Control of ionization in e-beam evaporators via optimum choice of focus-coil current

Abstract

e-beam evaporation is accompanied by production of a significant ionic component, which is a result of interaction of electrons with residual gas atoms as well as vapor atoms. In this study we show that the interaction of primary beam electrons with vapor atoms can be controlled to a certain extent by choosing the correct magnetic lens current. This technique can be used to reduce or enhance the extent of ionization depending upon the application.

How to solve problems in micro- and nanofabrication caused by the emission of electrons and charged metal atoms during e-beam evaporation

“…Finally, it should be kept in mind that the interaction of the ebeam with the vapor above the crucible can vary with the focal point and spot diameter of the e-beam. 17 2.) Removing contaminated evaporation material: The secondary electron yield can significantly increase in the presence of contaminants, an oxide layer, or adsorbates, which cover the material.…”

“…Therefore, electron-impact ionization between primary electrons and the vapor leads to the partial ionization of the vapor. [13][14][15][16][17][18][19] Several factors such as the alignment of the ebeam, chosen deposition parameters, and material constants of the evaporation material determine the total amount of this ionization, i.e. the ratio between the neutral and ionized vapor densities.…”

“…the ratio between the neutral and ionized vapor densities. 17,19,20 Especially at higher deposition rates, when a virtual source is created slightly above the actual crucible, 11,12 the amount of ionization increases, if the focus of the e-beam In an e-beam evaporator a hot filament emits electrons due to thermionic emission. These electrons are accelerated by a dc voltage V HV and focused onto the surface of the evaporation material by a magnetic field B.…”

“…moves into this viscous cloud. 17 The insertion of a crucible liner can reduce the amount of ionization. As the liner includes a thermal resistance between evaporation material and water cooled hearth, the heat loss will be reduced and the same evaporation rate can be achieved with less power, [1][2][3] i.e., less e-beam current and therefore less total electron-impact ionization.…”

“…Thirdly, focus the e-beam: We observe that decreasing the visible spot size of the e-beam on the surface of the evaporation material often reduces deposition problems, as this focussing can reduce the volume of space right above the crucible in which e-beam and vapor cloud overlap. 17…”