The effect of nitrogen incorporation into the gate oxide by using shallow implantation of nitrogen and drive-in process

The effect of nitrogen incorporation into the gate oxide by using shallow implantation of nitrogen, followed by drive-in annealing has been investigated. It is found that nitrogen distributed in the polysilicon and polysilicon/SiO ₂ can retard the diffusivity of boron in the polysilicon, and hence suppress the boron from reaching the bulk oxide and improve the charge to breakdown (Q _BD). However, too much incorporation of nitrogen during implantation or drive-in process might degrade the Q _BD, which is probably related to the nitrogen which is doubly bonded to Si atoms in the bulk oxide, with the remaining bond being a hydrogen or dangling bond. It is also found that furnace annealing and rapid thermal annealing (RTA) give different drive-in effect on as-implanted nitrogen, and therefore the gate oxide integrity.