U.S. patent application number 11/524509 was filed with the patent office on 2007-04-05 for apparatus and method for manufacturing positive or negative microlenses.
Invention is credited to Ulrich C. Boettiger, Jin Li.
Application Number | 20070076299 11/524509 |
Document ID | / |
Family ID | 35448608 |
Filed Date | 2007-04-05 |
United States Patent
Application |
20070076299 |
Kind Code |
A1 |
Boettiger; Ulrich C. ; et
al. |
April 5, 2007 |
Apparatus and method for manufacturing positive or negative
microlenses
Abstract
A variety of structures and methods used to adjust the shape,
radius and/or height of a microlens for a pixel array. The
structures affect volume and surface force parameters during
microlens formation. Exemplary microlens structures include a
microlens frame, base, material, protrusions or a combination
thereof to affect the shape, height and/or radius of the microlens.
The frame, base and/or protrusions alter the microlens flow
resulting from the heating of the microlens during fabrication such
that a height or radius of the microlens can be controlled. The
radius can be adjusted by the height differences between the
microlens and frame. The bigger the difference, the smaller the
radius will be.
Inventors: |
Boettiger; Ulrich C.;
(Boise, ID) ; Li; Jin; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
35448608 |
Appl. No.: |
11/524509 |
Filed: |
September 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10857948 |
Jun 2, 2004 |
|
|
|
11524509 |
Sep 21, 2006 |
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Current U.S.
Class: |
359/619 |
Current CPC
Class: |
H01L 27/14685 20130101;
H01L 27/14627 20130101; G02B 3/0018 20130101; G02B 27/10 20130101;
B29D 11/00278 20130101; B29D 11/00365 20130101; G02B 3/0056
20130101 |
Class at
Publication: |
359/619 |
International
Class: |
G02B 27/10 20060101
G02B027/10 |
Claims
1-64. (canceled)
65. A lens frame structure comprising: a plurality of frames
configured to receive and interact with a liquid-phase lens
material by tension and adhesion force to form a lens shape, each
frame comprising: a substantially vertical surface, the
substantially vertical surface comprising a substantially flat
portion.
66. The lens frame structure of claim 65, wherein the substantially
vertical surface slopes inwardly from a bottom of the substantially
flat portion.
67. The lens frame structure of claim 65, wherein the substantially
vertical surface comprises laterally sloping side end portions
below the substantially flat portion.
68. The lens frame structure of claim 65, wherein the substantially
vertical surface comprises a greater inward protrusion into the
space defined by each of the plurality of frames at a first point
than another point below the substantially flat portion.
69. The lens frame structure of claim 65, wherein each of the
plurality of frames is separated from each other.
70. The lens frame structure of claim 65, further comprising a
plurality of protrusions formed within the plurality of frames.
71. The lens frame structure of claim 65, wherein at least one of
the plurality of frames comprises a rectangular cavity.
72. The lens frame structure of claim 65, wherein the plurality of
frames cause a liquid-phase lens material to transition to a convex
shaped solid-phase lens structure after heat processing.
73. The lens frame structure of claim 65, wherein the plurality of
frames are configured to cause the liquid-phase lens material to
transition to a concave shaped solid-phase lens structure after
heat processing.
74. An image processing system, comprising: a semiconductor
substrate; a plurality of image pixels formed on the semiconductor
substrate; a plurality of lens structures respectively over each of
the plurality of image pixels, each of the plurality of lens
structures comprising a plurality of lens frames, each of the
plurality of lens frames comprising a substantially vertical
surface, the substantially vertical surface comprising a
substantially flat portion; and a lens formed within each of the
lens frames having a shape at least partially defined by surface
adhesion force interaction of a liquid-phase lens material with the
frames which solidifies as the lens.
75. The image processing system of claim 74, wherein the plurality
of surface interactions further include a plurality of forces
exerted against the liquid-phase lens material by a plurality of
the substantially vertical surfaces.
76. The image processing system of claim 74, wherein the
substantially vertical surface slopes inwardly from a bottom of the
substantially flat portion.
77. The image processing system of claim 74, wherein the
substantially vertical surface comprises laterally sloping side end
portions below the substantially flat portion.
78. The image processing system of claim 74, wherein the
substantially vertical surface comprises a greater inward
protrusion into the space defined by each of the plurality of lens
frames at a first point than another point below the substantially
flat portion.
79. The image processing system of claim 74, wherein each of the
plurality of lens frames is separated from each other.
80. The image processing system of claim 74, further comprising a
plurality of protrusions formed within the plurality of lens
frames.
81. An intermediate lens structure comprising: a planar layer
comprising a plurality of protrusions; a plurality of liquid-phase
lens material deposits disposed around the protrusions, whereby the
liquid-phase lens material has a shape related to a plurality of
surface interactions, a surface tension force and a geometric shape
of the plurality of protrusions.
