US-12619026-B2 - Waveguide escalators for a photonics chip

Abstract

Structures for a waveguide escalator, as well as methods of forming such structures. The structure comprises a first waveguide core on a substrate, a second waveguide core, and a back-end-of-line stack including a third waveguide core disposed between the first waveguide core and the second waveguide core. The third waveguide core comprises a layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer. The first layer and the second layer comprise a first dielectric material with a first refractive index, and the third layer comprises a second dielectric material with a second refractive index that is less than the first refractive index.

Inventors

• Avijit Chatterjee
• Ravi Prakash Srivastava
• Yusheng Bian
• Sujith Chandran
• Aneesh Dash
• Michal RAKOWSKI
• Riddhi Nandi
• Kenneth J. Giewont
• Theodore Letavic
• Mehrdad Djavid

Assignees

• GLOBALFOUNDRIES U.S. INC.

Dates

Publication Date

20260505

Application Date

20231220

Claims (20)

1. 1 . A structure comprising: a first substrate; a first waveguide core on the first substrate; a second waveguide core; a back-end-of-line stack including a third waveguide core disposed between the first waveguide core and the second waveguide core, the third waveguide core comprises a first layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer comprising a first dielectric material with a first refractive index, and the third layer comprising a second dielectric material with a second refractive index that is less than the first refractive index; and a fourth waveguide core on the first substrate, wherein the back-end-of-line stack includes a fifth waveguide core that is disposed between the second waveguide core and the fourth waveguide core, the fifth waveguide core comprises a second layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer of the second layer stack comprise the first dielectric material, and the third layer of the second layer stack comprises the second dielectric material.
2. 2 . The structure of claim 1 wherein the first layer and the second layer comprise nitrogen-doped silicon carbide or nitrogen-doped hydrogenated silicon carbide.
3. 3 . The structure of claim 1 wherein the first dielectric material of the first layer has a different composition than the second dielectric material of the second layer.
4. 4 . The structure of claim 1 wherein the second waveguide core includes a section that partially overlaps with the first layer stack.
5. 5 . The structure of claim 1 wherein the second waveguide core includes a section that fully overlaps with the first layer stack.
6. 6 . The structure of claim 1 wherein the first layer stack includes a fourth layer and a fifth layer between the second layer and the fourth layer, the fourth layer comprises the first dielectric material, and the fifth layer comprises the second dielectric material.
7. 7 . The structure of claim 1 wherein the back-end-of-line stack includes a dielectric layer, and the third waveguide core is embedded in the dielectric layer.
8. 8 . The structure of claim 7 wherein the dielectric layer comprises a third dielectric material having a different refractive index from the second dielectric material.
9. 9 . The structure of claim 8 wherein the third dielectric material has a different composition from the second dielectric material.
10. 10 . The structure of claim 7 wherein the dielectric layer comprises the second dielectric material.
11. 11 . The structure of claim 1 wherein the second waveguide core includes a first section that partially overlaps with the first layer stack and a second section that partially overlaps with the second layer stack.
12. 12 . The structure of claim 1 wherein the second waveguide core includes a first section that fully overlaps with the first layer stack and a second section that fully overlaps with the second layer stack.
13. 13 . The structure of claim 1 wherein the second waveguide core includes a first section that overlaps with the first layer stack and a second section that overlaps with the second layer stack, and further comprising: a sixth waveguide core disposed in a gap between the first layer stack and the second layer stack, wherein the second waveguide core includes a third section that connects the first section to the second section, and the third section of the second waveguide core bridges across the gap above the sixth waveguide core.
14. 14 . The structure of claim 13 wherein the sixth waveguide core is aligned orthogonal to the first waveguide core and the fourth waveguide core.
15. 15 . The structure of claim 1 further comprising: a second substrate, wherein the second waveguide core is disposed on the second substrate.
16. 16 . The structure of claim 15 further comprising: a first dielectric layer; and a second dielectric layer, wherein the second substrate is bonded to the first substrate along a bonding interface between the first dielectric layer and the second dielectric layer.
17. 17 . The structure of claim 16 wherein the bonding interface is disposed between the first layer stack and the second waveguide core.
18. 18 . The structure of claim 1 wherein the second waveguide core comprises silicon nitride.
19. 19 . A structure comprising: a substrate; a first waveguide core on the substrate; a second waveguide core; and a back-end-of-line stack including a third waveguide core disposed between the first waveguide core and the second waveguide core, the third waveguide core comprises a first layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer comprising a first dielectric material with a first refractive index, and the third layer comprising a second dielectric material with a second refractive index that is less than the first refractive index, wherein the third waveguide core comprises a second layer stack that is laterally and vertically offset from the first layer stack, the second layer stack includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer of the second layer stack comprise the first dielectric material, and the third layer of the second layer stack comprises the second dielectric material.
20. 20 . A method comprising: forming a first waveguide core on a substrate; forming a second waveguide core; forming a back-end-of-line stack that includes a third waveguide core disposed between the first waveguide core and the second waveguide core; and forming a fourth waveguide core on the substrate, wherein the third waveguide core comprises a layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer comprise a first dielectric material with a first refractive index, the third layer comprises a second dielectric material with a second refractive index that is less than the first refractive index, the back-end-of-line stack includes a fifth waveguide core that is disposed between the second waveguide core and the fourth waveguide core, the fifth waveguide core comprises a second layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer, the first layer and the second layer of the second layer stack comprise the first dielectric material, and the third layer of the second layer stack comprises the second dielectric material.

