Method of fabricating color filter substrate for liquid crystal display device

A method of fabricating a color filter substrate for a liquid crystal display device includes forming a black matrix on a substrate, adhering a color transcription film to the substrate, disposing a laser head over the color transcription film, repeatedly scanning a laser beam across a surface of the color transcription film using the laser head, removing the color transcription film so that a color filter pattern remains within color filter pattern regions defined by the black matrix, and polishing a surface of the color filter pattern to planarize a surface of the color filter pattern.

The present invention claims the benefit of Korean Patent Application No. P2002-077949 filed in Korea on Dec. 9, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of fabricating a display device, and more particularly, to a method of fabricating a color filter substrate for a liquid crystal display device.

2. Discussion of the Related Art

With rapid development within the information technology field, display devices have evolved to be able to process and display increasingly large amounts of information. Flat panel display technologies recently have been developed for display devices having small thickness, light weight, and low power consumption. Among these technologies, liquid crystal display (LCD) devices commonly have been used in notebook computers and desktop computer monitors due to their superior image resolution, color image display, and image quality.

In general, an LCD device includes an upper substrate, a lower substrate, and a liquid crystal layer disposed between the upper and lower substrates. The LCD device makes use of optical anisotropy of liquid crystal material and produces images by varying light transmittance according to the alignment of liquid crystal molecules by an electric field.

The lower substrate, which is commonly referred to as an array substrate, includes thin film transistors and pixel electrodes, and is fabricated using repeated photolithographic processes to pattern thin films. The upper substrate, which is commonly referred to as a color filter substrate, includes a color filter layer for displaying color images. The color filter layer commonly includes sub-color filters of red (R), green (G), and blue (B), and is formed by various methods including, for example, a dyeing method, an electro-deposition method, a pigment dispersion method, and a printing method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility.

FIGS. 1Ato1D are cross sectional views of a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art. Here, the pigment dispersion method is used.

InFIG. 1A, a black matrix15is formed on an insulating substrate10by depositing a metal material or coating a resin, and patterning the metal material or the resin through a photolithographic processes. The black matrix 15 blocks light leakage, which is caused by irregular operation of liquid crystal molecules, within regions except for pixel electrodes of an array substrate (not shown). The black matrix15also prevents light from being transmitted into a channel of a thin film transistor of the array substrate.

InFIG. 1B, a color resist17, which may be one of red, green, and blue resists, for example a red one, is coated onto the substrate10including the black matrix thereon by spin coating. A mask20having a light transmitting portion and a light blocking portion is disposed over the red resist17, and the red resist17is exposed to light using the mask20. Here, the red resist17is shown to have a negative property, i.e., a portion of the red resist17that is not exposed to light is removed.

InFIG. 1C, the red resist17(inFIG. 1B) is developed, and a red color filter pattern17ais formed. Then, the red color filter pattern17ais cured and hardened.

InFIG. 1D, green and blue color filter patterns17band17care formed on the black matrix15through similar processes, as shown inFIGS. 1B and 1C. Next, an overcoat layer23and a common electrode25are subsequently formed on the substrate10including the color filter patterns17a,17b, and17c. The overcoat layer23protects the color filter patterns17a,17b, and17c, and flattens the surface of the substrate10having the color filter patterns17a,17b, and17c. The common electrode25is made of a transparent conductive material, such as indium-tin-oxide and indium-zinc-oxide.

During the fabrication method of the color filter substrate using the pigment dispersion, since the color filter substrate is fabricated by repeated processes of coating, exposing, developing, and curing of a color resist, the fabrication method is complicated and requires significant amounts of time and numerous pieces of equipment. To solve the above problem, a fabrication method of a color filter substrate using thermal imaging has been proposed, as disclosed for example in U.S. Pat. No. 6,242,140, which is hereby incorporated by reference.

FIGS. 2Ato2D are cross sectional views of another method of fabricating a color filter substrate using thermal imaging according to the related art. InFIG. 2A, a black matrix35is formed on an insulating substrate30by depositing a metal material or coating a resin, and patterning the metal material or the resin by photolithographic processes.

InFIG. 2B, a first color transcription film40is disposed over the substrate30including the black matrix35. The first color transcription film40includes a supporting film40a, a light-to-heat conversion (LTHC) layer40b, and a color filter layer40c.

InFIG. 2C, the first color transcription film40is adhered to the substrate30without bubbles. A laser head50, from which a laser beam is generated, is disposed over the first color transcription film40. Then, the laser beam is applied to the first color transcription film40within a portion where a first color filter pattern will be formed later while the laser head50is reciprocated along a straight line. In the first color transcription film40exposed to the laser beam, the LTHC layer40btransforms light absorbed from the laser beam into thermal energy and emits the thermal energy. Accordingly, the color filter layer40cis transferred onto the substrate30due to the emitted thermal energy. Here, the color filter substrate may be a stripe type where color filter patterns are disposed along a line each having the same color. Thus, a first line is exposed to the laser beam by moving the laser head along a straight line, but second and third lines are skipped. Similarly, a fourth line is exposed to the laser beam. Using these processes, all the lines of the first color filter pattern are exposed, and the first color transcription film40is removed.

