Raman study of structural order of a-SiNx:H and its change upon thermal annealing

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been prepared by plasma-enhanced chemical-vapor deposition (PECVD) with a mixture of SiH4 and N2 at a substrate temperature of 250 °C. The structural properties of these films have been investigated using infrared absorption and Raman spectroscopy. In infrared-absorption measurement, two absorption peaks related to N atoms are observed. From Raman measurements, it is found that the frequency of the TO mode is not as sensitive to N content as the TA mode, and the bond angle distortion is increased slightly. After these samples were annealed in vacuum at 750 °C for 30 min, the bond configuration has been reconstructed to form Si3N bonds which are difficult to observe in as-deposited samples. The annealing results in a large redshift of both TO and TA bands and broadening of the TO mode.