U.S. patent application number 17/095295 was filed with the patent office on 2021-04-22 for test wafer with optical fiber with bragg grating sensors.
The applicant listed for this patent is iSenseCloud, Inc.. Invention is credited to An-Dien Nguyen, Huy D. Nguyen, William J. O'Banion, IV.
Application Number | 20210118654 17/095295 |
Document ID | / |
Family ID | 1000005251558 |
Filed Date | 2021-04-22 |
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United States Patent
Application |
20210118654 |
Kind Code |
A1 |
O'Banion, IV; William J. ;
et al. |
April 22, 2021 |
TEST WAFER WITH OPTICAL FIBER WITH BRAGG GRATING SENSORS
Abstract
An apparatuses relating generally to a test wafer, processing
chambers, and method relating generally to monitoring or
calibrating a processing chamber, are described. In one such an
apparatus for a test wafer, there is a platform. An optical fiber
with Fiber Bragg Grating sensors is located over the platform. A
layer of material is located over the platform and over the optical
fiber.
Inventors: |
O'Banion, IV; William J.;
(San Jose, CA) ; Nguyen; An-Dien; (Fremont,
CA) ; Nguyen; Huy D.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
iSenseCloud, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
1000005251558 |
Appl. No.: |
17/095295 |
Filed: |
November 11, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16036359 |
Jul 16, 2018 |
10861682 |
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17095295 |
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14814355 |
Jul 30, 2015 |
10033153 |
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16036359 |
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15458311 |
Mar 14, 2017 |
10209060 |
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14814355 |
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62310664 |
Mar 18, 2016 |
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62062429 |
Oct 10, 2014 |
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62031790 |
Jul 31, 2014 |
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62595515 |
Dec 6, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4204 20130101;
H01S 5/06804 20130101; H01J 2237/24585 20130101; G01J 3/18
20130101; G01K 1/14 20130101; G02B 6/0208 20130101; G01J 3/0208
20130101; G01N 29/14 20130101; G01N 29/2418 20130101; H01L 21/68742
20130101; H01S 5/0617 20130101; H01S 5/06808 20130101; H01J
37/32917 20130101; G01K 11/3206 20130101; G01N 29/2462 20130101;
H01S 5/4087 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; G02B 6/02 20060101 G02B006/02; G02B 6/42 20060101
G02B006/42; G01K 11/32 20060101 G01K011/32; G01N 29/24 20060101
G01N029/24; G01N 29/14 20060101 G01N029/14; G01K 1/14 20060101
G01K001/14; G01J 3/02 20060101 G01J003/02 |
Claims
1. An apparatus, comprising: a platform; an optical fiber with
Fiber Bragg Grating sensors located over the platform; patches of
adhesive located over the platform and over the optical fiber; and
at least a portion of the Fiber Bragg Grating sensors configured to
detect temperature-related information associated with the
platform.
2. The apparatus according to claim 1, wherein the at least the
portion of the Fiber Bragg Grating sensors is a first portion
thereof, the apparatus further comprising: a second portion of the
Fiber Bragg Grating sensors configured to detect strain-related
information associated with a structure to which the platform is
capable of being attached; wherein the second portion of the Fiber
Bragg Grating sensors are directly bonded to the platform.
3. The apparatus according to claim 1, wherein the optical fiber is
disposed to include a geometric pattern.
4. The apparatus according to claim 1, wherein the optical fiber is
disposed to include a spiral or spiral-like pattern.
5. The apparatus according to claim 1, wherein the optical fiber is
disposed to include a non-geometric pattern.
6. The apparatus according to claim 1, wherein: the platform has a
cavity defined therein; and the optical fiber is positioned at
least partially in the cavity.
7. The apparatus according to claim 6, wherein the cavity is a
groove or a channel.
8. The apparatus according to claim 1, wherein the optical fiber is
stripped of a coating.
9. The apparatus according to claim 1, wherein the optical fiber is
disposed over and directly on the platform.
10. The apparatus according to claim 1, wherein the Fiber Bragg
Grating sensors are positioned along curved portions of the optical
fiber.
11. The apparatus according to claim 10, wherein: the platform has
a cavity defined therein; the optical fiber is positioned at least
partially in the cavity; and the optical fiber is disposed in a
spiral or spiral-like pattern corresponding to the spiral or
spiral-like pattern formed as the cavity in the platform.
12. The apparatus according to claim 11, wherein the optical fiber
is located at least partially below an upper surface of the
platform.
13. The apparatus according to claim 1, wherein the platform is a
wafer.
14. The apparatus according to claim 13, wherein the wafer is a
silicon wafer.
15. The apparatus according to claim 1, wherein the optical fiber
has a coating.
16. The apparatus according to claim 15, wherein the coating is a
fiber coating.
17. The apparatus according to claim 15, wherein the fiber coating
is a polyimide coating.
18. The apparatus according to claim 1, further comprising a tube
having the optical fiber located therein.
19. The apparatus according to claim 18, wherein the optical fiber
is bare fiber inserted inside a hollow metal tube for the tube.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This nonprovisional application is a continuation
application of, and hereby claims priority to, pending U.S. patent
application Ser. No. 16/036,359, filed Jul. 16, 2018 (now U.S. Pat.
No. ______), which claims benefit under 35 U.S.C .sctn. 119(e) of
priority to provisional application 62/595,515, filed Dec. 6, 2017,
and which is a continuation-in-part of U.S. patent application Ser.
No. 15/458,311, filed Mar. 14, 2017 (now U.S. Pat. No. 10,209,060),
which claims the benefit of priority under 35 U.S.C. section 119(e)
to U.S. Provisional Patent Application No. 62/310,664, filed Mar.
18, 2016, and further is a continuation-in-part of pending U.S.
patent application Ser. No. 14/814,355, filed Jul. 30, 2015 (now
U.S. Pat. No. 10,033,153), which claims benefit of priority to
Provisional Patent Application Nos. 62/062,429, filed Oct. 10,
2014, and 62/031,790, filed Jul. 31, 2014, and the entirety of each
and all of the aforementioned provisional and nonprovisional
applications are incorporated by reference herein for all purposes
to the extent same is consistent herewith.
TECHNICAL FIELD
[0002] The following description relates to monitoring. More
particularly, the following description relates to monitoring using
fiber-optic sensors.
BACKGROUND
[0003] Precise control of internal chamber conditions, including
stability and uniformity of pressure, flow rate and/or temperature,
is useful in semiconductor processing. Test wafer devices ("test
wafers") are used in calibrating semiconductor industry processing
chambers. Such test wafers conventionally have a luminescent
material, such as a phosphor, that emits optically detectable
electromagnetic radiation ("optically detectable signal") based on
the temperature of such luminescent material. However, luminescent
material may be sensitive to other electromagnetic radiation
generated in a chamber, as such RF, UV and other electromagnetic
radiation, which may cause interference in detection of such an
optically detectable signal. This along with other limitations
associated with luminescent material sensors, and systems
associated therewith, makes their use problematic. Additionally,
temperature and other conditions within a processing chamber may be
monitored during manufacturing. It would be useful and desirable to
provide more sensors for such monitoring of temperature and/or
other conditions in a processing chamber.
SUMMARY
[0004] An apparatus relates generally to a test wafer. In such an
apparatus, there is a platform. An optical fiber with Fiber Bragg
Grating sensors is located over the platform. A layer of material
is located over the platform and over the optical fiber.
[0005] An apparatus relates generally to a processing chamber. In
such an apparatus, the processing chamber has a pedestal with at
least one lift pin of a plurality of lift pins configured to
include an optical eye and an optical waveguide for optical
communication.
[0006] An apparatus relates generally to another processing
chamber. In such an apparatus, the processing chamber has a chuck
and a showerhead or a lid. At least one of the chuck, the
showerhead, or the lid has at least one optical fiber with
sensors.
[0007] A method relates generally to monitoring or calibrating a
processing chamber. In such a method, the processing chamber has
therein an optical fiber with sensors configured for different
center frequencies for modulation responsive to at least
temperature. A broadband light source is optically transmitted from
a light-source based detection system to the optical fiber.
Reflected light is optically received from the optical fiber to the
light-source based detection system. The reflected light is
processed by the light-source based detection system to generate at
least temperature related data therefrom.
[0008] Other features will be recognized from consideration of the
Detailed Description and Claims, which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Accompanying drawings show exemplary apparatus(es) and/or
method(s).
[0010] However, the accompanying drawings should not be taken to
limit the scope of the claims, but are for explanation and
understanding only.
[0011] FIG. 1 is a signal diagram depicting an exemplary FBG
signal.
[0012] FIG. 2-1 is a block-perspective side view depicting an
exemplary test wafer.
[0013] FIG. 2-2 is a cross-sectional view of a portion of a
retention/alignment ring.
[0014] FIGS. 3-1 through 3-3 are optical signal-block diagrams
depicting cross-sectional views of respective exemplary optical
test systems.
[0015] FIG. 4 is a perspective-optical signal diagram depicting a
cross-sectional view of an exemplary bi-directional prism
assembly.
[0016] FIGS. 5-1 through 5-3 are a block-sectional diagrams
depicting examples of respective semiconductor processing chamber
systems ("processing chambers").
[0017] FIG. 6-1 is a block diagram of a sectional side view
depicting an exemplary lid assembly.
[0018] FIG. 6-2 is a top-down revealed view depicting an exemplary
enclosed portion of an optical fiber on a lower protective
layer.
[0019] FIG. 7-1 is a block diagram depicting an exemplary
fiber-optic strain system.
[0020] FIG. 7-2 is a block diagram depicting an exemplary
fiber-optic strain ("FOS") system.
[0021] FIG. 8 is a perspective side view depicting an exemplary
optical fiber and a corresponding reflected signal.
[0022] FIG. 9-1 is a block diagram of a perspective view depicting
an exemplary patch attached to a host structure.
[0023] FIG. 9-2 is a block diagram of a cross-sectional view along
A-A of the patch of FIG. 9-1.
[0024] FIG. 10 is a block diagram depicting an exemplary acoustic
emission ("AE") and FOS system.
[0025] FIG. 11-1 is a block diagram depicting an exemplary
single-channel laser tracking-based fiber optic voltage
conditioning system.
[0026] FIG. 11-2 is a block diagram depicting an exemplary
multichannel fiber optic voltage conditioning ("FOVC") system.
[0027] FIG. 12 is a block diagram depicting an exemplary wavelength
tracking system using fiber optic voltage conditioning for sensing
AE.
[0028] FIG. 13 is a flow diagram depicting an exemplary monitoring
or calibrating a processing chamber flow.
DETAILED DESCRIPTION
[0029] In the following description, numerous specific details are
set forth to provide a more thorough description of the specific
examples described herein. It should be apparent, however, to one
skilled in the art, that one or more other examples and/or
variations of these examples may be practiced without all the
specific details given below. In other instances, well known
features have not been described in detail so as not to obscure the
description of the examples herein. For ease of illustration, the
same number labels are used in different diagrams to refer to the
same items; however, in alternative examples the items may be
different.
[0030] Exemplary apparatus(es) and/or method(s) are described
herein. It should be understood that the word "exemplary" is used
herein to mean "serving as an example, instance, or illustration."
Any example or feature described herein as "exemplary" is not
necessarily to be construed as preferred or advantageous over other
examples or features.
[0031] Before describing the examples illustratively depicted in
the several figures, a general introduction is provided to further
understanding.
[0032] Fiber Bragg Gratings ("FBGs") may be used in a sensing
system. A Fiber Bragg Grating ("FBG") sensor array may be
interrogated by a broadband light source-based sensing system for
temperature and strain sensing and/or a laser-based detection
system for acoustic emission sensing. Such systems are described in
additional detail in U.S. patent application Ser. No. 14/814,355,
filed Jul. 30, 2015, and Ser. No. 15/458,311, filed Mar. 14, 2017,
each of which is incorporated by reference as though fully set
forth herein in its entirety for all purposes as indicated above.
Each such sensing and detection systems may generally be thought of
as a light source-based detection system, as described below in
additional detail.
[0033] An optical fiber may include multiple FBG sensors at
different wavelengths. FIG. 1 is a signal diagram depicting an
exemplary FBG signal 100. FBG signal 100, which has for a
horizontal or x-axis frequency 162 and a vertical or y-axis
amplitude 161, represents multiple FBG sensors in an optical fiber,
where each wavelet or signal notch 101 has a corresponding center
frequency, which may be sensitive to temperature, strain, and/or
pressure. A shift in frequency of a center frequency of a wavelet
or signal notch 101 may be related to a change in temperature,
strain, and/or pressure. As described below in additional detail,
an optical fiber with a number of FBG sensors, such as 17 or more
FBG sensors for example, may be used. Each of such FBG sensors may
be configured for a different center frequency or wavelength, and
so such FBG sensors may be used to provide 17 or more different
wavelets or signal notches 101. Each of such 17 or more wavelets or
signal notches 101 may be individually modulated responsive to
pressure, strain, and/or temperature such corresponding 17 or more
FBG sensors experience. Though an example of 17 or more different
wavelets or signal notches 101 is described, in other examples
fewer than 17 different wavelets or signal notches 101 may be
used.
[0034] For example, if pressure is held constant, changes in
temperature at 17 or more locations corresponding to positions of
such 17 or more FBG sensors in an optical fiber or other optical
waveguide may be determined from corresponding center frequencies
or wavelengths of such 17 or more wavelets or signal notches 101.
If, however, pressure is not held constant, then any and all
wavelength shifts of such 17 or more wavelets or signal notches 101
may be due to corresponding changes in pressure, strain, and/or
temperature. Changes in pressure, strain, and/or temperature may be
stored on a processing chamber-by-processing chamber basis in order
to determine profiles for each such processing chamber, as well as
correlate operation of processing chambers.