InFIG. 2D, the first color filter pattern45ais formed between the adjacent black matrixes35on the substrate30, wherein the first color filter pattern45amay be a red color filter. A second color filter pattern45band a third color filter pattern45care formed through the same process, as shown inFIGS. 2B and 2C, wherein the second and third color filer patterns45band45cmay be green and blue color filters, respectively. The substrate30having the color filter patterns45a,45b, and45cis placed in a hardening furnace, and the color filter patterns45a,45b, and45care hardened. An overcoat layer47is formed on the color filter patterns45a,45b, and45cin order to protect the color filter patterns45a,45b, and45c, and to flatten the surface of the substrate30otherwise having steps. Next, a common electrode49is formed on the overcoat layer47by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide.

During the thermal imaging method, manufacturing throughput of the color filter substrate is influenced by an application direction of the laser beam, wherein the laser beam is applied to the transcription film along a direction parallel to a pixel length of the LCD device. For example, in a color filter substrate of a video graphic array (VGA) LCD device, which has a resolution of 640 by 480, the VGA LCD device has sub-pixels of 640 by 3 lines (i.e., 1920 lines). Thus, the laser head50must scan 640 times for each color filter pattern, and a total number of scans is 1920. In addition, a size of the pixel depends on the resolution being used (e.g., VGA, SVGA (super video graphic array), XGA (extended graphic array), and so on), thereby making it problematic to have a laser beam fit for each different pixel size.

The scanning of the laser head50may be accomplished along a direction parallel to a pixel width of the LCD device, thereby reducing the scanning times. This may be referred to as a horizontal laser scan. The manufacturing throughput of the color filter substrate is improved due to reduction of the scanning times. However, in this case, there is a problem that scanning traces may be formed at pixel regions, thereby reducing image quality.

FIG. 3is a plan view of a color filter substrate fabricated by a thermal imaging method using a horizontal laser scan according to the related art. InFIG. 3, a substrate30includes a black matrix35and a color filter pattern45thereon, wherein the black matrix35has an opening in which the color filter pattern45is placed. The color filter pattern45is formed by the above-described thermal imaging method using a horizontal laser scan. A laser head50having a plurality of laser pixels52first scans the substrate30along a horizontal direction of the substrate30repeatedly turning the laser pixel52ON and OFF. After the first scan, the laser head50is moved along the vertical direction of the substrate30by a width of the first scan, and a second scan is accomplished. Here, a scanning trace55is formed along a border between first and second scanning regions, and is situated on the color filter pattern45.

FIG. 4Ais an enlarged view of a region A inFIG. 3according to the related art, andFIG. 4Bis a cross sectional view along IV—IV ofFIG. 4Aaccording to the related art.

InFIGS. 4A and 4B, after repeated laser scans, the scanning trace55is formed on the color filter pattern45because of scanning borders of the first and second scans. When a laser beam is applied to a light-to-heat conversion (LTHC) layer of a transcription film, photo energy from the laser beam applied to the LTHC layer is transformed into thermal energy. Accordingly, a color filter layer is transferred onto the substrate due to the thermal energy, wherein the color filter layer is actually transferred onto a larger area than the region actually exposed to the laser beam. In addition, due to difference in scanning times, spontaneous hardening of the color filter film, and the expansion rate of the color filter layer, the scanning trace55may have a certain thickness that protrudes over the surface of the color filter pattern45. Thus, the scanning trace55on the color filter pattern45lowers image quality.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of fabricating a color filter substrate for a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that improves image quality.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of fabricating a color filter substrate for a liquid crystal display device includes forming a black matrix on a substrate, adhering a color transcription film to the substrate, disposing a laser head over the color transcription film, repeatedly scanning a laser beam across a surface of the color transcription film using the laser head, removing the color transcription film so that a color filter pattern remains within color filter pattern regions defined by the black matrix, and polishing a surface of the color filter pattern to planarize a surface of the color filter pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5Ais a plan view of an exemplary laser head according to the present invention, andFIG. 5Bis a plan view showing an exemplary laser pixel of the laser head ofFIG. 5Aaccording to the present invention. InFIGS. 5A and 5B, a laser head160may have about 224 laser pixels162arranged along a line, wherein each of the laser pixels162may have a length L of about 5 μm to about 20 μm and a width W of about 3 μm to 5 μm. Of course, the laser pixel162may have a different size, i.e., larger or smaller, than the laser pixels162when the power of each of the laser pixels162is considered. For example, an entire size of the laser pixels162within the laser head160may be about 4480 μm by about 31 m, and a scan width of the laser head160may be about 4480 μm. The laser pixels162of the laser head160may be automatically operated by a computer system such that each of the laser pixels162turn ON and OFF according to red, green, and blue color filter patterns.

