U.S. patent application number 16/682502 was filed with the patent office on 2021-05-13 for non-planar grating couplers for antennas.
The applicant listed for this patent is GLOBALFOUNDRIES U.S. Inc.. Invention is credited to Yusheng Bian, Ajey Poovannummoottil Jacob, Bo Peng, Michal Rakowski.
Application Number | 20210141156 16/682502 |
Document ID | / |
Family ID | 1000005550570 |
Filed Date | 2021-05-13 |
![](/patent/app/20210141156/US20210141156A1-20210513\US20210141156A1-2021051)
United States Patent
Application |
20210141156 |
Kind Code |
A1 |
Bian; Yusheng ; et
al. |
May 13, 2021 |
NON-PLANAR GRATING COUPLERS FOR ANTENNAS
Abstract
Structures including a grating coupler and methods of
fabricating such structures. The structure includes a waveguide
core, a bend, and a grating coupler coupled to the waveguide core
by the bend. The grating coupler includes grating structures that
are positioned with a spaced relationship in a layer stack above
the bend.
Inventors: |
Bian; Yusheng; (Ballston
Lake, NY) ; Jacob; Ajey Poovannummoottil;
(Watervliet, NY) ; Rakowski; Michal; (Ballston
Spa, NY) ; Peng; Bo; (Wappingers Falls, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES U.S. Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
1000005550570 |
Appl. No.: |
16/682502 |
Filed: |
November 13, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/34 20130101 |
International
Class: |
G02B 6/34 20060101
G02B006/34 |
Claims
1. A structure comprising: a substrate; a waveguide core in a first
plane relative to the substrate; a bend that curves upwardly
relative to the waveguide core and away from the first plane; and a
first grating coupler coupled to the waveguide core by the bend,
the first grating coupler including a first plurality of grating
structures positioned with a spaced relationship above the bend in
a second plane that is oriented substantially perpendicular to the
first plane.
2. The structure of claim 1 wherein the first plurality of grating
structures have substantially equal dimensions.
3. The structure of claim 1 wherein the first plurality of grating
structures have unequal dimensions.
4. The structure of claim 1 wherein the bend includes a taper.
5. The structure of claim 1 wherein the first plurality of grating
structures have a uniform pitch and a uniform duty cycle.
6. The structure of claim 1 wherein the first plurality of grating
structures have a pitch that is apodized and/or a duty cycle that
is apodized.
7. The structure of claim 1 wherein the first plurality of grating
structures are spaced in a first direction in the second plane, and
further comprising: a second grating coupler including a second
plurality of grating structures that are spaced in a second
direction transverse to the first direction.
8. The structure of claim 1 wherein the waveguide core is comprised
of a first material, and the bend and the first grating coupler are
comprised of a second material having a different composition than
the first material.
9. The structure of claim 1 wherein the first plurality of grating
structures are positioned directly over a portion of the bend.
10. The structure of claim 1 wherein the first plurality of grating
structures are laterally offset from the bend.
11. The structure of claim 10 wherein at least one of the first
plurality of grating structures is laterally adjacent to a portion
of the bend.
12. The structure of claim 1 wherein the bend is arranged in part
over the waveguide core.
13. The structure of claim 1 wherein at least one of the first
plurality of grating structures is comprised of a first material,
and at least one of the first plurality of grating structures is
comprised of a second material having a different composition than
the first material.
14. The structure of claim 1 wherein the first grating coupler
includes a layer connecting the first plurality of grating
structures, and the layer is thinner than the first plurality of
grating structures.
15. The structure of claim 1 wherein the first grating coupler is
configured to function as an antenna for off-chip emission of laser
pulses at an emission angle.
16. (canceled)
17. The structure of claim 1 wherein a dielectric material fills
spaces between the first plurality of grating structures.
18. A method comprising: forming a waveguide core in a first plane
relative to a substrate; forming a bend that curves upwardly
relative to the waveguide core and away from the first plane; and
forming a grating coupler coupled to the waveguide core by the
bend, wherein the grating coupler includes a plurality of grating
structures positioned with a spaced relationship above the bend in
a second plane that is oriented substantially perpendicular to the
first plane.
19. The method of claim 18 wherein the plurality of grating
structures are positioned with the spaced relationship in a
vertical direction relative to the bend.