82. An imager lens structure comprising: a containing structure
formed over a pixel, the containing structure including a plurality
of sidewalls; and a lens the comprising a shape defined by an
interaction of the containing structure and surface tension force
of a liquid phase form of the lens material, the lens having a
height dependent on at least one dimension of the sidewalls.
83. An intermediate lens structure comprising: a plurality of lens
frames, each of the plurality of lens frames comprising a
substantially vertical surface, the substantially vertical surface
comprising a substantially flat portion; and a plurality of
liquid-phase lens material deposits disposed in respective ones of
the plurality of lens frames, whereby the liquid-phase lens
material has a shape related to a plurality of surface
interactions, a surface tension force and a geometric shape of the
respective ones of the plurality of lens frames.
Description
FIELD OF THE INVENTION
[0001] The invention relates to fabrication of microlens structures
for image capture or display systems, and more specifically to
structures and methods of manufacturing of microlens arrays for
solid state imager systems.
BACKGROUND OF THE INVENTION
[0002] Solid state imagers, including charge coupled devices (CCD)
and CMOS sensors, have been commonly used in photo imaging
applications. A solid state imager circuit includes a focal plane
array of pixel cells, each one of the cells including either a
photogate, photoconductor or a photodiode having a doped region for
accumulating photo-generated charge. Microlenses are commonly
placed over imager pixel cells. A microlens is used to focus light
onto the initial charge accumulation region. Conventional
technology uses a single microlens with a polymer coating, which is
patterned into squares or circles provided respectively over the
pixels which are then heated during manufacturing to shape and cure
the microlens.
[0003] Use of microlenses significantly improves the
photosensitivity of the imaging device by collecting light from a
large light collecting area and focusing it on a small
photosensitive area of the sensor. The ratio of the overall light
collecting area to the photosensitive area of the sensor is known
as the pixel's fill factor.
[0004] The use of smaller sized microlens arrays is of increasing
importance in microlens optics. One reason for increased interest
in reducing the size of microlenses is the increased need to reduce
the size of imager devices and increase imager resolution. However,
reductions in pixel sizes result in a smaller charge accumulation
area in individual pixels in the array. Reduced sizes of pixels
result in smaller accumulated charges which are read out and
processed by signal processing circuits.
[0005] As the size of imager arrays and photosensitive regions of
pixels decreases, it becomes increasingly difficult to provide a
microlens capable of focusing incident light rays onto the
photosensitive regions. This problem is due in part to the
increased difficulty in constructing a smaller microlens that has
the optimal focal characteristics for the imager device process and
that optimally adjusts for optical aberrations introduced as the
light passes through the various device layers. Also, it is
difficult to correct possible distortions created by multiple
regions above the photosensitive area, which results in increased
crosstalk between adjacent pixels. "Crosstalk" can result when
off-axis light strikes a microlens at an obtuse angle. The off-axis
light passes through planarization regions and a color filter,
misses the intended photosensitive region and instead strikes an
adjacent photo sensitive region.
[0006] Microlens shaping and fabrication through heating and
melting microlens materials also becomes increasingly difficult as
microlens structures decrease in size. Previous approaches to
control microlens shaping and fabrication do not provide sufficient
control to ensure optical properties such as focal characteristics,
radius of a microlens or other parameters needed to provide a
desired focal effect for smaller microlens designs. Consequently,
imagers with smaller sized microlenses have difficulty in achieving
high color fidelity and signal/noise ratios.
