It has been said that water would etch aluminum if it did not create
aluminum oxide, so the quick answer to your question is no, there is
no way to etch Cr without etching Al.  However, you should not be
having problems with doing your liftoff, try using 1827 instead of
1813, it is a thicker resist and should give you a larger separation
allowing for a better liftoff.

Nik

>Dear All,
>
>     I have similar problem like Terry Zhu.... I have aluminum
>interconnecting lines on my device.... After patterning and Sintering the
>Aluminum lines, i deposited Au/Cr seed layer (for doing electroplating) on
>top of it..... Now, I want to Etch the Au/Cr layer selectively. Etching Au
>is not a problem, since underlying Cr is protecting my Al lines. Now, I wish
>to etch Cr selectively. This selective etching of Cr includes the portion
>right above Al interconnecting lines.
>
>   Like Terry Zhu, we are also using Transene ethcant for Cr etching which
>is affecting aluminum lines. Do anyone knows the Al etch rate of Transene Cr
>etchant... i mean selectivity of the Cr etchant over Aluminum.
>
>  I tried lift-off method using S-1813 (Positive PR) and also with Su-8
>resist, But, it was not successful......
>
>  Can anyone tell how Aluminum lines be protected against Cr etchant...
>Whether dry etching will solve the purpose? Anyone has tried it?
>
>Regards,
>A. Ravi Shankar..