we have Vacuum system technologies(VST) evaporator in our clean room for metal evaporation. we are facing the problem with deposition of Aluminium with e-beam as well as thermal. most of the time aluminum is splitting out of the crucible when the deposition is happening ,can you please suggest to me any techniques or suggestions to get good aluminum metal deposition by evaporation?
Hello Bobby Bnm ,
Have you tried simply hanging hooks of pure aluminum on tungsten filaments? If you raise the temperature of the tungsten filaments slowly, by gradually increasing the current through them, until the aluminum melts and then wets the filament, you should be able to prevent spitting. Aluminum is such a low melting point and medium boiling point metal, 660ºC & 2,467ºC, respectively, that there is no reason to use e-beams. Tungsten's melting point is 3,410ºC. Please, consult the following book.
[1] L. Holland, Vacuum Deposition of Thin Films; John Wiley & Sons, Inc.; 1961.
Note, to get good adhesion of the deposited film, the substrate must first be mechanically and/or chemically cleaned, and then subjected to a low pressure, DC glow discharge using pure oxygen (observe the correct polarity) in the same vacuum chamber where the deposition is to occur, just prior to the actual deposition, see [1]. If the adhesion of the film is very good, it should almost survive the Scotch® tape pull test, although, the result would be much better with a SiO2 overcoat on the Al film.
Regards,
Tom Cuff
What rate are you depositing at? With our equipment, we can get rates as high as 10-20 A/sec with thermal (using a tungsten boat). E-beam evaporated aluminum in a fabmate crucible will spit if you push the rate above 5-6A/sec. I increase and decrease the power very slowly for both.
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