Abstract:
A mask inspection apparatus includes a mask transfer unit configured to transfer a mask in one of a first direction and a direction opposite to the first direction, a displacement sensor unit configured to measure a distance to a sheet of the mask transferred by the mask transfer unit, a photographic unit configured to photograph the sheet of the mask transferred by the mask transfer unit, a control unit configured to send a height control signal for controlling a height of the photographic unit according to the measured distance, and a height control unit configured to control the height of the photographic unit according to the height control signal sent by the control unit.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0146638, filed in the Korean Intellectual Property Office on Dec. 14, 2012, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present invention relates to a mask inspection apparatus and a method of controlling the same. 
     2. Description of the Related Art 
     Recently, there have been increased expectations for organic light emitting diode (OLED) displays, requiring attention to various apparatuses used in the manufacturing process, and requiring control of quality during the process. Particularly, masks used for forming organic materials of OLED displays are highly defined in view of the high resolution of displays. 
     However, when manufacturing OLED displays by using highly defined masks, if impurities exist on mask sheets or mask sheets are damaged, defect rates of displays may be increased. However, in general, mask inspection apparatuses and general methods of controlling the same are not well developed, as masks are inspected by using fixed cameras, thereby making it difficult or impossible to precisely inspect whether there are detects in the masks. 
     SUMMARY 
     Aspects of embodiments of the present invention include a mask inspection apparatus capable of inspecting a mask regardless of kind or in spite of a sag of a sheet of the mask, and a method of controlling the mask inspection apparatus. However, this aspect is merely exemplary, and the scope of the present invention is not limited thereto. 
     According to an aspect of the present invention, a mask inspection apparatus includes a mask transfer unit configured to transfer a mask in one of a first direction and a direction opposite to the first direction; a displacement sensor unit configured to measure a distance to a sheet of the mask transferred by the mask transfer unit; a photographic unit configured to photograph the sheet of the mask transferred by the mask transfer unit; a control unit configured to send a height control signal according to the distance measured by the displacement sensor unit; and a height control unit configured to control the height of the photographic unit according to the height control signal sent by the control unit. 
     The mask transfer unit may be configured to transfer the mask in the first direction under the displacement sensor unit and then to the photographic unit. The control unit may be configured to continuously send the height control signal for the photographic unit according to the distance measured by the displacement sensor unit, and the height control unit may be configured to continuously control the height of the photographic unit according to the height control signal. 
     The control unit may be configured to send the height control signal to control a distance from an area of the sheet of the mask photographed by the photographic unit to the photographic unit within a set range. 
     The mask inspection apparatus may further include a first position control unit configured to control a position of the displacement sensor unit in one of a second direction and a direction opposite to the second direction, the second direction intersecting the direction in which the height control unit controls the height of the photographic unit and intersecting the first direction. 
     The displacement sensor unit may include a plurality of displacement sensors separate from one another in a second direction, the second direction intersecting the direction in which the height control unit controls the height of the photographic unit and intersecting the first direction. The mask inspection apparatus may further include a second position control unit configured to control a position of the photographic unit in one of the second direction and a direction opposite to the second direction. The mask transfer unit may be configured to transfer the mask in the first direction under the displacement sensor unit and then to the photographic unit. After the mask transfer unit transfers the mask in the first direction, the control unit may be configured to send a position adjustment signal for adjusting the position of the photographic unit in one of the second direction and the direction opposite to the second direction, and the second position control unit may control the position of the photographic unit in one of the second direction and the direction opposite to the second direction, and after the second position control unit controls the position of the photographic unit, the mask transfer unit may be configured to transfer the mask in the direction opposite to the first direction, and while the mask transfer unit is transferring the mask in the direction opposite to the first direction, the control unit may be configured to send the height control signal to control the height of the photographic unit according to the height control signal sent by the control unit. 
