Liquid crystal display device and method of compensating for a defect

A liquid crystal display device and a method of compensating for a luminance point defect of the liquid crystal display device. After a detective luminance point pixel is detected, a laser beam is irradiated from an excimer laser oscillator on a portion of a surface of one of glass substrates of a liquid crystal panel on which an illuminating light is incident, the portion being located on the same irradiation path of the illuminating light with the luminance point pixel. In this way, the portion is laseretched, thereby forming a rough surface in the portion. When such a panel is used in a projection device, the light transmitted through the luminance point pixel is scattered and so reduced. Accordingly, the defective luminance point pixel is inconspicuous to normal pixels around the defective luminance point pixel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a liquid crystal display device comprising 
a transmission liquid crystal panel including a liquid crystal enclosed 
between a pair of transparent substrates and display pixels arranged in a 
matrix and a light source for irradiating an illuminating display light 
from a back of the transmission liquid crystal panel, and to a method of 
compensating for a luminance point defect of the transmission liquid 
crystal panel of the liquid crystal display device. 
2. Description of the Prior Art 
An example of this type of liquid crystal display device includes an 
active-matrix drive liquid crystal panel used for a projection device. 
This panel comprises a pair of glass substrates laminated to each other. 
One of the glass substrates has pixel electrodes arranged in a matrix on 
an inner surface thereof, and the pixel electrodes are connected to TFTS 
(thin film transistors). The pixel electrodes are selected by switching 
the TFTS, thereby displaying an image. In this construction, since no 
cross talk is generated as is generated in a simple matrix panel, a high 
quality display is realized. 
The TFT has a multiple layer construction, in which a gate electrode, a 
source electrode, a drain electrode and the like are laminated on the 
glass substrate. The production procedure of the TFT is a repetition of 
the step of laminating such thin metal films on the glass substrate and 
the step of patterning the thin metal films by the use of a pattern mask. 
Accordingly, the production of a perfect TFT requires a great amount of 
effort to maintain and control various conditions in the production 
procedure. 
It sometimes occurs that a defective TFT without normal TFT characteristics 
is produced. A defect which can be rectified is rectified in accordance 
with the type and the degree of the defect by the use of the appropriate 
rectifying technology. An example of a TFT defect is a luminance point 
defect, which is impossible to rectify on a circuit pattern and is 
recognized, for example, on a display screen in the form of a luminance 
point generated on pixels in correspondence with the pixel electrodes when 
the display screen is driven. 
FIGS. 26 and 27 illustrate a conventional method of compensating for the 
luminance defect. An opaque shading film 206 is formed on a portion of a 
surface of a glass substrate 202, the portion being in correspondence with 
a luminance point pixel 205 of a liquid crystal panel 201. A light emitted 
from a light source (not shown) and incident on the luminance point pixel 
205 is reduced by the opaque shading film 206, thereby making the 
luminance point pixel 205 inconspicuous. 
Selected as the portion on which the opaque shading film 206 is formed, 
namely, a luminance point defect compensation area, is a portion through 
which the light from the light source is irradiated on the luminance point 
pixel 205. More practically, among irradiation paths of the light which is 
emitted from the light source, incident on the panel 201 through a 
condenser lens 207 and converged to a projecting lens 208, an irradiation 
path A passing through the luminance point pixel 205 passes through the 
compensation portion. FIG. 27 schematically shows that the luminance point 
pixel 205 and the opaque shading film 206 are on the same irradiation 
path. Among a pair of glass substrates 202 and 227, the glass substrate 
202 is the one on which the light is incident. A liquid crystal as a 
display medium is enclosed between the glass substrates 202 and 227. 
The opaque shading film 206 is formed in the following way: An 
ultraviolet-ray hardened resin ink is put on a fine curved surface at a 
tip of a marking needle and is transferred to the compensation area. Then, 
the ink is hardened by irradiating an ultraviolet ray, whereby the ink is 
adhered on the surface of the glass substrate 202. The opaque shading film 
206 is extremely fine, although different in size depending on the type of 
the liquid crystal panel: the diameter is approximately 100 to 250 .mu.m 
and the thickness is approximately 10 .mu.m. 
The above conventional method is limited in eliminating affects of the 
luminance point defect due to the following disadvantages: 
(1) Since the opaque shading film 206 does not have an enough adhering 
force to the smooth glass substrate 202, the opaque shading film 206 is 
possibly peeled off from the glass substrate 202 or damaged when dust or 
the like is wiped off from the, glass substrate 202. Accordingly, it is 
poor in reliability. 
(2) Since the opaque shading film 206 shutters the light almost perfectly, 
the opaque shading film 206 is recognized as a black point with the human 
eye when an image brightens the display screen. Accordingly, the 
compensation area is restricted within an end portion of the display 
screen. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a liquid crystal 
display device and a method of compensating for a luminance point defect 
of a liquid crystal panel of the liquid crystal display device for 
improving the reliability of compensation for a luminance point defect and 
for eliminating the inconvenience of a luminance point defect compensation 
area being restricted. 
