Enlarged multilayer nitride waveguide for photonic integrated circuit

A structure, comprising:

• a semiconductor-on-insulator (SOI) substrate including a semiconductor-on-insulator (SOI) layer over a buried insulator layer over a semiconductor substrate;
• an inter-level dielectric (ILD) layer over the SOI substrate;
• a first multilayer nitride waveguide positioned in the ILD layer in a first region of the SOI substrate, the first multilayer nitride waveguide including a first nitride body, and a first cladding layer on at least a lower surface of the first nitride body, wherein the first cladding layer has a lower refractive index than the first nitride body;
• and
• a second multilayer nitride waveguide in the ILD layer in the first region of the SOI substrate, wherein the first and second multilayer nitride waveguides are optically side-coupled to one another, the second multilayer nitride waveguide including a second nitride body, and the first cladding layer on at least a lower surface of the second nitride body, wherein the first cladding layer has a lower refractive index than the second nitride body.

A method of forming a waveguide structure, the method comprising:

• forming a trench through an inter-level dielectric (ILD) layer in a first region of a substrate under the ILD layer;
• forming a first cladding layer and a nitride layer over the first cladding layer within the trench and over the ILD layer;
• planarizing an upper surface of the nitride layer, wherein the upper surface of the nitride layer remains within the ILD layer;
• and
• forming a first multilayer nitride waveguide by patterning the first cladding layer and the nitride layer within the trench to form a first nitride body having the first cladding layer thereunder,
• wherein the first cladding layer has a lower refractive index than the first nitride body.