Patterning method employing laser

A patterning method includes the steps of irradiating an excimer laser beam to a material layer so as to form a pattern on the material layer; and transferring onto a substrate, the material layer formed with the pattern; and irradiating the excimer laser beam to the material layer transferred onto the substrate so as to form a further pattern on the material layer.

BACKGROUND OF THE INVENTION 
The present invention relates to a patterning method for use in production 
of a color filter, etc. for a liquid crystal display. 
In a known method of forming a pattern on a color filter for a liquid 
crystal display, a pattern is formed by photolithography on a light 
shielding film of Cr or the like formed on a glass substrate so as to 
produce a black matrix and then, colored patterns of red, green and blue 
are formed on the substrate by dying, pigment dispersion, printing, etc. 
In dying, after photosensitive water-soluble resist such as gelatin has 
been coated on the glass substrate, a predetermined pattern is obtained by 
exposure and development. In addition, by dying and fixing, colored 
patterns are obtained. By repeating this process three times, colored 
layers of red, green and blue are formed. 
In pigment dispersion, colored photoresist in which pigment is dispersed is 
coated on the glass substrate and then, a predetermined pattern is 
obtained by exposure and development. By repeating this process three 
times, colored patterns of red, green and blue are formed. 
Such methods as litho offset printing and intaglio offset printing are used 
for printing. In litho offset printing, ink on a pattern portion of a 
print is transferred onto an elastic rubber member and then, is printed on 
the substrate. On the other hand, in intaglio offset printing, ink is 
filled on the pattern portion and unnecessary ink is scraped from the 
pattern portion by a scraper. Subsequently, ink is transferred onto an 
elastic rubber member and then, is printed on the substrate. In any one of 
the printing methods, colored inks of red, green and blue are sequentially 
printed on the same glass substrate so as to form colored patterns, 
respectively. 
In such conventional dying and pigment dispersion employing 
photolithography, the processes are complicated and production apparatuses 
are also expensive, thereby resulting in an increase in the production 
cost of the color filter. Meanwhile, in known printing, since the pattern 
has an arcuate sectional shape in which film thickness at it central 
portion is different from that of its opposite end portions, the pattern 
is not flat and thus, nonuniformity in film thickness is likely to take 
place. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide a 
patterning method in which a color filter can be produced highly 
accurately at low cost. 
In order to accomplish this object of the present invention, a patterning 
method according to the present invention comprises the steps of: 
irradiating an excimer laser beam to a material layer for patterning so as 
to form a pattern on the material layer; and transferring onto a 
substrate, the material layer formed with the pattern. 
In the above described patterning method, since the excimer laser beam is 
irradiated to the material layer so as to form the pattern on the material 
layer through laser ablation, the pattern can be formed on the material 
layer highly accurately without the need for performing wet development. 
Meanwhile, since the pattern formed on the material layer can be inspected 
prior to transfer, waste of the substrate is avoided. Furthermore, since 
the material layer is not required to be photosensitive, a wide range of 
materials having excellent heat resistance and solvent-resistance 
properties can be used for the material layer.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there are shown in FIGS. 1(a) to 1(e), steps 
of a patterning method according to a first embodiment of the present 
invention. In FIG. 1(a), a peel layer 2 and a red color filter 3 acting as 
a patterning material layer are formed on a support member 1. The support 
member 1 is formed by a polyester film, while the peel layer 2 is made of 
silicone rubber or silicone resin for peeling. The patterning material 
layer in which red, green and blue organic pigments are dispersed in resin 
such as epoxy resin, acrylic resin, etc. can be formed by spin coating, 
roll coating, spray coating or the like. 
In FIG. 1(b), an excimer laser beam 9 is irradiated to the red color filter 
3 so as to form a pattern. An excimer laser is of the discharge excitation 
type using a mixed gas of rare gas Xe and halogen gas Cl.sub.2 and can 
have an oscillation wavelength of 308 nm or an oscillation wavelength of 
248 nm of Kr and F.sub.2. Irradiation of the laser beam is performed by a 
mask imaging method. When the XeCl excimer laser beam 9 having an energy 
density of 1.2 J/cm.sup.2 per pulse is irradiated to the red color filter 
3 having a thickness of 2 .mu.m, portions of the red color filter 3, which 
are subjected to irradiation of the laser beam, can be removed through 
ablation by irradiation of four pulses and thus, a red color filter 
pattern 6 is obtained. 
