Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-11-13
2003-05-06
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000
Reexamination Certificate
active
06559917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective type liquid crystal display device, and more particularly, to a pattern formation method for forming an underlying insulating film and simplification of manufacturing process of a reflective electrode with ruggedness on its surface by utilizing the pattern formation method.
2. Description of the Prior Art
Japanese Published Unexamined Patent Application No. Hei 2000-171794 discloses a technology for simplifying the manufacturing process of a reflective type liquid crystal display device having configuration that a reflective electrode is disposed on the side of a liquid crystal in which an underlying pattern for forming the ruggedness of a reflective electrode and a contact hole pattern are formed simultaneously by one-time exposure by using a monolayer positive photosensitive resin.
FIG. 1
is a plan view of a conventional reflective type liquid crystal display device having the same type of TFT substrate as that of the reflective type liquid crystal display device described in the foregoing publication when viewing the TFT substrate from the side of the liquid crystal.
FIG. 2
is a cross sectional view when the TFT substrate, the liquid crystal, and a CF (Color Filter) substrate are cut along a plane through a cut line A-A′ of FIG.
1
and orthogonal to the TFT substrate.
The configuration of the reflective type liquid crystal display device will be described below in accordance with the manufacturing process of the reflective type liquid crystal display device.
First, on a first substrate
1
made of materials such as glass, a first bus wiring
2
also serving as a gate electrode
22
is formed, and subsequently, a first insulating film
3
also serving as a gate insulating film is formed. On the first insulating film
3
, a semiconductor region
4
constituting an active layer of TFT is formed, being located above the gate electrode
22
. Furthermore, on the first insulating film
3
, a second bus wiring
5
connected to one end of the semiconductor region
4
and a drain electrode
25
connected to the other end of the semiconductor region
4
are formed.
Then, a protective insulating film
6
is formed on the first insulating film
3
so as to cover the second bus wiring
5
and the drain electrode
25
. A part of the protective insulating film
6
is removed to form an opening
7
for ensuring connection to the drain electrode
25
.
Subsequently, aluminum is deposited on the protective insulating film
6
and patterned to form a reflective electrode
8
in a region excluding the first bus wiring
2
, the second bus wiring
5
, and a TFT region, thereby forming a TFT substrate
100
. In this case, although the reflective electrode
8
does not cover the TFT region, the reflective electrode
8
may cover the TFT region.
Then, on one surface of a second substrate
31
made of materials such as glass, color filters
41
,
42
, and
43
are formed so as to face the reflective electrode
8
of the TFT substrate
20
. Subsequently, a transparent electrode
44
is formed so as to cover the color filter
41
. Finally, on the opposite surface of the second substrate
31
, a polarizer
46
is formed, thereby forming a CF substrate
40
.
Thus obtained TFT substrate
20
and CF substrate
40
are processed in the following manner. That is, the uppermost surface on the TFT side of the TFT substrate
20
and the uppermost surface on the color filter side of the CF substrate
40
are printed with an alignment layer material by using offset printing method or the like, thereby completing the formation of the TFT substrate
20
and the CF substrate
40
.
Finally, the respective alignment layer materials of the TFT substrate
20
and the CF substrate
40
are subjected to a rubbing process to form alignment layers
9
. Then, a cell gap material (not shown) is interposed between the two substrates so that the two substrates are disposed so as to have a predetermined space from each other followed by the injection of a liquid crystal
10
into the space.
Japanese Published Unexamined Patent Application No. Hei 2000-171794 described above has its feature in the method for manufacturing the underlying pattern formed under the reflective electrode
8
, in which the reflective electrode
8
on the side of the TFT substrate
20
is formed in rugged shape. Therefore, a description will be performed focusing on the manufacturing process of the underlying pattern.
FIGS. 3A
to
3
C and
FIGS. 4A
to
4
C are cross sectional views of the TFT substrate in the manufacturing process, taken along a cut line B-B′ of FIG.
1
.
First, the gate electrode
22
and the first bus wiring
2
, the first insulating film
3
, the semiconductor region
4
, and the second bus wiring
5
and the drain electrode
25
are successively formed on the first substrate
1
. Thereafter, on the first insulating film
3
on which the second bus wiring
5
and the drain electrode
25
have been formed, a positive photosensitive resin
81
is coated (FIG.
3
A). Then, the photosensitive resin
81
is exposed at a low illuminance by using a photomask
75
in which light-shielding portions
85
have been patterned (FIG.
3
B). Subsequently, the photosensitive resin
81
is further exposed at a high illuminance by using a photomask
76
having a different pattern from that of the photomask
75
, in which light-shielding portions
86
have been patterned (FIG.
3
C). Thereafter, upon development of the photosensitive resin
81
, an opening
82
and concave portions
83
are formed in the photosensitive resin
81
(FIG.
4
A).
Then, the photosensitive resin
81
thus formed is heated, so that the photosensitive resin
81
undergoes thermal fluidity and is changed into a deformed resin
91
. Furthermore, the opening
82
and the concave portions
83
are changed into a contact hole
7
having a smaller opening area than that of the opening
82
and concave portions
93
each having a smoother angle than that of each concave portion
83
, respectively (FIG.
4
B).
Then, on the deformed resin
91
in which the contact hole
7
has been formed, aluminum is deposited and patterned so that aluminum is left in the region excluding the first bus wiring
2
, the second bus wiring
5
, and the TFT region, thereby forming the reflective electrode
8
and the TFT substrate
20
(
FIG. 4C
) Thereafter, the manufacturing steps in accordance with the manufacturing method already described are performed to complete a reflective type liquid crystal display device.
However, in the method for manufacturing a reflective electrode shown in
FIGS. 3A
to
3
C and
FIGS. 4A
to
4
C, the concave portions
83
are formed in the photosensitive resin
81
by exposure. The exposure condition at this step is critical, that is, the tolerance of the amount of light exposure, which is allowed to ensure the minimum thickness of the photosensitive resin film after development thereof is small. Therefore, there arises a problem that the film thickness of the photosensitive resin at the concave portions
83
is not uniform. Furthermore, an exposure process having a long process time has to be performed twice, thereby elongating the overall manufacturing process period.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for manufacturing a reflective type liquid crystal display device having an underlying film on which a reflective electrode is easily formed followed by the capability of providing good reflection characteristics.
A pattern formation method of the present invention includes, as its basic construction, the steps of:
forming an organic insulating film on a substrate, and opening predetermined regions of said organic insulating film to form first openings and second openings in the organic insulating film, the first openings being formed for forming contact holes in the organic insulating film, and the second openings each being a smaller opening area than that of each of the first openings and opened to a de
Kim Robert H.
Rude Timothy L
Sughrue & Mion, PLLC
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