BRIEF SUMMARY OF THE INVENTION
[0007] The various exemplary embodiments of the invention provide a
variety of structures and methods used to adjust the shape, radius
and/or height of a microlens for a pixel array. The embodiments use
structures that affect volume and surface force parameters during
microlens formation. Exemplary embodiments are directed to a
microlens structure that includes a microlens frame, base,
material, protrusions or a combination thereof to affect the shape,
height and/or radius of the microlens. The frame, base and/or
protrusions alter the microlens flow resulting from the heating of
the microlens during fabrication such that a height or radius of
the microlens can be controlled. The radius can be adjusted by the
height differences between the microlens and frame. The bigger the
difference, the smaller the radius will be.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Various exemplary embodiments of structures and methods of
their manufacture are discussed in detail below. These embodiments
and other features of the invention are described in more detail
below in connection with the accompanying drawings, in which:
[0009] FIG. 1 shows cross sectional view of a portion of an imager
structure constructed in accordance with an exemplary embodiment of
the invention;
[0010] FIG. 1A shows a cross sectional view of a portion of a
microlens structure constructed in accordance with an exemplary
embodiment of the invention;
[0011] FIG. 1B shows a cross sectional view of a portion of a
microlens structure constructed in accordance with another
exemplary embodiment of the invention;
[0012] FIG. 2 shows a perspective view of an imager structure
constructed in accordance with another exemplary embodiment of the
invention;
[0013] FIG. 3 shows a simplified perspective view of a portion of a
microlens structure constructed in accordance with an exemplary
embodiment of the invention;
[0014] FIG. 3A shows a perspective view of several FIG. 3 microlens
structures defined within a substrate;
[0015] FIG. 3B shows a perspective view of a FIG. 3 microlens
structure with lens material before heating within a frame defined
within a substrate;
[0016] FIG. 3C shows a perspective view of a FIG. 3 microlens
structure with lens material after heating within a frame defined
within a substrate;
[0017] FIG. 4 shows a portion of a microlens structure constructed
in accordance with an exemplary embodiment of the invention;
[0018] FIG. 5 shows a portion of a microlens structure constructed
in accordance with an exemplary embodiment of the invention;
[0019] FIG. 6 shows a top view of a portion of an imager structure
constructed in accordance with an exemplary embodiment of the
invention;
[0020] FIG. 7 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0021] FIG.8 shows a top view of a portion of an imager structure
constructed in accordance with an exemplary embodiment of the
invention;
[0022] FIG. 8A shows a cross sectional view of a portion of an
imager structure with a negative microlens constructed in
accordance with an exemplary embodiment of the invention;
[0023] FIG. 8B shows a cross sectional view of a portion of a FIG.
8A imager structure with a negative microlens after heating
constructed in accordance with an exemplary embodiment of the
invention;
[0024] FIG. 8C shows a top view of the FIGS. 8A and 8B imager
structures constructed in accordance with an exemplary embodiment
of the invention;
[0025] FIG. 9 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0026] FIG. 10 shows a top view of a portion of an imager structure
constructed in accordance with an exemplary embodiment of the
invention;
[0027] FIG. 11 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0028] FIG. 12 shows a perspective cross sectional view of a
portion of a microlens structure constructed in accordance with an
exemplary embodiment of the invention;
[0029] FIG. 13 shows a cross sectional view of a portion of a
microlens structure constructed in accordance with an exemplary
embodiment of the invention;
[0030] FIG. 14 shows a cross sectional view of a portion of a
microlens structure constructed in accordance with an exemplary
embodiment of the invention;
[0031] FIG. 15 shows a method of manufacturing an microlens
structure in accordance with an exemplary embodiment of the
invention;
[0032] FIG. 16 shows a method of manufacturing an microlens
structure in accordance with an exemplary embodiment of the
invention;
[0033] FIG.17 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0034] FIG. 18 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0035] FIG. 19 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0036] FIG. 20 shows a cross sectional view of a portion of an
imager structure constructed in accordance with an exemplary
embodiment of the invention;
[0037] FIG. 21 shows a method of manufacturing an microlens
structure in accordance with an exemplary embodiment of the
invention; and
[0038] FIG. 22 shows an image processing system constructed in
accordance with an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] Exemplary embodiments of the invention affect or adjust
microlens shapes or optical properties during lens formation (e.g.,
heating of lens material thereby causing lens material to flow or
settle into an intended microlens shape). Microlens frames and/or
other structures are used to affect or alter the flow behavior of
lens material to be different than otherwise would occur without
use of a microlens frame or other flow behavior altering
structures.
[0040] According to the invention, the focal characteristics of a
microlens can be adjusted by, among other things, forming boundary
walls around lens materials to contain/limit the outward flow of
lens material. This adjusts microlens flow behavior, e.g.,
increasing microlens height or defining a perimeter of the
microlens structures. Boundary walls can be formed by formation of
cavities or frame sidewalls with microlens material deposited
therein. Post-flow microlens shapes can also be adjusted or
affected by use of structures formed within the microlens materials
(for example, a microlens base within a microlens material) that
change flow behavior of the microlens during microlens flow
processing (e.g., altering a shape of the microlens or increasing
the height of the microlens from a planar layer or a microlens
cavity).
[0041] Radius, shape, height and optical properties of a microlens
can be adjusted independently of other microlens design parameters
by using structures, materials and/or fabrication processing
techniques to affect the microlens melting or flow behavior during
fabrication. As used herein, a positive microlens includes a
microlens extending above a layer or above a microlens cavity
(e.g., a convex microlens) and a negative microlens includes a
microlens that does not extend outside the microlens cavity or
below the layer (e.g., a concave microlens).
[0042] A first exemplary embodiment provides an alteration of the
balance of surface and volume related forces by creating a
microlens within an enclosure or frame; this results in an altered
radius, height or shape of the microlens (after heating and
subsequent flowing of melted microlens material). A variety of
enclosure or frame shapes and dimensions can be used to create the
microlens with a desired radius, height, shape and/or optical
property.
