PREVENTING BORON PENETRATION THROUGH 25-ANGSTROM GATE OXIDES WITH NITROGEN IMPLANT IN THE SI SUBSTRATES

For gate oxides thinner than 40 Angstrom, conventional schemes of inco rporating N in the oxides might become insufficient in stopping B pene tration, By implanting N into the Si substrates with a sacrificial oxi de layer, we have grown 25 Angstrom gate oxide and prevented B penetra tion in the presence of F after 90 min of 850 degrees C and 10 s of 10 50 degrees C anneals, SIMS analyses surprisingly reveal a N peak forme d within the thin oxide layer, while no N is left in the Si substrate beyond the oxide layer, In addition, no]B is seen in the substrate, ei ther, As a consequence, threshold voltage of pMOSFET's is shifted to a more negative value which agrees with calculations assuming no B pene tration. Meanwhile, threshold voltage of nMOSFET's is not affected by the N implant, which confirms that B penetration is the only explanati on for the pMOSFET data, Prevention of B peneitration also improves th e short-channel effects for 0.25-mu m pMOSFET's, while Pro difference is seen in nMOSFET's with and without N implant.