U.S. patent application number 15/895668 was filed with the patent office on 2019-08-15 for image sensors with deep silicon etch and related methods.
This patent application is currently assigned to SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC. The applicant listed for this patent is SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC. Invention is credited to Swarnal BORTHAKUR, Marc Allen SULFRIDGE.
Application Number | 20190252333 15/895668 |
Document ID | / |
Family ID | 67394090 |
Filed Date | 2019-08-15 |
United States Patent
Application |
20190252333 |
Kind Code |
A1 |
BORTHAKUR; Swarnal ; et
al. |
August 15, 2019 |
IMAGE SENSORS WITH DEEP SILICON ETCH AND RELATED METHODS
Abstract
Implementations of image sensors may include a silicon layer
having a first side and a second side opposite the first side, an
opening extending into the silicon layer from the first side of the
silicon layer toward the second side, a via extending into the
silicon layer from the second side of the silicon layer, and a
conductive pad within the opening. The conductive pad may be
coupled to the via. The opening may include a fill material. At
least a portion of the fill material may form a plane that is
substantially parallel with the first side of the silicon layer.
The conductive pad may be exposed through an opening in the fill
material.
Inventors: |
BORTHAKUR; Swarnal; (Boise,
ID) ; SULFRIDGE; Marc Allen; (Boise, ID) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC |
Phoenix |
AZ |
US |
|
|
Assignee: |
SEMICONDUCTOR COMPONENTS
INDUSTRIES, LLC
Phoenix
AZ
|
Family ID: |
67394090 |
Appl. No.: |
15/895668 |
Filed: |
February 13, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2224/05562
20130101; H01L 2224/0557 20130101; H01L 24/05 20130101; H01L
21/76898 20130101; H01L 2224/05571 20130101; H01L 27/1464 20130101;
H01L 2224/05557 20130101; H01L 23/481 20130101; H01L 2224/05567
20130101; H01L 27/14636 20130101 |
International
Class: |
H01L 23/00 20060101
H01L023/00; H01L 27/146 20060101 H01L027/146; H01L 23/48 20060101
H01L023/48; H01L 21/768 20060101 H01L021/768 |
Claims
1. An image sensor comprising: a silicon layer comprising a first
side and a second side opposite the first side; an opening
extending into the silicon layer from the first side of the silicon
layer toward the second side; a via extending into the silicon
layer from the second side of the silicon layer; and a conductive
pad within the opening, the conductive pad coupled to the via;
wherein the opening comprises a fill material; wherein at least a
portion of the fill material forms a plane that is substantially
parallel with a plane formed by the first side of the silicon
layer; and wherein the conductive pad is exposed through an opening
in the fill material.
2. The image sensor of claim 1, further comprising a dielectric
layer between the silicon layer and the via.
3. The image sensor of claim 1, further comprising a dielectric
layer between the fill material and the silicon layer.
4. The image sensor of claim 1, further comprising a high
dielectric constant dielectric layer between the fill material and
the silicon layer.
5. The image sensor of claim 1, further comprising a second via
extending into the silicon layer from the second side of the via,
the second via coupled to the conductive pad.
6. The image sensor of claim 1, wherein the silicon layer is 6
micrometers thick and the opening is 2.5 micrometers deep.
7. The image sensor of claim 1, wherein the via comprises
copper.
8. (canceled)
9. An image sensor comprising: a silicon layer comprising a first
side and a second side opposite the first side; a first opening
extending through the silicon layer; a second opening extending
into the silicon layer from the first side of the silicon layer; a
via extending into the silicon layer from the second side of the
silicon layer; and a conductive pad within the second opening, the
conductive pad coupled to the via; wherein the opening comprises a
fill material; wherein at least a portion of the fill material
forms a plane that is substantially parallel with a plane formed by
the first side of the silicon layer; and wherein the conductive pad
is exposed through an opening in the fill material.
10. (canceled)
11. The image sensor of claim 10, wherein the first opening further
comprises a first portion wider than a second portion.
12. The image sensor of claim 9, wherein the silicon layer is 6
micrometers thick and the opening is 2.5 micrometers deep.
13. The image sensor of claim 9, further comprising a dielectric
layer between the silicon layer and the via.
14. The image sensor of claim 9, further comprising a dielectric
layer between the fill material and the silicon layer.
15. The image sensor of claim 9, further comprising a high
dielectric constant dielectric layer between the fill material and
the silicon layer.
16. A method for forming a conductive pad in an image sensor, the
method comprising: etching an opening into a second side of a
silicon layer; forming a via within the opening in the second side
of the silicon layer; etching an opening into a first side of a
silicon layer; forming a dielectric layer over the first side of
the silicon layer; etching through the dielectric layer to expose
the via; forming a conductive pad within the opening in the first
side of the silicon layer, the conductive pad coupled to the via;
filling the opening in the first side of the silicon layer with a
fill material; planarizing the fill material to form a plane
substantially parallel with a planed formed by the first side of
the silicon layer; and etching an opening through the fill material
to expose the conductive pad.