[0043] A second exemplary embodiment creates a filler or base layer
that is covered with a microlens material layer. The radius, height
and/or shape at the microlens layer are affected by the base layer
during microlens formation.
[0044] A third exemplary embodiment forms columns or blocks on a
floor of a microlens enclosure or a microlens base layer. The
microlens is formed around and over the blocks or columns thereby
affecting microlens formation (e.g., flowing behavior).
[0045] A fourth exemplary embodiment employs asymmetrical, varied
or non-uniformed shaped enclosures, frames, base layers and/or
columns to alter microlens formation by changing flow behavior
during microlens formation.
[0046] Combinations of the exemplary embodiments may also be used
to control shaping of a microlens structure in order to adjust a
microlens shape, focal characteristics, radius or other microlens
attributes or properties.
[0047] Microlens material is heated and flowed during microlens
fabrication by melting the microlens material, resulting in a flow
of the deposited material into a desired shape. For example, a
rectangular block of microlens material formed on a planar surface
will assume a semi-spherical shaped microlens (e.g., microlens 11,
FIG. 7) after being heated to 170.degree. C. to 180.degree. C.
(depending on resist) due to the melting and flowing of the
microlens material. The term "flow", "flowing" or "reflowing"
refers to a change in shape of a material which is heated and melts
thereby producing a material flow or shape alteration in the
material caused by heating or other similar process. "Flow" is an
initial melting and "reflow" is a subsequent melting of a frame or
microlens material that has been previously flowed.
[0048] A first exemplary embodiment of the invention is now
described with reference to FIG. 1. FIG. 1 shows a cross section of
a microlens frame having openings 5, which are subsequently filled
with lens material to form a microlens. The frames 5 are formed
over a substrate 3 having photosensor devices 4 therein. The frame
openings 5 are formed within a planar layer 1 formed over the
substrate 3 using methods well known in the art such as etching or
patterning. Frame openings 5 are defined by frame opening sidewalls
2 and a flat floor portion 7. Frame openings 5 may be formed by
etching, by patterning photo resist for example. It should be
appreciated that other circuitry components and material layers are
not shown for purposes of simplifying the illustration of FIG. 1
and other figures herein.
[0049] FIG. 1A shows a view of a single exemplary frame opening 5
within the planar layer 1 of FIG. 1 having a flat floor portion 7.
Alternatively, FIG. 1B shows a FIG. 1 frame opening 5 with a curved
floor portion 7', which can be used to affect the after flowing
form (i.e., shape) of a microlens structure. The sidewalls 2 and
floor portion 7 define a volume within the frame opening 5. As is
discussed below, microlens material is deposited into the frame
opening 5 and then heated to flow or melt into a desired shape and
form.
[0050] As noted, FIG. 1B shows an exemplary embodiment of the
invention with a frame opening floor 7' that has a curved variable
depth from the plane formed by a top section of the frame opening
5. Microlens material is deposited onto the curved floor portion 7'
and into the frame opening 5 defined by sidewalls 2. For
sufficiently thin microlens films, the curved floor 7' affects the
flowing of microlens material in a similar manner as when a water
droplet is placed into a hollowed depression in a surface. When the
microlens material in curved floor portion 7' flows during heating,
the hollow of floor portion 7' will support or cup the microlens
material such that it will not settle as much as it would if the
microlens material were on a flat surface (e.g., floor portion 7,
FIG. 1A). A curved, convex or other non-planar shaped floor portion
can be used with any of the embodiments of the invention to achieve
a desired change to a flowed microlens material. Also, sidewalls 2
in any of the embodiments of the invention can be convex or concave
as well as other non-planar shapes as well.
[0051] FIG. 2 shows a perspective view of another embodiment of a
frame that has been formed with sidewalls 1 that are sloped in two
dimensions. The frame sidewalls 1 have a portion B that slopes down
and inwardly from a top center portion A of the sidewalls towards
the center of an opening 5 defined by the frame sidewalls 1. The
frame sidewalls 1 also have a portion C that slopes down laterally
on both sides towards corner areas from a center top portion A of
the sidewalls, thereby forming notch like openings D in the comer
areas of the frame. The multi-dimension sidewall shapes can be used
to selectively alter and direct flow behavior of microlens material
during liquid phase transitions of microlens materials deposited in
opening 5 during microlens flow processing.
