Carson,
You have to remember that SU-8 is a negative tone material - basically, where
you expose, the material will remain.
As such, this means that, the higher your exposure gets, the wider your
remaining linewidths will become. In the case of a massive overexposure (such as
your 100second, or 2 J/cm2), this can actually prevent narrow trench features
from developing out.
An optimal dose for the thickness you are exposing is ~300 mJ/cm2 (or, about 15
seconds). Unfortunately, the nature of the SU-8 will mean that some residual
stress will exist in the film, but with care taken during the baking steps, this
stress can be minimized.
One final comment (one I have made before) - be very careful that you are not
allowing the SU-8 to experience UV wavelengths below 350nm - this can cause
extremely unpredictable results during exposure.
Best Regards,
Chad Brubaker
EV Group invent * innovate * implement
Technology - Tel: 480.727.9635, Fax: 480.727.9700 e-mail:
[email protected], www.EVGroup.com
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of laetitia philippe
Sent: Wednesday, December 08, 2004 9:02 AM
To: [email protected]
Subject: [mems-talk] SU8 exposure time
Hello All,
I am trying to find the best exposure time for a SU8-2035 with a
thickness of around 50 um
This is not looking to be very easy. I am working with a UV i-line 365
nm, with 20 mW/cm2
For high exposure time (up to 100s ), I see that my structure does not
developp at all, i.e. the exposed polymer is not removed in the
developper although the sutructre is clearly visible with a color difference
between the exposed and non exposed part
For reasonnable exposure time (20 s), I have a good developpment but I
have always a resulting mould that is small as my mask. i.e some
feature of my pattern of 200 um would lead to only 100 um cavity in my
developped polymer and so one.
Finally, when I go down to 7 seconds, I have a good resulting mould,
with much better dimensions, but I have enormous stress on my polymer and
sometimes delamination which makes me thing I am under exposing of
course
Could someone share his own experience about that? especially about the
over-exposure'?
Many thanks
Carson
---------------------------------
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