Patent Publication Number: US-2022214531-A1

Title: Laser crystallization apparatus

Description:
This application claims priority to Korean Patent Application No. 10-2021-0000898, filed on Jan. 5, 2021, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to a laser crystallization apparatus. 
     2. Description of the Related Art 
     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 coverage is being extended to large-scale display devices. In particular, as a desire 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 operation characteristic, a channel part of a thin film transistor is formed using poly-silicon instead of amorphous silicon. 
     An annealing method using a laser is one of conventional methods for forming polycrystalline silicon. 
     Meanwhile, as the glass substrate for forming the display device becomes larger, it is important to irradiate a uniform laser beam over a wide area. 
     SUMMARY 
     Embodiments are to provide a laser crystallization apparatus capable of irradiating a uniform laser beam to a large-sized area. 
     It is apparent that the aspects of the embodiments are not limited to the above-described aspect, but may be variously extended within a range without departing from the spirit and scope of the embodiments. 
     A laser crystallization apparatus according to an embodiment includes: a light source unit which irradiates a laser beam; and a path conversion unit which converts the laser beam incident from the light source unit into a linear beam having a long axis parallel to a first direction and a short axis parallel to a second direction. The linear beam propagates in a third direction perpendicular to the first direction and the second direction, the path conversion unit includes an incident window extending parallel to a first length direction, an emission window extending parallel to a second length direction crossing the first length direction, a first reflection unit disposed at the same side with the incident window, and a second reflection unit disposed at the same side with the emission window, and the second length direction extends parallel to the first direction in a view of the third direction. 
     The first reflection unit and the second reflection unit may face each other along a direction perpendicular to the first length direction and the second length direction. 
     The incident window, the emission window, the first reflection unit, and the second reflection unit may be monolithic. 
     The laser crystallization apparatus may further include: a first heat sink disposed outside the first reflection unit; and a second heat sink disposed outside the second reflection unit. 
     A laser crystallization apparatus according to an embodiment includes: a plurality of light source units which irradiates a laser beam; and a first path conversion unit and a second path conversion unit which convert the laser beam incident from the light source units into a linear beam having a long axis parallel to a first direction and a short axis parallel to a second direction. The first path conversion unit may include a first incident window, a first emission window, a first reflection unit, and a second reflection unit, the second path conversion unit may include a second incident window, a second emission window, a third reflection unit, and a fourth reflection unit, the first incident window of the first path conversion unit, the first reflection unit of the first path conversion unit, the third reflection unit of the second path conversion unit, and the second incident window of the second path conversion unit may be sequentially positioned along the first direction, the first emission window of the first path conversion unit and the second reflection unit of the first path conversion unit may be sequentially positioned along the second direction, and the fourth reflection unit of the second path conversion unit and the second emission window of the second path conversion unit may be sequentially positioned along the second direction. 
     A laser crystallization apparatus according to an embodiment includes: a plurality of light source units which irradiates a laser beam; and a first path conversion unit and a second path conversion unit which convert the laser beam incident from the light source units into a linear beam having a long axis parallel to a first direction and a short axis parallel to a second direction. The first path conversion unit includes a first incident window, a first emission window, a first reflection unit, and a second reflection unit, the second path conversion unit includes a second incident window, a second emission window, a third reflection unit, and a fourth reflection unit, the first incident window and the second incident window extend parallel to a first length direction, and the first emission window and the second emission window extend parallel to a second length direction crossing the first length direction, the linear beam propagates in a third direction perpendicular to the first direction and the second direction, and the second length direction extends parallel to the first direction in a view of the third direction. 
     The first reflection unit and the second reflection unit may face each other along a direction perpendicular to the first length direction and the second length direction, and the second reflection unit and the fourth reflection unit may face each other along the direction perpendicular to the first length direction and the second length direction. 
     The first incident window, the first emission window, the first reflection unit, and the second reflection unit may be monolithic, and the second incident window, the second emission window, the third reflection unit, and the fourth reflection unit may be monolithic. 
     The first path conversion unit and the second path conversion unit may be separated from each other along the first direction. 
     According to the laser crystallization apparatus of the embodiments, the uniform laser beam may be irradiated to the large-sized area. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic layout view showing a laser crystallization apparatus according to an embodiment. 
         FIG. 2  is a view showing a part of a laser crystallization apparatus of  FIG. 1 . 
