U.S. patent application number 15/898357 was filed with the patent office on 2018-06-21 for photosensitive imaging devices and associated methods.
The applicant listed for this patent is SiOnyx, LLC. Invention is credited to Leonard Forbes, Homayoon Haddad, Jutao Jiang, Jeffrey McKee, Drake Miller, Chintamani Palsule.
Application Number | 20180175093 15/898357 |
Document ID | / |
Family ID | 54142870 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180175093 |
Kind Code |
A1 |
Haddad; Homayoon ; et
al. |
June 21, 2018 |
PHOTOSENSITIVE IMAGING DEVICES AND ASSOCIATED METHODS
Abstract
Photosensitive devices and associated methods are provided. In
one aspect, for example, a photosensitive imager device can include
a semiconductor substrate having multiple doped regions forming at
least one junction, a textured region coupled to the semiconductor
substrate and positioned to interact with electromagnetic
radiation, and an electrical transfer element coupled to the
semiconductor substrate and operable to transfer an electrical
signal from the at least one junction. In one aspect, the textured
region is operable to facilitate generation of an electrical signal
from the detection of infrared electromagnetic radiation. In
another aspect, interacting with electromagnetic radiation further
includes increasing the semiconductor substrate's effective
absorption wavelength as compared to a semiconductor substrate
lacking a textured region.
Inventors: |
Haddad; Homayoon;
(Beaverton, OR) ; Jiang; Jutao; (Tigard, OR)
; McKee; Jeffrey; (Tualatin, OR) ; Miller;
Drake; (Tigard, OR) ; Forbes; Leonard;
(Corvallis, OR) ; Palsule; Chintamani; (Lake
Oswego, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SiOnyx, LLC |
Beverly |
MA |
US |
|
|
Family ID: |
54142870 |
Appl. No.: |
15/898357 |
Filed: |
February 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14223938 |
Mar 24, 2014 |
9911781 |
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15898357 |
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|
12885158 |
Sep 17, 2010 |
8680591 |
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14223938 |
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61311004 |
Mar 5, 2010 |
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61311107 |
Mar 5, 2010 |
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61243434 |
Sep 17, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/1463 20130101;
H01L 27/14643 20130101; H01L 27/14609 20130101; H01L 27/14625
20130101; H01L 27/14689 20130101; H01L 27/14629 20130101; H01L
27/14698 20130101; H01L 27/14685 20130101; H01L 27/1462 20130101;
H01L 27/14638 20130101 |
International
Class: |
H01L 27/146 20060101
H01L027/146 |
Claims
1-28. (canceled)
29. A photosensitive imager pixel, comprising: a semiconductor
substrate having a radiation-receiving surface for receiving
incident electromagnetic radiation and multiple doped regions
forming at least one junction, a textured region associated with
the semiconductor substrate and positioned to receive at least a
portion of the incident electromagnetic radiation and interact with
said received electromagnetic radiation to cause at least a portion
of said electromagnetic radiation to experience multiple passes
within said semiconductor substrate so as to enhance quantum
efficiency of said imager device, and an electrical transfer
element coupled to the semiconductor substrate and operable to
transfer an electrical signal generated in response to absorption
of the electromagnetic radiation within said semiconductor
substrate.
30. The photosensitive imager pixel of claim 29, wherein said
semiconductor substrate comprises said textured region.
31. The photosensitive imager pixel of claim 29, wherein said
textured region is coupled to a surface opposite the
radiation-receiving surface.
32. The photosensitive imager pixel of claim 31, wherein said
surface opposite the radiation-receiving surface comprises said
textured region.
33. The photosensitive imager pixel of claim 31, further comprising
an additional textured region coupled to said radiation-receiving
surface of said semiconductor substrate.
34. The photosensitive imager pixel of claim 29, wherein said
textured region is coupled to said radiation-receiving surface of
said semiconductor substrate.
35. The photosensitive imager pixel of claim 29, wherein said
textured region comprises surface features selected from the group
consisting of cones, pillars, pyramids, microlenses, quantum dots,
inverted features, and combinations thereof.
36. The photosensitive imager pixel of claim 35, wherein said
surface features have a size in a range of about 50 nm to about 20
microns.
37. The photosensitive imager pixel of claim 29, wherein said
incident electromagnetic radiation comprises infrared radiation
having a wavelength in a range of about 800 nm to about 1300
nm.
38. The photosensitive imager pixel of claim 29, wherein said
transfer element is selected from the group consisting of a
transistor, a sensing node, a transfer gate, and combinations
thereof.
39. The photosensitive imager pixel of claim 29, further comprising
a lens optically coupled to said radiation-receiving surface and
positioned to focus the incident electromagnetic radiation into the
semiconductor substrate.
40. The photosensitive imager pixel of claim 29, wherein a side
surface of said semiconductor substrate comprises said textured
region.
41. The photosensitive imager pixel of claim 29, wherein said
semiconductor substrate comprises silicon.
42. A photosensitive imager array, comprising: at least two
neighboring photosensitive pixels, each of said photosensitive
pixels comprising: a semiconductor substrate having a
radiation-receiving surface for receiving incident electromagnetic
radiation and multiple doped regions forming at least one junction,
and a textured region coupled to the semiconductor substrate and
positioned to receive at least a portion of the incident
electromagnetic radiation and to interact with said received
electromagnetic radiation to cause any of diffusion and redirection
of the electromagnetic radiation so as to enhance the semiconductor
substrate's effective absorption length and increase the
photosensitive imager's quantum efficiency; and an electrical
transfer element coupled to the semiconductor substrate and
operable to transfer an electrical signal generated in response to
absorption of the electromagnetic radiation within said
semiconductor substrate.
43. The photosensitive imager array of claim 42, wherein the
textured region of each of said photosensitive pixels is configured
to cause at least a portion of the incident electromagnetic
radiation entering the semiconductor substrate to experience
multiple passes within the semiconductor substrate.
44. The photosensitive imager array of claim 42, wherein said
textured region is coupled to a surface opposite to said
radiation-receiving surface.
45. The photosensitive imager array of claim 42, wherein said
surface opposite said radiation-receiving surface comprises said
textured region.
46. The photosensitive imager array of claim 42, wherein at least
one of said photosensitive pixels comprises an additional textured
region.
47. The photosensitive imager array of claim 42, wherein said
textured region is coupled to said radiation-receiving surface of
said semiconductor substrate.
48. The photosensitive imager array of claim 42, wherein said
incident electromagnetic radiation comprises infrared radiation
having a wavelength in a range of about 800 nm to about 1300 nm.
Description
PRIORITY DATA
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/223,938, filed on Mar. 24, 2014, which is a
continuation of U.S. patent application Ser. No. 12/885,158, filed
on Sep. 17, 2010, now issued as U.S. Pat. No. 8,680,591, which
claims the benefit of U.S. Provisional Patent Application Ser. No.
61/243,434, filed on Sep. 17, 2009, U.S. Provisional Patent
Application Ser. No. 61/311,004 filed on Mar. 5, 2010, and U.S.
Provisional Patent Application Ser. No. 61/311,107, filed on Mar.
5, 2010, each of which is incorporated herein by reference.
BACKGROUND
[0002] The interaction of light with semiconductor materials has
been a significant innovation. Silicon imaging devices are used in
various technologies, such as digital cameras, optical mice, video
cameras, cell phones, and the like. Charge-coupled devices (CCDs)
were widely used in digital imaging, and were later improved upon
by complementary metal-oxide-semiconductor (CMOS) imagers having
increased performance. CMOS sensors are typically manufactured from
silicon and can covert visible incident light into a photocurrent
and ultimately into a digital image. Silicon-based technologies for
detecting infrared incident electromagnetic radiation have been
problematic, however, because silicon is an indirect bandgap
semiconductor having a bandgap of about 1.1 eV. Thus the absorption
of electromagnetic radiation having wavelengths of greater than
about 1100 nm is, therefore, very low in silicon.
