Abstract:
According to the present invention, an ion implantation system capable of implanting ions into a large substrate and reducing a manufacturing cost, and an ion implantation method using the same may be provided. The ion implantation system includes a plurality of ion implantation assemblies arranged in a line, each ion implantation assembly to implant ions into a partial region of the substrate. This allows for a compact ion implantation system to implant ions into a very large substrate. The substrate moves through the ion implantation system in a first direction, turns around, and then moves back through the ion implantation system in a second and opposite direction, where ions are implanted into the substrate while the substrate is moving in both directions. The path in the first direction can be spaced-apart from the path in the second direction to allow for two substrates to be processed simultaneously.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for ION IMPLANTATION SYSTEM AND ION IMPLANTATION METHOD USING THE SAME earlier filed in the Korean Intellectual Priority Office Korean Intellectual Priority Office on 21 Oct. 2010 and there duly assigned Serial No. 10-2010-0103059. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ion implantation system and an ion implantation method using the same. 
     2. Description of the Related Art 
     In flat panel display apparatuses such as organic light emitting display apparatuses and liquid crystal display apparatuses, a thin film transistor is used as a driving circuit. In particular, in an active organic light emitting display apparatus, a thin film transistor is formed on a substrate and an organic electroluminescent device is formed on the thin film transistor. 
     Currently, ion implantation apparatuses for implanting ions to form a semiconductor device such as a thin film transistor are used. An ion implantation apparatus includes an ion source unit for emitting ions into a chamber, electrode units, and other elements. The ion source unit ionizes gases into a plasma state to generate ions for implantation into a substrate or a wafer. 
     The ions generated by the ion source unit are accelerated by the electrode units. If a predetermined voltage is applied to the electrode units, the ions emitted from the ion source unit are accelerated, and proceed toward and are implanted into the substrate. 
     SUMMARY OF THE INVENTION 
     The present invention provides an ion implantation system capable of implanting ions into a large substrate and reducing manufacturing costs, and an ion implantation method using the same. 
     According to an aspect of the present invention, there is provided an ion implantation system for implanting ions into a substrate, the ion implantation system including a plurality of ion implantation assemblies arranged in a line to implant ions into the substrate, and a transfer assembly including a passage through which the substrate is moved, the transfer assembly to move the substrate through the passage, wherein each of the plurality of ion implantation assemblies implants ions into a partial region of the substrate, wherein, in the passage, the substrate is implanted with ions by the plurality of ion implantation assemblies while moving in a first direction, and is also implanted with ions by the plurality of ion implantation assemblies while moving in a second direction opposite to the first direction after moving in the first direction, and wherein the transfer assembly further includes a plurality of process chambers respectively connected to the plurality of ion implantation assemblies and to implant ions into the substrate, a return chamber to change a translational direction of the substrate, a holder to support the substrate, a first transfer guide to provide a path for moving the holder supporting the substrate through the process chambers in the first direction and a second transfer guide to provide a path for moving the holder supporting the substrate through the process chambers in the second direction. 
     The path in the first direction may be different from the path in the second direction, and the paths may be parallel to each other. A distance from the plurality of ion implantation assemblies to the path in the first direction may be different from a distance from the plurality of ion implantation assemblies to the path in the second direction. A total amount of ions implanted into the substrate may be a sum of a first implantation amount of ions implanted while the substrate moves in the first direction and a second implantation amount of ions implanted while the substrate moves in the second direction. The first and second implantation amounts may be the same. The return chamber to move the holder supporting the substrate from the first transfer guide to the second transfer guide. The first transfer guide may allow the holder supporting the substrate to be transferred from the first chamber to the return chamber, and the second transfer guide may allow the holder supporting the substrate to be transferred from the return chamber to the first chamber. The transfer assembly may also include a first chamber through which the substrate is initially loaded into the transfer assembly and is unloaded to an outside of the transfer assembly. The transfer assembly may also include a second chamber arranged between the first chamber and the plurality of process chambers to maintain a vacuum state upon the substrate being transferred from the first chamber. The ion implantation system may also include a robot arm to supply the substrate into the transfer assembly and to receive the substrate from the transfer assembly. The robot arm may load and unload the substrate into and from the transfer assembly, the robot arm may being arranged on a same side of the transfer assembly as the plurality of ion implantation assemblies. The robot arm may load and unload the substrate into and from the transfer assembly, the robot arm may be arranged on an opposite side of the transfer assembly from the plurality of ion implantation assemblies. The robot arm may load the substrate into the transfer assembly by tilting the substrate to have an acute angle to a ground surface. The ion implantation system may also include a Faraday unit arranged within the transfer assembly to measure an amount of ions emitted from one of plurality of ion implantation assemblies. The ion implantation system may also include a slit arranged in a side surface of each of the plurality of process chambers to allow ions emitted from the plurality of ion implantation assemblies to pass into the transfer assembly. 
