Patent Publication Number: US-2005118788-A1

Title: Mask, method for manufacturing thereof, method for manufacturing organic electroluminescent device, and organic electroluminescent device

Description:
RELATED APPLICATIONS  
      This application claims priority to Japanese Patent Application No. 2003-403070 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 mask, a method for manufacturing a mask, and a method for manufacturing an organic electroluminescent device (EL) and an organic EL device.  
      2. Related Art  
      As a method for manufacturing a low-molecular full-color organic EL panel, there is a method in which a deposition pattern is selectively formed through a mask so as to separately color each red, blue, and green luminescent layer on a glass substrate. For example, when a metal mask is used as the mask, deposition is conducted in a condition where the mask is adhered to one side of the glass substrate by a permanent magnet placed on the other side of the. glass substrate. However, when a large-size panel is manufactured with a metal mask, there is a problem in which a position of the mask deviates from that of the glass substrate, since there is a large difference between a thermal expansion coefficient of the mask and that of the glass substrate.  
      Therefore, there have been developments of a deposition mask that has less difference in the thermal expansion coefficient between the mask and the glass substrate and that uses a single crystalline Si wafer that can be more finely processed by micro electro mechanical systems (MEMS). Also, Japanese Unexamined Patent Publication No. 2003-100460, for example, discloses a technique in which the mask strength is increased by mounting a plurality of small Si mask chips on a large-size substrate material provided with apertures.  
      However, by the technique of the above-mentioned Japanese Unexamined Patent Publication No. 2003-100460, a slight bending occurs when fixing a Si mask chip to an aperture. Because of this bending, a gap is created between the mask and a glass substrate used as a material to be deposited on (a layer-formation object material), and the resulting deposition pattern may possibly be unclear.  
      In view of these issues, the present invention aims to provide a mask that is reliable, for example, for deposition and that can form a desired high-precision layer pattern on, for example, a glass substrate used as a layer-formation object material, and a method for manufacturing the mask. Further, the present invention aims to provide a method for manufacturing an organic EL device using the mask.  
     SUMMARY  
      To solve the problems, the mask of the present invention includes a first substrate having a first aperture and a plurality of second substrates each having second apertures serving as mask apertures of the mask of the invention, wherein the second apertures are placed inboard of the first aperture and the second substrate is partially bonded to the first substrate.  
      Upon a series of inquiries made by the present inventors, it has been discovered that the cause of the bending generated when fixing the above-mentioned Si mask chip to a large-size substrate material was in the fixation method, and thereby the present invention has been developed. That is to say, when a second substrate having an aperture for a mask is bonded to a first substrate having a first aperture, the problem of the bending created on the substrates is solved by partially bonding the second substrate to the first substrate even if an expansion and shrinkage of the substrates occur, since effect of the expansion and shrinkage of the substrates will be lessened at the non-bonded parts, and a desired high-precision layer pattern can be formed by, for example, depositing the mask. As a result, a gap between a mask and a layer-formation object material does not easily appear, and thereby a desired high-precision layer pattern can be formed. Moreover, because the second substrate is reinforced by the first substrate according to the present invention, the mask has very high strength.  
      Additionally, the second substrate and the first substrate can be bonded with an adhesive agent, which can be formed partially on one second substrate. In this case, also, a desired high-precision layer pattern can be formed. Moreover, since the bonding procedure using an adhesive agent is very simple, it is possible to provide the mask at low cost. Further, the second substrate can have a structure bonded to the first substrate over a plurality of points, and that, when an adhesive agent is used as described, the adhesive agent can be arranged over a plurality of places for one second substrate.  
      Further, the second substrate is formed rectangularly, and only a corner of the second substrate is bonded to the first substrate. Also, only one side each that opposes the other side of a primary surface of the second substrate is bonded partially to the first substrate (two adjacent sides are bonded). Moreover, only an area of the second substrate close to a center of a side having the largest expansion of all sides of a primary surface of the second substrate can be bonded to the first substrate. In any of these structures, a desired high-precision layer pattern can be formed using the mask.  