17. (canceled)
18. (canceled)
19. The method of claim 16, further comprising forming a dielectric
layer between the via and the silicon layer.
20. The method of claim 16, wherein the silicon layer is 6
micrometers thick and the opening is 2.5 micrometers deep.
Description
BACKGROUND
1. Technical Field
[0001] Aspects of this document relate generally image sensor
semiconductor packages (referred to herein as "image sensors").
More specific implementations involve the conductive pad region of
backside illumination (BSI) image sensors.
2. Background
[0002] Image sensors convey information related to an image by
communicating signals in response to incident electromagnetic
radiation. Image sensors are used in a variety of devices including
smart phones, digital cameras, night vision devices, medical
imagers, and many others. BSI image sensors may be used to improve
the light receiving efficiency of the image sensor, particularly
for specific light wavelengths.
SUMMARY
[0003] Implementations of image sensors may include a silicon layer
having a first side and a second side opposite the first side, an
opening extending into the silicon layer from the first side of the
silicon layer toward the second side, a via extending into the
silicon layer from the second side of the silicon layer, and a
conductive pad within the opening. The conductive pad may be
coupled to the via. The opening may include a fill material. At
least a portion of the fill material may form a plane that is
substantially parallel with the first side of the silicon layer.
The conductive pad may be exposed through an opening in the fill
material.
[0004] Implementations of image sensors may include one, all, or
any of the following:
[0005] A dielectric layer may be included between the silicon layer
and the via.
[0006] A dielectric layer may be included between the fill material
and the silicon layer.
[0007] A high dielectric constant dielectric layer may be included
between the fill material and the silicon layer.
[0008] A second via may be included that extends into the silicon
layer from the second side of the via, the second via electrically
coupled to the conductive pad.
[0009] A perimeter etch may be included through the silicon
layer.
[0010] The silicon layer may be substantially 6 micrometers thick
and the opening may be substantially 2.5 micrometers deep.
[0011] The via may include copper.
[0012] Implementations of image sensors may include a silicon layer
having a first side and a second side opposite the first side, a
first opening extending through the silicon layer, a second opening
extending into the silicon layer from the first side of the silicon
layer, a via extending into the silicon layer from the second side
of the silicon layer, and a conductive pad within the second
opening. The conductive pad may be coupled to the via. The opening
may include a fill material. At least a portion of the fill
material may form a plane that is substantially parallel with the
first side of the silicon layer. The conductive pad may be exposed
through an opening in the fill material.
[0013] Implementations of image sensors may include one, all, or
any of the following:
[0014] A dielectric layer may be included between the silicon layer
and the via.
[0015] A dielectric layer may be included between the fill material
and the silicon layer.
[0016] A high dielectric constant dielectric layer may be included
between the fill material and the silicon layer.
[0017] The first opening may extend around a perimeter of the
conductive pad.
[0018] The first opening may further include a first portion wider
than a second portion.
[0019] The silicon layer may be substantially 6 micrometers thick
and the opening may be substantially 2.5 micrometers deep.
[0020] Implementations of methods for forming conductive pad
regions of image sensors may include etching an opening into a
second side of a silicon layer, forming a via within the opening in
the second side of the silicon layer, etching an opening into a
first side of a silicon layer, forming a dielectric layer over the
first side of the silicon layer, etching through the dielectric
layer to expose the via, and forming a conductive pad within the
opening in the first side of the silicon layer. The conductive pad
may be coupled to the via. Implementations of methods for forming
conductive pad regions of image sensors may also include filling
the opening in the first side of the silicon layer with a fill
material, planarizing the fill material to form a plane
substantially parallel with the first side of the silicon layer,
and etching an opening through the fill material to expose the
conductive pad.
[0021] Implementations of methods for forming conductive pad
regions of image sensors may include one, all, or any of the
following:
[0022] The method may include forming a perimeter opening entirely
through the silicon layer.
[0023] The method may include forming a dielectric layer between
the via and the silicon layer.
[0024] The perimeter opening may be stepped.
[0025] The silicon layer may be substantially 6 micrometers thick
and the opening may be substantially 2.5 micrometers deep.
[0026] The foregoing and other aspects, features, and advantages
will be apparent to those artisans of ordinary skill in the art
from the DESCRIPTION and DRAWINGS, and from the CLAIMS.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Implementations will hereinafter be described in conjunction
with the appended drawings, where like designations denote like
elements, and:
[0028] FIG. 1 is a cross-section side view of a portion of an image
sensor;
[0029] FIG. 2A is a magnified cross-section side view of the
conductive pad region of an image sensor;
[0030] FIG. 2B is a top view of FIG. 2A.