     The photographic unit may include a plurality of cameras separate from one another in a second direction, the second direction intersecting the direction in which the height control unit controls the height of the photographic unit and intersects the first direction. The control unit may be configured to send height control signals for controlling a height of each of the plurality of cameras, and the height control unit may be configured to control the height of each of the plurality of cameras. 
     According to an aspect of the present invention, a method of controlling a mask inspection apparatus includes transferring a mask in a first direction; measuring a distance from a displacement sensor unit to a sheet of the mask; controlling a height of a photographic unit; and photographing the sheet of the mask according to the measured distance. 
     The transferring the mask in the first direction may include transferring the mask under the displacement sensor unit and to the photographic unit. In the transferring a mask in the first direction, the height of the photographic unit may be continuously controlled according to the measured distance continuously obtained by the displacement sensor unit. The height of the photographic unit may be controlled so that a distance from an area of the sheet of the mask photographed by the photographic unit to the photographic unit is controlled within a set range. 
     In the measuring a distance from a displacement sensor unit to a sheet of the mask, the distance from the displacement sensor unit to the sheet of the mask may be obtained in a plurality of areas separate from one another in a second direction, the second direction intersecting a direction for controlling the height of the photographic unit and intersecting the first direction. 
     The transferring the mask in the first direction may include transferring the mask under the displacement sensor unit and to the photographic unit, and the method may further include controlling a position of the photographic unit in one of a second direction and a direction opposite to the second direction, the second direction intersecting the direction for controlling the height of the photographic unit and intersecting the first direction; and transferring the mask in a direction opposite to the first direction, controlling the height of the photographic unit according to the measured distance. 
     The photographic unit may include a plurality of cameras separate from one another in a second direction, the second direction intersecting the direction for controlling the height of the photographic unit and intersecting the first direction, and the method may further include controlling the height of each of the plurality of cameras. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic side view illustrating a mask inspection apparatus according to an embodiment of the present invention; 
         FIGS. 2 and 3  are views illustrating a part of a photographic unit and a part of a mask sheet; and 
         FIG. 4  is a schematic perspective view illustrating a mask inspection apparatus according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and conveys aspects of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions may be exaggerated or contracted for convenience of description. 
     In the following embodiments, an x-axis, a y-axis, and a z-axis are limited to three axes on an orthogonal coordinate system, but it may be understood as a broader meaning including the same. For example, the x-axis, the y-axis, and z-axis may be orthogonal to one another but may indicate different directions that are not orthogonal to one another. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
       FIG. 1  is a schematic side view illustrating a mask inspection apparatus according to an embodiment of the present invention. 
     As illustrated, the mask inspection apparatus according to the present embodiment includes a mask transfer unit  10 , a displacement sensor unit, a photographic unit, a control unit, and a height-control unit. 
     The mask transfer unit  10  may transfer a mask  100  in one of a first direction that is a +x direction and a direction opposite to the first direction, which is a −x direction. In the drawing, the mask transfer unit  10  is shown to include a conveyer belt  11  and a roller  13  rotating the conveyer belt  11 , but it is not limited thereto and may be changed and, for example, include a rail extending along an x-axis and a carrier formed in the shape of a plate with rollers moving on the rail. 
     The displacement sensor unit may include a displacement sensor  21  as shown in  FIG. 1 . The displacement sensor unit may obtain information related to a distance to a sheet of the mask  100  transferred by the mask transfer unit  10 . For example, it is possible to obtain information related to a distance d 1  from a bottom of the displacement sensor  21  to the sheet of the mask  100 . The displacement sensor  21 , for example, may obtain the information related to the distance d 1  from the bottom of the displacement sensor  21  to the sheet of the mask  100  by emitting a laser beam to the sheet of the mask  100  and sensing the laser beam reflected to the displacement sensor  21 . 
     In this case, the mask  100  may include a frame with a tetragonal opening thereinside. The sheet may be coupled with the frame by welding or the like to shield the opening. The sheet may have a single aperture or a plurality of apertures through which evaporation materials pass. In this case, generally, a mask designates a sheet. However, the mask  100  may be considered a mask frame assembly formed of the mask (i.e., the sheet) and a frame coupled to each other. Hereinafter, for convenience, the mask  100  will be described as having a frame with a tetragonal opening thereinside and a sheet coupled with the frame. 
