Find out how much resist it takes to make the "wagon wheels" just disappear
and then add .5 ml to be on the safe side.
        Since resist is very expensive (anywhere from $300 - >$1000 per
gallon. High volume fabs go to great lengths to reduce the volume of resist
per coat.
        One mistake people make is they think they need to use more resist
for a thicker film. It takes the same amount of resist for a thick film as a
thin one. The only difference is the final spin speed.
   The amount required to coat a 8-inch wafer depends on your coat recipe,
and the surface of the wafer you are coating. I've seen layers that require
as much a 4ml. Others you can coat with as little as 1 ml. The easiest way
to reduce the amount of resist is increase the spin speed during dispense.
You have to be careful though because you lose vacuum and your wafer will
fly off. About 4000 rpm is about max you can go on a 8-inch wafer (on a good
coater)
   Another popular technique is to do a pre-wet with ebr before dispense.

Robert

-----Original Message-----
From: Wang Ziyang
Subject: RE: [mems-talk] Could someone tell me where I can
getsomeinformationabout wagon wheel pattern?

To avoid wagon wheel pattern, normally I put more resist onto wafer
surface than needed. However, I can observe that much of the resist has
been spinned to the plastic bowl and wasted. I am just wondering how I
can decide the roughly enough quantity of resist, say for an 8-inch
wafer, neither too much nor too little.