[0031] FIG. 3 is a cross-section side view of a portion of a
conductive pad region of the image sensor of FIG. 2A;
[0032] FIG. 4 is a cross-section side view of a portion of a
conductive pad region of an image sensor with a deep silicon etch
without a fill material;
[0033] FIG. 5 is a cross-section side view of a portion of an
implementation of a conductive pad region of an image sensor with a
deep silicon etch;
[0034] FIG. 6 is a cross-section side view of a portion of another
implementation of a conductive pad region of an image sensor with a
deep silicon etch;
[0035] FIG. 7 is a cross-section side view of a portion of an
implementation of a conductive pad region of an image sensor with a
deep silicon etch and a perimeter etch through the silicon
layer;
[0036] FIG. 8 is a cross-section side view of a portion of an
implementation of a conductive pad region of an image sensor with a
deep silicon etch and a stepped perimeter etch through the silicon
layer;
[0037] FIG. 9 is a cross-section side view of an implementation of
a portion of an image sensor coupled with other conductive portions
of the image sensor;
[0038] FIGS. 10A-10F are bottom and top views illustrating a
process flow of the method for forming the image sensor of FIG. 5;
and
[0039] FIGS. 11A-11I are cross-section side views illustrating a
process flow of the method for forming the image sensor of FIG.
5.
DESCRIPTION
[0040] This disclosure, its aspects and implementations, are not
limited to the specific components, assembly procedures or method
elements disclosed herein. Many additional components, assembly
procedures and/or method elements known in the art consistent with
the intended image sensors will become apparent for use with
particular implementations from this disclosure. Accordingly, for
example, although particular implementations are disclosed, such
implementations and implementing components may comprise any shape,
size, style, type, model, version, measurement, concentration,
material, quantity, method element, step, and/or the like as is
known in the art for such image sensors, and implementing
components and methods, consistent with the intended operation and
methods.
[0041] Referring to FIG. 1, a cross-section side view of a portion
of an image sensor is illustrated. While the FIG. 1 illustrates
many components of an image sensor 2, such as a pixel array 4, this
disclosure is primarily focused on region 6, referred to herein as
the conductive pad region as it includes a conductive pad 8 that
may be used to either test the image sensor or electrically couple
the image sensor to external devices. This conductive pad is
typically located on the edge or near the edge of the die or in the
scribeline area of the die in various implementations, though in
some implementations the conductive pad may be located in the
interior of the die. While the components and methods of this
document are primarily taught within the context of a BSI image
sensor, it is understood that the devices and methods disclosed
herein can be applied to image sensors that are not BSI image
sensors, and even to semiconductor packages that are not image
sensors.
[0042] Referring to FIGS. 2A-2B, magnified cross-section views of a
conductive pad region, similar to region 6 of FIG. 1, are
illustrated. Specifically, FIG. 2A illustrates a magnified
cross-section side view of the conductive pad region of an image
sensor. Referring to FIG. 2A, the image sensor may include a
silicon layer 10. It is understood that where this disclosure
refers to a silicon layer, the silicon layer could be any type of
silicon layer including by non-limiting example, an epitaxial
silicon layer, silicon on insulator, polysilicon, any combination
thereof, or any other silicon-containing substrate material.
Further, it is also understood that in various implementations a
substrate other than a silicon-containing substrate may be used,
such as, by non-limiting example, gallium arsenide, or a
metal-containing substrate.
[0043] The image sensor includes an opening 12 within the silicon
layer 10. In the implementation illustrated by FIG. 2A, the depth
of the opening, as well as the thickness of the semiconductor layer
10, is shallow and may be about 2.5 micrometers (um). In various
implementations, the length of the opening 12 may be about 100 um
long and about 80 um wide. FIG. 2A is not drawn to scale for the
purpose of clearly illustrating the different elements of FIG. 2A,
however, region 34 is shown drawn to scale in FIG. 3.
[0044] In various implementations, the image sensor may include a
first dielectric layer 14. The first dielectric layer may be an
interlayer dielectric (ILD), and in particular implementations, may
be SiO.sub.2. In various implementations, the image sensor may also
include a second dielectric layer 16 that may be formed over the
silicon layer 10 and within the opening 12. The second dielectric
layer may be SiO.sub.2 and may act as a sidewall passivation layer
as it covers the sidewalls of the opening 12. In various
implementations, the second dielectric layer may be about 300
nanometers (nm) thick.
[0045] The image sensor includes a conductive layer 18 that may be
within the first dielectric layer 14. In various implementations,
the conductive layer 18 may be metallic. In such implementations,
the conductive layer may be, by non-limiting example, copper, gold,
silver, aluminum, any other metal or metallic alloy, and any
combinations thereof. The conductive layer 18 may be coupled to a
conductive pad 20. In various implementations, the conductive pad
20 is a bond pad which may be used to couple external devices to
the image sensor. In other implementations, the conductive pad 20
may be a test pad used to electrically test the components of the
image sensor. In such implementations, the test pad may not be used
to couple the image sensor to external devices as would be done
with a bond pad. In still other implementations, the conductive pad
20 may be used as both a test pad and a bond pad. In various
implementations, and as illustrated by FIG. 2A, the conductive pad
20 may be directly coupled to the conductive layer 18. The
conductive pad 20 illustrated in FIG. 2A includes a first portion
22 and a second portion 24 which extend through the first 14 and
second 16 dielectric layers and couple to the conductive layer 18.
