25 October 1996 Optical properties of immersion objective lenses and collimation of secondary electrons in low-voltage SEM
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Abstract
Optical properties of two kinds of immersion lenses, i.e. the radial gap magnetic lens and the combined electric and magnetic field lens have been compared. When the specimen allows the application of a leakage electric field about 600 V and the accelerating voltage on the specimen is lower than 2 kV, the combined field lens is better than the radial gap lens, because the spherical and chromatic aberration coefficients are small and the collimation efficiency of secondary electrons is perfect. However, if the leakage electric field is not allowed, the radial gap lens is superior to the combined field lens. In the case of the radial gap lens, a weak electric field has to be applied to the specimen for collimating electrons emitted with large angle from the specimen. When the specimen is set lower than the magnetic field maximum position, a solenoid coil placed inside the yoke of the lens is useful to bring up the off axial electrons.
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Katsushige Tsuno, Katsushige Tsuno, Nobuo Handa, Nobuo Handa, Sunao Matsumoto, Sunao Matsumoto, A. Mogami, A. Mogami, "Optical properties of immersion objective lenses and collimation of secondary electrons in low-voltage SEM", Proc. SPIE 2858, Charged-Particle Optics II, (25 October 1996); doi: 10.1117/12.255512; https://doi.org/10.1117/12.255512
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