Low Field Electron Mobility Degradation in Silicon MOS Transistors Under Uniform Hot Electron Injection

Low field mobility of electrons in inversion layers of silicon n-type MOS transistors exposed to uniform (non-avalanche) hot electron injection is studied at ambient temperature. Mobility degradation by Coulomb scattering with stress induced charged states at the silicon/insulator interface and in the insulator bulk is investigated and interpreted on the basis of a numerical model. The model accounts for multi-subband transport and a detailed description of Coulomb scattering with charged centers including non-local screening by free-electrons in different subbands. Calculations are shown to be in good agreement with measured data. Exploiting Matthiessen's rule, mobility limited by Coulomb scattering with (stress induced) interface and insulator charges is extracted from measurements before and after stress and compared with calculations. The validity of Matthiessen's rule is discussed. Finally, a simple local model for mobility limited by Coulomb scattering with charged interface states, suitable for implementation in a commercial TCAD simulator, is proposed.