U.S. patent application number 14/961844 was filed with the patent office on 2016-03-24 for microlens array substrate.
The applicant listed for this patent is Seiko Epson Corporation. Invention is credited to Koichiro Akasaka.
Application Number | 20160084997 14/961844 |
Document ID | / |
Family ID | 50546039 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160084997 |
Kind Code |
A1 |
Akasaka; Koichiro |
March 24, 2016 |
MICROLENS ARRAY SUBSTRATE
Abstract
A microlens substrate has a tendency to warp when an oxide film
is formed and annealed before forming a mask in order to adjust the
etching rate of wet etching. A film exerting a stress that cancels
out this warping may be formed upon a microlens. This film
functions as an optical path length adjusting layer.
Inventors: |
Akasaka; Koichiro;
(Minowa-machi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiko Epson Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
50546039 |
Appl. No.: |
14/961844 |
Filed: |
December 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14044691 |
Oct 2, 2013 |
9234988 |
|
|
14961844 |
|
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Current U.S.
Class: |
359/738 ;
359/819 |
Current CPC
Class: |
G02B 3/0075 20130101;
G02B 5/003 20130101; G02B 3/0012 20130101; B29D 11/00019 20130101;
G02B 3/0056 20130101; G02F 1/133526 20130101 |
International
Class: |
G02B 3/00 20060101
G02B003/00; G02B 5/00 20060101 G02B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2012 |
JP |
2012-237561 |
Claims
1. A microlens array substrate comprising: a substrate; an oxide
film that has an aspheric-surfaced recess is disposed on the
substrate, the aspheric-surfaced recess has a tapered edge; a
microlens that has a higher refractive index than the substrate is
disposed in the aspheric-surfaced recess, the microlens has a
convex surface side and flat surface side opposite the convex
surface side; and an optical path length adjusting layer is
disposed on the flat surface side of the microlens, wherein the
substrate is warped in a concave shape by stress from at least one
of the oxide film or the microlens, the optical path length
adjusting layer includes a first film and a second film, the first
film receives a compressive stress in a direction orthogonal to a
normal direction of the substrate, and the second film receives a
tensile stress in the direction orthogonal to the normal direction
of the substrate.
2. The microlens array substrate according to claim 1, wherein the
optical path length adjusting layer includes a third film, the
third film receiving a compressive stress in a direction orthogonal
to a normal direction of the substrate.
3. The microlens array substrate according to claim 1, wherein the
substrate is a silica substrate and the oxide film is a silicon
oxide film.
4. The microlens array substrate according to claim 1, further
comprising: a light-blocking film disposed on the optical path
length adjusting layer, the light-blocking film receiving a tensile
stress in a direction orthogonal to a normal direction of the
substrate.
5. A microlens array substrate comprising: a substrate; an oxide
film that has an aspheric-surfaced recess is disposed on the
substrate, the aspheric-surfaced recess has a tapered edge; a
microlens that has a higher refractive index than the substrate is
disposed in the aspheric-surfaced recess, the microlens has a
convex surface side and flat surface side opposite the convex
surface side; and an optical path length adjusting layer is
disposed on the flat surface side of the microlens, wherein the
substrate is warped in a concave shape by stress from at least one
of the oxide film or the microlens, the optical path length
adjusting layer includes a first film and a second film, the first
film receives a tensile stress in a direction orthogonal to a
normal direction of the substrate, and the second film receives a
compressive stress in the direction orthogonal to the normal
direction of the substrate.
6. The microlens array substrate according to claim 5, wherein the
optical path length adjusting layer includes a third film, the
third film receiving a compressive stress in a direction orthogonal
to a normal direction of the substrate.
7. The microlens array substrate according to claim 5, wherein the
substrate is a silica substrate and the oxide film is a silicon
oxide film.
8. The microlens array substrate according to claim 5, further
comprising: a light-blocking film disposed on the optical path
length adjusting layer, the light-blocking film receiving a tensile
stress in a direction orthogonal to a normal direction of the
substrate.
9. The electronic device comprising the microlens array substrate
according to claim 1.
10. The electronic device comprising the microlens array substrate
according to claim 5.
Description
[0001] The present application is a continuation application of
U.S. patent application Ser. No. 14/044,691 filed on Oct. 2, 2013,
which claims priority from Japanese Patent Application No.
2012-237561 filed on Oct. 29, 2012, which are expressly
incorporated by reference herein.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to fabrication methods for
microlens array substrates.
[0004] 2. Related Art
[0005] Various types of electronic elements, including various
types of wires such as data lines, scanning lines, and capacitance
lines as well as thin-film transistors ("TFTs" hereinafter) are
built into image display regions of electro-optical apparatuses
such as liquid-crystal apparatuses. Accordingly, of the total
amount of parallel light incident upon such an electro-optical
apparatus, it is only possible to utilize an amount of light
allowed by the numerical aperture of the pixels, unless some kind
of measures are taken.
[0006] As one such measure, a microlens array containing
microlenses corresponding to respective pixels has in the past been
embedded into an opposing substrate, a microlens array substrate
has been affixed to an opposing substrate, and so on. Doing so
takes light that originally travels toward non-aperture regions
outside the aperture regions of the respective pixels and focuses
the light on a pixel-by-pixel basis so as to conduct the light to
the aperture regions of the pixels. The electro-optical apparatus
can produce a bright display as a result.
[0007] A high lens efficiency is a basic requirement in such
microlenses. As such, methods for fabricating microlenses having
aspheric surfaces have been proposed.
[0008] For example, JP-A-2004-70283 discloses a method for
fabricating a microlens that includes forming on a substrate a
first film that has an etching rate higher than the substrate,
forming on the first film a mask in which a hole is provided at a
position corresponding to a center of the microlens to be formed,
and forming in the substrate an aspheric recess that defines a
curved surface of the microlens by wet-etching the first film over
the mask.
[0009] According to JP-A-2004-70283, after being formed on the
substrate, the first film is subjected to annealing at a
predetermined temperature so as to bake the first film and control
the etching rate thereof. However, the inventors of this invention
discovered that the annealing in this method causes the substrate
to warp, causing problems in the subsequent steps of forming films
and the like. A large warp in the substrate makes it difficult to
position the element substrate and the opposing substrate when
affixing the substrates to each other, making it generally
difficult to affix the element substrate and the opposing substrate
to each other. A large warp in the substrate can also make it
impossible to carry out vacuum suction during the substrate
transportation, resulting in errors, and can furthermore result in
localized forces being applied when polishing the substrate surface
during a smoothing process, which can cause the film to peel
off.
SUMMARY
[0010] An advantage of some aspects of the invention is to provide
a fabrication method for a microlens array capable of suppressing
warps from arising in a substrate.
