Low loss optical waveguides fabricated by thermal nitridation of oxidized silicon

This letter describes the first optical waveguides fabricated by thermal nitridation of SiO2. This process has allowed us to create layers of silicon oxynitride of about 100‐nm thickness in 4.8‐μm‐thick silicon dioxide layers by exposing thermally oxidized silicon wafers to an ammonia atmosphere for times ranging from one to ten days. Ellipsometric measurements show that the refractive indices of the nitrided layers range from 1.67 to 1.75. Losses for nine optical waveguide samples fabricated with this process range from 0.06 to 0.31 dB/cm.