      Also, more than two second substrates can be bonded to the first substrate sharing the same adhesive agent. This can simplify the adhesive agent supply procedure at the same time as it can form a desired high-precision layer pattern using the mask.  
      Further, an alignment mark used when bonding the second substrate to the first substrate can be placed on each substrate, with each substrate being bonded in close proximity to the alignment mark. In this case, the procedure for aligning the first substrate and the second substrate will be relatively easy compared to when forming the bonding portion apart from an alignment mark.  
      For the mask of the present invention, the second substrate can be formed with a silicon wafer. By forming the second substrate with a silicon wafer, the difference between a thermal expansion coefficient of the mask and that of the glass substrate or the like as a layer-formation object material will be small, thereby preventing the position of the mask from deviating from the position of the layer-formation object material.  
      To solve the aforementioned problem, the method for manufacturing the mask of the present invention includes the steps of: laminating a first substrate having a first aperture and a plurality of second substrates each having second apertures serving as mask apertures so that the second apertures are placed inboard of the first aperture, and, in the laminating step, partially bonding the second substrates to the first substrate. By this manufacturing method, the above-described mask of the present invention can be suitably manufactured. Also, in the laminating step, the second substrate is partially bonded to the first substrate using an adhesive agent, which can be formed on a part of the first substrate and/or a part of the second substrate.  
      Further, by using a rectangular primary surface of a substrate as the second substrate, only a corner of the second substrate can be partially bonded to the first substrate in the laminating step. Also, in the laminating step, only one side each that opposes the other of the second substrate may be partially bonded to the first substrate (two adjacent sides are bonded). Moreover, in the laminating step, only an area of the second substrate close to a center of a side having the largest expansion coefficient of all sides of a primary surface of the second substrate may be partially bonded to the first substrate.  
      Next, the method of manufacturing an organic EL device according to the present invention includes forming an organic EL element using the mask of the present invention. Of organic EL elements, a luminescent material (organic material) that forms a luminescent layer, for example, can be formed into a layer by deposition. By conducting deposition through the mask, a highly reliable organic EL device having a luminescent layer in a predetermined pattern may be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      FIGS.  1 A-B are a flat pattern view and a cross sectional pattern view showing one embodiment of the mask of the present invention.  
      FIGS.  2 A-B are a flat pattern view and a cross sectional pattern view showing an enlarged principal part of the mask in  FIG. 1 .  
       FIG. 3  is a flat pattern view illustrating a general structure of a first substrate.  
       FIG. 4  is a flat pattern view illustrating a general structure of a second substrate.  
       FIG. 5  is a cross sectional pattern view for describing the method for manufacturing the mask in  FIG. 1 .  
       FIG. 6  is a cross sectional pattern view for describing the method for manufacturing the mask in  FIG. 1 .  
       FIG. 7  is a flat pattern view showing several altered examples of the mask of the present invention.  
      FIGS.  8 A-B are a flat pattern view and a cross pattern sectional view for describing one method for manufacturing the organic EL in accordance with the present invention.  
      FIGS.  9 A-C are cross sectional pattern views for describing one method for manufacturing the organic EL in accordance with the present invention.  
       FIG. 10  is a cross sectional pattern view showing one embodiment of the organic EL in accordance with the present invention.  
       FIG. 11  is a perspective view illustrating one embodiment of an electronic device. 
    
    
     DETAILED DESCRIPTION  
      Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.  
       FIG. 1 (A) is a flat pattern view of the mask according to an embodiment of the present invention, and  FIG. 1 (B) is a cross sectional view taken on a IB-IB line of  FIG. 1 (A).  FIG. 2 (A) is a flat pattern view of an enlarged principal part of the mask in accordance with the embodiment of the present invention, and  FIG. 2 (B) is a cross sectional view taken on a IIB-IIB line of  FIG. 2 (A). The mask of the present embodiment is composed of a first substrate  10  and at least one (in  FIG. 1 (A), a plurality of) second substrate  20 .  FIG. 3  is a flat pattern view showing a general structure of the first substrate  10 , and  FIG. 4  is a flat pattern view showing a general structure of the second substrate  20 .  
