Hi,

I would like to darken a sputtered Cu film on a Si wafer.

- For 1 minute on a hotplate with 195°C in ambient air works fine but is too
hot.
- H2O2 at room temperature and at up to 95°C for up to 30min does not work.
- NaCl + NaOH in H20 at 75°C oxidized too fast: in a few seconds the sputtered
film is gone. At
lower temparatures the solution does not work.
- In O2 plasma (parallel plate reactor and barrel reactor) I don't see any
effect.

After darkening the Cu I do UV lithography on top with extremely thick films
(1mm). Subsequently I
re-lighten the Cu in order to electroplate into the openings of the photoresist.
Thus, the darkened
Cu should not reflect during lithography and has to be set to initial
reflectivity and conductivity
after photolithography without getting etched too seriously.

Does anybody have an idea what I could try?

Kind regards

Felix