Abstract: A method for fabricating a photonic device is provided. The method includes forming an optical coupler and a waveguide structure connected to the optical coupler over a semiconductor substrate; forming a metal-dielectric stack over the optical coupler and the waveguide structure; etching a hole in the metal-dielectric stack and vertically overlapping the optical coupler; and forming a protection layer on a sidewall and a bottom of the hole.

Abstract: A method for fabricating a photonic device is provided. The method includes forming an optical coupler and a waveguide structure connected to the optical coupler over a semiconductor substrate; forming a metal-dielectric stack over the optical coupler and the waveguide structure; etching a hole in the metal-dielectric stack and vertically overlapping the optical coupler; and forming a protection layer on a sidewall and a bottom of the hole.

Abstract: A method for fabricating a photonic device is provided. The method includes patterning a semiconductor layer to form a waveguide structure, a semiconductor structure connected to the waveguide structure, and a dummy semiconductor structure disconnected from the waveguide structure and the semiconductor structure; epitaxially growing an epitaxial semiconductor feature over the semiconductor structure and a dummy epitaxial semiconductor feature over the dummy semiconductor structure; depositing a first capping film over the epitaxial semiconductor feature and the dummy epitaxial semiconductor feature; depositing a second capping film over the first capping film, wherein an oxide concentration of the second capping film is greater than an oxide concentration of the first capping film; and patterning the first and second capping films to form at least a dummy composite capping layer over the dummy epitaxial semiconductor feature.