Radiation enhanced oxidation of proton-irradiated copper thin-films: Towards a new concept of ultra-high radiation dosimetry

The effects of extreme radiation levels on the electrical resistivity of metal thin films made of copper were studied by means of electrical measurements and post irradiation imaging. Different 3x3 mm2 chips were produced by depositing 500 nm of meander shaped copper on top of a silicon substrate. A subset of samples was also passivated by sputtering 300 nm of SiO2. During irradiation with 23 GeV protons up to 1.2 x 1017 p/cm2 at the CERN IRRAD Proton Facility, only not-passivated copper samples have shown an increase of resistivity proportional to the particle fluence, indicating that the dominant factor of the resistivity increase is not directly an accumulation of displacement damage, but the radiation enhanced oxidation of the copper film exposed to air. Post-irradiation imaging of the chips cross sections has confirmed the presence of a grown copper oxide film on the surface as well as oxide wells that extended within the bulk following the grain boundaries. This permanent increase of resistance due to radiation enhanced oxidation, can be used for monitoring high energy particles fluence up to levels currently not reachable by standard silicon technology.