Structure for hybrid multilevel edge couplers and method for forming such a structure

Abstract

Structure for an edge coupler (10), the structure comprising: a first dielectric layer (24) having an edge (25); a first waveguide core region (18) on the first dielectric layer (24), the first waveguide core region (18) having an end face (28) and the first waveguide core region (18) being conical in the longitudinal direction towards the end face (28); a plurality of segments (12) on the first dielectric layer (24), the plurality of segments (12) being arranged between the first waveguide core region (18) and the edge (25) of the first dielectric layer (24); a waveguide core (32) having a first portion (34) disposed over the first waveguide core region (18) in an overlapping arrangement, the waveguide core (32) having an end face (38) and the first portion (34) being conical in the longitudinal direction toward the end face (38); a back-end-of-line stack (42) over the waveguide core (32); and a second dielectric layer (44) having an interface (43) with the back-end-of-line stack (42), the second dielectric layer (44) extending from the interface (43) to the edge (25) of the first dielectric layer (24), wherein the end surface (38) of the waveguide core (32) extends over the same distance as the interface (43).

Description

background

[0001] The present invention relates to photonic chips and, more particularly, to structures having an edge coupler and to methods for fabricating a structure having an edge coupler.

[0002] Photonic chips are used in many applications and systems, including data communication systems and data processing systems. A photonic chip integrates optical components, such as waveguides, optical switches, edge couplers, and polarizers, and electronic components, such as field-effect transistors, into a unified platform. Integrating both types of components can reduce layout area, cost, and operating overhead, among other benefits.

[0003] Typically, an edge coupler, also called a spot-size coupler, is used to couple light of a specific mode from an optical fiber to optical components on the photonic chip. The edge coupler may comprise a section of waveguide core defining an inverse cone adjacent to the edge of the photonic chip. According to the direction of propagation of the modes, an inverse cone refers to a conical section of a waveguide core characterized by a gradual increase in width along the direction of propagation of the modes. In the edge coupler design, the narrow end of the inverse cone is located at the top of the inverse cone near the optical fiber, and the wide end of the inverse cone is connected to another section of the waveguide core, which guides the light away from the edge coupler and toward optical components of the photonic chip.

[0004] The gradually changing cross-sectional area of ​​an inverse cone supports mode conversion and the variation in mode size associated with mode conversion as light is transmitted from the optical fiber to the photonic chip. The narrow end at the tip of the inverse cone is unable to fully confine the incident mode received by the optical fiber because the cross-sectional area of ​​the tip at its narrow end is smaller than the mode size. Consequently, a significant percentage of the electromagnetic field of the incident mode is distributed around the tip of the inverse cone. As the width increases, the inverse cone can support the entire incident mode and confine the electromagnetic field within the inverse cone.

[0005] Silicon-based edge couplers can experience power-dependent losses due to nonlinear mechanisms inherent in the silicon material. Furthermore, silicon-based edge couplers can be susceptible to irreversible damage at high optical input powers due to a combination of increased optical energy density and a change in thermal transfer away from the light path as the inverse taper widens. The inverse taper of the edge coupler can be the most vulnerable part of the edge coupler, which can be irreversibly damaged.

[0006] Improved edge coupler structures and methods for fabricating a structure with an edge coupler are needed.

[0007] The document US 2019 / 0 384 003 A1 relates to a spot size converter comprising a first part of a waveguide structure for coupling to a first waveguide to receive or transmit light from or to the first waveguide in a first propagation mode, the first part of the waveguide structure having a lower waveguide structure with a varying effective refractive index that decreases away from the first waveguide;and a second portion of the waveguide structure for coupling to a second waveguide to transmit light in a second propagation mode or to receive light from the second waveguide, the second portion of the waveguide structure comprising an upper waveguide structure having a plurality of high refractive index elements disposed therein, an overlap region between the first portion and the second portion, the first propagation mode progressively converting to the second propagation mode in the overlap region;

[0008] Document US 10 429 582 B1 relates to coupling elements between waveguides. A first waveguide is coupled to a first waveguide taper element, and a second waveguide is coupled to a second waveguide taper element. The first waveguide and the first waveguide taper element are made of silicon, and the second waveguide and the second waveguide taper element are made of silicon nitride. The second waveguide and the second waveguide taper element are arranged vertically above the first waveguide and the first waveguide taper element.

