Great silence at TN, or my box may miss the postings..anyway...here I have a topic about plasma cleaning. The aluminium trays, on which we place the ceramic substrates and other stuff for cleaning, they sometimes get discolored spots, blue, violet, brown, black. Most of these patterns occur along the edges. In light microscope you can see that parts of the aluminium is etched. The trays lay on a perforated stainless steel shelf that can be pushed in/out. There are numbers of such shelves in the chamber. As the homogenous stainless steel door is closed during operation, I can't see how the plasma works. I suspect that there are 'corona' lines, that bombard in concentrated areas and digs out the aluminium slowly atom by atom.

Q1: anyone who recognizes this?
Q2: what material is best as trays?
Q3: does the aluminium redeposit on the boards for cleaning? (don't think so myself)
Q4: what's best 'furniture' in the plasma chamber for spreading the argon ions best way?

Ingemar Hernefjord
Ericsson Microwave Systems

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