In various implementations, the conductive pad may have only one or
more than two portions that extend through the dielectric layers
and couple to the conductive layer.
[0046] The opening 12 may include a fill material 26. The fill
material may be the same material as or a different material from
the dielectric materials disclosed herein but is generally selected
of a material that is electrically insulative. As illustrated in
FIG. 2A, the surface 28 of the fill material may form a plane
substantially parallel with a plane formed by the surface 30 of the
silicon layer 10. The fill material 26 may have an opening 32
therein and the conductive pad 20 may be exposed through the
opening 32.
[0047] Referring to FIG. 2B, a top view of FIG. 2A is illustrated.
Though FIG. 2A and FIG. 2B are not drawn to scale with respect to
one another, FIG. 2B illustrates the perimeters of the elements of
FIG. 2A, specifically the opening 32 in the fill material 26, the
fill material 26, and the dielectric layer 16. Portions 22 and 24
of the conductive pad, though not technically exposed from a top
view, are illustrated in FIG. 2B to show the relative position of
such elements.
[0048] Referring now to FIG. 3, a cross-section side view of a
portion of the conductive pad region of the image sensor of FIG. 2A
is illustrated. FIG. 3 illustrates a magnified view of the region
34 of FIG. 2A, however, this region is drawn to scale in FIG. 3. As
illustrated by FIG. 3, the image sensor includes the silicon layer
10, the opening 12, the fill material 26, the conductive pad 20,
the conductive layer 18, the first dielectric layer 14, and the
second dielectric layers 16, all of which are cut off on the right
side of FIG. 3 in order to show the conductive pad region to scale.
This view of the conductive pad region is used through the
remaining figures in order to show what the conductive pad region
looks like as drawn to scale. It is understood that the conductive
pad region also includes an opening, which is not shown in FIG. 3,
such as opening 32 of FIG. 2A, through which the conductive pad is
exposed. It is also understood that the conductive pad may include
multiple portions of a conductive pad that are coupled to a
conductive layer rather than the one portion 22 illustrated in FIG.
3. Further, it is understood that though the left side of the
conductive pad region is shown in FIG. 3, the conductive pad region
may also include a symmetrical right side of the conductive pad
region, as illustrated in FIG. 2A. Lastly, only a portion of the
first dielectric layer 14 is illustrated by FIG. 3, though it is
understood that the first dielectric layer may extend beyond what
is shown in FIG. 3 (for example, the first dielectric layer 14 may
encapsulate the conductive layer 18).
[0049] As previously discussed, the silicon layer 10 of FIG. 3 is
substantially 2.5 um thick in various implementations. The surface
28 of the fill material 26 is planarized so that it is coplanar
with the top of the dielectric material 16, or so that it forms a
plane substantially parallel with a plane formed by the surface 30
of the silicon layer. Because the silicon layer is only about 2.5
um thick, it is feasible to include the fill material 26 in the
opening 12 and have it planarized.
[0050] Referring to FIG. 4, a cross-section side view of a portion
of a conductive pad region of an image sensor with a deep silicon
etch without a fill material is illustrated. The image sensor of
FIG. 4 is similar to the image sensor of FIG. 3, with the primary
difference being that the silicon layer 36 is substantially 6 um
thick rather than 2.5 um thick. In various implementations, it is
desirable to increase the thickness of the silicon layer for, among
other reasons, increasing the longer wavelengths (e.g. red,
near-infrared) response of the image sensor. However, if the
thickness of the silicon layer 36 is increased and the depth of the
opening 38 within the silicon layer 36 is increased, the opening 38
may become too deep to fill with a fill material. As illustrated by
FIG. 4, no fill material is included in the opening 38. The lack of
fill material, specifically the lack of fill material that is
coplanar with a surface of the dielectric layer 40 above the
silicon layer, may result in streaks, bands, and framing defects in
the image formed in subsequent processing of the image sensor and
may ultimately result in poor topography which may increase yield
loss by 6-18%.
[0051] Referring to FIG. 5, a cross-section side view of a portion
of an implementation of a conductive pad region of an image sensor
with a deep silicon etch is illustrated. The image sensor of FIG. 5
may include a silicon layer 42. The silicon layer 42 includes a
first side 44 and a second side 46 opposite the first side 44. In
various implementations, the silicon layer 42 is about 6 um thick,
however, in other implementations the silicon layer may be more or
less thick than about 6 um. The image sensor also includes an
opening 48 extending into the silicon layer 42 from the first side
44 of the silicon layer toward the second side 46 of the silicon
layer. In various implementations, the opening 48 may be about 2.5
um deep, and in various implementations, may be 100 um long and 80
um wide. In other implementations, the opening 48 may be more or
less deep than about 2.5 um, may be longer or less long than about
100 um, and may be wider or less wide than about 80 um.
