WO2006025639A1

WO2006025639A1 - Apparatus for cleaning a substrate and method thereof

Info

Publication number: WO2006025639A1
Application number: PCT/KR2005/001196
Authority: WO
Inventors: Il-Soon Kwak; Yoo-Chan Choi; Sung-Won Choi; In-Yong Seo
Original assignee: Sfa Engineering Corp.
Priority date: 2004-09-02
Filing date: 2005-04-26
Publication date: 2006-03-09
Also published as: KR100528286B1

Abstract

Disclosed herein are a method and an apparatus for cleaning a substrate using a mixture of electrolyzed water and ozone water during fabrication of a display device. The apparatus comprises a loading section, a cleaning section and an unloading section wherein the cleaning section includes electrolyzed water/ozone water cleaning means arranged adjacent to the loading section to spray electrolyzed water/ozone water on a substrate so as to clean the substrate, rinsing means arranged adjacent to the electrolyzed water/ozone water cleaning means to rinse the cleaned substrate using deionized water, drying means arranged adjacent to the rinsing means to dry the rinsed substrate, and substrate conveying means for passing the substrate through the loading section, the cleaning section and unloading section in this order.

Description

APPARATUSFORCLEANINGASUBSTRATEANDMETHOD

THEREOF

Technical Field

[1] The present invention relates to a method and an apparatus for cleaning a substrate during fabrication of a display device, and more particularly to a method and an apparatus for cleaning a substrate using a mixture of electrolyzed water and ozone water (hereinafter, referred to as "electrolyzed water/ozone water"). The method and the apparatus of the present invention can be applied to the fabrication of displays, semiconductors, printed circuit boards (PCBs), laser diodes (LDs), and light-emitting diodes (LEDs).

[2]

Background Art

[3] In general, examples of display substrates include glass substrates for liquid crystal displays (LCDs), glass substrates for plasma display panels (PDPs), and plastic substrates for organic electroluminescent displays (OELDs).

[4] With recent increasing demand for display substrates, much research has conducted to improve the functions of display substrates. In particular, a number of studies on display substrates have been devoted to large area, wide viewing angle and the like of display substrates since the 1990's. This tendency will be continued from now on.

[5] Display substrates are produced through two processes: a cell process for producing substrate panels and a module process for fabricating the panels into the finished products.

[6] In the cell process, cleaning, deposition and etching of an original substrate are r epeatedly carried out to produce a substrate having a particular pattern. Since the deposited pattern of the substrate is a product of micro-processes crucial to the production of a display substrate, cleaning for removing impurities present on the substrate is required in the respective sub-processes of the cell process.

[7] On the other hand, the module process is carried out to fabricate the finished substrate panel into one display module. For example, a display module is fabricated by forming driver ICs on a display substrate.

[8] As described above, cleaning is required in the respective sub-processes during the production of a display substrate. This cleaning is an important process influencing the production yield of the display substrate. Currently used cleaning processes are performed in the respective steps for the production of display substrates, and thus repeatedly several times through the overall procedure. [9] Deionized water (DIW) is commonly used as a cleaning solvent in conventional substrate cleaning methods. Mixtures of DIW and chemicals, e.g., surfactants, may be used as cleaning solutions.

[10] Chemicals are mainly used to remove cullet and particles causing short lines, short circuits and leakages in display substrates, organic materials, such as oils and fats, de¬ teriorating adhesion of thin films, and natural oxide films damaging the contact properties of display substrates.

[11] If contaminants are insufficiently removed by cleaning, pattern defects on array substrates and poor operation of transistors frequently occur, leading to low yields of the array substrates.

[12] Therefore, selection of cleaning methods, equipment and processes according to the purposes of cleaning is of great importance.

[13] Conventional cleaning methods comprise a first step of removing particles and metal impurities using chemicals, a second step of rinsing off the residual chemicals using DIW, and a third step of removing organic materials by UV cleaning.

[14] For example, a conventional cleaning method is accomplished by using the cleaning apparatus shown in Fig. 1. Referring to Fig. 1, the conventional cleaning apparatus 1 has a complicated structure consisting essentially of a loader 10, a UV cleaner 20, a deionized water rinser 30, a roll brasher 40, a cavitation jet 50, an ultrasonic cleaner 60, a final rinser 70, a drier 80, and an unloader 90, these units being connected con¬ secutively in this order. A cleaning operation is performed by passing a substrate through the stages where chemicals are used for cleaning.

[15] The conventional cleaning method has the problem that enormous costs for the respective processes are incurred. Particularly, since display substrates using low- temperature poly-Si TFTs require elaborate cleaning of the level required in semi¬ conductor manufacturing technologies, there exists a strong need to develop improved cleaning techniques.

[16] In actual processes, radicals may be generated during formation of a SiO film or a poly-Si layer on a substrate, during laser annealing after the formation, or during lithography. These radicals impede the formation of physical and chemical bonds between thin films and cause a decrease in the production yield of the substrate.

