David,
   I use SU-8 2050 and have had some similar problems.  For spinning,
download the microchem data sheet for SU-8 and look at the thickness vs.
spin speed curves.  You will need to spin at a slower rate and these curves
may be a good guide on how much slower to spin at.
   On my samples, I will get a large edge bead.  When I do the soft bake,
this edge bead migrates in towards the center.  If the soft bake finishes
before the edge bead smoothes out, I find non-uniformities like you speak
of.  Wiping off the edge bead may help a little, but I found I needed to
sit my sample on a table for some length of time and at a slightly elevated
temperature (I think I used 40C for an hour).  I also covered my sample to
reduce solvent evaporation during this time and keep dust off.  Be sure
your table is level or your SU-8 will be uneven.
   I use 2" wafers with 2mL of SU-8, so I use a disposable pipette.  I cut
the narrow tip off of the pipette so it doesn't take so long to fill.  Some
people I know pour it directly from a small bottle.
   Are you talking about bubbles in your bottle of SU-8?  I just wait a few
days after pouring and they go away.  I don't see why you can't heat it up,
except that if the solvent evaporates it will change the viscosity.

Glen

At 12:00 PM 8/22/2002, you wrote:
>Message: 1
>From: "dav ng" 
>To: [email protected]
>Date: Thu, 22 Aug 2002 09:50:44 +0000
>Subject: [mems-talk] su-8 2100 resist problems
>Reply-To: [email protected]
>
>hi,
>   for those who had used su-8 2100 before,can you pls read this and help me.
>   i am using the above mention to do a project.i understand that i have to
>coat about 3-4ml on the substrate to achieve 100 um thickness.But i can't
>achieve it.i can only achieve about 60 to 70 um and it is uneven .some part
>is 60um and the others parts are 70um.can u pls tell me how can i achieve a
>100 um thickness evenly?is there something wrong with the spinning rate
>recipe??i am also wondering how  microchem pour the 4ml of su-8.is it they
>use direct pouring onto the wafer or they use syringe.can u let me know too?
>
>i also noticed bubbles in the su-8.so i wish to heat the su-8 to get rid of
>the bubbles.is there any temperature and time i should follow??i thinking of
>heating the su-8 at a temperature of 75 degrees for 30 min becos i noticed
>that at that temperature ,the bubbles are gone.but i scared that i might
>have accidentally destroyed the characteristic of the su-8.is there such a
>possibility??will re-heat(heat more that once) of the su-8 do any damage to
>it?
>
>if i heat up the su-8 2100 to get rid of the bubbles,the su-8 will be
>fluid-like for sometimes.should i spin immediately to spread the su-8 2100
>or do i have to wait for a while.if i have to wait for a while,pls let me
>know how long shld i have to wait.
>
>thanks for reading.i hope someone can help to solve my questions.thank you
>dav
>
>david