Method of making a color filter plate with multi-gap for LCD

The method includes patterning red, green and blue pixels (R, G, B) on a substrate. A transparent positive type photoresist is coated on the color pixels. A first exposure is performed by an illumination using a photomask having an opening aligned to the red pixels (R). Next, the photomask is relatively shift to a position such that the opening is aligned to the green pixels (g). Then, a second exposure is carried out to expose the positive photoresist. Similarly, the photomask is also shift such that the opening is aligned to the blue pixels. Subsequently, the positive photoresist is exposed by the illumination by using the photomask. The positive photoresist is exposed by controlling the intensity of the illumination, exposure time or the combination thereof. Then, the positive photoresist is developed by conventional manner. Subsequently, a color filter plate with multi-gap for LCD is formed.

FIELD OF THE INVENTION 
The present invention relates to a method of making liquid crystal display, 
and more specifically, to a method of forming a color filter plate for a 
thin film transistor-liquid crystal display. 
BACKGROUND OF THE INVENTION 
Thin film transistor-liquid crystal display (TFT-LCD) is known as the 
display required for the high pixel density and quality. In general, the 
TFT-LCD includes a bottom plate formed with thin film transistors and 
pixel electrodes and a top plate formed with color filters. The liquid 
crystal is filled between the top plate and the bottom plate. In each unit 
pixel, a capacitor and a further capacitor are provided which are formed 
by virtue of the TFT serving as the switching element of the unit pixel. 
In the operation, a gate signal voltage is applied to the TFT that is the 
switching element of each unit pixel. The TFT receives the gate signal 
voltage, it is turn on so that data voltage carrying image information can 
be applied to the corresponding pixel electrode and the liquid crystal via 
the TFT. When the data voltage is applied to the TFT, the arrangement of 
the liquid crystal moleculers is change, thereby changing the optical 
properties and displaying the image. 
A color filter (CF) plate is used in the LCD to show the colored portion of 
the screen. In general, the viewing angle and the color performance are 
affected by the design of the color filter. Multi-gap structure is widely 
used to making the color filter plate for LCD and it has been applied in 
TN (TFT) and OCB (optical compensation bend) mode. FIG. 1 shows a 
conventional multi-gap LCD. In the structure, red, blue and green pixels 
are respectively formed on a glass 2. A first photoresist 4 is formed on 
the green and the blue pixels. Further, a second photoresist 6 is only 
formed on the top of the blue pixel. Between the glass 2 and a further 
glass 8 is liquid crystal 10. Thus, the gap spacing dR, dG and dB are 
difference. Namely, the color filter plate has a multi-gap structure. 
Typically, .DELTA. nd/.lambda. is designed to minimize or maximize the 
transmission, wherein the n is the integer number, the d is the gap 
spacing between the glass 8 and the color pixels, .lambda. indicates the 
wavelength of light. Thus, the red pixel has the largest .DELTA. nd, and 
the blue pixel has the smallest .DELTA. nd in the three color pixels. The 
object of the multi-gap structure is to keep the constant .DELTA. 
nd/.lambda. value. However, the proces for forming above structure needs 
at least two photoresist coating and two patterning steps. 
SUMMARY OF THE INVENTION 
A method is disclosed to form a color filter plate for TFT-LCD. The method 
includes patterning red, green and blue pixels (R, G, B) on a substrate. A 
transparent positive type photoresist is coated on the R, G, B pixels. A 
first exposure is performed by an illumination using a photomask having an 
opening aligned to the red pixels (R). Next, the photomask is relatively 
shift to a position such that the opening is aligned to the green pixels 
(g). Then, a second exposure is carried out to expose the positive 
photoresist. Similarly, the photomask is also shift such that the opening 
is aligned to the blue pixels. Subsequently, the positive photoresist is 
exposed by the illumination by using the photomask. The positive 
photoresist is exposed by controlling the intensity of the illumination, 
exposure time or the combination thereof. In detail, the first exposure 
has the highest illumination intensity, the third exposure has the lowest 
illumination intensity. The second exposure thus exhibits intermediate 
intensity of illumination. Another way is to control the time of exposure. 
