How about using HCl, just 1:1 ratio with water would etch Al very nicely. Why you want a complicated etching solution, I don't know but it my opinion HCl works fine and you can adjust the ratio to speed up or slow down your etch rate.
Many thanks Dr.Ata H Khalid for your reply, I will definitely go for your recipe. I just thought maybe H3Po4 is require to remove Al2O3 which may create because of oxidation.
CH3COOH is not compulsory for only etching Aluminum. CH3COOH is used to dilute the solution (in addition to H2O). HNO3 reacts with aluminum and creates Al2O3, which is dissolved in H3PO4. So, aluminum can be etched without adding CH3COOH in the solution. However, for fine features (etching of Al after lithography), addition of CH3COOH results in better etch uniformity.
Not only it is possible, but usually it is very desirable, because acetic acid causes photoresist detachment!
In my article on using aluminium as bulk material for micro fuel cells, I actually do deep etching using a H3PO4 + HNO3 formulation:
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6575144
As for "Why you want a complicated etching solution", I think that the phosphoric acid-based formulations are superior to the ones containing HCl for microfabrication, because HCl etching of aluminium is very exhotermic, which you want to avoid if you want to have control over the etch rates at the microscale.
Thanks everyone for your useful suggestions. I finally used this recipe
H3PO4:H2O:HNO3 ( ratio 20:5:1). The etching rate was ~ 1.9 nm/sec.
Does anyone know how to etch amorphous aluminium 6061? Would the same etchant be used as with the cast and wrought varieties?
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