Another object of the present invention is to provide a liquid crystal 
display device and a method of compensating for a luminance point defect 
of a liquid crystal panel of the liquid crystal display device for further 
improving an effect of reducing an illuminating light transmitted through 
a luminance point pixel and thus further improving an effect of a 
luminance point defect compensation. 
Still another object of the present invention is to provide a liquid 
crystal display device and a method of compensating for a luminance point 
defect of a liquid crystal panel of the liquid crystal display device 
which can be applied as a direct vision liquid crystal display device. 
Still another object of the present invention is to provide a method of 
compensating for a luminance point defect of a liquid crystal panel of the 
liquid crystal display device, by which surface-roughening is conducted 
easily and a highly precise rough surface can be formed without damaging a 
precise shape of a glass substrate including a concave portion. 
In the liquid crystal display device of this invention, which overcomes the 
above-discussed and numerous other disadvantages and deficiencies of the 
prior art, a processed concave portion is formed in a portion in the 
vicinity of a surface of one of transparent substrates on which an 
illuminating light is incident, the portion being located on an 
irradiation path of the illuminating light irradiated on a luminance point 
pixel having a luminance point defect, and the processed concave portion 
has a bottom which is rough so as to have a light scattering 
characteristic. 
In a preferred embodiment of the invention, the bottom of the processed 
concave portion comprises deep steps and shallow steps arranged 
alternately. 
In a preferred embodiment of the invention, the processed concave portion 
is formed to be narrower at the bottom thereof than at an upper opening 
thereof, and a side wall and the bottom of the processed concave portion 
are rough so as to have the light scattering characteristic. 
In a preferred embodiment of the invention, the wall has a sawtooth-like 
roughness and the bottom has a mesh-like roughness. 
In a preferred embodiment of the invention, the bottom of the processed 
concave portion is formed to have better light scattering characteristic 
at a central portion thereof than an ambient portion thereof. 
In a preferred embodiment of the invention, the central portion of the 
bottom has a mesh-like roughness. 
In a preferred embodiment of the invention, the central portion of the 
bottom has another processed concave portion which is deeper than the 
ambient portion and is narrower at a bottom thereof than at an upper 
opening thereof. 
Alternatively, in the liquid crystal display device, a processed concave 
portion is formed in a portion in the vicinity of a surface of one of 
transparent substrates on which an illuminating light is incident, the 
portion being located on an irradiation path of the illuminating light 
irradiated on a luminance point pixel having a luminance point defect, and 
the processed concave portion has a bottom which is deep so as to be close 
to the luminance point pixel and is rough so as to have a light scattering 
characteristic. 
In a preferred embodiment of the invention, the processed concave portion 
having the bottom which is rough so as to have a light scattering 
characteristic is formed by the use of an excimer laser beam. 
Alternatively, in the liquid crystal display device, a processed concave 
portion is formed in a portion in the vicinity of a surface of one of the 
transparent substrates from which the illuminating light is outgoing, the 
portion being located on an irradiation path of the illuminating light 
irradiated on a luminance point pixel having a luminance point defect, and 
the processed concave portion has a bottom which is rough so as to have a 
luminance reducing effect. 
In a preferred embodiment of the invention, the bottom of the processed 
concave portion comprises deep steps and shallow steps arranged 
alternately. 
In a preferred embodiment of the invention, the bottom of the processed 
concave portion is formed to have a more excellent light scattering 
characteristic at a central portion thereof than an ambient portion 
thereof. 
In a preferred embodiment of the invention, the central portion of the 
bottom has a-mesh-like roughness. 
Alternatively, the method of compensating for a defect of a liquid crystal 
display device of this invention, which overcomes the above-discussed and 
numerous other disadvantages and deficiencies of the prior art, comprises 
the steps of: detecting a luminance point defect by irradiating an 
illuminating light on a transmission liquid crystal display panel; forming 
a processed concave portion in a portion in the vicinity of a surface of 
one of transparent substrates on which the illuminating light is incident, 
the portion being located on an irradiation path of the illuminating light 
irradiated on a luminance point pixel having a luminance point defect; and 
forming a rough surface having a light scattering area by 
surfaceroughening a bottom of the processed concave portion. 
In a preferred embodiment of the invention, the method further comprises a 
step of forming deep steps and shallow steps arranged alternately on the 
bottom of the processed concave portion. 
Alternatively, the method of compensating for a defect of a liquid crystal 
display device of this invention, which overcomes the above-discussed and 
numerous other disadvantages and deficiencies of the prior art, comprises 
the steps of: detecting a luminance point defect by irradiating an 
illuminating light on a transmission liquid crystal display panel; forming 
a processed concave portion which is narrower at a bottom thereof than an 
upper opening thereof in a portion in the vicinity of a surface of one of 
transparent substrates on which the illuminating light is incident, the 
portion being located on an irradiation path of the illuminating light 
irradiated on a luminance point pixel having a luminance point defect; and 
forming a light scattering area by surface-roughening a wall and the 
bottom of the processed concave portion. 
