Focused ion beam metrology

In semiconductor device manufacturing, critical dimension (CD) metrology provides a measurement for precise line-width control during the lithographic process. Currently scanning electron microscope (SEM) tools are typically used for this measurement, because the resolution requirements for the CD measurements are outside the range of optical microscopes. While CD has been a good feedback control for the lithographic process, line-widths continue to shrink and a more precise measurement of the printed lines is needed. With decreasing line widths, the entire sidewall structure must be monitored for precise process control. Sidewall structure is typically acquired by performing a destructive cross sectioning of the device, which is then imaged with a SEM tool. Since cross sectioning is destructive and slow, this is an undesirable method for testing product wafers and only a small sampling of the wafers can be tested. We have developed a technique in which historical cross section/top down image pairs are used to predict sidewall shape from top down SEM images. Features extracted from a new top down SEM image are used to locate similar top downs within the historical database and the corresponding cross sections in the database are combined to create a sidewall estimate for the new top down. Testing with field test data has shown the feasibility of this approach and that it will allow CD SEM tools to provide cross section estimates with no change in hardware or complex modeling.

Focused Ion Beams offer a new method of measuring the size of polymer resist features on integrated circuits. The short penetration range of an ion relative to an electron is shown to offer fundamental advantages for critical dimension (CD) metrology. By confining the polymer damage to the very near surface, ion beams can induce less dimensional change than scanning electron microscopes during the measurement process. This can result in improved CD measurement precision. The erosion rate of polymers to various ion species is also presented, and we show that erosion is non-linear with ion dose. The use of FIB for forming resist cross sections is also demonstrated. An H20 gas assisted etching process for polymers has been developed, and is shown to significantly improve the quality of resist cross sections.

A novel analytical method applying combined electron beam induced current (EBIC) imaging based on scanning electron microscopy (SEM) and focused ion beam (FIB) cross sectioning in a SEM/FIB dualbeam system is presented. The method is demonstrated in several case studies for process characterization and failure analysis of thin film technology based Solar cells, including Silicon (CSG), Cadmium Telluride (CdTe) and Copper Indium Selenide (CIS) absorbers. While existing techniques such as electro-, photoluminescence spectroscopy and lock-in thermography are able to locate the larger, electrically active defects reasonably fast on a large area, the FIB-SEM EBIC system is uniquely capable of detecting sub-micron, sub-surface defects and of analysing these defects in the same system. In combination with a FIB, the localized region of interest can be easily cross sectioned and additional EBIC analysis can be applied for a three dimensional analysis of the p/n junction.

Micro-glass capillaries emerge as an important tool for the lossless guiding and focusing of ion beams (Kojima 2018 J. Phys. B: At. Mol. Opt. Phys. 51 042001). The self-focusing mechanism of the capillaries is primarily governed by charged patches induced on their inner walls by the incident beam (Stolterfoht et al 2002 Phys. Rev. Lett. 88 133201). However, the dominance of space charge forces over self-focusing forces in intense (J ≈ 1 A m−2) ion beams establishes a self-focusing limit (Maurya et al 2019 J. Phys. D: Appl. Phys. 52 055205), posing challenges to beam focusing beyond this limit. In this work, a novel method is introduced, demonstrating electrical control over the charge patch dynamics through an externally applied bias voltage, thereby enabling the focusing of Ar ion beams beyond the self-focusing limit. Experimental results reveal that adjusting the biasing voltage allows overcoming the self-focusing limit, resulting in the generation of a high-intensity ( Jout≈3.05×105 A m−2) nano-beam (∼160 nm). Furthermore, electrical control is shown to enhance the performance of both straight and tapered capillaries (SC/TC), with the TC being more effective for nano-beam generation. A Particle-In-Cell (PIC) simulation code has been developed to explain the experimental results. The implications of high-intensity nano ion beams in advancing nanopatterning, nanoscale material analysis, and matter wave interferometry, underscore significant contributions to research and innovation within electronics, materials science, nanotechnology, and emerging quantum technologies.

