Focused Ion Beam Thinning Research Articles

Weld-free mounting of lamellae for electrical biasing operando TEM

Recent advances in microelectromechanical systems (MEMS)-based substrates and sample holders for in situ transmission electron microscopy (TEM) are currently enabling exciting new opportunities for the nanoscale investigation of materials and devices. The ability to perform electrical testing while simultaneously capturing the wide spectrum of signals detectable in a TEM, including structural, chemical, and even electronic contrast, represents a significant milestone in the realm of nanoelectronics. In situ studies hold particular promise for the development of Metal-Insulator-Metal (MIM) devices for use in next-generation computing. However, achieving successful device operation in the TEM typically necessitates meticulous sample preparation involving focused ion beam (FIB) systems. Conducting contamination introduced during the FIB thinning process and subsequent attachment of the sample onto a MEMS-based chip remains a formidable challenge. This article delineates an improved FIB-based sample preparation methodology that results in good electrical connectivity and operational functionality across various MIM devices. To exemplify the efficacy of the sample preparation technique, we demonstrate preparation of a clean cross section extracted from a Au/Pt/BaSrTiO3/SrMoO3 tunable capacitor (varactor). The FIB-prepared TEM lamella mounted on a MEMS-based chip showed current levels in the tens of picoamperes range at 0.1 V. Furthermore, the electric response and current density of the TEM lamella device closely align with macro-scale devices. These samples exhibit comparable current densities to their macro-sized counterparts thus validating the sample preparation process and confirming device connectivity. The simultaneous operation and TEM characterization of electronic devices enabled by this process enables direct correlation between device structure and function, which could prove pivotal in the development of new MIM systems.

Coupled Si–Al Biogeochemistry: Occurrence of Aluminum in Diatom‐Derived Biogenic Silica

AbstractDiatoms play an important role in the biogeochemical cycling of aluminum (Al) in oceans. This occurs via the uptake of biological Al (Albio), which is incorporated into the structure of diatom‐derived biogenic silica (DBSi) and the formation of adsorbed Al (Alads) on the DBSi surface of post‐mortem diatoms. Al occurrence influences DBSi dissolution and thus diatom‐driven carbon sequestration. However, the mechanism of Al occurrence in DBSi remains unclear. In this study, Albio and Alads of DBSi from various diatom fossils in marine diatomaceous sediments were identified and quantified by combined focused ion beam thinning, elemental analysis, and the Al K‐edge X‐ray absorption near edge structure. Results showed the coexistence of Albio and Alads in all diatomaceous sediments and Al‐bearing DBSi thus constitutes a biological Al pool. Albio and Alads were mainly fourfold‐ and sixfold‐coordinated, respectively and Alads was much more abundant than Albio. Moreover, even at low concentrations (with an Al/Si atomic ratio of 0.0031), Albio can inhibit DBSi dissolution, effectively decreasing the extent of DBSi dissolution by ∼14%. Albio also significantly increased the mechanical strength of DBSi. The average Young's modulus (a measure of the stiffness of a material) of cribrum layers in Al‐incorporated DBSi was ∼1.4 times higher than that of Al‐free DBSi. Our results further demonstrate that diatoms play a dominant role in the biogeochemical cycling of Al in oceans, and the Al of DBSi participates in diatom‐driven Si and C coupled cycles in oceans, influencing the effectiveness of diatom‐driven carbon export by regulating the dissolution and mechanical strength of DBSi.

Self-marked preparation of site-specific transmission electron microscope lamellae of nanodevices using focusing ion beam technique.

The precise extraction of a thin slice (lamellae) from nano electronic devices using a focused ion beam (FIB) is crucial for transmission electron microscopy analysis, but it remains a challenge for 100nm and beyond scale device components. In this study, we introduce a new method that utilises the device's own features as markers during FIB thinning process by continuously monitoring the intermediate structures with secondary electron scanning electron microscopy (SE-SEM) imaging. This allows for the targeted extraction of the desired device component with high precision. We successfully demonstrate the effectiveness of this approach by extracting lamellae from 100nm length channel in arrayed carbon nanotube film field-effect transistors using FIB lift-out.

