Abstract:
A mask for deposition for forming a pattern on a transparent substrate according to the present invention includes a mask member having a mask alignment mark penetratedly formed so as to be aligned with a substrate alignment mark formed on the transparent substrate; and an unevenness region formed on one surface of the mask member so as to be adjacent to the mask alignment mark and having protrusions and depressions on a surface thereof. In accordance with embodiments of the present invention, it is possible to prevent the alignment error of the mask from occurring by increasing the recognition rate of the align marks formed on the substrate and the mask. As a result, it is possible to reduce the manufacturing costs by reducing the defective rate of the organic light emitting diode (OLED) display device.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application earlier filed in the Korean Intellectual Property Office on 31 Jul. 2012 and there duly assigned Serial No. 10-2012-0084200. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     An embodiment of the present invention relates generally to a mask for deposition and a method for aligning the same, and more particularly, to a mask for deposition and a method for aligning the same capable of precisely aligning a mask for deposition and a substrate. 
     Description of the Related Art 
     An organic light emitting diode (OLED) display device, which includes a hole injection electrode, an electron injection electrode, and an organic emission layer disposed therebetween, is a self-emitting type display device emitting light while annihilating holes injected from an anode and electrons injected from a cathode due to the recombination of the holes and electrons in the organic emission layer. In addition, the organic light emitting diode (OLED) display device exhibits high-quality characteristics such as lower power consumption, higher luminance, a wider viewing angle, and a higher reaction speed and therefore, has been focused as a next generation display device of a portable electronic device. 
     The organic light emitting diode (OLED) display device includes an organic light emitting display panel including a display substrate on which a thin film transistor and an organic light emitting element (OLED) are formed. The organic light emitting element includes an anode, a cathode, and an organic emission layer and emits light by forming excitons by holes and electrons injected from each of the anode and the cathode and shifting the excitons to a ground state. 
     In a flat panel display device such as the organic light emitting diode (OLED) display device, a vacuum deposition method for depositing corresponding materials such as an organic material or metals used as an electrode under the vacuum atmosphere to form a thin film on a flat panel, has been used. The vacuum deposition method is performed by disposing a substrate on which an organic thin film is grown in an interior of a vacuum chamber and by evaporating or sublimating the organic materials using a deposition source unit so as to be deposited on the substrate. 
     The deposition process is performed by aligning and attaching a mask for deposition including an open region, which is formed to correspond to a predetermined pattern to be formed on the substrate, on the substrate and performing a control so as to deposit a material for forming an evaporated pattern on the substrate through the open region. In the deposition process, it is important to correctly align and attach the mask for deposition on the substrate without errors. 
     When the substrate is a transparent substrate, however, a contrast difference between alignment marks, in particular, an angle alignment mark and a substrate (and a mask) is small due to the reflected light from the mask surface at the time of performing the measurement by the measuring device and therefore, it is difficult to confirm a location of the angle alignment mark. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a mask for deposition and a method for aligning the same capable of preventing an alignment error between a substrate and a mask from occurring. 
     Another aspect of the present invention provides a mask for deposition and a method for aligning the same capable of increasing a recognition rate of alignment marks formed on a substrate and a mask. 
     An embodiment of the present invention provides a mask for deposition for forming a pattern on a transparent substrate including: a mask member having a mask alignment mark penetratedly formed so as to be aligned with a substrate alignment mark formed on the transparent substrate; and an unevenness region formed on one surface of the mask member so as to be adjacent to the mask alignment mark and having protrusions and depressions on a surface thereof. 
     The unevenness region may diffused-reflect incident light. 
     The unevenness region may be coated with a diffused-reflection material. 
     The unevenness region may be formed at a height lower than one surface of the mask for deposition. 
     The unevenness region may be formed by half etching. 
     The mask for deposition may further include a flat region formed between the mask alignment mark and the unevenness region and having a flat surface. 
     The flat region may be formed along a periphery of the mask alignment mark. 
     The flat region may reflect incident light. 
     The flat region may be coated with a light reflection material. 
     Another embodiment of the present invention provides a method for aligning a mask, including steps of: preparing a transparent substrate having a substrate alignment mark and an angle alignment mark formed adjacent to the substrate alignment mark formed on one surface of the transparent substrate; disposing a mask for deposition on the transparent substrate, the mask including a mask member having a mask alignment mark penetratedly formed so as to be aligned with a substrate alignment mark formed on the transparent substrate and an unevenness region formed on one surface of the mask member so as to be adjacent to the mask alignment mark, the unevenness region having protrusions and depressions on a surface thereof, the unevenness region facing the transparent substrate; aligning the substrate alignment mark and the mask alignment mark at a predetermined location; and aligning the angle alignment mark so that the angle alignment mark is disposed at a predetermined location while overlapping the unevenness region. 
