U.S. patent application number 16/665995 was filed with the patent office on 2020-02-20 for bonded filter substrates.
The applicant listed for this patent is Hewlett Packard Enterprise Development LP. Invention is credited to Sagi Varghese Mathai, Georgios Panotopoulos, Paul K. Rosenberg, Wayne V. Sorin, Michael Renne Ty Tan.
Application Number | 20200057212 16/665995 |
Document ID | / |
Family ID | 56127170 |
Filed Date | 2020-02-20 |
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United States Patent
Application |
20200057212 |
Kind Code |
A1 |
Mathai; Sagi Varghese ; et
al. |
February 20, 2020 |
BONDED FILTER SUBSTRATES
Abstract
In the examples provided herein, an apparatus has a first
substrate upon which one or more first filters have been fabricated
on a first surface of the first substrate. The apparatus also has a
second substrate upon which one or more second filters have been
fabricated on a second surface of the second substrate, wherein the
one or more first filters and the one or more second filters each
transmit a different band of wavelengths. Additionally, the
apparatus has a bonding material that bonds the first substrate to
the second substrate.
Inventors: |
Mathai; Sagi Varghese;
(Sunnyvale, CA) ; Panotopoulos; Georgios;
(Berkeley, CA) ; Tan; Michael Renne Ty; (Menlo
Park, CA) ; Rosenberg; Paul K.; (Sunnyvale, CA)
; Sorin; Wayne V.; (Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hewlett Packard Enterprise Development LP |
Houston |
TX |
US |
|
|
Family ID: |
56127170 |
Appl. No.: |
16/665995 |
Filed: |
October 28, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15536130 |
Jun 14, 2017 |
10459174 |
|
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PCT/US2014/071367 |
Dec 19, 2014 |
|
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16665995 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4249 20130101;
G02B 6/4206 20130101; G02B 6/4214 20130101; G02B 6/4215
20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42 |
Claims
1. An apparatus comprising: a first substrate upon which one or
more first filters have been fabricated on a first surface of the
first substrate; a second substrate upon which one or more second
filters have been fabricated on a second surface of the second
substrate, wherein the one or more first filters and the one or
more second filters each transmit a different band of wavelengths;
and a bonding material, wherein the bonding material bonds the
first substrate to the second substrate.
2. The apparatus of claim 1, wherein the bonding material bonds the
first surface to the second surface such that the one or more first
filters and the one or more second filters are positioned between
the first substrate and the second substrate, and the apparatus
further comprises: absorbing material positioned between the first
substrate and the second substrate in areas not occupied by one of
the filters.
3. The apparatus of claim 1, wherein the first substrate has an
opposing surface that is on an opposite side of the first substrate
from the first surface, wherein the bonding material bonds the
opposing surface to the second surface such that the one or more
second filters are positioned between the first substrate and the
second substrate, and the one or more first filters are not
positioned between the first substrate and the second
substrate.
4. The apparatus of claim 1, wherein one of the first substrate and
the second substrate have been ground to pre-bow the substrate.
5. The apparatus of claim 1, further comprising a plurality of
standoffs positioned between the first substrate and the second
substrate to maintain a fixed separation between the first
substrate and the second substrate, wherein the first surface and
the second surface are coated with an anti-reflection coating, or
the bonding material is index-matched to a refractive index of the
first substrate and the second substrate.
6. The apparatus of claim 1, wherein the bonding material is a
two-sided sticky tape or epoxy film, or patternable material,
wherein the bonding material has multiple apertures, and wherein
each filter between the first substrate and the second substrate is
positioned in a different one of the apertures.
7.-13. (canceled)
14. A method comprising: fabricating a plurality of first filters
on a first surface of a first wafer, wherein the plurality of first
filters each transmit a first group of wavelengths; fabricating a
plurality of second filters on a second surface of a second wafer,
wherein the plurality of second filters each transmit a second
group of wavelengths, and further wherein the first group of
wavelengths and the second group of wavelengths are different;
determining which of the plurality of first filters and the
plurality of second filters meet specifications; dicing the first
wafer to produce first sections that include one first filter that
meets specifications; bonding each of some of the first sections
that include one first filter that meets specifications to one of
the second sections of the second wafer that includes one second
filter that meets specifications; and dicing the second wafer to
produce second sections with bonded first sections.