         FIG. 3  is a view conceptually showing a laser beam path conversion method of a path conversion unit of a laser crystallization apparatus according to an embodiment. 
         FIG. 4  is a view conceptually showing an arrangement of a path conversion unit of a laser crystallization apparatus according to an embodiment. 
         FIG. 5  is a perspective view conceptually showing a laser beam path conversion method of a path conversion unit of a laser crystallization apparatus according to an embodiment. 
         FIG. 6A  and  FIG. 6B  are views showing a result of an experimental example. 
         FIG. 7  is a view showing a result of another experimental example. 
         FIG. 8  is a view showing a part of a laser crystallization apparatus according to another embodiment. 
         FIG. 9  is a view showing an arrangement of a part of a laser crystallization apparatus according to another embodiment. 
         FIG. 10  is a view showing a path conversion unit of a laser crystallization apparatus according to another embodiment. 
         FIG. 11  is a view showing a result of an experimental example. 
         FIG. 12  is a graph showing a result of an experimental example. 
         FIG. 13  is a view showing a result of an experimental example. 
         FIG. 14  is a graph showing a result of an experimental example. 
         FIG. 15  and  FIG. 16  are graphs showing a result of an experimental example. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     The drawings and description are to be regarded as illustrative in nature and not restrictive, and like reference numerals designate like elements throughout the specification. 
     In the drawings, size and thickness of each element are arbitrarily illustrated for convenience of description, and the present invention is not necessarily limited to as illustrated in the drawings. In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, the thicknesses of layers and regions are exaggerated for convenience of description. 
     It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. Further, in the specification, the word “on” or “above” means positioned on or below the object portion, and does not necessarily mean positioned on the upper side of the object portion based on a gravitational direction. 
     It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “At least one” is not to be construed as limiting “a” or “an.” “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. In addition, unless explicitly described to the contrary, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10% or 5% of the stated value. 
     Throughout the specification, the phrase “on a plane” means viewing the object portion from the top, and the phrase “on a cross-section” means viewing a cross-section of which the object portion is vertically cut from the side. 
     In addition, in the specification, when referring to “connected to”, this does not mean only that two or more constituent elements are directly connected to each other, but the two or more constituent elements may be indirectly connected and physically connected through other constituent elements, and they may also be electrically connected or referred to by different names depending on the position or function, and may mean that they are one body. 
     Now, a laser crystallization apparatus according to an embodiment is described with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  is a schematic layout view showing a laser crystallization apparatus according to an embodiment, and  FIG. 2  is a view showing a part (i.e., path conversion unit) of a laser crystallization apparatus of  FIG. 1 . 
     First, referring to  FIG. 1 , the laser crystallization apparatus  100  according to the present embodiment includes a plurality of light source units LS 1  and LS 2 , a plurality of path conversion units M 1  and M 2 , and an optical unit OP. 
     The laser crystallization apparatus  100  supplies a laser beam LB on a substrate  10  including an amorphous silicon thin film  20 . 
     If the laser beam LB is supplied to the amorphous silicon thin film  20 , the amorphous silicon thin film  20  of the substrate  10  may be changed into polycrystalline silicon through solidification crystallization after melting. 
     The laser beam LB may propagate to the third direction DR 3  and have a line shape extending in a direction parallel to the first direction DR 1 . When an intensity of the laser beam is uniform in the first direction DR 1 , which is the length direction of the laser beam LB, and the second direction DR 2 , which is the width direction of the laser beam LB, a crystallization step of being changed into polycrystalline silicon may be uniformly performed. 
     The laser beams LB 1  and LB 2  supplied in the third direction DR 3  from a plurality of light source units LS 1  and LS 2  are diffused along the first direction DR 1  through a plurality of path conversion units M 1  and M 2  and are supplied as the laser beam LB of the line shape through the optical unit OP. 
     In the illustrated embodiment, the optical unit OP is illustrated as a lens, but the invention is not limited thereto, and the optical unit OP may include at least one of optical apparatuses such as a condenser lens for a long axis, a mirror, a projection lens for a short axis, and a window. 
     Now, a structure of a path conversion unit of a laser crystallization apparatus according to an embodiment is described with reference to  FIG. 2 .  FIG. 2  is a perspective view showing a part of a laser crystallization apparatus according to an embodiment. 
     Referring to  FIG. 2 , the path conversion units M 1  and M 2  of the laser crystallization apparatus  10  according to an embodiment have an integrated structure including an incident window IW into which the laser beam is incident, two reflection units Ra and Rb facing each other so that the incident laser beam is reflected several times through the reflection units Ra and Rb, and an emission window OW in which the reflected laser beam is emitted to the outside (i.e., to the substrate  10 ). 
