U.S. patent application number 15/964353 was filed with the patent office on 2019-05-16 for color filter uniformity for image sensor devices.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. The applicant listed for this patent is Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Yun-Wei Cheng, Chun-Hao Chou, Yi-Hsing Chu, Yin-Chieh Huang, Kuo-Cheng Lee.
Application Number | 20190148430 15/964353 |
Document ID | / |
Family ID | 66432433 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190148430 |
Kind Code |
A1 |
Chu; Yi-Hsing ; et
al. |
May 16, 2019 |
COLOR FILTER UNIFORMITY FOR IMAGE SENSOR DEVICES
Abstract
The present disclosure is directed to a method for reducing the
surface deformation of a color filter after a baking process in an
image sensor device. Surface deformation can be reduced by
increasing the surface area of the color filter prior to baking.
For example, forming a grid structure over a semiconductor layer of
an image sensor device, where the grid structure includes a first
region with one or more cells having a common sidewall; disposing
one or more color filters in a second region of the grid structure;
recessing the common sidewall in the first region of the grid
structure to form a group of cells with the recessed common
sidewall; and disposing another color filter in the group of
cells.
Inventors: |
Chu; Yi-Hsing; (Tainan City,
TW) ; Chou; Chun-Hao; (Tainan City, TW) ; Lee;
Kuo-Cheng; (Tainan City, TW) ; Huang; Yin-Chieh;
(Tainan City, TW) ; Cheng; Yun-Wei; (Taipei City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsinchu |
|
TW |
|
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
Hsinchu
TW
|
Family ID: |
66432433 |
Appl. No.: |
15/964353 |
Filed: |
April 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62586324 |
Nov 15, 2017 |
|
|
|
Current U.S.
Class: |
257/432 |
Current CPC
Class: |
H01L 27/1464 20130101;
H01L 27/14685 20130101; H01L 27/14627 20130101; H01L 27/14605
20130101; H01L 27/14621 20130101; H01L 27/1463 20130101 |
International
Class: |
H01L 27/146 20060101
H01L027/146 |
Claims
1. An image sensor device comprising: a grid structure configured
to receive one or more color filters over a semiconductor layer,
wherein the grid structure comprises: a first cell with a first
sidewall and a common sidewall; and a second cell with a second
sidewall and the common sidewall shorter than the first and second
sidewalls; and a color filter disposed in the first and the second
cells, wherein a top surface of the color filter is above the
common sidewall and below the first and the second sidewalls.
2. The image sensor device of claim 1, wherein the semiconductor
layer comprises one or more sensing regions configured to sense
radiation entering the semiconductor layer from the grid
structure.
3. The image sensor device of claim 1, wherein the common sidewall
is shorter than the first and second sidewalls by at least 10%.
4. The image sensor device of claim 1, further comprising: a
transparent material over the grid structure, wherein the
transparent material forms a micro-lens over the first and second
cells.
5. The image sensor device of claim 1, wherein the color filter
comprises a green color filter.
6. The image sensor device of claim 1, wherein each of the first
sidewall, common sidewall, and second sidewall comprises a bottom
layer and a top dielectric layer with the common sidewall being
shorter than the first and second sidewalls by at least 10%.
7. The image sensor device of claim 1 further comprising: an other
color filter in a third cell, wherein the other color filter is
different from the color filter in the first and second cells, and
wherein a top surface area of the other color filter is smaller
than the top surface area of the color filter disposed in the first
and second cells.
8. An image sensor system comprising: a semiconductor layer with
one or more radiation-sensing regions formed over an interconnect
layer and configured to convert light to electric charge; a grid
structure formed over the semiconductor layer and configured to
receive one or more color filters, wherein the grid structure
comprises: a first cell with a first sidewall and a common
sidewall; and a second cell with a second sidewall and the common
sidewall shorter than the first and second sidewalls; a color
filter disposed in the first and the second cells, wherein a top
surface of the color filter is above the common sidewall and below
the first and second sidewalls; and a micro-lens over each of the
first and second cells.
9. The image sensor system of claim 8, wherein a height of the
common sidewall is less than 90% of a height of the first and
second sidewalls.
10. The image sensor system of claim 8, wherein the interconnect
layer comprises a back-end of the line layer, a middle of the line
layer, a front-end of the line layer, or a combination thereof.
11. The image sensor system of claim 8, wherein each of the first
and second cells is aligned with a respective radiation-sensing
region of the one or more radiation-sensing regions of the
semiconductor layer.
12. The image sensor system of claim 8, wherein the grid structure
is configured to guide the light to the one or more
radiation-sensing regions of the semiconductor layer.