[0011] In order to achieve the stated advantage, the invention
employs the following methods.
[0012] 1. A fabrication method for a microlens array according to
one aspect of the invention includes: forming an oxide film on a
substrate; annealing the substrate on which the oxide film has been
formed; forming, on the oxide film, a mask having an opening in a
location corresponding to the center of a microlens that is to be
formed; forming an aspheric surfaced recess having tapered edges in
the substrate on which the oxide film has been formed by
wet-etching the oxide film and the substrate over the mask; forming
the microlens by depositing a material having a higher refractive
index than the substrate in the recess; and forming an optical path
length adjusting layer on the microlens. Here, the step of forming
the optical path length adjusting layer includes depositing a first
film that receives compressive stress in a direction orthogonal to
a normal direction of the substrate and a second film that receives
tensile stress in the direction orthogonal to the normal direction
of the substrate; and in the step of forming the optical path
length adjusting layer includes forming a film that exerts a stress
that warps the substrate in a direction that cancels out warping
produced in the substrate by the annealing and is selected from
among the first film and the second film, and the film that has
been selected is formed on the microlens first.
[0013] According to this method, a film that exerts a stress that
warps the substrate in a direction that cancels out the warping
produced in the substrate by the annealing is formed on the
microlens at the beginning of the step of forming the optical path
length adjusting layer, and thus the stress produced in the
substrate by the annealing can be greatly alleviated in the initial
stage of forming the optical path length adjusting layer.
[0014] For example, in the case where a film that exerts a stress
that warps the substrate in the opposite direction as the direction
that cancels out the warping produced in the substrate by the
annealing is formed on the microlens first, that film will cause
the substrate to warp in a direction that increases the warping
produced in the substrate by the annealing. As a result, the
substrate warps extensively in the initial stage of forming the
optical path length adjusting layer, which makes it difficult to
correct the warping in the substrate later. However, in the method
according to this aspect of the invention, the film that exerts a
stress that warps the substrate in a direction that cancels out the
warping produced in the substrate by the annealing is formed on the
microlens first, and thus the stated problem does not occur.
[0015] In addition, because the first film and the second film are
layered in an alternating manner, the warping in the substrate can
be corrected while adjusting the amount of stress to be alleviated
in the substrate by adjusting formation conditions such as the
thicknesses, materials, and so on of the first film and the second
film.
[0016] Accordingly, the substrate can be suppressed from
warping.
[0017] 2. In the fabrication method for the microlens array
according to 1 above, the substrate may be a silica substrate and
the oxide film may be a silicon oxide film; and in the step of
forming the optical path length adjusting layer, the first film may
be selected as the film that is formed on the microlens first.
[0018] 3. In the fabrication method for the microlens array
according to 2 above, the annealing may be performed at no less
than 800.degree. C. and no more than 1100.degree. C.
[0019] 4. In the fabrication method for the microlens array
according to any one of 1 to 3 above, in the step of forming the
optical path length adjusting layer, the substrate may be caused to
warp in a direction that cancels out warping in the substrate
caused by a later step performed after the step of forming the
optical path length adjusting layer.
[0020] According to this method, the substrate can, in the step of
forming the optical path length adjusting layer, be pre-warped in a
direction that alleviates stress produced in the substrate in a
later step. Accordingly, the microlens array substrate that is
ultimately fabricated can be prevented from warping.
[0021] 5. In the fabrication method for the microlens array
according to 4 above, the later step may be a step of forming a
light-blocking film on the optical path length adjusting layer; and
in the step of forming the optical path length adjusting layer, the
substrate may be caused to warp in a direction that cancels out
warping in substrate caused by the step of forming the
light-blocking film.
[0022] According to this method, the substrate can, in the step of
forming the optical path length adjusting layer, be pre-warped in a
direction that alleviates stress produced in the substrate in the
step of forming the light-blocking film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0024] FIG. 1 is a cross-sectional view of a microlens array
substrate according to an embodiment of the invention.
[0025] FIG. 2 is a cross-sectional partial enlargement of the
microlens array substrate.
[0026] FIGS. 3A through 3C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0027] FIGS. 4A through 4C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0028] FIGS. 5A through 5C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0029] FIGS. 6A through 6C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0030] FIGS. 7A through 7C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0031] FIGS. 8A through 8C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate.
[0032] FIG. 9 is a plan view illustrating a positional relationship
between a substrate and a mask.
[0033] FIGS. 10A through 10C are schematic diagrams illustrating
steps for fabricating a microlens array substrate and warping in
the substrate, according to a variation on the invention.
[0034] FIG. 11 is a diagram illustrating the overall configuration
of a projector.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0035] Hereinafter, an embodiment of the invention will be
described in detail with reference to the drawings. It should be
noted that in the appended drawings, the scale of the various
constituent elements has been changed as appropriate to make the
constituent elements more visibly recognizable.
Microlens Array Substrate
[0036] First, a microlens array substrate that can be fabricated
through the microlens array substrate fabrication method according
to the invention will be described with reference to FIGS. 1 and
2.
[0037] FIG. 1 is a cross-sectional view of a microlens array
substrate 1 according to an embodiment of the invention.
[0038] FIG. 2 is a cross-sectional partial enlargement of the
microlens array substrate 1 (that is, an enlarged cross-sectional
view of a microlens 14).
[0039] As shown in FIG. 1, the microlens array substrate 1
according to this embodiment is fabricated by forming a lens layer
13 configured of the plurality of microlenses 14 by depositing a
lens material on a substrate 10 in which is formed a plurality of
recesses 10b corresponding to the plurality of microlenses 14 so as
to form the plurality of microlenses 14, forming an optical path
length adjusting layer 15 upon the lens layer 13, and furthermore
forming a light-blocking film 19, a flattening film 20, and a
transparent conductive film 21 in that order upon the optical path
length adjusting layer 15.
[0040] Note that in the following descriptions, the substrate will
be referred to as a "substrate main body" prior to the recesses 10b
being formed, and will be referred to simply as a "substrate" after
the recesses 10b have been formed.
[0041] The plurality of recesses 10b are formed in the substrate 10
in a matrix. A transparent plate member configured of, for example,
a silica substrate or the like is used as the substrate main
body.
[0042] The microlenses 14 are formed of a highly transmissible
(that is, highly light-transmissible) material that has a higher
refractive index than the substrate 10.
[0043] The curved surfaces of the microlenses 14 are generally
defined by the substrate 10 and the lens layer 13, which have
different refractive indexes. Each microlens 14 is constructed as a
convex lens that protrudes downward in a convex shape.
