CN111103658A

CN111103658A - Device for optical coupling and system for communication

Info

Publication number: CN111103658A
Application number: CN201911021486.6A
Authority: CN
Inventors: 郭丰维; 周淳朴; 陈焕能; 卓联洲; 廖文翔
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2018-10-26
Filing date: 2019-10-25
Publication date: 2020-05-05

Abstract

The present disclosure discloses grating couplers with high coupling efficiency for optical communications. In one embodiment, an apparatus for optical coupling is disclosed. The apparatus comprises: a substrate; a grating coupler comprising a plurality of coupling gratings over a substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section with a central convex shape in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane; and a cladding layer comprising the optical medium, wherein the grating coupler is filled with the cladding layer.

Description

Device for optical coupling and system for communication

Technical Field

Embodiments of the present invention relate to devices for optical coupling and systems for communication.

Background

Optical gratings (optical gratings) are often used to enable communication between a light source and other components, such as a photodetector. For example, an optical grating may be used to redirect light from an optical fiber into an optical detector. Light coupled from one end of the optical grating that traverses the optical grating by reflecting from the inner surface at a shallow angle may be redirected such that the light strikes the inner surface at an acute angle that is greater than the critical angle of incidence, allowing the redirected light to escape from the other end of the optical grating. After escaping, light may impinge (imping) on the detector. The detected light may then be used for various purposes, such as for receiving encoded communication signals transmitted through an optical grating. Unfortunately, this process, as well as the reverse process of redirecting light from an on-chip light source to an optical fiber using an optical grating, may exhibit poor coupling efficiency, where most of the redirected light does not reach the detector. There is a need to develop a method and apparatus for efficient optical coupling using an optical grating.

Disclosure of Invention

In one embodiment, an apparatus for optical coupling is disclosed. The apparatus comprises: a substrate; a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section with an intermediate convex shape in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane; and a cladding layer comprising an optical medium, wherein the cladding layer fills on the grating coupler.

In another embodiment, an apparatus for optical coupling is disclosed. The apparatus comprises: a semiconductor photonics die; and a plurality of coupling gratings. Each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section with at least two layers in a second lateral direction. The at least two layers include a first layer on the semiconductor photonics die and a second layer on a middle portion of the first layer. The second layer of the plurality of coupling gratings has a duty cycle that varies along the second lateral direction.

In yet another embodiment, a system for communication is disclosed. The system comprises: a semiconductor photonics die located on a substrate, wherein the semiconductor photonics die includes at least one trench and a plurality of metal layers located over the at least one trench; an optical fiber array attached to the semiconductor photonic die; and at least one grating coupler located in the at least one trench on the semiconductor photonics die for transmitting optical signals between the semiconductor photonics die and the optical fiber array. Each of the plurality of metal layers has an opening located over the at least one grating coupler. The openings of the plurality of metal layers form channels extending in a first direction for passing optical signals between the optical fiber array and the at least one grating coupler. A non-zero angle is formed between the first direction and a second direction perpendicular to a surface of the substrate.

Drawings

Various aspects of the disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that the various features are not drawn to scale. In fact, the dimensions and geometries of the various features may be arbitrarily increased or reduced for clarity of illustration.

Fig. 1 illustrates an exemplary block diagram of an apparatus according to some embodiments of the present disclosure.

Fig. 2A illustrates a top view of an exemplary grating coupler, according to some embodiments of the present disclosure.

Fig. 2B illustrates a cross-sectional view of an exemplary grating coupler taken along the radial direction (a-a') shown in fig. 2A, according to some embodiments of the present disclosure.

Figure 2C illustrates a cross-sectional view of an exemplary grating coupler taken along the direction B-B' shown in figure 2A, according to some embodiments of the present disclosure.

Fig. 3 illustrates a cross-sectional view of an exemplary grating coupler including a plurality of coupled gratings according to some embodiments of the present disclosure.

Fig. 4 illustrates a cross-sectional view of another exemplary grating coupler including a plurality of coupled gratings according to some embodiments of the present disclosure.

Fig. 5 illustrates a cross-sectional view of yet another exemplary grating coupler including a plurality of coupled gratings according to some embodiments of the present disclosure.

Fig. 6A-6J illustrate cross-sectional views of an example grating coupler at various stages of a fabrication process according to some embodiments of the present disclosure.

Fig. 7 illustrates a cross-sectional view of an exemplary optical device according to some embodiments of the present disclosure.

Fig. 8 illustrates a cross-sectional view of an exemplary optical die having a tilted metal layer opening, according to some embodiments of the present disclosure.

Detailed Description

The following disclosure sets forth various exemplary embodiments for implementing different features of the disclosed subject matter. Specific examples of components and arrangements are set forth below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, it will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or one or more intervening elements may be present.

The coupling efficiency is the ratio of power coupled from waveguide mode to fiber mode (or from fiber mode to waveguide mode), and CE (1-R) η may be utilized_d*η_ovIs calculated, wherein η_dIs directivity (η)_ovIs the optical field overlap, and R is the back reflection, directionality η_dThe light field overlap η ov measures the integral of overlap (overlap integral) between the diffraction field profile and the Gaussian fiber mode, and the back reflection R measures the fraction of the power reflected back into the input portCoupling efficiency, improved directivity, increased overlap and reduced back reflection using a small index contrast. The present disclosure provides various embodiments of efficient fiber-to-chip grating couplers with high coupling efficiency.

In one embodiment, the disclosed grating coupler has a plurality of coupling gratings each having a cross-section in the shape of a central protrusion. A medium convex shape is a shape in which the middle part is convex or higher than the other parts of the shape, which results in each grating having a smoother curve. This reduces fiber light loss at the input/output (I/O) device and improves the coupling efficiency of the grating coupler.

