If I read this correctly you are using a compound containing radium in your
stack. I have no experience with these materials but I'd guess that it may be as
simple as the radioactivity of your radium is rendering your positive resists
soluble and negative resist insoluble to the developer. If this is the case I'd
resort to a liftoff technique for patterning the stack. Just verify that
whatever resist you use will give a re-entrant sidewall and will still be
soluble after direct contact with the RaAl. You photoresist supplier may be able
to make helpful suggestions and you can find an assortment of lift-off processes
online.

Cheers,
Rick Williston