     Light passes through the incident window IW and the emission window OW. 
     The incident window IW may have a rectangle shape elongated in a direction parallel to the first length direction DL 1 , and the emission window OW may have a rectangle shape elongated in a direction parallel to the second length direction DL 2 . The shapes of the incident window IW and the emission window OW are not limited to the rectangle shape and may be deformed to various shapes in another embodiment. 
     The first length direction DL 1  and the second length direction DL 2  may be directions perpendicular to each other. 
     The first length direction DL 1  of the incident window IW may be a direction approximately parallel to the second direction DR 2 , which is the width direction of the laser beam LB of the line shape irradiated to the substrate  10 , and the second length direction DL 2  of the emission window OW may be a direction almost parallel to the first direction DR 1 , which is the length direction (i.e., longitudinal direction) of the laser beam LB of the line shape irradiated to the substrate  10 . That is, when the second length direction DL 2  is projected on the major surface plane of the substrate  10 , the projected direction may be parallel to the first direction DR 1 . In other words, the emission window OW may extend in a direction parallel to the first direction DR 1  when viewed in the third direction DR 3  to which the laser beam LB may propagate. 
     Referring to  FIG. 2  along with  FIG. 1 , the first length direction DL 1  of the incident window IW may be a direction approximately parallel to the second direction DR 2 , which is the width direction of the laser beam LB of the line shape irradiated to the substrate  10 , and the second length direction DL 2  of the emission window OW may be a direction almost parallel to the first direction DR 1 , which is the length direction (i.e., longitudinal direction) of the laser beam LB of the line shape irradiated to the substrate  10 . 
     The laser beam LB may have the line shape extending in the direction parallel to the first direction DR 1 . When the intensity of the laser beam is uniform in the first direction DR 1 , which is the length direction of the laser beam LB and the second direction DR 2 , which is the width direction of the laser beam LB, the crystallization step of being changed into the polycrystalline silicon may be uniformly performed. 
     Two reflection units Ra and Rb face each other along a direction parallel to a direction perpendicular to the first length direction DL 1  and the second length direction DL 2 . 
     The reflection unit Ra and the incident window IW form the first surface of the path conversion units M 1  and M 2 , and the reflection unit Rb and the emission window OW form the second surface of the path conversion units M 1  and M 2 . The first surface and the second surface are surfaces facing each other, and the areas of the first surface and the second surface may be the same, but the areas are not limited thereto. 
     Two reflection units Ra and Rb facing each other include a layer that reflects light, and for example, may include a mirror. 
     The path conversion units M 1  and M 2  each have the shape in which the incident window IW and the emission window OW, and two reflection units Ra and Rb facing each other, are formed of one body (i.e., monolithic). For example, as shown in  FIG. 2 , the path conversion units M 1  and M 2  each have the hexahedron shape, and a surface including the reflection unit Ra and the incident window IW, and another surface including the reflection unit Rb and the emission window OW may face each other among six surfaces of the hexahedron. However, the present invention is not limited thereto, and the path conversion units M 1  and M 2  may have various other shapes in which the incident window IW and the emission window OW, and two reflection units Ra and Rb facing each other, are monolithic. 
     The path conversion units M 1  and M 2  of the laser crystallization apparatus according to an embodiment each includes two reflection units Ra and Rb facing each other while having the incident window IW and the emission window OW, respectively, so that the laser beam incident through the simple structure may be converted into the laser beam of the line shape extending in the direction parallel to the first direction DR 1 . 
     Also, the laser crystallization apparatus according to an embodiment includes a plurality of path conversion units M 1  and M 2 , so that the uniform laser beam may be converted to be symmetric in the first direction DR 1  and the second direction DR 2  perpendicular to the first direction DR 1 , that is, the long-axis direction and the short-axis direction of the laser beam, respectively. This is described in more detail later. 
     Hereinafter, the laser crystallization apparatus  100  according to an embodiment is described in more detail with reference to  FIG. 3  to  FIG. 5  along with  FIG. 1  and  FIG. 2 .  FIG. 3  is a view conceptually showing a laser beam path conversion method of a path conversion unit of a laser crystallization apparatus according to an embodiment,  FIG. 4  is a view conceptually showing an arrangement of a path conversion unit of a laser crystallization apparatus according to an embodiment,  FIG. 5  is a perspective view conceptually showing a laser beam path conversion method of a path conversion unit of a laser crystallization apparatus according to an embodiment. 
