Frank,

first of all you must avoid any bubbles when dispensing the SU-8 onto the
wafer. When you do a manual dispense, pour the resist carefully from a
bottle or a beaker with a wide opening only in the center of the substrate.
Use a moderate spinning speed to spread the SU-8 over the wafer before you
ramp up to the final coating speed. This should help to spin a defect free
layer, but bubbles may also appear during the soft bake step. When the
initial bake temperature is too high, the solvent is driven out of the
resist too fast and creates bubbles as well. For this reason, it is
essential to ramp up the bake temperature smoothly.

Another possible reason for bubbles in the resist layer is a rough or even
topographic surface of the substrate you are trying to coat, but I cannot
give process recommendations in this case without knowing more details.

Best Regards,

Frank.

--------------------------------------------
SUSS MicroTec
Applications Center Europe
Frank Runkel
Schleissheimer Str. 90
85748 Garching
Germany
Fon     +49 89 32007 - 302
Fax     +49 89 32007 - 390
email   f.runkel@suss.de


> ------------------------------
>
> Message: 6
> Date: Fri, 14 Mar 2003 11:07:41 cst
> From: "frank berisford" 
> Subject: [mems-talk] Bubbles in my SU-8
> To: mems-talk@memsnet.org
> Message-ID: <3e720c5d.7e4.0@email.uah.edu>
> Content-Type: text/plain; charset="iso-8859-1"
>
>
> Hello all,
>
> I've been trying several different techniques in an attempt to minimize
> bubbles
> in my SU-8.  At first I tried pippeting it onto my substrate using a large
> bore
> pippette.  I also tried dispensing from a syringe and pouring straight
> from
> the bottle.  The pouring seems to work best but I still get a sizable
> bubble
> count.  From here I've tried sucking the bubbles out with a needle and
> syringe
> but to no avail.
>
> I've read of others wiping the SU-8 across the wafers but have yet to try
> this
> method for fear of destroying the substrate.  For what it's worth I'm
> using
> SU-8 2035 with a target thickness of 50microns but I think I've got my
> spin
> recipe locked down.
>
> Thanks for  your time,
> Frank Berisford
>
>
>
>
>
> ------------------------------
>