     In the steps of aligning of the location or the aligning of the angle, after an alignment state is measured by a measuring device that is disposed so as to face the unevenness region, an alignment location of the transparent substrate or the mask for deposition may be adjusted. 
     The measuring device may be a measuring device mounted with a CCD camera. 
     According to the embodiments of the present invention, it is possible to prevent the alignment error of the mask from occurring by increasing the recognition rate of the alignment marks formed on the substrate and the mask. 
     As a result, it is possible to reduce the manufacturing costs by reducing the defective rate of the organic light emitting diode (OLED) display device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a schematic oblique view illustrating a mask for deposition and a method for aligning a substrate according to an embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view taken along line II-II of  FIG. 1 . 
         FIGS. 3 through 5  are top plan views illustrating a case in which an alignment of a mask for deposition and a transparent substrate is measured by a measuring device according to an embodiment of the present invention. 
         FIG. 6  is a schematic cross-sectional view illustrating a mask for deposition and a method for aligning a substrate according to an embodiment of the present invention. 
         FIG. 7  is a graph illustrating a recognition rate of an alignment mark after the mark for deposition according to the embodiment of the present invention and a transparent substrate are aligned and the alignment mark is photographed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a mask for deposition and a method for aligning the same according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the exemplary embodiments disclosed below but may be implemented in various types. Therefore, the present exemplary embodiments are provided to fully describe the present invention and fully inform those skilled in the art of the scope of the present invention. Like reference numerals designate like elements throughout the specification. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Further, the thicknesses of some layers and regions are exaggerated in the drawings for better understanding and ease of description. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. 
     In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     In addition, throughout the specification, “on” means one located above or below a targeted portion and does not necessarily mean one located on the top based on a gravity direction. 
       FIG. 1  is a schematic oblique view illustrating a mask for deposition and a method for aligning a substrate according to an embodiment of the present invention and  FIG. 2  is a schematic cross-sectional view taken along line II-II of  FIG. 1   
     In reference to  FIGS. 1 and 2 , a mask  100  for deposition according to an embodiment of the present invention is a mask for forming a pattern on a transparent substrate  200  and is configured to include a mask member  105  and an unevenness region  130 . 
     The transparent substrate  200  is a substrate for forming an organic light emitting diode (OLED) display device and may be further provided with a transparent barrier film  210 . The transparent substrate  200  may be made of a flexible material. Although not illustrated in  FIG. 1 , a first electrode layer serving as an anode is formed on the transparent barrier film  210 , an organic emission layer is formed on the first electrode layer, and a second electrode layer serving as a cathode is formed on the organic emission layer. 
     The first electrode layer may be formed to have a predetermined pattern on the transparent substrate  200  by vacuum deposition or sputtering and the second electrode layer may be molded to have a predetermined pattern by the vacuum deposition, and the like, after the first electrode layer and the organic emission layer are formed. Further, the organic emission layer may be formed by deposition, spin coating, inkjet printing, and the like. The organic emission layer may have a structure of a multilayered film at least including an emission layer. For example, an electron transport layer (ETL) may be disposed between the second electrode layer and the organic emission layer, a hole transport layer (HTL) may be disposed between the first electrode layer and the organic emission layer, a hole injection layer (HIL) may be disposed between the first electrode layer and the hole transport layer, an electron injection layer (EIL) may be disposed between the second electrode layer and the electron transport layer (ETL). Due to the foregoing multilayer structure, holes and electrons can be more smoothly transported into the organic emission layer. 
     In the manufacture of the organic light emitting diode (OLED) display device having the foregoing configuration, the mask  100  for deposition formed with an open region  150  so as to correspond to each pattern is used in a process of adopting a deposition method so as to form an electrode layer having a predetermined pattern and the organic emission layer. The mask for deposition adheres to the transparent substrate  200  by a vacuum adsorption means or a mask support means such as a magnet unit. 
