REFERENCE MARKERS ADJACENT TO A CAVITY IN A PHOTONICS CHIP

Structures including a cavity adjacent to an edge coupler and methods of forming such structures. The structure comprises a semiconductor substrate including a cavity with a sidewall, a dielectric layer on the semiconductor substrate, and an edge coupler on the dielectric layer. The structure further comprises a fill region including a plurality of fill features adjacent to the edge coupler. The fill region includes a reference marker at least partially surrounded by the plurality of fill features, and the reference marker has a perimeter that surrounds a surface area of the dielectric layer, and the surface area overlaps with a portion of the sidewall of the cavity.