Optical characterization of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition

An investigation of the optical properties of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition (LPCVD) from dichlorosilane (SiH2Cl2, DCS) and ammonia (NH3) mixtures has been performed. From TEM analysis, it was found that the excess Si forms nanocrystals the size of which depends on the temperature. The real and the imaginary part of the refractive index of the films were calculated using spectroscopic ellipsometry by fitting the ellipsometric data in the range 1000–250 nm using the Tauc–Lorentz model. It was found that the optical constants of the films mainly depend on their chemical composition which can be controlled by the DCS/NH3 flow ratio. Annealing at temperatures up to 1100 °C for 4 h does not considerably affect the refractive index of the films. Depending on their stoichiometry and the annealing conditions applied after growth, some of the films emitted light in the visible at room temperature. This was attributed to the quantum confinement of carriers in the Si nanocrystals contained in the films.