[mems-talk] Problems with Cr isotropic etching with Cr 7s

[Pua Shen]

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.