[17] Chemicals and physical cleaning employed to remove radicals causes the formation of crystallographic bonds of thin films and residual ions, resulting in deteriorated performance and low production yields of substrates.

[18] Thus, there is a demand for the introduction of new environmentally friendly wet- cleaning processes using electrolyzed water (EW) with no formation of ions.

[19] In recent years, reduced consumption of chemicals has been more and more important with a growing demand for environmental protection and low production costs. Under such circumstances, there is a demand to decrease the concentration of chemicals while maintaining the contaminant removal capacity in conventional liquid cleaning procedures and to develop novel cleaning solvents.

[20] Since the 1990's, a variety of physical cleaning [ultrasonic cleaning], wet cleaning and dry cleaning processes have been suggested for the purpose of adding new functions and lowering the cleaning costs.

[21] Of these, a cleaning method using tetramethylammonium hydroxide (TMAH) has been known, and a cleaning method using a cleaning solution of deionized water in TMAH is currently used in combination with physical cleaning.

[22] These cleaning methods are advantageous in terms of improved functions, but suffer from the problems associated with the use of a great amount of deionized water, poor cleaning functions, high running costs for cleaning and treatment of wastewater generated after cleaning when applied to the overall production procedure of display substrates on an industrial scale.

[23] In addition, since various kinds of chemicals are used in large quantities for the surface treatment of currently available TFT-LCD substrates, there always exist the problems of high-price chemicals, increased post-treatment costs, safety risks for operators, serious environmental pollution, and the like. That is, discharge of con¬ siderable amounts of wastewater and waste materials due to large quantities of water and various kinds of chemicals used for the cleaning processes causes the problems of increased costs, safety risks for operators, serious environmental pollution, and the like.

[24] It is desirable to prevent generation of pollutants rather than to treat already generated pollutants. In view of this, there is a strong need to develop a novel cleaning method which does not generate any generation of pollutants. The U.S. government began to take specific measures to restrict the generation of pollutants, and has dedicated to joint research through the SEMATECH government-industry partnership, and as a result, found satisfactory solutions to a considerable extent. In Japan, joint de¬ velopment projects in cooperation with the Ministry of International Trade and Industry have been undertaken, and as a result, achieved a reuse rate of chemicals and water higher than about 50%.

[25] Although trivial, Korean industries have reviewed related materials and data, and promoted basic research. However, such efforts largely depend on foreign countries due to releative technical inferiority in materials and equipment. Korean industries manage to respond to the problems related to the generation and prevention of pollutants through optimization of currently available processes. Namely, little research has been conducted, in Korea, to develop substitute technologies and process improvement technologies for reducing the discharge of pollutants during production. [26]

Disclosure of Invention Technical Problem

[27] It is one object of the present invention to provide a method and an apparatus for cleaning a substrate which are environmentally friendly without substantial use of chemicals and are highly economically advantageous due to reduced costs through process simplification.

[28] It is another object of the present invention to provide a method and an apparatus for cleaning a substrate in which cleaning water is reused, considerably reducing the amount of deionized water used.

[29]

Technical Solution

[30] In accordance with an aspect of the present invention for achieving the above objects, there is provided an apparatus for cleaning a substrate which comprises a loading section, a cleaning section and an unloading section wherein the cleaning section includes electrolyzed water/ozone water cleaning means arranged adjacent to the loading section to spray electrolyzed water/ozone water on a substrate so as to clean the substrate, rinsing means arranged adjacent to the electrolyzed water/ozone water cleaning means to rinse the cleaned substrate using deionized water, drying means arranged adjacent to the rinsing means to dry the rinsed substrate, and substrate conveying means for passing the substrate through the loading section, the cleaning section and unloading section in this order.

[31] Preferably, the electrolyzed water/ozone water cleaning means includes an ozone water generator for generating ozone and dissolving the ozone in water to generate ozone water, an electrolyzed water generator for electrolyzing deionized water to generate electrolyzed water, stirring units for mixing the ozone water generated from the ozone water generator and the electrolyzed water generated from the electrolyzed water generator and stirring the mixture to form electrolyzed water/ozone water, and sprayers for spraying the electrolyzed water/ozone water on a substrate.

[32] In accordance with another aspect of the present invention, there is provided a method for cleaning a substrate comprising the steps of:

[33] 1) spraying electrolyzed water/ozone water on a substrate to clean a substrate;

[34] 2) spraying deionized water on the cleaned substrate to rinse the substrate; and

[35] 3) spraying high-pressure air on the rinsed substrate to dry the substrate.

