Lifetime of thin oxide and oxide-nitride-oxide dielectrics withintrench capacitors for DRAMs

An investigation of the field acceleration of the time-dependent dielectric breakdown behavior of a thermal oxide and an oxide-nitride-oxide (ONO) dielectric on planar- and trench-cell MIS capacitors under a constant field stress of 5-9 MV/cm at 150°C is discussed. Defect-related and intrinsic failures are distinguished by a statistical analysis of the breakdown distributions. Planar- and trench-cell capacitors with an ONO dielectric exhibit reduced early failures and a more favorable field-acceleration behavior than capacitors with a thermal-oxide layer. A method which determines the number of intrinsic failures by extrapolation of the accelerated constant field stress data to the device area and down to the operational electric field strength is proposed. The extrapolation predicts, for trench-capacitor arrays with a 5-mm² active device area and a 13.5-nm oxide dielectric operating at 3 MV/cm and 150°C, a mean intrinsic failure rate slightly below 100 Fit in the first year, whereas trench structures with an ONO-dielectric reach the same number of cumulative failures after 1 million years