U.S. patent application number 16/297981 was filed with the patent office on 2020-06-18 for methods of producing slanted gratings.
This patent application is currently assigned to APPLIED Materials, Inc.. The applicant listed for this patent is APPLIED Materials, Inc.. Invention is credited to Megan Clark, Morgan Evans, Rutger Meyer Timmerman Thijssen.
Application Number | 20200192009 16/297981 |
Document ID | / |
Family ID | 71073563 |
Filed Date | 2020-06-18 |
United States Patent
Application |
20200192009 |
Kind Code |
A1 |
Evans; Morgan ; et
al. |
June 18, 2020 |
METHODS OF PRODUCING SLANTED GRATINGS
Abstract
Methods of producing gratings with trenches having variable
height and width are provided. In one example, a method includes
providing an optical grating layer atop a substrate, and providing
a patterned hardmask over the optical grating layer. The method may
include forming a mask over just a portion of the optical grating
layer and the patterned hardmask, and etching a plurality of
trenches into the optical grating layer to form an optical grating.
After trench formation, at least one of the following grating
characteristics varies between one or more trenches of the
plurality of trenches: a trench depth and a trench width.
Inventors: |
Evans; Morgan; (Manchester,
MA) ; Meyer Timmerman Thijssen; Rutger; (Sunnyvale,
CA) ; Clark; Megan; (Gloucester, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
APPLIED Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
APPLIED Materials, Inc.
Santa Clara
CA
|
Family ID: |
71073563 |
Appl. No.: |
16/297981 |
Filed: |
March 11, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62780138 |
Dec 14, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02164 20130101;
H01L 21/31105 20130101; H01L 21/3065 20130101; G02B 5/1842
20130101; H01J 37/3053 20130101; H01L 21/32136 20130101; G02B
5/1857 20130101 |
International
Class: |
G02B 5/18 20060101
G02B005/18 |
Claims
1. A method of forming a diffracted optical element, comprising:
providing an optical grating layer atop a substrate; providing a
patterned hardmask over the optical grating layer; forming a mask
over just a portion of the optical grating layer and the patterned
hardmask, wherein the mask is formed directly atop a top surface of
the optical grating layer; and etching a plurality of trenches into
the optical grating layer to form an optical grating, wherein a
first depth of a first trench of the plurality of trenches is
different than a second depth of a second trench of the plurality
of trenches.
2. The method of claim 1, wherein a first width of the first trench
of the plurality of trenches is different than a second width of
the second trench of the plurality of trenches.
3. The method of claim 1, further comprising patterning the mask
prior to etching the plurality of trenches into the optical grating
layer.
4. The method of claim 1, wherein the etching comprises performing
an angled ion etch.
5. The method of claim 4, wherein the angled ion etch is performed
by a reactive ion beam, and wherein the substrate is scanned along
a scan direction with respect to the reactive ion beam.
6. The method of claim 1, further comprising forming the patterned
hardmask as a plurality of hardmask elements each separated from
one another by a gap, wherein a first subset of the plurality of
hardmask elements is adjacent a second subset of the plurality of
hardmask elements, wherein each of the first subset of the
plurality of hardmask elements has a first width, wherein each of
the second subset of the plurality of hardmask elements has a
second width, and wherein the first width is greater than the
second width.
7. The method of claim 6, further comprising forming the mask to
include two or more heights relative to a top surface of the
optical grating layer.
8. The method of claim 6, further comprising forming the mask over
just the second subset of the plurality of hardmask elements.
9. The method of claim 6, wherein the first width of the first
trench of the plurality of trenches is approximately equal to the
second width of the second trench of the plurality of trenches.
10. A method of forming an optical grating component, comprising:
providing an optical grating layer atop a substrate; providing a
patterned hardmask over the optical grating layer; forming a mask
over just a portion of the optical grating layer and the patterned
hardmask, wherein the mask has a lower etch resistance than the
patterned hardmask, and wherein the mask is formed directly atop a
top surface of the optical grating layer; and etching a plurality
of trenches into the optical grating layer to form an optical
grating, wherein a trench depth varies between one or more trenches
of the plurality of trenches.
11. The method of claim 10, wherein the etching comprises
performing an angled ion etch.
12. The method of claim 11, wherein the angled ion etch is applied
to each of: the optical grating layer, the patterned hardmask, and
the mask.
13. The method of claim 11, wherein a first trench of the plurality
of trenches formed in the portion of the optical grating layer has
a first depth, wherein a second trench of the plurality of trenches
formed in a second portion of the optical grating layer has a
second depth, and wherein the second depth is greater than the
first depth.
14. The method of claim 10, further comprising patterning the mask
prior to etching the plurality of trenches into the optical grating
layer.
15. The method of claim 10, further comprising forming the
patterned hardmask as a plurality of hardmask elements each
separated from one another by a gap, wherein a first hardmask
element of the plurality of the hardmask elements has a different
width than a width of a second hardmask element of the plurality of
hardmask elements.
16. The method of claim 15, further comprising forming a first
subset of the plurality of hardmask elements adjacent a second
subset of the plurality of hardmask elements, wherein each of the
first subset of the plurality of hardmask elements has a first
width, wherein each of the second subset of the plurality of
hardmask elements has a second width, wherein the first width is
greater than the second width, wherein each of the plurality of
trenches has an approximately uniform width.
17. The method of claim 16, further comprising forming the mask
over just the second subset of the plurality of hardmask
elements.