13. A method comprising: forming a grid structure over a
semiconductor layer of an image sensor device, wherein the grid
structure comprises a first region with one or more cells having a
common sidewall; disposing one or more color filters in a second
region of the grid structure; recessing the common sidewall in the
first region of the grid structure to form a group of cells with
the recessed common sidewall; and disposing an other color filter
in the group of cells.
14. The method of claim 13, wherein the recessing the common
sidewall comprises a dry etch process that recesses the common
sidewall by at least 10%.
15. The method of claim 13, wherein the recessing the common
sidewall decreases a height of the common sidewall by at least
10%.
16. The method of claim 13, wherein the disposing the one or more
color filters comprises masking the first region of the grid
structure.
17. The method of claim 13, wherein the other color filter
comprises a green color filter.
18. The method of claim 13, wherein the one or more color filters
comprise a red color filter or a blue color filter.
19. The method of claim 13, wherein the grid structure comprises a
top passivation layer which is partially etched when recessing the
common sidewall in the first region.
20. The method of claim 13, further comprising performing a bake to
harden the other color filter.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/586,324, titled "Color filter uniformity
for image sensor devices," which was tiled on Nov. 15, 2017 and is
incorporated herein by reference in its entirety.
BACKGROUND
[0002] Semiconductor image sensors are used to sense visible or
non-visible radiation; such as, for example, visible light,
infrared light, etc. Complementary metal-oxide-semiconductor (CMOS)
image sensors (CIS) and charge-coupled device (CCD) sensors are
used in various applications such as digital still cameras, mobile
phones, tablets, goggles, etc. Arrays of pixels featured in CMOS
and CIS devices can sense incoming radiation that is projected
toward the sensor and convert it into electrical signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Aspects of the present disclosure are best understood from
the following detailed description when read with the accompanying
figures. It is noted that, in accordance with the common practice
in the industry, various features are not drawn to scale. In fact,
the dimensions of the various features may be arbitrarily increased
or reduced for clarity of illustration and discussion.
[0004] FIG. 1 is a cross-sectional view of a backside illuminated
image sensor device, according to some embodiments.
[0005] FIG. 2 is a top view of a composite grid structure
configured to receive color filters, according to some
embodiments.
[0006] FIG. 3 is a flow chart of a method to suppress surface
deformation of a color filter after a baking operation, according
to some embodiments.
[0007] FIG. 4 is a cross-sectional view of a composite grid
structure on a semiconductor layer of a partially fabricated image
sensor device, according to some embodiments.
[0008] FIG. 5 is a top view of a composite grid structure with a
group of unoccupied cells having common sidewalls, according to
sonic embodiments.
[0009] FIG. 6 is a cross-sectional view of a composite grid
structure after red and blue color filters have been disposed in
cells of a composite grid structure, according to some
embodiments.
[0010] FIG. 7 is a cross-sectional view of a composite grid
structure after a sidewall recess process, according to some
embodiments.
[0011] FIG. 8 is a top view of a composite grid structure with a
duster of unoccupied cells having recessed common sidewalls,
according to some embodiments.
[0012] FIG. 9 is a top view of a composite grid structure with a
group of cells having recessed common sidewalls and filled with a
green color filter, according to some embodiments.
[0013] FIG. 10 is a cross sectional view of a composite grid
structure after a green filter has been disposed in cells with
recessed common sidewalls, according to some embodiments.
[0014] FIG. 11 is a cross sectional view of a composite grid
structure with recessed top surfaces of its color filters,
according to some embodiments.
[0015] FIG. 12 is a top view of a composite grid structure with
recessed top surfaces of its color filters, according to some
embodiments.
DETAILED DESCRIPTION
[0016] The following disclosure provides many different
embodiments, or examples, for implementing different features of
the provided subject matter. Specific examples of components and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over a second feature in the description that follows may
include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features are disposed between the first and second
features, such that the first and second features are not in direct
contact.
[0017] Further, spatially relative terms, such as "beneath,"
"below," "lower," "above," "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. The spatially relative terms are intended to encompass
different orientations of the device in use or operation in
addition to the orientation depicted in the figures. The apparatus
may be otherwise oriented (rotated 90 degrees or at other
orientations) and the spatially relative descriptors used herein
may likewise be interpreted accordingly.
[0018] The term "about" as used herein indicates the value of a
given quantity that can vary based on a particular technology node
associated with the subject semiconductor device. Based on the
particular technology node, the term "about" can indicate a value
of a given quantity that varies within, for example, 10-30% of the
value (e.g., .+-.10%, .+-.20%, or .+-.30% of the value).
