Plasma diagnosis as a tool for the determination of the parameters of electron beam evaporation and sources of ionization

Abstract

The atomic vapor generated by electron beam heating is partially ionized due to atom-atom collisions (Saha ionization) and electron impact ionization, which depend upon the source temperature and area of evaporation as compared to the area of electron beam bombardment on the target. When electron beam evaporation is carried out by inserting the target inside an insulating liner to reduce conductive heat loss, it is expected that the area of evaporation becomes significantly more than the area of electron beam bombardment on the target, resulting in reduced electron impact ionization. To assess this effect and to quantify the parameters of evaporation, such as temperature and area of evaporation, we have carried out experiments using zirconium, tin and aluminum as a target. By measuring the ion content using a Langmuir probe, in addition to measuring the atomic vapor flux at a specific height, and by combining the experimental data with theoretical expressions, we have established a method for simultaneously inferring the source temperature, evaporation area and ion fraction. This assumes significance because the temperature cannot be reliably measured by an optical pyrometer due to the wavelength dependent source emissivity and reflectivity of thin film mirrors. In addition, it also cannot be inferred from only the atomic flux data at a certain height as the area of evaporation is unknown (it can be much more than the area of electron bombardment, especially when the target is placed in a liner). Finally, the reason for the lower observed electron temperatures of the plasma for all the three cases is found to be the energy loss due to electron impact excitation of the atomic vapor during its expansion from the source.

Properties on Yttrium-Doped/Undoped Barium Cerate and Barium Zirconate Thin Films Formed by E-Beam Vapor Deposition

“…However, accelerated electrons from the e-beam gun can interact with the high dense cloud to generate partial ionization and create defects on the film [18]. The vapor cloud density also is influenced by the evaporated material [19].…”

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

“…But it is exactly this region of high vapor density that the e-beam has to cross on its way to the crucible (see figure 1). 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 e-beam, chosen deposition parameters, and material constants of the evaporation material determine the total amount of this ionization, i.e.…”

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

“…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.…”

“…the area of sufficiently high temperature compared to the area of direct electron beam bombardment and, hence, decreases the chance of electron-impact ionization even further. 19 So far, the discussion about the amount of ionization has focused on the interaction of the vapor with the primary electrons of the e-beam. In addition, backscattered and secondary electrons, which are created by the interaction of the e-beam with the evaporation material, are important contributors to the overall ionization process, which will be discussed in the next subsection.…”