U.S. patent application number 14/084758 was filed with the patent office on 2015-05-21 for color filter array and micro-lens structure for imaging system.
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 Szu-Ying Chen, Tzu-Hsuan Hsu, Chen-Jong Wang, Dun-Nian Yaung.
Application Number | 20150137296 14/084758 |
Document ID | / |
Family ID | 53172452 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150137296 |
Kind Code |
A1 |
Chen; Szu-Ying ; et
al. |
May 21, 2015 |
Color Filter Array and Micro-Lens Structure for Imaging System
Abstract
A color filter array and micro-lens structure for imaging system
and method of forming the color filter array and micro-lens
structure. A micro-lens material is used to fill the space between
the color filters to re-direct incident radiation, and form a
micro-lens structure above a top surface of the color filters.
Inventors: |
Chen; Szu-Ying; (Toufen
Township, TW) ; Yaung; Dun-Nian; (Taipei City,
TW) ; Wang; Chen-Jong; (Hsin-Chu, TW) ; Hsu;
Tzu-Hsuan; (Kaohsiung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsin-Chu |
|
TW |
|
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
Hsin-Chu
TW
|
Family ID: |
53172452 |
Appl. No.: |
14/084758 |
Filed: |
November 20, 2013 |
Current U.S.
Class: |
257/432 ;
438/70 |
Current CPC
Class: |
H01L 27/14643 20130101;
H01L 27/14621 20130101; H01L 27/14627 20130101; H01L 27/14689
20130101; H01L 27/14685 20130101 |
Class at
Publication: |
257/432 ;
438/70 |
International
Class: |
H01L 27/146 20060101
H01L027/146 |
Claims
1. An imaging device comprising: a first color filter element on a
semiconductor substrate; a second color filter element on the
semiconductor substrate and spaced apart from the first color
filter element; a micro-lens structure arranged over a top surface
of the first color filter element; and a sidewall waveguide
structure arranged between neighboring sidewalls of the first and
second color filter elements, the sidewall waveguide structure and
micro-lens structure being made of the same material.
2. The imaging device of claim 1, the material of the micro-lens
structure and the sidewall waveguide structure being transparent
and having an index of refraction which is lower than that of the
first color filter element.
3. The imaging device of claim 1, wherein the material of the
sidewall waveguide structure and the micro-lens structure is photo
resist or oxide and has an index of refraction that is between 1.1
and 1.8.
4. The imaging device of claim 1, further comprising: a first
photodetector arranged under the first color filter element; and a
second photodetector arranged under the second color filter
element; the micro-lens structure being configured to focus both a
first incident ray, which has a first angle of incidence that is
less than a predetermined angle of incidence, and a second incident
ray, which has a second angle of incidence that is greater than the
predetermined angle of incidence, through the first color filter
element, and the sidewall waveguide structure being configured to
reflect the focused first incident ray to strike the first
photodetector and further configured to refract the focused second
incident ray to pass between the first and second
photodetectors.
5. A semiconductor imaging system comprising: a photodetector array
including a matrix of individual photodetectors; a color filter
array arranged over the photodetector array and including a matrix
of color filter elements which are arranged vertically over
respective photodetectors in the photodetector array; an array of
micro-lenses arranged over the color filter array and including a
matrix of micro-lens structures which are arranged vertically over
respective color filter elements of the color filter array; and a
sidewall waveguide structure laterally surrounding a color filter
element and configured to re-direct incident radiation striking a
micro-lens structure with a first angle of incidence, which is less
than a predetermined angle of incidence, toward an individual
photodetector that corresponds vertically to the color filter
element and the micro-lens structure.
6. The semiconductor imaging system of claim 5, the sidewall
waveguide structure being further configured to re-direct incident
radiation striking the micro-lens structure with a second angle of
incidence, which is greater than the predetermined angle of
incidence, to pass between neighboring photodetectors.
7. The semiconductor imaging system of claim 5, wherein the
sidewall waveguide structure has a first index of refraction, the
micro-lens structure has a second, different index of refraction,
and the color filter element has a third index of refraction that
is larger than the first index of refraction and larger than the
second index of refraction.
8. The semiconductor imaging system of claim 5, wherein the
sidewall waveguide structure and the micro-lens structure are made
of the same material.