     The photographic unit, as shown in the drawing, may include a camera  31 . The photographic unit photographs the sheet of the mask  100  transferred by the mask transfer unit  10 , thereby inspecting whether there are impurities on the sheet and/or whether the sheet is damaged. The camera  31  may be a charge-coupled device (CCD), a complementary metal-oxide semiconductor (CMOS), or the like. 
     The control unit (not shown) may output a height control signal to control a height of the photographic unit from the sheet of the mask  100  in a +z direction according to the distance-related information obtained by the displacement sensor unit. 
     When the height control signal is transferred to the height control unit  33 , the height control unit  33  may control a height of the photographic unit, that is, the camera  31  in the +z direction according to a corresponding signal. This may be understood as controlling a distance d 2  between the camera  31  and the sheet of the mask  100 . 
     The displacement sensor unit, the photographic unit, and the height control unit  33  may be supported by a frame (not shown) or the like. 
       FIGS. 2 and 3  are schematic views illustrating a part of the photographic unit of the mask inspection apparatus and a part of a sheet  110  of the mask  100 . As shown in the drawings, the photographic unit of the mask inspection apparatus may include a lighting unit  32  with light sources such as light emitting diodes (LED) formed thereon on an end that emit light in a direction of the sheet  10  of the mask  100 . The light unit  32  emits light to a part to be inspected by the camera  31  of the photographic unit to allow the photographic unit to obtain information related to the sheet  110  of the mask  100  with sufficient light. 
     As shown in  FIGS. 2 and 3 , distances between the bottom of the camera  31  of the photographic unit and the sheet  110  of the mask  100  are different, such as d 3  and d 4 . However, regardless of the distances, d 3  and d 4 , between the bottom of the camera  31  of the photographic unit and the sheet  110  of the mask  100 , the lighting unit  32  emits a certain or set amount of light to the sheet  110  of the mask  100 . Accordingly, if there is present an impurity  120  on the sheet  10  of the mask  100 , a reflecting angle at the impurity  120  varies depending on the distances d 3  and d 4  between the bottom of the camera  31  of the photographic unit and the sheet  110  of the mask  100  in such a way that inspection parameters obtained by the camera  31  of the photographic unit vary though the same shaped and sized impurity  120  is present, thereby deteriorating inspection ability of mask inspection apparatuses. 
     However, in case of the mask inspection apparatus according to the present embodiment, as described above, the displacement sensor  21  of the displacement sensor unit obtains distance-related information related to distance to the sheet of the mask  100 , the control unit outputs a height control signal to control a height from the sheet to the photographic unit in the +z direction according to the distance-related information obtained by the displacement sensor unit, and according thereto, the height control unit  33  controls a height of the photographic unit. That is, the height control unit  33  controls the height of the camera  31  in the +z direction in such a way that a distance from a spot (or area) of the sheet, photographed by the photographic unit, to the photographic unit is controlled within a previously determined or set range. Accordingly, the mask inspection apparatus may obtain accurate information related to the impurity on the sheet  110  of the mask  100  to allow the mask  100  to be smoothly maintained. 
     Particularly, as display apparatuses have become larger, the mask  110  has also become larger. To manufacture a plurality of display apparatuses at the same time on one mother glass, the mask  100  is typically enlarged. As the mask  100  has become large, a center of the sheet  110  may sag due to its own weight in the −z direction, that is, the direction in which gravity acts. As a result of this, the center of the sheet  110  of the mask  100  may sag in a range of about 120 μm to about 450 μm, relative to parts adjacent to the frame. However, general photographic units included in mask inspection apparatuses generally only obtain accurate information related to impurities, based on areas where focusing is performed, within ranges of less than 50 μm upwardly, that is, in the +z direction, and downwardly, that is, in the −z direction, respectively. Accordingly, when fixing a height of the photographic unit, it is difficult or impossible to precisely inspect the whole area of the sheet  110  of the mask  100 . 
