Recombination and thin film properties of silicon nitride and amorphous silicon passivated c-Si following ammonia plasma exposure

Recombination at silicon nitride (SiN_x) and amorphous silicon (a-Si) passivated crystalline silicon (c-Si) surfaces is shown to increase significantly following an ammonia (NH₃) plasma exposure at room temperature. The effect of plasma exposure on chemical structure, refractive index, permittivity, and electronic properties of the thin films is also investigated. It is found that the NH₃ plasma exposure causes (i) an increase in the density of Si N₃ groups in both SiN_x and a-Si films, (ii) a reduction in refractive index and permittivity, (iii) an increase in the density of defects at the SiN_x/c-Si interface, and (iv) a reduction in the density of positive charge in SiN_x. The changes in recombination and thin film properties are likely due to an insertion of N-H radicals into the bulk of SiN_x or a-Si. It is therefore important for device performance to minimize NH₃ plasma exposure of SiN_x or a-Si passivating films during subsequent fabrication steps.