Method for fabrication of vertically coupled integrated optical structures
A manufacturing process is provided for fabrication of vertically coupled integrated photonic devices by projection lithographic technique. A multi-layered structure is formed which includes a pair of core waveguiding layers separated by a coupling interlayer and sandwiched between cladding layers. Prior to forming optical features in the core layers, alignment marks are etched completely through the whole multi-layered structure with the alignment marks being visible on both sides of the multi-layered structure to a conventional projection stepper. After the alignment marks are formed, a “bottom level” optical features are made through the bottom cladding layer, bottom core layer, and portion of intervening coupling layer. The formed sample is then bonded by a polymer to a carrier and a “top level” optical features are defined through the top cladding, top core layer, and portion of the intervening coupling layer.
1. A method for fabrication of vertically coupled integrated photonics devices, including the steps of:
(a) forming a multi-layered structure having first and second levels and comprising: at least a first and a second waveguiding core layers, a coupling layer disposed between said at least first and second waveguiding core layers, and first and second cladding layers sandwiching said waveguiding core layers therebetween;
(b) forming alignment marks extending substantially through said multi-layered structure at predetermined areas thereof,
(c) forming first features at said first level of said multi-layered structure, said first features extending through said first cladding, said first waveguiding core layer and partially through said coupling layer; and
(d) forming second features at said second level of said multi-layered structure, said second features extending through said second cladding, said second waveguiding core layer and partially through said coupling layer; whereby said first and second features are disposed at predetermined location with reference to said alignment marks identifiable at both said first and second levels of said multi-layered structure.
2. The method of claim 1 , wherein in said steps (c) and (d), said first and second features are defined by means of a projection lithography technique.
3. The method of claim 2 , wherein in either of said steps (c) and (d), said projection lithography technique comprising the steps of:
depositing a photoresist on the external surface of a respective one of said cladding layers,
exposing said photoresist through a projection stepper prealigned with respect to said alignment marks, and
patterning a respective one of said waveguiding core layers.
4. The method of claim 3 , further comprising the steps of:
patterning said respective waveguiding core layer by means of etching through said respective cladding layer, said respective waveguiding core layer, and through portion of said coupling layer.
5. The method of claim 1 , further comprising the steps of:
in said steps (c) and (d), penetrating into said coupling layer to a predetermined depth to leave a portion of said coupling layer separating first and second features defined in said first and second waveguiding core layers, respectively.
6. The method of claim 5 , wherein said portion of said coupling layer is thinner than 0.3 μm.
7. The method of claim 1 , further comprising the steps of:
forming said multi-layered structure on a surface of a substrate structure, said substrate structure comprising a substrate layer and a stop-etch layer positioned between said substrate layer and a respective one of said cladding layers.
8. The method of claim 7 , further comprising the steps of:
subsequent to the completion of said step (c), adhering said multi-layered structure to a carrier structure in a predetermined alignment therewith with said first features extending towards said carrier structure.
9. The method of claim 8 , wherein in the step of adhering, said multi-layered structure is adhered to said carrier by a low temperature polymer bonding.
10. The method of claim 9 , wherein in said low temperature polymer bonding, said polymer is benzocyclobutene polymer.
11. The method of claim 8 , further comprising the steps of:
(E) upon completion of said step (d), removing said substrate structure.
12. The method of claim 11 , further comprising the steps of:
performing said step (e) after completion of said step (b);
encapsulating said second level of said multi-layered structure into a polymer, and
removing said carrier.
13. The method of claim 7 , further comprising the steps of:
after said step (b), forming metal films on said stop-etch layer within said alignment marks.
14. A vertically coupled integrated photonics device, comprising:
a multi-layered structure including:
(a) at least a pair of waveguiding core layers independently patterned to define respectively first and second waveguiding features therein,
(b) a coupling layer spacing said first and second waveguiding features,
(c) a pair of cladding regions sandwiching said first and second waveguiding features therebetween,
(d) a pair of spaced alignment marks extending through at least one of said cladding layers, at least one of said waveguiding core layers, and at least partially through said coupling layer, said first and second waveguiding features being located with respect to said alignment marks for acurate positioning of one with respect to the other, and
(e) a polymer envelope encapsulating said multi-layered structure therewithin.
15. The vertically coupled integrated photonics device of claim 14 , wherein the thickness of said coupling layer is less than approximately 0.3 μm.
16. The vertically coupled integrated photonics device of claim 14 , wherein said first waveguiding features include at least one microring.
17. The vertically coupled integrated photonics device of claim 14 , wherein said device includes a single microring resonator add/drop filter.
18. The vertically coupled integrated photonics device of claim 14 , wherein said device includes a double microring resonator.
19. The vertically coupled integrated photonics device of claim 14 , wherein said device includes GaAs/AlGaAs materials systems.
20. The vertically coupled integrated photonics device of claim 14 , wherein said polymer envelope has a low refractive index in the range of 1.53-1.55.