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March, 2014 Scanning Electron Microscopes Expand Fields of View By Jeffrey Paulownia
invaluable test tools in the electron- ics industry. Quite simply, they are microscopes that use electrons instead of light to “illuminate” a tar- get. They use an electron gun to pro- duce a beam of electrons that is focused by electromagnetic fields and lenses held in vacuum. The elec- tron beam strikes the sample, which then emits a variety of different elec- trons and x-ray signals. Different types of detectors are then used to read these signals and feed a display screen for viewing. Although not
S
canning electron microscopes (SEMs) are among the most exotic and, at the same time,
suited for all materials, SEMs can provide a great deal of insight with the proper targets and materials, and can produce images with resolu- tion of 1nm or better. While SEMs are often associat-
ed with research in physics and med- icine, they have increasingly been helping scientists to learn more about electronic materials and cir- cuits. Installations ranging from uni- versity research facilities to semicon- ductor foundries have installed SEM systems to provide high-resolution magnification of different subjects. One advantage that SEMs provides over optical microscopes, in addition
to the wide range of magnification, is a large depth of field, which allows a large amount of a specimen to remain in focus at the same time. Of course, SEMs also have their share of limitations. They are designed to work with solid specimens, which must fit within a relatively small SEM vacuum chamber. Samples that are wet or likely to outgas under vac- uum conditions are not suitable for use with an SEM.
Preparing Samples Because a SEM operates in a
vacuum, water must be removed from samples, otherwise it will
vaporize in the vacuum. SEMs work well with conductive materials, such as metals, but require specimens that are not conductive to be pre- treated to render them conductive and suitable for “viewing” in a SEM. Sputter coating is a pretreatment process typically used to prepare a sample for viewing. Although SEMs are radiation-producing systems, they are designed with sufficient shielding materials to make them quite safe under normal operating conditions. However, for safety rea- sons, the shielding must remain intact and must be properly main- tained on any SEM system. SEMs have traditionally been
physically large systems, comprised of an assortment of key components, including, an electron gun, electron lenses, a sample stage, detectors, a display, a vacuum system, and a power supply. For example, one of the leading
developers of SEM systems and tech- nology, the Nanotech nology Systems Division (NSD) of Hitachi High Technologies America, Inc. (www.hit -
achi-hta.com), recently announced that one of its latest and most advanced SEM systems, its model SU-3500, is now available with a four-axis motorized microscope stage, in addition to the initial version of the system, with its five-axis motorized microscope stage. This latest version of the SEM system was introduced to assist users in need of slightly small- er sample applications, with maxi- mum dimensions of about 200mm diameter and 70mm high. Its motor- ized stage helps to simplify three- dimensional (3D) viewing of samples and saving different vantage points of samples in digital form. JEOL (
www.jeolusa.com), sensi-
tive to the needs of its SEM users for a somewhat wider vacuum operating range to accommodate a wider range of samples, recently announced its model JSM-IT300LV SEM with low- vacuum mode. Capable of operating under vacuum pressure across a range of more than twice that of ear- lier models, this new system can pro- vide SEM imaging with such sam- ples that are typically wet, oily, suf- fer excessive outgassing, or are non- conductive, without pretreatment, by operating in low-vacuum mode. The SEM system, with an embedded charge-coupled-device (CCD) cam- era, uses the firm’s InTouchScope™ touch-screen control as part of its operating system, for simple, intu- itive operation. The system’s five- axis stage control provides imaging and analysis of samples over a wide range of angles and orientations with high accuracy and speed. The SEM also includes a large vacuum cham- ber for samples as large as 300mm in diameter and 80mm in high. It pro- vides a magnification range of 5X to 300,000X.
Another supplier of SEM sys-
tems, TESCAN (
www.tescan.com), is now offering the third generation of its VEGA series of SEM systems, with improvements made in SEM electronics, digital signal processing, and even in software control. These SEM systems perform in both high- and low-vacuum modes, with better than 3-nm resolution in high-vacuum mode and better than 3.5-nm resolu- tion in low-vacuum mode. They pro-
See at APEX, Booth 473 Continued on next page
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