     Referring to  FIG. 3  to  FIG. 5  along with  FIG. 1  and  FIG. 2 , a plurality of path conversion units M 1  and M 2  of the laser crystallization apparatus  100  according to an embodiment include a first path conversion unit M 1  and a second path conversion unit M 2  disposed to be separated along the first direction DR 1 . 
     The first laser beam LB 1  supplied from the first light source unit LS 1  among a plurality of light source units LS 1  and LS 2  of the laser crystallization apparatus  100  is incident through the first incident window IW 1  of the first path conversion unit M 1  and then is repeatedly reflected by the first reflection unit R 1  and the second reflection unit R 2  of the first path conversion unit M 1 , and then is emitted through the first emission window OW 1  of the first path conversion unit M 1 . For example, the first laser beam LB 1  incident from the first light source unit LS 1  to the first incident window IW 1  of the first path conversion unit M 1  is reflected multiple times at the surface of the first reflection unit R 1  and the surface of the second reflection unit R 2  and then is divided into a plurality of first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  and diffused into the first direction DR 1  and is emitted to the substrate  10 . A plurality of first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  may include a first beam LB 11   a,  a second beam LB 11   b,  a third beam LB 11   c,  a fourth beam LB 11   d,  a fifth beam LB 11   e,  and a sixth beam LB 11   f  in order away from the first incident window IW 1  of the first path conversion unit M 1  along the first direction DR 1 . 
     The first beam LB 11   a,  the second beam LB 11   b,  the third beam LB 11   c,  the fourth beam LB 11   d,  the fifth beam LB 11   e,  and the sixth beam LB 11   f  may be reflected with the number of the different reflections from the surface of the first reflection unit R 1  and the surface of the second reflection unit R 2 . In the illustrated embodiment, it is described that a plurality of first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  include the first beam LB 11   a  to the sixth beam LB 11   f,  but the invention is not limited thereto, and the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  may be a continuous beam emitted through the first emission window OW 1  and may include numerous beams. 
     Similarly, the second laser beam LB 2  supplied from the second light source unit LS 2  among a plurality of light source units LS 1  and LS 2  of the laser crystallization apparatus  100  is incident through the second incident window IW 2  of the second path conversion unit M 2  and then is repeatedly reflected by the third reflection unit R 3  and the fourth reflection unit R 4  of the second path conversion unit M 2 , and then is emitted through the second emission window OW 2  of the second path conversion unit M 2 . For example, the second laser beam LB 2  incident from the second light source unit LS 2  to the second incident window IW 2  of the second path conversion unit M 2  is reflected multiple times at the surface of the third reflection unit R 3  and the surface of the fourth reflection unit R 4 , and then is divided into a plurality of second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  and diffused along the first direction DR 1  to be emitted to the substrate  10 . A plurality of second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  may include a seventh beam LB 21   a,  an eighth beam LB 21   b,  a ninth beam LB 21   c,  a tenth beam LB 21   d,  an eleventh beam LB 21   e,  and twelfth beam LB 21   f  in order away from the second incident window IW 2  of the second path conversion unit M 2  along the direction parallel to the first direction DR 1 . 
     The seventh beam LB 21   a,  the eighth beam LB 21   b,  the ninth beam LB 21   c,  the tenth beam LB 21   d,  the eleventh beam LB 21   e,  and the twelfth beam LB 21   f  may be reflected with the different number of the reflections from the surface of the third reflection unit R 3  and the surface of the fourth reflection unit R 4 . In the illustrated embodiment, a plurality of second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  are shown to include the seventh beam LB 21   a  to the twelfth beam LB 21   f,  but the invention is not limited thereto, and the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  may be continuous beams emitted through the second emission window OW 2  and may include numerous beams. 
     A plurality of first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  and a plurality of second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  may be together irradiated to the substrate  10  through the optical unit OP of  FIG. 1  as the laser beam LB. 
     Referring to  FIG. 4 , based on the direction parallel to the first direction DR 1 , the first incident window IW 1  of the first path conversion unit M 1  may be positioned on the first side, for example, the right direction with respect to the first reflection unit R 1 , and the second incident window IW 2  of the second path conversion unit M 2  may be positioned on the second side opposite to the first side with respect to the third reflection unit R 3 , for example the left direction. That is, the first incident window IW 1  of the first path conversion unit M 1  and the second incident window IW 2  of the second path conversion unit M 2  may be disposed on the edges of the first path conversion unit M 1  and the second path conversion unit M 2  along the first direction DR 1 . 
