I once experienced adhesion problems with sputtered aluminum (~100-nm thick)
onto polished single crystal (100) silicon die. It turned out that only the bare
silicon die with poor silicon/aluminum lift-off adhesion, had been stored in
plastic containers (black plastic 4x4 snap clip packs) for over one month ...
apparently the plastic out-gassed onto the silicon. Other die from the same
plastic containers, when cleaned in a 1-minute piranha followed by an 10-sec HF
dip, had excellent adhesion after liftoff.

Thomas