U.S. patent application number 09/971732 was filed with the patent office on 2002-02-14 for reflector, method of fabricating the same, reflective display device comprising reflector, and method of fabricating the same.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Karasawa, Takeshi, Kawaguri, Mariko, Nishiyama, Seiji, Wakita, Naohide, Yamanaka, Yasuhiko.
Application Number | 20020018161 09/971732 |
Document ID | / |
Family ID | 26514310 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018161 |
Kind Code |
A1 |
Yamanaka, Yasuhiko ; et
al. |
February 14, 2002 |
Reflector, method of fabricating the same, reflective display
device comprising reflector, and method of fabricating the same
Abstract
A reflector comprises a substrate provided with a plurality of
projecting and depressed structures which are groups of columnar
portions each serving as a basic unit and composed of a plurality
of minute columnar portions, which are separate from each other or
at least partially connected to each other, and with a light
reflecting thin film provided over the projecting and depressed
structures. This allows incident light to be scattered and
reflected in a forward direction or the like, not in the regular
reflection direction, and provides a reflector having a superior
contrast property and a superior paper-white property, a
fabrication method therefor, and a reflective display device
comprising the reflector. The reflective display device has a
liquid crystal layer provided between a pair of substrates. One of
the pair of substrates is provided with projecting and depressed
portions covered with a metal film and with a support portion for
supporting the counter substrate, which are molded integrally. The
arrangement reduces reflection in the regular reflection direction
and enhances brightness and whiteness, while reducing the
occurrence of uneven display by providing a uniform cell gap.
Inventors: |
Yamanaka, Yasuhiko;
(Hirakata-shi, JP) ; Wakita, Naohide; (Suita-shi,
JP) ; Karasawa, Takeshi; (Suita-shi, JP) ;
Kawaguri, Mariko; (Moriguchi-shi, JP) ; Nishiyama,
Seiji; (Hirakata-shi, JP) |
Correspondence
Address: |
PARKHURST & WENDEL, L.L.P.
Suite 210
1421 Prince Street
Alexandria
VA
22314-2805
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
|
Family ID: |
26514310 |
Appl. No.: |
09/971732 |
Filed: |
October 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09971732 |
Oct 9, 2001 |
|
|
|
09619655 |
Jul 19, 2000 |
|
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Current U.S.
Class: |
349/112 |
Current CPC
Class: |
G02F 1/136227 20130101;
G02F 1/136236 20210101; G02F 1/133553 20130101 |
Class at
Publication: |
349/112 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 1999 |
JP |
11-204153 |
Aug 31, 1999 |
JP |
11-246656 |
Claims
What is claimed is:
1. A reflector comprising: a substrate provided with a plurality of
projecting and depressed structures each having a plurality of
projecting and depressed portions and serving as a basic unit: and
a light reflective thin film provided over the projecting and
depressed structures.
2. The reflector of claim 1, wherein the projecting and depressed
structures provided on the substrate are arranged randomly and
dispersively in an arbitrary direction.
3. The reflector of claim 1, wherein the projecting portions of the
projecting and depressed structures have top portions at different
heights and the depressed portions of the projecting and depressed
structures have bottom portions at different depths.
4. The reflector of claim 1, wherein the projecting and depressed
structures are groups of columnar portions each composed of a
plurality of minute columnar portions having different heights, the
columnar portions being separate from each other or at least
partially connected to each other.
5. The reflector of claim 4, wherein a height distribution of each
of the projecting and depressed structures has a peak at a position
deviated in a specified direction from a center portion of the
structure and tends to decrease with distance from the peak toward
a periphery thereof and the light reflecting thin film covering the
projecting and depressed structures has a curved surface having a
curvature larger in the specified direction than in a direction
opposite to the specified direction.
6. The reflector of claim 5, wherein at least one polymer resin
layer is provided between the projecting and depressed structures
and the light reflecting thin film.
7. The reflector of claim 1, wherein the projecting and depressed
structures are staircase structures each having a plurality of
stepped portions.
8. The reflector of claim 7, wherein a height distribution of each
of the projecting and depressed structures has a peak at a position
deviated in a specified direction from a center portion of the
structure and tends to decrease with distance from the peak toward
a periphery of the structure and the light reflecting thin film
covering the projecting and depressed structures has a curved
surface having a curvature larger in the specified direction than
in a direction opposite to the specified direction.
9. The reflector of claim 8, wherein at least one polymer resin
layer is provided between the projecting and depressed structures
and the light reflecting thin film.
10. The reflector of claim 1, wherein the reflector is a grating
reflector for reflecting and diffracting light, the grating
reflector having the plurality of projecting and depressed
structures provided periodically on the substrate.
11. The reflector of claim 1, wherein each of the projecting and
depressed structures in plan view has a size in the range of 1
.mu.m to 100 .mu.m.
12. The reflector of claim 1, wherein each of the plurality of
projecting and depressed structures has a periodic structure for
reflecting and diffracting light, the projecting and depressed
structures being provided such that positions thereof are random
and/or a direction in which periodicity is recognized is
random.
13. A reflector comprising: a substrate provided with a nonlinear
element; a photosensitive resin layer provided on the substrate,
the photosensitive resin layer having projecting and depressed
structures in specified regions; and a pixel electrode with a light
reflecting property provided on the photosensitive resin layer, the
pixel electrode being electrically connected to the nonlinear
element via a contact hole formed in the photosensitive resin
layer, wherein a light reflecting film is provided on a bottom
portion of the contact hole.
14. The reflector of claim 13, wherein a degree of crosslinking in
the photosensitive resin layer is higher in a surrounding portion
of an inner wall surface of the contact hole than in the other
portion thereof.
15. A reflector comprising: a substrate provided with a nonlinear
element; a photosensitive resin layer provided on the substrate,
the photosensitive resin layer having projecting and depressed
structures in specified regions; and a pixel electrode with a light
reflecting property provided on the photosensitive resin layer, the
pixel electrode being electrically connected to the nonlinear
element via a contact hole formed in the photosensitive resin
layer, wherein a thin film having a surface energy higher than that
of the photosensitive resin layer is provided on a bottom portion
of the contact hole.
16. A reflector comprising: a substrate provided with a nonlinear
element; a photosensitive resin layer provided on the substrate,
the photosensitive resin layer having projecting and depressed
structures in specified regions; and a pixel electrode with a light
reflecting property provided on the photosensitive resin layer, the
pixel electrode being electrically connected to the nonlinear
element via a contact hole formed in the photosensitive resin
layer, wherein the contact hole is provided such that a degree of
crosslinking is higher in a surrounding portion of an inner wall
surface of the contact hole than in the other portion thereof.
17. A reflector comprising: a substrate provided with a nonlinear
element and with a plurality of projecting and depressed portions;
and a pixel electrode with a light reflecting property provided
over the projecting and depressed portions, wherein the projecting
and depressed portions are composed of a single layer or a
plurality of layers selected arbitrarily from layers composing the
nonlinear element.
18. A reflective display device comprising: a counter substrate
with transparency; a reflector disposed in opposing relation to the
counter substrate, the reflector including a substrate provided
with a plurality of projecting and depressed structures each having
a plurality of projecting and depressed portions and serving as a
basic unit and a light reflecting thin film provided over the
projecting and depressed structures; and a liquid crystal layer
held between the counter substrate and the reflector.
19. The reflective display device of claim 18, wherein the
reflector is a grating reflector for reflecting and diffracting
light, the grating reflector having the plurality of projecting and
depressed structures provided periodically on the substrate.
20. The reflective display device of claim 18, wherein the
projecting portions of the projecting and depressed structures have
top portions at different heights and the depressed portions of the
projecting and depressed structures have bottom portions at
different depths.
21. The reflective display device of claim 18, wherein the
projecting and depressed structures are groups of columnar portions
each composed of a plurality of minute columnar portions having
different heights, the columnar portions being separate from each
other or at least partially connected to each other.
22. The reflective display device of claim 21, wherein a height
distribution of each of the projecting and depressed structures has
a peak at a position deviated in a specified direction from a
center portion of the structure and tends to decrease with distance
from the peak toward a periphery thereof and the light reflecting
thin film covering the projecting and depressed structures has a
curved surface having a curvature larger in the specified direction
than in a direction opposite to the specified direction.
23. The reflective display device of claim 22, wherein at least one
polymer resin layer is provided between the projecting and
depressed structures and the light reflecting thin film.
24. The reflective display device of claim 18, wherein the
projecting and depressed structures are staircase structures each
having a plurality of stepped portions.
25. The reflective display device of claim 24, wherein a height
distribution of each of the projecting and depressed structures has
a peak at a position deviated in a specified direction from a
center portion of the structure and tends to decrease with distance
from the peak toward a periphery thereof and the light reflecting
thin film covering the projecting and depressed structures has a
curved surface having a curvature larger in the specified direction
than in a direction opposite to the specified direction.
26. The reflective display device of claim 25, wherein at least one
polymer resin layer is provided between the projecting and
depressed structures and the light reflecting thin film.
27. The reflective display device of claim 18, wherein the
reflector is a grating reflector for reflecting and diffracting
light, the grating reflector having the plurality of projecting and
depressed structures provided periodically on the substrate.
28. The reflective display device of claim 18, wherein each of the
projecting and depressed structures in plan view has a size in the
range of 1 .mu.m to 100 .mu.m.
29. The reflective display device of claim 18, wherein each of the
plurality of projecting and depressed structures has a periodic
structure for reflecting and diffracting light, the projecting and
depressed structures being provided such that positions thereof are
random and/or a direction in which periodicity is recognized is
random.
30. A reflective display device comprising: a substrate provided
with a nonlinear element; a photosensitive resin layer provided on
the substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein a light reflecting film is
provided on a bottom portion of the contact hole.
31. The reflective display device of claim 30, wherein a degree of
crosslinking in the photosensitive resin layer is higher in a
surrounding portion of an inner wall surface of the contact hole
than in the other portion thereof.
32. A reflective display device comprising: a substrate provided
with a nonlinear element; a photosensitive resin layer provided on
the substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein a thin film having a surface
energy higher than that of the photosensitive resin layer is
provided on a bottom portion of the contact hole.
33. The reflective display device of claim 32, wherein a degree of
crosslinking in the photosensitive resin layer is higher in a
surrounding portion of an inner wall surface of the contact hole
than in the other portion thereof.
34. A reflective display device comprising: a substrate provided
with a nonlinear element; a photosensitive resin layer provided on
the substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein the contact hole is provided
such that a degree of crosslinking is higher in a surrounding
portion of an inner wall surface of the contact hole than in the
other portion thereof.
35. A reflective display device comprising: a substrate provided
with a nonlinear element and with a plurality of projecting and
depressed portions; and a pixel electrode with a light reflecting
property provided over the projecting and depressed portions,
wherein the projecting and depressed portions are composed of a
single layer or a plurality of layers selected arbitrarily from
layers composing the nonlinear element.
36.A reflective display device having a liquid crystal layer
provided between a pair of substrates, wherein one of the pair of
substrates is provided with projecting and depressed portions
covered with a metal film and with a support portion for supporting
the other of the pair of substrates, the projecting and depressed
portions and the support portion being molded integrally.
37. The reflective display device of claim 36, wherein the
projecting and depressed portions are pyramidal or conical.
38. The reflective display device of claim 37, wherein if an angle
formed between an inclined surface of the pyramidal projecting and
depressed portions and a horizontal surface or an angle formed
between a generating line of the conical projecting and depressed
portions and a horizontal surface is assumed to be a slope angle,
the projecting and depressed portions are dispersively arranged at
different slope angles and the slope angles are in the range of
4.degree. to 16.degree..
39. The reflective display device of claim 36, further comprising a
polymer resin layer molded integrally with the projecting and
depressed portions and with the support portion for supporting the
other of the substrates, the polymer resin layer being provided on
one of the substrates.
40. The reflective display device of claim 39, wherein a plurality
of nonlinear elements are provided on one of the substrates and a
contact hole for providing an electric connection between the
nonlinear elements and the metal film is provided in the polymer
resin layer.
41. The reflective display device of claim 36, wherein a resin film
molded integrally with the projecting and depressed portions and
with the support portion for supporting the other of the substrates
is laminated on one of the substrates.
42. The reflective display device of claim 41, wherein the resin
film is made of a photosensitive resin.
43. The reflective display device of claim 36, wherein one of the
substrates is a plastic substrate molded with the projecting and
depressed portions and with the support portion for supporting the
other of the substrates.
44. A reflective display device having a photosensitive resin layer
provided on a substrate and a metal film provided on the
photosensitive resin layer, wherein the photosensitive resin layer
is formed by exposing, to light, a photosensitive resin coated on
the substrate via a photomask and developing the exposed
photosensitive resin, the photosensitive resin layer having a
projecting and depressed surface formed by exposing the
photosensitive resin to the light via the photomask having a light
shielding pattern composed of groups of minute halftone dots
smaller than a resolution limit of an exposing device used for the
exposure and a resolution limit of the photosensitive resin, a mean
light transmittance of the light shielding pattern being nonuniform
over a surface of the photomask.
45.A method of fabricating a reflector, the method comprising: a
step of forming a photosensitive resin layer on a substrate; an
exposing step of irradiating the photosensitive resin layer with
light via a photomask having light shielding portions patterned
into specified configurations; a developing step of developing the
photosensitive resin layer irradiated with the light to form a
plurality of resist columns; a heat treatment step of performing a
heat treatment with respect to the substrate formed with the
plurality of resist columns and thereby forming groups of columnar
portions each composed of a plurality of minute columnar portions
having different heights, the columnar portions being separate from
each other or at least partially connected to each other; and a
step of forming a light reflecting thin film over the groups of
columnar portions, wherein as the photomask, a mask formed with a
plurality of unit components each composed of a plurality of minute
shielding portions having different heights is used.
46. A method of fabricating a reflector, the method comprising: a
step of forming a photosensitive resin layer on a substrate; an
exposing step of irradiating the photosensitive resin layer with
light via a photomask having light shielding portions each having a
progressively varying light shielding rate; a developing step of
developing the photosensitive resin layer irradiated with the light
to form a plurality of staircase resist columns; a heat treatment
step of performing a heat treatment with respect to the substrate
formed with the plurality of staircase resist columns to round off
respective angular edges of the resist columns and thereby forming
staircase structures each having a plurality of stepped portions;
and a step of forming a light reflecting thin film over the
staircase structures.
47. A method of fabricating a reflector, the method comprising: a
step of forming a photosensitive resin layer on a substrate; a step
of preparing a plurality of photomasks each having light shielding
portions patterned into specified configurations, each of the light
shielding portions of the different photomasks covering a light
shielding range which is different in size from one photomask to
another, each of the light shielding portions of any of the
photomasks covering a larger shielding range and each of the light
shielding portions of the photomask covering a next smaller
shielding range having a relationship therebetween such that the
next smaller light shielding range is included in the larger light
shielding range; an exposing step of irradiating the photosensitive
resin layer with light by successively using the photomasks in the
order of decreasing size of the light shielding range of the
shielding portion; a developing step of developing the
photosensitive resin layer irradiated with the light to form a
plurality of staircase resist columns; a heat treatment step of
performing a heat treatment with respect to the substrate formed
with the staircase resist columns to round off respective angular
edges of the resist columns and thereby forming staircase
structures each having a plurality of stepped portions; and forming
a light reflecting thin film over the staircase structures.
48. A method of fabricating a reflector having a substrate provided
with a nonlinear element, a photosensitive resin layer provided on
the substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a light-reflecting-film forming step of forming, at a
position at which the contact hole is to be formed, a light
reflecting film patterned into a specified configuration; a coating
step of coating a photosensitive resin material over the substrate
and the light reflecting film; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a heat treatment step of performing a
heat treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a post-baking step of
performing a heat treatment with respect to the photosensitive
resin layer and thereby curing the photosensitive resin layer; and
a pixel-electrode forming step of forming the pixel electrode with
the light reflecting property on the photosensitive resin
layer.
49. A method of fabricating a reflector having a substrate provided
with a nonlinear element, a photosensitive resin layer provided on
the substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a thin-film forming step of forming, at a position at
which the contact hole is to be formed, a frame-shaped thin film
having a surface energy higher than that of the photosensitive
resin layer; a coating step of coating a photosensitive resin
material over the substrate and the thin film; an exposing step of
irradiating the photosensitive resin material with light via a
photomask having light shielding portions patterned into specified
configurations; a developing step of developing the photosensitive
resin material irradiated with the light to form the photosensitive
resin layer comprising the contact hole and a plurality of resist
columns formed in specified regions; a heat treatment step of
performing a heat treatment with respect to the photosensitive
resin layer and thereby thermally deforming and rounding off
respective edge portions of the plurality of resist columns; a
post-baking step of performing a heat treatment with respect to the
photosensitive resin layer and thereby curing the photosensitive
resin layer; and a pixel-electrode forming step of forming the
pixel electrode with the light reflecting property on the
photosensitive resin layer.
50. A method of fabricating a reflector having a substrate provided
with a nonlinear element, a photosensitive resin layer provided on
the substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a thin-film forming step of forming, on a drain
electrode of the nonlinear element, a thin film having a surface
energy higher than that of the photosensitive resin layer; a
coating step of coating a photosensitive resin material over the
substrate and the thin film; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a heat treatment step of performing a
heat treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a removing step of
removing the thin film by ashing; a post-baking step of performing
a heat treatment with respect to the photosensitive resin layer and
thereby curing the photosensitive resin layer; and a
pixel-electrode forming step of forming the pixel electrode with
the light reflecting property on the photosensitive resin
layer.
