Method of aligning a substrate, mask to be aligned with the same, and flat panel display apparatus using the same

A method of aligning a substrate includes forming a first alignment hole in the substrate, preparing a mask with a second alignment hole narrower than the first alignment hole, modifying a surface reflectance around either the first alignment hole or the second alignment hole to form a treatment region, positioning the mask below the substrate, such that the first and second alignment holes overlap, and operating a sensor unit above the first alignment hole to examine alignment of the first and second alignment holes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of aligning a substrate, a mask to be aligned with the substrate, and a flat panel display apparatus using the same. More particularly, the present invention relates to a method of providing efficient alignment of an opaque substrate with a patterning/deposition mask.

2. Description of the Related Art

Generally, flat panel display apparatuses have thin and light display panels exhibiting superior display characteristics as compared to other display devices, e.g., excellent visibility, wide viewing angles, high contrast, and high response speed. For example, an organic electroluminescent (EL) display device, i.e., a display device employing voltage between two electrodes to excite electrons in an organic light emitting layer between the electrodes, may further exhibit high luminance and driving voltage to enable improved color purity and display.

Manufacturing of flat panel apparatuses may require, inter alia, deposition and patterning of thin films. Conventional methods of thin film deposition on a substrate may include a vacuum evaporation method, an ion plating method, a sputtering method, a chemical vapor deposition method, and so forth. Conventional methods of patterning may include wet etching. For example, manufacturing of the conventional organic EL display device may require deposition of at least one electrode, i.e., a first electrode, and an organic light emitting layer by the vacuum evaporation method, followed by patterning via wet etching, e.g., photolithography. In order to minimize deterioration of the organic light emitting layer during the wet etching, e.g., due to contact with moisture and oxygen, simultaneous film deposition and patterning may be performed. For example, the conventional method of simultaneous film deposition and patterning may provide attachment of a mask with a predetermined pattern to a substrate, so that material deposited onto the substrate via the mask may be formed at the predetermined pattern of the mask.

However, simultaneous deposition and patterning may require accurate alignment between the substrate and the mask. For example, a conventional alignment of a mask and a flexible substrate, e.g., a synthetic resin, may require a complex procedure for aligning multiple layers, e.g., a light emitting layer, a driving thin film transistor layer, an electrode layer, and so forth, while imparting minimized deformation to the flexible substrate. On the other hand, a conventional alignment of a mask and an opaque substrate, e.g., a metal substrate, may require accurate alignment via alignment holes in the opaque substrate and the mask.

However, due to the opaque material employed to form the opaque substrate, the reflectance thereof may be similar to the reflectance of the mask, thereby reducing visibility of a boundary line between the substrate and the mask. As such, accurate alignment of the substrate and the mask may be difficult, while a confirmation of a proper alignment via optical devices, e.g., an optical sensor, may be incorrect. Accordingly, there exists a need for a method capable of providing effective alignment of an opaque substrate with a mask.

SUMMARY OF THE INVENTION

The present invention is therefore directed to a method of aligning a substrate, a mask, and a flat panel display apparatus using the same, which substantially overcome one or more of the disadvantages of the related art.

It is therefore a feature of an embodiment of the present invention to provide a method capable of providing effective alignment of an opaque substrate with a patterned mask.

At least one of the above and other features and advantages of the present invention may be realized by providing a method of aligning a substrate, including forming a first alignment hole in the substrate, preparing a mask with a second alignment hole, the second alignment hole having a smaller width than the first alignment hole, modifying a surface reflectance around either the first alignment hole or the second alignment hole to form a treatment region, positioning the mask below the substrate, such that the first and second alignment holes overlap, and operating a sensor unit above the first alignment hole to examine alignment of the first and second alignment holes.

The substrate may be made of an opaque material. The opaque material may be metal. Operating a sensor unit may include operating a CCD camera. Modifying the surface reflectance may include modifying a surface roughness or a surface color. Forming the treatment region may include forming a region having an inner boundary concentric with a corresponding first or second alignment hole.

Forming the treatment region may include irradiating an area on an upper surface of the substrate around the first alignment hole. Forming the treatment region may include irradiating an area having a distance between the inner boundary and the outer boundary of about 1 mm or less. Forming the treatment region may include etching or melting. Forming the treatment region may include irradiating an area to a thickness of about 30 μm to about 100 μm.