18. A method of forming an optical grating component, comprising:
providing an optical grating layer atop a substrate; providing a
patterned hardmask over the optical grating layer; forming a mask
over just a portion of the optical grating layer and the patterned
hardmask, and wherein the mask is formed directly atop a top
surface of the optical grating layer; and forming a plurality of
trenches in the optical grating layer by etching the optical
grating layer, the patterned hardmask, and the mask, wherein at
least one of the following grating characteristics varies between
one or more trenches of the plurality of trenches: a trench depth
and a trench width.
19. The method of claim 18, further comprising: forming a first
trench of the plurality of trenches in the portion of the optical
grating layer to a first depth; and forming a second trench of the
plurality of trenches in a second portion of the optical grating
layer to a second depth, wherein the second depth is greater than
the first depth.
20. The method of claim 18, further comprising forming the
patterned hardmask as a plurality of hardmask elements each
separated from one another by a gap, wherein a first hardmask
element of the plurality of the hardmask elements has a different
width than a width of a second hardmask element of the plurality of
hardmask elements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional patent
application Ser. No. 62/780,138, filed Dec. 14, 2018, the entire
contents of which is incorporated by reference herein.
FIELD OF THE DISCLOSURE
[0002] Embodiments of the present disclosure generally relate to
methods of producing gratings. More specifically, the disclosure
relates to methods of producing gratings with trenches having
variable height and width.
BACKGROUND OF THE DISCLOSURE
[0003] Optical elements such as optical lenses have long been used
to manipulate light for various advantages. Recently,
micro-diffraction gratings have been utilized in holographic and
augmented/virtual reality (AR and VR) devices. One particular AR
and VR device is a wearable display system, such as a headset,
arranged to display an image within a short distance from a human
eye. Such wearable headsets are sometimes referred to as head
mounted displays, and are provided with a frame displaying an image
within a few centimeters of the user's eyes. The image can be a
computer-generated image on a display, such as a micro display. The
optical components are arranged to transport light of the desired
image, where the light is generated on the display to the user's
eye to make the image visible to the user. The display where the
image is generated can form part of a light engine, so the image
generates collimated light beams guided by the optical component to
provide an image visible to the user.
[0004] Different kinds of optical components have been used to
convey the image from the display to the human eye. To properly
function in an augmented reality lens or combiner, the geometries
of an optical grating may be designed to achieve various effects.
In some devices, multiple different regions, such as two or more
different regions, are formed on the surface of a lens, wherein the
grating geometries in one region are different from the grating
geometries in other regions.
[0005] Angled surface relief optical gratings can be produced by
the direct etching of angled trenches into a substrate or a film
stack on a substrate. One of the parameters controlling the
efficiency of the optical grating is the trench depth.
Unfortunately, current approaches of forming optical gratings with
varied heights, widths, and/or shapes across diffracting and
viewing fields have proved challenging.
[0006] Therefore, there is a need for improved methods of producing
gratings having trenches with variable height and width.
SUMMARY
[0007] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended as an aid in determining the scope of the
claimed subject matter.
[0008] Embodiments of the present disclosure provide a method of
forming a diffracted optical element, the method including
providing an optical grating layer atop a substrate, providing a
patterned hardmask over the optical grating layer, and forming a
mask over just a portion of the optical grating layer and the
patterned hardmask. The method may further include etching a
plurality of trenches into the optical grating layer to form an
optical grating, wherein a first depth of a first trench of the
plurality of trenches is different than a second depth of a second
trench of the plurality of trenches.
[0009] Embodiments of the present disclosure further provide a
method of forming an optical grating component, the method
including providing an optical grating layer atop a substrate, and
providing a patterned hardmask over the optical grating layer. The
method may further include forming a mask over just a portion of
the optical grating layer and the patterned hardmask. The method
may further include etching a plurality of trenches into the
optical grating layer to form an optical grating, wherein at least
one of the following grating characteristics varies between one or
more trenches of the plurality of trenches: a trench depth and a
trench width.
[0010] Embodiments of the present disclosure further provide a
method of forming an optical grating component, the method
including providing an optical grating layer atop a substrate, and
providing a patterned hardmask over the optical grating layer. The
method may further include forming a mask over just a portion of
the optical grating layer and the patterned hardmask. The method
may further include forming a plurality of trenches in the optical
grating layer by etching the optical grating layer, the patterned
hardmask, and the mask, wherein at least one of the following
grating characteristics varies between one or more trenches of the
plurality of trenches: a trench depth and a trench width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings illustrate exemplary approaches of
the disclosure, including the practical application of the
principles thereof, as follows:
[0012] FIG. 1 is a schematic, cross-sectional view of a display
apparatus according to embodiments of the disclosure;
[0013] FIG. 2A depicts a side cross sectional view of an optical
grating component according to embodiments of the disclosure;
[0014] FIG. 2B depicts a top plan view of the optical grating
component of FIG. 1A according to embodiments of the
disclosure;
[0015] FIG. 3A shows a processing apparatus, depicted in schematic
form, in accordance with embodiments of the present disclosure;
[0016] FIG. 3B shows an extraction plate component and substrate in
top plan view in accordance with embodiments of the present
disclosure;
[0017] FIGS. 4A-D are side cross-sectional views of angled
structures as formed in an optical grating layer in accordance with
embodiments of the present disclosure;
[0018] FIG. 5 shows is an etch process to form an optical grating
according to embodiments of the present disclosure;
[0019] FIG. 6 shows is an etch process to form an optical grating
according to embodiments of the present disclosure; and
[0020] FIG. 7 depicts a process flow in accordance with embodiments
of the disclosure.