[0035] For an upstream broadband light source providing a broadband
light signal for an optical fiber with FBGs, each FBG sensor acts
as a filter. So for example, an upstream FBG sensor may filter out
a frequency or wavelength of such broadband light allowing
remaining frequencies or wavelengths to pass. In the example below,
FBGs filter wavelengths in a range of 1500 to 1600 nanometers. This
range may be used to avoid a typical UV range emitted by a plasma
in order to avoid a possibility of UV interference from such plasma
emission. Thus, for example, a broadband light source coupled to an
optical fiber with FBGs may have: a first of such FBGs configured
to reflect back light at a wavelength of 1500 nanometers, a second
of such FBGs configured to reflect back light at a wavelength of
1505 nanometers, and so on up to 1600 nanometers.
[0036] With such reflected light from each of such FBG sensors, an
individual spectrum associated with each such reflected wavelength
wavelet 101 peak may be detected for purposes of detecting changes
in pressure and/or temperature corresponding to each shift in
wavelength corresponding to such reflected wavelength. Along those
lines, an interrogation system may be coupled to receive reflected
wavelets or signal notches 101 from FBG sensors of an optical
fiber. Such an interrogation system may be configured to detect
wavelength shifts, such as in a range from 10 pico-meters to 90
nanometers for example. An interrogation system may be a broadband
light-source based detection system, as described below in
additional detail.
[0037] Along those lines, each FBG sensor may shift approximately
10 pico-meters per degree Celsius change. For approximately 60 FBG
sensors for a 100 nanometer wavelength range, there may be a shift
of approximately 1500 pico-meters, effectively about 150 degrees C.
of shift, of spacing between adjacent pairs of such 60 FBG sensors.
This spacing allows for all 60 FGB sensors to be monitored
together, with sufficient spacing between adjacent FBG sensors to
allow for movement, or expansion of FGB sensors, without negatively
impacting sensing.
[0038] As described herein, a reflected spectrum from FBG sensors
in an optical fiber sensed at an optically proximal end to a
broadband light source is described. However, in another example, a
reverse or inverse of a reflected spectrum from FBG sensors in an
optical fiber sensed at an optically distal end to a broadband
light source may be used in accordance with the description herein.
Thus, a reflection mode or a transmission mode, or both, may be
used for sensing changes in wavelengths corresponding to changes in
pressure and/or temperature. For purposes of clarity by way of
example and not limitation, a reflection mode is described
below.
[0039] By using an optical fiber with multiple sensors, a single
port and a single interface therefor, namely an opening of an
optical fiber for receiving broadband light and detecting reflected
FGB sensor wavelets 101, may be used. By having the capacity to
sense multiple locations along an optical fiber with a single port
opening and a single photo-detector interface, a test wafer may be
more robust and have multiple sensors.
[0040] FBGs may be used for leak detection and/or other structural
monitoring. Along those lines, a known failure mechanism of a wafer
chuck in a chamber is a vacuum leak, where a wafer chuck may vent
to atmosphere. However, it may take some time for a vacuum leak to
grow large enough for a wafer chuck to vent to atmosphere, and a
narrow band light source-based system, such as a laser-based
system, may be used for fiber optic acoustic emission leak
detection monitoring, and such fiber optic acoustic emission leak
detection monitoring may be used with a test wafer as described
herein for early detection of such leakage.
[0041] With the above general understanding borne in mind, various
configurations for a test wafer, as well as other structures for
fiber optic sensors, are generally described below. Though the
description herein is for FBG sensors, it should be understood that
other optical sensors in an optical fiber may be used in accordance
with the description herein.
[0042] FIG. 2-1 is a block-perspective side view depicting an
exemplary test wafer 200. This is just one example of a test wafer
200. In another example, a groove or other cavity, such as a
channel 222 shown in part, may be formed in a polyimide
wafer-shaped sheet to receive an optical fiber with FBG sensors,
which can be adhered in such cavity, such as with an adhesive, to
be below an upper surface of such polyimide wafer-shaped sheet. In
another example, patches may be used to hold an optical fiber in
place at different locations.
[0043] In this example, test wafer 200 may include a first low
durometer layer 201, such as 4-5 mil silicone or other cured or
uncured polysiloxane sheet, bonded onto a more rigid test wafer
platform 202, such as a silicon wafer for example. In another
example, layer 201 may be omitted and a coated optical fiber may be
disposed over and directly on test wafer platform 202. Such first
low durometer layer 201 may be smaller in diameter than such test
wafer platform 202, such as by 1 to 15 millimeters, in order to
more readily fit within a retention/alignment ring 207 of a wafer
chuck, generally indicated with block 206.
[0044] As is known, wafer chuck 206 may be an electrostatic wafer
chuck. Furthermore, wafer chuck 206 may be configured for heating
and/or cooling wafer support surface 210, as well as vacuum ports
(not shown), all of which is known.
[0045] An optical fiber 205 may be laid on such silicon sheet 201,
followed by laying a second low durometer layer 203, such as
another 4-5 mil silicone or other polysiloxane sheet, on and over
such optical fiber 205 and onto such first low durometer layer 201.
In another example, second layer 203 may be a polyimide layer. In
yet another example, a second layer 203 may be reinforced with a
synthetic fiber, such as Kevlar for example. A portion of optical
fiber 205 may extend out from test wafer 200 for subsequent
interconnection, such as with a connector to a light-source based
detection system external to a processing chamber, as described
below in additional detail for embedded optical fibers, or a
portion of optical fiber 205 may be vertically aligned for having
an end thereof downward for alignment with an optical lift pin, as
described below in additional detail.
[0046] Such optical fiber 205 between silicone sheets 201 and 203
may then be adhered to one another with a polyimide or other
sealant 204 for at least sealing edges of such sheets and a gap
therebetween, to provide a hermetic or environmental seal.
Polyimide absorbs UV, and so optical fiber 205 having FGB sensors,
some of which are generally indicated with dots 212, may be
shielded from UV and other environmental factors along an edge or
edges 213. Though the example of a cylindrically or
circularly-shaped test wafer 200 is depicted, in another example a
different shape may be used.
[0047] Optionally, in another example, a polytetrafluoroethylene
(PTFE) layer may be used in addition to silicone sheet 203. In
another example, a coated fiber or the like may be used instead of
or in addition to using a protective layer 201 in order to mitigate
against strain induced errors.
[0048] In this example, test wafer 200 may be loaded, such as with
a robotic arm as is known, into a semiconductor or other processing
chamber through a transfer chamber. Test wafer 200, like a
production wafer, may be positioned for alignment, such as by
having an alignment mark optically encoded on such test wafer 200.
However, for a test wafer 200, such alignment may be for alignment
to an optical lift pin 208p, as described below in additional
detail. Conventionally, as much as a 100 micron misalignment is
allowed, and so an optical lift pin 208p to optical fiber 205
opening end 211 alignment may operate with a misalignment of as
much as 100 microns.
[0049] Lift pins 208 may rise toward such test wafer 200, and such
robotic arm may release such test wafer 200 onto such lift pins
208. Such lift pins 208 may be lowered to lower such test wafer 200
onto a wafer support surface 210 of a wafer chuck 206. Even though
a wafer chuck 206 is described, a susceptor may be used. Such lift
pins 208 may further recess below such wafer support surface 210
creating a gap between a lower surface 320 of test wafer 200 and
wafer support surface 210. In other words, lift pins 208 in this
example are not in direct contact with test wafer 200 while test
wafer 200 is in process or in use.
[0050] However, as described below in additional detail, test wafer
200 is in communication with an optical lift pin 208p during use of
test wafer 200. Additionally, test wafer 200 may be completely
passive, namely test wafer 200 may operate without a power source
other than an optical signal passed from optical lift pin 208p, as
described below in additional detail.
[0051] Recessed below an upper-inner wafer support surface 210
inside retention/alignment ring 207 of wafer chuck 206 may be a
plurality of lift pins 208 in recesses 209 defined in wafer chuck
206. Lift pins 208 may be used for lowering test wafer 200 into
position, namely into ring 207, and for raising test wafer 200 out
of ring 207, as generally indicated with arrow 214. One of such
lift pins 208 may include an optical waveguide, namely optical lift
pin 208p. An opening end 211 of optical fiber 205 may be aligned
for optical communication across a gap, namely "free space", with
optical lift pin 208p. In another example, lift pins 208 may stay
in contact with test wafer 200, so as to have little to no gap.
[0052] Even though a spiral or spiral-like pattern is
illustratively depicted for optical fiber 205, another geometric
pattern, combination of geometric patterns, random positioning
pattern, and/or a combination of any of the above, may be used.
However, for purposes of clarity by way of example and not
limitation, it shall be assumed that a spiral pattern is used.
[0053] Lift pins 208 are conventionally made of sapphire, alumina,
or quartz. Optical lift pin 208p is configured as an optical
waveguide for providing broadband light from a broadband light
source to an opening end 211 of optical fiber 205. Optical lift pin
208p is further configured as an optical waveguide for receiving
reflected wavelets or signal notches 101 for detection by a
downstream interrogation system.
[0054] At this point, it should be understood that only optical
components are present in test wafer 200. Along those lines, there
are no electronic components in test wafer 200 in contrast to a
conventional test wafer. As strong RF fields may be generated in
some chambers, including without limitation plasma chambers, which
quickly degrade electronic components, avoidance of such components
in a test wafer may be useful. In other words, an optical-only
passive test wafer without electronic components embedded therein
may have a longer life cycle in comparison to a test wafer with
embedded electronic components.
[0055] In another example, an optical lift pin 208p may be used
with or omitted in favor of a more direct connection. For example,
a well-known fiber optic feedthrough connector may be used to
provide an optical feed through, such as from internal vacuum
pressure in a processing chamber to external pressure with respect
to a processing chamber. Examples of known fiber optic connectors
include FC/PC and FC/APC connectors.
[0056] FIG. 2-2 is a cross-sectional view of a portion of a
retention/alignment ring 220. A two layer/piece retention/alignment
ring 220 may be used instead of retention/alignment ring 207 of
FIG. 2-1. Lower ring 221 of retention/alignment ring 220, which may
be formed of quartz or other material, may include a passage for an
optical fiber 205 with FBG sensors. An upper tuning ring 223, which
may be formed of silicon carbide or another material, may rest on
an upper surface of lower ring 221, and upper and lower rings 223
and 221 may be raised or lowered with lift pins. In another
example, upper tuning ring 223 may include an optical fiber 205
with FBG sensors, and in yet another example, both tuning rings 221
and 223 may include an optical fiber 205 with FBG sensors. An end
of optical fiber 205 may feed into a fiber optic connector 227,
such as an FC/PC or FC/APC feedthrough connector.
[0057] FIG. 3-1 is an optical signal-block diagram depicting a
cross-sectional view of an exemplary optical test system 300. In
optical test system 300, an optical lift pin 208p is for optical
communication with an optical fiber 205 across a gap 301. Gap 301
may represent "free space" between an aligned optical lift pin 208p
and an opening end 211 of optical fiber 205. This gap may represent
some signal loss, which may affect length of optical fiber 205
and/or number of FBG sensors thereof. Along those lines, a distance
such an optical eye 302 of optical lift pin 208p is recessed below
a wafer support surface 210 of wafer pedestal or chuck 206 may vary
between different types or different tools within a same type of
semiconductor processing equipment. Moreover, such equipment is not
limited to semiconductor processing, but may be used in formation
of solar panels or other electronic components.
[0058] Broadband light, generally indicated with arrow 305, is
provided via an optical waveguide 303 of optical lift pin 208p to
an optical "eye" 302 of optical lift pin 208p. Optical "eye" 302
may be a configuration of one or more lenses for collimating
broadband light 305 into transmitted light 304 for transmission
across gap 301 for entry via opening end 211 of optical fiber 205.
Opening end 211 of optical fiber 205 may optionally include a taper
and lens 321. Such an optional lens 321 may be formed as part of
optical fiber 205.
[0059] After being reflected by one or more FBG sensors 212,
reflected light, as generally indicated with arrow 306, is
reflectively transmitted across gap 301 to optical eye 302. Optical
eye 302 may collimate reflected light 306 into collimated light 307
for communication via optical waveguide 303 for an interrogator
system.
[0060] Accordingly, optical lift pin 208p may operate as a lift pin
and an optical transceiver and bi-directional optical waveguide.
However, in another configuration, a dedicated optical
transceiver/bi-directional optical waveguide 208p may be used,
independently from use of a lift pin 208.
[0061] FIG. 3-2 is the same diagram as in FIG. 3-1, except in this
example optical eye 302 is in test wafer platform 202 of test wafer
200 of an exemplary optical test system 330. Test wafer platform
202 may be formed of a silicon or other material wafer with a
through hole formed therein for receipt of optical eye 302. An open
end 323 of optical waveguide 303 may be formed to include an
optional taper and lens 322. Thus, an optical transceiver lens or
lens assembly, such contained in and retained by optical eye 302,
may form part of a test wafer 200. Moreover, a collimated-tapered
fiber may be used for an optical waveguide 303. Along those lines,
an end of an optical fiber used for optical waveguide 303 may have
a lens formed at an opening end 308 thereof for providing all or a
portion of optical "eye" 302.
[0062] FIG. 3-3 is a combination of an upper portion of FIG. 3-1
and a lower portion of FIG. 3-2 to provide an example of a
single-mode fiber-to-single mode fiber optical test system 350. For
optical communication across a gap 301, an opening end 211 of an
optical fiber 205 may have an optional taper and a lens 321 in
order to receive and collimate dispersed light 304 and transmit
collimated reflected light 306.
[0063] Likewise, an opening end 323 of an optical waveguide 303,
such as another optical fiber, may be aligned to face opening end
211, namely with sufficient overlap for optical communication
across a gap 301. Such opening end 323 of an optical waveguide 303
may have an optional taper and a lens 322 in order to receive and
collimate dispersed reflected light 307 and transmit collimated
light 305.