Alternatively, forming the treatment region may include treating an area on an upper surface of the mask around the second alignment hole. Forming the treatment region may include laser irradiation, metal deposition, chemical mechanical polishing or sand blasting. Forming the treatment region may include forming a region having the inner boundary spaced apart from the second alignment hole. Forming the treatment region may include forming the inner boundary to have a narrower width than a width of the first alignment hole. Forming the treatment region may include forming the outer boundary to have a wider width than the first alignment hole upon alignment of the substrate with the mask.

At least one of the above and other features and advantages of the present invention may be further realized by providing a display device, including a substrate having an alignment hole and a treatment region around the alignment hole, the treatment region exhibiting a substantially different reflectance as compared to an upper surface of the substrate, and a light display element on the upper surface of the substrate. The light display element may be an organic light emitting diode.

At least one of the above and other features and advantages of the present invention may be also realized by providing a mask to be aligned with a substrate having a first alignment hole, the mask including a second alignment hole smaller than the first alignment hole of the substrate, and a treatment region around the second alignment hole, the treatment region exhibiting a substantially different reflectance as compared to the mask. The treatment region may have an inner boundary having a width smaller than a width of the first alignment hole, and an outer boundary having a width wider than a width of the first alignment hole. The treatment region may include a thin metal layer having a higher reflectance as compared to the mask.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 10-2006-0046575, filed on May 24, 2006, No. 10-2006-0067105, filed on Jul. 18, 2006, and No. 10-2006-0077822, filed on Aug. 17, 2006, in the Korean Intellectual Property Office, and entitled: “Method of Aligning Substrate and Flat Panel Display Apparatus Using the Same,” are incorporated by reference herein in their entirety.

In the figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers or elements may also be present. Further, it will be understood that when a layer or element is referred to as being “under” another layer or element, it can be directly under, and one or more intervening layers or elements may also be present. In addition, it will also be understood that when a layer or element is referred to as being “between” two layers or elements, it can be the only layer or element between the two layers or elements, or one or more intervening layers or elements ay also be present. Like reference numerals refer to like elements throughout.

Hereinafter, an exemplary embodiment of a method of aligning a substrate and a mask according to the present invention will be described in more detail with reference toFIGS. 1-5.

As illustrated inFIG. 1, a first alignment hole210with a treatment region250may be formed in a substrate200. Next, a mask220with a second alignment hole230may be positioned below the substrate200, so that the first alignment hole210and the second alignment hole230may be substantially aligned. Finally, a sensor unit240may be positioned above the first alignment hole210of the substrate200in order to determine proper alignment of the first and second alignment holes210and230.

The substrate200may be any suitable substrate employed in a flexible flat panel display device as determined by one of ordinary skill in the art. The substrate200may be made of an opaque material, such as metal, e.g., steel use stainless (SUS).

The first alignment hole210may be formed through the substrate200and in close proximity to an edge thereof. In other words, the first alignment hole210may be formed sufficiently close to an edge of the substrate200to avoid an overlap between the treatment region250of the substrate200with any essential components of the flat panel display device. On the other hand, the first alignment hole210may be formed sufficiently far from the edge of the substrate200to avoid an overlap between the treatment region250with the edge of the substrate200. The first alignment hole210may have a first width w1, as measured along a horizontal direction and illustrated inFIG. 2, e.g., if the first alignment hole210has a circular shape, the first width w1may equal a diameter of the first alignment hole210.

The treatment region250may be formed on an upper surface of the substrate200around the first alignment hole210. For example, as illustrated inFIG. 1, the treatment region250may have a shape of a ring having an inner boundary250aand an outer boundary250b, so that the outer boundary250bmay have a larger width than the inner boundary250a. The first alignment hole210of the substrate200may be concentric to the inner boundary250a, and the inner boundary250aof the treatment region250may be in communication with an edge of the first alignment hole210.

The treatment region250may be formed to exhibit a substantially different surface reflectance as compared to a surface reflectance of the substrate200. In this respect, it should be noted that the substantially different surface reflectance refers to a difference in reflectance capable of being detected by a standard optical sensor as may be used by one of ordinary skill in the art, e.g., a charged coupled device (CCD) camera. The surface reflectance may be modified by a laser beam of a laser ablation device. For example, as illustrated inFIG. 2, an area surrounding the first alignment hole210may be irradiated to modify a surface texture thereof, e.g., visually and/or physically, to form the treatment region250with a second width w2and a rougher surface texture as compared to a surface texture of the substrate200, i.e., a higher average roughness values with respect to height of bumps on a surface. The treatment region250formed by the laser beam may also have a surface color that is different from the color of the substrate200.

