I second the Piranha safety warning. But also, according to "Etch Rates
for Micromachining Processing - Part II" Piranha eats evaporated Cr at
over 16 nm/min. I've used Piranha to clean masks before, but only as a
last resort and for short times. I would start with the oxygen asher and
exhaust that option before trying the Piranha. If the power was high
enough I can imagine that there's a small chance you could sputter off
Cr, but the rate would be immeasurably slow and I think you'd be risking
more harm to the mask with Piranha.

-Joe

On 3/26/2010 10:04 AM, Andrew Irvine wrote:
> Just to re-visit a wise warning from a recent poster, Piranha etch (at
> 110C or not) is seriously hazardous, and we need to be flagging up
> safety advice when suggesting stuff.
>
> I don't see a problem with using an oxygen asher, and if there is no
> problem (anyone?), do that instead, Mikas!
>
> Andy


--
Joseph Grogan
Graduate Student
Department of Mechanical Engineering&  Applied Mechanics
University of Pennsylvania
220 South 33rd st
Room 229, Towne Building
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Lab Phone: 215-898-1380