In a preferred embodiment of the invention, the wall is surface-roughened 
to be sawtooth-like and the bottom is surface-roughened to be mesh-like. 
Alternatively, the method of compensating for a defect of a liquid crystal 
display device of this invention, which overcomes the above-discussed and 
numerous other disadvantages and deficiencies of the prior art, comprises 
the steps of: detecting a luminance point defect by irradiating an 
illuminating light on a transmission liquid crystal display panel; forming 
a processed concave portion which has a rough bottom having a light 
scattering characteristic by surfaceroughening a portion in the vicinity 
of a surface of one of transparent substrates on which the illuminating 
light is incident, the portion being located on an irradiation path of the 
illuminating light irradiated on a luminance point pixel having a 
luminance point defect; and forming another processed concave portion at a 
central portion of the rough bottom of the processed concave portion, the 
forming another processed concave portion being deeper than the rough 
surface. 
Alternatively, the method of compensating for a defect of a liquid crystal 
display device of this invention, which overcomes the above-discussed and 
numerous other disadvantages and deficiencies of the prior art, comprises 
the steps of: detecting a luminance point defect by irradiating an 
illuminating light on a transmission liquid crystal display panel; and 
forming a processed concave portion having a bottom which is close to a 
luminance point pixel having a luminance point defect and which is rough 
so as to have a light scattering characteristic by surfaceroughening a 
portion in the vicinity of a surface of one of transparent substrates on 
which the illuminating light is incident, the portion being located on an 
irradiation path of the illuminating light irradiated on the luminance 
point pixel. 
In a preferred embodiment of the invention, the portion is 
surface-roughened by way of laser etching by the use of an excimer laser 
beam. 
In a preferred embodiment of the invention, the excimer laser beam is 
irradiated on the a defect compensation area by way of 
reduction-slit-exposure through a slit pattern having a slit of an 
enlarged shape of an outline of the defect compensation area. 
Alternatively, the method of compensating for a defect of a liquid crystal 
display device of this invention, which overcomes the above-discussed and 
numerous other disadvantages and deficiencies of the prior art, comprises 
the steps of: detecting a luminance point defect by irradiating an 
illuminating light on a transmission liquid crystal display panel; and 
forming a processed concave portion in a portion in the vicinity of a 
surface of one of transparent substrates from which the illuminating light 
is outgoing, the portion being located on an irradiation path of the 
illuminating light irradiated on a luminance point pixel having a 
luminance point defect and surfaceroughening a bottom of the processed 
concave portion to form a rough surface having a luminance reducing area. 
In a preferred embodiment of the invention, the method further comprises a 
step of forming deep steps and shallow steps arranged alternately on the 
bottom of the processed concave portion. 
In a preferred embodiment of the invention, the portion is 
surface-roughened by the use of an excimer laser beam. 
In the state where the concave portion having the surface-roughened bottom 
is formed on the abovementioned portion, the illuminating light incident 
on the portion is scattered in ambient directions. As a result, the 
luminance of the luminance point pixel is lowered so as to be 
inconspicuous against ambient normal pixels. The scattered illuminating 
light is transmitted through the ambient normal pixels in the vicinity of 
the luminance point pixel, and is further scattered slightly when 
transmitting through a liquid crystal layer. Accordingly, the gradation 
level of the luminance point pixel is close to that of the ambient normal 
pixels. This also results in a situation where the luminance point pixel 
is inconspicuous against the ambient normal pixels. This means the 
luminance point defect is virtually compensated for. 
In the state where the concave portion whose bottom is narrower than the 
upper opening is formed in the above-mentioned portion and the wall and 
the bottom of the concave portion are surface-roughened so as to have the 
light scattering characteristic, the illuminating light incident on the 
portion is scattered in ambient directions. Accordingly, the illuminating 
light transmitted through the luminance point pixel and projected on a 
display screen is reduced. Such a light reducing effect is also obtained 
in the state where the polygonal concave portion is formed in the above 
portion and the bottom thereof is surface-roughened. 
In the case of the former in which the concave has the bottom narrower than 
the upper opening, a light scattering area per beam of the illuminating 
light is larger than in the case of the latter. Therefore, the light 
scattering characteristic is especially excellent in the former by the 
difference in the size of the light scattering area. Consequently, the 
former has an excellent light reducing effect as well as virtually 
compensating for the luminance point defect. 
In the state where the central portion of the bottom of the concave portion 
has a better light scattering characteristic than the ambient portion, an 
amount of the illuminating light transmitted through the ambient portion 
can be approximated to an amount of the illuminating light transmitted 
through the normal pixels without sacrificing the compensation for the 
luminance point defect, as well as improving the light reducing effect at 
the central portion. Accordingly, the difference which is recognized 
between the ambient portion of the luminance point pixel and the normal 
pixels on the display screen is reduced. As a result, the luminance point 
pixel is inconspicuous against the normal pixels. 