[0021] FIG. 8 depicts a diffracted optical element over a series of
etch cycles according to embodiments of the present disclosure.
[0022] FIG. 9 depicts a diffracted optical element over a series of
etch cycles according to embodiments of the present disclosure.
[0023] The drawings are not necessarily to scale. The drawings are
merely representations, not intended to portray specific parameters
of the disclosure. The drawings are intended to depict exemplary
embodiments of the disclosure, and therefore are not be considered
as limiting in scope. In the drawings, like numbering represents
like elements.
[0024] Furthermore, certain elements in some of the figures may be
omitted, or illustrated not-to-scale, for illustrative clarity. The
cross-sectional views may be in the form of "slices", or
"near-sighted" cross-sectional views, omitting certain background
lines otherwise visible in a "true" cross-sectional view, for
illustrative clarity. Furthermore, for clarity, some reference
numbers may be omitted in certain drawings.
DETAILED DESCRIPTION
[0025] Methods in accordance with the present disclosure will now
be described more fully hereinafter with reference to the
accompanying drawings, where embodiments of the methods are shown.
The methods may be embodied in many different forms and are not to
be construed as being limited to the embodiments set forth herein.
Instead, these embodiments are provided so the disclosure will be
thorough and complete, and will fully convey the scope of the
system and method to those skilled in the art.
[0026] FIG. 1 is a schematic, cross-sectional view of a waveguide
104 implemented in a display apparatus 100. The display apparatus
100 may be configured for augmented, virtual, and mixed or merged
reality applications as well as other display applications, for
example, hand held display devices.
[0027] The display apparatus 100 uses the waveguide 104 for
transparent viewing of an ambient environment 130 through the
waveguide 104, such as for a user viewing the environment 130 from
a user perspective 101. When implemented in the display apparatus
100, a first surface 122 of the waveguide 104 is disposed adjacent
to, and facing, a user's eye 111. A second surface 124 of the
waveguide 104 is disposed opposite the first surface 122 and
adjacent to and facing the ambient environment 130. Although
illustrated as being planar, the waveguide 104 may be curved,
depending upon the desired application.
[0028] The display apparatus 100 further includes an image
microdisplay 128 to direct light 120 of a generated, virtual image
into the waveguide 104. The light 120 of the virtual image is
propagated in the waveguide 104. Generally, the waveguide 104
includes an input coupling region 106, a waveguide region 108, and
an output coupling region 110. The input coupling region 106
receives light 120 (a virtual image) from the image microdisplay
128 and the light 120 travels through the waveguide region 108 to
the output coupling region 110 where the user's perspective 101 and
field of view enable visualization of a virtual image overlaid on
the ambient environment 130. The image microdisplay 128 is a high
resolution display generator, such as a liquid crystal on silicon
microdisplay operable to project the light of the virtual image
into the waveguide 104.
[0029] The waveguide 104 includes input grating structures 112 and
output grating structures 114. The input grating structures 112 are
formed on the waveguide 104 in an area corresponding to the input
coupling region 106. The output grating structure 114 are formed on
the waveguide 104 in an area corresponding to the output coupling
region 110. The input grating structures 112 and output grating
structure 114 influence light propagation within the waveguide 104.
For example, the input grating structure 112 couples in light from
the image microdisplay 128 and the output grating structure couples
out light to the user's eye 111.
[0030] For example, the input grating structures 112 influence the
field of view of a virtual image displayed at the user's eye 111.
The output grating structures 114 influence the amount of light 120
collected and outcoupled from the waveguide 104. In addition, the
output grating structures 114 modulate the field of view of a
virtual image from a user's perspective 101 and increase the
viewing angle a user can view the virtual image from the image
microdisplay 128. In another example, a grating structure (not
shown) is also formed in the waveguide region 108 between the input
coupling region 106 and the output coupling region 110.
Additionally, multiple waveguides 104, each with desired grating
structures formed therein, can be used to form the display
apparatus 100.
[0031] FIG. 2A depicts a side cross sectional view of an optical
grating component 200, according to embodiments of the disclosure.
FIG. 2B depicts a top plan view of the optical grating component
200. The optical grating component 200 may be used as an optical
grating to be placed on an eyeglass or formed integrally in the
eyeglass in accordance with various embodiments of the disclosure.
The optical grating component 200 includes a substrate 202, and an
optical grating 206 disposed on the substrate 202. The optical
grating 206 may be the same or similar to the input grating
structure 112 and/or the output grating structure 114 of FIG. 1. In
some embodiments, the substrate 202 is an optically transparent
material, such as a known glass. In some embodiments, the substrate
202 is silicon. In the latter case, the substrate 202 is silicon,
and another process is used to transfer grating patterns to a film
on the surface of another optical substrate, such as glass or
quartz. The embodiments are not limited in this context. The
optical grating 206 may be disposed in an optical grating layer
207, as described further below. In the non-limiting embodiment of
FIG. 2A and FIG. 2B, the optical grating component 200 further
includes an etch stop layer 204, disposed between the substrate 202
and optical grating layer 207. According to some embodiments of the
disclosure, the optical grating layer 207 may be an optically
transparent material, such as silicon oxide, silicon nitride,
glass, TiO.sub.2, or other material.
