Focused Ion Beam Sample Preparation Research Articles

Operando electrical biasing TEM experiments of Ge-rich GST thin films with FIB sample preparation

Ge-Sb-Te (GST) ternary alloy is the core material for phase-change memory (PCM). Compared with Ge2Sb2Te5 (GST-225), Ge-rich GST (GGST) has a higher crystallization temperature (about 400°C) and thereby an improved thermal stability. In this paper, we propose a methodology dedicated to studying the phase changes by operando transmission electron microscopy (TEM). The methodology combines focused ion beam (FIB) specimen preparation and injection of electrical pulses for in-situ studies. We show how the microstructure is correlated to the electrical switching dynamics in GGST nanobridges. The electrical pulse modification, the electrochemical migration, local current density, void formation and the corresponding switching mechanism are discussed.

Enabling focused ion beam sample preparation for application in reverse tip sample scanning probe microscopy

Focused ion beam (FIB) has become a powerful tool for transmission electron microscopy sample preparation in the nanoelectronics industry and has in recent years also shown its benefits for specific preparation steps in electrical scanning probe microscopy (SPM). Most recently, a novel SPM approach – so-called reverse tip sample (RTS) SPM – has been proposed in which the position of sample and tip are switched compared to standard SPM; in RTS SPM the sample is attached to the end of a cantilever beam. To achieve this configuration, the region of interest must first be extracted from a substrate and then needs to be reliably fixed to the cantilever by FIB. Therefore, we have explored and developed dedicated FIB preparation methods for RTS SPM in this work. Our established procedures ensure a strong mechanical and good electrical connection of the sample to the cantilever for both cross-section and top view sample preparation. Furthermore, we introduce an approach for mounting samples from a full wafer size workflow. This paper presents the developed FIB procedures and discusses the quality and stability of all mounted samples and their electrical evaluation in RTS SPM.

Operando two-terminal devices inside a transmission electron microscope

Advanced nanomaterials are at the core of innovation for the microelectronics industry. Designing, characterizing, and testing two-terminal devices, such as metal-insulator-metal structures, is key to improving material stack design and integration. Electrical biasing within in situ transmission electron microscopy using MEMS-based platforms is a promising technique for nano-characterization under operando conditions. However, conventional focused ion beam sample preparation can introduce parasitic current paths, limiting device performance and leading to overestimated electrical responses. Here we demonstrate connectivity of TEM lamella devices obtained from a novel electrical contacting method based solely on van der Waals forces. This method reduces parasitic leakage currents by at least five orders of magnitude relative to reported preparation approaches. Our methodology enables operation of stack devices inside a microscope with device currents as low as 10 pA. We apply this approach to observe in situ biasing-induced defect formation, providing valuable insights into the behavior of an SrTiO3-based memristor.

Ga+ Focused Ion Beam Damage in n-type Ga2O3 and Its Recovery after Annealing Treatment

In this study, the focused ion beam (FIB) Ga+ irradiation damage on β-Ga2O3 Schottky diode structure under different ion energies were tested, and the effective recovery of diode characteristics after rapid thermal annealing (RTA) post-annealing were also studied.β-Ga2O3 based Schottky diodes have attracted increasing attention because of the prospects for use in next-generation high-power electronics. Focused ion beam (FIB) machining is one of the newest processing techniques, which is mainly used in semiconductor and chip manufacture and transmission electron microscopy (TEM) sample preparation. During FIB sample preparation, the energetic Ga ions are incident onto the sample to induce physical sputtering of the material, which in turn, modifies its chemical composition, crystallinity and electrical properties. It has been found in many studies that 20-30 nm amorphous layer can form on silicon after irradiation with 30 keV Ga ions. From our previous study, the FIB ion beam induced damages could cause significant degradation on diode on-resistance and turn-on voltage. Milling at lower energy has been used to reduce the electrical damage. However low energy milling is more time consuming and less precise. Short-time, high-temperature post-annealing treatments, such as RTA has been proved could remove the crystal damage. Thus, there is a great need to determine the maximal ion beam energy and post-annealing temperature for FIB without degrading diode characteristics.In this work, energies ranging from 2 keV to 30 keV were employed to mill off a part of Ga2O3 epi-layer and Schottky diodes were fabricated on milled surface. Forward IV characteristic shows less degradations with lower ion beam energies. For the diodes exposed to 2, 5, and 10 keV Ga+ ion beams exhibited significant recovery of diode on resistance and turn-on voltage after 300°C RTA annealing. For the diodes exposed to 30 keV Ga+ ion beams recovered significantly after 400 °C annealing. In conclusion, decreasing the FIB energy shows effective alleviations on the FIB damage, and post annealing treatment effectively recovered the damage from Ga+ implantation.This is the first time the thermal annealing treatment was performed for Ga2O3 Schottky diode recovering from FIB cutting, it is an effective and simple way to mitigate the degradation, especially for higher ion beam energies. This work could broaden the FIB’s usability and release tremendous potential as a specimen preparation and imaging tool in materials science applications. Figure 1