     In addition, based on the direction parallel to the second direction DR 2 , the first emission window OW 1  of the first path conversion unit M 1  may be positioned on the third side of the second reflection unit R 2 , for example, in the downward direction, and the second emission window OW 2  of the second path conversion unit M 2  may be positioned on the fourth side opposite to the third side with respect to the fourth reflection unit R 4 , for example, in the upward direction. That is, the first emission window OW 1  of the first path conversion unit M 1  and the second emission window OW 2  of the second path conversion unit M 2  may be disposed in the positions opposite to each other along the second direction DR 2 . 
     As such, by differently disposing the relative positions of the first incident window IW 1  and the first emission window OW 1  of the first path conversion unit M 1  and the second incident window IW 2  and the second emission window OW 2  of the second path conversion unit M 2 , the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  may be symmetrical to each other along the first direction DR 1  and the second direction DR 2 , and accordingly, the laser beam LB having a constant intensity may be emitted along the first direction DR 1  and the second direction DR 2 . 
     Referring to  FIG. 3 , the first path conversion unit M 1  and the second path conversion unit M 2  may each be disposed to form a predetermined angle with respect to the first direction DR 1  and another predetermined angle with respect to the third direction DR 3 , the predetermined angles formed between the first path conversion unit M 1 , and the first direction DR 1  and the third direction DR 3  may be the same as or different from the corresponding angles formed between the second path conversion unit M 2 , and the first direction DR 1  and the third direction DR 3 . 
     Also, referring to  FIG. 5 , the first path conversion unit M 1  and the second path conversion unit M 2  may each be disposed to achieve a predetermined angle with respect to the second direction DR 2 , and the angle between the first path conversion unit M 1  and the second direction DR 2  may be the same as or different from the angle between the second path conversion unit M 2  and the second direction DR 2 . 
     As such, the first path conversion unit M 1  and the second path conversion unit M 2  may each be disposed not to be parallel to the first direction DR 1 , the second direction DR 2 , and the third direction DR 3 , and may be disposed in a direction parallel to the first direction DR 1  according to an embodiment. The arrangement of the first path conversion unit M 1  and the second path conversion unit M 2  may be changed depending on the positions of the incident laser beams LB 1  and LB 2  and the optical unit OP, and the position of the substrate  10 . 
     Referring to  FIG. 5  along with  FIG. 3 , along the first direction DR 1 , the first incident window IW 1  of the first path conversion unit M 1 , the first reflection unit R 1  of the first path conversion unit M 1 , the third reflection unit R 3  of the second path conversion unit M 2 , and the second incident window IW 2  of the second path conversion unit M 2  may be sequentially positioned, along the second direction DR 2 , the first emission window OW 1  of the first path conversion unit M 1  and the second reflection unit R 2  of the first path conversion unit M 1  may be sequentially positioned, similarly, along the second direction DR 2 , and the fourth reflection unit R 4  of the second path conversion unit M 2  and the second emission window OW 2  of the second path conversion unit M 2  may be sequentially positioned. 
     According to the embodiment shown in  FIG. 5 , the first emission window OW 1  of the first path conversion unit M 1  and the second emission window OW 2  of the second path conversion unit M 2  are shown to be disposed side by side along the first direction DR 1 , but the invention is not limited thereto, and the first emission window OW 1  of the first path conversion unit M 1  and the second emission window OW 2  of the second path conversion unit M 2  may be disposed to be offset from each other along the first direction DR 1 , by adjusting the angle between the first emission window OW 1  and the second direction DR 2  and the angle between the second emission window OW 2  and the second direction DR 2 . So, the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  and the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  may be emitted to have approximately the same width along the second direction DR 2 . 
     Next, a simulation result according to an embodiment is described with reference to  FIG. 6A ,  FIG. 6B , and  FIG. 7  along with  FIG. 3  to  FIG. 5 .  FIG. 6A  and  FIG. 6B  are views showing a result of an experimental example, and  FIG. 7  is a view showing a result of another experimental example. 
