U.S. patent application number 12/885138 was filed with the patent office on 2011-03-24 for photodiodes and methods for fabricating photodiodes.
This patent application is currently assigned to INTERSIL AMERICAS INC.. Invention is credited to Joy Jones, Dong Zheng.
Application Number | 20110068426 12/885138 |
Document ID | / |
Family ID | 43755801 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110068426 |
Kind Code |
A1 |
Zheng; Dong ; et
al. |
March 24, 2011 |
PHOTODIODES AND METHODS FOR FABRICATING PHOTODIODES
Abstract
A photodiode includes an opening over an active photodiode
region so that a top passivation layer and interlayer dielectric
layers (ILDs) do not affect the spectral response of the
photodiode. A dielectric reflective optical coating filter, which
includes a plurality of dielectric layers, fills at least a portion
of the opening and thereby covers the active photodiode region, to
shape a spectral response of the photodiode. Alternatively, the
dielectric reflective optical coating filter is formed prior to the
opening, and the opening is formed by removing a top passivation
coating and ILDs to expose the dielectric reflective optical
coating filter.
Inventors: |
Zheng; Dong; (San Jose,
CA) ; Jones; Joy; (Fremont, CA) |
Assignee: |
INTERSIL AMERICAS INC.
Milpitas
CA
|
Family ID: |
43755801 |
Appl. No.: |
12/885138 |
Filed: |
September 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61244817 |
Sep 22, 2009 |
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61259475 |
Nov 9, 2009 |
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61257595 |
Nov 3, 2009 |
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Current U.S.
Class: |
257/432 ;
257/461; 257/E31.001; 257/E31.127; 438/69 |
Current CPC
Class: |
H01L 27/14623 20130101;
G01J 1/4228 20130101; H01L 27/14621 20130101; G01J 1/0488 20130101;
H01L 27/1446 20130101; G01J 1/4204 20130101 |
Class at
Publication: |
257/432 ; 438/69;
257/E31.127; 257/E31.001; 257/461 |
International
Class: |
H01L 31/0232 20060101
H01L031/0232; H01L 31/18 20060101 H01L031/18 |
Claims
1. A photodiode, comprising: a first semiconductor type surface
region; a second semiconductor type surface layer formed in a
portion of said first semiconductor type surface region, wherein an
active photodiode region is formed by a PN junction of said first
semiconductor type surface region and said second semiconductor
type surface layer; a passivation coating on said second
semiconductor surface layer; an etch stop coating on a portion of
said passivation coating; an opening over at least a portion of
said active photodiode region, said opening extending through said
etch stop coating down to said passivation coating; a dielectric
reflective optical coating filter, comprising a plurality of
dielectric layers, that fills at least a portion of said opening
and thereby covers the at least a portion of said active photodiode
region; wherein said opening allows a portion of light incident on
the photodiode to be received by said active photodiode region; and
wherein said dielectric reflective optical coating filter reflects
a portion of light incident on the photodiode and thereby shapes a
spectral response of the photodiode.
2. The photodiode of claim 1, wherein said dielectric reflective
optical coating filter fills the entire said opening.
3. The photodiode of claim 1, wherein: said dielectric reflective
optical coating filter includes a top surface that is generally
parallel to a top surface of said passivation coating and sidewalls
that extend from said top surface of said dielectric reflective
optical coating filter towards said passivation coating; and
further comprising a dark mirror covering said top surface and said
sidewalls of said dielectric reflective optical coating filter.
4. The photodiode of claim 1, wherein: said first semiconductor
type is one of P type and N type; and said second semiconductor
type is the other one of P type and N type.
5. The photodiode of claim 1, wherein: said passivation coating
comprises an oxide layer on said second semiconductor type surface
layer and a second dielectric layer different from said oxide layer
on said oxide layer; and said second dielectric layer, of said
passivation coating, extends beyond said second semiconductor type
surface layer.
6. The photodiode of claim 1, wherein said etch stop coating, on
the portion of said passivation coating, comprises a layer
resistant to oxide etch on an oxide layer.
7. The photodiode of claim 1, wherein the portion of said
passivation coating, on which is said etch stop coating, comprises
a peripheral portion of said passivation coating.
8. The photodiode of claim 1, wherein said etch stop coating
comprises at least one of silicon nitride and polysilicon, and
overlies and extends beyond a peripheral portion of said second
semiconductor surface layer.
9. A photodiode, comprising: a first semiconductor type surface
region; a second semiconductor type surface layer formed in a
portion of said first semiconductor type surface region, wherein an
active photodiode region is formed by a PN junction of said first
semiconductor type surface region and said second semiconductor
type surface layer; an etch stop coating formed on a portion of
said first semiconductor type surface region that surrounds said
second semiconductor type surface layer; an opening over at least a
portion of said active photodiode region, said opening extending
through said etch stop coating down to said second semiconductor
type surface layer or down to a thin oxide layer on said second
semiconductor type surface layer; a dielectric reflective optical
coating filter, comprising a plurality of dielectric layers, that
covers said opening; wherein said opening allows a portion of light
incident on the photodiode to be received by said active photodiode
region; and wherein said dielectric reflective optical coating
filter reflects a portion of light incident on the photodiode and
thereby shapes a spectral response of the photodiode.
10. The photodiode of claim 9, wherein: said dielectric reflective
optical coating filter fills at least a portion of said opening;
said dielectric reflective optical coating filter includes a top
surface that is generally parallel to a top surface of said
passivation coating and sidewalls that extend from said top surface
of said dielectric reflective optical coating filter towards said
second semiconductor type surface layer; and further comprising a
dark mirror covering said top surface and said sidewalls of said
dielectric reflective optical coating filter.
