Bond density and physicochemical properties of a hydrogenated silicon nitride film

Abstract

Hydrogenated silicon nitride films of 100–300 nm in thickness were prepared on GaAs and Si wafers by plasma enhanced chemical vapor deposition. The number of Si and N atoms in the film was measured by Rutherford backscattering. The number of H atoms was determined by an energy recoil detection (ERD) technique. A zero dose extrapolation method was employed to eliminate the effect of undesirable decrease in ERD count during ion-beam irradiation. The atomic density was determined by dividing the number of atoms by the film thickness obtained from ellipsometry. Infrared absorption cross sections of the SiH and NH bonds were obtained by using a correlation curve between IR band areas and the number of hydrogen atoms from ERD. The density of chemical bonds such as SiSi, SiN SiH and NH was obtained by equating the atomic density with the absorption cross-section of the bonds. Investigation of the refractive index of films with different chemical structures suggests that a concept of the bond refraction can explain a relatively high refractive index (1.8–2.3) and low density (2.1–2.7g/cm −3) of the Si-rich silicon nitride films, as compared with a stoichiometric compound Si 3N 4. The etch rate of the silicon nitride film in buffered oxide etchant solution showed a linear relation against the density of silicon atoms that were not bonded to hydrogen.