Principle of FESEM

FESEM Principle
A field-emission cathode in the electron gun of a scanning electron microscope provides narrower probing beams at low as well as high electron energy, resulting in both improved spatial resolution and minimized sample charging and damage. Under vacuum, electrons generated by a Field Emission Source are accelerated in a field gradient. The beam passes through Electromagnetic Lenses, focussing onto the specimen. As result of this bombardment different types of electrons are emitted from the specimen. A detector catches the secondary electrons and an image of the sample surface is constructed by comparing the intensity of these secondary electrons to the scanning primary electron beam. Finally the image is displayed on a monitor.

Applications include
Semiconductor device cross section analyses for gate widths, gate oxides, film thicknesses, and construction details Advanced coating thickness and structure uniformity determination Small contamination feature geometry and elemental composition measurement

Why Field Emission SEM?
FESEM produces clearer, less electrostatically distorted images with spatial resolution down to 1 1/2 nm. That's 3 to 6 times better than conventional SEM.
Smaller-area contamination spots can be examined at electron accelerating voltages compatible with Energy Dispersive X-ray Spectroscopy.
Reduced penetration of low kinetic energy electrons probes closer to the immediate material surface.
High quality, low voltage images are obtained with negligible electrical charging of samples. (Accelerating voltages range from 0.5 to 30 kV.) Need for placing conducting coatings on insulating materials is virtually eliminated.

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