Patent Publication Number: US-2022212291-A1

Title: Laser crystallization apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and the benefit of Korean Patent Application No. 10-2021-0000899, filed on Jan. 5, 2021, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND 
     Field 
     Embodiments of the invention relate generally to a laser crystallization apparatus. 
     Discussion of the Background 
     A liquid crystal display (LCD) and an organic light emitting diode (OLED) display, which are types of flat panel display devices, can be fabricated to be thin and light, so they are commonly used as a display device for mobile electronic devices, and their application is coverage is being extended to large-scale display devices. In particular, as the necessity for a display device requiring high speed operational characteristics emerges, research for such a display device is actively ongoing. 
     In order to satisfy the high speed operational characteristics of a display device, a channel region of a thin film transistor (TFT) is formed by using polycrystalline silicon instead of amorphous silicon. 
     As a method of forming polycrystalline silicon, an annealing method using a laser has been disclosed. 
     Meanwhile, as a glass substrate for forming the display device is becoming larger, it is important to irradiate a laser beam over a wide area. 
     The above information disclosed in this Background section is only for understanding of the background of the inventive concepts, and, therefore, it may contain information that does not constitute prior art. 
     SUMMARY 
     An embodiment is to provide a laser crystallization apparatus capable of irradiating a laser beam to a large area without increasing a manufacturing cost. 
     Additional features of the inventive concepts will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the inventive concepts. 
     A laser crystallization apparatus according to an embodiment includes a light source unit irradiating a laser beam; and an optical unit to which the laser beam is incident in an incident direction. The optical unit includes a first portion and a second portion bonded to each other on a bonded surface, and a first width of the first portion and a second width of the second portion are the same as each other on the bonded surface based on a direction parallel to the incident direction of the laser beam. 
     Based on a direction perpendicular to the incident direction of the laser beam, the first length of the first portion and the second length of the second portion may be different from each other. 
     The first portion and the second portion may be bonded by optical contact bonding or welding. 
     The bonded surface may be parallel to the incident direction of the laser beam. 
     The bonded surface may be inclined to form a predetermined angle with the incident direction of the laser beam. 
     Based on a direction perpendicular to the incident direction of the laser beam, the width of the bonded surface may be about 0.3% to about 0.6% of the length of the optical unit. 
     The length of the optical unit may be about 2000 mm to about 2500 mm based on the direction perpendicular to the incident direction of the laser beam. 
     A laser crystallization apparatus according to another embodiment includes a light source unit irradiating a laser beam; and an optical unit to which the laser beam is incident in an incident direction and including a plurality of sub-optical units, wherein each of a plurality of sub-optical units includes a first portion and a second portion bonded to each other on a bonded surface, and a plurality of sub-optical units are sequentially arranged based on a direction parallel to the incident direction of the laser beam. 
     A plurality of sub-optical units may include a first sub-optical unit and a second sub-optical unit, and the length of the first portion of the first sub-optical unit may be different from the length of the first portion of the second sub-optical unit. 
     The bonded surface of the first sub-optical unit and the bonded surface of the second sub-optical unit may be disposed to offset each other in the direction parallel to the incident direction of the laser beam. 
     Based on the direction parallel to the incident direction of the laser beam, the first width of the first portion and the second width of the second portion may be the same as each other on the bonded surface. 
     The bonded surface of the first sub-optical unit and the bonded surface of the second sub-optical unit may be parallel to the incident direction of the laser beam. 
     The bonded surface of the first sub-optical unit and the bonded surface of the second sub-optical unit may be inclined to form a predetermined angle with the incident direction of the laser beam. 
     Based on the direction perpendicular to the incident direction of the laser beam, the width of the bonded surface of the first sub-optical unit may be about 0.3% to about 0.6% of the length of the first sub-optical unit. 
     The length of the first sub-optical unit may be about 2000 mm to about 2500 mm. 
     A plurality of sub-optical units may be disposed to be bonded along the incident direction of the laser beam. 
     A plurality of sub-optical units may be disposed to be separated from each other along the incident direction of the laser beam. 
     A laser crystallization apparatus according to an embodiment includes a light source unit irradiating a laser beam and an optical unit to which the laser beam is incident in an incident direction, the optical unit includes a first portion and a second portion bonded to each other on a bonded surface, and the bonded surface is inclined to form a predetermined angle with the incident direction of the laser beam. 
     According to the laser crystallization apparatus according to the embodiments, the laser beam may be irradiated to a large-sized area without increasing a manufacturing cost. 
     The effects of the embodiments are not limited to the above-described effect, and it is obvious that it may be variously extended in a range that does not deviate from the spirit and scope of the embodiments. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the inventive concepts. 
         FIG. 1  is a schematic perspective view illustrating a laser crystallization apparatus according to an embodiment. 
         FIG. 2  is a view illustrating a part of a laser crystallization apparatus of  FIG. 1 . 
         FIG. 3  is a layout view illustrating a laser crystallization apparatus according to an embodiment. 
         FIG. 4  is a perspective view conceptually illustrating an optical unit of a laser crystallization apparatus of  FIG. 3 . 
         FIG. 5  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to another embodiment. 
         FIG. 6  is an exploded perspective view of optical units of  FIG. 5 . 
         FIG. 7  is a graph conceptually illustrating changes in intensity of a laser beam passing through an optical unit of a laser crystallization apparatus according to an embodiment. 
         FIG. 8  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to another embodiment. 
         FIG. 9  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to another embodiment. 
         FIG. 10  is an exploded perspective view of optical units of  FIG. 9 . 
         FIG. 11  is a graph conceptually illustrating changes in intensity of a laser beam passing through an optical unit of a laser crystallization apparatus according to another embodiment. 
         FIG. 12  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments or implementations of the invention. As used herein “embodiments” and “implementations” are interchangeable words that are non-limiting examples of devices or methods employing one or more of the inventive concepts disclosed herein. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are illustrated in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments. Further, various exemplary embodiments may be different, but do not have to be exclusive. For example, specific shapes, configurations, and characteristics of an exemplary embodiment may be used or implemented in another exemplary embodiment without departing from the inventive concepts. 
     Unless otherwise specified, the illustrated exemplary embodiments are to be understood as providing exemplary features of varying detail of some ways in which the inventive concepts may be implemented in practice. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions, and/or aspects, etc. (hereinafter individually or collectively referred to as “elements”), of the various embodiments may be otherwise combined, separated, interchanged, and/or rearranged without departing from the inventive concepts. 