[0032] According to some embodiments of the disclosure, the optical
grating 206 may comprise a grating height H in the range of 100 nm
to 1000 nm. As such, the optical grating 206 may be appropriate for
use in an eyepiece of an AR &VR apparatus. Embodiments herein
are not limited in this context. In accordance with some
embodiments, the etch stop layer 204 may be an optically
transparent material and may have a thickness of 10 nm to 100 nm.
The embodiments are not limited in this context. Examples of a
suitable material for the etch stop layer 204 include SiN, SiO2,
TiN, SiC, and other materials. In embodiments where the optical
grating 206 is to be applied to or incorporated in an eyepiece of
an eyeglass, an especially appropriate material is an optically
transparent material. In embodiments where the optical grating
component 200 forms a master for fabricating optical gratings for
an eyepiece, the etch stop layer 204 need not be optically
transparent. Moreover, the etch stop layer 204 may be omitted in
some embodiments.
[0033] As further shown in FIG. 2A, the optical grating 206 may
comprise a plurality of angled structures, shown as angled
components or structures 212, disposed at a non-zero angle of
inclination with respect to a perpendicular to a plane (e.g., x-y
plane) of the substrate 202. The angled structures 212 may be
included within one or more fields of slanted gratings, the slanted
grating together forming "micro-lenses." In the example of FIG. 2A,
define a uniform height along the direction parallel to the Y-axis
of the Cartesian coordinate system shown, where the first direction
(y-axis) is parallel to the plane of the substrate 202, in this
case the x-y plane. In other embodiments, the angled structures 212
may define a variable height along the direction parallel to the
y-axis. The plurality of trenches 214 may be disposed at a non-zero
angle of inclination with respect to a perpendicular to a plane,
such as a top surface of the substrate 202 or a top surface of
optical grating layer 207. As will be described in greater detail
below, the depth `d` and/or the width `w` of one or more trenches
of the plurality of trenches 214 may vary due to the presence of a
mask layer provided over the optical grating 206 prior to
etching.
[0034] In some embodiments, the width of the optical grating 206
along the Y-direction may be on the order of several millimeters to
several centimeters, while the grating height H may be on the order
of 1 micrometer or less. Accordingly, the variation in grating
height H may range on the order of several hundred nanometers or
less. An example of a smooth variation in grating height H or depth
d is where a change in grating height H or depth d between adjacent
lines of a grating is less than 10%, less than 5%, or less than 1%.
The embodiments are not limited in this context. Thus, in an
eyepiece, the grating height H may vary continuously and in a
non-abrupt fashion in a given direction along the surface of the
eyepiece over a distance of, for example, millimeters to
centimeters. More particularly, a change in grating height H of 50%
over a 5 mm distance may entail changing the grating height H
continuously over approximately 5.times.10.sup.3 lines having a
pitch of one micrometer. The change entails an average change in
relative height of adjacent lines of 0.5/5.times.10.sup.4 or
approximately 0.01%.
[0035] Turning now to FIG. 3A, there is shown a processing
apparatus 300, depicted in schematic form. The processing apparatus
300 represents a processing apparatus for etching portions of a
substrate, or depositing on a substrate, to generate, for example,
the optical gratings of the present embodiments. The processing
apparatus 300 may be a plasma based processing system having a
plasma chamber 302 for generating a plasma 304 therein by any
convenient method as known in the art. An extraction plate 306 may
be provided as shown, having an extraction aperture 308, where a
non-uniform etching or non-uniform deposition may be performed to
reactively etch or deposit an optical grating layer 207 (FIGS.
2A-2B). A substrate 202, including, for example, the aforementioned
optical grating structure, is disposed in the process chamber 324.
A substrate plane of the substrate 202 is represented by the X-Y
plane of the Cartesian coordinate system shown, while a
perpendicular to the plane of the substrate 202 lies along the
Z-axis (Z-direction).
[0036] As further shown in FIG. 3A, an ion beam 310 may be
extracted when a voltage difference is applied using bias supply
320 between the plasma chamber 302 and substrate 202, or substrate
platen 314, as in known systems. The bias supply 320 may be coupled
to the process chamber 324, for example, where the process chamber
324 and substrate 202 are held at the same potential.
[0037] According to various embodiments, the ion beam 310 may be
extracted along the perpendicular 326 or may be extracted at a
non-zero angle of incidence, shown as .PHI., with respect to the
perpendicular 326.
[0038] The trajectories of ions within the ion beam 310 may be
mutually parallel to one another or may lie within a narrow angular
spread range, such as within 10 degrees of one another or less. In
other embodiments, as will be discussed below, the trajectory of
ions within the ion beam 310 may converge or diverge from one
another, for example, in a fan shape. Thus, the value of.sub.1 may
represent an average value of incidence angle where the
individually trajectories vary up to several degrees from the
average value. In various embodiments, the ion beam 310 may be
extracted as a continuous beam or as a pulsed ion beam as in known
systems. For example, the bias supply 320 may be configured to
supply a voltage difference between the plasma chamber 302 and the
process chamber 324, as a pulsed DC voltage, where the voltage,
pulse frequency, and duty cycle of the pulsed voltage may be
independently adjusted from one another.
[0039] In various embodiments, gas, such as reactive gas, may be
supplied by the source 322 to plasma chamber 302. The plasma 304
may generate various etching species or depositing species,
depending upon the exact composition of species provided to the
plasma chamber 302.