[36] Preferably, step 1) includes the sub-steps of:

[37] a) generating ozone and dissolving the ozone in deionized water to generate ozone water (ozone water generation step); [38] b) electrolyzing deionized water to generate electrolyzed water (electrolyzed water generation step); [39] c) mixing the ozone water and the electrolyzed water, and stirring the mixture to form electrolyzed water/ozone water; and

[40] d) spraying the electrolyzed water/ozone water on a substrate to clean the substrate.

[41]

Advantageous Effects

[42] The electrolyzed water/ozone water used in the present invention contains electrolyzed water generated by electrolysis of deionized water (DIW) without substantial use of chemicals. In addition, the cleaning method of the present invention uses a lesser amount of deionized water than conventional methods.

[43] Since the present invention uses cleaning water having a very broad range of pH and oxidation reduction potential (ORP) without addition of any chemical, the degree of cleaning is optimized, leading to improved productivity of display substrates and enabling environmentally friendly cleaning.

[44] Further, according to the present invention, the cost of chemicals can be reduced due to the use of electrolyzed water, and the failure of the final product can be markedly lowered, thus attaining economical cost-effectiveness.

[45] Further, according to the cleaning method of the present invention, pH and oxidation reduction potential required in the respective steps during cleaning of the display substrate are imparted to the cleaning water, allowing the cleaning water to have superior cleaning capability. Particularly, since the electrolyzed water molecules contain smaller H⁺ and OH^" ions in size than common water, they exhibit a lower surface tension than common water, thus enabling penetration into microholes. As a result, the present invention enables cleaning of fine sites and high degree of in¬ tegration on the display substrate, when compared to conventional techniques.

[46] Further, according to the cleaning method of the present invention, since the number of repeated cleaning processes can be decreased, the overall procedure is simplified and the amount of deionized water used is reduced.

[47] Further, according to the cleaning method of the present invention, since deionized water is reused during cleaning by recirculation, the amount of deionized water used can be greatly reduced. Accordingly, since the cleaning method of the present invention can reduce the amount of environmental pollutants generated from the display substrate production processes, it can basically solve the industrial envi¬ ronmental problems, aiding efficient response to governmental environmental regulations in developed countries. Further, the ozone water generator used in the present invention is a low-price, high-efficiency apparatus, and has the advantage that it can be freely used anywhere using a common power supply. Therefore, since the ozone water generator is economically advantageous, poorly-equipped farmers and small- and medium-enterprises can widely employ the apparatus without economical burden. [48]

Brief Description of the Drawings [49] Theabove and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[50] Fig. 1 is a conceptual diagram of a conventional substrate cleaning apparatus;

[51] Fig. 2 is a conceptual diagram of a substrate cleaning apparatus according to one embodiment of the present invention; [52] Fig. 3 is a conceptual diagram showing the configuration of electrolyzed water/ ozone water cleaning means used in one embodiment of the present invention; [53] Fig. 4 is a view showing the structure of a sprayer used in one embodiment of the present invention; [54] Fig. 5 is a fragmentary perspective view showing the structure of a substrate mounting plate used in one embodiment of the present invention; [55] Figs. 6a to 6c show side views and a plan view showing the structures of drying means used in respective embodiments of the present invention; [56] Fig. 7 is a cross-sectional view showing the configuration of ultrasonic cleaning means used in one embodiment of the present invention; [57] Fig. 8 is a cross-sectional view showing the configuration of plasma cleaning means used in one embodiment of the present invention; and [58] Fig. 9 is a process chart showing the procedure of a substrate cleaning method according to one embodiment of the present invention. [59]

Mode for the Invention [60] Hereinafter, specific embodiments of the present invention will be described with reference to the attached drawings. [61]

[62] <Embodiment 1>

[63] A substrate cleaning apparatus 100 of this embodiment comprises a loading section, a cleaning section, and an unloading section. [64] The loading section 110 acts to continuously provide each display substrate S to the cleaning section in which the display substrate is to be cleaned. The loading section

110 includes conveying means (not shown) for delivering the display substrate S provided from the outside to the cleaning section. In this embodiment, the conveying means is composed of a plurality of rollers in the shape of a wheel and spaced at fixed intervals from a rotatory shaft so that it minimize the contact area with display substrate in the conveying process and prevent any contamination on the substrate.

[65] Next, the unloading section 120 serves to discharge the display substrate S cleaned in the cleaning section to the outside. Like in the loading section 110, the unloading section 120 includes conveying means (not shown) for conveying the cleaned display substrate. The display substrate conveyed by the action of the unloading section is mounted on a substrate loading system (for example, a cassette).

[66] The cleaning section plays a role in cleaning the display substrate so as to remove contaminants from the substrate surface. The cleaning section includes electrolyzed water/ozone water cleaning means 130, rinsing means 140, drying means 150, and conveying means R.

