Atomic level modeling of boron diffusion through silicon oxide before and after plasma nitridation

Abstract

Ab initio quantum chemical calculations on model systems containing one siloxane bond have been employed to get insight into the mechanisms of boron diffusion in silicon oxide and suppression of boron penetration into gate oxide by plasma-induced nitridation. Calculated energies of insertion of various dopants into siloxane bond show a certain correlation with experimental diffusion activation energies through silicon oxide. Plasma-induced nitridation leads to incorporation of nitrogen atoms into siloxane bond. Energy gain for B insertion into a nitridized siloxane bond dramatically increases compared to its insertion into a regular siloxane bond: from ≈3 eV to more than 10 eV. This might be a plausible explanation of the B diffusion retardation after plasma nitridation. Semi-empirical quantum chemical methods showed a qualitative agreement with ab initio ones for insertion energies and have been applied to larger model systems. Model calculation of the neutral N atom interaction with a siloxane bond containing the hydroxyl group suggested a possible explanation for an absence of nitridation of oxide fluxes composed only of low energy neutral N atoms.