[0019] One type of image sensor device is a back side illuminated
image sensor device. In a back side illuminated image sensor
device, color filters and micro-lenses are positioned on the back
side of a substrate (e.g., on an opposite side of the substrate's
circuitry), so that the image sensor device can collect light with
minimal or no obstructions. As a result, back side illuminated
image sensor devices are configured to detect light from the back
side of the substrate, rather than from a front side of the
substrate where the color filters and micro-lenses of the image
sensor device are positioned between the substrate's circuitry and
the pixels. Compared to front side illuminated image sensor
devices, back side illuminated image sensor devices have improved
performance under low light conditions and higher quantum
efficiency (QE) (e.g., photon to electron conversion
percentage).
[0020] Image sensor devices use color filters to capture color
information from incident light rays. For example, the image sensor
device through the use of color filters can detect the red, green,
and blue (RGB) regions of the visible light spectrum. A composite
grid structure, which includes cells that can be filled with color
filter material, is used to position the color filter material
above pixels of the image sensor device.
[0021] Once the composite grid structure is tilled with color
filters (e.g., red, green, or blue), a. bake is performed to harden
the color filter material. As the color filter material hardens,
its top surface area shrinks by an amount. Further, each color
filter can exhibit a different shrinkage amount. For example, the
green color filter can shrink from about 14% to about 18% (e.g.,
about 14.7% to about 18%), the red color filter can shrink from
about 13% to about 16% (e.g., about 13.2% to about 16.2%), and the
blue color filter can shrink from about 7% to about 9% (e.g., about
7.5% to about 9%). As the color filters shrink, their top surface
deforms and changes from flat to convex. The degree of the top
surface deformation can be proportional to the shrinkage amount.
For example, the green color filter, which shrinks the most, can be
more prone to deformation compared to the red or blue color
filters. Further, color filter shrinkage can impact color shielding
uniformity (CSU), which is an indicator of color uniformity across
a pixel area (e.g., an index to check color uniformity on photo
diagonals). Poor color shielding uniformity can result in
performance degradation of the image sensor device.
[0022] Various embodiments in accordance with this disclosure
provide a method to reduce the top surface deformation of a color
filter after a baking process. This can be accomplished by allowing
the color filter to expand to one or more adjacent cells and thus
increase the color filter's top surface area. In an example,
assuming that two same-color color filters occupy two adjacent
cells of a composite grid structure, a common sidewall of the
adjacent cells can be selectively recessed so that the two color
filters can be combined into a single color filter with a larger
top surface area that stretches across the two adjacent cells. The
common top surface can be, for example, double the size of the
individual top surfaces of the color filters.
[0023] FIG. 1 is a simplified cross-sectional view of a back side
illuminated image sensor device 100, according to some embodiments
of the present disclosure. Back side illuminated image sensor
device 100 includes a semiconductor layer 102 with
radiation-sensing areas 104. By way of example and not limitation,
semiconductor layer 102 includes a silicon material doped with a
p-type dopant, such as boron. Alternatively, semiconductor layer
102 can include silicon that is doped with an n-type dopant, such
as phosphorous or arsenic. Semiconductor layer 102 can also include
other elementary semiconductors, such as germanium or diamond.
Semiconductor layer 102 can optionally include a compound
semiconductor and/or an alloy semiconductor. Further, semiconductor
layer 102 can include an epitaxial layer, which may be strained for
performance enhancement. Semiconductor layer 102 can include a
silicon-on-insulator (SOI) structure.
[0024] Semiconductor layer 102 has a front side (also referred to
as a "bottom surface") 106 and a back side (also referred to as a
"top surface") 108. Semiconductor layer 102 has a thickness that
can range from about 100 .mu.m to about 3000 .mu.m.
[0025] Radiation-sensing regions or pixels 104 are formed in the
semiconductor layer 102. As disclosed herein, the terms
"radiation-sensing regions" and "pixels" may be used
interchangeably. Pixels 104 are configured to sense radiation, such
as incident light rays impinging semiconductor layer 102 from back
side 108. Each of the radiation-sensing regions or pixels 104
include a photodiode that can convert photons to charge, according
to some embodiments of the present disclosure. In some embodiments
of the present disclosure, pixels 104 can include photodiodes,
transistors, amplifiers, other similar devices, or combinations
thereof. Pixels 104 may also be referred to herein as
"radiation-detection devices" or "light-sensors."
