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Subject:
From:
"Creswick, Steven" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Creswick, Steven
Date:
Wed, 20 Oct 2004 12:15:36 -0400
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Ingemar,

Hello there!  Here are my thoughts.  

Q1 - Yes, it happens.  I always associated colorations with plasma "hot spots" producing differing 'oxide' thicknesses, or literal heating - hence color fringing.  

I have always had reservations about parts coming out of the plasma cleaner being too hot to handle.  If they ever became too hot to handle, I considered that to be too much 'energy' and would try to optimize the process away from the 'hot' settings and down to something 'cooler'.  Seems like I could always get there [thus far] - see second to last paragraph.

Q2 - I prefer stainless, but most often use aluminum.  It is cheaper, easier to make fixtures from, lighter [for the ladies].  Being so soft, aluminum has a nasty habbit of creating unwanted particulates/shavings, however.

If you were going really high volumes and VERY frequent load/unload cycles, I would consider stainless simply due to the ruggedness.  Have to tell the ladies to 'beef up' a little.

Q3 - I differ from you slightly.  I feel the aluminum does re-deposit.  It is just a question of 'How much?'  The trick is to keep the plasma 'density' high enough to actually clean something, but also low enough to suck that which was dislodged, out the vacuum line.

From an atomic level viewpoint, I never really considered aluminum being re-deposited onto aluminum bond pads to be all that much of a risk [at least it was not foreign to the surface ...]  Maybe Dave Hillman will have some comments.  He is sharper on this than I.

On the other hand, if I used stainless fixtures, and chrome, or iron, or some such element came to rest on the bond pad - that would be foreign to the pad!! 

The last two plasma cleaners I have used have an aluminum chamber, so I have not been too worried about additional re-deposition by the fixtures.....

I like to run the plasma chamber with oxygen every so often to ash out any organics and 'toughen up' the aluminum surface.  

At my previous employer we used to actually scrub down the chamber with a steel wool equivalent at periodic intervals.  I have not gotten that desperate  .... yet, but we never had problems either...  At least not that we could associate with the plasma cleaner.   :-)

Q4 - Best furniture is pretty much defined by the manufacturers internal layout.  I try to clutter it up as little as possible internally.  If their electrodes are positioned such that they allow for racks and trays, then go for it!

Having a water droplet contact angle test set up allows  you to determine if there are 'hot' or 'cold' spots in the chamber .... or within your fixturing.  That is about the only way that I can tweak in the process parameters and check for uniformity across/within the chamber.  If someone else has another approach, I sure would like to learn about it!

Am actually working on optimizing a third plasma unit [well, I should be, but am writing this instead] so alternative ideas will be considered.  Thanks

Hope this helps a little.

Steve








                 Are into the cool, wet season now which limits aerial activities.  
                 Colors are great, however!


-----Original Message-----
From: Ingemar Hernefjord (KC/EMW)
[mailto:[log in to unmask]]
Sent: Wednesday, October 20, 2004 10:57 AM
To: [log in to unmask]
Subject: [TN] Argon plasma cleaning


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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