U.S. patent application number 11/275171 was filed with the patent office on 2007-06-21 for funneled light pipe for pixel sensors.
Invention is credited to James William Adkisson, Jeffrey Peter Gambino, Robert Kenneth Leidy, Richard John Rassel.
Application Number | 20070138380 11/275171 |
Document ID | / |
Family ID | 36124628 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070138380 |
Kind Code |
A1 |
Adkisson; James William ; et
al. |
June 21, 2007 |
FUNNELED LIGHT PIPE FOR PIXEL SENSORS
Abstract
A photo sensing structure and methods for forming the same. The
structure includes (a) a semiconductor substrate and (b) a photo
collection region on the semiconductor substrate. The structure
also includes a funneled light pipe on top of the photo collection
region. The funneled light pipe includes (i) a bottom cylindrical
portion on top of the photo collection region of the photo
collection region, and (ii) a funneled portion which has a tapered
shape and is on top and in direct physical contact with the bottom
cylindrical portion. The structure further includes a color filter
region on top of the funneled light pipe.
Inventors: |
Adkisson; James William;
(Jericho, VT) ; Gambino; Jeffrey Peter; (Westford,
VT) ; Leidy; Robert Kenneth; (Burlington, VT)
; Rassel; Richard John; (Colchester, VT) |
Correspondence
Address: |
SCHMEISER, OLSEN & WATTS
22 CENTURY HILL DRIVE
SUITE 302
LATHAM
NY
12110
US
|
Family ID: |
36124628 |
Appl. No.: |
11/275171 |
Filed: |
December 16, 2005 |
Current U.S.
Class: |
250/227.11 |
Current CPC
Class: |
G01J 1/04 20130101; G01J
1/0407 20130101; G01J 1/0488 20130101; G01J 1/0422 20130101 |
Class at
Publication: |
250/227.11 |
International
Class: |
G01J 1/04 20060101
G01J001/04 |
Claims
1. A pixel sensor structure, comprising: (a) a semiconductor
substrate; (b) a photo collection region on the semiconductor
substrate; and (c) a funneled light pipe on top of the photo
collection region, wherein the funneled light pipe comprises (i) a
bottom cylindrical portion on top of the photo collection region of
the photo collection region, and (ii) a funneled portion which has
a tapered shape and is on top and in direct physical contact with
the bottom cylindrical portion.
2. The structure of claim 1, further comprising a color filter
region on top of the funneled light pipe.
3. The structure of claim 2, further comprising a micro-lens on top
of the color filter region.
4. The structure of claim 1, further comprising a micro-lens on top
of the funneled light pipe.
5. The structure of claim 1, wherein a first horizontal
cross-section of the funneled portion is larger in area than a
second horizontal cross-section of the bottom cylindrical
portion.
6. The structure of claim 1, wherein a cross-section of the
funneled portion has a concave shape.
7. The structure of claim 6, wherein the concave shape has a
hyperbolic shape.
8. The structure of claim 6, wherein the concave shape has a
parabolic shape.
9. The structure of claim 1, wherein a cross-section of the
funneled portion has a convex shape.
10. The structure of claim 9, wherein the convex shape has a
hyperbolic shape.
11. The structure of claim 9, wherein the convex shape has a
parabolic shape.
12. The structure of claim 1, wherein a cross-section of the
funneled portion has a shape of a straight line.
13. The structure of claim 1, further comprising a BEOL (Back End
Of Line) layer on top of the photo collection region and the
semiconductor substrate, wherein the funneled light pipe resides in
the BEOL layer, and wherein the BEOL layer comprises M interconnect
layers, M being a positive integer.
14. The structure of claim 13, wherein the funneled portion resides
in only one interconnect layer of the M interconnect layers.
15. The structure of claim 13, wherein the funneled portion resides
in K interconnect layers of the M interconnect layers, wherein K is
an integer, and wherein 1<K<M.
16. The structure of claim 13, wherein the funneled light pipe
comprises a transparent material whose refractive index is higher
than a refractive index of a material of the BEOL layer.
17. The structure of claim 1, further comprising a light reflective
layer on side walls of the funneled light pipe.
