U.S. patent application number 14/270309 was filed with the patent office on 2015-11-05 for backside illuminated color image sensors and methods for manufacturing the same.
This patent application is currently assigned to OmniVision Technologies, Inc.. The applicant listed for this patent is OmniVision Technologies, Inc.. Invention is credited to Dyson Hsin-Chih Tai, Vincent Venezia, Wei Zheng.
Application Number | 20150318327 14/270309 |
Document ID | / |
Family ID | 54355817 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150318327 |
Kind Code |
A1 |
Zheng; Wei ; et al. |
November 5, 2015 |
BACKSIDE ILLUMINATED COLOR IMAGE SENSORS AND METHODS FOR
MANUFACTURING THE SAME
Abstract
A method for manufacturing a backside illuminated color image
sensor includes (a) modifying the frontside of an image sensor
wafer, having pixel arrays, to produce electrical connections to
the pixel arrays, wherein the electrical connections extend
depth-wise into the image sensor wafer from the frontside, and (b)
modifying the backside of the image sensor wafer to expose the
electrical connections.
Inventors: |
Zheng; Wei; (Los Gatos,
CA) ; Tai; Dyson Hsin-Chih; (San Jose, CA) ;
Venezia; Vincent; (Los Gatos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OmniVision Technologies, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
OmniVision Technologies,
Inc.
Santa Clara
CA
|
Family ID: |
54355817 |
Appl. No.: |
14/270309 |
Filed: |
May 5, 2014 |
Current U.S.
Class: |
438/70 |
Current CPC
Class: |
H01L 27/14685 20130101;
H01L 27/14636 20130101; H01L 27/14645 20130101; H01L 21/76898
20130101; H01L 27/14603 20130101; H01L 21/76224 20130101; H01L
27/14687 20130101; H01L 21/762 20130101; H01L 27/1464 20130101;
H01L 23/481 20130101; H01L 27/14621 20130101; H01L 27/14638
20130101; H01L 2924/00 20130101; H01L 2924/0002 20130101; H01L
2924/0002 20130101; H01L 21/76829 20130101 |
International
Class: |
H01L 27/146 20060101
H01L027/146; H01L 21/768 20060101 H01L021/768; H01L 21/762 20060101
H01L021/762 |
Claims
1. A method for manufacturing a backside illuminated color image
sensor, comprising: modifying frontside of an image sensor wafer,
including pixel arrays, to produce electrical connections to the
pixel arrays, the electrical connections extending depth-wise into
the image sensor wafer from the frontside; exposing the electrical
connections from backside of the image sensor wafer; after the step
of exposing, flattening the backside of the image sensor wafer to
provide a flat backside surface; and after the step of flattening,
applying a color filter to the flat backside surface.
2. (canceled)
3. A method for manufacturing a backside illuminated color image
sensor, comprising: modifying frontside of an image sensor wafer,
including pixel arrays, to produce electrical connections to the
pixel arrays, the electrical connections extending depth-wise into
the image sensor wafer from the frontside; flattening backside of
the image sensor wafer to provide a flat backside surface; after
the step of flattening, applying a color filter to the flat
backside surface; and after the step of applying, exposing the
electrical connections.
4. The method of claim 1, the step of modifying frontside
comprising forming recesses and the electrical connections, each of
the electrical connections connecting bottom of recesses to
circuitry of one of the pixel arrays.
5. A method for manufacturing a backside illuminated color image
sensor, comprising: modifying frontside of an image sensor wafer,
including pixel arrays, to produce electrical connections to the
pixel arrays, the electrical connections extending depth-wise into
the image sensor wafer from the frontside, the step of modifying
the frontside including: (a) etching recesses, (b) forming lined
recesses by depositing electrically insulating liner inside the
recesses, (c) depositing the electrical connections, each of the
electrical connection connecting a portion of bottom of one of the
lined recesses to electrical interconnects of one of the pixel
arrays, and (d) depositing electrically insulating material, the
insulating material filling the lined recesses; and modifying
backside of the image sensor wafer to expose the electrical
connections.
6. The method of claim 5, the step of etching recesses comprising
etching recesses at least to depth beyond location of photodiodes
of the pixel arrays.
7. The method of claim 6, further comprising: uniformly thinning
the electrically insulating material; and bonding the electrically
insulating material to a carrier wafer.
8. The method of claim 1, the step of exposing the electrical
connections comprising etching portions of the backside to gain
access to the electrical connections.
9. The method of claim 8, the step of etching comprising etching
portions of a dielectric layer to gain access to the electrical
connections.
10. The method of claim 1, in the step of modifying frontside, the
electrical connections being disposed on an electrically insulating
liner; and the step of flattening the backside comprising (a)
uniformly thinning the backside to depth of the electrically
insulating liner, and (b) producing electrically insulating layer,
on the backside, the electrically insulating layer providing the
flat backside surface.
11. The method of claim 10, the step of flattening the backside
further comprising producing elements for modifying incident light,
the elements being at least partially encapsulated by the
electrically insulating layer.
12. The method of claim 10, the step of flattening the backside
comprising: depositing oxide layer with elements for modifying
incident light; and uniformly thinning the oxide layer to provide
the flat backside surface.
13. The method of claim 3, further comprising: in the step of
modifying frontside, disposing the electrical connections on an
electrically insulating liner; before the step of exposing the
electrical connections, (a) uniformly thinning the backside to
depth of the electrically insulating liner, and (b) producing
electrically insulating layer on the backside; in the step of
exposing, etching portions of the electrically insulating layer to
gain access to the plurality of electrical connections; and in the
step of flattening, filling the portions with electrically
conductive material and uniformly thinning the backside to provide
the flat backside surface.
14. The method of claim 3, the step of modifying frontside
comprising forming recesses, each of the electrical connections
connecting bottom of recesses to circuitry of one of the pixel
arrays.
15. The method of claim 3, the step of exposing the electrical
connections comprising etching portions of the backside to gain
access to the electrical connections.
16. The method of claim 15, the step of etching comprising etching
portions of a dielectric layer to gain access to the electrical
connections.