Possible Approaches for Combined Use of Xenon and Gallium Ion Sources for Task Specific Focused Ion Beam Sample Preparation

Possible Approaches for Combined Use of Xenon and Gallium Ion Sources for Task Specific Focused Ion Beam Sample Preparation

Cryogenic Focused Ion Beam Sample Preparation for the Analysis of Hydrogen in Zr Alloy APT Experiments

Cryogenic Focused Ion Beam Sample Preparation for the Analysis of Hydrogen in Zr Alloy APT Experiments

FIB and Wedge Polishing Sample Preparation for TEM Analysis of Sol-Gel Derived Perovskite Thin Films

In ceramic thin films, choosing an appropriate sample preparation method for transmission electron microscopy (TEM) analyses is of paramount importance to avoid preparation-induced damage and retain nanoscale features that require investigation. Here we compare two methods of TEM thin film sample preparation, namely conventional wedge polishing and focused ion beam (FIB) based lift out preparation applied to ferroelectric barium titanate (BaTiO3, BT) thin films made by chemical solution deposition (CSD). The aim of the work is to determine the pros and cons of each method considering not only the quality of the TEM specimen, but also aspects such as availability, ease of use, and affordability. Besides some limitations on the selection of visualized area due to thickness constraints on the FIB-made sample, both methods offer the capability to prepare samples with very comparable quality, as indicated by achieving the same thickness, a largely agreeing microstructure, no secondary phases on the diffraction pattern, and good atomic resolution. This last observation is especially important in the current context of material science, where more nanoscale phenomena are becoming the subject of study. The wedge polishing method, however, is deemed more affordable in terms of instrumentation, as it only requires a tripod polisher, a polishing wheel, and a precision ion polishing system, whereas the lift out method requires a scanning electron microscope (SEM) equipped with an FIB system. We believe that this work serves groups working on ferroelectric thin films in preparing TEM samples in a more effective and uncomplicated manner, facilitating progress in understanding this fascinating class of materials.

Optimization of the In Situ Biasing FIB Sample Preparation for Hafnia-Based Ferroelectric Capacitor.

Hafnia-based ferroelectric (FE) thin films have received extensive attention in both academia and industry, benefitting from their outstanding scalability and excellent CMOS compatibility. Hafnia-based FE capacitors in particular have the potential to be used in dynamic random-access memory (DRAM) applications. Obtaining fine structure characterization at ultra-high spatial resolution is helpful for device performance optimization. Hence, sample preparation by the focused ion beam (FIB) system is an essential step, especially for in situ biasing experiments in a transmission electron microscope (TEM). In this work, we put forward three tips to improve the success rate of in situ biasing experiments: depositing a carbon protective layer to position the interface, welding the sample on the top of the Cu column of the TEM grid, and cutting the sample into a comb-like shape. By these means, in situ biasing of the FE capacitor was realized in TEM, and electric-field-induced tetragonal (t-) to monoclinic (m-) structure transitions in Hf0.5Zr0.5O2 FE film were observed. The improvement of FIB sample preparation technology can greatly enhance the quality of in situ biasing TEM samples, improve the success rate, and extend from capacitor sample preparation to other types.

