Sputtered silicon oxynitride for microphotonics : a materials study

Abstract

Silicon oxynitride (SiON) is an ideal waveguide material because the SiON materials system provides substantial flexibility in composition and refractive index. SiON can be varied in index from that of silicon dioxide (n=1.46) to that of silicon-rich silicon nitride (n-2.3). This flexibility in refractive index allows for the optimization of device performance by allowing trade-offs between the advantages of low-index contrast systems (low scattering losses and easy fiber-to-waveguide coupling) and the benefits of high-index-contrast systems (small waveguide size and tight bending radii). This work presents sputter processing as an alternative to traditional CVD processing. Two room-temperature SiON sputter processes are explored. The first process is a co- sputtered deposition from a silicon oxide and a silicon nitride target. The second is a reactive sputtering process from a silicon nitride target in an oxygen ambient. Silicon nitride sputtered from a silicon nitride target is also investigated. Models are provided that predict the index and composition in both the reactive and co- sputtered depositions. The cosputtered deposition is shown to follow a mixture model, while the reactive sputter deposition is shown to be either Si-flux limited or O-flux limited, depending on the partial pressure of oxygen in the reaction chamber and the power applied to the silicon nitride target. A materials study is provided that shows sputtered SiON to be a homogeneous material that gives good control of refractive index. Reactively sputtered SiON is shown to be Si-rich. These sputtered materials investigated for use in waveguides and in Er-doped waveguide amplifiers.

(cont.) Low loss waveguides are demonstrated for both co-sputtered and reactively sputtered depositions. Losses below 1 dB/cm are shown for co-sputtered deposition (n=1.65). Photoluminescence of Er-doped material shows lifetimes comparable to commercial EDFA material for both co-sputtered SiON and sputtered silicon dioxide.