11. A photodiode, comprising: a first semiconductor type surface
region; a second semiconductor type surface layer formed in a
portion of said first semiconductor type surface region, wherein an
active photodiode region is formed by a PN junction of said first
semiconductor type surface region and said second semiconductor
type surface layer; a dielectric reflective optical coating filter,
comprising a plurality of dielectric layers, above said second
semiconductor type surface layer; an etch stop coating on a portion
of said dielectric reflective optical coating filter; an opening
over at least a portion of said active photodiode region, said
opening extending through said etch stop coating down to said
dielectric reflective optical coating filter; wherein said opening
allows a portion of light incident on the photodiode to be received
by said active photodiode region; and wherein said dielectric
reflective optical coating filter reflects a portion of light
incident on the photodiode and thereby shapes a spectral response
of the photodiode.
12. The photodiode of claim 11, wherein said dielectric reflective
optical coating filter is on said second semiconductor type surface
layer.
13. The photodiode of claim 11, further comprising: a passivation
coating between said second semiconductor surface layer and said
dielectric reflective optical coating filter.
14. The photodiode of claim 13, wherein: said passivation coating
comprises an oxide layer on said second semiconductor type surface
layer and a second dielectric layer different from said oxide layer
on said oxide layer; and said second dielectric layer, of said
passivation coating, extends beyond said second semiconductor type
surface layer.
15. The photodiode of claim 11, wherein said etch stop coating, on
the portion of said passivation coating, comprises a layer
resistant to oxide etch on an oxide layer.
16. The photodiode of claim 11, wherein: said first semiconductor
type is one of P type and N type; and said second semiconductor
type is the other one of P type and N type.
17. A method of a fabricating a photodiode, comprising: (a)
implanting and thereby forming a second semiconductor type shallow
surface layer into a portion of a first semiconductor type surface
region, wherein an active photodiode region is formed by a PN
junction of the first semiconductor type surface region and the
second semiconductor type shall surface layer; (b) forming a
passivation coating on said shallow surface layer, wherein said
passivation coating comprises a thin oxide layer on said shallow
surface layer and a second dielectric layer different from said
thin oxide layer on said thin oxide layer; (c) forming an etch stop
coating on said second dielectric layer, wherein said etch stop
coating comprises at least one layer resistant to oxide etch; (d)
performing at least some of interlayer dielectric (ILD) processing,
metal processing, contact processing, via processing and
passivation processing, which results in multiple layers being
formed above said etch stop coating; (e) removing at least a
portion of said multiple layers formed at step (d) and at least a
portion of said etch stop coating to produce an opening that
extends down to said passivation coating over at least a portion of
said active photodiode region; and (f) filling at least a portion
of said opening with a dielectric reflective optical coating filter
so that said dielectric reflective optical coating filter covers
said at least a portion of said active photodiode region.
18. The method of claim 17, wherein step (f) comprising filling the
entire said opening with said dielectric reflective optical coating
filter.
19. The method of claim 17, wherein after step (f) said dielectric
reflective optical coating filter includes a top surface that is
generally parallel to a top surface of said passivation coating and
sidewalls that extend from said top surface towards said
passivation coating, and further comprising: (g) covering said top
surface and said sidewalls of said dielectric reflective optical
coating filter with a dark mirror.
20. A method of a fabricating a photodiode, comprising: (a)
implanting and thereby forming a second semiconductor type shallow
surface layer into a portion of a first semiconductor type surface
region, wherein an active photodiode region is formed by a PN
junction of the first semiconductor type surface region and the
second semiconductor type shallow surface layer; (b) forming an
etch stop coating over said second semiconductor type shallow
surface layer, wherein said etch stop coating comprises at least
one layer (316) resistant to oxide etch; (c) performing at least
some of interlayer dielectric (ILD) processing, metal processing,
contact processing, via processing and passivation processing,
which results in multiple layers being formed above said etch stop
coating; (d) removing at least a portion of said multiple layers
formed at step (c) and at least a portion of said etch stop coating
to produce an opening, over at least a portion of said active
photodiode region, that extends down to said second semiconductor
type shallow surface layer or down to a thin oxide that covers said
second semiconductor type shallow surface layer; and (e) filling at
least a portion of said opening with a dielectric reflective
optical coating filter so that said dielectric reflective optical
coating filter covers said at least a portion of said active
photodiode region.
21. The method of claim 20, wherein step (e) comprising filling the
entire said opening with said dielectric reflective optical coating
filter.
22. The method of claim 20, wherein after step (e) said dielectric
reflective optical coating filter includes a top surface that is
generally parallel to a top surface of said passivation coating and
sidewalls that extend from said top surface towards said
passivation coating, and further comprising: (f) covering said top
surface and said sidewalls of said dielectric reflective optical
coating filter with a dark mirror.
23. A method of a fabricating a photodiode, comprising: (a)
implanting and thereby forming a second semiconductor type shallow
surface layer into a portion of a first semiconductor type surface
region, wherein an active photodiode region is formed by a PN
junction of the first semiconductor type surface region and the
second semiconductor type shall surface layer; (b) forming a
dielectric reflective optical coating filter over at least a
portion of said active photodiode region; (c) forming an etch stop
coating over said dielectric reflective optical coating filter,
wherein said etch stop coating comprises at least one layer
resistant to oxide etch; (d) performing at least some of interlayer
dielectric (ILD) processing, metal processing, contact processing,
via processing and passivation processing, which results in
multiple layers being formed above said etch stop coating; and (e)
removing at least a portion of said multiple layers formed at step
(d) and at least a portion of said etch stop coating to produce an
opening that extends down to said dielectric reflective optical
coating filter over at least a portion of said active photodiode
region.
24. The method of claim 23, further comprising: between steps (a)
and (b), forming a passivation coating on said shallow surface
layer, wherein said passivation coating comprises a thin oxide
layer on said shallow surface layer and a second dielectric layer
different from said thin oxide layer on said thin oxide layer; and
wherein step (b) comprises forming said dielectric reflective
optical coating filter on said passivation coating.
