DETERMINATION OF THE COLLECTION EFFICIENCY FOR COMBINED MAGNETIC-ELECTROSTATIC SEM OBJECTIVE LENSES

In this paper the calculation of the collection efficiency for a combi ned magnetic-electrostatic objective lens is presented. We have assume d that a rotationally symmetric, coaxially arranged detector is mounte d above the lens (through-lens detection). Designing a lens, one shoul d ensure that the image planes of secondary electrons are not located too close to the detector plane, because in these cases very high dete ction losses would occur. The comparison of two lens variants, which h ave only slight differences with regard to primary electron optics, sh ows large differences in collection characteristics in the case of a p rimary electron energy of 1 keV. The proportion of backscattered elect rons on the detector signal is discussed.