[0026] For simplicity, two pixels 104 are illustrated in FIG. 1,
but additional pixels 104 can be implemented in semiconductor layer
102. By way of example and not limitation, pixels 104 can be formed
using an ion implant process on semiconductor layer 102 from front
side 106. Pixels 104 can also be formed by a dopant diffusion
process.
[0027] Pixels 104 are electrically isolated from each other with
isolation structures 110. Isolation structures 110 can be trenches
etched into semiconductor layer 102 and filled with a dielectric
material, such as silicon oxide, silicon nitride, silicon
oxynitride, fluorine-doped silicate glass (FSG), a low-k dielectric
material (e.g., a material with a k value lower than 3.9), and/or a
suitable insulating material. According to some embodiments of the
present disclosure, isolation structures 110 on back side 108 of
semiconductor layer 102 have an anti-reflective coating (ARC) 112.
ARC 112 is a liner layer that can prevent incoming light rays from
being reflected away from radiation-sensing areas/pixels 104. ARC
112 can include a high-k material (e.g., a material with a k-value
lower than 3.9), such as hafnium oxide (HfO.sub.2), tantalum
pentoxide (Ta.sub.2O.sub.5), zirconium dioxide (ZrO.sub.2),
aluminum oxide (Al.sub.2O.sub.3), or any other high-k material. ARC
112 can be deposited using a sputtering process, a chemical vapor
deposition (CVD)-based process, an atomic layer deposition
(ALD)-based techniques, or any other suitable deposition technique.
In some embodiments of the present disclosure, the thickness of ARC
112 can range from about 10 .ANG. to about 500 .ANG..
[0028] Back side illuminated image sensor device 100 also includes
a capping layer 114 formed over the semiconductor layer 102, such
as over the ARC 112, as illustrated in FIG. 1. In some embodiments
of the present disclosure, capping layer 114 can provide a planar
surface on which additional layers of back side illuminated image
sensor device 100 can be formed. Capping layer 114 can include a
dielectric material, such as silicon oxide (SiO.sub.2), silicon
nitride (Si.sub.3N.sub.4), silicon oxy-nitride (SiON), or any other
suitable dielectric material. Further, capping layer 114 can be
deposited using CVD or any other suitable deposition technique. In
some embodiments of the present disclosure, the thickness of
capping layer 114 can range between about 500 .ANG. and about 2000
.ANG..
[0029] Further, back side illuminated image sensor device 100
includes a composite grid structure 116 formed over capping layer
114. According to some embodiments of the present disclosure,
composite grid structure 116 includes cells 118 arranged in columns
and rows, where each cell 118 is aligned to a respective
radiation-sensing area 104. As mentioned above, cells 118 can
receive a red, green, or blue color filter 120.
[0030] FIG. 2 is a top view of composite grid structure 116,
according to some embodiments. Each cell 118 of composite grid
structure 116 is filled with a single color filter 120. By way of
example and not limitation, neighboring cells 118 may be filled
with the same-color color filter. For example, as shown in FIG. 2,
four adjacent cells 118 can be filled with the same color filter
120--e.g., four adjacent cells 118 have a filter with the same
color (red, green, or blue). Consequently, cells 118--which are
part of a quadrant share four sidewalls a, b, c, and d. In this
example, the color filters in each cell 118 are kept isolated from
one another via common sidewalls a, b, c, and d. The number of
cells 118 filled with the same color filter 120, as depicted in
FIG. 2, is exemplary and not limiting. Therefore, a group of
neighboring cells 118 filled with the same color filter 120 can be
larger or smaller (e.g., two, six, etc.)
[0031] Referring to FIG. 1, cells 118 of composite grid structure
116 can be formed by depositing a bottom layer 122 and a top
dielectric layer 124 and selectively etching away portions of the
bottom layer and top dielectric layer to form cells 118. By way of
example and not limitation, composite grid structure 116 can be
formed as follows: bottom layer 122 and top dielectric layer 124
can be blanket deposited on capping layer 114. One or more
photolithography and etch operations can be used to pattern bottom
layer 122 and top dielectric layer 124 to form the sidewalls of
cells 118. The photolithography and etch operations can be
performed so that each cell 118 of composite grid structure 116 is
aligned to respective pixels 104 of semiconductor layer 102. In
some embodiments, the sidewall height of each cell 118 of composite
grid structure 116 can range from about 200 nm to about 1000
nm.
[0032] Bottom layer 122 of cell 118 can be made of titanium,
tungsten, aluminum, or copper. However, bottom layer 122 of cells
118 may not be limited to metals and may include other suitable
materials or stack of materials that can reflect and guide incoming
visible light towards radiation-sensing areas 104. In some
embodiments of the present disclosure, bottom layer 122 of cells
118 is formed using a sputtering process, a plating process, an
evaporation process, or any other suitable deposition method.