[0064] Such taper and lenses 321 and 322 are optional, as for some
applications gap 301 may be too small for sufficient dispersion to
warrant a taper and lens at opposing opening ends of optical
fibers. In above example with dispersion due to a gap 301, such
taper may generally be to expand average fiber optical mode field
diameter from 10 microns to approximately 1.3 millimeters with
unchanged numerical aperture for the above example to receive
dispersed light. Though such taper is present for transmission of
light, such light is collimated upon exit with a lens. For optical
alignment, an optical eye assembly 326 may surround an opening end
211 of optical fiber 205, and an optical eye assembly 327 may
surround an opening end 323 of optical fiber 303.
[0065] Furthermore, in the above example for having one fiber
generally orthogonal to another fiber with respect to internal
communications of optical signals, one or both such lenses 321 and
322 may include a reflective surface, such as a mirrored surface
such as surfaces 328 and 329, respectively, to re-direct light, for
a 90 degree or right angle redirection. For example, Single Mode
SMF-28 fiber of gold coated fiber with Fiber Bragg Grating of 5 mm
in length with separation of 2 cm of 17 or more, such as 50 for
example, channel/arrays with pitch of 2 cm and one side
perpendicular lensed fiber with 500 .mu.m collimated beam diameter
and stripped length of 10 to 12 mm and wavelength between 1510 and
1590 nm may be used. For such a fiber, other or distal end may be
plain cleaved, and remaining fiber may be bare for an overall
length of approximately 1.3 meters.
[0066] For this separation between each FBG sensors, a 2 cm spacing
between each adjacent gratings may be used to minimize optical
crosstalk. However, in another example, a minimum spacing may be 1
cm between adjacent gratings. Furthermore, a fiber polyimide
coating stripping and a gold overcoat coating may be separate
operations, designed to enhance mechanical strength for fiber
handling. However, a polyimide stripping may be used without a gold
coating to minimize thermal crosstalk.
[0067] However, in another example, a prism may be used with an
optical fiber. FIG. 4 is a perspective-optical signal diagram
depicting a cross-sectional view of an exemplary bi-directional
prism assembly 400. Bi-directional prism assembly 400 may include a
conical or conical-like tip 401 configured to collimate light, such
as for an optical transmission 411 to free space and an optical
reception 412 from free space.
[0068] An optical prism waveguide portion 402 of bi-directional
prism assembly 400 may be fused, such as with ARC or other fusion
405, to an optical fiber 404. A right angle surface 403 of
bi-directional prism assembly 400 have a reflective coating 406,
such as to provide a mirror, for re-directing optical signals 411
and 412. In another example for free space transmission with a
significant gap between two single mode fibers, more than one prism
can be used as beam shaper to significantly increase a beam size
for effective mode overlap to enhance coupling alignment tolerance.
For example, spherical or aspherical lenses together with a pair of
prisms, or cascaded prisms, can be used to collimate an exiting
beam from a first fiber, expand beam size, and redirect the beam
through a gap, then reduce the beam size, and focus the beam to the
second fiber. This combined lens and cascaded prisms facilitates
free space transmission between two non-colinear single mode fibers
with high coupling alignment tolerance.
[0069] An optical transmission signal 411 may be 10 microns wide at
exit for example; however, such optical transmission signal 411 may
diverge or disperse in free space into a much wider signal.
Furthermore, other sizes of optical transmission widths may be used
in other examples.
[0070] An optional lens 322 may be used to receive such dispersed
optical transmission signal 411 for collimation into an optical
fiber 205. Likewise, tip 401 may be configured to receive an
optical reflection transmission 412, collimated at exit from an
optional lens 322 and dispersed across free space for reception at
tip 401, and then tip 401 may collimate such received dispersed
optical reflection transmission 412 from FBG sensors 212 of an
optical fiber 205.
[0071] Optionally, optical prism waveguide 402 may incorporate a
lens 409 and/or a lens 408. Optical prism waveguide 402 may
functions as a compact beam shaping component such as expanding or
reducing a collimated beam size and/or redirecting a beam's
direction. A lens 409 optionally can be bonded or integrally made
as part of optical prism waveguide 402 as a single element unit.
Optionally, an optical fiber 404 may be with integrated ball lens
408, which then can be combined with a optical prism waveguide 402
for further expanding a beam size and bending or redirecting, such
as by 90 degree, a beam for enhancing orthogonal coupling alignment
tolerance.
[0072] FBG sensors in optical fibers may be used with an
interrogation system. An FBG sensor array may be interrogated by a
broadband light source detection system. In this example, an LED
may be used as a broadband light source. Furthermore, because FBGs
do need the signal strength that other devices do in order to
operate, a larger free space gap may be tolerated. Furthermore,
because only shifts in wavelength may be detected to determine a
pressure and/or temperature change, weak signals may be used for
such detection. For example, up to a 90% signal loss may be
tolerated in such a system, because a frequency shift and not an
amplitude loss is detected.
[0073] Returning to FIG. 2, a test wafer 200 may be used in a
processing chamber. In this example, a bi-directional 214 arrow
indicates a device in a through hole in a silicon wafer substrate
base, such as of a wafer chuck, for engagement with a test wafer
platform 202.
[0074] In this example, a bi-directional prism optical interface,
such as of FIG. 4, is used, as generally indicated with such a
bi-directional arrow 214 disposed in such a silicon wafer substrate
base. Additionally, such bi-directional prism optical interface may
be used to collimate light in an upward direction for a test wafer
optical fiber 205, as well as in a downward direction for
communication via an optical waveguide 303, such as an optical
fiber. Along those lines, a bi-direction prism optical interface is
an example of an optical eye 302. Such a bi-directional prism may
be for transmission of collimated light for communication with a
test wafer and/or to receive collimated light for downstream
communication to a photo-sensitive array of an interrogation
system.
[0075] In this example, layers 201 and 203 are respective low
durometer vulcanized fiber layers. Furthermore, in this example, a
polyimide or other corrosion protection layer 204 covers an upper
layer 203 as well as sides of layers 201 and 203. Covering layers
201 and 203 with a polyimide layer for example may be useful to
capture any outgassing of layers 201 and 203. Along those lines, an
underside of layer 201 may be exposed, as vacuum ports of a wafer
chuck may be used to remove such outgassing from negatively
impacting chamber chemistries. However, in another example, all of
test wafer 200 may be covered with a polyimide layer 204, except
where bare optical fiber 205 opening end 211 is accessible to
incoming and outgoing light. Bare fiber can optionally be inserted
inside a hollow metal tube with inner diameter slightly larger than
the fiber diameter itself, such as between 300 um and 500 um, to
allow for FBG to freely expand inside such a metal tube without any
or any significant restriction imposed by such metal tube. Such a
metal or other shielding tube can be a UV barrier or additional UV
barrier with respect to protecting light in an optical fiber.
Moreover, such a metal or other shielding tube may provide a
pressure isolation layer for FBG sensors for focusing on
temperature sensing.
[0076] Even though this example is for 48 FBG sensors using one of
three lift pins, in another example more FBG sensors per lift pin
may be used. Furthermore, in another example, more than one lift
pin and more than one optical fiber may be used. However, use of
multiple lift pins and multiple optical fibers may be understood
from a single lift pin and single optical fiber example, except an
optical multiplexer may be used to multiplex multiple signals input
to an interrogation system.
[0077] An optical patch cord may run through a raceway to an
interrogation system. Because a lift pin under carriage frame is
generally driven from the bottom, a patch cord with some amount of
slack may be used above such lift mechanism to track vertical
movement up and down without binding such optical fiber.
Additionally, an optical lift pin 208p may be a replaceable item,
like a test wafer 200, after a number of uses in order to ensure a
high quality of result.
[0078] While the above-description has generally been for a test
wafer having an optical fiber with FBG sensors, use of FBG sensors
in semiconductor processing and/or semiconductor processing
calibration equipment is not limited to test wafers. As FBG sensors
may be used for leak detection and structural monitoring, such FBG
sensors may be used to determine if a chamber is structurally sound
and/or leaking, such as leaking to atmosphere in a clean room.
Along those lines, FGB sensors may be used in chamber shower heads,
chamber walls, wafer pedestals, chamber lids, and/or wafer chucks,
among other semiconductor processing equipment structures.
[0079] FIG. 5-1 is a block-sectional diagram depicting an example a
semiconductor processing chamber system ("processing chamber") 500.
A component in an interior volume 506 of processing chamber 500 is
substrate support assembly 548, such as for supporting an
in-process substrate 536 disposed in a retention ring 546.
Substrate support assembly 548 may include an electrostatic chuck
("wafer cuck") for a wafer or other substrate for example. Even
though a wafer chuck is described, a susceptor may be used. For
purposes of clarity by way of example and not limitation, a
substrate support assembly 548 may be allowed to have a helium leak
rate for example of 1.5 SCCM (Standard Cubic Centimeters per
Minute) or less for a lifespan thereof, generally measured in RFHrs
(radio frequency hours).
[0080] Various manufacturing processes, including cleaning, may
expose semiconductor process chamber 500 and components thereof,
including substrate support assembly 548, to high temperatures,
high energy plasmas, mixtures of corrosive gases, high stresses,
near vacuum pressures, and combinations thereof. These extreme
conditions may erode, corrode, and increase susceptibility to
defects with respect to one or more of such processing chamber 500
components. Accordingly monitoring for structural and other defects
due to erosion, corrosion, and/or general wear and tear may avoid
costly damage to a chamber and/or products formed in such chamber.
Along those lines, structural monitoring, leak detection, pressure
monitoring, temperature monitoring, and other forms of monitoring
and detection may be used.
[0081] Processing chamber 500 may be used for processes in which a
corrosive plasma environment having plasma processing conditions is
created in such chamber. For example, processing chamber 500 may be
a chamber for a plasma etcher or plasma etch reactor, a plasma
cleaner, and so forth. Examples of processing chamber 500
components include substrate support assembly 548, an electrostatic
chuck (ESC), a ring (e.g., a process kit ring or single ring), a
chamber wall, a base, a gas distribution plate, a gas distribution
assembly ("showerhead") 530, gas lines, a nozzle, a lid, a liner, a
liner kit, a shield, a plasma screen, a flow equalizer, a cooling
base, a chamber viewport, a chamber lid 504, and so on.
[0082] In this example, processing chamber 500 includes a chamber
body 502, a gas distribution assembly 530, and a chamber lid 504.
Chamber body 502, gas distribution assembly 530, and chamber lid
504 define at least in part an interior volume 506 for
processing.
[0083] Chamber body 502 generally includes sidewalls 508 and a
bottom 510. Chamber body 502 may be fabricated from aluminum,
stainless steel or other suitable material.
[0084] An outer liner 516 with respect to interior volume 506 may
be disposed adjacent to interior surfaces of side walls 508 to
protect chamber body 502. Outer liner 516 may be fabricated and/or
coated with a coating, such as for example a plasma or
halogen-containing gas resistant material. In an example, outer
liner 516 is fabricated from aluminum oxide. In another example,
outer liner 516 is fabricated from or coated with yttria, a yttrium
alloy, or an oxide thereof.
[0085] Gas distribution assembly 530 may have multiple gas delivery
holes or apertures 532 on a downstream surface of a gas
distribution plate ("GDP") 531 of gas distribution assembly 530 to
direct gas flow into interior volume 506. GDP 531 may be bonded to
an aluminum showerhead base or an anodized aluminum showerhead
base. GDP 531 may be made from Si or SiC, or may be a ceramic such
as Y.sub.2O.sub.3, Al.sub.2O.sub.3, YAG, and so forth. Showerhead
530 and delivery holes 532 may be coated with a multi-component
coating.
[0086] Additionally, gas distribution assembly 530 can have a
center hole where gases are fed, such as through a ceramic gas
nozzle, into an interior distribution region 533 of gas
distribution assembly 530. Gas distribution assembly 530 may be
fabricated and/or coated by a ceramic material, such as silicon
carbide, yttria, or other material to provide resistance to
halogen-containing chemistries to prevent or mitigate corrosion. In
another example, gas distribution assembly 530 may be replaced by a
lid and a nozzle. Any of gas distribution assembly 530 (or lid
and/or nozzle), sidewalls 508 and/or bottom 510 may be coated to
prevent corrosion. Gas distribution assembly 530 in this example is
for a dielectric etch, namely etching of dielectric materials, in
processing chamber 500.
[0087] For processing chamber 500 used for a conductor etch, namely
etching of conductive materials, a lid may be used rather than a
gas distribution assembly 530. Such a lid may include a center
nozzle that fits into a center hole of such lid. Such lid may be a
ceramic such as Al.sub.2O.sub.3, Y.sub.2O.sub.3, YAG, or a ceramic
compound including Y.sub.4Al.sub.2O.sub.9 and a solid-solution of
Y.sub.2O.sub.3-ZrO.sub.2. Such nozzle may also be a ceramic, such
as Y.sub.2O.sub.3, YAG, or the ceramic compound including
Y.sub.4Al.sub.2O.sub.9 and a solid-solution of
Y.sub.2O.sub.3-ZrO.sub.2. Such lid, gas distribution assembly 530
(e.g., including showerhead base, GDP and/or gas delivery
conduits/holes) and/or nozzle may all be coated with a
multi-component coating.
[0088] An exhaust port 526 may be defined in bottom 510 of chamber
body 502. Exhaust port 526 may provide a conduit between interior
volume 506 and a pump system 528. Pump system 528 may include one
or more pumps and throttle valves utilized to evacuate and
otherwise regulate pressure in interior volume 506 of processing
chamber 500. This pressure for semiconductor processing may be
close to a vacuum, such as for example in a range of 0.1 to 20
millitorr ("mTorr"; 0.01 Pascals ("Pa") to 2.67 Pa).