     However, when the mask inspection apparatus according the present embodiment is used, as described above, the displacement sensor  21  of the displacement sensor unit obtains information related to the distance to the sheet of the mask  100  and the height control unit  33  controls the height of the photographic unit (that is, the height of the camera  31  is controlled in the +z direction according to the distance information) so that the distance between the area of the sheet  110  of the mask  100  to be photographed by the photographic unit is within a previously determined or set range. Accordingly, the mask inspection apparatus according to the present embodiment obtains accurate information related to an impurity on the sheet  110  of the mask  100 , to allow the mask  100  to be smoothly maintained. 
     When inspecting a mask, while the mask transfer unit  10  transfers the mask  100  in the first direction that is the +x direction, the transferred mask  100 , as shown in  FIG. 1 , may pass under the displacement sensor  21  of the displacement sensor unit and approach the camera  31  of the photographic unit. Accordingly, it is possible to continuously transfer the mask  100  in the first direction, that is the +x direction, in such a way that the sheet  110  of the mask  100  may be precisely inspected by the camera  31  of the photographic unit. 
     That is, while the mask transfer unit  10  transfers the mask  100  in the first direction that is the +x direction, the control unit may continuously output the height control signal for the camera  31  of the photographic unit according to distance-related information continuously obtained by the displacement sensor  21  of the displacement sensor unit. The height control unit  33  may continuously control the height of the camera  31  of the photographic unit in the +z direction according to the height control signal. As such, while inspecting the sheet  110  of the mask, a transfer of the mask  100  does not stop and the sheet  110  of the mask  100  is continually inspected, thereby quickly and accurately inspecting the mask  100 . 
     The mask inspection apparatus may further include a first position control unit  25 . The first position control unit  25  may control a position of the displacement sensor unit, that is, a position of the displacement sensor  21  in a second direction (+y direction) or in a direction opposite to the second direction. Here, the second direction (+y direction) may intersect both a direction (+z direction) in which the height control unit  33  controls the height of the camera  31  of the photographic unit and the first direction that is the +x direction. The first direction, the second direction, and the direction in which the height control unit  33  controls the height of the camera  31  of the photographic unit may be orthogonal to one another. As shown in  FIG. 1 , the displacement sensor  21  may be connected to the first position control unit  25  by a sensor supporting unit  23 . In such a configuration, the first position control unit  25  controls a position of the sensor supporting unit  23  in one of the second direction, that is the +y direction, and the −y direction opposite to the second direction. 
     The first position control unit  25  controls the position of the sensor supporting unit  23  in one of the second direction, that is +y direction, and the −y direction opposite to the second direction, so that the displacement sensor unit may obtain information related to the distance to the sheet  110  of the mask  100  corresponding to a part to be inspected by the camera  31  of the photographic unit (among areas of the sheet  110  of the mask  100 ). 
     In some embodiments, when the photographic unit includes a plurality of cameras, for example, two cameras, the first position control unit  25  may control the position of the displacement sensor  21  in such a way that the mask transfer unit  10  transfers the mask  100  in the first direction (that is the +x direction) and one displacement sensor  21  is moved to different parts of the sheet  110  of the mask  100  that are to be inspected by the two cameras of the photographic unit. As such, the displacement sensor  21  alternately obtains information related to distances to the sheet  110  at corresponding parts. In this way, when the photographic unit includes two cameras, it is possible to allow distances from the respective cameras to parts of the sheet  110  to be photographed by corresponding cameras to be within a previously determined or set range. Using the displacement sensor  21 , the control unit outputs height control signals to control respective heights of the plurality of cameras, and the height control unit  33  individually controls the respective heights of the plurality of cameras. 