51. A method of fabricating a reflector having a substrate provided
with a nonlinear element, a photosensitive resin layer provided on
the substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a coating step of coating a photosensitive resin
material on the substrate; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a light irradiating step of
irradiating a surrounding portion of the contact hole with light at
a shorter wavelength; a heat treatment step of performing a heat
treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a post-baking step of
performing a heat treatment with respect to the photosensitive
resin layer; and a pixel-electrode forming step of forming the
pixel electrode with the light reflecting property on the
photosensitive resin layer, wherein a degree of crosslinking is
higher in a surrounding portion of an inner wall surface of the
contact hole.
52. The method of claim 51, further comprising, after the heat
treatment step, a light irradiating step of irradiating the
surrounding portion of the contact hole with light at a shorter
wavelength.
53. A method of fabricating a reflector, the method comprising: a
step of forming a photosensitive resin layer on a substrate; an
exposing step of irradiating the photosensitive resin layer with
light via a first photomask having light shielding portions
patterned into specified configurations; a developing step of
developing the photosensitive resin layer irradiated with the light
to form a plurality of resist columns; an irradiating step of
irradiating respective specified regions of the plurality of resist
columns with light at a shorter wavelength via a second photomask
having openings patterned into specified configurations; a heat
treatment step of performing a heat treatment with respect to the
resist columns and thereby thermally deforming respective edge
portions of the plurality of resist columns to form projecting and
depressed structures each having an asymmetrical cross-sectional
configuration; a post-baking step of performing a heat treatment
with respect to the photosensitive resin layer; and a
pixel-electrode forming step of forming a pixel electrode with a
light reflecting property on the photosensitive resin layer.
54. The method of claim 53, further comprising, after the heat
treatment step, a light irradiating step of irradiating the
plurality of projecting and depressed structures with light at a
shorter wavelength.
55. A method of fabricating a reflective display device comprising
a light modulating layer between a pair of substrates, the method
comprising the steps of: forming a polymer resin layer on one of
the pair of substrates; pressing a platen provided with a
projecting and depressed pattern composed of a group of minute
projecting and depressed patterns and a hole against the polymer
resin layer; curing the polymer resin layer and mold releasing the
platen from the polymer resin layer; forming a metal film on the
polymer resin layer; and thereby shaping the polymer resin layer
into the projecting and depressed pattern to integrally mold minute
projecting and depressed portions in a surface of the polymer resin
layer with a support portion for supporting the other of the pair
of substrates.
56. The method of claim 55, wherein, if the polymer resin layer
formed on one of the substrates is a photosensitive resin layer, a
platen with transparency is used as the platen and the polymer
resin layer is cured by irradiating the photosensitive resin layer
with light via the platen.
57. The method of claim 55, wherein, if the polymer resin layer
formed on one of the substrates is a thermoplastic resin layer, the
platen is pressed against the thermoplastic resin layer with the
application of heat.
58. The method of claim 55, wherein a nonlinear element is provided
on one of the substrates and a platen having a projecting portion
for forming a contact hole at a position corresponding to an output
terminal portion of the nonlinear element is used as the
platen.
59. The method of claim 58, wherein a bottom portion of the contact
hole in the polymer resin layer is etched immediately after the
platen is mold released from the polymer resin layer till the
output terminal portion of the nonlinear element is exposed.
60. A method of fabricating a reflective display device comprising
a light modulating layer between a pair of substrates, the method
comprising the steps of: pressing a platen provided with a
projecting and depressed pattern composed of a group of minute
projecting and depressed patterns and a hole against one of the
pair of substrates; curing one of the substrates and mold releasing
the platen from one of the substrates; forming a metal film on one
of the substrates; and thereby shaping one of the substrates into
the projecting and depressed pattern to integrally mold minute
projecting and depressed portions in a surface of one of the
substrates with a support portion for supporting the other of the
substrates.
61. The method of claim 60, wherein, if one of the substrates is
made of a photosensitive resin, a platen with transparency is used
as the platen and one of the substrates is cured by irradiating one
of the substrates with light via the platen.
62. The method of claim 60, wherein, if one of the substrates is
made of a thermoplastic resin, the platen is pressed against one of
the substrates with the application of heat.
63. A method of fabricating a reflective display device comprising
a light modulating layer between a pair of substrates, the method
comprising the steps of: forming a polymer resin layer over a mold
provided with a projecting and depressed pattern composed of a
group of minute projecting and depressed patterns; bonding the mold
to one of the pair of the substrates such that the polymer resin
layer faces the substrate and releasing the mold from the polymer
resin layer to laminate the polymer resin layer on one of the
substrates; forming a metal film over the polymer resin layer; and
thereby shaping the polymer resin layer into the projecting and
depressed pattern to form minute projecting and depressed portions
in a surface of the polymer resin layer.
64. The method of claim 63, wherein a base film made of a polymer
resin is used as the mold.
65. The method of claim 63, wherein a mold having, at a specified
position, a hole for forming a support portion for supporting the
other of the pair of substrates is used as the mold.
66. A method of fabricating a reflector, the method comprising the
steps of: coating a photosensitive resin layer on a substrate;
exposing the photosensitive resin layer to light via a photomask;
developing the exposed photosensitive resin layer to form
projecting and depressed portions in the photosensitive resin
layer; and forming a reflective film over the projecting and
depressed surface, wherein the photomask has a light shielding
pattern composed of groups of minute half-tone dots smaller than a
resolution limit of an exposing device used in the exposing step
and a resolution limit of the photosensitive resin layer and a mean
light transmittance of the light shielding pattern is nonuniform
over a surface of the photomask.
67. The method of claim 66, wherein a nonlinear element is provided
on the substrate and a mask having a light shielding portion or a
light non-shielding portion provided at a portion corresponding to
an output portion of the non-linear element is used as the
photomask.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a reflector for use in a
reflective liquid crystal display device which displays an image by
reflecting external light when used in OA equipment, a personal
computer, a mobile phone, a mobile data terminal, or the like, to a
method of fabricating the same, to the reflective display device,
and a method of fabricating the same.
BACKGROUND OF THE INVENTION
[0002] As AV equipment and data equipment has been scaled down to
have a reduced thickness in recent years, there has been growing
demand for a liquid crystal display device as a light-receiving
display device. For the data equipment, a liquid crystal display
device that can be mounted on a notebook personal computer with
higher portability has been in increasing demand with the advent of
a multimedia society. In the field of mobile data terminals, a
liquid crystal display device which is lower in profile, weight,
and power consumption has been required.
[0003] Such liquid crystal display devices are subdivided into a
transmissive type having a backlight disposed on the rear surface
of a liquid crystal panel and a reflective type having a reflector
disposed therein and using external light as illuminating light.
There is also a semitransmissive type comprising a half mirror,
which uses external light reflected by a reflector as illuminating
light in a bright environment, while using a backlight in
combination in a dark environment. Since a reflective liquid
crystal display device and a semitransmissive liquid crystal
display device use a mode of displaying an image by reflecting
external light and normally do not need a light source such as a
backlight unit, they can be reduced particularly in power
consumption, profile, and weight compared with a conventional
transmissive liquid crystal display device. In a typical reflective
liquid crystal display device, a scattering reflector made of
aluminum or silver is disposed behind a liquid crystal panel. In a
monochrome display device used in a wrist watch, a scattering
reflector with a sheet polarizer is bonded to the outside of glass.
As a display mode of the reflective liquid crystal display device,
a TN (Twisted Nematic) mode, a STN (Super Twisted Nematic) mode, a
GH (Guest-Host) mode involving the use of a dichroic dye have been
used predominantly.
[0004] To achieve brighter and more satisfactory display in the
reflective liquid crystal display device, it is required to reflect
and scatter incident light in the normal viewing angle direction
which is perpendicular to a display screen and thereby increase the
intensity of the light. In addition to reflecting and scattering,
in the normal viewing angle direction, external light incident at a
specified angle from a specified direction, it is also desirable to
similarly reflect and scatter, in the normal viewing angle
direction, external light incident at arbitrary angles from
different directions. As a result, it becomes necessary to
fabricate a reflector having optimum reflecting properties which
allow external light incident from an arbitrary direction to be
used efficiently as display light. The optimum reflecting
properties used here indicate the properties of the reflector with
which incident light is reflected in a wide range and with a high
reflectance.
[0005] In the case of using a conventional reflector such as one
having a specular metal film formed on a substrate, incident light
is reflected only in the direction of regular reflection so that
the reflectance is low in a direction other than the regular
reflection direction. This causes the problem that a screen
displayed is extremely dark in a direction of visual recognition of
a viewer, such as the normal viewing angle direction, which
significantly degrades the display quality.
[0006] To solve the problem, a reflective liquid crystal display
panel comprising a scattering reflector having a rough
configuration is disclosed in, e.g., Japanese Unexamined Patent
Publication No. HEI 4-243226. The scattering reflector disclosed in
the publication is fabricated in accordance with the following
method such that a reflecting surface thereof has a uniform
configuration and is formed with high reproducibility. That is, as
shown in FIG. 33A, a resist film 202 is coated on a glass substrate
201. Then, as shown in FIG. 33B, the resist film 202 is covered
with a photomask 203 patterned into a specified configuration and
exposed to light. Subsequently, the exposed resist film 202 is
developed with a developing solution, whereby numerous projecting
portions 204 as shown in FIG. 33C are formed. Since the projecting
portions 204 have generally right-angled edges in cross section,
the edges of the projecting portions 204 should be rounded off. By
performing a heat treatment, therefore, a configuration as shown in
FIG. 33D is obtained. Further, Ag is vapor-deposited over the glass
substrate 201 formed with the projecting portions 204 to form a
metal reflective film 206 (FIG. 33E). By the foregoing process, the
scattering reflector has been fabricated.
[0007] To solve the foregoing problem, a pixel electrode having
reflecting properties with which reflection of incident light in
the region of regular reflection is reduced is also disclosed in,
e.g., Japanese Unexamined Patent Publication No. HEI 6-27481.
According to the publication, a reflector 210 comprises: a
substrate 211 formed with a plurality of projecting portions 212a
and 212b; a polymer resin film 214 provided over the substrate 211;
and a pixel electrode 215 disposed on the polymer resin film 214,
as shown in FIG. 34. The surface of the pixel electrode 215 has a
continuously undulating configuration.
[0008] To form the reflector 210, the following method has been
used (FIGS. 35). First, as shown in FIG. 35A, a resist film 212
made of a photosensitive resin is coated on the substrate 211 by
spin coating and pre-baked at a specified processing temperature.
Subsequently, the resist film 212 is exposed to light by using a
photomask 213 positioned thereabove, as shown in FIG. 35B. Then,
development is performed by using a developing solution to form the
projecting portions 212a and 212b having different heights on the
substrate 211, as shown in FIG. 35C. Subsequently, a heat treatment
is performed by heating the projecting portions 212a and 212b for
one hour at a specified temperature, as shown in FIG. 35D. The heat
treatment rounds off the respective angular edge portions of the
projecting portions 212a and 212b to form projecting portions 212a
and 212b with rounded edge portions. Then, as shown in FIG. 35E, a
polymer resin is spin-coated on the substrate 211 after the heat
treatment to form the polymer resin film 214. Finally, the pixel
electrode 215 is formed by sputtering on the polymer resin film 214
(FIG. 35F).
[0009] On the other hand, Japanese Unexamined Patent Publication
No. HEI 9-292304 discloses that, if the angle formed between an
extremely small surface at the surface of a pixel electrode having
a projecting and depressed configuration and a substrate surface is
defined as a slope angle, the reflecting properties of a reflector,
i.e., the reflectance and brightness thereof in a direction normal
to a substrate, are determined by the slope angle distribution.
[0010] However, since the conventional reflector has formed the
projecting and depressed configuration by forming the projecting
portions by using the photoresist and melting and rounding the
projecting portions with the application of heat, the configuration
is determined by the roundness of the projecting portions shaped
naturally by the heat-melting process so that it is difficult to
precisely control the configuration. It is therefore evident that
the slope angle distribution of the projecting portions has not
been produced actually such that specified reflecting properties
are provided. As a result, the light reflected by the conventional
reflector in the regular reflection direction is increased so that
brightness in the viewing angle direction is insufficient and a
satisfactory paper-white property is not provided in a wide range.
The conventional reflector also has the problem of seemingly
metallic display because of its large dependence on an exit angle.
Moreover, since the projecting portions are formed by
photolithography, an extra step is added to a normal fabrication
process, which causes the problem of a larger number of process
steps.
[0011] To provide a uniform cell gap, a liquid crystal display
device comprises spacers each having a given size or height between
a pair of substrates. Specifically, it is common to use not only
ball-shaped (spherical) spacers in the cell of a display element
but also ball-shaped or fiber-like spacers which are blended in a
seal resin coated into a frame-like configuration on the periphery
of the substrate. If the spacers are scattered on the substrate of
the conventional reflective liquid crystal display device
comprising the scattering reflector, however, it is difficult to
provide a uniform cell gap with accuracy in a specified range since
the scattering reflector has a projecting and depressed
configuration.
[0012] If a switching element 216 such as a thin-film transistor
(hereinafter referred to as TFT) or a thin-film diode (hereinafter
referred to as TFD) is provided on the conventional scattering
reflector, it is required to provide an electric connection between
the pixel electrode 215 and the switching element 216, so that a
contact hole 217 is formed (FIG. 36E). In accordance with the
following conventional method, however, the contact hole 217 may be
clogged or have an aperture area smaller than required and intended
during the formation thereof That is, as shown in FIGS. 36A to 36C,
the contact hole 217 is formed simultaneously with the formation of
the projecting portions 212a and 212b. However, there are cases
where the contact hole 217 has a smaller opening or is clogged due
to thermal deformation during a heat treatment performed in the
process of forming the projecting portions 212a and 212b, as shown
in FIG. 36D. This increases contact resistance between the pixel
electrode 215 and the switching element 216 and causes a serious
problem such as the degradation of the display quality of the
reflective liquid crystal display device comprising the
reflector.
[0013] The present invention has been achieved in view of the
foregoing problems and it is therefore a first object of the
present invention to provide a reflector having superior reflecting
properties such as a contrast property and a paper-white property,
a fabrication method therefor, and a reflective liquid crystal
display device comprising the reflector.
[0014] A second object of the present invention is to provide a
reflector having superior reflecting properties, a fabrication
method therefor, and a reflective liquid crystal display device
comprising the reflector wherein a uniform cell gap is
provided.
[0015] A third object of the present invention is to provide a
method of fabricating a reflector wherein a contact hole for
providing an electrical connection between a pixel electrode and a
switching element has a sufficiently large opening irrespective of
the provision of the reflector.
SUMMARY OF THE INVENTION
[0016] The present invention may be broadly subdivided into first
and second groups based on closely related aspects thereof. In the
first group of the invention, a description will be given to a
reflector comprising a plurality of projecting and depressed
structures each having projecting and depressed portions and
serving as a basic unit. In the second group of the invention, a
description will be given to a reflector having projecting and
depressed portions covered with a metal film and a support portion
serving as a spacer, which are formed integrally.
First Group of the Invention
[0017] To solve the foregoing problems, a reflector in the first
group of the present invention comprises: a substrate provided with
a plurality of projecting and depressed structures each having a
plurality of projecting and depressed portions and serving as a
basic unit: and a light reflective thin film provided over the
projecting and depressed structures.
[0018] The light reflecting thin film is provided over the
projecting and depressed structures so that the surface
configuration of the light reflecting thin films is conformal to
the configuration of the projecting and depressed structures. Since
each of the projecting and depressed structures has the plurality
of projecting and depressed portions, the plan and cross-sectional
configurations of the projecting and depressed structure can be
controlled easily by varying, e.g., the distribution of the
projecting and depressed portions. This allows light incident from
an arbitrary direction to be reflected and scattered in the forward
direction of the reflector or the like, not in the regular
reflection direction.
[0019] In the foregoing arrangement, the projecting and depressed
structures provided on the substrate may be arranged randomly and
dispersively in an arbitrary direction.
[0020] In the arrangement, the projecting and depressed structures
as the basic units are not observed repetitively with a given
period so that light interference is suppressed and a phenomenon
of, e.g., colored reflected light is suppressed.
[0021] In the foregoing arrangement, the projecting portions of the
projecting and depressed structures may have top portions at
different heights and the depressed portions of the projecting and
depressed structures have bottom portions at different depths.
[0022] This allows the light reflecting thin film provided over the
projecting and depressed structures to be formed with an inclined
surface. By increasing or reducing a level difference between the
adjacent top portions or the adjacent bottom portions, the angle
formed between the inclined surface and the substrate surface
(hereinafter referred to as a slope angle) can be adjusted larger
or smaller. As a result, the surface of the light reflecting thin
film is capable of scattering and reflecting light in directions
within an anisotropic range and light can be reflected brightly in
directions in a given angular range, not in the regular reflection
direction. If three or more top portions are provided in the
projecting and depressed structure, the top portions have different
heights so that the slope angle distribution is controlled and an
asymmetric cross-sectional configuration is provided. If the three
or more top portions are arranged such that the heights thereof
become progressively higher and that different level differences
are provided between the adjacent top portions, a distribution of
slope angles is produced. By varying the level difference, a
desired slope angle distribution is obtained. If the three or more
top portions are arranged discontinuously such that the heights
thereof become progressively higher, reach a peak somewhere, and
become progressively lower, the projecting and depressed structure
has an asymmetric cross-sectional configuration.
[0023] In the foregoing arrangement, the projecting and depressed
structures may be groups of columnar portions each composed of a
plurality of minute columnar portions having different heights, the
columnar portions being separate from each other or at least
partially connected to each other.
[0024] In the arrangement, the plurality of minute columnar
portions are formed to have different heights arranged in a
specified distribution such that the slope angle distribution of
the light reflecting thin film provided over the groups of columnar
portions is controlled precisely. This provides a reflector having
reflecting properties including a superior paper-white
property.
