High resolution low-kV STEM imaging is getting more and more attention in the materials research and semiconductor industry, as well as in life sciences research [1]. This has been driven by the need to work with thinner TEM lamella, and with samples containing low-Z and beam sensitive materials. Decreasing electron energies is often favorable from a radiation damage point of view, moreover it improves scattering contrast. In this contribution we focus on STEM imaging extended by diffraction analysis, by integration of pixelated detectors into the FIB/SEM platform.There are two main types of STEM instrumentationdedicated S/TEM systems (which can typically perform in both STEM and TEM modes) and general purpose FIB/SEM systems with a STEM option. The dedicated S/TEM instruments offer higher ultimate imaging performance, usually can go to higher accelerating voltages, might use correctors and advanced analytical techniques such as EELS. In contrast, FIB/SEM platforms offer high system versatility, combining sample preparation with imaging and analysis. However, the STEM options have historically been limited to ~6Å or more, limiting their usefulness on the most challenging samples. Significant improvements in this field was achieved by introducing the Helios G4 platform which brings 3Å STEM resolution, as well in-situ site specific ultrathin lamellas with damage below 1 nm and maximum cut fidelity [2].Resolution of a 30 kV field emission SEM is mainly limited by spherical aberration of the objective lens. The easiest way how to reduce the spherical aberration is to shorten the focal length of the objective lens. In SEMs with conventional lenses the minimum focal length is usually more than 10 mm, in instruments with immersion magnetic (single pole) lenses more than 4 mm. On the other hand, in TEMs where the objective lens utilizes two pole pieces with small gap in between (an in-lens configuration), the focal length can be several times shorter and consequently the coefficients of axial aberrations smaller. The presented accomplishment of STEM performance improvement in a SEM is to equip the system with a second (lower) pole piece in such a way that the system is in-situ configurable and can be operated both in a traditional single-pole SEM (or FIB/SEM) mode and in a high resolution in-lens STEM mode. In order to have the system user-configurable the lower pole piece with integrated multi-segment solid state detector is mounted on a retractable mechanism, which also assures precise mechanical alignment to avoid unwanted aberrations. Improvements in resolution at 30 kV was demonstrated by lattice planes visualizations on several materials such as carbon nanotubes (0.34 nm), silicon (0.31 nm) or tungsten disulfide (0.27 nm) as shown in Figure 1c.To augment the STEM imaging it is desirable to view the diffraction pattern from the sample (as would typically be the case in a conventional S/TEM), which can provide information about sample crystallography, as well as lamella orientation. To investigate this, a pixelated d...
Shrinking sizes of observed features and advancements in (S)TEM techniques requires higher quality TEM sample preparation as well as extended low-kV STEM-in-SEM analysis. In this contribution we present a new generation of the FEI Helios family, configured for ultimate sample preparation and improved STEM-in-SEM imaging. The main improvements to the system can be summarized in sample handling, improved electron and ion optics, and in the introduction of a brand new workflow combining advanced TEM sample preparation and high-resolution STEM imaging in a single instrument.Common workflows include top-down, plan view, and inverted lamellas as well as tomography sample preparation. Sample handling is achieved by a combination of the well-established piezo stage to manipulate and observe bulk samples in combination with newly developed TEM-like rod for sample thinning and STEM imaging. The dual-tilt rod has a long tilt axis perpendicular to the electron and ion columns and second axis allowing sample flip. Opening of the rod from one side facilitates sample milling and cleaning using FIB, and enables optimized signal collection by EDS. The sample rod can be automatically inserting and retracting into the specimen chamber, permitting automated switching from bulk stage to STEM operation. Sample lift-out is achieved by the EasyLift TM manipulator.The focused ion beam (FIB) is an established and powerful technology for site-specific sample preparation. The newly developed Phoenix FIB column brings significant improvement over all existing columns by achieving the possibility to precisely position the low energy ion beam during final lamella thinning and cleaning at 500eV (Figure 1c), while maintaining high milling rates at high energies. The column allows operators to create site specific ultra-thin lamellas with damage below 1 nm and maximum cut fidelity.The improved SEM/STEM is based on the FEI Elstar column; including a Schottky field emission electron gun with improved monochromator performance allows usage the monochromated beam at higher beam currents for improved low-energy imaging. In order to improve the STEM performance the system is equipped with a retractable second (lower) pole piece in such a way that the system can be operated both as a traditional SEM in a FIB/SEM configurations as well in a high-resolution in-lens SEM/STEM mode (Figure 1a,b). The lower part of the STEM objective is equipped with an integrated solid state segmented STEM. The presented developments enable a significant improvement in the STEM resolution of the original system by a factor of two, with the possibility to simultaneously acquire various SEM and STEM signals to provide surface information as well as structural and compositional information as demonstrated on the Figure 2.We are able to demonstrate resolution of lattice planes on several materials such as carbon nanotubes (0.34 nm at 20-30 kV) or Tungsten Disulfide (0.27 nm at 30kV). Configurability of the system opens the space for in-situ experiments, improving existing workf...