In addition, although each grating has a raised portion in the middle, the raised portions may have different widths for different gratings. The duty cycle of the grating means the ratio between the width of the convex portion and the width of the grating. That is, different gratings may have different duty cycles. This also helps to increase the coupling efficiency of the grating coupler, since different duty cycles can cause apodization of the optical coupling, where the effective index of refraction is reduced.

In addition, the height and angle of the fiber array can be adjusted to obtain better grating coupling efficiency. Once the optimal or desired input angle of the optical signal is determined, the structure of the grating coupler can also be designed to ensure good coupling efficiency. For example, a metal layer above the grating may be etched to form optical channels aligned with an optimal or desired input angle. This ensures that the optical signal received through the optical channel will have an optimal or desired input angle for the grating coupler to enjoy good coupling efficiency.

The disclosed grating coupler has high coupler efficiency and is easy to implement in any suitable silicon photonic input/output and high speed applications. The disclosed grating coupler facilitates wafer level testing as well as low cost packaging.

Fig. 1 illustrates an exemplary block diagram of an apparatus 100 according to some embodiments of the present disclosure. It should be noted that the apparatus 100 is merely an example and is not intended to limit the present disclosure. It is therefore to be understood that additional functional blocks may be provided in the device 100 shown in fig. 1 or may be coupled to the device 100 shown in fig. 1, and that some other functional blocks may only be briefly described herein.

Referring to fig. 1, apparatus 100 includes an electronic die 102, a light source die 104, a photonics die 106, an interposer 110, and a Printed Circuit Board (PCB) substrate 114. Electronic die 102, light source die 104, and photonics die 106 are coupled together through input/output interfaces (not shown) on interposer 110. In some embodiments, interposer 110 is fabricated using silicon. In some embodiments, interposer 110 includes at least one of: interconnect lines, Through Silicon Vias (TSVs), and contact pads. In some embodiments, interposer 110 integrates all components including electronic die 102, light source die 104, and photonics die 106. In some embodiments, each of the dies 102/104/106 is coupled to the interposer 110 using a flip-chip (controlled collapse chip connection, C4) interconnection method. In some embodiments, high density solder micro-bumps are used to couple die 102/104/106 to interposer 110. In addition, interposer 110 is coupled to PCB substrate 114 by wire bonds 112 or Through Silicon Vias (TSVs) 116 using solder balls. The TSVs 116 may include conductive paths that extend vertically through the interposer 110 and provide electrical connections between the electronic die 102 and the PCB substrate 114. In some embodiments, PCB substrate 114 may include support structures for device 100, and may include both insulating materials for isolating devices and conductive materials that provide electrical contact to active devices on photonic die 106 and circuits/devices on electronic die 102 via interposer 110. In addition, the PCB substrate 114 may provide a thermal conduction path to carry away heat generated by devices and circuitry in the electronic die 102 and the light source die 104.

In some embodiments, the electronic die 102 includes circuitry (not shown) including amplifiers, control circuitry, digital processing circuitry, and the like. The electronic die 102 also includes at least one electronic circuit (not shown) that provides the required electronic functions of the apparatus 100 as well as driver circuitry for controlling elements in the light source die 104 or photonics die 106.

In some embodiments, the light source die 104 includes a plurality of components (not shown), such as at least one light emitting element (e.g., a laser or a light emitting diode), a transmission element, a modulation element, a signal processing element, a switching circuit, an amplifier, an input/output coupler, and a light sensing/detection circuit. In some embodiments, each of the at least one light-emitting element in the light source die 104 may include a solid inorganic semiconductor material, an organic semiconductor material, or a combination of inorganic/organic hybrid semiconductor materials to generate light. In some embodiments, light source die 104 is located on photonics die 106.

In some embodiments, the photonics die 106 includes an optical fiber array 108, an optical interface, and a plurality of fiber-to-chip grating couplers 118. In some embodiments, the plurality of fiber-to-chip grating couplers 118 are configured to couple the photonics die 106 with the fiber array 108. In some embodiments, fiber array 108 includes a plurality of optical fibers and each of the plurality of optical fibers may be a single-mode (single-mode) or a multi-mode (multi-mode) optical fiber. In some embodiments, the fiber array 108 may be epoxied on the photonics die 106.

In some embodiments, photonic die 106 also includes components (not shown) such as laser drivers, digital control circuitry, photodetectors, waveguides, small form factor pluggable (SFP) transceivers, High-speed phase modulators (HSPMs), calibration circuitry, distributed Mach-Zehnder interferometers (MZIs), grating couplers, light sources (i.e., lasers), and so forth. Each of the plurality of fiber-to-chip grating couplers 118 is capable of coupling an optical signal between the fiber array 108 and a corresponding photodetector on the light source die 104 or the photonic die 106. Each of the plurality of fiber-to-chip grating couplers 118 includes a plurality of gratings and waveguides whose design reduces refractive index contrast to reduce back reflection losses, providing improved coupling efficiency between optical fibers on corresponding waveguides, discussed in detail below in various embodiments of the present disclosure.

During operation, optical signals received from a remote server affixed to one end of the fiber array 108 may be coupled to corresponding photodetectors on the photonic die 106 through fiber-to-chip grating couplers 118 affixed to the other end of the fiber array 108. Alternatively, the optical signals received from the light source die 104 may be coupled to the fiber array 108 through a fiber-to-chip grating coupler 118, which may be further transmitted to a remote server.

