Reliability of Thin Oxide Grown on Heavily Doped Polysilicon

The reliability of 100 - 200 A poly-oxide grown on heavily doped polysilicon was investigated mainly by TDDB measurements, compared with ~ 100 A tunnel oxide grown on high dose implanted Si substrate. For the lower phosphorus concentration polyoxide, cumulative failure rate is high at short stress time, slightly depending on stress electric field. The poly-oxide for the higher concentration wears out under the high stress electric field. The wearout phenomenon is considered to be attributed to positive charge generation, due to phosphorus atoms incorporated into poly-oxide. No wearout is observed for tunnel oxide on high dose implanted Si substrate. The TDDB characteristics can be explained by reduction in effective thickness for stoichiometric oxide.