Solar energetic particle tracks in lunar samples: A transmission electron microscope calibration and implications for lunar space weathering

AbstractTransmission electron microscope (TEM) imaging techniques combined with focused ion beam sample preparation were used to calibrate the solar energetic particle track production rate in lunar samples. Track density measurements by TEM as a function of depth were obtained from lunar rock 64455 that has a well‐constrained exposure age of 2 Myr giving a track production rate of 4.4 ± 0.4 × 104 tracks cm−2 yr−1 for a 2π exposure at 1 AU. The typical space weathering effects in mature lunar soils (both vapor‐deposited rims and solar wind‐damaged rims) accumulate in ˜106 yr based on the new calibration applied to track densities in individual grains. Solar wind‐damaged rim widths in anorthite and olivine follow a power law relationship with track density and achieve steady‐state widths in a few Myr. Vapor‐deposited rim widths show no correlation with exposure age suggesting that their formation is episodic with the full width of vapor‐deposited rims accumulating in a single or a few rare impact events. Solar wind‐damaged rim development was modeled using the stopping range of ions in matter code. Modeling shows that the solar wind‐damaged rims develop rapidly and approach steady‐state values in 105–106 yr. Anorthite and olivine record similar track densities for similar exposure ages, but their structural response to solar wind irradiation differs significantly. Solar wind‐damaged rims on olivine are not amorphous in contrast to modeling and high flux laboratory experiments and a model is proposed to account for their different response to solar wind irradiation.

Expanding the Capability of Xe Plasma Focused Ion Beam Sample Preparation for Transmission Electron Microscopy

Expanding the Capability of Xe Plasma Focused Ion Beam Sample Preparation for Transmission Electron Microscopy

Improved Focused Ion Beam Sample Preparation Techniques for Transmission Electron Microscopy and Failure Analysis of Memristor Devices

Improved Focused Ion Beam Sample Preparation Techniques for Transmission Electron Microscopy and Failure Analysis of Memristor Devices

A novel approach to index site-specific grain boundary plane

A novel approach using focused ion beam (FIB) and electron backscatter diffraction (EBSD) or transmission Kikuchi diffraction (TKD) was developed to characterize all five parameters of the individual grain boundary. With this approach, the grain orientations and the grain boundary trace angles on two perpendicular surfaces can be measured. Then the grain boundary plane normal in the sample coordinate system can be determined and transformed to plane indices in the two crystal coordinate systems. FIB-TKD is a viable alternative to FIB-EBSD when EBSD measurement can't be conducted on the sample surface which is degraded by oxidation or corrosion. This approach was verified on a coherent twin boundary in alloy 690. The accuracy of the present FIB-EBSD method is better than 3°. This approach provides a convenient and efficient solution for measuring all five parameters of a site-specific grain boundary during FIB sample preparation.

A versatile cryo-transfer system, connecting cryogenic focused ion beam sample preparation to atom probe microscopy.

Atom probe tomography (APT) is a powerful technique to obtain 3D chemical and structural information, however the 'standard' atom probe experimental workflow involves transfer of specimens at ambient conditions. The ability to transfer air- or thermally-sensitive samples between instruments while maintaining environmental control is critical to prevent chemical or morphological changes prior to analysis for a variety of interesting sample materials. In this article, we describe a versatile transfer system that enables cryogenic- or room-temperature transfer of specimens in vacuum or atmospheric conditions between sample preparation stations, a focused ion beam system (Zeiss Crossbeam 540) and a widely used commercial atom probe system (CAMECA LEAP 4000X HR). As an example for the use of this transfer system, we present atom probe data of gallium- (Ga)-free grain boundaries in an aluminum (Al) alloy specimen prepared with a Ga-based FIB.

