Field mode provides an enhanced field of view, as well as very high depth of focus.
The electron beam is focused on the specimen surface by means of the intermediate lens IML, while the objective lens is off. The final angular aperture of the incident beam is so small and the depth of focus so large that the image is focused in all accessible positions of the specimen stage. Because the objective lens is off, it does not affect the electron beam, which can pass through the lens without being restricted to the paraxial (center) area. The position of the scanning pivot point is optimized in order to reach the maximum field of view, which is limited only by the bore of the final lens. The field of view is substantially larger than in Resolution or Depth modes.
Field mode can also be used to produce a well-collimated beam, which can be useful in lithographic and electron channeling applications.
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