[0052] The dimensions, shape, volume of lens frame opening (e.g.,
opening 5), focal length and other focal characteristics in all
embodiments herein that use frames are determined by one or more
microlens and imager design parameters including: (1) the distance,
width or size of the photosensor 4 underneath the frame opening 5
the microlens focuses light upon; (2) the viscosity of the
microlens material used to form the microlenses during heating; (3)
the structures or frame opening sidewall dimensions (e.g., sidewall
2 height profiles) that affect microlens formation; (4) the
alterations in flow behavior of the microlens material resulting
from microlens structures affecting microlens material flow
behavior during heating; (5) the effects of pre-heating or pre-flow
treatment of frame or microlens materials; (6) the desired
approximate radius of the microlens structure after heating of the
microlens material is completed; and (7) the effects of a base
layer within microlens material that alters flow properties of the
microlens material.
[0053] Pre-flow treatment of frame or microlens materials can
include UV exposure which cross-links the material resulting in
less flow and better shape retention of "as printed" microlens
shapes. Reflow properties of microlens materials, frames structures
receiving microlens material and microlens base layers embedded in
microlens material are determined by, among other things, initial
polymer material properties of microlens material, frame opening
structures and/or microlens base layers. Also, temperature profile
over time for reflow, pre-flow treatment of material and pre-bake
of microlens, frame or layer materials (or a combination thereof)
at temperatures below glass transition temperatures for a specified
time that tends to harden a material so treated. Ultraviolet (UV)
or light exposure before reflow can affect the viscosity of
microlens material or frame material during flow reflow processing.
Pre-baking results in less reflow and better "as printed" shape
retention of microlens material, material which frame openings are
formed into (e.g., planar layer 1) or both. Determination of design
parameters can be done by a cycle of selecting of a set of design
parameters, producing a lens structure with the design parameters
and evaluating resulting lens structure to determine if the
resulting lens structure meets design requirements as will be
further described below.
[0054] FIG. 3 shows a perspective view of a simplified frame
opening 5 with exemplary sidewalls 6 enclosing the frame opening 5
and a floor portion 7, such as those shown in FIGS. 1-2. FIG. 3
shows how frame sidewalls 6 can have laterally sloping sides, which
have a higher portion in the middle of the sidewalls 6 and another
portion that slopes downward from a portion approximately mid-way
from a center portion toward an end segment of the sidewalls 6. The
FIG. 3 sidewalls 6 have a downward sloping height from a top
section of the sidewall 6 to the end of the sidewall 6 on both ends
in a symmetrical fashion. The sidewalls 6 have a sidewall height
which is at a maximum height in a center portion and a minimum
height at both end portions of the sidewalls 2. FIG. 3A shows an
expanded perspective view of the FIG. 1 and FIG. 3 exemplary
embodiments with more than one frame opening 5. Each frame opening
5 is defined by sidewalls 6 and frame opening floor 7 within the
planar layer 1.
[0055] Frame opening 5 depths can also be varied from one point of
a floor of the frame opening 5 to another portion of the floor in
the opening 5 thereby causing a portion of a flowed microlens
within the opening 5 to be tilted, flattened or raised with respect
to other portions of the flowed microlens.
[0056] Both positive and negative lens structures can be produced
with frame or other structures described herein that affect
formation of lens structures during fabrication. For example, FIG.
3B shows a frame structure formed by coating a substrate 3 with
positive resist 17 to form a frame with a varying sidewall 6
thickness of about 0.5 .mu.m to about 0.25 .mu.m, as measured from
a floor portion to a top portion of frame opening 5. A deposited
microlens layer 17 has a, thickness within the frame opening 5 of
about 0.8.mu.m before reflow. In the FIG. 3B embodiment, frame
sidewalls 6 have a sloping end portion that slopes down to a corner
area of the frame. FIG. 3C shows the FIG. 3B structure after reflow
of the deposited microlens layer 17, wherein the microlens layer
melts and flows such that it assumes a shape of about 1.4 .mu.m at
a center portion and a width of about 3.12 .mu.m. The height of the
resulting flowed microlens layer 17 in FIG. 3C is higher than it
would be without the frame structure. In such a manner, microlenses
can be formed with a radius independent of the microlens' size
(e.g., height).
[0057] A negative microlens, such as shown in FIGS. 13-14, can have
a frame layer thickness of about 1.4 .mu.m at a center portion and
microlens layer thickness of about 0.8 .mu.m before reflow (about
0.7 .mu.m after reflow with a radius of about -3.8 .mu.m below the
frame and from a center point above the microlens' concave shaped
curvature). Forces including surface tension from surfaces
including the sidewalls and floor as well as gravity in this
example cause the melting photoresist to reflow to a volume that is
semi-spherically shaped. Surface tension and gravity have a similar
effect on flowing photoresist as is found when a droplet of water
forms on a flat portion of a table or in a dip/sink portion in the
table. Negative microlens are further discussed below.
