Nitrogen bonding environments and local order in hydrogenated amorphous silicon nitride films studied by Raman spectroscopy

Hydrogenated amorphous silicon nitride (a-SiNx:H) films prepared by plasma-enhanced chemical vapor deposition in silane-ammonia radio frequency glow discharge were studied around the stoichiometry by Raman spectroscopy. The properties of these films were investigated using a micro-Raman setup and a reflector substrate to enhance the recorded signal. A spectroscopic signature that discriminates among the different amorphous films showed a gradual building up of the phonon density of states when increasing the level of nitrogenation up to N/Si=1.4. For this composition, a-SiN:H keeps the memory of the corresponding Si3N4 crystal modes. Besides, the Si–N stretching modes of the Nn–Si–H(4−n) evidenced the stages of the substitution of H by NH bonds allowing to ascribe the lines located at 1050, 1015, and 820 cm−1 to SiN4, N3–Si–H, and N2–Si–H2 groups, respectively.