Rajib,
    With a wet etch, the thicker photo probably won't help too much with the
undercut.  The etch is likely to move about as fast sideways as it does down
depending on any anisotropy of your film and the exact fluid mechanics of
the situation.  If you really need that little undercut, you probably need
to RIE, ion mill, or simply bloat your features on the mask after doing an
experiment to see how much undercut you will get.  But you can probably use
a thinner (1-2 um) resist that will easily give you the dimensions you want.

-Lou


>From: "Rajib mukherjee" 
>Reply-To: General MEMS discussion 
>To: mems-talk@memsnet.org
>Subject: [mems-talk] Need 2u thick PZT etching with minimum undercut (<1u)
>Date: Sun, 21 Aug 2005 13:22:04 -0500
>
>Hi all,
>
>I am trying to make PZT/Pt/Cr/SiO2/Si with a 2u thick PZT. The problem is
>the  feature size I have is 10u wide and etching  PZT with normal wet
>etchant gives a huge undercut,So I have to use a very thick resist (20u)
>and achieving a 10u feature size on such resist is really a problem. I am
>using AZ 9260 for the purpose. I have an option of using a negative resist
>with a dark field mask but am not sure whether this would help (I have SU8
>but I would need to strip it too). Anyone having an experience in this
>field, please suggest some solution to this problem in an optimized high
>resolution thick resist deposition.Any alternate etchant of PZT which gives
>minimal undercut with a thin resist will also do the job. Any help would be
>greatly appreciated.