15. The method of claim 14, further comprising performing one of
the following: placing absorbing epoxy or index-matching material
between the first sections and the second sections in areas not
occupied by one of the filters; grinding the first wafer prior to
dicing the first wafer; and grinding the second wafer prior to
dicing the second wafer.
Description
BACKGROUND
[0001] Wavelength division multiplexing (WDM) is useful for
increasing communication bandwidth by sending multiple data
channels down a single fiber. For example, a 100 gigabit per second
(Gbps) link can be constructed by using four channels operating at
25 Gbps per channel, with each channel operating at a different
wavelength. A multiplexer is used to join the signals together
before transmitting them down the waveguide, and a demultiplexer is
subsequently used to separate the signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The accompanying drawings illustrate various examples of the
principles described below. The examples and drawings are
illustrative rather than limiting.
[0003] FIG. 1 depicts a block diagram of an example multiplexer
system that includes four wavelength-selective filters fabricated
on two different substrates, and the substrates are bonded together
such that the filters are positioned between the substrates.
[0004] FIG. 2 depicts example filter die substrates.
[0005] FIG. 3 depicts an example of bonded filter substrates where
the filters fabricated on the substrates have equal
thicknesses.
[0006] FIG. 4 depicts an example of bonded filter substrates where
the filters fabricated on the substrates have dissimilar filter
thicknesses.
[0007] FIG. 5 depicts a block diagram of an example multiplexer
system that includes four wavelength-selective filters fabricated
on two different substrates, and the substrates are bonded together
such that two of the filters are not positioned between the
substrates.
[0008] FIGS. 6A, 6B, 6C1, 6C2, 6D1, 6D2, 6E1, and 6E2 depict steps
of different fabrication techniques for fabricating bonded filter
substrates.
[0009] FIG. 7 depicts a flow diagram illustrating an example
process of fabricating bonded filter substrates having four
different types of filters, where the substrates are bonded prior
to dicing the substrates.
[0010] FIG. 8 depicts a flow diagram illustrating an example
process of fabricating bonded filter substrates having two
different types of filters, where the substrates are bonded prior
to dicing the substrates.
[0011] FIGS. 9A-9B depict a flow diagram illustrating an example
process of fabricating bonded filter substrates having four
different types of filters, where the filters are tested prior to
bonding the substrates.
[0012] FIG. 10 depicts a flow diagram illustrating an example
process of fabricating bonded filter substrates having two
different types of filters, where the filters are tested prior to
bonding the substrates.
DETAILED DESCRIPTION
[0013] In a WDM optical system, optical signals from two or more
sources are multiplexed together for transmission down an optical
waveguide. Each optical signal has a different peak wavelength.
After traveling through the waveguide, the signals are separated.
By multiplexing multiple signals on a single waveguide, the
transmission capacity of the waveguide can be increased.
[0014] In some WDM system configurations, multiple
wavelength-selective optical filters having different passbands can
be used to multiplex and demultiplex optical signals. The different
optical filters for a WDM system can be fabricated as a monolithic
filter array. However, the aggregate yield for a monolithic filter
array with multiple different optical filters can be low. The
techniques presented below enable manufacturing of filter arrays
with a higher aggregate yield. In one configuration, the assembly
of a filter array that has multiple different wavelength-selective
filters includes a first substrate upon which one or more first
filters have been fabricated on a first surface of the first
substrate, and a second substrate upon which one or more second
filters have been fabricated on a second surface of the second
substrate. The one or more first filters and the one or more second
filters each transmit a different band of wavelengths. Further, a
bonding material bonds the first substrate to the second
substrate.
WDM Optical System
[0015] FIG. 1 depicts a block diagram of an example system 100 that
includes multiple different wavelength-selective filters 122, 124,
126, 128 fabricated on two substrates 120, 130, where the
substrates 120, 130 are bonded together, and the
wavelength-selective filters 122, 124, 126, 128 are positioned
between the substrates 120, 130 that form a filter array 101.
Multiple optical sources 112, 114, 116, 118 can each emit a light
beam carrying data, and the light beams are multiplexed by the
system 100. The optical sources 112, 114, 116, 118 can be any type
of light source that emits a light beam in a band of wavelengths,
such as a vertical-cavity surface-emitting laser (VCSEL), a
distributed feedback laser, or a fiber laser. The optical sources
may include lenses to tilt and collimate the light beams.