According to some embodiments of the present disclosure, the
thickness of bottom layer 122 of each cell 118 can range from about
100 .ANG. to about 3000 .ANG..
[0033] Top dielectric layer 124 can include one or more dielectric
layers. In some embodiments, top dielectric layer 124 can protect
previously-formed layers of back side illuminated image sensor
device 100 (e.g., bottom layer 122 and capping layer 114). Top
dielectric layer 124 can allow incoming light to pass through and
reach radiation-sensitive areas (or pixels) 104. Top dielectric
layer 124 can be made of a transparent material or materials. In
some embodiments of the present disclosure, top dielectric layer
124 can be made of SiO.sub.2, Si.sub.3N.sub.4, SiON, or any other
suitable transparent dielectric material. Top dielectric layer 124
can be deposited by CVD or ALD and can have a deposited thickness
range from about 1000 .ANG. to about 3000 .ANG., according to some
embodiments.
[0034] Cells 118 can also include a passivation layer 126, which is
interposed between color filter 120 and the sidewalls of cells 118
(e.g., bottom layer 122 and dielectric layer 124). In some
embodiments of the present disclosure, passivation layer 126 can be
conformally deposited by a CVD-based or an ALD-based deposition
technique. Passivation layer 126 can be formed from a dielectric
material, such as SiO.sub.2, Si.sub.3N.sub.4, or SiON. Further,
passivation layer 126 can have a thickness between about 375 .ANG.
to about 625 .ANG..
[0035] In some embodiments, the top surface of color filters 120
can be aligned to the top surface of passivation layer 126 on
dielectric layer 124. Alternatively, color filters 120 can be
formed above the top surface of passivation layer 126 on dielectric
layer 124. For example and explanation purposes, the top surface of
color filters 120 will be described as being aligned to the top
surface of passivation layer 126 on dielectric layer 124.
[0036] Referring to FIG. 1, after cells 118 of composite grid
structure 116 receive their respective color filters 120, a
transparent material layer 128 can be formed over composite grid
structure 116 and color filters 120. Transparent material layer 128
can be in contact with passivation layer 126 if the top surface of
color filters 120 is aligned to the top surface of passivation
layer 126 over dielectric layer 124. Alternatively, transparent
material layer 128 may not be in contact with passivation layer 126
if the top surface of color filters 120 is above the top surface of
passivation layer 126 over dielectric layer 124. In some examples,
transparent material layer 128 forms a micro-lens 130 over each
cell 118 of composite grid structure 116. Micro-lenses 130 are
aligned with respective radiation-sensing areas 104 and are formed
so they cover the top surface of color filters 120 within the
boundaries of cell 118 (e.g., contained within the sidewalls of
each cell 118). Transparent material layer 128 can be an oxide
deposited by CVD, according to some embodiments.
[0037] Micro-lenses 130, due to their curvature, are thicker than
other areas of transparent material layer 128 (e.g., areas between
micro-lenses 130 above dielectric layer 124). For example,
referring to FIG. 1, transparent material layer 128 is thicker over
color filter 120 (e.g., where micro-lens 130 is formed) and thinner
in areas between micro-lenses 130 (e.g., above dielectric layer
124).
[0038] Referring to FIG. 1, back side illuminated image sensor
device 100 can also include an interconnect structure 132.
Interconnect structure 132 can include patterned dielectric layers
and conductive layers that form interconnects (e.g., wiring)
between pixels 104 and other components (not shown in FIG. 1).
Interconnect structure 132 may, for example be, one or more
multilayer interconnect (MLI) structures 134 embedded in an
interlayer dielectric (ILD) layer 136. According to some
embodiments of the present disclosure, MLA structures 134 can
include contacts/vias and metal lines. For purposes of
illustration, multiple conductive lines 138 and vias/contacts 140
are shown in FIG. 1. The position and configuration of conductive
lines 138 and vias/contacts 140 can vary depending on design needs
and are not limited to the depiction of FIG. 1. Further,
interconnect structure 132 can include sensing devices 142. Sensing
devices 142 can be, for example, an array of field effect
transistors (FETs) and/or memory cells that are electrically
connected to respective radiation-sensing areas (or pixels) 104 and
configured to read the electrical signal produced in those areas as
a result of a light-to-charge conversion process,
[0039] In some embodiments of the present disclosure, interconnect
structure 132 can be a top layer of a partially-fabricated
integrated circuit (IC) or of a fully-fabricated IC that can
include multiple layers of interconnects, resistors, transistors,
and/or other semiconductor devices. As a result, interconnect
structure 132 can include front end of the line (FEOL) and middle
of the line (MOL) layers. Furthermore, interconnect structure 132
can be attached via a buffer layer (not shown in FIG. 1) to a
carrier substrate (not shown in FIG. 1) that can provide support to
the structures fabricated thereon (e.g., interconnect layer 132,
semiconductor layer 102, etc.). The carrier substrate can be, for
example, a silicon wafer, a glass substrate, or any other suitable
material.