[67] The electrolyzed water/ozone water cleaning means 130is arranged adjacent to the loading section 110 and is an element for spraying electrolyzed water/ozone water on the substrate to clean the substrate. Particularly, the electrolyzed water/ozone water cleaning means 130 used in this embodiment is an important element capable of replacing cleaning means using chemicals in conventional cleaning apparatuses. The electrolyzed water/ozone water cleaning means 130 includes an ozone water generator 132, an electrolyzed water generator 134, stirring units 136, and sprayers 138.

[68] The ozone water generator 132 is a unit that induces an electric discharge in air to generate ozone and dissolves the ozone in water to generate ozone water. In this embodiment, the ozone water generator 132 includes a discharger (not shown) for causing a corona discharge in oxygen and a gas diffuser (not shown) for delivering the ozone and oxygen to the discharger. The ozone generated from the discharger is released in the form of gas bubbles through the gas diffuser into water and then the ozone molecules are dissolved in the water to form ozone water.

[69] The electrolyzed water generator 134 is a unit where water is electrolyzed to generate electrolyzed water. In this embodiment, deionized water is electrolyzed, and is then separated into water containing hydrogen ions (H⁺) and oxidative ions and water containing hydroxide ions (OH^") and reductive ions via an ion-exchange membrane. Electrolyzed water has a very broad range of pH and oxidation reduction potential even in the absence or presence of slight amounts of chemicals. Accordingly, the use of electrolyzed water in this embodiment optimizes the degree of cleaning of display substrates, leading to improved productivity and enabling environmentally friendly cleaning. In this embodiment, as shown in Fig. 3, electrolyzed water obtained in a cathode cell 134a and electrolyzed water obtained in an anode cell 134b are separately activated and sprayed to maximize the cleaning capability. [70] The stirring units 136 are units for mixing the ozone water generated from the ozone water generator 132 and the electrolyzed water generated from the electrolyzed water generator 134 to form electrolyzed water/ozone water.

[71] The sprayers 138 are units for spraying the electrolyzed water/ozone water on the display substrate S. In this embodiment, the sprayers 138 may have various structures.

[72] The sprayers are provided with an atomizing nozzle for degrading the electrolyzed water/ozone water to a water molecular size and spraying it on the substrate. That is, the atomizing nozzle degrades the electrolyzed water/ozone water to a size sub¬ stantially equal to that of water molecules before spraying at high speed. Accordingly, the atomizing nozzle is suitable for the removal of small-sized particles adhered to the display substrate. Small-sized particles are not readily removed by drops of water sprayed from general nozzles because the force of the sprayed water is dispersed. For this reason, only when the particles collid with drops of water having a size equal to or smaller than that of the particles, are they separated from the display substrate.

[73] Particularly, in the case where the sprayers are provided with a two-phase flow nozzle as shown in Fig. 4, the particles separated from the display substrate are moved by an air so that the particles are completely removed from the substrate. The term "two-phase flow nozzle" used herein refers to a nozzle that mixes a liquid and a gas and sprays the mixture. Specifically, a mixer is arranged in front of the atomizing nozzle to enable simultaneous spraying of a gas and a liquid.

[74] In this embodiment, the sprayers 138 may be provided with a pressure control nozzle that can control the spraying pressure of a liquid. The pressure control nozzle has the advantage that the pressure of a liquid sprayed from the nozzle can be varied from low to high pressure. Accordingly, the spray pressure of the liquid is controlled depending on the type of the display substrate to be cleaned and the kind of con¬ taminants to be removed, thus attaining satisfactory cleaning effects.

[75] It is preferred that the electrolyzed water/ozone water cleaning means 130 further includes a substrate mounting plate 139 for rotating the display substrate while being fixed. Specifically, the display substrate S is fixed on the substrate mounting plate 139 and is rotated at high speed while it is cleaned by the electrolyzed water/ozone water. Spraying of the electrolyzed water/ozone water in the direction opposite to that of the substrate rotating at high speed increases the relative speed of the electrolyzed water/ ozone water and the substrate, and as a result, the impulse on the particles adhered to the substrate is further increased and thus satisfactory cleaning of the substrate is obtained.

[76] In this embodiment, fixing of the display substrate S on the substrate mounting plate 139 is accomplished by vacuum adsorption. That is, a plurality of vacuum holes are formed on the mounting surface of the substrate mounting plate and are connected to a vacuum pump. Suction of a gas via the vacuum holes allows the substrate to be firmly fixed on the mounting plate.

[77] A grab is provided on the periphery of the substrate mounting plate in such a manner that the plate is bound and fix to the side of the substrate. In this case, the substrate is physically fixed to the substrate mounting plate.

[78] It is preferred that the electrolyzed water/ozone water cleaning means 130 further includes a cleaning water regeneration unit 131. The cleaning water regeneration unit 131 is a unit where the cleaning water used for the cleaning is collected, filtered, and then supplied to the electrolyzed water generator 134 and the ozone water generator 132. Since the display substrate cleaning apparatus 100 of this embodiment uses deionized water as raw water, the apparatus requires a filter system that can performs a filtering process for removing fine particles and a deionization process for removing ions.