Substrates 120, 130 can transmit a high percentage of the
wavelengths of the light emitted by the optical sources 112, 114,
116, 118. In the example of FIG. 1, four optical sources 112, 114,
116, 118 are shown, but the light emitted by any number of optical
sources can be multiplexed with an appropriate system similar to
system 100, for example, having a one-to-one correspondence between
the number of optical sources and the number of
wavelength-selective filters.
[0016] The optical sources 112, 114, 116, 118 can be positioned so
that each emitted light beam is received at a different
wavelength-selective filter 122, 124, 126, 128, and the
wavelength-selective filters 122, 124, 126, 128 can be positioned
in a row. Each wavelength-selective filter 122, 124, 126, 128 can
reflect light at a first set or group of wavelengths and transmits
light at a second set or group of wavelengths. The first set of
wavelengths is different from the second set of wavelengths for a
given wavelength-selective filter, and each wavelength-selective
filter 122, 124, 126, 128 transmits a different second set of
wavelengths. For example, the set of wavelengths emitted by optical
source 112 that is transmitted by wavelength-selective filter 122
is different from the set of wavelengths emitted by optical source
114 that is transmitted by wavelength-selective filter 124 and is
also different from the set of wavelengths emitted by optical
source 116 that is transmitted by wavelength-selective filter 126,
and yet further, is different from the set of wavelengths emitted
by optical source 118 that is transmitted by wavelength-selective
filter 128. Also, the set of wavelengths emitted by a particular
optical source 112, 114, 116, 118 is reflected by each of the
wavelength-selective filters 122, 124, 126, 128 that do not
transmit that particular set of emitted wavelengths. For example,
the set of wavelengths emitted by optical source 112 is reflected
by each of the wavelength-selective filters 124, 126, 128.
[0017] Additionally, in the system 100, the light beams from the
three optical sources 112, 114, 116 can be focused and reflected by
relay mirrors 142, 144, 146 toward the next successive
wavelength-selective filter in the row of wavelength-selective
filters. The relay mirrors 142, 144, 146 are coupled to substrate
140 which can transmit a high percentage of light at the
wavelengths emitted by the optical sources 112, 114, 116, 118.
Thus, in example system 100, the light beam emitted by optical
source 112 is first transmitted by substrate 120 and then
transmitted by wavelength-selective filter 122, focused and
reflected by relay mirror 142, reflected by wavelength-selective
filter 124, focused and reflected by relay mirror 144, reflected by
wavelength-selective filter 126, focused and reflected by relay
mirror 146, reflected by wavelength-selective filter 128 and
finally exits the system 100 at output location 148. In some
implementations, an output lens can be placed at output location
148 to tilt, focus, or collimate the exiting light. Note that as a
light beam bounces between the relay mirrors 142, 144, 146 and the
wavelength-selective filters 124, 126, 128 before exiting the
system 100, the light beam travels with low loss multiple times
through substrates 130, 140. The light beams emitted by the other
optical sources 114, 116, 118 can bounce between the appropriate
relay mirrors and wavelengths-selective filters in a similar manner
until exiting from system 100 at output location 148. Thus, the
light exiting system 100 at output location 148 can include
multiplexed light beams from each of the optical sources 112, 114,
116, 118. In some instances, substrates 130, 140 may be a single
substrate.
[0018] A similar system can also perform a demultiplexing function
if a multiplexed light beam enters system 100 from the output
location 148 and travels through the system 100 in the opposite
direction from the light beams in the multiplexing configuration
described above. Additionally, for the demultiplexing
configuration, four photodetectors can be used, one photodetector
is positioned where each of the optical sources 112, 114, 116, 118
are located. The photodetectors may include lenses to focus the
incoming light beams onto the light absorbing areas of the
photodetectors. For example, light having wavelengths in the set of
wavelengths transmitted by wavelength-selective filter 122 is
reflected by filter 128, focused and reflected by relay mirror 146,
reflected by filter 126, focused and reflected by relay mirror 144,
reflected by filter 124, focused and reflected by relay mirror 142,
and transmitted by filter 122 to a photodetector. Thus, in this
example, a multiplexed light beam can be separated into light beams
having different wavelengths for detection by different
photodetectors, in this case, four photodetectors. However, a light
beam can be demultiplexed into any number of light beams with
different wavelengths with an appropriate number of
wavelength-selective filters and photodetectors.