     The plurality of ion implantation assemblies may include a first ion implantation assembly and a second ion implantation assembly, wherein the plurality of process chambers comprise a first process chamber and a second process chamber, wherein the first ion implantation assembly is connected to the first process chamber, the first ion implantation assembly to emits ions into the first process chamber, and wherein the second ion implantation assembly is connected to the second process chamber, the second ion implantation assembly to emits ions into the second process chamber. The first ion implantation assembly may emit ions toward a lower portion of the substrate, and wherein the second ion implantation assembly may emit ions toward an upper portion of the substrate. The first direction may be a direction from the first process chamber toward the second process chamber and the second direction may be a direction from the second process chamber toward the first process chamber. A lower portion of the substrate may be implanted with ions emitted by the first ion implantation assembly and an upper portion of the substrate may be implanted with ions emitted by the second ion implantation assembly while the substrate is transferred in the first direction, and the upper portion of the substrate may be implanted with ions emitted by the second ion implantation assembly and the lower portion of the substrate may be implanted with ions emitted by the first ion implantation assembly while the substrate is transferred in the second direction. The first process chamber may be connected to the first ion implantation assembly, and may include a first slit through which ions generated by the first ion implantation assembly pass, and the second process chamber may be connected to the second ion implantation assembly, and may include a second slit through which ions generated by the second ion implantation assembly pass. The first slit may be arranged to correspond to the lower portion of the substrate, and the second slit may be arranged to correspond to the upper portion of the substrate. 
     Each of the first and second ion implantation assemblies may include an ion supply unit to generate ions by ionizing a gas received from an outside of the ion implantation system, a mass spectrometry unit to divide ions according to mass and a ion beam deflection unit to accelerate the ions divided by the mass spectrometry unit. The first and second ion implantation assemblies may be arranged symmetrically with respect to a direction that ions are emitted. The substrate may be divided into a plurality of implantation regions corresponding to the plurality of ion implantation assemblies, and each of the implantation regions may be implanted with ions by a corresponding one of the plurality of ion implantation assemblies. The implantation regions may include a lower portion and an upper portion of the substrate arranged in a direction perpendicular to a direction in which the plurality of ion implantation assemblies are arranged. While the substrate is being transferred, one of the lower implantation region and the upper implantation region of the substrate is first implanted with ions, and then another of the lower implantation region and the upper implantation region of the substrate is implanted with ions. The plurality of ion implantation assemblies may emit ions into the transfer assembly at different heights. The plurality of ion implantation assemblies may be aligned in parallel at different heights corresponding to the implantation regions of the substrate. 
     The ion implantation system may also include a plurality of supporting members having different heights are arranged under ones of the plurality of ion implantation assemblies to maintain the plurality of ion implantation assemblies at different heights. The plurality of ion implantation assemblies may emit ion beams at different heights due to a difference in heights of the supporting members. According to a transfer direction of the substrate, the supporting members may be sequentially aligned from a supporting member having one of a smallest height and a largest height to another supporting member having another of a smallest height and a largest height. The plurality of ion implantation assemblies may be aligned to alternate with each other between neighboring ion implantation assemblies. The plurality of ion implantation assemblies may include a plurality of upper ion implantation assemblies and a plurality of lower ion implantation assemblies, wherein the plurality of upper and lower ion implantation assemblies may be aligned to alternate with each other between neighboring ion implantation assemblies, and wherein the plurality of upper ion implantation assemblies may be arranged at a greater height than the plurality of lower ion implantation assemblies. The plurality of upper ion implantation assemblies may implant ions into an upper portion of the substrate, and wherein the plurality of lower ion implantation assemblies may implant ions into a lower portion of the substrate. 
     According to another aspect of the present invention, there is provided an ion implantation method, including transferring a substrate into a transfer assembly of an ion implantation assembly, implanting a first region of the substrate with ions while the substrate is being transferred in a first direction, implanting a second region of the substrate with ions while the substrate is being transferred in the first direction, changing a translational direction of the substrate from the first direction to a second direction opposite to the first direction, implanting the second region of the substrate with ions while the substrate is being transferred in the second direction and implanting the first region of the substrate with ions while the substrate is being transferred in the second direction. 
     The substrate may be transferred in the first and second directions on different paths. The substrate may move through the transfer assembly in the first and second directions. The transfer assembly may include a first process chamber, a second process chamber, and a return chamber arranged in a line. The first region of the substrate may be implanted with ions while the substrate passes through the first process chamber, and wherein the second region of the substrate may be implanted with ions while the substrate passes through the second process chamber. The first region of the substrate may be a lower portion of the substrate and wherein the second region of the substrate may be an upper portion of the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIGS. 1A through 1C  are cross-sectional views for describing a process of manufacturing a thin film transistor for driving a pixel in an active-matrix-type organic light emitting display apparatus; 
         FIG. 2  is a perspective view of an ion implantation system according to a first embodiment of the present invention; 
         FIG. 3  is a plan view of the ion implantation system illustrated in  FIG. 2 ; 
         FIG. 4  is a schematic diagram showing the alignment of a substrate and first and second slits in the ion implantation system illustrated in  FIGS. 2 and 3 ; 
         FIG. 5  is a schematic diagram showing a path of the substrate in a transfer assembly in the ion implantation system illustrated in  FIGS. 2 through 4 ; 
         FIG. 6  is a plan view of an ion implantation system according to a second embodiment of the present invention; 
         FIG. 7  is a plan view of an ion implantation system according to a third embodiment of the present invention; 
         FIG. 8  is a perspective view of an ion implantation system according to a fourth embodiment of the present invention; and 
         FIG. 9  is a schematic diagram showing the alignment of slits of the ion implantation system illustrated in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While exemplary embodiments of the invention are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit exemplary embodiments of the invention to the particular forms disclosed, but conversely, exemplary embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear. 
