Résumé
Electronic devices used in many space, military, accelerator and nuclear power plants systems may be exposed to Total Ionizing Dose (TID). For the use of these devices, it is essential to have test methods to determine the hardness in a radiative environment. Cobalt-60 (60-Co) is the most common radiation source used for total ionizing dose testing of electronic components. 60-Co is usually considered as the reference ionizing radiation source to perform TID tests on electronic devices and systems. In order to perform TID testing at system-level or for screening, we propose to study in this paper the use of a high-energy X-ray generator with voltage up to 320kV allowing to obtain photons up to 320keV. For the photoelectric effect, low energy photons have a low penetration depth but have a significant impact on the absorbed dose due to the variability of the mass energy-absorption coefficients depending on the atomic number Z of the materials. These conditions are far from optimal for component testing where the goal is to achieve a high penetration depth and an energy deposition that does not depend on the Z of the material. This is the reason why we have decided to cut the low energy photons. This cut is realized with a lead (Pb) filter. We first simulated the effect of such a filter. The TASMICS tool has been used to simulate 3 conditions: (1) no filter, (2) a 2mm aluminum (Al) filter and (3) a 2mm aluminum plus 1mm lead (Pb) filter. As expected, we observe that the Pb filter can cut low energy photons below 90keV. This result has also been verified experimentally. As obtained for the simulation results, we observe experimentally that the Pb filter cuts low energy photons.In order to provide some answers, two references of electronic components have been irradiated within 3 conditions: 60-Co irradiation, X-ray irradiation with Al filter, and X-ray irradiation with Al + Pb filter. Degradation closer to 60-Co has been obtained with X-ray irradiation when photons with low energy photons were cut (i.e. when a lead filter is used). But a difference of degradation remains. The degradation difference can be attributed to several factors: the contributions of packaging or backscattered photons in Back End Of Line (BEOL) stack (contacts, metal layers, insulating layers) that can induce a significant TID contribution in the sensitive oxide . Another explanation can be Time Dependent Effect (TDE) due to the use of different dose rates for 60-Co and X-ray in our experiments. However, the first annealing results seem to indicate that charges detrapping is very low. This point will be further investigated.