      The first substrate  10  may be composed of a transparent substrate such as a glass substrate. On the first substrate  10 , at least one (in  FIG. 1 (A), a plurality of) aperture  12  is formed rectangularly so that the second substrates  20  can be fit relative to the apertures  12 . Therefore the first substrate  10  may be called frames. Here, an area of the aperture  12  is structured to be smaller than an area of a primary surface of the second substrate  20 . However, the aperture  12  is larger than a region on the second substrate  20  on which a plurality of through-holes  22  are formed, as will be described later.  
      On the first substrate  10 , a first alignment mark  14  is formed. The first alignment mark  14  is used for aligning the first substrate  10  with the second substrate  20  when bonding them together. The first alignment mark  14  may be formed with a metal film or by etching. Also, on the first substrate  10 , a mask-positioning mark  16  is formed. The mask-positioning mark  16  is used for positioning the mask of the present embodiment when conducting deposition using the mask. The mask-positioning mark  16  can also be formed with a metal material. Further, the mask-positioning mark  16  may be formed on the second substrate  20 .  
      The second substrate  20  is formed rectangularly, similarly outlining the aperture  12 , and a plurality of through-holes  22  (see  FIG. 2 (A) and  FIG. 2 (B)) are formed therein. The through-holes  22  may be in any shape as square, parallelogram, or circular. A mask pattern is structured relative to the shape, arrangement, and quantity of the through-holes  22 . Therefore, the second substrate  20  may be called a screen board.  
      On the second substrate  20 , a second alignment mark  24  is formed. The first and the second substrates  10  and  20  are aligned with each other using the first and the second alignment marks  14  and  24 . The second alignment mark  24  may be formed by etching the second substrate  20  or may be formed with a metal film.  
      A plurality of second substrates  20  are mounted on the first substrate  10 . As shown in  FIG. 2 (A), the second substrate  20  is mounted on the first substrate  10  so that a plurality of through-holes  22  are arranged inboard the aperture  12  on the first substrate  10 . More precisely, a periphery of the second substrate  20  is mounted along a rim of the aperture  12  of the first substrate  10 , and one second substrate  20  is mounted corresponding to one aperture  12 . The second substrate  20  is mounted on a surface of the first substrate  10  opposite the surface of the other side where the first alignment mark  14  is formed. In the present embodiment, the first and the second substrates  10  and  20  are laminated with an adhesive agent  91 , and the second substrate  20  is composed of a material adhesive to the first substrate  10  (such as silicon).  
      The adhesive agent  91  is confined to a corner of the second substrate  20 , which is bonded to the first substrate  10  only at the corner. Therefore, a degree of freedom of the substrates increases in comparison with a structure in which the entire periphery of the second substrate  20  is adhered to the first substrate  10 . Even if there is a case in which the second substrate  20  is expanded due to heat or the like in the adhering procedure, a problem of the bending of the second substrate  20  does not easily take place.  
      Next,  FIG. 5  shows a cross sectional pattern view for describing the method for manufacturing the mask in accordance with the present embodiment. Prepared first is the first substrate  10  composed of glass and the second substrate  20  composed of single crystalline silicon. For the formation of the aperture  12  on the first substrate  10 , sandblasting may be applied. Also, the first. alignment mark  14  or the mask-positioning mark  16  on the first substrate  10  may be formed by, for example, sputtering or deposition, or by etching.  