[0009] Document DE 10 2019 117 173 A1 relates to a photonic semiconductor component comprising a plurality of oxide layers over a substrate, a plurality of first waveguides, and a plurality of second waveguides in the oxide layers, wherein the first waveguides are optically coupled to the second waveguides, and wherein the first waveguides comprise silicon and the second waveguides comprise silicon nitride. Furthermore, a routing structure is provided over at least a portion of a first waveguide of the plurality of first waveguides, wherein the routing structure comprises a plurality of insulating layers and conductive structural elements in the insulating layers. Summary

[0010] In one embodiment of the invention, a structure for an edge coupler is provided. The structure comprises a dielectric layer having an edge, a waveguide core region on the dielectric layer, and a plurality of segments on the dielectric layer. The waveguide core region has an end face, and the waveguide core region is tapered longitudinally toward the end face. The plurality of segments are arranged between the waveguide core region and the edge of the dielectric layer. The structure further comprises a waveguide core having a portion disposed over the waveguide core region in an overlapping arrangement. The waveguide core has an end face, and the portion of the waveguide core is tapered longitudinally toward the end face.The structure further comprises a back-end-of-line stack over the waveguide core and a second dielectric layer having an interface with the back-end-of-line stack, the second dielectric layer extending from the interface to the edge of the first dielectric layer, the end face of the waveguide core extending the same distance as the interface.

[0011] In one embodiment of the invention, a method for forming a structure for an edge coupler is provided. The method comprises forming a waveguide core region on a dielectric layer, forming a plurality of segments on the dielectric layer, and forming a waveguide core having a portion disposed over the waveguide core region in an overlapping arrangement. The plurality of segments are disposed between the waveguide core region and an edge of the dielectric layer. The waveguide core region has an end face, and the waveguide core region is tapered longitudinally toward the end face. The waveguide core has an end face, and the portion is tapered longitudinally toward the end face.The method further comprises forming a back-end-of-line stack over the waveguide core; removing a first portion of the back-end-of-line stack; and forming a second dielectric layer having an interface with a second portion of the back-end-of-line stack, wherein the second dielectric layer extends from the interface to the edge of the first dielectric layer (24) and the end face of the waveguide core has the same extent as the interface. Short description of the drawings

[0012] The accompanying drawings, which are incorporated in this specification, illustrate various embodiments of the invention and, together with the general description of the invention above and the detailed description of the embodiments below, serve to explain embodiments of the invention. In the drawings, like reference numerals refer to like features throughout the several views. Fig. 1 is a plan view of a structure in a first manufacturing phase of a method according to embodiments of the invention. Fig. Figure 2 is a cross-sectional view of the structure taken generally along line 2-2 in Fig. 1 runs. Fig. Figure 2A is a cross-sectional view of the structure taken generally along line 2A-2A in Fig. 1 runs. Fig. Figure 2B is a cross-sectional view of the structure taken generally along line 2B-2B in Fig. 1 runs. Fig. 3 is a plan view of the structure in a manufacturing phase of the processing method according to Fig. 1. Fig. Figure 4 is a cross-sectional view of the structure taken generally along line 4-4 in Fig. 5 runs. Fig. Figure 4A is a cross-sectional view of the structure taken generally along line 4A-4A in Fig. 3 runs. Fig. Figure 4B is a cross-sectional view of the structure taken generally along line 4B-4B in Fig. 3 runs. Fig. 5 is a plan view of the structure in a manufacturing phase of the processing method according to Fig. 3. Fig. Figure 6 is a cross-sectional view of the structure taken generally along line 6-6 in Fig. 5 runs. Fig. Figure 6A is a cross-sectional view of the structure taken generally along line 6A-6A in Fig. 5 runs. Fig. Figure 6B is a cross-sectional view of the structure taken generally along line 6B-6B in Fig. 5 runs. Fig. 7 is a plan view of a structure according to alternative embodiments of the invention. Fig. 8 is a plan view of a structure according to alternative embodiments of the invention. Description