9. The semiconductor imaging system of claim 8, wherein the
material of the sidewall waveguide structure and the micro-lens
structure is photoresist or oxide and has an index of refraction
that is between 1.1 and 1.8.
10. The semiconductor imaging system of claim 5, wherein the color
filter array comprises primary color filter elements arranged in a
matrix.
11. The semiconductor imaging system of claim 10, wherein the
primary color filter elements include a red color filter, a green
color filter, and a blue color filter.
12. The semiconductor imaging system of claim 5, wherein the
individual photodetectors are made of a silicon-containing
material.
13. The semiconductor imaging system of claim 5, wherein the color
filter element is made of photoresist and has an index of
refraction that is between 1.6 and 2.0.
14. The semiconductor imaging system of claim 5, wherein a ratio of
a height of a color filter element to a space between neighboring
color filter elements is about 1:7.
15. The semiconductor imaging system of claim 5, wherein the
individual photodetectors are complementary
metal-oxide-semiconductor (CMOS) photodetectors.
16-20. (canceled)
21. An imaging device disposed over a semiconductor substrate
comprising: first and second photodetectors arranged at least
partially in the semiconductor substrate; first and second color
filter elements disposed above the first and second photodetectors,
respectively; first and second micro-lens structures covering top
surfaces of the first and second color filter elements,
respectively; and a sidewall waveguide structure separating the
first and second color filter elements; wherein the sidewall
waveguide structure has an index of refraction that is smaller than
that of the first and second color filter elements.
22. The imaging device of claim 21, wherein the material of the
sidewall waveguide structure is photoresist.
23. The imaging device of claim 21, wherein the material of the
sidewall waveguide structure is silicon dioxide.
24. The imaging device of claim 21, wherein the sidewall waveguide
structure has an index of refraction that is between 1.1 and
1.8.
25. The imaging device of claim 21, wherein the sidewall waveguide
structure and the first and second micro-lens structures are made
of the same material.
Description
BACKGROUND
[0001] Digital cameras and other digital imaging devices use arrays
of millions of tiny photodetectors or pixels to record an image.
For example, when a cameraman or camerawoman presses his or her
camera's shutter button and exposure begins, each photodetector in
the array is uncovered to detect the presence or absence of photons
at the individual array locations. To end the exposure, the camera
closes its shutter, and circuitry in the camera assesses how much
light (e.g., how many photons) fell into each photodetector while
the shutter was open. The relative quantity or intensity of photons
that struck each photodetector are then stored according to a bit
depth (0-255 for an 8-bit pixel). The digital values for all the
pixels are then stored and are used to form a resultant image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] FIG. 1 illustrates a cross-sectional view of a color filter
array and micro-lens structure for imaging system in accordance
with some embodiments.
[0003] FIG. 2 illustrates a cross-sectional views of some
alternative embodiments of a method of forming a color filter array
and micro-lens structure for imaging system.
[0004] FIG. 3 illustrates a top view of some alternative
embodiments of a method of forming a color filter array and
micro-lens structure for imaging system and an arrangement method
of different color filters.
[0005] FIG. 4 illustrates a flow diagram of some embodiments of a
method for forming a color filter array and micro-lens structure
for imaging system.
[0006] FIGS. 5-9b illustrate cross-sectional views of some
alternative embodiments of a substrate upon which a method of
forming a color filter array and micro-lens structure for imaging
system is performed.
DETAILED DESCRIPTION
[0007] The description herein is made with reference to the
drawings, wherein like reference numerals are generally utilized to
refer to like elements throughout, and wherein the various
structures are not necessarily drawn to scale. In the following
description, for purposes of explanation, numerous specific details
are set forth in order to facilitate understanding. It will be
appreciated that the details of the figures are not intended to
limit the disclosure, but rather are non-limiting embodiments. For
example, it may be evident, however, to one of ordinary skill in
the art, that one or more aspects described herein may be practiced
with a lesser degree of these specific details. In other instances,
known structures and devices are shown in block diagram form to
facilitate understanding.
[0008] Individual photodetectors are often, in-and-of themselves,
unable to differentiate between different colors of light.