20. The method of claim 18 wherein the plurality of grating
structures are patterned from a plurality of layers deposited to
form a layer stack, and the plurality of layers are composed of one
or more materials.
21. The method of claim 18 wherein the waveguide core is comprised
of a first material, and the bend and the grating coupler are
comprised of a second material having a different composition than
the first material.
Description
BACKGROUND
[0001] The present invention relates to photonics chips and, more
particularly, to structures including a grating coupler and methods
of fabricating such structures.
[0002] Light Detection and Ranging (LIDAR) is a laser-mapping
technology that measures distance to a target by illuminating the
target with pulsed laser light and measuring pulses reflected from
the target with a sensor. LIDAR is used in, for example, autonomous
robots and self-driving cars. A LIDAR system may be embodied in a
photonics chip that integrates optical components, such as
waveguides and bends, and electronic components, such as
field-effect transistors, into a unified platform. Among other
factors, layout area, cost, and operational overhead may be reduced
by the integration of both types of components in the photonics
chip.
[0003] Grating couplers are commonly used in photonics chips to
provide antennas in LIDAR systems, as well as to provide antennas
in silicon photonics phased arrays. Grating couplers are planar
structures that direct laser pulses off-chip at a given emission
angle. Due to limitations placed on the emission angle by their
planar construction, grating couplers inherently have a restricted
vertical field of view. For example, the emission angle out of the
plane of a grating coupler may be limited to +/-15 degrees.
[0004] Improved structures including a grating coupler and methods
of fabricating such structures are needed.
SUMMARY
[0005] In an embodiment of the invention, a structure includes a
waveguide core, a bend, and a grating coupler coupled to the
waveguide core by the bend. The grating coupler includes a
plurality of grating structures positioned with a spaced
relationship in a layer stack above the bend.
[0006] In an embodiment of the invention, a method includes forming
a waveguide core, forming a bend, and forming a grating coupler
coupled to the waveguide core by the bend. The grating coupler
includes a plurality of grating structures positioned with a spaced
relationship in a layer stack above the bend.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] 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.
[0008] 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.
[0009] FIG. 2 is a cross-sectional view of the structure at a
fabrication stage subsequent to FIG. 1.
[0010] FIG. 3 is a cross-sectional view taken generally along line
3-3 in FIG. 2.
[0011] FIGS. 3A-3C are cross-sectional views of structures in
accordance with alternative embodiments of the invention.
[0012] FIG. 4 is a cross-sectional view of the structure at a
fabrication stage subsequent to FIG. 3.
[0013] FIGS. 5-8 are cross-sectional views of structures in
accordance with alternative embodiments of the invention.
DETAILED DESCRIPTION
[0014] With reference to FIG. 1 and in accordance with embodiments
of the invention, a layer stack 10 is formed in a region of a
silicon-on-insulator (SOI) wafer. The SOI wafer may include a
device layer (not shown), a buried insulator layer 14, and a
substrate 16 separated from the device layer by the buried
insulator layer 14. The buried insulator layer 14 may be composed
of a dielectric material, such as silicon dioxide, and the device
layer and substrate 16 may be composed of a single-crystal
semiconductor material, such as single-crystal silicon.
[0015] The layer stack 10 includes layers 18, 20, 22, 24 that are
composed of a given material and layers 19, 21, 23 that are
composed of a given material having a different composition than
the material of the layers 18, 20, 22, 24. The layers 18, 20, 22,
24 and the layers 19, 21, 23 alternate with position in a vertical
direction within the layer stack 10 such that the materials also
alternate. In an embodiment, the layers 18, 20, 22, 24 may be
composed of a dielectric material, such as silicon nitride,
deposited by chemical vapor deposition. In an alternative
embodiment, the layers 18, 20, 22, 24 may be composed of silicon
carbon nitride (e.g., nitrogen-doped silicon carbide (SiCN)),
commonly known as NBloK, deposited by chemical vapor deposition. In
an embodiment, the layers 18, 20, 22, 24 may be composed of a
non-dielectric material, such as polycrystalline silicon (i.e.,
polysilicon) or amorphous silicon, deposited by chemical vapor
deposition. The layers 19, 21, 23 may be composed of a dielectric
material, such as silicon dioxide, having a lower index of
refraction than the material constituting the layers 18, 20, 22,
24. The layer stack 10 may be arranged directly on the buried
insulator layer 14 or, in an alternative embodiment, on one or more
dielectric layers (not shown) positioned between the layer stack 10
and the buried insulator layer 14.
