Dear, Everyone,

I would be very grateful for some advice on this subject: I'm dealing
with a GaAs wafer, coated with PMMA and the PMMA is sputter coated
with ~10nm of Al.  The idea is to prevent charging effects during
e-beam write.

Before development, Al needs to be etched off, because MIBK will not
penetrate it.  I was hoping HCl would quickly etch away Al, but it
appears to be very slow even at high concentration.  Could anyone
suggest a different etchant, hopefully something simple, that would
not attack GaAs too badly (I can afford to lose some GaAs on the back
side but it has to be kept to a minimum)?

Alternatively, suggestions of other metal coatings are welcome, if
they can be etched easily without attacking GaAs.

Thank you,
-mikas