Manufacturing method of a color filter substrate

A light-blocking black matrix is applied to a transparent substrate, then several coats of negative photoresists, with optimal spectral properties, are applied over the black matrix to create red, blue and green color filters. Then, the surface of the black matrix and the red, blue and green filters are preheated using infrared (IR) rays to remove any residual moisture or gas. Next, the surfaces of the black matrix and color filters are irradiated by ultraviolet (U.V.) rays to remove pigment residue remaining on the black matrix. This is followed by a UV irradiating step in which high-density ozone molecules (O.sub.3) are injected into a UV chamber and any final traces of pigment remaining on the surface are dissolved and volatilized in reaction to active oxygen from the ozone.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to manufacturing method of a color filter
 substrate, and more particularly, facing a thin film transistor substrate
 in a liquid crystal display.
 2. Description of the Related Art
 In general, a liquid crystal display includes two substrates that have
 electrodes and face each other, a liquid crystal material therebetween,
 and a sealant sealing the liquid crystal material.
 One of the two substrates has a black matrix and red, green and blue color
 filter, and the other has a plurality of thin film transistors (TFTs) and
 pixel electrodes.
 FIG.1 is a cross-sectional view of two substrates in a liquid crystal
 display (LCD).
 As shown in FIG.1, a black matrix 2, partially covered by color filters 3
 in the display region P and another black matrix 21 are formed on a color
 filter substrate 1. An indium tin oxide (ITO) layer 4 is overlaid on the
 color filters 3 and the black matrices 2 and 21.
 A thin film transistor substrate 5, which is facing opposite the foregoing
 substrate 1, has a passivation layer 6 on the facing side.
 A sealant 8 joins the two opposing substrates 1 and 5. A liquid crystal
 material 7 is then injected into the space between the two facing
 substrates 1 and 5.
 Referring to FIG. 1, a conventional manufacturing method of an LCD will be
 described, emphasizing a manufacturing method of a color filter substrate.
 A layer of chromium is sputtered on a transparent substrates 1 to a
 thickness between 500 to 2000 .ANG. to create black matrices 2 and 21,
 which prevent TFTs from being degraded from exposure to light.
 A photoresist, with optimal spectral properties, is coated thereover, and
 developed to form a red color filter 3.
 Blue and green color filters 3 are formed in the same manner as the red
 color filter 3.
 An ITO layer 4 is formed on the substrate 1 having color filters 3, thus
 completing the color filter substrate 1.
 Finally, a liquid crystal display is completed by applying a sealant 8 on
 the edge of one of the two substrates 1 and 5, joining the two facing
 substrates 1 and 5, and injecting a liquid crystal material 7 between the
 two opposing substrates 1 and 5.
 However, in the application of conventional manufacturing methods of LCDs,
 the adhesive strength between the color filters, the black matrices, and
 the ITO layer is compromised by either residual pigment remaining on the
 surface of the black matrix, and/or any moisture or gas in the color
 filters remaining from the evaporation when forming the ITO layer.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to reinforce the adhesive strength
 between color filters and a black matrix, and an ITO layer.
 In a manufacturing method of a color filter substrate according to the
 present invention to achieve this object, the surfaces of a black matrix
 and color filters are sequentially ashed by infrared (I.R.) rays and
 ultraviolet (U.V.) rays before forming an ITO layer.
 The I.R. irradiation step is used as a preheating process before U.V.
 irradiation to remove any the moisture or gas remaining in the color
 filters.
 Furthermore, ozone molecules (O.sub.3) are injected into the ultraviolet
 chamber in the U.V. irradiation step so that any pigment residue,
 remaining on the surface of the black matrix, are dissolved and
 volatilized in action to active oxygen from ozone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention will now be described more fully hereinafter with
 reference to the accompanying drawings, in which preferred embodiments of
 the present invention are shown. This invention may, however, be embodied
 in different forms and should not be construed as limited to the
 embodiments set forth herein. Rather, these embodiments are provided so
 that this disclosure will be thorough and complete, and will fully convey
 the scope of the invention to those skilled in the art. In the drawings,
 the thickness of layers and regions are exaggerated for clarity.
 FIGS. 2A.about.2F are cross-sectional views illustrating the manufacturing
 method of a color filter substrate for an LCD according to the present
 invention.
 As shown in FIG. 2A, a layer of preferably chromium, but opaque metal or
 resin can also suffice, is sputtered onto a transparent substrate 100 to a
 thickness between 500 to 2000 .ANG. to create a black matrix 200. This
 prevents the TFTs on the opposing substrate from being degraded from
 exposure to light.
 Next, as shown in FIG. 2B, a negative photoresist 300, with an optimal red
 spectral property, is coated over the black matrix 200, which is adhered
 to the substrate 100.
 The negative photoresist 300 transmits light only having a red-color
 wavelength, and absorbs all other light. It is made from a color
 photosensitive acrylic resin with a dispersion of a pigment.
