Integrated SOI rib waveguide using inductively coupled plasma reactive ion etching

To achieve the integration of self-alignment connection between single-mode fiber and rib waveguide in a silicon-on-insulator (SOI) wafer, a three-mask lithography process was used. Micrographs revealed uniform U-grooves and accurate self-alignment between the U-groove and the rib waveguide. An atomic force microscope with an ultrasharp tip was used to directly measure the endface profile of the SOI rib waveguide etched using inductively coupled plasma reactive ion etching (ICPRIE). The rms roughness of the SOI rib waveguide endface was compared with that of a conventional chemical mechanical polishing endface. As an attractive single layer antireflection coating on silicon substrate, HfO₂ film reduced the Fresnel reflection losses from 2.55 to 0.022 dB. After depositing HfO₂ films onto waveguide endfaces, the rms roughness difference between the two SOI rib waveguides was also investigated. The rms endface roughness was influenced by the highly directional waveguide endface etched by ICPRIE. The results indicated that the three-mask lithography ICPRIE process is easy, cost-effective, and acceptable in a mass production environment.