[0019] Returning to the multiplexing configuration shown in FIG. 1,
in general, the emission wavelength spectrum of each of the optical
sources 112, 114, 116, 118 can be matched to the passband
transmission wavelengths of the corresponding wavelength-selective
filter 122, 124, 126, 128 to minimize optical power loss in the
system 100. Wavelength-selective filters 122, 124, 126, 128 can be
made of multiple layers of thin film dielectric material having
different refractive indices.
[0020] Generally, the yield for each fabricated
wavelength-selective filter that meets filter specifications is not
100%, and, in fact, can be substantially lower than 100%. As a
result, the greater the number of different filters that are formed
on the same substrate of a filter array, the lower the total yield.
The total yield can be so low that it may not be practical to
manufacture the filter array at a reasonable cost. In the example
system 100 shown in FIG. 1, four different wavelength-selective
filters are used in the filter array 101. Techniques are presented
below that improve the yield of the filter array 101 by limiting
the number of filters fabricated on a given substrate or wafer.
[0021] In one implementation, a plurality of first filters and a
plurality of second filters can be fabricated on a first substrate,
and a plurality of third filters and a plurality of fourth filters
can be fabricated on a second substrate. FIG. 2 depicts two example
die substrates, substrate 1 210 and substrate 2 220, which were
diced from a larger first substrate and a larger second substrate,
respectively. One first filter 212 and one second filter 214 are
fabricated on substrate 1 210, and one third filter 223 and one
fourth filter 225 are fabricated on substrate 2 220. In this
example, two filters are fabricated, and then the two substrates,
each having two good filters, are bonded together. However, any
number of filters can be fabricated on each of two or more
substrates that are subsequently bonded together. The die
substrates 210, 220 can be any type of material, such as silicon,
glass, ceramic, or organic materials.
[0022] When the substrates are bonded together, the substrates
should be maintained as parallel as possible. Referring to FIG. 1,
if the substrates 120, 130 are not parallel or close to being
parallel, the light beams emitted by the optical sources 112, 114,
116, 118 may not be reflected at the correct angles from the
wavelength-selective filters 124, 126, 128 or from the relay
mirrors 142, 144, 146. As a result the light beams may not be
directed toward the output location 148 of system 100.
[0023] There are two cases for bonding together the substrates 120,
130 if the filters 122, 124, 126, 128 are positioned between the
two substrates 120, 130, as shown in the example of FIG. 1. In the
first case, the filters have equal thicknesses, and in the second
case, the filters have dissimilar thicknesses.
Equal Filter Thicknesses
[0024] FIG. 3 depicts an example of bonded filter substrates 310,
320 where the filters 312, 316 fabricated on a first substrate 310
and the filters 314, 318 fabricated on a second substrate 320 have
equal thicknesses. The substrates 310, 320 should both be
sufficiently flat so that the substrates 310, 320 can be brought
into intimate contact and bonded. Methods of bonding the substrates
310, 320 will be described below.
[0025] When filters are fabricated on a substrate, the substrate
might bow due to thin film stresses. To mitigate bowing of the
substrate, coatings can be placed on the opposite surface of the
substrate from the surface where the filters are fabricated so that
the material of the coatings compensates for the stress induced by
the filters and flattens the substrate. Alternatively or
additionally, the substrate can be pre-bowed in the opposite
direction by grinding and/or polishing the substrate so that
deposition of the filters on the pre-bowed substrate results in
flattening of the substrate; and/or a coefficient of thermal
expansion of the first substrate, the second substrate, and thin
films used to create the filters 312, 314, 316, 318 can be matched.
These techniques can be applied to at least one of the first
substrate 310 and the second substrate 320, or to both substrates
310, 320.
[0026] To reduce potential crosstalk of light beams and absorb any
stray light that might be reflected off a filter or substrate at an
undesired angle, absorbing bonding material 331, 332, 333, 334, 335
can be positioned between the first substrate 310 and the second
substrate 320 in areas not occupied by one of the filters 312, 314,
316, 318.