Fig. 2A illustrates a top view of an exemplary fiber-to-chip grating coupler 200 according to some embodiments of the present disclosure. In some embodiments, a fiber-to-chip grating coupler (hereinafter "grating coupler") 200 includes a grating region 202 and a waveguide 210. The grating region 202 includes a plurality of periodic gratings 204. In the illustrated embodiment, the curve is an edge 208 of the plurality of gratings 204 in the grating coupler 200. Any number of edges 208 in each grating 204 and any number of gratings 204 in the grating coupler 200 may be used and are within the scope of the present disclosure.

In the illustrated embodiment, the grating coupler 200 scatters an incident light field 220 received from the waveguide 210 in a radial direction in a direction perpendicular to the grating 204, and the refractive index contrast between the waveguide 210 and the grating region 202 enhances the scattering from the grating 204. The plurality of periodic gratings 204 in the grating region 202 produce an exponentially decaying intensity distribution (exponentially decaying intensity profile) in the propagation direction along the radial direction at a given angle 222 with respect to one end of the grating coupler 200. The exponentially decaying intensity profile may determine the position of an optical fiber (not shown) in the fiber array 108 atop the grating coupler 200 to efficiently couple the optical field from the chip to the optical fiber. In some embodiments, the number of periodic gratings 204 may be determined based on the shape, geometry, and material of the gratings and the desired operating wavelength range.

Referring to fig. 2A, grating region 202 and waveguide 210 include

lengths

206 and 212, respectively, in the radial direction. In some embodiments, each of the plurality of gratings 204 includes a radius of curvature 214 according to its position relative to the center "O" and an arc length 216. In some embodiments, each of the plurality of gratings 204 in the grating coupler 200 has no curvature, i.e., the gratings are straight and have the same length 216.

Fig. 2B illustrates a cross-sectional view of the exemplary grating coupler 200 taken along the radial direction (a-a') shown in fig. 2A, according to some embodiments of the present disclosure. In the illustrated embodiment, the grating coupler 200 fabricated on the silicon substrate 224 comprises a multi-layer structure including a bottom reflective layer 290, a silicon oxide layer 226, a silicon layer 228, and a top reflective layer 292.

In the illustrated embodiment, a silicon oxide layer 226 is fabricated on the silicon substrate 224 using chemical vapor deposition, physical vapor deposition, or the like. In some embodiments, silicon oxide layer 226 has a thickness 230 of 500 nanometers to 3000 nanometers. In some embodiments, this layer may be made of other types of dielectric materials (e.g., Si) depending on the various embodiments of the present disclosure₃N₄、SiO₂(e.g., quartz and glass), Al₂O₃And H₂O) instead.

In some embodiments, silicon layer 228 is deposited on silicon oxide layer 226 using chemical vapor deposition. In some embodiments, the silicon layer 228 is 270 nanometers thick. In some other embodiments, the thickness of the silicon layer 228 is in a range of 250 nanometers to 350 nanometers, depending on various embodiments of the present disclosure.

In some embodiments, the bottom reflective layer 290 includes at least one of: al, Cu, Ni, and combinations thereof. In some embodiments, the thickness of the bottom reflective layer 290 is in the range of 0.1 microns to 10 microns. In some embodiments, the top reflective layer 292 includes at least one of: al, Cu, Ni, and combinations thereof. In some embodiments, the thickness of the top reflective layer 292 is in the range of 0.1 microns to 10 microns. In some embodiments, the top reflective layer 292 covers only the waveguides 210. In some embodiments, the top reflective layer 292 is equal to or greater than 20 × 20 microns.

In some embodiments, the waveguide 210 comprises the same material used in the plurality of gratings 204. In some other embodiments, the waveguide 210 comprises a second material different from the material used in the plurality of gratings 204.

In the embodiment shown, each of the plurality of gratings 204 has a sidewall profile of a central convex shape for achieving low back reflection and high directivity. In some embodiments, the intermediate convex shape has an intermediate convex portion 246 that is farther from the substrate 224 than other portions of the intermediate convex shape. As shown in fig. 2B, the central convex shape of each grating 204 includes, in addition to the central convex portion 246, a left portion 247, a right portion 249, and a central base portion 248 directly below the central convex portion 246.

As shown in FIG. 2B, left portion 247 has a width 240, middle raised portion 246 has a width 242, and right portion 249 has a width 244. In some embodiments, the intermediate convex shape is symmetric about a Z-direction perpendicular to the grating plane or the top surface of the silicon oxide layer 226. That is, the width 240 may be the same as the width 244, with the middle convex portion 246 being located just in the middle of the middle convex shape of the grating 204. In other embodiments, the middle convex portion 246 may not be exactly in the middle of the middle convex shape of the grating 204, and the width 240 may be different than the width 244.

As shown in FIG. 2B, left side portion 247 and right side portion 249 have a thickness 234, and middle raised portion 246 has a thickness 236. Thus, the sidewalls of the grating 204 have a total thickness 238 equal to the sum of the

thicknesses

234 and 236. The sidewalls are perpendicular to the substrate surface (i.e., the top surface of silicon oxide layer 226). The dimensions of the plurality of periodic gratings 204 will be discussed in further detail below.

In some embodiments, the intermediate convex shape is formed by a multi-step etching process. For example, shallow trenches are formed on each side of the middle protruding portion 246 in the silicon layer 228 by an etching step; and a deep or full trench is formed between two adjacent gratings 204 in the silicon layer 228 by an etching step. In the illustrated embodiment, one period 241 of the sidewall profile of the plurality of periodic gratings 204 includes a full trench, a middle bump shape, and two shallow trenches. In some embodiments, in the radial direction, grating region 202 has a length 206 (as shown in fig. 2A) and waveguide 210 has a length 212.