Description
PRIORITY CLAIM
[0001] This application claims priority under 35 U.S.C. 119(e) to
the following provisional patent applications, each of which is
incorporated herein by reference: U.S. Provisional Patent
Application No. 61/244,817, entitled WAFER-LEVEL COATING FOR
AMBIENT SENSOR AND PROXIMITY SENSOR, filed Sep. 22, 2009; U.S.
Provisional Patent Application No. 61/259,475, entitled OPTICAL
SENSOR INCLUDING WAFER-LEVEL OPTICAL COATINGS AND TINTED PACKAGING
EPDXY TO SHAPE SPECTRAL RESPONSE, filed Nov. 9, 2009; and U.S.
Provisional Patent Application No. 61/257,595, entitled INFRARED
SUPPRESSING PHOTO-PATTERNABLE COATING FOR PHOTODETECTING
SEMICONDUCTOR DIE GLASS APPLICATIONS, filed Nov. 3, 2009.
BACKGROUND
[0002] Photodiodes can be used as ambient light sensors (ALSs),
e.g., for use as energy saving light sensors for displays, for
controlling backlighting in portable devices such as mobile phones
and laptop computers, and for various other types of light level
measurement and management. For more specific examples, ambient
light sensors can be used to reduce overall display-system power
consumption and to increase Liquid Crystal Display (LCD) lifespan
by detecting bright and dim ambient light conditions as a means of
controlling display and/or keypad backlighting. Without ambient
light sensors, LCD display backlighting control is typically done
manually whereby users will increase the intensity of the LCD as
the ambient environment becomes brighter. With the use of ambient
light sensors, users can adjust the LCD brightness to their
preference, and as the ambient environment changes, the display
brightness adjusts to make the display appear uniform at the same
perceived level; this results in battery life being extended, user
eye strain being reduced, and LCD lifespan being extended.
Similarly, without ambient light sensors, control of the keypad
backlight is very much dependent on the user and software. For
example, keypad backlight can be turned on for 10 second by a
trigger which can be triggered by pressing the keypad, or a timer.
With the use of ambient light sensors, keypad backlighting can be
turned on only when the ambient environment is dim, which will
result in longer battery life. In order to achieve better ambient
light sensing, ambient light sensors preferably have a spectral
response close to the human eye response and have excellent
infrared (IR) noise suppression.
SUMMARY
[0003] In accordance with certain embodiments, a photodiode
includes a first semiconductor type surface region (e.g., 302), and
a second semiconductor type surface layer (e.g., 303) formed in a
portion of the first semiconductor type surface region (e.g., 302),
such that an active photodiode region is formed by a PN junction of
the first semiconductor type surface region (e.g., 302) and the
second semiconductor type surface layer (e.g., 303). A passivation
coating (e.g., 314) is on the second semiconductor surface layer
(e.g., 303). An etch stop coating (e.g., 315) is on a portion of
the passivation coating (e.g., 314). The photodiode also includes
an opening (e.g., 340) over at least a portion of the active
photodiode region, where the opening (e.g., 340) extends through
the etch stop coating (e.g., 315) down to the passivation coating
(e.g., 314). A dielectric reflective optical coating filter (e.g.,
350), which includes a plurality of dielectric layers, fills at
least a portion of the opening (e.g., 340) and thereby covers the
active photodiode region. The opening (e.g., 340) allows a portion
of light incident on the photodiode to be received by the active
photodiode region. The dielectric reflective optical coating filter
(e.g., 350) reflects a portion of light incident on the photodiode
and thereby shapes a spectral response of the photodiode. The
dielectric reflective optical coating filter (e.g., 350) includes a
top surface that is generally parallel to a top surface of the
passivation coating (e.g., 314) and sidewalls (e.g., 355) that
extend from the top surface towards the passivation coating (e.g.,
314). In accordance with an embodiment, a dark mirror (e.g., 360)
covers the top surface and the sidewalls (355) of the dielectric
reflective optical coating filter (e.g., 350).
[0004] In accordance with alternative embodiments, there is no
passivation coating (e.g., 314) on the second semiconductor surface
layer (e.g., 303). In such embodiments, the opening (e.g., 340)
over at least a portion of the active photodiode region extends
down to the second semiconductor type surface layer (e.g., 303) or
a thin oxide layer on the second semiconductor type surface layer
(e.g., 303).
[0005] In other embodiments, the dielectric reflective optical
coating filter (e.g., 350) is formed above the second semiconductor
type surface layer (e.g., 303), and an etch stop coating (e.g.,
315) is on a portion of the dielectric reflective optical coating
filter (e.g., 350). In such embodiments, an opening (e.g., 340) is
over at least a portion of the active photodiode region, with the
opening (e.g., 340) extending through the etch stop coating (315)
down to the dielectric reflective optical coating filter (e.g.,
350). In such embodiments, a passivation coating (e.g., 314) may or
may not be between the second semiconductor surface layer (e.g.,
303) and the dielectric reflective optical coating filter (e.g.,
350).