SUMMARY
[0003] The present disclosure provides photosensitive devices and
associated methods. In one aspect, for example, a photosensitive
imager device can include a semiconductor substrate having multiple
doped regions forming at least one junction, a textured region
coupled to the semiconductor substrate and positioned to interact
with electromagnetic radiation, and an electrical transfer element
coupled to the semiconductor substrate and operable to transfer an
electrical signal from the at least one junction. In one aspect,
the textured region is operable to facilitate generation of an
electrical signal from the detection of infrared electromagnetic
radiation. In another aspect, interacting with electromagnetic
radiation further includes increasing the semiconductor substrate's
effective absorption length as compared to a semiconductor
substrate lacking a textured region. In one specific aspect, the
transfer element is selected from the group consisting of a
transistor, a sensing node, a transfer gate, and combinations
thereof.
[0004] The textured region can be positioned in a variety of
locations relative to the doped regions. In one aspect, for
example, the textured region is positioned on a surface of the
semiconductor substrate that is opposite the multiple doped
regions. In one specific aspect, the textured region has a surface
morphology operable to direct electromagnetic radiation into or out
of the semiconductor substrate. The surface morphology of the
textured region relative to the semiconductor substrate can include
a variety of configurations, including, without limitation,
sloping, pyramidal, inverted pyramidal, spherical, parabolic,
asymmetric, symmetric, and the like, including combinations
thereof.
[0005] In another aspect, the textured region can be positioned on
a surface of the semiconductor substrate that is adjacent the
multiple doped regions. In a more specific aspect, an additional
textured region can be positioned on a surface of the semiconductor
substrate that is opposite the multiple doped regions. In this
manner, textured regions can thus be positioned adjacent to
multiple doped regions and opposite the multiple doped regions.
[0006] Various aspects of the textured region can vary depending on
the desired configuration of the device. In one aspect, however,
the textured region includes surface features having a size
selected from the group consisting of micron-sized, nano-sized, and
combinations thereof. Numerous surface feature morphologies are
contemplated, nonlimiting examples of which include cones, pillars,
pyramids, micolenses, quantum dots, inverted features, and
combinations thereof. Additionally, the textured region can be
formed by a variety of processes. Nonlimiting examples of such
texturing processes can include lazing, chemical etching (e.g.
anisotropic etching, isotropic etching), nanoimprinting, material
deposition, and combinations thereof.
[0007] Additional layers and/or structures can be included in
various devices according to aspects present disclosure. In one
aspect, for example, a reflective layer can be coupled to the
semiconductor substrate and positioned to maintain the
electromagnetic radiation in the semiconductor substrate. In
another aspect, a lens can be optically coupled to the
semiconductor substrate and positioned to focus incident
electromagnetic radiation into the semiconductor substrate.
[0008] In another aspect of the present disclosure, a method of
making a photosensitive imager device is provided. Such a method
can include forming a textured region on a semiconductor substrate
having multiple doped regions forming a least one junction, wherein
the textured region is formed in a position to interact with
electromagnetic radiation and coupling an electrical transfer
element to the semiconductor substrate such that the electrical
transfer element is operable to transfer an electrical signal from
the at least one junction.
[0009] In one aspect, the photosensitive imager device can be tuned
to be selected to filter out specific electromagnetic radiation
wavelengths. In one specific aspect, tuning includes forming
surface features to have dimensions that selectively diffuse or
selectively absorb a desired wavelength of electromagnetic
radiation. In another aspect, tuning is accomplished through a
factor selected from the group consisting of placement of the
textured region, material type and/or thickness of the textured
region, dopant type of the textured region, doping profile of the
texture region, dopant profile of the semiconductor substrate,
material type and/or thickness of the semiconductor substrate, and
combinations thereof.
[0010] In another aspect of the present disclosure, a
photosensitive imager device is provided. Such a device can include
a semiconductor substrate having multiple doped regions forming a
least one junction, a textured region coupled to the semiconductor
substrate and positioned to interact with electromagnetic
radiation, and at least 4 transistors coupled to the semiconductor
substrate and with at least one of the transistors electrically
coupled to the at least one junction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of a photosensitive device in
accordance with one aspect of the present disclosure;
[0012] FIG. 2 is a schematic view of a photosensitive device in
accordance with another aspect of the present disclosure;
[0013] FIG. 3 is a schematic view of a photosensitive device in
accordance with yet another aspect of the present disclosure;
[0014] FIG. 4 is a schematic view of a photosensitive device in
accordance with a further aspect of the present disclosure;
[0015] FIG. 5 is a schematic view of a photosensitive device in
accordance with yet a further aspect of the present disclosure;
[0016] FIG. 6 is a schematic view of a photosensitive device in
accordance with another aspect of the present disclosure;
[0017] FIG. 7 is a schematic view of a photosensitive pixel device
in accordance with yet another aspect of the present
disclosure;
[0018] FIG. 8 is a schematic view of a photosensitive pixel device
in accordance with a further aspect of the present disclosure;
[0019] FIG. 9 is a schematic view of a photosensitive pixel device
in accordance with yet a further aspect of the present
disclosure;
[0020] FIG. 10 is a schematic view of a photosensitive pixel device
in accordance with another aspect of the present disclosure;
[0021] FIG. 11 is a schematic view of a photosensitive pixel device
in accordance with yet another aspect of the present
disclosure;
[0022] FIG. 12 is a schematic view of a photosensitive pixel device
in accordance with a further aspect of the present disclosure;
[0023] FIG. 13 is a schematic view of a photosensitive pixel device
in accordance with another aspect of the present disclosure;
[0024] FIG. 14 is a schematic view of a photosensitive imager
device in accordance with yet another aspect of the present
disclosure;
[0025] FIG. 15 is a schematic view of a photosensitive pixel device
in accordance with a further aspect of the present disclosure;
[0026] FIG. 16 is a schematic view of a photosensitive pixel device
in accordance with another aspect of the present disclosure;
and
[0027] FIG. 17 is a depiction of a method of making a
photosensitive imager device in accordance with yet another aspect
of the present disclosure.
DETAILED DESCRIPTION
[0028] Before the present disclosure is described herein, it is to
be understood that this disclosure is not limited to the particular
structures, process steps, or materials disclosed herein, but is
extended to equivalents thereof as would be recognized by those
ordinarily skilled in the relevant arts. It should also be
understood that terminology employed herein is used for the purpose
of describing particular embodiments only and is not intended to be
limiting.
Definitions
[0029] The following terminology will be used in accordance with
the definitions set forth below.
[0030] It should be noted that, as used in this specification and
the appended claims, the singular forms "a," and, "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a dopant" includes one or more of
such dopants and reference to "the layer" includes reference to one
or more of such layers.
[0031] As used herein, the term "low oxygen content" refers to any
material having an interstitial oxygen content that is less than or
equal to about 60 ppm atomic.
[0032] As used herein, the terms "disordered surface" and "textured
surface" can be used interchangeably, and refer to a surface having
a topology with nano- to micron-sized surface variations formed by
the irradiation of laser pulses. While the characteristics of such
a surface can be variable depending on the materials and techniques
employed, in one aspect such a surface can be several hundred
nanometers thick and made up of nanocrystallites (e.g. from about
10 to about 50 nanometers) and nanopores. In another aspect, such a
surface can include micron-sized structures (e.g. about 2 .mu.m to
about 60 .mu.m). In yet another aspect, the surface can include
nano-sized and/or micron-sized structures from about 5 nm and about
500 .mu.m.
[0033] As used herein, the term "fluence" refers to the amount of
energy from a single pulse of laser radiation that passes through a
unit area. In other words, "fluence" can be described as the energy
density of one laser pulse.