Development in semiconductor industry as well as in materials research has lead to a further decrease in observed features sizes. STEM in SEM imaging has been a well based and widely used technique to address this type of work. As a consequence of reducing feature size, there have been parallel requirement increases for high quality TEM sample preparation as well as for improved optical and detection performance of SEM/FIB systems. Here we introduce the very new generation of the FEI Helios product family, which addresses both of upper demands (preparation and resolution). Helios G4 introduces a brand new workflow, which combines ultrathin TEM sample preparation and high resolution STEM imaging in a single instrument. Newly introduced Helios system enables the preparation of all common sampling methods: top‐down, plan view, inverted and tomography. It integrates three sample manipulation devices, the well‐established piezo stage for sample bulk processing, nanomanipulator for sample lift‐out and double‐tilt STEM Rod (TEM‐like manipulator) for lamella thinning and high‐resolution STEM imaging. All manipulators are controlled via the microscope controller software, which allows automated switching between each manipulator and enables automation of the complete workflow. STEM Rod design with opening from one side enables access to sample by Focus Ion Beam (FIB), gas injection system, nanomanipulator and also provides optimized signal collection by analytical detector such as X‐Ray EDS. Focus Ion Beam is a known and commonly used technology for thin sample preparation. Helios G4 family employs the newly developed Phoenix FIB, which brings an advancement in low kV performance, allowing for precise beam placement at low acceleration voltage down to 500 V without compromising milling rates at high voltages. As a result, operator can create site‐specific TEM samples with thickness below 10 nm with damage layer less than 1 nm. Sample lift‐out and transfer from bulk sample to the liftout grid is realized using FEI EasyLift TM nanomanipulator. The grid is loaded in the STEM Rod with double‐tilt functionality for SEM to access both sides of the lamella for precise end‐pointing. STEM Rod is used for final thinning and cleaning and for subsequent high‐resolution STEM imaging of prepared sample. The whole process is done in a system chamber without breaking vacuum. STEM Rod is also designed for sample transfer out of the specimen chamber for further analysis. The option is also to load previously prepared sample into the system and run the STEM imaging. Helios G4, namely FX configuration, introduces the most advanced STEM imaging capability in existing SEM/FIB product portfolio. It is based on proven Elstar SEM column equipped with Schottky field emission gun with improved monochromator, delivering better resolution at higher beam currents. Elstar column works in a setup with configurable objective lens geometry and can be operated in conventional SEM/FIB mode, STEM/FIB end‐pointing mode and high‐resolution STEM imaging mode. Design of new STEM imaging and detection system brings significant leap forward in resolution and also improvement in STEM contrast. Helios G4 FX capabilities can be demonstrated on imaging of lattice planes on several materials as Carbon nanotubes (CNT, 0.34 nm at 20–30 kV) or Tungsten Disulfide (0.27 nm at 30kV). Users can benefit from simultaneous collection of various SEM/STEM signal types and acquire information about sample surface, structure and composition in a single scan.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.