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Ion channeling through the poly-Si gate is investigated using Monte Carlo simulations. It is shown that even at very low energies, channeling may lead to dopant penetration through the gate oxide, resulting in large threshold voltage variations, in particular, of narrow-channel, submicron devices, Unlike thermally activated dopant diffusion through the gate dielectric that is severe only in the case of B, direct penetration due to channeling is a potential problem with all commonly used dopants. The maximum channeling range (minimum poly-Si thickness to prevent dopant penetration) is calculated as a function of implant energy for B, P, and As ions.
Date of Publication: July 1999