[0034] As used herein, the terms "surface modifying" and "surface
modification" refer to the altering of a surface of a semiconductor
material using laser radiation. In one specific aspect, surface
modification can include processes using primarily laser radiation
or laser radiation in combination with a dopant, whereby the laser
radiation facilitates the incorporation of the dopant into a
surface of the semiconductor material. Accordingly, in one aspect
surface modification includes doping of a semiconductor
material.
[0035] As used herein, the term "target region" refers to an area
of a semiconductor material that is intended to be doped or surface
modified using laser radiation. The target region of a
semiconductor material can vary as the surface modifying process
progresses. For example, after a first target region is doped or
surface modified, a second target region may be selected on the
same semiconductor material.
[0036] As used herein, the term "detection" refers to the sensing,
absorption, and/or collection of electromagnetic radiation.
[0037] As used herein, the term "substantially" refers to the
complete or nearly complete extent or degree of an action,
characteristic, property, state, structure, item, or result. For
example, an object that is "substantially" enclosed would mean that
the object is either completely enclosed or nearly completely
enclosed. The exact allowable degree of deviation from absolute
completeness may in some cases depend on the specific context.
However, generally speaking the nearness of completion will be so
as to have the same overall result as if absolute and total
completion were obtained. The use of "substantially" is equally
applicable when used in a negative connotation to refer to the
complete or near complete lack of an action, characteristic,
property, state, structure, item, or result. For example, a
composition that is "substantially free of" particles would either
completely lack particles, or so nearly completely lack particles
that the effect would be the same as if it completely lacked
particles. In other words, a composition that is "substantially
free of" an ingredient or element may still actually contain such
item as long as there is no measurable effect thereof.
[0038] As used herein, the term "about" is used to provide
flexibility to a numerical range endpoint by providing that a given
value may be "a little above" or "a little below" the endpoint.
[0039] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
[0040] Concentrations, amounts, and other numerical data may be
expressed or presented herein in a range format. It is to be
understood that such a range format is used merely for convenience
and brevity and thus should be interpreted flexibly to include not
only the numerical values explicitly recited as the limits of the
range, but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. As an illustration, a
numerical range of "about 1 to about 5" should be interpreted to
include not only the explicitly recited values of about 1 to about
5, but also include individual values and sub-ranges within the
indicated range. Thus, included in this numerical range are
individual values such as 2, 3, and 4 and sub-ranges such as from
1-3, from 2-4, and from 3-5, etc., as well as 1, 2, 3, 4, and 5,
individually.
[0041] This same principle applies to ranges reciting only one
numerical value as a minimum or a maximum. Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0042] The Disclosure
[0043] Electromagnetic radiation can be present across a broad
wavelength range, including visible range wavelengths
(approximately 350 nm to 800 nm) and non-visible wavelengths
(longer than about 800 nm or shorter than 350 nm). The infrared
spectrum is often described as including a near infrared portion of
the spectrum including wavelengths of approximately 800 to 1300 nm,
a short wave infrared portion of the spectrum including wavelengths
of approximately 1300 nm to 3 micrometers, and a mid to long wave
infrared (or thermal infrared) portion of the spectrum including
wavelengths greater than about 3 micrometers up to about 30
micrometers. These are generally and collectively referred to
herein as "infrared" portions of the electromagnetic spectrum
unless otherwise noted.
[0044] Traditional silicon photodetecting imagers have limited
light absorption/detection properties. For example, infrared light
is mostly transparent to such silicon based detectors. While other
materials (e.g. InGaAs) can be used to detect infrared
electromagnetic radiation having wavelengths greater than about
1000 nm, silicon is still commonly used because it is relatively
cheap to manufacture and can be used to detect wavelengths in the
visible spectrum (i.e. visible light, 350 nm-800 nm). Traditional
silicon materials require substantial absorption depths to detect
photons having wavelengths longer than approximately 700 nm. While
visible light can be absorbed at relatively shallow depths in
silicon, absorption of longer wavelengths (e.g. 900 nm) in silicon
of a standard wafer depth (e.g. approximately 750 .mu.m) is poor if
at all. The devices of the present disclosure increase the
absorption of semiconductor materials by decreasing the effective
absorption length to longer wavelengths as compared to traditional
materials. For example, the absorption depth of silicon can be
reduced such that these longer wavelengths can be absorbed at
depths of less than or equal to about 850 .mu.m. In other words, by
decreasing the effective absorption length these devices are able
to absorb longer wavelengths (e.g. >1000 nm for silicon) within
a thin semiconductor material. In addition to increasing the
effective absorption length, the response rate or response speed
can also be increased using thinner semiconductor materials.
[0045] The present disclosure additionally provides broadband
photosensitive diodes, pixels, and imagers capable of detecting
visible as well as infrared electromagnetic radiation, including
associated methods of making such devices. A photosensitive diode
can include a semiconductor substrate having multiple doped regions
forming at least one junction, and at least one textured region
coupled to the semiconductor substrate and positioned to interact
with electromagnetic radiation. In one aspect the multiple doped
regions can include at least one cathode region and at least one
anode region. In some aspects, doped regions can include an n-type
dopant and/or a p-type dopant as is discussed below, thereby
creating a p-n junction. In other aspects, a photosensitive device
can include an i-type region to form a p-i-n junction.
[0046] A photosensitive pixel can include a semiconductor substrate
having multiple doped regions forming at least one junction, at
least one textured region coupled to the semiconductor substrate
and positioned to interact with electromagnetic radiation, and an
electrical transfer element coupled to the semiconductor substrate
and operable to transfer an electrical signal from the at least one
junction. A photosensitive imager can include multiple
photosensitive pixels. Additionally, an electrical transfer element
can include a variety of devices, including without limitation,
transistors, sensing nodes, transfer gates, transfer electrodes,
and the like.
[0047] Photosensitive or photodetecting imagers include photodiodes
or pixels that are capable of absorbing electromagnetic radiation
within a given wavelength range. Such imagers can be passive pixel
sensors (PPS), active pixel sensors (APS), digital pixel sensor
imagers (DPS), or the like, with one difference being the image
sensor read out architecture. For example, a semiconducting
photosensitive imager can be a three or four transistor active
pixel sensor (3T APS or 4T APS). Various additional components are
also contemplated, and would necessarily vary depending on the
particular configuration and intended results. As and example, a 4T
configuration can additionally include, among other things, a
transfer gate, a reset, a source follower, and row select
transistors. Additionally, devices having greater than 4
transistors are also within the present scope.
[0048] Photosensitive imagers can be front side illumination (FSI)
or back side illumination (BSI) devices, and there are advantages
and disadvantages to both architecture types. In a typical FSI
imager, incident light enters the semiconductor device by first
passing by transistors and metal circuitry. The light, however, can
scatter off of the transistors and circuitry prior to entering the
light sensing portion of the imager, thus causing optical loss and
noise. A lens can be disposed on the topside of a FSI pixel to
direct and focus the incident light to the light sensing active
region of the device, thus partially avoiding the circuitry. In one
aspect the lens can be a ulens. BSI imagers, one the other hand,
are configured to have the depletion region of the junction
extending to the opposite side of the device. In one aspect, for
example, incident light enters the device via the light sensing
portion and is mostly absorbed prior to reaching the circuitry. BSI
designs allow for smaller pixel architecture and a high fill factor
for the imager. As mentioned, the present disclosure can be adapted
for either configuration. It should also be understood that devices
according to aspects of the present disclosure can be incorporated
into complimentary metal-oxide-semiconductor (CMOS) imager
architectures or charge-coupled device (CCD) imager
architectures.
