Greg:

The problem you are having has little to do with the PRIMARY stripping
ingredients, MEA and Choline, but rather with the other "wiffle dust"
ingredients, and specifically the chelating agent(s).

When photoresist is put on metal there is always some oxide on the metal, and
this oxide reacts with the resist.   And in fact, today, this is the
principal bonding mode of photoresist.   This reaction product (of oxide and
resist) is completely insoluble, and must be destroyed to be removed.  The
easy way to destroy it is to "suck" the metal out of the compound, which is
what chelates do well, and the reason resist strippers have chelates.  And
incidentally, MEA is a very weak chelate, not strong enough for this task.

When you use RTF, there is A LOT more oxide available to react with the
photoresist, and you need A LOT of chelate.  This is even more so with modern
resists, that have a higher metal loading capacity than older films.

We are formulating for this problem, and finding that levels of chelate 5-10
fold what we used to find adequate are required.   (I could be a wise A here,
and say, "or you could throw the current chemistry out 5 to 10 times more
often.....")

To test this concept, you may want to simply ask your stripper vendor to give
you some of the chelate he uses, and you add it yourself, to prove that this
is required.

This makes waste treatment more difficult, but it seems the only way to deal
with the problem.

Rudy Sedlak
RD Chemical Company
www.rdchem.com

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