I've seen the same thing when etching silicon dioxide with a chromium mask.
I think that some of the oxide got sputtered onto the Cr.
The solution was a quick HF dip to remove the oxide before stripping the Cr
mask.

In your case, the solution would be a quick dip in a silicon etchant before
stripping the Cr.
The etchant could be hot KOH or an isotropic silicon etchant.

    --Kirt Williams, Ph.D.        consultant
----- Original Message -----
From: Patrick Carlberg 
To: 
Sent: Tuesday, April 15, 2003 7:27 AM
Subject: [mems-talk] Si post etch process problems


> Dear all
>
> I use RIE with different SF6/O2 ratios to etch Si. I have Cr as an etch
> mask. The problem is that after the etching I cannot remove the Cr etch
> mask. Is there risk for deposition on the Cr-oxide? Can the S molecules
> react somehow? Is there risk for polymerization? Do you have any
> suggestions for solutions?
>
> Sincerely
> Patrick Carlberg
> __________________________________________________
> Patrick Carlberg, Ph.D Student, MSc
> Lund University, Solid State Physics/Nanometer Consortium
> Box 118, SE-221 00 LUND, Sweden
>
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