     The use of cross-hatching and/or shading in the accompanying drawings is generally provided to clarify boundaries between adjacent elements. As such, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, dimensions, proportions, commonalities between illustrated elements, and/or any other characteristic, attribute, property, etc., of the elements, unless specified. Further, in the accompanying drawings, the size and relative sizes of elements may be exaggerated for clarity and/or descriptive purposes. When an exemplary embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. Also, like reference numerals denote like elements. 
     When an element, such as a layer, is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. To this end, the term “connected” may refer to physical, electrical, and/or fluid connection, with or without intervening elements. Further, the dx-axis, the dy-axis, and the dz-axis are not limited to three axes of a rectangular coordinate system, such as the x, y, and z-axes, and may be interpreted in a broader sense. For example, the dx-axis, the dy-axis, and the dz-axis may be perpendicular to one another, or may represent different directions that are not perpendicular to one another. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms “first,” “second,” etc. may be used herein to describe various types of elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the teachings of the disclosure. 
     Spatially relative terms, such as “beneath,” “below,” “under,” “lower,” “above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), and the like, may be used herein for descriptive purposes, and, thereby, to describe one elements relationship to another element(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and/or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms, “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It is also noted that, as used herein, the terms “substantially,” “about,” and other similar terms, are used as terms of approximation and not as terms of degree, and, as such, are utilized to account for inherent deviations in measured, calculated, and/or provided values that would be recognized by one of ordinary skill in the art. 
     Various exemplary embodiments are described herein with reference to sectional and/or exploded illustrations that are schematic illustrations of idealized exemplary embodiments and/or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not necessarily be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. In this manner, regions illustrated in the drawings may be schematic in nature and the shapes of these regions may not reflect actual shapes of regions of a device and, as such, are not necessarily intended to be limiting. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
     First, referring to  FIG. 1 , the laser crystallization apparatus according to the present embodiment includes a light source unit LS, a first optical unit OP 1 , a second optical unit M, a third optical unit OP 2 , a fourth optical unit W 1 , a fifth optical unit W 2 , and a transporting stage  18 . 
     According to a third direction dz, a substrate  14  including an amorphous silicon thin film  16  is disposed on a transporting stage  18 , and a laser beam  20  of a line type generated from the laser crystallization apparatus according to the present embodiment is irradiated to the amorphous silicon thin film  16  from top to bottom in a direction parallel to the third direction dz to be scanned along a scan direction. 
     At this time, the position of the laser beam  20  is fixed, and the transporting stage  18  may move in the transporting direction a 2 . That is, by the movement of the transporting stage  18 , the laser beam  20  scans the amorphous silicon thin film  16  to be irradiated in the scan direction of the opposite direction to the transporting direction a 2 , and the amorphous silicon of the scanned region  16   a  may be converted into polycrystalline silicon through a solidification process after the melting. 
     The laser beam  20  may have a line shape extending in the first direction (dx), and the crystallization operation that changes to the polycrystalline silicon may be uniformly done when the laser beam of the uniform intensity is irradiated in the first direction dx and the second direction dy. 
     The first optical unit OP 1  may be a long-axis lens, the second optical unit M may be a mirror, the third optical unit OP 2  may be a short-axis lens, and the fourth optical unit W 1  and fifth optical unit W 2  may be windows. The short-axis lens may be a condenser lens or an image formation lens, but embodiments are not limited thereto. The first optical unit OP 1 , the second optical unit M, the third optical unit OP 2 , the fourth optical unit W 1 , and the fifth optical unit W 2  are not limited thereto and may be different optical apparatuses. 
     The laser beam B supplied from the light source unit LS passes through the first optical unit OP 1  and is condensed in the long-axis direction, and passes through the third optical unit OP 2  and diffuses in the short axis direction after the path thereof is converted in the second optical unit M to be supplied as the laser beam  20  of the line shape through the fourth optical unit W 1  and the fifth optical unit W 2 . As illustrated in  FIG. 2 , the laser beam B may include a plurality of collinear beams. 
     According to the laser crystallization apparatus according to the illustrated embodiment, the laser crystallization apparatus is described to include the first optical unit OP 1 , the second optical unit M, the third optical unit OP 2 , the fourth optical unit W 1  and the fifth optical unit W 2 , however embodiments are not limited thereto. A plurality of different optical systems may be further included, and some of the first optical unit OP 1 , the second optical unit M, the third optical unit OP 2 , the fourth optical unit W 1  and the fifth optical unit W 2  may be omitted. 
     Next, the optical unit of the laser crystallization apparatus according to an embodiment is described in more detail with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  is a layout view of a laser crystallization apparatus according to an embodiment, and  FIG. 4  is a perspective view conceptually illustrating an optical unit of a laser crystallization apparatus of  FIG. 3 . 
     Referring to  FIG. 3 , the laser crystallization apparatus according to an embodiment includes the first optical unit OP 1 , the second optical unit M, the third optical unit OP 2 , the fourth optical unit W 1 , and the fifth optical unit W 2  through which the laser beam B supplied from the light source unit LS passes. 
     The first optical unit OP 1  includes a first portion OP 1   a  and a second portion OP 1   b . The first portion OP 1   a  of the first optical unit OP 1  and the second portion OP 1   b  of the first optical unit OP 1  are bonded to each other. The first portion OP 1   a  of the first optical unit OP 1  and the second portion OP 1   b  of the first optical unit OP 1  may be bonded to each other through optical contact bonding or welding. 
     The first length La of the first portion OP 1   a  of the first optical unit OP 1  and the second length Lb of the second portion OP 1   b  of the first optical unit OP 1  may be different from each other, but embodiments are not limited thereto. The first length La of the first portion OP 1   a  of the first optical unit OP 1  and the second length Lb of the second portion OP 1   b  of the first optical unit OP 1  may be the same as each other. Here, the first length La and the second length Lb are lengths measured based on a direction perpendicular to the direction in which the laser beam B is incident. 
     The sum La+Lb of the first length La of the first portion OP 1   a  of the first optical unit OP 1  and the second length Lb of the second portion OP 1   b  of the first optical unit OP 1  may be about 2000 mm to 2500 mm. 
     The bonded part of the first portion OP 1   a  of the first optical unit OP 1  and the second portion OP 1   b  of the first optical unit OP 1  may be parallel to the incidence direction of the laser beam B, at the bonded part of the first portion OP 1   a  of the first optical unit OP 1  and the second portion OP 1   b  of the first optical unit OP 1 , and the width of the first portion OP 1   a  of the first optical unit OP 1  and the width of the second portion OP 1   b  of the first optical unit OP 1 , which are measured in the direction parallel to the incident direction of the laser beam B, may be the same. Also, the widths of the first portion OP 1   a  and second portion OP 1   b  may vary as the surface of the first optical unit curves downward from a center to outward edges thereof. 