 In FIG. 2C, an aperture 910 of a mask 900 is aligned over the substrate 100
 to expose only a small portion of the photoresist 300, which is overlaid
 on the black matrix 200. The photoresist 300 is then exposed to light and
 developed to form a red color filter 310 as illustrated in FIG. 2D.
 A blue filter 320 and a green filter 330 are formed following the same
 steps illustrated in FIG. 2C and FIG. 2D, but with slight adaptations. A
 photoresist with optimal blue spectral properties are used for the blue
 filter 320, and a photoresist with optimal green spectral qualities are
 used for the green filter 330. The mask 900 is shifted slightly over the
 substrate 100 each time to properly align the aperture 910 for each color.
 Thus, the red, blue and green color filters 310, 320 and 330 are separated
 from each other, yet overlap the edges of the black matrix 200.
 Next, the surfaces of the black matrix 200 and color filters 310, 320 and
 330 are sequentially ashed by I.R. and U.V. rays to reinforce the adhesive
 strength between the black matrix 200 and the color filters 310, 320 and
 330, and also to an ITO layer, whose formation is described below.
 The l.R. irradiating step is a preheating process before the U.V.
 irradiation. This process removes any the moisture or gas remaining in the
 red, blue and green color filters 310, 320 and 330.
 Furthermore, ozone molecules (O.sub.3) are injected into the U.V. chamber
 in the U.V. irradiation procedure where any residual traces of pigment
 remaining on the surface of the black matrix 200 are dissolved and
 volatilized in reaction to active oxygen from ozone.
 The preferred roughness of the surface of the color filters 310, 320 and
 330 is less than 1,000 .ANG. when executing the I.R. and the U.V. ashing
 procedure.
 Next, to complete the color filter substrate 100, an ITO layer 400 is
 formed with a thickness of 500 to 2,500 .ANG. over the red, blue and green
 color filter layers 310, 320 and 330, and over the black matrix 200.
 Since any residual moisture, gas or pigment remaining in the red, blue and
 green color filters 310, 320 and 330 or on the surfaces of the black
 matrix 200 are removed, the adhesive strength between the black matrix 200
 and the color filters 310, 320 and 330, and the ITO layer 400 is
 reinforced.
 The adhesive strength of the ITO layer 400 was measured by using a scratch
 tester, which is described below.
 In FIG. 3, the chart shows how often the ITO layer detaches from the color
 filter substrate according to the embodiment of the present invention when
 pressure is applied using a scratch tester. FIG. 4 charts the adhesive
 strength of the ITO layer.
 The results in FIG. 4 show that when a scratch test with a pressure of 15
 gf is applied to the ITO layer, more than 90% of the ITO layer detach from
 the color substrate. That is, when slight pressure is applied, the
 adhesive strength is weak. When a pressure of 15-20 gf is applied, 85% of
 the ITO layer detach. The adhesive strength does not increase
 substantially when slightly more pressure is applied. However, when even
 more pressure is applied, 20-30 gf, only 1% of the ITO layer detach. And
 finally, in cases where the pressure exceeds 30 gf, there is no detachment
 at all. As more pressure is applied to the ITO layer, the integrity of the
 adhesion increases. Therefore, to increase adhesive strength, a pressure
 of more than 20 gf should be applied.
 The horizontal axis in FIG. 4 indicates a pressure applied to the pin which
 is connected to the scratch tester in gf, and the vertical axis indicates
 the output voltage rate of the scratch tester in %.
 As shown in the graph, the pressure of the adhesive strength was 11.8gf and
 13.9 gf respectively in absence of l.R. and U.V. ashing. The pressure was
 21.4 gf and 29.8 gf respectively in case of applying l.R. and U.V. ashing.
 It acknowledges that the adhesive strength becomes stronger.
 Furthermore, the contact resistance between the ITO layer 400 and the black
 matrix 200 is remarkably reduced since executing the l.R. and U.V. ashing
 eliminates any traces of pigment residual from the surface of the black
 matrix 200.
 FIG. 2F illustrates the structure of the color filter substrate of a LCD
 manufactured according to the embodiment of the present invention.
 As shown in FIG. 2F, a substrate 100 has a first layer of a black matrix
 200 spaced evenly apart. In the second layer, the red, blue, and green
 color filters 310, 320 and 330, respectively, made of photosensitive
 resist, are overlaid so they are spaced evenly apart on the same plane and
 the edges overlap the edges of the black matrix. On the final layer, the
 ITO layer 400 covers both the color filters 310, 320, 330 and the black
 matrix 200.
 In the manufacturing method of the color filter substrate according to the
 present invention, traces of moisture, gas or pigment residue remaining in
 the color filters or on the surfaces of the black matrix are removed by
 executing I.R. and U.V. ashing on the surfaces of the black matrix and the
 color filters before forming the ITO layer. Accordingly, the quality of a
 liquid crystal display is improved by reinforcing the adhesive strength of
 the color filters and the black matrix, to the ITO layer. Any separation
 between the two substrates, or detachment of the ITO layer from the color
 filters and the black matrix disappear. Furthermore, contact resistance
 between the ITO layer and the black matrix is reduced by removing any
 pigment residue on the surface of the black matrix.