A Review of the Use of Electron Beam Machines for Thermal Milling

The factors which influence the size of the heat-affected zone of a material on which a focused electron beam is incident are reviewed. These include the limitation of current density in the focused spot, which is given by the Langmuir relation, and also the limitation imposed by the spherical aberrations of the lens which focuses the beam. The peak temperature rise in the material, with due allowance for the source penetration and backscatter effects, is discussed. The design requirements for electron beam machines are then considered. These are followed by brief descriptions of a number of machines which have been used for the machining of thin films, deposited on substrates, and for the machining of self-supporting thin foils. The principal features of the machined films and foils are described. The review concludes with an account of the various explanations which have been put forward to account for the observed experimental results.