[0049] In one aspect, as is shown in FIG. 1, a photosensitive diode
10 can include a semiconductor substrate 12 having multiple doped
regions 14, 16 forming at least one junction, and at least one
textured region 18 coupled to the semiconductor substrate and
positioned to interact with electromagnetic radiation. The
different doped regions can have the same doping profile or
different doping profiles, depending on the device. Such an
architecture is a FSI design where light enters the semiconductor
substrate from the direction of the multiple doped regions. While
the device shown in FIG. 1 contains three doped regions, it should
be noted that aspects containing one or more doped regions are
considered to be within the present scope. Additionally, the
semiconductor substrate can be doped, and thus can be considered to
be a doped region in some aspects. It should also be noted that the
photosensitive diode can be configured with a BSI architecture, and
thus electromagnetic radiation would enter the semiconductor
substrate from the direction of the textured region.
[0050] The various devices according to aspects of the present
disclosure can exhibit increased quantum efficiency over
traditional photosensitive devices. Any increase in the quantum
efficiency makes a large difference in the signal to noise ratio.
More complex structures can provide not only increased quantum
efficiency but also good uniformity from pixel to pixel. In
addition, devices of the present disclosure exhibit increased
responsivity as compared to traditional photosensitive devices. For
example, in one aspect the responsivity can be greater than or
equal to 0.8 A/W for wavelengths greater than 1000 nm for
semiconductor substrate that is less than 100 .mu.m thick.
[0051] Photosensitive imagers can be maintained under constant
conditions (fixed voltage or current) to provide enhanced linearity
and uniformity. Connections between the imager and the underlying
device layers can be achieved using vias fabricated from a
refractory metal, such as tungsten or tantalum. Placing storage
elements under the imager may provide various photonic benefits.
For example, the entire pixel array may be dedicated to signal
processing. This may enable higher performance by permitting access
to low level pixel signals. Furthermore, massively parallel
operations can be performed by pixel processors. For example,
analog to digital conversion, noise reduction (ie., true correlated
double sampling), power conditioning, nearest neighbor pixel
processing, compression, fusion, and color multiplexing operations
can be performed.
[0052] A variety of semiconductor materials are contemplated for
use with the devices and methods according to aspects of the
present disclosure. Non-limiting examples of such semiconductor
materials can include group IV materials, compounds and alloys
comprised of materials from groups II and VI, compounds and alloys
comprised of materials from groups III and V, and combinations
thereof. More specifically, exemplary group IV materials can
include silicon, carbon (e.g. diamond), germanium, and combinations
thereof. Various exemplary combinations of group IV materials can
include silicon carbide (SiC) and silicon germanium (SiGe). In one
specific aspect, the semiconductor material can be or include
silicon. Exemplary silicon materials can include amorphous silicon
(a-Si), microcrystalline silicon, multicrystalline silicon, and
monocrystalline silicon, as well as other crystal types. In another
aspect, the semiconductor material can include at least one of
silicon, carbon, germanium, aluminum nitride, gallium nitride,
indium gallium arsenide, aluminum gallium arsenide, and
combinations thereof.
[0053] Exemplary combinations of group II-VI materials can include
cadmium selenide (CdSe), cadmium sulfide (CdS), cadmium telluride
(CdTe), zinc oxide (ZnO), zinc selenide (ZnSe), zinc sulfide (ZnS),
zinc telluride (ZnTe), cadmium zinc telluride (CdZnTe, CZT),
mercury cadmium telluride (HgCdTe), mercury zinc telluride
(HgZnTe), mercury zinc selenide (HgZnSe), and combinations
thereof.
[0054] Exemplary combinations of group III-V materials can include
aluminum antimonide (AlSb), aluminum arsenide (AlAs), aluminum
nitride (AlN), aluminum phosphide (AlP), boron nitride (BN), boron
phosphide (BP), boron arsenide (BAs), gallium antimonide (GaSb),
gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide
(GaP), indium antimonide (InSb), indium arsenide (InAs), indium
nitride (InN), indium phosphide (InP), aluminum gallium arsenide
(AlGaAs, Al.sub.xGa.sub.1-xAs), indium gallium arsenide (InGaAs,
In.sub.xGa.sub.1-xAs), indium gallium phosphide (InGaP), aluminum
indium arsenide (AlInAs), aluminum indium antimonide (AlInSb),
gallium arsenide nitride (GaAsN), gallium arsenide phosphide
(GaAsP), aluminum gallium nitride (AlGaN), aluminum gallium
phosphide (AlGaP), indium gallium nitride (InGaN), indium arsenide
antimonide (InAsSb), indium gallium antimonide (InGaSb), aluminum
gallium indium phosphide (AlGaInP), aluminum gallium arsenide
phosphide (AlGaAsP), indium gallium arsenide phosphide (InGaAsP),
aluminum indium arsenide phosphide (AlInAsP), aluminum gallium
arsenide nitride (AlGaAsN), indium gallium arsenide nitride
(InGaAsN), indium aluminum arsenide nitride (InAlAsN), gallium
arsenide antimonide nitride (GaAsSbN), gallium indium nitride
arsenide antimonide (GaInNAsSb), gallium indium arsenide antimonide
phosphide (GaInAsSbP), and combinations thereof.
[0055] The semiconductor material can be of any thickness that
allows electromagnetic radiation detection and conversion
functionality, and thus any such thickness of semiconductor
material is considered to be within the present scope. In some
aspects the laser processed region of the semiconductor increases
the efficiency of the device such that the semiconductor material
can be thinner than has previously been possible. Decreasing the
thickness of the semiconductor reduces the amount of semiconductor
material required to make such a device. In one aspect, for
example, the semiconductor material has a thickness of from about
500 nm to about 50 .mu.m. In another aspect, the semiconductor
material has a thickness of less than or equal to about 500 .mu.m.
In yet another aspect, the semiconductor material has a thickness
of from about 1 .mu.m to about 10 .mu.m. In a further aspect, the
semiconductor material can have a thickness of from about 5 .mu.m
to about 750 .mu.m. In yet a further aspect, the semiconductor
material can have a thickness of from about 5 .mu.m to about 100
.mu.m.
[0056] Additionally, various types of semiconductor material are
contemplated, and any such material that can be incorporated into
an electromagnetic radiation detection device is considered to be
within the present scope. In one aspect, for example, the
semiconductor material is monocrystalline. In another aspect, the
semiconductor material is multicrystalline. In yet another aspect,
the semiconductor material is microcrystalline. It is also
contemplated that the semiconductor material can be amorphous.
Specific nonlimiting examples include amorphous silicon or
amorphous selenium.
[0057] The semiconductor materials of the present disclosure can
also be made using a variety of manufacturing processes. In some
cases the manufacturing procedures can affect the efficiency of the
device, and may be taken into account in achieving a desired
result. Exemplary manufacturing processes can include Czochralski
(Cz) processes, magnetic Czochralski (mCz) processes, Float Zone
(FZ) processes, epitaxial growth or deposition processes, and the
like. Whether or not low oxygen content is desired in the device
can also affect the choice of a manufacturing process for the
semiconductor material. Various processes produce semiconductor
materials containing varying amounts of oxygen, and as such, some
applications having more stringent tolerances with respect to
oxygen levels may benefit more from specific manufacturing
procedures as compared to others. For example, during CZ crystal
growth oxygen from the containment vessel, usually a quartz
crucible, can become incorporated into the crystal as it is pulled.
Additionally, other sources of oxygen contamination are also
possible with the CZ process. Such contamination may be reduced,
however, through the use of non oxygen-containing crucible
materials, as well as the development of other crystal growth
methods that do not utilize a crucible. One such process is the FZ
process.
