Ab initio quantum-chemical calculations of model systems which contained 1 siloxane bond were used to obtain insights into the mechanisms of B diffusion in the oxide, and the suppression of B penetration into gate oxide by means of plasma-induced nitridation. The calculated energies of insertion of various dopants into the siloxane bond revealed a correlation with experimental activation energies for diffusion through the oxide. Plasma-induced nitridation led to the incorporation of N atoms into the siloxane bond. The energy gain for B insertion into a nitrided siloxane bond increased markedly (from about 3eV to more than 10eV) as compared to its insertion into a regular siloxane bond. This was suggested to be a plausible explanation for B diffusion retardation following plasma nitridation. Semi-empirical quantum-chemical methods yielded qualitative agreement with ab initio ones, for insertion energies, and were applied to larger model systems. Calculations of the neutral N atom interaction with a siloxane bond that contained the hydroxyl group suggested a possible explanation for the absence of nitridation of oxide fluxes which were composed only of low-energy neutral N atoms.

Atomic Level Modelling of Boron Diffusion through Silicon Oxide before and after Plasma Nitridation. V.Zubkov, S.Aronowitz, V.Sukharev: Materials Science in Semiconductor Processing, 2000, 3[1-2], 41-5