[79] The rinsing means 140 is arranged adjacent to the electrolyzed water/ozone water cleaning means 130, and is an element for removing contaminants remaining on the surface of the substrate after cleaning by rinsing using the electrolyzed water/ozone water. In this embodiment, deionized water is used in the rinsing means 140.

[80] The drying means 150 is arranged adjacent to the rinsing means 140, and is an element for removing the deionized water sprayed from the rinsing means 140 to dry the display substrate. That is, high-pressure air is sprayed on the cleaned display substrate S to remove moisture present on the substrate surface in the drying means. Prompt drying of the cleaned substrate enables rapid application to subsequent processes, advantageously shortening the overall process time.

[81] In this embodiment, the drying means 150 is composed of at least one air knife for spraying high-pressure air to dry one side of the display substrate, as shown in Figs. 6a to 6c. Referring to Fig. 6a, two air knives are preferably provided on upper and lower sides of a line through which the display substrate passes to simultaneously dry the top and bottom surfaces of the substrate. Referring to Fig. 6b, for more complete drying of the substrate, two or more air knives are preferably provided rather than one air knife on each side.

[82] Referring to Fig. 6c, the air knives preferably move in the direction slanted to the substrate so as to perform the drying step.

[83] If necessary, it is preferred that an ionizer (not shown) is further provided to completely remove a static electricity remaining on the cleaned substrate S so as to be suitable for the subsequent processes.

[84] Like in the loading section 110 and the unloading loading section 120, the cleaning section includes conveying means R for conveying the display substrate S. The conveying means R conveys the display substrate to the unloading section 120 through the respective parts of the cleaning section.

[85] Preferably, the substrate cleaning apparatus 100 of this embodiment further comprises ultrasonic cleaning means 160 arranged between the electrolyzed water/ ozone water cleaning means 130 and the rinsing means 140. The ultrasonic cleaning means 160 is an element for sonicating the surface of the display substrate to remove contaminants remaining on the surface of the display substrate. In this embodiment, as shown in Fig. 7, the ultrasonic cleaning means 160 consists of an ultrasonic- wave transmission plate 162 and an ultrasonic wave generator 164. First, a sound wave having a frequency of 1-5 MHz is generated from the ultrasonic wave generator 164. It is generally known that an ultrasonic wave refers to a sound wave having a frequency of 20-1,000 KHz, which is a frequency band inaudible to humans. In this embodiment, a sound wave having a frequency band higher than 20-1,000 KHz is used. Specifically, a sound wave (i.e., megasonic wave) having a frequency of 1-5 MHz is used. The megasonic wave having a high energy is used to remove impurities present on the substrate. Of course, an ultrasonic wave having a frequency band lower than that of the megasonic wave may be used. A sound wave having a frequency of several MHz is applied to special glass substrates, causing damage to the substrates. If needed, the frequency of the sound wave is changed in order to prevent the damage. The ultrasonic-wave transmission plate 162 is a unit for transmit the ultrasonic wave generated from the ultrasonic wave generator 164 to the substrate surface. Water is used as a medium to transmit the ultrasonic wave. In this embodiment, as shown in Fig. 7, the substrate S is approached to the ultrasonic- wave transmission plate 162 to a spacing of several millimeters, and deionized water is injected therebetween in such a manner that the deionized water W is interposed between the substrate and the ultrasonic-wave transmission plate 162. When the ultrasonic wave generator 164 is driven to generate an ultrasonic wave, the ultrasonic- wave transmission plate 162 uniformly transmits the ultrasonic wave to all sides of the display substrate S.

[86] Preferably, the substrate cleaning apparatus 100 of this embodiment further comprises plasma cleaning means 170 arranged between the loading section 110 and the electrolyzed water/ozone water cleaning means 130. The plasma cleaning means 170 is an element for removing organic contaminants from the display substrate S using atmospheric pressure plasma. Accordingly, the plasma cleaning means 170 replaces a UV cleaner used in conventional cleaning apparatuses.

[87] As shown in Fig. 8, the plasma cleaning means 170 includes an electrode unit 172, protrusion-type radiation plates 174, a raw gas supply unit 176, plasma discharge ports 178, and suction/exhaust units 179. Referring to Fig. 8, the plasma cleaning means 170 is provided with a central space in which the electrode unit 172, the raw gas supply unit 176 and the plasma discharge ports 178 are formed, and left and right spaces in which the protrusion-type radiation plates 174 and the suction/exhaust units 179 are formed.