[0040] In various embodiments, the ion beam 310 may be provided as
a ribbon reactive ion beam having a long axis extending along the
X-direction of the Cartesian coordinate system shown in FIG. 3B. By
scanning a substrate platen 314 including substrate 202 with
respect to the extraction aperture 308, and thus with respect to
the ion beam 310 along the scan direction 330, the ion beam 310 may
etch the substrate 202 or deposit upon the substrate 202. The ion
beam 310 may be composed of any convenient gas mixture, including
inert gas, reactive gas, and may be provided in conjunction with
other gaseous species in some embodiments. In particular
embodiments, the ion beam 210 and other reactive species may be
provided as an etch recipe to the substrate 202 so as to perform a
directed reactive ion etching of a layer, such as the optical
grating layer 307. Such an etch recipe may use known reactive ion
etch chemistries for etching materials such as oxide or other
material, as known in the art. In other embodiments, the ion beam
310 may be formed of inert species where the ion beam 310 is
provided to etch the substrate 202 or more particularly, the
optical grating layer 207, by physical sputtering, as the substrate
202 is scanned with respect to ion beam 310.
[0041] In the example of FIG. 3B, the ion beam 310 is provided as a
ribbon reactive ion beam extending to a beam width along the
X-direction, where the beam width is adequate to expose an entire
width of the substrate 202, even at the widest part along the
X-direction. Exemplary beam widths may be in the range of 10 cm, 20
cm, 30 cm, or more while exemplary beam lengths along the
Y-direction may be in the range of 2 mm, 3 mm, 5 mm, 10 mm, or 20
mm. The embodiments are not limited in this context.
[0042] Notably, the scan direction 330 may represent the scanning
of substrate 202 in two opposing (180 degrees) directions along the
Y-direction, or just a scan toward the left or a scan toward the
right. As shown in FIG. 3B, the long axis of ion beam 310 extends
along the X-direction, perpendicularly to the scan direction 330.
Accordingly, an entirety of the substrate 202 may be exposed to the
ion beam 310 when scanning of the substrate 202 takes place along a
scan direction 330 to an adequate length from a left side to right
side of substrate 202.
[0043] The grating features, such as the angled structures 212 of
FIGS. 2A-2B, may be accomplished by scanning the substrate 202 with
respect to the ion beam 310 using a processing recipe. In brief,
the processing recipe may entail varying at least one process
parameter of a set of process parameters, having the effect of
changing, e.g., the etch rate or deposition rate caused by the ion
beam 310 during scanning of the substrate 202. Such process
parameters may include the scan rate of the substrate 202, the ion
energy of the ion beam 310, duty cycle of the ion beam 310 when
provided as a pulsed ion beam, the spread angle of the ion beam
310, and rotational position of the substrate 202. In at least some
embodiments herein, the processing recipe may further include the
material(s) of the optical grating layer 207, and the chemistry of
the etching ions of the ion beam 310. In yet other embodiments, the
processing recipe may include starting geometry of the optical
grating layer 207, including dimensions and aspect ratios. The
embodiments are not limited in this context.
[0044] FIGS. 4A-4D demonstrate a method for forming a diffracted
optical element 400 according to embodiments of the present
disclosure. As shown in FIG. 4A, an optical grating layer 407 may
be formed over a substrate 402. Although not shown, in some
embodiments, an etch stop layer may be provided between the
substrate 402 and the optical grating layer 407. The substrate 402
may be made from an optically transparent material, such as
silicon. When present, the etch stop layer may be formed, for
example, by a chemical vapor deposition (CVD) process, a physical
vapor deposition (PVD) process, or a spin-on process. The etch stop
layer is formed from a material, such as titanium nitride or
tantalum nitride, among others, resistant to an etching
process.
[0045] The grating layer 407 may be formed from an optically
transparent material. In one example, the grating layer 407 is
formed from a silicon-based material, such as silicon nitride or
silicon oxide, or a titanium-based material, such as titanium
oxide. The material of the grating layer 407 has a high refractive
index, such as approximately 1.3 or higher, like 1.5, or even
higher. Generally, the grating layer 407 has a thickness less than
approximately 1 micrometer, such as between approximately 150 nm
and 700 nm.
[0046] As shown in FIG. 4B, a patterned hardmask 410 may be formed
over the optical grating layer 407. In some embodiments, the
patterned hardmask (hereinafter "hardmask") 410 is formed from a
photoresist stack (not shown), wherein a hardmask layer is
conformally formed over the grating layer 407. The hardmask layer
is, for example, formed from titanium nitride using a chemical
vapor deposition process. As shown, the hardmask 410 is formed as a
plurality of hardmask elements 410A-F separated from one another by
a gap 411. Each of the gaps 411 may be formed using an etch process
selective to a top surface 413 of the optical grating layer 407. In
some embodiments, the plurality of hardmask elements 410A-F is
formed by etching a photoresist stack. In some embodiments, each of
the plurality of hardmask elements 410A-F has a same height `hmh`
and/or width `hmw`. In other embodiments, one or more of the
plurality of hardmask elements 410A-F has a different or
non-uniform height and/or thickness.