     Similarly, the second optical unit M includes a first portion Ma and a second portion Mb which are bonded to each other, and the first length La of the first portion Ma of the second optical unit M and the second length Lb of the portion Mb of the second optical unit M may be different, but embodiments are not limited thereto. The first length La of the first portion Ma of the second optical unit M and the second length Lb of the second portion Mb of the second optical unit M may be the same as each other. The sum La+Lb of the first length La of the first portion Ma of the second optical unit M and the second length Lb of the second portion Mb of the second optical unit M may be about 2000 mm to 2500 mm. Here, the first length La and the second length Lb are lengths measured based on a direction perpendicular to the direction in which the laser beam B is incident. 
     In addition, the bonded part of the first portion Ma of the second optical unit M and the second portion Mb of the second optical unit M may be parallel to the incident direction of the laser beam B, at the bonded part of the first portion Ma of the second optical unit M and the second portion Mb of the second optical unit M. The width of the first portion Ma of the second optical unit M and the width of the second portion Mb of the second optical unit M, which are measured in the direction parallel to the incident direction of the laser beam B, may be the same. 
     Similarly, the third optical unit OP 2  includes a first portion OP 2   a  and a second portion OP 2   b  bonded to each other, and the first length La of the first portion OP 2   a  of the third optical unit OP 2  and the second length Lb of the second portion OP 2   b  of the third optical unit OP 2  may be different, but embodiments are not limited thereto. The first length La of the first portion OP 2   a  of the third optical unit OP 2  and the second length Lb of the second portion OP 2   b  of the third optical unit OP 2  may be the same as each other. The sum La+Lb of the first length La of the first portion OP 2   a  of the third optical unit OP 2  and the second length Lb of the second portion OP 2   b  of the third optical unit OP 2  may be about 2000 mm to 2500 mm. Here, first length La and the second length Lb are lengths measured based on a direction perpendicular to the direction in which the laser beam B is incident. 
     In addition, the bonded portion of the first portion OP 2   a  of the third optical unit OP 2  and the second portion OP 2   b  of the third optical unit OP 2  may be parallel to the incident direction of the laser beam B, at the bonded portion of the first portion OP 2   a  of the third optical unit OP 2  and the second portion OP 2   b  of the third optical unit OP 2 , the width of the first portion OP 2   a  of the third optical unit OP 2  and the width of the second portion OP 2   b  of the third optical unit OP 2 , which are measured in the direction parallel to the incident direction of the laser beam B, may be the same as each other. 
     In addition, the fourth optical unit W 1  includes a first portion W 1   a  and a second portion W 1   b  bonded to each other, and the first length La of the first portion W 1   a  of the fourth optical unit W 1  and the second length Lb of the second portion W 1   b  of the fourth optical unit W 1  may be different, but embodiments are not limited thereto. The first length La of the first portion W 1   a  of the fourth optical unit W 1  and the second length Lb of the second portion W 1   b  of the fourth optical unit W 1  may be the same as each other. The sum La+Lb of the first length La of the first portion W 1   a  of the fourth optical unit W 1  and the second length Lb of the second portion W 1   b  of the fourth optical unit W 1  may be about 2000 mm to 2500 mm. Here, the first length La and the second length Lb are lengths measured based on a direction perpendicular to the direction in which the laser beam B is incident. 
     In addition, the bonded portion of the first portion W 1   a  of the fourth optical unit W 1  and the second portion W 1   b  of the fourth optical unit W 1  may be parallel to the incident direction of the laser beam B, and at the bonded portion of the first portion W 1   a  of the fourth optical unit W 1  and the second portion W 1   b  of the fourth optical unit W 1 , the width of the first portion W 1   a  of the fourth optical unit W 1  and the width of the second portion W 1   b  of the fourth optical unit W 1 , which are measured in the direction parallel to the incident direction of the laser beam B, may be the same as each other. 
     Similarly, the fifth optical unit W 2  includes a first portion W 2   a  and a second portion W 2   b  bonded to each other, and the first length La of the first portion W 2   a  of the fifth optical unit W 2  and the second length Lb of the second portion W 2   b  of the fifth optical unit W 2  may be different, but embodiments are not limited thereto. The first length La of the first portion W 2   a  of the fifth optical unit W 2  and the second length Lb of the second portion W 2   b  of the fifth optical unit W 2  may be the same as each other. The sum La+Lb of the first length La of the first portion W 2   a  of the fifth optical unit W 2  and the second length Lb of the second portion W 2   b  of the fifth optical unit W 2  may be about 2000 mm to 2500 mm. Here, the first length La and the second length Lb are lengths measured based on a direction perpendicular to the direction in which the laser beam B is incident. 
     Also, the bonded portion of the first portion W 2   a  of the fifth optical unit W 2  and the second portion W 2   b  of the fifth optical unit W 2  may be parallel to the incident direction of the laser beam B, and at the bonded portion of the first portion W 2   a  of the fifth optical unit W 2  and the second portion W 2   b  of the fifth optical unit W 2 , the width of the first portion W 2   a  of the fifth optical unit W 2  and the width of the second portion W 2   b  of the fifth optical unit W 2 , which are measured in a direction parallel to the incident direction of the laser beam B, may be the same as each other. 
     The first length La of the first portion OP 1   a  of the first optical unit OP 1  may be different from or may be the same as the first length La of the first portion Ma of the second optical unit M. In addition, the second length Lb of the second portion OP 1   b  of the first optical unit OP 1  may be different from or may be the same as the second length Lb of the second portion Mb of the second optical unit M. 
     The first length La of the first portion Ma of the second optical unit M may be different from or may be the same as the first length La of the first portion OP 2   a  of the third optical unit OP 2 . In addition, the second length Lb of the second portion Mb of the second optical unit M may be different from or may be the same as the second length Lb of the second portion OP 2   b  of the third optical unit OP 2 . 
     The first length La of the first portion OP 2   a  of the third optical unit OP 2  may be different from or may be the same as the first length La of the first portion W 1   a  of the fourth optical unit W 1 . In addition, the second length Lb of the second portion OP 2   b  of the third optical unit OP 2  may be different from or may be the same as the second length Lb of the second portion W 1   b  of the fourth optical unit W 1 . 