       FIG. 6A  is an image showing the simulation result of the laser beam intensity of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first emission window OW 1  of the first path conversion unit M 1 , and  FIG. 6B  is an image showing the simulation result of the laser beam intensity of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second emission window OW 2  of the second path conversion unit M 2 .  FIG. 7  is an image showing a simulation result of intensity of a laser beam summing a first emission beam and a second emission beam. 
     Referring to  FIG. 6A  and  FIG. 6B , along with  FIG. 3  to  FIG. 5 , the first beam LB 11   a  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the seventh beam LB 21   a  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other along the first direction DR 1  and the second direction DR 2 . 
     Similarly, the second beam LB 11   b  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the eighth beam LB 21   b  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other with respect to the first direction DR 1  and with respect to the second direction DR 2 . 
     Similarly, the third beam LB 11   c  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the ninth beam LB 21   c  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other along the first direction DR 1  and the second direction DR 2 , and the fourth beam LB 11   d  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the tenth beam LB 21   d  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other with respect to the first direction DR 1  and with respect to the second direction DR 2 . 
     In addition, the fifth beam LB 11   e  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the eleventh beam LB 21   e  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other along the first direction DR 1  and the second direction DR 2 , and the sixth beam LB 11   f  of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the twelfth beam LB 21   f  of the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other with respect to the first direction DR 1  and with respect to the second direction DR 2 . 
     Accordingly, the laser beam LB of the sum of the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2 , as shown in  FIG. 7 , have the intensities that are symmetrical to each other along the first direction DR 1  and the second direction DR 2 . 
     As above-described, according to the laser crystallization apparatus  100  according to the embodiment, by differentially disposing the relative positions of the first incident window IW 1  and the first emission window OW 1  of the first path conversion unit M 1  and the second incident window IW 2  and the second emission window OW 2  of the second path conversion unit M 2 , the first emission beams LB 11   a,  LB 11   b,  LB 11   c,  LB 11   d,  LB 11   e,  and LB 11   f  emitted through the first path conversion unit M 1  and the second emission beams LB 21   a,  LB 21   b,  LB 21   c,  LB 21   d,  LB 21   e,  and LB 21   f  emitted through the second path conversion unit M 2  may be symmetrical to each other with respect to the first direction DR 1  and with respect to the second direction DR 2 , and accordingly, the laser beam LB having the constant intensity may be emitted along the first direction DR 1  and the second direction DR 2 . 
     Next, a part of the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a view showing a part of a laser crystallization apparatus according to another embodiment, and  FIG. 9  is a view showing an arrangement of a part of a laser crystallization apparatus according to another embodiment. 
     Referring to  FIG. 8 , the path conversion unit of the laser crystallization apparatus according to the present embodiment includes the first path conversion unit M 1 , the second path conversion unit M 2 , and the third path conversion unit M 3 . 
     The first path conversion unit M 1  and the second path conversion unit M 2  of  FIG. 8  may be the same as the first path conversion unit M 1  and the second path conversion unit M 2  of the laser crystallization apparatus according to the above-described embodiment. The detailed description of this is omitted. 
     The third path conversion unit M 3  of the laser crystallization apparatus according to the present embodiment, as shown in  FIG. 2  above, may include two reflection units Ra and Rb facing each other, the incident window IW of the shape elongated in the first length direction DLL and the emission window OW of the shape elongated in the second length direction DL 2 . As mentioned above, the second length direction DL 2  is parallel to the first direction DR 1  in a view of the third direction DR 3 . 
     Referring to  FIG. 9 , the third incident window IW 3  and the third emission window OW 3  of the third path conversion unit M 3  of the laser crystallization apparatus according to the present embodiment may have the same arrangement as the first incident window IW 1  and the first emission window OW 1  of the first path conversion unit M 1 , respectively. However, differently, the third incident window IW 3  and the third emission window OW 3  of the third path conversion unit M 3  may have the same arrangement as the second incident window IW 2  and the second emission window OW 2  of the second path conversion unit M 2  in another embodiment. Also, differently from this, the third path conversion unit M 3  may have the arrangement different from the first path conversion unit M 1  and the second path conversion unit M 2  in still another embodiment. 
     The first emission beam LB 11  passing through the first path conversion unit M 1 , the second emission beam LB 21  passing through the second path conversion unit M 2 , and the third emission beam LB 31  passing through the third path conversion unit M 3  may be diffused in the first direction DR 1  and emitted to the substrate  10  with the shape of the laser beam LB having the long axis (i.e., longitudinal direction) parallel to the first direction DR 1 . 
