GaAs/AlGaAs Etching: High & Low Aspect Ratios

[Gokul43201]

I'm looking for reliable (anisotropic) wet etch techniques that give high (~ 10^2) and low aspect ratios for GaAs on Al(0.3)Ga(0.7)As. I have a few in hand, but would be glad for any additional inputs, especially from someone with personal experience, or at least word-of-mouth knowledge.

I'm aware of the citric acid/peroxide (which we use) and the ammonia/proxide wet etches. I'm checking to make sure there's not some other wet etch that has been found to be far superior. Any opinions on HCl/H2O2 or others ?

 

[anorlunda]

You probably know all of these.

Several anisotropic wet etchants are available for silicon, all of them hot aqueous caustics. For instance, potassium hydroxide (KOH) displays an etch rate selectivity 400 times higher in <100> crystal directions than in <111> directions. EDP (an aqueous solution of ethylene diamine and pyrocatechol), displays a <100>/<111> selectivity of 17X, does not etch silicon dioxide as KOH does, and also displays high selectivity between lightly doped and heavily boron-doped (p-type) silicon. Use of these etchants on wafers that already contain CMOS integrated circuits requires protecting the circuitry. KOH may introduce mobile potassium ions into silicon dioxide, and EDP is highly corrosive and https://en.wikipedia.org/w/index.php?title=Cancer_causing&action=edit&redlink=1, so care is required in their use. Tetramethylammonium hydroxide (TMAH) presents a safer alternative than EDP, with a 37X selectivity between {100} and {111} planes in silicon.