[0044] In this embodiment, the microlens array is fabricated using
a fabrication method that will be described later, and thus a film
12 (an oxide film) remains on a top surface of the substrate 10
near the edges of the microlenses 14 and in regions where the
microlenses 14 are not formed. The film 12 is configured of, for
example, a transparent silicon oxide film (SiO.sub.2).
[0045] The optical path length adjusting layer 15 is formed of a
highly transmissible (that is, highly light-transmissible) material
such as SiO.sub.2. The refractive index of the optical path length
adjusting layer 15 is approximately the same as that of the
substrate 10, for example.
[0046] The optical path length adjusting layer 15 is configured by
forming a first film 16, a second film 17, and a third film 18 in
that order upon the lens layer 13. The first film 16, the second
film 17, and the third film 18 will be described in detail
later.
[0047] The microlens array substrate 1 is disposed so that during
use, the microlenses 14 correspond to respective pixels in, for
example, an electro-optical apparatus such as a liquid-crystal
apparatus. Accordingly, due to the refraction effects of the
microlenses 14 and the adjustment effect of the optical path length
adjusting layer 15, light incident near the center of the
microlenses 14 is focused toward the centers of the corresponding
pixels in the electro-optical apparatus.
[0048] The light-blocking film 19 defines the non-aperture regions
in the electro-optical apparatus to which the microlens array
substrate 1 is attached. Specifically, the light-blocking film 19
employs a grid-shaped planar pattern so as to define individual
non-aperture regions in grid form. Note that the light-blocking
film 19 may instead have a stripe-shaped planar pattern and may be
used along with another light-blocking film to define the
non-aperture regions in grid form.
[0049] Through this, the non-aperture regions for each pixel can be
defined with more certainty, and light leakage and the like between
the respective pixels can be suppressed. Furthermore, light can be
prevented from being incident on electronic elements that are built
into the non-aperture regions of the electro-optical apparatus,
such as TFTs, whose characteristics change when photo-leakage
current is produced under photoelectric effects occurring when
light is incident thereon.
[0050] Note that as shown in FIG. 1, the flattening film 20 is
formed covering the light-blocking film 19 on the optical path
length adjusting layer 15, and the transparent conductive film 21
is formed upon the flattening film 20. Furthermore, an orientation
layer may be formed upon the transparent conductive film 21. In
addition, in the microlens array substrate 1, R (red), G (green),
or B (blue) color filters may be built into the aperture regions of
the pixels defined by the light-blocking film 19.
[0051] As shown in FIG. 2, edge areas of the microlenses 14 are
formed from the film 12, which has a different etching rate from
the substrate 10. The edge areas of the microlenses 14 have steeper
pitches than that of the curved surfaces in the microlenses 14 of
the substrate 10.
[0052] The curved lens surfaces of the microlenses 14 are aspheric
surfaces having tapers at the side edges thereof. Specifically, the
curved lens surfaces of the microlenses 14 in the substrate 10 are
aspheric surfaces having shallower bases than spherical surfaces,
or in other words, have semi-elliptical shapes when viewed along a
cross-section. The curved lens surfaces of the microlenses 14 in
the film 12 are steeper-pitched surfaces than the shallow-based
aspheric surfaces, or in other words, follow straight lines when
viewed along a cross-section. Accordingly, in each microlens 14,
the curvature radius near the center thereof is greater than the
curvature radius in a spherical lens.
[0053] The lens efficiency is improved depending on the degree of
the aspheric surface. That is, unlike a spherical lens whose
aperture diameter and lens depth are the same, a lens having a
curved surface only near the center thereof, as in this embodiment,
can have a larger curved surface (that is, a smaller curvature
radius), which makes it possible to reduce the focal length.
[0054] Furthermore, spherical aberration can be reduced and the
focal point can be kept constant, as compared to when a spherical
lens is employed.
[0055] In FIG. 2, reference numeral Lt1 indicates a line tangent at
an area in the substrate 10 where the curved lens surface of the
microlens 14 is sloped the most, or in other words, at the upper
edge of the curved lens surface of the microlens 14 in the
substrate 10. A reference numeral Lt2 indicates a line tangent at
an area in the film 12 where the curved lens surface of the
microlens 14 is sloped the most, or in other words, at the upper
edge of the curved lens surface of the microlens 14 in the film 12.
An angle .theta. is an angle formed by the line tangent Lt1 and the
line tangent Lt2.
[0056] In this embodiment, the curved lens surfaces of the
microlenses 14 are defined so that the angle .theta. is 30.degree.
to 50.degree., for example. Note that the angle .theta. can be
controlled, depending on the light source and the projection-side
lens design, from an angle that provides a gentle slope in the
curved lens surface to an angle that provides a steep slope in the
curved lens surface.
[0057] Furthermore, setting the angle .theta. as desired based on
the specifications of the electro-optical apparatus makes it
possible to ensure that light focused through the edges of the
microlenses 14 in addition to the vicinity of the centers thereof
can pass through the aperture regions of the corresponding
pixels.
[0058] According to this configuration, incident light such as
projected light incident from below the substrate in FIG. 2 can,
due to the light-focusing effects of the microlenses 14, be
efficiently utilized as display light. This makes it possible to
achieve a bright and clear image display.
Fabrication Method for Microlens Array Substrate
[0059] Next, a fabrication method for the microlens array substrate
1 according to this embodiment of the invention will be described
with reference to FIGS. 3A through 9.
[0060] FIGS. 3A through 8C are schematic diagrams illustrating
steps for fabricating the microlens array substrate 1 and warping
in the substrate.
[0061] FIG. 9 is a plan view illustrating a positional relationship
between the substrate 10 and a mask M.
[0062] Note that in FIGS. 3A through 8C, the left sides are
diagrams illustrating steps for fabricating the microlens array
substrate 1 as cross-sectional views, and the right sides indicate
the state of warping in the substrate.
[0063] Furthermore, for the sake of simplicity, "warping in the
substrate" may refer not only to warping in the substrate 10 but
also to warping in the substrate main body 10a in the following
descriptions.
[0064] "Warping amount" refers to the distance from the center of
the substrate to the area of the substrate that is the most warped
(that is, an end edge of the substrate) in a normal direction of
the substrate (that is, the thickness direction of the substrate
when the substrate is not warped). Here, the warping amount is a
value obtained by adding the distance from the center of the
substrate to the left end edge of the substrate in the normal
direction of the substrate to the distance from the center of the
substrate to the right end edge of the substrate in the normal
direction of the substrate and dividing the result by 2, or in
other words, is the mean value of right and left warping
amounts.
[0065] Although there are cases where the warping of the substrate
is concave (that is, protrudes downward) and cases where the
warping of the substrate is convex (that is, protrudes upward), the
warping amount is an absolute value.