[0013] With reference to the Fig. 1, Fig. 2, Fig. 2A, Fig. 2B and according to embodiments of the invention, a structure 10 for an edge coupler includes a plurality of segments 12, a plurality of segments 14, and a waveguide core region 16 overlaid with the segments 14, as well as a conical waveguide core region 18 adjacent to the segments 14 and the waveguide core region 16. The segments 12, the segments 14, the waveguide core region 16, and the conical waveguide core region 18 may be arranged longitudinally aligned along a longitudinal axis 21. The segments 14 and the waveguide core region 16 are arranged longitudinally between the segments 12 and the conical waveguide core region 18.

[0014] Laser light can be directed onto structure 10 from an optical fiber (not shown). The laser light can have a specific wavelength, intensity, mode shape, and mode size, and structure 10 provides spot conversion for the laser light. The gap or space between the optical fiber and structure 10 can be filled with air or, alternatively, with an index-matched material or a lens. The light propagates within structure 10 from segments 12 toward the conical waveguide core 18.

[0015] The segments 12, the segments 14, the waveguide core region 16, and the conical waveguide core region 18 may be disposed over a dielectric layer 24. In one embodiment, the dielectric layer 24 may be formed of silicon dioxide. In one embodiment, the dielectric layer 24 may be a buried oxide layer of a silicon-on-insulator substrate, and the silicon-on-insulator substrate may further include a handle substrate 26 formed of a single-crystal semiconductor material (e.g., single-crystal silicon). The segments 12, the segments 14, the waveguide core region 16, and the conical waveguide core region 18 may be formed of a single-crystal semiconductor material, e.g., single-crystal silicon.In one embodiment, the segments 12, the segments 14, the waveguide core region 16, and the conical waveguide core region 18 may be patterned by lithography and etching processes from a single-crystal silicon device layer of a silicon-on-insulator wafer.

[0016] The segments 12 are arranged in a section of the structure 10 that initially receives the laser light from the optical fiber. The segments 12 are discrete and not interconnected. The segments 12 are separated from each other by grooves 13, defining a grid-like structure. The segments 12 can have a width dimension in a direction transverse to the longitudinal axis 21 that varies with the position along the longitudinal axis 21.

[0017] The segments 14 and the waveguide core region 16 are arranged in a section of the structure 10 that transmits the laser light from the segments 12 to the conical waveguide core region 18. The segments 14, connected by the waveguide core region 16, may have a width dimension in a direction transverse to the longitudinal axis 21 that varies with position along the longitudinal axis 21. Portions of each segment 14 protrude outwardly from the opposite side edges of the waveguide core region 16 to accommodate the variation in the width dimension.

[0018] The segments 12, 14 can be arranged at such a close pitch that they do not emit or reflect light at the operating wavelength and act as an effective optical material, thus defining a metamaterial waveguide. In one embodiment, the pitch and duty cycle of the segments 12 can be uniform to define a periodic array. In alternative embodiments, the pitch and / or duty cycle of the segments 12 can be apodized (i.e., non-uniform) to define a non-periodic array. In one embodiment, the pitch and duty cycle of the segments 14 can be uniform to define a periodic array. In alternative embodiments, the pitch and / or duty cycle of the segments 14 can be apodized (i.e., non-uniform) to define a non-periodic array.

[0019] The conical waveguide core region 18 has a sidewall 20 and a sidewall 22 that extend from the intersection with the waveguide core region 16 to an end face 28. The conical waveguide core region 18 can be directly connected to the waveguide core region 16. The conical waveguide core region 18 extends longitudinally from the waveguide core region 16 along the longitudinal axis 21 and terminates at the end face 28. The conical waveguide core region 18 has a length L1 that can be measured from the intersection with the waveguide core region 16 to the end face 28.