Low-damage laser scribing of thin films to perform series interconnection (external and integrated) of thin-film CIGS solar cells for module fabrication is still a challenge. In consequence, the influence of laser scribing parameters on the electrical characteristics of thin-film CIGS solar cells must be studied in addition to standard analytical techniques for imaging and spectroscopy. Hence, CIGS solar cells were scribed with ultrashort Ti:Sapphire laser pulses with a wavelength of 775 nm and a pulse length of 150 fs. The I-V curves with the open circuit voltage, parallel, and series resistance were measured directly after the laser-scribing process and were compared with initial cell parameters. Apart from studying the influence of laser fluence etc. also various laser-scribing geometries were examined. The most significant effect of the laser-scribing procedure can be found for the parallel resistance. Laser ablation and laser-induced material modifications during scribing results in (i) alterations of the material properties of the films, e.g. the CIGS, and (ii) material modifications outside of the laser scribe, where the interfaces, e.g. p-n junction, primarily are effected; both effects are leading to the sudden decrease in parallel resistance. Morphology, topography, geometry and material modifications of the laser-scribed areas were analyzed by scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX) and focused ion beam (FIB) cross sectioning. The results of the laserscribing induced alterations are discussed in relation to the applied scribing parameters. A model is introduced to improve the understanding of the physical reasons of the measured solar cell degradation while scribing.

There is currently great interest in combining focused ion beam (FIB) and scanning electron microscopy technologies for advanced studies of polymeric materials and biological microstructures, as well as for sophisticated nanoscale fabrication and prototyping. Irradiation of electrically insulating materials with a positive ion beam in high vacuum can lead to the accumulation of charge, causing deflection of the ion beam. The resultant image drift has significant consequences upon the accuracy and quality of FIB milling, imaging and chemical vapour deposition. A method is described for suppressing ion beam drift using a defocused, low-energy primary electron beam, leading to the derivation of a mathematical expression to correlate the ion and electron beam energies and currents with other parameters required for electrically stabilizing these challenging materials.

A gallium (Ga) focused ion beam (FIB) has been applied increasingly to 'site-specific' preparation of cross-sectional samples for transmission electron microscopy (TEM), scanning TEM, scanning electron microscopy and scanning ion microscopy. It is absolutely required for FIB cross-sectioning to prepare higher-quality samples in a shorter time without sacrificing the site specificity. The present paper clarifies the parameters that impose limitation on the following performances of the FIB cross-sectioning: milling rate, cross-sectioning at a right angle with respect to the sample surface, curtain structures formed on the cross sections, ion implantation and ion damage. All of these are discussed from the viewpoint of ion-sample interaction. Improvements for these performances achieved by diminishing their limiting origins or by correcting the resultants are described. Especially, the FIB scanning speed is significantly utilizable to improve the milling rate. A microsampling method, which allows the FIB incidence in a sidewards or upwards direction as well as downwards with respect to the microsample surface, is very effective to minimize the curtain structures.