      In the second substrate  20 , a plurality of through-holes  22  are formed. For their formation, etching (e.g. anisotropic etching having crystal-surface orientation dependency) may be applied. A wall surface of the through-hole  22  may be perpendicular to the surface (primary surface) of the second substrate  20  or may be tapered. As shown in  FIG. 4 , when forming the second substrate  20  using a silicon wafer  26 , the second substrate  20  can be obtained by cutting the silicon wafer  26  into a desired shape. By this method, a flatness (greatest height)−(smallest height) of the second substrate  20  is around 5 μm. Further, the second alignment mark  24  on the second substrate  20  may be formed by etching, or by sputtering or deposition, for example.  
      Next, the adhesive agent  91  is applied to one corner of the periphery of each aperture  12  of the first substrate  10 . For the adhesive agent  91 , a highly adhesive, epoxy UV curing adhesive agent (light curing resin) with low outgas in a vacuum may be employed, or a heat curing resin may be employed. In addition, the adhesive agent  91  may be applied, for example, to one corner of the rectangular second substrate  20  or to both a corner of the first substrate  10  and a corner of the second substrate  20 .  
      The thus prepared first substrate  10  and the second substrate  20  are then aligned with each other, bonded with the adhesive agent  91  which has been applied thereon. Here, a plurality of second substrates  20  are arranged on one surface of the first substrate  10  in such a way that the second substrates  20  do not overlap one another. Additionally, for their alignment, the first and the second alignment marks  14  and  24  are used. After aligning, the first and the second substrates  10  and  20  are adhered to each other by illuminating the adhesive agent  91 .  
      By this method, the second substrate  20  is reinforced by the first substrate  10 , enabling a mask to be manufactured with a high strength. Further, even when expansion or shrinkage occurs on the first and/or the second substrate  10  and/or  20 , the effect of expansion or shrinkage on the substrates will be lessened at the non-bonded (non-adhered) part since the adhesive agent  91  is applied to only one corner for bonding, and, therefore, a problem such as the bending of the substrates will be solved. As a result, a gap between a layer-formation object material and the mask will not easily appear, and thereby the mask of the present embodiment having a desired high-precision layer pattern can be formed by, for example, deposition.  
      In addition, as shown in  FIG. 6 , if a plurality of second substrates  20  do not have a uniform height due to a thickness variation therebetween, the surfaces of the second substrates  20  may be polished by a whetstone  40  or the like. This enables the flattening of a plurality of the surfaces of the second substrates  20 , thereby increasing adhesion to objects to which deposition, for example, is conducted.  
       FIG. 7  is a diagram showing alternative examples of the present embodiment. That is,  FIG. 7  illustrates various places at which the adhesive agent  91  may be applied. An adhesive agent  91   a  may be applied not only on a corner of the aperture  12  as shown in  FIG. 1 (A), but also on one side of the aperture  12  as shown in  FIG. 7  at (a). Further, as shown in  FIG. 7  at (b), an adhesive agent  91   b  may be applied close to the center of one side of the aperture  12 .  
      Furthermore, as shown in  FIG. 7  at (c), an adhesive agent  91   c  may be applied on more than one side of the aperture  12 , particularly only on one side each that opposes the other side (on two adjacent sides). In this case, an adhesive agent  91   c  is to be applied on two sides constituting a corner. In addition, in this case, the adhesive agent  91   d  may be applied close to the center of each side of the aperture  12  as shown in  FIG. 7  at (d). In particular, by applying an adhesive agent close to the center of the side having the largest expansion coefficient of all sides of the aperture  12 , a degree of freedom of the substrates increases further, which can prevent or restrain the bending of the substrates caused by, for example, heat expansion. Further, as shown in  FIG. 7  at (e) and (f), an adhesive agent  91   e  may be applied and shared among a plurality of apertures  12 .  
       FIG. 8 (A) and  FIG. 8 (B) illustrate the method for manufacturing the organic EL in accordance with the embodiment of the present invention. On a mask  50  (e.g. the second substrate  20 ) shown in  FIG. 8 (A), a magnetic material layer  52  is formed. The magnetic material layer  52  may be formed with a strongly magnetic material such as iron, cobalt, or nickel. Alternatively, a magnetic metal material such as Ni, Co, Fe, or a stainless steel alloy containing Fe, or a combination of a magnetic metal material and a non-magnetic metal material may be used to form the magnetic material layer  52 . Other details on the mask  50  are as described above.  