[0016] The bottommost layer 18 in the layer stack 10 is deposited
conformally over a mandrel 25. In that regard, the mandrel 25 may
be patterned by lithography and etching processes from a dielectric
layer deposited on the buried insulator layer 14. The bottommost
layer 18, which is deposited after the mandrel 25 is formed,
includes sections 26 on and adjacent to the side surfaces 25a (FIG.
2) of the mandrel 25 and a section 28 on and adjacent to the top
surface 25b (FIG. 2) of the mandrel 25. The sections 26 of the
layer 18 may include a concave curvature, which is not shown for
simplicity of illustration, at and near the lower corners of the
mandrel 25 defined by the intersections between the side surfaces
25a and the buried insulator layer 14.
[0017] With reference to FIGS. 2, 3 in which like reference
numerals refer to like features in FIG. 1 and at a subsequent
fabrication stage, the layers 20, 21, 22, 23, 24 of the layer stack
10 are patterned with lithography and etching processes in which an
etch mask is formed over the layer stack 10 and the masked layers
20, 21, 22, 23, 24 are etched with an etching process, such as
reactive ion etching. The patterning of the layers 20, 22, 24
defines a grating coupler 30 with the patterned layers 20, 22, 24
providing grating structures that are positioned in a vertical
direction relative to the SOI wafer. The patterned layers 20, 22,
24 of the grating coupler 30 have a spaced relationship in which
the grating structures are located at different distances in the
layer stack 10 from the buried insulator layer 14.
[0018] The patterned layers 20, 22, 24 of the grating coupler 30
are disconnected from each other, and the spaces between the
patterned layers 20, 22, 24 are filled by the dielectric material
of the patterned layers 21, 23. In an embodiment, the patterned
layers 20, 22, 24 may have equal dimensions. For example, the
patterned layers 20, 22, 24 may have equal widths, w. In an
alternative embodiment and as shown in FIG. 3A, the patterned
layers 20, 22, 24 may have unequal dimensions that are provided by
individually patterning the layers 20, 22, 24.
[0019] The layers 18, 19 of the layer stack 10 are patterned, after
patterning the grating coupler 30, with lithography and etching
processes in which an etch mask is formed over the grating and
layers 18, 19, and the masked layers 18, 19 are etched with an
etching process, such as reactive ion etching. The patterning of
the layer 18 defines a waveguide core 32 and a bend 34 that couples
the waveguide core 32 to the grating coupler 30.
[0020] The bend 34, which is located adjacent to the mandrel 25,
may include one of the sections 26 of the layer 18 and the entirety
of the section 28 of the layer 18. In an alternative embodiment,
the bend 34 may only include one of the sections 26 of the layer 18
and not include the section 28 of the layer 18. In an alternative
embodiment, the bend 34 may include one of the sections 26 of the
layer 18 and a portion of the section 28 of the layer 18.
[0021] The dimensions (i.e., the length and width) of the patterned
layers 20, 22, 24 may be adjusted to be equal or substantially
equal to the dimensions of the bend 34. For example, the dimensions
of each of the patterned layers 20, 22, 24 may be equal or
substantially equal to the dimensions of the top surface of the
patterned section 28 of the layer 18. For example, the patterned
layers 20, 22, 24 and the patterned section 28 of the layer 18 may
have equal widths, w. In an embodiment, the grating structures of
the grating coupler 30 may be arranged at least in part directly
over the bend 34. In an embodiment, the waveguide core 32 may be
narrower in width than the bend 34.
[0022] The waveguide core 32 guides optical signals (e.g.,
modulated laser pulses) from a laser 41 to the grating coupler 30.
