Definition of e-beam evaporation
E-beam evaporation is a type of PVD (physical vapor deposition) techniques, which directly heats the evaporation material (usually pellets) by using an electron beam under vacuum, and transports the vaporized material to the substrate to form a film.
Working process of e-beam evaporation
Electron beam evaporation is based on the evaporation of tungsten filaments. A current about 5 to 10 kV is sent through a tungsten filament (located outside the deposition area to avoid contamination) and heats it to the point where thermionic emission of electrons takes place. The electrons are focused and directed toward the evaporation materials (placed in a crucible) using permanent magnets or electromagnets. During the process when the electron beam hits the surface of the evaporation pellets, its kinetic energy is transformed to heat, and high energy (more than several million watts per square inch) is released. Thus, the hearth which holds the evaporation materials must be water-cooled to avoid from melting.
Difference between e-beam evaporation and thermal evaporation
The biggest difference between electron beam evaporation and thermal evaporation is: the former bombards an object with a beam of electrons which cause high energy for doing the evaporation, and the latter finishes the process by heating. Compared to thermal evaporation, e-beam evaporation gives a high energy; but it will be difficult to control the thickness of of the film the order of 5 nm. In this case, a good thermal evaporator with thickness monitor will be more suitable.
Pros and cons of e-beam evaporation
Electron beam evaporation can evaporate high melting point materials, which is more efficient than general resistance heating and evaporation. It can be widely used for optical coating such as high purity film and conductive glass. It also has potential industrial application for wear-resistant and thermal barrier coatings in aerospace industries, hard coatings for cutting and tool industries.
However, e-beam evaporation cannot be used to coat the inner surface of complex geometries. Besides, the filament degradation in the electron gun may result in a non-uniform evaporation rate.
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