In the state where the concave portion whose bottom is close to the 
luminance point pixel is formed, the illuminating light incident on the 
luminance point pixel can be recognized with the human eye as a displaying 
light outgoing from an outer surface of the glass substrate even when 
observed from a different angle. In other words, the luminance point pixel 
can be observed in the form of being compensated for with any angle. This 
type of liquid crystal display device can be used not only as a projection 
device but also as a direct vision device. The projection device is 
equipped with a backlight as an illuminating device. The illuminating 
light, which is emitted from the backlight, is incident on one of the 
transparent substrates and is outgoing from the other of the transparent 
substrates through a twisted nematic liquid crystal layer, is recognized 
by a user as the displaying light (displayed image) of the liquid crystal 
display device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described by way of illustrating embodiments 
with reference to the accompanying drawings. 
EXAMPLE 1 
FIG. 1 schematically shows an example of a luminance point defect 
compensating method of a liquid crystal display device according to the 
present invention. Hereinafter, the liquid crystal display will be 
referred to as the "LCD display". A laser (light amplification of 
stimulated emission of radiation) beam 10 emitted from an excimer laser 
oscillator 9 passes through a slit pattern 11, is reflected by an 
ultraviolet reflective mirror 12, passes through a lens 13, and is 
converged to a luminance point defect compensation area 16 of a liquid 
crystal panel 1 placed on a table 14, whereby the laser beam 10 is 
irradiated on the luminance point defect compensation area 16. The liquid 
crystal panel 1 will be referred to as the "panel", and the luminance 
point defect compensation area 16 will be referred to as the "compensation 
area", hereinafter. As indicated by a shaded portion of FIG. 2, the 
compensation area 16 is on the same path of an illuminating light 40 with 
a luminance point pixel 5 generating a luminance point. 
As shown in FIG. 3, the panel 1 comprises a pair of glass substrates. One 
of the glass substrates on which an illuminating light 40 emitted from a 
light source is incident will be referred to as the glass substrate 2. The 
other glass substrate from which the illuminating light 40 is outgoing 
will be referred to as the glass substrate 27. In Example 1, the 
compensation area 16 is located in the vicinity of an outer surface of the 
glass substrate 2. Inside the glass substrate 2, color filters 24 and a 
black matrix 25 are arranged in correspondence with pixels, and a counter 
electrode 26 is provided for applying a voltage to a liquid crystal. 
Inside the glass substrate 27, pixel electrodes 28 arranged in a matrix and 
TFTs 29 for switching the voltage supply to the pixel electrodes 28 are 
provided. Enclosed between the glass substrates 2 and 27 is a twisted 
nematic liquid crystal layer 30 twisted by 90.degree. or more. 
The panel 1 of Example 1 is for use in a three panel-system projection LCD 
device. The color filters 24 are turned into the same color when 
incorporated in the panel 1. The three panels are composed, thereby 
realizing an RGB color display. The color filters 24 may be provided on 
the outer surface of the glass substrate 2. The incident direction of the 
laser beam 10 is identical with the incident direction of the illuminating 
light 40 on the panel 1. 
The slit pattern 11 has a slit having an enlarged shape of the outline of 
the compensation area 16 so that the laser beam 10 passed through the slit 
pattern 11 is reduction-slit-exposed to be irradiated on the compensation 
area 16 with high precision. The use of such a slit pattern 11 has an 
advantage of forming a rough surface 17 of various shapes as will be 
described later. The table 14 is movable, for example, on a horizontal 
plane in X and Y directions which are perpendicular to each other so that 
the laser beam 10 is irradiated on a desired compensation area 16 by 
moving the table 14. 
The luminance point pixel 5 is detected in a preceding step in the 
following way. The illuminating light 40 is irradiated on the panel 1 from 
the light source, an image displayed on the driven panel 1 is projected on 
a display screen, and the projected image on the display screen is 
inspected with the human eye. 
The laser beam 10 is irradiated on the compensation area 16 of the glass 
substrate 2 in the direction shown by arrow 1, whereby the compensation 
area 16 is etched to form a concave portion 18 and simultaneously a bottom 
of the concave portion 18 is surface-roughened to form the rough surface 
17 comprising a microscopic concave and convex pattern. The formation of 
the concave portion 18 and the rough surface 17 are both done by the use 
of an excimer laser beam. The rough surface 17 has a light scattering 
characteristic. When the illuminating light 40 is irradiated from the 
light source to the rough surface 17 in this state, the illuminating light 
40 is scattered by the rough surface 17, whereby the luminance level of 
the luminance point pixel 5 is lowered on the display screen to a level 
close to that of normal pixels 50 disposed around the luminance point 
pixel 5. 
Moreover, since the scattered illuminating light 40 is then slightly 
scattered in the liquid crystal layer 30, the illuminating light 40 is 
partially transmitted through the normal pixels 50 and then is returned 
toward the luminance point pixel 5. Consequently, the gradation level of 
the luminance point pixel 5 is lowered to be close to that of the normal 
pixels 50 on the display screen. For the above reasons, the luminance 
point pixel 5 is not recognized as the luminance point pixel 5, which 
means the luminance point defect of the luminance point pixel 5 is 
virtually compensated for. 