More specifically, as illustrated inFIG. 3, the substrate200may be etched to a predetermined thickness to form the treatment region250. In other words, the laser beam intensity may be adjusted to remove portions from the substrate200, so the treatment region250may have a thickness t, i.e., a vertical distance as measured in a downward direction from an upper surface of the substrate200that is lower than a thickness of the substrate200. For example, the thickness t of the treatment region250may equal half a thickness of the substrate200. The thickness t may be in the range of about 30 μm to about 100 μm. The thickness t of the irradiation region250may be controlled by adjusting the intensity of the laser beam of the laser ablation device or by using a mask. As further illustrated inFIG. 3, the treatment region250may further have the second width w2, i.e., a horizontal distance as measured between the inner and outer boundaries250aand250b, having a value of about 1 mm or less.

Alternatively, as illustrated inFIG. 4, the substrate200may be heat treated by a laser beam to form the treatment region250. In other words, the intensity of the laser beam may be adjusted to partially melt the upper surface of the substrate200to the thickness t and the second width w2. The thickness t and second width w2of the treatment region250formed by surface melting may be similar to the thickness t and second width w2of the treatment region250formed by surface etching. Similarly, the color and roughness of the surface of the treatment region250formed by heat treatment may be different as compared to the substrate200. For example, the surface of the treatment region250formed by melting may be darker as compared to the substrate200.

Without intending to be bound by theory, it is believed that forming the treatment region250with a surface roughness and/or surface color different than the surface of the substrate200may facilitate optical distinction therebetween. For example, the increased surface roughness in the treatment region250may provide different reflectance as compared to the reflectance of the substrate200. Different reflectance values may facilitate improved optical detection of a boundary line between the treatment region250and the substrate200and, thereby, enable location of the first alignment hole210with respect to a center of the treatment region250.

The mask220positioned below the substrate200, as illustrated inFIG. 1, may be made of metal, e.g., nickel or stainless steel, and may include a predetermined pattern to be imparted to a film deposited on the substrate200. The predetermined pattern may be formed in the mask220, e.g., by etching. The second alignment hole230may be formed through the mask220, e.g., by punching. The second alignment hole230may have a third width w3, as illustrated inFIG. 5, that is smaller than the first alignment hole210. It is believed that different widths of the first and second alignment holes210and230may facilitate optical recognition of each of the first and second alignment holes210and230. It should be noted, however, that other types and configurations of masks for depositing a pattern on the substrate200are not excluded from the scope of the present invention.

The sensor unit240may be disposed above the upper surface of the substrate200, so that the substrate200may be positioned between the sensor unit240and the mask220. More specifically, the sensor unit240may be positioned directly above the first alignment hole210, and may include a camera, e.g., a CCD, to check alignment between the substrate200and the mask220, i.e., alignment between the first and second alignment holes210and230. Proper alignment between the first and second alignment holes210and230may vertically line up centers of the first and second alignment holes210and230, so that the second alignment hole230may be seen through the first alignment hole210due to the difference of widths thereof.

More specifically, as illustrated inFIG. 5, the treatment region250may surround the first alignment hole210of the substrate200, while the second alignment hole230may be seen through the first alignment hole210. Accordingly, proper alignment of the first and second alignment holes210and230may enable the sensor unit240to capture and display an image of the first and second alignment holes210and230. Further, the different surface reflectance of the treatment region250as compared to the substrate200may facilitate proper visual identification of the first alignment hole210in the image produced by the sensor unit240. Visual identification of the first alignment hole210, e.g., due to darker surface color of the irradiation region250, by the sensor unit240may provide a convenient method of confirming positioning of the second alignment hole230of the mask220with respect to the center of the first alignment hole210of the substrate200. Accordingly, the substrate200may be easily aligned with the mask220.

Once the substrate200is aligned with the mask220, a light display element may be mounted on the substrate200. For example, as illustrated inFIG. 6, a light display element300may be deposited and patterned on an upper surface of the substrate200to form a flat display device310. The light display element300may be a light emitting element, e.g., a light emitting diode, or a liquid crystal display element.

According to another exemplary embodiment of the present invention, an EL display device may be manufactured by, inter alia, aligning the substrate200with the mask220according to the embodiment described previously with respect toFIGS. 1-5. For example, as illustrated inFIG. 7, an EL display device400may include the substrate200and a light emitting element470on the substrate200. In this respect it should be noted that the EL display device400depicts an active matrix (AM) light emitting display device with a thin film transistor (TFT). However, other types of light emitting display devices are not excluded from the scope of the present invention.

