Molecular models and activation energies for bonding rearrangement in plasma-deposited alpha-SiNx : H dielectric thin films treated by rapid thermal annealing

Abstract

Hydrogen and nitrogen release processes in amorphous silicon nitride dielectrics have been studied by MeV ion scattering spectrometry in combination with infrared spectroscopy. The outdiffusion of those light constituents was activated by the thermal energy supplied to the samples by rapid thermal annealing treatments. Molecular models of how these reactions proceed have been proposed based on the information obtained from the infrared spectra, and the validity of the models has been tested by an analysis of the activation energy of the desorption processes. For this purpose, the evolution of the hydrogen concentration versus the annealing temperature was fitted to an Arrhenius-type law obtained from a second-order kinetics formulation of the reactions that are described by the proposed structural models. It was found that the low values of the activation, energies can be consistently explained by the formation of hydrogen bonding interactions between Si-H or N-H groups and nearby doubly occupied nitrogen orbitals. This electrostatic interaction debilitates the Si-H or N-H bond and favors the release of hydrogen. The detailed mechanism of this process and the temperature range in which it takes place depend on the amount and the proportion of hydrogen in SI-H and N-H bonds. Samples with higher nitrogen content, in which all bonded hydrogen is in the form of N-H bonds, are more stable upon annealing than samples in which both Si-H and N-H bonds are detected. in those nitrogen-rich films only a loss of hydrogen is detected at the highest annealing temperatures.