[0066] First, as indicated on the left side of FIG. 3A, a film 11a
configured of amorphous silicon (.alpha.-Si) is formed on the
substrate main body 10a through, for example, chemical vapor
deposition ("CVD" hereinafter), sputtering, or the like. A
disc-shaped transparent plate member configured of silica or the
like is used as the substrate main body 10a. The substrate main
body 10a is, for example, approximately 200 mm in diameter and 1.2
mm thick.
[0067] The substrate is not warped in this step, as indicated in
the right side of FIG. 3A.
[0068] Next, as indicated on the left side in FIG. 3B, the film 11a
is removed from regions aside from areas corresponding to marks 11
that are to be formed, by patterning the film 11a using
photolithography and etching. This forms the marks 11, which
function as alignment marks for excavating openings Mh in locations
of a mask Ma (mentioned later) that correspond to the centers of
the microlenses to be formed.
[0069] The substrate is not warped in this step, as indicated in
the right side of FIG. 3B.
[0070] Next, as indicated in the left side of FIG. 3C, a film
(oxide film) 12a, whose etching rate under a predetermined type of
etchant such as a hydrofluoric acid is higher than the etching rate
of the substrate main body 10a, is formed so as to cover the film
11a on the substrate main body 10a. The film 12a is formed from a
transparent silicon oxide film or the like, through CVD,
sputtering, or the like. The film 12a is, for example, no less than
400 .ANG. and no more than 600 .ANG. thick. In this embodiment, the
film 12a is approximately 500 .ANG. thick.
[0071] After this, the substrate main body 10a on which the film
12a is formed is subjected to annealing in, for example, a nitrogen
gas (N.sub.2 gas) atmosphere at no less than 800.degree. C. and no
more than 1100.degree. C. This determines the etching rate of the
film 12a.
[0072] The substrate is warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 3C. The warping amount at this time is approximately 20 .mu.m.
The substrate main body 10a experiencing thermal deformation due to
the annealing can be thought of as a reason for the substrate
warping in this manner. The warping can also be thought to be
caused by the substrate main body 10a being supported on both ends
and sagging under its own weight.
[0073] Next, as indicated in the left side of FIG. 4A, the mask Ma,
configured of a polysilicon film, is formed upon the film 12a
through CVD, sputtering, or the like.
[0074] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 4A. In other words, the warping amount at this time is
approximately 20 .mu.m.
[0075] Next, as indicated on the left side in FIG. 4B, the openings
Mh are excavated in locations corresponding to the centers of the
microlenses to be formed, by patterning over the mask Ma using
photolithography and etching. At this time, the positions of the
openings Mh are determined based on the positions of the marks 11.
This forms the mask M, which has the openings Mh in the locations
that correspond to the centers of the microlenses to be formed.
Note that the left side in FIG. 4B corresponds to a cross-sectional
view taken along the IVB-IVB line shown in FIG. 9.
[0076] As shown in FIG. 9, diameters R1 of the openings Mh are
smaller than diameters R2 of the recesses 10b (that is, the
diameters of the microlenses 14 to be formed). In FIG. 9, reference
numeral W1 indicates a first width of a single pixel that is
rectangular in shape when viewed from above; reference numeral W2
indicates a second width that is orthogonal to the first width, and
reference numeral W3 indicates a third width taken along the
diagonal direction of the pixels. For example, the first width W1
and the second width W2 are each 4 .mu.m to 30 .mu.m. Furthermore,
the sizes of the diameters R1 of the openings Mh are greater than 1
.mu.m but are shorter than approximately 80% the length of the
third width W3. Likewise, the sizes of the diameters R2 of the
recesses 10b are greater than the diameters R1 of the openings Mh
but are shorter than approximately 95% the length of the third
width W3.
[0077] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 4B. In other words, the warping amount at this time is
approximately 20 .mu.m.
[0078] Next, as indicated in the left side of FIG. 4C, the film 12a
and the substrate main body 10a are wet-etched over the mask M
using a hydrofluoric acid-type etchant. Because the etching rate of
the etchant on the film 12a is higher than the etching rate on the
substrate main body 10a, the film 12a is etched at a higher
rate.
[0079] In other words, spherical surfaced recesses are excavated in
the film 12a in the periphery of the openings Mh in the mask M
during a period leading up to openings 12h being etched in the film
12a, but the film 12a is then etched more quickly after the
openings 12h have been formed in the film 12a. Accordingly, the
etching spreads outward from the openings Mh faster than in the
depth direction. In other words, there is a relatively higher
amount of side-etching. Through this, the aspheric surfaced
recesses 10b having tapered side edges are excavated in the
substrate main body 10a on which the film 12a has been formed.
Specifically, the recesses 10b having bases that are shallower than
spherical surfaces are excavated in the substrate main body
10a.
[0080] After this, time is managed so that the etching stops at a
stage where the recesses 10b have been excavated to sizes
corresponding to the microlenses 14. In other words, the substrate
10, in which the shallow-base recesses 10b have been excavated on a
microlens-by-microlens basis, is completed.
[0081] Although the substrate remains warped in a concave shape
(that is, protrudes downward) in this step, as indicated in the
right side of FIG. 4C, the amount of warping in the substrate
changes slightly as a result of the wet etching. The warping amount
at this time is approximately 25 .mu.m.
[0082] In this embodiment, the etching rate is controlled by
setting at least one of the following conditions: the type of the
film 12a, such as the material, density, and porosity thereof; the
technique used to form the film 12a, such as CVD, sputtering, or
the like; the temperature at which the film 12a is formed, such as
no more than 400.degree. C. or no less than 400.degree. C. and no
more than 1000.degree. C.; and the processing temperatures employed
during the heat treatment or annealing after the film 12a has been
formed.
[0083] For example, of CVD and sputtering, sputtering results in a
finer film 12a, which makes it possible to reduce the etching rate.
Likewise, during the heat treatment following the formation of the
film 12a, increasing the processing temperature results in a finer
film 12a, which makes it possible to reduce the etching rate,
whereas reducing the processing temperature makes it possible to
increase the etching rate. Controlling the etching rate in this
manner makes it comparatively easy to adjust the curvature factors
or the curvature factor distribution among the aspheric surfaces
defined by the recesses 10b that are ultimately obtained.
[0084] Note that the curvature factors or the curvature factor
distribution among the aspheric surfaces defined by the recesses
10b that are ultimately obtained can also be adjusted comparatively
easily based on the thickness of the film 12a.
[0085] The various conditions for controlling the etching rate, the
thickness of the film 12a, and so on may be set on an individual
basis experimentally, experientially, or theoretically, or may be
set specifically based on the sizes of the microlenses 14 that are
actually used and the capabilities, apparatus specifications, and
so on required of the microlenses 14.