Efficient removal of Cd2+ by diatom frustules self-modified in situ with intercellular organic components

The organic modification of three-dimensional porous diatom frustules (biosilica) and their fossils (diatomite) is promising in heavy metal adsorption. However, the preparation of such materials involves complex processes, high costs, and environmental hazards. In this study, organic-biosilica composites based on in situ self-modification of diatoms were prepared by freeze-drying pretreatment. Freeze-drying resulted in the release of the intercellular organic components of diatoms, followed by loading on the surface of their diatom frustules. The bio-adsorbent exhibits outstanding Cd2+ adsorption capacity (up to 220.3 mg/g). The adsorption isotherms fitted the Langmuir model and the maximum adsorption capacity was 4 times greater than that of diatom biosilica (54.1 mg/g). The adsorption kinetics of Cd2+ was adequately described by a pseudo-second-order model and reached equilibrium within 30 min. By combining focused ion beam thinning with transmission electron microscopy–energy dispersive X-ray spectroscopy, the internal structure of the composite and the Cd2+ distribution were investigated. The results showed that the organic matter of the composite adsorbed approximately 10 times more Cd2+ than inorganic biosilica. The adsorption mechanism was dominated by complexation between the abundant organic functional groups (amide, carboxyl, and amino groups) on the surfaces of composite and Cd2+. The bio-adsorbent was demonstrated to have wide applicability in the presence of competitive cations (Na+, K+, Ca2+, and Mg2+) and under a wide range of pH (3–10) conditions. Thus, the self-modification of diatoms offers a promising organic–inorganic composite for heavy metal remediation.

Fabrication of Vertical Array CNTs/Polyaniline Composite Membranes by Microwave-Assisted In Situ Polymerization.

A vertical array carbon nanotubes (VACNTs)/polyaniline (PANi) composite membrane was prepared by microwave-assisted in situ polymerization. With microwave assistance, the morphology of PANi revealed a smaller diameter and denser connection. Meanwhile, thermogravimetric analysis showed improved thermal stability of microwave-assisted PANi for higher molecular weight. Focused ion beam thinning method was used to cut the VACNTs/PANi membrane into dozen-nanometer thin strips along the cross-sectional direction, and transmission electron microscopy observation showed seamless deposition of PANi between VACNT gaps, without damaging the vertical status of CNTs. Meanwhile, stronger conjugate interaction between the quinoid ring of PANi and VACNTs of the composite membrane were prompted by microwave-assisted in situ polymerization. By using nanoindentation technology, the VACNTs/PANi composite membrane showed exponential increasing of modulus and hardness. Meanwhile, the elasticity was also improved, which was proved by the calculated plastic index. The results can provide helpful guidance for seamlessly infiltrating matrix into CNT array and also demonstrate the importance of structural hierarchy for getting proper behavior of nanostructures.

Purity and resistivity improvements for electron-beam-induced deposition of Pt

Electron-beam-induced deposition (EBID) of platinum is used by many researchers. Its main application is the formation of a protective layer and the “welding material” for making a TEM lamella with a focused ion beam thinning process. For this application, the actual composition of the deposition is less relevant, and in practice, both the mechanical strength and the conductivity are sufficient. Another important application is the creation of an electrical connection to nanoscale structures such as nano-wires and graphene. To serve as an electrical contact, the resistivity of the Pt deposited structure has to be sufficiently low. Using the commonly used precursor MeCpPtMe3 for deposition, the resistivity as created by the basic process is 10+5–10+6 higher than the value for bulk Pt, which is 10.6 µΩ cm. The reason for this is the high abundance of carbon in the deposition. To improve the deposition process, much attention has been given by the research community to parameter optimization, to ex situ or in situ removal of carbon by anneal steps, to prevention of carbon deposition by use of a carbon-free precursor, to electron beam irradiation under a high flux of oxygen and to the combination with other techniques such as atomic layer deposition (ALD). In the latter technique, the EBID structures are used as a 1-nm-thick seed layer only, while the ALD is used to selectively add pure Pt. These techniques have resulted in a low resistivity, today approaching the 10–150 µΩ cm, while the size and shape of the structure are preserved. Therefore, now, the technique is ready for application in the field of contacting nano-wires.