[0047] As shown in FIG. 4C, a mask 420 may then be formed over the
optical grating layer 407 and the hardmask 410. In some
embodiments, the mask 420 is a "soft" mask formed over just a
portion of the optical grating layer 407 and the hardmask 410. For
example, the mask 420 may be formed over the hardmask elements
410A-410C, while the hardmask elements 410D-410F remain uncovered
and exposed. In non-limiting embodiments, the mask 420 may be a
photoresist-type material formed over the diffracted optical
element 400 using 3-D printing. In other embodiments, the mask 420
may be "imaged" during photolithography, or formed by subtractive
methods, such as ion etching, reactive or sputter, and laser
oblation. For example, the entire etch depth profiling or a portion
thereof may be achieved via a patterned mask process. In this case,
the angled etch may be a uniform process. The mask 420 may have a
uniform height `hi` or a variable height. For example, the mask 420
may include one or more sloped sections 422. The shape of the
sloped section 422 in the mask 420 may be transferred to the shape
of the bottom of the trenches, as will be described in greater
detail below.
[0048] In some embodiments, the mask 420 may be formed over the
optical grating layer 407 and the hardmask 410 by first shaping the
mask 420, and then transferring the shape to the diffracted optical
element 400. By shaping the mask 420, precision may be improved.
Furthermore, in some embodiments, the mask 420 may then be
patterned, e.g., using a subtractive technique such as etching.
[0049] As shown in FIG. 4D, the diffracted optical element 400 is
then etched 425. In some embodiments, the etch 425 is an angled ion
etch, wherein the angled ion etch is performed by a reactive ion
beam. The substrate may be scanned along a scan direction with
respect to the reactive ion beam. During the etch process, the
hardmask 410 functions as a pattern guide for formation of the
slanted grating structures. In examples where the mask 420 has also
been patterned, the mask 420 also acts as a pattern guide for
formation of the slanted grating structures.
[0050] Turning now to FIG. 5, a diffracted optical element 500 over
a series of etch cycles according to embodiments of the present
disclosure will be described. At process point (PP) 1, the mask 520
is formed over just a first portion 505 of the optical grating
layer 507 and the hardmask 510. As shown, the hardmask elements
510E-510G above a second portion 506 of the optical grating layer
507 remain exposed. Furthermore, gaps 511A and 511B are left
uncovered by the mask 520. At PP 2, the etch process begins,
causing a first set of trenches 514A to be formed in the second
portion 506 of the optical grating layer 507. Because the gaps 511A
and 511B are left uncovered by the mask 520, the etching is
permitted to more quickly impact the optical grating layer 507 in
those areas. Although, in those areas of the optical grating layer
507 covered by the mask 520, no trench formation has begun at PP 2.
Although non-limiting, the ratio of etch selectivity between the
substrate 502, the hardmask 510 and the mask 520 is approximately
1:20:2.
[0051] As shown at PP 3, as the etch process continues, the first
set of trenches 514A deepen in the second portion 506 of the
optical grating layer 507, while the mask 520 is recessed in an
area above the first portion 505 of the optical grating layer 507.
At PP 4, a second set of trenches 514B is formed into the first
portion 505 of the optical grating layer 507, between each of the
plurality of hardmask elements 510A-510D. The etching continues at
PPS until the first set of trenches 514A reach the substrate 502,
thus forming each of the plurality of angled structures 512 from
the optical grating layer 507. As shown, the second set of trenches
514B does not extend to the substrate 502. Said another way, a
first depth `d1` of one or more trenches of the first set of
trenches 514A may be greater than a second depth `d2` of one or
more trenches of the second set of trenches 514B. Furthermore, a
first width `w1` of one or more trenches of the first set of
trenches 514A may be greater than a second width `w2` of one or
more trenches of the second set of trenches 514B. The presence of
the mask 520 in PP1-PP3 causes the etch process to impact the
second portion 506 of the optical grating layer 507 before
impacting the first portion 505 of the optical grating layer,
resulting in more shallow and/or narrow trenches in the first
portion 505.
[0052] By controlling the shape of each of the angled structures
512, changes in the diffractions of different wavelengths (i.e.,
different colors) may be controlled to improve the image quality.
The optical efficiency (i.e., projection of desired wavelengths to
a user's perspective) is greatly improved due to the increased
control provided by the angled structures 512. Further, the
projection of undesired wavelengths is reduced. thus increasing the
clarity and quality of the projected image.
[0053] Turning now to FIG. 6, a diffracted optical element 600 over
a series of etch cycles according to embodiments of the present
disclosure will be described. The diffracted optical element 600 is
similar to the diffracted optical element 500 of FIG. 5. As such,
not all details of the diffracted optical element 600 will be
described for the sake of brevity. At PP 1 the hardmask 610
includes a first subset of hardmask elements 610A formed adjacent a
second subset of hardmask elements 610B. The mask 620 is formed
over just the first portion 605 of the optical grating layer 607
and over just the second subset of hardmask elements 610B. As
shown, each of the first subset of hardmask elements 610A has a
first hardmask width `hmw1` and each of the second subset of
hardmask elements 610B has a second hardmask width `hmw2`. In this
embodiment, hmw1 is greater than hmw2. In other embodiments, more
than two different hardmask widths may be present. By making
hmw1>hmw2, a first width `w1` of one or more trenches of the
first set of trenches 614A may be approximately equal to a second
width `w2` of one or more trenches of the second set of trenches
614B, as shown by the diffracted optical element 600 at PP 6. Said
another way, the width and shape of the plurality of angled
structures 612 may be more uniform. The variable hardmask 610 width
compensates for loss of grating width.