[88] The electrode unit 172 is provided with three electrodes spaced parallel at fixed intervals in the central portion of the plasma cleaning means 170. Referring to Fig. 8, the protrusion-type radiation plates 174 are formed in such a manner that they are in contact with the outer electrodes 172a and 172c. The raw gas supply unit 176 is formed on top of the electrodes 172a, 172b and 172c, and includes a temporary raw gas storage tank 176a, a raw gas diffusion member 176b formed in the middle of the temporary raw gas storage tank 176a to uniformly diffuse a plasma raw gas, and a raw gas supply port 176c formed at a predetermined position on the upper portion of the temporary raw gas storage tank 176a. Referring to Fig. 8, the plasma discharge ports are formed at the lower portion of the electrodes 172a, 172b and 172c. Plasma generated from the spaces formed between the electrodes is discharged through the plasma discharge ports. Referring to Fig. 8, the suction/exhaust units 179 are formed in the spaces formed at left and right sides of the space in which the raw gas supply unit 176, the electrode unit 172 and the plasma discharge ports 178 are formed. Each of the suction/exhaust units 179 is provided with a first gas passage 179a formed on top of the suction/exhaust unit to connect to the outside and a second gas passage 179b formed on the bottom of the suction/exhaust unit to connect to the outside.

[89]

[90] Embodiment 2>

[91] Hereinafter, a method for cleaning a display substrate according to this embodiment will be explained.

[92] First, display substrate loading step Sl 10 is carried out to supply a display substrate to a cleaning section.

[93] Preferably, the display substrate cleaning method of this embodiment further comprises roll brush cleaning step S 120. Step S 120 is carried out to remove relatively large-sized particle adhered to the surface of the substrate by scratching the substrate surface using a roll brush.

[94] Next, plasma cleaning step S 130 is preferably carried out. Step S 130 is carried out to remove organic contaminants present on the surface of the display substrate using atmospheric pressure plasma. Step S 130 replaces a UV cleaning process of con¬ ventional cleaning methods.

[95] Cleaning step S 140 is then carried out to spray electrolyzed water/ozone water on the display substrate. Step S 140 includes the sub-steps of an electrolyzed water generation step, an ozone water generation step, an electrolyzed water/ozone water formation step, and a cleaning step.

[96] The sub-steps will now be described. [97] The electrolyzed water generation step is to generate electrolyzed water using the electrolyzed water generator. Electrolyzed water is generated by electrolysis of deionized water, followed by separation into ionized water containing H⁺ ions and oxidative ions, and ionized water containing OHT ions and reductive ions via an ion- exchange membrane. Electrolyzed water has a very broad range of pH and oxidation reduction potential even in the absence or presence of slight amounts of chemicals. Ac¬ cordingly, the use of electrolyzed water in this embodiment optimizes the degree of cleaning of display substrates, leading to improved productivity and enabling envi¬ ronmentally friendly cleaning.

[98] In addition, since electrolyzed water has pH and oxidation reduction potential required in the respective steps during cleaning of the display substrate, it has superior cleaning capability. Furthermore, since electrolyzed water molecules contain smaller H ⁺ and OH^" ions in size than common water, they exhibit a lower surface tension than common water, thus enabling penetration into microholes. As a result, fine sites can be cleaned when compared to conventional cleaning methods.

[99] Accordingly, the degree of integration on the display substrate can be increased and cleaning effects can be improved.

[100] Next, the ozone water generation step is carried out to generate ozone water using the ozone water generator. Ozone is commonly generated by electric discharge in oxygen. Many kinds of ozone generators have been developed and introduced into the market. However, such conventional ozone generators are disadvantageous in terms of their high price and large volume. A representative conventional ozone generation method is a dielectric barrier discharge. The dielectric barrier discharge is a kind of corona discharge and refers to a method wherein a dielectric material is interposed between electrodes and an alternating-current discharge is induced. The dielectric material serves to prevent induction of an arc discharge so as to continue the al¬ ternating-current discharge.

[101] This embodiment discloses two ozone water generation methods. The first method is to generate a large amount of ozone by corona discharge induced in oxygen. The generated ozone is delivered to a gas diffuser in water through an exhaust pipe attached to a discharger. The ozone and oxygen molecules are released in the form of small gas bubbles into water through the diffuser. At this time, the ozone molecules are dissolved in water to form ozone water.

[102] The second method is to directly induce an electric discharge in water surface. An ozone water generator for implementing the second method has a structure wherein a high- voltage power supply is connected to a net electrode under which a resistor is attached. In the ozone water generator, oxygen passes between the water surface and the bottom surface of the resistor to create a corona discharge between the net electrode and the earthed water surface through the resistor. By the corona discharge, the oxygen dissociates to form ozone. The ozone thus formed is dissolved in water to form ozone water. Water continuously flows below the resistor to generate a large amount of highly concentrated ozone water.

[103] Since the ozone water used in this embodiment contains ozone dissolved in water, it exhibits strong oxidizing power and disinfecting power. In addition, since little or no ozone is released into the atmosphere, the ozone water is harmless to humans. Furthermore, since the ozone water contains no secondary pollutants, the method of this embodiment is environmentally friendly.

