Hello Micro Fab,

Thanks for the things that you pointed out.
About the dimensions of the undercut that you wonder:

The undercut is usually (but not always!) ~2.5 to 3.0 microns from each
side of my pattern. But there are two more interesting things other than
the dimensions of the undercut:

1. I am etching only ~30nm thick Cr, and I am observing the change of
the surface color to understand that the ~30nm thick Cr is completely
etched form the upper surface of my wafer (I have large patterns in
other regions of my wafer that help me easily see the change in the
color during etching ~30nm thick Cr). The confusing part is that: While
I am etching only 30nm from top of my wafer, I am having ~2.5 to 3.0
microns of undercut Cr (thickness of this undercut Cr layer is ~10nm).
So, this is really interesting... i had an interesting discussion with
one of the microfab guys in my lab, and he told me that surface tension
and capillary forces (and etc etc...) may be playing important factors
in my case.

2. At some regions, the undercut is relatively larger than ~2.5 to 3.0
microns. I did not do an exact measurement, but the undercut sometimes
is ~10 microns from each side of patterns.

Thanks a lot, and if I can not succeed in the end of my next trial, I
guess I will ask more questions to the mems-talk community.

Mehmet
Mechanical Engineer