[0054] Turning now to FIG. 7, a method 700 for forming an optical
grating component according to embodiments of the present
disclosure will be described in greater detail. As shown, at block
701, the method 700 may include providing an optical grating layer
atop a substrate. At block 703, the method 700 may include
providing a patterned hardmask over the optical grating layer. In
some embodiments, the patterned hardmask is a plurality of hardmask
elements each separated from one another by a gap, wherein a first
hardmask element of the plurality of the hardmask elements has a
different width than a width of a second hardmask element of the
plurality of hardmask elements. In some embodiments, the method
includes forming a first subset of the plurality of hardmask
elements adjacent a second subset of the plurality of hardmask
elements, wherein each of the first subset of the plurality of
hardmask elements has a first width. Furthermore, each of the
second subset of the plurality of hardmask elements may have a
second width, wherein the first width is greater than the second
width.
[0055] At block 705, the method 700 may include forming a mask over
just a portion of the optical grating layer and the patterned
hardmask. In some embodiments, the mask is a soft mask more easily
etched than the hardmask. Said another way, the hardmask is more
resistant to an etch that the mask. In some embodiments, the mask
may be formed over just a subset of hardmask elements, while
another subset of hardmask elements remains uncovered and exposed.
In non-limiting embodiments, the mask may be a photoresist-type
material formed over the diffracted optical element using 3-D
printing. In some embodiments, the mask may then be patterned to
form a plurality of hardmask elements each separated from one
another by a gap.
[0056] At block 707, the method 700 may include etching a plurality
of trenches into the optical grating layer to form an optical
grating, wherein at least one of the following grating
characteristics varies between one or more trenches of the
plurality of trenches: a trench depth and a trench width. In some
embodiments, a first width of a first trench of the plurality of
trenches is different than a second width of a second trench of the
plurality of trenches. In some embodiments, the plurality of
trenches may be etched to form a third trench having a different
width than a width of: the first trench or the second trench. In
some embodiments, the mask layer may be patterned, or partially
patterned, prior to the etching process. In other embodiments, the
mask and the optical grating layer between each of the exposed
hardmask elements may begin to be recessed at the same time.
[0057] Turning now to FIG. 8, a diffracted optical element 800 over
a series of etch cycles according to embodiments of the present
disclosure will be described. The diffracted optical element 800 is
similar to the diffracted optical element 500 of FIG. 5 and the
diffracted optical element 600 in FIG. 6. As such, not all details
of the diffracted optical element 800 will be described for the
sake of brevity. In the embodiment shown, at PP 1 the hardmask 810
includes a first subset of hardmask elements 810A formed adjacent a
second subset of hardmask elements 810B. The mask 820 is formed
over just the first portion 805 of the optical grating layer 807
and over just the second subset of hardmask elements 810B. As
shown, the mask 820 may have a sloped surface profile 822
subsequently transferred (shown as 822') to the shape of the bottom
of the trenches 814, for example, as shown in PP2.
[0058] Turning now to FIG. 9, a diffracted optical element 900 over
a series of etch cycles according to embodiments of the present
disclosure will be described. The diffracted optical element 900 is
similar to the diffracted optical elements 500, 600, and 800
described above. As such, not all details of the diffracted optical
element 900 will be described for the sake of brevity. In the
embodiment shown, at PP 1, the mask 920 is provided over just the
first portion 905 of the optical grating layer 907 and over just a
first subset 910A and a second subset 910B of the hardmask elements
910. The mask 920 may not be formed over a third subset 910C of the
hardmask elements 910. Although, in other embodiments, the mask 920
may extend over both the first portion 905 and the second portion
906 of the optical grating layer 907.
[0059] As shown, the mask 920 may have one or more levels or
heights, H1 and H2, as measured from a top surface of the optical
grating layer 907. Additionally, the first subset 910A of the
hardmask elements 910 may each have a first width w1, the second
subset 910B of the hardmask elements 910 may each have a second
width w2, and the third subset 910C of the hardmask elements 910
may each have a third width w3. As shown, w3>w2>w1, wherein
the width of the hardmask elements 910 is generally proportional to
the height of the mask 920. Varying the width of the hardmask
elements 910 at the start of processing (e.g., PP 1) result in more
uniform-withed angled structures 912 at the end of processing, for
example, at PP 4.
[0060] In this embodiment, the mask 920 may also be softer than the
optical grating layer 907. Making the mask 920 softer than the
optical grating layer 907 and the hardmask elements 910 enables a
taller layer of the mask 920, in turn enabling more methods to
shape the mask 920, such as 3D printing. In other embodiments, the
optical grating layer 907 may be softer than the mask 920.
[0061] At PP 2, the etch process begins, causing one or more first
set of trenches 914A to be formed in the second portion 906 of the
optical grating layer 907, between a second subset 910B of the
hardmask elements 910. Because the second portion 906 of the
optical grating layer 907 is left uncovered by the mask 520, the
etching is permitted to more quickly impact the optical grating
layer 907 in the second portion 906. Although, in those areas of
the optical grating layer 907 covered by the mask 920, no trench
formation has begun at PP 2.
[0062] As shown at PP 3, as the etch process continues, the first
set of trenches 914A deepen in the second portion 906 of the
optical grating layer 907, while the mask 920 is recessed in an
area above the first portion 905 of the optical grating layer 907.