     In the embodiment shown in  FIG. 8 , it is described that the third path conversion unit M 3  is further included as well as the first path conversion unit M 1  and the second path conversion unit M 2 , however it is not limited thereto, and the laser crystallization apparatus may further include an additionally path conversion unit. That is, the laser crystallization apparatus according to an embodiment may include a plurality of path conversion units, and a plurality of path conversion unit may include at least two path conversion units. 
     Many features of the laser crystallization apparatus according to the embodiment described above are applicable to all of the laser crystallization apparatus according to the present embodiment. 
     Next, the structure of the path conversion unit of the laser crystallization apparatus according to another embodiment is described with reference to  FIG. 10 .  FIG. 10  is a view showing a path conversion unit of a laser crystallization apparatus according to another embodiment. 
     Referring to  FIG. 10 , the structure of the path conversion unit of the laser crystallization apparatus according to the present embodiment is similar to the structure of the path conversion unit of the laser crystallization apparatus according to the embodiment described with reference to  FIG. 2 . 
     The path conversion unit M of the laser crystallization apparatus according to the present embodiment includes the incident window IW to which the laser beam is incident, two reflection units Ra and Rb facing each other so as to reflect the incident laser beam, and the emission window OW to which the reflected laser beam is emitted to the outside. 
     The incident window IW may have a shape elongated in the direction approximately parallel to the second direction DR 2  of the width direction of the laser beam LB of the line shape irradiated to the substrate  10 , and the emission window OW may have a shape elongated in the direction (i.e., the second length direction DL 2 ) approximately parallel to the first direction DR 1  of the length direction of the laser beam LB of the line shape irradiated to the substrate  10 . As mentioned above, the emission window OW may have a shape elongated in the direction parallel to the first direction DR 1  in a view of the third direction DR 3 . 
     Two reflection units Ra and Rb face each other, the reflection unit Ra and the incident window IW form the first surface of the path conversion units M 1  and M 2 , and the reflection unit Rb and the emission window OW form the second surface of the path conversion units M 1  and M 2 . 
     Two reflection units Ra and Rb facing each other include a layer that reflects light, and for example, may include a mirror. 
     The path conversion unit M of the laser crystallization apparatus according to the present embodiment, differently from the path conversion units M 1 , M 2 , and M 3  according to the embodiment described with reference to  FIG. 2 , may further include a first heat sink HS 1  and a second heat sink HS 2  attached to the outside of two reflection units Ra and Rb. 
     The first heat sink HS 1  and the second heat sink HS 2  prevent the heating of two reflection units Ra and Rb from which the laser beam is reflected, and thus it may be prevented that the position of the emitted laser beam is changed by the thermal lens effect due to a heating of the reflection units Ra and Rb. 
     Like this, according to the path conversion unit of the laser crystallization apparatus according to the present embodiment, by attaching two heat sinks on the outside of two reflection units facing each other, the heating of the reflection unit may be prevented without affecting the reflection of the laser beam, thereby the laser beam may be uniformly emitted. 
     The features of the path conversion unit according to the embodiment described with reference to  FIG. 10  are all applicable to the laser crystallization apparatus according to the embodiment described above. 
     Next, an experimental example is described with reference to  FIG. 11  and FIG.  12 .  FIG. 11  is a view showing a result of an experimental example, and  FIG. 12  is a graph showing a result of an experimental example. 
     In the present experimental example, like the laser crystallization apparatus according to an embodiment, a plurality of path conversion units M 1  and M 2  are formed, the intensity according to the positions of the emission beams LB 11  and LB 21  passing through a plurality of path conversion units M 1  and M 2  is measured, the simulation result according to the long axis and the short axis of the linear laser beam LB is shown in  FIG. 11 , and the graph of the intensity for the short axis of the linear laser beam LB is shown in  FIG. 12 . 
     Referring to  FIG. 11 , as above-described, it may be confirmed that the first emission beam LB 11  emitted through the first path conversion unit M 1  and the second emission beam LB 21  emitted through the second path conversion unit M 2  are symmetrical to each other with respect to the first direction DR 1  parallel to the long-axis direction of the linear laser beam LB and with respect to the second direction DR 2  parallel to the short-axis direction of the linear laser beam LB. 
     Therefore, even if the first path conversion unit M 1  and the second path conversion unit M 2  are heated by the laser beam so that the thermal lens effect occurs, the linear laser beam LB of which the first emission beam LB 11  emitted through the first path conversion unit M 1  and the second emission beam LB 21  emitted through the second path conversion unit M 2  are summed and may have the uniform symmetrical intensity along the first direction DR 1  and the second direction DR 2 . 