FIGS. 1(c) and 1(d) show a step in which the red color filter pattern 6 is 
transferred onto a substrate through an adhesive layer 12. A glass 
substrate 10 formed with a black matrix 11 is used as the substrate. The 
black matrix 11 is obtained by patterning light shielding material such as 
Cr by photolithography or forming a light shielding pattern in a pigment 
dispersion method by using resin. The black matrix 11 may also be obtained 
by a method in, which after a light shielding film having carbon dispersed 
in resin has been formed on a glass substrate, a pattern is formed by 
irradiating an excimer laser beam to the light shielding film. The 
adhesive layer 12 should have an adhesive property for peeling the red 
color filter pattern 6 from the peel layer 2. Furthermore, after transfer, 
the adhesive layer 12 desirably has a sufficient adhesive property, heat 
resistance and resistance against solvent. In this embodiment, 
ultraviolet-curing epoxy resin is employed as the adhesive layer 12. After 
the adhesive layer 12 has been coated on the glass substrate 10, a proper 
quantity of ultraviolet ray is irradiated to the adhesive layer 12 so as 
to impart an adhesive property to the adhesive layer 12 and then, transfer 
of the red color filter pattern 6 is performed. 
In FIG. 1(e), a green color filter and a blue color filter are formed in 
the same manner as the steps of FIGS. 1(a) and 1(b) and then, a green 
color filter pattern 7 and a blue color filter pattern 8 are transferred 
onto the glass substrate 10 as in the step of FIG. 1(d). Thereafter, an 
ultraviolet ray is irradiated to the glass substrate 10 so as to cure the 
adhesive layer 12. As a result, a color filter for liquid crystal is 
obtained. 
Meanwhile, in FIGS. 1(c), 1(d) and 1(e), the color filter pattern is 
transferred onto the glass substrate 10 through the adhesive layer 12. 
However, by thermal contact bonding, the color filter pattern may also be 
transferred directly onto the glass substrate 10 formed with the black 
matrix 11. Namely, after the color filter pattern formed as in the steps 
of FIGS. 1(a) and 1(b) has been contact bonded to the glass substrate 10 
and then, heated, the support member 1 formed with the peel layer 2 is 
peeled from the color filter pattern. As a result, the color filter 
pattern is transferred onto the glass substrate 10. By transferring the 
remaining color filter patterns of other colors onto the glass substrate 
10 successively, a color filter for a liquid crystal display is obtained. 
When the color filter for liquid crystal produced by the patterning method 
according to the first embodiment of the present invention is used for a 
liquid crystal display, the liquid crystal display has good display 
quality and reliability of the color filter is also excellent. 
FIGS. 2(a) to 2(g) show steps of a patterning method according to a second 
embodiment of the present invention. In FIG. 2(a), the peel layer 2, the 
red color filter 3, a green color filter 4 and a blue color filter 5 are 
piled on the support member 1. In FIG. 2(b), by irradiating the excimer 
laser beam 9 to the red color filter 3 and the green color filter 4, a 
pattern is formed on the red color filter 3 and the green color filter 4. 
Meanwhile, in FIG. 2(c), by irradiating the excimer laser beam 9 to only 
the red color filter 3, a pattern is formed on only the red color filter 
3. By changing energy density of the excimer laser beam 9, depth of the 
color filters removable by irradiation of one pulse can be adjusted and 
one or two of the color filters can be removed by the number of irradiated 
pulses. 
Meanwhile, a buffer layer of about 1 .mu.m in thickness may also be 
provided between neighboring ones of the piled color filters in order to 
prevent, when one of the color filters is removed through irradiation of 
the laser beam, damage to its adjoining color filter. The buffer layer 
should not have a light absorbing property in a visible light region but 
should exhibit a light absorbing property in an ultraviolet region having 
the wavelength of the excimer laser beam. The buffer layer may be obtained 
by dispersing an ultraviolet absorber in resin. The ultraviolet absorber 
includes, for example, benzophenone compounds such as 
2-hydroxy-4-methoxybenzophenone or benzotriazole compounds such as 
hydroxyphenyl benzotriazole. 