At PP 4, a second set of trenches 914B is formed into the first
portion 905 of the optical grating layer 907, between each of the
subset 910A of the hardmask elements 910. The etching may continue
until the first set of trenches 914A reach the substrate 902, thus
forming each of the plurality of angled structures 912 from the
optical grating layer 907. As shown, the second set of trenches
914B may not extend to the substrate 902. By controlling the shape
of each of the angled structures 912, changes in the diffractions
of different wavelengths (i.e., different colors) may be controlled
to improve the image quality. The optical efficiency (i.e.,
projection of desired wavelengths to a user's perspective) is
greatly improved due to the increased control provided by the
angled structures 912. Further, the projection of undesired
wavelengths is reduced thus increasing the clarity and quality of
the projected image.
[0063] For the sake of convenience and clarity, terms such as
"top," "bottom," "upper," "lower," "vertical," "horizontal,"
"lateral," and "longitudinal" will be used herein to describe the
relative placement and orientation of components and their
constituent parts as appearing in the figures. The terminology will
include the words specifically mentioned, derivatives thereof, and
words of similar import.
[0064] As used herein, an element or operation recited in the
singular and proceeded with the word "a" or "an" is to be
understood as including plural elements or operations, until such
exclusion is explicitly recited. Furthermore, references to "one
embodiment" of the present disclosure are not intended as limiting.
Additional embodiments may also incorporate the recited
features.
[0065] Furthermore, the terms "substantial" or "substantially," as
well as the terms "approximate" or "approximately," can be used
interchangeably in some embodiments, and can be described using any
relative measures acceptable by one of ordinary skill in the art.
For example, these terms can serve as a comparison to a reference
parameter, to indicate a deviation capable of providing the
intended function. Although non-limiting, the deviation from the
reference parameter can be, for example, in an amount of less than
1%, less than 3%, less than 5%, less than 10%, less than 15%, less
than 20%, and so on.
[0066] Still furthermore, one of ordinary skill will understand
when an element such as a layer, region, or substrate is referred
to as being formed on, deposited on, or disposed "on," "over" or
"atop" another element, the element can be directly on the other
element or intervening elements may also be present. In contrast,
when an element is referred to as being "directly on," "directly
over" or "directly atop" another element, no intervening elements
are present.
[0067] As used herein, "depositing" and/or "deposited" may include
any now known or later developed techniques appropriate for the
material to be deposited including although not limited to, for
example: chemical vapor deposition (CVD), low-pressure CVD (LPCVD),
and plasma-enhanced CVD (PECVD). "Depositing" and/or "deposited"
may also include semi-atmosphere CVD (SACVD) and high-density
plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum
CVD (UHVCVD), limited reaction processing CVD (LRPCVD), and
metal-organic CVD (MOCVD). "Depositing" and/or "deposited" may also
include sputtering deposition, ion beam deposition, electron beam
deposition, laser assisted deposition, thermal oxidation, thermal
nitridation, spin-on methods, and physical vapor deposition (PVD).
"Depositing" and/or "deposited" may also include atomic layer
deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE),
plating, evaporation.
[0068] In various embodiments, design tools can be provided and
configured to create the datasets used to pattern the layers of
diffracted optical elements 400, 500, 600, 800, and 900 e.g., as
described herein. For example, data sets can be created to generate
photomasks used during lithography operations to pattern the layers
for structures as described herein. Such design tools can include a
collection of one or more modules and can also be comprised of
hardware, software or a combination thereof. Thus, for example, a
tool can be a collection of one or more software modules, hardware
modules, software/hardware modules or any combination or
permutation thereof. As another example, a tool can be a computing
device or other appliance running software, or implemented in
hardware.
[0069] As used herein, a module might be implemented utilizing any
form of hardware, software, or a combination thereof. For example,
one or more processors, controllers, ASICs, PLAs, logical
components, software routines or other mechanisms might be
implemented to make up a module. In implementation, the various
modules described herein might be implemented as discrete modules
or the functions and features described can be shared in part or in
total among one or more modules. In other words, as would be
apparent to one of ordinary skill in the art after reading the
description, the various features and functionality described
herein may be implemented in any given application. Furthermore,
the various features and functionality can be implemented in one or
more separate or shared modules in various combinations and
permutations. Although various features or elements of
functionality may be individually described or claimed as separate
modules, one of ordinary skill in the art will understand these
features and functionality can be shared among one or more common
software and hardware elements.
[0070] By utilizing the embodiments described herein, a waveguide
having slanted grating structures is formed. A first technical
advantage of the slanted grating structures of the present
embodiments includes improved function of the waveguide by better
collecting and directing light passing through the waveguide, thus
improving clarity of a projected image. A second technical
advantage of the slanted grating structures of the present
embodiments includes increased control over the wavelengths of
light projected to a desired image plane. The uniformity of the
power of light outcoupled by the waveguide is significantly more
uniform. A third technical advantage of the slanted grating
structures of the present embodiments includes improved
manufacturing of a waveguide by eliminating manufacturing
processes, such as mechanical polishing, thus reducing damage to
layers used to form the waveguide. Further, a fourth technical
advantage of the slanted grating structures of the present
embodiments includes providing a two dimensional or a
three-dimensional shape, enabling use of the waveguide in an
increased range of applications.
[0071] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Furthermore, the present disclosure has been described
herein in the context of a particular implementation in a
particular environment for a particular purpose. Those of ordinary
skill in the art will recognize the usefulness is not limited
thereto and the present disclosure may be beneficially implemented
in any number of environments for any number of purposes. Thus, the
claims set forth below are to be construed in view of the full
breadth and spirit of the present disclosure as described
herein.
* * * * *