Nanostructural defects evidenced in failing silicon-based NMOS capacitors by advanced failure analysis techniques

STMicroelectronics, Avenue C´elestin Coq, 13106 Rousset, FranceReceived: 25 August 2013 / Received in final form: 11 February 2014 / Accepted: 6 March 2014Published online: 21 April 2014 – ⃝c EDP Sciences 2014Abstract. An experimental methodology compliant with industrial constraints was deployed to uncover theorigin of soft breakdown events in large planar silicon-based NMOS capacitors. Complementary advancedfailure analysis techniques were advantageously employed to localize, isolate and observe structural defectsat nanoscale. After an accurate localization of the failing area by optical beam-induced resistance change(OBIRCH), focused ion beam (FIB) technique enabled preparing thin specimens adequate for transmissionelectron microscopy (TEM). Characterization of the gate oxide microstructure was performed by high-resolution TEM imaging and energy-filtered spectroscopy. A dedicated experimental protocol relying oniterative FIB thinning and TEM observation enabled improving the quality of electron imaging of defectsat atom scale. In that way, the gate oxide integrity was evaluated and an electrical stress-induced siliconepitaxy was detected concomitantly to soft breakdown events appearing during constant voltage stress.The growth of silicon hillocks enables consuming a part of the breakdown energy and may prevent the softbreakdown event to evolve towards a hard breakdown that is catastrophic for device functionality.

Mineralogy and defect microstructure of an olivine-dominated Itokawa dust particle: evidence for shock metamorphism, collisional fragmentation, and LL chondrite origin

We report here detailed analytical scanning and transmission electron microscopic investigations on an olivine-dominated dust particle (RB-QD04-0042) from the surface of asteroid 25143 Itokawa. The dust particle was returned to Earth by the Hayabusa spacecraft and was made available in the context of the first announcement of opportunity for Hayabusa sample investigation. Multiple thin slices were prepared from the precious particle by means of focused ion beam thinning, providing a unique three-dimensional access to its interior. The 40 × 50 μm sized olivine particle contains a spherical diopside inclusion and an intimate intergrowth of troilite and tetrataenite. The compositions of olivine (Fo69Fa31) and diopside (En48Wo42Fs10), as well as the high Ni content of the sulfide-metal alloy, indicate a LL ordinary chondrite origin in accord with previous classifications. Although no impact crater exists at the surface of RB-QD04-0042, transmission electron microscopy revealed the presence of various shock defects in constituent minerals. These defects are planar fractures and [001] screw dislocations in olivine, multiple {101} deformation twins in tetrataenite and basal (0001) stacking faults in troilite. These diagnostic shock indicators occur only in a small zone on one concave side of the dust particle characterized by a high fracture density. These observations can be explained by a collisional event that spalled off material from the particle's surface. Alternatively, the dust particle itself could be a spallation fragment of an impact into a larger regolith target. This suggests that Itokawa dust particles lacking visible microcraters on their surfaces might have still experienced shock metamorphism and were involved in collisional fragmentation that resulted in the formation of regolith.

