Determination of the collection efficiency for combined magnetic-electrostatic SEM objective lenses

摘要

In this paper the calculation of the collection efficiency for a combined magnetic-electrostatic objective lens is presented. We have assumed that a rotationally symmetric, coaxially arranged detector is mounted above the lens (through-lens detection). Designing a lens, one should ensure that the image planes of secondary electrons are not located too close to the detector plane, because in these cases very high detection losses would occur. The comparison of two lens variants, which have only slight differences with regard to primary electron optics, shows large differences in collection characteristics in the case of a primary electron energy of 1 keV. The proportion of backscattered electrons on the detector signal is discussed. [References: 12]