In some embodiments, the grating coupler 200 is further covered by a cladding layer 272. In some embodiments, the cladding layer 272 comprises silicon oxide and has a thickness 274 from the top surface of the cladding layer 272 to the top surface of the underlying unpatterned silicon layer 228. In some embodiments, the cladding layer 272 has a thickness of 2 microns. In some embodiments, the thickness 274 of the cladding layer 272 may be in the range of 0.6 microns to 3 microns, depending on the various applications. In some embodiments, cladding layer 272 may comprise other types of dielectric materials, including polysilicon and silicon nitride, depending on the application. In some other embodiments, the cladding layer 272 comprises a plurality of layers having a gradient in index (i.e., the refractive index of the plurality of layers in the cladding layer 272 increases). In some embodiments, the thicknesses of the multiple layers may be adjusted individually according to various applications. It should be noted that this is merely an example, and that the optimized thickness of the cladding layer 272 is a function of the effective index (i.e., material property) of the cladding layer 272 in combination with the underlying gradient structure. Thus, any thickness of cladding layer 272 may be used to achieve optimized coupling efficiency at the desired wavelength, and such any thickness of cladding layer 272 is within the scope of the present disclosure.

In some embodiments, the radiated optical field 270 from the grating coupler 200 with an electric field orthogonal to the plane of incidence (i.e., transverse electric TE polarization) is collected by an optical fiber 252 having a core diameter 260. In one example, the fiber core diameter (fiber diameter)260 is less than 10 microns. In some embodiments, the core of the optical fiber 252 is located a distance 262 from the center of its core to the top surface of the cladding 272. In some embodiments, the optical fiber 252 receives the optical field 270 at an angle 258 (between the axis 254 of the optical fiber 252 and a z-axis 256 that is perpendicular to the surface of the substrate). In some embodiments, angle 258 is 12 degrees. In some other embodiments, the angle 258 of the optical fiber 252 may be configured to be in the range of 5 degrees to 15 degrees, depending on the structural/geometric/material properties of the grating coupler 200 and cladding 272. In some embodiments, the optical fiber 252 may be a single mode optical fiber or a multimode optical fiber.

FIG. 2C illustrates a cross-sectional view of the exemplary fiber-to-chip grating coupler 200 taken along the direction B-B' shown in FIG. 2A, according to some embodiments of the present disclosure. The cross-sectional view shows that the medium relief-shaped grating 204 in the silicon layer 228 in fig. 2B is continuous over the entire length 216. In the embodiment shown, grating 204 includes 2 etched steps, and each of the two steps has a

step height

234 and 236, respectively. In some embodiments, thickness 232 of silicon layer 228 is equal to the sum of

step heights

234 and 236. In some embodiments, the thickness 232 of the silicon layer 228 is 270 nanometers. In some other embodiments, the thickness 232 of the silicon layer may be in the range of 180 nanometers to 400 nanometers.

Fig. 3 illustrates a cross-sectional view of an example grating coupler 300 including a plurality of coupled gratings 304 according to some embodiments of the present disclosure. As shown in fig. 3, grating coupler 300 has a silicon layer 320 disposed on a silicon oxide layer 310. Each of the plurality of coupling gratings 304 is located in the silicon layer 320. In this embodiment, the silicon layer 320 includes three sublayers: the first sublayer 321; a second sublayer comprising a plurality of stacks 322 located on the first sublayer 321; and a third sublayer comprising a plurality of stacks 323 each located on a corresponding stack 322.

The stacks 323 may have different widths from one another. As shown in fig. 3, the

width

351, 352, 353, 354, 355 of the stack 323 decreases from left to right. The width of the stack 323 may also increase from left to right, increase first and then decrease from left to right, or decrease first and then increase from left to right, according to various embodiments. In some embodiments, width 353 is equal to 220 nanometers. In some embodiments, the

widths

351, 352, 353, 354, 355 are in the range of 0 nanometers to 500 nanometers, depending on the application with different operating wavelengths.

Each of the plurality of stacks 322 in the second sublayer has a width 344, the width 344 being equal to the sum of the left-side portion width 342, the right-side portion width 343, and the width (351, 352, 353, 354, or 355) of the corresponding stack 323. The corresponding stack 323 is a central raised portion on top of the stack 322. In some embodiments, the stack 323 is located just in the middle of the stack 322, which means that the left portion width 342 is the same as the right portion width 343. In other embodiments, the stack 323 is not located exactly in the middle of the stack 322, meaning that the left portion width 342 may be different than the right portion width 343. In some embodiments, each of the left portion width 342 and the right portion width 343 are equal to 120 nanometers. In some embodiments, each of the left-side portion width 342 and the right-side portion width 343 is greater than 0 nanometers and less than 250 nanometers, depending on the application with different operating wavelengths.

As shown in fig. 3, each two adjacent stacks 322 are separated by a trench 302 having a width 341. According to various embodiments, the width 341 is greater than 0 nanometers and less than 250 nanometers, depending on the application with different operating wavelengths. In some embodiments, the width 341 is different for different pairs of adjacent stacks 322.

The total width 301 of each grating 304 is the sum of the width 341 and the width 344. According to various embodiments, the total width 301 is greater than 0 nanometers and less than 1250 nanometers, depending on the application with different operating wavelengths. For example, for an operating wavelength of 1310 nanometers, the total width 301 is designed to be less than 600 nanometers.

As described above, the

widths

351, 352, 353, 354, 355 of the stacks 323 are different from one another. This means that stack 323 has a different duty cycle relative to the corresponding stack 322. The duty cycle of the stack 323 on the corresponding stack 322 is measured as the ratio between the width (351, 352, 353, 354, or 355) of the stack 323 and the width 344 of the corresponding stack 322. Thus, the duty cycle of the stack 323 may vary from left to right in the lateral direction. For example, the duty cycle of stack 323 decreases from left to right in the lateral direction in fig. 3. According to various embodiments, the duty cycle of stack 323 is in the range of 0% to 50%.