     Referring to  FIG. 12 , it may be confirmed that the linear laser beam LB has the uniform intensity along the short-axis direction (a Y-coordinate). 
     Next, another experimental example is described with reference to  FIG. 13  and  FIG. 14 .  FIG. 13  is a view showing a result of an experimental example, and  FIG. 14  is a graph showing a result of an experimental example. 
     In the present experimental example, for a case that a plurality of path conversion units M 1  and M 2  are formed like the laser crystallization apparatus according to an embodiment and the heat sinks HS 1  and HS 2  are installed outside two reflection units Ra and Rb facing each other of a plurality of path conversion units M 1  and M 2 , like the embodiment shown in  FIG. 10 , the intensity depending on the position of the emission beams LB 11  and LB 21  passing through a plurality of path conversion units M 1  and M 2 , the simulation result according to the long axis and the short axis of the linear laser beam LB is shown in  FIG. 13 , and the graph of the intensity for the short axis of the linear laser beam LB is shown in  FIG. 14 . 
     Referring to  FIG. 13 , as above-described, it may be confirmed that the first emission beam LB 11  emitting through the first path conversion unit M 1  and the second emission beam LB 21  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other with respect to the first direction DR 1  parallel to the long-axis direction of the linear laser beam LB and with respect to the second direction DR 2  parallel to the short-axis direction of the linear laser beam LB. Like this, by installing the heat sinks HS 1  and HS 2  outside of two reflection units Ra and Rb facing each other of a plurality of path conversion units M 1  and M 2 , the first emission beam LB 11  emitted through the first path conversion unit M 1  and the second emission beam LB 21  emitted through the second path conversion unit M 2  have the intensities that are symmetrical to each other with respect to the first direction DR 1  and with respect to the second direction DR 2 . 
     In this way, even when the laser beam of strong energy is irradiated to the first path conversion unit M 1  and the second path conversion unit M 2 , it may be confirmed that the thermal lens effect is not generated by the heat sink, so that the linear beam of uniform intensity may be irradiated over the wide area. 
     Referring to  FIG. 14 , it may be confirmed that the linear laser beam LB has uniform intensity along the short-axis direction (the Y-coordinate). 
     Next, another experimental example is described with reference to  FIG. 15  and  FIG. 16 .  FIG. 15  and  FIG. 16  are graphs showing a result of an experimental example. 
     In the present experimental example, like the laser crystallization apparatus according to the embodiment, a first case of forming a plurality of path conversion units M 1  and M 2  and a second case of using a plurality of mirrors like a conventional art, the intensity for the short axis of the emission beam passing through a plurality of path conversion units M 1  and M 2  and the emission beam reflected by a plurality of mirrors, and a result thereof is shown in  FIG. 15  and  FIG. 16 .  FIG. 15  shows the result of the first case, and  FIG. 16  shows the result of the second case. 
     Referring to  FIG. 15 , it may be confirmed that the first case like the laser crystallization apparatus accord to the embodiment has the constant intensity according to the short-axis direction (the Y-coordinate), however referring to  FIG. 16 , it may be confirmed that the intensity of the emission beam is not constant according to the short-axis direction in the second case like the conventional art. 
     As such, according to the laser crystallization apparatus according to the embodiment, it may be confirmed that the incident beam may be converted into the linear emission beam through the simple structure by including the integrated path conversion unit including two reflection units facing each other, the incident window, and the emission window, and the linear laser beam having the uniform intensity may be provided along the long-axis direction and the short-axis direction of the linear laser beam by including a plurality of path conversion units of which the relative positions of the incident window, the emission window, and two reflection units are different from each other. 
     While this disclosure has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
       10 : substrate 
       100 : laser crystallization apparatus 
     HS 1 , HS 2 : heat sink 
     IW,  1 W 1 , IW 2 , IW 3 : incident window 
     LB, LB 1 , LB 2 : laser beam 
     LB 11 , LB 21 , LB 31 : emission beam 
     LS 1 , LS 2 : light source unit 
     M, M 1 , M 2 , M 3 : path conversion unit 
     OP: optical unit 
     OW, OW 1 , OW 2 , OW 3 : emission window 
     R 1 , R 2 , R 3 , R 3 , Ra, Rb: reflection unit