Hi Ramesh:

If you are using Silicon as your sacrificial material then isotropic dry etching
of Si with XeF2 will be the best solution as suggested by David of Xactics. If
you are using some organic materials as you sacrificial material then you have
to look for an alternate solution like one suggested by Behraad.

Good luck.

David Springer  wrote:

>As the replies show there are several reasons why this is happening.
>Certainly the suggested stiction problem is a high probability candidate.
>The best way to fix this is to move to a dry process. Using a silicon
>sacrificial layer and etching it with xenon difluoride may be the best
>solution. The etch has no attack on aluminum and is capable of very long
>undercuts.