Atomic resolution top-down nanofabrication with low-current focused-ion-beam thinning

► Developed a technique of size reduction to sub-ten nanometers by FIB milling. ► FIB milling is a top-down and site-specific approach with atomic resolution. ► No remarkable morphology and microstructure changes of W composite nanowires were observed after thinning. ► FIB thinning is an effective method towards size and quantum effects observation. Techniques for scalable fabrication of one-dimensional or quasi-one-dimensional nanowires are of great importance to observe quantum size effects and build quantum information devices. In this work, we developed a technique for size reduction of both lateral and freestanding tungsten composite nanostructures using focused-ion-beam (FIB) thinning. Different exposure times and ion-beam currents were used to control the final size and the thinning rate and accuracy of a group of nanowires, an individual nanowire and a portion of a nanowire by low-current site-specific milling. A transmission electron microscope image of a thinned superconducting tungsten composite nanowire with width reduced from 80 nm to 50 nm shows uniform shrinking along the length of the wire and high resolution image shows no obvious changes of the morphology after thinning. The variation of the superconducting critical current density upon thinning is insignificant; it is 1.7 × 10 5 and 1.4 × 10 5 A/cm 2 at 4.26 K for the as-deposited and wire with width reduced to 50 nm, respectively. These results suggest that FIB-milling is a potential approach for controllable size reduction enabling the observation of size- and quantum effects.

Optimization of the preparation of GaN-based specimens with low-energy ion milling for (S)TEM

We report on optimization of electron transparent GaN based specimens for transmission electron microscopy (TEM) and scanning TEM (STEM) studies by combining focused ion beam thinning and low-energy (≤500eV) Ar-ion milling. Energy dependent ion milling effects on GaN based structures are investigated and the quality of ion milled samples is compared with that of specimens prepared by wet chemical etching. Defects formed during ion milling lead to amorphization of the specimen. The experimental results are compared with Monte-Carlo simulations using the SRIM (stopping and range of ions in matter) software. Specimen thickness was deduced from high-angle annular dark field STEM images by normalization of measured intensities with respect to the intensity of the scanning electron probe and comparison with multislice simulations in the frozen lattice approach. The results show that the thickness of the amorphous surface layer can be successfully reduced below 1nm by low energy ion milling, leading to a homogeneous image contrast in TEM and STEM, so that good conditions for quantitative analysis can be achieved. For an ion energy of 400eV the thickness measurements resulted in an etching rate of about 6–8nm/min.

Atomic-scale effects behind structural instabilities in Si lamellae during ion beam thinning

The rise of nanotechnology has created an ever-increasing need to probe structures on the atomic scale, to which transmission electron microscopy has largely been the answer. Currently, the only way to efficiently thin arbitrary bulk samples into thin lamellae in preparation for this technique is to use a focused ion beam (FIB). Unfortunately, the established FIB thinning method is limited to producing samples of thickness above ∼20 nm. Using atomistic simulations alongside experiments, we show that this is due to effects from finite ion beam sharpness at low milling energies combined with atomic-scale effects at high energies which lead to shrinkage of the lamella. Specifically, we show that attaining thickness below 26 nm using a milling energy of 30 keV is fundamentally prevented by atomistic effects at the top edge of the lamella. Our results also explain the success of a recently proposed alternative FIB thinning method, which is free of the limitations of the conventional approach due to the absence of these physical processes.

Micromachining tools and correlative approaches for cellular cryo-electron tomography

A principal limitation of cryo-transmission electron microscopy performed on cells or tissues is the accessible specimen thickness. This is exacerbated in tomography applications, where the aspect ratio (and thus the apparent specimen thickness) changes considerably during specimen tilting. Cryo-ultramicrotomy is the most obvious way of dealing with this problem; however, frozen-hydrated sections suffer from potentially inconsistent compression that cannot be corrected with certainty, and furthermore, yields of sections that satisfy all of the conditions necessary for tomographic imaging are poor. An alternative approach that avoids mechanical deformations is the use of focused ion beam (FIB) instrumentation, where thinning of the frozen-hydrated specimen occurs through the process of sputtering with heavy ions, typically gallium. Here, we use correlative cryo-fluorescence microscopy to navigate large cellular volumes and to localize specific cellular targets. We show that the selected targets in frozen-hydrated specimens can be accessed directly by focused ion beam milling. We also introduce a novel cryo-planing procedure as a method that could facilitate thinning of large areas of vitreous ice prior to cryo-fluorescence, FIB thinning, and cryo-electron tomography.

