It all depends on the metal and lateral dimensions you are looking to
release (and the facilities you have).  The only all around solution
I can give is silicon since you can remove that in XeF2 (a non-plasma
based isotropic gas etch)...but that won't work well if you have gold
as your metal.  If you are using a polymer as a sacrificial layer
though, you should be able to easily create an isotropic oxygen
plasma in RIE, especially if you don't have a very "good" etcher
(since bad is generally used to describe etchers that are not
anisotropic).

Nik

>Dear All,
>I am trying to deposit a suspended metal layer over a sacrificial
>layer. Is any material that can be used as a sacrifical layer that:
>1) Can be removed without using ultrasonic bath. The ultrasonic bath
>seem to liftoff my metal structure as well.
>2) Can be removed without RIE etching. The RIE etching has to be
>isotropic in order to etch out the underneath sacrificial layer. Our
>nanofacility doesn't have a very good etcher.
>
>I tried NR7, but it is pretty sticky, without utlrasonic, it is very
>hard to remove completely. Can I use SU-8 ?
>
>Any help and suggestion will be highly appreciated.
>