Wave Optical Calculation of Probe Size in Low Energy Scanning Electron Microscope

0431331 - ÚPT 2015 CZ eng A - Abstrakt
Radlička, Tomáš
Wave Optical Calculation of Probe Size in Low Energy Scanning Electron Microscope.
9th International Conference on Charged Particle Optics. Book of Abstracts. Brno: Institute of Scientific Instruments AS CR, v. v. i, 2014. s. 26. ISBN 978-80-87441-11-4.
[International Conference on Charged Parrticle Optics /9./. 31.08.2014-05.09.2014, Brno]
Institucionální podpora: RVO:68081731
Kód oboru RIV: JA - Elektronika a optoelektronika, elektrotechnika

The probe size is commonly used as a measure of the resolution of the scanning electron microscope (SEM). There are several ways how to determine. The most used approach is the work of Barth & Kruit, which allows computing the probe size containing a given fraction of current (FC) of a round beam. Even if this approach is in a good agreement with wave optical calculations, it is not optimized for the use at very low energies of several eV. The paper presents a comparison of this approach with a full wave optical calculation and suggests a simple modification to optimize it for a low energy of the electrons. We used wave optical calculations covering the effect of the axial aberrations of an axially symmetrical system and an electron beam of finite brightness. As the resolution is mainly influenced by chromatic aberrations, we consider them up to the second degree, but only the effect of the primary geometrical aberrations is needed. We use a standard formula for the point spread function (PSF) of the axial point, which we extend for the second-degree chromatic aberration. The effect of the finite brightness was computed by a 2-D convolution of the PSF with the 2-D current density distribution in the virtual source plane. As we assume the Gaussian distribution, it is possible to obtain the result in the form of a simple 1-D integral. The approach was implemented in Matlab and tested for a new SLEEM system built at the ISI. The figure shows a comparison of the optimal resolution computed by the wave calculation with the results obtained using. The contribution will also cover the effect of the deflection aberration on the spot size.
Trvalý link: http://hdl.handle.net/11104/0236391