FCC Surface Precipitation in Cu-Zn-Al after Low Angle GA<SUP>+</SUP> Ion Irradiation

The precipitation of a disordered FCC surface structure after low angle Ga + ion irradiation during focused ion beam thinning of a B2 Cu-Zn-Al alloy with e/a = 1.48 is reported. Conventional as well as high-resolution transmission electron microscopy techniques reveal FCC layers on both sides of the thinned sample. The occurrence of this structure is attributed to disordering and dezincification of the alloy resulting from the sputtering process during the irradiation. Changes in crystallographic sample orientation with respect to the incoming ion beam do not have a significant effect on the appearance of the FCC surface structure.

Stress-induced curvature of focused ion beam fabricated microcantilevers

Microcantilevers with very low spring constants, as required to measure the short-range Casimir force, can be fabricated by focused ion beam thinning of conventional atomic force microscope cantilevers, but the resulting beams have a stress-induced curvature. This can be explained by consideration of the implanted gallium ions and associated damage effects in the etched surface. The problem can be overcome by using a complementary etch method in which top and bottom surfaces of the microcantilever are etched by the same amount.

Evaluation of commercial ultra-thin Si-on-insulator wafers using laser confocal inspection system

Commercially available ultra-thin (50 nm) Si-on-insulator (SOI) wafers were evaluated using a laser confocal inspection system. The defect distribution and defects were observed for both bonded SOI and separation-by-implanted-oxygen (SIMOX) wafers. Some of defects were marked using the system's marking function and evaluated using transmission electron microscopy after the samples were prepared using focused ion beam thinning. The most serious defects observed in both types of wafers were voids. Small defects such as dislocations were also detected. The inspection system is non-destructive and therefore promising for use in pre- and in-line monitoring systems.

Study of the near-surface of hot- and cold-rolled AlMg0.5 aluminium alloy

Rolling is known to alter the surface properties of aluminium alloys and to introduce disturbed near-surface microcrystalline layers. The near-surfaces of mostly higher alloyed materials were investigated by various techniques, often combined with a study of their electrochemical behaviour. Cross-sectional transmission electron microscopy (TEM), after ion milling or ultramicrotomy, indicated the presence of disturbed layers characterized by a refined grain structure, rolled-in oxide particles and a fine distribution of intermetallics. Those rolled-in oxide particles reduce the total reflectance of rolled Al alloys. Furthermore, various depth profiling techniques, such as AES, XPS, SIMS and qualitative glow discharge optical emission spectroscopy (GD-OES) have been used to study the in-depth behaviour of specific elements of rolled Al alloys. Here, the surface and near-surface of AlMg0.5 (a commercially pure rolled Al alloy with addition of 0.5 wt.% Mg) after hot and cold rolling, and with and without additional annealing is studied with complementary analytical techniques. Focused ion beam thinning is introduced as a new method for preparing cross-sectional TEM specimens of Al surfaces. Analytical cross-sectional TEM is used to investigate the microstructure and composition. Measuring the total reflectance of progressively etched samples is used as an optical depth profiling method to derive the thickness of disturbed near-surface layers. Quantitative r.f. GD-OES depth profiling is introduced to study the in-depth behaviour of alloying elements, as well as the incorporation of impurity elements within the disturbed layer. The GD-OES depth profiles, total reflectance and cross-sectional TEM analyses are correlated with SEM/energy-dispersive x-ray observations in GD-OES craters. Copyright © 2005 John Wiley & Sons, Ltd.

