Excuse me, I have the next question: Where it come from the electrons in sputtering system that ionized the argon gas? Because in the literature say that are electrons "ever free" but I don´t know where they come from because I have vacuum in the chamber and I can't understand that. If we have vacuumm, how could be present electrons?
Thank you.
Dear Esteban,
the electrons arise from a (heated) filament mounted within the head of the ion gun. Please see for example page 7 of the attached manual in the link.
http://www.src.wisc.edu/users/scienta_info/Scienta_200U/Instruction%20Manuals/OCI%20Ion%20Sputtering%20Gun%20and%20Power%20Supply.pdf
In the previous response by Dr. Gerhard Martens, was referring to Ion beam sputtering, where you can have a filament which is heated up and produces electrons.
Nowadays there are filament less ion beam guns as well.
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You are right while doing sputtering, In the chamber you do have a good vacuum initially, but in vacuum you don't see any plasma, and you cannot even strike a plasma.
Only after you fill up some argon gas and raise the chamber pressure to a certain level, you are able to strike the plasma, and in this plasma as the argon gas breaks down you will now get argon ions ((+ve) and electrons (e-). You need to understand how an inert gas breaks down under a high field between two electrodes, which are very close to each other (the distance).
the product p.d is a constant, '"p" is pressure and "d" is the distance between the electrodes. When the pressure is high, d should be very small, and pressure p is low, the d can be large. Of course it all depends on the voltage applied between the electrode.
Before you understand the process of sputtering, I would suggest you should basically understand "glow discharge phenomena" thoroughly. This will clear many of your doubts.
Refer to the book by Maissel and R. Glang "handbook of thin film technology", a very old book, but describes everything in great detail.
K. Sreenivas
Dear Esteban,
The basics of Ion sources is described in the following document:
http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/26/001/26001458.pdf
Thank you so much to all of you. You have been of big help. The point is: how an inert gas breaks down under a high field between two electrodes, which are very close to each other (the distance)? So, I will research that. Thank you, again!!
Dear Esteban,
arcing even in an inert gas starts from an initial ionization of the gas molecule/atoms. The very first of this ionization processes is performed either by a) environmental radio activity, b) cosmic radiation, c) thermal and/or field emissson of electrons from the electrode (cathode) which are accelerated in the high electric field or d) by photoemission from the electrodes due to cosmic radiation and environmental radioactivity. It is a random process.
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