As described above, the widths 341 of the trenches 302 in different gratings 304 may be different from one another. This means that the stack 322 may also have a different duty cycle with respect to the grating 304. The duty cycle of the stack 322 in the corresponding grating 304 is measured as the ratio between the width 344 of the stack 322 and the total width 301 of the corresponding grating 304. Thus, the duty cycle of the stack 322 may vary from left to right in the lateral direction. For example, the duty cycle of the stack 322 may decrease, increase, decrease first and increase second, or increase first and decrease second, from left to right in the lateral direction in fig. 3. According to various embodiments, the duty cycle of the stack 322 is in the range of 20% to 50%.

As shown in fig. 3, each stack 323 has a thickness 363, each stack 322 has a thickness 362, and the first sub-layer 321 has a thickness 331. Thus, the total thickness 333 of each grating 304 is equal to the sum of thickness 363, thickness 362, and thickness 331. In some embodiments, each grating 304 is formed by a multi-step etch process. For example, shallow trenches are formed on each side of the stack 323; and deep trenches are formed between each two adjacent stacks 322.

As shown in fig. 3, each grating 304 has a first etch thickness 331, a second etch thickness 332 equal to the sum of the first etch thickness 331 and the thickness 362, and a third etch thickness 333 equal to the sum of the second etch thickness 332 and the thickness 363. According to various embodiments, the first etch thickness 331 is in a range of 0 nanometers to 200 nanometers, depending on various applications having different operating wavelengths. The first etch thickness 331 in the example of fig. 3 is greater than 0 nanometers. According to various embodiments, the second etch thickness 332 is in the range of 0 nanometers to 270 nanometers, depending on various applications having different operating wavelengths. The second etch thickness 332 in the example of fig. 3 is greater than 70 nanometers. According to various embodiments, the third etch thickness 333 is in a range of 250 nanometers to 350 nanometers, depending on various applications having different operating wavelengths. The third etch thickness 333 in the example shown in figure 3 is greater than 270 nanometers to ensure that the coupler efficiency of the grating coupler 300 is above the threshold.

While the edge pattern of the

stacks

322, 323 follows a right angle of 90 degrees, it is also a possible fabrication process that the vertical edge pattern and the horizontal edge pattern of the

stacks

322, 323 may follow an arcuate pattern having less than 90 degrees.

Fig. 4 illustrates a cross-sectional view of another exemplary grating coupler 400 including a plurality of coupled gratings 404 according to some embodiments of the present disclosure. As shown in fig. 4, grating coupler 400 has a silicon layer 420 disposed on a silicon oxide layer 410. Similar to the embodiment shown in fig. 3, each of the plurality of coupling gratings 404 in fig. 4 is located in a silicon layer 420.

Unlike the embodiment shown in fig. 3, the silicon layer 420 in fig. 4 includes two sublayers: a first sublayer comprising a plurality of stacks 421 on the silicon oxide layer 410; and a second sublayer comprising a plurality of stacks 422 each located on a corresponding stack 421. The widths 451 of the stacks 422 may be different from one another, such as decreasing from left to right (as shown in fig. 4), increasing from left to right, increasing first and then from left to right, or decreasing first and then from left to right. Thus, the stacks 422 have different duty cycles relative to the corresponding stacks 421. The duty cycle of the stack 422 on the corresponding stack 421 is measured as the ratio between the width 451 of the stack 422 and the width 442 of the corresponding stack 421. The duty cycle of the stack 422 may vary (e.g., increase, decrease, or a mixture of both) from left to right in the lateral direction in fig. 4. According to various embodiments, the duty cycle of the stack 422 is in the range of 0% to 50%. In some embodiments, width 451 is in the range of 0 nanometers to 500 nanometers, depending on the application with different operating wavelengths. Each of the plurality of stacks 421 in the first sublayer has a width 442. Each stack 422 is a central raised portion on top of the corresponding stack 421. In some embodiments, width 442 is greater than 0 nanometers and less than 1000 nanometers, depending on the application with the different operating wavelengths.

As shown in fig. 4, each two adjacent stacks 421 are separated by a trench 402 having a width 441. Unlike the embodiment shown in fig. 3, the trench 402 in fig. 4 is a complete trench that extends down onto the silicon oxide layer 410. According to various embodiments, width 441 is greater than 0 nanometers and less than 250 nanometers, depending on the application having different operating wavelengths. In some embodiments, the width 441 is different for different pairs of adjacent stacks 421. The total width 401 of each grating 404 is the sum of width 441 and width 442. Thus, the stack 421 may also have a different duty cycle relative to the grating 404. The duty cycle of the stack 421 in the corresponding grating 404 is measured as the ratio between the width 442 of the stack 421 and the total width 401 of the corresponding grating 404. The duty cycle of the stack 421 may vary (e.g., increase, decrease, or a mixture of both) from left to right in the lateral direction in fig. 4. According to various embodiments, the duty cycle of the stack 421 is in the range of 20% to 50%.

In some embodiments, each grating 404 is formed by a multi-step etch process. For example, shallow trenches are formed on each side of the stack 422; and a complete trench is formed between every two adjacent stacks 421. As shown in fig. 4, each stack 421 in grating 404 has a thickness 431, and each grating 404 has a total thickness 432. According to some embodiments, thickness 431 is in the range of 0 nanometers to 270 nanometers, depending on various applications having different operating wavelengths. According to some embodiments, total thickness 432 is in the range of 250 nanometers to 350 nanometers, depending on various applications having different operating wavelengths.