Structure of unepitaxial crystallites in a homoepitaxial diamond film

Unepitaxial crystallites (UC, non-epitaxial crystallites) were spontaneously grown in a homoepitaxial diamond film deposited by chemical vapor deposition (CVD) method at a high growth rate. Degradation of electrical and optical properties of the deposited films was attributed to the growth of the UC. In order to investigate the structure of the UC, electron microscopic analysis was performed on the UC. Focused ion beam thinning (FIB), a field emission scanning electron microscopy (FESEM) and a high-resolution transition electron microscopy (HRTEM) were employed for the investigation. Dislocations were observed in the growth region in the 〈001〉 direction. Nanometer-sized grains were observed in the growth region in the 〈111〉 direction. Most of the grains rotated by 70.53° around the 〈110〉 axis, corresponding to ∑3 coincidence site lattice (CSL) relation. The (111̄) ∑3 grain boundary was dominant in number and was extremely long in length. Incoherent ∑3 boundaries connected to the {111} ∑3 boundary were much shorter.

Automated TEM Sample Preparation

Abstract The rising demand in the semiconductor industry for higher spatial resolution in the analysis of device defects has focused attention on the use of transmission electron microscopy (TEM). However, conventional TEM sample preparation can be difficult and time-consuming, and, depending on the operator, may result in a low yield of quality specimens. One solution to this problem is the use of focused ion beam (FIB) milling for the final stage of TEM sample preparation. However, specimens have to be mechanically thinned prior to FIB and the need to characterize specific devices requires a pre-FIB preparation method that can target specific features on the wafer. We will discuss an innovative and automated solution that isolates specific devices and prepares TEM specimens for subsequent FIB thinning. The complete pre-FIB preparation takes less than 30 minutes and yields a sample in which the targeted feature is positioned a specific distance from the sample edge, thereby minimizing final FIB milling time. The output specimen is automatically packaged for FIB milling and TEM analysis. We also present drawings of the process flow and examples showing TEM results from tungsten filled vias.

Physical and chemical analysis of advanced interconnections using energy filtering transmission electron microscopy

Our newest method for interconnection analysis using focused ion beam (FIB) specimen thinning and energy filtering transmission electron microscopy (EFTEM) is presented. It is shown that using the site-specific capability and the controlled thinning effect of the FIB in addition with the high spatial resolution of the EFTEM technique, fast chemical analysis of materials with nanometre spatial resolution can be obtained. This is the only method for the observation of very thin diffusion barriers and interfaces in the presence of drastic topography. Application examples are given concerning firstly, the in-depth analysis of tungsten aluminum technology, barrier integrity and interdiffusion of elements near interfaces and secondly, the surface contamination of copper in copper interconnection technology with high aspect ratio contacts. In this case, photoresist spin-coating is carried out prior to FIB thinning. This method is an alternative to surface analysis techniques and offers the best spatial resolution without topography limitations.

Role of the twin boundary for the occurrence of peak effect in Y-Ba-Cu-O superconducting bulks melt grown under varied oxygen pressure

A novel melt-growth technique, i.e. melt growth under varied oxygen pressure (MGVOP) in which the oxygen partial pressure is increased to solidify the initial melt, has been employed to prepare melt-textured superconducting bulks of the Y-Ba-Cu-O system. The obtained textured bulk samples consisted of two phases, i.e. superconducting and non-superconducting (Y-211). The critical current density of the samples reached as high as 40 kA (at 65 K) at a high magnetic field of T to exhibit a peak in the versus relation, i.e. a peak effect. To elucidate the causes of the peak effect and the high values of at high magnetic fields, submicron structures of the MGVOP-processed samples were examined by transmission electron microscopy (TEM), and the distributions of both Y-211 particles and twin boundaries were studied. In order to collect sufficient data for statistical analyses, specimens for `large-area TEM observations' were prepared using a focused ion beam thinning technique such that the TEM-observable area of the specimen was as wide as . Statistical analyses of the TEM images yielded the volume fraction of Y-211 phase, the average size of Y-211 grains and the inter-twin-boundary distance for each sample. It was concluded that a sample that had a higher twin-boundary density possessed a higher value at the peak in the versus characteristics, while fine Y-211 particles were likely to contribute to the value only at low magnetic fields.