Andreas,
How did the test go? One of the problems we ran into when doing early
adhesion tests was how to qualify total dehydration. A major problem is the
moisture gets trapped in the silicon surface and requires more dehydration than
you would think. That is why on a standard vacuum vapor primer we spend 11
minutes doing the dehydration. The time and the help of the vacuum give us
total dehydration. Let me know if your test has problems. If you send me test
wafers I can vacuum vapor prime them and because this makes the wafers totally
hydrophobic I can mail them back with no loss of adhesion. I know this is
difficult to believe but the best report of this was a company in Ireland who
shipped me problem wafers. Irish customs held them for 8 weeks before releasing
them to the customer. The resist stuck like glue. Let me know if I can help.
Bill
-----Original Message-----
From: Andreas Jahn [mailto:[email protected]]
Sent: Thursday, March 06, 2003 11:14 AM
To: General MEMS discussion
Subject: RE: [mems-talk] Adhesion problems after etching with TMAH
Bill,
thanks for you prompt answer. I do a dehydration of 2 minutes @ 115degrees
Centigrade on a hotplate, just before I spin coat the HMDS. I guess I have
to increase the dehydration time when I pattern the SiO2 a second time. But
everything worked well ont the first SiO2 patterning. Does any chemical
reaction take place on the SiO2 surface? I know TMAH etches SiO2 as well,
but with a much slower etch rate than Si. If it is just the moisture of the
SiO2 it should work with a longer dehydration time. I will run a test
tomorrow and let you know the results.
Andreas Jahn
-----Original Message-----
From: Bill Moffat [mailto:[email protected]]
Sent: Wednesday, March 05, 2003 11:49 AM
To: General MEMS discussion
Subject: RE: [mems-talk] Adhesion problems after etching with TMAH
Andreas,
The TMAH process leaves a wafer with moisture in the Si02. If your
HMDS process does not do a good job of dehydrating the wafer the HMDS reacts
with the moisture leaving an easy to remove adhesion molecule. If you use
vacuum vapor prime, the wafer is totally dehydrated and the HMDS can only
react with hydroxyl ions on the wafer. This produces a tight bond that
moisture can not break. This is almost identical to a process I ran back at
AMD, 15,000 Angstroms of SiO2, wet etch in buffered HF for 17 minutes. With
my old bake then spray HMDS process I had problems with adhesion if I went
more than 4 hours between bake and HMDS. With vacuum vapor prime I ran
tests up to 7 days old with no problems. Contact me directly and I will
give you some more ides. Bill Moffat.
-----Original Message-----
From: Andreas Jahn [mailto:[email protected]]
Sent: Tuesday, March 04, 2003 1:36 PM
To: [email protected]
Subject: [mems-talk] Adhesion problems after etching with TMAH
To all,
does anyone know, what could cause adhesion problems of photoresist on SiO2
after etching in TMAH?
I oxidize a Si-wafer (double polished) and pattern the SiO2 on the backside.
Then I etch it in TMAH. If I want to pattern the
same SiO2 on the frontside, the HF undercuts the photoresist even with the
use of HMDS as an adhesion promoter.
It is the same procedure than the backside. Thanks for your help.
-Andreas
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