[0058] Frame opening and microlens material design parameters are
determined by fabrication of microlenses within frame openings with
different design parameters and then evaluating the resulting
effects of altering design parameters. Empirical test data obtained
from the evaluation is used to determine the shape, dimensions,
material selection and flow/reflow time as well as other
fabrication or design parameters used to fabricate a microlens in
accordance with the invention. Changes in design parameters result
in different flow or reflow of microlens materials. Accordingly,
varying design parameters to affect a balance between surface and
volume forces affecting flow or reflow behavior of a microlens
material during heating results in different microlens shapes,
radius and/or heights after flowing or reflowing.
[0059] Frame openings 5 can be designed with a variety of sidewalls
(e.g., sidewall 2, FIG. 1) having different profiles that affect
the microlens material deposited and flowed within the frame
opening 5. FIGS. 3-5 show examples of different sidewalls for a
lens structure frame enclosure, e.g., sidewalls 6, 8, 10 that can
be used to define different exemplary frame openings (e.g., frame
opening 5) used to affect the flow of microlens material.
[0060] FIG. 4 shows another exemplary sidewall 8 that has a
non-uniform or asymmetrical height profile across one portion of
its length, but not the remaining portion. The FIG. 4 sidewall 8
defines a frame opening in a manner, for example, as shown in FIG.
3A. The FIG. 4 sidewall 8 has one end that is depressed as
contrasted to the other end which is not. Other shapes can be used
to adjust flow behavior of lens material including other
asymmetrically shaped sidewalls or containing structures of lens
material.
[0061] FIG. 5 shows another exemplary sidewall 10 that has two
symmetrically shaped top portions, which begin and slope downward
gradually from a center point of the sidewall to an opposing end
segment of the sidewall 10. A different sidewall shape will affect
the shape and radius of a microlens formed on or within the opening
defined by the particular sidewall.
[0062] In addition, frame opening sidewalls (e.g., sidewalls 2, 6,
8, 10) can be symmetrical or asymmetrical with respect to opposing
sides of a sidewall. In other words, a sidewall can be formed with
different or irregular shaped end portions. Frame opening sides,
e.g., symmetrical sides can have a side which is not mirrored by an
opposing side, such as if one sidewall is lower than an opposing
sidewall.
[0063] For thin microlens films, depths of the frame opening 5 can
also be varied from one point of a floor of the frame opening 5 to
another portion of the floor, thereby causing a portion of a flowed
microlens within the opening 5 to be tilted, flattened or raised
with respect to other portions of the flowed microlens. Also,
non-symmetrical microlenses can provide focal points that are not
directly underneath a microlens if needed for a particular
design.
[0064] A frame sidewall (e.g., FIGS. 1-5) can be further designed
based on a three-dimensional model of the effects of varying
multiple microlens structure design parameters including frame
opening (e.g., opening 5) or volume affecting structures (e.g.,
FIG. 9, protrusion 12; FIG. 18, layer 45) in order to design a
frame opening volume, floor and sidewalls that suitably alter
microlens material flow behavior towards a desired microlens shape.
A three-dimensional profile of a frame opening 5 can be designed
based on design layout as well as adjusting photolithography tool
characteristics. For example, three-dimensional profiles can be
obtained as the result of a limited resolution of a
photolithography tool and process used to print or form the frame
openings 5. A rounded shape or sloped wall of a frame opening 5 can
be obtained by exceeding photolithography resolution limits so a
mask produces less than a well defined print image during
photolithography. A three-dimensional profile of a frame opening 5
can be designed to alter multiple aspects of a microlens shape or
optical properties such as focal characteristics (e.g., focal
length) and focal point. Three-dimensional modeling and designs for
microlenses can be produced by use of commercial and proprietary
optical property modeling tools that simulate optical
characteristics of microlenses, such as Lighttools.RTM.. Other
tools are available to provide modeling of flow/reflow behavior of
microlenses during heating processing. Together, the tools can be
used to predict how different three-dimensional designs of frame
openings, as well as other structures affecting microlens material
flow, alter microlens shapes and optical properties.
[0065] FIG. 6 shows a top view of the FIG. 1 imager with
substantially rectangular frame openings 5 defined by frame opening
sidewalls 2 defined within planar layer 1 formed on a substrate
with an image pixel underneath the frame opening 5 (not shown). An
alternative embodiment will have other shapes including circular
shaped (e.g., frame openings 5 of FIG. 8).
[0066] FIG. 7 shows a cross-sectional view of the FIG. 1 imager
structure after microlens material is deposited and flowed/reflowed
into the frame openings 5. The illustrated microlenses 11 have been
formed as positive microlenses 11 by overfilling the frame openings
5 with microlens material. However, a negative microlens can be
formed by depositing less microlens material before the flowing
process, such as is shown in FIGS. 8A-8C, 13 and 14. It should be
noted that the second coat in FIGS. 8A-8C can be uniform as shown
or imaged into patters to achieve a desired shape after reflow.