(Invited) Understanding the Corrosion of SS316L in Molten LiCl-Li2O-Li Using 3D Transmission X-Ray Microscopy and 3D XANES

Pyrochemical reprocessing (pyroprocessing) of used nuclear fuel (UNF) is a promising pathway towards closing the nuclear fuel cycle and providing the means to generate durable wasteforms for portions of the UNF that are not able to be recycled. To incorporate commercial UNF (UO2) into the pyroprocessing scheme, the ceramic UNF must be converted to a metallic form at the head end of the process, which can be accomplished via electrolytic reduction of the UNF in LiCl-Li2O molten salt electrolyte. During the electrolytic reduction of UO2 at the cathode, metallic Li is inevitably co-reduced from the electrolyte due to the proximity of the reduction potential of the U4+ in UO2 and Li+ in the electrolyte. Metallic Li disperses into the LiCl electrolyte and can then interact with the process vessel and other apparatus in contact with the electrolyte, altering the rate and mechanism of the degradation of those materials.Our group has previously shown that the presence of metallic Li in the electrolyte creates a reducing condition where the surface oxide layer of SS316 is removed, and extensive intergranular corrosion takes place. To further the understanding of the mechanism and morphology of the intergranular corrosion, transmission X-ray microscopy (TXM) at Brookhaven National Laboratory’s National Synchrotron Light Source II (NSLSII) beamline 18-ID was used to examine ~20 μm diameter focused-ion beam (FIB) milled pillars of the cross-section of SS316L exposed to LiCl-Li2O-Li with 0 wt.%, 0.3 wt.%, 0.6 wt.% and 1 wt.% Li. Computed Tomographic (CT) images were obtained at X-ray energies above and below the absorption edges of alloying elements of interest, providing insight into the distribution of alloying elements after exposure to the molten salt. 3D X-ray absorption near edge spectroscopy (XANES) tomography at the Cr K-edge was also attempted. This analysis provided additional evidence of the formation of Cr-rich intermetallic phases and 3D CT images of the void structure of the exposed samples, strengthening the evidence that the sensitization of SS316L at process temperatures and the subsequent dissolution of the Cr carbide precipitates into the electrolyte is the primary driver of the deep intergranular corrosion of SS316L in LiCl-Li2O-Li. To our knowledge, this is the first application of this FIB milling technique and TXM imaging of the FIB-milled pillars to corrosion samples and lessons learned regarding the sample preparation and analysis will be presented.Acknowledgements: The authors thank Zachary Karmiol, research scientist at Materials Characterization Nevada, for technical assistance with the FIB sample preparation. This work was performed under the auspices of the Department of Energy (DOE) under contracts DE- NE0008236, and the US Nuclear Regulatory Commission (USNRC) under contract NRC-HQ-13-G-38-0027. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively. This research used beamline 18-ID of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy (US-DOE), Office of Science, Basic Energy Sciences, at Idaho National Laboratory under contract DE-AC07-05ID14517. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1447692. One of the authors, JM, acknowledges the Graduate Research Fellowship from the US National Science Foundation.

Anomalous enhancement of focused ion beam etching by single raster propagating toward ion beam at glancing incidence

Focused ion beam (FIB) sample preparation for electron microscopy often requires large volumes of materials to be removed. Prior efforts to increase the rate of bulk material removal were mainly focused on increasing the primary ion beam current. Enhanced yield of etching at glancing ion beam incidence is known but has not found widespread use in practical applications. In this study, etching at glancing ion beam incidence was explored for its advantages in increasing the rate of bulk material removal. Anomalous enhancement of material removal at glancing angles of ion beam incidence was observed with single-raster etching in along-the-slope direction with toward-FIB direction of raster propagation. Material removal was inhibited in an away-from-FIB direction of raster propagation. The effects of glancing angles and ion doses on depth of cut and volume of removed materials were also recorded. We demonstrated that the combination of single-raster FIB etching at glancing incidence in along-the-slope direction with toward-FIB raster propagation and a “staircase” type of etching strategy holds promise for reducing the processing time for bulk material removal in FIB sample preparation applications.

