Aluminium etching mechanisms involve formation of aluminium oxide using aluminium etchant. Yet, if we want to selectively etch aluminium, can some recipe be made for that? Is it possible the other way round?
Yes, it is definitely possible to etch Al selectively which is on top of Al2O3 using dry etching. This is one of the most commonly used process and should be able to find quite easily online. But, when it comes to wet etch it could be an issue for such structures to etch.