[0006] Embodiments of the present invention are also directed to
methods for fabricating photodiodes. In accordance with an
embodiment, a method include implanting and thereby forming a
second semiconductor type shallow surface layer (e.g., 303) into a
portion of a first semiconductor type surface region (e.g., 302),
wherein an active photodiode region is formed by a PN junction of
the first semiconductor type surface region and the second
semiconductor type shallow surface layer. A passivation coating
(e.g., 314) is formed on the shallow surface layer (e.g., 303),
wherein the passivation coating (e.g., 314) comprises a thin oxide
layer (e.g., 311) on the shallow surface layer (e.g., 303) and a
second dielectric layer (e.g., 312) different from the thin oxide
layer on the thin oxide layer. An etch stop coating (e.g., 315) is
formed on the second dielectric, wherein the etch stop coating
(e.g., 315) comprises at least one layer (e.g., 316) resistant to
oxide etch. At least some of interlayer dielectric (ILD)
processing, metal processing, contact processing, via processing
and passivation processing are then performed, which results in
multiple layers being formed above the etch stop coating (e.g.,
315). The method further includes removing at least a portion of
the multiple layers formed above the etch stop coating (e.g., 315)
and at least a portion of the etch stop coating (e.g., 315) to
produce an opening (e.g., 340) that extends down to the passivation
coating (e.g., 314) over at least a portion of the active
photodiode region. At least a portion of the opening (340) is
filled with a dielectric reflective optical coating filter (350) so
that the dielectric reflective optical coating filter (350) covers
the at least a portion of the active photodiode region.
Additionally, a top surface (e.g., 357) and sidewalls (e.g., 355)
of the dielectric reflective optical coating filter (350) can be
covered with a dark mirror (360).
[0007] In alternative embodiments, there is no passivation coating
(e.g., 314) formed on the second semiconductor surface layer (e.g.,
303). In such an embodiment, an opening (e.g., 340) is formed by
removing at least a portion of the multiple layers formed above the
remaining etch stop coating (e.g., 315) and at least a portion of
the remaining etch stop to produce an opening that extends down to
the second semiconductor type surface layer (e.g., 303) or a thin
oxide layer on the second semiconductor type surface layer (e.g.,
303).
[0008] In other embodiments, the dielectric reflective optical
coating filter (350) is formed over at least a portion of the
active photodiode region, before an opening (e.g., 340) is
formed.
[0009] Further and alternative embodiments, and the features,
aspects, and advantages of the embodiments of invention will become
more apparent from the detailed description set forth below, the
drawings and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates an exemplary spectral response of a
photodiode without any spectral response shaping.
[0011] FIG. 2 illustrates the typical spectral response of a human
eye.
[0012] FIG. 3A illustrates a cross section of a photodiode 300a
after a window has been opened over an active photodiode region
down to a passivation coating, in accordance with an
embodiment.
[0013] FIG. 3B illustrates a cross section of a photodiode 300b,
according to an embodiment, which includes a dielectric reflective
optical coating filter filling a portion of a window opened over an
active photodiode region down to a passivation coating.
[0014] FIG. 3C illustrates a cross section of a photodiode 300c
that is similar to the photodiode 300b of FIG. 3B, but with a dark
mirror added to cover sidewall and a top surface of the dielectric
reflective optical coating filter, in according with an
embodiment.
[0015] FIG. 3D illustrates a cross section of a photodiode 300d
that is similar to the photodiode 300b of FIG. 3B, but with the
area of the diffusion region (and thus, the active photodiode
region) made substantially smaller than the opening formed by the
sidewalls 355 of the dielectric reflective optical coating filter,
in accordance with an embodiment.
[0016] FIG. 3E illustrates a cross section of a photodiode 300e
that is similar to the photodiode 300c of FIG. 3C, but where the
dielectric reflective optical coating filter fills the entire
window and extends above the window, in accordance with an
embodiment.
[0017] FIG. 4 illustrates a cross section of a photodiode 400,
according to an embodiment, where the dielectric reflective optical
coating filter is formed before the window is opened.
[0018] FIG. 5A illustrates a cross section of a photodiode 500a
after a window has been opened over an active photodiode region
down to a diffusion region of the photodiode or down to a thin
oxide covering the diffusion region.
[0019] FIG. 5B illustrates a cross section of a photodiode 500b,
according to an embodiment, which includes a dielectric reflective
optical coating filter filling a portion of a window opened over an
active photodiode region down to a diffusion region of the
photodiode or down to a thin oxide covering the diffusion
region.
[0020] FIG. 5C illustrates a cross section of a photodiode 500c
that is similar to the photodiode 500b of FIG. 5B, but with a dark
mirror added to cover sidewalls and a top surface of the dielectric
reflective optical coating filter, in according with an
embodiment.
[0021] FIG. 5D illustrates a cross section of a photodiode 500d
that is similar to the photodiode 500b of FIG. 5B, but with the
area of the diffusion region (and thus, the active photodiode
region) made substantially smaller than the opening formed by the
sidewalls 355 of the dielectric reflective optical coating filter,
in accordance with an embodiment.
[0022] FIG. 5E illustrates a cross section of a photodiode 500e
that is similar to the photodiode 500c of FIG. 5C, but where the
dielectric reflective optical coating filter fills the entire
window and extends above the window, in accordance with an
embodiment.
[0023] FIG. 6 illustrates a cross section of a photodiode 600,
according to an embodiment, where the dielectric reflective optical
coating filter is formed above the diffusion region before the
window is formed.
[0024] FIG. 7 illustrates how that a filter response (F) can be
shifted relative to a target response (T), so that when the filter
is used with a photodiode having a photodiode response (P), the
target response (T) is achieved.
DETAILED DESCRIPTION
[0025] FIG. 1 shows an exemplary spectral response of a photodiode
without any spectral response shaping, e.g., using a filter to
covering an active photodiode region. FIG. 2 illustrates the
typical spectral response of a human eye. As can be appreciated
from FIGS. 1 and 2, a problem with using a photodiode as an ambient
light sensor is that it detects both visible light and non-visible
light, such as infrared (IR) light, which starts at about 700 nm.
By contrast, notice from FIG. 2 that the human eye does not detect
IR light. Thus, the response of a photodiode can significantly
differ from the response of a human eye, especially when the light
is produced by an incandescent light, which produces large amounts
of IR light. This would provide for significantly less than optimal
adjustments if the photodiode were used as an ambient light
detector, e.g., for adjusting backlighting, or the like.
