TID Effects Induced by ARACOR, ⁶⁰Co, and ORIATRON Photon Sources in MOS Devices: Impact of Geometry and Materials

Total ionizing dose (TID) effects induced by different photon sources are studied in MOS devices. The dose factor (DF), defined as the ratio between dose deposition in dosimeter and actual dose deposition in MOS-sensitive oxides (SOs), is estimated using Monte-Carlo simulations of energetic photons striking simple device structures. An effective TID approach is proposed to account for both the real ionizing dose depositions in small volumes and the charge yield. This method is applied to a silicon-on-insulator (SOI) technology using three photon sources: the usual ARACOR and ⁶⁰ Co sources, which deliver several tens of kiloelectron volt photons and ~1.25-MeV photons, respectively, and a third facility named ORIATRON, a 6-MeV electron linear accelerator that produces photons on a wide energy spectrum. This topic, investigated intensively in the literature a few decades ago, is revisited in the context of several evolutions including: new radiation sources, novel simulation tools, and device scaling, which all impact ionizing dose deposition in microsensitive volumes of current electronic technologies. Dedicated numerical simulations demonstrate the importance of taking into account the entire stack of materials in order to get the most accurate estimations of TID in the SO. Descriptions of the back-end-of-line (BEOL) layers (especially when the technology uses copper), the polysilicon gate, the Buried OXide (BOX) (for SOI devices), but also of the substrate and package are mandatory in these simulations, since dose enhancement and/or backscattered photons can be a significant source of TID variation in the gate oxide. Also the package lid composition and its thickness can be major TID contributors. The results show that the use of a prefilter with lead and aluminum can optimize ionizing dose deposition