     The first length La of the first portion W 1   a  of the fourth optical unit W 1  may be different from or may be the same as the first length La of the first portion W 2   a  of the fifth optical unit W 2 , 
     In addition, the second length Lb of the second portion W 1   b  of the fourth optical unit W 1  may be different from or may be the same as the second length Lb of the second portion W 2   b  of the fifth optical unit W 2 . 
     The first length La of the first portion W 2   a  of the fifth optical unit W 2  may be different from or may be the same as the first length La of the first portion OP 1   a  of the first optical unit OP 1 . In addition, the second length Lb of the second portion W 2   b  of the fifth optical unit W 2  may be different from or may be the same as the second length Lb of the second portion OP 1   b  of the first optical unit OP 1 . 
     According to the embodiment of  FIG. 3 , it is described that each of the optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus includes the first portion and the second portion bonded to each other, however it is not limited thereto, and at least one of the optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus may include the first portion and the second portion bonded to each other. 
     Now, the structure of the optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus according to the third embodiment is described in more detail with reference to  FIG. 4 . 
     The optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus according to the embodiment of  FIG. 3  may have the same structure as the optical unit OP illustrated in  FIG. 4 . 
     Referring to  FIG. 4 , the optical unit OP of the laser crystallization apparatus according to the embodiment includes a first portion Pa and a second portion Pb bonded to each other. The first portion Pa and the second portion Pb of the optical unit OP may include glass. 
     The first portion Pa and the second portion Pb of the optical unit OP may be bonded to each other at a boundary between the first portion Pa and the second portion Pb through a bonding element such as optical contact bonding or welding. A bonded surface Sab of the first portion Pa and the second portion Pb of the optical unit OP may be parallel to the incident direction of the laser beam B. 
     The bonded surface Sab at the boundary between the first portion Pa and the second portion Pb includes a material layer combination that includes a part of the first portion Pa adjacent the boundary, the bonding element, and a part of the second portion Pb adjacent the boundary. The bonded surface Sab may have a thickness as described herein. 
     In the bonded surface Sab of the first portion Pa and the second portion Pb of the optical unit OP, the first width Wa of the first portion Pa and the second width Wb of the second portion Pb measured in a direction parallel to the incident direction of the laser beam B may be the same. 
     As the glass substrate for forming the display device becomes larger, the laser crystallization apparatus may irradiate a laser beam over a wide area, and for this purpose, the size of the optical unit of the laser crystallization apparatus may be increased. When forming the optical unit having a large size using one glass, a manufacturing cost increases. 
     The laser crystallization apparatus according to the embodiment includes the optical unit including the first portion and the second portion bonded to each other, and the bonded portions of the first portion and the second portion may be bonded to each other through the optical contact bonding or the welding. Accordingly, using the bonded surfaces that include a plurality of parts instead of larger monolithic parts, it is possible to more easily diversify shapes and sizes of the optical units and form the laser crystallization apparatus including the optical units having large sizes without increasing the manufacturing cost of the laser crystallization apparatus. 
     Next, the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 5 .  FIG. 5  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to an embodiment. 
     As described herein, the laser crystallization apparatus according to the present embodiment includes a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2 , and at least one among a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus may have the structure of the optical unit OP illustrated in  FIG. 5 . 
     Referring to  FIG. 5 , the optical unit OP of the laser crystallization apparatus according to the present embodiment may include a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 . 
     The first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP may be connected to each other. 
     The first sub-optical unit O 1  of the optical unit OP may include a first portion Ola and a second portion O 1   b  bonded to each other, the second sub-optical unit O 2  of the optical unit OP may include a third portion O 2   a  and a fourth portion O 2   b  bonded to each other, the third sub-optical unit O 3  of the optical unit OP may include a fifth portion O 3   a  and a sixth portion O 3   b  bonded to each other, the fourth sub-optical unit O 4  of the optical unit OP may include a seventh portion O 4   a  and an eighth portion O 4   b  bonded to each other, the fifth sub-optical unit O 5  of the optical unit OP may include a ninth portion O 5   a  and a tenth portion O 5   b  bonded to each other. 
     The first portion O 1   a  and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP are bonded to each other on the first bonded surface Sab 1 , the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP are bonded to each other on the second bonded surface Sab 2 , the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP are bonded to each other on the third bonded surface Sab 3 , the seventh portion O 4   a  of the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP are bonded to each other on the fourth bonded surface Sab 4 , and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP are bonded to each other on the fifth bonded surface Sab 5 . 
     The first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may be parallel to the incident direction of the laser beam B of the optical unit OP. Also, based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     Now, the sub-optical units of the optical unit of 5 are described in more detail with reference to  FIG. 6  along with  FIG. 5 .  FIG. 6  is an exploded perspective view of optical units of  FIG. 5 . 
     Referring to  FIG. 6  along with  FIG. 5 , the optical unit OP of the laser crystallization apparatus according to the present embodiment includes a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 . 
     The first sub-optical unit O 1  of the optical unit OP includes a first portion O 1   a  and a second portion O 1   b  bonded to each other on the first bonded surface Sab 1 , and the first length L 01  of the first portion Ola of the first sub-optical unit O 1  of the optical unit OP and the second length L 11  of the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP may be different from each other or may be the same. 
     The first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP may be a surface parallel to the incident direction of the laser beam B, based on the direction parallel to the incident direction of the laser beam B, and the first width Wa of the first portion Ola of the first sub-optical unit O 1  and the second width Wb of the second portion O 1   b  of the first sub-optical unit O 1  may be the same as each other on the first bonded surface Sab 1 . 
     The second sub-optical unit O 2  of the optical unit OP includes a third portion O 2   a  and a fourth portion O 2   b  bonded to each other on the second bonded surface Sab 2 , and the third length L 02  of the third portion O 2   a  of the second sub-optical unit O 2  of the optical unit OP and the fourth length L 12  of the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP may be different from or the same as each other. 
     The second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP may be parallel to a surface almost parallel to the incident direction of the laser beam B, based on the direction parallel to the incident direction of the laser beam B, and the first width Wa of the third portion O 2   a  of the second sub-optical unit O 2  and the second width Wb of the fourth portion O 2   b  of the second sub-optical unit O 2  may be the same as each other on the second bonded surface Sab 2 . 
     The third sub-optical unit O 3  of the optical unit OP may include a fifth portion O 3   a  and the sixth portion O 3   b  bonded to each other on the third bonded surface Sab 3 , and the fifth length L 03  of the fifth portion O 3   a  of the third sub-optical unit O 3  of the optical unit OP and the sixth length L 13  of the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP may be different from or the same as each other. 