17. The method of claim 5, the step of modifying backside of the
image sensor wafer to expose the electrical connections comprising
etching portions of the backside to gain access to the electrical
connections.
18. The method of claim 17, the step of etching portions of the
backside comprising etching portions of a dielectric layer to gain
access to the electrical connections.
Description
BACKGROUND
[0001] The demand for advances in digital camera performance is
ever increasing. Consumers wish to capture photos and videos with
high resolution and high sensitivity. Improved spatial resolution
may be achieved by reducing the area of individual image sensor
pixels, such that a greater number of pixels may be accommodated by
the same image sensor area. However, a reduction in pixel size
generally reduces the light collected by each pixel and thus leads
to a decrease in light sensitivity. Decreased light sensitivity
adversely affects camera performance in low-light situations, for
example nighttime photography, and in capture of dynamic scenes
with fast moving objects, such as scenes of sporting events. One
solution to this problem, which is implemented in commonly
available digital single-lens reflex camera, is to provide an image
sensor with a significantly larger area. This allows for
incorporating a larger number of pixels without reducing the area
of individual pixels. Unfortunately, such sensors are associated
with greater cost, both for the image sensor itself and for the
imaging objective required for properly imaging a scene onto the
enlarged sensor, which precludes use in many applications.
[0002] Backside illuminated image sensors offer an alternative
solution. In conventional frontside illuminated image sensors light
incident on a pixel must pass through a layer of electrical
connections before reaching the photosensitive element. This is
associated with a loss of light. Backside illuminated image sensors
are oriented, seen from the point of view of incident light, such
that the layer of electrical connections is located below the
photosensitive element. Accordingly, incident light may reach the
photosensitive elements without being affected by the electrical
connections, which results in greater light collection efficiency
and, thus, improved sensitivity.
[0003] Color image capture is provided by disposing a color filter
on top of the image sensor pixel array. Different pixels are
associated with different color coatings, where each type of color
coating transmits a certain color. For example, in a Bayer type
color image sensor, the color filter includes three different types
of color coatings, R, G, and B, configured for transmission of red,
green, and blue light, respectively. Color pixels, providing color
data, may be formed by grouping together one pixel with R-type
coating, two pixels with G-type coating, and one pixel with B-type
coating.
SUMMARY
[0004] In an embodiment, a method for manufacturing a backside
illuminated color image sensor includes (a) modifying the frontside
of an image sensor wafer, having pixel arrays, to produce
electrical connections to the pixel arrays, wherein the electrical
connections extend depth-wise into the image sensor wafer from the
frontside, and (b) modifying the backside of the image sensor wafer
to expose the electrical connections.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 illustrates a backside illuminated image sensor
pixel, according to an embodiment.
[0006] FIGS. 2A and 2B illustrate, in top plan view and
cross-sectional side view, respectively, a backside illuminated
color image sensor, according to an embodiment.
[0007] FIG. 3 illustrates an image sensor wafer including a
plurality of backside illuminated color image sensors, according to
an embodiment.
[0008] FIG. 4 illustrates a method for manufacturing an image
sensor wafer including a plurality of backside illuminated color
image sensors, wherein the method optionally includes manufacturing
a plurality of backside illuminated color image sensors, according
to an embodiment.
[0009] FIG. 5 illustrates certain steps of the method of FIG. 4,
according to an embodiment.
[0010] FIG. 6 illustrates a method for modifying the frontside of
an image sensor wafer, to perform a portion of the method of FIG.
4, according to an embodiment.
[0011] FIG. 7 illustrates certain steps of the method of FIG. 4,
according to an embodiment.
[0012] FIG. 8 is a diagram that illustrates a method for applying a
color filter to an image sensor wafer, which may be used in the
method of FIG. 4, according to an embodiment.
[0013] FIG. 9 illustrates a method for modifying the backside of an
image sensor wafer, to perform a portion of the method of FIG. 4,
wherein a color filter is applied to the backside of the image
sensor wafer before exposing electrical connections, according to
an embodiment.
[0014] FIG. 10 illustrates steps of the method of FIG. 9, according
to an embodiment.
[0015] FIG. 11 illustrates a backside illuminated image sensor
pixel manufactured using the methods of FIGS. 4, 6, and 9,
according to an embodiment.
[0016] FIG. 12 illustrates a method for modifying the backside of
an image sensor wafer, to perform a portion of the method of FIG.
4, wherein a color filter is applied to the backside of the image
sensor wafer after exposing electrical connections, according to an
embodiment.
[0017] FIG. 13 illustrates steps of the method of FIG. 12,
according to an embodiment.
[0018] FIG. 14 illustrates a backside illuminated image sensor
pixel manufactured using the methods of FIGS. 4, 6, and 12,
according to an embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0019] FIG. 1 illustrates one exemplary backside illuminated (BSI)
pixel 100 that represents an individual pixel in a BSI color image
sensor. BSI pixel 100 has a backside 110 and a frontside 120. BSI
pixel 100 includes a photodiode 131, located in a photodiode layer
130, metal interconnects 141 located in a pixel array circuitry
layer 140, and a color filter 150. Photodiode layer 130, pixel
array circuitry layer 140, and color filter 150 span the extent of
an array of BSI pixels 100 in a BSI color image sensor. Metal
interconnects 141 are a portion of the electrical circuitry
required to read out electrical signals generated by the array of
photodiodes 100. For clarity of illustration, not all metal
interconnects 141 are labeled in FIG. 1. BSI pixel 100 may include
fewer or more metal interconnects 141, and/or differently arranged
metal interconnects 141, than illustrated in FIG. 1, without
departing from the scope hereof. BSI pixel 100 includes a color
filter 150 for selecting a desired spectral portion of illumination
160 incident on backside 110, for example red, green, or blue
light. Optionally, BSI pixel 100 further includes an additional
layer, not illustrated in FIG. 1, located between photodiode layer
130 and color filter 150, for modifying illumination 160. This
optional layer may include opaque elements for preventing
illumination 160 incident on one BSI pixel 100 from reaching a
photodiode 131 of a neighboring BSI pixel 100, and/or include an
anti-reflective coating. Pixel array circuitry layer 140 may be
bonded to a carrier substrate 145.
