I've seen several questions lately concerning spinning of SU-8, especially
without bubbles.  I have spun several batches of this material and in all but
the most viscous material, #50 I believe, I have used an Eppendorf pipette
system with 50 ml cups.  They do come with a rather small tip which I cut of
about 15 mm from the barrel.  The SU-8 material is poured into the cup and I
then put the unit together and let stand, tip upwards, for about 5 minutes
before use.  I know of some other people that use a syringe, without a needle,
and they also fill the unit, then put the plunger in.  Using this method there
are no bubbles in the material before dispense.

To dispense I recommend spinning the wafer at a low speed, about 25-50 rpm, and
dispensing the material in a spiral pattern from the center out.  This gets the
material spread out on the wafer and centered.  Then we ramp the wafer up to
speed very slowly to get the material to spread followed by the final speed.  At
the end of the cycle if you perform an edge bead removal using acetone followed
by a high acceleration, speed, for a short time you will have a substrate with
little or no edge bead.  I do not let the substrate sit on the spinner for any
length of time after the spin cycle.

We bake the substrate using a proximity / contact hot plate at about 100'C;
starting at about 6 mm from the plate to about 0.5 mm in three steps of about
40-60 seconds each followed by a contact bake for about 4 to 8 minutes depending
on the thickness.

Post exposure bake is on the same hot plate for 5 minutes at a 6 mm proximity.
This bake temperature must be less than the post apply bake temperature.

That's all for now.  If you have more questions contact me.

Clifford J. Hamel
Applications Engineer
Karl Suss America

Clif

>>> Bernard Hao-Chih Liu  10/09 1:39 PM >>>
Tiziana Lepidi wrote:

> i have problems with SU-8 photoresist. in particular i don't have idea
> to spin the photoresist on the silicon subtrate without form bubbles. Do
> you Know how to apply this photoresist avoiding this problem and have a
> uniform layer of photoresist?
> Thanks Vanessa la Cecilia
> Dr. Vanessa la Cecilia
> e-mail: vanessa.lacecilia@aquila.infn.it  or alaceci@tin.it
> tel. +393388424257
>
>

Dear Dr. Cecilia,

I have the same problem as yours. Furthermore, sometimes I got several
basin
area instead of bubbles.
Could you share the information with me once you get the answers?
Thank you!

Sincerely,

Bernard Hao-Chih Liu
Rapid Prototyping Lab
Stanford University
www-rpl.stanford.edu