     The third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP may be a surface almost parallel to the incident direction of the laser beam B, and based on the direction parallel to the incident direction of the laser beam B, the first width Wa of the fifth portion O 3   a  of the third sub-optical unit O 3  and the second width Wb of the sixth portion O 3   b  of the third sub-optical unit O 3  may be the same as each other on the third bonded surface Sab 3 . 
     The fourth sub-optical unit O 4  of the optical unit OP includes a seventh portion O 4   a  and an eighth portion O 4   b  bonded to each other on the fourth bonded surface Sab 4 , and the seventh length L 04  of the seventh portion O 4   a  of the fourth sub-optical unit O 4  of the optical unit OP and the eighth length L 14  of the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP may be different from or the same as each other. 
     The fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP may be a surface almost parallel to the incident direction of the laser beam B, and based on the direction parallel to the incident direction of the laser beam B, the first width Wa of the seventh portion O 4   a  of the fourth sub-optical unit O 4  and the second width Wb of the eighth portion O 4   b  of the fourth sub-optical unit O 4  may be the same as each other on the fourth bonded surface Sab 4 . 
     The fifth sub-optical unit O 5  of the optical unit OP may include a ninth portion O 5   a  and a tenth portion O 5   b  bonded to each other on the fifth bonded surface Sab 5 , and the ninth length L 05  of the ninth portion O 5   a  of the fifth sub-optical unit O 5  of the optical unit OP and the tenth length L 15  of the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP may be different from or the same as each other. 
     The fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may be a surface almost parallel to the incident direction of the laser beam B, and based on the direction parallel to the incident direction of the laser beam B, the first width Wa of the ninth portion O 5   a  of the fifth sub-optical unit O 5  and the second width Wb of the tenth portion O 5   b  of the fifth sub-optical unit O 5  may be the same as each other on the fifth bonded surface Sab 5 . 
     The first length L 01  of the first portion Ola of the first sub-optical unit O 1  of the optical unit OP, the third length L 02  of the third portion O 2   a  of the second sub-optical unit O 2  of the optical unit OP, the fifth length L 03  of the fifth portion O 3   a  of the third sub-optical unit O 3  of the optical unit OP, the seventh length L 04  of the seventh portion O 4   a  of the fourth sub-optical unit O 4  of the optical unit OP, and the ninth length L 05  of the ninth portion O 5   a  of the fifth sub-optical unit O 5  of the optical unit OP may be different from each other. Here, the first length L 01 , the third length L 02 , the fifth length L 03 , the seventh length L 04 , and the ninth length L 05  may be lengths measured in the direction perpendicular to the incident direction of the laser beam B. 
     Similarly, the second length L 11  of the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP, the fourth length L 12  of the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP, the sixth length L 13  of the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP, the eighth length L 14  of the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP, and the tenth length L 15  of the tenth portion O 5   b  of the fifth sub-optical unit O 5  optical unit OP may be different from each other. Here, the second length L 11 , the fourth length L 12 , the sixth length L 13 , the eighth length L 14 , and the tenth length L 15  may be lengths measured in the direction perpendicular to the incident direction of the laser beam B. 
     The first portion Ola and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the seventh portion O 4   a  and the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding. 
     Also, the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP may be sequentially disposed along the direction of the incident direction of the laser beam B, and the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding. 
     Based on the direction parallel to the incident direction of the laser beam B of the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in a line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     According to the embodiment illustrated in  FIG. 5  and  FIG. 6  above, it is described that the optical unit of the laser crystallization apparatus according to the embodiment includes five sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 , however it is not limited thereto, and the number of the plurality of sub-optical units may be changed. 
     A change in intensity of a laser beam passing through the optical unit of the laser crystallization apparatus according to an embodiment is described with reference to  FIG. 7  along with  FIG. 5  and  FIG. 6 .  FIG. 7  is a graph conceptually illustrating changes in intensity of a laser beam passing through an optical unit of a laser crystallization apparatus according to an embodiment. 
     Referring to  FIG. 7  along with  FIG. 5  and  FIG. 6 , while the laser beam B passes through the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP, the intensity BL of the laser beam B may be reduced on the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP. 
     As described herein with reference to  FIG. 5  and  FIG. 6 , based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP of the laser crystallization apparatus according to the embodiment, because the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in line with each other, but are disposed to be offset from each other, the first bonded surface Sab 1 , the second bonded surface Sab 2 , the third bonded surface Sab 3 , the fourth bonded surface Sab 4 , and the fifth bonded surface Sab 5 , in which the intensity BL of the laser beam B is changed, do not overlap each other. 
     Accordingly, the change of the intensity BL of the laser beam B passing through the optical unit OP is not concentrated at a specific position, therefore by spacing the bonded surfaces evenly about the width of the laser beam B, the intensity of the uniform laser beam B may be supplied evenly to the substrate  14  according to the positions of the bonded surfaces. 
     Next, the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 8 .  FIG. 8  is a view illustrating one example of an optical unit of a laser crystallization apparatus according to another embodiment. 
     As described herein, the laser crystallization apparatus according to the present embodiment includes a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2 , at least one among a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus may have the structure of the optical unit OP illustrated in  FIG. 8 . 
     Referring to  FIG. 8 , the optical unit OP of the laser crystallization apparatus according to the present embodiment may include a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5  separated from each other. 
     The first sub-optical unit O 1  of the optical unit OP may include the first portion Ola and the second portion O 1   b  bonded to each other, the second sub-optical unit O 2  of the optical unit OP may include the third portion O 2   a  and the fourth portion O 2   b  bonded to each other, the third sub-optical unit O 3  of the optical unit OP may include the fifth portion O 3   a  and the sixth portion O 3   b  bonded to each other, the fourth sub-optical unit O 4  of the optical unit OP may include the seventh portion O 4   a  and the eighth portion O 4   b  bonded to each other, and the fifth sub-optical unit O 5  of the optical unit OP may include the ninth portion O 5   a  and the tenth portion O 5   b  bonded to each other. 
     The first portion Ola and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP are bonded to each other on the first bonded surface Sab 1 , the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP are bonded to each other on the second bonded surface Sab 2 , the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP are bonded to each other on the third bonded surface Sab 3 , the seventh portion O 4   a  and the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP are bonded to each other on the fourth bonded surface Sab 4 , and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP are bonded to each other on the fifth bonded surface Sab 5 . 