[0025] In the foregoing arrangement, the projecting and depressed
structures are staircase structures each having a plurality of
stepped portions.
[0026] In the arrangement, each of the projecting and depressed
structures is formed as the staircase structure having the stepped
portions at different heights such that the slope angle
distribution is controlled precisely. This provides a reflector
having reflecting properties including a superior paper-white
property.
[0027] In the foregoing arrangement, a height distribution of each
of the projecting and depressed structures has a peak at a position
deviated in a specified direction from a center portion of the
structure and tends to decrease with distance from the peak toward
a periphery thereof and the light reflecting thin film covering the
projecting and depressed structures has a curved surface having a
curvature larger in the specified direction than in a direction
opposite to the specified direction.
[0028] In the foregoing arrangement, at least one polymer resin
layer is provided between the projecting and depressed structures
and the light reflecting thin film.
[0029] In the arrangement, even if the clearance between the
adjacent projecting and depressed structures is large, a flat
portion parallel to the substrate surface can be formed to have a
gently curved configuration. Consequently, a flat region parallel
to the substrate is not formed so that light reflected in the
regular reflection direction is reduced. If each of the projecting
and depressed structures is a group of columnar portions and a deep
valley portion is formed between the adjacent columnar portions,
the polymer resin layer is buried in the valley portion so that a
gently curved configuration with a continuously changing height
distribution is provided. If each of the projecting and depressed
structures is a staircase structure, a gently curved configuration
with a continuously changing height distribution can be provided
such that the stepped configuration is not reflected in the surface
configuration of the light reflecting thin film.
[0030] In the foregoing arrangement, the reflector may be a grating
reflector for reflecting and diffracting light, the grating
reflector having the plurality of projecting and depressed
structures provided periodically on the substrate.
[0031] In the foregoing arrangement, each of the projecting and
depressed structures in plan view has a size in the range of 1
.mu.m to 100 .mu.m.
[0032] To solve the foregoing problems, a reflector according to
the present invention comprises: a substrate provided with a
nonlinear element; a photosensitive resin layer provided on the
substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein a light reflecting film is
provided on a bottom portion of the contact hole.
[0033] In the arrangement, the light reflecting thin film is
provided at the position at which the contact hole is to be formed
so that light is reflected by the vicinity of the light reflecting
film during exposure. This achieves a higher exposure dose at the
position at which the contact hole is to be formed than in the
other exposed region. As a result, a contact hole having a
generally trapezoidal cross section is formed by development so
that, even if a thermal deformation is caused by, e.g., a heat
treatment step, the bottom portion of the contact hole is prevented
from being clogged. This implements a reflector in which an
increase in contact resistance and faulty operation are
suppressed.
[0034] In the foregoing arrangement, a degree of crosslinking in
the photosensitive resin layer is higher in a surrounding portion
of an inner wall surface of the contact hole than in the other
portion thereof.
[0035] In the arrangement, irradiation of a surrounding portion of
the inner wall surface of the contact hole with, e.g., UV light at
a shorter wavelength or an electron beam at a shorter wavelength
advances cross-linking in the irradiated region, so that it is
cured. As a result, a thermal deformation resulting from a heat
treatment can be prevented more positively.
[0036] To solve the foregoing problems, a reflector according to
the present invention comprises: a substrate provided with a
nonlinear element; a photosensitive resin layer provided on the
substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein a thin film having a surface
energy higher than that of the photosensitive resin layer is
provided on a bottom portion of the contact hole.
[0037] In the arrangement, the frame-shaped thin film having the
surface energy higher than that of the photosensitive resin layer
is provided at the position at which the contact hole is to be
formed. Even if a thermal deformation is caused by, e.g., a heat
treatment step, the photosensitive resin layer is prevented from
flowing and clogging the bottom portion of the contact hole. This
implements a reflector in which an increase in contact resistance
and faulty operation are suppressed.
[0038] To solve the foregoing problems, a reflector according to
the present invention comprises: a substrate provided with a
nonlinear element, a photosensitive resin layer provided on the
substrate, the photosensitive resin layer having projecting and
depressed structures in specified regions; and a pixel electrode
with a light reflecting property provided on the photosensitive
resin layer, the pixel electrode being electrically connected to
the nonlinear element via a contact hole formed in the
photosensitive resin layer, wherein the contact hole is provided
such that a degree of crosslinking is higher in a surrounding
portion of an inner wall surface of the contact hole than in the
other portion thereof.
[0039] In the arrangement, irradiation of surrounding portion of
the inner wall surface of the contact hole with, e.g., UV light at
a shorter wavelength or an electron beam at a shorter wavelength
advances cross-linking in the irradiated region. As a result, a
thermal deformation resulting from a heat treatment can be
prevented more positively.
[0040] To solve the foregoing problems, a reflective display device
according to the present invention comprises: a counter substrate
with transparency; a reflector disposed in opposing relation to the
counter substrate, the reflector including a substrate provided
with a plurality of projecting and depressed structures each having
a plurality of projecting and depressed portions and serving as a
basic unit and a light reflecting thin film provided over the
projecting and depressed structures; and a liquid crystal layer
held between the counter substrate and the reflector.
[0041] The arrangement provides a reflective liquid crystal display
device comprising a reflector having a superior contrast property
and a superior paper-white property.
[0042] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention comprises: a step of
forming a photosensitive resin layer on a substrate; an exposing
step of irradiating the photosensitive resin layer with light via a
photomask having light shielding portions patterned into specified
configurations; a developing step of developing the photosensitive
resin layer irradiated with the light to form a plurality of resist
columns; a heat treatment step of performing a heat treatment with
respect to the substrate formed with the plurality of resist
columns and thereby forming groups of columnar portions each
composed of a plurality of minute columnar portions having
different heights, the columnar portions being separate from each
other or at least partially connected to each other; and a step of
forming a light reflecting thin film over the groups of columnar
portions, wherein, as the photomask, a mask formed with a plurality
of unit components each composed of a plurality of minute shielding
portions having different heights is used.
[0043] In accordance with the method, the photosensitive resin
layer formed on the substrate is initially exposed and then
developed to form the resist columns having heights in a uniform
distribution. The resist columns are then thermally deformed by
performing the heat treatment with respect to the substrate formed
with the resist columns, thereby forming the plurality of minute
columns having different heights. The columnar portions have
different heights because the resist columns have different plan
configurations prior to the heat treatment step in response to the
configurations and sizes of the light shielding portions. If a
photosensitive resin material in which the area occupied by the
plan configuration of the resist column and the height of the
resist column thermally deformed (i.e., the height of the columnar
portion) satisfy a linearly functional relationship is used and the
processing temperature is set within a specified range, the resist
column occupying a larger area can form a higher columnar portion.
By varying the area, therefore, the columnar portion can be formed
to have a controlled height so that a reflector is produced in
which the light reflecting thin film provided over the group of
columnar portions has a precisely controlled slope angle
distribution.
[0044] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention comprises: a step of
forming a photosensitive resin layer on a substrate; an exposing
step of irradiating the photosensitive resin layer with light via a
photomask having light shielding portions each having a
progressively varying light shielding rate; a developing step of
developing the photosensitive resin layer irradiated with the light
to form a plurality of staircase resist columns; a heat treatment
step of performing a heat treatment with respect to the substrate
formed with the plurality of staircase resist columns to round off
respective angular edges of the resist columns and thereby forming
staircase structures each having a plurality of stepped portions;
and a step of forming a light reflecting thin film over the
staircase structures.
[0045] In accordance with the method, the photosensitive resin
layer is irradiated with light based on the light shielding rates
of the light shielding portions of the photomask. Accordingly,
optical decomposition and cross-linking proceed to different
degrees in different regions so that resist columns each having a
staircase cross-sectional configuration are formed after the
development step. By further performing the heat treatment step,
the staircase structures each having the plurality of stepped
portions can be formed. By thus varying the light shielding rate in
the photomask, the staircase structures having the stepped portions
at controlled heights are formed so that the light reflecting thin
film provided over the staircase structures has a precisely
controlled slope angle distribution.
[0046] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention comprises: a step of
forming a photosensitive resin layer on a substrate; a step of
preparing a plurality of photomasks each having light shielding
portions patterned into specified configurations, each of the light
shielding portions of the different photomasks covering a light
shielding range which is different in size from one photomask to
another, each of the light shielding portions of any of the
photomasks covering a larger shielding range and each of the light
shielding portions of the photomask covering a next smaller
shielding range having a relationship therebetween such that the
next smaller light shielding range is included in the larger light
shielding range; an exposing step of irradiating the photosensitive
resin layer with light by successively using the photomasks in the
order of decreasing size of the light shielding range of the
shielding portion; a developing step of developing the
photosensitive resin layer irradiated with the light to form a
plurality of staircase resist columns; a heat treatment step of
performing a heat treatment with respect to the substrate formed
with the staircase resist columns to round off respective angular
edges of the resist columns and thereby forming staircase
structures each having a plurality of stepped portions; and forming
a light reflecting thin film over the staircase structures.
[0047] In accordance with the method, the cumulative exposure dose
is controlled for each of the regions by performing at least two or
more exposing steps and using the photomask covering a light
shielding range which decreases as the exposing steps are performed
one after another. As a result, optical decomposition and
cross-linking proceed to different degrees from one region to
another so that the staircase resist columns are formed by the
developing step. This allows formation of the staircase structures
each having the plurality of stepped portions.
[0048] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention is a method of
fabricating a reflector having a substrate provided with a
nonlinear element, a photosensitive resin layer provided on the
substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a light-reflecting-film forming step of forming, at a
position at which the contact hole is to be formed, a light
reflecting film patterned into a specified configuration; a coating
step of coating a photosensitive resin material over the substrate
and the light reflecting film; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a heat treatment step of performing a
heat treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a post-baking step of
performing a heat treatment with respect to the photosensitive
resin layer and thereby curing the photosensitive resin layer; and
a pixel-electrode forming step of forming the pixel electrode with
the light reflecting property on the photosensitive resin
layer.
[0049] In accordance with the method, the light reflecting film is
formed preliminarily at the position at which the contact hole is
to be formed so that light is reflected by the vicinity of the
light reflecting film when light is radiated in the exposing step.
Accordingly, the exposure dose in the vicinity of the light
reflecting film is higher than in the other region. In addition,
the developing step allows formation of the contact hole having a
generally trapezoidal cross section. The configuration and size of
the opening portion of the contact hole nearly correspond to the
pattern configuration of the photomask and become larger with
approach toward the bottom portion thereof.
[0050] Subsequently, the heat treatment is performed with respect
to the plurality of resist columns each formed in the specified
region to deform the respective edge portions thereof. Although the
opening portion and inner wall surface of the contact hole are
thermally deformed, there can be formed a contact hole having an
unclogged bottom portion because of the trapezoidal cross-sectional
configuration. This allows formation of a reflector in which an
increase in contact resistance and faulty operation are
suppressed.
[0051] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention is a method of
fabricating a reflector having a substrate provided with a
nonlinear element, a photosensitive resin layer provided on the
substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a thin-film forming step of forming, at a position at
which the contact hole is to be formed, a frame-shaped thin film
having a surface energy higher than that of the photosensitive
resin layer; a coating step of coating a photosensitive resin
material over the substrate and the thin film; an exposing step of
irradiating the photosensitive resin material with light via a
photomask having light shielding portions patterned into specified
configurations; a developing step of developing the photosensitive
resin material irradiated with the light to form the photosensitive
resin layer comprising the contact hole and a plurality of resist
columns formed in specified regions; a heat treatment step of
performing a heat treatment with respect to the photosensitive
resin layer and thereby thermally deforming and rounding off
respective edge portions of the plurality of resist columns; a
post-baking step of performing a heat treatment with respect to the
photosensitive resin layer and thereby curing the photosensitive
resin layer; and a pixel-electrode forming step of forming the
pixel electrode with the light reflecting property on the
photosensitive resin layer.
[0052] In accordance with the method, the thin film having the
surface energy higher than that of the photosensitive resin layer
has been formed preliminarily at the position at which the contact
hole is to be formed. Even if the opening portion and inner wall
surface of the contact hole are thermally deformed, they are
prevented from flowing as a result of the thermal deformation. This
prevents the bottom portion of the contact hole from being clogged
and allows formation of a reflector in which an increase in contact
resistance and faulty operation are suppressed. The thin film has
been formed into a frame-shaped configuration to provide an
electric connection between the switching element and the pixel
electrode.
[0053] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention is a method of
fabricating a reflector having a substrate provided with a
nonlinear element, a photosensitive resin layer provided on the
substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a thin-film forming step of forming, on a drain
electrode of the nonlinear element, a thin film having a surface
energy higher than that of the photosensitive resin layer; a
coating step of coating a photosensitive resin material over the
substrate and the thin film; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a heat treatment step of performing a
heat treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a removing step of
removing the thin film by ashing; a post-baking step of performing
a heat treatment with respect to the photosensitive resin layer and
thereby curing the photosensitive resin layer; and a
pixel-electrode forming step of forming the pixel electrode with
the light reflecting property on the photosensitive resin
layer.
[0054] In accordance with the method, even if the thin film which
is not frame-shaped is formed, an electric connection is provided
between the nonlinear element and the pixel electrode and the
bottom portion of the contact hole is prevented from being clogged
if the thin film is removed by ashing. This allows formation of a
reflector in which an increase in contact resistance and faulty
operation are suppressed.
[0055] To solve the foregoing problems, a method of fabricating a
reflector according to the present invention is a method of
fabricating a reflector having a substrate provided with a
nonlinear element, a photosensitive resin layer provided on the
substrate and having projecting and depressed structures in
specified regions, and a pixel electrode with a light reflecting
property provided on the photosensitive resin layer, the pixel
electrode being electrically connected to the nonlinear element via
a contact hole formed in the photosensitive resin layer, the method
comprising: a step of forming the nonlinear element on the
substrate; a coating step of coating a photosensitive resin
material on the substrate; an exposing step of irradiating the
photosensitive resin material with light via a photomask having
light shielding portions patterned into specified configurations; a
developing step of developing the photosensitive resin material
irradiated with the light to form the photosensitive resin layer
comprising the contact hole and a plurality of resist columns
formed in specified regions; a light irradiating step of
irradiating a surrounding portion of the contact hole with light at
a shorter wavelength; a heat treatment step of performing a heat
treatment with respect to the photosensitive resin layer and
thereby thermally deforming and rounding off respective edge
portions of the plurality of resist columns; a post-baking step of
performing a heat treatment with respect to the photosensitive
resin layer; and a pixel-electrode forming step of forming the
pixel electrode with the light reflecting property on the
photosensitive resin layer, wherein a degree of crosslinking is
higher in a surrounding portion of an inner wall surface of the
contact hole.
[0056] In accordance with the method, irradiation of a surrounding
portion of the contact hole that has been formed by the exposing
and developing steps with light at a shorter wavelength advances
cross-linking in the opening portion and inner wall surface of the
contact hole, so that curing proceeds to a higher degree than in
the other portion. Even if the heat treatment step is performed,
therefore, the surrounding portion of the contact hole is inhibited
from being thermally deformed. This prevents the bottom portion of
the contact hole from being clogged and allows formation of a
reflector in which an increase in contact resistance and faulty
operation are suppressed.
[0057] The foregoing arrangement further comprises, after the heat
treatment step, a light irradiating step of irradiating the
surrounding portion of the contact hole with light at a shorter
wavelength.
[0058] By thus performing again the light irradiating step after
the heat treatment step, thermal deformation during the post-baking
step is suppressed and an increase in contact resistance and faulty
operation are further suppressed.
[0059] To solve the foregoing problems, a method of fabricating a
reflector comprises: a step of forming a photosensitive resin layer
on a substrate; an exposing step of irradiating the photosensitive
resin layer with light via a first photomask having light shielding
portions patterned into specified configurations; a developing step
of developing the photosensitive resin layer irradiated with the
light to form a plurality of resist columns; an irradiating step of
irradiating respective specified regions of the plurality of resist
columns with light at a shorter wavelength via a second photomask
having openings patterned into specified configurations; a heat
treatment step of performing a heat treatment with respect to the
resist columns and thereby thermally deforming respective edge
portions of the plurality of resist columns to form projecting and
depressed structures each having an asymmetrical cross-sectional
configuration; a post-baking step of performing a heat treatment
with respect to the photosensitive resin layer; and a
pixel-electrode forming step of forming a pixel electrode with a
light reflecting property on the photosensitive resin layer.
[0060] In accordance with the method, irradiation of the respective
specified regions of the resist columns that have been formed by
performing the exposing and developing steps with the light at a
shorter wavelength advances cross-linking in the irradiated
regions, so that curing proceeds to a higher degree than in the
other portion. As a result, unirradiated regions undergo
significant thermal deformation, while the cured portions undergo a
lower degree of thermal deformation. This allows formation of the
projecting and depressed structures each having an asymmetric
cross-sectional configuration and fabrication of a reflector
capable of scattering and reflecting light in directions within an
anisotropic range. If conditions for irradiation in the light
irradiating step are determined properly, the projecting and
depressed structures each having the asymmetric cross-sectional
configuration and a desired slope angle can be formed with ease and
controllability.
[0061] The foregoing arrangement further comprises, after the heat
treatment step, a light irradiating step of irradiating the
plurality of projecting and depressed structures with light at a
shorter wavelength.
[0062] By thus performing again the light irradiating step after
the heat treatment step, the projecting and depressed structures
each having an asymmetric cross-sectional configuration are
prevented from being thermally deformed in the post-baking step and
there can be fabricated a reflector having desired reflecting
properties.