Therefore a color filter array (CFA) with color filter elements for
different colors is often aligned over a photodetector array so
that photodetectors detect light intensity of different colors.
Traditionally, indexes of refraction of the different color filter
elements are similar, such that when an incident light ray has a
large angle of incidence, the light could easily pass through one
color filter into other neighboring color filters and/or other
neighboring photodetectors underneath the color filters. In this
way, crosstalk can happen between photodetectors for different
color filters, ultimately causing noise that distorts the resultant
digital images.
[0009] In general, the present disclosure is related to an
optimized semiconductor color filter array and micro-lens structure
that alleviates crosstalk between neighboring photodetectors
underlying different color filters. These disclosed techniques
improve signal-to-noise ratios (SNR) for imaging systems. More
particularly, a sidewall waveguide structure is formed between
neighboring color filter elements and works in conjuction with a
color filter element and a micro-lens structure to limit crosstalk.
In some embodiments, the sidewall waveguide structure and
micro-lens structure can be made of the same material to limit the
number of manufacturing steps. In some embodiments, when incident
radiation reaches a waveguide structure between two neighboring
color filter elements, the waveguide re-directs the incident
radiation back to one of the color filter elements and away from
the other color filter element. With some incident angles, for
example, total internal reflection happens at the contact surface
of the color filter element and the sidewall waveguide structure,
which prevents light from passing through neighboring color filter
elements. With other incident angles, for example, the sidewall
waveguide structure refracts light between neighboring
photodetector elements so the light does not inadvertently strike a
neighboring photodetector. As a result, larger portion of the
incident radiance strikes a photodiode underneath its corresponding
color filter element and less light "strays" to neighboring
photodiodes, such that SNR is improved.
[0010] FIG. 1 illustrates a cross-sectional view of some
embodiments of an example semiconductor substrate 100 upon which a
semiconductor color filter array and micro-lens structure for
imaging system has been applied. Substrate 100 includes a first
color filter element 102 and a second color filter element 104,
which are different. For example, in some embodiments, first color
filter element 102 is a blue filter, which allows blue light to
pass there through while blocking other wavelengths of light (e.g.,
blue filter 102 blocks red and green light), and second color
filter element 104 can be a green filter, which allows green light
to pass there through while blocking other wavelengths of light
(e.g. green filter 104 blocks red and blue light). The color filter
elements 102, 104 can have different sizes, spacings or materials
to provide the desired wavelength specificities. The color filter
elements 102 and 104 may be made of a kind of photo resist which
has similar index of refraction (n.sub.cf), for example between 1.6
and 2.0. A first micro-lens structure 106 is arranged over a top
surface of the first color filter element 102; and a second
micro-lens structure 108 is arranged over a top surface of the
second color filter element 104. A space 110 between the color
filter elements 102 and 104 is filled with the same material used
to form the first and second micro-lens structures 106, 108. When
filled with this material, the space 110 acts as a sidewall
waveguide structure that allows both reflectance and refraction of
incident radiance.
[0011] When incident radiance (see e.g., incident rays 112, 116)
strikes this structure, the incident radiance is focused by a
micro-lens structure towards its corresponding color filter
element, and is re-directed when reaching an internal contact
surface 114 at which the color filter element 102 meets the
micro-lens material 110. In some embodiments, the micro-lens
material 110 could be photo resist or oxide with an index of
refraction (n.sub.r) smaller than the index of refraction of the
color filter elements 102, 104 (n.sub.cf). In an embodiment, the
index of refraction of the micro-lens material is between 1.1 and
1.8. If the incident radiance has an angle of incidence that is
less than some critical angle (see incident ray 112), the incident
radiance experiences total internal reflectance at the internal
contact surface 114 and is therefore bounced back into the color
filter element 102. On the other hand, if the incidence radiance
has an angle of incidence that is larger than the critical angle
(see incident ray 116), the incident radiance is refracted at the
internal surface 114 and therefore is re-directed closer to the
color filter element 102. In some embodiments, the critical angle
for total internal reflection at the internal contact surface 114
can be larger than 30 degrees.
[0012] FIG. 2 illustrates a cross-sectional view of some
embodiments of an example substrate upon which a semiconductor
imaging system 200 has been applied. The imaging system 200 could
be a complimentary metal-oxide-semiconductor (CMOS) imaging system.