[0020] Photodiode layer 130 is located between backside 110 and
pixel array circuitry layer 140, such that illumination 160
incident on BSI pixel 100 may reach photodiode 131 without having
to pass through pixel array circuitry layer 140. Accordingly, BSI
pixel 100 has a light acceptance cone 170 which is unaffected by
metal interconnects 141. A hypothetical frontside acceptance cone
180 illustrates the light acceptance cone for a corresponding
frontside illuminated image sensor receiving illumination through
frontside 120. Due to the presence of metal interconnects 141,
hypothetical frontside acceptance 180 cone is significantly smaller
than light acceptance cone 170. Thus, BSI pixel 100 is more
photosensitive than the corresponding hypothetical frontside
illuminated pixel.
[0021] One challenge associated with BSI color image sensors is
gaining access to metal interconnects 141, as pixel array circuitry
layer 140 is not readily accessible from backside 110. Typically,
BSI image sensor manufacturing includes gaining access to pixel
array circuitry layer 140 by etching deep trenches from backside
110 into pixel array circuitry layer 140. According to one
conventional method, the deep trenches is etched prior to applying
color filter 150. However, the deep trenches affect the process for
applying color filter 150 and cause non-uniform thickness of color
filter 150. This in turn leads to striations in color images
captured using the sensor. According to another conventional
method, color filter 150 is applied prior to etching the deep
trenches and then masked while etching the deep trenches.
Generally, the deep trenches must be etched into silicon, which
imposes challenging requirements to the masking of color filter
150.
[0022] Disclosed herein are methods that overcome these challenges.
In the presently disclosed methods, trenches with electrical
connections to metal interconnects 141 are formed from frontside
120, prior to bonding pixel array circuitry layer 140 to carrier
substrate 145. The trenches extend through pixel array circuitry
layer 140 and into photodiode layer 130. In a subsequent step,
backside 110 is modified, using less invasive processes than those
associated with conventional methods, to gain access to the
electrical connections of the trenches. The methods disclosed
herein further allow for applying color filter 150 to a flat
surface, as opposed to a surface with deep trenches.
[0023] FIGS. 2A and 2B illustrate one exemplary BSI color image
sensor 200. FIG. 2A shows BSI color image sensor 200 in top plan
view. FIG. 2B shows a portion of BSI color image sensor 200 in
cross-sectional side view, where the cross section is taken along
line 2B-2B in FIG. 2A. FIGS. 2A and 2B are best viewed together.
FIGS. 2A and 2B are not drawn to scale. BSI color image sensor 200
includes a pixel array 210 of BSI pixels such as BSI pixel 100 of
FIG. 1, a peripheral area 220 located next to pixel array 210, and
electrical connection pads 231. For clarity of illustration, not
all electrical connection pads 231 are labeled in FIG. 2A.
Electrical connection pads 231 provide electrical connections to
the circuitry associated with pixel array 210. Electrical
connection pads 231 may be used, for example, to readout signals
generated by photodiodes, such as photodiode 131, of pixels of
pixel array 210, and/or apply voltages to the photodiodes.
[0024] BSI color image sensor 200 may include fewer or more
electrical connection pads 231 than illustrated in FIG. 2A, without
departing from the scope hereof. Likewise, BSI color image sensor
200 may include more peripheral areas 220 than illustrated in FIG.
2A, without departing from the scope hereof. Additionally pixel
array 210, peripheral area 220, and electrical connection pads 231
may be arranged differently from what is shown in FIG. 2A, without
departing from the scope hereof.
[0025] As illustrated in FIG. 2B, BSI color image sensor 200 has a
backside 290. BSI color image sensor 200 includes a photodiode
layer 240, which includes a plurality of photodiodes 211, each
photodiode 211 corresponding to a different pixel of pixel array
210. Photodiode layer 240 is disposed on a circuitry layer 250,
which includes metal interconnect layers 212 located in pixel array
210 and metal interconnect layers 222 located in peripheral area
220. Metal interconnect layers 212 are an embodiment of metal
interconnects 141 of FIG. 1. In an embodiment, metal interconnect
layers 212 include three layers of metal interconnects, and metal
interconnect layers 222 include four layers of metal interconnects.
However, metal interconnect layers 212 and 222 may include other
numbers of layers of metal interconnects, without departing from
the scope hereof. At least a portion of metal interconnect layers
222 are communicatively coupled with metal interconnect layers 212.
Photodiode layer 240 and circuitry layer 250 are embodiments of
photodiode layer 130 and pixel array circuitry layer 140,
respectively, of FIG. 1. In an embodiment, photodiode layer 240 is
a silicon layer with embedded photodiodes 211. In an embodiment,
circuitry layer 250 is a silicon oxide layer with embedded metal
interconnect layers 212 and 222.
[0026] Each of at least a portion of electrical connection pads 231
are formed by manufacturing an electrical connection 230 from a
front-facing surface of circuitry layer 250 to a location
accessible from backside 290. Electrical connection 230 is formed
during frontside processing of BSI color image sensor 200.
Electrical connection 230 may be a layer of aluminum-copper alloy
with thickness of, for example, between 0.5 micron and 1.5 micron.
Electrical connection 230 contacts the front-most layer of metal
interconnect layers 222. In an embodiment, the interface between
photodiode layer 240 and circuitry layer 250 includes, in the
region adjacent to electrical connection 230, a shallow layer of
electrically insulating material 245 such as silicon oxide.
Electrically insulating material 245 may be located in photodiode
layer 240, as illustrated in FIG. 2B, in circuitry layer 250, or in
a combination thereof, without departing from the scope hereof.
