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.

Figures:

Figure 1. Typical BrightField (BF) STEM image of a semiconductorfin finished with low kV cleaning, insert FFT from silicon region taken from higher magnification picture, {111} planes are clearly resolved.

Figure 2. Helios G4 imaging of a multiwall CNT at 30kV showing (a) secondary electron image, (b, d) BF STEM and (c) High Angle Annular Dark Field (HAADF) STEM image. Simultaneous imaging shows surface details on secondary electron image (a), structural information on BF STEM (b) and compositional information on HAADF STEM (c) note the catalytic particle is easily resolved on HAADF, the scale bar represents 50nm in images (a) to (c) and 10 nm in high resolution BF STEM image (d).

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EMC Abstracts - https://emc-proceedings.com/abstract/helios-g4-combination-of-ultrathin-damage-free-tem-sample-preparation-and-high-resolution-stem-imaging-in-a-single-instrument/