[0089] Chamber lid 504 may be supported on one or more sidewalls
508 of chamber body 502. Chamber lid 504 may be opened to allow
access to interior volume 506 of processing chamber 500 in some
examples, and chamber lid 504 may be closed to provide a seal for
processing chamber 500. A gas panel 538 may be coupled such as via
a conduit to processing chamber 500 to provide process and/or
cleaning gases to interior volume 506 through gas distribution
assembly 530. In this example, gas distribution assembly 530 is
part of chamber lid 504.
[0090] Examples of processing gases which may be used in
semiconductor fabrication in processing chamber 500 include
halogen-containing gases, such as C.sub.2F.sub.6, SF.sub.6,
SiCl.sub.4, HBr, NF.sub.3, CF.sub.4, CHF.sub.3, CH.sub.2F.sub.3,
Cl.sub.2 and SiF.sub.4, among others, and other gases such as
O.sub.2, or N.sub.2O. Examples of carrier gases include N.sub.2,
He, Ar, and other gases inert to process gases (e.g., non-reactive
gases). Examples of cleaning gases that may be used to clean
components in interior volume 506 include chlorine, fluorine,
bromine, and other corrosive gases that are usable to produce a
plasma suitable for cleaning.
[0091] Substrate support assembly 548 is located in interior volume
506 of processing chamber 500 below a gas distribution assembly 530
or a lid. Substrate support assembly 548 may be used to hold a
substrate during processing. Substrate support assembly 548 may
include an electrostatic chuck bonded to a cooling plate.
[0092] An inner liner 518 with respect to outer liner 516 may be
coated on a periphery surface of substrate support assembly 548.
Inner liner 518 may be a halogen-containing gas resistant material
such as those discussed with reference to outer liner 516. In one
example, inner liner 518 may be fabricated from the same materials
as outer liner 516.
[0093] In this example, substrate support assembly 548 includes a
lower mounting plate 562 with a threaded through hole for threaded
engagement with a pedestal 552. Substrate support assembly 548
further includes an electrostatic chuck 550. Pedestal 552 may be
controllably raised, lowered, and/or rotated within interior volume
506 in order to raise, lower, and/or rotate electrostatic chuck
550
[0094] Electrostatic chuck 550 includes a thermally conductive base
564 bonded to an electrostatic body ("electrostatic puck") 566 via
a bond 538. Electrostatic puck 566 may be fabricated from a ceramic
material such as aluminum nitride (AlN) or aluminum oxide
(Al.sub.2O.sub.3). Mounting plate 562 may be attached or coupled to
bottom 510 of chamber body 502. Mounting plate 562, and bottom 510,
may include passages for routing utilities (e.g., fluids, power
lines, sensor leads, etc.) to the thermally conductive base 564 and
electrostatic puck 566. Along those lines, sensor leads may include
fiber optic lines in accordance with the description herein.
[0095] Thermally conductive base 564 and/or electrostatic puck 566
may include one or more optional embedded heating elements 576,
embedded thermal isolators 574 and/or conduits 568, 570, such as to
control a lateral temperature profile of support assembly 548.
Along those lines, conduits 568, 570 may be coupled to a fluid
source 572 for flow of fluid to circulate a temperature regulating
fluid through conduits 568, 570. An embedded thermal isolator 574
may be located at least in part between conduits 568, 570 in this
example.
[0096] Heater 576 may be regulated by a heater power source 578.
Circulation of fluid through conduits 568, 570 and regulation of
heater 576 may be utilized to control temperature of thermally
conductive base 564, such as through thermal conduction, to heat
and/or cool electrostatic puck 566 and a substrate (e.g., a wafer)
being processed. Temperature of electrostatic puck 566 and
thermally conductive base 564 may be monitored using a plurality of
temperature sensors 592, which may be monitored using a thermal
controller 595, and thermal controller 595 may be used to control
heater power source 578 and fluid source 572 to regulate thermal
conditions of electrostatic puck 566 and/or thermally conductive
base 564.
[0097] Instead of or in addition to temperature sensors 592, one or
more optical fibers or fiber optic cables 205 having FBG sensors
may be located in electrostatic puck 566, a retention/alignment
ring (as previously described), and/or thermally conductive base
564. Optionally, a fiber optic cable 205 having FBG sensors may be
located in gas distribution assembly 530 and/or a chamber lid 504.
Such one or more fiber optic cables 205 may be coupled to a light
source-based detection system 591 to generate data 597 in response.
Optical fiber 404 of FIG. 4, not shown in this figure for clarity,
may extend from electrostatic chuck 550 down to be coupled to light
source-based detection system 591. Reflections from a FBG sensor
array may be interrogated by a laser-based detection system such as
described in additional detail in U.S. patent application Ser. No.
14/814,355, filed Jul. 30, 2015, and Ser. No. 15/458,311, filed
Mar. 14, 2017, each of which is incorporated by reference as though
fully set forth herein in its entirety for all purposes, and such
laser-based detection systems may be used for a light source-based
detection system 591.
[0098] Data 597 may be used to indicate temperature detected using
such FBG sensors, and such data 597 or results therefrom may be fed
to thermal controller 595. Thermal controller 595 may be used to
control heater power source 578 and fluid source 572 to regulate
thermal conditions of electrostatic puck 566 and/or thermally
conductive base 564.
[0099] Thermal data and/or other information, such as pressure,
flow rate, leak detection and/or structural information, in data
597 may be provided to a computer system for monitoring
temperature, flow rate, structural integrity, and/or pressure for
processing chamber 500. Along those lines, even though FBG sensors
in one or more fiber optic cables 205 may be located within
processing chamber 500, optionally there may be FBG sensors in one
or more fiber optic cables 205 external to processing chamber 500,
such as for sensing acoustic emissions for leak detection for
example. Moreover, an embedded or enclosed portion of a fiber optic
cable or optical fiber 205, whether in an electrostatic puck 566,
thermally conductive base 564, gas distribution assembly 530, or
chamber lid 504, may be generally disposed in a spiral, spiral
like, or other pattern as described herein.
[0100] Electrostatic puck 566 may further include multiple gas
passages such as grooves, mesas and/or other surface features that
may be formed in an upper surface of electrostatic puck 566. Along
those lines, a fiber optic cable 205 may be positioned in grooves
or other surface features formed in an upper surface of
electrostatic puck 566. Such gas passages may be coupled to a fluid
source 572, such as via holes drilled in electrostatic puck 566 for
passage of a thermally conductive gas. In operation, gas may be
provided at a controllable pressure into such gas passages to
enhance thermal transfer between electrostatic puck 566 and a
chucked substrate 544. In addition to fiber optic cable 205 being
used to sense temperature of electrostatic puck 566 for example,
such fiber optic cable 205 may be positioned to sense temperature
and/or flow rate of gas moving in such grooves and/or other surface
features.
[0101] Electrostatic puck 566 includes at least one clamping
electrode 580 controlled by a chucking power source 582. Electrode
580, or other electrode disposed in puck 566 or base 564, may
further be coupled to one or more RF power sources 584, 586 through
a matching circuit 588 for maintaining a plasma formed from
processes and/or other gases within processing chamber 500. RF
power sources 584, 586 may generally capable of producing RF signal
having a frequency from about 50 kHz to about 3 GHz and a power of
up to about 10,000 Watts.
[0102] Substrate 544 may have a disc shape, a flat square shape, a
flat rectangular shape, or other appropriate shape. Substrate 544
may include a conductive portion that allows substrate 544 to be
secured or chucked by electrostatic chuck 550 during a
semiconductor fabrication or chamber cleaning process.
[0103] FIG. 5-2 is the block-sectional diagram of FIG. 5-1
depicting another example of a processing chamber 500. In this
example, gas distribution assembly 530 is replaced with a chamber
lid 561. Chamber lid 561 may have centrally disposed therein a
nozzle 563 coupled at an end for gas(es) ("gas") flow from gas
panel 538. Another end of nozzle 563 may be exposed to interior
volume 506 for spraying or otherwise distributing gas flow in
interior volume 506. Other details regarding processing chamber 500
are the same as in processing chamber 500 of FIG. 5-1, and thus are
not repeated. Optionally, a fiber optic cable 205 having FBG
sensors may be located in chamber lid 561, and information from
such FBG sensors may be coupled to light source-based detection
system 591 for generating thermal data or other information in data
597, which may be provided to a computer system for monitoring
temperature, flow rate, structural integrity, and/or pressure for
processing chamber 500.
[0104] Processing chambers 500 of FIGS. 5-1 and 5-2 are examples
representative of etch or deposition chambers. Known details
regarding processing chambers 500 are not described in unnecessary
detail for purposes of clarity and not limitation. Along those
lines, even though particular examples of processing chambers 500
are depicted, other designs of processing chambers 500 may have
coupled thereto a light source-based detection system 591 by one or
more fiber optic cables 205 having FBG sensors. Such fiber optic
cables 205 may be located in electrostatic puck 566, thermally
conductive base 564, gas distribution assembly 530/chamber lid 561,
and/or elsewhere in a processing chamber 500. Such fiber optic
cables 205 in puck 566, thermally conductive base 564, and/or gas
distribution assembly 530/chamber lid 561 may have a spiral pattern
or spiral-like pattern, such as for example as in FIG. 2.
[0105] FIG. 5-3 is a block-sectional diagram depicting yet another
example of a processing chamber 500. Processing chamber 500 is an
etcher, which in this example is representative of a Decoupled
Plasma Source chamber, also known as an inductively coupled plasma
etch chamber. Known details regarding processing chamber 500 are
not described in unnecessary detail for purposes of clarity and not
limitation. Along those lines, even though an inductively coupled
plasma etcher is depicted, a capacitively coupled parallel plate
etch chamber, a magnetically enhanced ion etch chamber, or other
etch processing chambers 500 may be used with fiber optic cables
205 having FBG sensors, as described herein. Such one or more fiber
optic cables 205 may be coupled to a light source-based detection
system 591 for generating data 597, where such fiber optic cables
205 may be located in electrostatic puck 566, thermally conductive
base 564, chamber lid 561, and/or elsewhere in a processing chamber
500. Such fiber optic cables 205 in puck 566, thermally conductive
base 564, and/or showerhead chamber lid 561 may have a spiral
pattern or spiral-like pattern, such as for example as in FIG.
2.
[0106] Precise control of internal chamber conditions, including,
temperature, pressure/vacuum, gas flow, leakage of vacuum and/or
gases, spectral characteristics, vibration/acoustics, chemical
composition, and/or thermodynamic uniformity may be used for
semiconductor processing. A test apparatus, such as a Test Wafer,
with FBG sensors in an optical fiber 205 and/or a fiber optic cable
205 which may be a bi-directional optical cable, built into a
process chamber 500 can be used for both calibration and/or
monitoring of existing or permanently installed peripheral process
control components, such as but not limited to heaters, sensors,
flow meters, and/or RF generators as used in a processing chamber
500. An optical fiber 205 and/or a fiber optic cable 205 may be
interconnected to light source-based detection system 591 directly
or via an FC-APC or other optical connection interface. In this
example, optical fiber 205 is a bi-directional optical cable, where
reflections from FBG sensors are used in response to laser-beam
generated signals. Along those lines, only one end of optical fiber
205 is connected to light source-based detection system 591, as
reflections may be used. However, in another implementation, a
negative signature of such reflections may be used, namely by
having both ends of fiber optic cable 205 interconnected to light
source-based detection system 591. Use of these and such peripheral
process control components may combine to create a uniform plasma
or other semiconductor processing environment within a chamber for
a wafer on a pedestal or chuck, as well as for the use of capturing
data that can be used to determine certain trends of these
peripherals. This captured information may allow chamber operators
to make improvements that can both improve quality and/or volume of
a wafer's yield of integrated circuit dies. A wafer may have
integrated circuit dies, such as processors, microcontrollers,
memory, optical mux/demux, waveguides, and other integrated
circuits and/or other discrete devices, which are used in today's
global industries. Such global industries include cellular phones,
tablets, notebook computers, onboard space rocket/satellite
telemetry control computers, and missile guidance systems, among
others.
[0107] Test wafers as described here use FBG sensors, such as for
capturing one or more aforementioned process control parameter data
points. Moreover, such FBG sensors do not suffer from one or more
limitations associated with conventional use of mineral luminescent
material and Fabry Perot-based systems. As the control parameters
of a semiconductor process controller environment change, an
optical signal and/or optical system is not limited by one or more
limitations of mineral luminescent material-based and Fabry
Perot-based systems, such as signal decay associated with
conventional luminescent material, UV sensitivity associated with
conventional luminescent material, and/or calibration parameter
variation associated with Fabry Perot-based interferometry.
[0108] Additionally, RF immunity is useful in a semiconductor
chamber due to an extremely high level of RF power used to strike
an exothermic plasma which enhances certain processes such as ALD,
PVD, CVD, EPI, Etch, and SRP, among others. An FBG-based optical
system as described herein provides such immunity.
[0109] FIG. 6-1 is a block diagram of a side sectional view
depicting an exemplary lid assembly 600. Lid assembly 600 may be
used for a chamber lid 561 or a gas distribution assembly 530, as
previously described. However, for purposes of clarity and not
limitation, a chamber lid 561 of processing chamber 500 of FIG. 5-3
is assumed.
[0110] Lid assembly 600 includes a lid 610. Lid 610 may be made of
an alumina for example. Lid assembly 600 may include a heater
dielectric layer 611. Heater dielectric layer 611 may be made of a
high durometer polyimide. A heating element 612 may be positioned
in heater dielectric layer 611. Heating element 612 may be
separately controlled (not shown in this figure). Heating element
612 may be a phosphor bronze alloy foil or film, where same is
located in an etched channel in heater dielectric layer 611.