[0026] Referring to FIG. 3A, in accordance with an embodiment, a
photodiode 300a can be fabricated by starting with a substrate,
e.g., P+ substrate 301, having a first semiconductor type surface
region, e.g., P- surface region 302 on at least a portion of the
substrate 301. Alternatively, the surface region 302 can simply be
a surface of the substrate 301. A second semiconductor type shallow
surface layer, e.g., N+ diffusion layer 303 (also referred to as a
diffusion region), can be formed into a portion of the surface
region 302 to thereby form an active PN junction photodiode region.
The P+ substrate 301, the P- surface region 302, and the N+
diffusion layer 303 can be formed from Silicon (Si), but are not
limited thereto. The N+ diffusion layer 303 can be formed, e.g., by
doping Si with As or Sb, but is not limited thereto.
[0027] In FIG. 3A, a passivation coating 314 is formed on the
shallow surface layer 303. In accordance with an embodiment, the
passivation coating 314 includes two dielectric layers. The top
layer 312 of the passivation coating 314 can be a nitride, e.g.,
silicon nitride (Si3N4). In accordance with an embodiment of the
present invention, when used for an optical application, the
nitride layer preferably has a thickness in the range of about
20-40 nm (e.g., 30 nm) so that the nitride layer does not adversely
affect the spectral response of the photodiode. However, the
relatively shallow thickness of the nitride layer may cause
stopping on the nitride as an etch stop to be difficult. To
overcome this, the thickness of the nitride can be increased so
that during the etching some of the nitride is etched, leaving a
nitride layer within the desired thickness range. Alternatively, a
sacrificial etch stop layer (e.g., a metal) can be added to protect
an area that is not already covered by a top metal. This
sacrificial etch stop layer can then be removed by another masking
step. The bottom layer 311 of the passivation coating 314 can be a
thin silicon dioxide (SiO.sub.2) layer. The thin silicon dioxide
(SiO.sub.2) layer 311 (e.g. 1.5 to 8 nm) reduces tension/stress
between the underlying Si and the silicon nitride (Si.sub.3N.sub.4)
layer 312 or other second dielectric layer of the passivation
coating 314. The second dielectric layer (e.g., Si.sub.3N.sub.4)
312 seals the N+ diffusion layer 303 from moisture. Although the
second dielectric layer 312 of the passivation coating 314 is
generally described herein as being silicon nitride, the invention
is not limited to silicon nitride as the second dielectric layer
312. For example, the second dielectric layer 312 can be silicon
rich SiO.sub.2, silicon rich SiO.sub.N or silicon rich
Si.sub.3N.sub.4. An exemplary known technique for depositing such
silicon rich layers is using plasma enhanced deposition
systems.
[0028] In FIG. 3A, an etch stop coating 315 is formed on the
passivation coating 314. In accordance with an embodiment, the etch
stop coating 315 includes at least one layer resistant to oxide
etch 316, e.g., silicon nitride (Si.sub.3N.sub.4) or polysilicon,
above an oxide (e.g., SiO.sub.2) layer 317.
[0029] After the passivation coating 314 and the etch stop coating
315 are formed, a portion of the etch stop coating 315 and the
passivation coating 314 is removed outside the active photodiode
region down to the first semiconductor type surface region, e.g.,
the P- surface region 302, to make room for metalization. Such
removal can be performed, e.g., using resist patterning followed by
an etch and resist removal. The etch stop coating should also be
cleared from a CMOS gate topography (not shown). In the case of a
Si etch stop layer a variety of plasma etches stopping on the
underlying oxide can be used. In the case of a Si.sub.3N.sub.4 etch
stop layer, plasma or wet etches can be employed, the latter
generally including an oxide hard mask material (about 30 nm or
thicker) deposited over the Si.sub.3N.sub.4 etch stop layer. The
oxide layer 317 between the passivation coating 314 and the etch
stop layer resistant to oxide etch 316 can be removed using wet
chemistry prior to the photo resist mask removal, but is not
limited thereto.
[0030] Thereafter, interlayer dielectric (ILD), metal, contact, via
and passivation processing can be performed to add interlayer
dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization
330, and a top passivation layer 326 (e.g., an oxide layer capped
with a nitride layer). The ILD layers 321, 322, 323, 324 and 325
are typically oxides, portions of which can be removed using an
oxide etch. In FIG. 3A, metallization 330 is coupled to a P+
contact 305 for low resistance contact to the P-surface region 302.
An N+ diffusion contact is not shown in FIG. 3A. The N+ diffusion
contact can be referred to as the cathode of the photodiode, and
the P+ contact 305 can be referred to as the anode of the
photodiode.
[0031] At this point, there are numerous ILD layers (e.g., layers
321, 322, 323, 324 and 325) and a top passivation layer 326 over
the active photodiode region, which layers affect the spectral
response of the underlying active photodiode region. Even if there
was an attempt to optimize the thicknesses of these ILD layers to
achieve a desired spectral response (e.g., a spectral response
similar to that of a human eye), because normal semiconductor
fabrication thickness control is in the range of +/-10 to 20%,
there is too much thickness variation to provide for a well
controlled and predictable spectral response. Accordingly, in
accordance with specific embodiments of the present invention, the
ILD layers and the top passivation layer over the active photodiode
region are removed. In other words, a window 340 is formed over the
active photodiode region. Thereafter, as will be described below,
an optical filter is formed within the window 340, to provide for
the desired spectral response (e.g., a spectral response similar to
that of a human eye).