Dissimilar Filter Thicknesses
[0027] FIG. 4 depicts an example of bonded filter substrates 410,
420 where the filters 422, 424 fabricated on a first substrate 410
and the filters 423, 425 fabricated on a second substrate 420 have
dissimilar filter thicknesses. A plurality of standoffs 431, 432
can be fabricated on one or both of the substrates 410, 420 and
positioned between the first substrate 410 and the second substrate
420 to maintain a fixed separation between the first substrate 410
and the second substrate 420. For example, the standoffs 431, 432
can be fabricated using a glass material, metal, deposited thin
films, or electroplated materials, or the substrates 410, 420 can
be etched to form a recess in which the filters 422, 423, 424, 425
are fabricated. Another method is to insert shims between the
substrates 410, 420.
[0028] Yet another method is to use two-sided tape, epoxy film, or
patternable material, such as photoresist, BCB (benzocyclobutene),
polyimide, or SU8 epoxy polymer, as the bonding material. Multiple
apertures, one corresponding to each of the filters, can be created
in the bonding material, and each filter 422, 423, 424, 425 can be
positioned in a different one of the apertures between the first
substrate 410 and the second substrate 420. Although four filters
are shown in the example of FIG. 4, more or fewer filters can be
used.
[0029] As with the case of equal thickness filters (FIG. 3), for
dissimilar filter thicknesses, bonding material 441 can be
positioned between the first substrate 410 and the second substrate
420 in areas not occupied by one of the filters 422, 423, 424, 425,
where the bonding material absorbs incident light.
[0030] In areas corresponding to the filter apertures, the first
surface 411 of the first substrate 410 on which the filters 422,
424 are fabricated and a second surface 421 of the second substrate
420 on which the filters 423, 425 are fabricated can be coated with
an anti-reflection coating (not shown) to minimize reflections at
the air-substrate interfaces. As another alternative, the bonding
material 441 can be selected to be index-matched to a refractive
index of the first substrate 410 and the second substrate 420.
[0031] FIG. 5 depicts a block diagram of an example system 500 that
includes a series of four wavelength-selective filters 522, 524,
526, 528 fabricated on two different substrates 520, 530, where the
substrates 520, 530 are bonded such that two of the filters 524,
528 not located between the substrates. That is, in contrast to
system 100 in FIG. 1 where all of the optical filters 122, 124,
126, 128 are co-planar, in system 500, optical filters 522, 526 are
not co-planar with optical filters 524, 528. Specifically, filters
522 and 526 have been fabricated on substrate 530, and filters 524,
528 have been fabricated on substrate 520, and the filters 524, 528
are not positioned between the substrates 520, 530. The substrates
520, 530 and filters 522, 524, 526, 528 form a filter array
501.
[0032] In some configurations, such as in system 100 of FIG. 1, the
distance between a relay mirror 142, 144, 146 and the filters
closest to each relay mirror can be designed to be approximately a
Rayleigh range, such that the relay mirror performs one-to-one
imaging of the light beams between those filter locations. For the
system 500 in FIG. 5, the distances between the filters closest to
a relay mirror and the relay mirror is not the same, for example
the distance between filter 522 and relay mirror 542 is less than
the distance between relay mirror 542 and filter 524. To
approximately maintain the one-to-one imaging of the light beams
between filter locations by the relay mirrors, the distance 505
should be small relative to the Rayleigh range. Because filters are
fabricated on a thick substrate for ease of handling, and a
Rayleigh range may be on the order of a millimeter, the substrate
520 may be much less than a millimeter, for example, approximately
200 microns. Thus, the thickness of the substrate 520 is reduced to
an appropriate thickness after filters 524, 528 are fabricated and
prior to bonding substrate 520 to substrate 530.
[0033] Similar to system 100 in FIG. 1, system 500 includes four
optical sources 512, 514, 516, 518 that emit light beams having
different peak wavelengths, and the optical sources are coupled to
a substrate 510. Substrates 520, 530 can transmit a high percentage
of the wavelengths of the light beams emitted by the optical
sources 512, 514, 516, 518. The light beam emitted by each optical
source 512, 514, 516, 518 is received at a different
wavelength-selective filter 522, 524, 526, 528. Each
wavelength-selective filter can reflect light at a first set or
group of wavelengths and transmit light at a second set or group of
wavelengths. The first set of wavelengths is different from the
second set of wavelengths, and each wavelength-selective filter
522, 524, 526, 528 transmits a different second set of wavelengths.
Additionally, the set of wavelengths emitted by a particular
optical source 512, 514, 516, 518 can be reflected by each of the
wavelength-selective filters 522, 524, 526, 528 that do not
transmit that particular set of emitted wavelengths.