The EL display device400may include a TFT on the substrate200and a buffer layer (not shown) formed as an insulator between the substrate200and the TFT. More specifically, a semiconductor layer410may be formed on the substrate200. Once the semiconductor layer410is formed, a gate insulating film420and a gate electrode430may be formed sequentially on the semiconductor layer410. Next, an interlayer insulating film440may be formed on the gate electrode430to coat the gate electrode430and the gate insulating film420. Contact holes may be formed in the interlayer insulating film440and the gate insulating film420, so that upon formation of source/drain electrodes450on the interlayer insulating film, electrical contact may be established between the source/drain electrodes450and the semiconductor layer410. In this respect, it should be noted that even though the TFT described above is a top-gate type TFT, other types of TFTs are not excluded from the scope of the present invention.

The EL display device400may further include a passivation film460on the TFT, the light emitting element470on the passivation film460, and a pixel defining film465to coat the passivation film460. The passivation film460may be made of an inorganic and/or organic material, and may have a flat upper surface regardless of a curvature of a lower surface. Alternatively, the passivation film460may have a curved upper surface, so that a curvature of the upper surface may be identical to the curvature of the lower surface. The pixel defining film465may be a non-continuous layer, so that an opening may be formed therein to expose a portion of the light emitting element470.

The light emitting element470of the EL display device400may include a pixel electrode472, a light emitting layer474, and an opposite electrode476. The pixel electrode472may be formed on the passivation film460and be in electric communication with the drain electrode450of the TFT through a via hole in the passivation film460. Next, the light emitting layer474, e.g., made of an organic material, and the opposite electrode476may be sequentially deposited on the pixel electrode472, i.e., the pixel and opposite electrodes472and476may be separated from each other by the light emitting layer474. The pixel electrode472may function as an anode electrode, and the opposite electrode476may function as a cathode electrode. The polarities of the pixel electrode472and the opposite electrode476may be switched. Accordingly, voltage may be applied to the pixel and opposite electrodes472and476to trigger excitation of the light emitting layer474therebetween. Once the pixel electrode472, light emitting layer474, and opposite electrode476are formed, the light emitting element470may be hermetically sealed.

The pixel electrode472may be made of a material having a high work function, e.g., a transparent conductive material, such as indium-tin-oxide (ITO), indium-zinc-oxide (IZO), indium oxide (In2O3), zinc oxide (ZnO), and so forth. The opposite electrode476may include a metal having a low work function, e.g., silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), or a combination thereof.

The light emitting layer474may be deposited by vacuum evaporation method, and may be made of a low molecular weight organic molecule or a polymer. When the light emitting layer474includes a low molecular weight organic molecule, e.g., copper phthalocyanine (CuPc), N,N′-di-(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3), and so forth, a hole injection layer (HIL), a hole transport layer (HTL), a light emitting layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL) may be formed therein in a single or a composite structure. The HIL, ETL and EIL of the light emitting layer474may be used for depositing red, green and blue pixels. Accordingly, the light emitting layer474may be formed to coat the entire pixel defining film465(not shown).

Alternatively, when the light emitting layer474is made of the polymer, the light emitting layer474may include a HTL and an EML. The HTL may include, e.g., poly-3,4-ethylenedioxythiophene (PEDOT), and the EML may include, e.g., poly-phenylenevinylene (PPV) based material and/or a polyfluorene based material. The HTL and the EML may be formed by using a screen printing or an inkjet printing method. It should be noted, however, that other materials for forming the light emitting layer474are not excluded from the scope of the present invention.

According to yet another exemplary embodiment of the present invention illustrated inFIGS. 8-13, a method of aligning a substrate with a mask may include formation of a first alignment hole510in a substrate500, formation of a second alignment hole530with a treatment region535in a mask520, and aligning the first and second alignment holes510and530, so that the sensor unit240may be positioned above the substrate500to determine proper alignment of the first and second alignment holes510and530.

In this respect, it should be noted that the mask520and the substrate500, with the exception of formation of the treatment region therein, are similar to the mask220and the substrate200described previously with respect toFIGS. 1-5and, therefore, their description will not be repeated herein. Similarly, formation of the respective first and second alignment holes, their size ratio, and location are similar in both embodiment and, therefore, will not be repeated herein. In other words, the method illustrated inFIGS. 8-13is similar to the method illustrated inFIGS. 1-5, with the exception that a treatment region is formed in the mask520and not in the substrate500.

