Is it possible caused by the humidity layer on the surface? Maybe a hot baking
will be
helpful to keep the photoresist.

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From: "de la Fuente, Pablo" 
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Date: Fri, 9 Jul 2004 13:19:42 +0200
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Subject: [mems-talk] problems with photolitography after diffusion step
Message: 10

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 350=BAC in O2 flow
60' at 950=BAC 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, Secci=F3n de Microelectr=F3nica.=20
Paseo de Manuel Lardiz=E1bal, 15.=20
20018 San Sebasti=E1n, Spain=20
Tel.: (34) 943 212 800=20
Fax.: (34) 943 213 076=20




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Regards,
Yilei Zhang