     A mask inspection apparatus according to another embodiment of the present invention may further include a second position control unit capable of controlling positions of respective cameras of a plurality of cameras of the photographic unit in one of the second direction, that is the +y direction, and the −y direction opposite to the second direction. The second position control unit, for example, may be formed together with the height control unit  33  in a single body or may be an additional control unit different from the height control unit  33 . The second position control unit may control the position of the photographic unit by receiving a position adjustment signal outputted by the control unit, and thereby adjust the position of respective cameras in one of the second direction that is the +y direction and the −y direction opposite to the second direction. 
     The mask transfer unit  10  transfers the mask  100  in the first direction, that is the +x direction, to allow the transferred mask  100  to pass under the displacement sensor unit, including a displacement sensor  21 . As the transferred mask is passed under the displacement sensor unit, the first position control unit  25  controls the displacement sensor  21  to be alternately located in two areas separate from each other in the second direction, that is the +y direction, and therefore to alternately obtain information related to distances from the corresponding areas of the sheet  110  of the mask. Then, the transferred mask is passed under the photographic unit (including one camera  31 ). 
     A height of the camera  31  of the photographic unit in the +z direction is controlled by the height control unit  33  in an area corresponding to one of the two areas to perform an inspection of the sheet  110 . The position of the camera  31  of the photographic unit is then adjusted to an area corresponding to the other of the two areas. Then, the mask transfer unit  10  transfers the mask  100  in the −x direction opposite to the first direction to perform an inspection of the mask  100  in the other of the two areas. A height of the camera  31  of the photographic unit in the other area may be controlled by the height control unit  33  by using the information related to the distance to the sheet  110  of the mask obtained by the displacement sensor  21  of the displacement sensor unit in the other two areas when the mask  100  was initially transferred in the first direction that is the +x direction. 
     Using the configuration described above, when the mask transfer unit  10  transfers the mask  100  in the −x direction opposite to the first direction, in addition to the first direction, a distance between the photographic unit and the sheet  110  of the mask  100  may be controlled within a previously determined or set range to precisely and quickly perform a mask inspection at the other areas. 
       FIG. 4  is a perspective view schematically illustrating a mask inspection apparatus according to another embodiment of the present invention. In the mask inspection apparatus according to the present embodiment, a displacement sensor unit  20  includes a plurality of displacement sensors  21  disposed separate from one another in the second direction, that is the +y direction. In the drawing, there the displacement sensor unit  20  includes four displacement sensors  21 , however, it is not limited thereto. In addition, a photographic unit  30  also includes a plurality of cameras  31  disposed separate from one another in the second direction, that is the +y direction. The number of cameras  31  may be less than the number of the displacement sensors  21 , and in the drawing, the photographic unit  30  includes two cameras  31 , however, the number of cameras is not limited thereto. 
     In the mask inspection apparatus according to the present embodiment, the mask transfer unit  10  transfers the mask  100  in the first direction, that is the +x direction, so that the transferred mask  100  passes under the displacement sensor unit  20  including the four displacement sensors  21  and approaches the photographic unit  30  including the two cameras  31 . The four displacement sensors  21  separate from one another in the second direction, that is the +y direction, obtain information related to distances to the sheet  110  of the mask  100  at respective areas (e.g., spots). Heights of the two cameras  31  of the photographic unit  30  in the +z direction may be controlled by the height control unit  33  in areas corresponding to a first area and a second area where two of the four displacement sensors  21  are located, respectively, to perform an inspection on the sheet  110  of the mask  100 . 
     After that, the transfer of the mask  100  in the first direction is finished and the inspection on the mask  100  in the areas corresponding to the first area and the second area is finished. Then, positions of the cameras  31  of the photographic unit  30  are controlled by the second position control unit to areas corresponding to a third area and a fourth area, where two other displacement sensors  21  of the four displacement sensors  21  were located. Then, the mask transfer unit  10  transfers the mask  100  in the −x direction opposite to the first direction to perform an inspection on the mask  100 . In this case, heights of the cameras in the third area and the fourth area may be controlled by the height control unit  33  by using information related to distances to the sheet  110  of the mask  100  previously obtained by the two displacement sensors  21  in the third area and the fourth area while initially transferring the mask  100  in the first direction. 