In some embodiments, SNR=10 of the system is less than 115 lux,
which represents an improvement of approximately 7%. As appreciated
by persons of ordinary skill in the art, the luminance where a
given target SNR is reached is used as a one-number performance
metric. SNR=10 is a commonly used target SNR.
[0013] An array of photodetectors 202, which is made up of
individual photodetectors (e.g., 202a, 202b, 202c, 202d), is
arranged as a matrix of pixels to collect incident radiance coming
through an array of color filter elements 204, which is made up of
individual color filter elements (e.g., 204a, 204b, 204c, 204d). As
shown, the individual color filter elements are vertically aligned
with the individual photodetectors. The color filter array 204
comprises color filter elements for different colors. It could
comprise primary color filter elements arranged in a matrix. For
example, first color filter element 204a could be a blue filter and
second color filter element 204b could be a green filter. Sidewall
waveguide structure 206 is arranged between neighboring color
filter elements. Similar as previously described with regards to
FIG. 1, when incident radiance (see e.g., incident rays 210, 212)
strikes this system 200, the incident radiance is focused or
directed by a micro-lens structure (e.g., 208a) towards its
corresponding color filter element (e.g., 204a) and its
corresponding photodetector (e.g., 202a). If the incident radiance
has an angle of incidence that is less than some critical angle
(see incident ray 210), the incident radiance experiences total
internal reflectance at the internal contact surface 214 and is
therefore bounced back into the color filter element 204a and its
corresponding photodetector 202a. On the other hand, if the
incidence radiance has an angle of incidence that is larger than
the critical angle (see incident ray 212), the incident radiance is
refracted at the internal surface 114 and therefore still passes
into the sidewall waveguide structure 206 and passes between
photodetectors 202a, 202b without striking either photodetector
202a, 202b.
[0014] Advantageously, in either case of total internal reflection
or refraction by the sidewall waveguide structure 206, the sidewall
waveguide structure 206 diverts the incident light away from
neighboring photodetectors (e.g., away from photodetector 202b).
Thus, in cases of total internal reflection such as shown by
incident ray 210, the sidewall waveguide structure 206 is helpful
in that it improves the collection efficiency of photodetector
202a, but also helps to limit cross-talk experienced by the
neighboring photodetector 202b. Further, even in cases of
refraction as shown by incident ray 212 which do not necessarily
improve the collection efficiency of photodetector 202a, by
refracting the incident ray 212 away from the neighboring
photodetector 202b, the sidewall waveguide structure 206 still
helps to limit cross-talk between neighboring photodetectors.
[0015] FIG. 3 shows a top view 300 of one example arrangement of
pixels corresponding to the cross-sectional view 200 illustrated in
FIG. 2. In this example, color filter elements 204b and 204d are a
first type of filter (e.g., blue filters); color filter element
204a is a second, different type of filter (e.g., green filter) and
306 is a third, still different type of filter (e.g., red filter).
A space between neighboring color filter elements is formed
laterally which is filled by a sidewall waveguide structure 206.
The sidewall waveguide structure 206 re-directs incident radiance
back toward a color filter element and its vertically aligned or
corresponding photodetector. An array of micro-lenses 208 includes
individual lenses (e.g., 208a, 208b, 208c, 208d) aligned with the
individual color filter elements in the color filter array 204 and
the individual photodetectors in the photodetector array 202.
Sidewall waveguide structure 206 converges projecting incident
radiance.
[0016] In an embodiment, in order to have total internal reflection
at an internal contact surface at which the sidewall waveguide
structure 206 meets a color filter element, a first index of
refraction of the sidewall waveguide structure (n1) and a second
index of refraction of the micro-lens structure (n2) are smaller
than a third index of refraction of the color filter element (n3).
In an embodiment, the index of refraction of the sidewall waveguide
structure, micro-lens structure, and the color filter element are
different. In an embodiment, the material of the photodetector 202
could be or contains silicon. The color filter element 204 could be
formed by photo resist with index of refraction n3, which can be
between 1.6 and 2.0. The micro-lens structure 208 and the sidewall
waveguide structures 206 could be formed by transparent photo
resist or oxide. The ratio of a height of color filter element to a
space between two adjacent color filter elements (or a distance
between at least one of the opposing surfaces of two adjacent color
filter elements, e.g. 202a and 202b) could be around 1:7.