The bend 34, which curves upwardly in a vertical direction relative
to the waveguide core 32, guides optical signals arriving from the
waveguide core 32 to the grating coupler 30. The grating coupler 30
may operate as an antenna for directing the optical signals
off-chip at an emission angle, .theta., that has a significant
component parallel to the top surface of the buried insulator layer
14. The bend 34 provides a change in direction that redirects the
optical signals from being guided within the plane of the waveguide
core 32 to being guided in a plane containing the grating coupler
30. The plane containing the grating coupler 30 may be oriented in
a vertical or substantially vertical position relative to a
horizontal plane containing the waveguide core 32.
[0023] The emission angle of the optical signals from the grating
coupler 30 is sloped or inclined relative to the horizontal plane.
The ability to provide an emission angle in a direction that is
substantially horizontal contrasts with conventional grating
coupler antennas, which are limited to emission angles in a
direction that is substantially vertical. In embodiments, a
substantially horizontal emission angle may be less than or equal
to 30.degree. relative to the horizontal plane. For comparison, a
substantially vertical emission angle may be greater than or equal
to 60.degree. relative to the horizontal plane. The substantially
horizontal emission angle may be provided without the need to
mechanically rotate the photonics chip carrying the antenna. The
grating coupler 30 may be replicated on the photonics chip to
provide an array of antennas that feature different emission
angles.
[0024] In an alternative embodiment and as shown in FIG. 3B, the
bend 34 may include a taper that widens with increasing distance
from the waveguide core 32. In an embodiment, the patterned layers
20, 22, 24 of the grating coupler 30 may be periodically arranged
with a uniform pitch and duty cycle. In an alternative embodiment
and as shown in FIG. 3C, the patterned layers 20, 22, 24 of the
grating coupler 30 may have apodized (i.e., aperiodic) positions
with a pitch and/or a duty cycle that varies as a function of
distance from the bend 34. The thickness of the layers 20, 21, 22,
23, 24 may be used to determine the pitch and duty cycle of the
grating structures of the grating coupler 30. In an alternative
embodiment, the patterned layers 20, 22, 24 of the grating coupler
30 may be laterally offset relative to the bend 34 in a
"stair-step" arrangement.
[0025] In an embodiment, the grating coupler 30, the waveguide core
32, and the bend 34 may be composed of the same material. For
example, the grating coupler 30, the waveguide core 32, and the
bend 34 may be composed of the same dielectric material, such as
silicon nitride. In an alternative embodiment, the grating coupler
30, the waveguide core 32, and the bend 34 may be composed of
different materials. For example, the waveguide core 32 may be
composed of single-crystal silicon, and the bend 34 and grating
coupler 30 may be composed of, for example, polysilicon. In an
alternative embodiment, the grating structures of the grating
coupler 30 may be composed of different materials. For example, the
patterned layers 20 and 24 providing some of the grating structures
may be composed of silicon nitride, and the patterned layer 22
providing another of the grating structures may be composed of
polysilicon.
[0026] With reference to FIG. 4 in which like reference numerals
refer to like features in FIG. 2 and at a subsequent fabrication
stage, an interconnect structure 36 may be formed by middle-of-line
and back-end-of-line processing over the entire SOI wafer. The
interconnect structure 36 may include dielectric layers and
metallization that is coupled with electronic components and active
optical components that are integrated into a photonics chip that
includes the antenna. For example, the electronic components may
include field-effect transistors that are fabricated by
front-end-of-line processing.
[0027] The interconnect structure 36 should be free of
metallization on the emission side of the grating coupler 30 in
order to avoid blocking or obstructing the modulated laser pulses
emitted from the antenna. The distance between the grating coupler
30 and the chip edge can be in the range of several microns to
tens, or even hundreds, of microns.
[0028] With reference to FIG. 5 in which like reference numerals
refer to like features in FIG. 4 and in accordance with alternative
embodiments of the invention, a waveguide core 40 may be formed
independently from the formation of the bend 34 and the waveguide
core 40 may be coupled by the bend 34 to the grating coupler 30.
The grating coupler 30 and bend 34 are located above the waveguide
core 40 in the antenna. The waveguide core 40 may be formed by
patterning the single-crystal semiconductor material of the device
layer of the SOI wafer with lithography and etching processes in
which an etch mask is formed over the device layer and the masked
device layer is etched with an etching process, such as reactive
ion etching. Optical signals are coupled from the waveguide core 40
upward to the bend 34 and then directed by the bend 34 to the
grating coupler 30.