Fig. 5 illustrates a cross-sectional view of yet another example grating coupler 500 including a plurality of coupled gratings 504, according to some embodiments of the present disclosure. As shown in fig. 5, grating coupler 500 has a silicon layer 520 disposed on a silicon oxide layer 510. Similar to the embodiment shown in FIG. 3, each grating 504 located in the silicon layer 520 includes three sub-layers: the first sublayer 521; a second sublayer including a plurality of stacks 522 on the first sublayer 521; and a third sublayer comprising a plurality of stacks 523 each located on a corresponding stack 522.

Unlike the embodiment shown in fig. 3, the width 551 of the stack 523 increases from left to right in fig. 5. Thus, for a given width 542 of the stack 522, the duty cycle of the stack 523 also increases from left to right in the lateral direction in fig. 5. According to some embodiments, the duty cycle of the stack 523 is in the range of 0% to 50%. Each two adjacent stacks 522 are separated by a trench 502 having a width 541, and the width 541 may be different for different pairs of adjacent stacks 522. The total width 501 of each grating 504 is the sum of the

widths

541 and 542.

Unlike the embodiment shown in fig. 3, the width 541 of the trench 502 decreases from left to right in the lateral direction in fig. 5. Thus, the duty cycle of the stack 522 increases from left to right in the lateral direction in fig. 5.

In some embodiments, each grating 504 is formed by a multi-step etch process. For example, shallow trenches are formed on each side of the stack 523; and deep trenches are formed between each two adjacent stacks 522. Each grating 504 has a first etched thickness 531 of the first sublayer 521, a second etched thickness 532 equal to the total thickness of the first sublayer 521 and the second sublayer 522, and a third etched thickness 533 equal to the total thickness of the grating 504. According to some embodiments, the first etch thickness 531 is in a range of 0nm to 200 nm, the second etch thickness 532 is in a range of 0nm to 270 nm, and the third etch thickness 533 is in a range of 250 nm to 350 nm, depending on various applications having different operating wavelengths.

Fig. 6A-6J illustrate cross-sectional views of an example grating coupler 600 at various stages of a fabrication process according to some embodiments of the present disclosure. Fig. 6A is a cross-sectional view of a grating coupler 600 according to some embodiments of the present disclosure, the grating coupler 600 including a first layer 610 and a second layer 620 disposed on the first layer 610 at one of various stages of fabrication. The first layer 610 may be formed of silicon oxide (as shown in fig. 6A) or another oxide material. The second layer 620 may be formed of silicon (as shown in fig. 6A) or another semiconductor material.

Figure 6B is a cross-sectional view of grating coupler 600 including mask layer 630, mask layer 630 being formed on silicon layer 620 at one of the various stages of fabrication, according to some embodiments of the present disclosure. The coating mask layer 630 on the silicon layer 620 may include a Photoresist (PR) material.

Figure 6C is a cross-sectional view of grating coupler 600 including middle portion 632 of mask layer 630, middle portion 632 of mask layer 630 being formed on silicon layer 620 at one of the various stages of fabrication, according to some embodiments of the present disclosure. The mask layer 630 is patterned to leave a middle portion 632 on the silicon layer 620, for example by removing the left side portion 633 and the right side portion 631 based on waveguide lithography and development.

Figure 6D is a cross-sectional view of a grating coupler 600 including an intermediate portion 622 of a silicon layer 620, the silicon layer 620 being formed at one of various stages of fabrication, according to some embodiments of the present disclosure. Since the mask layer 630 is patterned to have openings over the left and

right portions

623, 621 of the silicon layer 620, the left and

right portions

623, 621 exposed by the mask layer are removed, for example, by a wet or dry etch process.

Fig. 6E is a cross-sectional view of the grating coupler 600 with the mask layer 632 removed at one of the various stages of fabrication, according to some embodiments of the present disclosure. For example, the mask layer 632 may be removed by resist stripping.

Figure 6F is a cross-sectional view of the grating coupler 600 including another mask layer 640 formed on the remaining silicon layer 622 at one of the various stages of fabrication, according to some embodiments of the present disclosure. The coating mask layer 640 on the silicon layer 622 may include a Photoresist (PR) material. As shown in fig. 6F, the coating mask layer 640 covers not only the silicon layer 622 but also left and right portions of the first layer 610.

Fig. 6G is a cross-sectional view of a grating coupler 600 including a plurality of trenches 646, the trenches 646 being formed in the silicon layer 622 at one of the various stages of fabrication, according to some embodiments of the present disclosure. Based on waveguide lithography and development, the mask layer 640 is patterned to include a plurality of stacks 645 formed on the silicon layer 622, for example by etching the mask layer 640 to form a plurality of trenches 646 between the plurality of stacks 645.

Fig. 6H is a cross-sectional view of a grating coupler 600 including a plurality of gratings 625, the plurality of gratings 625 formed at one of various stages of fabrication, according to some embodiments of the present disclosure. Since the mask layer 640 is patterned to have openings 646 over the silicon layer 622, the exposed portions of the silicon layer 622 are removed (e.g., by a wet etch process or a dry etch process) to form the plurality of gratings 625.

Fig. 6I is a cross-sectional view of the grating coupler 600 with the mask layer 640 removed at one of the various stages of fabrication, according to some embodiments of the present disclosure. For example, the mask layer 640 may be removed by photoresist stripping. In the embodiment shown in fig. 6I, the silicon layer 622 includes a grating portion 651 and a waveguide portion 652 coupled to the grating portion 651. The grating portion 651 includes a plurality of coupling gratings 625 separated by shallow trenches 626. The shallow trenches 626 may be formed by a single step etch process.

