Patent Publication Number: US-8968477-B2

Title: Deposition mask and method for manufacturing organic light emitting display using the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/180,653, filed on Jul. 14, 2005, and claims the benefit of Korean Patent Application No. 10-2004-0055072, filed on Jul. 15, 2004, which are incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a deposition mask for manufacturing an organic light emitting display (OLED) using the deposition mask. More particularly, the invention relates to a deposition mask that can be used in depositing an organic emission layer (EML) and the OLED with such an EML. 
     2. Description of the Related Art 
     An OLED typically includes a first electrode formed in a predetermined pattern on a transparent insulation substrate, an organic film formed by, for example, vacuum deposition on the first electrode, and a second electrode formed on an upper surface of the organic film. 
     The first electrode is generally made of a transparent conductor such as indium tin oxide (ITO) or indium zinc oxide (IZO) and pattering of the transparent conductor is typically performed by a photolithography method. 
     Photolithography can be used before the organic film is formed but may not be used after the organic film is formed. This is because the organic film may be very vulnerable to moisture and thus may require thorough isolation from moisture during and after the manufacturing process. Therefore, photolithography that exposes the organic film to moisture during a resist exfoliation or etching may not be appropriate for patterning the organic film and the second electrode. 
     To solve the above-described problem, the organic film and the second electrode layer may be manufactured by vacuum deposition using a mask having a predetermined pattern. Particularly, the second electrode can be patterned using a cathode separator which is a predetermined isolation wall. However, a small molecular organic film may be most appropriately patterned by vacuum deposition using a deposition mask. 
     An emission layer (EML) may be manufactured by a method in which respective pixels of red (R), green (G), and blue (B) are independently deposited on a substrate so as to provide a full color display. Since the respective colors are independently deposited, separate masks may be required for each color. 
     As shown in  FIG. 1 , four panel regions  11  may be deposited on a substrate  10 . The respective panel regions  11  can be formed on one substrate  10  and can be cut off and used separately. Only four panel regions have been formed in  FIG. 1 , but a further larger number of panel regions can be simultaneously manufactured in a real process. A panel region can refer to a region where an OLED is formed on the substrate. 
     In  FIG. 1 , the OLEDs formed on the respective panel regions  11  can have an icon part  12  and a main image part  13 . The icon part  12  can have red, green, and blue light emission regions  12 R,  12 G, and  12 B. The main image part  13  can be configured so as to realize full color display. 
     To deposit EMLs of these elements red, green, and blue masks  14 R,  14 G, and  14 B may be used, as illustrated in  FIGS. 2A through 2C . The respective masks  14 R,  14 G, and  14 B may have icon masking parts  15 R,  15 G, and  15 B for depositing the icon part  12  and may have main masking parts  16 R,  16 G, and  16 B for depositing the main image part  13 . 
     If the EMLs are deposited using the respective masks  14 R,  14 G, and  14 B, only portions that correspond to the respective colors of the EMLs may be opened and the other portions may be blocked off in the mask as illustrated in  FIGS. 2A through 2C . The portions blocked-off by the mask might be touched by the EML already deposited or other hole transport layer (HTL) or hole injection layer (HIL) during deposition process of the EML. This can damage the organic film. The damage might act as a dark spot afterwards. 
     As described above, the blocked-off portion of the mask can contact the organic film. In such a case, particles of material forming the organic film might fall onto a region where light emission occurs and have a negative influence on the organic film. 
     Japanese patent publication No. 2003-257650 discloses a structure in which a spacer (made of insulation body) is formed in a region where light emission does not occur. However, even in that case, a blocked-off portion of the mask may touch the spacer and thus small fragments (and fragments of the spacer) and outgasing may have a negative influence on the organic film. 
     SUMMARY OF THE INVENTION 
     The present invention provides a deposition mask and a method for manufacturing an organic light emitting display (OLED) using the same capable of preventing an organic film from being destroyed or chemical transition from occurring due to contact of sealed portion of the mask and an EML already deposited during a deposition process of an organic EML. 
     The present invention may inure various advantages. First, the indented portion of the mask may not touch already deposited organic EML, thereby preserving the organic EML. Second, it may be possible to prevent chemical transition from occurring at the organic EML. Third, the deposition mask can be obtained in a simple method and additional processes may not be required for the OLED manufacturing process. Thus, productivity can be improved. 
     The present invention provides, for example, a deposition mask that can include a generally planar portion, an opening in the planar portion adapted to permit deposition of an organic emission layer on a substrate of an organic light emitting display, and an indentation in the planar portion indented, having a predetermined depth on a side of the planar portion facing the substrate. Only a portion of the mask may contact the substrate, and that portion may firmly contact the substrate. 
