Color filter substrate with color filter pattern and protective layers containing photosensitive polyamide resins

An electrode plate structure for a liquid crystal color display is produced by forming a color filter layer of a photosensitive polyamide resin containing a colorant dispersed therein; disposing a protective layer of a photosensitive polyamide resin on the color filter layer; forming an ITO (indium-tin-oxide) film on the protective layer, preferably at an elevated temperature of at most 270.degree. C.; post-annealing the ITO film at a temperature of 200.degree.-300.degree. C. for improving the crystallinity of the ITO film suitable for etching; and selectively etching the ITO film patternwise with an etchant of hydroiodic acid or a hydroiodic acid-ferric chloride aqueous solution mixture to leave an ITO electrode pattern.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to a process for producing a substrate or 
electrode plate structure for a liquid crystal color display device, 
particularly a process for producing an electrode plate structure for a 
liquid crystal display device having an electrode pattern of ITO 
(indium-tin-oxide) formed on a color filter. 
As a conventional type of color filter, there has been known a dyed color 
filter which is obtained by coating a substrate with a dyeable layer of a 
hydrophilic polymer, such as gelatin, casein, glue or polyvinyl alcohol, 
and dyeing the layer with a colorant to form a colored layer. 
Such a color filter obtained through a dyeing process encounters a 
difficulty when it is subjected to a heat treatment as by formation of a 
transport conductor film of ITO, etc., thereon, because the colorant used 
in the dyeing has a relatively low heat resistance on the order of 
150.degree. C. 
In the case of forming a layer of ITO, etc., on a color filter, it has been 
a usual practice to form such a layer at a low temperature in 
consideration of the insufficient heat resistance of the color filter. If 
the formation of an ITO film is effected at a low temperature, however, 
the crystalline structure of the ITO is not specified, thus requiring a 
long time for etching thereof when an ordinary etching liquid for ITO, 
such as a hydrochloric acid-ferric chloride mixture, or a hydrochloric 
acid-nitric acid mixture. As a result, it is extremely difficult to 
control the shape of an ITO electrode pattern and also the color filter 
layer formed below the ITO can be damaged due to such a long time of 
etching. These difficulties have provided a serious obstacle to practical 
utilization a dyed color filter for a liquid crystal device. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the problems accompanying 
the conventional process, i.e., poor heat resistance of a color filter, 
low-temperature formation of an ITO film required thereby and 
corresponding difficulty in etching thereof. 
Another object of the present invention is to provide a substrate or 
electrode plate structure for a liquid crystal color display device 
wherein a heat-resistant color filter is patterned in a simple step and an 
ITO film formed at a low temperature is then post-treated to have a good 
etching characteristic. 
A further object of the present invention is to provide an electrode plate 
structure for a liquid crystal color display device wherein an ITO 
electrode pattern is formed on a color filter through etching without 
damaging the color filter. 
According to the present invention, there is provided a process for 
producing an electrode plate structure for a liquid crystal color display, 
comprising the steps of: 
forming on a substrate a color filter layer comprising a photosensitive 
polyamide resin containing a colorant dispersed therein, 
coating the color filter layer with a protective layer comprising a 
photosensitive polyamide resin, 
coating the protective layer with an ITO (indium-tin-oxide) film, 
heat-treating the ITO film, and 
selectively etching the ITO film patternwise with an etchant comprising 
hydroiodic acid or a hydroiodic acid-ferric chloride aqueous solution 
mixture to leave an ITO electrode pattern. 
According to the present invention, it is possible to form a 
well-controlled ITO electrode pattern which has been difficult to provide. 
Further, it is possible to prevent a color filter pattern of a colored 
photosensitive polyamide resin formed below an ITO film from being damaged 
during etching, thus providing a reliable electrode plate structure for a 
liquid crystal color display device at a high yield. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

EXAMPLE 1 
An electrode plate structure was prepared through the steps as described 
with reference to FIGS. 1A-1M. 