Electrically insulating material 245 reduces the risk of electrical
shortage between photodiode layer 240 and circuitry layer 250 in
the region adjacent to electrical connection 230. In some
embodiments, for clarity not illustrated in FIG. 2B, electrical
connection 230 is electrically insulated from photodiode layer 240
and circuitry layer 250. Such electrical insulation may be
provided, for example, by including an insulating liner at the
interfaces of electrical connection 230 with photodiode layer 240
and circuitry layer 250.
[0027] An electrically insulating layer 260, such as silicon oxide,
is disposed on circuitry layer 250 and electrical connection 230.
An optical layer 280 is disposed on photodiode layer 240. Optical
layer 280 includes a color filter, for providing color image
capture capability. Optionally, optical layer 280 includes
additional elements for modifying illumination incident on backside
290, such as opaque elements for preventing illumination incident
on one pixel from reaching a photodiode of a neighboring pixel
and/or an anti-reflective coating. Optical layer 280 may have
extent different from what is shown in FIG. 2B and, for example,
cover larger portions of photodiode layer 240, without departing
from the scope hereof. In an embodiment, electrically insulating
layer 260 is bonded to a carrier substrate 270. Carrier substrate
270 may serve to provide structural stability and robustness during
manufacturing, and may be significantly thicker than what is
indicated by FIG. 2B.
[0028] FIG. 3 illustrates one exemplary image sensor wafer 300
manufactured using methods disclosed herein. Image sensor wafer 300
includes a plurality of BSI color image sensors 200 (FIGS. 2A and
2B). A close-up 310 of image sensor wafer 300 shows a group of four
BSI color image sensors 200. Between BSI color image sensors are
streets 330. When singulating BSI color image sensors 200 from
image sensor wafer 300, image sensor wafer 300 is cut along streets
300. Streets 300 may include electrical connection pads 331 for
testing of BSI color image sensors 200 during manufacturing.
Electrical connection pads 331 may be formed using the same methods
as electrical connection pads 231, or other methods known in the
art.
[0029] FIG. 4 illustrates one exemplary method 400 for
manufacturing a BSI color image sensor, such as BSI color image
sensor 200 (FIGS. 2A and 2B), or a wafer of BSI color image
sensors, such as image sensor wafer 300 (FIG. 3). FIG. 5
schematically shows examples of certain steps of method 400. FIGS.
4 and 5 are best view together.
[0030] In a step 410, method 400 receives an image sensor wafer.
For example, method 400 receives an image sensor wafer with a
plurality of image sensors 501 (FIG. 5). In the present disclosure,
the term "image sensor" may refer to a finished image sensor or the
state of the same during manufacturing thereof. FIG. 5 shows image
sensor 501 in a cross-sectional side-view, where the cross-section
is taken along line 2B-2B in FIG. 2A. Image sensor 501 includes
circuitry layer 250 (FIG. 2B), a photodiode layer 540, and an
electrically insulating liner 510. Image sensor 501 has frontside
550 and backside 560. Photodiode layer 540 is an embodiment of
photodiode layer 240 (FIG. 2B), and includes a plurality of
photodiodes 211 (FIG. 2B). Optionally, photodiode layer 540
includes electrically insulating material 245 (FIG. 2B).
Electrically insulating liner 510 has an opening that exposes a
portion of metal interconnect layer 222 (FIG. 2B). Electrically
insulating liner 510 is, for example, silicon oxide, silicon
nitride, a combination thereof, or a material that includes silicon
oxide and/or silicon nitride. Electrically insulating liner 510 may
have thickness in the range between 50 nanometers and 500
nanometers.
[0031] In a step 420, the frontside of the image sensor wafer is
modified to produce electrical connections to the pixel arrays,
wherein the electrical connections extend depth-wise into the
interior of the image sensor wafer. For example, an image sensor
wafer including a plurality of image sensors 501 having frontsides
550 is modified to produce, from each image sensor 501, an image
sensor 502 having a frontside 550' and electrical connections 230
(FIGS. 2 and 5). In an embodiment, step 420 includes a step 422,
wherein the electrical connections are produced to extend to a
depth at least beyond the location of the photodiodes of the pixel
arrays. For example, as illustrated by image sensor 502, electrical
connection 230 extends depth-wise into the interior of image sensor
502 to a depth that is beyond the location of photodiode 211. In an
embodiment, step 420 includes a step 424, wherein the electrical
connections are electrically insulated. For example, frontsides 550
of image sensors 501 are modified to include electrically
insulating liners 520, as shown for image sensor 502. Electrically
insulating liner 520 insulates one or more electrical connections
230 from circuitry layer 250 and photodiode layer 540. Electrically
insulating layer 520 includes a portion of electrically insulating
layer 510. Electrically insulating liner 520 is, for example,
silicon oxide, silicon nitride, a combination thereof, or a
material that includes silicon oxide and/or silicon nitride.
Electrically insulating liner 520 may have thickness in the range
between 50 nanometers and 500 nanometers. In an embodiment, step
420 includes a step 426, wherein an electrically insulating layer
is formed on the frontside of the image sensor wafer. The
electrically insulating layer has a flat front-facing surface,
which is bonded to a carrier wafer. For example, as illustrated by
image sensor 502, an electrically insulating layer 530 is deposited
on the frontside of the image sensor wafer to cover the frontside
including electrical connections 230 and exposed portions of
electrically insulating liners 520 of all image sensors 502 on the
image sensor wafer. Subsequently, the image sensor wafer is bonded
to a carrier wafer 535, as shown for image sensor 502 which is
bonded to a portion of carrier wafer 535. Electrically insulating
layer 530 includes, for example, silicon oxide. Electrically
insulating layer 530 and carrier wafer 535 are embodiments of
electrically insulating layer 260 (FIG. 2B) and carrier wafer 270
(FIG. 2B).
[0032] In a step 430, the backside of the image sensor wafer is
modified to expose the electrical connections formed in step 420,
thereby gaining access to the electrical connections from the
backside. Step 430 includes a step 432, wherein a color filter is
applied to the image sensor wafer backside. For example, the
backside of the image sensor wafer is modified to expose electrical
connections 230 through backsides 560 of image sensors 502, and
apply a color filter to backsides 560. This results in the
production of an embodiment of image sensor wafer 300.
