Optimization of SiON/SiOx structures fabrication process for optical waveguides

Abstract

We have investigated the deposition and etching process of silicon oxynitride (SiON) films for optical waveguides on silicon wafer. SiON films were deposited using plasma-enhanced chemical vapor deposition (PECVD) system. Thickness, uniformity and refractive index was measured by micro-spot spectroscopic reflectometry and confirmed by ellipsometry. Aluminum (Al) mask was fabricated for etching purpose using lift-off process. SiON films were etched in low pressure inductively coupled plasma - reactive ion etching (ICP-RIE) chamber using CF4 gas. The effect of oxygen (O2) flow rate and source power on etch rate and profile of SiON waveguide was investigated. Scanning electron microscope (SEM) has been used to study the overall structure quality of SiON optical waveguide core. Deposition of SiOx cladding layer was also investigated. SiOx cladding layer was deposited using PECVD system. We investigated the impact of total gas flow rate, N2O/SiH4 ratio and power on the refractive index, growth rate, and uniformity of thickness of the deposited SiOx layer. Micro-trenching occurred in all cases, and their variation was explained by combination of variations in the plasma density and profile angles. The SiO2 cladding layer deposited with N2O/SiH4 ratio of 8,353, total gas flow rate of 1000 sccm and power P = 100W yielded the best results in terms of refractive index.