Method for fabricating a photonic chip
The fabrication of a first waveguide made of stoichiometric silicon nitride, of a second waveguide made of crystalline semiconductor material and of at least one active component optically coupled to the first waveguide via the second waveguide. The method includes: a) the formation of an aperture which passes through an encapsulation layer of the first waveguide and emerges in or on a substrate made of monocrystalline silicon, then b) the deposition by epitaxial growth of a crystalline seeding material inside the aperture until this crystalline seeding material forms a crystalline seed on a top face of the encapsulation layer, then c) a lateral epitaxy, of a crystalline semiconductor material from the crystalline seed formed to form a layer made of crystalline semiconductor material wherein the second waveguide is then produced.
1. A method for fabricating a photonic chip comprising a first waveguide made of stoichiometric silicon nitride, a second waveguide made of crystalline semiconductor material and at least one active component optically coupled to the first waveguide via the second waveguide, said method comprising:
providing a substrate made of monocrystalline silicon on which is deposited a layer made of dielectric material, said substrate extending primarily in a plane called “plane of the substrate”, then
vapour depositing, on the layer made of dielectric material, a layer of stoichiometric silicon nitride followed by an annealing at a temperature of between 1000° C. and 1400° C., then
producing the first waveguide in said deposited and annealed layer of stoichiometric silicon nitride, then
encapsulating the first waveguide in a dielectric material to obtain an encapsulation layer wherein the first waveguide is encapsulated, said encapsulation layer having a top face on the side opposite the substrate, then
creating a layer made of crystalline semiconductor material directly on the top face of the encapsulation layer, then
producing the second waveguide in said layer made of crystalline semiconductor material, said second waveguide being optically coupled to the first waveguide by an evanescent coupling, then
producing the active optical component, said active optical component being connected optically to the first waveguide via the second waveguide, then
producing electrical ports to electrically connect the active optical component to an electrical power source,
wherein the creating of the layer made of crystalline semiconductor material comprises the following operations:
a) forming an aperture which passes through the encapsulation layer and emerges in or on the substrate, then
b) depositing by epitaxial growth of a crystalline seeding material inside the aperture until said crystalline seeding material reaches the top face and forms a crystalline seed on said top face, said crystalline seeding material having mesh parameters that are identical, to within plus or minus 5%, to those of the crystalline semiconductor material, then
c) a lateral epitaxy, of the same crystalline semiconductor material as that wherein the second waveguide is produced, from the crystalline seed formed to form the layer made of crystalline semiconductor material wherein the second waveguide is then produced.
2. The method according to claim 1 , wherein, before the creating of the layer made of crystalline semiconductor material, the method comprises structuring the top face to form, in said top face, a hollow recess having a bottom parallel to the plane of the substrate and walls at rights angle to the bottom, then, during the creating of the layer made of crystalline semiconductor material:
the aperture is formed in the bottom of the hollow recess, then
the lateral epitaxy completely fills said hollow recess.
3. The method according to claim 1 , wherein the lateral epitaxy comprises:
depositing a layer made of amorphous semiconductor material on the crystalline seed formed on the top face, then
an annealing at a temperature suitable for provoking the crystallization of the amorphous semiconductor material from the crystalline seed.
4. The method according to claim 3 , wherein the aperture is a trench with a length two times greater than its width.
5. The method according to claim 1 , wherein the lateral epitaxy consists in directly depositing the crystalline semiconductor material on the top face by epitaxial growth from the crystalline seed formed on said top face.
6. The method according to claim 5 , wherein the aperture is a trench with a length two times greater than its width.
7. The method according to claim 1 , wherein:
during the producing of the first waveguide, said first waveguide is produced between a first lower plane and a first upper plane, these first planes being parallel to the plane of the substrate,
during the producing of the second waveguide, said second waveguide is produced between a second lower plane and a second upper plane, these second planes being parallel to the plane of the substrate and both situated above the first planes in a direction at right angles to the plane of the substrate.
8. The method according to claim 1 , wherein the crystalline seeding material is monocrystalline silicon.
9. The method according to claim 1 , wherein the crystalline semiconductor material is chosen from the group composed of:
silicon,
germanium,
SiGe alloy, and
a III-V material.
10. The method according to claim 9 , wherein the method comprises:
executing the operations a) to c) to create a first layer made of crystalline semiconductor material, and
executing the operations a) to c) to create a second layer made of crystalline semiconductor material, said second layer made of crystalline semiconductor material being produced in a crystalline semiconductor material different from that of the first layer, then
producing the second waveguide in the first layer made of crystalline semiconductor material and the production of a third waveguide in the second layer made of semiconductor material.
11. The method according to claim 1 , wherein:
the crystalline seeding material deposited inside the aperture by epitaxial growth is different from the crystalline silicon, and
the width of the aperture is adapted to trap, inside said aperture, the majority of the defects of the crystalline seeding material thus deposited by epitaxial growth.
12. The method according to claim 1 , wherein the vapour deposition of the layer of stoichiometric silicon nitride is performed under a pressure lower than 300 mTorr (39 996 mPa).
13. A photonic chip obtained by a fabrication method according to claim 1 , said photonic chip comprising:
a substrate made of monocrystalline silicon extending primarily in a plane called “plane of the substrate”,
a first waveguide made of stoichiometric silicon nitride exhibiting propagation losses of less than 4 dB/m for wavelengths of between 1530 nm and 1565 nm, the core of said first waveguide extending, in a direction at right angles to the plane of the substrate, from a first lower plane to a first upper plane, these first planes being parallel to the plane of the substrate and the first lower plane being the plane closest to the substrate,
a second waveguide made of crystalline semiconductor material optically coupled to the first waveguide by an evanescent coupling, the core of said second waveguide extending, in the direction at right angles to the plane of the substrate, from a second lower plane to a second upper plane, these second planes being parallel to the plane of the substrate and the second lower plane being the plane closest to the substrate, and
at least one active component optically coupled to the first waveguide via the second waveguide, said active component comprising electrical ports suitable for electrically connecting it to an electrical power source,
wherein the photonic chip comprises a stud which extends from the substrate made of monocrystalline silicon to the second lower plane, said stud being produced in a crystalline seeding material which forms a crystalline seed on the second lower plane, said crystalline seeding material having mesh parameters identical, to within plus or minus 5%, to those of the crystalline semiconductor material of the second waveguide.
14. The photonic chip according to claim 13 , wherein the second lower plane is situated above the first upper plane.
15. The photonic chip according to claim 13 , wherein the height of the stud made of crystalline seeding material is greater than 4 μm.