Gap-fill and bond film interface opening in optical applications

A method comprising:

• forming a photonic die comprising a grating coupler;
• replacing portions of a plurality of dielectric layers with a transparent region that overlaps the grating coupler;
• bonding an electronic die to the photonic die;
• depositing a dielectric barrier comprising a first portion over the electronic die, and a second portion over the photonic die;
• etching the second portion of the dielectric barrier to form an opening in the second portion, wherein the opening is vertically aligned to the grating coupler;
• forming a gap-fill region, wherein the gap-fill region fills the opening;
• and
• planarizing the gap-fill region.

A method comprising:

• forming a photonic die comprising:
• forming a grating coupler;
• forming a plurality of dielectric layers over the grating coupler;
• etching the plurality of dielectric layers to form a first opening, wherein the etching is stopped at a position higher than and spaced apart from the grating coupler;
• and
• forming a transparent region in the opening;
• depositing a barrier layer over and contacting the photonic die;
• etching the barrier layer to form a second opening vertically aligned to the transparent region and the grating coupler;
• and
• forming a gap-fill region filling the second opening, wherein the gap-fill region comprises a transparent material.