     Before describing an ion implantation system and an ion implantation method according to embodiments of the present invention, the structure of a thin film transistor included in an active-matrix-type organic light emitting display apparatus for performing an ion implanting process will now be described. 
     Turning now to  FIGS. 1A through 1C ,  FIGS. 1A through 1C  are cross-sectional views for describing a process of manufacturing a thin film transistor for driving a pixel in an active-matrix-type organic light emitting display apparatus. Referring now to  FIG. 1A ,  FIG. 1A  is a cross-sectional view showing a channel doping operation in the thin film transistor manufacturing process. As illustrated in  FIG. 1A , a buffer layer  11  is formed on a substrate  10 , and an active layer  12  and a lower electrode  19  of a capacitor are formed on the buffer layer  11 . 
     Both the active layer  12  and the lower electrode  19  of the capacitor are formed by forming a semiconductor layer on the buffer layer  11  and then patterning the semiconductor layer. The semiconductor layer may be made out of amorphous silicon or polysilicon. Accordingly, the active layer  12  and the lower electrode  19  of the capacitor are made out of amorphous silicon or polysilicon. An ion dopant may be implanted into the active layer  12 . As a result, a Vth shift effect may occur. 
     Referring now to  FIG. 1B ,  FIG. 1B  is a cross-sectional view showing a source and drain doping operation in the thin film transistor manufacturing process. Referring to  FIG. 1B , a first insulating layer  13  is stacked on the structure illustrated in  FIG. 1A , and a pixel electrode  14 , first and second gate electrodes  15   a  and  16   a  of the thin film transistor, and first and second upper electrodes  15   b  and  16   b  of the capacitor are formed on the first insulating layer  13 . 
     The first and second gate electrodes  15   a  and  16   a  of the thin film transistor, and the first and second upper electrodes  15   b  and  16   b  of the capacitor may be formed by sequentially stacking a transparent conductive layer and a metal layer on the first insulating layer  13 , and then patterning the transparent conductive layer and the metal layer. 
     Ion impurities are doped into the active layer  12  by using the first and second gate electrodes  15   a  and  16   a  as a self-alignment mask. As a result, the active layer  12  includes source and drain regions  12   a  and  12   b  doped with the ion impurities, and a channel region  12   c  between the source and drain regions  12   a  and  12   b  that remains undoped. 
     Referring now to  FIG. 1C ,  FIG. 1C  is a cross-sectional view showing a lower electrode doping operation of the capacitor in the thin film transistor manufacturing process. Referring to  FIG. 1C , a second insulating layer  17  is formed on the structure illustrated in  FIG. 1B , and then first and second openings  17   a  and  17   b  for exposing the pixel electrode  14 , first and second contact holes  17   c  and  17   d  for respectively exposing the source and drain regions  12   a  and  12   b  of the thin film transistor, and a third opening  17   e  for exposing the first upper electrode  15   b  of the capacitor are formed on the second insulating layer  17 . After that, source and drain electrodes  18   a  and  18   b  respectively contacting the source and drain regions  12   a  and  12   b  of the active layer  12  are formed. Then, ion impurities are doped into the lower electrode  19  of the capacitor. As such, the lower electrode  19  of the capacitor may have an increased conductivity, may form a metal-insulator-metal (MIM) capacitor together with the first upper electrode  15   b , and thus may increase the capacity of the capacitor. 
     With reference to the description above, an ion implantation system according to an embodiment of the present invention may be used in doping the source and drain regions  12   a  and  12   b  of the active layer  12 , and in doping the lower electrode  19  of the capacitor. 
     Turning now to  FIGS. 2 and 3 ,  FIG. 2  is a perspective view of an ion implantation system  100  according to a first embodiment of the present invention and  FIG. 3  is a plan view of the ion implantation system  100  illustrated in  FIG. 2 . The ion implantation system  100  may include first and second ion implantation assemblies  110  and  120 , a transfer assembly  150 , and a robot arm  170 . 
     The ion implantation system  100  may include a plurality of ion implantation assemblies. For example, as illustrated in  FIGS. 2 and 3 , the ion implantation system  100  may include two ion implantation assemblies, i.e., the first and second ion implantation assemblies  110  and  120 , however the present invention is not limited thereto as the ion implantation system  100  may instead include three or more ion implantation assemblies. 
     The first and second ion implantation assemblies  110  and  120  may generate ions and may emit the ions into the transfer assembly  150 . The first and second ion implantation assemblies  110  and  120  may respectively include ion supply units  111  and  121 , mass spectrometers  112  and  122 , and ion beam deflection units  113  and  123 . The ion supply units  111  and  121  generate ions by Ionizing a gas received from outside the ion implantation system  100 . In general, cations to be used as a dopant may be, for example, B + , P + , As + , or Sb + . In order to reduce harm caused by an emission of source gas, a material for forming a dopant may be diluted with hydrogen (H) gas. As such, in general, a source gas for supplying atoms of the dopant may be, for example, B 2 H 6 , BF 3 , PH 3 , or AsH 3 . 