In terms of the amount of light, the light which is incident on the panel 
after the rough surface is formed can appropriately be controlled to be 
within a range of 80 to 10% of the light incident before the rough surface 
17 is formed. In Example 1, the amount of light incident after the rough 
surface 17 is formed is reduced to 50%.+-.10% of the amount of light 
incident before the rough surface 17 is formed, thereby obtaining a 
satisfactory light reducing, namely, defect compensation effect. 
The rough surface 17 may be formed by laser etching by the use of CO.sub.2 
or direct impression by the use of a diamond needle or a hard metal 
needle. However, excimer laser etching has the following advantages over 
the above methods. 
Compared with the direct impression, the rough surface 17 can be formed 
more easily and with more uniform size of concave portions and convex 
portions. 
While the laser etching by the use of CO.sub.2 which uses heat and 
therefore damages the glass substrate in the vicinity of the compensation 
area 16, the excimer laser etching has no such problem. 
Accordingly, excimer laser etching is most preferable in forming the rough 
surface 17. 
Excimer laser etching employs, as a filler gas, ArF having an oscillating 
wavelength of 193 nm, KrF having an oscillating wavelength of 248 nm, XeCl 
having an oscillating wavelength of 308 nm or the like. Depending on the 
type of the filler gas, the pulse energy of the excimer laser oscillator 9 
is different, and therefore the roughness of the rough surface 17 is 
different. It has been found out through the following experiment 
conducted by a team of researchers including the inventors that KrF is 
most preferable as the filler gas for the excimer laser etching to 
compensate for the luminance point defect. 
In order to determine the most preferable filler gas, the rough surface was 
formed using various types of gas under the same pulse shot conditions. 
The surface was roughest when KrF was used and second roughest when ArF 
was used. When XeCl was used, the rough surface was not formed since the 
laser beam 10 was transmitted through the glass substrate 2. When observed 
with a microscope, the rough surface formed by the use of KrF was 
sand-like so as to satisfactorily restrict the luminance of the 
illuminating light 40. 
Thereafter, the whole part of the compensation area 16 was uniformly 
irradiated by the laser beam 10 by the use of KrF in order to confirm that 
the luminance point disappeared. The luminance level of the luminance 
point was lowered to be close to that of the normal pixels 50. 
EXAMPLE 2 
FIG. 4 shows a second example according to the present invention. A 
semi-spherical concave portion 180 is formed in the compensation area 16, 
and then the rough surface 17 is formed on a bottom of the concave portion 
180. This construction has the same light reducing effect, namely, the 
effect of lowering the luminance level of the rough surface 17 as in 
Example 1. 
EXAMPLE 3 
FIGS. 5 and 6 show a third example according to the present invention. A 
plurality of concave portions 181 (shaded) and convexes 20 (not shaded) 
are formed in a fine portion of the compensation area 16, and the rough 
surface 17 is formed on a bottom of each concave portion 181 and on a 
surface of each convex 20. The size of the fine portion, which is 
different depending on the type of the panel 1, is approximately 120 
.mu.m.times.100 .mu.m at the minimum and approximately 250 .mu.m.times.230 
.mu.m at the maximum. 
In this construction, since the rough surface 17 is formed in two steps, 
the illuminating light 40 from the light source can be further scattered 
and so reduced. This construction is convenient in conforming to the 
future technological trend. Since it is predicted that the metal halide 
lamp used As the light source will be increased in luminance in the 
future, it is necessary to further improve the light reducing effect. 
In this construction, the luminance point defect is compensated for by 
irradiating the laser beam 10 on the whole part of the compensation area 
16 uniformly and irradiating the laser beam 10 again through a mesh slit 
pattern mask. 
EXAMPLE 4 
FIGS. 7 and 8 show a fourth example according to the present invention. A 
plurality of concave portions 182 (shaded) are formed in the compensation 
area 16, and the rough surface 17 is formed on a bottom of each concave 
portion 182. In this construction, the luminance point defect is 
compensated for in the same way and the same light reducing effect is 
obtained as in Example 3. 
EXAMPLE 5 
FIG. 9 shows a fifth example according to the present invention. A 
plurality of concave portions 183 are formed in a tapered state in the 
compensation area 16, and the rough surface 17 is formed on a bottom of 
each concave portion 183. In this construction, the luminance point defect 
is compensated for in the same way and the same light reducing affect is 
obtained as in Example 3. 
EXAMPLE 6 
FIG. 10 shows a sixth example according to the present invention. A 
plurality of concave portions 184 and convexes 20 extended diagonally are 
formed in the compensation area 16 by irradiating the laser beam 10 with a 
specified angle with respect to a surface of the compensation area 16, and 
the rough surface 17 is formed on a bottom of each concave portion 184 and 
a surface of each convex 20. In this construction, the same light reducing 
effect as in Example 3 is obtained. 
EXAMPLE 7 
FIGS. 11 and 12 show a seventh example according to the present invention. 
