Hi Lisen,
that is very well know phenomenon. Novolak (positive
PR) developer is 3.9% solution of TMAH, which indeed
does etch Aluminum.
Normal developing removes about 40 - 50 nm of Al,
which typically does not matter too much as a
conventional layer thickness in CMOS is 1 um and
besides that, you pattern Al in order to etch it
anyway.
The problem is, when you find out that you have to
rework the litho step. In such a case, you have to
strip Al and re-sputter it.
If you have exposed htink layer Al later on, think
about its protection or make it thicker.
Pavel

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