[0067] FIG. 8 shows a top view of the FIG. 7 structure. Microlens
material is deposited within and above frame openings 5 such that
when the microlens material is heated, a positive microlens 11
having an approximate convex upper shape is formed. FIG. 8 shows
circular shaped microlenses 11 with an upper portion that is above
planar layer 1 and having a larger diameter than frame openings 5
after microlens material has been deposited into frame openings 5
and the microlens material flowed/reflowed.
[0068] Another exemplary embodiment of the invention is shown in
FIGS. 9-11 where base layers 12 (FIG. 9) are formed on a floor
portion of the frame opening 5. FIG. 10 shows a top view of the
FIG. 9 exemplary embodiment with the base layers 12 formed as a
pattern of protrusions on the floor of the frame opening 5. The
base layers 12 and sidewalls 2 have the effect of cooperatively
changing flow properties of the microlens material. Referring to
FIG. 11, microlens material is formed over the base layers 12 and
then heated to flow the microlens material into a desired microlens
11. Shape, materials and dimensions of base layers 12 and frame
openings are determined based on design parameters including
effects on deposited microlenses forming around and over
protrusions in frame openings 5 and those described above for the
FIGS. 1-8. Base layers 12 can be formed from the planar layer 1 or
by depositing additional layers on the floor of the frame opening
(e.g., frame 5). A three-dimensional profile of the frame opening 5
can be made to include effects of both base layer 12 and frame
opening 5 along with other design factors such as photolithographic
processing characteristics.
[0069] FIGS. 12-14 show an exemplary embodiment of the invention
used to form negative microlenses. FIG. 12 shows a perspective view
of a portion of an imager structure having substrate 13 with frame
openings 14. FIG. 13 shows microlens material 15 that has been
deposited into the frame openings 14. The microlens material 15 has
been under-filled into frame openings 14. FIG. 14 shows microlens
material 15 after heating and flowing which resulted in a negative
(concave) microlens.
[0070] An exemplary process for manufacturing an exemplary
embodiment of the invention, such as the ones shown in FIGS. 1-8,
is shown in FIG. 15. At processing segment S21, a substrate is
formed or provided. At processing segment S22, a plurality of
pixels are formed in the substrate. At processing segment S23, a
planar layer is deposited over the plurality of pixels. At
processing segment S24, a plurality of containing structures are
formed from the planar layer comprising a plurality of sidewalls
respectively formed over the plurality of pixels, the plurality of
containing structures defines an outer boundary of the microlens
structure. At processing segment S25, a microlens structure is
formed in each containing structure from lens material deposited
therein where each of the sidewalls are adapted to exert a force on
the lens material during a liquid-phase of the lens material that
alters the lens material shape during the liquid-phase of the lens
material.
[0071] An exemplary process for manufacturing another exemplary
embodiment of the invention, such as the ones shown in FIGS. 9-11,
is shown in FIG. 16. At processing segment S28, a substrate 3 is
formed. At processing segment S29, a plurality of pixels 4 are
formed in the substrate 3. At processing segment S30, a planar
layer 1 is formed over the pixels 4. At processing segment S31, a
plurality of containing structures are formed respectively over the
plurality of pixels. Each of the plurality of containing structures
is formed with a plurality of sidewalls formed from the planar
layer such that the plurality of containing structures defines an
outer boundary of the microlens structure. At processing segment
S32, a plurality of protrusions are formed on an upwardly facing
surface of the planar layer within each of the enclosures. At
processing segment S33, a microlens structure is formed within each
containing structure from lens material deposited therein where
each of the sidewalls are adapted to exert a force on lens material
deposited within the containing structures during a liquid-phase of
the lens material.
[0072] FIG. 17 shows microlens structures formed over imager pixels
in accordance with another exemplary embodiment of the invention.
Microlens base layers 45, convex shaped in this embodiment, are
formed on a planar layer 1 over pixels 4. Microlens material 49 is
formed over the microlens base layers 45. The microlens base layer
45 and microlens material 49 dimensions, shape and volume are
determined by a number of design parameters including those
described with respect to FIGS. 1-8 above. The design parameters of
microlens base layer 45 and microlens material 49 are determined by
the fabrication of microlenses with embedded microlens base layers
45 having different design parameters and then evaluating the
resulting effects of altering design parameters from one design to
another. As with the FIGS. 1-8 exemplary embodiments, empirical
test data obtained from the evaluation is then used to determine
the shape, dimensions, material selection and flow/reflow time as
well as other fabrication or design parameters used to fabricate a
microlens in accordance with the invention.
