Characterization of ‘ARE’ deposited silicon nitride films and their feasibility as antireflection coating

Silicon nitride films are deposited in presence of nitrogen gas plasma by ‘Activated Reactive Evaporation (ARE)’ process on silicon substrates maintained at room temperature. Silicon powder was evaporated by e-beam evaporation in the presence of nitrogen gas plasma excited by a radio frequency (RF) power source (13.56 MHz). Depositions were carried out at different RF plasma powers. The deposited films were characterized by X-ray diffraction, X-ray photoelectron and UV–Visible spectroscopy, scanning electron microscopy and ellipsometry techniques. The X-ray diffraction pattern reveals the polycrystalline nature of the films with characteristics of hexagonal structure. X-ray photoelectron spectroscopy showed formation of silicon-rich silicon nitride. Observation of the films under scanning electron microscope shows a smooth and pinhole-free surface. The film deposited at 70 W RF plasma power for 18-min deposition time showed the refractive index (‘η’ at λ = 632.8 nm) and the thickness (d) 1.98 and 68.5 nm, respectively. The minimum reflectivity R = 1.74% is obtained from UV–Visible spectroscopy at λ = 547 nm. For the condition of near quarter wavelength single layer antireflection coating the optical thickness of the layer was taken as a quarter wavelength d = λ/4η at the minimum reflectivity observed for the film. The above results show the feasibility of using ‘ARE’ silicon nitride as antireflection coating.