     Each of the ion supply units  111  and  121  may include a filament (not shown). If a high current flows through the filament, plasma is formed around the filament. If active electrons and molecules of the source gas collide with each other due to the energy of the plasma, cations to be used as a dopant may be generated. The ion supply units  111  and  121  may collect the generated cations to form ion beams. 
     The mass spectrometers  112  and  122  select certain ions by using a difference in mass from among the ions generated by the ion supply units  111  and  121 . Each of the mass spectrometers  112  and  122  includes a spectrometer magnet (not shown) having a refraction angle of for example, 90°, and the magnetic field of the spectrometer magnet provides a force for deflecting an ion beam including impurities or various cations, to follow a curved orbit. The ions are spread according to mass units of atoms of the ions. Ions having a relatively large mass in comparison to the intensity of a given magnetic field are curved less than ions having a relatively small mass. The radius of curvature of the curved orbit is determined according to the intensity of the magnetic field of the spectrometer magnet, and only ions having a desired mass may reach and pass through a slit at an end of the spectrometer magnet by adjusting the intensity of the magnetic field of the spectrometer magnet. 
     The ions selected by the mass spectrometers  112  and  122  may be accelerated or decelerated by an acceleration apparatus (not shown). When cations move relatively fast, the cations may have relatively high kinetic energy and may be deeply implanted into a substrate  10  when they collide with a surface of the substrate  10 . The acceleration apparatus forms an electric field for providing additional energy to the ions selected by the mass spectrometers  112  and  122 . Cations have positive charges, and thus are pulled toward an electric field having a negative polarity. An acceleration voltage is applied to form the electric field having a negative polarity and, if the intensity of the electric field is increased, cations move faster. On the other hand, if a deceleration voltage is applied by changing the polarity of the electric field, the ions selected by the mass spectrometers  112  and  122  may be decelerated. 
     The ion beam deflection units  113  and  123  may focus the ions accelerated or decelerated by the acceleration apparatus, and may scan the surface of the substrate  10  by deflecting the focused ions while the substrate moves through first and second process chambers  154  and  155  of the transfer assembly  150 . 
     The first and second ion implantation assemblies  110  and  120  may be aligned in a line and may be connected to the transfer assembly  150 . In particular, the first ion implantation assembly  110  may be connected to the first process chamber  154  of the transfer assembly  150 , and the second ion implantation assembly  120  may be connected to the second process chamber  155  of the transfer assembly  150 . The first ion implantation assembly  110  may be connected to a first slit  154   a  (see  FIG. 4 ) of the first process chamber  154 , and ions generated by the first ion implantation assembly  110  may be emitted into the first process chamber  154  through the first slit  154   a . Also, the second ion implantation assembly  120  may be connected to a second slit  155   a  (see  FIG. 4 ) of the second process chamber  155 , and ions generated by the second ion implantation assembly  120  may be emitted into the second process chamber  155  through the second slit  155   a.    
     Referring now to  FIG. 4 , the first and second ion implantation assemblies  110  and  120  may implant ions into different regions of the substrate  10 , e.g., first and second implantation regions  11  and  12 . That is, the substrate  10  may be divided into a plurality of implantation regions corresponding to the number of ion implantation assemblies included in the ion implantation system  100 . For example, if the ion implantation system  100  includes the first and second ion implantation assemblies  110  and  120  as illustrated in  FIGS. 2 and 3 , the substrate  10  may be divided into the first and second implantation regions  11  and  12  as illustrated in  FIG. 4 . Alternatively, if the ion implantation system  100  includes three or more ion implantation assemblies, the substrate  10  may be divided into three or more implantation regions. 
     The first and second implantation regions  11  and  12  may be formed on the substrate  10  in a direction (Y direction) perpendicular to a direction (X direction) in which the first and second ion implantation assemblies  110  and  120  are aligned. That is, the first implantation region  11  may be a lower portion of the substrate  10 , and the second implantation region  12  may be an upper portion of the substrate  10 . Alternatively, the first implantation region  11  may instead be the upper portion of the substrate  10 , and the second implantation region  12  may be the lower portion of the substrate  10 . 
     The first implantation region  11  (the lower portion) of the substrate  10  may be implanted with ions by the first ion implantation assembly  110 , and the second implantation region  12  (the upper portion) of the substrate  10  may be implanted with ions by the second ion implantation assembly  120 . The substrate  10  is supported by a holder  160  and is implanted with ions while moving through the transfer assembly  150 . In more detail, the substrate  10  is loaded into a first chamber  151  by the robot arm  170 , is supported by the holder  160 , and is transferred through the transfer assembly  150  along a first or second transfer guide  158  or  159 . Initially, the substrate  10  departs from the first chamber  151  and is transferred through the first and second process chambers  154  and  155 . While the substrate  10  is transferred through the first process chamber  154 , ions emitted from the first ion implantation assembly  110  are implanted into the first implantation region  11  of the substrate  10 . After that, the substrate  10  is transferred to the second process chamber  155  and, while the substrate  10  is transferred through the second process chamber  155 , ions emitted from the second ion implantation assembly  120  are implanted into the second implantation region  12  of the substrate  10 . 