Description

BACKGROUND The disclosure relates to photonics chips and, more specifically, to structures for a waveguide escalator, as well as methods of forming such structures. Photonics chips are used in many applications and systems including, but not limited to, data communication systems and data computation systems. A photonics chip includes a photonic integrated circuit comprised of photonic components, such as modulators, polarizers, and optical couplers, that are used to manipulate light received from a light source, such as an optical fiber or a laser. A waveguide crossing array may include waveguide core crossings that are arranged on a photonics chip. For example, the waveguide crossing array may include waveguide cores in a lower level, and waveguide cores in an upper level that are routed over and across the waveguide cores in the lower level. Direct crossings of waveguide cores may result in adverse consequences, such as high insertion loss and crosstalk, due to strong light scattering induced by the close local proximity of the waveguide cores in the upper and lower levels. Conventional waveguide crossings are unable to avoid the occurrence of these negative consequences. Improved structures for a waveguide escalator, as well as methods of forming such structures, are needed. SUMMARY In an embodiment of the invention, a structure comprises a first waveguide core on a substrate, a second waveguide core, and a back-end-of-line stack including a third waveguide core disposed between the first waveguide core and the second waveguide core. The third waveguide core comprises a layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer. The first layer and the second layer comprise a first dielectric material with a first refractive index, and the third layer comprises a second dielectric material with a second refractive index that is less than the first refractive index. In an embodiment of the invention, a method comprises forming a first waveguide core on a substrate, forming a second waveguide core, and forming a back-end-of-line stack that includes a third waveguide core disposed between the first waveguide core and the second waveguide core. The third waveguide core comprises a layer stack that includes a first layer, a second layer, and a third layer between the first layer and the second layer. The first layer and the second layer comprise a first dielectric material with a first refractive index, and the third layer comprises a second dielectric material with a second refractive index that is less than the first refractive index. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the embodiments of the invention. In the drawings, like reference numerals refer to like features in the various views. FIG. 1 is a cross-sectional view of a structure at an initial fabrication stage of a processing method in accordance with embodiments of the invention. FIG. 2 is a cross-sectional view of the structure at a fabrication stage of the processing method subsequent to FIG. 1. FIG. 3 is a top view of a structure at an initial fabrication stage of a processing method in accordance with embodiments of the invention. FIG. 3A is a cross-sectional view taken generally along line 3A-3A in FIG. 3. FIG. 4 is a top view of the structure at a fabrication stage of the processing method subsequent to FIGS. 3, 3A. FIG. 4A is a cross-sectional view taken generally along line 4A-4A in FIG. 4. FIG. 5 is a top view of the structure at a fabrication stage of the processing method subsequent to FIGS. 4, 4A and in which overlying layers are omitted for purposes of illustration. FIG. 5A is a cross-sectional view taken generally along line 5A-5A in FIG. 5. FIG. 6 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 7 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 8 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 9 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 10 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 11 is a cross-sectional view of a structure in accordance with alternative embodiments of the invention. FIG. 12 is a top view of a structure in accordance with alternative embodiments of the invention. FIG. 13 is a top view of a structure in accordance with alternative embodiments of the invention. DETAILED DESCRIPTION With reference to FIG. 1 and in accordance with embodiments of the invention, a structure 10