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

Ab initio quantum chemical calculations on model systems containing one sil oxane bond have been employed to gel insight into the mechanisms of boron d iffusion in silicon oxide and suppression of boron penetration into gate ox ide by plasma-induced nitridation. Calculated energies of insertion of vari ous dopants into siloxane bond show a certain correlation with experimental diffusion activation energies through silicon oxide. Plasma-induced nitrid ation leads to incorporation of nitrogen atoms into siloxane bond. Energy g ain for B insertion into a nitridized siloxane bond dramatically increases compared to its insertion into a regular siloxane bond: from approximate to 3 eV to more than 10 eV. This might be a plausible explanation of the B di ffusion retardation after plasma nitridation. Semi-empirical quantum chemic al 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 hydro xyl group suggested a possible explanation for an absence of nitridation of oxide fluxes composed only of low energy neutral N atoms. (C) 2000 Elsevie r Science Ltd. All rights reserved.