Thin Film Deposition Process
In an EBPVD system, the deposition chamber must be evacuated to a pressure of at least 7.5 x 10−5 Torr (10−4 hPa) to allow passage of electrons from the electron gun to the evaporation material which can be in the form of an ingot or rod. Multiple types of evaporation materials and electron guns can be used simultaneously in a single EBPVD system, each having a power from tens to hundreds of kW. Electron beams can be generated by thermionic emission, field electron emission or the anodic arc method. The generated electron beam is accelerated to a high kinetic energy and directed towards the evaporation material. Upon striking the evaporation material, the electrons will lose their energy very rapidly. The kinetic energy of the electrons is converted into other forms of energy through interactions with the evaporation material. The thermal energy that is produced heats up the evaporation material causing it to melt or sublimate. The resulting vapor can then be used to coat surfaces. Accelerating voltages can be between 3 kV – 40 kV. When the accelerating voltage is between 20 kV – 25 kV and the beam current is a few amperes, 85% of the electron's kinetic energy can be converted into thermal energy. Some of the incident electron energy is lost through the production of X-rays and secondary electron emission.
There are three main EBPVD configurations, electromagnetic alignment, electromagnetic focusing and the pendant drop configuration. Electromagnetic alignment and electromagnetic focusing use evaporation material that is in the form of an ingot while the pendant drop configuration uses a rod. Ingots will be enclosed in a copper crucible or hearth while a rod will be mounted at one end in a socket. Both the crucible and socket must be cooled. This is typically done by water circulation. In the case of ingots, molten liquid can form on its surface which can be kept constant by vertical displacement of the ingot. The evaporation rate may be on the order of 10−2 g/cm2 sec.
Read more about this topic: Electron Beam Physical Vapor Deposition
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