[0058] Materials grown with the CZ method can also be made to have
lowered oxygen concentration through enhancements to the crystal
growth process, such as growing the crystal in the presence of a
magnetic field (i.e. the mCz process). Also, gettering techniques
can be employed to reduce the impact of oxygen or other impurities
on the finished device. These gettering techniques can include
thermal cycles to liberate or nucleate impurities, or selective ion
implantation of species to serve as gettering sites for the
impurities. For example, oxygen concentrated in the semiconductor
can be removed by the performing a furnace cycle to form a denuded
zone. During heating with an inert gas, oxygen near the surface of
the semiconductor diffuses out of the material. During the furnace
cycle but after the denuding step, nucleating and growing steps may
be performed. Nucleating sites for precipitates are formed during
the nucleating step, and the precipitates are grown from the
nucleating sites during a growing step. The precipitates are formed
from interstitial oxygen within the bulk of the semiconductor
material and beneath the denuded zone. The precipitation of oxygen
in the bulk of the semiconductor material can be desired because
such precipitates can act as gettering sites. Such precipitate
formation can also be performed to "lock up" interstitial oxygen
into the precipitates and reduce the likelihood that such oxygen
can migrates from the bulk of the semiconductor material into the
denuded zone.
[0059] In those aspects where low oxygen content of the device is
desired, further processing of the semiconductor material can be
performed so as to minimize the introduction of oxygen. Oxygen can
exist in different states or at different sites (for example,
interstitially or substitutionally) within a semiconductor such as
silicon, dependent upon the thermal processing the semiconductor
has received. If the semiconductor is subjected to temperatures
higher than, for example, about 1000.degree. C., oxygen can form
aggregates or clusters that serve as defect sites in the crystal
lattice. These sites may result in trap states and a reduction in
carrier lifetime within the semiconductor material and device can
occur. At lower temperatures (for example, around 400.degree. C. to
700.degree. C.), oxygen can behave as electrically active thermal
donors. Thus, oxygen can have a negative impact on carrier lifetime
and on carrier mobility. In a device fabricated to have
photoconductive gain, the presence of oxygen causing reduced
carrier lifetime may result in reduced levels of photoconductive
gain.
[0060] It may be beneficial, therefore, to produce semiconductor
devices such that a low oxygen content is obtained or maintained.
This can be accomplished in a variety of ways, including using
semiconductor materials having low levels of oxygen contained
therein to begin with, processing these materials in a manner that
minimizes the uptake of oxygen into the semiconductor lattice, and
utilizing techniques that eliminate or reduce oxygen that may be
present in the semiconductor. Such processes and techniques can
include, for example, annealing the semiconductor material and any
laser treated region to lower temperatures as compared to previous
annealing procedures. Annealing processes are discussed more fully
below.
[0061] Additionally, texture processing of the semiconductor
material and/or any annealing process can be performed in a
substantially oxygen-depleted environment in order to minimize the
introduction of oxygen into the semiconductor. An oxygen-depleted
or substantially oxygen-depleted environment can include a variety
of environments. In one aspect, for example, the oxygen-depleted
environment can be an environment whereby oxygen from the air or
other sources has been replaced with a gas or other fluid
containing little to no oxygen. In another aspect, processing can
occur in a vacuum environment, and thus contain little to no
oxygen. Additionally, oxygen-containing materials or materials that
introduce oxygen into the semiconductor, such as, for example,
quartz crucibles, can be avoided. As a practical matter, the term
"oxygen-depleted environment" can be used to describe an
environment with low levels of oxygen, provided a semiconductor
material can be processed therein within the desired tolerances.
Thus, environments having low oxygen, or little to no oxygen, are
environments in which a semiconductor can be processed as a
low-oxygen content semiconductor while maintaining oxygen levels
within the tolerances of the present disclosure. In one aspect, an
oxygen-depleted environment can be an oxygen-free environment.
Further details regarding low-oxygen content semiconductor
materials can be found in U.S. patent application Ser. No.
12/771,848, filed on Apr. 30, 2010, which is incorporated herein by
reference.
[0062] The semiconductor material can have varying levels of
interstitial oxygen depending on the desired efficiency of the
device. In some aspects, oxygen content may be of no concern, and
thus any level of oxygen within the lattice is acceptable. In other
aspects, a low oxygen content is desired. In one aspect a
semiconductor material can have an oxygen content that is less than
or equal to about 50 ppm atomic. In another aspect, a semiconductor
material can have an oxygen content that is less than or equal to
about 30 ppm atomic. In yet another aspect, the semiconductor
material can have an oxygen content less than or equal to about 10
ppm atomic. In another aspect the semiconductor can have an oxygen
content less than about 5 ppm atomic. In yet another aspect the
semiconductor can have an oxygen content less than about 1 ppm
atomic.
[0063] As has been described, the textured region can function to
diffuse electromagnetic radiation, to redirect electromagnetic
radiation, and to absorb electromagnetic radiation, thus increasing
the quantum efficiency of the device. The textured region can
include surface features to increase the effective absorption
length of the photosensitive pixel. The surface features can be
cones, pyramids, pillars, protrusions, microlenses, quantum dots,
inverted features and the like. Factors such as manipulating the
feature sizes, dimensions, material type, dopant profiles, texture
location, etc. can allow the diffusing region to be tunable for a
specific wavelength. In one aspect, tuning the device can allow
specific wavelengths or ranges of wavelengths to be absorbed. In
another aspect, tuning the device can allow specific wavelengths or
ranges of wavelengths to be reduced or eliminated via
filtering.
[0064] Tuning can also be accomplished through the location of the
texture region within the device, modifying the dopant profile(s)
of regions within the device, dopant selection, and the like.
Additionally, material composition near the textured region can
create a wavelength specific photosensing pixel device. It should
be noted that a wavelength specific photosensing pixel can differ
from one pixel to the next, and can be incorporated into an imaging
array. For example a 4.times.4 array can include a blue pixel, a
green pixel, a red pixel, and infrared light absorbing pixel, or a
blue pixel, two green pixels, and a red pixel.
[0065] Textured regions according to aspects of the present
disclosure can allow a photosensitive device to experience multiple
passes of incident electromagnetic radiation within the device,
particularly at longer wavelengths (i.e. infrared). Such internal
reflection increases the effective absorption length to be greater
than the thickness of the semiconductor substrate. This increase in
absorption length increases the quantum efficiency of the device,
leading to an improved signal to noise ratio.
[0066] The textured region can be formed by various techniques,
including lasing, chemical etching (e.g. anisotropic etching,
isotropic etching), nanoimprinting, additional material deposition,
and the like. For example, pillar features can be incorporated into
pixels by thinning or removing material from the backside of a FSI
semiconductor substrate by using deep trench isolation and etching
techniques. In one aspect material can be removed to a thickness of
about 20 .mu.m. Anisotropic etching can be used to produce a
sloping backside pyramid structure, spherical, structure parabolic
structure, a lens structure with reflectors, and the like. Such
features on the backside of pillars will also serve to diffuse and
reflect electromagnetic radiation.
[0067] In one aspect, the texturing process can be performed during
the manufacture of the photosensitive device. In another aspect,
the texturing process can be performed on a photosensitive device
that has previously been made. For example, a CMOS, CCD, or other
photosensitive element can be textured following manufacture. In
this case, material layers may be removed from the photosensitive
element to expose the semiconductor substrate or bulk material upon
which a textured region may be formed.
[0068] One effective method of producing a textured region is
through laser processing. Such laser processing allows discrete
locations of the semiconductor substrate to be textured. A variety
of techniques of laser processing to form a textured region are
contemplated, and any technique capable of forming such a region
should be considered to be within the present scope. Laser
treatment or processing can allow, among other things, enhanced
absorption properties and thus increased electromagnetic radiation
focusing and detection. The laser treated region can be associated
with the surface nearest the impinging electromagnetic radiation,
or the laser treated surface can be associated with a surface
opposite in relation to impinging electromagnetic radiation,
thereby allowing the radiation to pass through the semiconductor
material before it hits the laser treated region.
