You should be able to buildup 30 microns in a single spin with 4903.  both
hotplate ad owen work well for soft bake.  if you have steps then vacuum
bake works better.

Hope this helps

At 02:04 PM 10/26/99 +1000, P.Leech@mst.csiro.au wrote:
>Dear Colleagues,
>in the use of multiple layers of 4620 and 4903 resists, is there a
>preferred method of  softbake? We are talking of total of 30 microns thick
>built up in 5 layers. I have both vacuum oven bake and hotplate available.
>
>Yours sincerely,
>
>Patrick Leech,
>CSIRO CMST,
>Private Bag 33, Clayton South MDC,
>Victoria , Australia.
>
>
Shekhar Bhansali Ph.D.
Research Assistant Professor
Center for Microelectronic Sensors and MEMS
University of Cincinnati
Cincinnati OH 45221-0030
Ph: (513) 556 0903  fx:  (513) 556 7326