     Using the configuration described above, when the mask transfer unit  10  transfers the mask  100  the −x direction opposite to the first direction, in addition to the first direction, the distance between the photographic unit  30  and the sheet  110  of the mask  100  may be controlled within a previously determined or set range to precisely and quickly perform a mask inspection of the third area and the fourth area. 
     As described above, when manufacturing a small display apparatus, it is possible to manufacture a plurality of display apparatuses on one mother glass at the same time. In this case, each area on the one mother glass, which will become a small display apparatus, may be designated as a cell. In the mask inspection apparatuses according to the described embodiments and variations thereof, when a displacement sensor of a displacement sensor unit obtains distance-related information for changing a position of the photographic unit in a second direction (or a plurality of displacement sensors of a displacement sensor unit separate from one another in the second direction) in corresponding areas, the distance-related information may correspond to each cell. 
     The mask inspection apparatuses according the embodiments of the present invention have been described, but the present invention is not limited thereto. Various embodiments and variations thereof, such a method of controlling the mask inspection apparatuses or the like, may be included therein. 
     In a method of controlling the mask inspection apparatus according to an embodiment of the present invention, referring to  FIG. 1 , the mask  100  is transferred in the first direction (that is the +x direction) and information related to the distance d 1  from the displacement sensor unit to the sheet of the mask  100  is obtained by the displacement sensor  21 , and the height of the photographic unit inspecting the sheet of the mask  100  is thereby controlled. In this case, while transferring the mask  100  in the first direction (that is the +x direction), the transferred mask  100  may pass under the displacement sensor unit and then approach the photographic unit. When transferring the mask  100  in the first direction (that is the +x direction), the height of the photographic unit is controlled according to the distance-related information obtained by the displacement unit so that the distance from the area of the sheet of the mask  100  photographed by the photographic unit to the photographic unit is within a previously determined or set range. 
     When obtaining the information related to the distance to the sheet of the mask by the displacement sensor unit, the displacement sensor unit may obtain (e.g., be controlled to obtain) information related to a distance from the displacement sensor unit to the sheet of the mask  100  in each of a plurality of areas separate from one another in the second direction (that is the +y direction). The second direction (that is the +y direction) intersects both the direction for controlling the height of the photographic unit (which is the +z direction) and the first direction (that is the +x direction). 
     Similar to the mask inspection apparatus as described above, in the method of controlling the mask inspection apparatus, the mask  100  is transferred in the first direction (that is the +x direction) to pass under the displacement sensor unit and then approach the photographic unit, in which the sheet of the mask  100  is inspected. The height of the photographic unit is controlled according to the distance-related information obtained by the displacement sensor unit while transferring the mask in the first direction. After that, the position of the photographic unit may be controlled in one of the second direction which is +y direction and the direction opposite to the second direction. After that, the mask  100  is transferred in the −x direction opposite to the first direction and the sheet of the mask  100  is inspected. The height of the photographic unit in this area is controlled according to the previously obtained distance-related information. The displacement sensor unit may change position in the second direction and obtain distance-related information at different positions or may include a plurality of displacement sensors to obtain distance-related information at different positions. 
     The photographic unit of the mask inspection apparatus includes a plurality of cameras disposed separate from one another in the second direction (that is the +y direction). 
     As described above, when manufacturing a small display apparatus, it is possible to manufacture a plurality of display apparatuses on one mother glass at the same time. In this case, each area on the one mother glass, which will become a small display apparatus, may be designated as a cell. In the method of controlling the mask inspection apparatuses according to described embodiments and variations thereof, a displacement sensor of a displacement sensor unit may obtain distance-related information by changing a position of displacement sensors of a displacement sensor unit in a second direction (that is a +y direction), or by using a plurality of displacement sensors separately disposed in the +y direction. Thereby, distance-related information may be identified for each cell. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as defined by the following claims and equivalents thereof.