Second Group of the Invention
[0063] To solve the foregoing problems, a reflective display device
according to the present invention is a reflective display device
having a liquid crystal layer provided between a pair of
substrates, wherein one of the pair of substrates is provided with
projecting and depressed portions covered with a metal film and
with a support portion for supporting the other of the pair of
substrates, the projecting and depressed portions and the support
portion being molded integrally.
[0064] In the case where one of the substrates is provided with the
projecting and depressed portions, as in the foregoing arrangement,
if spacers are scattered to provide a specified cell gap between
the pair of substrates, the cell gap therebetween becomes
nonuniform over a surface of the substrate so that uneven display
is recognized visually. However, if the projecting and depressed
portions and the support portion for supporting the other of the
substrates are formed integrally, there is no need to scatter the
spacers and a uniform cell gap is provided. This reduces the
occurrence of uneven display and provides a high display
quality.
[0065] In the foregoing arrangement, the projecting and depressed
portions may be pyramidal or conical.
[0066] In the foregoing arrangement, if an angle formed between an
inclined surface of the pyramidal projecting and depressed portions
and a horizontal surface or an angle formed between a generating
line of the conical projecting and depressed portions and a
horizontal surface is assumed to be a slope angle, the projecting
and depressed portions may be dispersively arranged at different
slope angles and the slope angles are in the range of 4.degree. to
16.degree..
[0067] The foregoing arrangement may further comprises a polymer
resin layer molded integrally with the projecting and depressed
portions and with the support portion for supporting the other of
the substrates, the polymer resin layer being provided on one of
the substrates.
[0068] In the foregoing arrangement, a plurality of nonlinear
elements may be provided on one of the substrates and a contact
hole for providing an electric connection between the nonlinear
elements and the metal film is provided in the polymer resin
layer.
[0069] In the foregoing arrangement, a resin film molded integrally
with the projecting and depressed portions and with the support
portion for supporting the other of the substrates may be laminated
on one of the substrates.
[0070] In the foregoing arrangement, the resin film may be made of
a photosensitive resin.
[0071] In the foregoing arrangement, one of the substrates may be a
plastic substrate molded with the projecting and depressed portions
and with the support portion for supporting the other of the
substrates.
[0072] To solve the foregoing problems, a reflective display device
according to the present invention is a reflective display device
having a photosensitive resin layer provided on a substrate and a
metal film provided on the photosensitive resin layer, wherein the
photosensitive resin layer is formed by exposing, to light, a
photosensitive resin coated on the substrate via a photomask and
developing the exposed photosensitive resin, the photosensitive
resin layer having a projecting and depressed surface formed by
exposing the photosensitive resin to the light via the photomask
having a light shielding pattern composed of groups of minute
halftone dots smaller than a resolution limit of an exposing device
used for the exposure and a resolution limit of the photosensitive
resin, a mean light transmittance of the light shielding pattern
being nonuniform over a surface of the photomask.
[0073] In the foregoing arrangements, the projecting and depressed
portions are formed in the photosensitive resin layer by using the
photomask having the light shielding pattern capable of half-tone
representation which cannot be implemented with a conventional
chromium mask or the like and finely controlling the configuration
of the projecting and depressed portions. This permits light
incident from an arbitrary direction to be scattered and reflected
in the forward direction of the reflective display device or the
like, not in the regular reflection direction, and enables bright
image display with excellent whiteness.
[0074] To solve the foregoing problems, a method of fabricating a
reflective display device according to the present invention is a
method of fabricating a reflective display device comprising a
light modulating layer between a pair of substrates, the method
comprising the steps of forming a polymer resin layer on one of the
pair of substrates; pressing a platen provided with a projecting
and depressed pattern composed of a group of minute projecting and
depressed patterns and a hole against the polymer resin layer;
curing the polymer resin layer and mold releasing the platen from
the polymer resin layer; forming a metal film on the polymer resin
layer; and thereby shaping the polymer resin layer into the
projecting and depressed pattern to integrally mold minute
projecting and depressed portions in a surface of the polymer resin
layer with a support portion for supporting the other of the pair
of substrates.
[0075] In the conventional reflector, the projecting and depressed
configurations have been formed by forming the projecting portions
by using a photoresist, heat-melting the projecting portions, and
thereby rounding off the respective angular edges thereof.
Therefore, it has been difficult to control the curved
configurations of the projecting and depressed portions. However,
the foregoing method allows formation of the projecting and
depressed portions having precisely controlled curved
configurations in the polymer resin layer because it performs
shaping by using the platen provided with the projecting and
depressed pattern composed of the group of minute projecting and
depressed patterns and the hole. This reduces reflection in the
regular reflection direction and allows fabrication of a reflective
display device with excellent brightness and whiteness. Moreover,
since the projecting and depressed portions and the support portion
for supporting the counter substrate are formed integrally, there
is no need to scatter spacers and a uniform cell gap is provided.
This reduces the occurrence of uneven display and provides a
reflective display device with a high display quality.
[0076] In the foregoing method, if the polymer resin layer formed
on one of the substrates is a photosensitive resin layer, a platen
with transparency is used as the platen and the polymer resin layer
may be cured by irradiating the photosensitive resin layer with
light via the platen.
[0077] In the foregoing method, if the polymer resin layer formed
on one of the substrates is a thermoplastic resin layer, the platen
may be pressed against the thermoplastic resin layer with the
application of heat.
[0078] In the foregoing method, a nonlinear element is provided on
one of the substrates and a platen having a projecting portion for
forming a contact hole at a position corresponding to an output
terminal portion of the nonlinear element may be used as the
platen.
[0079] In the foregoing method, a bottom portion of the contact
hole in the polymer resin layer may be etched immediately after the
platen is mold released from the polymer resin layer till the
output terminal portion of the nonlinear element is exposed. This
satisfactorily exposes the output terminal portion of the nonlinear
element even if the contact hole to be formed by shaping has an
insufficient opening area and suppresses an increase in contact
resistance. As a result, there can be fabricated a reflective
display device with a particularly high display quality in a motion
picture display.
[0080] To solve the foregoing problems, a method of fabricating a
reflective display device according to the present invention is a
method of fabricating a reflective display device comprising a
light modulating layer between a pair of substrates, the method
comprising the steps of: pressing a platen provided with a
projecting and depressed pattern composed of a group of minute
projecting and depressed patterns and a hole against one of the
pair of substrates; curing one of the substrates and mold releasing
the platen from one of the substrates; forming a metal film on one
of the substrates; and thereby shaping one of the substrates into
the projecting and depressed pattern to integrally mold minute
projecting and depressed portions in a surface of one of the
substrates with a support portion for supporting the other of the
substrates.
[0081] In the fabrication of a substrate, the step of pressing a
platen with satisfactory flatness against the substrate has been
performed conventionally to smooth the surface thereof. The
foregoing method achieves a reduction in the number of process
steps and lower cost by shaping the substrate into the projecting
and depressed pattern with the use of the platen provided with the
projecting and depressed pattern and smoothing the substrate.
[0082] In the foregoing method, if one of the substrates is made of
a photosensitive resin, a platen with transparency is used as the
platen and one of the substrates may be cured by irradiating one of
the substrates with light via the platen.
[0083] In the foregoing method, if one of the substrates is made of
a thermoplastic resin, the platen may be pressed against one of the
substrates with the application of heat.
[0084] To solve the foregoing problems, a method of fabricating a
reflective display device according to the present invention is a
method of fabricating a reflective display device comprising a
light modulating layer between a pair of substrates, the method
comprising the steps of forming a polymer resin layer over a mold
provided with a projecting and depressed pattern composed of a
group of minute projecting and depressed patterns; bonding the mold
to one of the pair of the substrates such that the polymer resin
layer faces the substrate and releasing the mold from the polymer
resin layer to laminate the polymer resin layer on one of the
substrates; forming a metal film over the polymer resin layer; and
thereby shaping the polymer resin layer into the projecting and
depressed pattern to form minute projecting and depressed portions
in a surface of the polymer resin layer.
[0085] If a polymer resin is coated on the substrate and the
polymer resin is shaped into the projecting and depressed pattern
by using the platen, e.g., the substrate may be damaged in pressing
the platen against the substrate. However, if the polymer resin
layer that has been shaped into the projecting and depressed
pattern by using the platen provided with the projecting and
depressed pattern is prepared in advance and formed on the
substrate, the substrate will not be broken. This allows
fabrication of a reflective display device with an improved
production yield. The foregoing method also achieves a reduction in
fabrication cost since the process of forming the polymer resin
layer over the platen can be performed in a shorter time than the
process of shaping the polymer resin formed on the substrate by
pressing the platen thereagainst.
[0086] In the foregoing method, a base film made of a polymer resin
may be used as the mold.
[0087] In the foregoing method, a mold having, at a specified
position, a hole for forming a support portion for supporting the
other of the pair of substrates may be used as the mold.
[0088] To solve the foregoing problems, a method of fabricating a
reflector comprises the steps of: coating a photosensitive resin
layer on a substrate; exposing the photosensitive resin layer to
light via a photomask; developing the exposed photosensitive resin
layer to form projecting and depressed portions in the
photosensitive resin layer; and forming a reflective film over the
projecting and depressed surface, wherein the photomask has a light
shielding pattern composed of groups of minute half-tone dots
smaller than a resolution limit of an exposing device used in the
exposing step and a resolution limit of the photosensitive resin
layer and a mean light transmittance of the light shielding pattern
is nonuniform over a surface of the photomask.
[0089] Since the foregoing method uses the photomask having the
light shielding pattern composed of the groups of minute halftone
dots smaller than the resolution limit of the exposing device and
the resolution limit of the photosensitive resin layer, it can
implement halftone representation that has been impossible with a
conventional photomask and the ability to represent details is
improved remarkably. As a consequence, the projecting and depressed
portions having, e.g., a gently inclined surface can be formed and
fine control of the configurations of the projecting and depressed
portions can be effected properly. Since a normal exposing device
or the like can be used, there is no need to introduce new
equipment.
[0090] Since the light shielding pattern has a nonuniform mean
transmittance over a surface of the photomask, projecting and
depressed portions having different heights and depth can be formed
in a variety.
[0091] In the foregoing method, a nonlinear element is provided on
the substrate and a mask having a light shielding portion or a
light non-shielding portion provided at a portion corresponding to
an output portion of the non-linear element may be used as the
photomask.
[0092] The method allows formation of a contact hole in the portion
of the photosensitive resin layer corresponding to the output
portion of the nonlinear element. If the photomask is provided with
the light shielding portion, a photosensitive resin layer composed
of a negative resist can be used as the photosensitive resin layer.
If the photomask is provided with a light non-shielding portion, a
photosensitive resin layer composed of a positive resist can be
used as the photosensitive resin layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0093] These and other objects and features of the present
invention will become apparent from the following description of
preferred embodiments thereof taken in conjunction with the
accompanying drawings, in which:
[0094] FIG. 1 is a cross-sectional view showing a structure of a
reflector according to EMBODIMENT 1 of the present invention;
[0095] FIG. 2A is a plan view of groups of columnar portions in the
reflector of EMBODIMENT 1 and FIG. 2B is a cross-sectional view
taken along the line A-A' of FIG. 2A;
[0096] FIG. 3 is a perspective view of a light reflecting thin film
in the reflector according to EMBODIMENT 1;
[0097] FIG. 4 illustrates the scattering and reflection of light by
the reflector according to EMBODIMENT 1;
[0098] FIGS. 5 are cross-sectional views illustrating the process
of fabricating the reflector according to EMBODIMENT 1;
[0099] FIG. 6 is a plan view schematically showing a pattern
configuration of a shielding portion of a photomask used in the
process of fabricating the reflector;
[0100] FIG. 7 is a graph showing the relationship between the
maximum width of a resist column and the height of a projecting
portion;
[0101] FIG. 8 is a cross-sectional view showing a structure of a
reflective liquid crystal display device comprising the reflector
according to EMBODIMENT 1;
[0102] FIG. 9A is a cross-sectional view showing a structure of a
reflector according to EMBODIMENT 2 of the present invention and
FIG. 9B is a plan view showing a staircase structure in the
reflector;
[0103] FIGS. 10 are cross-sectional views illustrating a method of
fabricating the reflector according to EMBODIMENT 2;
[0104] FIG. 11 is a plan view schematically showing a pattern
configuration of a shielding portion of a photomask used in the
process of fabricating the reflector;
[0105] FIGS. 12 are cross-sectional views illustrating another
method of fabricating the reflector according to EMBODIMENT 2;
[0106] FIGS. 13 are plan views schematically showing pattern
configurations of respective shielding portions of photomasks used
in the process of fabricating the reflector, of which FIG. 13A
shows the photomask used in a first exposing step, FIG. 13B shows
the photomask used in a second exposing step, and FIG. 13C shows
the photomask used in a third exposing step;
[0107] FIGS. 14 are cross-sectional views illustrating a method of
fabricating a reflector according to EMBODIMENT 3 of the present
invention;
[0108] FIGS. 15 are plan views schematically showing photomasks
used in the process of fabricating the reflector, of which FIG. 15A
shows the photomask used in an exposing step and FIG. 15B shows the
photomask used in a deep UV irradiating step;
[0109] FIG. 16 is a cross-sectional view showing a structure of a
reflective liquid crystal display device according to EMBODIMENT 4
of the present invention;
[0110] FIGS. 17 are cross-sectional views illustrating a method of
fabricating a reflector in the reflective liquid crystal display
device;
[0111] FIG. 18 is a cross-sectional view showing a structure of a
reflective liquid crystal display device according to EMBODIMENT 5
of the present invention;
[0112] FIG. 19A is a cross-sectional view illustrating a principal
portion of a reflector in the reflective liquid crystal display
device and FIG. 19B is a plan view showing a thin film and a pixel
electrode in the reflector;
[0113] FIGS. 20 are cross-sectional views illustrating a method of
fabricating the reflector;
[0114] FIG. 21 is a flow chart illustrating a method of fabricating
a reflector according to EMBODIMENT 6 of the present invention;
[0115] FIG. 22 is a cross-sectional view schematically showing
projecting and depressed structures on another reflector of the
present invention;
[0116] FIG. 23A is a plan view showing the arrangement of groups of
columnar portions as the projecting and depressed structures on
still another reflector and FIG. 23B is a cross-sectional view
taken along the line B-B' of FIG. 23A;
[0117] FIG. 24A is a plan view showing the arrangement of groups of
columnar portions as the projecting and depressed structures on yet
another reflector of the present invention and FIG. 24B is a
cross-sectional view taken along the line C-C' of FIG. 24A;
[0118] FIGS. 25 are views illustrating a structure of a grating
reflector, of which FIG. 25A is a partial cross-sectional view
showing the grating reflector and FIG. 25B is a plan view showing
the arrangement of projecting and depressed structures;
[0119] FIG. 26A is a cross-sectional view showing a cross-sectional
configuration of each of projecting portions when each of the
projecting and depressed structures is a diffraction grating and
FIG. 26B is a plan view of the projecting and depressed structures
in the form of a plurality of diffraction gratings;
[0120] FIG. 27 is a cross-sectional view schematically showing a
structure of still another reflector of the present invention;
[0121] FIG. 28 is a perspective view showing a surface
configuration of a platen used in a method of fabricating a
reflective display device according to EMBODIMENT 7 of the present
invention;
[0122] FIGS. 29A to 29C are views illustrating the process steps in
accordance with the method of fabricating the display device of the
present invention;
[0123] FIG. 30 is a cross-sectional view showing the reflective
display device according to EMBODIMENT 7;
[0124] FIG. 31A is a view illustrating a molding process in which a
base film is thermally pressed with a metal roll, FIG. 31B is a
cross-sectional view showing a laminated film resist, and FIG. 31C
is a cross-sectional view showing a resist resin film shaped by
using the base film and formed on a substrate;
[0125] FIG. 32 is a plan view schematically showing a halftone dot
pattern of a photomask used in EMBODIMENT 8 of the present
invention;
[0126] FIG. 33A is a cross-sectional view of a resist film coated
on a glass substrate, FIG. 33B is a cross-sectional view
illustrating exposure of the resist film, FIG. 33C is a
cross-sectional view illustrating the development of the exposed
resist film, FIG. 33D is a cross-sectional view illustrating a heat
treatment performed with respect to projecting portions, and FIG.
33E is a cross-sectional view illustrating the step of forming a
metal reflective film over the projecting portions after the heat
treatment;
[0127] FIG. 34 is a cross-sectional diagram showing a schematic
structure of a conventional reflector;
[0128] FIGS. 35A to 35E are cross-sectional views illustrating a
method of fabricating the conventional reflector, of which FIG. 35A
is a cross-sectional view of a resist film coated on a substrate,
FIG. 35B is a cross-sectional view illustrating exposure of the
resist film, FIG. 35C is a cross-sectional view illustrating the
development of the exposed resist film, FIG. 35D is a
cross-sectional view illustrating a heat treatment performed with
respect to projecting portions, FIG. 35E is a cross-sectional view
illustrating the step of forming a polymer resin film over the
projecting portions after the heat treatment; and FIG. 35F is a
cross-sectional view illustrating the step of forming a pixel
electrode over the projecting portions after the heat treatment;
and
[0129] FIGS. 36A to 36E are cross-sectional views illustrating the
formation of a contact hole in the conventional reflector.
DESCRIPTION OF THE EMBODIMENTS
First Group of the Invention
[0130] Referring now to the drawings, the embodiments of the
present invention will be described.
Embodiment 1
[0131] An embodiment of the present invention will be described
with reference to FIGS. 1 to 8. FIG. 1 is a cross-sectional view
illustrating a reflector according to the present embodiment. As
shown in the drawing, a reflector 10 is composed of plural groups
12 of columnar portions (projecting and depressed structures); a
polymer resin layer 14; and a light reflecting thin film 15, which
are stacked successively on a substrate 11.