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

The global energy landscape is undergoing a profound transformation, shifting from traditional fossil fuel-based systems to sustainable, renewable energy sources like wind, solar, bioenergy, hydroelectric, and tidal energy. This transition signifies a significant evolution in global energy generation and consumption patterns, necessitating advanced energy storage solutions to manage the intermittent nature of renewables and ensure a stable and reliable energy supply. Advanced energy storage technologies, including batteries, supercapacitors, and other innovative systems, play a pivotal role in this transition by enabling effective load balancing, supporting the electrification of transportation through electric vehicles and charging infrastructure, managing peak demand, and facilitating the seamless integration of renewable energy into the grid. This evolution not only advances sustainability goals but also enhances energy security and independence. [1]Advanced analytical techniques are essential for developing energy storage systems, especially batteries, by providing critical insights into their complex chemical and physical processes. Battery materials' microstructure, composition, and operational dynamics can be explored using analytical techniques like scanning electron microscopy (SEM), focused ion beam (FIB), transmission electron microscopy (TEM), X-ray diffraction (XRD), and spectroscopy. The detailed analysis through these techniques is crucial for optimizing material properties, enhancing energy density, improving safety, and extending battery lifespan. By identifying degradation mechanisms and optimizing electrode and electrolyte materials, these techniques contribute to precise battery engineering. As demand grows for more efficient and higher-capacity batteries, these sophisticated tools are indispensable for advancing energy storage technology. [2]At Shell Technology Center Houston, we have developed air-controlled and cryogenic electron microscopy (EM) workflows for studying advanced energy storage systems in preparation for the energy transition. The air-controlled EM workflow, employing SEM, FIB, TEM, and XRD, plays a pivotal role in battery research by providing a controlled environment that prevents exposure to atmospheric elements that could alter material properties. These techniques are essential for examining the fine structural details and chemical compositions of battery components under near-native conditions. The cryo-EM workflow using SEM, FIB, and TEM is vital in battery research for studying materials and interfaces sensitive to environmental conditions or rapid degradation upon exposure. These cryogenic techniques involve rapid freezing of battery components to preserve their structure in a close-to-native state and prevent deleterious effects of air exposure such as oxidation or moisture interaction. [3]In our study, we present comprehensive results obtained using both air-controlled EM and cryogenic EM workflows to investigate advanced energy storage systems, including lithium-ion batteries (LIBs) and beyond-LIBs such as multivalent rechargeable batteries. The utilization of air-controlled EM techniques such as SEM, FIB, TEM, and XRD allows us to examine battery components under controlled environmental conditions, ensuring accurate analysis of structural details and chemical compositions without the risk of atmospheric contamination. Additionally, the use of cryo-EM techniques, including cryo-SEM, cryo-FIB, and cryo-TEM, enables the study of sensitive battery materials and interfaces in a preserved, near-native state. These cryogenic methods prevent degradation effects such as oxidation and moisture interaction, providing unprecedented insights into the ultrastructural properties and operational dynamics of battery materials at atomic or molecular levels. By leveraging both air-controlled and cryogenic EM workflows, we have achieved a comprehensive understanding of battery mechanics and chemistry, paving the way for improved battery design and enhanced performance in energy storage applications.Reference[1] International Renewable Energy Agent (IRENA) 2021 https://www.irena.org/publications/2021/Aug/Renewable-energy-statistics-2021[2] Tarascon, J.-M., Armand, M., Nature 414, 359–367 (2001). https://doi.org/10.1038/35104644[3] Cheng, D., Lu, B., Raghavendran, G., Zhang, M., and Meng, Y. S., Matter, Volume 5, Issue 1, p26-42, 2022 https://doi.org/10.1016/j.matt.2021.11.019

Optical fibers have been the basis of the modern information technology since Kao and Hockham proposed glass waveguides as a practical medium for communication in 1965. A lot of different optical fiber active/passive devices including couplers, interferometers, gratings, resonators and amplifiers have been widely employed for applications on telecommunications and sensing networks (Agrawal, 2002). For a number of applications, it is important to reduce the device’s size. Small size is often attractive for particular sensing applications because of some benefits such as fast response to detecting small objection with little perturbation on the object being measured. There are two steps to obtain fiber devices as small as possible. First, it is to taper or etch the fiber and reduce its diameter. A subwavelength-scale microfiber is the basic element of miniature fiber devices and subsystems (Tong et al., 2003; Brambilla et al., 2004, 2005, 2010). The second is to engineer the microfiber to realize miniature version of conventional fiber devices. There are various fabrication methods to engineer the microfiber, such as CO2 laser, femtosecond (fs) laser, HF acid etching, arc splicing and focused ion beam (FIB). Most of these techniques have the difficulties in carving the microfiber freely because of the resolution. The latest progress in FIB technique has opened a new widow for ultra-small size fiber devices. So far, FIB is the most flexible and powerful tool for patterning, cross-sectioning or functionalizing a subwavelength circular microfiber due to its small and controllable spot size and high beam current density. FIB systems have been produced commercially for approximately thirty years, primarily for large semiconductor manufacturers. FIB systems operate in a similar fashion to a scanning electron microscope (SEM) except, rather than a beam of electrons and as the name implies, FIB systems use a finely focused beam of ions that can be operated at low beam currents for imaging or high beam currents for site specific sputtering or milling (http://en.wikipedia.org/wiki/Focused_ion_beam). The fine and controllable ion spot size and high beam current density are perfect for microand nano-fabrications with high spatial resolution (~ 10 nm). As a result, FIB has recently become a popular candidate for fabricating high-quality micro-devices or high-precision microstructures. Originally, FIB processing was used for mask repair (Liang et al., 2000), integrated circuit chip repair/modification (Liu et al., 2006), cross-sectional imaging of critical parts of

