Drain current decrease in MOSFETs after heavy ion irradiation

In this work, we have focused our attention on MOSFETs, which are the real basic elements of all CMOS applications. We have studied the immediate and latent effects produced by heavy ion irradiation on MOSFETs with ultrathin gate oxide, even after electrical stresses subsequent to irradiation. We found that a single ion can generate a physically damaged region (PDR) localized in the Si-SiO₂ interface, which may hamper the surface channel formation. In order to generate a PDR the ion hit must be close enough to MOSFET borders, i.e., in correspondence with the STI or the LDD spacer. Consequently, if both MOSFET W and L are large enough only few ion hits may give place to a PDR, mitigating the radiation damage. Finally we have developed an original model to describe the impact of the PDR on channel conductance in the ohmic linear region. On the basis of this model, we predict a PDR size around 0.2-1 μm.