Time dependent dielectric wearout (TDDW) technique for reliability of ultrathin gate oxides

The degradation of ultrathin oxides is measured and characterized by the dual voltage time dependent dielectric wearout (TDDW) technique. Compared to the conventional time-dependent dielectric breakdown (TDDB) technique, a distinct breakdown can be determined at the operating voltage I-t curve. A noisy, soft prebreakdown effect occurs for 1.8-2.7 nm ultrathin oxides at earlier stress times. The different stages of wearout of 1.8-2.7 nm oxides are discussed. The wearout of oxide is defined when the gate current reaches a critical current density at the circuit operating voltage. Devices still function after the soft breakdowns occur, but are not functional after the sharp breakdown. However, application of the E model to project the dielectric lifetime shows that this is more than 20 y for thermal oxides in the ultrathin regime down to 1.8 nm.