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 incorporating N in the oxides might become insufficient in stopping B penetration, By implanting N into the Si substrates with a sacrificial oxide layer, we have grown 25 Angstrom gate oxide and prevented B penetration in the presence of F after 90 min of 850 degrees C and 10 s of 1050 degrees C anneals, SIMS analyses surprisingly reveal a N peak formed 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, either, As a consequence, threshold voltage of pMOSFET's is shifted to a more negative value which agrees with calculations assuming no B penetration. Meanwhile, threshold voltage of nMOSFET's is not affected by the N implant, which confirms that B penetration is the only explanation for the pMOSFET data, Prevention of B peneitration also improves the short-channel effects for 0.25-mu m pMOSFET's, while Pro difference is seen in nMOSFET's with and without N implant.