[0111] An optical fiber cable 205 may be sandwiched between a lower
protective layer 615 and an upper protective layer 614 of a low
durometer material, such as for example a vulcanized rubber. An end
616 of optical fiber 205 may be interconnected to a connector, such
as with an FC-APC connector, for connection to a light source-based
detection system 591. Optionally, a rigid top or cover plate 617,
such as made of a polyimide, may be located over upper layer 614,
as well as down along sides of protective layers 614 and 615 and
sides of dielectric layer 611 for attachment to a surface 618 of
lid 610. Optionally, an insulation layer 619 may be located over
top 617.
[0112] FIG. 6-2 is a top-down revealed view depicting an exemplary
portion of an optical fiber 205 on a lower protective layer 615. In
this example, optical fiber 205 starts with a spiral or spiral-like
pattern followed by what appears as a "random" pattern. However,
such "random" pattern may be for working with particular locations
of wavelength specific laser scribed FBG sensors along optical
fiber 205. Thus, a combination of a geometric and a non-geometric
pattern may be used.
[0113] Though the above examples have generally been associated
with processing chambers for wafers, such processing chambers may
be for a display, such as an LED or other display, screen, a solar
panel, or other substrates. Additionally, examples of light
source-based detection systems 591 are described below with
reference to FIGS. 7-1, 7-2, 10, 11-1, 11-2, and 12.
[0114] FIG. 7-1 is a block diagram depicting an exemplary
fiber-optic strain system A100. Fiber-optic strain ("FOS") system
A100 may be configured to convert optical signals from FBG
fiber-optic sensors A111 in a rosette or rosette-like pattern into
analog voltage outputs that may be directly interfaced with strain
instrumentation. FOS system A100 may include a subsystem, namely
fiber-optic system for sensing ("fiber-optic sensing system")
A119.
[0115] Along those lines, an example FBG interrogation system may
have broadband super-luminescent light-emitting diodes ("SLED"), an
optical circulator, and a spectral engine A112, such as for example
an InGaAs spectral engine. A commercially available spectral engine
A112 may include a Volume Phase Grating ("VPG") for a spectral
element A107 and a multi-element array detector A108, such as for
example an InGaAs CCD (charge-coupled device) array detector. In
such system, an optical signal reflected back from FBG fiber-optic
sensors A111 may be spectrally dispersed with such a VPG, such that
reflected power from each VPG may extend over only a few pixels of
a CCD array detector. This reflected power extending to just a few
pixels may represent a sufficient number of data points for a
downstream digital signal processor or digital signal processing
algorithms of a general-purpose processor to be applied to provide
higher resolutions. Using a multi-element array detector
facilitates high-speed parallel processing, real time spectrum
inspection with sub-millisecond ("sub-ms") response times, and
sub-pico meter ("sub-pm") spectral resolution.
[0116] Strain-induced wavelength shifts experienced by one or more
of FBG fiber-optic sensors A111 may be converted to analog voltage
signals ("analog output") A102 that resemble parametric outputs of
a conventional strain gauge signal conditioner. This allows an FOS
system A100 to work as a high-performance "drop-in" replacement for
a signal conditioner in conventional strain measurement systems, as
described below in additional detail. Additionally, analog output
A102 may be used to provide temperature measurements.
[0117] FOS system A100 may include an FBG Analyzer ("FBGA") module
A110, a System-on-Chip ("SoC") module A120, FBG fiber-optic sensors
A111 in an optical fiber A101, an optical fiber-to-structure
bonding material A104, and a digital-to-analog ("D/A") converter
A130. Optionally, FOS system A100 may be coupled to a network A190,
which may include the Internet or other network, for Cloud
storage/computing A191. Optionally, one or more web-browser enabled
devices A192 may be used to communicate with such Cloud
storage/computing A191 via such network A190.
[0118] FBG fiber-optic sensors A111 in optical fiber A101 housing
may be coupled to receive and provide an optical signal via such
optical fiber A101, the former of which may be for optical
transmission of light from a broadband light source A105. A bonding
material A104 may be used to couple optical fiber A101 having FBG
fiber-optic sensors A111, namely bonding FBG fiber-optic sensors
A111 to a material or structure under test A103. A cyanoacrylate or
other adhesive may be used for example for a bonding material A104.
Optionally, rather than direct bonding to a material or structure
under test A103, a polymer substrate may be used as described below
in additional detail.
[0119] A broadband light source A105, such as an LED light source,
including an SLED, of FBGA module A110 may provide light to an
optical circulator A106 of FBGA module A110, and such light may be
sent through to optical fiber A101 via passing through optical
circulator A106 through to FBG fiber-optic sensors A111. Responsive
to strain-induced wavelength shifts experienced by one or more of
FBG fiber-optic sensors A111, reflected light from FBG fiber-optic
sensors A111 may be provided as returned optical signals via
optical fiber A101 to optical circulator A106 for spectral element
A107 of FBGA module A110. As described below in additional detail,
more than one optical fiber A101 may be coupled to provide a
rosette or rosette-like pattern of FBG fiber-optic sensors A111,
which may be coupled to a spectral element A107 through optical
circulator A106.
[0120] Reflected light may be spectrally dispersed through spectral
element A107, which in this example is one or more VPGs of a
spectral engine A112 of FBGA module A110. Such dispersed light may
be detected by a photodiode array A108 of FBGA module A110, which
in this example is an InGaAs photodiode array; however, other types
of photodiode arrays may be used in other implementations. As
described above, a spectral engine A112 may include a CCD array
detector A108. Along those lines, a CCD array detector A108 may
include or perform the function of an analog-to-digital converter
("A/D") converter A109 as part of spectral engine A112. In another
example, a separate ND converter A109 may be used, as either an
analog or digital array detector A108 may be used. For purposes of
clarity and not limitation, it shall be assumed that a photodiode
array A108 is used that does not incorporate an ND converter
A109.
[0121] Data output of photodiode array A108 may be digitized using
an ND converter A109 of FBGA module A110 to provide digital data
output A113. Digital data output A113 of ND converter A109 may be
packetized by an on-board integrated circuit packetizer A139 of
FBGA module A110, which in this example is separate from an FPGA of
SoC module A120. However, in another implementation, packetizer
A139 and/or ND converter A109 may be implemented in an FPGA of SoC
module A120. Such packetized information may be forwarded from
packetizer A139 to SoC module A120 for post-processing. Packetizer
A139 may be for hardwired Ethernet or other hardwired
communication, or packetizer A139 may be for wireless
communication, such as for WiFi, WLAN, or other wireless traffic.
Moreover, even though a single channel system is illustratively
depicted, a multi-channel system may be implemented as described
below in additional detail.
[0122] SoC module A120 may include a CPU complex A121, a
programmable gate array device A122, and main memory A123. In this
example, such programmable gate array device A122 is an FPGA;
however, in other implementations, other types of integrated
circuits, whether programmable gate array devices or not, may be
used to provide a digital-to-analog ("D/A") interface A124 and
digital signal processing ("DSP") hardware A125.
[0123] CPU complex A121, which may be on a same FPGA as D/A
interface A124 and DSP hardware A125 in another implementation, in
this implementation includes a dual-core CPU A127 running firmware
A126. However, a single core or other types of multi-core CPUs may
be used in other implementations. Generally, a signal conversion
block A150, which may be in CPU complex A121, may include a peak
detector A129, a Web socket A136, firmware stored in memory
("firmware") A126, and a spectral power converter A131. Firmware
A126 may receive data from packetizer A139 of FBGA A110 into a ring
buffer A128 of SoC module A120, which may also be of CPU complex
A121.
[0124] Ring buffer A128 may be used to store a continuous stream of
samples from packetizer A139 of FBGA A110 to in effect allow FOS
system A100 to plot outputs of FBG fiber-optic sensors A111 in a
rosette or rosette-like pattern over a period of time. Firmware
A126 may be configured to clean up data from ring buffer A128. Data
from ring buffer A128 may be provided to a peak detector A129, and
detected peaks may be provided from peak detector A129 to spectral
power block A131 to quantify spectral power associated with each of
such peaks detected. Along those lines, firmware A126 may quantify
wavelength shifts, which are directly proportional to the amount of
strain experienced and spectral power sensed by each of FBG
fiber-optic sensors A111 in a rosette or rosette-like pattern. This
post-processed data A132 may be stored in main memory A123.
[0125] In this implementation, programmable gate array A122, which
is coupled to main memory A123, is configured to provide hardware
that reads data A132 that firmware A126 has placed in main memory
A123 and that performs signal processing tasks on such data A132
using DSP hardware A125. An example of a signal processing task may
be an FFT and/or the like to measure any vibration components in
data A132.
[0126] Output of DSP hardware A125, such as an FFT output for
example, may be written back to main memory A123 as data A133 for
use by CPU complex A121. D/A interface A124 of programmable gate
array device A122 may be used to send FBG sensor data A132 to an
external D/A converter A130 to mimic a parametric output of a
conventional strain signal conditioner. FOS system A100 may work as
a high-performance "drop-in" replacement for a signal conditioner
in conventional strain measurement systems, and so analog output
A102 may be provided to conventional strain measurement
instrumentation (not shown). Each output of D/A converter A130 may
represent an output of one FBG fiber-optic rosette sensor of FBG
fiber-optic sensors A111.
[0127] CPU complex A121 via firmware A126 may be configured to read
strain data A133 that programmable gate array A122 has placed in
main memory A123. CPU complex A121 may optionally include either or
both an Ethernet interface A134 or a USB WiFi interface A135 to
forward strain data A133 to one or more remote computers connected
over network A190. Optionally, an external Cloud server or servers
for providing Cloud storage/computing A191 may take outputs from
multiple FOS systems A100 and store them in a database for further
analysis by software running on such Cloud server(s). In this
example, such computers may include multiple HTML5-compliant Web
browsers A192 to communicate with such Cloud servers and/or to
communicate with one or more FOS systems A100 to access strain data
A133, which may allow users to make business decisions and/or
configure individual FOS systems A100 using corresponding optional
Web sockets A136 of CPU complexes A121 of such systems. However, in
another or this implementation data may be wirelessly transferred,
using for example a TCP/IP protocol, to a remote or local notebook
computer for data analysis.
[0128] For portability, SoC module A120 and one or more fiber-optic
sensing systems A119 may be powered with a battery-based power
supply ("battery") A138, which in this example may be a 5 volt
battery power supply. Along those lines, because of an ability to
multiplex data from FBG sensors, more than one fiber-optic sensing
system A119 may optionally be coupled to a same SoC module A120.
Such one or more fiber-optic sensing systems A119 may be coupled to
a same ring buffer A128, such as using USB or other type of
communication connection. However, for purposes of clarity and not
limitation, only one-to-one relationship between fiber-optic
sensing system A119 and SoC module A120 is described below.
[0129] FIG. 7-2 is a block diagram depicting an exemplary FOS
system A200. FOS system A200 is the same as FOS system A100 of FIG.
7-1, except SoC module A120 is replaced with a network interface
A201, and functions associated with SoC module A120 may be
performed by Cloud storage/computing A191.
[0130] Fiber-optic sensing system A119 may optionally be a
standalone system, such as without an interrogator node directly
mechanically coupled thereto. Along those lines, a smaller battery
power supply ("battery") A118 than battery A138 may be used to
power fiber-optic sensing system A119.
[0131] Network interface A201 may be an Ethernet or other type of
network interface configured for hardwired and/or wireless
communication with a network A190. In this example, network
interface A201 is for wirelessly communicating with network A190
for sending packetized data from packetizer A139 to network A190
for Cloud storage/computing A191. Along those lines, data sourced
from FBG fiber-optic sensors A111 may be stored and processed
remotely with respect to FBGA module A110. Processing operations,
including associated processing functions, provided with SoC module
A120 may be provided with Cloud storage/computing A191. Moreover,
network interface A201 may be configured to include packetizer
A139. Network interface A201 may be incorporated into FBGA module
A110 or may be separate therefrom.
[0132] To recapitulate, multifunctional integrated FBG fiber-optic
sensors A111 may be coupled to an FBGA module A110, as part of an
interrogation system. FBG fiber-optic rosettes as described herein
can be interrogated by a compact, wireless, battery powered
fiber-optic interrogator for both strain and AE detection, such as
by SoC module A120. Optionally or additionally, such interrogation
system may be remotely provided using Cloud storage/computing A191.
A fiber-optic rosette array may be field deployed with a
multichannel wireless interrogator node to allow data to be
remotely recorded, analyzed, and displayed for visualization and
large scale damage prognostics. Along those lines, a fiber-optic
rosette array, such as of FBG fiber-optic sensors A111, may be used
with Cloud storage/computing A191 for storage and/or analysis of
such data obtained.
[0133] In the former example implementation, FBG fiber-optic
sensors A111 may be used with a miniaturized interrogation device,
including a stand-alone compact multichannel fiber-optic strain/AE
interrogator with wireless data acquisition capability for strain
and damage monitoring. In the latter example implementation, FBG
fiber-optic sensors A111 may be used with only an FBGA module A110
of such a miniaturized interrogation device with wired and/or
wireless data acquisition capability for strain and damage
monitoring.
[0134] The latter example implementation facilitates wide spread
deployment of FBG fiber-optic sensors A111 coupled to an FBGA
module A110. Such FBG fiber-optic sensors A111 and FBGA module A110
systems may be compact and low power. Such FBG fiber-optic sensors
A111 and FBGA module A110 systems may be deployed with only
battery-based power systems and wireless connectivity. Moreover,
use of a broadband light source for collecting a signal for strain
measurement may reduce cost, size and power consumption in
comparison with a narrowband light source.