[0034] Light beams from the three optical sources 512, 514, 516 can
be focused and reflected by relay mirrors 542, 544, 546 toward the
next successive wavelength-selective filter in the series of
wavelength-selective filters. The relay mirrors 542, 544, 546 are
coupled to substrate 540 which can also transmit a high percentage
of light at the wavelengths emitted by the optical sources 512,
514, 516, 518. Thus, in example system 500, optical source 512
emits a light beam that is transmitted through substrate 520,
transmitted by wavelength-selective filter 522, focused and
reflected by relay mirror 542, reflected by wavelength-selective
filter 524, focused and reflected by relay mirror 544, reflected by
wavelength-selective filter 526, focused and reflected by relay
mirror 546, reflected by wavelength-selective filter 528 and
finally exits system 500 at output location 548. Note that as a
light beam bounces between the relay mirrors 542, 544, 546 and the
wavelength-selective filters 524, 526, 528 before exiting system
500, the light beam is transmitted with low loss multiple times
through the substrates 520, 530, 540. The light beams emitted by
the other optical sources 514, 516, 518 travel through the system
500 in a similar manner, and the light exiting from system 500 at
output location 548 includes multiplexed light beams from the
optical sources 512, 514, 516, 518.
[0035] Thus, the main difference between system 500 in FIG. 5 and
system 100 shown in FIG. 1 is that in system 500, not all of the
wavelength-selective filters are positioned between a first
substrate 530 and a second substrate 520. In some implementations,
the first substrate 520 and the second substrate 520 can be bonded
directly to each other so that none of the filters are positioned
between the first substrate 530 and the second substrate 520, and
the filters are not co-planar.
Fabricating Bonded Filter Substrates
[0036] FIGS. 6A, 6B, 6C1, 6C2, 601, 6D2, 6E1, and 6E2 pictorially
depict steps of different fabrication techniques for fabricating
bonded filter substrates having four different filters. However,
these fabrication steps are applicable to substrates having any
number of different types of filters. These figures will be
referenced in the flow diagram descriptions of FIGS. 7 and 9A-9B
below.
Fabrication Process for Bonded Filter Substrates--Bonding
Substrates Prior to Dicing Substrates
[0037] FIG. 7 depicts a flow diagram illustrating an example
process 700 of fabricating bonded filter substrates having four
different types of filters, where the substrates are bonded prior
to dicing the substrates.
[0038] At block 705 of FIG. 7, a plurality of first filters and a
plurality of second filters are fabricated on a first surface of a
first substrate or wafer, where the plurality of first filters each
transmit a first group of wavelengths, and the plurality of second
filters each transmit a second group of wavelengths. FIG. 6A
illustrates the plurality of first filters 612 and the plurality of
second filters 614 fabricated on a first surface 618 of a first
substrate 610.
[0039] And at block 710, a plurality of third filters and a
plurality of fourth filters are fabricated on a second surface of a
second substrate or wafer, where the plurality of third filters
each transmit a third group of wavelengths, and the plurality of
fourth filters each transmit a fourth group of wavelengths. Also,
the first group of wavelengths, the second group of wavelengths,
the third group of wavelengths, and the fourth group of wavelengths
are different. FIG. 6A illustrates the plurality of third filters
622 and the plurality of fourth filters 624 fabricated on a second
surface 621 of a second substrate 620. While in the example of FIG.
6A, two different types of filters are fabricated on each of two
substrates, more or fewer different types of filters can be
fabricated on each substrate, and more than two substrates can be
bonded together.
[0040] Then at block 715, the first substrate is bonded to the
second substrate. In some implementations, positions of the
plurality of first filters, the plurality of second filters, the
plurality of third filters, and the plurality of fourth filters are
not stacked when the substrates are bonded. Further, in some
implementations, the plurality of first filters, the plurality of
second filters, the plurality of third filters, and the plurality
of fourth filters can be aligned relative to each other, as shown,
for example, in FIG. 1. Non-limiting examples of methods of bonding
substrates include glass-to-glass bonding, adhesive bonding,
oxide-to-oxide bonding, eutectic bonding, solder bonding,
thermocompression bonding, and glass frit bonding.
