I've also had problems with AZ351 developer etching thin ~500A Al films during
liftoff. I'd suggest sputtering a thin ~50A overlayer of Pd on top of the Al.
This has worked fo rme. Does anyone know the developer etch rates for aluminum?
I suspect it's on the orer of 10A/sec, based upon my process.

Good luck.

Thomas E Wilson
Marshall University
Phyiscs