[0135] FIG. 8 is a perspective side view depicting an exemplary
optical fiber A101 and a reflected signal 620. Optical fiber A101
may have a fiber core 601. Fiber core 601 may include FBG
fiber-optic sensors A111 inscribed on single-mode photosensitive
silica-based fibers, such as Ge/B doped silica fibers for example.
Input edge-to-input edge spacing 602 between neighboring FBG
fiber-optic sensors A111 may be .LAMBDA., and refractive indexes n
of FBG fiber-optic sensors A111 may be different from one another,
such as .eta..sub.0 through .eta..sub.3 for example, for forming a
Bragg grating.
[0136] A sensor rosette patch, such as previously described, may be
coupled to a miniaturized interrogation device including a
stand-alone compact multichannel fiber optic strain interrogator
with optional wireless data acquisition. Optionally, such
interrogator may be coupled to an energy harvesting device. Such a
fiber-optic sensor may be: only a few grams in weight (e.g., 10
grams or less for sensor weight); compact (e.g., 0.2 mm.times.2
mm.times.1 cm or smaller); responsive (e.g., a response time of
measured in a few milliseconds or less); immune to EM interference;
and highly sensitive to strain and stress wave signals from DC to
ultrasonic frequency with flat (e.g., no resonance) response. Such
a sensor may be passive, so as not to consume power. Such a sensor
size may be multiplexed along length of an optical fiber A101. Such
a sensor may have an AE resolution of sub-nanostrain and a load
resolution of sub-microstrain.
[0137] A core refractive index of fiber core 601 may have a digital
clock-like pattern corresponding to FBG fiber-optic sensors A111
and spacings 602. Spectral response of an input signal may be
different than spectral response of a transmitted signal, and
spectral response of a transmitted signal may be different than
spectral response of a reflected signal.
[0138] With respect to a spectral response of a reflected signal
620 from FBG fiber-optic sensors A111, under an unstrained or
baseline condition for optical fiber A101, such reflected spectral
response 610 may appear as an impulse 603 centered at a Bragg
wavelength 604 or .lamda.B. However, under a strained or
non-baseline condition for optical fiber A101, such reflected
spectral response may appear as an impulse centered at a wavelength
other than a Bragg wavelength, such as generally indicated by an
example impulse 605 shifted in wavelength away from impulse 603.
This wavelength shift may be detected and correlated to strain
causing such wavelength shift.
[0139] Discrete sensing using FBG fiber-optic sensors A111 as point
sensors, with a laser or broadband light source, may be implemented
to measure strain, temperature, pressure, vibration, and/or AE.
However, distributed sensing using FBG fiber-optic sensors A111 may
be implemented using a pulse laser light source and generally an
entire sensing length of an optical fiber A101, such as a silica
fiber (e.g., a pure silica fiber) as a sensing medium. Such
distributed sensing may be used to measure strain, distributed
temperature sensed ("DTS"), and/or distributed acoustics sensed
("DAS").
[0140] FIG. 9-1 is a block diagram of a perspective view depicting
an exemplary patch 700 attached to a host structure, such as a
processing chamber 500 for example. FIG. 9-2 is a block diagram of
a cross-sectional view along A-A of patch 700 of FIG. 9-1. With
simultaneous reference to FIGS. 7-1 through 9-2, patch 700 is
further described.
[0141] Patch 700 may have a single FBG sensor or more than one FGB
sensor. One or more patches 700 may be used to provide a rosette or
rosette-like pattern. A rosette or rosette-like pattern may be
formed by having one or more optical fibers A101 coupled and/or
taped down to a backing 705.
[0142] In this example, backing 705 may be formed using one or more
flexible thin films with an FBG baseline strain after embedding.
Backing 705 thickness, width, and/or length may be adjusted
according to an application. For example, a bond ply used in
flexible printed circuit industry or other suitable flexible
substrates may be use together with epoxies to bond an entire FBG
sensor rosette pattern, including the grating and non-grating fiber
sections of three optical fibers A101. Thus even though only one
optical fiber A101 is illustratively shown for purposes of clarity,
it should be understood that more than one optical fiber A101 may
be attached to a patch 700. Moreover, an input end 701 of a section
of optical fiber A101 may be used for receiving a transmitted
optical signal, and an output end 702 of such section of optical
fiber A101 may be used for reflecting back a reflected optical
signal associated with such transmitted optical signal.
[0143] Patch 700 may be bonded directly with a bonding material
A104 to a surface of a host structure, such as a processing chamber
500 for example, to be monitored. A bonding material A104 layer may
be used to couple backing 705 to host structure.
[0144] An encapsulation material suitable for use with FBG sensors
may optionally be used for a stronger strain coupling to a host
structure to be monitored. Such encapsulation material may be for
additional protection from environmental forces and/or structural
integrity. In this example, an encapsulation layer 703 is used to
encapsulate a section of optical fiber A101, including at least the
entirety of an FBG sensor thereof. Optionally, an adhesive film 704
may be used to couple a section of optical fiber A101 to backing
705 prior to encapsulation by encapsulation layer 703.
[0145] For example, Dupont Kapton.RTM. polyimide film backing from
CS Hyde Company coupled with Henkel-Adhesives Hysol.RTM. 9696
adhesive film may be implemented optionally with a polyurethane
protective film layer for encapsulation. Hysol.RTM. film parameters
published by the vendor include a thickness of 0.001 in. and a
tensile strength of 30 ksi. A polyurethane protective film layer
can be thermoformed around a section of optical fiber A101 to
provide protection from environmental factors while minimizing any
effects on structural coupling of one or more FBG fiber-optic
sensors A111 to a host structure, such as a processing chamber 500
for example.
[0146] Geometry may be optimized for maximum strain transfer from a
host structure to FBG fiber-optic sensors A111. For example,
positioning of patch edges with respect to FBG fiber-optic sensors
A111 may be used to reduce or minimize edge effects at the location
of FBG fiber-optic sensors A111. Accordingly, distances d1, d2, and
d3 from outer edges of optical fiber A101 to corresponding outer
edges of encapsulation layer 703 or backing layer 705, as
applicable, may be adjusted to reduce or minimize edge effects.
[0147] Thickness and material properties of a backing and one or
more adhesive layers may impact the transfer of strain. Along those
lines, backing 705 may be expanded to allow integration of FBG
fiber-optic sensors A111 to form a rosette or rosette-like pattern
on a single patch. Once a geometric arrangement for FBG fiber-optic
sensors A111 of a patch 700 is determined, such as by finite
element analysis, at least two FBG fiber-optic sensors A111 may be
encapsulated in a rosette or rosette-like pattern.
[0148] For example, to precisely control the orientation of FBG
fiber-optic sensors A111 to create a rosette pattern, a stencil may
be created, such as by laser cutting a thin sheet of plastic in a
desired geometry for example. Adhesive may be placed within
stenciled areas, and FBG fiber-optic sensors A111 may be set in
place in such stenciled areas. Such stencil may be removed while
adhesive is curing. A protective encapsulation layer may be
applied, and a heat gun may be used to provide sufficient
temperature to thermoform such protective encapsulation layer to
such patch assembly, including eliminating any air-gaps.
[0149] With respect to AE and strain, FIG. 10 is a block diagram
depicting an exemplary AE and FOS system 800. In this example,
there are N, for N a positive integer greater than one, FBG
fiber-optic sensors A111-1 through A111-N coupled through
corresponding optical multiplexers or optical circulators 801-1
through 801-N to a multi-channel fiber optic voltage conditioning
("FOVC") 810M and a multi-channel FBG analyzer Al 10M. Even though
a multi-channel FOVC 810M and a multi-channel FBG analyzer Al 10M
are described, a single-channel FOVC 810 and a single-channel FBG
analyzer A110 may be used in another implementation as follows from
the more complex description of a multi-channel implementation.
[0150] Multi-channel FOVC 810M and multi-channel FBG analyzer A110M
may be operated out-of-phase with respect to one another in order
to share FBG fiber-optic sensors A111-1 through A111-N. For
example, multi-channel FOVC 810M and multi-channel FBG analyzer Al
10M may be operated or active on opposite states of a sync control
signal 811 coupled to multi-channel FOVC 810M and multi-channel FBG
analyzer A110M.
[0151] A detailed description of a multi-channel FOVC may be found
in U.S. patent application Ser. No. 14/814,355. However, this or
another type of multi-channel FOVC compatible with an FBG sensor
may be used.
[0152] On a timing interval of control signal 811 for which
multi-channel FOVC 810M is to be active, multi-channel FOVC 810M
may transmit signals to FBG fiber-optic sensors A111-1 through
A111-N to receive corresponding returned signals. Multi-channel
FOVC 810M may process such returned signals to provide ADC
converted voltage analog outputs as digital data outputs 805-1
through 805-N corresponding to such returned signals. Such digital
data outputs 805-1 through 805-N may be provided to a data
multiplexer ("mux") 809.
[0153] Control signal 811 may optionally be used for providing a
control select to mux 809 for selecting either digital data outputs
805-1 through 805-N or digital data outputs A113-1 through A113-N
for an interval of a cycle of control signal 811. Along those
lines, a 50-50 duty cycle or other duty cycle commensurate with
timing of operations of multi-channel FPVC 810M and multi-channel
FBG analyzer A110M may be used.
[0154] On a timing interval of control signal 811 for which
multi-channel FBG analyzer A110M is to be active, multi-channel FBG
analyzer A110M may transmit signals to FBG fiber-optic sensors
A111-1 through A111-N to receive corresponding returned signals.
Multi-channel FBG analyzer Al 10M may process such returned signals
to provide ADC converted voltage analog outputs as digital data
outputs A113-1 through A113-N corresponding to such returned
signals. Such digital data outputs A113-1 through A113-N may be
provided to a mux 809.
[0155] A selected output of mux 809 may be provided to a packetizer
A139, which may be time-slice shared by multi-channel FPVC 810M and
multi-channel FBG analyzer A110M for wireless transmission of data,
such as previously described and not repeated here for purposes of
clarity and not limitation.
[0156] FIG. 11-1 is a block diagram depicting an exemplary
single-channel laser tracking-based fiber optic voltage
conditioning system 850. In order to provide voltage conditioning
for acoustic emissions ("AEs") measurements, an open/closed loop
control 851 of FOVC 810 of fiber optic voltage conditioning system
850 may be used to actively track a laser to Bragg wavelength of an
FBG fiber-optic sensor A111.
[0157] A function of laser tracking-based FOVC 810 may be to
provide fiber optic voltage conditioning of returned optical signal
803 coupled to FBG sensors (collectively and singly "FBG sensor")
A111 via a fiber optic cable or line, as described below in
additional detail. Along those lines, a multifunction fiber optic
sensor, such as fiber Bragg grating sensor, may be used. For AE
measurements, using a fiber Bragg grating sensor in a fiber optic
housing, an entire sensing area can be bonded directly to a surface
of a structure ("measurement surface") such as with a permanent
epoxy or other bonding material. The direct bonding of a bare fiber
to a measurement surface may provide a high-level of stress wave
coupling from such measurement surface to a sensing area.
[0158] However, over time such bonding material may result in local
stress along such Bragg grating sensor, such as along a grating
length for example, and this may lead to creation of an unstable
optical cavity formed by multiple gratings, such as along such
grating length for example. These optical cavities may negatively
affect FOAE sensor performance by changing the slope of a Bragg
reflection spectrum and/or increasing Fabry-Perot noise. To address
this issue, an overhanging ridge configuration may be used, where a
grating under tension may be used for hanging over two stand-offs
bonded to a structure's surface to address the above-described
problem, such as for AE and/or strain sensing. Moreover, for an
overhanging ridge configuration, a grating may be used for hanging
over shear wave-coupling gel, on either or both sides thereof, to
provide a flexible bonding to a structure's surface to address the
above-described problem, such as for AE and/or temperature sensing.
Optionally, a package sensor multiplexing two or more FBG sensors
on the same package with different Bragg wavelengths installed can
be multiplexed in serial or parallel. Such a package sensor may be
used for AE, strain, and/or temperature sensing. Moreover,
optionally a multiplexed-multi-sensing package sensor may be used.
For example, two or more different types of sensors (e.g.,
AE/strain and AE/temperature) can be multiplexed on the same
package for multi-sensing.
[0159] Optionally, another function of such laser tracking-based
FOVC 810 may be to convert returned optical signal 803 from FBG
sensor A111 to an optional AC voltage analog output 855 that may
directly interface with conventional AE instrumentation, which is
illustratively depicted as optional AE data acquisition system 830.
An optional analog signal output 855 of FOVC 810 may resemble that
of a piezo-electric sensor used in conventional AE measurements,
facilitating sensor "drop in replacement". Optionally, analog
output signal A102, as previously described herein, may be provided
to AE data acquisition system 830 in order to trigger operation
thereof.
[0160] Along those lines, conventional piezo-electric
sensors/preamplifier signal conditioners can be completely replaced
with a combination of FBG sensor A111 and FOVC 810 as described
herein without changing existing AE software and electronics of
conventional AE data acquisition systems, such as AE data
acquisition system 830 for example, leading to significant cost
saving through minimizing additional hardware/software
installation. In other words, a high-frequency, high-gain
photodetector output 805 carrying a high frequency signal may be
interfaced directly to an analog input of a conventional AE data
acquisition system 830, such as a Mistras PCI-2 DAQ board from
Mistras Group, Inc. of Princeton Junction, N.J., for example.
[0161] Light 804, which may be from a compact, commercially
available distributed feedback ("DFB") laser or other laser 882,
may be passed via an optical circulator 813 to an FBG sensor A111.
A returned optical signal 803 from FBG sensor A111 passing through
optical circulator 813 may be routed to a photodetector 814.
Current control 816, which may be separate from or part of DFB
laser 882, may be initially set at a midrange value between a
lasing threshold and a maximum current limit, and a thermoelectric
cooler ("TEC") control 885, which may be separate from or part of
DFB laser 882, may be tuned to move laser wavelength to a
mid-reflection point ("V REF") of a Bragg wavelength of FBG sensor
A111.