[0033] Optionally, method 400 includes a step 440, wherein BSI
image sensors are singulated from the image sensor wafer. For
example, image sensor wafer 300 (FIG. 3), is cut along streets 330
(FIG. 3) to cingulate BSI color image sensors 200 (FIGS. 2 and
3).
[0034] FIG. 6 illustrates one exemplary method 600 for modifying
the frontside of an image sensor wafer to produce electrical
connections that may be made accessible from the backside of the
image sensor wafer. Method 600 is an embodiment of step 420 of
method 400 (FIG. 4). FIG. 7 schematically shows, together with FIG.
5, examples of certain steps of method 600. FIGS. 5, 6, and 7 are
best view together. In a step 610, recesses are etched from the
image sensor wafer frontside into the interior of the image sensor
wafer. In an embodiment, step 610 includes a step 612, wherein the
recesses are etched to a depth that is beyond the location of
photodiodes of the pixel arrays of the image sensor wafer. For
example, recesses are etched into frontsides 550 of image sensors
501 (FIG. 5) to produce image sensors 701 (FIG. 7). Image sensor
701 has a frontside 550'', which includes at least one recess 710.
Recess 710 extends through circuitry layer 250 (FIGS. 2 and 5) into
photodiode layer 540 (FIG. 5), beyond the location of photodiodes
211 (FIGS. 2 and 5). In an embodiment, recess 710 extends between 2
micron and 4 micron into photodiode layer 540. In an embodiment,
the bottom of recess 710, i.e., the portion of recess 710 closest
to backside 560 of image sensor 701, is planar.
[0035] In a step 620, an electrically insulating liner is deposited
in the recesses to form lined recesses. In one embodiment, all
surface portions of the recesses are lined. In another embodiment,
only surface portions of the recesses, which are associated with
electrical connections formed in subsequent step 630 are lined. For
example, an electrically insulating liner is deposited inside each
recess 710 to form, together with portions of electrically
insulating liner 510 (FIG. 5), electrically insulating liner 520
(FIG. 5) of image sensor 702 (FIG. 7). Although image sensor 501
(FIG. 5) is illustrated as including electrically insulating liner
510, electrically insulating line 510 may be omitted from image
sensor 510 and instead produced in step 620, without departing from
the scope hereof.
[0036] In a step 630, electrical connections are deposited on the
frontside of the image sensor wafer, such that each electrical
connection connects a portion of the bottom of a lined recess,
formed in step 620, to the electrical interconnects of a pixel
array. For example, electrical connections 230 are deposited on
electrically insulating liners 520 (FIG. 5), as shown for image
sensor 702, such that each electrical connection 230 contacts metal
interconnect layer 222 and the portion of recess 710 closest to
backside 560. This results in image sensor 702 having a frontside
surface 550' and recess 710'. In one embodiment, a plurality of
electrical connections are deposited in a single recess. For
example, recess 710 is an elongated trench having a longer
dimension in the plane of the image sensor wafer, and a plurality
of electrical connections 230 are deposited in recess 710 at a
respective plurality of positions along the longer dimension of
recess 710. In another embodiment, electrical connections are
deposited such that no recess contains more than one electrical
connection. For example, each electrical connection 230 is
deposited in a different recess 710.
[0037] In a step 640, an electrically insulating layer is deposited
on the image sensor wafer frontside. The electrically insulating
layer fills the recesses formed in step 610 through 630. The
electrically insulating layer provides structural support for the
electrical connections formed in step 630, when these electrical
connections are exposed from the backside in subsequent step 430 of
method 400 (FIG. 4). In an example, electrically insulating layer
530 (FIG. 5) is deposited on the frontside of an image sensor wafer
including a plurality of image sensors 702 (FIG. 7) having
frontsides 550'. As illustrated for image sensor 502 (FIG. 5),
electrically insulating layer 530 fills recess 710'. Optionally,
step 640 includes a step 642, wherein the electrically insulating
layer is deposited such that it covers the frontside of the image
sensor wafer. This is illustrated by electrically insulating layer
530 (FIG. 5) that covers the entire frontside of image sensor 502
(FIG. 5).
[0038] In an optional step 650, relevant for embodiments of method
600 that include optional step 642, the electrically insulating
layer is uniformly thinned to provide a flat frontside surface,
such as that illustrated by electrically insulating layer 530 (FIG.
5). Chemical-mechanical polishing methods may be utilized to
uniformly thin the electrically insulating layer. In a subsequent
optional step 660, the flat frontside surface is bonded to a
carrier wafer. For example an image sensor wafer including a
plurality of image sensors 502 (FIG. 5), without carrier wafer 535
(FIG. 5), is bonded to carrier wafer 535.
[0039] FIG. 8 is a diagram 800 illustrating application of a color
filter to an image sensor wafer 810 that includes a plurality of
image sensors 820. The general color filter formation process
typically consists of (a) applying photoresist to image sensor
wafer 810, (b) develop portions of the applied photoresist, by
exposing these portions to light, to form respective color filter
portions, and (c) removing undeveloped photoresist. In the case of
forming a Bayer type color filter, steps (a), (b), and (c) are
repeated for three different color types of photoresist, where each
color type is developed for portions of image sensor wafer 810
corresponding to different pixels of image sensor 820. Diagram 800
thus illustrates one exemplary method for performing at least a
portion of step 432 of method 400 (FIG. 4). For clarity of
illustration, only one image sensor 820 is labeled in FIG. 8. FIG.
8 shows image sensor wafer 810 and image sensors 820 in top plan
view. Photoresist is applied to a local area 830 of image sensor
wafer 810. The support structure is spun about a rotation axis 840
in a direction 850. Rotation axis 840 is substantially
perpendicular to the plane of image sensor wafer 810, and the
backside surfaces of image sensors 820. In this example, local area
830 and rotation axis 840 are centered on image sensor wafer 810.