Fig. 6J is a cross-sectional view of the grating coupler 600 with the mask layer 640 removed at one of the various stages of fabrication, according to some embodiments of the present disclosure. In the embodiment shown in fig. 6J, the silicon layer 622 includes a grating portion 651 and a waveguide portion 652 coupled to the grating portion 651. The grating portion 651 comprises a plurality of coupling gratings 625 separated by deep trenches 626. The deep trench 626 may be formed by a multi-step etch process. For example, using the patterned mask layer 640 shown in fig. 6H over the silicon layer 622, at least two or three etching steps may be performed on the exposed portions of the silicon layer 622 to form the plurality of high gratings 625 shown in fig. 6J.

Fig. 7 illustrates a cross-sectional view of an exemplary optical device 700, according to some embodiments of the present disclosure. As shown in fig. 7, optical device 700 includes an electronic die 710 and a photonic die 720, where electronic die 710 and photonic die 720 are connected by an interposer 740, via bumps 742 and bonding pads 741. Electronic die 710, photonic die 720, and interposer 740 are covered by an encapsulation material 730, encapsulation material 730 having an opening atop trench 750 of photonic die 720. Optical device 700 also includes a grating coupler 751 in trench 750 for transmitting optical signals between semiconductor photonics die 720 and optical fiber array 760. Grating coupler 751 is used herein as an optical input/output (I/O) device for optical device 700.

According to some embodiments, grating coupler 751 is configured to receive optical signals from fiber array 760 at an angle measured between the axis of fiber array 760 and a direction perpendicular to the surface of grating coupler 751. According to various embodiments, the height of fiber array 760 compared to grating coupler 751 can be adjusted between 0 and 100 microns; and the angle of fiber array 760 can be adjusted between 0 and 20 degrees. The fiber angle may be modified to improve the coupler efficiency of grating coupler 751.

Fig. 8 illustrates a cross-sectional view of an exemplary optical die 800 with tilted metal layer openings, according to some embodiments of the present disclosure. As shown in fig. 8, the optical die 800 includes a substrate 810, a silicon oxide layer 820 disposed on the substrate 810, and a grating coupler 830 disposed on the silicon oxide layer 820. A grating coupler 830 located on the optical die 800 is configured to transmit optical signals between the optical die 800 and the optical fiber array 860. The optical fiber array 860 may be bonded to the semiconductor photonics die 800 by a transparent epoxy adhesive.

As shown in fig. 8, optical die 800 also includes a plurality of metal layers M1841, M2842 … M _ top845 located over grating coupler 830. Each of the plurality of metal layers has an opening over the grating coupler 830 such that the openings of the plurality of metal layers form a channel 850 extending in a first direction for passing optical signals between the optical fiber array 860 and the grating coupler 830. A non-zero angle θ in851 is formed between the first direction and a second direction (Z direction in fig. 8) perpendicular to the surface of the substrate 810. According to some embodiments, the angle θ _ in851 is between 5 and 20 degrees. In one embodiment, channel 850 includes empty space for transmitting optical signals. In another embodiment, the channel 850 comprises a dielectric material, such as: oxide material to form a small waveguide for guiding the optical signal along the tilt angle θ _ in 851.

During fabrication of the channel 850, the angle θ _ in851 may be determined based on at least two of: a total height H _ n872 in the Z direction, a grating position D _ n871 in the R direction, and a channel length M _ n 873 of the plurality of metal layers M1841, M2842 … M _ top 845. Grating position D _ n871 is the shift distance in the lateral R direction between the opening of the lowest metal layer M1841 and the opening of the top metal layer M _ top 845. For example, a cosine value of angle θ _ in851 may be calculated based on a ratio between height H _ n872 and channel length M _ n 873, such that angle θ _ in851 may be determined based on the cosine value. In another example, the tangent value of the angle θ _ in851 may be calculated based on the ratio between the raster position D _ n871 and the height H _ n872, such that the angle θ _ in851 may be determined based on the tangent value.

On the other hand, once the desired angle θ _ in851 is determined, each of the three may be determined given any of the raster position D _ n871, the height H _ n872 and the channel length M _ n 873. For example, based on a given height H _ n872, raster position D _ n871 may be determined based on the tangent value of angle θ _ in851, and channel length M _ n 873 may be determined based on the cosine value of angle θ _ in 851.

Fiber array 860 also has a fiber angle θ _ fiber861 measured between the axis of fiber array 860 and the Z-direction perpendicular to the surface of substrate 810. Once the channel 850 is formed at the desired angle θ _ in851 for good grating coupling efficiency, the optical signal passing through the channel 850 will follow the desired angle θ _ in851 regardless of the fiber angle θ _ fiber861, and even if the fiber array 860 is not accurately aligned with the openings of the top metal layer M _ top845 in the Y-direction and/or the R-direction. In one embodiment, the desired angle θ _ in851 is maintained when each metal layer is formed over first metal layer M1841. For example, the position of the opening at the second metal layer M2842, the distance between the first metal layer M1841 and the second metal layer M2842, and the desired angle θ _ in851 are determined based on the position of the opening at the first metal layer M1841. When a dielectric layer is present between every two adjacent metal layers, the dielectric layer may also be patterned to maintain the desired angle θ _ in851 as the dielectric layer is formed. In another embodiment, the dielectric layer is not patterned and the dielectric material fills the openings at each metal layer to form dielectric vias 850. The dielectric via 850 is defined by the metal material of the metal layer and the vias V1, V2 … V _ top, and forms a waveguide with a desired angle θ _ in851 to guide the optical signal through the dielectric via 850.

