Gate oxide thinning in MOS structures with shallow trench isolation

摘要

Gate oxide thinning was observed near the STI edge even when the trench-fill dielectric densification was performed in a dry oxidizing ambient. Thinning did not occur in the case of densification in a non-oxidizing ambient. The gate oxide breakdown voltage distribution correlates well with the physical thinning effects. The thinning is explained as a result of the reaction between residual H_2 in the CVD trench-fill oxide and O_2 during the densification process to form H_2O. The H_2O in turn can react with the Si_3N_4 to form NH_3 which would lead to nitridation of Si as in the case of classical Kooi effect.