[0069] In one aspect, for example, a target region of the
semiconductor material can be irradiated with laser radiation to
form a textured region. Examples of such processing have been
described in further detail in U.S. Pat. Nos. 7,057,256, 7,354,792
and 7,442,629, which are incorporated herein by reference in their
entireties. Briefly, a surface of a semiconductor material is
irradiated with laser radiation to form a textured or surface
modified region. Such laser processing can occur with or without a
dopant material. In those aspects whereby a dopant is used, the
laser can be directed through a dopant carrier and onto the
semiconductor surface. In this way, dopant from the dopant carrier
is introduced into the target region of the semiconductor material.
Such a region incorporated into a semiconductor material can have
various benefits in accordance with aspects of the present
disclosure. For example, the target region typically has a textured
surface that increases the surface area of the laser treated region
and increases the probability of radiation absorption via the
mechanisms described herein. In one aspect, such a target region is
a substantially textured surface including micron-sized and/or
nano-sized surface features that have been generated by the laser
texturing. In another aspect, irradiating the surface of
semiconductor material includes exposing the laser radiation to a
dopant such that irradiation incorporates the dopant into the
semiconductor. Various dopant materials are known in the art, and
are discussed in more detail herein.
[0070] Thus the surface of the semiconductor material is chemically
and/or structurally altered by the laser treatment, which may, in
some aspects, result in the formation of surface features appearing
as microstructures or patterned areas on the surface and, if a
dopant is used, the incorporation of such dopants into the
semiconductor material. In some aspects, the features or
microstructures can be on the order of 50 nm to 20 .mu.m in size
and can assist in the absorption of electromagnetic radiation. In
other words, the textured surface can increase the probability of
incident radiation being absorbed by the semiconductor
material.
[0071] The type of laser radiation used to surface modify a
semiconductor material can vary depending on the material and the
intended modification. Any laser radiation known in the art can be
used with the devices and methods of the present disclosure. There
are a number of laser characteristics, however, that can affect the
surface modification process and/or the resulting product
including, but not limited to the wavelength of the laser
radiation, pulse width, pulse fluence, pulse frequency,
polarization, laser propagation direction relative to the
semiconductor material, etc. In one aspect, a laser can be
configured to provide pulsatile lasing of a semiconductor material.
A short-pulsed laser is one capable of producing femtosecond,
picosecond and/or nanosecond pulse durations. Laser pulses can have
a central wavelength in a range of about from about 10 nm to about
8 .mu.m, and more specifically from about 200 nm to about 1200 nm.
The pulse width of the laser radiation can be in a range of from
about tens of femtoseconds to about hundreds of nanoseconds. In one
aspect, laser pulse widths can be in the range of from about 50
femtoseconds to about 50 picoseconds. In another aspect, laser
pulse widths can be in the range of from about 50 picoseconds to
100 nanoseconds. In another aspect, laser pulse widths are in the
range of from about 50 to 500 femtoseconds.
[0072] The number of laser pulses irradiating a target region can
be in a range of from about 1 to about 2000. In one aspect, the
number of laser pulses irradiating a semiconductor target region
can be from about 2 to about 1000. Further, the repetition rate or
frequency of the pulses can be selected to be in a range of from
about 10 Hz to about 10 .mu.Hz, or in a range of from about 1 kHz
to about 1 MHz, or in a range from about 10 Hz to about 1 kHz.
Moreover, the fluence of each laser pulse can be in a range of from
about 1 kJ/m.sup.2 to about 20 kJ/m.sup.2, or in a range of from
about 3 kJ/m.sup.2 to about 8 kJ/m.sup.2.
[0073] A variety of dopant materials are contemplated, and any such
material that can be used in the laser treatment process to surface
modify a semiconductor material according to aspects of the present
disclosure is considered to be within the present scope. It should
be noted that the particular dopant utilized can vary depending on
the semiconductor material being laser treated, as well as the
intended use of the resulting semiconductor material. For example,
the selection of potential dopants may differ depending on whether
or not tuning of the photosensitive device is desired.
[0074] A dopant can be either electron donating or hole donating.
In one aspect, non-limiting examples of dopant materials can
include S, F, B, P, N, As, Se, Te, Ge, Ar, Ga, In, Sb, and
combinations thereof. It should be noted that the scope of dopant
materials should include, not only the dopant materials themselves,
but also materials in forms that deliver such dopants (i.e. dopant
carriers). For example, S dopant materials includes not only S, but
also any material capable being used to dope S into the target
region, such as, for example, H.sub.2S, SF.sub.6, SO.sub.2, and the
like, including combinations thereof. In one specific aspect, the
dopant can be S. Sulfur can be present at an ion dosage level of
between about 5.times.10.sup.14 and about 1.times.10.sup.16
ions/cm.sup.2. Non-limiting examples of fluorine-containing
compounds can include ClF.sub.3, PF.sub.5, F.sub.2 SF.sub.6,
BF.sub.3, GeF.sub.4, WF.sub.6, SiF.sub.4, HF, CF.sub.4, CHF.sub.3,
CH.sub.2F.sub.2, CH.sub.3F, C.sub.2F.sub.6, C.sub.2HF.sub.5,
C.sub.3F.sub.8, C.sub.4F.sub.8, NF.sub.3, and the like, including
combinations thereof. Non-limiting examples of boron-containing
compounds can include B(CH.sub.3).sub.3, BF.sub.3, BCl.sub.3, BN,
C.sub.2B.sub.10H.sub.12, borosilica, B.sub.2H.sub.6, and the like,
including combinations thereof. Non-limiting examples of
phosphorous-containing compounds can include PF.sub.5, PH.sub.3,
and the like, including combinations thereof. Non-limiting examples
of chlorine-containing compounds can include Cl.sub.2,
SiH.sub.2Cl.sub.2, HCl, SiCl.sub.4, and the like, including
combinations thereof. Dopants can also include arsenic-containing
compounds such as AsH.sub.3 and the like, as well as
antimony-containing compounds. Additionally, dopant materials can
include mixtures or combinations across dopant groups, i.e. a
sulfur-containing compound mixed with a chlorine-containing
compound. In one aspect, the dopant material can have a density
that is greater than air. In one specific aspect, the dopant
material can include Se, H.sub.2S, SF.sub.6, or mixtures thereof.
In yet another specific aspect, the dopant can be SF.sub.6 and can
have a predetermined concentration range of about
5.0.times.10.sup.-8 mol/cm.sup.3 to about 5.0.times.10.sup.-4
mol/cm.sup.3. SF.sub.6 gas is a good carrier for the incorporation
of sulfur into the semiconductor material via a laser process
without significant adverse effects on the semiconductor material.
Additionally, it is noted that dopants can also be liquid solutions
of n-type or p-type dopant materials dissolved in a solution such
as water, alcohol, or an acid or basic solution. Dopants can also
be solid materials applied as a powder or as a suspension dried
onto the wafer.
[0075] The semiconductor substrate can be annealed for a variety of
reasons, including dopant activation, semiconductor material damage
repair, and the like. In those aspects including a laser textured
region, the semiconductor material can be annealed prior to laser
treatment, following laser treatment, during laser treatment, or
both prior to and following laser treatment. Annealing can enhance
the semiconductive properties of the device, including increasing
the photoresponse properties of the semiconductor materials.
Additionally, annealing can reduce damage done by the lasing
process. Although any known anneal can be beneficial and would be
considered to be within the present scope, annealing at lower
temperatures can be particularly useful. Such a "low temperature"
anneal can greatly enhance the photoconductive gain and external
quantum efficiency of devices utilizing such materials. In one
aspect, for example, the semiconductor material can be annealed to
a temperature of from about 300.degree. C. to about 1100 C.degree..
