I too looked into the possibility of wet-etching polyimide and came to the
same conlusion as Andy (dry is better). There was some discussion on this
same topic on the board a few years ago; below are two of the more helpful
replies I received. A company called JT Baker were quite helpful also.
Regards,
Conor
NMRC Ireland.
Hi Conor:
Most of the replies I received indicated the
same method you are using: dry etching. Almost all
of the responses used a O2 barrel etcher of some sort.
I contacted DuPont and they said the only way
to remove cured polyimide was using hot fuming sulfuric
acid! Of course that is unacceptable since it would
attack everything else on the wafer. I tried hot TMAH,
EDP, and pure hot Ethelynediamine, but without success.
All of the above wet etchants attacked the field areas
very fast, but were unable to undercut my pads (now these
pads were very large 200 microns on each side). Of course
I had included access holes, but I was still having problems.
Therefore, I contact Dr. Mark Allen at the Georgia
Institute of Technology. He does a lot of work with sensors
and polyimide. The advice was to cure polyimide only if
the material was going to be an integral part of the sensor
or structure you are building. If the polyimide is being
used as a sacrificial layer and needs to be removed later,
do not cure, but softbake it. Of course, not completely
curing the polyimide entails that it is not as stable and
can be attacked more easily by strong bases (i.e. PR developer),
and solvents (IPA, ACE).
In my process, I bake the PI2545 at 150C for approximately
30 mins and then remove it later using a very strong base (hot).
Of course, since the PI is no longer cure, in order to pattern
or etch it, a wet etch process is necessary instead of dry
etching.
In summary, I would not completely cure the polyimide. However,
depending on your cure temperature and time, you could try using
a very hot (fuming even) strong base (TMAH) to see if it would attack
the polyimide. If your bridges are narrow or contain many access
holes it may be possible to etch the polyimide away.
Good luck and if you have any other questions, let me know.
***************************
The ease with which we can etch the polyimide depends on the degree of cross
linking of the polyimide. PRS-2000 may work fine, but we have had people
use some of our other PRS products as well. If you want to send us a sample
we could quickly check several products and make a recommendation for you.
If necessary later on we can decide
to do a quick test in the US for some other strippers.
Hoping to have informed you sufficiently.
http://www.jtbaker.nl <http://www.jtbaker.nl>
-----Original Message-----
From: mems-talk-***@memsnet.org
[mailto:mems-talk-***@memsnet.org]On Behalf Of Andy Scholes
Sent: 16 April 2003 08:17
To: mems-***@memsnet.org
Subject: Re: [mems-talk] wet-etching of polyimide
I did some work a few months ago on wet etching polyimide as a release
process rather than for patterning. After extensive searching we finally
identified an etch which would remove the polyimide. The results were mixed,
however, and the etch we found was very aggressive. Careful thought must be
given to the other layers on the wafer when using the etch, so it may not
suit your needs.
Although I haven't given up completely with the wet etch, a dry etch is
much easier to control and is more production friendly. There have been
postings in the past on dry etching which you can find in the archives.
An alternative could be to use a photosensitive polyimide which you can
pattern and develop. We have used PI2723 from HD Microsystems for several
years and are very happy with the results. (
www..hdmicrosystems.com/conn/offices.html for contact details).
If you could give more details of the process you are running I may be able
to offer a few tips.
Andy Scholes, Ph.D.
Utvecklingsingenjör
ACREO AB
SE 164 40 Kista
Sweden
Dear All,
Does anybody happen to know about the wet-etching of
polyimide? Is there any "standard" etchant to wet-etch
polyimide layers?
Appreciating any hint,
Sh.Farhangfar
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