As image sensor wafer 810 spins about rotation axis 840, the
photoresist disperses from local area 840 in a radially outward
direction indicated by arrows 860 (only one arrow labeled in FIG.
8). This results in coating of the backside surfaces of image
sensors 820, as well as other exposed portions of image sensor
wafer 810. If deep recesses are present on the surface of image
sensor wafer 810, to which the photoresist is applied, these
recesses may distort the radially outward from of photoresist
indicated by arrows 860. For example, if the recesses are elongated
trenches, photoresist may preferably travel along these trenches.
Distortion of the radially outward flow may in turn lead to a
non-uniform coating thickness, and thus degraded performance of the
color filter. Accordingly, it is preferred to apply the color
filter to a flat surface.
[0040] FIG. 9 illustrates one exemplary method 900 for modifying
the backside of an image sensor wafer, wherein a color filter is
applied prior to exposing electrical connections formed during
frontside processing of the image sensor wafer. Method 900 is an
embodiment of step 430 of method 400 (FIG. 4). FIG. 10
schematically illustrates, by example, steps of method 900. FIGS. 9
and 10 are best view together.
[0041] In a step 910, at least a portion of the image sensor wafer
is flattened to provide a flat backside surface of the image sensor
wafer. In one embodiment, the full backside surface of the image
sensor wafer is made flat. In another embodiment, portions of the
backside surface near the perimeter of the wafer in areas not
occupied by image sensors may deviate from flatness. Image sensor
1001 of FIG. 10 is an embodiment of image sensor 502 of FIG. 5, and
is identical to image sensor 502 at least from backside 560 (FIG.
5) to the interface between photodiode layer 540 and circuitry
layer 250. Image sensor 1001 is shown in the same view as image
sensor 502. However, for illustrative clarity, only the portion of
image sensor 1001 from backside 560 to the interface between
photodiode layer 540 and circuitry layer 250 is shown in FIG. 10.
Image sensor 1001 may be identical to image sensor 502 (FIG. 5). In
an example of step 910, the backside of an image sensor wafer
including a plurality of image sensors 1001 is processed to provide
a flat backside surface. This results in the production of an image
sensor wafer including a plurality of image sensors 1002 having a
flat backside surfaces 560'. Accordingly, each image sensor 1001 of
the image sensor wafer is modified to form image sensor 1002.
[0042] In an embodiment, step 910 includes a step 912, wherein the
backside of the image sensor wafer is uniformly thinned to provide
a flat surface. Chemical-mechanical polishing methods may be
utilized to uniformly thin the backside of the image sensor wafer.
For example, an image sensor wafer including a plurality of image
sensors 1001 is uniformly thinned until electrically insulating
liner 520 (FIG. 5) is exposed. As a result, for each image sensor
1001, photodiode layer 540 is uniformly thinned to produce an image
sensor 1002. Image sensor 1002 has flat backside surface 560' and a
photodiode layer 540' that is thinner than photodiode layer 540 of
image sensor 1001.
[0043] Optionally, step 910 further includes a step 914, wherein an
optical layer is formed on the backside of the image sensor wafer.
The optical layer may include elements for modifying incident
light, for example to prevent or reduce cross talk between
neighboring pixels of individual pixel arrays. In embodiments of
step 910 that include step 914, the optical layer provides the flat
backside surface. Step 914 is illustrated by the inclusion of an
optical layer 1010 in image sensor 1002. Manufacturing of optical
layer 1010 includes (a) depositing elements for modifying light
incident on flat backside surface 560' such that optical layer 1010
provides flat backside surface 1010. For example, an
anti-reflective coating may be deposited on the image sensor wafer
backside, followed by deposition of a metal grid encapsulated in an
electrically insulating material. The metal grid serves to reduce
or prevent illumination incident on one pixel from reaching a
photodiode of a neighboring pixel. The electrically insulating
material may be or include silicon oxide. Finally, the electrically
insulating material is uniformly thinned, for example using
chemical-mechanical polishing methods, to provide flat backside
surface 560'.
[0044] In a step 920, a color filter is applied to the flat
backside surface formed in step 910. In an embodiment, step 920
includes three, or more, sequential steps of applying a different
color filter coating to the flat backside surface of the image
sensor wafer, using the method illustrated in FIG. 8. For example,
green, red, and blue color filter coatings are sequentially applied
to form a Bayer-type color filter. In an example, step 920 results
in the formation of a color filter 1020 on flat backside surface
560' of each image sensor 1002 of an image sensor wafer. Thus, at
least some of image sensors 1002, of an image sensor wafer, are
modified to produce respective image sensors 1003. Each image
sensor 1003 has a backside surface 560'' that includes color filter
1020.
[0045] In a step 930, the electrical connections formed in step 420
of method 400 (FIG. 4) are exposed. For example, backside 560'' of
each image sensor 1003 is modified to gain access to electrical
connections 230, as illustrated for image sensor 1004. Image sensor
1004 has backside surface 560'''. In an embodiment, step 930
includes a step 932, wherein portions of the backside surface of
the image sensor wafer are etched to expose the electrical
connections. For example, for each image sensor 1003, portions of
backside surface 560'' are etched to the depth of electrical
connection 230 to produce image sensor 1004. This includes etching
through optional optical layer 1010 and electrically insulating
liner 520 at locations coinciding with electrical connections 230,
thus forming electrically insulating layer 520' and optical layer
1010'. Although FIG. 10 shows image sensor 1004 as having all of
the bottom of electrical connection 231 exposed, image sensor 1004
may have only a portion of the bottom of electrical connection 231
exposed, without departing from the scope hereof. The etching
process in step 932 does not involve etching a deep layer of
silicon. Therefore, the masking of the color filters, such as color
filters 1020, is less demanding than the corresponding masking
required in conventional methods where electrical access is
achieved by etching several micron into silicon.