[0020] The conical waveguide core region 18 has a width dimension that changes with position along the longitudinal axis 21 in a light propagation direction (specifically, it is conical in the longitudinal direction). The width dimension of the conical waveguide core region 18 increases with increasing distance from the segments 14 and the waveguide core region 16 and decreases with decreasing distance from the end face 28. The conical waveguide core region 18 has a minimum width w1 that occurs at the end face 28. For example, the conical waveguide core region 18 can taper from a width of 280 nanometers at the intersection with the waveguide core region 16 to a width of 90 nanometers at the end face 28.In one embodiment, the width dimension of the conical waveguide core region 18 may be narrowest at the end face 28 and may vary along its length L1 based on a linear function, resulting in a trapezoidal shape. In an alternative embodiment, the width dimension of the conical waveguide core region 18 may be narrowest at the end face 28 and may vary along its length L1 based on a nonlinear function, such as a quadratic, parabolic, or exponential function.

[0021] With reference to the Fig. 3, Fig. 4, Fig. 4A, Fig. 4B, in which like reference numerals refer to like features in the Fig. 1, Fig. 2, in a subsequent manufacturing phase, a dielectric layer 30 is formed over the segments 12, the segments 14, the waveguide core region 16, the conical waveguide core region 18, and the dielectric layer 24. The dielectric layer 30 may be formed from silicon dioxide, which may be deposited by chemical vapor deposition and planarized by chemical mechanical polishing.

[0022] A waveguide core 32 is disposed on the dielectric layer 30. The waveguide core 32 includes a conical section 34 above the conical waveguide core region 18 and a non-conical section 33 connected to the conical section 34. The waveguide core 32 extends longitudinally along a longitudinal axis 35 and terminates at an end face 38. The conical section 34 may completely overlap with the conical waveguide core region 18. The conical section 34 may be arranged to partially overlap with the conical waveguide core region 18 and partially overlap with the segments 14 and the waveguide core region 16 adjacent the end face 38 of the waveguide core 32. In one embodiment, the conical section 34 of the waveguide core 32 may be centered over the conical waveguide core region 18.The conical section 34 has a sidewall 36 and a sidewall 37 extending from the end face 38 of the waveguide core 32 to the intersection with the non-conical section 33. The conical section 34 has a length L2 that can be measured from the end face 38 to the intersection with the non-conical section 33. The length L2 of the conical section 34 can be greater than the length L1 (. Fig. 1).

[0023] The width of the conical section 34 may increase with increasing distance from the end face 38. The conical section 34 has a width dimension that varies with position along the longitudinal axis 35. The conical section 34 gradually widens with increasing distance from the end face 38 in a direction along the longitudinal axis 35 and has a minimum width w2 at the end face 38. For example, the conical section 34 may widen from a width of 120 nanometers at the end face 38 to a width of 800 nanometers at the end of the conical shape. In one embodiment, the conical section 34 defines an inverse cone shape that tapers in the opposite direction with respect to the conical shape of the conical waveguide core region 18.An inverse cone, as used herein, is a conical portion of a waveguide core having a gradual increase in width along the direction of light propagation. In one embodiment, the width dimension of the conical portion 34 may be narrowest at the end face 38 and vary along its length L2 based on a linear function, resulting in a trapezoidal shape. In an alternative embodiment, the width dimension of the conical portion 34 may be narrowest at the end face 38 and vary along its length L2 based on a non-linear function, such as a quadratic, parabolic, or exponential function. In one embodiment, the width dimension of the conical portion 34 may be greater than the width dimension of the conical waveguide core region 18 at any longitudinal position where an overlap exists.