     Also, the substrate  10  is transferred from the second process chamber  155  to a return chamber  157  and then is transferred back to the first chamber  151  sequentially through the second and first process chambers  155  and  154 . While the substrate  10  is transferred is sequentially through the second and first process chambers  155  and  154  on the way back to the first chamber  151 , the second and first implantation regions  12  and  11  are implanted with ions by the second and first ion implantation assemblies  120  and  110 , respectively. The ion implantation process of the substrate  10  will be described later. 
     As illustrated in  FIG. 4 , the first slit  154   a  may be formed to correspond to the first implantation region  11  of the substrate  10 , and the second slit  155   a  may be formed to correspond to the second implantation region  12  of the substrate  10 . That is, the first and second slits  154   a  and  155   a  are located at different heights. For example, as illustrated in  FIG. 4 , the second slit  155   a  may be arranged higher than the first slit  154   a . In order to emit ions from the second slit  155   a , the second ion implantation assembly  120  is disposed at a higher position than the first ion implantation assembly  110 . According to an embodiment of the present invention, a supporting member  130  (see  FIG. 2 ) may be disposed under the second ion implantation assembly  120  so that second ion implantation assembly  120  may be higher than first ion implantation assembly  110  so that ions emitted from second ion implantation assembly  120  may pass through second slit  155   a.    
     As illustrated in  FIG. 3 , the transfer assembly  150  provides a passage through which the substrate  10  moves. The transfer assembly  150  may include the first chamber  151 , a second chamber  152 , a gate valve  153 , the first process chamber  154 , the second process chamber  155 , a third chamber  156 , the return chamber  157 , the first transfer guide  158 , the second transfer guide  159 , and the holder  160 . 
     The first chamber  151  loads the substrate  10  from an outside of the ion implantation system  100  into the transfer assembly  150 , or unloads the substrate  10  from the transfer assembly  150  to an outside of the ion implantation system  100 . If the substrate  10  is loaded into the first chamber  151 , the substrate  10  is supported by the holder  160  and is transferred through the second chamber  152 , the first process chamber  154 , third chamber  156 , the second process chamber  155 , and the return chamber  157  along the first transfer guide  158 . Also, if the substrate  10  is transferred to the return chamber  157 , the holder  160  supporting the substrate  10  moves from the first transfer guide  158  to the second transfer guide  159 , and holder supporting the substrate  10  is transferred through the second process chamber  155 , the third chamber  156 , the first process chamber  154 , the second chamber  152 , and the first chamber  151  along the second transfer guide  159 . The substrate  10  transferred to the first chamber  151  may be unloaded to an outside of the ion implantation system  100 . 
     The second chamber  152  is disposed between the first chamber  151  and the first process chamber  154 , and functions as a buffer in which the substrate  10  transferred from the first chamber  151  or the substrate  10  transferred from the first process chamber  154  is on standby. The second chamber  152  is maintained in a vacuum state. 
     The substrate  10  transferred from the second chamber  152  may be transferred to the first process chamber  154  through the gate valve  153 . The first process chamber  154  may be connected to the first ion implantation assembly  110 . The first process chamber  154  may include the first slit  154   a  as illustrated in  FIG. 4 . Ions generated by the first ion implantation assembly  110  are emitted into the first process chamber  154  through the first slit  154   a . The substrate  10  may be implanted with ions while being within the first process chamber  154 . 
     The first slit  154   a  may be arranged to correspond to a partial region of the substrate  10 . Referring to  FIG. 4 , the first slit  154   a  may be arranged to correspond to the first implantation region  11 , that is, the lower portion of the substrate  10 . Accordingly, an ion beam passed through the first slit  154   a  may be implanted into the first implantation region  11  of the substrate  10 . 
     While the substrate  10  moves through the first process chamber  154 , the first implantation region  11  may be implanted with ions. The first implantation region  11  of the substrate  10  may be implanted with ions in the first process chamber  154  while the substrate  10  moves in a first direction F (see  FIG. 5 ), towards the return chamber  157 , and may also be implanted with ions while within the first process chamber  154  while the substrate  10  is transferred in a second direction B (see  FIG. 5 ) towards the first chamber from the return chamber  157 . The ion implantation process of the substrate  10  will be described later. 
     The first process chamber  154  may include a Faraday unit  161 . The Faraday unit  161  may measure the amount of ions emitted in the form of an ion beam from the first ion implantation assembly  110  and the uniformity of the ions emitted in the form of an ion beam. 
     The substrate  10  transferred from the first process chamber  154  may be transferred to the second process chamber  155  through the third chamber  156 . The second process chamber  155  may be connected to the second ion implantation assembly  120 . The second process chamber  155  may include the second slit  155   a  as illustrated in  FIG. 4 . Ions generated by the second ion implantation assembly  120  may be emitted into the second process chamber  155  through the second slit  155   a . The substrate  10  may be implanted with ions while within the second process chamber  155 . 
     The second slit  155   a  may be arranged to correspond to a partial region of the substrate  10 . Referring to  FIG. 4 , the second slit  155   a  may be arranged to correspond to the second implantation region  12 , that is, the upper portion of the substrate  10 . Accordingly, an ion beam passing through the second slit  155   a  may be implanted into the second implantation region  12  of the substrate  10 . 