     The present invention also provides, for example, a method of manufacturing an organic light emitting display. The method may include forming a first electrode on a substrate, forming an organic emission layer on an upper portion the first electrode, and forming an organic emission layer on the first electrode by firmly contacting a mask to the substrate and depositing emission layer material through the mask. The mask may have an opening and an indentation that does not contact the substrate, and the emission layer material may be deposited through the opening. The method may also include forming a second electrode on an upper portion of the organic emission layer and sealing the substrate. 
     The present invention also provides, for example, a method of manufacturing an organic light emitting display. The method may include, for example, forming a first electrode on a plurality of panel regions of a substrate, and forming an organic emission layer on the first electrode by firmly contacting a mask to the substrate and depositing emission layer material through the mask. The mask may have an opening and an indentation that does not contact the substrate, and the emission layer material may be deposited through the opening. The method may also include forming a second electrode on an upper portion of the organic emission layer, sealing the substrate, and dividing the substrate by panel region unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a state in which an OLED is formed on the substrate. 
         FIG. 2A ,  FIG. 2B , and  FIG. 2C  are plan views of deposition masks for depositing red, green, and blue organic EMLs, respectively. 
         FIG. 3  is a cross-sectional view of a main image part of  FIG. 1 . 
         FIG. 4  is an exploded perspective view of a deposition mask according to a preferred embodiment of the present invention. 
         FIG. 5  is a plan view more simply illustrating the deposition mask of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of  FIG. 5  taken along line I-I. 
         FIG. 7  is a cross-sectional view of  FIG. 5  taken along line II-II. 
         FIG. 8  is a cross-sectional view illustrating a state in which an icon part is deposited using the deposition mask of  FIG. 5 . 
         FIG. 9  is a cross-sectional view illustrating a state in which a main image part is deposited using the deposition mask of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
     The present invention can be used to manufacture an OLED as illustrated in  FIG. 1 . As described above, the substrate  10  of  FIG. 1  has four panel regions but the present invention is not necessarily limited to this. The present invention can have a plurality of panel regions and have the OLED formed on the respective panel regions. 
     As described above, the OLED of the respective panels  11  can include an icon part  12  and a main image part  13 . The icon part  12  can include a red emission region  12 R, a green emission region  12 G, and a blue emission region  12 B. The main image part  13  can have a red sub-pixel, a green sub-pixel, and a blue sub-pixel so as to realize full color. 
     At this point, the icon part  12  and the main image part  13  can have the structure illustrated in  FIG. 3 . This structure is further detailed below. 
     First, the first electrode layer  20  may be formed in a predetermined pattern on the substrate  10  and an insulation layer  21  may be formed thereon so that a predetermined portion of the first electrode layer  20  may be exposed. An organic film may be formed on an upper portion of the first electrode layer  20 . For the organic film, a hole transport layer (HTL)  22  and an electron transport layer (ETL)  24  may be used as a common layer. A red organic emission layer  23 R, a green organic emission layer  23 G, and a blue organic emission layer  23 B may be formed between the HTL  22  and the ETL  24 . The second electrode layer  25  may be formed on an upper portion of the organic film. 
     The substrate  10  can have a plurality of thin film transistors (TFTs) and storage capacitors on a glass substrate. A buffer layer by SiO2 can be formed on the glass substrate. 
     The first electrode layer  20  can be used as a hole injection electrode of the OLED. The first electrode layer  20  can be formed using transparent electrodes or reflection-type electrodes. If the transparent electrodes are used for the first electrode layer  20 , the transparent electrodes can be made of ITO, IZO, ZnO, or In 2 O 3 . If the reflection-type electrodes are used for the first electrode layer  20 , a reflection film may be formed using Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, and combinations thereof first and then ITO, IZO, ZnO, or In 2 O 3  can be formed on the reflection film. 
     Any organic film that can be used for the OLED can be all applied for the organic film including the organic emission layers  23 R,  23 G, and  23 B. As described above, a hole injection layer (HIL) or an electron injection layer (EIL) can be further provided besides the HTL, the organic EML, and the ETL. Further, for the organic material available, a variety of materials such as copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminum (Alq3) can be used. 
     The second electrode layer  25  can also be used as a hole injection electrode of the OLED and can also be formed using transparent electrodes or reflection-type electrodes. If transparent electrodes are used for the second electrode layer  25 , metal having low work function such as Li, Ca, LiF/Ca, LiF/Al, Al, Mg, and compound thereof may be deposited to be oriented to a direction of the ETL  24 . After that, auxiliary electrodes or bus electrode lines can be formed thereon using material for transparent electrode formation such as ITO, IZO, ZnO, or In 2 O 3 . Alternatively, if reflection-type electrodes are used for the second electrode layer  25 , a metal such as Li, Ca, LiF/Ca, LiF/Al, Al, Mg, or a compound thereof may be deposited so that the electrode layer  25  may be formed. 