More specifically, the treatment region535may be formed on an upper surface of the mask520around the second alignment hole530, so that the second alignment hole530may be positioned in a center of the treatment region535. The treatment region535may be formed to have a surface having a reflectance substantially different from a reflectance of the upper surface of the mask520. For example, as illustrated inFIG. 9, the treatment region535may be formed by using a laser ablation device.

In detail, a laser beam may be used to irradiate an area surrounding the second alignment hole530to form the treatment region535, so that the treatment region535may have a surface texture that is rougher than a surface texture of the mask520, i.e., a higher average roughness values with respect to height of bumps on a surface. The treatment region530formed by the laser beam may also have a surface color that is different from the color of the mask520. As further illustrated inFIG. 9, the treatment region535may have the thickness t. The thickness t may be determined by one of ordinary skill in the art with respect to a material used to form the mask520, so that a strength of the mask520is not affected. For example, the thickness t may equal about half a thickness of the mask520. The thickness t of the treatment region535may be formed by removing, i.e., etching, portions of the mask520, applying a mask, and so forth. Upon etching, an upper surface of the treatment region535may have a modified surface roughness as compared to the mask520.

Alternatively, the mask520may be heat treated by the laser beam to form the treatment region535. In other words, the intensity of the laser beam may be increased to partially melt the upper surface of the mask520to the thickness t. The thickness t and surface roughness of the treatment region535formed by surface melting may be similar to the thickness t of the treatment region535formed by surface etching.

As illustrated inFIG. 9, the treatment region535may have a shape of a ring having an inner boundary535aand an outer boundary535b, so that the second alignment hole530of the mask520may be concentric to the inner boundary535a. The outer boundary535bmay have a larger width than the inner boundary535a, so that the treatment region535may have a width corresponding to a horizontal distance as measured between the inner and outer boundaries535aand535b. It should be noted, however, that the treatment region535should be spaced apart from the second alignment hole530, i.e., the inner boundary535aof the treatment region535should be positioned at a predetermined distance from the interface between the second alignment hole530and the mask520. If the inner boundary535aof the treatment region535overlaps with the interface between the second alignment hole530and the mask520, i.e., the inner boundary535ais in communication with the second alignment hole530, it may be difficult to distinguish the second alignment hole530and the treatment region535from each other in images produced by the sensor unit240due to low reflectance difference therebetween. In other words, the sensor unit240may not identify the second alignment hole530and/or confirm alignment between the first and second alignment holes510and530and, thereby, fail to facilitate alignment between the substrate500and the mask520.

In further detail, as illustrated inFIG. 12, the inner boundary535amay have a fourth width w4that is larger than a third width w3of the second alignment hole530and smaller than a first width w1of the first alignment hole510. The fourth width w4of the inner boundary535amay be smaller than the first width of the first alignment hole510to allow the treatment region535to be seen through the sensor unit240. The outer boundary535bmay have a width that is larger than the first width w1to facilitate detection of the first alignment hole510of the substrate500through the sensor unit240upon alignment of the substrate500with the mask520.

In order to facilitate detection of the first alignment hole510further, the outer boundary535bof the treatment region535may be formed in any shape as determined by one of ordinary skill in the art as long as its width is larger than the first width w1of the first alignment hole510upon alignment of the first and second alignment holes510and530. For example, the outer boundary535bof the treatment region535may have a circular perimeter, as illustrated inFIG. 10. Alternatively, the outer boundary535bof the treatment region535may have a rectangular perimeter, as illustrated inFIG. 11. Although the outer boundary535bof the treatment region535may not be seen through the first alignment hole530upon alignment of the substrate500and the mask520, as illustrated inFIG. 13, a portion of the treatment region535within the first width w1of the first alignment hole510may be seen through the first alignment hole510and, therefore, be displayed via the sensor unit240. As such, the portion of the treatment region535exposed through the first alignment hole510may be aligned with the first alignment hole510and facilitate visual distinction therebetween.

The treatment region535may be formed by metal deposition onto the mask520. More specifically, any mental having a higher reflectance as compared to the mask520, e.g., aluminum (Ag), silver (Ag), chromium (Cr), platinum (Pt), or an alloy thereof, may be used. Alternatively, the treatment region535may be formed via chemical mechanical polishing (CMP). In yet another alternative, the treatment region535may be formed using sand blasting, so that the surface roughness of the treatment region535may be increased by jetting sand under a high pressure. When the treatment region535is formed via metal deposition or CMP, the reflectance of the treatment region535may be higher than the reflectance of the surface of the mask520. Accordingly, the treatment region535may appear as a brighter region as compared to the mask520when viewed via the sensor unit240and, therefore, facilitate alignment of the substrate500with the mask520.