     The first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may be respectively parallel to the incident direction of the laser beam B incident to the optical unit OP. Also, based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in a line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     According to the embodiment illustrated in  FIG. 8 , it is described that the optical unit of the laser crystallization apparatus according to an embodiment includes the five sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 , however it is not limited thereto, and the number of a plurality of sub-optical units may be changed. 
     Many characteristics of the optical units of the laser crystallization apparatuses according to the embodiment described with reference to  FIG. 1  to  FIG. 7  above may be applied to the optical unit of the laser crystallization apparatus according to the present embodiment. 
     Next, the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 9 .  FIG. 9  is a view illustrating one example of an optical unit of a laser crystallization apparatus according to another embodiment. 
     As described herein, the laser crystallization apparatus according to embodiments described herein includes a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2 , and at least one among a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus may have the structure of the optical unit OP illustrated in  FIG. 9 . 
     Referring to  FIG. 9 , the optical unit OP of the laser crystallization apparatus according to the present embodiment may include a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 . 
     The first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  may be sequentially disposed according to the direction parallel to the incident direction of the laser beam B of the optical unit OP. 
     The first sub-optical unit O 1  of the optical unit OP may include the first portion Ola and the second portion O 1   b  bonded to each other, the second sub-optical unit O 2  of the optical unit OP may include the third portion O 2   a  and the fourth portion O 2   b  bonded to each other, the third sub-optical unit O 3  of the optical unit OP may include the fifth portion O 3   a  and the sixth portion O 3   b  bonded to each other, the fourth sub-optical unit O 4  of the optical unit OP may include the seventh portion O 4   a  and the eighth portion O 4   b  bonded to each other, and the fifth sub-optical unit O 5  of the optical unit OP may include the ninth portion O 5   a  and the tenth portion O 5   b  bonded to each other. 
     The first portion Ola and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP are bonded to each other on the first bonded surface Sab 1 , the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP are bonded to each other on the second bonded surface Sab 2 , the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP are bonded to each other on the third bonded surface Sab 3 , the seventh portion O 4   a  and the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP are bonded to each other on the fourth bonded surface Sab 4 , and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP are bonded to each other on the fifth bonded surface Sab 5 . 
     The bonded surfaces Sab at the boundaries between the respective portions include a material composition including a part of a first portion adjacent the boundary, the bonding element, and a part of a second portion adjacent the boundary extending perpendicular to the direction of the beam B. 
     The first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP may form a first angle θ 1  with the incident direction of the laser beam B, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP may form a second angle θ 2  with the incident direction of the laser beam B, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP may form a third angle θ 3  with the incident direction of the laser beam B, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP may form a fourth angle θ 4  with the incident direction of the laser beam B, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may form a fifth angle θ 5  with the incident direction of the laser beam B. 
     The first angle θ 1 , the second angle θ 2 , the third angle θ 3 , the fourth angle θ 4 , and the fifth angle θ 5  may be smaller than about 45 degrees, and may be equal to or different from each other. 
     Also, based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in a line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     Next, the sub-optical units of the optical unit of  FIG. 9  are described in detail with reference to  FIG. 10  along with  FIG. 9 .  FIG. 10  is an exploded perspective view of optical units of  FIG. 9 . 
     Referring to  FIG. 10  along with  FIG. 9 , the optical unit OP of the laser crystallization apparatus according to the present embodiment includes a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 . 
     The first sub-optical unit O 1  of the optical unit OP includes the first portion Ola and the second portion O 1   b  bonded to each other on the first bonded surface Sab 1 , and a first length L 01  of the first surface of the first portion Ola of the first sub-optical unit O 1  and a second length L 11  of the first surface of the second portion O 1   b  may be different from a first length (L 01 -L) of the second surface facing the first surface of the first portion Ola of the first sub-optical unit O 1  and a second length (L 11 +L) of the second surface of the second portion O 1   b  of the first sub-optical unit O 1 . 
     In detail, the first length L 01 -L of the second surface of the first portion Ola of the first sub-optical unit O 1  may be shorter by the length difference L than the first length L 01  of the first surface of the first portion Ola of the first sub-optical unit O 1 . The second length L 11 +L of the second surface of the second portion O 1   b  of the first sub-optical unit O 1  may be longer by the length difference L than the second length L 11  of the first surface of the second portion O 1   b  of the first sub-optical unit O 1 . That is, based on the direction perpendicular to the incident direction of the laser beam B, the width of the first bonded surface Sab 1  of the first sub-optical unit O 1  may be the same as the length difference L. 
     The length difference L and the width of the first bonded surface Sab 1  may be about 0.3% to about 0.6% of the entire length of the first sub-optical unit O 1 . For example, the entire length of the first sub-optical unit O 1  is about 2200 mm, and the length difference L and the width of the first bonded surface Sab 1  may be about 10 mm. 
     The width of the first bonded surface Sab 1  refers to a combined width including part of the first portion Ola, part of the second portion O 1   b , and the bonding element area at the boundary of the first portion Ola and the second portion 0 lb. This composition is representative of the other bonded surfaces discussed herein. 
     As described herein, lengths measured in the direction perpendicular to the incident direction of the laser beam B. 
     Also, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP may form the first angle θ 1  with the incident direction of the laser beam B, and based on the direction parallel to the incident direction of the laser beam B, the first width Wa of the first portion O 1   a  of the first sub-optical unit O 1  and the second width Wb of the second portion O 1   b  of the first sub-optical unit O 1  may be the same as each other on the first bonded surface Sab 1 . 
     Similarly, the second sub-optical unit O 2  of the optical unit OP includes the third portion O 2   a  and the fourth portion O 2   b  bonded to each other on the second bonded surface Sab 2 , and the third length L 02  of the first surface of the third portion O 2   a  of the second sub-optical unit O 2  and the fourth length L 12  of the first surface of the fourth portion O 2   b  of the second sub-optical unit O 2  may have the difference from the third length L 02 -L of the second surface of the third portion O 2   a  of the second sub-optical unit O 2  and the fourth length L 12 +L of the second surface of the fourth portion O 2   b  of the second sub-optical unit O 2  by the length difference L. That is, based on the direction perpendicular to the incident direction of the laser beam B, on the second sub-optical unit O 2 , the width of the second bonded surface Sab 2  may be the same length difference L. 
     The length difference L and the width of the second bonded surface Sab 2  may be about 0.3% to about 0.6% of the entire length of the second sub-optical unit O 2 . For example, when the entire length of the second sub-optical unit O 2  is about 2200 mm, the length difference L and the width of the second bonded surface Sab 2  may be about 10 mm. 
