Dear Khaled Ramadan,

Thank you very much for your suggestion. Yes, I often take the spin coating
after pour PR out and put the sample on a hot bake immediately. In fact, the
soft baking temperature is set about  65 (C), lasting 1 hr. And then I change
the temperature of soft baking to 95 (C) for another hour. I have discovered
that the bubbles appear after several minutes of first soft baking stage. They
will disappear in the second stage gradually. But the thickness of the edges of
sample is larger than that of inner area. That mean, it will make a small gap
between mask and sample surface when exposure, it may cause to some error on the
pattern.

For PR removal, I will try with piranha clean. I do hope it can be removed
without any damage of structure.


Thanks,

Best regards,

Le Hong

PhD student
Department of Mechanical Engineering
National Central University, Taiwan




________________________________
From: Khaled Mohamed Ramadan 
To: Le Hong Hanh ; General MEMS discussion 
Sent: Wednesday, June 8, 2011 9:12 PM
Subject: Re: [mems-talk] Su-8 cannot be removed!


Dear Le Hong,

        It is very true that with a non circular wafer, you cant get a uniform
thickness especially with large thicknesses. for the bubbles, try to do the
spinning immediately after you put the SU8 on the wafer.with very large
thicknesses, I recommend you bake at smaller temperature with longer times. This
will decreases the issue of bubbles appearing while soft baking and will reduce
the internal stress on the film. If you bake only at 65, "Longer Times" would
mean triple to 4 times the soft baking at 95.

      For removal, once you cross-link the su-8 with exposure, it is very hard
to remove it with any thing. For me honestly, nothing removes Cross-linked SU8
but piranha clean. This is because cross linked SU-8 is meant to be remaining as
a structure.

Thanks
Regards,
Khaled Ramadan