[0132] The substrate 11 is composed of an insulating substrate made
of, e.g., glass (under the trade name 1737, which is commercially
available from Corning Co.). The substrate 11 has a thickness of,
e.g., 1.1 mm.
[0133] Each of the groups 12 of columnar portions is composed of a
plurality of minute columnar portions (projecting portions) 13a to
form a basic unit for determining the reflective properties of the
reflector 10. As shown in the drawing, the groups 12 of columnar
portions are positioned irregularly on the substrate 11 in parallel
relation to each other. What results is a structure in which the
groups 12 of columnar portions as the basic units are not observed
repetitively with a given period. This suppresses interference of
light which occurs due to a repetitive pattern in which the
projecting and depressed structures are arranged regularly and
suppresses a phenomenon of colored reflected light. The groups 12
of columnar portions may also be contiguous to each other without
having clearance therebetween in a portion or in a plurality of
portions. If the clearance is excessively large, on the other hand,
a flat surface parallel to a substrate surface is formed
undesirably to increase light reflected in the regular reflection
direction.
[0134] If a plan configuration of a region in which columnar
portions 13a are distributed is regarded approximately as those of
the groups 12 of columnar portions, the groups 12 of columnar
portions are formed to have elliptical plan configurations, as
indicated by the dot circles in FIG. 2A. Accordingly, the plan
configuration and size of each of the groups 12 of columnar
portions can be adjusted freely and accurately as required by
changing the distribution of the plurality of columnar portions 13a
isotropically or anisotropically in such a manner as to impart a
specified directionality to the distribution. The size of the group
12 of columnar portions can be changed appropriately provided that
the lengths of the long and short axes thereof are in the range of
1 .mu.m to 100 .mu.m. Compared with a conventional reflector (as
disclosed in Japanese Unexamined Patent Publication No. HEI
9-292504) having such a structure that projecting portions are
provided between a substrate and a metal thin film, the group 12 of
columnar portions as a basic unit has a size comparable to that of
the projecting portion of the conventional reflector. Preferably,
the maximum width of the columnar portion 13a in plan view is in
the range of 0.5 .mu.m to 20 .mu.m. If the maximum width is smaller
than 0.5 .mu.m, it is difficult to form the columnar portion of
this size since an exposure limit is exceeded. If the maximum width
is larger than 20 .mu.m, on the other hand, the level difference
between the projecting and depressed portions is increased to
aggravate the nonuniformity of a cell gap so that uneven display is
visually recognized undesirably.
[0135] Each of the groups 12 of columnar portions is composed of
the plurality of minute columnar portions 13 having different
heights which are collectively placed on a residual film 13b. By
forming the columnar portions 13a having different heights at
specified positions, therefore, the height distribution of the
groups 12 of columnar portions can be varied finely. This enables
precise control of the slope angle distribution of the light
reflecting thin film 15 formed over the groups 12 of columnar
portions. In the present embodiment, the heights has a peak
deviated, in the direction indicated by the arrow X, from a center
portion of the region in which the columnar portions 13a are
distributed. The columnar portions 13a having different heights are
arranged such that the heights thereof tend to decrease gradually
with distance from the peak toward the periphery. Preferably, the
height of the columnar portion 13a is in the range to 1 .mu.m to 5
.mu.m. The height of the column portion 13a is a level difference
between the residual film 13b and a top of the columnar portion
13a. If the height is smaller than 1 .mu.m, the level difference
between the projecting and depressed portions on the surface of the
light reflecting thin film 15 is reduced to undesirably increase
light reflected in the regular reflection direction. If the height
is larger than 5 .mu.m, on the other hand, the nonuniformity of the
cell gaps is aggravated so that uneven display is visually
recognized undesirably to degrade the display quality. The number
of columnar portions 13a distributed per unit area of 1 mm.sup.2 is
appropriately in the range of about 100 to 500000. If the number of
the columnar portions 13a distributed per unit area is smaller than
100/mm.sup.2, the scattering property deteriorates. If the number
of the columnar portions 13a distributed per unit area is larger
than 500000/mm.sup.2, on the other hand, regularity is produced
undesirably to form a repetitive structure. The respective peak
heights of the groups 12 of columnar portions may be the same or
different from each other.
[0136] The columnar portions 13a are made of, e.g., a
photosensitive resin, example of which are a positive resist, an
electron beam resist, and the like. The present embodiment has used
a low-.gamma. positive resist (under the trade name PC409, which is
commercially available from JSR Corporation). The columnar portion
13a is configured as a column having a circular or elliptical cross
section in a direction parallel to a substrate surface and a
roundly curved tip portion. This allows the light reflecting thin
film 15 provided over the columnar portions 13a to have a smooth,
curved surface. In accordance with the present invention, the
cross-sectional configuration in the direction parallel to the
substrate surface is not limited to a circle or an ellipse and may
be a polygon or the like.
[0137] The residual film 13b is composed of the same material as
composing the columnar portions 13a. The residual film 13b is a
film undeveloped and left in forming the columnar portions 13a by
the developing step in the photolithographic process.
[0138] The polymer resin layer 14 is composed of, e.g., a resist.
The same material composing the columnar portions 13a may also be
used to compose the polymer resin layer 14. By providing the
polymer resin layer 14, a gently curved surface configuration can
be imparted to a flat portion parallel to the substrate surface if
the clearance between the groups 12 of columnar portions is large.
Since the flat region parallel to the substrate 11 is not formed,
light reflected in the regular reflection direction is suppressed.
Even if deep valley portions are formed between the columnar
portions 13a due to a large level difference between the top
portions of the columnar portions 13a and the residual film 13b,
the polymer resin layer 14 is filled in the valley portions to
provide a gently curved surface configuration in which the height
distribution varies continuously. The polymer resin layer 14 is not
limited to a single-layer structure. In consideration of the film
thickness, the polymer layer 14 may also have a multi-layer
structure in which a plurality of layers are stacked.
[0139] The light reflecting thin film 15 has a light reflecting
function and is composed of a metal thin film made of aluminum (Al)
or the like. The light reflecting thin film 15 has an anisotropic
scattering surface which scatters and reflects light in directions
within an anisotropic range. Specifically, the light reflecting
thin film 15 has a projecting and depressed surface which does not
have a flat region parallel to a surface of the substrate 11. The
surface configuration of the light reflecting thin film 15 is
curved to have a curvature which is locally larger in the
X-direction than in the Y-direction opposite to the X-direction.
That is, a deflection is produced in a cross-sectional
configuration of the slope angle distribution in the X-to-Y
direction, so that an asymmetrical structure is provided. As a
result, light incident from a certain direction can be reflected
not in the regular reflection direction but in a direction of
visual recognition of the viewer, such as a direction perpendicular
to the reflector 10. The surface configuration of the light
reflecting thin film 15 is determined by the height distribution of
the columnar portions 13a composing the groups 12 of columnar
portions and the two-dimensional distribution thereof. Therefore,
the magnitude of the slop angle, the slope angle distribution, and
the surface configuration of the light reflecting thin film 15 can
be controlled precisely by controlling the height distribution of
the columnar portions 13a. If slight reflection of light in the
regular reflection direction is permitted, the proportion of the
flat region to the entire region may be at least about 20% or
lower. As the material of the light reflecting thin film 15, there
can be listed silver (Ag), chromium (Cr), nickel (Ni), or a
multilayer film consisting of a plurality of stacked metal thin
films in addition to Al mentioned above.
[0140] As shown in FIG. 4, the reflector 10 according to the
present embodiment thus structured is disposed to have a curved
surface with a lower curvature facing upward such that it has a
high reflectance in a wide range and scattering and reflecting
properties including a superior paper-white property.
[0141] A description will be given below to a method of fabricating
the reflector 10 according to the present embodiment. FIGS. 5 are
cross-sectional views illustrating the process of fabricating the
reflector 10.
[0142] First, as shown in FIG. 5A, a photosensitive resin material
(under the trade name PC409, which is a low-.gamma. positive resist
commercially available from JSR Corporation) is coated by spin
coating on the substrate 11 (under the trade name 1737, which is
available from Corning Co.) (coating step). For example, spin
coating is performed at a revolution speed of 700 rpm for 30
seconds such that a coated film with a thickness of 3.6 .mu.m is
formed. The substrate 11 having a coating of the photosensitive
resist material is then pre-baked at 105.degree. C. for 90 seconds
such that a solvent in the coated film is evaporated, whereby the
photosensitive resin layer 16 is formed.
[0143] Next, as shown in FIG. 5B, a photomask 18 is positioned
above the photosensitive resin layer 16 such that the
photosensitive resin layer 16 is exposed to UV light via the
photomask 18 (exposing step). As shown in FIG. 6, the photomask 18
has circular or elliptical shielding portions 18a formed
irregularly to occupy specified areas. More specifically, the
shielding portions are formed so as to occupy larger areas at
portions where higher columnar portions are to be formed (a
detailed description will be given later to the reason for this).
For example, the UV light is radiated at an intensity of 10 to 300
mJ/cm.sup.2 for an exposure time of 1 to 30 seconds. As for pattern
data for implementing the pattern configuration shown in FIG. 6, it
has been predetermined by simulation or the like such that the
columnar portions 13a of different sizes have a specified height
distribution.
[0144] Subsequently, development is performed by using an aqueous
solution containing 0.4% of NMD-3.TM. (commercially available from
Tokyo Ohka Kogyo Co., Ltd.) as a developing solution and an
unwanted portion is dissolved away (developing step). The
development time is, e.g., about 60 seconds. By the developing
step, resist columns 17 and the residual film 13b are formed on the
substrate 11, as shown in FIG. 5C. In plan view, the resist columns
17 occupy different areas depending on the sizes of the shielding
portions 18a of the photomask 18. The resist columns 17 have a
uniform height (which is a height measured on the basis of the
resist film 13b), since the developing speeds are nearly the
same.
[0145] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 17 and the like at a temperature
of, e.g., 120.degree. C. for 5 minutes. As a consequence, the
respective angular edges of the tip portions of the resist columns
17 are heat-melted, which allows the formation of the columnar
portions 13 having smoothly curved configurations and the groups 12
of columnar portions composed of the group of the columnar portions
13a, as shown in FIG. 5D.
[0146] The columnar portions 13a composing the groups 12 of
columnar portions are formed to have different heights which are
measured from the residual film 13b. This is because the present
embodiment has used a photosensitive resin material such that the
maximum widths (.mu.m) of the resist columns and the heights
[0147] (.mu.m) of the columnar portions formed by heat-melting the
resist column satisfy such a linearly functional relationship as
shown in FIG. 7. The drawing shows the result of measuring, from
the residual film, the heights of the columnar portions formed by
heat-melting the resist columns having different maximum widths in
plan view. In plan view, the resist columns in use have a
geometrically similar relationship therebetween and nearly equal
heights. As will be understood from the drawing, the heights of the
columnar portions after the heat-melting process are larger as the
maximum widths of the resist columns are increased, i.e., as the
areas occupied by the resist columns in plan view are increased. By
properly setting the maximum widths of the resist columns 17,
therefore, the heights of the individual columnar portions 13a can
be controlled, which allows precise control of the height
distribution of the groups 12 of columnar portions. Depending on
the temperature range set in the heating step, however, there are
cases where the resist columns that are melted and softened are apt
to elongate in a direction vertical to the substrate 11 due to the
affinity between the photosensitive resin material and the
substrate 1. In other words, there are cases where the relationship
between the maximum widths (.mu.m) of the resist columns and the
heights (.mu.m) of the columnar portions formed after the
heat-melting process are represented by a curve protruding upwardly
and having an inflexion point.
[0148] The overall height of the columnar portions 13a and the
thickness of the residual film 13b can be controlled by adjusting
the thickness and material of the photosensitive resin layer 16,
the cumulative exposure dose, the exposure time, and the
development time. Specifically, a larger thickness increases the
overall height of the resist columns 17 so that the overall height
of the columnar portions 13a is also increased. The heights of the
resist columns 17 can be controlled by varying the exposure time
since the cumulative exposure dose is varied thereby. If the
cumulative exposure dose is increased by, e.g., increasing the
exposure time, the heights of the resist columns 17 are increased.
This increases the heights of the columnar portions 13a and
planarizes the depressed portions between the adjacent columnar
portions 13a or reduces the thickness of the residual film 13b. It
is also possible to reduce the overall height of the resist columns
17 by increasing the development time. Moreover, the present
embodiment has used the low-.gamma. positive resist PC409, which is
such a photosensitive resin material as to reduce the thickness of
the residual film on a linear function basis as the cumulative
exposure dose increases. If a normal photosensitive resin material
is used, the thickness of the residual film presents a fixed value
till a certain cumulative exposure dose is reached. However, the
film thickness reduces drastically if the cumulative exposure dose
is exceeded. If such a normal photosensitive resin material is
used, it is difficult to control the thickness of the residual
film, i.e., the heights of the columnar portions 13. Hence, it is
preferable to use a photosensitive resin material having such
physical properties as shown in the present embodiment in terms of
controllability over the heights of the columnar portions 13a.
[0149] Further, the same photosensitive resin material (under the
trade name PC409, which is a positive resist commercially available
from JSR Corporation), as composing the columnar portions 13a and
the residual film 13b is coated thereon by spin coating.
[0150] Next, the coated film is cured by, e.g., applying heat at a
specified temperature for a given time, thereby forming a polymer
resin layer 14. Further, aluminum is vapor-deposited on the polymer
resin layer 14, whereby the light reflecting thin film 15 having a
thickness of about 2000 .ANG. is formed (light-reflecting-thin-film
forming step).
[0151] By the foregoing process, the reflector 10 according to the
present embodiment can be formed. A description will be given next
to a reflective liquid crystal display device comprising the
reflector 10 thus fabricated. FIG. 8 is a cross-sectional view of
the reflective liquid crystal display device.
[0152] As shown in the drawing, the reflective liquid crystal
display device has: the reflector 10; a counter substrate 20 (the
display surface side); and a liquid crystal layer 21 held between
the reflector 10 and the counter substrate 20. An alignment film 22
for orienting adjacent liquid crystal molecules in a specified
direction is formed on the reflector 10. In this case, the light
reflecting thin film 15 functions as a pixel electrode.
[0153] A transparent electrode 23 made of ITO (Indium Tin Oxide) is
provided on the counter substrate 20. An alignment film 24 is
further provided on the transparent electrode 23. The counter
substrate 20 is composed of a light transmitting substrate.
[0154] The liquid crystal layer 21 is composed of a guest-host
liquid crystal containing a black dichroic dye dissolved in a
liquid crystal. The alignment films 22 and 24 are made of e.g., a
polyimide resin and have been oriented in opposite directions.
Between the substrates, the liquid crystal molecules are aligned to
twist by about 360 degrees.
[0155] As a result of examining the display condition on the
reflective liquid crystal display device thus structured,
anisotropy was observed in the range in which the reflected light
was scattered. The display obtained had a particularly excellent
paper-white property in a direction of visual recognition of the
viewer, remarkable brightness, and superior contrast.
[0156] Although the present embodiment has described the case where
the groups 12 of columnar portions are formed directly on the
substrate 11, the photosensitive resin layer may also be formed
preliminarily on the substrate 11. For example, the photosensitive
resin layer may be formed prior to the formation of the
photosensitive resin layer 16 composed of the low-.gamma. positive
resist PC409 by coating the same material on the substrate 11 and
performing a heat treatment with respect to the coated film.
Alternatively, another photosensitive resin layer may also be
formed of a material different from PC409. This varies the affinity
between the substrate 11 and the photosensitive resin layer 16 and
the heat treatment performed with respect to the resist columns 17
allows the heights of the columnar portions 13a to be controlled
during the formation thereof.
[0157] Although the present embodiment has described the case where
the groups 12 of columnar portions are formed on the substrate 11,
there may also be used a depressed structure which can be formed by
exposing the photosensitive resin layer 16 via a photomask having a
circular or elliptical opening. From a different viewpoint, a
structure which is a continuity of projecting and depressed
structures in which a plurality of gaps at different depths are
provided may also be used. In this case, the projecting portions
mean the portions which are higher in level than the lowermost
portion in the depressed structure. The depth of the structure can
be controlled by varying the cumulative exposure dose.
Embodiment 2
[0158] A reflector according to EMBODIMENT 2 is different from the
reflector according to EMBODIMENT 1 in that it has staircase
structures each formed unitarily in place of the groups of columnar
portions each formed of the plurality of minute columnar
portions.
[0159] FIG. 9 illustrates a structure of the reflector according to
the present embodiment. FIG. 9A shows a cross-sectional
configuration of the reflector. FIG. 9B shows plan configurations
of the staircase structures in the reflector. As shown in the
drawings, a reflector 30 is composed of a plurality of staircase
structures 31a; a polymer resin layer 14; and a light reflecting
thin films 15, which are stacked successively on a substrate
11.
[0160] Each of the staircase structure 31a forms a basic unit for
determining the reflective properties of the reflector 30 according
to the present embodiment. As shown in FIG. 9B, the staircase
structures 31a are positioned irregularly on the substrate 11 in
parallel relation to each other. What results is a structure with
reduced regularity in which the staircase structures 31a as the
basic units are not observed repetitively with a given period. This
suppresses interference of light which occurs due to the repetitive
pattern of the staircase structures 31a and suppresses a phenomenon
of, e.g., colored reflected light. The staircase structures 31a may
also be contiguous to each other without having clearance
therebetween in a portion or in a plurality of portions. If the
clearance is excessively large, on the other hand, a flat surface
parallel to a substrate surface is formed undesirably to increase
reflected light in the regular reflection direction.