FIG. 6is a cross sectional view of an exemplary color transcription film according to the present invention. InFIG. 6, a color transcription film110may include three layers: a supporting film110a; a light-to-heat conversion (LTHC) layer110b; and a color filter layer110c. The supporting film110a, which may support the LTHC layer110band the color filter layer110c, may include a high molecular substance, such as polyester and polyethylene, having transparent and high transmittance characteristics in order to transmit a laser beam to the LTHC layer110b. The LTHC layer110bmay be formed on the supporting film110aand may be made of a material that can efficiently convert light into heat energy. Accordingly, the LTHC layer110bmay convert light energy from a laser head into heat energy. The LTHC layer110bmay include an organic material, such as carbon black and IR (infrared) pigments, or an inorganic material, such as a metal material (i.e., aluminum (Al), metallic oxide, or alloy of the above materials). The color filter layer110c, which may be the layer to be transferred, may be formed on the LTHC layer110band may include one of red, green, and blue colors.

FIGS. 7Ato7E are cross sectional views of an exemplary method of fabricating a color filter substrate according to the present invention. Here, a color filter substrate ofFIGS. 7Ato7E shows pixels along a line having the same color, for example red, and for convenience of explanation, a laser head may be illustrated to be shortened as compared with a region between black matrixes of a substrate.

InFIG. 7A, a black matrix105may be formed on an insulating substrate100by depositing a metal material, such as chromium (Cr), or coating a resin, such as an epoxy. Then, the metal material or resin may be patterned through photolithographic processes.

InFIG. 7B, a first color transcription film120, which may include a supporting film120a, a light-to-heat conversion (LTHC) layer120b, and a color filter layer120c, may be disposed over the substrate100including the black matrix105with the color filter layer120cfacing the substrate100. The first color transcription film120may be adhered to the substrate100without bubbles, and a laser head160may be disposed at a distance over the first color transcription film100. Then, a laser beam of the laser head160may be applied to the first color transcription film120in a portion where a first color filter pattern will be formed later as the laser head160scans the substrate130by reciprocating the laser head160along a straight line or moving a stage fixing the substrate100thereon along a straight line. In the first color transcription film120exposed to the laser beam, the LTHC layer120bmay transform light absorbed from the laser beam into thermal energy, thereby emitting thermal energy. Then, the color filter layer120cmay be transferred onto the substrate100due to the emitted thermal energy.

InFIGS. 7Ato7E, the color filter substrate may be a stripe-type, wherein color filter patterns along a line may have the same color. Accordingly, a first line may be exposed to the laser beam by moving the laser head along a straight line. However, second and third lines may be skipped. Similarly, a fourth line may be exposed to the laser beam. In this manner, all the lines of the first color filter pattern may be exposed. After a first scan, one of the substrate100and the laser head160is transferred, and the second, third, and fourth scans may be sequentially performed.

InFIG. 7C, the first color transcription film120(inFIG. 7B) may be removed after the whole substrate100is scanned. Here, the color filter layer120ccorresponding to the LTHC layer120bexposed to the laser beam may be transferred onto the substrate100, while the color filter layer120ccorresponding to the LTHC layer120bnot exposed to the laser beam may be removed together with the color transcription film120(in FIG.7B). Accordingly, a first color filter pattern125may be formed both between the adjacent black matrixes105on the substrate100and on the black matrixes105. In the example shown, the first color filter pattern125may be a red color filter.

Scanning traces130may be formed along borders between the first, second, third, and fourth scans on the color filter pattern125. The scanning traces130protrude over the color filter pattern125. Next, although not shown in the figures, a second color filter pattern and a third color filter pattern may be formed through the same process shown inFIGS. 7B and 7C. The second and third color filter patterns may be green and blue color filters, respectively. Next, the substrate100having the color filter pattern125may be placed into a hardening furnace, and the color filter pattern125may be hardened under temperatures within a range of about 200 degrees of Celsius to about 300 degrees of Celsius.

InFIG. 7D, the substrate100including the hardened color filter pattern125may be situated onto a stage (not shown), and the surface of the color filter pattern125may be polished by a chemical mechanical polishing (CMP) process using a polisher150moved along the surface of the color filter pattern125or by moving the stage. Accordingly, the scanning traces130may be removed and the surface of the color filter pattern125may be flattened (or planarized). In addition, a surface roughness of the color filter pattern125may be improved. The polishing process may be accomplished along an entire surface of the color filter pattern125, or may be performed within specified portions of the color filter pattern125.

InFIG. 7E, a common electrode140may be formed on the color filter pattern125by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide. Thus, an overcoat layer may be formed between the color filter pattern125and the common electrode140may be omitted since the color filter pattern125has a flat surface due to the polishing process.

According to the present invention, since the scanning traces formed along a border between adjacent scans may be removed through a polishing process, such as a CMP process, a liquid crystal display device having high quality images may be provided. In addition, manufacturing costs may be reduced since the overcoat layer may be omitted.

It will be apparent to those skilled in the art that various modifications and variations can be made in the color filter substrate and method of fabricating a color filter substrate of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.