An inverted trapezoidal pyramid shaped concave portion 185 narrowing at a 
bottom thereof is formed in the compensation area 16 in correspondence 
with the luminance point pixel 5, and rough surfaces 170 and 171 are 
formed on a bottom and a slanted wall of the concave portion 185. In this 
way, the illuminating light 40 transmitted through the luminance point 
pixel 5 is further reduced. This construction is also convenient in 
conforming to the aforementioned future technological trend. The concave 
portion 185 and the rough surfaces 170 and 171 are formed in the following 
way by the use of excimer laser etching. 
First, the reduction ratio of slit-exposing the laser beam 10 through the 
slit pattern 11 (FIG. 1) and the energy density of the laser beam 10 (FIG. 
1) are set to an appropriate level. Then, the laser beam 10 is irradiated 
from the excimer lager oscillator 9 on the compensation area 16, thereby 
forming the concave portion 185. A mesh slit pattern mask 60 having round 
holes 61 as shown in FIG. 13 is inserted into the slit pattern 11, and the 
laser beam 10 is again irradiated on the concave portion 185, thereby 
simultaneously forming the sawtooth rough surfaces 171 on the wall and the 
mesh-like rough surface 170 on the bottom of the concave portion 185. 
In this construction, in which the compensation area 16 has the concave 
portion 185 with the rough surfaces 170 and 171, a scattering area of the 
illuminating light 40 incident on the compensation area 16 per beam is 
larger than of FIG. 3. Accordingly, the light scattering characteristic, 
by which the illuminating light 40 is scattered in ambient directions, is 
improved by the difference in the size of the scattering areas, thereby 
also improving the effect of reducing the illuminating light 40, namely, 
of lowering the luminance. 
The concave portion 185 preferably has an upper opening of approximately 
250 .mu.m.times.250 .mu.m, a slanting angle of approximately 5.degree. to 
20.degree., and a depth of approximately 200 .mu.m or more. It has been 
found out that the light reducing effect can be set at approximately 80% 
or more by forming the concave portion 185 having such specifications. The 
light reducing effect of the construction shown in FIG. 3 is approximately 
50%. 
In Example 7, the panel 1 for use in the three panel-system projection LCD 
device is used. 
EXAMPLE 8 
FIG. 14 shows an eighth example according to the present invention. A 
mesh-like central rough surface 172 is formed in a central portion of the 
bottom of the rough surface 17, the central rough surface 172 being deeper 
than the rough surface 17. 
The central rough surface 172 is formed in the following way. As shown in 
FIG. 14, the laser beam 10 is irradiated on the compensation area 16 in 
the direction of arrow 1. The compensation area 16 is etched to form a 
concave portion 186 and simultaneously a bottom of the concave portion 186 
is surface-roughened to form the rough surface 17 comprising a microscopic 
concave and convex pattern. 
Then, the mesh slit pattern mask 60 (FIG. 13) is inserted into the slit 
pattern 11, and the laser beam 10 is irradiated only on the central 
portion of the rough surf ace 17, thereby forming the mesh central rough 
surface 172 which is deeper than the rough surface 17. 
In this construction, since the central portion of the rough surface 17 has 
deeper concave portions than an ambient portion thereof, the light 
scattering area of the central portion is larger than that of the ambient 
portion. In other words, the light reducing effect of the central portion 
is better than that of the ambient portion. Accordingly, a center of the 
luminance point pixel 5 is not conspicuous against the normal pixels 50 
around the luminance point pixel 5. 
Moreover, since the amount of light transmitted through an ambient portion 
of the luminance point pixel 5 can be slightly reduced compared with the 
amount of light transmitted through the normal pixels 50, the difference 
recognized between the ambient portion of the luminance point pixel 5 and 
the normal pixels 50 is reduced. 
For the above reasons, the construction of Example 8 makes the luminance 
point pixel 5 inconspicuous against the normal pixels 50 around the 
luminance point pixel 5. The further light reducing effect realized in the 
central portion of the luminance point pixel 5 is convenient in conforming 
to the future technological trend. 
It has been found out that the amount of light is set to approximately 80% 
by setting the light reducing effect at approximately 20 to 40%. 
EXAMPLE 9 
FIG. 15 shows a ninth example according to the present invention. A 
rectangular pyramid central concave portion 187 narrowing at a bottom 
thereof is formed in a central portion of the rough surface 17, and rough 
surfaces 173 and 174 are formed on a bottom and a slanted wall of the 
concave portion 187. In this way, the illuminating light 40 transmitted 
through the luminance point pixel 5 is further reduced. The concave 
portion 187 and the rough surfaces 173 and 174 are formed in the following 
way by the use of excimer laser etching. 
First, the laser beam 10 is reduction-slit-exposed on the rough surface 17 
in the same way as in Example 6, thereby forming the central concave 
portion 187. A mesh slit pattern mask 60 (FIG. 13) is inserted into the 
slit pattern 11, and the laser beam 10 is again irradiated only on the 
central portion of the rough surface 17, thereby simultaneously forming 
the central concave portion 187, the sawtooth rough surfaces 174 on the 
wall and the mesh-like rough surface 173 on the bottom of the concave 
portion 187. This construction has the same effect of reducing the 
Illuminating light 40 as in Example 8. 