     The mask  100  for deposition and the transparent substrate  200  are accurately disposed at a predetermined location so as to accurately form the pattern at a desired location. In  FIG. 1 , line A indicates an alignment line for aligning the mask  100  for deposition and the transparent substrate  200 . A substrate alignment mark  230  and an angle alignment mark  220  are formed on one surface of the transparent substrate  200  for alignment. The substrate alignment mark  230 , which is a mark for confirming an alignment state with a mask, is a means for determining whether or not to be matched with the mask alignment mark  110  to be described below. The present embodiment describes that the mark is formed in a cross (+) shape, but is not limited thereto and therefore, the mark may be formed in various shapes of diagrams. The angle alignment mark  220  may be disposed while an angle of a substrate deviates from a predetermined reference even though the substrate alignment mark  230  is matched with the mask alignment mark  110 . Therefore, the angle alignment mark  220  is adjacently formed to the substrate alignment mark  230  which is a means for preventing a warpage of a substrate. The present embodiment describes that the mark is formed in a quadrangular shape, but is not limited thereto, and therefore the mark may be formed in various shapes of diagrams. The substrate alignment mark  230  and the mask alignment mark  110  are adjacently formed to each other but are spaced apart from each other with a predetermined distance. 
     The mask member  105  is a plate-shaped member including the open region (i.e., a deposition pattern region)  150  formed to correspond to a pattern of an object to be deposited and a material of the mask member  105  may be a metal material such as metal or alloy, a functional polymer, or a mixture of polymer and metal. The open region  150  may be provided with a plurality of slits that are formed by penetrating through the mask  100  for deposition. The open region  150  may have a pattern corresponding to the first electrode layer, the organic emission layer, and the second electrode layer. 
     The mask alignment mark  110 , which is a mark for aligning the transparent substrate  200  and the mask  100  for deposition, is formed as the open region by penetrating the mask member  105 . The present embodiment of the present invention describes that the mask alignment mark  110  has a circular shape, but is not limited thereto, and therefore the mask alignment mark  110  may have various shapes of polygons, such as triangle, quadrangle, and the like. When the mask alignment mark  110  and the substrate alignment mark  230  are aligned, an area of the mask alignment mark  110  may be larger than that of the substrate alignment mark  230  so that the substrate alignment mark  230  may be disposed within a region of the mask alignment mark  110 . Further, for the precise alignment with the transparent substrate  200 , at least two mask alignment marks  110  may be formed at an outside of the mask member  105 . 
     The unevenness region  130  is formed on one surface of the mask member  105  so as to be adjacent to the mask alignment mark  110  and the unevenness region  130  having protrusions and depressions is formed on a surface thereof. As shown in  FIG. 2 , the unevenness region  130  has a bent surface on which a plurality of ridges and valleys are repeated. Due to the foregoing features, the unevenness region  130  may diffuse-reflect incident light. At the time of performing measurement by a measuring device  300  (in reference to  FIG. 6 ), the unevenness region  130  appears darker than periphery by diffused-reflecting incident light from the measuring device. When the angle alignment mark  220  is disposed in a region rather than in the unevenness region  130 , it is difficult to recognize the angle alignment mark  220  due to light reflected from the surface of the mask  100  for deposition. In other words, in the present embodiment where the angle alignment mark  220  is disposed within the unevenness region  130  as shown in  FIG. 2 , it is possible to prevent the angle alignment mark  220  of the transparent substrate  200  disposed on the unevenness region  130  from not being recognized by the measuring device  300  due to reflected light, by preventing the incident light from the measuring device  300  from being reflected from the unevenness region  130 . 
       FIGS. 3 through 5  are top plan views illustrating the case in which the alignment of the mask for deposition and the transparent substrate is measured by the measuring device according to an embodiment.  FIGS. 3( b ) and 4( b )  illustrate photographs in which the mask for deposition according to the embodiment of the present invention is taken by a charge-coupled device (CCD) camera. 
     As illustrated in  FIG. 3( a ) , an unevenness region  131  may be formed around the mask alignment mark  110  by being divided into at least two while being spaced apart from the mask alignment mark  110 ; as illustrated in  FIGS. 4( a )  and  5 , an unevenness region  132 ,  133  may be formed as a continuous element to surround the periphery of the mask alignment mark  110  while being spaced apart from the mask alignment mark  110 . 
     The present embodiments of the present invention describe that the entire shape of the unevenness region  130  has an oval shape, but are not limited thereto. Therefore, the unevenness region  130  may have various shapes. The area of the unevenness region  130  may be formed to be larger than that of the angle alignment mark  220  so that the angle alignment mark  220  disposed within the unevenness region  130  may be easily differentiated. 
     As shown in  FIG. 2 , the unevenness region  130  may be formed to have a height lower than one surface of the mask  100  for deposition by partially cutting the surface of the mask  100  for deposition. In this case, the unevenness region  130  may be formed by one selected from various processes, such as half etching, laser, a photolithography process, a sand blast process, and the like. When the unevenness region  130  is formed at a height lower than one surface of the mask  100  for deposition, the unevenness region  130  is not damaged even though the mask  100  for deposition adheres to the transparent substrate  200 . 
