Photonic device

A photonic device, comprising:

• a semiconductor substrate;
• an optical coupler over the semiconductor substrate;
• a waveguide structure over the semiconductor substrate and laterally connected to the optical coupler;
• and
• a metal-dielectric stack over the optical coupler and the waveguide structure, wherein the metal-dielectric stack has a hole above the optical coupler, wherein a portion of the metal-dielectric stack below the hole has a convex top surface, wherein the convex top surface of the metal-dielectric stack is laterally aligned with a bottommost one of a plurality of metal layers of the metal-dielectric stack.

A photonic device, comprising:

• a semiconductor substrate;
• an optical coupler over the semiconductor substrate;
• a waveguide structure over the semiconductor substrate and laterally connected to the optical coupler;
• an interlayer dielectric layer over the optical coupler and the waveguide structure;
• a metal-dielectric stack over the interlayer dielectric layer, wherein the metal-dielectric stack has a hole above the optical coupler;
• and
• a protection layer extending in the interlayer dielectric layer and directly above the optical coupler, wherein the protection layer comprises a side portion in contact with a sidewall of the interlayer dielectric layer and a bottom portion extending laterally from a bottom end of the side portion of the protection layer and in contact with the interlayer dielectric layer, wherein the protection layer and the interlayer dielectric layer comprise a same material.