[0032] A photoresist can be patterned to open the window 340 (also
referred to as an opening or a trench) over the active photodiode
region. More specifically, a portion of top passivation coating
326, ILD layers and the etch stop coating 315 is removed so that
the opening 340 extends all the way down to the passivation coating
314 over at least a portion of the active photodiode region. This
can include removing at least a portion of the oxide layer 317
using an oxide etch, and removing at least a portion the etch step
coating 315 that is over the active photodiode region to expose at
least a portion of the passivation coating 314 that is over the
active photodiode region. In accordance with an embodiment, the
area of the opening 340 is less than the area of the active
photodiode region, as shown in FIG. 3A.
[0033] After the above described trench 340 is formed, an optical
filter 350 can be formed above the passivation coating 314. In
contrast to thickness control for semiconductor fabrication,
thickness control for optical filters is typically in the range of
+/-1%. In accordance with an embodiment, a wafer including a
plurality of the photodiodes 300a having the window 340 over the
active photodiode region is manufactured at a semiconductor
fabrication plant (commonly called a fab). Thereafter, the wafer is
transferred to an optoelectronic and/or optical device fabrication
facility, where the optical filters 350 are added. The wafer with
filters can then be returned to a semiconductor fab where the wafer
can be diced into photodiode dies, and packaging can be added to
produce photodiode integrated circuit (IC) chips. It is also
possible that all of the above steps occur within the same
facility, if such facility is appropriately equipped to perform
both semiconductor and optical fabrication.
[0034] In accordance with an embodiment, the optical filter 350 is
a dielectric reflective optical coating filter. Depending on the
depth for the trench 340, and the thickness of the dielectric
reflective optical coating filter 350, the dielectric reflective
optical coating filter 350 can fill only a portion of the trench,
or can fill the entire trench and even extend above the trench. In
FIG. 3B the dielectric reflective optical coating filter 350 is
shown as filling only a portion of the trench 340 of the photodiode
300b.
[0035] The dielectric reflective optical coating filter 350 can be
constructed from thin layers of materials such as, but not limited
to, zinc sulfide, magnesium fluoride, calcium fluoride, and various
metal oxides (e.g., titanium dioxide), which are deposited onto the
underlying optical substrate. By careful choice of the exact
composition, thickness, and number of these layers, it is possible
to tailor the reflectivity and transmissivity of the filter 350 to
produce almost any desired spectral characteristics. For example,
the reflectivity can be increased to greater than 99.99%, to
produce a high-reflector (HR) coating. The level of reflectivity
can also be tuned to any particular value, for instance to produce
a mirror that reflects 90% and transmits 10% of the light that
falls on it, over some range of wavelengths. Such mirrors have
often been used as beam splitters, and as output couplers in
lasers. Alternatively, the filter 350 can be designed such that the
mirror reflects light only in a narrow band of wavelengths,
producing a reflective optical filter.
[0036] High-reflection coatings work the opposite way to
antireflection coatings. Generally, layers of high and low
refractive index materials are alternated one above the other.
Exemplary high refractive index materials include zinc sulfide
(n=2.32) and titanium dioxide (n=2.4), and exemplary low refractive
index materials include magnesium fluoride (n=1.38) and silicon
dioxide (n=1.49). This periodic or alternating structure
significantly enhances the reflectivity of the surface in the
certain wavelength range called band-stop, which width is
determined by the ratio of the two used indices only (for
quarter-wave system), while the maximum reflectivity is increasing
nearly up to 100% with a number of layers in the stack. The
thicknesses of the layers are generally quarter-wave (then they
yield to the broadest high reflection band in comparison to the
non-quarter-wave systems composed from the same materials),
designed such that reflected beams constructively interfere with
one another to maximize reflection and minimize transmission. Using
the above described structures, high reflective coatings can
achieve very high (e.g., 99.9%) reflectivity over a broad
wavelength range (tens of nanometers in the visible spectrum
range), with a lower reflectivity over other wavelength ranges, to
thereby achieve a desired spectral response. By manipulating the
exact thickness and composition of the layers in the reflective
stack, the reflection characteristics can be tuned to a desired
spectral response, and may incorporate both high-reflective and
anti-reflective wavelength regions. The coating can be designed as
a long-pass or short-pass filter, a bandpass or notch filter, or a
mirror with a specific reflectivity.
[0037] In accordance with specific embodiments of the present
invention, dielectric reflective optical coating filter 350 is used
to shape the spectral response of a photodiode to obtain a spectral
response that is similar to that of a typical human eye response
(shown in FIG. 2). Alternative spectral responses are possible, and
within the scope of the present invention.
[0038] Referring now to the photodiode 300c of FIG. 3C, in
accordance with an embodiment of the present invention, in order to
reduce and preferably minimize light piping effects, a dark mirror
coating 360 (also referred to simply as a dark mirror) can be added
to cover the sidewalls 355 of the dielectric reflective optical
coating filter 350. The dark mirror 360 can also cover the top
surface 357 of the dielectric reflective optical coating filter
350, from which the sidewalls 355 extend downward from. The dark
mirror coating 360 is patterned so that there is an opening in the
dark mirror coating over the active photodiode region. A dark
mirror is a low reflective, low transmissive filter. In an
embodiment, the dark mirror coating 360 provides a low reflectivity
surface that absorbs visible light.
[0039] Referring now to the photodiode 300d of FIG. 3D, another way
to reduce and preferably minimize light piping effects, is to make
the area of the N+ diffusion region 303 (and thus, the active
photodiode region) substantially smaller than the opening formed by
the sidewalls 355 of the dielectric reflective optical coating
filter 350. The embodiments of FIGS. 3C and 3D can also be combined
so that the area of the N+ diffusion region 303 (and thus, the
active photodiode region) is substantially smaller than the opening
formed by the sidewalls 355 of the dielectric reflective optical
coating filter 350, and a dark mirror coating 360 is added to cover
the sidewalls 355 and top surface 357 of the dielectric reflective
optical coating filter 350.