[0161] In cross section, each of the staircase structures 31a is
configured as a staircase having a plurality of stepped portions.
The height of the staircase structure 31a has a peak deviated in a
direction indicated by the arrow X from the center portion thereof
and tends to decrease with distance from the peak toward the
periphery. By controlling the height of each of the stepped
portions measured from the bottom portion of the staircase
structure 31a, the height distribution of the staircase structure
31a can be varied finely. This enables precise control of the slope
angle distribution of the light reflecting thin film 15 formed over
the staircase structures 31a. The stepped portions and top portion
of the staircase structure 31a have a roundly curved configuration.
This imparts a more smoothly curved surface configuration to the
light reflecting thin film 15 provided over the staircase
structures 31a.
[0162] The peak height of the staircase structure 31a is preferably
in the range of 1 .mu.m to 5 .mu.m. If the height is smaller than 1
.mu.m, the level difference between the projecting and depressed
portions at the surface of the light reflecting thin film 15 is
reduced so that light reflected in the regular reflection direction
is increased undesirably. If the height is larger than 5 .mu.m, on
the other hand, the nonuniformity of the cell gap is aggravated and
uneven display is visually recognized, which degrades the display
quality. The peak heights of the individual staircase structures
31a may be equal to or different from each other.
[0163] Each of the staircase structures 31a has, e.g., an
elliptical plan configuration. In the present invention, the plan
configuration of the staircase structure 31a is not limited to an
ellipse described above and may be a polygon.
[0164] The staircase structure 31a is composed of, e.g., a
photosensitive resin, example of which are a positive resist, an
electron beam resist, and the like. The present embodiment has used
a low-.gamma. positive resist (under the trade name PC409, which is
commercially available from JSR Corporation).
[0165] A residual film 31b is composed of the same material as
composing the staircase structures 31a. The residual film 31b is a
film undeveloped and left in forming the staircase structures 31a
by the developing step in the photolithographic process.
[0166] The reflector 30 according to the present embodiment thus
structured is disposed to have a curved surface with a low
curvature facing upward such that it has a high reflectance in a
wide range and reflecting and scattering properties including an
excellent paper-white property.
[0167] A description will be given below to a method of fabricating
the reflector 30 according to the present embodiment. FIGS. 10 are
cross-sectional views illustrating the process of fabricating the
reflector 30.
[0168] First, the low-.gamma. positive resist PC409 as the
photo-sensitive resin material is coated by spin coating on the
substrate 11, similarly to EMBODIMENT 1. The thickness of the
coated film is adjusted to 3.6 .mu.m. The substrate 11 having a
coating of the photosensitive resist material is then pre-baked at
105.degree. C. for 90 seconds such that a solvent in the coated
film is evaporated, whereby a photosensitive resin layer 16 is
formed (see FIG. 10A).
[0169] Next, as shown in FIG. 10B, a photomask 32 is positioned
above the photosensitive resin layer 16 such that the
photosensitive resin layer 16 is exposed to UV light via the
photomask 32 (exposing step). As shown in FIG. 11, the photomask 32
is formed to have different light shielding rates in the respective
regions of each of Light shielding portions 33. Specifically, the
shielding rate is highest in the region 33a and decreases gradually
in the regions 33b and 33c in this order. Since the respective
regions have different light shielding rates, the regions of the
photosensitive resin layer 16 corresponding to the respective
regions 33a to 33c are exposed with different cumulative exposure
doses even if they are irradiated with UV light at an equal
intensity. As for pattern data for implementing the pattern
configuration of the shielding portion composed of the regions 33a
to 33c, it has been predetermined by simulation or the like.
[0170] Subsequently, development is performed by using a developing
solution, whereby an unwanted portion is removed (developing step).
As a consequence, the residual film 31b and the resist columns 34
are formed on the substrate 11, as shown in FIG. 10C.
[0171] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 34 or the like at a temperature
of, e.g., 120.degree. C. for 5 minutes (heat treatment step). As a
consequence, the respective angular edges of the resist columns 34
are heat-melted to have smoothly curved configurations, as shown in
FIG. 10D.
[0172] The heights of the stepped portions of the staircase
structure 31a can be controlled by varying the light shielding
rates in the photomask 32. The heights of the staircase structures
31a and the thickness of the remaining film 31b can be controlled
by adjusting the thickness and material of the photosensitive resin
layer 16, the cumulative exposure dose, the exposure time, and the
development time. Specifically, a larger thickness increases the
heights of the staircase structures 31a. The height of the
staircase structure 31a can also be controlled by varying the
exposure time since the cumulative exposure dose is varied thereby.
For example, the cumulative exposure dose is increased by
increasing the exposure time so that the residual film 31b is
thinned. As a result, the heights of the staircase structures 31a
can be increased. On the other hand, the heights of the staircase
structures 31 can be reduced by increasing the development
time.
[0173] Further, the low-.gamma. positive resist PC409 as the
photo-sensitive resin material is coated by spin coating over the
staircase structure 31a and the residual film 31b. The coating may
be performed under the same conditions as in EMBODIMENT 1.
[0174] Next, the coated film is cured by, e.g., applying heat at a
specified temperature for a given time by the same step as
performed in EMBODIMENT 1, thereby forming the polymer resin layer
14. Further, aluminum is vapor-deposited on the polymer resin layer
14, whereby the light reflecting thin film 15 is formed
(light-reflecting-thin-film forming step).
[0175] By the foregoing process, the reflector 30 according to the
present embodiment can be formed.
[0176] The staircase structures 31a may also be formed by
performing a plurality of exposing steps in another method of
fabricating the reflector 30 according to the present embodiment,
which will be described in greater detail as follows. FIGS. 12 are
cross-sectional views illustrating another process of fabricating
the reflector 30.
[0177] First, similarly to the process mentioned above, the
low-.gamma. positive resist PC409 as the photosensitive resin
material is coated on the substrate 11 (coating step), which is
then pre-baked at a specified temperature for a given time to form
the photosensitive resin layer 16 (see FIG. 12A).
[0178] Next, as shown in FIG. 12B, a first photomask 35 is
positioned above the photosensitive resin layer 16 so that the
photosensitive resin layer 16 is exposed to UV light via the first
photomask 35 (first exposing step). The first photomask 35 is
formed such that elliptical first light shielding portions 35a are
in a specified pattern, as shown in FIG. 13A.
[0179] Further, as shown in FIG. 12C, a second photomask 36 is
positioned above the photosensitive resin layer 16 so that the
photosensitive resin layer 16 is exposed to UV light in the same
manner as described above (second exposing step). The second
photomask 36 is formed such that elliptical second light shielding
portions 36a are located within the respective light shielding
ranges of the first shielding portions 35a, as shown in FIG.
13B.
[0180] Subsequently, as shown in FIG. 12D, a third photomask 37 is
positioned above the photosensitive resin layer 16 such that the
photosensitive resin layer 16 is exposed to UV light in the same
manner as described above (third exposing step). The third
photomask 37 is formed such that elliptical third shielding
portions 37a are located within the respective light shielding
ranges of the second shielding portions 36a, as shown in FIG.
13C.
[0181] As stated previously, the first to third exposing steps
provide different cumulative exposure doses in the specified
regions of the photosensitive resin layer 16. In positioning the
first to third photomasks 35 to 37 above the substrate 11, the
two-dimensional positions of the first to third photomasks 35 to 37
relative to the substrate 11 are determined with accuracy in a
specified range. As for pattern data for implementing the pattern
configuration of the first to third light shielding portions 35a to
37a, it has been predetermined by simulation or the like.
[0182] Subsequently, development is performed by using a developing
solution, whereby an unwanted portion is removed (developing step).
The development was performed under the same conditions as
described above. As a consequence, the residual film 31b and
staircase resist columns 34 are formed on the substrate 11, as
shown in FIG. 12E. The formation of the stepped portions in the
resist columns 34 is attributable to the different cumulative
exposure doses achieved in the respective regions by the first to
third exposing steps. The heights of the resist columns 34 and the
thickness of the residual film 31b can be controlled by adjusting
the thickness and material of the photosensitive resin layer 16,
the cumulative exposure dose, the exposure time, and the
development time, similarly to the foregoing method.
[0183] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 34 and the like at a temperature
of, e.g., 120.degree. C. for 5 minutes (heat treatment step). As a
consequence, the respective angular edges of the resist columns 34
are heat-melted to have smoothly curved configurations, as shown in
FIG. 12F, whereby the staircase structures 31a are formed.
[0184] Further, the low-.gamma. positive resist PC409 is coated by
spin coating over the staircase structures 31a and the residual
film 31b in the same manner as described above and the coated film
is cured with the application of heat, thereby forming the polymer
resin layer 14. Subsequently, aluminum is vapor-deposited on the
polymer resin layer 14, whereby the light reflecting thin film 15
is formed.
[0185] By the foregoing process, the reflector 30 according to the
present embodiment can be formed.
Embodiment 3
[0186] The present embodiment fabricates a reflector comprising
projecting and depressed structures each having an asymmetric
cross-sectional configuration in accordance with a deep UV method.
FIGS. 14 are cross-sectional views illustrating the fabrication
method.
[0187] As shown in FIG. 14A, a photosensitive resin material is
coated on a substrate 11 by spin coating. The thickness of the
coated film is adjusted to 3.6 .mu.m. The substrate 11 having a
coating of the photosensitive resist material is then pre-baked at
105.degree. C. for 90 seconds such that a solvent in the coated
film is evaporated, whereby a photosensitive resin layer 16 is
formed. Further, as shown in FIG. 14B, a photomask 41 is positioned
above the photosensitive resin layer 16 such that the
photosensitive resin layer 16 is exposed to UV light via the
photomask 41 (exposing step). As shown in FIG. 15A, the photomask
41 has a plurality of elliptical light shielding portions 41a which
are equal-sized and formed irregularly.
[0188] Subsequently, development is performed by using a developing
solution, whereby an unwanted portion is removed (developing step).
As a consequence, resist columns 42 each having an elliptical plan
configuration are formed on the substrate 11, as shown in FIG.
14C.
[0189] Next, as shown in FIG. 14D, a photomask 43 is positioned
above the substrate 11 provided with the resist columns 42 and the
substrate 11 is irradiated with UV (deep UV) light at a shorter
wavelength (in the range of 250 nm to 365 nm (i-line)) via the
photomask 43 (irradiating step). As a consequence, cross-linking
further proceeds in the portions of the resist columns 42
irradiated with deep UV so that they are cured to a higher degree
than the other portions. As shown in FIG. 15B, the photomask 43 has
a plurality of elliptical openings 43a which are equal-sized and
formed irregularly. The opening 43a and the light shielding portion
41a are geometrically similar to each other and have a dimensional
ordering relationship therebetween such that the long axis of the
opening 43a corresponds to half the long axis of the light
shielding portion 41a. The two-dimensional position of the
substrate 11 relative to the position of the photomask 43 have been
determined such that one end on the long axis of the shielding
portion 41 coincides with one end on the long axis of the opening
portion 43a. In the irradiating step, an electron beam at a shorter
wavelength may also be used for irradiation instead of the UV light
at a shorter wavelength.
[0190] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 42 at a temperature of, e.g.,
120.degree. C. for 5 minutes (heat treatment step). As a
consequence, projecting portions 44 composing the projecting and
depressed structures each having an asymmetric cross-sectional
configuration are formed, as shown in FIG. 14E. In this case, since
the portions irradiated with the deep UV have been cured to a
higher degree than the other portions, as described above, the
irradiated portions undergo a lower degree of thermal deformation
so that the edge portions of the irradiated portions are slightly
rounded. By contrast, the regions unirradiated with deep UV undergo
a higher degree of thermal deformation so that inclined surfaces
having smoothly curved configurations are formed.
[0191] Subsequently, the reaction of an unreacted substance
contained in the projecting portions 44 is completed and a
post-baking step is performed to suppress the production of an
impurity or a contaminant in the step of forming the light
reflecting thin film 15, which will be described later. Further, a
photosensitive resin material is coated over the projecting
portions 44 and the substrate 11 by spin coating and the coated
film is cured with the application of heat, thereby forming a
polymer resin layer 14. Subsequently, aluminum is vapor-deposited
on the polymer resin layer 14 to form the light reflecting thin
film 15, whereby the reflector according to the present embodiment
is formed.
[0192] Thus, the method of fabricating the reflector according to
the present embodiment allows easy formation of the projecting
portions composing the projecting and depressed structures each
having an asymmetric cross-sectional configuration.
[0193] For reference purposes, there may also be considered a
method in which the projecting and depressed structures each having
an asymmetric cross-sectional configuration are formed by
performing a heat treatment with respect to the substrate which is
held inclined to cause a heat sag, instead of irradiating the
substrate with deep UV. In such a method, however, it is difficult
to properly cause the heat sag for a desired slope angle so that
the method has a room for improvement in terms of controllability.
By contrast, if the exposure dose and the like are set properly for
irradiation with deep UV in the method of fabricating the reflector
according to the present embodiment, the projecting and depressed
structures each having an asymmetric cross-sectional configuration
and a desired slope angle can be formed easily with excellent
controllability.
[0194] In accordance with the method of fabricating the reflector
according to the present embodiment, it is also possible to improve
controllability over the slope angle distribution by performing a
plurality of irradiating steps using UV light at a shorter
wavelength or an electron beam at a shorter wavelength and varying
the exposure dose in each of the irradiating steps.
[0195] In the present embodiment, it is also possible to perform a
deep UV irradiating step for further curing the projecting portions
44 after the heat treatment step. Specifically, the projecting
portions 44 are irradiated with UV light at a shorter wavelength
(in the range of 250 nm to 365 nm (i-line)) or an electron beam at
a shorter wavelength by using a mask having openings corresponding
to the projecting portions 44. As a result, cross-linking further
proceeds in the portions irradiated with UV light or the like so
that the degree of cure is increased. Even if a post-baking step
for heating the projecting portions 44 is performed, therefore, the
thermal deformation of the projecting portions 44 is prevented and
the controlled slope angle distribution is retained.
Embodiment 4
[0196] A reflective liquid crystal display device according to
EMBODIMENT 4 is structurally different from the liquid crystal
display device according to EMBODIMENT 1 in that a switching
element (nonlinear element) is provided on the reflector side and a
light reflecting thin film is formed on the bottom portion of a
contact hole for providing an electrical connection between the
switching element and the light reflecting thin film. Referring to
FIG. 16, a detailed description will be given to specific
components. FIG. 16 is a cross-sectional view schematically showing
a principal portion of the reflector in the liquid crystal display
device.
[0197] As shown in the drawing, the liquid crystal display device
has: a substrate 11; a counter substrate 20 (display surface side);
and a liquid crystal layer 21 held between the substrate 11 and the
counter substrate 20.
[0198] On the substrate 11, a thin-film transistor (hereinafter
referred to as TFT) 51 as the switching element, a source line (not
shown), a gate line (not shown), and the like are formed. A metal
film (light reflecting film) 52 and a photosensitive resin layer 53
are formed thereover. A light reflecting thin film 15 is further
formed over the photosensitive resin layer 53 and the metal film
52. An alignment film 22 is provided on the light reflecting thin
film 15. The light reflecting thin film 15 is electrically
connected to a drain electrode 51a via a contact hole 54 provided
in the photosensitive resin layer 53 and the metal film 52.
[0199] On the TFT 51, the photosensitive resin layer 53 functions
as a planarizing film for planarizing a rough configuration
resulting from the provision of the TFT 51 and also functions as a
protective film. In the region other than the portion formed with
the TFT 51, plural groups 12 of columnar portions are provided to
function as a part of the reflector. It will easily be appreciated
that each of the groups 12 of columnar portions is composed of a
plurality of minute columnar portions 13a which are collectively
placed, as described in EMBODIMENT 1. Although the TFT 51 and the
photosensitive resin layer 53 have been described separately for
convenience, the photosensitive resin layer 53 usually composes the
TFT 51.
[0200] The light reflecting thin film 15 functions as a part of the
reflector, while functioning as a pixel electrode in the region
provided with the groups 12 of columnar portions.
[0201] The metal film 52 has a light reflecting property and is
made of Al, Ag, Cr, Ni, or an alloy thereof (e.g., an Ag--Cu alloy
or the like).
[0202] A description will be given below to a method of fabricating
the liquid crystal display device according to the present
embodiment. FIGS. 17 are cross-sectional views illustrating the
process of fabricating the reflector associated with the liquid
crystal display device.
[0203] First, the TFT 51, a metal interconnect, and the like are
formed on the substrate 11 by a conventionally known method. Then,
as shown in FIG. 17A, the metal film 52 is formed to have at least
one part thereof overlapping the drain electrode 51a of the TFT 51
by a conventionally known method.
[0204] Next, a photosensitive resin material is coated on the
substrate 11 by spin coating (coating step) and the substrate 11
having a coating of the photosensitive resist material is then
pre-baked at 105.degree. for 90 seconds such that a solvent in the
coated film is evaporated, whereby the photosensitive resin layer
16 is formed (see FIG. 17B), similarly to EMBODIMENT 1.
[0205] Next, as shown in FIG. 17C, a photomask 55 is positioned
above the photosensitive resin layer 16 and the photosensitive
resin layer 16 is exposed to UV light via the photomask 55
(exposing step). In the case where a residual film 13b is to be
formed, a region in which a contact hole is to be formed should be
formed at a position deeper than the residual film 13b. Therefore,
the cumulative exposure dose should be higher at the position at
which the contact hole is to be formed than in the other region.
Since the radiated UV light is reflected by the metal film 52 in
the vicinity of the metal film 52, the cumulative exposure dose is
higher than in the other exposed region. The photomask 55 has
circular or elliptical light shielding portions which are formed to
occupy specified areas. The photomask 55 also has an opening for
forming the contact hole 54 which is formed in a region of the
photosensitive resin layer 16 corresponding to the metal film
52.