[0041] FIG. 6B illustrates an example configuration where the first
surface 618 of the first substrate 1 610 on which the first filters
612 and second filters 614 are fabricated is brought close to the
second substrate 2 620 so that the filters on the first surface 618
can be bonded to the second surface 621 on which the third filters
622 and fourth filters 624 are fabricated. In this case, the
orientation of substrate 610 in FIG. 68 is upside down relative to
its orientation in FIG. 6A. The configuration of the substrates
610, 620 shown in FIG. 6B is used to generate filter arrays for the
system 100 shown in FIG. 1, where the filters are positioned
between the substrates 120, 130.
[0042] FIG. 6C2 illustrates another example configuration for
bonding substrates 610a. 620 to generate filter arrays for the
system 500 shown in FIG. 5 where two of the filters are not
positioned between the substrates 520, 530. As shown in FIG. 6A,
the first substrate 610 has an opposing surface 619 that is on an
opposite side of the first substrate 610 from the first surface 618
on which filters 612, 614 are fabricated. As discussed previously,
the thickness of the first substrate 610 is reduced, resulting in a
thinned first substrate 610a that has a new opposing surface 619a
(shown in FIG. 6C1). FIG. 6C2 illustrates how the new opposing
surface 619a is brought close to the second substrate 620 so that
the new opposing surface 619a can be bonded to the filters on the
second surface 621.
[0043] Next, at block 720, the bonded first substrate and second
substrate are diced into sections that include one first filter,
one second filter, one third filter, and one fourth filter. For the
example configuration shown in FIG. 6B, the bonded first substrate
610 and second substrate 620 are diced along the dotted lines to
produce individual filter array dies 625a, 625b, 625c, 625d, where
the filters are positioned between the substrates 610, 620. For the
example configuration shown in FIG. 6C2, the bonded first substrate
610a and second substrate 620 are diced along the dotted lines to
produce individual filter array dies 633a, 633b, 633c, 633d, where
two of the filters are not positioned between the substrates 610a,
620. In some implementations, the first substrate and/or the second
substrate can be ground and/or polished prior to dicing.
[0044] The process 700 in FIG. 7 is applicable to the case where
two different types of filters 612, 614 are fabricated on a first
substrate 610, and two different types of filters 622, 624 are
fabricated on a second substrate 620, as shown in the example of
FIG. 6A. FIG. 8 depicts a flow diagram illustrating an example
generalized process 800 of fabricating bonded filter substrates
having a total of two different types of filters, where the
substrates are bonded together prior to dicing.
[0045] At block 805 of FIG. 8, a plurality of first filters are
fabricated on a first surface of a first substrate, where the
plurality of first filters each transmit a first group of
wavelengths. And at block 810, a plurality of second filters are
fabricated on a second surface of a second substrate, where the
plurality of second filters each transmit a second group of
wavelengths. Also, the first group of wavelengths and the second
group of wavelengths are different.
[0046] Then at block 815, the first substrate is bonded to the
second substrate, where positions of the plurality of first filters
and the plurality of second filters are not stacked. And at block
820, the bonded first substrate and second substrate are diced into
sections that include one first filter and one second filter.
Fabrication Process for Bonded Filter Substrates--Testing Filters
Prior to Bonding
[0047] FIGS. 9A-9B depict a flow diagram illustrating another
example process 900 of fabricating bonded filter substrates having
four different types of filters, where the filters are tested prior
to bonding the substrates.
[0048] At block 905, a plurality of first filters and a plurality
of second filters are fabricated on a first surface of a first
substrate or wafer, where the plurality of first filters each
transmit a first group of wavelengths, and the plurality of second
filters each transmit a second group of wavelengths.
[0049] And at block 910, a plurality of third filters and a
plurality of fourth filters are fabricated on a second surface of a
second substrate or wafer, where the plurality of third filters
each transmit a third group of wavelengths, and the plurality of
fourth filters each transmit a fourth group of wavelengths, and
further where the first group of wavelengths, the second group of
wavelengths, the third group of wavelengths, and the fourth group
of wavelengths are different. Block 905 is similar to block 705,
and block 910 is similar to block 710, thus the illustration of
FIG. 6A is also applicable to blocks 905 and 910.
[0050] Further, at block 915, a determination is made of which of
the plurality of first filters, the plurality of second filters,
the plurality of third filters, and the plurality of fourth filters
meet their respective filter specifications. The determination can
be made by testing the spectral response of each of the
filters.
