Effect of N/sub 2/O or NO annealing of wet oxide at different times on TDDB characteristics

Abstract

Wet oxide films nitrided in N/sub 2/O and NO ambient have been investigated to clarify the effect of the annealing time and temperature on electrical characteristics, charge trapping properties and TDDB (Time Dependent Dielectric Breakdown) characteristics. It was found that the electrical characteristics do not change significantly with annealing until constant current stress is applied. After stressing, the maximum increase of current is observed in wet oxide film nitrided in NO ambient, whereas the wet oxide nitrided in N/sub 2/O ambient at 900/spl deg/C for 10 min. shows least change. NO annealed wet oxide has less positive charge trapping during the constant current stressing compared to N/sub 2/O annealed oxide. TDDB results show that initial failure rate in NO annealed oxide is larger than that in N/sub 2/O annealed oxide. Even wet oxide annealed in N/sub 2/O ambient at 900/spl deg/C for 10 min. shows longer t/sub BD/. For the same process conditions, NO annealing incorporates more nitrogen compared to N/sub 2/O annealing. The initial failure in the TDDB of NO samples seems to be due to impurities from the gas sources or N related defects in the bulk oxide. Nitridation of oxides brings benefit in the radiation hardness of devices, but annealing conditions such as gas species, temperature and time must be carefully chosen to obtain the optimum effect.