That is the exposure time of the first exposure is the longest, while the 
one of the third exposure is the shortest. The second exposure thus 
exhibits intermediate time of exposure. 
Then, the positive photoresist is developed by conventional manner. The 
result of the present invention after the three exposure steps is a color 
filter plate having a multi-gap structure. Finally, an indium tin oxide 
(ITO) layer, liquid crystal, a alignment film, a further ITO and a further 
glass are respectively formed by conventional technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A method is disclosed to form a color filter plate for TFT-LCD. The present 
invention needs only one photoresist coating and one photomask. As will be 
seen below, this technique can be used for the formation of a TFT device. 
Referring to FIG. 2, in the preferred embodiment, a substrate 100 formed 
of glass, quartz or the like is used as an insulating transparent 
substrate. Red, green and blue pixels (R, G, B) are patterned on the 
substrate 100 by using conventional manner. Generally, these color pixels 
are formed of resin. 
Subsequently, still referring to FIG. 2, a transparent positive type 
photoresist 104 is coated on the color pixels. As well known in the art, 
the characteristic of the negative photoresist is opposite to the one of 
the positive photoresist. Next steps are used to create a multi-level 
structure formed in the photoresist. It can be controlled by multi-step of 
exposure procedure by controlling the illumination intensity and exposure 
time. The photoresist can be exposed with three difference intensities of 
an illumination such that regions of the photoresist respectively on said 
red pixel, said green pixel and said blue pixel are exposed by difference 
intensity. Then, the photoresist is developed to form a multi-level 
structure on the color pixels due to different exposure intensity. 
Alternatively, the procedures includes exposing the photoresist with three 
difference exposure time such that regions of said photoresist 
respectively on the color pixels are exposed by difference time. The 
embodiment can be seen as follow. 
Turning to FIG. 3, a first exposure is performed by an illumination using a 
photomask 106 having an opening 108 aligned to the red pixels (R). Next, 
the photomask 106 is relatively shift to a position such that the opening 
108 is aligned to the green pixels (g), as shown in FIG. 4. Then, a second 
exposure is carried out to expose the positive photoresist 104. The 
illumination will expose the photoresist 104 through the opening 108 as 
known in the art. 
Referring to FIG. 5, similarly, the photomask 106 is also shift such that 
the opening 108 is aligned to the blue pixels (B). Subsequently, the 
positive photoresist 104 is exposed by the illumination by using the 
photomask 106. The key of the present invention is that the three exposure 
steps are respectively performed with difference level of exposure. In 
order to achieve this, the positive photoresist 104 is exposed by 
controlling the intensity of the illumination, exposure time or the 
combination thereof. In detail, the first exposure has the highest 
illumination intensity, the third exposure has the lowest illumination 
intensity. The second exposure thus exhibits intermediate intensity of 
illumination. Another way is to control the time of exposure. That is the 
exposure time of the first exposure is the longest, while the one of the 
third exposure is the shortest. The second exposure thus exhibits 
intermediate time of exposure. 
Then, the positive photoresist 104 is developed by conventional manner. The 
result of the present invention after the three exposure steps is shown in 
FIG. 6. As can be seen in the figure, the color filter plate according to 
the present invention has a multi-gap structure. Finally, an ITO (indium 
tin oxide) layer 102, an alignment film 112, liquid crystal 110, a further 
ITO 114, a further alignment film 118 and a further glass 116 are 
respectively formed by conventional technology, as shown in FIG. 7. 
However, it is not the feature of the present invention. Therefore, the 
color filter plate has difference gap spacing dR, dG and dB. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that various changes can be made therein 
without departing from the spirit and scope of the invention.