     The unevenness region  130  may be coated with a diffused reflection material that may diffused-reflect light according to the reaction of a wavelength of light with a molecular particle of a material. In this case, it is possible to more effectively diffused-reflect the incident light. 
     A flat region  120  ( 121 ,  122 ,  123  as shown respectively in  FIG. 3( a )  and  FIG. 4( a )  and  FIG. 5 ) with a flat surface may be further disposed between the mask alignment mark  110  and the unevenness region  130 . The flat region  120  may reflect the incident light. The mask alignment mark  110  is opened to transmit light that is incident in a substrate direction, while the flat region  120  reflects light that is incident in the substrate direction, such that the mask alignment mark  110  is displayed at low brightness and the flat region  120  is displayed at high brightness at the time of performing the measurement by the measuring device  300 . As such, the difference in contrast between the mask alignment mark  110  and the flat region  120  is distinct so that the mask alignment mark  110  can be easily differentiated. The flat region  120  has a difference in contrast from the diffused reflection region  130  according to the foregoing principle, such that the mask alignment mark  110  and the unevenness region  130  can be easily differentiated. 
     The flat region  120  may be formed along a boundary of the mask alignment mark  110  so as to easily differentiate the mask alignment mark  110  and may be formed by being coated with a light reflection material reflecting light that is incident according to the reaction of a wavelength of light with a molecular particle of a material. 
     As shown in  FIG. 3( a ) , when the unevenness region  131  is formed around the mask alignment mark  110  by being divided into at least two, the flat region  121  is formed to surround the boundary of the mask alignment mark  110  to geometrically isolate the unevenness region  131  and the mask alignment mark  110 ; as illustrated in  FIGS. 4( a )  and  5 , the flat regions  122  and  123  are formed to surround the boundary of the mask alignment mark  110  but may be formed in some region of the inside of the unevenness regions  132  and  133 . 
     The present embodiment of the present invention describes that the entire shape of the flat region  120  surrounding the mask alignment mark  110  has a quadrangle  122  (see  FIG. 4 ) and a circle  123  (see  FIG. 5 ), but is not limited thereto and may be variously changed among shapes that can space between the mask alignment mark  110  and the flat region  130  while surrounding the mask alignment mark  110 . 
     Hereinafter, the use of the mask for deposition and the method for aligning the same according to the exemplary embodiment will be described with reference to the accompanying drawings. 
       FIG. 6  is a schematic view illustrating a mask for deposition and a method for aligning a substrate according to an embodiment of the present invention. 
     Referring to  FIGS. 1 and 6 , the transparent substrate  200  having one surface S 1  on which the substrate alignment mark  230  and the angle alignment mark  220  adjacently formed to the substrate alignment mark  230  are formed is prepared and then, the transparent substrate  200  is seated on a substrate support member (not shown). The features of the substrate alignment mark  230  and the angle alignment mark  220  adjacently formed thereto are already described. 
     The mask  100  for deposition according to the embodiment of the present invention is disposed on the transparent substrate  200  and the transparent substrate  200  is adhered to the mask  100  for deposition by the mask support means. In this case, the mask  100  for deposition on which the unevenness region  130  is formed is disposed so that one surface S 2  thereof faces the transparent substrate  200 . 
     Next, the substrate alignment mark  230  and the mask alignment mark  110  are aligned so as to be disposed at a predetermined location. In this case, the locations of the substrate alignment mark  230  and the mask alignment mark  110  are confirmed by measuring the alignment state by the measuring device  300  that is disposed so as to face the unevenness region  130 . The predetermined location refers to a location that is input to the measuring device  300  mounted with a CCD camera in advance and may correspond to, for example, reference lines  310 ,  315 , and  320  illustrated in  FIGS. 3 through 5 . A central portion of the substrate alignment mark  230  having a cross shape is disposed at a central portion at which a vertical reference line  310  intersects a vertical reference line  315 , and a circular central line  320  may be formed to have the same size as the circular mask alignment mark  110  so as to match the mask alignment mark  110  (for convenience, shown in the drawings so as not to match each other). The shapes of the reference lines  310 ,  315 , and  320  are by way of example and therefore, the reference lines  310 ,  315 , and  320  may be formed to have various shapes according to colors, shapes, and the like, of the alignment mark. 
