Mopa,

Try the following.

1)  HMDS treat the wafer before coat.
2)  Bake the wafer for 1hr at 100c before etch to improve the resist.
3)  A good KI/I2/H2O mix 2 grams/0.5 grams/75 ml

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-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of X.P. Zhu
Sent: Tuesday, February 14, 2006 2:55 AM
To: [email protected]
Subject: [mems-talk] Undercut uniformity of Gold wet etching

Hi,
    I am using KI/I2 to etch gold pattern. The
thickness of the gold layer which is on 2 inch wafer
is more than 1.5 micron. The etching rate at the edge
of the wafer is faster and in center it is slower. So
when the pattern in center is OK the undercut at the
edge will be not accepted (often > 3 micron). How to
reduce the undercut? Thank you for any advice.