[0040] In some embodiments of the present disclosure, to fabricate
back side illuminated image sensor device 100, semiconductor layer
1.02 can be formed on a silicon substrate (e.g., silicon wafer) and
interconnect structure 132 can be subsequently formed over front
side 106 of semiconductor layer 102. Interconnect structure 132 can
undergo multiple photolithography, etch, deposition, and
planarization operations before it is completed. Once interconnect
structure 132 is formed, a carrier substrate, as discussed above,
can be attached to the top of interconnect structure 132. For
example, a buffer layer can act as an adhesion medium between the
carrier substrate and interconnect structure 132. The silicon
substrate can be turned upside down, and the silicon substrate can
be mechanically grinded and polished until back side 108 of
semiconductor layer 102 is exposed. Isolation structures 110 on
back side 108 of semiconductor layer 102 can be subsequently formed
to further electrically isolate radiation-sensing areas or pixels
104. Capping layer 114, along with the composite grid structure
116, can be formed on back side 108 of semiconductor layer 102.
[0041] Composite grid structure 116 can be formed so that each of
its cells 118 is aligned to respective radiation-sensing areas or
pixels 104. Alignment of composite grid structure 116 and
radiation-sensing areas, or pixels, 104 can be achieved with
photolithographic operations based on, for example, alignment marks
present on back side 108 of semiconductor layer 102. The formation
of composite grid structure 116 can include the deposition and
subsequent patterning of bottom layer 122 and dielectric layer 124
using photolithography and etch operations to form cells 118.
Passivation layer 126 is subsequently deposited over the exposed
surfaces of bottom layer 122 and dielectric layer 124. Color
filters 120 can fill cells 118, and transparent material layer 128
can be deposited thereon to form micro-lenses 130. Fabrication of
back side illuminated image sensor device 100 is not limited to the
operations described above and additional or alternative operations
can be performed.
[0042] FIG. 3 is a flowchart of an exemplary method 300 for
disposing one or more color filters in a composite grid structure
of a back side illuminated image sensor device with minimal top
surface deformation of the color filters. For example purposes,
method 300 will be described in the context of back side
illuminated image sensor device 100 of FIG. 1.According to some
embodiments, method 300 utilizes an etch process that can recess
commonly shared sidewalls between a selected group of cells 118 so
that the color filter occupying the group of cells 118 has a larger
surface area. Method 300 is not limited to the operations described
below. Other fabrication operations can be performed between the
various operations of method 300 and are omitted merely for
clarity.
[0043] Method 300 begins with operation 302, where one or more
color filters are disposed into a subset of cells (e.g., one or
more cells) in a composite grid structure. FIG. 4 shows a partially
fabricated back side illuminated image sensor device, such as back
side illuminated image sensor device 100 of FIG. 1. One or more
color filters can be disposed into cells of composite grid
structure 116. In some embodiments, the selection of the color
filters is based on surface deformation characteristics after a
baking process. For example, color filters exhibiting low surface
deformation (e.g., with a top surface shrink percentage less than
15) can be candidates for operation 302 as opposed, for example, to
color filters that exhibit high surface deformation (e.g., with a
top surface shrink percentage greater than 15). In some
embodiments, candidate color filters for operation 302 are, for
example, the red and blue color filters.
[0044] In referring to FIG. 5, which is a top view of composite
grid structure 116 shown in FIG. 4, red color filters 120R and blue
color filter 120B are disposed into one or more cells 118. By way
of example and not limitation, selective placement of a color
filter (e.g., blue, red, or green) into cells 118 of composite grid
structure 116 can be accomplished by selectively covering areas
(e.g., cells 118) of composite grid structure 116 that receive a
different color filter. For example, if red color filter 120R is
the first color filter that will be introduced into cells 118 of
composite grid structure 116, a photoresist or a mask layer (not
shown in FIG. 5) can be disposed and patterned on composite grid
structure 116 so that the patterned photoresist or mask layer masks
the cells 118 that will receive a different color filter (e.g.,
blue or green). Subsequently, exposed cells 118 of composite grid
structure 116 can be filled with red color filter 120R, according
to a desired design. The same process can be repeated to introduce
blue color filter 120B in one or more predetermined cells 118 of
composite grid structure 116. In some embodiments, red color
filters 120R and blue color filters 120B cover portions of
passivation layer 126 above dielectric layer 124, shown as area 600
in FIG. 6. After the red and blue color filters are being disposed
into their respective cells 118, the photoresist or mask layer can
be removed from composite grid structure 116.
