Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-14
2004-08-24
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S005000
Reexamination Certificate
active
06781650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for producing the same. More particularly, it relates to a reflection-type liquid crystal light valve for a liquid crystal projection display device.
2. Description of the Related Art
Recently, a super high definition active matrix projection LCD (liquid crystal display) has attracted widespread attention for its ability to meet high definition and large-screen display requirements and its potential to replace CRTs (cathode ray tubes). Generally, an active matrix LCD comprises: a semiconductor substrate on which switching elements and display electrodes connected to the switching elements are formed; and a counter substrate on which counter electrodes are formed above the semiconductor substrate, where a liquid crystal fills the region between the semiconductor substrate and the counter substrate (the cell gap).
A projection LCD device comprises a light source, a light valve, a screen, an optical filter, and a projection lens. There are two types of light valves which are used for the LCD device. One is a transmission-type liquid crystal light valve for projecting an image on a screen by letting in the light from the light source, and the other is a reflection-type liquid crystal light valve for projecting an image on the screen by reflecting the light from the light source.
FIG. 11
is a schematic sectional view of one example of a reflection-type liquid crystal light valve. As shown in
FIG. 11
, the reflection-type liquid crystal light valve
200
has: a transistor
204
formed in a semiconductor substrate
202
; a counter substrate
206
provided on a light-incident side; a plurality of light-reflecting films
210
connected electrically to the semiconductor substrate with a space
208
therebetween; and liquid crystal
212
filled in a cell gap between the light-reflecting films and the counter substrate. Over the transistor
204
, a light-reflecting film
210
which acts as a reflecting electrode is formed on an interlayer insulating layer
214
and the like. The liquid crystal
212
is filled in a cell gap between these light-reflecting films
210
(which films act as reflecting electrodes), and the counter substrate
206
consisting of a counter electrode
216
and a glass cover plate
218
. The light-reflecting films
210
which act as reflecting electrodes are formed for each pixel region including each transistor
204
. Between mutually adjacent light-reflecting films
210
, a space
208
is formed. In such a liquid crystal light valve, a voltage between the light-reflecting films
210
and the counter electrode
216
is controlled in accordance with a display signal, and thereby an array of the liquid crystal
212
placed therebetween is properly controlled.
In the case of a reflection-type liquid crystal light valve, incident light passes through the space between the reflecting electrodes and is transmitted into the interlayer insulating layer, and then propagates through the interlayer insulating layer by multipath reflections. When this light comes near the transistor, it causes a leakage current as a result of the photoconductive effect, and thus degrades the contrast of the LCD. The photoconductive effect becomes more pronounced as the patterning of pixels becomes finer. Therefore, like the LCD light valve
200
shown in
FIG. 11
, a liquid crystal light valve is generally provided with a light-blocking layer
220
and an insulating layer
222
formed on the light-blocking layer
220
in order to avoid the above-mentioned photoconductive effect and to block the incident light.
In various steps of forming the above-mentioned semiconductor substrate, residual reactive products generated in the deposition process used, such as a CVD (Chemical Vapor Deposition) process, and foreign particles such as metal powders and organic pieces generated in the course of the operation of an apparatus, may all be left and deposited in the apparatus, adhering to the surface of the substrate. For example, foreign particles may be generated during a photolithographic process and adhere to a surface of a resist layer or a metal layer. FIG.
12
(
a
) shows a case where a foreign particle
230
adheres to an insulating layer
214
in the liquid crystal light valve. If the light-blocking layer
220
is formed on the insulating layer
214
with a foreign particle thereon, a protrusion is formed on its surface as shown in FIG.
12
(
b
), and thus the smoothness of the surface is spoiled. As a result, the insulating layer
222
formed on the light-blocking layer
220
is substantially thinned near the foreign particle, and therefore insulation between the light-blocking layer
220
and the reflecting electrode
210
cannot be assured.
However, there is a method to keep the insulation. In that method, after the light-blocking layer
220
is formed, the protrusion including a foreign particle is removed by a physical method such as CMP (chemical mechanical polish) to flatten the surface of the light-blocking layer
220
, and then the insulating layer
222
is formed on the light-blocking layer
220
, as shown in FIG.
12
(
c
).
However, since the light-blocking layer itself is also removed by this method, an underlying transistor fails to work properly due to incident light, and thus pixel failure occurs. More specifically, since the light shield and light-reflecting electrode are formed almost all over the semiconductor substrate, the foreign particle causes a short circuit between the light-blocking layer and a reflecting electrode or light leakage causes the malfunction of a transistor, which leads to the pixel failure.
Published Japanese Patent Application No. 8-328034 discloses a liquid crystal light valve comprising a plurality of light-blocking layers to inhibit a leakage current due to the photoconductive effect. For example, as shown in
FIG. 13
, two metal layers
304
and
306
are formed by sandwiching the insulating layer
222
therebetween, so that they can shield the surface of the semiconductor substrate from the light incident from a space
208
between the reflecting electrodes
210
. These metal layers
304
and
306
are each provided with a slit
308
. Since these slits
308
are staggered, the incident light is reflected by either of metal layers
304
or
306
, so that it cannot reach the semiconductor substrate.
As the number of light-blocking layers such as metal layers
304
and
306
increases, more shielding effects are produced. However, since a step of forming the metal layer
304
or
306
has to be repeated, the process becomes more complicated and increases in number, which leads to higher manufacturing costs.
Published Japanese Patent Application No. 9-33952 discloses a liquid crystal light valve
400
shown in
FIG. 14
, which can solve the above problems. In this liquid crystal light valve
400
, the space
402
between the light-reflecting films
210
(reflecting electrodes) are filled with a light-blocking insulating layer
404
consisting of two color resists selected from red, blue, and green. The light of wavelengths in a specific region may pass though the space
402
between the light-reflecting films
210
, however, the light is completely blocked by the light-blocking insulation layer
404
before it reaches an MOS (Metal Oxide Semiconductor) transistor and thus the leakage current can be prevented. The light-reflecting films
210
of the liquid crystal light valve described in the above patent application should be thick enough to form two colored resist layers of uniform thickness, however, it may often cause a problem in terms of the formation of thinner layers.
Moreover, as the demand for higher definition and higher production efficiency increases, the simplification of processes, the reduction of power consumption of pixels, and high-speed operation are always required in the process of forming a liquid crystal light valve.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to pro
Colgan Evan George
Shinohara Masami
Uda Mitsuru
Akkapeddi P. R.
International Business Machines - Corporation
Kim Robert H.
Trepp Robert M.
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