ABSTRACT
This work presents a "half-etch" horizontal slot waveguide design based on SiN, where only the upper SiN layer is etched to form a strip that confines the mode laterally. The numerical modeling, fabrication, and characterization of passive waveguiding components are described. This novel slot waveguide structure was designed with on-chip light amplification in mind, for example with an Er-doped oxide spacer layer. Proof-of-concept racetrack resonators were fabricated and characterized, showing quality factors up to 50,000 at critical coupling and residual losses of 4â dB/cm at wavelengths away from the N-H bond absorption peak in SiN, demonstrating the high potential of these horizontal slot waveguides for use in active integrated photonics.
ABSTRACT
Silicon nitride is used for many technological applications, but a quantitative knowledge of its surface chemistry is still lacking. Native oxynitride at the surface is generally removed using fluorinated etchants, but the chemical composition of surfaces still needs to be determined. In this work, the thinning (etching efficiency) of the layers after treatments in HF and NH4F solutions has been followed by using spectroscopic ellipsometry. A quantitative estimation of the chemical bonds found on the surface is obtained by a combination of infrared absorption spectroscopy in ATR mode, X-ray photoelectron spectroscopy, and colorimetry. Si-F bonds are the majority species present at the surface after silicon nitride etching; some Si-OH and a few Si-NHx bonds are also present. No Si-H bonds are present, an unfavorable feature for surface functionalization in view of the interest of such mildly reactive groups for achieving stable covalent grafting. Mechanisms are described to support the experimental results, and two methods are proposed for generating surface SiH species: enriching the material in silicon, or submitting the etched surface to a H2 plasma treatment.