     While the substrate  10  moves through the second process chamber  155 , the second implantation region  12  may be implanted with ions. The second implantation region  12  of the substrate  10  may be implanted with ions in the second process chamber  155  while the substrate  10  is transferred in the first direction F, that is, from the first chamber  151  to the return chamber  157 , and may also be implanted with ions in the second process chamber  155  while the substrate  10  is transferred in the second direction B, that is, from the return chamber  157  to the first chamber  151 . The ion implantation of the second implantation region  12  of the substrate  10  will be described later. 
     The second process chamber  155  may also include a Faraday unit  162 . The Faraday unit  162  may measure the amount of ions emitted in the form of an ion beam from the second ion implantation assembly  120  and the uniformity of the ions emitted in the form of an ion beam. 
       FIG. 4  is a schematic diagram showing the alignment of the substrate  10  and. the first and second slits  154   a  and  155   a  in the ion implantation system  100  illustrated in  FIGS. 2 and 3 . As described above, the first slit  154   a  may be formed to correspond to the first implantation region  11  of the substrate  10 , and the second slit  155   a  may be formed to correspond to the second implantation region  12  of the substrate  10 . Accordingly, the first ion implantation assembly  110  connected to the first slit  154   a  may implant ions into only the first implantation region  11  of the substrate  10 , and the second ion implantation assembly  120  connected to the second slit  155   a  may implant ions into only the second implantation region  12  of the substrate  10 . Because each of the first and second ion implantation assemblies  110  and  120  implants ions into only a partial region of the substrate  10 , the ion implantation system  100  is able to implant ions into a relatively large substrate that may not be completely implanted with ions by a single operation by using only one ion implantation assembly. As such, a relatively large ion implantation assembly is not necessary to process large substrates, as any-size substrate may be implanted with ions by using a plurality of relatively small ion implantation assemblies according to the present invention. 
     The return chamber  157  may be disposed at an end of the second process chamber  155  and may change the translational direction of the substrate  10  transferred from the second process chamber  155 . That is, the substrate  10  is transferred from the first chamber  151  to the return chamber  157  through the first and second process chambers  154  and  155 , and once the substrate  10  reaches the return chamber  157 , the translational direction of the substrate  10  is changed by the return chamber  157 , and the substrate  10  is then transferred to the first chamber  151  through the second and first process chambers  155  and  154 . The substrate  10  is implanted with ions while the substrate  10  is transferred in the first direction F from the first chamber  151  to the first and second process chambers  154  and  155 , and is again implanted with ions while the substrate  10  is transferred in the second direction B to the first chamber  151  through the second and first process chambers  155  and  154 . 
     Turning now to  FIG. 5 ,  FIG. 5  is a schematic diagram showing a path of the substrate  10  in the transfer assembly  150  in the ion implantation system  100  illustrated in  FIGS. 2 through 4 . Referring to  FIG. 5 , the substrate  10  is transferred from the first chamber  151  toward the return chamber  157  in the first direction F, and is transferred from the return chamber  157  in the second direction B opposite to the first direction F. The second direction B is a direction from the return chamber  157  toward the first chamber  151 . While the substrate  10  is transferred in the first direction F, the first implantation region  11  is implanted with ions in the first process chamber  154  and the second implantation region  12  is implanted with ions in the second process chamber  155 . Also, while the substrate  10  is transferred in the second direction B, the second implantation region  12  is again implanted with ions in the second process chamber  155  and the first implantation region  11  is again implanted with ions in the first process chamber  154 . That is, the substrate  10  may be implanted with ions while the substrate  10  is transferred in the first direction F, and may also be implanted with ions while the substrate  10  is transferred in the second direction B. Since the substrate  10  is implanted with ions twice as described above, the uniformity of the ions implanted over the whole substrate  10  may be improved. 
     A sum of a first implantation amount of ions implanted while the substrate  10  moves in the first direction F and a second implantation amount of ions implanted while the substrate  10  moves in the second direction B is a total amount of ions implanted into the substrate  10 . For example, the first and second implantation amounts may be the same. 
     The substrate  10  may be transferred through the transfer assembly  150  along paths in the first and second directions F and B. The paths in the first and second directions F and B may not be the same path but may be different paths. That is, the paths in the first and second directions F and B may be separated from the first and second ion implantation assemblies  110  and  120  by different distances t 2  and t 1 , respectively. In more detail, although not shown in  FIG. 5 , as described above in relation to  FIGS. 2 through 4 , the first ion implantation assembly  110  is connected to the first process chamber  154 , and the second ion implantation assembly  120  is connected to the second process chamber  155 . The distance t 2  between the first ion implantation assembly  110  and the path in the first direction F may be greater than the distance t 1  between the second ion implantation assembly  120  and the path in the second direction B. The substrate  10  may be initially transferred on the path in the first direction F separated relatively further from the first and second ion implantation assemblies  110  and  120  in comparison to the path in the second direction B, and then the translational direction of the substrate  10  may change to the second direction B in the return chamber  157 . As such, since the substrate  10  in the transfer assembly  150  is transferred in the first and second directions F and B on different paths, a plurality of substrates  10  may be sequentially loaded into the transfer assembly  150  and thus a tact time for implanting ions may be improved. 