     The above-described lengths are the lengths measured in the direction perpendicular to the incident direction of the laser beam B. 
     Also, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP may form the second angle θ 2  with the incident direction of the laser beam B, based on the direction parallel to the incident direction of the laser beam B, and the first width Wa of the third portion O 2   a  of the second sub-optical unit O 2  and the second width Wb of the fourth portion O 2   b  of the second sub-optical unit O 2  may be the same as each other on the second bonded surface Sab 2 . 
     The third sub-optical unit O 3  of the optical unit OP includes the fifth portion O 3   a  and the sixth portion O 3   b  bonded to each other on the third bonded surface Sab 3 , and the fifth length L 03  of the first surface of the fifth portion O 3   a  of the third sub-optical unit O 3  and the sixth length L 13  of the first surface sixth portion O 3   b  of the third sub-optical unit O 3  may have the difference from the fifth length L 03 -L of the second surface of the fifth portion O 3   a  of the third sub-optical unit O 3  and the sixth length L 13 +L of the second surface of the sixth portion O 3   b  of the third sub-optical unit O 3  by the length difference L. That is, based on the direction perpendicular to the incident direction of the laser beam B, on the third sub-optical unit O 3 , the width of the third bonded surface Sab 3  may be the same as the length difference L. 
     The length difference L and the width of the third bonded surface Sab 3  may be about 0.3% to about 0.6% of the entire length of the third sub-optical unit O 3 . For example, when the entire length of the third sub-optical unit O 3  is about 2200 mm, the length difference L and the width of the third bonded surface Sab 3  may be about 10 mm. 
     All lengths described above are lengths measured in the direction perpendicular to the direction in which the laser beam B is incident. 
     Also, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP may form the third angle θ 3  with the incident direction of the laser beam B, based on the direction parallel to the incident direction of the laser beam B, and the first width Wa of the fifth portion O 3   a  of the third sub-optical unit O 3  and the second width Wb of the sixth portion O 3   b  of the third sub-optical unit O 3  may be the same as each other on the third bonded surface Sab 3 . 
     The fourth sub-optical unit O 4  of the optical unit OP includes the seventh portion O 4   a  and the eighth portion O 4   b  bonded to each other on the fourth bonded surface Sab 4 , and the seventh length L 04  of the first surface of the seventh portion O 4   a  of the fourth sub-optical unit O 4  and the eighth length L 14  of the first surface of the eighth portion O 4   b  of the fourth sub-optical unit O 4  may have the difference from the seventh length L 04 -L of the second surface seventh portion O 4   a  of the fourth sub-optical unit O 4  and the eighth length L 14 +L of the second surface of the eighth portion O 4   b  of the fourth sub-optical unit O 4  by the length difference L. That is, based on the direction perpendicular to the incident direction of the laser beam B, the width of the fourth bonded surface Sab 4  may be the same as the length difference L on the fourth sub-optical unit O 4 . 
     The length difference L and the width of the fourth bonded surface Sab 4  may be about 0.3% to about 0.6% of the entire length of the fourth sub-optical unit O 4 . For example, when the entire length of the fourth sub-optical unit O 4  is about 2200 mm, the length difference L and the width of the fourth bonded surface Sab 4  may be about 10 mm. 
     All lengths described above are lengths measured in the direction perpendicular to the direction in which the laser beam B is incident. 
     Also, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP may form the fourth angle θ 4  of the incident direction of the laser beam B, based on the direction parallel to the incident direction of the laser beam B, and the first width Wa of the seventh portion O 4   a  of the fourth sub-optical unit O 4  and the second width Wb of the eighth portion O 4   b  of the fourth sub-optical unit O 4  may be the same as each other on the fourth bonded surface Sab 4 . 
     Similarly, the fifth sub-optical unit O 5  of the optical unit OP includes the ninth portion O 5   a  and the tenth portion O 5   b  bonded to each other on the fifth bonded surface Sab 5 , and the ninth length L 05  of the first surface of the ninth portion O 5   a  of the fifth sub-optical unit O 5  and the tenth length L 15  of the first surface tenth portion O 5   b  of the fifth sub-optical unit O 5  may have the difference from the ninth length L 05 -L of the second surface of the ninth portion O 5   a  of the fifth sub-optical unit O 5  and the tenth length L 15 +L of the second surface of the tenth portion O 5   b  of the fifth sub-optical unit O 5  by the length difference L. That is, based on the direction perpendicular to the direction in which the laser beam B is incident, the width of the fifth bonded surface Sab 5  may be equal to the length difference L on the fifth sub-optical unit O 5 . 
     The length difference L and the width of the fifth bonded surface Sab 5  may be about 0.3% to about 0.6% of the entire length of the fifth sub-optical unit O 5 . For example, when the entire length of the fifth sub-optical unit O 5  is about 2200 mm, the length difference L and the width of the fifth bonded surface Sab 5  may be about 10 mm. 
     All lengths described above are lengths measured in the direction perpendicular to the direction in which the laser beam B is incident. 
     The fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may form the fifth angle θ 5  with the incident direction of the laser beam B, and based on the direction parallel to the incident direction of the laser beam B, the first width Wa of the ninth portion O 5   a  of the fifth sub-optical unit O 5  and the second width Wb of the tenth portion O 5   b  of the fifth sub-optical unit O 5  may be the same as each other on the fifth bonded surface Sab 5 . 
     The first length L 01  of the first portion Ola of the first sub-optical unit O 1  of the optical unit OP, the third length L 02  of the third portion O 2   a  of the second sub-optical unit O 2  of the optical unit OP, the fifth length L 03  of the fifth portion O 3   a  of the third sub-optical unit O 3  of the optical unit OP, the seventh length L 04  of the seventh portion O 4   a  of the fourth sub-optical unit O 4  of the optical unit OP, and the ninth length L 05  of the ninth portion O 5   a  of the fifth sub-optical unit O 5  of the optical unit OP may be different from each other. Here, the first length L 01 , the third length L 02 , the fifth length L 03 , the seventh length L 04 , the ninth length L 05  may be lengths measured in the direction perpendicular to the incident direction of the laser beam B. 
     Similarly, the second length L 11  of the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP, the fourth length L 12  of the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP, the sixth length L 13  of the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP, the eighth length L 14  of the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP, and the tenth length L 15  of the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP may be different from each other. Here, the second length L 11 , the fourth length L 12 , the sixth length L 13 , the eighth length L 14 , and the tenth length L 15  may be lengths measured in the direction perpendicular of the incident direction of the laser beam B. 