[0040] In FIGS. 3B-3D, the dielectric reflective optical coating
filter 350 was shown as filling only a portion of the trench 340.
FIG. 3E shows an embodiment where the dielectric reflective optical
coating filter 350 fills the entire opening 340 of the photodiode
300e, and even extends above the trench 340. To reduce and
preferably minimize light piping effects, the dark mirror coating
360 covers sidewalls 355 and a top surface 357 of the dielectric
reflective optical coating filter 350. Alternatively, or
additionally, the area of the N+ diffusion region 303 (and thus,
the active photodiode region) can be made substantially smaller
than the opening formed by the sidewalls 355 of the dielectric
reflective optical coating filter 350, as was explained above with
reference to the photodiode 300d of FIG. 3D.
[0041] In the embodiments of FIGS. 3B-3E, the dielectric reflective
optical coating filter 350 was shown as being formed after the
trench 340 was formed. In accordance with an alternative
embodiment, described with reference to FIG. 4, the dielectric
reflective optical coating filter 350 of the photodiode 400 is
formed before the trench is formed. In FIG. 4, the dielectric
reflective optical coating filter 350 is formed on the passivation
coating 314. Thereafter, the etch stop coating 315 is formed on the
dielectric reflective optical coating filter 350. In accordance
with an embodiment, the etch stop coating 315 includes at least one
layer resistant to oxide etch 316, e.g., silicon nitride
(Si.sub.3N.sub.4) or polysilicon, above an oxide (e.g., SiO.sub.2)
layer 317. After the passivation coating 314, the dielectric
reflective optical coating filter 350, and the etch stop coating
315 are formed, a portion of the etch stop coating 315 and the
passivation coating 314 is removed outside the active photodiode
region down to the first semiconductor type surface region, e.g.,
the P- surface region 302, to make room for metalization.
Thereafter, ILD, metal, contact, via and passivation processing can
be performed to add interlayer dielectric (ILD) layers 321, 322,
323, 324 and 325, metalization 330, and a top passivation layer 326
(e.g., an oxide layer capped with a nitride layer).
[0042] At this point, there are numerous ILD layers (e.g., layers
321, 322, 323, 324 and 325) and a top passivation layer 326 over
the active photodiode region, which layers affect the spectral
response of the underlying active photodiode region. The ILD layers
and the top passivation layer over the active photodiode region are
removed. In other words, a window 340 is formed over the active
photodiode region, with the window extending down to the dielectric
reflective optical coating filter 350. In a similar manner as was
discussed above with regards to FIG. 3A, a photoresist can be
patterned to open the window 340 (also referred to as an opening or
a trench).
[0043] In accordance with an embodiment, a wafer including a
plurality of active photodiode regions (i.e., PN junctions between
regions 302 and 303) is manufactured at a semiconductor a fab.
Thereafter, the wafer is transferred to an optoelectronic and/or
optical device fabrication facility, where the dielectric
reflective optical coating filter 350 is formed over substantially
the entire wafer. The wafer with dielectric reflective optical
coating filter can then be returned to a semiconductor fab where
patterning can be performed, and ILD, metal, contact, via and
passivation processing can be performed to add interlayer
dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization
330, and a top passivation layer 326 (e.g., an oxide layer capped
with a nitride layer) for each active photodiode region. The window
340 can then be opened for each photodiode region. The wafer can
then be diced into photodiode dies, and packaging can be added to
produce photodiode integrated circuit (IC) chips. It is also
possible that all of the above steps occur within the same
facility, if such facility is appropriately equipped to perform
both semiconductor and optical fabrication.
[0044] In the embodiments described with reference to FIGS. 3B-3E
and 4, the dielectric reflective optical coating filter 350 was
described as being formed on top of a passivation coating 315. In
accordance with alternative embodiments, the dielectric reflective
optical coating filter 350 is formed directly on top of the
diffusion layer 303, or a thin oxide layer on the diffusion layer
303, as will now be described with reference to FIGS. 5A-5E and 6.
In such embodiments, the bottom layers of the dielectric reflective
optical coating filter 350 can be designed to perform the function
of the passivation coating 315. For example, the lowest layer of
the dielectric reflective optical coating filter 350 can be an
oxide (e.g., SiO.sub.2) to provide stress relief, and the second
from the lowest layer can be a nitride (e.g., Si.sub.3N.sub.4), to
protect the active photodiode region from moisture.
[0045] FIG. 5A illustrates that the etch stop coating 315 can be
formed directly on top of the diffusion layer 303 such that it
extends beyond the boundary of the diffusion layer 303. A portion
of the etch stop coating 315 is removed outside the active
photodiode region down to the first semiconductor type surface
region, e.g., the P- surface region 302, to make room for
metalization. Thereafter, ILD, metal, contact, via and passivation
processing can be performed to add interlayer dielectric (ILD)
layers 321, 322, 323, 324 and 325, metalization 330, and a top
passivation layer 326 (e.g., an oxide layer capped with a nitride
layer). At this point, there are numerous ILD layers (e.g., layers
321, 322, 323, 324 and 325) and a top passivation layer 326 over
the active photodiode region, which layers affect the spectral
response of the underlying active photodiode region. A window 340
is then formed over the active photodiode region, with the window
extending down to the diffusion region 303, or alternatively, a
thin layer of the oxide 317 of the etch stop coating 315 can be
kept. In a similar manner as was discussed above with regards to
FIG. 3A, a photoresist can be patterned to open the window 340
(also referred to as an opening or a trench).
[0046] Referring now to FIG. 5B-5E, the dielectric reflective
optical coating filter 350 can then be added. Depending on the
depth for the trench 340 and the thickness of the dielectric
reflective optical coating filter 350, the dielectric reflective
optical coating filter 350 can fill only a portion of the trench
(as in the photodiode 500b of FIG. 5B), or can fill the entire
trench and even extend above the trench (as in the photodiode 500e
of FIG. 5E). As shown in FIGS. 5C and 5E, the dark mirror coating
360 can be added to cover the sidewalls 355 and top surface 357 of
the dielectric reflective optical coating filter 350.
