Hello Kirt,

It turns out you're right, the copper etched much slower than aluminum on
which it was deposited - so we basically obtained a partial lift-off
of copper. This is an unexpected but actually positive outcome, for
our experiment.

Thank you (and Shay),


m

On Wed, Jun 15, 2011 at 8:44 PM, Kirt Williams
 wrote:
> Ditto what Shay said.
>
> In the first etch-rates paper I listed a variety of reasons for etch-rate
> *variation*. One is a galvanic effect when two metal are on contact with
> each other and also with the etchant. The less electronegative metal
> (aluminum in this case) gives up electrons more easily and will probably
> etch much faster when in contact with copper than aluminum sitting on an
> insulator.
>
>   --Kirt Williams
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf
> Of Shay
> Sent: Wednesday, June 15, 2011 6:47 AM
> To: 'General MEMS discussion'
> Subject: Re: [mems-talk] aluminum etchant vs. copper vs. aluminum
>
> Hi,
>
> You should be careful with etch rates of structures. Two materials that are
> in contact behave very different in etching environment because of the
> different electro chemical potential.
>
> I suggest that you run a test on a real small area. Also, try using copper
> etchant. The FeCl stuff. It might work better.
>
> Shay