The action of the photo sensitive part of the resist is to change the
hydrophobic/hydrophilic  property of the Novolac. The pure
Novolac, dissolves in high PH solutions. When the photoactive compound is
added, the matrix becomes highly hydrophobic so water based developer has a
hard time entering the matrix and the un-exposed resist has a very low
removal rate in the developer. Once the PAC has carboxylic groups, it
becomes hydrophilic so the developer has ha much easier access into the
matrix. The fact that there is also an exothermic reaction between the base
and the acid makes it even faster so the matrix removal rate is much higher.
Regarding your strip post iodine or permanganate exposure - these might
create a on soluble cap on top of the resist. Increasing OH concentration
would help only if the other wet process do not cause some level of cross
linking which I suspect both material may cause.

Shay

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of rmartin@systron.com
Sent: Wednesday, September 03, 2008 12:45 AM
To: General MEMS discussion
Subject: [mems-talk] Positive Resist Development Mechanism

      I did some research on positive resist development but could not find
any literature that shows what the development mechanism is of the
indene-carboxylic acid photoproduct.  Am I to assume that it's a straight
redox reaction (we use NaOH for our developer) producing a soluble salt
by-product and water?

      On a related note, I am trying to develop a flood expose and develop
strip system to remove photoresist (using a mercury arc lamp as an exposure
source and our current developer to strip).  It worked well in the initial
stages, but now we are getting some residue which seems to be a result of
the photoresist being affected by other wet processes involving permanganate
and/or iodine.  Would increasing NaOH concenration help dissolve the resist?
Your thoughts are appreciated.