Time dependent dielectric breakdown at 210 Å oxides

Time-dependent dielectric breakdown (TDDB) data on 210-Å oxide films made with a 1.25-μm CMOS process using large-area test capacitors (0.3 cm²) are presented. Stress temperatures of 60°C and 150°C were used while the electric field stress was varied from near-operation conditions (3 MV/cm) to highly accelerated conditions (8 MV/cm). Approximately 14000 test capacitors have been aged. In an attempt to model electric field functionality, an abrupt change in the standard deviation (sigma) of the log-normal failure distribution was observed at moderate stress conditions. At high stress conditions, a field dependent activation energy and a temperature-dependent acceleration parameter were observed. However, at low-stress conditions, an activation energy independent of field and an acceleration parameter independent of temperature were observed. The change in the behavior of the sigma, the activation energy, and the acceleration parameter occur at the same stress condition. It is believed that these changes may indicate a change in the physical failure mechanism at moderate stress conditions