The concave portion 187 preferably has an upper opening of approximately 
250 .mu.m.times.250 .mu.m, a slanting angle of approximately 5 to 20%, and 
a depth of approximately 250 .mu.m, it has been found out that the light 
reducing effect can be set at approximately 80% or more by forming the 
concave portion 187 having such specifications. 
EXAMPLE 10 
FIGS. 16 and 17 show a tenth example according to the present invention. In 
the panel 1 of Example 10, red (R), green (G) and blue (B) color filters 
24' are alternately arranged. The panel 1 of Example 10 is usable in a 
direct vision LCD device as well as in the projection LCD device. 
RGB color filters 24' and a black matrix 25 are arranged in correspondence 
with the pixels, and the counter electrode 26 is provided for applying a 
voltage to the liquid crystal. The RGB color filters 24' may be provided 
on the outer surface of the glass substrate 2. 
Inside the glass substrate 27, the pixel electrodes 28 arranged in a matrix 
and the TFTs 29 for switching the voltage supply to the pixel electrodes 
28 are provided. Enclosed between the glass substrates 2 and 27 is the 
twisted nematic liquid crystal layer 30 twisted by 90.degree. or more. 
The luminance point pixel 5 is generated in a portion of the pixel 
electrodes 28. In FIG. 16, the thickness of the twisted nematic liquid 
crystal layer 30 with respect to the thicknesses of the glass substrates 2 
and 27 are larger than the real one. FIG. 17 illustrates the relationship 
among the above thicknesses which is closer to the real one. Although not 
shown in FIGS. 16 and 17, polarizing plates are disposed outside of the 
glass substrates 2 and 27. 
The compensation area 16 has a concave portion 188 having the rough surface 
17. As shown in FIG. 17, the rough surface 17 is close to the luminance 
point pixel 5. The concave portion 188 is formed in the following way so 
as to locate a bottom thereof close to the luminance point pixel 5. 
As shown in FIG. 16, the laser beam 10 Is irradiated on the compensation 
area 16 in the direction of arrow I, whereby the irradiated portion is 
laser-etched and a bottom of the compensation area 16 is made close to a 
bottom of the glass substrate 2. In other words, the laser etching forms 
the concave portion 188 having the bottom close to the luminance point 
pixel 5 and further forms the rough surface 17 comprising microscopic 
concave portions and convexes. The shape and the depth of the concave 
portion 188 and the roughness of the rough surface 17 can be adjusted by 
employing an appropriate slit pattern 11 (FIG. 1) and setting the energy 
density of the laser beam 10 to an appropriate level. 
When the illuminating light 40 is Irradiated on the concave portion 188 
having the rough surface 17 from a backlight, the incident light is 
scattered by the rough surface 17, thereby reducing the light transmitted 
through the luminance @point pixel 5 which is closely opposed to the rough 
surface 17. Accordingly, the illuminating light 40 transmitted through the 
luminance point pixel 5, namely, the luminance level of the light 
transmitted through the luminance point pixel 5 obtained when the panel 1 
is used in the projection LCD device is confirmed as being as low as the 
luminance level of the light transmitted through the normal pixels 50 when 
viewed with the human eye from outside of the glass substrate 27. 
Further, a rough surface is formed even on a portion of the compensation 
area 16 opposed to the normal pixel 50 adjacent to the luminance point 
pixel 5. A portion of the light transmitted through such a rough surface 
is partially scattered toward the adjacent normal pixel 50. Consequently, 
the tone of the adjacent normal pixel 50 is overlapped on the luminance 
point pixel 5 when observed by the human eye, whereby the gradation level 
of the luminance point pixel 5 is close to that of the normal pixels 50 
around the luminance point pixel 5. This means that the luminance point 
defect of the luminance point pixel 5 is compensated for so as to be 
inconspicuous. 
Since the rough surface 17 is close to the luminance point pixel 5, the 
illuminating light 40 Incident on the luminance point pixel 5 can be 
confirmed with the human eye as displaying light outgoing from an outer 
surface of the glass substrate 27 even when observed from different 
angles. Since the illuminating light 40 can be observed in the state where 
the calescence point defect is compensated for, the panel 1 of Example 10 
can be used In the direct vision LCD device as well as in the projection 
LCD device. 
The panel 1 of Example 10 may be equipped with a glass substrate including 
TFTs disposed on a light incident side and a glass substrate including the 
color filters disposed on a light outgoing side. In such a case, the 
compensation area 16 is formed in the glass substrate including the color 
filters. 
EXAMPLE 11 
FIG. 18 shows an eleventh example according to the present invention. In 
this and all the following examples, the compensation area 16 is located 
in the vicinity of the outer surface of the glass substrate 27 from which 
the illuminating light 40 is outgoing. The compensation area 16 is on the 
same irradiation path of the illuminating light 40 with the luminance 
point pixel 5. 
Inside the glass substrate 2 on which the illuminating light 40 is 
incident, the color filters 24 and the black matrix 25 are arranged in 
correspondence with the pixels, and the counter electrode 26 is provided 
for applying a voltage to the liquid crystal. The color filters 24 may be 
provided on the outer surface of the glass substrate 2. 