[104] Accordingly, the method of this embodiment replaces conventional UV cleaning processes for removing organic substances, which are adsorbed on the surface of wafers, damaging the performance of semiconductor devices and display substrates, and the use of the ozone water can simply solve the problems, e.g., washing of various industrial equipment, sterilization and disinfection of hospital laundry and removal of residual agricultural chemicals, which previously have been difficult to treat.

[105] Next, an electrolyzed water/ozone water generation step is carried out to form electrolyzed water/ozone water by mixing the electrolyzed water generated from the electrolyzed water generator and the ozone water generated from the ozone water generator, and stirring the mixture. Specifically, alkali water generated from a cathode cell of the electrolyzed water generator and the ozone water are mixed, and separately acidic water generated from an anode cell of the electrolyzed water generator and the ozone water are mixed. Each of the mixtures is stirred in a stirring unit to form electrolyzed water/ozone water according to the respective electrolyzed water.

[106] An electrolyzed water/ozone water spraying step is carried out to clean con¬ taminants present on the substrate by spraying the electrolyzed water/ozone water on the display substrate S. Specifically, the electrolyzed water/ozone water is sprayed on the surface of the substrate S using sprayers to remove contaminants. At this step, the electrolyzed water/ozone water is sprayed through a spray nozzle arranged in each sprayer. It is preferred that holes of the spray nozzle have a diameter of from about 0.5 mm to about 3 mm.

[107] It is preferred that the distance between the end of the spray nozzle and the surface of the substrate S is adjusted to 2-13 mm and the angle between the central line of the spray nozzle and the display substrate S is adjusted to 85°~90°.

[108] The mixture of the alkali water and the ozone water can replace chemicals used for removal of particles and metal impurities in conventional cleaning methods.

[109] The mixture of the acidic water and the ozone water can replace UV cleaners for removal of organic substances, which are adsorbed on the surface of display substrates, damaging the performance of the display substrates in conventional cleaning methods. [110] In this embodiment, it is preferred that the electrolyzed water/ozone water is degraded to a water molecular size before spraying. Impact of the water droplets on the substrate is advantageous to remove fine particles adhered to the substrate.

[Ill] Preferably, the display substrate cleaning method of this embodiment further comprises a regeneration step of collecting and filtering the electrolyzed water/ozone water used for cleaning in the electrolyzed water/ozone water spraying step. Specifically, the regeneration step is carried out to collect and filter the electrolyzed water/ozone water used for the cleaning of the surface of the substrate S in the electrolyzed water/ozone water spraying step so as to reuse the filtrate in the electrolyzed water generation step and the ozone water generation step.

[112] Almost all the electrolyte and the ozone contained in the used electrolyzed water/ ozone water are consumed during cleaning, thus becoming similar to the initially used- deionized water. However, since the collected electrolyzed water/ozone water contains a variety of contaminants and impurities generated during cleaning, it is not suitable to reuse for cleaning. The regeneration step entails filtering the collected electrolyzed water/ozone water using a filtration unit so as to reuse the filtrate in the electrolyzed water generation step and the ozone water generation step. Since the electrolyzed water generation step and the ozone water generation step require highly pure deionized water, the filtration unit used in the filtering is operated to remove fine particles using a filter and to remove ions (deionization).

[113] Even in the case where the used electrolyzed water/ozone water is directly discharged without reuse, the wastewaters (i.e. the acidic water and the alkali water) generated after cleaning are neutral without involving the formation of salts when mixed, thus making it possible to discharge to the outside without any additional treatment. Therefore, the method of this embodiment is very environmentally friendly.

[114] Preferably, the method of this embodiment further comprises ultrasonic cleaning step S 150. This step is to sonicate the display substrate so as to clean the display substrate. In this embodiment, an ultrasonic wave having a frequency of 1-5 MHz is used to clean the display substrate. In a specific case, the ultrasonic wave may cause damage to the substrate or a device formed on the substrate. In this embodiment, the frequency of the ultrasonic wave can be varied in order to clean the substrate without any damage.

[115] Subsequently, rinsing step S 160 is carried out to remove liquid and particles remaining after cleaning by spraying deionized water on the substrate. This step is to remove foreign materials remaining on the display substrate by spraying deionized water on the substrate.

[116] Next, drying step S 170 is carried out to dry the display substrate by spraying high- pressure air on the display substrate. In this embodiment, air is sprayed on both sides of the substrate to simultaneously dry both sides of the substrate. Finally, unloading step S 180 is carried out to continuously receive display substrates from the cleaning section and mount the display substrates on a mounting plate.

