Pablo, have you tried an SC1, SC2 rca clean, after the HF.  I think that
might very well help you. Gary

Gary Hillman
Service Support Specialties, Inc.
9 Mars Court
PO Box 365
Montville, NJ 07045
973-263-0640
973-263-8888.



-----Original Message-----
From:   de la Fuente, Pablo [SMTP:[email protected]]
Sent:   Friday, July 09, 2004 7:20 AM
To:     [email protected]
Subject:        [mems-talk] problems with photolitography after diffusion step

Hi all, I am having some problems when trying to perform a typical
photolitographic step after a n-type difussion.
Prior to difussion an oxidation step is performed to grow a 500 nm SiO2
layer to serve as a barrier for the difussion. Then difussion is performed,
with the following parameters:

20' at 350oC in O2 flow
60' at 950oC in N2 flow

We use a liquid dopant source. After this predeposition step (we don't
redistribute) remaining dopant oxide is removed by inmersion in diluted HF
(1:9). After that a typical photolitographic step has to be performed, but
the photoresist lifts-off in critical point of the geometries (the zones
surrounding the insolated places) so we can't define any geometry.
The problem is not the photolitography parameters as we only have this
problem after a difussion step.

We though the SiO2 surface could be damaged or contained impurities as a
result of the difussion step and that this could lead to photoresist
lifting (we don't understand how it coud be, but it happens), so we tried
to etch the surface of the SiO2 layer by wet etching (HF).

If any of you could give me any idea about what happens and how to avoid
this effect I would be very grateful. Thanks to everybody,

Pablo.

Pablo de la Fuente Prado
[email protected]
CEIT, Seccion de Microelectronica.
Paseo de Manuel Lardizabal, 15.
20018 San Sebastian, Spain
Tel.: (34) 943 212 800
Fax.: (34) 943 213 076
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