Microstructure modifications induced by bonded hydrogen in N-rich SiNx:H films

Abstract

The effect of bonded hydrogen in the atomic microstructure of nitrogen-rich SiNx:H films is investigated using extended x-ray-absorption fine-structure spectroscopy (EXAFS). The hydrogen concentration in the examined films, as measured by elastic recoil detection analysis, takes values in the range 25–33 at. %. It is shown that hydrogen, which is mostly bonded to N, alters the film microstructure, as that is determined by the nearest-neighbor distances and coordination numbers. The measured N–Si nearest-neighbor distance is modified by the presence of N—H bonds and it is shorter than that corresponding to Si3N4 by 3%. This bond length reduction is attributed to the higher electronegativity of hydrogen than that of the replaced Si atoms. In addition, the coordination number N in the nearest-neighbor shell, consisting of Si atoms, is reduced to 2 from the expected coordination of 3 in Si3N4. Furthermore, EXAFS detects the presence of partially reacted Si (a-Si:N) phase, embedded in the SiN matrix, the concentration of which depends on the deposition conditions (rf power and gas flow ratio). The existence of the a-Si:N phase is confirmed by plane-view transmission electron microscopy measurements.