[0086] Next, as indicated in the left side of FIG. 5A, the mask M
is removed through an etching process. Note that this step (the
step indicated in the left side of FIG. 5A) can be omitted if the
thickness of the mask M can be set so that the mask M is completely
removed by the etching performed in the step of forming the
recesses 10b (the step indicated in the left side of FIG. 4C).
[0087] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 5A. In other words, the warping amount at this time is
approximately 25 .mu.m.
[0088] Next, as indicated in the left side of FIG. 5B, silicon
oxynitride (SiON) is deposited in the recesses 10b by performing,
for example, plasma-enhanced chemical vapor deposition ("PECVD"
hereinafter) using a source gas such as SiH.sub.4, N.sub.2O,
NH.sub.3, or the like. A lens layer 13a including the microlenses
14 configured of SiON is formed as a result of this step.
[0089] Here, changing the ratio of N.sub.2O to NH.sub.3 used as the
source gas makes it possible to adjust the refractive index of the
microlenses 14. This in turn makes it possible to achieve a focal
position suited to the pixel size, TFT shape, and F value of the
projection lens.
[0090] For example, assume that a flow ratio between N.sub.2O and
NH.sub.3 (that is, the flow rate of N.sub.2O:the flow rate of
NH.sub.3) is 1:1. Note that the flow ratio is not limited thereto
and can be set as desired, using only N.sub.2O, using only
NH.sub.3, or the like. Note also that varying the flow ratio will
have almost no influence on the warping in the substrate.
[0091] It is desirable for the thickness of the lens layer 13a (a
distance from the upper surface of the film 12 to the upper surface
of the lens layer 13a) to be 5 .mu.m to 20 .mu.m. In this
embodiment, the lens layer 13a is approximately 8 .mu.m thick. Note
that a set plate temperature for setting the substrate 10 is set to
150.degree. C. to 370.degree. C. The thickness of the lens layer
13a that is layered in this step is controlled by the depth of the
recesses 10b, so that the upper surface of the lens layer 13a (and
more specifically, the lowest area of the upper surface of the lens
layer 13a) is positioned higher than the upper surface of the
substrate 10.
[0092] Although the substrate remains warped in a concave shape
(that is, protrudes downward) in this step, as indicated in the
right side of FIG. 5B, the amount of warping in the substrate
changes slightly as a result of the lens layer 13a being formed.
The warping amount at this time is approximately 15 .mu.m. In other
words, the lens layer 13a functions as a film that receives
compressive stress in a direction orthogonal to the normal
direction of the substrate 10. The film that receives compressive
stress in the direction orthogonal to the normal direction of the
substrate 10 will be described in detail later.
[0093] As indicated in the left side of FIG. 5B, when the lens
layer 13a is formed through PECVD on the substrate 10 that has the
recesses 10b, the layer is formed having a shape in which the
respective hemispheres are shifted from each other by half a unit
of pitch.
[0094] Accordingly, an upper area of the lens layer 13a is then
smoothed using, for example, chemical mechanical polishing ("CMP"
hereinafter), as indicated in the left side of FIG. 5C. The lens
layer 13, whose upper surface has been smoothed, is formed as a
result. The thickness of the lens layer 13 (a distance from the
upper surface of the film 12 to an upper surface of the lens layer
13) is approximately 3 .mu.m, for example.
[0095] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 5C. In other words, the warping amount at this time is
approximately 15 .mu.m.
[0096] Note that it is preferable to remove an outer peripheral
area of the lens layer 13a through dry etching prior to smoothing
the upper area of the lens layer 13a through CMP. Doing so makes it
possible to suppress steps from being produced between microlens
areas (areas where the recesses 10b that form the microlenses 14
are formed) and flat areas (areas where the recesses 10b are not
formed) when smoothing the upper area of the lens layer 13a through
CMP.
[0097] Next, the optical path length adjusting layer 15 is formed
upon the lens layer 13. The step of forming the optical path length
adjusting layer 15 includes steps of layering, in an alternating
manner, the first film 16 that receives the compressive stress in
the direction orthogonal to the normal direction of the substrate
10 and the second film 17 that receives tensile stress in the
direction orthogonal to the normal direction of the substrate 10.
In the step of forming the optical path length adjusting layer 15,
the first film 16 is first formed upon the lens layer 13 so that
the substrate 10 warps in a direction that cancels out the warping
that occurred in the substrate 10 as a result of the annealing.
[0098] Here, "receiving the compressive stress in the direction
orthogonal to the normal direction of the substrate 10" refers to a
compressive force acting on the first film 16 in the direction
orthogonal to the normal direction of the substrate 10 due to the
substrate 10 attempting to return to its original flat state (a
restorative force of the substrate 10). In other words, this refers
to a force that pushes extendingly the substrate 10 outward acting
on the first film 16.
[0099] "Receiving the tensile stress in the direction orthogonal to
the normal direction of the substrate 10", meanwhile, refers to an
extending force acting on the second film 17 in the direction
orthogonal to the normal direction of the substrate 10 due to the
restorative force of the substrate 10. In other words, this refers
to a force that pulls back the substrate 10 inward acting on the
second film 17.
[0100] In this embodiment, the following steps are employed in the
step for forming the optical path length adjusting layer 15.
[0101] First, as indicated in the left side of FIG. 6A, the first
film 16 is formed upon the lens layer 13 from SiO.sub.2 under
predetermined plasma conditions through, for example, PECVD using a
source gas such as SiH.sub.4, N.sub.2O, or the like.
[0102] A high-frequency plasma source and a low-frequency plasma
source are employed when forming the first film 16. This is because
the warping in the substrate can change as a result. Specifically,
the first film 16 becomes finer when a low-frequency plasma source
is employed, and the first film 16 receives the compressive stress
in the direction orthogonal to the normal direction of the
substrate 10.
[0103] For the plasma conditions, a ratio between the frequency of
the high-frequency plasma source and the frequency of the
low-frequency plasma source (high-frequency plasma source
frequency:low-frequency plasma source frequency) is set to 2:1, for
example.
[0104] In this embodiment, the high-frequency plasma source
frequency is assumed to be 13.56 MHz and the low-frequency plasma
source frequency is assumed to be 300 kHz. The high-frequency
plasma source frequency and the low-frequency plasma source
frequency are not, however, limited to these frequencies, and can
be set as desired. Warping in the substrate can be changed by
changing the ratio between the high-frequency plasma source
frequency and the low-frequency plasma source frequency.
[0105] In this embodiment, the first film 16 is approximately 4
.mu.m thick. Note however that the thickness of the first film 16
is not limited thereto and can be set as desired. Varying the
thickness of the first film 16 makes it possible to change the
warping in the substrate.
