Along with the recent advances in nanotechnology there is a growing need for a SEM combining ultra-high resolution optics and analytical performance. Here we introduce a new design of a SEM column where recently-developed high-resolution optics [1] is brought together with traditional analytical capabilities.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

1. TESCAN Brno, Brno, Czech Republic. For most current Scanning Electron Microscopes (SEM), the traditional Everhart-Thornley secondary electron (SE) detector and annular backscattered electron (BSE) detector are complemented with several detectors placed in the column. To choose the right system suitable for appropriate application is a challenging task. TESCAN introduced two ultra-high-resolution SEM columns [1], [2] in the last two years. Here, we present a comparison of both systems and introduce recent improvements. Both systems allow angular filtering of SE, energy-filtering of BSE and angular BSE selection.The BrightBeam TM SEM column [1] combines a high-potential tube with a magnetic-electrostatic objective lens delivering ultra-high resolving power when the specimen is in the magnetic-field-free mode. Two specialized detectors in the SEM column together with in-chamber detectors enable the selection of multiple signals for angular SE and BSE (see Figure 1). The Multidetector acquires wide-angle SEs while the Axial detector collects the axial part of the SE signal responsible for enhanced surface sensitivity. Wide angle BSEs impact the BSE detector in the chamber and/or are converted to a SE3 signal with topography BSE information detected on the in-chamber E-T detector. The potential applied on the grid of the Multidetector allows for filtering out the low-energy signal electrons to collect narrow-angle BSEs with good Z-contrast or low-loss BSEs created in the top layer of the sample. The angular BSE filtration is completed with a dedicated imaging mode, where the Axial detector collects the portion of the BSE signal close to the optical axis, which is shown to yield increased surface sensitivity with minimized topography at higher beam energies.The Triglav TM SEM column [2] is equipped with the TriLens TM triple objective lens system to enable ultra-high resolution imaging when the specimen is immersed in the magnetic field, analysis in field-free mode and multiple display modes combining all three lenses. The detection system includes a triplet of complementary BSE detectors (TriBE TM ) that provides angular selection of BSEs (see Figure 2). Inchamber BSE with enhanced sensitivity in the low-energy region (down to 200 eV) provides a strong signal as well as mixed material and topographic contrast due to wide-angle BSEs. The Mid-angle detector placed in the column utilizes the conversion effect and has excellent signal at low energies < 2 keV. The imaging capabilities of the system are significantly enriched by adding a filtering grid to the In-Beam BSE detector collecting axial electrons, enabling surface-sensitive BSE imaging in the normal mode, as well as in the beam deceleration mode.Sample topography is mapped using TriSE TM -a triplet of secondary electron detectors. The in-chamber SE detector is dedicated to observation in the analytical mode. In the ultra-high-resolution mode, secondary electrons are effectively driven into the column where they are attracted to the In-Beam SE detector. The u...

No abstract

The need for increased SEM resolution and the simultaneous demand for enhanced analytical capability have led to the development of increasingly sophisticated instruments. Here we describe the design of a novel SEM column where recently‐developed high‐resolution optics [1] is brought together with traditional analytical capabilities. Combined with FIB it greatly enlarges the capability for 3D tomography inspection of a specimen especially when used in combination with other analytical techniques like EDS or EBSD. The SEM column comprises a triple objective lens design. The first objective lens is optimized to yield an image resolution of less than 1.1 nm at 1 kV. The design retains a single‐pole lens [2] which creates a strong magnetic field around the sample, dramatically decreasing optical aberrations. However, the leaking magnetic field distorts ion trajectories of the FIB and causes beam splitting of ion‐isotopes. To overcome this, FIB processing is performed in a magnetic‐field‐free mode, where the second objective lens of a conventional type with a resolution of 2.5 nm is used. The third objective lens enables a large field of view. A combination of all three objective lenses allows for multiple display modes, e.g. for enlarged field of view, greater depth of field or optimizing resolution at high probe currents. To prevent thermal instability due to changes of lens excitation when switching between the imaging, analytical and other modes, the column works in a regime where constant thermal power dissipation is maintained independent of lens excitation. It significantly reduces image drift and enables stable, long‐term, automatic 3D analysis. 3D BSE tomography of an SERS‐active structure of gold‐coated, partially‐etched polystyrene spheres (Figure 1) was performed maintaining stable operation over a 13 hour period [3]. The sample was sliced using FIB and each cross‐section was automatically imaged at 2 kV using one of the three dedicated back‐scattered electrons (BSE) detectors to obtain the gold distribution on the polystyrene surface. InBeam BSE detector placed in the column acquires high‐angle BSE signal, whereas the two other detectors collect BSE with lower angles. The BSE detector triplet thus enables angle filtration. Furthermore, energy‐filtering of the BSE signal enhances material contrast, (Figure 2), where low‐loss 1.95‐2 keV BSEs reveal details not observable in the integral BSE signal. The redesigned electron gun further enhances the analytical capabilities of the column. It allows probe currents as high as 400 nA for structural analysis and ten times faster beam energy alternation compared to the previous generation. The sharp conus of the objective pole‐piece enables FIB processing of large tilted samples, e.g. 8 inch wafers. The new SEM column will be used in the Mark II generation of the TESCAN MAIA electron microscope and the dual FIB‐SEM instruments GAIA and XEIA [4].