Thus, once the channels 850 are formed at the desired angle θ _ in851 according to the operating wavelength, the optical die 800 can be used with a variety of fiber arrays having a variety of fiber angles, which can reduce the cost and complexity of the semiconductor device. In one example, depending on the operating wavelength, the channel 850 is formed at a desired angle θ _ in851 equal to 12 degrees, and the fiber angle θ _ fiber861 may be capable of being adjusted between 0 and 20 degrees.

As shown in fig. 8, vias V1, V2 … V _ top are used to connect the multiple metal layers M1841, M2842 … M _ top 845. In some embodiments, the metal layers and vias may comprise materials such as copper, aluminum, silver, silicon, etc. to reduce optical loss during optical I/O coupling.

In some embodiments, the central convex shape is symmetrical about a direction perpendicular to the grating plane. In some embodiments, the medial convex shape comprises at least three layers. In some embodiments, the grating coupler is configured to receive optical signals from an optical fiber array at a non-zero angle, wherein the non-zero angle is measured between an axis of the optical fiber array and a direction perpendicular to the grating plane. In some embodiments, the non-zero angle is between 0 degrees and about 15 degrees. In some embodiments, the grating coupler comprises silicon and silicon oxide; and the silicon in the grating coupler has a thickness between 250 nm and 350 nm.

In some embodiments, the first lateral direction and the second lateral direction are parallel to a surface of the semiconductor photonics die and perpendicular to each other in a grating plane. In some embodiments, the plurality of coupling gratings are configured to couple light received from the waveguide, and the light propagates along the second lateral direction. In some embodiments, the second layer of the plurality of coupled gratings has a duty cycle that increases along the second lateral direction. In some embodiments, the second layer of the plurality of coupled gratings has a duty cycle that decreases along the second lateral direction. In some embodiments, the second layer of the plurality of coupling gratings has a duty cycle that first increases and then decreases in the second lateral direction. In some embodiments, the second layer of the plurality of coupling gratings has a duty cycle that first decreases and then increases along the second lateral direction. In some embodiments, the second layer of the plurality of coupling gratings has a duty cycle between about 20% and about 50%. In some embodiments, the first layer of the plurality of coupled gratings has a duty cycle that varies along the second lateral direction.

In some embodiments, the non-zero angle is between 5 and 20 degrees. In some embodiments, the at least one grating coupler comprises a plurality of coupled gratings; each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section in a second lateral direction having a medial convex shape; and a total width of the intermediate convex shape in the second lateral direction is less than 600 nm. In some embodiments, the height of the array of optical fibers compared to the at least one grating coupler is adjustable between 0 and 100 microns; and an angle of the array of optical fibers is adjustable between 0 and 20 degrees, wherein the angle of the array of optical fibers is measured between an axis of the array of optical fibers and the second direction perpendicular to the surface of the substrate. In some embodiments, the optical fiber array is bonded to the semiconductor photonics die by a transparent epoxy adhesive.

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the various aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

[ description of symbols ]

100: device for measuring the position of a moving object

102: electronic die/die

104: light source tube core/tube core

106: photonic die/die

108. 760, 860: optical fiber array

110. 740: intermediary article

112: wire bonding

114: printed Circuit Board (PCB) substrate

116: through Silicon Via (TSV)

118: fiber to chip grating coupler

200: fiber-to-chip grating coupler/grating coupler

202: grating area

204: periodic grating/grating

206. 212, and (3): length of

208: edge of a container

210: waveguide

214: radius of curvature

216: arc length/length

220: incident light field

222. 258: angle of rotation

224: silicon substrate/substrate

226. 310, 410, 510, 820: silicon oxide layer

228. 320, 420, 520: silicon layer

232. 274, 362, 363, 431: thickness of

234. 236: thickness/step height

238. 432: total thickness of

240. 242, 244, 341, 344, 351, 352, 353, 354, 355, 441, 442, 451, 541, 542, 551: width of

241: period of time

246: middle convex part

247. 623 and 633: left side part

248: intermediate base part

249. 621, 631: right side part

252: optical fiber

254: axial line

256: z axis

260: core diameter/optical fiber core diameter

262: distance between two adjacent plates

270: radiation field/light field

272: coating layer

290: bottom reflective layer

292: top reflective layer

300. 400, 500, 600, 751, 830: grating

couplers

301, 401, 501: total width

302. 402, 502: groove

304. 404, 504: coupled grating/grating

321. 521: first sublayer

322. 323, 421, 422, 523, 645: stacking

331: thickness/first etch thickness

332. 532: second etching thickness

333: total thickness/third etch thickness

342: left side partial width

343: width of right side part

522: stack/second sublayer

531: first etching thickness

533: third etching thickness

610: first layer

620: second layer/silicon layer

622: intermediate part/silicon layer

625: grating/coupling grating/high grating

626: shallow/deep trench

630: mask layer/coating mask layer

632: intermediate part/mask layer

640: mask layer/coating mask layer/patterning mask layer

646: trench/opening

651: light grid part

652: waveguide section

700: optical device

710: electronic die

720: photonic die/semiconductor photonics die

730: packaging material

741: bonding pad

742: bump

750: groove

800: optical die/semiconductor photonic die

810: substrate

841. M1: metal layer/lowest metal layer

842. 843, 844, M2, M3, M4: metal layer

845. M _ top: metal layer/top metal layer

850: channel

851. θ _ in: non-zero/desired angle

861. θ _ fiber: angle of optical fiber

871. D _ n: position of grating

872. H _ n: total height/height

873. M _ n: length of channel

A-A': radial direction

B-B', R, Y, Z: direction of rotation

O: center of a ship

V1, V2, V3, V _ top: through hole

Claims

1. An apparatus for optical coupling, comprising:

a substrate;

a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section in a second lateral direction of an intermediate convex shape, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane; and

a cladding layer comprising an optical medium, wherein the cladding layer fills on the grating coupler.