[0029] With reference to FIG. 6 in which like reference numerals
refer to like features in FIG. 4 and in accordance with alternative
embodiments of the invention, the grating coupler 30 may be
integrated on a photonics chip with a grating coupler 42 having a
planar construction to provide a more complex antenna. The grating
structures of the grating coupler 30 are spaced in a direction
(e.g., the vertical direction) relative to the SOI wafer, and the
grating structures 43 of the grating coupler 42 are spaced in a
direction (e.g., the horizontal direction) that is transverse to
the direction of the spaced relationship of the grating structures
of the grating coupler 30.
[0030] The combination of the grating couplers 30, 42 may permit
optical signals to be emitted over a widened range of emission
angles, which provides an antenna having an expanded field of view.
In an embodiment, the grating coupler 30 may emit optical signals
over a given range of emission angles, and the grating coupler 42
may emit optical signals over a different range of emission angles.
In an embodiment, the grating coupler 30 may emit optical signals
over a given range of emission angles, and the grating coupler 42
may emit optical signals over a similar range of emission angles.
An additional grating coupler like grating coupler 30, but with a
different emission angle as tailored by, for example, pitch and/or
duty cycle, may be added to the antenna to further expand the field
of view. The grating couplers 30, 42 may be replicated to provide a
heterogeneous array of antennas.
[0031] With reference to FIG. 7 in which like reference numerals
refer to like features in FIG. 4 and in accordance with alternative
embodiments of the invention, the grating coupler 30 may include a
layer 44 that is positioned adjacent to the bend 34 and patterned
when the layers 20, 22, 24 are patterned. Optical signals are
transferred from the bend 34 to the patterned layer 44. Because of
the addition of the patterned layer 44, the grating coupler 30 may
be offset laterally from the bend 34 and no longer directly over
the bend 34. In an embodiment, the grating coupler 30 may be
composed of a dielectric material, such as silicon nitride, and the
waveguide core 32 and bend 34 may be composed of polysilicon.
[0032] With reference to FIG. 8 in which like reference numerals
refer to like features in FIG. 4 and in accordance with alternative
embodiments of the invention, the patterned layers 20, 22, 24
providing the grating structures of the grating coupler 30 may be
connected together by a layer 46. In an embodiment, the layer 46 is
arranged at aligned side edges of the grating structures of the
grating coupler 30. The layer 46 may directly connect the grating
structures of the grating coupler 30 to the bend 34. The layer 46
may be thinner than the grating structures of the grating coupler
30.
[0033] The methods as described above are used in the fabrication
of integrated circuit chips. The resulting integrated circuit chips
can be distributed by the fabricator in raw wafer form (e.g., as a
single wafer that has multiple unpackaged chips), as a bare die, or
in a packaged form. The chip may be integrated with other chips,
discrete circuit elements, and/or other signal processing devices
as part of either an intermediate product or an end product. The
end product can be any product that includes integrated circuit
chips, such as computer products having a central processor or
smartphones.
[0034] References herein to terms modified by language of
approximation, such as "about", "approximately", and
"substantially", are not to be limited to the precise value
specified. The language of approximation may correspond to the
precision of an instrument used to measure the value and, unless
otherwise dependent on the precision of the instrument, may
indicate +/-10% of the stated value(s).
[0035] References herein to terms such as "vertical", "horizontal",
etc. are made by way of example, and not by way of limitation, to
establish a frame of reference. The term "horizontal" as used
herein 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 horizontal, as just defined. The
term "lateral" refers to a direction within the horizontal
plane.
[0036] A feature "connected" or "coupled" to or with another
feature may be directly connected or coupled to or with the other
feature or, instead, one or more intervening features may be
present. A feature may be "directly connected" or "directly
coupled" to or with another feature if intervening features are
absent. A feature may be "indirectly connected" or "indirectly
coupled" to or with another feature if at least one intervening
feature is present. A feature "on" or "contacting" another feature
may be directly on or in direct contact with the other feature or,
instead, one or more intervening features may be present. A feature
may be "directly on" or in "direct contact" with another feature if
intervening features are absent. A feature may be "indirectly on"
or in "indirect contact" with another feature if at least one
intervening feature is present.
[0037] The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
* * * * *