Packages with photonic engines and method of forming the same

A method comprising:

• patterning a top silicon layer in a substrate to form a plurality of photonic devices, wherein the substrate comprises the top silicon layer, a first dielectric layer under the top silicon layer, and a semiconductor layer under the first dielectric layer;
• forming a second dielectric layer to embed the plurality of photonic devices therein;
• forming an interconnect structure over and signally coupled to the plurality of photonic devices;
• bonding an electronic die to the interconnect structure;
• thinning the semiconductor layer;
• patterning the semiconductor layer that has been thinned to form openings;
• forming a reflector in one of the openings in the semiconductor layer, wherein the reflector is configured to reflect an optical signal received by the reflector to an edge coupler adjacent to the reflector;
• filling the openings with a dielectric material to form dielectric regions;
• and
• forming through-vias penetrating through the dielectric regions to electrically couple to the interconnect structure.

A method comprising:

• patterning a top silicon layer in a substrate to form a plurality of photonic devices, wherein the substrate comprises the top silicon layer, a first dielectric layer under the top silicon layer, and a semiconductor layer under the first dielectric layer;
• forming a second dielectric layer to embed the plurality of photonic devices therein;
• forming an interconnect structure over and signally coupled to the plurality of photonic devices;
• bonding an electronic die to the interconnect structure;
• thinning the semiconductor layer;
• patterning the semiconductor layer that has been thinned to form openings;
• filling the openings with a dielectric material to form dielectric regions;
• and
• forming through-vias penetrating through the dielectric regions to electrically couple to the interconnect structure, wherein at a time after the through-vias are formed, a portion of the semiconductor layer remains.