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

Georgi Gorine,Federico Ravotti,Didier Bouvet,Giuseppe Pezzullo,Jean-Michel Sallese

doi:10.1063/1.5096606

Abstract

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.

Highlights

IntroductionThe effects of radiation on metals have been considered in a number of studies aimed to understand and predict radiationinduced degradation of materials and components used in nuclear reactors as well as in high-energy physics experiments. Several property variations were reported like: changes in the material stiffness, generation of internal voids, surface swelling, as well as changes in the electrical resistivity of the irradiated metal and/or alloy. In the latter, a qualitative trend in increasing copper resistivity was observed, explained as result of transmutations (e.g. decay of 64Cu into 64Zn and 64Ni by beta emission), and defects generation in the lattice due to displacement damage. Such experiments were carried out on relatively thick metal samples (several mm thickness), and not on thin-film samples of sub-μm size, where the effects of very high fluences of energetic particles (>1020p/cm2), to the best of our knowledge, have never been studied in detail.In this work, we analyze and explain the effects of radiation on 500 nm thin copper layers, by direct electrical characterization before, during, and after irradiation, as well as by morphological observations combining Focused Ion Beam (FIB) milling with Scanning Electron Microscopy (SEM).This paper is structured as follows
In order to overcome these limitations of silicon devices, we have focused our research on a new dosimetry concept based on the change of resistance of metal nanolayers, which could share the same electrical readout principle as the change of resistance of p-i-n diodes
We have shown and discussed the results from the irradiation tests performed on several devices made of copper

Summary

Introduction

The effects of radiation on metals have been considered in a number of studies aimed to understand and predict radiationinduced degradation of materials and components used in nuclear reactors as well as in high-energy physics experiments. Several property variations were reported like: changes in the material stiffness, generation of internal voids, surface swelling, as well as changes in the electrical resistivity of the irradiated metal and/or alloy. In the latter, a qualitative trend in increasing copper resistivity was observed, explained as result of transmutations (e.g. decay of 64Cu into 64Zn and 64Ni by beta emission), and defects generation in the lattice due to displacement damage. Such experiments were carried out on relatively thick metal samples (several mm thickness), and not on thin-film samples of sub-μm size, where the effects of very high fluences of energetic particles (>1020p/cm2), to the best of our knowledge, have never been studied in detail.In this work, we analyze and explain the effects of radiation on 500 nm thin copper layers, by direct electrical characterization before, during, and after irradiation, as well as by morphological observations combining Focused Ion Beam (FIB) milling with Scanning Electron Microscopy (SEM).This paper is structured as follows. Several property variations were reported like: changes in the material stiffness, generation of internal voids, surface swelling, as well as changes in the electrical resistivity of the irradiated metal and/or alloy.3 In the latter, a qualitative trend in increasing copper resistivity was observed, explained as result of transmutations (e.g. decay of 64Cu into 64Zn and 64Ni by beta emission), and defects generation in the lattice due to displacement damage.. A qualitative trend in increasing copper resistivity was observed, explained as result of transmutations (e.g. decay of 64Cu into 64Zn and 64Ni by beta emission), and defects generation in the lattice due to displacement damage.4 Such experiments were carried out on relatively thick metal samples (several mm thickness), and not on thin-film samples of sub-μm size, where the effects of very high fluences of energetic particles (>1020p/cm2), to the best of our knowledge, have never been studied in detail.

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