Effects of nitrogen incorporation during growth on thin oxide wearout and breakdown

Abstract

Thin oxides, 6.4–7.6 nm thick, have been formed in oxygen with varying levels of nitrogen incorporated into the oxidation ambient. In addition to films with no nitrogen, the nitrogen concentration was varied from 0.00001 to 10% in decade increments. The wearout and breakdown characteristics of these oxides were measured. Wearout was quantified by measuring the changes in the low-level leakage currents, the changes in the mid-gap interface trap densities, the shifts in the flat-band voltages, and the number of traps generated inside of the oxides, all by high voltage stresses. Breakdown was characterized by measuring the time-zero-breakdown voltage distributions. It was found that the wearout was independent of the nitrogen concentration but the breakdown voltages decreased as the nitrogen concentration increased. The average breakdown voltage dropped by |1 V| for oxides with 0.1% N 2 and by |3 V| for oxides with 10% N 2, with the number of low-voltage breakdowns also increasing as the nitrogen concentration increased. It was felt that the nitrogen was incorporated into the oxide both relatively uniformly throughout the oxide and in local non-uniform regions. The uniform distribution inside of the oxide did not affect the wearout properties of the oxide, which were determined by high-field, bond breaking of silicon-oxygen bonds. The regions with non-uniform concentrations of nitrogen introduced local asperities that affected the breakdown voltage distributions by generating local high field regions and locally high trap concentrations.