[0024] With reference to the Fig. 5, Fig. 6, Fig. 6A, Fig. 6B, in which like reference numerals refer to like features in the Fig. 3, Fig. 4, in a subsequent manufacturing stage, a dielectric layer 40 is formed over the dielectric layer 30 and the waveguide core 32. The dielectric layer 40 may be formed from silicon dioxide deposited by chemical vapor deposition and planarized by chemical mechanical polishing. A back-end-of-line stack 42 comprising a stack of interlayer dielectric layers is formed over the dielectric layer 40, and a portion of the back-end-of-line stack 42 proximate the structure 10 is removed and replaced with a dielectric layer 44. The dielectric layer 44 may be formed from silicon dioxide deposited by chemical vapor deposition and planarized by chemical mechanical polishing.The back-end-of-line stack 42 and the dielectric layer 44 converge along an interface 43, where a transition occurs from the dielectric interlayers of the back-end-of-line stack 42 to the dielectric layer 44. The end face 38 of the waveguide core 32 may coincide with the interface 43 (in particular, have a common boundary).

[0025] A groove 46 is formed in the handle substrate 26, extending from an edge 27 of the handle substrate 26 to an edge 25 of the dielectric layer 24 and then further under the dielectric layer 24 and a portion of the structure 10 as an undercut. The edge 25 represents a side surface at a boundary of the dielectric layer 24. The edge 27 represents a surface at a boundary of the handle substrate 26, which is horizontally spaced by a distance d from the edge 25 of the dielectric layer 24. The edge 27 is also horizontally spaced by a distance d2 from the interface 43.

[0026] The groove 46 can be manufactured in a multi-step process. Lithography and etching processes can be used to form a rectangular opening extending through the dielectric layers 24, 30, 40 and into the handle substrate 26 between the edges 25, 27, and also to form holes (not shown) extending through the dielectric layers 24, 30, 40 and into the handle substrate 26 adjacent to the structure 10. The formation of the rectangular opening defines the edge 25 of the dielectric layer 24. The rectangular opening in the handle substrate 26 can then be masked with a resist, and the handle substrate 26 below the portion of the structure 10 can be etched through the holes using an etching process, for example, using a sulfur hexafluoride plasma, to create an initial undercut.After removing the resist, a wet chemical etchant can be used to V- or U-shape the portion of the groove 46 between the edges 25, 27 and the portion of the groove 46 forming the undercut. The wet chemical etchant can exhibit selectivity with respect to the crystal orientation of the semiconductor material of the handle substrate 26 and can be characterized by different etching rates along different crystal directions, creating the V- or U-shape. The wet chemical etchant can be, for example, a solution comprising tetramethylammonium hydroxide (TMAH).

[0027] A portion of the groove 46 in the handle substrate 26 is located near the edge 25 of the dielectric layer 24 and thus near the structure 10. An optical fiber tip can be inserted and at least partially supported by the sidewalls of the portion of the groove 46 adjacent to the structure 10. A low-index adhesive can be used to mount the optical fiber tip, which can completely or partially fill the groove 46. A portion of the groove 46 is located below a portion of the structure 10, and a portion of the dielectric layer 24 is located between the groove 46 and the structure 10. The portion of the dielectric layer 24 located above the groove 46 defines a membrane that is undercut by the groove 46.

[0028] In any of the embodiments described herein, structure 10 can be integrated into a photonic chip comprising electronic components and additional optical components. The electronic components can, for example, comprise field-effect transistors manufactured using the CMOS process.

[0029] The edge coupler structure 10 includes an intrinsic transition between the conical waveguide core region 18 and the conical section 34, which are located at different elevation levels above the dielectric layer 24. The edge coupler structure 10 has a hybrid construction with materials of different compositions located at the different levels. Incorporating the multi-level transition between the conical waveguide core region 18 and the conical section 34 within the structure 10 can provide fast mode conversion and enable improved power handling, making the conical waveguide core region 18 less susceptible to damage.The introduction of a material other than silicon into the structure 10 can reduce power-dependent losses in the transmission of optical power from the optical fiber through the structure to the optical components on the photonic chip.

