of a helium beam in such a FIB instrument the authors have tested a room-temperature electron beam ion trap coupled with a high resolution FIB machine. In this letter they present their first results in target imaging using a helium beam with a resolution that allows to account for a beam diameter in the submicrometer range.

FIB technology applied to the improvement of the crystal quality of GaN and to the fabrication of organised arrays of quantum dots

In this paper we demonstrate the possibility of achieving selective epitaxy and epitaxial lateral overgrowth (ELO) using nanometric openings patterned with a focused ion beam (FIB). The test structure we used in this work consists of an AlN buffer layer on 6H–SiC with very high crystal quality close to pseudomorphism. This substrate is first covered with a thin (∼2 nm) silicon nitride mask deposited by CVD. Then a high resolution FIB was used to create regular openings with a range of sizes (lowest 100 nm) and organisation. Finally, GaN was grown on the structure by metal-organic vapour phase epitaxy (MOVPE). The relatively low ion dose (2.7 × 1016 ions/cm2) required to remove the surface layer allows reasonable patterning speeds (0.45 ms/pt) and minimises FIB-induced defect extension in the vicinity of the patterned GaN structures.

FIB technology applied to the improvement of the crystal quality of GaN and to the fabrication of organised arrays of quantum dots

In this paper we demonstrate the possibility of achieving selective epitaxy and epitaxial lateral overgrowth (ELO) using nanometric openings patterned with a focused ion beam (FIB). The test structure we used in this work consists of an AlN buffer layer on 6H–SiC with very high crystal quality close to pseudomorphism. This substrate is first covered with a thin (∼2 nm) silicon nitride mask deposited by CVD. Then a high resolution FIB was used to create regular openings with a range of sizes (lowest 100 nm) and organisation. Finally, GaN was grown on the structure by metal-organic vapour phase epitaxy (MOVPE). The relatively low ion dose (2.7 × 10 16 ions/cm 2) required to remove the surface layer allows reasonable patterning speeds (0.45 ms/pt) and minimises FIB-induced defect extension in the vicinity of the patterned GaN structures.

Plane-view observation technique of silicon nanowires by transmission electron microscopy

We have developed a novel technique of the plane-view transmission electron microscopy (TEM) observation of silicon (Si) nanowires by covering them firmly with a holding layer of Si3N4. The use of the Si3N4 holding layer is shown to be effective to fix the fine structure of the sample without deformation during a focused ion beam (FIB) thinning process, to protect the sample from a high energy FIB, and to give high contrast in the TEM image of the crystalline fine structure. The Si3N4 holding layer is quite suitable, therefore, for plane-view TEM observation of the fine structure such as a Si nanowire. By means of the proposed observation technique, we have successfully observed clear features in the direction of length of narrow (16 nm) Si nanowires fabricated by using SiO2 sidewall masks and the extremely fine (3–5 nm) Si nanowires obtained by the successive self-limiting oxidation. Moreover, the plane-view TEM lattice image of the ultrafine Si nanowire was also observed. The plane-view TEM observation technique described here is useful to analyze various fine nanostructures and contributes to develop nanofabrication technology.

Tandem accel lens advantageous in producing a small spot focused ion beam

This article presents a novel electrostatic lens which is particularly advantageous in producing a smaller spot focused ion beam (FIB). The lens has a tandem structure made up of conventional einzel lenses operated in the acceleration (accel) mode. The structure allows the lens to work under significantly lower excitation voltages compared with conventional accel lenses, making it possible to converge high energy FIB at short focal lengths to minimize aberrations. The minimum spot size obtainable for a 30 keV FIB with 1 pA current has been calculated for various objective lens applications under a restriction where the excitation voltage should be below the beam voltage (30 kV). Spot sizes are 7.3, 6.6, and 4.8 nm for the conventional accel, decel, and tandem accel lenses discussed in this article, respectively.

FIB repair of defects in rim and attenuated phase shift masks

The feasibility of using focused ion beam (FIB) to repair defects in rim and attenuated phase shift masks (PSM) was investigated. Contact holes of rim and attenuated PSMs with programmed opaque edge defects were fabricated and printed by g-line and i-line steppers after FIB repair. The post-repair ghost defects, associated with high FIB sputtering yield from the free edge of an opaque defect, were analysed by computer simulation and experimental lithography.

High Conductivity FIB Deposited Metal

AbstractThe ion beam induced metal deposition processes now employed by commercial focused ion beam (FIB) tools all demonstrate less than optimal characteristics for use in circuit repair, a major application of these tools. In particular, the processes have low efficiencies, the metals produced have poor conductivity, and some form of clean up is generally required to remove excess material surrounding the repair site. The gold deposition process developed for x-ray mask repair, in contrast, exhibits efficiencies 10-50 times higher with significantly less material deposited in unwanted areas. Unfortunately, the conductivity of the gold is even poorer than that of materials now used for FIB circuit repair.In this paper, an annealing step which improves the conductivity of FIB deposited Au is described. Results are presented demonstrating resistivities of 5-15 μΩ-cm while maintaining the high efficiency of the gold deposition process. The suitability of the process for use in FIB circuit repair is discussed.

High current FIB system for micromechanics application

A high current Focused Ion Beam (FIB) system, designed to achieve current densities above 10 A/cm 2 is presented. The system parameters and properties are discussed and first applications in the field of micromechanics are shown.