I would like some advice on the best etchant to use to thin an
Al(x)Ga(1-x)As (x=30%) layer. We need to remove ~400nm of a 520nm thick
layer. The sample area is about 0.5 cm^2 with a mirror-like finish.
We currently use H2O2-NH4OH to remove our GaAs. Using a 60:1 mix, we
etch the GaAs at about 2 um/min, stopping on the AlGaAs layer which
etches at ~0.2 um/min. Now we need to thin the AlGaAs while preserving
the surface quality.
We need a slow etch rate for the AlGaAs - preferably slower than
100nm/min, that will preserve the mirror-like surface quality. I do not
know if a citric acid solution or NH4OH-type solution is best, or if
there is anything better for our purposes.