[0045] As a result of operation 302, a select number of cells 118
(e.g., in composite grid structure 116) is left unoccupied (e.g.,
without a color filter). In some embodiments, unoccupied cells 118
are clustered together to form groups of cells that include two,
four, six, or any even number of cells 118. Based on the above
description, FIG. 5 shows an exemplary group 500 of unoccupied
cells 118 in composite grid structure 116. Group 500 includes four
unoccupied cells 118 clustered together after red and blue color
filters 120R and 120B have been disposed in composite grid
structure 116. As discussed above, red color filters 120R and blue
color filters 120B have been disposed into composite grid structure
116 so that they cover passivation layer 126 of their respective
cells 118. However, passivation layer 126 remains exposed for group
500 of cells 118 since these cells were previously covered by
photoresist or a masking layer.
[0046] Further, each cell 118 of group 500 shares at least two
sidewalls with two other cells in the group. For example, in FIG. 5
the cells in group 500 share sidewalls a, b, c, and d. For
illustration purposes, FIG. 5 shows four unoccupied cells 118
clustered together in group 500. However this is not limiting, and
group 500 can include fewer or additional cells. Further,
additional groups of cells, such as group 500, are possible across
composite grid structure 116. In some embodiments, the size and/or
number of unoccupied groups of cells--after operation 302--can
depend on the design and/or specifications of the image sensor
device. FIG. 6--which is a cross section of FIG. 5 across line
A-B--shows the exposed common sidewall d between two adjacent empty
cells 118 of group 500.
[0047] In referring to FIG. 3, method 300 continues with operation
304, where an etch process is used to recess common sidewalls a, b,
c, and d of cells 118 in group 500 (shown in FIG. 5). In some
embodiments, and in referring to FIGS. 5 and 6, areas of the image
sensor exposed to the etch process include the top surfaces of
color filters 120R and 120B, and common sidewalls a, b, c, and d of
unoccupied cells 118 in group 500.
[0048] In operation 304, color filters 120R and 120B are used as
masking layers so that the sidewalls of underlying cells 118 in
composite grid structure 116 are not recessed. On the other hand,
any exposed sidewall of a cell 118 (e.g., not occupied by a color
filter) that is subjected to the etch process of operation 304 will
be recessed. For example, FIG. 7 shows the partially fabricated
structure of FIG. 6 after the etch process of operation 304, where
the common sidewall d between adjacent cells 118 has been recessed.
The recessed height H2 of sidewall d is shorter than its original
height H1. In some embodiments, the etch process of operation 304
is timed so that the height ratio H2/H1 is less than 0.9. For
example, if an exposed sidewall is subjected to the timed etch
process of operation 304, its height will be reduced by at least
10%. The 10% height reduction, or more, ensures that the recessed
sidewalls will be submerged under the color filter when cells 118
are filled. As discussed above, and referring to FIG. 5, common
sidewalls a, b, and c of cells 118 within group 500 can be
similarly recessed during the etch process of operation 304. For
example, FIG. 8 shows the recessed common sidewalls a, b, c, and
d.
[0049] In some embodiments, the etch process of operation 304 can
partially remove exposed portions of passivation layer 126; for
example, and referring to FIG. 7, exposed portions of passivation
layer 126 include the top and sides surfaces of sidewall d and the
bottom surfaces of cell 118. By way of example and not limitation,
a new deposition of passivation layer 126 into available cells 118
can be performed to recover any etched portions of passivation
layer 126 prior to the next operation of method 300 (e.g.,
operation 306).