[0206] Subsequently, development is performed by using, as a
developing solution, an aqueous solution containing 0.4% of
NMD-3.TM. (commercially available from Tokyo Ohka Kogyo Co., Ltd.)
and an unwanted portion is dissolved away (developing step). By the
step, resist columns 17 and the residual film 13b are formed on the
substrate 11, while a cavity portion 56 is formed therein, as shown
in FIG. 17D. The cavity portion 56 has a trapezoidal cross section
which diverges with approach toward the bottom portion thereof In
other words, the size of the void portion 56 increases gradually
with approach toward the bottom portion thereof, compared with the
size of the light shielding portion, though the configuration and
size of the opening portion of the cavity portion 56 correspond to
those of the photomask 55. This is because the cumulative exposure
dose is increased in the vicinity of the metal film 52 due to the
reflection of the UV light by the metal film 52, so that optical
decomposition occurs in a wider range, as mentioned above in the
description of the exposing step.
[0207] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 17 and the like at 120.degree. C.
for 5 minutes, thereby forming the photosensitive resin layer 53,
as shown in FIG. 17E. More specifically, the groups 12 of columnar
portions composed of the plurality of columnar portions 13a are
provided in the region other than the portion formed with the TFT
51. In the cavity portion 56 also, the opening portion and inner
wall surface thereof are melted and thermally deformed but the
bottom portion thereof is prevented from being clogged since the
cavity portion 56 is formed inherently to have a trapezoidal cross
section. What results is the contact hole 54 having a generally
rectangular cross section and a sufficient diameter to provide an
electric connection between the TFT 51 and the light reflecting
thin film 15. This suppresses a faulty operation and an increase in
contact resistance.
[0208] Further, the reaction of an unreacted substance contained in
the photosensitive resin layer 53 is completed and a post-baking
step is performed to suppress the production of an impurity and a
contaminant under constant pressure in the step of forming the
light reflecting thin film 15 or in the step of injecting a liquid
crystal. The processing temperature, time, and the like in the step
are set appropriately as required.
[0209] Next, as shown in FIG. 17F, aluminum is vapor-deposited on
the photosensitive resin layer 53 to form the light reflecting thin
film 15 (light-reflecting-thin-film forming step).
[0210] Next, a polyimide resin is coated on the light reflecting
thin film 15 and a rubbing process is performed with respect
thereto, thereby forming the alignment film 22. On the other hand,
a transparent electrode 23 is formed on the counter substrate 20 by
a conventionally known method and the alignment film 24 is formed
on the transparent electrode 23 in the same manner as described
above. Subsequently, the substrate 11 and the counter substrate 20
are bonded to each other and a guest-host liquid crystal composed
of a chiral nematic liquid crystal containing a black dichroic dye
dissolved therein is injected from a liquid crystal injection port
to form the liquid crystal layer 21. By the foregoing process, the
reflective liquid crystal display device according to the present
embodiment can be fabricated.
[0211] Thus, since the method of fabricating the reflective liquid
crystal display device according to the present embodiment can
suppress an increase in the contact resistance between the light
reflecting thin film 15 and the TFT 51, there can be fabricated a
reflective liquid crystal display device having a particularly high
display quality in a motion picture display.
[0212] In the present embodiment, a deep UV irradiating step for
further advancing the curing of a surrounding portion of the inner
wall surface of the contact hole 54 may also be performed after the
heat treatment step. Specifically, the contact hole 54 is
irradiated with UV light at a shorter wavelength (in the range of
200 to 400 nm) via a mask having an opening corresponding to the
contact hole 54. As a result, cross-linking further proceeds to
increase the degree of cure in the portions irradiated with the UV
light. If the post-baking steps for heating the photosensitive
resin layer 53 is performed, therefore, the thermal deformation of
the contact hole 54 is prevented and a more satisfactory electric
connection is provided between the TFT 51 and the light reflecting
thin film 15.
Embodiment 5
[0213] As shown in FIG. 18, a liquid crystal display device
according to EMBODIMENT 5 is structurally different from the
reflective liquid crystal display device according to EMBODIMENT 4
in that a thin film having a surface energy higher than that of the
photosensitive resin in the photosensitive resin layer 53
(hereinafter referred to as a thin film) 61 is used in place of the
metal film.
[0214] As shown in FIG. 19, the thin film 61 is configured as a
rectangular frame in plan view and has a surface energy higher than
that of the photosensitive resin layer 53. The thin film 61 is
configured as the rectangular frame such that a cavity formed in a
center portion thereof provides an electric connection between the
light reflecting thin film 15 and the drain electrode 51a.
Accordingly, the plan configuration of the thin film 61 is not
limited to the rectangular frame and may be a circle or an ellipse.
The reason that the thin film 61 has a surface energy higher than
that of the photosensitive resin layer 53 will be described
later.
[0215] As an example of the material of the thin film 61, a polymer
resin having a functional group containing a fluorine atom may be
listed.
[0216] A description will be given below to a method of fabricating
the liquid crystal device according to the present embodiment.
FIGS. 20 are cross-sectional views illustrating the process of
fabricating a reflector associated with the liquid crystal display
device.
[0217] First, a TFT 51, a metal interconnect, and the like are
formed on a substrate 11 by a conventionally known method. Then, as
shown in FIG. 20A, the thin film configured as a rectangular frame
is formed to have at least one part thereof overlapping a drain
electrode 51a of the TFT 51.
[0218] Next, a photosensitive resin material is coated on the
substrate 11 by spin coating (coating step) and the substrate 11
having a coating of the photosensitive resist material is then
pre-baked at 105.degree. C. for 90 seconds such that a solvent in
the coated film is evaporated, whereby the photosensitive resin
layer 16 is formed (see FIG. 20B), similarly to EMBODIMENT 1.
[0219] Next, as shown in FIG. 20C, a photomask 55 is positioned
above the photosensitive resin layer 16 and the photosensitive
resin layer 16 is exposed to UV light via the photomask 55
(exposing step).
[0220] Subsequently, development is performed by using, as a
developing solution, an aqueous solution containing 0.4% of
NMD-3.TM. (commercially available from Tokyo Ohka Kogyo Co., Ltd.)
(developing step). By the step, resist columns 17 and the residual
film 13b are formed on the substrate 11, while a contact hole 62 is
formed therein, as shown in FIG. 20D.
[0221] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 17 and the like at 120.degree. C.
for 5 minutes (heat treatment step), thereby forming the
photosensitive resin layer 53, as shown in FIG. 20E. During the
heat treatment, the inner walls of the contact hole 62 are also
thermally deformed and tend to clog the contact hole 62. However,
since the thin film 61 has a surface energy higher than that of the
photosensitive resin material, the inner walls are prevented from
flowing over to the thin film 61. This suppresses the clogging of
the contact hole 62 and a reduction in the opening portion of the
contact hole 62 and allows the formation of the contact hole 62
having a sufficient diameter to provide an electric connection
between the TFT 51 and the light reflecting thin film 15. As a
result, an increase in the contact resistance between the light
reflecting thin film 15 and the TFT 51 is suppressed.
[0222] Next, as shown in FIG. 20F, a post-baking step is performed
and aluminum is vapor-deposited on the photosensitive resin layer
53, whereby the light reflecting thin film 15 is formed
(light-reflecting-thin-film forming step).
[0223] Next, an alignment film 22 is formed on the light reflecting
thin film 15, similarly to EMBODIMENT 4. On the other hand, a
transparent electrode 23 is formed on a counter substrate 20 by a
conventionally known method and an alignment film 24 is formed on
the transparent electrode 23 in the same manner as described above.
Subsequently, the substrate 11 and the counter substrate 20 are
bonded to each other and a liquid crystal material or the like is
injected from a liquid crystal injection port to form a liquid
crystal layer 20. By the foregoing process, the reflective liquid
crystal display device according to the present embodiment can be
fabricated.
[0224] Thus, since the method of fabricating the reflective liquid
crystal display device according to the present embodiment can
suppress an increase in the contact resistance between the light
reflecting thin film 15 and the TFT 51, there can be fabricated a
reflective liquid crystal display device having a particularly high
display quality in a motion picture display.
[0225] In the present embodiment, a deep UV irradiating step for
further advancing the curing of the surrounding portion of the
inner wall surface of the contact hole 54 may also be performed
after the heat treatment step, similarly to EMBODIMENT 4. If the
post-baking step for heating the photosensitive resin layer 53 is
performed, therefore, the thermal deformation of the contact hole
54 is prevented and a more satisfactory electric connection is
provided between the TFT 51 and the light reflecting thin film
15.
[0226] Although the present embodiment has described the case where
the thin film 61 has a frame-like configuration, it is possible to
prevent the thermal deformation of the contact hole and provide an
electric connection between the drain electrode 51a and the light
reflecting thin film 15 even if a normal thin film which does not
have a frame-like configuration is used. Specifically, after the
photosensitive resin layer 53 is formed by the heat treatment step,
the thin film is decomposed and ashed by performing ashing using an
O.sub.2 asher or the like so that the thin film 61 is removed
appropriately. This further reduces the contact resistance and
allows fabrication of a reflective liquid crystal display device
having a remarkably high display quality.
Embodiment 6
[0227] A method of fabricating a reflective liquid crystal display
device according to EMBODIMENT 6 is for fabricating a reflective
liquid crystal display device having a contact hole formed into a
desired configuration by a deep UV method. FIG. 21 is a flow chart
illustrating the fabrication method.
[0228] First, a TFT 51, a metal interconnect, and the like are
formed on a substrate 11 (TFT forming step S1), similarly to
EMBODIMENT 4. Then, a photosensitive resin material is coated on
the substrate 11 (coating step S2) and the substrate 11 having a
coating of the photosensitive resin material is pre-baked at
105.degree. C. for 90 seconds (pre-baking step S3) such that a
solvent in the coated film is evaporated, whereby a photosensitive
resin layer 16 is formed.
[0229] Next, a photomask 55 is positioned above the photosensitive
resin layer 16 and the photosensitive resin layer 16 is exposed to
UV light via the photomask (exposing step S4). Subsequently,
development is performed by using, as a developing solution, an
aqueous solution containing 0.4% of NMD-3.TM. (commercially
available from Tokyo Ohka Kogyo Co., Ltd.) (developing step S5). By
the step, resist columns 17 and a residual film 13b are formed on
the substrate 11, while a contact hole 62 is formed therein.
[0230] At this stage, a deep UV irradiating step (S6) is performed
to further advance the curing of the surrounding portion of the
inner wall surface of the contact hole 54. Specifically, the
contact hole 62 is irradiated with UV light at a shorter wavelength
(in the range of 200 to 365 nm (i-line)) via a mask having an
opening corresponding to the contact hole 62. As a result,
cross-linking further proceeds to increase the degree of cure in
the portions irradiated with the UV light. In the irradiating step,
an electron beam at a shorter wavelength can also be used instead
of the UV light at a shorter wavelength.
[0231] Next, a heat treatment is performed by heating the substrate
11 formed with the resist columns 17 and the like at 120.degree. C.
for 5 minutes (heat treatment step S7), thereby forming the
photosensitive resin layer 53, as shown in FIG. 20E. Since
cross-linking has proceeded to a higher degree in the inner wall
surface of the contact hole 62 than in the other portion, the
degree of cure is higher so that the thermal deformation is less
likely to occur even in the heat treatment step. As a consequence,
the contact hole 62 has a sufficient diameter to provide an
electric connection between the TFT 51 and the light reflecting
thin film 15.
[0232] Further, a post-baking step (S8) is performed and aluminum
is vapor-deposited on the photosensitive resin layer 53, whereby
the light reflecting thin film 15 is formed
(light-reflecting-thin-film forming step S9).
[0233] Next, an alignment film 22 is formed on the light reflecting
thin film 15, similarly to EMBODIMENT 4. On the other hand, a
transparent electrode 23 is formed on a counter substrate 20 by a
conventionally known method and an alignment film 24 is formed on
the transparent electrode 23 in the same manner as described
above.
[0234] Subsequently, the substrate 11 and the counter substrate 20
are bonded to each other and a liquid crystal material or the like
is injected from a liquid crystal injection port to form a liquid
crystal layer 20. By the foregoing process, the reflective liquid
crystal display device according to the present embodiment can be
fabricated.
[0235] Thus, since the method of fabricating the reflective liquid
crystal display device according to the present embodiment can
suppress an increase in the contact resistance between the light
reflecting thin film 15 and the TFT 51, there can be fabricated a
reflective liquid crystal display device having a particularly high
display quality in a motion picture display.
[0236] In the present embodiment, a deep UV irradiating step for
further advancing the curing of the surrounding portion of the
inner wall surface of the contact hole 54 may also be performed
after the heat treatment step and prior to the post-baking step. As
a result, cross-linking further advances in the portions irradiated
with the UV light so that the degree of cure becomes higher than in
the other portion. By performing the post-baking step, therefore,
the thermal deformation of the contact hole 54 can be
prevented.
Others
[0237] Although the projecting and depressed structures (groups of
columnar portions or staircase structures) as the principal part of
the present invention has been described in each of the foregoing
embodiments, the size, material, shape, and relative arrangement
thereof are only for illustrative purposes and are not for the
purpose of limiting the scope of the invention thereto unless
otherwise specified.
[0238] For example, the form in which the groups of columnar
portions exist is not limited to those described in the individual
embodiments. The groups of columnar portions may also be embodied
in a form such that the individual columnar portions 13a are
separate from each other in the absence of the residual film 13b.
The group of columnar portions may also be embodied in a form such
that the columnar portion 13a are connected to each other with a
reduced level difference between the projecting and depressed
portions by adjusting the heating temperature higher in the heat
treatment step. In either case, the same operations and effects as
achieved in each of the embodiments are achievable.
[0239] Although each of the embodiments has described the case
where the plural groups of columnar portions or the plurality of
staircase structures are positioned irregularly in parallel
relation to each other, the present invention is not in the least
limited thereto and may be embodied in the foregoing form. That is,
the plural groups 12 of columnar portions may be arranged such that
the light reflecting thin film 15 has a projecting and depressed
surface configuration inclined toward the demarcation line P which
halves the display screen into the upper and lower parts, as shown
in FIG. 23. Alternatively, the plural groups 12 of columnar
portions may also be arranged such that the light reflecting thin
film 15 has a projecting and depressed surface configuration
inclined toward the center portion of the display screen, as shown
in FIG. 24.
[0240] Although each of the embodiment has described the case of
using the plurality of projecting and depressed structures which
are arranged irregularly, the present invention is not limited
thereto. For example, there may also be used a grating reflector
having projecting and depressed structures regularly arranged in a
concentric configuration, as shown in FIG. 25. Since the magnitude
of the slope angle, the slope angle distribution, and the
distribution density thereof can be controlled in accordance with
the present invention, there can be produced a grating reflector in
a color reproducible range.
[0241] Although each of the embodiments has described the reflector
provided with only one type of projecting and depressed structures,
the same operations and effects as achieved in each of the
embodiments are achievable even if plural types of projecting and
depressed structures in different configurations are provided.
[0242] The projecting and depressed structure as a basic unit may
also be configured as a diffraction grating. Specifically, the
projecting portions composing the projecting and depressed
structure may have, e.g., the same height measured from the
substrate and the same cross-sectional configuration. FIG. 26A is a
cross-sectional view showing the cross-sectional configurations of
the projecting portions when the projecting and depressed structure
is a diffraction grating. FIG. 26B is a plan view of a plurality of
projecting and depressed structures, each configured as a
diffraction grating. As shown in FIGS. 26A and 26B, projecting and
depressed structures 80 as basic units are arranged in a mosaic
pattern. The plan configuration and area of each of the projecting
and depressed structures 80 are random and the direction in which
periodicity is recognized (the direction in which the projecting
portions are arranged) is also random. Each of the projecting and
depressed structures 80 is a striped diffraction grating that has
been formed to have a size in the range of about 20 to 50 .mu.m.
Projecting portions 81 composing the projecting and depressed
structures 80 are composed of silicon nitride films 82 arranged
periodically and equidistantly. The pitch of the projecting
portions 81 is about 4 .mu.m and the respective heights thereof
measured from the substrate 11 are equally about 0.25 .mu.m. A
light reflecting film 83 is provided over the projecting portions
81. The light reflecting film 83 functions as a pixel electrode. By
thus forming the projecting and depressed structures as diffraction
gratings, it becomes possible to reduce regularly reflected light
by utilizing the phenomenon of diffraction and increase scattered
light even if flat portions exist between the projecting portions
81. If the number of process steps is to be reduced in the case
where the basic unit is composed of one projecting or depressed
portion, as in the conventional reflector, the flat portions are
formed between the projecting or depressed portions so that
regularly reflected light is increased. This leads to insufficient
brightness in a viewing angle direction so that a satisfactory
paper-white property is not obtained. In the foregoing structure,
the projecting portions 81 need not necessarily be arranged with a
strictly fixed period. If a disturbance in the period is smaller
than an average period, the effect of reducing regularly reflected
light is achievable, similarly to the above, by providing the
projecting and depressed structures 80 in which a plurality of
projecting portions 81 form a basic unit, though they are arranged
with a certain degree of irregularity. However, since coloring is
more likely to occur due to dependency on wavelength in the
phenomenon of diffraction as the periodicity of the projecting
portions 81 is higher, the occurrence of coloring should be
suppressed by rendering both the positions at which the projecting
and depressed structures 80 are scattered and the direction in
which periodicity is recognized or either one of the above. The
occurrence of coloring can also be suppressed by using projecting
and depressed structures composed of projecting portions 81 having
a different pitch in combination.