[0106] The substrate is warped in a convex shape (that is,
protrudes upward) in this step due to the effect of the first film
16, as indicated in the right side of FIG. 6A. In other words, the
direction of the warp produced in the substrate by the annealing is
the reverse of the direction of the warp produced in the substrate
by the effect of the first film 16. The warping amount at this time
is approximately 20 .mu.m.
[0107] Next, as indicated in the left side of FIG. 6B, the second
film 17 is formed upon the first film 16 from SiO.sub.2 under
predetermined plasma conditions through, for example, PECVD using a
source gas such as SiH.sub.4, N.sub.2O, or the like.
[0108] A high-frequency plasma source is employed when forming the
second film 17. This is because the warping in the substrate can
change as a result. Specifically, the second film 17 receives the
tensile stress in the direction orthogonal to the normal direction
of the substrate 10 when a high-frequency plasma source is
employed.
[0109] For the plasma conditions, a ratio between the frequency of
the high-frequency plasma source used when forming the first film
16 and the frequency of the high-frequency plasma source used when
forming the second film 17 (high-frequency plasma source frequency
when forming first film 16:high-frequency plasma source frequency
when forming second film 17) is set to 2:3, for example.
[0110] In this embodiment, the second film 17 is approximately 3
.mu.m thick. Note however that the thickness of the second film 17
is not limited thereto and can be set as desired. Varying the
thickness of the second film 17 makes it possible to change the
warping in the substrate.
[0111] The substrate is warped in a concave shape (that is,
protrudes downward) in this step due to the effect of the second
film 17, as indicated in the right side of FIG. 6B. In other words,
the direction of the warp produced in the substrate due to the
effect of the first film 16 is the reverse of the direction of the
warp produced in the substrate by the effect of the second film 17.
The warping amount at this time is approximately 5 .mu.m.
[0112] Next, as indicated in the left side of FIG. 6C, the third
film 18 is formed upon the second film 17 from SiO.sub.2 under
predetermined plasma conditions through, for example, PECVD using a
source gas such as SiH.sub.4, N.sub.2O, or the like. The optical
path length adjusting layer 15 is completed as a result.
[0113] As in the step of forming the first film 16, a
high-frequency plasma source and a low-frequency plasma source are
employed when forming the third film 18. Accordingly, the third
film 18 receives the compressive stress in the direction orthogonal
to the normal direction of the substrate 10.
[0114] For the plasma conditions, a ratio between the frequency of
the high-frequency plasma source and the frequency of the
low-frequency plasma source (high-frequency plasma source
frequency:low-frequency plasma source frequency) is set to 2:1, for
example.
[0115] The high-frequency plasma source frequency and the
low-frequency plasma source frequency are not, however, limited to
these frequencies, and can be set as desired. Warping in the
substrate can be changed by changing the ratio between the
high-frequency plasma source frequency and the low-frequency plasma
source frequency.
[0116] In this embodiment, the third film 18 is approximately 4
.mu.m thick. Note however that the thickness of the third film 18
is not limited thereto and can be set as desired. Varying the
thickness of the third film 18 makes it possible to change the
warping in the substrate.
[0117] The substrate returns to its original flat shape in this
step due to the effect of the third film 18, as indicated in the
right side of FIG. 6C. In other words, the warping is eliminated
from the substrate.
[0118] Although this embodiment has described forming three layers
in the step of forming the optical path length adjusting layer 15,
namely the first film 16, the second film 17, and the third film
18, it should be noted that the configuration is not limited
thereto.
[0119] For example, the configuration may be such that two layers
are formed, namely the first film 16 and the second film 17.
Alternatively, the configuration may be such that a film that
receives the compressive stress in the direction orthogonal to the
normal direction of the substrate 10 (this corresponds to a first
film) and a film that receives the tensile stress in the direction
orthogonal to the normal direction of the substrate 10 (this
corresponds to a second film) are layered in an alternating manner
to form four or more layers.
[0120] In terms of improving production efficiency, however, it is
preferable to have a low number of layers (a low number of
depositions).
[0121] Although this embodiment gives an example of a configuration
in which the substrate 10 is a silica substrate and the oxide film
12 is a silicon oxide film, and the first film 16 is selected as
the first film to be formed upon the lens layer 13 in the step of
forming the optical path length adjusting layer 15, the invention
is not limited thereto. In the step of forming the optical path
length adjusting layer 15, a film that exerts a stress for warping
the substrate in a direction that cancels out the warping in the
substrate caused by the annealing may be selected from among the
first film 16 and the second film 17, and that film may then be
formed upon the lens layer 13 first.
[0122] In other words, of the film that receives the compressive
stress in the direction orthogonal to the normal direction of the
substrate 10 and the film that receives the tensile stress in the
direction orthogonal to the normal direction of the substrate 10,
one film that exerts a stress for warping the substrate in a
direction that cancels out the warping in the substrate caused by
the annealing is formed as the lowermost layer of the optical path
length adjusting layer 15, and the other film is then formed on top
of the one film. The one film and the other film may then be formed
in an alternating manner upon the first instance of the other
film.
[0123] Here, forming a thick optical path length adjusting layer 15
can roughen the surface of the layer and cause clouding.
Accordingly, the upper area of the optical path length adjusting
layer 15 (the third film 18) is smoothed through CMP, for example.
The optical path length adjusting layer 15, whose upper surface has
been smoothed, is formed as a result. The amount of grinding of the
optical path length adjusting layer 15 is no more than 1 .mu.m, for
example.
[0124] Next, a film 19a configured of aluminum (Al) is formed upon
the optical path length adjusting layer 15 (the third film 18)
through sputtering, for example, as indicated in the left side of
FIG. 7A. The film 19a is approximately 1500 .ANG. thick, for
example.
[0125] The substrate is not warped in this step, as indicated in
the right side of FIG. 7B.
[0126] Next, as indicated in the left side of FIG. 7B, the film 19a
is removed from regions in locations corresponding to the marks 11
(that is, regions that overlap with the marks 11 when viewed from
above) so as to excavate openings 19h1, by patterning the film 19a
using photolithography and etching. A film 19b, which has the
openings 19h1 that serve as windows for viewing the marks 11, is
formed as a result.
[0127] After this, a resist mask (not shown) used for the
patterning is removed at an atmospheric temperature of
approximately 250.degree. C. through etching using a chlorine
etchant or the like.
[0128] The substrate is warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 7B. The warping amount at this time is approximately 80 .mu.m.
The film 19a contracting due to the atmospheric temperature when
removing the resist mask can be thought of as a reason for the
substrate warping in this manner.
