Refractive index and thickness analysis of planar interfaces by prism coupling technique

Since 2022, various foundries are offering the manufacture of integrated photonic structures for the visible spectrum. As this technology continues to enter the market, there will be an increasing demand for accurate optical and dimensional characterization of these structures. To meet this demand, we have developed a highly precise optical characterization system based on the prism coupling technique, also known as m-lines spectroscopy, to investigate the optical properties of hydrogenated amorphous silicon nitride planar waveguides deposited by plasma-enhanced chemical vapor deposition. In this work, by combining visible spectroscopy with the prism coupling technique to excite modes that propagate resonantly in the waveguide via frustrated total internal reflection, using either parallel or perpendicularly polarized light beams, we were able to analyze the waveguide properties of silicon nitride thin films with an interfacial oxide layer. Furthermore, through numerical simulation of the bilayer structure, we calculate the waveguide's refractive index and thickness, and determine the characteristics of the interfaces in terms of refractive index and thickness.