Mirror energy filter for electron beam apparatus

Abstract

One embodiment relates to an apparatus for forming an electron image using electrons with a narrow range of electron energies from an electron beam with a wide range of energies. An electron beam source is configured to generate an electron beam, and condenser lenses collimate the beam into an objective lens configured to illuminate the specimen. The illuminating electrons are scattered by the specimen and form an electron beam with a range of energies that enter a magnetic prism separator. After a 90 degree deflection, the prism separator introduces an angular dispersion that disperses the incoming electron beam according to its energy. A knife-edge plate removes either the high or low energy tail from the propagating beam. An electron lens is configured to focus the electron beam into an electron mirror so that after the reflection, the other energy tail is stopped on the same knife-edge plate. The remaining nearly monochromatic beam reenters the prism separator and is deflected toward the projection system and used to form a two-dimensional electron image on an electron detector. By adjusting the strength of the prism separator, the specific electron energy used for imaging is selected from the energy distribution of the scattered electrons. Other embodiments are also disclosed.