[0046] FIG. 11 illustrates one exemplary BSI color image sensor
1100 formed by method 400 (FIG. 4), including step 440 and with
steps 420 and 430 implemented according to methods 600 (FIG. 6) and
900 (FIG. 9), respectively. BSI color image sensor 1100 is an
embodiment of BSI color image sensor 200 (FIG. 2). BSI color image
sensor 1100 is shown in cross-sectional side view along line 2B-2B
of FIG. 2A. BSI color image sensor 1100 is composed of (a) the
portion of image sensor 1004 (FIG. 10) that is between backside
surface 560''' and the interface of photodiode layer 540' and
circuitry layer 250, as discussed in connection with image sensor
1001 of FIG. 10, and (b) the portion of image sensor 502 (FIG. 5)
that is between frontside 550' and the interface of photodiode
layer 540 and circuitry layer 250. The exposed portion of
electrical connection 230 forms an electrical connection pad 1110,
such that BSI color image sensor 1100 may include a plurality of
electrical connection pads 1110.
[0047] FIG. 12 illustrates one exemplary method 1200 for modifying
the backside of an image sensor wafer, wherein a color filter is
applied after exposing electrical connections formed during
frontside processing of the image sensor wafer. Method 1200 is an
embodiment of step 430 of method 400 (FIG. 4). FIG. 13
schematically illustrates, by example, steps of method 1200. FIGS.
12 and 13 are best view together.
[0048] In an optional step 1210, method 1200 performs step 912 of
method 900 (FIG. 9). For example, an image sensor wafer including a
plurality of image sensors 1001 (FIG. 10) is uniformly thinned
until electrically insulating liners 520 (FIGS. 5 and 10) are
exposed. This is illustrated by image sensor 1301 (FIG. 13) having
backside 1360. FIG. 13 illustrates image sensor 1301 in a view
equivalent to the view of image sensor 1001 of FIG. 10. In a
subsequent optional step 1220, method 1200 performs step 914 of
method 900 (FIG. 9). Step 1220 is illustrated by the inclusion of
an optional optical layer 1310 in image sensor 1301. Optical layer
1310 is similar to optical layer 1010 (FIG. 10) but may, for
example, have thickness different from optical layer 1010.
[0049] In a step 1230, the backside of the image sensor wafer is
modified to expose the electrical connections formed in step 420 of
method 400 (FIG. 4). For example, an image sensor wafer including a
plurality of image sensors 1301 is modified to produce, from each
of at least some of image sensors 1301, an image sensor 1302. Image
sensor 1302 has backside 1360', optical layer 1310', and
electrically insulating liner 520', which provide access to
electrical connections 230. In an embodiment, step 1230 includes a
step 1232, wherein method 1200 performs step 932 of method 900, as
discussed in connection with FIGS. 9 and 10.
[0050] In a step 1240, a flat backside surface of the image sensor
is provided. In one embodiment, the full backside surface of the
image sensor wafer is made flat. In another embodiment, portions of
the backside surface near the perimeter of the wafer in areas, not
occupied by image sensors, may deviate from flatness. In an
example, the backside of an image sensor wafer, including a
plurality of image sensors 1302, is modified to have a flat
backside surface. In an embodiment, step 1240 includes steps 1242
and 1244. In step 1242, backside access areas to the electrical
connections are filled with an electrically conductive material.
For example, for each image sensor 1302 of an image sensor wafer,
areas above electrical connections 230 are filled with an
electrically conductive material 1320, to form an image sensor
1303. Image sensor 1303 has backside 1360'', which includes
electrically conductive material 1320 located on the exposed
portion of electrical connection 230. Electrically conductive
material 1320 may be an aluminum-copper alloy. While FIG. 13
illustrates electrically conductive material 1320 as only partially
filling the access area above electrical connection 1320,
electrically conductive material 1320 may completely fill the
access area and even extend beyond the backside-facing surface of
optical layer 1310. In step 1244, the backside of the image sensor
wafer is uniformly thinned, using for example chemical-mechanical
polishing methods, to form a flat backside surface of the image
sensor wafer. For example, an image sensor wafer, including a
plurality of image sensors 1303, is uniformly thinned to form a
flat backside surface of the image sensor wafer. As a result,
backside 1360'' of each image sensor 1303 is uniformly thinned to
produce an image sensor 1304. Image sensor 1304 has a flat backside
surface 1360''', which includes optical layer 1310'' and
electrically conductive material 1320'. Optical layer 1310'' is a
thinned version of optical layer 1310'. Electrically conductive
material 1320' is either the same as electrically conductive
material 1320' or a thinned version thereof.
[0051] In a step 1250, method 1200 performs step 920 of method 900.
For example, method 1200 applies a color filter 1330 to backside
surface 1360' of each image sensor 1304 to form image sensors 1305.
Each image sensor 1305 has backside 1360'''', which includes color
filter 1330.
[0052] FIG. 14 illustrates one exemplary BSI color image sensor
1400 formed by method 400 (FIG. 4), including step 440 and with
steps 420 and 430 implemented according to methods 600 (FIG. 6) and
1200 (FIG. 12), respectively. BSI color image sensor 1400 is an
embodiment of BSI color image sensor 200 (FIG. 2). BSI color image
sensor 1400 is shown in cross-sectional side view along line 2B-2B
of FIG. 2A. BSI color image sensor 1400 is composed of (a) the
portion of image sensor 1305 (FIG. 13) that is between backside
surface 1360'''' and the interface of photodiode layer 540' and
circuitry layer 250, and (b) the portion of image sensor 502 (FIG.
5) that is between frontside 550' and the interface of photodiode
layer 540 and circuitry layer 250. The exposed portion of
electrically conductive material 1320' forms an electrical
connection pad 1410, such that BSI color image sensor 1400 may
include a plurality of electrical connection pads 1410.
[0053] Combinations of Features
[0054] Features described above as well as those claimed below may
be combined in various ways without departing from the scope
hereof. For example, it will be appreciated that aspects of one
backside illuminated color image sensor, or method for
manufacturing the same, described herein may incorporate or swap
features of another backside illuminated color image sensor, or
method for manufacturing the same, described herein. The following
examples illustrate possible, non-limiting combinations of
embodiments described above. It should be clear that many other
changes and modifications may be made to the methods and device
herein without departing from the spirit and scope of this
invention:
[0055] (A) A method for manufacturing a backside illuminated color
image sensor may include (i) modifying frontside of an image sensor
wafer, including pixel arrays, to produce electrical connections to
the pixel arrays, wherein the electrical connections extend
depth-wise into the image sensor wafer from the frontside, and (ii)
modifying backside of the image sensor wafer to expose the
electrical connections.