[0052] In various implementations, the image sensor may include a
via 50 extending into the silicon layer 42 from the second side 46
of the silicon layer. In various implementations the via extends
about 4 um deep into the silicon layer 42 and has a width of about
5 um, however, in other implementations the via 50 may have a width
greater or less than about 5 um and may extend deeper or shallower
than about 4 um into the silicon layer 42. The via 50 may have a
length (extending into the page as illustrated by FIG. 5) that is
about 52 um long, however, in other implementations the length may
be more or less than about 52 um. The via 50 includes an
electrically and/or thermally conductive material and may include,
in various implementations, a metallic material. In such
implementations, the via may include, by non-limiting example,
copper, gold, silver, aluminum, any other metal or metallic alloy,
and any combination thereof. In various implementations the via may
be the same as or a different material from the material of the
conductive layer 52. In various implementations, the image sensor
may include only a single via 50 coupling the conductive layer 52
to a conductive pad 54, however, in other implementations, the
image sensor may include two or more vias extending into the
silicon layer 42 from the second side 46 of the silicon layer,
coupling the conductive layer 52 to the conductive pad 54. In such
implementations, the two or more vias may be similar to or the same
as any via described herein.
[0053] Still referring to FIG. 5, in various implementations the
image sensor may include a first dielectric layer 56. The first
dielectric layer 56 may be an ILD layer. Though not illustrated by
FIG. 5, the first dielectric layer 56 may at least partially
encapsulate the conductive layer 52 as is illustrated by FIG. 2A.
The first dielectric layer 56 may also separate the material of the
via 50 from the silicon layer 42 as illustrated by FIG. 5. In
various implementations, the thickness of the dielectric layer at
the portion of the dielectric layer that separates the via 50 from
the silicon layer 42 may be about 300 nm thick, however, in other
implementations it may be more or less thick than about 300 nm. In
various implementations, the dielectric layer may be SiO.sub.2, or
any other type of dielectric material.
[0054] As illustrated by FIG. 5, the image sensor includes a
conductive pad 54 within the opening 48. In various
implementations, the conductive pad 54 is coupled directly to the
via 50, however, in other implementations there may be other
electrically/thermally conductive elements or layers between the
via 50 and the conductive pad 54. In implementations where the
conductive pad is directly coupled to the via, the conductive pad
may extend through the first dielectric layer 56 and a second
dielectric layer 66. The conductive pad is formed of a
electrically/thermally conductive material, and may be, by
non-limiting example, aluminum, gold, copper, titanium, other
metals or metallic alloys, other conductive non-metal materials, or
any combination thereof. In various implementations, the conductive
pad 54 may include an opening 58 therein which may facilitate
adhesion of a fill material 60 to the conductive pad 54.
[0055] In various implementations, the image sensor may include a
fill material 60 within the opening 48. At least a surface 62 of
the fill material may form a plane that is substantially parallel
with a plane formed by the first side of the silicon layer 44.
Further, the surface 62 of the fill material may be substantially
coplanar with a plane formed by the surface of the dielectric layer
64 over the first side 44 of the silicon layer 42. By having the
fill material coplanar with the dielectric layer 64, yield loss due
to poor topography may be reduced. The fill material may be, by
non-limiting example, an epoxy, a resin, SiO.sub.2, or any other
type of fill material. Though not illustrated by FIG. 5, the fill
material includes an opening therein through which the conductive
pad 54 is exposed, similar to the opening 32 of FIG. 2A.
[0056] In various implementations, the image sensor may include a
second dielectric layer 66 which extends along the sides of the
opening 48 and separates the fill material 60 from the silicon
layer 42. In such implementations the second dielectric layer 66
may serve as a sidewall passivation layer for the sidewalls of the
opening 48. The second dielectric layer may also separate the
conductive pad 54 from the silicon layer 42. In various
implementations, the second dielectric layer 66 may be an adhesion
layer to facilitate bonding of the conductive pad 54 to the silicon
layer 42. In various implementations, the second dielectric layer
66 may be the same as or include similar materials to any other
dielectric layer disclosed herein. Further, in various
implementations, the second dielectric layer 66 may include the
structure of the dielectric layer 64 over the first side 44 of the
silicon layer 42.
[0057] Referring to FIG. 6, a cross-section side view of a portion
of another implementation of a conductive pad region of an image
sensor with a deep silicon etch is illustrated. The conductive pad
region illustrated in FIG. 6 is essentially the same in structure
as the conductive pad region illustrated in FIG. 5, with the
difference being that the image sensor of FIG. 6 includes a high
dielectric constant dielectric layer 68 lining the silicon layer
70. As used herein, a high dielectric constant layer means a
dielectric layer having a dielectric constant which is higher than
the dielectric constant of SiO.sub.2, which is approximately 3.9.
Use of a high dielectric constant layer may reduce the amount of
dark current traveling through the image sensor. In various
implementations, the high dielectric constant material may include,
by non-limiting example, tantalum pentoxide (Ta.sub.2O.sub.5),
aluminum oxide (Al.sub.2O.sub.3), hafnium dioxide (HfO.sub.2),
HfO.sub.x, any combination thereof, and any other material with a
dielectric constant higher than that of SiO.sub.2.
[0058] Referring to FIG. 7, a cross-section side view of a portion
of an implementation of a conductive pad region of an image sensor
with a deep silicon etch and a perimeter etch through the silicon
layer is illustrated. Similar to the image sensor of FIG. 5, the
image sensor illustrated by FIG. 7 includes a silicon layer 72
which has a first side 74 and a second side 76. The thickness of
the silicon layer may be about 6 um, however, in other
implementations the thickness of the silicon layer may be more or
less than about 6 um. In various implementations, the image sensor
includes a first opening 78 which extends through the silicon layer
72. The first opening 78 isolates the conductive pad 80 from the
bulk of the silicon layer 72. In various implementations, the first
opening may be lined with a high dielectric constant dielectric
layer which may facilitate the reduction of dark current flowing
within the image sensor. The high dielectric constant material may
be any high dielectric material disclosed herein. The opening may
be filled with a fill material. The fill material may be SiO.sub.2.
In various implementations, the first opening is not lined with the
high dielectric constant material but may just be filled with the
fill material. Though not illustrated in FIG. 7, the first opening
78 may surround the conductive pad 80, and may be formed as a
perimeter etch around the conductive pad. This is more easily
visualized by imagining a trench etched into the silicon layer all
around the perimeter of the conductive pad as viewed from above,
such as the view of FIG. 2B. In this manner, the conductive pad 80
may be completely isolated from the remainder of the silicon layer
72. In various implementations, the first opening may be about 3 um
wide, while in other implementations it may be more or less wide
than about 3 um.
[0059] In various implementations, the first opening may be fully
included within the full thickness of the silicon layer 72. For
example, in implementations where the thickness of the silicon
layer is about 6 um, the entirety of the first opening may extend
through the about 6 um portion of the silicon layer. In other
implementations, the first opening may partially or fully extend
through the thinner portion of the silicon layer 72 which the
second opening 82 is over. In such an implementation, the image
sensor would not include the portion 94 of the silicon layer
separating the first opening 78 from the second opening 82.
[0060] The remainder of the conductive pad region illustrated by
FIG. 7 may be the same structure and material or of similar
structure and material to the conductive pad region illustrated by
FIG. 5. Specifically, the image sensor includes a second opening
82, a via 84, a conductive layer 86, a first dielectric layer 88, a
conductive pad 80, a second dielectric layer 90 or a high
dielectric constant layer 68 like that illustrated in FIG. 6, and a
fill material 92. In various implementations, because the
conductive pad and the via are isolated from the remainder of the
silicon layer 72 due to the first opening 78, the image sensor may
not necessarily include a first dielectric layer 88 which separates
the via 84 from the silicon layer 72 or a second dielectric layer
90 which separates the conductive pad 80 from the silicon layer
72.
[0061] Referring to FIG. 8, a cross-section side view of a portion
of another implementation of a conductive pad region of an image
sensor with a deep silicon etch and a perimeter etch through the
silicon layer is illustrated. The conductive pad region illustrated
by FIG. 8 is similar in structure and materials to the conductive
pad region of FIG. 7, with the only differences found in the first
opening 96. Unlike the first opening 78 of FIG. 7, the first
opening 96 is not separated from the second opening 98 by a portion
of the silicon layer similar to portion 94 of FIG. 7. Further, the
first opening 96 of FIG. 8 is stepped. In the implementation
illustrated by FIG. 8, a first portion 100 of the first opening 96
adjacent to the first side 102 of the silicon layer 104 may be
wider than the second portion 106 of the first opening adjacent to
the second side 108 of the silicon layer. In other implementations,
the second portion 106 may be the same size as, or wider, than the
first portion 100. Further, in the implementation illustrated by
FIG. 8, a high dielectric constant dielectric layer 110 is
illustrated as separating the first portion 100 from the second
portion 106. In various implementations, however, the dielectric
layer 110 may not be used to separate the first portion 100 from
the second portion 106. Further, in various implementations, the
dielectric layer 110 may extend into the second portion 106 and
cover the sidewalls of the portion 106 of the first opening 96. In
various implementations, the second portion 106 may be formed from
the second side 108, and may be formed during processing of the
first side 102 of the silicon layer. Likewise, the first portion
100 may be formed from the first side 102, and may be formed during
processing of the second side 108. In various implementations, the
opening necessary to form the first portion 100 may be etched into
the silicon layer. In such implementations, the second portion 106
may serve as an etch stop. The etched opening may then be coated
with dielectric layer 110, which may be a high dielectric constant
dielectric material, filled with an oxide as described later
herein, and planarized through using chemical mechanical polishing
(CMP) techniques as described later herein.
[0062] Referring to FIG. 9, a cross-section side view of the
portion of the image sensor coupled with other conductive portions
of the image sensor is illustrated. In various implementations, the
image sensor may include a via 150 directly coupled to a conductive
pad 152 and coupled to one or more other vias 154 extending from
other conductive layers. In this manner, an entire network of
conductive elements, such as conductive layer 156, may be
electrically coupled to the conductive pad 152. The vias and
conductive layers or traces illustrated by FIG. 9 may be similar to
or the same as any other via or conductive layer or trace disclosed
herein. Further, in various implementations, the via 150 may be
coated with a barrier layer 158 to prevent migration of copper and
other metals from the via into the silicon and other structures of
the device. In implementations where the second opening in the
silicon layer and the opening in the dielectric layer are etched,
the barrier layer 158 may also act as an etch stop during the
backside etch of the silicon layer and the dielectric layer. This
may prevent the exposure of the vias during the etch, and may
prevent contamination of the etch chamber by the vias. The barrier
layer may also serve as an adhesion layer for the via. In various
implementations, the barrier layer may include tantalum, tantalum
nitride, titanium, titanium nitride, tungsten, tungsten nitride, or
any other barrier layer material. In particular implementations,
the barrier layer may coat portions of multiple vias and conductive
layers.
[0063] FIGS. 10-11 illustrate a method of forming the conductive
pad region illustrated in FIG. 5. Specifically, FIGS. 10A-10F
illustrate a process flow of the method for forming the image
sensor of FIG. 5 as seen from bottom and top views. Referring to
FIG. 10A, the method for forming a conductive pad region in an
image sensor may include forming one or more openings 112 into a
second side 114 of a silicon layer 116. In various implementations,
the openings may be etched. In such implementations, the openings
may be etched using, by non-limiting example, plasma etching,
deep-reactive ion etching, or wet chemical etching. In various
implementations, a process marketed under the tradename BOSCH.RTM.
by Robert Bosch GmbH, Stuttgart Germany (the "Bosch process"), may
be used to form the openings 112 in the silicon layer 116. As the
conductive pad region is oriented in FIG. 5, the view of FIG. 10A
corresponds to a bottom view. The method includes forming one or
more vias 118 within the one or more openings 112.
[0064] Referring to FIG. 10B, the method includes forming an
opening 120 within the first side 122 of the silicon layer 116. The
opening may be formed using any etching technique disclosed herein.
The view of FIG. 10B (as well as FIGS. 10C-10F) corresponds to a
top view of FIG. 5 based on the orientation illustrated in FIG. 5.
In various implementations, the opening may be formed deep enough
to expose the vias 118 from the first side 122 of the silicon layer
116.
[0065] Referring to FIG. 10C, the method may include forming a
dielectric layer 124 over the first side 122 of the silicon layer
116. The dielectric layer covers the one or more vias, though the
vias are still visible in FIG. 10C. Referring to FIG. 10D, the
method of forming the conductive pad region may include etching
through the dielectric layer to expose the vias. In various
implementations, and as illustrated by FIG. 10D, a portion of the
dielectric layer may remain over the edges of the vias 118, thus
only a middle portion of the vias 118 are exposed.
[0066] Referring to FIG. 10E, the method for forming a conductive
pad region includes forming a conductive pad 126 over the vias 118.
Though the vias 118 are still illustrated in FIG. 10E, it is
understood that the conductive pad covers the vias 118. The method
may also include filling the opening 114 in the first side of the
silicon layer 116 with a fill material 128, and etching through the
fill material 128 to expose the conductive pad 126, as illustrated
by FIG. 10F. In various implementations, the method may include
planarizing the fill material in a manner that allows it to be
coplanar with the dielectric layer 124 covering the silicon layer.
In other implementations, the fill material may be planarized in a
manner that allows it to be coplanar with a separate dielectric
layer over the silicon layer 116. The surface of the fill material
seen in FIG. 10F may form a plane substantially parallel with the
semiconductor layer.
[0067] In various implementations, the method for forming the
conductive pad region may include forming an opening around a
perimeter of the conductive pad using a perimeter etch. The opening
may be etched using any etching technique previously disclosed
herein. This may be formed before or after the conductive pad is
coupled to the one or more vias. In various implementations, the
opening around the perimeter of the conductive pad extends entirely
through the silicon layer and may be etched from either the first
side, the second side, or both the first and the second side.
[0068] Referring to FIGS. 11A-11I, cross section side views
illustrating a process flow of the method for forming the
conductive pad region illustrated by FIG. 5 is shown. The process
flow illustrated by FIGS. 11A-11I essentially covers the same
process illustrated by FIGS. 10A-10F, just from a different
perspective. Referring to FIG. 11A, a cross-section side view of a
silicon layer 130 is illustrated. In this particular
implementation, the silicon layer may be an epitaxial silicon layer
which may be part of a much thicker wafer made of silicon. The
silicon layer includes a first side 132 and a second side 134. The
silicon layer may be about 6 um thick, though in other
implementations it may be more or less thick than about 6 um.
Referring to FIG. 11B, the method may include forming a first
opening 136 into a second side 134 of the silicon layer 130. The
opening may be etched using any etching technique previously
disclosed herein. In various implementations, and as illustrated by
FIG. 11C, the method for forming the conductive pad region may
include forming a first dielectric layer 138 over the second side
134 of the silicon layer 136. The first dielectric layer may also
extend along the sides of the opening 136 as illustrated by FIG.