Alternatively, or additionally, as shown in FIG. 5D, the area of
the N+ diffusion region 303 (and thus, the active photodiode
region) can be made substantially smaller than the opening formed
by the sidewalls 355 of the dielectric reflective optical coating
filter 350, in a similar manner as was explained above with
reference to FIG. 3D. The embodiments of FIGS. 5C and 5D can be
combined so that the area of the N+ diffusion region 303 (and thus,
the active photodiode region) is made substantially smaller than
the opening formed by the sidewalls 355 of the dielectric
reflective optical coating filter 350, and a dark mirror coating is
added to cover the sidewalls 355 and the top surface 357 of the
dielectric reflective optical coating filter 350.
[0047] In accordance with an alternative embodiment, described with
reference to FIG. 6, the dielectric reflective optical coating
filter 350 of the photodiode 600 is formed on the diffusion region
303 before the trench is formed. Thereafter, the etch stop coating
315 is formed on the dielectric reflective optical coating filter
350. A portion of the etch stop coating 315 and the dielectric
reflective optical coating filter 350 is removed outside the active
photodiode region down to the first semiconductor type surface
region, e.g., the P- surface region 302, to make room for
metalization. Thereafter, ILD, metal, contact, via and passivation
processing can be performed to add interlayer dielectric (ILD)
layers 321, 322, 323, 324 and 325, metalization 330, and a top
passivation layer 326 (e.g., an oxide layer capped with a nitride
layer).
[0048] At this point, there are numerous ILD layers (e.g., layers
321, 322, 323, 324 and 325) and a top passivation layer 326 over
the active photodiode region, which layers affect the spectral
response of the underlying active photodiode region. The ILD layers
and the top passivation layer over the active photodiode region are
removed. In other words, a window 340 is formed over the active
photodiode region, with the window extending down to the dielectric
reflective optical coating filter 350, in a similar manner as was
discussed above with regards to FIG. 4. In a similar manner as was
discussed above with regards to FIG. 3A, a photoresist can be
patterned to open the window 340 (also referred to as an opening or
a trench).
[0049] Referring back to FIG. 1, it can be appreciated that the
spectral response of the photodiode (not covered by a dielectric
reflective optical coating filter) is not flat. Thus, if the desire
is to provide a photodiode with a spectral response similar to that
of a typical human eye (shown in FIG. 2), then the spectral
response of the reflective optical coating filter should be
appropriately offset to compensate for the underlying photodiode
response. In other words, if F is the response the filter made up
of the dielectric reflective optical coating, T is the target
response (i.e., a response similar to that of a typical human eye
shown in FIG. 2), and P is the response of the photodiode (e.g.,
similar to the response shown in FIG. 1), then the response of the
filter F should be designed such that F=T/P. This is illustrated in
FIG. 7, which shows that the filter response (F) is shifted
relative to the target response (T), so that when the filter is
used with a photodiode having a photodiode response (P), the target
response (T) is achieved. In accordance with an embodiment, the
target response (so that the response resembles that of a human
eye) has a low frequency 50% cut-off at about 500 nm (+/-10 nm), a
peak at about 550 nm (+/-10 nm), and a high frequency 50% cut-off
at about 600 nm (+/-10 nm).
[0050] There have been previous attempts to cover a silicon wafer
with a dielectric reflective optical coating filter. However, such
attempts have placed the dielectric reflective optical coating
filter above a top passivation coating (e.g., similar coating 326),
which has resulted in a spectral response that includes undesirable
ripples due to interference effects at the top passivation layers.
The embodiments of the invention described herein significantly
reduce (or eliminate) the thickness of passivation coatings used in
standard processes, therefore reducing such ripples in the spectral
response. While described as being especially useful for producing
an ambient light sensor (ALS), the photodiode structures described
herein can be used with alternative dielectric reflective optical
coating filter designs for other applications, such as, but not
limited to, red (R), green (G) and blue (B) sensors.
[0051] In the embodiments described above, the target response was
often described as being similar to that of a typical human eye
viewing diffused light. However, that need not be the case. For
example, other target responses can be for an optical sensor to
only detect light of a specific color, such as red, green or blue.
Such photodiodes can be used, e.g., in digital cameras, color
scanners, color photocopiers, and the like. In these embodiments,
the dielectric reflective optical coating filter 350 can be
optimized for the specific color to be detected, and can be used
alone or in combination with the various techniques for filtering
out IR light that happens to make it through the dielectric
reflective optical coating filter 350. For example, one or more
photodiode(s) can be optimized to detect green light, one or more
further photodiode(s) can be optimized to detect red light, and one
or more further photodiode(s) can be optimized to detect blue
light, with one or more of these photodiode(s) including a
dielectric reflective optical coating filter.
[0052] In the above described embodiments, N regions are described
as being implanted in a P region. For example, the N+ diffusion
region 303 is implanted in P.sup.- region 302. In alternative
embodiments, the semiconductor conductivity materials are reversed.
That is, a P region is implanted in an N region. For a specific
example, a heavily doped P.sup.+ region is implanted in a lightly
doped N.sup.- region, to form the active photodiode region.
[0053] Certain embodiments of the present invention are also
directed to methods of producing photocurrents that are primarily
indicative of target wavelengths of light, e.g., wavelengths of
visible light. In other words, embodiments of the present invention
are also directed to methods for providing a photodiode having a
target spectral response, such as, a response similar to that of
the human eye. Additionally, embodiments of the present invention
are also directed to methods of using the above described
photodiodes.
[0054] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention.
[0055] The breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *