Patent Publication Number: US-RE42248-E

Title: Cleaning method, cleaning apparatus and electro optical device

Description:
RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2003-403071 filed Dec. 2, 2003 which is hereby expressly incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a cleaning method, a cleaning apparatus and an electro optical device. 
     2. Related Art 
     In a low molecular weight organic electro luminescence (EL) device, light emitting layers composed of low molecular weight organic materials are formed on a glass substrate. The light emitting layers composed of low molecular weight organic materials are formed by vapor-deposition. Vapor-deposition is a method in which a small piece of a material is heated and evaporated in a high vacuum so as to, be deposited on a substrate as a thin film. When light emitting layers are formed by vapor-deposition, a vapor-deposition mask needs to be disposed in order to prevent organic materials from attaching to regions other than the regions on which the light emitting layers are desired to be formed. In addition, protection plates need to be disposed in order to prevent organic materials from attaching to an inner wall and so forth of a vapor-deposition chamber. 
     Here, multiple vapor-deposition treatments results in a state in which organic substances are deposited on the surfaces of a protection plate, a vapor-deposition mask and so forth, which are manufacturing devices for organic EL devices. If a protection plate on which organic substances are deposited is permitted to repeatedly remain standing, the inside of a vapor-deposition chamber is contaminated. Also, the vapor-deposition mask that is formed of a metal thin plate or the like bends greatly because of the weight of the organic substances, thereby affecting the accuracy of patterning. Therefore, it is essential to remove the organic substances deposited on the protection plate, vapor-deposition mask and so forth periodically. 
     Thus, manual scrubbing away of organic substances deposited on a protection plate, a vapor-deposition mask and so forth is carried out by human hands. Also, in Japanese Unexamined Patent Publication No. 8-319586, a method in which a mixed gas plasma is generated in a treatment chamber after etching treatment so as to remove residual reaction products in the treatment chamber has been proposed. Furthermore, in Japanese Unexamined Patent Publication No. 2000-282219, a method in which organic films attached to a mask through organic-film vacuum deposition are removed by heat treatment without breaking a vacuum has been proposed. 
     The method of manual scrubbing (by human hands), however, suffers from a problem in that many workers are required. Thus, the establishment of a cleaning process that needs no human hands and is favorable in terms of working efficiency has been desired. 
     In both methods proposed in the above patent documents, organic films and so forth are removed in a treatment chamber (chamber), and therefore the modification of a vapor-deposition apparatus is required. Accordingly, there is a problem in that a large cost is required. 
     The present invention is devised in order to solve the above problems and is intended to provide a cleaning method and a cleaning apparatus that can easily remove organic substances attached to a manufacturing device for electro optical devices. Also, the present invention is intended to provide a high quality electro optical device. 
     SUMMARY 
     To this end, a cleaning method of the present invention comprises cleaning an organic substance attached to a manufacturing device of an electro optical device by using a derivative of pyrrolidone. 
     Derivatives of pyrrolidone utilized for resist removal and so forth are superior in decomposing organic substances. 
     Thus, organic substances can be removed without requiring physical treatment such as scrub-cleaning and the modification of a manufacturing device. Therefore, organic substances attached to a manufacturing device of an electro optical device can easily be removed. 
     Furthermore, a cleaning method of an organic substance attached to a manufacturing device of an electro optical device comprises: treating the manufacturing device with a derivative of pyrrolidone; treating the manufacturing device with water; and treating the manufacturing device with ethanol. 
     Organic substances attached to a manufacturing device are removed through treatment with derivatives of pyrrolidone. Also, the derivatives of pyrrolidone attached to the manufacturing device are removed through treatment with water. Furthermore, treatment with ethanol allows the water attached to the manufacturing device to be replaced by ethanol. 
     Then, the ethanol, which has a low boiling point, attached to the manufacturing device can be dried rapidly. Therefore, organic substances attached to a manufacturing device of an electro optical device can easily be removed. 
     The derivative of pyrrolidone is preferably N-methyl-2-pyrrolidone. 
     N-methyl-2-pyrrolidone is superior in the action of removing organic substances particularly. Therefore, organic substances attached to a manufacturing device of an electro optical device can easily be removed. 
     The manufacturing device of the electro optical device may be a protection plate used for vapor-deposition treatment of a functional layer of an organic EL device. 
     With this configuration, organic substances attached to the protection plate can be removed easily, and thus contamination in the vapor-deposition chamber can be prevented. 
     The manufacturing device of the electro optical device may be a mask used for vapor-deposition treatment of a functional layer of an organic EL device. 
     With this configuration, organic substances attached to the mask can be removed easily, and thus the bending of the mask due to the weight of the organic substances is avoided. Therefore, the accuracy of vapor-deposition treatment can be ensured. 
     The manufacturing device is preferably cleaned at room temperature. 
     With this configuration, the deformation of the manufacturing device as a result of heating can be avoided, and therefore an electro optical device can be manufactured with high accuracy. 
     The manufacturing device is preferably cleaned using ultrasonic waves. 
     With this configuration, organic substances attached to a manufacturing device of an electro optical device can be removed effectively. 
     A cleaning apparatus of the present invention is a cleaning apparatus of an organic substance attached to a manufacturing device of an electro optical device, and comprises: a stage for treating the manufacturing device with a derivative of pyrrolidone; a stage for treating the manufacturing device with water; a stage for treating the manufacturing device with ethanol; a stage for drying the manufacturing device; and carrying means that carries the manufacturing device to each stage in sequence. 
     With this configuration, organic substances attached to a manufacturing device of an electro optical device can be removed easily. 
     An electro optical device of the present embodiment is manufactured by cleaning a manufacturing device of the electro optical device by using the above described cleaning methods, and then using the manufacturing device of the electro optical device that has been cleaned. 
     With this configuration, the accuracy of vapor-deposition treatment can be ensured by removing organic substances attached to a manufacturing device of an electro optical device, and thus a high quality electro optical device can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory diagram showing the schematic structure of a cleaning apparatus of an embodiment of the invention. 
         FIG. 2  is a side sectional view of a low molecular weight organic EL device. 
         FIG. 3  is an explanatory diagram of a vapor-deposition apparatus. 
         FIG. 4  is an explanatory diagram of vapor-deposition treatment for a substrate. 
         FIG. 5  shows treatment ways and conditions of each process in a cleaning method of the present embodiment. 
         FIG. 6  shows results of cleaning by each cleaning fluid in a working example and the safety of each cleaning fluid. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described below with reference to the drawings. It is understood that the scale of each of the members in the drawings used in the following description is adequately changed so that they are easily visible. 
     Organic EL Device 
     A cleaning method of the present embodiment is a method of cleaning organic substances attached to a vapor-deposition mask when forming light emitting layers of a low molecular weight organic EL device. First, the schematic structure of a low molecular weight organic EL device will be described referring to FIG.  2 . 
       FIG. 2  is a side sectional view of a low molecular weight organic EL device. An organic EL device  200  includes a plurality of pixel regions R, G and B arranged in a matrix. A circuit part  220  driving each pixel region is formed on the surface of a substrate  210  composed of a glass material and so forth. In  FIG. 2 , the illustration of detailed structure of the circuit part  220  is omitted. A plurality of pixel electrodes  240  composed of ITO and so forth is formed on the surface of the circuit part  220 , in a matrix corresponding to each of the pixel regions R, G and B. A hole injection layer  250  composed of copper phthalocyanine and so forth is formed so as to cover the pixel electrodes  240  functioning as anodes. In some cases, a hole transport layer composed of N,N-di(1-naphthyl)-N,N-diphenylbenzidine (NPB) may be provided on the surface of the hole injection layer  250 . 
     Light emitting layers  260  corresponding to each of the pixel regions R, G and B are formed in a matrix on the surface of the hole injection layer  250 . The light emitting layers  260  are composed of low molecular weight organic materials whose molecular weight is about 1000 or less. Specifically, the light emitting layers  260  are composed of Alq3 (aluminum complex) and so forth as a host material and rubrene and so forth as a dopant. Also, an electron injection layer  270  composed of lithium fluoride and so forth is formed so as to cover each light emitting layer  260 . A cathode  280  composed of Al and so forth is formed on the surface of the electron injection layer  270 . A sealing substrate (not shown) is attached to an end of the substrate  210  so as to hermetically seal the entire device. 
     When a voltage is applied between the pixel electrodes  240  and the cathode  280 , the hole injection layer  250  injects holes into the light emitting layers  260 , and the electron injection layer  270  injects electrons into the light emitting layers  260 . Then, the holes and electrons recombine in the light emitting layers  260 , and thereby dopants are excited so as to emit light. A low molecular weight organic EL device that thus includes light emitting layers composed of low molecular weight organic materials has a long lifetime and is superior in luminous efficiency. 
     Vapor-Deposition Apparatus 
     The above light emitting layers are formed by vapor-deposition treatment using a vapor-deposition apparatus. A vapor-deposition apparatus will be described with using FIG.  3 . 
       FIG. 3  is an explanatory diagram of a vapor-deposition apparatus. A resistance-heating vacuum deposition apparatus will be illustrated below by way of example. A vapor-deposition apparatus  100  comprises a chamber  104  connected to a vacuum pump  102 . A substrate holder  110  is provided inside the chamber  104 . The substrate holder  110  holds the substrate  210  to be treated with vapor-deposition so that the substrate  210  faces downwardly. Meanwhile, a crucible  120  in which a vapor-deposited material  124  is contained is provided so as to face the substrate holder  110 . A filament  122  is wired for the crucible  120  so that the vapor-deposited material  124  in the crucible can be heated. Also, a protection plate  130  is provided in order to prevent the evaporated material from attaching to the inside wall and so forth of the chamber  104 . 
     In order to carry out vapor-deposition treatment by using this vapor-deposition apparatus, first the substrate  210  is loaded on the substrate holder  110 , and the vapor-deposited material  124  is placed in the crucible  120 . Then, the vacuum pump  102  connected to the chamber  104  is operated so as to evacuate the chamber  104 . Next, a current is applied to the filament  122  wired for the crucible  120  so as to make the filament  122  generate heat, and thereby heating the vapor-deposited material  124  in the crucible. Then, the vapor-deposited material  124  is evaporated so as to attach to the surface of the substrate  210 . The vapor-deposited material that scatters toward directions other than the direction to the substrate attaches to the surface of the protection plate  130 . 
       FIG. 4  is an explanatory diagram of vapor-deposition treatment for a substrate. In  FIG. 4 , the substrate  210  faces downwardly. Here, the process of forming the light emitting layer  260  for the pixel region G will be exemplified by way of example. When the light emitting layer  260  is formed, the substrate  210  is loaded on the substrate holder of the vapor-deposition apparatus with the vapor-deposition mask being disposed on the surface of the substrate  210 . The vapor-deposition mask  140  is formed of a metal thin plate of stainless steel or the like, and has an aperture  142  corresponding to the formation region of the light emitting layer  260 . Meanwhile, a constituent material of the light emitting layer  260  as a vapor-deposited material is placed in the crucible of the vapor-deposition apparatus. Then, when the vapor-deposited material  124  is evaporated, the vapor-deposited material  124  passes through the aperture  142  of the vapor-deposition mask  140  so as to attach to the formation region of the light emitting layer  260  above the surface of the substrate  210 . Since the vapor-deposition mask  140  is placed above regions other than the formation region of the light emitting layer  260 , the vapor-deposited material  124  attaches to the surface of the vapor-deposition mask. Thus, the light emitting layer  260  can be formed by attaching the vapor-deposited material  124  only to the formation region of the light emitting layer  260 . 
     Moreover, if the aperture  142  of the vapor-deposition mask  140  is moved to above the pixel region B and then vapor-deposition treatment is carried out in the same way as above, a light emitting layer can also be formed in the pixel region B. In this case, the constituent materials of the light emitting layers  260  in each of the pixel regions R, G and: B are sequentially deposited on the surface of the vapor-deposition mask  140 . Also, organic substances are deposited on the protection plate similarly. Therefore, the organic substances attached to the vapor-deposition mask  140 , the protection plate and so forth need to be cleaned. 
     Cleaning Apparatus 
       FIG. 1  is an explanatory diagram showing the schematic structure of a cleaning apparatus of the present embodiment. A cleaning apparatus  1  of the present embodiment comprises a first stage  10  for treating the vapor-deposition mask  140  with a derivative of pyrrolidone, a second stage  20  for rinsing the vapor-deposition mask  140  with water, and a third stage  30  for rinsing the vapor-deposition mask  140  with flowing water. The cleaning apparatus  1  also comprises a fourth stage  40  for treating the vapor-deposition mask  140  with ethanol, a fifth stage  50  for drying the vapor-deposition mask  140 , and a carrier (carrying means)  5  that carries the vapor-deposition mask  140  to each stage in sequence. Each stage is provided inside a cleaning chamber  2 . 
     The first stage  10  is a stage for treating the vapor-deposition mask  140  with a derivative of pyrrolidone. Therefore, a treatment bath is provided in the first stage  10  and the inside thereof contains a derivative of pyrrolidone. Derivatives of pyrrolidone are chemicals utilized for resist removal and so forth, and are superior in decomposing organic substances. As derivatives of pyrrolidone, there are 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone and so forth. Out of them, the use of N-methyl-2-pyrrolidone expressed by Chemical formula 1 exhibits a high cleaning effect at room temperatures. 
                 
 
     The treatment bath of the first stage  10  may be provided with an ultrasonic cleaner (cleaning means)  16 . The ultrasonic cleaning means  16  radiates ultrasonic waves in a cleaning fluid so as to generate standing waves, thereby cleaning objects by means of the action of sound pressure. The ultrasonic cleaning means  16  can preferably radiate ultrasonic waves of 800 kHz or more for example, and more preferably sweep frequency periodically. This allows the distribution of standing waves in the cleaning bath to change so that a high cleaning effect is displayed. 
     The second and third stages  20  and  30  are stages for treating the vapor-deposition mask  140  with water. Water therefore is contained in treatment baths of the second and third stages  20  and  30 . Particularly, a stirring means  36  for water is provided in the treatment bath of the third stage  30 . The stirrer (stirring means)  36  allows a water flow to be generated in the treatment bath. 
     The fourth stage  40  is a stage for treating the vapor-deposition mask  140  with ethanol. Ethanol therefore is contained in the treatment bath of the fourth stage  40 . 
     The fifth stage  50  is a stage for drying the vapor-deposition mask  140 . The provision of a blower  50  in the fifth stage  50  permits rapid drying of the vapor-deposition mask. In addition, the use of the blower  56  employing an inactive gas such as nitrogen gas prevents the oxidation and so forth of the vapor-deposition mask  140 . 
     Furthermore, the carrying means  5  that carries the vapor-deposition mask  140  to each stage in sequence is provided. The carrying means  5  is formed into a box shape and the walls thereof are formed of a punched metal, a net material or the like. This allows fluid to freely move from and into the carrying means  5  through the walls. The carrying means  5  is formed into such a size that one or more vapor-deposition masks  140  can be contained therein, and that the-carrying means  5  can be immersed in the treatment bath of each stage. In addition, a driving means (not shown) for transferring the carrying means  5  to each stage in sequence and immersing it in the treatment bath of each stage in sequence is provided. 
     Cleaning Method 
     A method of cleaning a vapor-deposition mask by using the above cleaning apparatus will now be described referring to  FIGS. 5 and 1 .  FIG. 5  shows treatment ways and conditions of each process in the cleaning method of the present embodiment. The cleaning method of the present embodiment comprises a first process for treating the vapor-deposition mask  140  with a derivative of pyrrolidone, a second process for rinsing the vapor-deposition mask  140  with water, and a third process for rinsing the vapor-deposition mask  140  with flowing water. The cleaning method also comprises a fourth process for treating the vapor-deposition mask  140  with ethanol and a fifth process for drying the vapor-deposition mask  140 . 
     In the first process, the vapor-deposition mask  140  is treated with a derivative of pyrrolidone. Specifically, the vapor-deposition mask  140  is contained in the carrying means  5  and the carrying means  5  is moved to the first stage  10 . Then, the both vapor-deposition mask  140  and the carrying means  5  are immersed in the treatment bath of the first stage  10 . The immersing temperature and time are room temperature and three minutes, respectively, for example. This immersion removes organic substances attached to the vapor-deposition mask  140 . In the case of providing the ultrasonic cleaning means  16  in the treatment bath of the first stage  10 , organic substances can be removed effectively by using the ultrasonic cleaning in combination with the immersion. In the case of a protection plate or the like that has been allowed to stand in the atmosphere for a long period after used in vapor-deposition treatment, organic substances may not be removed even by immersion cleaning for ten minutes. However, using ultrasonic cleaning in combination with immersion permits the complete removal of organic substances attached to such a protection plate or the like. 
     In the second process, the vapor-deposition mask  140  is rinsed with water. Specifically, the carrying means  5  is moved to the second stage  20 , and then both the vapor-deposition mask  140  and the carrying means  5  are immersed in the treatment bath. The immersing temperature and time are room temperature and five minutes, respectively, for example. This immersion removes most of the derivative of pyrrolidone attached to the vapor-deposition mask  140 . 
     In the third process, the vapor-deposition mask  140  is rinsed with flowing water. Specifically, the stirring means  36  provided in the treatment bath of the third stage  30  is driven so as to generate a water flow in the treatment bath previously. Then, the carrying means  5  is moved to the third stage  30 , and then both the vapor-deposition mask  140  and the carrying means  5  are immersed in the treatment bath. The immersing temperature and time are room temperature and five minutes, respectively, for example. This immersion completely removes the derivative of pyrrolidone attached to the vapor-deposition mask  140 . 
     In the fourth process, the vapor-deposition mask  140  is treated with ethanol. Specifically, the carrying means  5  is moved to the fourth stage  40 , and then both the vapor-deposition mask  140  and the carrying means  5  are immersed in the treatment bath. The immersing temperature and time are room temperature and three minutes, respectively, for example. This immersion allows water attached to the vapor-deposition mask  140  to be replaced by ethanol. 
     In the fifth process, the vapor-deposition mask  140  is dried. Specifically, the carrying means  5  is moved to the fifth stage  50 , and then the vapor-deposition mask  140  is allowed to stand for ten minutes. Since ethanol, which has a low boiling point (evaporating temperature), is disposed on the surface of the vapor-deposition mask  140 , the mask can be air dried rapidly. In the case of providing the blower  56  in the fifth stage  50 , the blower  56  blows the vapor-deposition mask  140 , thereby drying the mask more rapidly. 
     As described above in detail, in the cleaning method of the present embodiment, organic substances attached to a vapor-deposition mask are cleaned by using a derivative of pyrrolidone. Derivatives of pyrrolidone utilized for resist removal and so forth are superior in decomposing organic substances. Therefore, organic substances can be removed in a short time without requiring physical treatment such as scrub-cleaning and the modification of a manufacturing device. Thus, organic substances attached to a vapor-deposition mask can easily be removed. Accordingly, the bending of a vapor-deposition mask due to the weight of organic substances can be prevented. Therefore, the accuracy of vapor-deposition treatment can be ensured. 
