You CAN lift-off an oxide mask if the oxide is deposited by
electron-beam lithography.  I don't know if thermal evaporation is
possible--I have not tried it.  However, the quality will not be nearly as
good as a grown oxide.  Grown oxide, such as PECVD, cannot be lifted off
because it would grow conformably around the resist.  In addition, the
growth temperature may well destroy the resist.
         -Bill