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E-Beam & thermal evaporation

In thermal evaporation the materials to be evaporated is put on conductive (graphite or tungsten) crucibles which are intensely heated by Joule effect, until its evaporation.
In the e-beam evaporation the necessary vapours for the production of the coating are obtained by focussing an energetic electron beam on the crucible containing the material, and heating it until reaching its evaporation.
The electrons dissipate their kinetic energy in the material, the power of the e-beam has to be regulated in such a way to reach the temperature at which the vapour tension is enough in order to obtain the desired speed of evaporation. In the e-gun evaporation the speed of evaporation of the material is unstable and can vary even quickly; in order to maintain an adequately constant speed of deposition, it is necessary to control in real time the growth rate of the film and to use it as a feedback for the power of the e-beam. This is obtained thanks to an instrument, called quartz microbalance, consisting of a piezoelectric quartz crystal placed in vibration at its background frequency and exposed to the flow of condensing material. The material deposited progressively adds to the weight of the quartz, lowering its background frequency. Measuring in real time the oscillation frequency of the quartz, the power of the electronic beam can be regulated and correspondingly the instantaneous speed of growth of the film will be regulated.
The evaporated material diffuses into the deposition chamber following linear trajectories and reaches therefore only the areas in line of sight with the crucible. Given the above limitation on the positioning of the crucible, the obtainment of a suitable coating uniformity imposes, in this technique, the adoption of complex manipulation of substrates. In e-gun evaporation, the important amount of melted material causes a rather high heating of the pieces to coat, hence it is not suited to use under a deposition temperature of 350° C. The condensation of vapours happens eventually in the presence of reactive gases (O2, N2) introduced in a controlled way in the deposition chamber, leading to the so called process of reactive evaporation.

 

In the more sophisticated applications, the growing film is subjected to ion bombardment, either by ion beams (IBAD process) or by creating a plasma in the chamber (Ion Plating process).

 

Features:

  • Resistance heated wire spiral and boat evaporators
  • Ion beam or plasma assistance possible
  • E-gun power feedback by quartz microbalance
  • Water-cooled multi-crucible (2,3,4
  • E-beam sweeper and feedback controls
  • Evaporators for Organic Materials

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