The impact of an external sodium diffusion source on the reliability of MOS circuitry

Data retention studies were conducted on nonvolatile devices exposed to an external sodium diffusion source (sodium bicarbonate). A time-to-failure model is presented and the kinetics of failure are discussed. In this mobile ion contamination study, the integrity of the passivation overcoat (PO) was identified as the major factor affecting data loss. Even under a heavy concentration of sodium (3 wt.% Na sol.), pinhole-free PO units baked at 300°C were observed to fail due to intrinsic charge loss before sodium compensation of the floating gate occurred. Units which had anomalies in the PO were found to fail rapidly with localized regions of failing bits appearing as circular areas. These circles of failed bits were found to grow in radius with the square root of time. Arrhenius plots of the rate of circular growth yielded an average value of 1.8 eV for the activation energy