[0129] Next, as indicated in the left side of FIG. 7C, the film 19b
is removed from regions corresponding to the aperture regions of
the respective pixels (that is, regions that overlap with the
aperture regions when viewed from above) so as to excavate openings
19h2, by patterning the film 19b using photolithography and
etching. The light-blocking film 19 that has the openings 19h1 and
the openings 19h2 is formed as a result.
[0130] Note that films 19c located on both ends of the
light-blocking film 19 function as alignment marks for positioning
the element substrate and the opposing substrate when affixing
those substrates to each other.
[0131] Next, as indicated in the left side of FIG. 8A, a film 20a
is formed from SiO.sub.2 under predetermined plasma conditions
through, for example, PECVD using a source gas such as SiH.sub.4,
N.sub.2O, or the like, so as to cover the light-blocking film 19 on
the optical path length adjusting layer 15 (the third film 18).
[0132] As in the step of forming the first film 16, a
high-frequency plasma source and a low-frequency plasma source are
employed when forming the film 20a.
[0133] For the plasma conditions, a ratio between the frequency of
the high-frequency plasma source and the frequency of the
low-frequency plasma source (high-frequency plasma source
frequency:low-frequency plasma source frequency) is set to 2:1, for
example.
[0134] The high-frequency plasma source frequency and the
low-frequency plasma source frequency are not, however, limited to
these frequencies, and can be set as desired. Warping in the
substrate can be changed by changing the ratio between the
high-frequency plasma source frequency and the low-frequency plasma
source frequency.
[0135] In this embodiment, the thickness of the film 20a (a
distance from the upper surface of the light-blocking film 19 to
the upper surface of the film 20a) is approximately 2 .mu.m. Note
however that the thickness of the film 20a is not limited thereto,
and can be set as desired. Varying the thickness of the film 20a
makes it possible to change the warping in the substrate.
[0136] Although the substrate remains warped in a concave shape
(that is, protrudes downward) in this step, as indicated in the
right side of FIG. 8A, the amount of warping in the substrate
changes slightly as a result of the film 20a being formed. The
warping amount at this time is approximately 70 .mu.m. In other
words, the film 20a functions as a film that receives the
compressive stress in a direction orthogonal to the normal
direction of the substrate 10.
[0137] When the film 20a is formed through PECVD so as to cover the
light-blocking film 19 on the optical path length adjusting layer
15 (the third film 18) as indicated in the left side of FIG. 8A,
the film 20a is formed in a shape conforming to areas where the
light-blocking film 19 is formed and areas where the light-blocking
film 19 is not formed (that is, the openings 19h1 and 19h2).
[0138] Accordingly, an upper area of the film 20a is then smoothed
through CMP, for example, as indicated in the left side of FIG. 8B.
The flattening film 20, whose upper surface has been smoothed, is
formed as a result. The thickness of the flattening film 20 (a
distance from the upper surface of the light-blocking film 19 to
the upper surface of the flattening film 20) is approximately 1
.mu.m, for example.
[0139] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 8B. In other words, the warping amount at this time is
approximately 70 .mu.m.
[0140] Next, the transparent conductive film 21 is formed from
indium tin oxide ("ITO" hereinafter) upon the flattening film 20
through sputtering or the like, as indicated in the left side of
FIG. 8C. The transparent conductive film 21 is approximately 1,460
.ANG. thick, for example.
[0141] The substrate remains warped in a concave shape (that is,
protrudes downward) in this step, as indicated in the right side of
FIG. 8C. In other words, the warping amount at this time is
approximately 70 .mu.m.
[0142] The microlens array substrate 1 according to this embodiment
of the invention is completed through the steps described thus
far.
[0143] According to the method for fabricating the microlens array
substrate 1 according to this embodiment, the first film 16 that
receives the compressive stress in the direction orthogonal to the
normal direction of the substrate 10 is first formed upon the lens
layer 13 in the step of forming the optical path length adjusting
layer 15, and thus stress produced in the substrate by the
annealing can be alleviated in the initial stage of forming the
optical path length adjusting layer 15.
[0144] In, for example, the case where the second film 17 that
receives the tensile stress in the direction orthogonal to the
normal direction of the substrate 10 is formed on the lens layer 13
first, the second film 17 will act on the substrate in a direction
that increases the warping in the substrate caused by the
annealing. As a result, the substrate warps extensively in the
initial stage of forming the optical path length adjusting layer
15, which makes it difficult to correct the warping in the
substrate later. However, the method according to this embodiment
forms the first film 16 on the lens layer 13 first, and thus the
stated problem does not occur.
[0145] In addition, because the first film 16 and the second film
17 are layered in an alternating manner, the warping in the
substrate can be corrected while adjusting the amount of stress to
be alleviated in the substrate by adjusting formation conditions
such as the thicknesses, materials, and so on of the first film 16
and the second film 17.
[0146] Accordingly, the substrate can be suppressed from
warping.
[0147] With the microlens array substrate 1 according to this
embodiment, the substrate remains warped in a concave shape (that
is, protrudes downward), as indicated in the right side of FIG. 8C.
This is to conform to warping in the element substrate to which the
opposing substrate is to be affixed.
[0148] As long as the warping amount in the substrate is no greater
than 100 .mu.m, the warping will have no effect on the process for
affixing the element substrate and the opposing substrate to each
other, or in other words, it will not be difficult to position the
element substrate and the opposing substrate when affixing those
substrates to each other. In this embodiment, the warping amount in
the substrate is approximately 70 .mu.m, which is lower than the
stated 100 .mu.m, and thus the element substrate and the opposing
substrate can be positioned with ease when affixing the substrates
to each other.
[0149] This embodiment describes an example in which the microlens
array substrate 1 is fabricated by forming the lens layer 13
configured of the plurality of microlenses 14 by depositing a lens
material on the substrate 10 in which is formed the plurality of
recesses 10b corresponding to the plurality of microlenses 14 so as
to form the plurality of microlenses 14, forming the optical path
length adjusting layer 15 upon the lens layer 13, and furthermore
forming the light-blocking film 19, the flattening film 20, and the
transparent conductive film 21, in that order, upon the optical
path length adjusting layer 15. However, the invention is not
limited thereto.
[0150] For example, the microlens array substrate may be configured
without the light-blocking film 19, the flattening film 20, and the
transparent conductive film 21. Variation
[0151] Next, a fabrication method for a microlens array substrate 2
according to a variation of the invention will be described with
reference to FIGS. 10A through 10C.
[0152] FIGS. 10A through 10C are schematic diagrams illustrating
steps for fabricating the microlens array substrate and warping in
the substrate.
[0153] Note that in FIGS. 10A through 10C, the left sides are
diagrams illustrating steps for fabricating the microlens array
substrate as cross-sectional views, and the right sides indicate
the state of warping in the substrate. Note also that in FIGS. 10A
through 10C, steps identical to those in the aforementioned
embodiment are not shown, and descriptions thereof will be
omitted.