     When being photographed by the CCD camera that is mounted in the measuring device  300 , the brightness is reduced by transmitting the incident light from the CCD camera through the mask alignment mark  110  of the mask  100  for deposition that is an opened region, while the brightness is increased due to the reflection of the incident light from the flat region  120 . The mask alignment mark  110  may be easily identified due to the distinct difference in contrast between the mask alignment mark  110  and the flat region  120 , such that it may be detected whether the mask  100  for deposition is disposed at a desired location. In addition, the substrate alignment mark  230  located at a center of the mask alignment mark  110  reflects the incident light to increase the brightness, such that it is possible to easily differentiate the mask alignment mark  110 . When the substrate alignment mark  230  or the mask alignment mark  110  are not disposed at a predetermined location, the substrate support member moves or the transparent substrate  200  or the mask  100  for deposition moves through a mask driving member (not shown) so as to be disposed at a predetermined location. 
     Next, the angle alignment mark  220  is aligned so as to be disposed at a predetermined location while the angle alignment mark  220  overlaps the unevenness region  130 . In this case, the locations of the angle alignment mark  220  and the unevenness region  130  are confirmed by measuring the alignment state by the measuring device  300  that is disposed so as to face the unevenness region  130 . The predetermined location refers to a location that is input to the measuring device  300  mounted with the CCD camera and may correspond to, for example, the vertical reference line  310  illustrated in  FIGS. 3 through 5 . Both of the substrate alignment mark  230  and the angle alignment mark  220  are aligned so as to match the vertical reference line  310  so that it is possible to prevent the transparent substrate  200  from being disposed while being deviated from the mask  100  for deposition. When the angle alignment mark  220  is not disposed at the predetermined location, the substrate support member moves or the transparent substrate  200  or the mask  100  for deposition moves through the mask driving member so as to be disposed at the predetermined location. 
     When being photographed by the CCD camera mounted with the measuring device, the incident light from the CCD camera is diffused-reflected la the unevenness region  130  to reduce the brightness and is reflected by the flat region adjacent to the unevenness region  130  to increase the brightness, such that the difference in brightness between the unevenness region  130  and the flat region  120  is distinct. When the brightness is reduced by the unevenness region  130  so as to dispose the angle alignment mark  220  within the unevenness region  130 , the angle alignment mark  220  can be easily recognized. 
     By the foregoing method, a process of aligning the transparent substrate  200  to the mask  100  for deposition and then, deposition of the organic material is performed. 
     Hereinafter, the use of the mask for deposition and an effect of the method for aligning the same according to the exemplary embodiment will be described with reference to the accompanying drawings. 
       FIG. 7  is a graph illustrating a recognition rate of an alignment mark after the mark for deposition according to the embodiment of the present invention and a transparent substrate are aligned and the alignment mark is photographed. 
     A recognition rate shows how much the shape of the stored image and the shape actually measured by the measuring device overlap each other after an image for the shapes of the alignment marks  220  and  230  formed on the transparent substrate  200  and the mask alignment mark  110  is stored in the measuring device  300 , that is, a ratio of an overlapping area with the entire area of the shape. That is, when the shape of the stored image and the actually measured shape completely overlap, the recognition rate corresponds to 100% and when the shape of the stored image and the actually measured shape completely do not overlap, the recognition rate corresponds to 0%. It is preferable that the recognition rate is experimentally 95% or more. 
     Experimental Example 1 of  FIG. 7  is an alignment mark recognition rate after being aligned using the mask for deposition formed as shown in  FIG. 3  and Experimental Example 2 is an alignment mark recognition rate after being aligned using the mask for deposition formed as shown in  FIG. 4 . The deposition mask of Comparative Example 1 is formed to have the same shape as Experimental Example 1, but does not have the unevenness region. The deposition mask of Comparative Example 2 is formed to have the same shape as Experimental Example 2, but does not have the unevenness region. Further, each of the masks for deposition of Experimental Examples and Comparative Examples includes two mask alignment marks  110  and includes the substrate alignment mark  230 , the angle alignment mark  220 , the unevenness region  130 , the flat region  120 , and the like, to correspond to the mask alignment mark  110 . The two alignment marks  110  are measured by the two measuring device  300 , which are each shown by C 1  and C 2  in  FIG. 7 . 
     It may be appreciated that Comparative Example 1 and Comparative Example 2 show a distribution of the recognition rate of 88 to 96% according to the experimental frequency, while both of the Experimental Example 1 and Experimental Example 2 show the recognition rate of 96% or more. It may be appreciated that the alignment mark recognition rates of the masks for deposition formed according to the embodiments of the present invention are higher by diffused-reflecting the incident light in the unevenness region. 
     While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.