      In the present embodiment, a luminescent material is formed into a layer on a substrate (layer-formation object material)  54  using the mask  50 . The substrate  54  is used for forming a plurality of organic EL devices and is a transparent substrate such as a glass substrate. On the substrate  54 , as shown in  FIG. 9 (A), an electrode (e.g. a transparent electrode composed of an ITO, for example)  56  or a hole transport layer  58  is formed, or, alternatively, an electron transport layer may be formed.  
      As shown in  FIG. 8 (A), the mask  50  is arranged so that the second substrate  20  is placed on one side of the substrate  54 . On the other side of the substrate  54 , a magnet  48  is placed so as to attract the magnetic material layer  52  formed on the mask  50  (the second substrate  20 ).  
       FIG. 8 (B) is a diagram for describing the method for positioning the mask. As described above, the mask-positioning mark  16  is formed on the first substrate  10 . Also, on the substrate  54 , a positioning mark  55  is formed. Using the mask-positioning mark  16  and the positioning mark  55 , the first substrate  10  and the substrate  54  are aligned with each other.  
       FIG. 9 (A) to  FIG. 9 (C) are diagrams for describing the method for forming a layer using a luminescent material. The luminescent material is an organic material, for example. As a low-molecular organic material, there is tri(8-hydrooxyquinoline) aluminum (Alq 3 ), and as a high-molecular organic material, there is poly(para-phenylene vinylene) (PPV). The luminescent material may be formed into a layer by deposition. For example, as shown in  FIG. 9 (A), a red luminescent material is patterned through the mask to form a red luminescent layer  60 . Then, as shown in  FIG. 9 (B), by moving the mask  50  and patterning a green luminescent material, a green luminescent layer  62  is formed. Also, as shown in  FIG. 9 (C), by moving the mask  50  again and by patterning a blue luminescent material, a blue luminescent layer  64  is formed.  
      In the present embodiment, the second substrate  20  serving as a screen is partially bonded to the first substrate  10 . Therefore, the second substrate  20  has a high degree of freedom and does not easily bend or deform and shows a high repeatability in selective deposition and high productivity. With the mask  50  of the present embodiment, a plurality of apertures  12  are formed on the first substrate  10 , and the second substrates  20  are placed corresponding to each aperture  12 . Each second substrate  20  corresponds to one organic EL device. In other words, by using the mask  50 , a plurality of unified organic EL devices can be manufactured. By cutting the substrate  54 , separate. organic EL devices can be obtained.  
       FIG. 10  is a cross-sectional pattern view illustrating a general structure of the organic EL device manufactured by following the above-described method for forming the layers of the luminescent materials. The organic EL device includes the substrate  54 , the electrode  56 , the hole transport layer  58 , and the luminescent layers  60 ,  62 , and  64 . On the luminescent layers  60 ,  62 , and  64 , an electrode  66  is formed. The electrode  66  is a cathode electrode, for example. The organic EL device such as this is suitable for a display device (or a display), and by using the luminescent layers  60 ,  62 , and  64 , a highly reliable display with a very little pattern shifting can be provided.  
      As an example of an electronic apparatus having the organic EL device, a mobile phone  500  is illustrated in  FIG. 11 . The mobile phone has a structure having a display unit  501  which includes the organic EL device of the above-described embodiment, thereby a very highly reliable display can be provided.  
      Additionally, it is to be understood that the present invention is not limited to any of the embodiments as herein described, that modifications can be properly effected within the entire scope and spirit of the invention, and that any method for manufacturing a substrate used for an electro-optical device, any substrate used for electro-optical device, any electro-optical device, and any electronic apparatus associated with such modifications shall be included in the scope of the present invention.