[0030] With reference to Fig. 7, in which the same reference numerals refer to the same features in Fig. 1, and according to alternative embodiments of the invention, the tapered waveguide core region 18 may be modified to extend lengthwise along the longitudinal axis 21 beyond the tapered portion 34 of the waveguide core 32 such that a portion of the tapered waveguide core region 18 is overlapped by the tapered portion 34 of the waveguide core 32 and another portion of the tapered waveguide core region 18 is overlapped by the non-tapered portion 33 of the waveguide core 32. The end face 28 of the extended tapered waveguide core region 18 is disposed below the non-tapered portion 33 of the waveguide core 32, rather than below the tapered portion 34 of the waveguide core 32.

[0031] With reference to Fig. 8, in which the same reference numerals refer to the same features in Fig.3, and according to alternative embodiments of the invention, the conical portion 34 of the waveguide core 32 may be modified such that the end face 38 is disposed over the conical waveguide core region 18 rather than over the segments 14 and the waveguide core portion 16. In one embodiment, the end face 38 may be disposed directly over the transition from the segments 14 and the waveguide core region 16 to the conical waveguide core region 18. The end face 38 is longitudinally offset from the segments 14 and the waveguide core region 16 without any overlap.

[0032] The processes described above are used in the manufacture of integrated circuits. The resulting integrated circuit chips can be distributed by the manufacturer in raw wafer form (e.g., a single wafer containing multiple unpackaged chips), as a bare chip, or in packaged form. The chip can be integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of an intermediate or final product. The final product can be any product containing integrated circuit chips, such as computer products with a central processor or smartphones.

[0033] References in this document to terms modified by imprecise terms such as "approximately," "about," and "substantially" are not intended to be limited to the exact value. The imprecise term may be consistent with the accuracy of an instrument used to measure the value and, unless otherwise dependent upon the instrument's accuracy, may indicate + / -10% of the stated value(s).

[0034] References to terms such as "vertical," "horizontal," etc., are used herein only as examples and not as limitations, to provide a frame of reference. As used herein, "horizontal" is defined as a plane parallel to a conventional plane of a semiconductor substrate, regardless of its actual three-dimensional spatial orientation. The terms "vertical" and "normal" refer to a direction perpendicular to the just-defined horizontal direction. The term "lateral" refers to a direction within the horizontal plane.

[0035] A feature that is "connected" or "coupled" to another feature may be directly connected or coupled to the other feature, or there may instead be one or more intervening features. A feature may be "directly connected" or "directly coupled" to another feature if there are no intervening features. A feature may be "indirectly connected" or "indirectly coupled" to another feature if there is at least one intervening feature. A feature that is "on" or "in contact" with another feature may be directly on or in direct contact with the other feature, or there may instead be one or more intervening features. A feature may be "directly on" or in "direct contact" with another feature if there are no intervening features.A feature may be "indirectly on" or in "indirect contact" with another feature if there is at least one intervening feature. Different features may overlap if one feature extends over another feature and touches a portion of it, either directly or indirectly.

[0036] The descriptions of the various embodiments of the present invention are for illustrative purposes only and are not intended to limit the invention to the described embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope of the described embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, practical application, or technical improvement over current technologies, or to enable others not skilled in the art to understand the embodiments described herein.