Thermal approach of defects generation on copper/organic dielectric interface due to SEM inspections

In this work, an improved methodology of cross-sectional scanning electron microscopy (SEM) analysis of thin-film Ti/V/Ti multilayers was described. Multilayers with various thicknesses of the vanadium middle layer were prepared by magnetron sputtering. The differences in cross sections made by standard fracture, focused ion beam (FIB)/Ga, and plasma focused ion beam (PFIB)/Xe have been compared. For microscopic characterization, the Helios NanoLab 600i microscope and the Helios G4 CXe with the Quanta XFlash 630 energy dispersive spectroscopy detector from Bruker were used. The innovative multi-threaded approach to the SEM preparation itself, which allows us to retain information about the actual microstructure and ensure high material contrast even for elements with similar atomic numbers was proposed. The fracture technique was the most noninvasive for microstructure, whereas FIB/PFIB results in better material contrast (even than EDS). There were only subtle differences in cross sections made by FIB-Ga and PFIB-Xe, but the decrease in local amorphization or slightly better contrast was in favor of Xe plasma. It was found that reliable information about the properties of modern nanomaterials, especially multilayers, can be obtained by analyzing a two-part SEM image, where the first one is a fracture, while the second is a PFIB cross section.

High resolution investigation of the microstructure of materials and devices is very often restricted to the study of the very surface of the sample. This is because most high resolution analytical and imaging techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM) or scanning tunnelling microscopy (STM) only provide information about the surface microstructure of the sample. To locally investigate the internal microstructure of the sample at high resolution, the sample has to be opened up. This can be done very precisely by the use of a focused ion beam (FIB) for cutting into the sample and the use of a field emission SEM for high resolution imaging of the internal structure. The combination of FESEM and FIB is a future key technology for semiconductor and material science related applications. A new CrossBeam tool is discussed in this presentation. Through the combination of the well known Gemini ultrahigh resolution field emission SEM column and the well known Canion31+ high performance FIB column a wide field of applications can now be accessed. This includes structural cross-sections for SEM and TEM applications, device modification, failure analysis, sublayer measurement and examination, as well as SEM and FIB related analytical techniques such as EDS, WDS, SIMS etc. Real time high resolution SEM imaging of the cutting and deposition process enables the researcher to perform very accurate three dimensional structural examinations and device modifications.

Combined Focused Ion Beam – Scanning Electron Microscope and Synchrotron X-ray Fluorescence analysis of multi-solid and melt inclusions from the super-giant Grasberg Cu[sbnd]Au deposit, Indonesia

ABSTRACTKnowledge of the composition of many cultural heritage objects is limited, resulting in many unanswered questions in regards to the provenance, composition, and production methods. In this paper, our objective is to show that dual beam scanning electron microscope (SEM) and focused ion beam (FIB) can be used rapidly and non-destructively to determine the surface and bulk metal compositions in small cultural heritage objects. We show, for the first time, that this novel FIB technique can be successfully applied non-destructively to cultural heritage objects by examining three representative silver plated objects (Candelabra, “Century” spoon, and New York World’s Fair spoon) from the Dallas Museum of Art’s unparalleled collection of modern American silver. In each case, we successfully reveal and characterize the bulk metal as well as the Ag-plating, up to ∼80 µm deep and show that there is no visual damage resulting from the milling process of the FIB. This novel characterization technique can be applied, due to its ease of availability and rapid use, to many other problems in addition to silver plated objects, making dual beam SEM/FIB a possible cornerstone technique in the study of cultural heritage objects.