[0017] Further, as will be appreciated in more detail herein, the
micro-lens structure 208 and the sidewall waveguide structure 206
could be formed by same manufacturing step and/or made of same
material. FIG. 4 illustrates a flow diagram of some example
embodiments of a method for forming a color filter array and
micro-lens structure for imaging system, wherein a micro-lens
structure and a sidewall waveguide structure is formed by a same
manufacture step and same material.
[0018] At 402, a photodetector array is patterned.
[0019] At 404, a color filtering array is patterned onto the
photodetector array. The color filter elements are patterned
separately wherein a space exists between two color filter
elements. The color filter elements are patterned so that a ratio
of a height of a color filter element to a distance between two
color filter elements is about 1:7. The color filter array
comprises primary color filter elements arranged in a matrix. The
primary colors could be red, green and blue.
[0020] At 406, a micro-lens material is applied above the color
filter array. In an embodiment, a height of the micro-lens material
is larger than a sum of a height and width of the color filter
element. The micro-lens material could be coated for example by
either spin-on method or deposition.
[0021] At 408, a micro-lens shape is patterned above the micro-lens
material. Varies methods could be used to pattern micro-lens shape.
For example, a photo resist could be exposed, developed and baked
to form a rounding shape which will be utilized as micro-lens shape
in following steps.
[0022] At 410, a back etching is performed to form micro-lens.
[0023] One example of FIG. 4's method is now described with regards
to a series of cross-sectional views as shown in FIGS. 5-9b.
Although FIGS. 5-9b are described in relation to method 400, it
will be appreciated that the structures disclosed in FIGS. 5-9b are
not limited to such a method, but instead may stand alone as a
structure.
[0024] At FIG. 5, a color filter array 500, which includes color
filter elements 502 and 504, is patterned onto the photodetector
array 510. The individual color filter elements are aligned with
corresponding photodetectors so that a photodetector is covered or
overlapped by a color filter element. A color filter element has
height H, width W, and the distance between two color filter
elements is D (measured from the opposing side walls of two
adjacent or neighboring color filter elements). In some
embodiments, the value for H is in a range of about 3,000 .ANG. to
about 10,000 .ANG.. In some embodiments the value of D is in a
range of about 1,500 .ANG. to about 3,000 .ANG.. In some
embodiments, the value of W is in a range of about 8000 .ANG. to
about 10,000 .ANG. with a pixel pitch about 1.1 .mu.m.
[0025] Space 506 exists between neighboring color filter elements
502, 504. In some embodiments, this space 506 extends downward from
an upper surface of the color filter elements to the substrate. In
some embodiments, this space 506 can be formed by performing an
etch when a mask is placed or disposed over the color filter
elements. In other embodiments, the color filter elements can be
selectively grown over the photodetector array such that the space
506 is a result of the selective growth.
[0026] At FIG. 6, a micro-lens material 600 is applied above the
color filter array 500 In an embodiment, a height of the micro-lens
material is larger than a sum of a height H and width W of the
color filter element. The micro-lens material extends downward into
the space 506 as shown by 604 to establish sidewall waveguide
structures, and also forms over an upper surface of the individual
color filter elements as shown by 602.
[0027] At FIG. 7, a bottom anti-reflection layer 702 is coated
above the micro-lens material 602, 604.
[0028] At FIG. 8, a micro-lens template 802 is patterned above the
bottom anti-reflection layer with photo resist. The micro-lens
template has a curved upper surface whose curvature determines the
extent which incident light is to be bent by the micro-lens to be
formed. Thus, different curvatures can be used for micro-lens
template 802 depending on the wavelengths of incident light that
are targeted, as well as the underlying geometries for the color
filter elements, sidewall waveguides, and photodetectors. The
curved upper surface is applied by distributing exposing light dose
to photo resist. For example, the photo resist can be negative
material, relative more light is exposed at the bottom of the
curvature and relative less light is exposed at the top of the
curvature.