[0050] In referring to FIG. 3, method 300 continues with operation
306, where a third color filter is disposed in unoccupied cells 118
of the composite grid structure 116. As discussed above, the third
color filter can be a green color filter since it exhibits the
highest level of surface deformation during baking. In some
embodiments, due to recessed common sidewalls a, b, c, and d (shown
in FIG. 8), green color filter 120G is allowed expand to more than
one unoccupied cells 118 of group 500 in composite grid structure
116--provided that its top surface is above recessed height H2. In
other words, recessed sidewalls a, b, c, and d allow green color
filter 120G to expand to all of the cells of group 500 and form a
single green color filter 120G with an enlarged common surface
area. Further, a height ratio H2/H1 of less than 0.9 ensures that
the recessed sidewalls will be submerged under green color filter
120G, as discussed earlier. For example, in FIG. 9, which is a top
view of composite grid structure 116 after operation 306, green
filter 120G is disposed in composite grid structure 116 across all
cells 118 of group 500. This means that color filter 120G can
occupy a larger surface area on composite grid structure 116, as
opposed to red and blue color filters (e.g., 120R and 120B). In
FIG. 10, which is a cross section of FIG. 9 along line C-D, top
surface 900 of green color filter 120G is below height HI and above
height H2, according to some embodiments.
[0051] In some embodiments, a bake is performed to harden the color
filters. A subsequent etch process recesses the top surfaces of the
color filters (e.g., 120R, 120G, and 120B) so that passivation
layer 126 of the cells with red and blue color filters is exposed
over areas of dielectric layer 124, as shown in FIG. 11. According
to FIG. 11, the top surface of green color filter 120G is below the
top surfaces of red and blue color filter 120R and 120B. FIG. 12 is
a top view of composite grid structure 116 after the aforementioned
etch process.
[0052] In some embodiments, method 300 is not limited to green
color filters. For example, sidewalls of any number of cells (e.g.,
an even number of cells) of any section of the composite grid
structure can be recessed to provide a larger surface area for any
color filter depending on the image sensor design and
characteristics and the shrinkage amount of the color filter's
surface after the bake process.
[0053] Various embodiments in accordance with this disclosure
provide a method to reduce the surface deformation of a color
filter after a baking process. Surface deformation can be reduced
by recessing the sidewalls of selected sections of a composite grid
structure so that a color filter occupying these sections can
expand in cells with recessed sidewalls and enlarge its surface
area. The proposed method is not limited to single color filter or
a specific area of the composite grid structure. Recessing is
performed in selected areas of the composite grid structure using
photolithography and etch operations. For example, the
photolithography and etch operations can isolate sections of the
composite grid structure and etch common sidewalls of adjacent
cells within the selected area of the composite grid structure.
[0054] In some embodiments, an image sensor device includes a grid
structure configured to receive one or more color filters over a
semiconductor layer, where the grid structure includes a first cell
with a first sidewall and a common sidewall, a second cell with a
second sidewall and the common sidewall the common sidewall being
shorter than the first and second sidewalls. The image sensor
device further includes a color filter disposed in the first and
the second cells, where a top surface of the color filter is above
the common sidewall and below the first and the second
sidewalls.
[0055] In some embodiments, an image sensor system includes: a
semiconductor layer with one or more radiation-sensing regions
formed over an interconnect layer and configured to convert light
to electric charge; and a grid structure formed over the
semiconductor layer and configured to receive one or more color
filters, where the grid structure includes a first cell with a
first sidewall and a common sidewall and a second cell with a
second sidewall and the common sidewall--the common sidewall being
shorter than the first and second sidewalls. The image sensor
system further includes a color filter disposed in the first and
the second cells, where a top surface of the color filter is above
the common sidewall and below the first and second sidewalls; and a
micro-lens over each of the first and second cells.
[0056] In some embodiments, a method includes: forming a grid
structure over a. semiconductor layer of an image sensor device,
where the grid structure includes a first region with one or more
cells having a common sidewall; disposing one or more color filters
in a second region of the grid structure; recessing the common
sidewall in the first region of the grid structure to form a group
of cells with the recessed common sidewall; and disposing another
color filter in the group of cells.
[0057] It is to be appreciated that the Detailed Description
section, and not the Abstract of the Disclosure, is intended to be
used to interpret the claims. The Abstract of the Disclosure
section may set forth one or more but not all exemplary embodiments
contemplated and thus, are not intended to be limiting to the
subjoined claims.
[0058] The foregoing disclosure outlines features of several
embodiments so that those skilled in the art may better understand
the aspects of the present disclosure. Those skilled in the art
will appreciate that they may readily use the present disclosure as
a basis for designing or modifying other processes and structures
for carrying out the same purposes and/or achieving the same
advantages of the embodiments introduced herein. Those skilled in
the art will also realize that such equivalent constructions do not
depart from the spirit and scope of the present disclosure, and
that they may make various changes, substitutions, and alterations
herein without departing from the spirit and scope of the subjoined
claims.
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