[0051] Then at block 920, the first substrate is diced to produce
first sections that include one first filter and one second filter
that each meet their respective filter specifications.
[0052] Next, at block 925 each of at least some of the first
sections of the first substrate that includes one first filter and
one second filter that meet specifications are bonded to a
different one of the second sections of the second substrate that
include one third filter and one fourth filter that meet
specifications. Bonding of the substrates can be performed, for
example, by using one of the previously described techniques.
Bonding is performed in such a way as to precisely align and
maintain a specific pitch from filter to filter.
[0053] In the example of FIG. 6D1, three known good dies 610a,
610b. 610c from the first substrate 1 610 have each been tested and
determined to have a first filter 612 and a second filter 614 that
meet specifications. The three known good dies 610a, 610b, 610c are
shown bonded to sections of substrate 2 620 that have a third
filter 622 and fourth filter 624 that have been tested and
determined to meet specifications. Substrate 2 620 has a section
with a third filter 605 and a fourth filter 606. One or both of
these filters have been determined to not meet specifications. In
the case of this section with one or both bad filters that do not
meet specifications, known good dies from the first substrate are
not wasted by being bonded to a known bad section of substrate 2
620. This method prevents known good dies from substrate 1 from
being bonded to areas on substrate 2 that do not meet
specifications, and therefore, increases the yield of the filter
arrays.
[0054] In the example of FIG. 6E1, there are three tested known
good dies 611a, 611b, 611c, each with a first filter 612 and a
second filter 614 that meet specifications. Prior to dicing the
first substrate 610, the substrate 610 is thinned so that the
original opposing surface 619 (shown in FIG. 6A) becomes a new
opposing surface 619a. Then bonding material, such as
index-matching epoxy, is placed between the new opposing surface
619a of the known good dies 611a, 611b, 611c and the second surface
629 of sections of substrate 2 that have a third filter 622 and
fourth filter 624 that have been tested and determined to meet
specifications. Additionally, index-matching material can be placed
between one of the good third filters and/or one of the good fourth
filters and the new opposing surface 619a if the good third filter
and/or the good fourth filter does not contact the opposing
surface.
[0055] Then at block 930, the second substrate is diced to produce
second sections with bonded first sections. For the example
configuration shown in FIG. 6D2, the second substrate 620 is diced
to produce individual filter array dies 630a, 630b, 630c.
Similarly, for the example configuration shown in FIG. 6E2, the
second substrate 620 is diced to produce individual filter array
dies 635a, 635b, 635c.
[0056] The process 900 in FIG. 9 is applicable to the case where
two different types of filters 612, 614 are fabricated on a first
substrate 610, and two different types of filters 622, 624 are
fabricated on a second substrate 620, as shown in the example of
FIG. 6A. FIG. 10 depicts a flow diagram illustrating an example
generalized process 1000 of fabricating bonded filter substrates
having a total of two different types of filters, where the filters
are tested prior to bonding the substrates.
[0057] At block 1005, a plurality of first filters are fabricated
on a first surface of a first substrate, where the plurality of
first filters each transmit a first group of wavelengths. And at
block 1010, a plurality of second filters are fabricated on a
second surface of a second substrate, where the plurality of second
filters each transmit a second group of wavelengths, and further
where the first group of wavelengths and the second group of
wavelengths are different.
[0058] Further, at block 1015, a determination is made of which of
the plurality of first filters and the plurality of second filters
meet their respective filter specifications. Then at block 1020,
the first substrate is diced to produce first sections that include
one first filter that meets filter specifications.
[0059] Next, at block 1025 each of at least some of the first
sections of the first substrate that includes one first filter that
meets specifications are bonded to one of the second sections of
the second substrate that includes one second filter that meets
specifications.
[0060] Then at block 1030, the second substrate is diced to produce
second sections with bonded first sections.
[0061] Not all of the steps or features presented above are used in
each implementation of the presented techniques. Steps can be
performed and features can be created in a different order than
presented.
[0062] It should be noted that the above description illustrates
rather than limits the examples described herein, and that those
skilled in the art will be able to design alternative examples
without departing from the scope of the appended claims. The word
"comprising" does not exclude the presence of elements or steps
other than those listed in a claim. Further, "a" or "an" does not
exclude a plurality, and "a plurality" does not exclude multiple
pluralities.
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