Deposited films of amorphous silicon nitride, Si3N4, which are used for surface protection or as an insulating interlayer in microelectronic devices, have been studied by IR. The observed changes in the vibrational frequency location of the broad infrared Si-N antisymmetrical stretching absorption in the spectra of various plasma deposited Si3N4 films indicate the formation and inclusion of impurities within the silicon nitride network. The deposited films are composed principally of amorphous Si3N4, but trace amounts of hydrogen-, oxygen-, and nitrogen-containing moieties were found which contributed to the displacement of the Si-N absorption. The associated functional groups were identified as Si-H, NH, SiOx, and Si-O-Nx. IR was used to measure quantitatively the hydrogen-containing impurities. The method provides a means of identifying and correlating impurity levels with properties of the films.
J. P. Luongo, "IR Study of Amorphous Silicon Nitride Films," Appl. Spectrosc. 38, 195-199 (1984)