Claims

[1] Structure for an edge coupler (10), the structure comprising: a first dielectric layer (24) having an edge (25); a first waveguide core region (18) on the first dielectric layer (24), the first waveguide core region (18) having an end face (28) and the first waveguide core region (18) being conical in the longitudinal direction towards the end face (28); a plurality of segments (12) on the first dielectric layer (24), the plurality of segments (12) being arranged between the first waveguide core region (18) and the edge (25) of the first dielectric layer (24); a waveguide core (32) having a first portion (34) disposed over the first waveguide core region (18) in an overlapping arrangement, the waveguide core (32) having an end face (38) and the first portion (34) being conical in the longitudinal direction toward the end face (38); a back-end-of-line stack (42) over the waveguide core (32); and a second dielectric layer (44) having an interface (43) with the back-end-of-line stack (42), the second dielectric layer (44) extending from the interface (43) to the edge (25) of the first dielectric layer (24), wherein the end surface (38) of the waveguide core (32) extends over the same distance as the interface (43). [2] The structure of claim 1, wherein the first portion (34) of the waveguide core (32) is centered over the first waveguide core region (18). [3] The structure of claim 1, wherein the waveguide core (32) is formed of silicon nitride and the first waveguide core region (18) and the plurality of segments (12) are formed of single-crystal silicon. [4] The structure of claim 1, wherein the end face (28) of the first waveguide core region (18) is disposed below the first portion (34) of the waveguide core (32). [5] The structure of claim 4, further comprising: a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is disposed over the second waveguide core region (16) and the plurality of segments (12). [6] The structure of claim 4, further comprising: a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is arranged above the first waveguide core region (18). [7] The structure of claim 1, further comprising: a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is disposed over the second waveguide core region (16) and the plurality of segments (12). [8] The structure of claim 1, further comprising: a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is arranged above the first waveguide core region (18). [9] The structure of claim 1, wherein the first waveguide core region (18) and the plurality of segments (12) are formed of silicon, the waveguide core (32) is formed of silicon nitride, and further comprising: a second dielectric layer (30) disposed between the first waveguide core region (18) and the first portion (34) of the waveguide core (32). [10] The structure of claim 1, wherein the first dielectric layer (24) is disposed on a substrate (26), and the substrate (26) includes a groove (46) extending below the edge (25) of the first dielectric layer (24) and below the plurality of segments (12). [11] The structure of claim 1, wherein the first waveguide core region (18) and the first portion (34) of the waveguide core (32) taper in opposite directions. [12] The structure of claim 1, wherein the plurality of segments (12) and the first waveguide core region (18) are aligned along a longitudinal axis and the plurality of segments (12) are spaced apart from each other along the longitudinal axis. [13] The structure of claim 1, wherein the interface (43) and the end face (38) of the waveguide core (32) are disposed over the plurality of segments (12). [14] The structure of claim 1, wherein the waveguide core (32) has a second portion (33) adjacent to the first portion (34), the first portion (34) is disposed between the second portion (33) and the end face (38), and the end face (38) of the first waveguide core region (18) is disposed below the second portion (33) of the waveguide core (32). [15] A method of forming a structure for an edge coupler (10), the method comprising: forming a first waveguide core region (18) on a first dielectric layer (24), the first waveguide core region (18) having an end face (28) and the first waveguide core region (18) being conical in the longitudinal direction toward the end face (28); forming a plurality of segments (12) on the first dielectric layer (24), the plurality of segments (12) being arranged between the first waveguide core region (18) and an edge (25) of the first dielectric layer (24); forming a waveguide core (32) having a portion (34) disposed over the first waveguide core region (18) in an overlapping arrangement, the waveguide core (32) having an end face (38) and the portion (34) being conical in the longitudinal direction toward the end face (38); forming a back-end-of-line stack (42) over the waveguide core (32); removing a first portion of the back-end-of-line stack (42); and forming a second dielectric layer (44) having an interface (43) to a second portion of the back-end-of-line stack (42), wherein the second dielectric layer (44) extends from the interface (43) to the edge (25) of the first dielectric layer (24) and the end surface (38) of the waveguide core (32) has the same extent as the interface (43). [16] The method of claim 15, wherein the end face (28) of the first waveguide core region (18) is disposed below the portion (34) of the waveguide core (32). [17] The method of claim 15, further comprising: forming a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is disposed over the second waveguide core region (16) and the plurality of segments (12). [18] The method of claim 15, further comprising: forming a second waveguide core region (16) overlaid with the plurality of segments (12), the second waveguide core region (16) being connected to the first waveguide core region (18), wherein the end face (38) of the waveguide core (32) is arranged above the first waveguide core region (18).

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