Summary For the first time a scanned focused ion beam of approximately 50 nm diameter has been used to prepare biological material. Small defined areas of the surface were removed by ion etching to allow examination of the underlying structures with a scanning electron microscope. Different milling procedures were carried out on two anatomical features in mites of the genus Halarachne (Halarachnidae: Mesostigmata). In the first, square holes were milled into the surface of the peritrematal plate to reveal the structure of the underlying respiratory peritrematal groove. In the second, transverse cuts were made across the shafts of the sensory sensilli which make up the sensory Haller's organ on tarsus I. This latter procedure revealed detail both within the core and walls of sensilli. Details of specimen preparation and milling procedures, as well as suitability and interpretation of results, are presented.

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"Extreme high-resolution" (XHR) scanning electron microscopy (SEM) has the potential to change the way we look at SEM. Anyone in the SEM world knows that you don't do high-resolution SEM at low accelerating voltages because of chromatic aberration limitations. The XHR design offers a new way to deal with chromatic aberration and realize the huge benefit of reduced beam penetration.The new Magellan 400 SEM family is the first to offer subnanometer resolution over the entire electron energy range from 1 keV to 30 keV, effectively establishing a new performance category known as XHR SEM (Figure 1). To achieve this unprecedented performance, the Magellan combines novel electron optical design elements with technologies developed for the industry-leading Titan (scanning) transmission electron microscope (S/TEM) and DualBeam (focused ion /SEM) platforms.beam/SEM) platforms. Unique CapabilityThe system's extraordinary low-voltage performance provides high-resolution, surface-specific information that is simply unavailable from other techniques. Although SEM is considered a surface imaging technique, it would be more accurately called near-surface since the signals it uses may originate as much as a micrometer below the surface, depending upon the beam energy used. S/TEM images, in contrast, are projections presenting information generated as the 200-300 kV electrons travel through a thin section. They can reveal detailed internal structure at atomic resolution, and in some cases, using advanced three-dimensional (3D) tomography reconstruction techniques, some detail about internal surfaces and interfaces. The XHR SEM's low-voltage capabilities allow it to provide exquisitely-detailed images of complex 3D surfaces that are difficult or impossible to obtain any other way. XHR ApplicationsA key driver for the development of the XHR SEM came from the semiconductor market. Whether for research, process development, process control, or for failure analysis, semiconductor device manufacturers have made heavy use of SEMs throughout the history of their industry. With new processes being introduced at design rules of 45 nm and below, the drive for high-resolution information of their ever smaller layers and structures pushes them in two main directions -lower beam energies in the SEM (to allow for more surface sensitive imaging) and to more S/TEM analysis.Each technique has its own benefits -SEM generally has simpler sample preparation, and lends itself to high-throughput imaging of cleaved sections and of complex 3D surfaces, while S/TEM offers atomic level imaging and chemical analysis, unmatched by SEM, but requires much more sample preparation and is not well suited to inspecting 3D surface features. Therefore, it is to be expected that both XHR SEM and S/TEM will become more prevalent and critical with the progression to each new, smaller technology node. Figure 2 shows an XHR SEM application, where a deprocessed sample has been stripped back to the poly-silicon level. Here the benefits of using XHR SEM to inspect the com...

Low voltage SEM image resolution is predominantly limited by chromatic aberration. In order to strongly reduce this effect, FEI has incorporated a monochromator in its latest XHR SEM system (called the Magellan). This enables the reduction of energy spread to 0.15 eV FWHM. To illustrate the potential of a monochromator for low voltage SEM, figure 1 shows the probe size as a function of energy spread, for accelerating voltages U = 0.5 and 1 kV. Sub-nm resolution Magellan images at low voltage have revealed unprecedented information, such as fine surface details and nanoparticle distributions, without any sample preparation [1].An electrostatic Schottky-FEG module has been developed that can provide a monochromatized beam for XHR imaging, and which can also provide large probe currents for analysis. The three modes of operation of this module are shown in figure 2. The extractor contains a first aperture plane with two apertures, defining an axial and offaxial beam. An electrode below the extractor serves as gun lens. This electrode is segmented, so it can also be used for deflection and stigmation. The second aperture plane has an axial aperture and a small, off-axial slit [2]. The latter is used to monochromatize the off-axial beam. A deflector below the second aperture plane is used to direct either the axial or off-axial beam into the column, where a final beam limiting aperture is used to determine the probe current. Unwanted electrons are blocked.In the first mode of operation, the axial beam is used with gun lens off. The axial aperture in the second aperture plane limits the beam current. In the second mode of operation, the gun lens is turned on to deliver more beam current, which can go up to 22 nA. The third mode (called UC mode) uses the off-axial monochromatized beam. Voltages on the gun lens segments are used to position, focus and stigmate the off-axial beam on the energy selecting slit. The beam is dispersed due to the off-axial traversal through the strong gun lens. The spherical aberration of the gun lens results in coma in the off-axial beam. However, the effect of this coma on the energy spread is negligible for useful probe currents, i.e. < 100 pA. For larger probe currents, the loss of brightness becomes more important than the reduction in energy spread.

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