     The insulation film  21  may be a region whose predetermined region opens to form a pixel and thus corresponds to a pixel-define film. For the insulation film  21 , polyimide, acryl, BCB, SiO 2 , SiN x , and the like can be used. 
     In the OLED, the icon part  12  may be configured such that the respective organic EMLs  23 R,  23 G, and  23 B form one region and the respective emission regions emit colors of the relevant organic EMLs. The main image part  13  may be configured such that the organic EMLs are provided for the respective sub-pixels to realize full color. Of course, the icon part  12  can be so configured as to realize full color. 
     In the OLED, the organic EML may be formed by being deposited with the deposition mask as illustrated in  FIG. 4 . 
     As shown in  FIG. 4 , the deposition mask according to a preferred embodiment of the present invention can deposit an organic EML of one color and can have a plurality of unit masks  31 . The respective unit masks  31  can have an icon masking part  32  for depositing the icon part and a main masking part  33  for depositing the main image part. 
     The deposition mask  30  may be made of a magnetized thin panel and can be made of nickel or nickel alloy and may be made of nickel-cobalt alloy with which fine patterns are easily formed and whose surface roughness is excellent. 
     The deposition mask  30  can form openings of the respective icon masking parts  32  and the main masking parts  33  using an electro forming method to obtain fine patterns and excellent surface planarization. Of course, the openings can be manufactured by an etching method. In such a case, after a resist layer having the same patterns as the openings of the respective icon masking parts  32  and main masking parts  33  is formed on a thin panel using a photoresist, or a film having the patterns of the openings is attached to the thin panel first, the thin panel may be etched so that the openings can be manufactured. 
     The deposition mask  30  manufactured as described above may be given tensile force with its edge fixed by a clamp or an adhesive and joined to a mask frame  40 . At this point, the mask frame  40  may have a cavity part  41  so that edge portions except the portions where the respective unit masks  31  are formed can be supported. Though a variety of methods such as joining by an adhesive, laser welding, or resistor heating welding can be applied, laser welding may be preferred because of its accuracy. 
     Further, though not illustrated in the drawing, to solve a problem of accuracy variations due to bad welding when the deposition mask  30  is welded to the mask frame  40 , a cover frame (not shown) may cover an upper portion of the deposition mask  30  where the mask frame  40  and the deposition mask  30  are welded. Thus the welded portion may be secured. 
       FIG. 5  is a simpler plan view illustrating the deposition mask in more detail. As shown, only four unit masks  31  are provided and the icon masking parts  32  have an opening for deposition of one color (such as red, green, or blue). The deposition mask illustrated in  FIG. 5  is intended for depositing a green organic EML. Since the deposition mask can be applied in the same way for red or blue, only the green organic EML&#39;s deposition will be described. 
     The icon masking part  32  may have a first opening  34 G for depositing the green organic EML. The rest (regions  35 R and  35 B that correspond to red and blue emission regions respectively) may be blocked off. 
     Also, in the main masking part  33 , the second opening  36 G may be provided for depositing a green organic EML and regions that correspond to the rest of the colors are blocked off. 
     An indentation indented to a predetermined depth may be formed on a side of the mask facing the substrate lest the organic EML should be damaged by the mask. 
       FIG. 6  is a cross-sectional view of the icon making part  32  in  FIG. 5  taken along line I-I and  FIG. 7  is a cross-sectional view of the main masking part  33  in  FIG. 5  taken along line II-II. A plane facing upward in  FIGS. 6 and 7  is a plane facing the substrate. 
     First, as shown in  FIG. 6 , in the icon masking part  32 , the first opening  34 G may be formed so as to deposit the green organic EML. The regions  35 R and  35 B that correspond to red and blue emission regions, respectively, are blocked off and the first indentation  37  indented a predetermined depth is formed. This first indentation  37  is formed with a corresponding area in the regions  35 R and  35 B that correspond to the red and blue emission regions. The area of the first indentation  37  may be more than areas of the regions  35 R and  35 B that correspond to the red and the blue emission regions so that the surface of the mask may not touch the organic EML of the red and the blue regions when the green organic EML is deposited. 
     As shown in  FIG. 7 , in the main masking part  33 , the second opening  36 G may be formed so as to deposit the green organic EML. The second indentation  38  may be formed on regions of other colors except a portion where the second opening  36 G is formed. For example, this second indentation  38  may be formed over regions that correspond to the blue and the red organic EMLs in the deposition mask where the opening for the green organic EML is formed. 
     The indentation can be formed in the mask by a half etching. As described above, if the mask is formed by an etching method, the indentation may be formed by half etching when an opening is etched. If the mask is formed by an electro forming method, the indentation can be formed by half etching after going through a separate etching process. However, formation of the indentation is not necessarily limited to this. The indentation can be formed by attaching a separate member without an etching process. 
