Optimal control on composition and optical properties of silicon oxynitride thin films

Abstract

The desire to merge the most advantageous physical and chemical properties of both SiO2 and Si3N4 in an optimum combination tailored to various applications in electrical, optical, and optoelectronic thin films has pushed a continuous interest in the processing of SiOxNy thin films. Inhomogeneous thin film filters have had an increasing importance in the industry as optical filters. Silicon oxynitride, SiOxNy, is a very interesting material for multiple applications, including graded refractive index films. The refractive index can be changed from pure silicon dioxide (1.47) to silicon nitride (2.4) by just varying the film composition. We report the growth of SiOxNy films by reactive laser ablation using two different solid targets, Si3N4 and Si, in the ambient of N2 and O2 at various pressures, introduced separately in the growth chamber, as the film is monitored by real time ellipsometry. The oxidation rate in the films is studied for both targets. The composition of the films is in situ determined by Auger-electron spectroscopy and x-ray photoemission spectroscopy. The evolution of the chemical bonding of the species in the film is done by Fourier transform infrared. The SiOxNy film stoichiometry, bonding character, and optical properties are compared as a function of O2 pressure while N2 pressure is maintained fixed as either the Si3N4 or Si target is ablated.