Referring to the figures, a glass substrate 1 was provided with color 
filter patterns of R(4), G(5) and B(6) each in a thickness of about 1.5 
micron (FIG. 1E) through repetition of ordinary lithographic steps 
including application of a colored photosensitive polyamide resin 
("PA-1012R", "PA-1012G" and "PA-1012B", available from Ube Kosan K.K.) 
dissolved in N-methyl-2-pyrrolidone at a viscosity of 90 to 130 cP by 
spinner coating (FIG. 1A), pattern exposure to ultraviolet rays from an 
ultra high-voltage mercury lamp to form a photocured part 2a (FIG. 1B and 
1C), and development with a cyclohexane-based developer solution (FIG. 
1D). Then, the color filter layer including the color filter patterns 4-6 
was further coated with a solution of a photosensitive polyamide resin 
("PA-1000C", available from Ube Kosan K.K.), followed by drying, 
ultraviolet exposure and post-curing at 200.degree. C. to form an about 2 
micron-thick protective layer 7. 
Then, the above-treated substrate having a color filter pattern thereon was 
subjected to sputtering of ITO at a substrate temperature of 250.degree. 
C. at a deposition pressure of 3.times.10.sup.-3 Torr under Ar stream of 
200 sccm and O.sub.2 stream of 2 sccm to form an about 1000 .ANG.-thick 
ITO film 8. Then, the substrate having the ITO film 8 was placed in a 
clean oven, heated to 250.degree. C. in 2 hours, held at that temperature 
for 1 hour and cooled gradually in 4 hours (FIG. 1G). 
Then, the ITO film on the substrate was coated with a 1 micron-thick 
photoresist film 9 (FIG. 1H), which has then exposed through a prescribed 
electrode pattern mask (FIG. 1I) and developed with a prescribed developer 
(FIG. 1J). Then, the substrate having the thus-developed photoresist 
pattern 9 was dipped in a hydroiodic acid solution with a concentration of 
about 56 wt. % at 40.degree. C. for 2 minutes under a light-shielding 
condition (FIG. 1K), and then the photoresist pattern 9 was peeled off to 
form an ITO electrode pattern (FIG. 1L and 1M). 
The thus formed ITO electrode pattern 9 (FIG. 1M) was free from thinning or 
irregularity of the pattern due to the etching to retain an accurate 
shape, and occurrence of short circuit between adjacent electrodes were 
extremely rare. 
Further, as a result of the use of hydroiodic acid as the etchant, the 
color filter pattern comprising the cured photosensitive polyamide was not 
damaged at all. 
EXAMPLE 2 
An electrode plate structure was prepared in the same manner as in Example 
1 except that the etching of the ITO film was performed for 2.5 minutes by 
using a 70/30-volume mixture of about 56 wt. %-hydroiodic acid solution/35 
wt. %-ferric chloride at 40.degree. C. as the etchant. 
The thus prepared electrode plate structure has an ITO electrode pattern 
which was free from thinning or irregularity of the pattern due to the 
etching to retain an accurate shape, and occurrence of short-circuit 
between adjacent electrodes were extremely rare. 
Further, as a result of the use of a hydroiodic acid-ferric chloride 
aqueous solution mixture as the etchant, the color filter pattern 
comprising the cured photosensitive polyamide was not damaged at all. 
Comparative Example 
An electrode plate structure was prepared in the same manner as in Example 
1 except that the etching of the ITO film was performed for 4 minutes by 
using a mixture of 60 vol. % of hydrochloric acid and 40 vol. % of ferric 
chloride aqueous solution (Fe.sub.2 Cl.sub.3 35 wt. %) at 47.degree. C. 
The thus-prepared electrode plate structure had an ITO electrode pattern 
which was accompanied with remarkable thinning of the pattern due to side 
etching, thus failing to provide a prescribed electrode width. 
Further, as a result of the use of the hydrochloric acid-ferric chloride 
aqueous solution mixture, the color filter pattern comprising the cured 
photosensitive polyamide was accompanied with partial peeling or lifting 
along with a damage of the protective film, so that the resultant 
electrode plate structure was practically unacceptable at all.