I think using a syringe may be the reason of the problem. The SU-8 may mix
with the air when you load the SU-8 to the syringe and inject it on the
wafer via the narrow inlet of syringe. I would suggest just pour the SU-8
directly from the bottle onto the wafer. Do this as slow as possible and
make sure the bottle is closer to the wafer.

If this won't solve your problem, you may try ramped heating. If the
baking is too fast, the su-8 will dry out before bubbles could escape from
the su-8 bulk phase. This traps the bubbles inside. I work with high
aspect ratio su-8 fabrication. I never see bubbles under SEM.

Peng


> Hi Abdou,
>
> The dispensing is done using a syringe , distributing manually the SU-8
> over the whole wafer surface beginning from the center towards the edge.
> When completely covered, the spinner is started.
>
> To fill the syringe (10 ml), I open it at the back and pore the SU-8
> into it directly from the bottle.

--
Peng Li
Research Assistant
Department of Mechanical Engineering & Applied Mechanics
University of Rhode Island
133D Kirk, 92 Upper College Road,
Kingston, RI  02881
Phone: (401) 874-2247