Inside the glass substrate 27, the pixel electrodes 28 arranged in a matrix 
and the TFTs 29 for switching the voltage supply to the pixel electrodes 
28 are provided. Enclosed between the glass substrates 2 and 27 is the 
twisted nematic liquid crystal layer 30 twisted by 90.degree. or more. The 
panel 1 of Example 11 is for use in the three panel-system projection LCD 
device. 
The laser beam 10, the intensity of which is controlled, is irradiated on 
the compensation area 16 of the glass substrate 27 in the direction shown 
by arrow I.sub.1, whereby the compensation area 16 is etched to form a 
concave portion 19 and simultaneously a bottom of the concave portion 19 
is surface-roughened to form the rough surface 17 comprising a microscopic 
concave and convex pattern. When the illuminating light 40 is Irradiated 
from the light source in the direction of arrow I.sub.2 to the rough 
surface 17 in this state, the illuminating light 40 is transmitted through 
the luminance point pixel 5, is scattered by the rough surface 17, and 
radiates toward the display screen. Therefore, the amount of light sent 
from the luminance point pixel 5 to the observer is reduced in accordance 
with the roughness of the rough surface 17, so that the luminance level of 
the luminance point pixel 5 is lowered to be close to that of the normal 
pixels 50. As a result, the luminance point pixel 5 is not recognized as 
the luminance point pixel 5. This means the luminance point defect of the 
luminance point pixel 5 is virtually compensated for. 
In terms of the amount of light, the light which is incident on the panel 1 
after the rough surface 17 is formed can appropriately be controlled to be 
within a range of 80 to 10% of the light incident before the rough surface 
17 is formed. In Example 11, the amount of light incident after the rough 
surface 17 lo is formed is reduced to 50%.+-.10% of the amount of light 
Incident before the rough surface 17 is formed, thereby obtaining a 
satisfactory light reducing, namely, defect compensation effect. 
The rough surface 17 may be formed by laser etching by the use Of CO.sub.2 
Or direct impression by the use of a diamond needle or a hard metal 
needle. However, excimer laser etching has the aforementioned advantages 
over the above methods. 
EXAMPLES 12 
FIG. 19 shows a twelfth example according to the present invention. A 
semi-spherical concave portion 190 is formed in the compensation area 16, 
and then the rough surface 17 is formed on a bottom of the concave portion 
190. This construction has the same light reducing effect as in Example 
11. 
EXAMPLE 13 
FIGS. 20 and 21 show a thirteenth example according to the present 
invention. A plurality of concave portions 191 (shaded) and convexes 200 
(not shaded) are formed in a fine portion of the compensation area 16, and 
the rough surface 17 is formed on a bottom of each concave portion 191 and 
on a surface of each convex 200. The size of the fine portion, which is 
different depending on the type of the panel 1, is approximately 120 
.mu.m.times.100 .mu.m at the minimum and approximately 250 .mu.m.times.230 
.mu.m at the maximum. 
In this construction, since the rough surface 17 is formed in two steps, 
the illuminating light 40 from the light source can be further scattered 
and so reduced. This construction is convenient in conforming to the 
future technological trend. 
In this construction, the luminance point defect is compensated for by 
irradiating the laser beam 10 on the whole part of the compensation area 
16 uniformly and irradiating the laser beam 10 again through a mesh slit 
pattern mask 60 (FIG. 13). 
EXAMPLE 14 
FIGS. 22 and 23 show a fourteenth example according to the present 
invention. A plurality of concave portions 192 (shaded) are formed in the 
compensation area 16, and the rough surface 17 is formed on a bottom of 
each concave portion 192. In this construction, the luminance point defect 
is compensated for in the same way and the same light reducing effect is 
obtained as in Example 13. 
EXAMPLE 15 
FIG. 24 shows a fifteenth example according to the present invention. A 
plurality of concave portions 193 are formed in a tapered state In the 
compensation area 16, and the rough surface 17 is formed on a bottom of 
each concave portion 193. In this construction, the luminance point defect 
is compensated for in the same way and the same light reducing effect is 
obtained as in Example 13. 
EXAMPLE 16 
FIG. 25 shows a sixteenth example according to the present invention. A 
plurality of concave portions 194 extended diagonally and convexes 200 are 
formed in the compensation area 16 by irradiating the laser beam 10 with a 
specified angle with respect to a surface of the compensation area 16, and 
the rough surface 17 is formed on a bottom of each concave portion 194 and 
a surface of each convex 200. In this construction, the same light 
reducing effect as in Example 13 is obtained. 
It is understood that various other modifications will be apparent to and 
can be readily made by those skilled in the art without departing from the 
scope and spirit of this invention. Accordingly, it is not intended that 
the scope of the claims appended hereto be limited to the description as 
set forth herein, but rather that the claims be construed as encompassing 
all the features of patentable novelty that reside in the present 
invention, including all features that would be treated as equivalents 
thereof by those skilled in the art to which this invention pertains.