Investigation of hydrogen evolution and dangling bonds creation mechanism in amorphous silicon nitride thin films

We have investigated the hydrogen evolution and its consequent impact on the silicon and nitrogen dangling bond density in Si- and N-rich amorphous hydrogenated silicon nitride films prepared by plasma-enhanced chemical vapor deposition. This investigation was done under different thermal annealing conditions through a combination of the Fourier transform infrared spectroscopy and electron spin resonance (ESR) measurements. We have found that the rate of hydrogen evolution from each bond depends on the film stoichiometry, and the N-H bonds are thermally less or more stable than the Si:H bonds in Si- and N-rich films, respectively. In N-rich silicon nitride, for example, the dissociation temperature of the Si-H bond is about 500 and 700°C for the films deposited at 250 and 400°C, respectively; and almost all of the N-H bonds are dissociated above 1000°C. The IR and ESR results suggest that the thermal annealing of the N-rich films creates both K- and N-centers. But the K-center would be passivate during the thermal annealing to form new Si-N bonds, which are observed in the IR spectra