     In each of the first and second process chambers  154  and  155 , only one substrate  10  may be implanted with ions while being transferred. That is, although the substrate  10  may be transferred through the first or second process chamber  154  or  155  in the first or second direction F or B, one substrate  10  moving in the first direction F and another substrate  10  moving in the second direction B may not be simultaneously transferred through one of the first and second process chambers  154  and  155 . If one substrate  10  is transferred in the first direction F and another substrate  10  is transferred in the second direction B at the same time through one of the first and second process chambers  154  and  155 , implantation of ions into the substrate  10  transferred in the first direction F is disturbed by the substrate  10  transferred in the second direction B. 
     With the arrangement of  FIG. 5 , it may be possible to implant ions from a first ion implantation assembly  110  into a first substrate  10  in first process chamber  154  and traveling in first direction F while second ion implantation assembly  120  implants ions into a second substrate  10  in second process chamber  155  and traveling in second direction B. Because the path in the second direction B is spaced apart from the path in the first direction F, it is possible to move the first substrate  10  in the first direction F to the second process chamber  155  while the second substrate  10  moves in the second direction B to the first process chamber  154  without the two substrates colliding with each other. Then, the first substrate  10  is implanted with ions from the second ion implantation assembly  120  while the second substrate  10  is implanted with ions from the first ion implantation assembly  110 . Consequently, by spacing the paths of the first and second directions F and B apart from each other as in  FIG. 5 , it is possible to increase throughput of the ion implantation system  100 . 
     The robot arm  170  is connected to the first chamber  151 , and supplies the substrate  10  from an outside of the ion implantation system  100  into the first chamber  151 , or from the first chamber  151  to an outside of the ion implantation system  100 . The robot arm  170  supplies the substrate  10  into the first chamber  151  by vertically tilting the substrate  10  with respect to the ground, as illustrated in  FIG. 2 . 
     The robot arm  170  and the first and second ion implantation assemblies  110  and  120  may be disposed at opposite sides of the transfer assembly  150  as illustrated in  FIG. 3 . That is, the robot arm  170  may be disposed at one side  150   b  of the transfer assembly  150 , and the first and second ion implantation assemblies  110  and  120  may be disposed at another side  150   a  of the transfer assembly  150 . 
     Turning now to  FIG. 6 ,  FIG. 6  is a plan view of an ion implantation system  200  according to a second embodiment of the present invention. Referring to  FIG. 6 , the robot arm  170  and the first and second ion implantation assemblies  110  and  120  may all be disposed on a same side  150   a  of the transfer assembly  150 . As such, a space occupied by the ion implantation system  200  may be reduced. In comparison to a case when the first and second ion implantation assemblies  110  and  120  and the robot arm  170  are disposed at opposite sides of the transfer assembly  150 , if the first and second ion implantation assemblies  110  and  120  and the robot arm  170  are disposed on a same side of the transfer assembly  150 , an area occupied by the ion implantation system  200  may be reduced and thus an installation cost of the ion implantation system  200  may also be reduced. 
     Turning now to  FIG. 7 ,  FIG. 7  is a plan view of an ion implantation system  300  according to a third embodiment of the present invention. Referring to  FIG. 7 , the ion implantation system  300  is different from the ion implantation system  100  illustrated in  FIGS. 2 and 3  in that the first and second ion implantation assemblies  110  and  120  are disposed symmetrically. That is, the first and second ion implantation assemblies  110  and  120  may be disposed symmetrically with respect to a direction (Y direction) for emitting ions. As such, an overall length of the transfer assembly  150  may be reduced. In more detail, the first and second ion implantation assemblies  110  and  120  may respectively include the ion supply units  111  and  121 , the mass spectrometers  112  and  122 , and the ion beam deflection units  113  and  123 . Since each of the mass spectrometers  112  and  122  includes a spectrometer magnet having a refraction angle of 90° as described above in relation to  FIGS. 2 and 3 , if the mass spectrometer  112  of the first ion implantation assembly  110  and the mass spectrometer  122  of the second ion implantation assembly  120  are disposed asymmetrically as illustrated in  FIG. 3 , the ion supply unit  121  of the second ion implantation assembly  120  is disposed between the mass spectrometer  112  of the first ion implantation assembly  110  and the mass spectrometer  122  of the second ion implantation assembly  120 , and thus the third chamber  156  is disposed between the first and second process chambers  154  and  155  in the transfer assembly  150 . However, in the ion implantation system  300 , the first and second ion implantation assemblies  110  and  120  may be disposed symmetrically with respect to the direction (Y direction) perpendicular to a direction (X direction) in which the transfer assembly  150  extends. That is, the mass spectrometers  112  and  122  are now disposed between the ion supply unit  111  of the first ion implantation assembly  110  and the ion supply unit  121  of the second ion implantation assembly  120  and are disposed symmetrically with respect to the perpendicular direction (Y direction), and thus the first and second process chambers  154  and  155  may directly contact each other without interposing a third chamber  156  therebetween. Accordingly, a manufacturing cost of the ion implantation system  300  may be reduced. Also, since an overall length of the transfer assembly  150  is reduced and thus an area occupied by the ion implantation system  300  is also reduced, a cost for building a factory that requires the ion implantation system  300  may be reduced. Also, due to the reduction in length of the transfer assembly  150  through which the substrate  10  is transferred, a tact time for an ion implantation process may be reduced and thus throughput and productivity may be improved. 