An in-situ method for protecting internal cracks/pores from ion beam damage and reducing curtaining for TEM sample preparation using FIB

Focused ion beam (FIB) milling has evolved to be one of the most important Transmission Electron Microscope (TEM) site specific sample preparation techniques. However, this technique still poses challenges, such as the structural damage and potential curtaining issues often observed for thin TEM lamella. These artefacts can negatively affect the TEM analysis results. In particular, structures such as internal cracks and pores in FIB prepared TEM samples can often be damaged during sample preparation. This is commonly regarded as an unavoidable problem, even though microstructurally intact thin lamellae TEM samples are widely needed for the investigation of crack tips or pore morphologies in many different materials. This presents a strong driver for the development of innovative methods to overcome damage and curtaining issues during FIB sample preparation. Here we report on a new methodology developed to protect internal cracks and pores from ion beam damage. Our proposed method also mitigates curtaining issues, which often make TEM analysis more difficult. This method uses the FIB to sputter and redeposit material onto the edges of any cracks or pores in order to fill these features in-situ prior to lamella thinning. Case studies showcasing this method are presented, demonstrating the approach on a modular pure iron sample and on a porous laser treated Al/B4C composite sample. Our proposed ‘filling’ method has demonstrated a two key benefits; it preserves the integrity of the edges of any cracks and pores and it reducing curtaining. The results also demonstrate that this technique can be an alternative to conventional Gas Injection System (GIS) deposition for protecting the external top surface.

Wet-chemical etching of FIB lift-out TEM lamellae for damage-free analysis of 3-D nanostructures

Reducing ion beam damage from the focused ion beam (FIB) during fabrication of cross sections is a well-known challenge for materials characterization, especially cross sectional characterization of nanostructures. To address this, a new method has been developed for cross section fabrication enabling high resolution transmission electron microscopy (TEM) analysis of 3-D nanostructures free of surrounding material and free of damage detectable by TEM analysis. Before FIB processing, nanopillars are encapsulated in a sacrificial oxide which acts as a protective layer during FIB milling. The cross sectional TEM lamella containing the nanopillars is then mounted and thinned with some modifications to conventional FIB sample preparation that provide stability for the lamella during the following wet-chemical dip etch. The wet-chemical etch of the TEM lamella removes the sacrificial oxide layer, freeing the nanopillars from any material that would obscure TEM imaging. Both high resolution TEM and aberration corrected scanning TEM images of Si/SiGe pillars with diameters down to 30 nm demonstrate the successful application of this approach.

Characterization of AlN Inclusion Particles Formed in Commercial Purity Aluminum

The detailed characterization of nitride inclusion particles formed in the commercial purity Al melt has been carried out using advanced analytical electron microscopy assisted with pressure melt filtration and focused ion beam sample preparation techniques. It is found that the nitride inclusion particles have short rod-like morphology with an average length of 375 nm and an average width of 104 nm. Moreover, these nitride particles are identified to be hexagonal wurtzite AlN particles with the most close-packed plane, {0001}, as the exposed broad plane. Based on the crystallographic information, the potency of AlN as nucleation substrate for α-Al grain has been theoretically estimated from the lattice matching point of view. It is revealed that the interatomic spacing misfit along the close-packed directions on the close-packed planes between AlN and Al is 6.66 pct, indicating relatively strong potency of AlN as nucleation substrate for α-Al. However, it is suggested that AlN particles would rarely be involved in the nucleation and initiation of α-Al grains when competing with other oxide and boride inclusion particles normally present in the Al melt because AlN particles have larger misfit with Al, comparable or even smaller size, and lower number density than oxides and borides.

Effect of focused ion beam sample preparation on the phase composition of zirconia

The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30 kV, 30 nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30 kV and 30 nA is 700 K for ZrO2. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083 °C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5 kV, 4.8 nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia.

A contribution to the characterization of the silicate-water interface – Part II: Atom Probe Tomography of tricalcium silicate

This work explores the possibility to investigate the nanoscale cement-water interface by means of atom-probe tomography (APT). For this purpose, the main compound of Ordinary Portland Cement, tricalcium silicate, and its hydration product calcium-silicate-hydrate have been analyzed by APT. Of special interest was the surface of anhydrous and hydrated tricalcium silicate. The results show, that a nanoscale characterization of tricalcium silicate with APT is possible by carefully controlling the various measurement parameters. Furthermore, our results indicate, that the conditions during focused ion beam sample preparation, especially the high vacuum and energy input, are potentially harmful to calcium-silicate-hydrate. Future developments in cryo sample preparation will greatly enhance the applicability of APT on cement and its hydration products.