     The first portion Ola and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, the seventh portion O 4   a  and the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding, and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding. 
     Also, the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP may be sequentially disposed along the direction parallel to the incident direction of the laser beam B, and the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP may be bonded to each other through the optical contact bonding or the welding. 
     Based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in a line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     According to the embodiment illustrated in  FIG. 9  and  FIG. 10 , it is described that the optical unit of the laser crystallization apparatus according to the embodiment includes five sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 , however it is not limited thereto, and the number of a plurality of sub-optical units may be changed. 
     Now, a change in intensity of a laser beam passing through the optical unit of the laser crystallization apparatus according to an embodiment is described with reference to  FIG. 11  along with  FIG. 9  and  FIG. 10 .  FIG. 11  is a graph conceptually illustrating changes in intensity of a laser beam passing through an optical unit of a laser crystallization apparatus according to another embodiment. 
     Referring to  FIG. 11  along with  FIG. 9  and  FIG. 10 , while the laser beam B passes through the first sub-optical unit O 1 , the second sub-optical unit O 2 , the third sub-optical unit O 3 , the fourth sub-optical unit O 4 , and the fifth sub-optical unit O 5  of the optical unit OP, the intensity BL of the laser beam B may be reduced in the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP. 
     As described with reference to  FIG. 9  and  FIG. 10 , based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP of the laser crystallization apparatus according to the embodiment, because the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in one line and are disposed to be offset from each other, the first bonded surface Sab 1 , the second bonded surface Sab 2 , the third bonded surface Sab 3 , the fourth bonded surface Sab 4 , and the fifth bonded surface Sab 5 , in which the intensity BL of the laser beam B is changed, do not overlap each other. 
     Accordingly, the change of the intensity BL of the laser beam B passing through the optical unit OP is not concentrated at a specific position, therefore the uniform laser beam B may be supplied substantially evenly to the substrate  14  according to the position of the bonded surfaces. 
     Next, the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 12 .  FIG. 12  is a view illustrating an example of an optical unit of a laser crystallization apparatus according to another embodiment. 
     As described herein, the laser crystallization apparatus according to the present embodiment includes a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2 , and at least one among a plurality of optical units OP 1 , M, OP 2 , W 1 , and W 2  of the laser crystallization apparatus may have the structure of the optical unit OP illustrated in  FIG. 12 . 
     Referring to  FIG. 12 , the optical unit OP of the laser crystallization apparatus according to the present embodiment may include a plurality of sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5  separated from each other. 
     The first sub-optical unit O 1  of the optical unit OP may include the first portion Ola and the second portion O 1   b  bonded to each other, the second sub-optical unit O 2  of the optical unit OP may include the third portion O 2   a  and the fourth portion O 2   b  bonded to each other, the third sub-optical unit O 3  of the optical unit OP may include the fifth portion O 3   a  and the sixth portion O 3   b  bonded to each other, the fourth sub-optical unit O 4  of the optical unit OP may include the seventh portion O 4   a  and the eighth portion O 4   b  bonded to each other, and the fifth sub-optical unit O 5  of the optical unit OP may include the ninth portion O 5   a  and the tenth portion O 5   b  bonded to each other. 
     The first portion Ola and the second portion O 1   b  of the first sub-optical unit O 1  of the optical unit OP are bonded to each other on the first bonded surface Sab 1 , the third portion O 2   a  and the fourth portion O 2   b  of the second sub-optical unit O 2  of the optical unit OP are bonded to each other on the second bonded surface Sab 2 , the fifth portion O 3   a  and the sixth portion O 3   b  of the third sub-optical unit O 3  of the optical unit OP are bonded to each other on the third bonded surface Sab 3 , the seventh portion O 4   a  and the eighth portion O 4   b  of the fourth sub-optical unit O 4  of the optical unit OP are bonded to each other on the fourth bonded surface Sab 4 , and the ninth portion O 5   a  and the tenth portion O 5   b  of the fifth sub-optical unit O 5  of the optical unit OP are bonded to each other on the fifth bonded surface Sab 5 . 
     The first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP may respectively form the first angle θ 1 , the second angle θ 2 , the third angle θ 3 , the fourth angle θ 4 , and the fifth angle θ 5  by the incident direction of the laser beam B incident to the optical unit OP. In addition, the first angle θ 1 , the second angle θ 2 , the third angle θ 3 , the fourth angle θ 4 , and the fifth angle θ 5  may be the same as or different from each other. 
     Also, based on the direction parallel to the incident direction of the laser beam B incident to the optical unit OP, the first bonded surface Sab 1  of the first sub-optical unit O 1  of the optical unit OP, the second bonded surface Sab 2  of the second sub-optical unit O 2  of the optical unit OP, the third bonded surface Sab 3  of the third sub-optical unit O 3  of the optical unit OP, the fourth bonded surface Sab 4  of the fourth sub-optical unit O 4  of the optical unit OP, and the fifth bonded surface Sab 5  of the fifth sub-optical unit O 5  of the optical unit OP are not disposed in a line with each other, but may be disposed to be offset from each other in a direction perpendicular to the emission of the laser beam B. 
     According to the embodiment illustrated in  FIG. 12 , it is described that the optical unit of the laser crystallization apparatus according to an embodiment incudes five sub-optical units O 1 , O 2 , O 3 , O 4 , and O 5 , however it is not limited thereto, and the number of a plurality of sub-optical units may be changed. 
     Many characteristics of the optical units of the laser crystallization apparatus according to the embodiments described herein are applicable to all of the optical units of the laser crystallization apparatus according to the present embodiment. 
     As described herein, the laser crystallization apparatuses according to the embodiments include a plurality of optical units, and at least one among a plurality of optical units includes the first portion and the second portion bonded to each other, at least one among a plurality of optical units may include a plurality of sub-optical units including the first portion and the second portion bonded to each other, and a plurality of sub-optical units may be bonded to each other or separated from each other. In addition, the bonded surfaces of a plurality of sub-optical units may be disposed to be deviated or offset from each other without being disposed in one line along the direction parallel to the incident direction of the laser beam. Accordingly, it is possible to form the laser crystallization apparatus including the optical unit having a large size without increasing the manufacturing cost of the laser crystallization apparatus and to reduce the uniformity reduction of the laser beam. 
     Although certain embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. Accordingly, the inventive concepts are not limited to such embodiments, but rather to the broader scope of the appended claims and various obvious modifications and equivalent arrangements as would be apparent to a person of ordinary skill in the art.