[0073] FIG. 18 shows the FIG. 17 lens structures after the flowing
of microlens material 49. Microlens material 49 has been flowed
into a shape, in this case a convex shaped lens 49, that is
determined in part by the shape, viscosity, dimensions and volume
of microlens base layer 45.
[0074] FIG. 19 shows an imager in accordance with another exemplary
embodiment of the invention. A squared microlens base layer 51 is
formed on a planarized substrate 53 having photosensitive
photosensors 4 formed therein. A microlens material 55 is formed
over and around the microlens base layers 51. The microlens base
layer 51 and microlens materials' 55 size, shape and volume are
determined based on design parameters including volume and flow
parameters as well as design parameters discussed with respect to
the FIG. 14 microlens base layers 51.
[0075] FIG. 20 shows the FIG. 19 imager after the microlens
material 55 has been shaped through processes such as flowing.
Microlens material 55 and microlens base layer 51 are both affected
by each other during flowing of lens material 55, lens base layer
51 or both.
[0076] Three-dimensional designs of the structures illustrated in
FIGS. 17-20 can also be designed using principles and design
parameters discussed above. Lens base layers 45 and microlens
material 49 can be formed which alter flow or reflow behavior of
microlens material 49 by exerting forces on the liquid-phase lens
material to shape of liquid-phase lens material during flowing of
lens material to produce a desired microlens shape.
[0077] FIG. 21 shows a method of forming an imager structure in
accordance with another exemplary embodiment of the invention. At
processing segment S61, a plurality of pixels are formed in a
substrate. At processing segment S63, a planar layer is formed over
the pixels and the substrate. At processing segment S65, a
plurality of protrusions are formed from the planar layer, each of
the protrusions are formed over one of the plurality of pixels. At
processing segment S67, a plurality of lens material is formed over
and around each of the protrusions. At processing segment S69, the
lens material is heated to transition the lens material to a
liquid-phase, each of the plurality of liquid-phase lens materials
assumes a shape related to a geometric shape of the protrusion
embedded in the liquid-phase material as well as a plurality of
surface interactions with an embedded protrusion and planar layer.
The plurality of surface interactions include a surface tension
force, an effect of a change in volume on said liquid-phase lens
material caused by a presence of one of said plurality of
protrusions within each of said plurality of liquid-phase lens
materials, an adhesive force with said protrusions and a
gravitational force. The protrusions can be formed as rectangular
protrusions extending vertically from the planar surface.
[0078] Microlens base layer and microlens layer shape and volume
are determined such that the combination thereof determines one or
more final dimensions and one or more optical properties of the
microlens layer respectively formed over the underlying base
layers. The microlens layers can be rectangular or circular shaped
microlens layers. Additional blocks or protrusions can be formed
above the microlens base layers or the microlens base layer can be
formed into separate smaller blocks or protrusions. The microlens
base layers and microlens layers dimensions, shape and materials
determination are based in part on microlens layer flow properties
and desired microlens layer optical properties after formation.
[0079] The apparatus and process for manufacturing an apparatus
aspects of the invention can be used to construct a system 69 shown
in FIG. 22. An imager 73 with a pixel array 77 comprising a
microlens structure in accordance with any of the embodiments of
the invention is coupled with a sample and hold circuit 83. An
analog to digital (A/D) 85 is receives signals from the sample and
hold circuit 83 and outputs digital signals to an image processor
85. The imager 71 then outputs image data to a data bus 75. A
central processing unit coupled to the data bus 75 receives image
data.
[0080] It should be noted that the structures shown in the figures
show both rounded sidewalls (e.g., FIG. 1A, sidewall 1) as well as
squared or non-rounded sidewalls (e.g., FIG. 1, sidewall 1). A
person skilled in the art would recognize that a variety of
sidewall shapes are capable of being used with different
embodiments of the invention.
[0081] It is also possible to form a microlens layer relative to a
frame layer to allow additional influences, such as a
non-equilibrium based design parameter, on a final shape of the
completed microlens. For example, a microlens can be formed based
on non-equilibrium flow conditions such as heating a lens material
such that it begins a phase change to a liquid and begins flowing,
then allow the lens material to solidify during the flow process
before it reaches its final equilibrium shape as defined by surface
and volume forces. Such non-equilibrium based design influences
provide additional means for defining a final shape of a
microlens.
[0082] Frame material can be transparent with a certain refractive
index to help guide incident light onto a microlens. Frame material
can also be absorbing to act as a black matrix outer containment
layer. Transparent material or light absorbing material embodiments
would aid in reducing crosstalk.
[0083] While exemplary embodiments of the invention have been
described and illustrated, it should be apparent that many changes
and modifications can be made without departing from the spirit or
scope of the invention. Accordingly, the invention is not limited
by the description above, but is only limited by the scope of the
appended claims.
* * * * *