[0243] In accordance with the present invention, the reflector may
also be fabricated by forming the projecting portions composed of a
layer selected appropriately from a semiconductor layer, a metal
film, an insulating film, and the like, which compose a nonlinear
element, simultaneously with the formation of the nonlinear
element. Specifically, the reflector having a structure as shown in
FIG. 27 may be listed as an example. On the substrate 11 shown in
the drawing, a TFT 51 and a plurality of projecting portions 90 are
formed. The TFT 51 is composed of: a gate electrode 81; a gate
insulating film layer 92; an amorphous silicon (a-Si) layer 93a; a
semiconductor layer 93 composed of an n+a-Si layer 93b;
source/drain electrodes 94; and an insulating film layer 96
(corresponding to a protective film), which are formed on the
substrate 11 and are stacked in layers. The projecting portions 90
have been formed simultaneously with the formation of the TFT 51 by
patterning or like method. Each of the projecting portions 90
consists of the layer of the gate electrode 91' and the gate
insulating film layer 92. A plurality of pixel electrodes 95 having
a light reflecting property are provided over the projecting
portions 90. The pixel electrode 95 also has a flat portion at a
surface thereof. Since the projecting portions 90 are formed
simultaneously with the formation of the TFT 51, the reflector
having the foregoing structure can be fabricated in a smaller
number of process steps at lower fabrication cost.
[0244] As described above, since the reflectors in the first group
of the present invention are provided with the projecting and
depressed structures each composed of a plurality of projecting and
depressed portions to serve as a basic unit and having, e.g., at
least two projecting portions the top portions of which are at
different heights, they can be formed to have asymmetric
cross-sectional configurations and the slope angle distribution
thereof can be controlled precisely. This allows the surface of the
light reflecting thin film to scatter and reflect light in
directions within an anisotropic range, not in the regular
reflection direction, and provides bright reflection in directions
within a specified angular range. Even if the heights of the top
portions are uniform, light in the regular reflection direction can
be reduced by allowing the basic unit to function as the
diffraction grating, which increases scattering light in the
forward direction of the panel and provides bright display. As a
result, there is provided a reflector having satisfactory
reflecting properties including a superior paper-while property and
excellent controllability over the reflecting properties.
[0245] By providing the reflectors in the reflective liquid crystal
display devices in the first group of the invention, remarkably
bright display is achieved and display quality with a superior
contrast property is provided. Even if active matrix driving is
performed by providing a switching element, display quality
particularly high in a motion picture display is provided since a
contact hole for providing an electric connection between the
switching element and the pixel electrode is prevented from being
clogged and an increase in contact resistance is suppressed.
Second Group of the Invention
Embodiment 7
[0246] Referring to FIGS. 28 to 31, EMBODIMENT 7 of the present
invention will be described. FIG. 28 is an enlarged overhead view
of a platen used to fabricate a reflector in a method of
fabricating a liquid crystal display device according to the
present embodiment. FIGS. 29 are views illustrating the process
steps in accordance with the method of fabricating the display
device of the present invention.
[0247] First, a platen 105 shown in FIG. 28 was produced by cutting
aluminum to form a mold, stacking a low-melting glass and the mold,
and pressing the laminate. The platen 105 has a surface shaped
inversely to a shape to be obtained. Specifically, a large number
of depressed portions 101 each engraved in the form of a hexagonal
pyramid having 10-.mu.m sides are formed all over without clearance
in each of regions 102 corresponding to one pixel. The depressed
portions 101 are formed to have different depths and distributed
randomly. However, the angle .theta. (slope angle) formed between
an inclined surface of each of the depressed portions 101 and a
horizontal surface had been adjusted to the range of 4 to 16
degrees. This is because, if the slope angle is smaller than 4
degrees, scattering in the regular reflection direction increases.
Conversely, if the slope angle is larger than 16 degrees, the
disadvantages of an excessively enhanced scattering property and
insufficient brightness arise. The depressed portions having equal
slope angles are formed in equal numbers.
[0248] The platen 105 is also provided with projecting portions 103
each configured as a square prism for forming a contact hole in
each of pixel regions and with holes 104 for forming support
portions serving spacers. The projecting portions are provided at
respective corner portions of the regions 102 to correspond to the
drain electrodes of TFT elements, which will be described later.
The holes 104 are provided diagonally to the positions at which the
projecting portions 103 are formed. Each of the projecting portions
103 has a height of 3 .mu.m and a rectangular cross section having
8-.mu.m sides in a horizontal direction. Each of the holes 104 has
a depth of 5 .mu.m and has a rectangular opening configuration
having 15-.mu.m sides. FIG. 28A depicts only the depressed portions
101 each engraved in the form of a hexagonal pyramid in a part of
each of the regions 102 corresponding to one pixel, while omitting
the depiction of the depressed portions 101 in the other part
thereof.
[0249] Next, a pre-mold releasing treatment was performed in such a
manner that a monomolecular film 106 was formed on the surface of
the platen 105 formed with the depressed portions 101 each
configured as a hexagonal pyramid by chemically adsorbing a
fluorine-based silane coupler, whereby the wetting property of the
surface of the platen 105 was reduced.
[0250] On the other hand, an acrylic resin was coated by a roll
coater method on a substrate 108 made of glass and preliminarily
formed with a TFT element 107 to form a coated film 109 with a
thickness of 4 .mu.m (see FIG. 29A).
[0251] Subsequently, the platen 105 and the substrate 108 were
aligned and stacked such that the surface subjected to the pre-mold
releasing treatment faced the coated film 109 and then pressed
under a pressure of 0.3 atmospheres. The platen 105 and the
substrate 108 held under the pressure were irradiated with UV light
from the platen side, whereby the coated film 109 made of the
acrylic resin was cured. Thereafter, the platen 105 was peeled off
so that a polymer resin layer 113 having the contact hole 110, the
support portion 111 as a spacer, and the depressed portions 112
each configured as a hexagonal pyramid is formed for each pixel, as
shown in FIG. 29C. To ensure exposure of a surface of the drain
electrode 107a of the TFT element 107 at the bottom portion of the
contact hole 110, a surface layer portion of the entire polymer
resin layer 113 was scraped away by using an oxygen plasma asher by
a thickness of about 0.2 .mu.m.
[0252] Next, an aluminum film with a thickness of 0.3 .mu.m was
formed by sputtering on the substrate 108 comprising the polymer
resin layer 113 having a projecting and depressed surface that had
been formed by using the platen 105 as a shaper and patterned to
form a pixel electrode (reflecting film) 114. An alignment film 115
was further formed over the pixel electrode 114 by a conventionally
known method and subjected to a rubbing process.
[0253] On the other hand, a counter substrate 116 with transparency
was prepared and a transparent electrode 117 as a counter electrode
was formed on the counter substrate 116 by a conventionally known
method. Then, an alignment film 115 was formed over the transparent
electrode 117 by repeating the same step as described above and
subjected to a rubbing process.
[0254] Subsequently, a seal resin was coated on the peripheral
portion of the substrate 108 to have a frame-like configuration
having a cut-away portion corresponding to a liquid crystal
injection port. The counter substrate 116 and the substrate 108
were bonded to each other and pressed with the application of heat
such that the seal resin was cured. A liquid crystal was injected
from the liquid crystal injection port to form a liquid crystal
layer 120 as a light modulating layer, whereby a liquid crystal
panel was fabricated.
[0255] Since the fabrication method according to the present
embodiment has thus formed the depressed portion 101 by shaping, it
can be formed into a desired configuration in accordance with a
desired scattering property so that the configuration is controlled
with high flexibility. Moreover, the firming step is easy and
simple. Since the fabrication method according to the present
embodiment has formed the supporting portion 111 functioning as a
spacer integrally with the polymer resin layer 113 having a
projecting and depressed surface, the dispersive distribution of
spacers that has been performed conventionally is no more required.
This reduces the fabrication cost. In the case of controlling the
cell gap by using, e.g., spherical spacers, a uniform cell gap has
not necessarily been provided because of the projecting and
depressed surface of the alignment film 115 on the substrate 108.
However, when the spacer was formed integrally with the polymer
resin layer 113 as in the foregoing structure, the liquid crystal
layer 120 was formed uniformly to have a mean thickness of 5 .mu.m
for each pixel. In addition, the scattering property of the
reflective film (pixel electrode 114) was such that light incident
at an angle of 30 degrees was reflected to have a constant
intensity within a range subtending an angle of about 25 degrees in
each of forward, rearward, leftward, and rightward directions about
the front side of the panel and the reflected light gave the sense
of whiteness to both eyes. Moreover, brightness obtained was
several-fold or more higher than the brightness of white paper so
that an excellent paper-white property was recognized.
[0256] At this stage, a 1/4 wave plate 118 was provided externally
of the counter substrate 116 and a polarizer 119 was provided
externally of the 1/4 wave plate 118, whereby the reflective liquid
crystal display device was fabricated (see FIG. 30). When the
reflective liquid crystal display device was driven, a screen
displayed was bright and high in whiteness. This proved that the
liquid crystal display device fabricated by the fabrication method
according to the present embodiment had a high display quality.
[0257] Although the present embodiment has described the case where
the polymer resin layer 113 formed on the substrate 108 was molded
by shaping, the present invention is not in the least limited
thereto. It is also possible to provide, as spacers, projecting and
depressed portions and the like by, e.g., directly molding a
surface of a plastic substrate made of a resin. If a UV
polymerizable acrylic resin is used to compose the plastic resin,
e.g., molding can be performed in the same manner as described
above. If a thermoplastic material such as polycarbonate or
polyethersulfone is used, heating is performed appropriately during
press molding. In the case of using the plastic substrate, the step
of smoothing a surface of the substrate by pressing a platen with
excellent flatness against the surface has been performed in the
conventional process of producing the substrate. However, since the
present invention allows the support portions as spacers and the
projecting and depressed portions to be formed simultaneously with
the production of the substrate, the number of steps can be reduced
and lower cost is achieved.
[0258] It is also possible to laminate a resin film preliminarily
provided with support portions as spacers and projecting and
depressed portions on a substrate. Specifically, a base film (mold)
121 made of PET (polyethylene terephthalate) and having a thickness
of 100 .mu.m is molded by thermally pressing, against the base film
121, a metal roll 122 engraved with projecting and depressed
portions for molding the projecting and depressed portions and the
support portions for spacers, so that desired projecting and
depressed portions are formed in the surface of the base film 121,
as shown in FIG. 31A. Subsequently, a resist resin film 123 is
coated on the base film 121 by a roll coater method. The thickness
of the coated film is adjusted to, e.g., about several micrometers
to several tens of micrometers, whereby a laminated film resist 124
is produced (FIG. 31B). The film resist 124 is further laminated on
the substrate 108 formed with the TFT element 107 and the base film
121 is peeled off. As a result, the resist resin film 123 shaped by
the base film 121 is formed on the substrate 108, as shown in FIG.
31C. A contact hole for providing an electric connection between
the drain electrode 107a of the TFT element 107 and the pixel
electrode formed as a reflective film on the resist resin film 123
is formed by a photolithographic process. By thus forming a resin
film by another process, the breakage of the substrate due to
defective molding, which might occur if the projecting and
depressed portions were formed above the substrate by shaping, is
prevented and the production yield is improved. In addition, the
process of molding the resist film can be performed in a shorter
period of time than the process of performing molding above the
substrate by shaping, so that lower cost is achieved.
Embodiment 8
[0259] A method of fabricating a reflective display device
according to the present embodiment is different from the
fabrication method according to EMBODIMENT 7 in that the polymer
resin layer 113 is formed by photolithography. By using a
photolithographic method, the present embodiment has obviated the
necessity for various manufacturing apparatus that have been
necessary to perform molding in EMBODIMENT 7. Since these
manufacturing apparatus are not used in the process of fabricating
a normal liquid crystal display device, the present embodiment can
achieve lower fabrication cost.
[0260] The method of fabricating the reflective display device
according to the present embodiment will be described in detail.
FIG. 32 is a schematic plan view of a photomask used to form the
polymer resin layer 113.
[0261] First, a negative photoresist (under the trade name OMR85,
which is commercially available from Tokyo Ohka Kogyo Co., Ltd.)
was coated on a substrate formed with a TFT element, an
interconnect, and the like by spin coating. The thickness of a
resist film formed by coating was adjusted to 3.0 .mu.m.
[0262] Next, the resist film was exposed to UV light with an
exposure energy of 20 mJ/cm.sup.2 via the photomask.
[0263] Since a plurality of depressed portions, each configured as
a hexagonal pyramid, are formed in the individual pixel regions 102
as shown in FIG. 32, the photomask is provided with a light
shielding pattern having a plurality of hexagonal halftone dot
patterns formed therein. The hexagonal halftone dot patterns are
such that the density of halftone dots distributed in a hexagon 130
increases gradually with approach toward the center portion
thereof. Accordingly, transmittance decreases gradually with
approach toward the center portion of the hexagon 130. This enables
halftone representation, which cannot be implemented with a
conventional mask. Each of halftone dots composing the halftone dot
patterns is a 1.0-.mu.m rectangular window. By varying the
densities of the halftone dots distributed in the individual
hexagons 130, transmittances at the respective center portions of
the hexagons 130 are varied The hexagon 130 has a side of, e.g.,
about several tens of micrometers. A rectangular light shielding
window (a light shielding portion) 131 is also provided in each
region corresponding to a pixel region.
[0264] The exposure was performed by using a mirror projection
aligner (exposing device), thereby rending the portion exposed to
UV light undissolvable. By further performing development (for a
development time of 60 seconds), the plurality of depressed
portions each configured as a hexagonal pyramid and the contact
hole were formed.
[0265] The resolution of the negative photoresist OMR85 was about 4
.mu.m and the resolution of the mirror projection aligner was 1 to
2 .mu.m. It follows therefore that a resolution limit when exposure
is performed by using the resist and the exposing device in
combination is about 4 .mu.m. However, since the present embodiment
has used the photomask having the 1-.mu.m halftone dot patterns,
geometries smaller than the resolution limit can be defined.
Accordingly, the projecting portion having a gently inclined
surface can be formed. Actually, the portion other than the light
shielding portion 131 is entirely filled with the hexagonal
halftone dot patterns, though they are not depicted in FIG. 32.
[0266] Subsequently, the developed resist film was sintered at a
specified temperature and the pixel electrode as the reflective
film made of aluminum was formed on the resist film and patterned.
After the alignment film was formed on the pixel electrode, a
rubbing process was performed with respect to the alignment
film.
[0267] On the other hand, the counter substrate 116 was prepared,
similarly to EMBODIMENT 7. The transparent electrode and the
alignment film were formed successively on the counter substrate
116 and a rubbing process was performed with respect to the
alignment film.
[0268] Subsequently, spacers were scattered over the substrate, a
seal resin was coated on the substrate, and a panel was assembled
by bonding the counter substrate and the substrate to each other,
similarly to EMBODIMENT 7. After injecting a liquid crystal into
the panel, the 1/4 wave plate and the polarizer were provided
successively externally of the counter substrate, whereby the
reflective liquid crystal display device according to the present
embodiment was fabricated. As a result of examining the display
properties of the liquid crystal display device, it was proved that
the intensity of reflected light when viewed from a position
adjacent the front of the panel was constant and a superior display
quality with high whiteness was obtained.
[0269] Thus, since the method of fabricating the reflective display
device according to the present embodiment has used the photomask
having a shielding pattern composed of the minute halftone dot
patterns, a minute surface configuration can be controlled, which
has been impossible with a conventional chromium mask. It is also
possible to easily control the projecting and depressed
configuration by varying the pattern configuration of the halftone
dot patterns. Since it is sufficient to use conventional equipment
including an exposing device, a conventional material, and the
like, there is no need to introduce new equipment and the like.
Others
[0270] Although the reflective liquid crystal display devices have
been described in EMBODIMENTS 7 and 8, the present invention is not
in the least limited thereto. The present invention is applicable
to any device provided that it is a light-receiving device which
requires a scattering reflective film and uniform layer
formation.
[0271] Although EMBODIMENTS 7 and 8 have described the cases where
the depressed portions are configured as hexagonal pyramids, the
present invention is not limited thereto. The depressed portions
may have pyramidal or conical configurations. Preferably, the slope
angle is in the range of 4 to 16 degrees. In the case of a
pyramidal configuration, the slope angle is defined as the angle
formed between a horizontal surface and an inclined surface. In the
case of a conical configuration, the slope angle is defined as the
angle formed between a horizontal surface and a generating
line.
[0272] Thus, in the second group of the invention, the projecting
and depressed portions of the reflector can be formed in a
precisely controlled configuration since the projecting and
depressed portions are molded by shaping. This reduces reflection
in the regular reflection direction and provides a reflective
display device with superior brightness and superior whiteness.
Since the projecting and depressed portions and the support
portions as spacers are formed integrally, there can be provided a
reflective display device with a uniform cell gap and reduced
uneven display and a fabrication method therefor.
[0273] In the second group of the invention, the projecting and
depressed portions are formed by using the photomask having a
shielding pattern composed of halftone dots smaller than the
respective resolution limits of the exposing device and the
photosensitive resin layer. As a result, projecting and depressed
portions having gently curved configurations can be formed and the
configuration can be controlled properly. This allows light
incident from an arbitrary direction to be scattered and reflected
in the forward direction of the reflective display device, not in
the regular reflection direction, and thereby provides a reflective
display device capable of displaying an image with excellent
whiteness and a fabrication method therefor.
[0274] While the specific embodiments have been described in
detail, such description is strictly for the purpose of clarifying
the art of the present invention. It is to be understood that
present invention is not construed as limited to the specific
embodiments and various changes and modifications may be made in
practicing the invention without departing from the spirit thereof
and the scope of the following claims.
* * * * *