HYDROGEN DIFFUSION AND PASSIVATION PROCESSES IN P-TYPE AND N-TYPE CRYSTALLINE SILICON

Several deuteration experiments on crystalline silicon have been performed for various shallow dopant impurities (B and Al for p-type silicon; P and As for n-type silicon) and for different temperatures and times of plasma exposure. Deuterium diffusion depth profiles obtained by secondary-ion mass spectroscopy (SIMS) were simulated with an improved version of a previously reported model. A careful analysis of the SIMS data has allowed the reduction of the number of fit parameters, by excluding the H2-molecule formation and by a rough estimate of the neutral-deuterium diffusion coefficient and of the surface concentration of neutral deuterium. The diffusion coefficients and related activation energies of the hydrogen species H0, H-, and H+ were determined, leading to a stated ranking of the mobilities in the order H0 < H- < H+. The dissociation energies of BH, A1H, and PH complexes were also calculated and have allowed us to deduce the corresponding bonding energies of the complexes, which suggest a scaling of the complex stability in the order PH < BH < AlH. Free-carrier depth profiles obtained by high-frequency capacitance-voltage measurements, combined with chemical etching, provided direct evidence of the rate of passivation of the shallow p-type-dopant impurities. The comparison between both couples of depth profiles (deuterium diffusion and carrier concentrations), in the case of p-type silicon, showed good agreement between the deactivation process of dopants and the corresponding depth penetration of deuterium.