[0056] (B) In the method denoted as (A), the step of modifying
backside may include (i) flattening the backside of the image
sensor wafer to provide a flat backside surface, (ii) applying a
color filter to the flat backside surface, and (iii) exposing the
electrical connections.
[0057] (C) In the method denoted as (B), the step of exposing may
be performed before the step of flattening.
[0058] (D) In the method denoted as (B), the step of exposing may
be performed after the step of applying.
[0059] (E) In the methods denoted as (A) through (D), the step of
modifying frontside may include forming recesses and the electrical
connections, wherein each of the electrical connections connect
bottom of recesses to circuitry of one of the pixel arrays.
[0060] (F) In the methods denoted as (A) through (E), the step of
modifying frontside may include etching recesses.
[0061] (G) In the method denoted as (F), the step of modifying
frontside may further include depositing electrical connections,
each electrical connection connecting a portion of bottom of one of
the recesses to electrical interconnects of one of the pixel
arrays.
[0062] (H) In the method denoted as (G), the step of modifying
frontside may further include depositing electrically insulating
material, the insulating material filling the recesses.
[0063] (I) In the method denoted as (F), the step of modifying
frontside may further include forming lined recesses by depositing
electrically insulating liner inside the recesses.
[0064] (J) In the method denoted as (I), the step of modifying
frontside may further include depositing electrical connections,
each electrical connection connecting a portion of bottom of one of
the lined recesses to electrical interconnects of one of the pixel
arrays.
[0065] (K) In the method denoted as (J), the step of modifying
frontside may further include depositing electrically insulating
material, the insulating material filling the lined recesses.
[0066] (L) In the methods denoted as (F) through (K), the step of
etching recesses may include etching recesses at least to depth
beyond location of photodiodes of the pixel arrays.
[0067] (M) The methods denoted as (I) and (K), may further include
uniformly thinning the electrically insulating material, and
bonding the electrically insulating material to a carrier
wafer.
[0068] (N) In the methods denoted as (A) through (M), the step of
exposing the plurality of electrical connections may include
etching portions of the backside to gain access to the plurality of
electrical connections.
[0069] (O) In the method denoted as (N), the step of etching may
include etching portions of a dielectric layer to gain access to
the plurality of electrical connections.
[0070] (P) In the method denoted as (D), the step of modifying
frontside may include disposing the electrical connections on an
electrically insulating liner.
[0071] (Q) In the method denoted as (P), the step of flattening may
include (i) uniformly thinning the backside to depth of the
electrically insulating liner, and (ii) producing electrically
insulating layer, on the backside, wherein the electrically
insulating layer provides the flat backside surface.
[0072] (R) In the method denoted as (Q), the step of flattening may
further include producing elements for modifying incident light,
wherein the elements may be at least partially encapsulated by the
electrically insulating layer.
[0073] (S) In the methods denoted as (Q) and (R), the step of
flattening may include depositing an oxide layer with elements for
modifying incident light and uniformly thinning the oxide layer to
provide the flat backside surface.
[0074] (T) In the method denoted as (D), the step of modifying
frontside may include disposing the electrical connections on an
electrically insulating liner.
[0075] (U) In the method denoted as (T), the step of modifying
backside may further include, before the step of exposing: (i)
uniformly thinning the backside to depth of the electrically
insulating liner, and (ii) producing electrically insulating layer
on the backside.
[0076] (V) In the method denoted as (U), the step of exposing may
include etching portions of the electrically insulating layer to
gain access to the plurality of electrical connections.
[0077] (W) In the method denoted as (V), the step of flattening may
include filling the portions with electrically conductive material
and uniformly thinning the backside to provide the flat backside
surface.
[0078] (X) A backside illuminated color image sensor may include
(i) a plurality of electrical connection pads located on backside
of image sensor, (ii) a respective plurality of electrical
connections connecting the plurality of electrical connection pads
to front-facing portion of pixel array circuitry of the image
sensor, and (iii) a color filter disposed on backside of the image
sensor.
[0079] (Y) In the backside illuminated color image sensor denoted
as (X), each of the plurality of electrical connections, for all
portions thereof away from the plurality of electrical connection
pads and not contacting the pixel array circuitry, may be
surrounded by electrically insulating material.
[0080] (Z) The backside illuminated color image sensors denoted as
(X) and (Y) may include a pixel array layer that has a photodiode
sublayer with a photodiode array, and a circuitry sublayer of
electrical interconnects for the photodiode array; wherein each of
the plurality of electrical connections may be located in a
front-facing recess of the pixel array sublayer and on a
front-facing portion of the circuitry sublayer.
[0081] (AA) In the backside illuminated color image sensor denoted
as (Z), the front-facing recess may span full depth of the pixel
array layer.
[0082] (AB) The backside illuminated color image sensors denoted as
(Z) and (AA) may include a frontside layer covering front-facing
surface of the pixel array layer and spanning separation between
back-facing surface of the backside and the pixel array layer
[0083] (AC) In the backside illuminated color image sensor denoted
as (AB), the frontside layer may have uniform thickness in all
areas not coinciding with one of the plurality of electrical
connection pads.
[0084] (AD) In the backside illuminated color image sensors denoted
as (X) through (AD), the surface of the backside of the image
sensor may be flat.
[0085] Changes may be made in the above systems and methods without
departing from the scope hereof. It should thus be noted that the
matter contained in the above description and shown in the
accompanying drawings should be interpreted as illustrative and not
in a limiting sense. The following claims are intended to cover
generic and specific features described herein, as well as all
statements of the scope of the present method and device, which, as
a matter of language, might be said to fall therebetween.
* * * * *