Hi all,

I have some problems regarding about Cr isotropic etching. I'm currently deposit
Cr with DC sputtering system as a metal mask. The Cr layer thickness is around
400nm to 500nm on a 4" silica on silicon wafer. After the PR patterned, i use
Cr-7s etchant from rockwood to etch the Cr layer. From the information i found
from internet, the etch rate of Cr-7s is around 7mins/micron. But i'm using
around 20 minutes to etch the 450nm Cr layer completely, have anyone face the
problem like this? When the etching goes on, the Cr layer will change to dark
color before it etch off, is this a normal phenomena? The etching is start from
side to the centre of the wafer, when the etching is end at the centre the
pattern on the side will be over etched. Anyway to prevent this or overcome this
problem? Thanks for reading my mail, it will be great if anyone of you can
answer my question. Thanks alot.

Best Regards,
Shen
Photonic Laboratory,
University of Malaya.