In FIGS. 2(d) and 2(e), the piled color filters are transferred onto the 
glass substrate 10 through the adhesive layer 12. In this embodiment, 
ultraviolet-curing epoxy resin is used as the adhesive layer 12. The piled 
color filters are attached to the glass substrate 10 and the adhesive 
layer 12 is cured by irradiating an ultraviolet ray thereto. Subsequently, 
the support member 1 and the peel layer 2 are peeled from the color 
filters. 
In FIG. 2(f), by irradiating the excimer laser beam 9 to only the blue 
color filter 5, a pattern is formed on only the blue color filter 5. 
Meanwhile, in FIG. 2(g), a pattern is formed on the green color filter 4 
and the blue color filter 5. 
The color filter obtained by the above described steps has portions where 
the red color filter 3, the green color filter 4 and the blue color filter 
5 are piled on one another and other portions which are each occupied by 
only one of the red color filter 3, the green color filter 4 and the blue 
color filter 5. In the color filter, since the portions where the color 
filters are piled on one another function as a black matrix, it is not 
necessary to form the black matrix additionally. 
When the color filter produced by the patterning method according to the 
second embodiment of the present invention is used for a liquid crystal 
display, the liquid crystal display has good display quality and the 
reliability of the color filter is also excellent. 
In the course of the steps of production of the color filter, defects such 
as entry of foreign matter, damage, etc. are generated. FIGS. 3(a) to 3(g) 
show steps for remedying the defects of the color filter generated in a 
patterning method according to a third embodiment of the present 
invention. FIG. 3(a) shows a state in which foreign matter 13 adheres to 
the produced blue color filter pattern 8. In FIG. 3(b), the excimer laser 
beam 9 is irradiated to the defective portion so as to obviate the 
defective portion. An excimer laser is of discharge excitation type using 
mixed gas of rare gas Xe and halogen gas Cl.sub.2 and has an oscillation 
wavelength of 308 nm. Irradiation of the laser beam is performed by a mask 
imaging method. When the XeCl excimer laser beam 9 having an energy 
density of 1.0 J/cm.sup.2 per pulse is irradiated to the foreign matter 
13, the foreign matter 13 and the corresponding blue color filter pattern 
8 can be removed by irradiation of six pulses. FIG. 3(c) shows a state in 
which the foreign matter 13 and the corresponding blue color filter 
pattern 8 have been removed. 
FIGS. 3(d) to 3(g) show steps in which a color filter is newly formed at 
the removed blue color filter pattern 8. In FIG. 3(d), the peel layer 2 
and the blue color filter 5 are formed on the support member 1 and the 
excimer laser beam 9 is irradiated to the blue color filter 5 so as to 
form the desired blue color filter pattern 8 on the blue color filter 5. 
FIG. 3(e) shows the formed blue color filter pattern 8. FIGS. 3(f) and 
3(g) show steps in which the blue color filter pattern 8 is transferred 
onto the glass substrate 10. Initially, as shown in FIG. 3(f), the blue 
color filter pattern 8 is contact bonded to the glass substrate 10 and 
then, is heated. Subsequently, as shown in FIG. 3(g), the support member 1 
formed by a polyester film is peeled from the glass substrate 10 and thus, 
the blue color filter pattern 8 has been transferred onto the glass 
substrate 10. 
By the above described steps, the defective color filter can be corrected. 
When the corrected defective color filter is used for a liquid crystal 
display, the liquid crystal display has good display quality and the 
reliability of the color filter is also excellent. 
Meanwhile, in this embodiment, the XeCl excimer laser having the 
oscillation wavelength of 308 nm is employed but a KrF excimer laser 
having an oscillation wavelength of 248 nm may be likewise effective for 
obviating the defects or forming the patterns. 
Furthermore, in this embodiment, the defect that the foreign matter adheres 
to the color filter is remedied. However, in this embodiment, it is 
likewise possible to remedy also such defects as entry of foreign matter 
into the color filter patterns, pin holes or damage produced in the color 
filter patterns, etc. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.