     Turning now to  FIGS. 8 and 9 ,  FIGS. 8 and 9  schematically illustrate an ion implantation system  400  according to a fourth embodiment of the present invention. In more detail,  FIG. 8  is a perspective view of an ion implantation system  400  according to the fourth embodiment of the present invention and  FIG. 9  is a schematic diagram showing the alignment of first through fourth slits  254   a ,  354   a ,  255   a , and  355   a  of the ion implantation system  400  illustrated in  FIG. 8 . 
     Referring to  FIG. 8 , the ion implantation system  400  may include four ion implantation assemblies that are aligned in an alternate manner. For example, the ion implantation system  400  may include first and second upper ion implantation assemblies  210  and  310  and first and second lower ion implantation assemblies  220  and  320 , wherein the first upper and lower ion implantation assemblies  210  and  220  are adjacent to each other and are aligned in different rows, the first lower ion implantation assembly  220  and the second upper ion implantation assembly  310  are adjacent to each other and are aligned in different rows, and the second upper and lower ion implantation assemblies  310  and  320  are adjacent to each other and are aligned in different rows. The first and second upper ion implantation assemblies  210  and  310  may implant ions into the second implantation region  12  (see  FIG. 4 ) of the substrate  10 , and the first and second lower ion implantation assemblies  220  and  320  may implant ions into the first implantation region  11  (see  FIG. 4 ) of the substrate  10 . The second implantation region  12  of the substrate  10  is the upper portion of the substrate  10 , and the first implantation region  11  of the substrate  10  is the lower portion of the substrate  10 . 
     The first and second upper ion implantation assemblies  210  and  310  are installed at an upper portion of a side wall of a transfer assembly  250  and at a predetermined height from a bottom surface of the transfer assembly  250 , in order to implant ions into the second implantation region  12  of the substrate  10 . Also, the first and second lower ion implantation assemblies  220  and  320  are installed at lower portion of the side wall of the transfer assembly  250 , in order to implant ions into the first implantation region  11  of the substrate  10 . 
     The first and second upper and lower ion implantation assemblies  210 ,  220 ,  310 , and  320  are connected to the first through fourth slits  254   a ,  354   a ,  255   a , and  355   a  respectively formed in the side wall of the transfer assembly  250 , and ions generated by the first and second upper and lower ion implantation assemblies  210 ,  220 ,  310 , and  320  are emitted into the transfer assembly  250  through the first through fourth slits  254   a ,  354   a ,  255   a , and  355   a . The first and second upper ion implantation assemblies  210  and  310  are respectively connected to the first and second slits  254   a  and  354   a , and the first and second lower ion implantation assemblies  220  and  320  are respectively connected to the third and fourth slits  255   a  and  355   a.    
     An ion implantation method according to an embodiment of the present invention will now be described. Initially, the substrate  10  transferred from an outside of the ion implantation system  100  is loaded into the first chamber  151  by the robot arm  170 . The robot arm  170  supplies the substrate  10  into the first chamber  151  by vertically tilting the substrate  10  with respect to the ground. 
     Then, the substrate  10  passes through the first chamber  151 , the second chamber  152 , and the gate valve  153 , and then reaches the first process chamber  154  along the first direction F. The substrate  10  is transferred through the first process chamber  154  in the first direction F, and ions emitted from the first ion implantation assembly  110  are implanted into one region (the first implantation region  11 ) of the substrate  10  while the substrate  10  is transferred through the first process chamber  154 . 
     After that, the substrate  10  passed through the first process chamber  154  passes through the third chamber  156  and then is implanted with ions within the second process chamber  155 . Another region (the second implantation region  12 ) of the substrate  10  is implanted with ions in the second process chamber  155 . The second implantation region  12  of the substrate  10  is implanted with ions while the substrate  10  is transferred through the second process chamber  155  in the first direction F. 
     The substrate  10 , having been passed through second process chamber  155 , reaches the s return chamber  157 . In the return chamber  157 , the translational direction of the substrate  10  is changed from the first direction F into the second direction B. That is, the substrate  10  moves from the second process chamber  155  toward the first chamber  151 . 
     The substrate  10 , of which the translational direction is changed into the second direction B in the return chamber  157 , reaches the second process chamber  155 . The second implantation region  12  of the substrate  10  is implanted with ions while the substrate  10  is transferred through the second process chamber  155  in the second direction B. 
     Then, the substrate  10  passes through the third chamber  156  and then reaches the first process chamber  154 . The first implantation region  11  of the substrate  10  is implanted with ions while the substrate  10  is transferred through the first process chamber  154  in the second direction B. 
     After passing through the first process chamber  154  in second direction B, substrate  10  is transferred sequentially through the gate valve  153 , the second chamber  152 , and the first chamber  151 , and reaches the robot arm  170 . The robot arm  170  unloads the substrate  10  to an outside of the ion implantation system  100 . 
     According to the present invention, ions may be implanted into a relatively large substrate from a relatively small piece of equipment, a time for an ion implantation process may be reduced, throughput and productivity are improved, and a manufacturing cost of an ion implantation system may also be reduced. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.