[0162] With laser current and TEC control voltages settled at
initial set points, namely V TEC SET and V CUR SET 821, laser
wavelength may be locked to a mid-reflection point of FBG sensor
A111 using simultaneous TEC and current tracking through a closed
loop 851 proportional-integral-derivative ("PID") feedback
control.
[0163] For adjustment for real-time laser tracking control, a
chip-based data acquisition ("DAQ") board 820, such as an
FPGA-based or other System-on-Chip-based ("SoC-based") circuit
board, may be used to record at least one of a low-gain and/or
low-frequency of photodetector output signal 806, namely as
associated with an analog input to analog-to-digital converter
("ADC") 817 and to generate a PID control signal 807 of DAC
818.
[0164] By "low-gain" and "low-frequency", it is generally meant an
analog output signal being below both a threshold gain and a
threshold frequency, respectively, where such thresholds represent
an external environmental change and/or perturbation, including
without limitation a change in one or more of temperature, strain,
pressure, and/or stress of a structure under test, including a
structure being monitored, as sensed by one or more FGB sensors
coupled to one or more optical fibers. Accordingly, such thresholds
may vary from application-to-application depending upon the type of
structure being tested, as well as use of such structure.
[0165] An analog output signal 806 of photodetector 814 may be
converted to a digital data output signal 805 by ADC 817, and a
digital output of ADC 817 may additionally feed an input of a
voltage set and store block 819. A digital output of voltage set
and store block 819 may feed an input of DAC 818 to provide an
analog PID control signal 807. PID control signal 807 may include a
PID current error ("CUR ERR") signal and a PID TEC error ("ERR")
signal. PID control signal 807 may be output from DAC 818.
[0166] For purposes of clarity by way of example and not
limitation, it shall be assumed that an FPGA is used to set and
store voltages; however, in another implementation another type of
SoC may be used, including without limitation an ASSP, ASIC, or
other IC. Along those lines, voltage set and store block ("FPGA")
819 may be used to set and store a laser current voltage and a TEC
control voltage, namely V TEC SET and V CUR SET 821, and FPGA 819
may be used to store a mid-reflection point V REF of a Bragg
wavelength of FBG sensor A111. FPGA 819 may be coupled to receive a
digital output 823 from ADC 817, where such digital output 823 is a
conversion of an analog photodetector output signal 806. FPGA 819
may be configured to generate and store TEC and laser current error
voltages, namely a V TEC ERR and a V CUR ERR, using such digital
output 823 received. FPGA 819 may provide a digital PID control
signal 824, where such digital PID control signal includes a V CUR
ERR signal and a V TEC ERR signal, to DAC 818, and DAC 818 may
convert such digital PID control signal 824, namely a V TEC ERR
signal and a V CUR ERR signal, to analog PID control signal 807
having analog PID CUR ERR and PID TEC ERR signals.
[0167] PID CUR and TEC error signals from PID control 807 may be
correspondingly added to CUR and TEC set voltages 821 by adder 822,
and respective sums 808 output from adder 822 may be fed into a
controller 850 for adjustment of control information provided to
laser 882. In this example, for purposes of clarity and not
limitation controller 850 is broken out into three controllers or
modules, namely a laser controller 853 coupled to a current
controller 816 and a TEC controller 885. However, in another
implementation, current controller 816 and/or TEC controller 885
may be part of a laser, such as DFB laser 882 for example. Sums 808
may be used together to compensate for drift of a Bragg wavelength,
such as due to external environmental changes and/or perturbation
including without limitation changes in one or more of temperature,
strain, pressure, and/or stress, by actively tuning laser
wavelength responsive to such current and TEC control. Even though
a DFB laser 882 is used, in another implementation a broadband
light source or other type of light source may be used.
[0168] In this example, both laser TEC and current are used
simultaneously to compensate for FBG wavelength drift from DC up to
approximately 20 kHz for photodetector output signal 806. TEC
tracking may be provided by changing temperature of DFB laser 882
via TEC control 885 to compensate for FBG sensor A111 wavelength
drift caused by environmental changes. While providing large
dynamic range, such as for example approximately several thousand
microstrains for strain monitoring, TEC compensation may be slow,
with a maximum response time in the order of seconds or longer.
[0169] In this example, fast, such as for example a few Hz to 20
kHz or higher, real time compensation may not be possible with TEC
tracking. Along those lines, laser current compensation, as
described herein, may be used with a much higher response time,
possibly up to approximately 20 kHz or higher, subject to
limitations of response time of electronics of laser controller
853, and such laser current compensation may be used simultaneously
with TEC tracking. Tracking by changing laser injection current may
cause changes in both laser wavelengths and intensity, although
with much more limited dynamic range, such as for example
approximately several hundred microstrains for dynamic strain
tracking. For larger dynamic strain monitoring, such as more than
approximately a thousand microstrains, commercially available
distributed Bragg reflector ("DBR") lasers can be used in place of
DFB lasers. However, it should be appreciated that using TEC and
current tracking in combination provides extended dynamic range and
fast response for laser tracking.
[0170] Long-distance AE measurement using a laser-based FBG
interrogation may be subject to presence of high amounts of optical
noise associated with the Fabry-Perot effect generated by an
optical cavity created by two or more reflective mirrors. By
"interrogation," it is generally meant providing a light signal to
an optical sensor coupled to a material or structure under test and
obtaining a light signal in return from such optical sensor to
obtain information therefrom regarding such material or structure
under test. A Bragg grating itself may be considered a highly
reflective mirror. In the presence of another reflective surface
from an optical component, such as for example an optical
circulator or a scattering center such as a local defect present in
a long optical fiber, unstable, unwanted constructive optical
interferences can be generated due to laser coherence. Accordingly
such interferences may contribute to increased AE background noise,
and as a consequence can significantly reduce a signal-to-noise
ratio ("SNR") in AE measurements.
[0171] To suppress this optical noise, a combination of circulators
and optical isolators between reflection and/or scattering surfaces
may be used to provide unidirectional optical paths and avoid
bidirectional optical paths between any two reflective optical
components, such as described below in additional detail.
[0172] FIG. 11-2 is a block diagram depicting an exemplary
multichannel FOVC system 850. Multichannel FOVC system 850 is
further described with simultaneous reference to FIGS. 11-1 and
11-2.
[0173] In multichannel FOVC system 850, an N-channel FOVC 810M is
respectively coupled to FBG sensors A111-1 through A111-N via
corresponding optical circulators 883-1 through 883-N, for N a
positive integer greater than one. FBG sensors A111-1 through
A111-N may be respective discrete FOAE sensors or an array
thereof.
[0174] DFB1 through DFBN lasers 882-1 through 882-N and
corresponding photodetectors ("PD") PD1 884-1 through PDN 884-N may
be respectively coupled to optical circulators 883-1 through 883-N.
Each of DFB lasers 882-1 through 882-N may deliver corresponding
laser lights 804-1 through 804-N respectively into FBG sensors
A111-1 through A111-N via corresponding circulators 883-1 through
883-N. Circulators 883-1 through 883-N may then be used to pass
corresponding returned optical signals 803-1 through 803-N
respectively from sensors A111-1 through A111-N on a per channel
basis. Returned optical signals 803-1 through 803-N may be
respectively provided onto photodetectors 884-1 through 884-N.
[0175] Each of the outputs of photodetectors 884-1 through 884-N,
which may be implemented in an example implementation as
photodiodes ("PD") PD1 through PDN, may be split into two sections,
namely analog signals 806-1 through 806-N and optionally analog
signals 805-1 through 805-N. One group, namely a low frequency
signal output group of signals 806-1 through 806-N, may be input
into an analog input interface 852, such as respective analog input
ports for example, of an FPGA-based data acquisition system 820 for
laser tracking control generation as previously described herein.
Another optional group, namely a high frequency signal output group
of analog signals 805-1 through 805-N, may optionally be input to a
conventional multichannel AE DAQ system 830 for AE measurement.
[0176] Even though an FPGA 819 is used as described herein for DAQ
820, another type of SoC, an ASSP, an ASIC, or other VLSI type of
integrated circuit device may be used instead of FPGA 819. However,
for purposes of clarity and not limitation, it shall be assumed
that an FPGA 819 is used. Furthermore, DAC 820 may exist in a
single integrated circuit device, whether such device is a
monolithic integrated circuit or an integrated circuit formed of
two or more integrated circuit dies packaged together.
[0177] An FPGA 819 may have sufficient resources for integration of
one or more ADCs 817, one or more DACs 818, and/or one or more
adders 822 therein for providing a multichannel FOVC 810M. However,
an FPGA may lack sufficient analog resources, and so a separate
analog chip, such as for providing digital-to-analog conversions,
may be used. However, for purposes of clarity by way of example and
not limitation, it shall be assumed that FPGA 819 has a sufficient
number of ADCs 817 for converting analog signals 806-1 through
806-N into corresponding digital data outputs 805-1 through 805-N.
FPGA 819 may include a digital interface 859 for outputting digital
data outputs 805-1 through 805-N. Optionally, FPGA 819 may be
configured with a control signal generator circuit to generate and
output a control signal 811.
[0178] In this example, FOVC 810M includes a DAQ 820 having an FPGA
819 configured for inputs 1 through N of an analog input interface
852 ("inputs 852") and outputs 1 through 2N of an analog output
interface 856 ("outputs 856"), for example separate analog output
ports. Inputs 852 may correspond to a group of signals 806-1
through 806-N. Pairs 808-1 through 808-N of outputs may
respectively be provided to laser controllers 853-1 through 853-N.
Laser controllers 853-1 through 853-N may provide respective pairs
of TEC and current control signals 885-1, 816-1 through 885-N,
816-N to DFBs 882-1 through 882-N, respectively.
[0179] For purposes of clarity by way of example and not
limitation, laser controllers 853-1 through 853-N are
illustratively depicted as including corresponding pairs of current
and TEC controllers, which were illustratively depicted as separate
controllers 816 and 885, respectively, in FIG. 11-1 for purposes of
clarity. However, it should be understood that controllers 885 and
816 may be incorporated into a laser controller 853.
[0180] For purposes of scaling an FOVC 810, it should be
appreciated that a single FPGA 819 may be used by a DAQ 820
configured to support N channels. In this example, FOVC 810M does
not include optical circulators 883-1 through 883-N; however, in
another configuration, FOVC 810M may include optical circulators
883-1 through 883-N.
[0181] Generally, FPGA 819 generates respective sets, such as pairs
for example, of TEC and current control signals 808-1 through 808-N
via analog output ports 856 of DAQ 820, and such respective sets of
TEC and current control signals 808-1 through 808-N may be used to
provide corresponding pairs of TEC control and current control
signals 885-1, 816-1 through 885-N, 816-N to respectively lock DFB
lasers 882-1 through 882-N to their respective FBG sensors A111-1
through A111-N by adding respective error signals. Such respective
error signals may be generated from FPGA 819 generated PID control
to provide current and TEC set points via digital summing as
previously described herein, though on a per-channel basis in this
example of FOVC 810M. For long distance measurements, N fiber
extenders, whether all transmission fiber extenders, all reflection
fiber extenders, or a combination thereof may be used in
conjunction with multichannel FOVC 810M.
[0182] FIG. 12 is a block diagram depicting an exemplary wavelength
tracking system 1000 using fiber optic voltage conditioning, as
described above, for sensing AE. Wavelength tracking system 1000
uses a broadband light source system ("BLS system") 1022, such as
previously described for measuring microstrain. BLS system 1022
provides a monitoring subsystem for wavelength tracking system 1000
to provide an initial FBG position for FOAE tracking recovery.
Along those lines, BLS system 1022 may have multiple wavelengths
within a BLS. For example, each color in broadband light from a
broadband light source represents a different wavelength.
Wavelength multiplexing may be used to feed information to a
controller 1021. Controller 1021 may be implemented to include a
finite state machine ("FSM"). In an example implementation,
controller 1021 may be implemented with a microcontroller. For
purposes of clarity by way of example and not limitation,
controller 1021 shall be assumed to be a microcontroller 1021.
Microcontroller 1021 may be a trusted "supervisor microcontroller",
and microcontroller 1021 may be used to prompt BLS system 1022 to
feed information for a particular wavelength for tracking
recovery.
[0183] One or more lasers may be used with BLS system 1022 for
dynamic configuration or reconfiguration. In order to provide
voltage conditioning for acoustic emissions ("AE") measurements, an
open/closed loop control system may be used to actively track a
wavelength of a narrowband tunable light source, such as a
distributed feedback ("DFB") laser, to a Bragg wavelength of a
fiber Bragg grating ("FBG") sensor. A wavelength tracking-based
fiber optic acoustic emission voltage conditioner ("FOVC") may be
used to convert an optical signal from FBG sensors to an AC voltage
output that can directly interface with conventional AE
instrumentation. The signal output of such an FOVC resembles that
of a piezo-electric sensor used in convention AE measurements,
facilitating sensor "drop in replacement".
[0184] However, AE with laser tracking is sensitive, and thus more
likely to lose tracking. To quickly recover tracking or moving to
another wavelength, a laser may be tuned to lock to a different FBG
wavelength of one of FBG sensors A111. For example, if there is a
"hot spot" indicated by microstrain measurements obtained from BLS
system 1022, one or more lasers may be directed to such "hot spot"
using dynamic reconfiguration by dynamically retuning such one or
more lasers to lock to one or more corresponding different FBG
wavelengths. For example, when a rosette principal direction drifts
from a nominal value indicating presence of damage, one or more
lasers may be tuned to one or more FBG wavelengths associated with
such rosette. Independently or in addition to retuning for
microstrain detected damage, one or more lasers of an AE data
acquisition system may be locked to one or more FBG wavelengths for
a "wake up" mode and/or when a load exceeds a load threshold.