In another aspect, the semiconductor material can be annealed to a
temperature of from about 500.degree. C. to about 900.degree. C. In
yet another aspect, the semiconductor material can be annealed to a
temperature of from about 700.degree. C. to about 800.degree. C. In
a further aspect, the semiconductor material can be annealed to a
temperature that is less than or equal to about 850.degree. C.
[0076] The duration of the annealing procedure can vary according
to the specific type of anneal being performed, as well as
according to the materials being used. For example, rapid annealing
processes can be used, and as such, the duration of the anneal may
be shorter as compared to other techniques. Various rapid thermal
anneal techniques are known, all of which should be considered to
be within the present scope. In one aspect, the semiconductor
material can be annealed by a rapid annealing process for a
duration of greater than or equal to about 1 .mu.s. In another
aspect, the duration of the rapid annealing process can be from
about 1 .mu.s to about 1 ms. As another example, a baking or
furnace anneal process can be used having durations that may be
longer compared to a rapid anneal. In one aspect, for example, the
semiconductor material can be annealed by a baking anneal process
for a duration of greater than or equal to about 1 ms to several
hours. As has been described, if low oxygen content semiconductor
materials are used it may be beneficial to anneal such materials in
a substantially oxygen-depleted environment.
[0077] As has been described, annealing can help reduce defects
inherent to the semiconductor substrate and otherwise reduce
electron/hole recombination. In other words, the annealing can help
create electron states that effectively reduce the undesirable
recombination processes. Annealing the semiconductor material may
also improve the responsivity or photoconductive gain of the
device. Photoconductive devices can have dopants, impurities, or
defects that can introduce energy levels that can trap carriers.
Trapping carriers and reducing recombination of photocarriers can
lead to an increase in photoconductive gain of the device. The
relationship of photoconductive gain and trapping time can be
represented by Equation (I):
Gain=.tau..sub.L/.tau..sub.t (I)
where ".tau..sub.L" is the lifetime of an excess carrier and
".tau..sub.t" is the transit time of the carriers across the
device. It is understood that the lifetime of an excess carrier can
be increased by trapping a carrier species and reducing the
recombination rate. An increase in gain can be achieved by trapping
centers in the semiconductor that have millisecond trapping times
at room temperature and short transit times in thinned lightly
doped wafers. These trapping locations can decrease the
recombination of carriers and therefore improve or increase the
photoconductive gain of the device by allowing more electrons to
traverse the different regions without being recombined.
[0078] Turning to FIG. 2, a reflecting layer 20 can be coupled to
the semiconductor substrate 12. The reflecting layer can be coupled
to any side or portion of the semiconductor substrate in order to
reflect electromagnetic radiation back into the device.
Accordingly, in one aspect the reflecting layer can be located on
the semiconductor substrate opposite the incoming electromagnetic
radiation. Thus, as is shown in FIG. 2, electromagnetic radiation
passing though the semiconductor substrate and the textured region
16 can be reflected back into the semiconductor substrate.
Additionally, a passivation layer 22 can be coupled to the
semiconductor substrate. The passivation layer is shown coupled to
the side of the semiconductor substrate facing the incoming
electromagnetic radiation, however a passivation layer can be
located anywhere on the device and still be within the present
scope.
[0079] As has been described, location of the textured region can
be used to provide enhancement and/or filtering of the incoming
electromagnetic radiation. For example, a textured region located
at the point of entry of the electromagnetic radiation into the
photosensitive device tends to bend the electromagnetic radiation,
particularly the blue wavelengths. Accordingly, one level of tuning
can be accomplished by locating the textured region on the surface
adjacent the incident electromagnetic radiation to purposely
effectuate the filtering of blue wavelengths. Additionally,
absorption of particular wavelengths of electromagnetic radiation
occurs at different depths in the semiconductor layer and/or
textured region. By increasing the absorption to green wavelengths,
for example, the electrical signal as a result of green wavelengths
can be increased in a diode or pixel. Certain traditional 4 pixel
imagers have one red, one blue, and two green pixels, with the
greater number of green pixels to account for increased sensitivity
of the human eye to green colors. Thus in one aspect, a 4 pixel
imager can have one blue, one red, and one green pixel having an
increased green wavelength absorption. The fourth pixel can be used
for an IR or other wavelength selective pixel depending on the
desired application of the imager.
[0080] FIG. 3 shows a photosensitive device having textured regions
30 located on the sides of the semiconductor substrate 12. Such a
configuration allows electromagnetic radiation normally exiting
through the sides of the device to be further defused and absorbed
within semiconductor substrate. The textured region(s) can be
located on one or more sides to facilitate the enhanced
absorption.
[0081] FIG. 4 shows a photosensitive device having a textured
region 40 having a nonparallel surface with respect to the
semiconductor substrate 12. Thus the overall configuration of the
textured region can be designed to further enhance absorption
and/or selectively tune the device. As has been described, the
nonparallel surface can have a variety of configurations, such as,
without limitation, nonparallel slope, a pyramid, an inverted
pyramid, a concave shape, a convex shape, and the like. In some
cases the configuration of the textured region can function to
direct or focus electromagnetic radiation into the semiconductor
substrate, and in other cases the configuration of the textured
region can function to direct or focus electromagnetic radiation
away from the semiconductor substrate.
[0082] As is shown in FIG. 5, a lens 50 can be coupled to the
semiconductor substrate 12 on a side facing incoming
electromagnetic radiation. Thus the lens can focus the
electromagnetic radiation into the semiconductor substrate. In
those aspects having circuitry or other structures disposed on the
incoming electromagnetic radiation surface, the lens can further
focus light around such structures, thereby reducing optical
scattering and noise.
[0083] As is shown in FIG. 6, a textured region 60 is located on
the semiconductor substrate 12 adjacent to the multiple doped
regions 14, 16. The textured region can be associated with at least
one of the doped regions as is shown, or the textured region can be
distinct from the doped regions (not shown). Electromagnetic
radiation can enter the photosensitive device at the side adjacent
the doped regions, or alternatively at the side opposite the doped
regions.
[0084] FIGS. 7-11 show various steps in the manufacture of a
photosensitive pixel according to aspects of the present
disclosure. FIG. 7 shows a cross-section of a front side
illumination (FSI) photosensitive pixel device. The photosensitive
pixel device can include a semiconductor substrate 72, and can be
referred to as bulk semiconductor material. The semiconductor
substrate includes at least one doped region 74 that can be doped
with an electron donating or hole donating species to cause the
region to become more positive or negative in polarity as compared
to the semiconductor substrate. In one aspect, for example, the
doped region can be p doped. In another aspect the doped region can
be n doped. A highly doped region 76 can be formed on or near the
doped region to create a pinned diode. In one example, the
semiconductor substrate can be negative in polarity, and the doped
region and the highly doped region can be doped with p+ and n-
dopants respectively. In some aspects, variations of n(--), n(-),
n(+), n(++), p(--), p(-), p(+), or p(++) type doping of the regions
can be used. It should be noted that in one aspect the highly doped
region can be the textured region. In other words, textured surface
features can be formed on or in the highly doped region.
[0085] The device of FIG. 7 can further include various metal
regions 78, at least one via 80, a passivation layer 82, trench
isolation 84, and an electrical transfer element 86. Trench
isolation elements can maintain pixel to pixel uniformity by
reducing optical and electrical crosstalk. The trench isolation can
be shallow (FIG. 7) or deep (FIG. 12) trench isolation. The trench
isolation can include various materials, including, without
limitation, dielectric materials, reflective materials, conductive
materials, light diffusing features, and the like. These trench
isolation regions can be configured to reflect incident light until
it is absorbed, thereby increase the effective absorption length of
the device.
