Electric field dependent dielectric breakdown of intrinsic SiO/sub 2/ films under dynamic stress

Time-dependent dielectric breakdown (TDDB) characteristics are reported for 6.5 nm, 9 nm, 15 nm, and 22 nm intrinsic silicon dioxide films stressed under dc and bipolar pulsed bias conditions for a wide range of electric fields and temperatures. Our results show that the increased lifetime observed under bipolar pulsed stress conditions diminishes as the stress electric field and oxide thickness are reduced. Similar electric field and temperature dependencies of TDDB are observed under both static and dynamic stress conditions. It is observed that lifetime enhancement only occurs for electric fields and thicknesses where charge trapping is significant. Contradictory to the conventional notion, TDDB tests on intrinsic thin oxides indicate that static stress testing cannot be considered as a conservative test of bipolar stressing for estimating oxide reliability. These results also confirm the existence of two separate failure mechanisms for TDDB that are functions of electric field and oxide thickness.