[0185] Different wavelengths may be in a rosette including
different FBG wavelengths. Moreover, a BLS light may share a fiber
with a laser source light, where a BLS and a laser use same or
different wavelengths, as a laser source can overwhelm a BLS
source. Furthermore, with different FBG wavelengths, lasers may
share a same fiber.
[0186] Wavelength tracking system 1000 includes a SoC 1020, which
optionally may be used for edge computing. SoC 1020, may be an FPGA
with one or more FPGA-based microprocessors, which may be coupled
to a cloud-based computing system 1009 through a network interface
1003 of such SoC 1020. Such a cloud-based computing system 1009 may
include data storage 1006, such as may include database ("DB")
software, and one or more processors 1007 configured with analytics
software, such as SaaS for example, for processing raw and feature
extracted data obtained from SoC 1020. Optionally, such SoC 1020
may be configured for local processing of raw data, such as for
extraction of information from such raw data, in an optional
FPGA-based edge computing configuration. Along those lines, SoC
1020 may send results and/or information obtained from local
processing of raw data, rather than, or optionally in addition to,
sending raw data in order to conserve bandwidth and/or enhance
overall processing capacity. One or more web browser computers or
other web-configured devices 1008 may be put in communication with
cloud-based computing system 1009 for accessing stored data,
whether raw and/or processed data.
[0187] SoC 1020, in addition to network interface 1003, may include
a laser controller 1001, memory 1002, and one or more electronic
data acquisition ("eDAQ") controllers, such as eDAQ controllers
1005 for example. Laser controller 1001 may be configured with
laser control software 1004.
[0188] Laser controller 1001 and network interface 1003 may be
coupled through and share memory 1002. Additionally, eDAQ
controllers 1005 may be coupled to and share memory 1002. While two
eDAQ controllers 1005 are illustratively depicted, in another
example fewer or more than two eDAQ controllers 1005 may be
used.
[0189] A supervisor microcontroller 1021 may be coupled through bus
1024 to SoC 1020 for communication therewith. However, in another
implementation, supervisor microcontroller 1021 may be incorporated
into SoC 1020. Memory 1002 may be configured with a look-up table
1025. Look-up table 1025 may include predetermined settings for
different FBG wavelengths for one or more eDAQ controllers 1005,
eDAQ converters 1010, laser drivers 1013, photodetectors 1017,
and/or other components of wavelength tracking system 1000. Such
settings in lookup table 1025 may be used for tuning one or more
modules of wavelength tracking system 1000 for optimum performance
for a variety of applications.
[0190] To provide supervised wavelength tracking, a multichannel
sensor interrogation array may be used. Different and/or same types
of logistics sensors 1023, such as a GPS sensor, an accelerometer
sensor, and/or a liquid monitoring sensor, among other types of
sensors, may be used for logistics for an AE sensing application.
Additionally or optionally, logistics sensors 1023 may include one
or more controllers for pulse generators. Such one or more
controllers for pulse generators may be configured to generate
predefined periodic pulses of stress waves for individual automated
sensor testing ("AST"). These stress waves may be used to provide
acousto-ultrasonic testing to capture a principal strain and a
principal direction of each sensor rosette using pitch catch and/or
pulse-echo processing. Along those lines, for example a
piezo-electric actuator may be placed remotely from or proximate to
supervisor microcontroller 1021, and a controller for pulse
generation may be in wireless communication with such an actuator
for causing such actuator to pulse for propagation of such pulse
along a monitored structure. Such a controller for pulse generation
and/or other logistics sensors 1023 may be coupled to supervisor
microcontroller 1021 for obtaining different sensing inputs
associated with logistics, multi-sensing data collection and/or
sensor fusion analytics, which may include one or more of finite
state machine states including wake-up call triggering, system
initialization, wavelength tuning, tracking control, wavelength
monitoring, tracking recovery, system shut-down, and dynamic
re-configuration for on-demand new sensor selection.
[0191] A BLS system 1022 may be coupled to supervisor
microcontroller 1021 for providing wavelength tracking. A front
panel and user interface 1013 may be coupled through bus 1024 to
SoC 1020 and supervisor microcontroller 1021 for unlocking those
components, if locked. Along those lines, SoC 1020 and supervisor
microcontroller 1021 may be protected with boot protection, which
may be hardware and/or software based protection. Additionally,
front panel and user interface 1013 may be coupled through bus 1024
to SoC 1020 and supervisor microcontroller 1021 for initializing
and monitoring status of those components.
[0192] In a trusted mode of operation, a trusted supervisor
microcontroller 1021 may be responsible for unlocking and
initializing hardware sub-modules. With a trusted boot of
supervisor microcontroller 1021, SoC 1020, an array of laser
drivers 1014, and an array of photodetectors ("PDs") 1016 may be
unlocked and initialized under control of supervisor
microcontroller 1021. A locked state may be present at power-up or
reset of wavelength tracking system 1000. A look-up table 1026 in
memory 1002, or in memory of microcontroller 1021 in another
implementation, may be preloaded with specific information to
prohibit functioning of wavelength tracking system 1000 responsive
to a failure of authentication of one or more module components of
such system. In other words, authentication may be performed at
initialization to validate a system configuration of wavelength
tracking system 1000.
[0193] Additionally, supervisor microcontroller 1021 may be
configured to monitor system statistics of wavelength tracking
system 1000 to ensure proper operation, such as operation within
predefined parameters for example. If a module or other portion of
wavelength tracking system 1000 is not operating within predefined
parameters, supervisor microcontroller 1021 may halt or shut down
such module or other portion not operating within predefined
parameters.
[0194] Supervisor microcontroller 1021 may additionally provide
"black box" functionality by allowing an external device to view
logged events, which may be periodically logged by supervisor
microcontroller 1021. Such an event log may be used to view a state
of wavelength tracking system 1000, including an ability to
determine for example whether an anomalous event has occurred.
Supervisor microcontroller 1021 may communicate with front panel
and user interface 1013 to illuminate status LEDs or other devices
used to communicate status to allow a user to have up-to-date
information about operation of wavelength tracking system 1000.
[0195] Supervisor microcontroller 1021 may be used to offload
system management tasks from SoC 1020 from real-time control
processes running on SoC 1020, which in this example is implemented
with an FPGA. These real-time control processes may be used for
controlling eDAQ converters 1010.
[0196] Crack growth and/or damage hot spot monitoring using an FBG
rosette may be used to distinguish between damage and its effect on
principal strain direction and/or changes in loading by comparing
with neighboring rosettes. Principal strain direction at one or
more FBG rosettes may shift in the presence of a local crack for
example, while one or more nearest neighbor FBG rosettes may not
indicate any change. Thus, one or more FBG rosettes touching or
proximate to such local damage may be used to indicate damage.
[0197] Along those lines, in an example for a local crack or other
detectable damage, the principal direction of a rosette touching or
proximate to a crack may show change independent of temperature,
geometry or any other background change. In addition to being
independent of environmental conditions, a nearest neighbor damage
index may be baseline free, which may be useful in applications
with more or less arbitrary loading conditions. In other words, no
pristine or other background information need be used, such as
measured and subtracted out, because local information may be
directly compared to global information. In other words, one or
more rosettes local to a damage site may be directly compared to
one or more nearest neighbors absent a baseline. Such a direct
comparison may be used to avoid false positives, as comparison with
nearest neighbor rosettes may be used to indicated damage without
being confounded by load direction and/or load magnitude. Any
change in load direction may change principal strain vectors at all
rosettes in an array; however, with nearest neighbor comparisons,
local damage may only change the principal strain vector at such
local location.
[0198] For a nearest neighbor comparison, damage severity may be
quantified by using a normalized damage index ("DI") formula as
follows:
D I = sin | .theta. i - 1 n k = 1 n .theta. k | ##EQU00001##
where i is a rosette immediately at or adjacent to a damage
instance, such as a crack for example, and k are one or more
nearest neighbor rosettes. The larger the difference between i and
k may indicated a larger amount of damage.
[0199] For a grid or array of rosettes, both near field and far
field effects of loading may be detected. A damage index value for
DI may range from 0 to 1, inclusive, with 0 being no crack and with
1 being for a rosette directly on a crack. Along those lines, a DI
value may be compared or otherwise processed against other DI
values of other rosettes in a grid to identify a damage region, or
at least a probability of a damage region relative to such DI
value. However, as indicated above, a baseline-free DI value is an
absolute value for an FBG, and not a relative value as compared to
some existing DI-based damage detection techniques that requires
knowledge of the pristine condition as a baseline reference for
background subtraction. This means that a baseline-free DI value
obtained from a local discontinuity in a principal direction
compared to one or more of its nearest neighbors may generally be
insensitive to changes in a local environment, boundary conditions,
loading conditions, and may be used to indicate a "permanent" shift
in a principal direction due to damage.
[0200] Moreover, rosettes may be used to provide damage imaging for
real-time visualization and/or post damage evaluation. Rosettes may
be placed on interior and/or exterior surfaces of a structure to
form a two-dimensional and/or three-dimensional image. Rosettes may
be provided in a single layer or multiple layers.
[0201] eDAQ controllers 1005 may respectively control eDAQ
converters 1010. While two eDAQ converters are illustratively
depicted, in another implementation more or fewer eDAQ converts
1010 may be used. Each eDAQ converter 1010 may include an ADC 1011
and a DAC 1012.
[0202] eDAQ converters 1010 may be used for providing analog
signals to laser drivers 1013. In this example, there are laser
drivers 1013-1 and 1013-2 fed by one eDAQ converter 1010, and there
are laser drivers 1013-3 and 1013-4 fed by another eDAQ converter
1010. Laser drivers 1013 may be set to different FBG wavelengths.
So in this example, four different wavelengths for laser light
outputs may be used with analog information from two eDAQ
converters 1010.
[0203] Outputs from laser drivers 1013 may be provided to
respective optical LEDs of an array of LEDs 1015. Outputs from LEDs
1015 may respectively be input to FBG fiber-optic sensors A111-1
through A111-4, with each FBG fiber-optic sensor A111 in a rosette
or rosette-like pattern. Outputs for FBG fiber-optic sensors A111-1
through A111-4 may be respectively input to photodiodes 1017-1
through 1017-4 of an array of photodiodes 1016. Output of each of
photodiodes 1017-1 through 1017-4 is corresponding AE information
1019-1 through 1019-4. AE information 1019-1 and 1019-2 may be fed
back to a corresponding source eDAQ converter 1010, and AE
information 1019-3 and 1019-4 may be fed back to another
corresponding source eDAQ converter 1010.
[0204] Because BLS may be more easily tracked than laser light and
may consume less power, BLS system 1022 may be used as an initial
interrogator of FBG fiber-optic sensors A111, which may be shared
with lasers 1013 (though not shown in this FIG. 12 for purposes of
clarity and not limitation). If such interrogation results in
detection of damage by microstrain information and/or one or more
DIs for corresponding FBG fiber-optic sensors A111, lasers 1013 may
be used to obtain more precise AE information 1019. SoC 1020 may be
coupled to receive an output signal from BLS system 1022 and
configured to clean up such output signal, detect peaks in such
output signal, and quantify power associated with one or more peaks
detected in such output signal. This information from such an
output signal may be used by SoC 1020, as SoC may be configured to
quantify wavelength shifts in such output signal as being directly
proportional to amounts of strain and spectral power sensed by
fiber-optic sensors in a rosette or rosette-like pattern. These
wavelength shifts may be used to provide one or more wavelength
adjustment information for one or more wavelength adjustments to
shift one or more laser drivers to corresponding FBG wavelengths of
FBG sensors 111 associated with such output indicating a damage
area. Such FBG sensors 111, and thus fiber-optic lines associated
therewith, may be shared as between lasers and a BLS, as previously
described.
[0205] In another implementation, such output signal from BLS
system 1022 may be combined with information output from one or
more logistics sensors 1023, such as by supervisor microcontroller
1021, for providing to SoC 1020, and optionally subsequently to
cloud-based computing system 1009, for analysis by either or both
SoC 1020 or analytics processors 1007. Analysis results from
cloud-based processing at cloud-based computing system 1009 may be
communicated to SoC 1020. Such analysis results from either or both
SoC 1020 or analytics processors 1007 may be used to identify which
one or more FBG sensors 111 to target to obtain AE information 1019
and to shift one or more wavelengths for one or more laser drivers
1013, as previously described, associated with such identified FBG
sensors 111. Again, for example, this shift may be for obtaining AE
information 1019 for an identified hot spot.
[0206] FIG. 13 is a flow diagram depicting an exemplary monitoring
or calibrating a processing chamber flow 1100. At operation 1101,
an optical fiber 205 with sensors, such as FBG sensors 212, is
located in a processing chamber 500. FBG sensors 212 may be
configured for different center frequencies for modulation
responsive to at least temperature, as previously described.
[0207] At operation 1102, a broadband light source from a
light-source based detection system 591 may be optically
transmitted to optical fiber 205. An example of a broadband light
source may have a spectrum as previously described herein from 1500
to 1600 nanometers.
[0208] At operation 1103, reflected light may be optically received
from optical fiber 205 to a light-source based detection system
591. At 1104, such reflected light may be processed by light-source
based detection system 591 to generate data at least related to
temperature. Such processing may include detection of a shift or
other modulation in a Bragg frequency of an FBG sensor, or Bragg
frequencies of corresponding FBG sensors.
[0209] While the foregoing describes exemplary apparatus(es) and/or
method(s), other and further examples in accordance with the one or
more aspects described herein may be devised without departing from
the scope hereof, which is determined by the claims that follow and
equivalents thereof. Claims listing steps do not imply any order of
the steps. Trademarks are the property of their respective
owners.
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