     The deposition mask can be modified in various ways by patterns of the organic EML of the OLED to be deposited. An indentation of various patterns can be formed as far as the indentation has a structure that allows the organic EML not to be touched to the blocked-off region of the mask. 
     For that purpose, the depth the first and the second indentations  37  and  38  are indented should be at least larger than the thickness of the organic EML. If the depth is smaller than this, the organic EML is touched to the mask part and an effect of forming the indentation cannot be obtained. The indentations may have the deposition mask stick to a substrate direction by a magnet member and have a thickness more than 25 μm with consideration of a minimum etched thickness. 
     The depth of the indentations probably should not exceed about a half of a thickness of the deposition mask. If, for example, the indentations are formed deeply (including more than half a thickness of the deposition mask), the indentations can include protrusions in their ends when the deposition masks are pulled to the substrate direction by the magnet member. 
     Further, if a tensile force is applied to the deposition mask, the deposition mask can be transformed. 
     The deposition mask may cover the organic film such that the region where light emission occurs does not touch the mask. Accordingly, the organic film such as the organic EML may not be damaged by roughness of the mask&#39;s surface. Additionally, surface impurities and further chemical transition of the surface can be prevented. 
     Next, a method for manufacturing the OLED using the deposition mask will be described. 
     First, as shown in  FIGS. 1 and 3 , the first electrode  20  may be formed on a plurality of panel regions  11  provided on a substrate  10 . 
     If an active matrix-type OLED is to be created, a plurality of thin film transistors and storage capacitors may be pre-formed on the substrate  10 . The first electrode  20  may be connected with a drain electrode of the driving TFT and may be so formed as to correspond to a region where light emission occurs. 
     If a passive matrix-type OLED is to be created, the first electrode  20  can be formed in a predetermined pattern. 
     The first electrode  20  manufactured using the above-described material and patterning can be formed by photolithography. 
     After the first electrode  20  is formed, an insulation film  21  may be spread and patterning may be performed. The insulation film  21  may expose a predetermined portion of the first electrode  20  and may be patterned so that the opening (exposed area) can be covered with an organic film including an organic EML. Since a pixel can be defined during this patterning, the patterned insulation film can be a pixel define layer. This insulation film  21  may have photosensitivity such that the patterning process can be performed easily. 
     After the insulation film  21  is formed, a HTL  22  may be deposited as a common layer. At this point, a HIL can be further deposited and formed before deposition of the HTL  22 . 
     After the HTL  22  is formed, organic EMLs  23 R,  23 G, and  23 B may be deposited. The organic EMLs can be formed as red, green, and blue organic EMLs  23 R,  23 G, and  23 B. The icon part  12  can allow red, green, and blue emission regions  12 R,  12 G, and  12 B to have a single color, respectively. As shown in  FIG. 3 , the main image part  13  can allow a sub-pixel having a red organic EML  23 R, a sub-pixel having a green organic EML  23 G, and a sub-pixel having a blue organic EML  23 B to form one pixel so as to realize full color. 
     Though not shown in the drawing, the deposition may be performed in the following way. Organic material evaporating from a deposition source arranged at a lower point inside a vacuum chamber may pass through the mask and be deposited on a substrate in a predetermined pattern. A magnet member positioned on a plane of the substrate opposite the mask may allow the mask to stick to the substrate. 
     As shown in  FIG. 8 , the icon part  12  may be deposited by the first opening  34 G. The mask may include first indentation  37  that may correspond to a location where icon part  12  is to be (or was previously) deposited.  FIG. 8  illustrates a situation in which a green emission region  12 G is being deposited, a red emission region  12 R was previously deposited, and a blue emission region  12 B is about to be deposited. 
     As shown in  FIG. 8 , the first indentations  37  may be formed on regions that correspond to the blue emission region  12 B and the red emission region  12 R. Accordingly, even if the mask sticks to the substrate, the mask may not touch the organic EML already deposited. Thus, the organic EML may not be damaged. 
     As shown in  FIG. 9 , for the main image part  13 , the deposition mask may have a second indentation  38 , and thus the organic EML already deposited may not touch the mask. The second indentation  38  may extend to correspond to a plurality of regions, such as a plurality of sub-pixel regions. 
       FIGS. 8 and 9  illustrate a case of a green deposition mask but similar masks may be used for red and blue deposition masks. 
     After the organic EML is formed, an EIL  24  may be deposited as a common layer and the second electrode layer  25  may be deposited. The second electrode layer  25  may be deposited on an entire portion of the main image part among the panel regions in an active matrix (AM) structure. It may be deposited in a predetermined pattern so as to be perpendicular to the first electrode  20  in a passive matrix (PM) structure. 
     After the second electrode layer  25  is formed, the respective panel regions  11  may be sealed using a separate glass member or a metal cap and the substrate  10  may be divided by panel region unit. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, various changes may be made without departing from the scope of the present invention.