Marc,

I assume you wet etch the Cr under Au.  The undercut problem is due to an
electrochemical reaction known as "galvanic reaction".  The reaction occurs
whenever there are two dissimilar metals in contact and one of them is
being wet etched.  The etching of Cr, in your case, is accelerated by the
existence of Au.  Try TiW (10/90) as an adhesion layer and etch it in
H2O2.  It works well for us.

Good luck,

Jamie Yao

Marc Llaguno wrote:

> I'm having problems with etching a 10 nm Cr adhesion layer under 200
> nm of gold. we always seem to get several microns of undercut. Is this
> because of the gold thickness? Could there be adhesion problems between
> gold and chrome for this thickness?
> any suggestions/comments will be appreciated.
>
> Marc Llaguno
> University of Pennsylvania
>
>