[0086] As is shown in FIG. 8, a carrier substrate or carrier wafer
88 can be coupled to the photosensing pixel. In one aspect, the
carrier substrate can be disposed on the passivation layer 82,
although the carrier substrate can be disposed on any surface of
the device. In one aspect, for example, the carrier substrate can
be disposed on the semiconductor substrate (not shown). The carrier
substrate can be coupled to the photosensing pixel by various
techniques, and any such coupling mechanism is within the present
scope. In one aspect, for example, the coupling can occur by way of
a bonding layer or adhesive layer disposed on the device, for
example, on the passivation layer. The support substrate can
provide support to the semiconductor device both during and after
manufacture, depending on whether or not the support is removed.
The carrier substrate can be made of a semiconductor material that
is the same or similar to the bulk semiconductor material, or it
can be made of a different material.
[0087] As is shown in FIG. 9, a textured region 90 is coupled to
the semiconductor substrate 72 opposite the doped regions 74,76.
Thus light entering from the direction of the doped regions passes
through the semiconductor substrate prior to contacting the
textured region. The textured region can be disposed across an
entire surface of the semiconductor substrate, as is shown in FIG.
9, or it can be disposed on one or more discrete regions (not
shown).
[0088] As is shown in FIG. 10, an additional carrier support
substrate 100 can be coupled to the device on an opposing side from
the carrier support substrate 88. The additional carrier support
substrate can be utilized for a variety of purposes, including
providing additional support to the device, facilitating the
removal of the first carrier support substrate, and the like. A
reflective layer 102 can be disposed between the textured region 90
and the carrier support substrate. Thus the reflective layer can
reflect electromagnetic radiation that passes through the textured
region back toward the semiconductor substrate 72, thus reducing
optical loss and backscattering. Thus, in some aspects a reflective
layer can increase the quantum efficiency of the device. The
reflective layer material can be any reflective material that can
be incorporated into such a device. Nonlimiting examples can
include materials such as silver, aluminum, and the like.
[0089] As is shown in FIG. 11, the carrier support substrate can be
removed to expose the passivation layer 82 or any other material
layer that was previously covered by the carrier support substrate.
The additional carrier substrate 100 can be maintained in the
device, removed from the device, or thinned to reduce the thickness
of the substrate depending on the intended use of the device. The
removal of material from the device, including the carrier support
substrate and the additional carrier substrate, can be accomplished
by a variety of methods including, without limitation, etching,
chemical mechanical polishing, ion implanting (i.e. smart cut), and
the like.
[0090] Various types of trench isolation are contemplated, and any
such isolation is considered to be within the present scope. As has
been described, trench isolation can be shallow (FIG. 7, 84) or
deep (FIG. 12, 120) trench isolation. The trench isolation can also
include depths between shallow and deep, depending on the device
design. Trench isolation can include dielectric materials,
reflective materials, conductive materials, and combinations
thereof, including textured regions and other light diffusing
features. Thus the trench isolation layer can be configured to
reflect incident electromagnetic radiation, in some cases until it
is absorbed, thereby increasing the effective absorption length of
the device. Additionally, in some aspects pillar features can be
incorporated into pixels by thinning or removing material from the
semiconductor substrate using deep trench isolation and etching
techniques. As is shown in FIG. 13, the textured region 130 can
have a nonparallel surface with respect to the semiconductor
substrate 72 as has been described. This nonparallel morphology,
when included with the deep trench isolation 120, can effectively
focus electromagnetic radiation into the semiconductor substrate
from multiple sides.
[0091] It is also contemplated, that a non-bulk material can be
formed or disposed near a doped region in the device. The addition
of the non-bulk material can allow for electromagnetic radiation
diffusing features to be formed on or in the non-bulk material. A
metal layer defining an aperture can also be included in one aspect
of the present disclosure. The metal layer can be formed near the
doped regions and can have a light entering region that defines an
aperture. This light entering region can also include an
antireflecting material.
[0092] FIG. 14 shows a photosensitive imager comprising two
photosensitive pixels 140. Each photosensitive pixel includes a
boundary region 142 that can include metal circuitry and a textured
region 144. Each photosensitive pixel can include at least one
transistor 146 or other electrical transfer element. Additional
read out and circuitry elements 148 can be utilized and shared by
both photosensitive pixels.
[0093] Turning to FIG. 15, a backside illuminated (BSI)
photosensitive pixel according to one aspect present disclosure is
provided. A lens 150 and an anti-reflective coating 152 are
disposed on the backside of the pixel following thinning and trench
isolation. A color filter 154 can be optically coupled to the lens
to allow specific wavelengths filtering of the electromagnetic
radiation. A textured region 156 can be coupled to the
semiconductor substrate 72 opposite the lens in order to provide
diffusive scattering and reflection of the incident electromagnetic
radiation that passes through to the front side of the pixel. Thus
the electromagnetic radiation can be focused within the
semiconductor substrate to the combined action of the textured
region and the trench isolation 120
[0094] FIG. 16 shows a front side illuminated (FSI) imager
according to another aspect of the present disclosure. A lens 160
and an antireflecting passivation layer on 62 are coupled to the
front side of the pixel. A textured region 90 and a reflecting
layer 102 are coupled to the semiconductor substrate 72 opposite
the lens to provide diffusive scattering and reflection of the
incident electromagnetic radiation that passes through the
semiconductor substrate. An aperture 164 formed in a metal or other
reflective material layer 166 can increase the effectiveness of the
optical cavity. Thus the lens focuses electromagnetic radiation
through the aperture.
[0095] In other aspects of the present disclosure, various methods
of making photosensitive diodes, pixels, and imagers, are
contemplated. In one aspect, as is shown in FIG. 17, a method of
making a photosensitive imager device can include forming a
textured region on a semiconductor substrate having multiple doped
regions forming a least one junction, wherein the textured region
is formed in a position to interact with electromagnetic radiation
170. The method also includes coupling an electrical transfer
element to the semiconductor substrate such that the electrical
transfer element is operable to transfer an electrical signal from
the at least one junction 172. In one aspect, multiple pixels can
be associated together to form an imager. A passivation layer can
also be disposed on the photosensitive imager device to protect
and/or reduce the dark current of the device.
[0096] In another aspect of the present disclosure, a method for
making a photosensitive diode is provided. Such a method can
include forming at least one cathode and at least one anode on a
surface of a semiconductor substrate, coupling a textured region to
the semiconductor substrate, and coupling a support substrate to
the semiconductor substrate. The textured region can be located
adjacent to the anode and cathode, opposite the anode and cathode,
or both adjacent and opposite the anode and cathode. An electrical
transfer on the can be electrically coupled to at least one of the
anode and cathode to form a photosensitive pixel. In another
aspect, the semiconductor substrate can be thinned to improve the
response rate and/or speed of the device. A passivation layer can
also be disposed on the photosensitive diode to protect and/or
reduce the dark current of the device. An additional support
substrate can be attached to the device to provide additional
support. In one aspect, the additional support substrate can be
located on the opposite side of the photosensitive diode from the
support substrate. The support substrate can subsequently be
removed to allow for further processing.
[0097] Of course, it is to be understood that the above-described
arrangements are only illustrative of the application of the
principles of the present disclosure. Numerous modifications and
alternative arrangements may be devised by those skilled in the art
without departing from the spirit and scope of the present
disclosure and the appended claims are intended to cover such
modifications and arrangements. Thus, while the present disclosure
has been described above with particularity and detail in
connection with what is presently deemed to be the most practical
embodiments of the disclosure, it will be apparent to those of
ordinary skill in the art that numerous modifications, including,
but not limited to, variations in size, materials, shape, form,
function and manner of operation, assembly and use may be made
without departing from the principles and concepts set forth
herein.
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