18. A semiconductor structure fabrication method, comprising:
providing a structure that includes (i) a semiconductor substrate,
(ii) a photo collection region on the semiconductor substrate, and
(iii) a BEOL (Back End Of Line) layer on the photo collection
region and the semiconductor substrate; etching the BEOL layer so
as to form a funneled cavity in the BEOL layer, wherein a
cross-section of the funneled cavity has a tapered shape; after
said etching the BEOL layer so as to form the funneled cavity in
the BEOL layer, further etching the BEOL layer through the funneled
cavity so as to form a cylindrical cavity in the BEOL layer,
wherein the cylindrical cavity are directly above the photo
collection region and directly beneath the funneled cavity; and
forming a funneled light pipe in the cylindrical cavity and the
funneled cavity.
19. The method of claim 18, further comprising forming a color
filter region on top of the funneled light pipe.
20. The method of claim 19, further comprising the step of forming
a micro-lens on top of the color filter region.
21. The method of claim 18, further comprising the step of forming
a micro-lens on top of the funneled light pipe region.
22. The method of claim 18, wherein said etching the BEOL layer so
as to form the funneled cavity in the BEOL layer is isotropic
etching.
23. The method of claim 22, wherein said further etching the BEOL
layer through the funneled cavity so as to form the cylindrical
cavity in the BEOL layer is anisotropic etching.
24. The method of claim 18, wherein said forming the funneled light
pipe in the cylindrical cavity and the funneled cavity comprises
filling the funneled cavity and the cylindrical cavity with a
transparent material whose refractive index is higher than a
refractive index of a material of the BEOL layer.
25. The method of claim 18, wherein said forming the funneled light
pipe in the cylindrical cavity and the funneled cavity comprises:
forming a light reflective layer on side walls of the cylindrical
cavity and the funneled cavity; and after said forming the light
reflective layer is performed, filling the funneled cavity and the
cylindrical cavity with a transparent material.
26. A pixel sensing structure, comprising: (a) a semiconductor
substrate; (b) a photo collection region on the semiconductor
substrate; (c) a BEOL (Back End Of Line) layer on the semiconductor
substrate and the photo collection region; and (d) a funneled light
pipe on top of the photo collection region and in the BEOL layer,
wherein the funneled light pipe comprises (i) a bottom cylindrical
portion on top of the photo collection region of the photo
collection region, (ii) a funneled portion which has a tapered
shape and is on top and in direct physical contact with the bottom
cylindrical portion, and (iii) a light reflective layer on side
walls of the bottom cylindrical portion and the funneled
portion.
27. The structure of claim 26, further comprising a color filter
region on top of the funneled light pipe.
28. The structure of claim 27, further comprising a micro-lens on
top of the color filter region.
29. The structure of claim 26, further comprising a micro-lens on
top of the funneled light pipe.
30. The structure of claim 26, wherein a first horizontal
cross-section of the funneled portion is larger in area than a
second horizontal cross-section of the bottom cylindrical portion.
Description
BACKGROUNG OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to pixel sensors, and more
specifically, to pixel sensors that have funneled light pipes.
[0003] 2. Related Art
[0004] Some advanced pixel sensors implement vertical light pipes
with micro-lenses, wherein the micro-lenses are used to focus light
into the light pipes. Therefore, there is a need for a pixel sensor
structure that does not have the micro-lenses of the prior art.
SUMMARY OF THE INVENTION
[0005] The present invention provides a pixel sensor structure,
comprising (a) a semiconductor substrate; (b) a photo collection
region on the semiconductor substrate; and (c) a funneled light
pipe on top of the photo collection region, wherein the funneled
light pipe comprises (i) a bottom cylindrical portion on top of the
photo collection region of the photo collection region, and (ii) a
funneled portion which has a tapered shape and is on top and in
direct physical contact with the bottom cylindrical portion.
[0006] The present invention also provides a semiconductor
structure fabrication method, comprising providing a structure that
includes (i) a semiconductor substrate, (ii) a photo collection
region on the semiconductor substrate, and (iii) a BEOL (Back End
Of Line) layer on the photo collection region and the semiconductor
substrate; etching the BEOL layer so as to form a funneled cavity
in the BEOL layer, wherein a cross-section of the funneled cavity
has a tapered shape; after said etching the BEOL layer so as to
form the funneled cavity in the BEOL layer, further etching the
BEOL layer through the funneled cavity so as to form a cylindrical
cavity in the BEOL layer, wherein the cylindrical cavity are
directly above the photo collection region and directly beneath the
funneled cavity; and forming a funneled light pipe in the
cylindrical cavity and the funneled cavity.
[0007] The present invention also provides a photo sensing
structure, comprising (a) a semiconductor substrate; (b) a photo
collection region on the semiconductor substrate; (c) a BEOL (Back
End Of Line) layer on the semiconductor substrate and the photo
collection region; and (d) a funneled light pipe on top of the
photo collection region and in the BEOL layer, wherein the funneled
light pipe comprises (i) a bottom cylindrical portion on top of the
photo collection region of the photo collection region, (ii) a
funneled portion which has a tapered shape and is on top and in
direct physical contact with the bottom cylindrical portion, and
(iii) a light reflective layer on side walls of the bottom
cylindrical portion and the funneled portion.
[0008] The present invention provides a pixel sensor structure that
does not have the micro-lens of the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A-1I show cross-section views of a pixel sensor going
through different fabrication steps of a fabrication process, in
accordance with embodiments of the present invention.
[0010] FIGS. 2, 3, and 4 show other embodiments of the pixel sensor
of FIG. 1I, in accordance with embodiments of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] FIGS. 1A-1I show cross-section views of a pixel sensor 100
going through different fabrication steps of a fabrication process,
in accordance with embodiments of the present invention.
[0012] With reference to FIG. 1A, in one embodiment, the
fabrication process starts out with a semiconductor substrate 110.
Illustratively, the semiconductor substrate 110 comprises a
semiconductor material such as silicon Si, germanium Ge, etc.
[0013] Next, in one embodiment, four photo collection region 112a,
112b, 112c, and 112d are formed on top of the semiconductor
substrate 110 as shown in FIG. 1A. Illustratively, the four photo
collection region 112a, 112b, 112c, and 112d are formed by using
any conventional method. In one embodiment, the four photo
collection region 112a, 112b, 112c, and 112d are photo diodes or
photo gates 112a, 112b, 112c, and 112d, respectively.
[0014] Next, with reference to FIG. 1B, in one embodiment, a
nitride layer 116 is formed on top of the semiconductor substrate
110 and the photo diodes 112a, 112b, 112c, and 112d. More
specifically, the nitride layer 116 can be formed by CVD (Chemical
Vapor Deposition) of silicon nitride on top of the structure 100 of
FIG. 1A.
[0015] Next, in one embodiment, a dielectric layer 122 is formed on
top of the nitride layer 116. Illustratively, the dielectric layer
122 comprises an electrically insulating material such as USG
(Undoped Silicate Glass).
[0016] Next, in one embodiment, metal lines 124 are formed in the
dielectric layer 122. Illustratively, the metal lines 124 comprise
copper, aluminum, or any other electrically conductive metal. In
one embodiment, the metal lines 124 are formed by using a
conventional method.
[0017] Next, in one embodiment, a nitride layer 126 is formed on
top of the dielectric layer 122. Illustratively, the nitride layer
126 is formed by CVD of silicon nitride on top of the dielectric
layer 122. The dielectric layer 122, the metal lines 124, and the
nitride layer 126 are collectively referred to as an interconnect
layer 120.
[0018] Next, with reference to FIG. 1C, in one embodiment,
interconnect layers 130, 140, and 150 similar to the interconnect
layer 120 are formed in that order on top of each other to provide
interconnect multi-layers 155 as shown in FIG. 1C. The interconnect
multi-layers 155 can also be referred to as a BEOL (Back End Of
Line) layer 155. In one embodiment, the formation of each of the
interconnect layers 130, 140, and 150 is similar to the formation
of the interconnect layer 120. In one embodiment, the nitride
layers 126, 136, and 146 separate the adjacent interconnect layers
120, 130, 140, and 150.
[0019] Next, with reference to FIG. 1D, in one embodiment, a
patterned photo-resist layer 160 is formed on top of the nitride
layer 156. In one embodiment, the patterned photo-resist layer 160
is formed by using a conventional lithographic process.
[0020] Next, with reference to FIG. 1E, in one embodiment, the
patterned photo-resist layer 160 is used as a blocking mask to etch
the interconnect multi-layers 155 stopping at the nitride layer 146
to form funnels 164a, 164b, 164c, and 164d in the interconnect
multi-layers 155. This etching step is represented by arrows 162
and hereafter is referred to as the etching step 162. In one
embodiment, the etching step 162 is performed isotropically such
that the cross-section of each of side walls 165a, 165b, 165c, and
165d of the funnels 164a, 164b, 164c, and 164d, respectively, has a
shape of a concave hyperbola as shown in FIG. 1E.
[0021] Next, with reference to FIG. 1F, in one embodiment, the
patterned photo-resist layer 160 is used as a blocking mask to
further etch through the interconnect multi-layers 155 stopping at
the nitride layer 116 to form cavities 168a, 168b, 168c, and 168d.
This etching step is represented by arrows 166 and hereafter is
referred to as the etching step 166. In one embodiment, the etching
step 166 is an anisotropic etching process. Because the etching
step 166 is anisotropic, so side walls 169a, 169b, 169c, and 169d
of the cavities 168a, 168b, 168c, and 168d, respectively, are
vertical. The funnel 164a and the cavity 168a can be collectively
referred to as a funneled pipe 164a, 168a. Similarly, the funnel
164b and the cavity 168b can be collectively referred to as a
funneled pipe 164b, 168b. The funnel 164c and the cavity 168c can
be collectively referred to as a funneled pipe 164c, 168c. The
funnel 164dand the cavity 168d can be collectively referred to as a
funneled pipe 164d, 168d.
[0022] Next, in one embodiment, the patterned photo-resist layer
160 is removed by using a wet etching step, resulting in the
structure 100 of FIG. 1G. Alternatively, the patterned photo-resist
layer 160 is removed by using an oxygen based plasma etch.
[0023] Next, with reference to FIG. 1H, in one embodiment, the
funneled pipes 164a, 168a; 164b, 168b; 164c, 168c; and 164d, 168d
(in FIG. 1G) are filled with a transparent material so as to form
funneled light pipes 170a, 170b, 170c, and 170d, respectively.
Illustratively, the funneled light pipes 170a, 170b, 170c, and 170d
are formed by depositing the transparent material on top of the
entire structure 100 of FIG. 1G (including in the funneled pipes
164a, 168a; 164b, 168b; 164c, 168c and 164d, 168d) and then
polishing by a CMP (Chemical Mechanical Polishing) step to remove
excessive transparent material outside the funneled pipes 164a,
168a; 164b, 168b; 164c, 168c and 164d, 168d. In an alternative
embodiment, the funneled pipes 164a, 168a; 164b, 168b; 164c, 168c;
and 164d, 168d (in FIG. 1G) are filled with a spin-on photo-resist,
and then the excessive photo-resist outside the funneled pipes
164a,168a; 164b,168b; 164c,168c and 164d,168d can be removed by
using a standard lithographic process. In one embodiment, the
spin-on photo-resist is a clear material.
[0024] In one embodiment, the transparent material of the funneled
light pipes 170a, 170b, 170c, and 170d has a refractive index: (a)
which is higher than the refractive index of the material of the
dielectric layers 122, 132, 142, and 152 surrounding the funneled
light pipes 170a, 170b, 170c, and 170d, and (b) but which is lower
than the refractive index of the material of the nitride layer 116
above the photo diodes 112a, 112b, 112c, and 112d. In one
embodiment, the transparent material of the funneled light pipes
170a, 170b, 170c, and 170d can be BPSG (boro-phospho-silicate
glass), or silicon nitride.
[0025] In an alternative embodiment, the side walls 165a, 165b,
165c, 165d, 169a, 169b, 169c, and 169d of the funneled pipes
164a,168a; 164b,168b; 164c,168c and 164d,168d are coated with a
light reflective material (such as aluminum) so as to form a light
reflective layer (not shown) before the funneled light pipes 170a,
170b, 170c, and 170d are formed as described above. More
specifically, the aluminum layer is formed by depositing aluminum
on top of the entire structure 100 of FIG. 1G (including on the
side walls 165a, 165b, 165c, 165d, 169a, 169b, 169c, and 169d of
the funneled pipes 164a,168a; 164b,168b; 164c,168c and 164d,168d)
by CVD and then etching back to remove excessive aluminum outside
the funneled pipes 164a,168a; 164b,168b; 164c,168c and 164d,168d.
As a result, the aluminum layer remains on the side walls 165a,
165b, 165c, 165d, 169a, 169b, 169c, and 169d after the etching
step. In this alternative embodiment, because of the aluminum layer
on the side walls 165a, 165b, 165c, 165d, 169a, 169b, 169c, the
refractive index of the transparent material does not need to be
higher than the refractive index of the material of the dielectric
layers 122, 132, 142, and 152.
[0026] In yet another alternative embodiment, the side walls 165a,
165b, 165c, 165d, 169a, 169b, 169c, and 169d of the funneled pipes
164a,168a; 164b,168b; 164c,168c and 164d,168d can be first coated
with a nitride film (not shown) so as to form a "cladding" and then
an oxide material or a clear polymer can be used to fill the
funneled pipes 164a, 168a; 164b,168b; 164c,168c and 164d,168d as
described above.
[0027] Next, with reference to FIG. 1I, in one embodiment, CFA
(Color Filter Array) regions 180a, 180b, 180c, and 180d are formed
on top of the funneled light pipes 170a, 170b, 170c, and 170d,
respectively. More specifically, the CFA regions 180a and 180c
comprise a green color filter material that allows only green
photons to pass through it. The CFA region 180b comprises a blue
color filter material that allows only blue photons to pass through
it. The CFA region 180d comprises a red color filter material that
allows only red photons to pass through it. In one embodiment, the
CFA regions 180a, 180b, 180c, and 180d are formed as follows.
First, the green CFA regions 180a and 180c are formed by using any
conventional method. Then, in a similar manner, the blue CFA region
180b and the red CFA region 180d are formed in turn. The resulting
structure 100 is shown in FIG. 1I. It should be noted that the
green, red, blue colors are used for illustration only and other
colors can be used. In one embodiment, the arrangement of the CFA
regions 180a, 180b, 180c, and 180d can be different.
[0028] In one embodiment, the operation of the pixel sensor 100 of
FIG. 1I is as follows. Assume that a light beam (not shown) which
comprises blue, red, and green photons is incident on the surface
186 of the structure 100 of FIG. 1I. The CFA regions 180a, 180b,
180c, and 180d ensure that only green photons pass through the
green CFA regions 180a and 180c, only blue photons pass through the
blue CFA region 180b, and only red photons pass through the red CFA
region 180d. FIG. 1I' shows paths of photons in the funneled light
pipe 170a of FIG. 1I, for illustration. With reference to FIGS. 1I
and 1I', some of the green photons that pass through the CFA region
180a (like photon 182) will travel down the funneled light pipe
170a to arrive at the photo diode 112a without hitting the side
walls 165a and 169a of the funneled light pipe 170a. Some others of
the green photons that pass through the CFA region 180a (like a
photon 184) will hit the side walls 165a and 169a at possibly
different incident angles. In the representative case of the photon
184, the photon 184 travels along a path i and hits the side wall
165a at an incident angle .theta. (.theta. is the angle between the
path i and an imaginary line n, called a normal line, that is
perpendicular to the side wall 165a at the incident point of the
photon 184). If the incident angle .theta. of the photon 184 is
less than a critical angle .theta..sub.0 (not shown), the photon
184 will refract into the BEOL layer 155. The critical angle
.theta..sub.0 is determined by the mathematical formula: .theta. 0
= sin - 1 .function. ( n dielectric .times. .times. material n
transparent .times. .times. material ) ##EQU1## wherein
n.sub.dielectric material is refractive index of the material of
the dielectric layers 122, 132, 142, and 152 and n.sub.transparent
material is refractive index of the transparent material of the
funneled light pipe 170a. If the incident angle .theta. of the
photon 184 is greater than the critical angle .theta..sub.0, the
photon 184 will bounce back (i.e., reflect) into the funneled light
pipe 170a. Then, the photon 184 can travel down the funneled light
pipe 170a and arrive at the photo diode 112a, or hit the side walls
165a and 169a one or more times at possibly different incident
angles (not shown). If these incident angles are also greater than
the critical angle .theta..sub.0, the photon 184 will travel down
the funneled light pipe 170a and arrive at the photo diode 112a.
The greater n.sub.transparent material is, the smaller the critical
angle .theta..sub.0 is, and therefore, the more green photons (like
the photon 184) that arrive at the photo diode 112a. Blue photons
of the light beam that pass through the blue CFA region 180b will
travel down along the funneled light pipe 170b and reach the photo
diodes 112b in a similar manner. Red photons of the light beam that
pass through the red CFA region 180d will travel down along the
funneled light pipe 170d and reach the photo diodes 112d in a
similar manner. As a result, the greater n.sub.transparent material
is, the more photons of the light beam that arrive at the photo
diodes 112a, 112b, 112c and 112d. It should be noted that the
description above is for the case where there is no light
reflective coating layer on side walls 165a, 165b, 165c, 165d,
169a, 169b, 169c, and 169d. If the side walls 165a, 165b, 169a,
169b, 169c, and 169d of the funneled pipes 164a,168a; 164b,168b;
164c,168c and 164d,168d are coated with the light reflective
material (such as aluminum) and then filled with the transparent
material as describe above with reference to FIG. 1H, the photon
184 will reflect back regardless of the incident angle .theta..
[0029] FIG. 2 shows a cross-section view of a pixel sensor 200, in
accordance with embodiments of the present invention. In one
embodiment, the pixel sensor 200 is similar to the pixel sensor 100
of FIG. 1I, except that the cross-section of each of side walls
265a, 265b, 265c, and 265d of the funnels 264a, 264b, 264c, and
264d has a shape of a convex hyperbola as shown in FIG. 2 (as
opposed to the concave hyperbolic shape of the side walls 165a,
165b, 165c, and 165d of the funnels 164a, 164b, 164c, and 164d,
respectively, as shown in FIG. 1I). For simplicity, similar regions
and layers will have the same reference numeral. In one embodiment,
the convex hyperbolic side walls 265a, 265b, 265c, and 265d of the
funnels 264a, 264b, 264c, and 264d, respectively, are formed by
etching with a changing component of chemical substance or another
chemical substance. In one embodiment, the convex hyperbolic side
walls 265a, 265b, 265c, and 265d of the funnels 264a, 264b, 264c,
and 264d are formed by polymerizing RIE process (fluorocarbon
chemistry with CHF3 or C4F8 for example), and then the lower
portions of light pipes are formed by non-polymerizing RIE process
(CF4 or CHF3/02 or C4F8/O2).
[0030] In one embodiment, the operation of the pixel sensor 200 is
similar to the operation of the pixel sensor 100 of FIG. 1I as
described above. More specifically, when a light beam (not shown)
is incident on the surface 286 of the structure 200, most of the
photons of the light beam that pass through the CFA regions 180a,
180b, 180c, and 180d will arrive at the photo diodes 112a, 112b,
112c and 112d, respectively.
[0031] FIG. 3 shows a cross-section view of a pixel sensor 300, in
accordance with embodiments of the present invention. In one
embodiment, the pixel sensor 300 is similar to the pixel sensor 100
of FIG. 1I, except that the cross-section of each of side walls
365a, 365b, 365c, and 365d of the funnels 364a, 364b, 364c, and
364d is a slant straight line as shown in FIG. 3. In one
embodiment, the straight side walls 365a, 365b, 365c, and 365d of
the funnels 364a, 364b, 364c, and 364d, respectively, are formed by
etching with a changing component of chemical substance or another
chemical substance. In one embodiment, the straight funnels 364a,
364b, 364c, and 364d are formed by polymerizing RIE process
(fluorocarbon chemistry with CHF3 or C4F8 for example), and then
the lower portions of light pipes are formed by non-polymerizing
RIE process (CF4 or CHF3/O2 or C4F8/O2). In one embodiment, the
straight funnels 364a, 364b, 364c, and 364d can also be formed by
anisotropic RIE to form non-tapered light pipe (including lower
portions) and followed by sputter etch (in Ar for example) to form
tapered upper portions of light pipes.
[0032] In one embodiment, the operation of the pixel sensor 300 is
similar to the operation of the pixel sensor 100 of FIG. 1I as
described above. More specifically, when a light beam (not shown)
is incident on the surface 386 of the structure 300, most of the
photons of the light beam that pass through the CFA regions 180a,
180b, 180c, and 180d will arrive at the photo diodes 112a, 112b,
112c, and 112d, respectively.
[0033] FIG. 4 shows a cross-section view of a pixel sensor 400, in
accordance with embodiments of the present invention. In one
embodiment, the formation of the pixel sensor 400 is similar to the
formation of the structure 100 of FIG. 1H, except for the formation
of funneled light pipes 168a,480a; 168b,480b; 168c,480c; and
168d,480d. More specifically, the cavities 168a, 168b, 168c, and
168d of the funneled light pipes 168a,480a; 168b,480b; 168c,480c;
and 168d,480d are filled with the transparent material which is
then etched back down to the filled cavities 168a, 168b, 168c, and
168d. Next, in one embodiment, CFA funneled regions 480a, 480b,
480c, and 480d are formed in the funnels 164a, 164b, 164c, and
164d, respectively, by using any conventional method, resulting in
the structure 400 of FIG. 4. More specifically, the funnels 164a
and 164c are filled with a green color filter material to form the
green CFA funneled regions 480a and 480c that allow only green
photons to pass through them. Then, the funnel 164b is filled with
a blue color filter material to form the blue CFA funneled region
480b that allows only blue photons to pass through it. Then, the
funnel 164d is filled with a red color filter material to form the
red CFA funneled region 480d that allows only red photons to pass
through it.
[0034] In one embodiment, the operation of the pixel sensor 400 of
FIG. 4 is similar to the operation of the pixel sensor 100 of FIG.
1I. It should be noted that the CFA funneled regions 480a, 480b,
480c, and 480d play two roles: (a) the role of color filter regions
(similar to the role of the CFA regions 180a, 180b, 180c, and 180d
of FIG. 1I) and (b) the role of funneled regions (similar to the
role of the filled funnels 164a, 164b, 164c, and 164d of FIG.
1I).
[0035] FIG. 4' shows a cross-section view of a pixel sensor 400',
in accordance with embodiments of the present invention. In one
embodiment, the formation of the pixel sensor 400' is similar to
the formation of the pixel sensor 400 of FIG. 4, except that
micro-lenses 490a, 490b, 490c, and 490d are formed on top of the
CFA funneled regions 480a, 480b, 480c, and 480d, respectively. The
micro-lenses 490a, 490b, 490c, and 490d are used to focus light
into the CFA funneled regions 480a, 480b, 480c, and 480d,
respectively. It should be noted that the micro-lenses 490a, 490b,
490c, and 490d can be applied to all the embodiments, including
with and without color filter arrays (like the CFA regions 180a,
180b, 180c, and 180d of FIG. 1I).
[0036] In the embodiments described above, with reference to FIGS.
1A-1I, there are four photo diodes 112a, 112b, 112c, and 112d. In
general, the pixel sensor 100 can have N photo diodes, and wherein
N is a positive integer.
[0037] In the embodiments described above, with reference to FIG.
1E, the etching step 162 stops at the nitride layer 146 of the
interconnect layer 140. In an alternative embodiment, the etching
step 162 stops before the nitride layer 146 is exposed to
surrounding ambient. In yet another alternative embodiment, the
etching step 162 etches through the nitride layer 146 and stops at
the nitride layer 136. In general, the etching step 162 can stop at
anywhere in the interconnect multi-layers 155.
[0038] In the embodiments described above, the side walls of the
funnels 164a, 164b, 164c, and 164d (FIG. 1G), the funnels 264a,
264b, 264c, and 264d (FIG. 2), and the funnels 364a, 364b, 364c,
and 364d (FIG. 3) have a hyperbolic shape. Alternatively, they have
a parabolic shape.
[0039] While particular embodiments of the present invention have
been described herein for purposes of illustration, many
modifications and changes will become apparent to those skilled in
the art. Accordingly, the appended claims are intended to encompass
all such modifications and changes as fall within the true spirit
and scope of this invention.
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