     Derivatives of pyrrolidone exhibit an excellent cleaning effect even at normal room temperatures. Therefore, organic substances attached to a vapor-deposition mask can be removed without heating. Also, a frame having a thermal expansion rate different from that of the body of a vapor-deposition mask is formed in the peripheral part of the vapor-deposition mask. Heating of the vapor-deposition mask may cause the deformation of body of the vapor-deposition mask because of the difference in thermal expansion rates between the body of the vapor-deposition mask and the frame. In this regard, the cleaning method of the present invention enables the cleaning of a vapor-deposition mask without heating, and thus prevents the deformation of the vapor-deposition mask. It should be noted that heat-cleaning can enhance a cleaning effect if there is no need to take the deformation of a cleaned object into account. 
     Here, it should be understood that the technical scope of the present invention is not limited to the above embodiments but includes various kinds of modifications of the above embodiments without departing from the scope and spirit of the present invention. 
     In other words, specific materials and structures described in the embodiments are just examples, and therefore can be modified accordingly. In the embodiments, cleaning of organic substances attached to a vapor-deposition mask for light emitting layers of a low molecular weight organic EL device has been described. The present invention, however, can be widely applied to cleaning of organic substances attached to a manufacturing device of an electro optical device. For example, besides low molecular weight organic EL devices, the present invention can be widely applied to manufacturing devices of high molecular weight organic EL devices, liquid crystal display devices, plasma display devices, field emission display (FED) devices and so forth. Also, besides manufacturing devices used in vapor-deposition treatment, the present invention can be widely applied to manufacturing devices used for film-deposition treatment other than vapor-deposition treatment, etching treatment and so forth. 
     Working Example 1 
     With respect to some cleaning fluids, the comparison of cleaning effects against organic substances was made. As the cleaning fluids, ten kinds of solvents and aqueous alkaline solutions were selected. A protection plate used for vapor-deposition treatment was adopted as a cleaned object. The protection plate has been used in a process of forming functional layers of low molecular weight organic EL devices. Organic substances such as copper phthalocyanine, N,N-di (1-naphthyl)-N,N-diphenylbenzidine (NPB), tris(8-hydroxyquinolinolato) aluminum(Alq3), rubrene, and coumarin were attached to the surface of the protection plate. This protection plate was immersed in each cleaning fluid for ten minutes at room temperature. Physical cleaning such as ultrasonic cleaning and scrub-cleaning was not carried out. The protection plate was rinsed with flowing water for five minutes, and dried by nitrogen blowing. 
       FIG. 6  shows the results of cleaning by each cleaning fluid and the safety of each cleaning fluid. In the case of adopting N-methyl-2-pyrrolidone as a cleaning fluid, the organic substances attached to the protection plate ware all removed, which confirmed that N-methyl-2-pyrrolidone exhibits the most favorable cleaning effect. Here, a resist remover from Shipley Co. was adopted as N-methyl-2-pyrrolidone. 
     On the contrary, in the case of using a mixture of dimethylsulfoxide and monoethanolamine that is a resist remover from Tokyo Ohka Kogyo Co., the speed of cleaning organic substances was slow, and therefore a lot of organic substances remained after the immersion for ten minutes. Also, monoethanolamine is a chemical relevant to pollutant release and transfer register (PRTR) and has concern for influence on the human body. It therefore is difficult to adopt this mixture as a cleaning fluid. 
     Ketone and alcohol such as acetone, ethanol and isopropyl alcohol can also clean organic substances. However, since the reattachment of removed organic substances was confirmed, there is a need to change the cleaning fluid frequently. Also, a number of remaining stains on the protection plate were observed. In addition, when these chemicals are used as a cleaning fluid, large-scale safety enhanced facilities are required. It therefore is difficult to adopt these chemicals as a cleaning fluid. 
     In the case of using alkaline cleaning fluids such as tetra methyl ammonium hydroxide (TMAH) and potassium hydroxide (KOH), a good cleaning effect could not be obtained. 
     The above results confirmed that N-methyl-2-pyrrolidone, which is a derivative of pyrrolidone, is most favorable as a cleaning fluid against organic substances attached to a protection plate and so forth.