[0029] At FIG. 9a and FIG. 9b, a back etching is performed to form
micro-lens 900. Notably, the etching chemical used for back etching
process is able to etch the photo resist making the micro-lens
template as well. Therefore, the portion of the micro-lens material
corresponding to bottom of the curvature is etched more than the
portion of the micro-lens material corresponding to top of the
curvature relatively such that the resultant curvature of the
micro-lens 900 substantially follows that of the micro-lens
template 802.
[0030] Thus, some embodiments relate to a semiconductor device. The
device includes a first color filter element on a semiconductor
substrate. A second color filter element is formed on the
semiconductor substrate and spaced apart from the first color
filter element. A micro-lens structure is arranged over a top
surface of the first color filter element. A sidewall waveguide
structure is arranged between neighboring sidewalls of the first
and second color filter elements. The sidewall waveguide structure
and micro-lens structure are made of the same material.
[0031] Other embodiments relate to a semiconductor imaging system.
The semiconductor imaging system includes a photodetector array
including a matrix of individual photodetectors. A color filter
array is arranged over the photodetector array and includes a
matrix of color filter elements which are arranged vertically over
respective photodetectors in the photodetector array. An array of
micro-lenses are arranged over the color filter array and includes
a matrix of micro-lens structures which are arranged vertically
over, or overlap, respective color filter elements of the color
filter array. A sidewall waveguide structure laterally surrounds a
color filter element. The sidewall waveguide structure re-directs
incident radiation striking a micro-lens structure with a first
angle of incidence, which is less than a predetermined angle of
incidence, toward an individual photodetector that corresponds
vertically to the color filter element and the micro-lens
structure. In an embodiment, the micro-lens structure is configured
to focus a first incident ray with an angle of incidence that is
less than a predetermined angle of incidence, and a second incident
ray with an angle of incidence that is greater than the
predetermined angle of incidence, through a color filter element.
In another embodiment, the sidewall waveguide structure is
configured to reflect the focused first incident ray to strike the
photodetector and further configured to refract the focused second
incident ray to pass between neighboring photodetectors.
[0032] Still another embodiment relates to a method of forming a
semiconductor imaging system structure. In this method, a
photodetector array is patterned on a semiconductor substrate. A
color filter array is patterned over the photodetector array. The
color filter array, after being patterned, has spaces between
neighboring color filter elements of the color filter array. A
micro-lens material is applied to the patterned color filter array.
The micro-lens material fills the spaces between neighboring color
filter elements to establish sidewall waveguide structures and also
covers upper surfaces of the color filter elements to establish
micro-lens structures.
[0033] It will be appreciated that while reference is made
throughout this document to exemplary structures in discussing
aspects of methodologies described herein (e.g., the structure
presented in FIGS. 5-9b, while discussing the methodology set forth
in FIG. 4), that those methodologies are not to be limited by the
corresponding structures presented. Rather, the methodologies (and
structures) are to be considered independent of one another and
able to stand alone and be practiced without regard to any of the
particular aspects depicted in the Figures. Additionally, layers
described herein, can be formed in any suitable manner, such as
with spin on, sputtering, growth and/or deposition techniques,
etc.
[0034] Also, equivalent alterations and/or modifications may occur
to those skilled in the art based upon a reading and/or
understanding of the specification and annexed drawings. The
disclosure herein includes all such modifications and alterations
and is generally not intended to be limited thereby. For example,
although the figures provided herein, are illustrated and described
to have a particular doping type, it will be appreciated that
alternative doping types may be utilized as will be appreciated by
one of ordinary skill in the art.
[0035] In addition, while a particular feature or aspect may have
been disclosed with respect to only one of several implementations,
such feature or aspect may be combined with one or more other
features and/or aspects of other implementations as may be desired.
Furthermore, to the extent that the terms "includes", "having",
"has", "with", and/or variants thereof are used herein, such terms
are intended to be inclusive in meaning--like "comprising." Also,
"exemplary" is merely meant to mean an example, rather than the
best. It is also to be appreciated that features, layers and/or
elements depicted herein are illustrated with particular dimensions
and/or orientations relative to one another for purposes of
simplicity and ease of understanding, and that the actual
dimensions and/or orientations may differ substantially from that
illustrated herein.
* * * * *