11C. The first dielectric layer may be an ILD and may be any type
of material previously disclosed herein. In other implementations,
the method may not include forming a first dielectric layer.
[0069] Referring to FIG. 11D, the method may include forming the
material of a via within the opening 136 in the second side 134 of
the silicon layer 130. While only a single via is illustrated in
FIG. 11D, it is understood that the method may include forming
other vias not illustrated by FIG. 11D. The materials included in
the via may be the same as or similar to any type of via previously
disclosed herein. The perimeter of the via may be, by non-limiting
example, circular, ovate, elliptical, a square, rectangular, or any
other closed shape.
[0070] Referring to FIG. 11E, the method may include etching an
opening 142 into the first side 132 of the silicon layer 130. In
various implementations, the depth of the opening 142 may be etched
about 2.5 um into the silicon layer 130, while in other
implementations it may be etched deeper or less deep than about 2.5
um. The opening may be etched deep enough to expose the first
dielectric layer 138 in implementations with a first dielectric
layer. In implementations without a first dielectric layer, the
opening may be etched deep enough to expose the via 140. The
opening may be etched using any etching technique disclosed
herein.
[0071] Referring to FIG. 11F, the method may include forming a
second dielectric layer 144 over the first side 132 of the silicon
layer 130. The second dielectric layer may be the same as or
similar to any type of dielectric layer previously disclosed
herein. In particular implementations, the second dielectric layer
may include a high dielectric constant dielectric layer. Referring
to FIG. 11G, the method for forming the conductive pad region
illustrated in FIG. 5 includes etching through the first dielectric
layer 138 and the second dielectric layer 144 to expose the via
140. In various implementations the etch will stop at a barrier or
adhesion layer (not illustrated) that encapsulates the via 140.
Referring to FIG. 11H, the method may include forming a conductive
pad 146 within the opening 142 within the first side 132 of the
silicon layer 130. In the implementation illustrated, the
conductive pad 146 is directly coupled to the via 140. The
conductive pad may be the same as or similar to any conductive pad
disclosed herein.
[0072] Referring to FIG. 11I, the method may include filling the
opening 142 in the first side 132 of the silicon layer 130 with a
fill material 148. The fill material may be the same as or similar
to any fill material disclosed herein. The method may include
planarizing the fill material 148 to form a plane substantially
parallel with the first side 132 of the silicon layer 130. In
various implementations, the fill material 148 is planarized to be
coplanar with a surface of a dielectric layer 144 over the first
side 132 of the silicon layer 130. While FIG. 11I illustrates the
dielectric layer 144 being over the first side 132 of the silicon
layer 130, in other implementations a dielectric layer separate
from the second dielectric layer 144 may be over the first side 132
of the silicon layer 130. The fill material may be planarized using
chemical mechanical polishing CMP techniques or any other
planarizing technique. Though not illustrated by FIG. 11I, the
method may also include etching an opening through the fill
material 148 to expose the conductive pad 146.
[0073] The method for forming a conductive pad region like those
illustrated in FIGS. 7-8 may be carried out using processes similar
to the method illustrated by FIGS. 10A-10I, with the difference
being that the method may include forming a perimeter etch through
the entire thickness of the silicon layer which extends around the
conductive pad. In various implementations, it may be formed before
or after the conductive pad is coupled to the via. Specifically,
referring to FIG. 11B and FIG. 11E, it may be formed at the same
time the opening 136 is formed into the second side 134 of the
silicon layer 130, at the same time the opening 142 is formed into
the first side 132 of the silicon layer, or at both the time the
opening 136 and the opening 142 are formed. In other
implementations, the perimeter etch may be formed before and/or
after either the opening 136 or the opening 142 is formed. Further,
the perimeter etch may be formed from the first side of the silicon
layer, the second side of the silicon layer, or from both the first
and the second side of the silicon layer. In various
implementations, the perimeter etch may be formed using any etching
technique disclosed herein or any etching technique disclosed in
U.S. Pat. No. 7,544,592 to Kirby et al., entitled "Method for
increasing etch rate during deep silicon dry etch," issued Jun. 9,
2009, and U.S. Pat. No. 8,110,488 to Kirby et al., entitled "Method
for increasing etch rate during deep silicon dry etch," issued Feb.
7, 2012, the disclosures of each of which are hereby incorporated
entirely herein by reference. In other implementations, the
perimeter etch may be stepped. In such implementations, the
perimeter etch may be formed by partially etching through the
silicon layer from the first side, and partially etching through
the silicon layer from the second side in a manner that the etch
from the second side connects with the etch from the first side,
thus forming an opening through the entirety of the silicon layer.
The etch from the first side may be wider than, smaller than, or
the same size as the etch from the second side of the silicon
layer. In other implementations the stepped etch may be formed from
a single side of the silicon layer.
[0074] In places where the description above refers to particular
implementations of image sensors and implementing components,
sub-components, methods and sub-methods, it should be readily
apparent that a number of modifications may be made without
departing from the spirit thereof and that these implementations,
implementing components, sub-components, methods and sub-methods
may be applied to other image sensors.
* * * * *