Claims

[1] An apparatus for cleaning a substrate, comprising a loading section, a cleaning section and an unloading section, wherein the cleaning section includes: electrolyzed water/ozone water cleaning means arranged adjacent to the loading section to spray electrolyzed water/ozone water on a substrate so as to clean the substrate; rinsing means arranged adjacent to the electrolyzed water/ozone water cleaning means to rinse the cleaned substrate using deionized water; drying means arranged adjacent to the rinsing means to dry the rinsed substrate; and substrate conveying means for passing the substrate through the loading section, the cleaning section and unloading section in this order.

[2] The apparatus according to claim 1, wherein the electrolyzed water/ozone water cleaning means includes: an ozone water generator for generating ozone and dissolving the ozone in water to generate ozone water; an electrolyzed water generator for electrolyzing deionized water to generate electrolyzed water; stirring units for mixing the ozone water generated from the ozone water generator and the electrolyzed water generated from the electrolyzed water generator and stirring the mixture to form electrolyzed water/ozone water; and sprayers for spraying the electrolyzed water/ozone water on a substrate.

[3] The apparatus according to claim 2, wherein the sprayers are provided with an atomizing nozzle for degrading the electrolyzed water/ozone water to a water molecular size, followed by spraying on the substrate.

[4] The apparatus according to claim 2, wherein the sprayers are provided with a pressure control nozzle capable of controlling the spraying pressure of a liquid.

[5] The apparatus according to claim 2, wherein the sprayers are provided with a two-phase flow nozzle for mixing a liquid and a gas and spraying the mixture.

[6] The apparatus according to claim 2, wherein the electrolyzed water/ozone water cleaning means further includes a substrate mounting plate for rotating the substrate while being fixed.

[7] The apparatus according to claim 6, wherein the substrate mounting plate fixes the substrate by vacuum adsorption.

[8] The apparatus according to claim 6, wherein the substrate mounting plate fixes the substrate using a grab.

[9] The apparatus according to claim 2, wherein the electrolyzed water/ozone water cleaning means further includes a cleaning water regeneration unit for collecting and filtering the cleaning water used for the cleaning and supplying the filtrate to the electrolyzed water generator and the ozone water generator.

[10] The apparatus according to claim 1, wherein the drying means is one or more air knives for spraying high-pressure air to dry one side of the substrate.

[11] The apparatus according to claim 10, wherein the air knives are provided on upper and lower sides of a line through which the substrate passes to simul¬ taneously dry top and bottom surfaces of the substrate.

[12] The apparatus according to claim 1, further comprising ultrasonic cleaning means arranged between the electrolyzed water/ozone water cleaning means and the rinsing means to remove contaminants present on the surface of the substrate by sonication.

[13] The apparatus according to claim 12, wherein the ultrasonic cleaning means generates a sound wave having a frequency of 1-5 MHz.

[14] The apparatus according to claim 1, further comprising plasma cleaning means arranged between the loading section and the electrolyzed water/ozone water cleaning means to remove organic contaminants from the substrate using at¬ mospheric pressure plasma.

[15] A method for cleaning a substrate comprising the steps of:

1) spraying electrolyzed water/ozone water on a substrate to clean a substrate;

2) spraying deionized water on the cleaned substrate to rinse the substrate; and

3) spraying high-pressure air on the rinsed substrate to dry the substrate.

[16] The method according to claim 15, wherein step 1) includes the sub-steps of: a) generating ozone and dissolving the ozone in deionized water to generate ozone water (ozone water generation step); b) electrolyzing deionized water to generate electrolyzed water (electrolyzed water generation step); c) mixing the ozone water and the electrolyzed water, and stirring the mixture to form electrolyzed water/ozone water; and d) spraying the electrolyzed water/ozone water on a substrate to clean the substrate.

[17] The method according to claim 16, wherein step d) is carried out to degrade the electrolyzed water/ozone water to a water molecular size, followed by spraying.

[18] The method according to claim 16, wherein step d) is carried out to spray the electrolyzed water/ozone water while rotating the substrate at high speed.

[19] The method according to claim 16, further comprising, after step d), a re¬ generation step of collecting and filtering the electrolyzed water/ozone water used for cleaning so as to reuse the filtrate. [20] The method according to claim 15, further comprising, before step 1), a plasma cleaning step of removing organic contaminants present on the surface of the substrate using atmospheric pressure plasma. [21] The method according to claim 15, further comprising, before step 1), the step of cleaning the substrate using a roll brush while spraying deionized water or a sodium hydroxide solution on the surface of the substrate. [22] The method according to claim 15, further comprising, after step 1), an ultrasonic cleaning step of sonicating the substrate to clean the substrate. [23] The method according to claim 22, wherein the ultrasonic cleaning step is carried out to apply an ultrasonic wave having a frequency of 1-5 MHz to the substrate to clean the substrate. [24] The method according to claim 15, further comprising, before step 1), a loading step of continuously supplying substrates, and after step 3), an unloading step of continuously receiving substrates and mounting the substrates on a mounting plate.