[0154] In a step of forming an optical path length adjusting layer
25 according to this variation, the substrate is caused to warp in
a direction that cancels out warping in the substrate occurring in
the steps that follow the step of forming the optical path length
adjusting layer 25.
[0155] In this variation, the following steps are employed in the
step for forming the optical path length adjusting layer 25.
[0156] First, as indicated in the left side of FIG. 10A, a first
film 26, a second film 27, and a third film 28 are formed upon the
lens layer 13 from SiO.sub.2 under predetermined plasma conditions
through, for example, PECVD using a source gas such as SiH.sub.4,
N.sub.2O, or the like. The optical path length adjusting layer 25
is formed upon the lens layer 13 as a result.
[0157] In this variation, the substrate is warped in a convex shape
(that is, protrudes upward) as indicated in the right side of FIG.
10A, by varying the frequency of the plasma source, the
thicknesses, and so on as desired while forming the first film 26,
the second film 27, and the third film 28. In other words, the
optical path length adjusting layer 25 has an effect of warping the
substrate in the opposite direction as the direction of warping
produced in the substrate in the subsequent steps.
[0158] Next, as indicated in the left side of FIG. 10B, the film
19a is removed from regions in locations corresponding to the marks
11 (that is, regions that overlap with the marks 11 when viewed
from above) so as to excavate the openings 19h1, by patterning the
film 19a using photolithography and etching. The film 19b, which
has the openings 19h1 that serve as windows for viewing the marks
11, is formed as a result.
[0159] After this, a resist mask (not shown) used for the
patterning is removed at an atmospheric temperature of
approximately 250.degree. C. through etching using a chlorine
etchant or the like.
[0160] The substrate returns to its original flat shape in this
step due to the effect of the atmospheric temperature when removing
the resist mask, as indicated in the right side of FIG. 10B. In
other words, the warping is eliminated from the substrate.
[0161] The microlens array substrate 2 according to this variation
is then completed by carrying out the steps of forming the
light-blocking film 19, the flattening film 20, and the transparent
conductive film 21, as indicated in the left side of FIG. 10C.
[0162] According to the microlens array substrate 2 fabrication
method in this variation, the substrate can, in the step of forming
the optical path length adjusting layer 25, be pre-warped in a
direction that alleviates stress produced in the substrate in a
later step (the step of forming the film 19b). Accordingly, the
microlens array substrate 2 that is ultimately fabricated can be
prevented from warping.
[0163] Although this variation describes an example in which the
later step is the step of forming the film 19b that serves as the
light-blocking film 19, and in which in the step of forming the
optical path length adjusting layer 25 the substrate is caused to
warp in a direction that cancels out warping produced in the step
of forming the film 19b, the invention is not limited thereto. As
long as there is another later step that produces warping in the
substrate after the step of forming the optical path length
adjusting layer 25, the substrate may, when the optical path length
adjusting layer 25 is formed, be pre-warped in a direction that
cancels out the warping produced in that later step.
Electronic Device
[0164] The aforementioned microlens array substrate is used as an
opposing substrate that partially configures an optical modulation
apparatus in a projector 100 such as that shown in FIG. 11.
[0165] FIG. 11 is a diagram illustrating the overall configuration
of a projector.
[0166] As shown in FIG. 11, the projector 100 includes a light
source 101, dichroic mirrors 102 and 103, a red light optical
modulation apparatus 104, a green light optical modulation
apparatus 105, a blue light optical modulation apparatus 106, a
light guiding optical system 107, reflecting mirrors 110 to 112, a
cross dichroic prism 113, and a projection lens 114. Color image
light emitted from the projector 100 is projected onto a screen
115.
[0167] The light source 101 includes a lamp 101a such as a metal
halide lamp and a reflector 101b that reflects light from the lamp
101a.
[0168] The dichroic mirror 102 is configured to allow red light
from the white light emitted by the light source 101 to pass while
reflecting green light and blue light. The dichroic mirror 103 is
configured to allow blue light from the blue light and green light
reflected by the dichroic mirror 102 to pass through while
reflecting green light.
[0169] The red light optical modulation apparatus 104, the green
light optical modulation apparatus 105, and the blue light optical
modulation apparatus 106 include the aforementioned microlens array
substrate as their opposing substrates.
[0170] The red light optical modulation apparatus 104 is configured
to modulate, based on a predetermined image signal, red light that
has passed through the dichroic mirror 102 and is incident on the
red light optical modulation apparatus 104.
[0171] The green light optical modulation apparatus 105 is
configured to modulate, based on a predetermined image signal,
green light that has been reflected by the dichroic mirror 103 and
is incident on the green light optical modulation apparatus
105.
[0172] The blue light optical modulation apparatus 106 is
configured to modulate, based on a predetermined image signal, blue
light that has passed through the dichroic mirror 103 and is
incident on the blue light optical modulation apparatus 106.
[0173] The light guiding optical system 107 is configured of an
incoming lens 107a, a relay lens 107b, and an outgoing lens 107c,
and is provided to suppress optical loss caused by the length of
the optical path for the blue light.
[0174] The reflecting mirror 110 is configured to reflect the red
light that has passed through the dichroic mirror 102 toward the
red light optical modulation apparatus 104.
[0175] The reflecting mirror 111 is configured to reflect the blue
light that has passed through the dichroic mirror 103 and the
incoming lens 107a toward the relay lens 107b.
[0176] The reflecting mirror 112 is configured to reflect the blue
light emitted from the relay lens 107b toward the outgoing lens
107c.
[0177] The cross dichroic prism 113 is configured by affixing four
right-angle prisms to each other; a dielectric multilayer film that
reflects red light and a dielectric multilayer film that reflects
blue light are formed in an X shape at the borders between the
right-angle prisms. The three colors of light are combined by these
dielectric multilayer films, forming light that expresses a color
image.
[0178] The projection lens 114 is configured to enlarge the color
image produced by the cross dichroic prism 113 and project the
enlarged image onto the screen 115.
[0179] Although a preferable exemplary embodiment of the invention
has been described thus far with reference to the drawings, it goes
without saying that the invention is not intended to be limited to
the aforementioned embodiment. The forms, combinations, and so on
of the various constituent elements described in the aforementioned
embodiment are merely examples, and many variations based on design
requirements and the like are possible without departing from the
essential spirit of the invention.
[0180] Likewise, the specific details of the shapes, numbers,
locations, materials, formation methods, and so on of the
constituent elements in the microlens array substrate are not
intended to be limited to the aforementioned embodiment, and can be
changed as desired.
* * * * *