Patent Publication Number: US-2006017904-A1

Title: Method and apparatus for photolithographic exposure using a redirected light path for secondary shot regions

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims priority under 35 USC § 119 to Korean Patent Application No. 2004-57631, filed on Jul. 23, 2004, the contents of which are herein incorporated by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to methods and apparatus for exposing photosensitive materials and, more particularly, to methods and apparatus for exposing photosensitive material on a microelectronic substrate.  
      Semiconductor devices are typically manufactured using a plurality of processes, such as an ion implantation process, a deposition process, a diffusion process, and a photolithography process. A pattern may be formed on a semiconductor substrate by a photolithography process. A photolithography process typically includes a coating process for coating a photoresist solution on the semiconductor substrate, a baking process for baking the photoresist solution to form a photoresist film, an exposure process for transcribing a reticle pattern onto the photoresist film, and a developing process for forming a photoresist pattern corresponding to the reticle pattern on the semiconductor substrate.  
      An apparatus for performing an exposure process typically includes a light source, an illumination unit for converting a spot light into a surface light to condense the surface light, a first stage for supporting a reticle having a reticle pattern, a projection optical unit for irradiating the surface light passing through the reticle onto the semiconductor substrate, and a second stage for supporting the semiconductor substrate. The reticle typically is positioned over the projection optical unit. The semiconductor substrate typically is arranged under the projection optical unit.  
      Light emitted from the light source passes through the illumination unit and is converted into surface light. The surface light typically is then focused. The focused surface light typically is irradiated to the reticle. The light passing through the reticle includes image information of the reticle pattern. The light including the image information is irradiated onto the semiconductor substrate through the projection optical unit.  
      Shot regions of the semiconductor substrate into which the reticle pattern is transcribed typically have dimensions and numbers in accordance with the kinds of semiconductor devices being manufactured. The exposure process may be classified into a primary exposure process performed on the device regions and a secondary exposure process performed on edge portions of the semiconductor substrate. The secondary exposure process may be carried out on edge shot regions adjacent to the edge portions of the semiconductor substrate to selectively remove a photoresist film on the edge portions of the semiconductor substrate.  
      According to a conventional exposure process, a patterned reticle having a single pattern area may be used in the primary exposure process as an exposure mask. A non-patterned reticle without a pattern may be used in the secondary exposure process as an exposure mask.  
      Thus, to perform the secondary exposure process on a first semiconductor substrate, the patterned reticle may need to be exchanged for the non-patterned reticle after completing the primary exposure process. Also, to perform the primary exposure process on a second semiconductor substrate, the non-patterned reticle may be exchanged for the patterned reticle. Additionally, after the patterned reticle is exchanged for the non-patterned reticle and vice versa, an alignment process between the substrate and the exchanged reticle may need to be carried out. For example, when a unit lot includes twenty-five semiconductor substrates, fifty exchanging processes may be required to perform the exposure process on the twenty-five semiconductor substrates. Also, fifty alignment processes for the patterned reticle and the non-patterned reticle may also need to be carried out. This may cause decreasing accuracy in the exposure process and loss of time and money. As semiconductor devices have become highly integrated, the above-mentioned problem may become increasingly significant.  
     SUMMARY OF THE INVENTION  
      According to some embodiments of the present invention, photolithographic exposure methods are provided. Light from an illumination source is processed to produce light beams having substantially parallel paths and substantially identical densities. The light beams are passed through a reticle to expose a first object on a microelectronic substrate. The light beams are redirected to bypass the reticle and expose a second object on the microelectronic substrate. The first object may include a first shot region, such as a device region, defined on a photoresist film on the substrate. The second object may include a second shot region, such as an edge shot region, defined on the photoresist film.  
      In further embodiments, processing light from an illumination source to produce light beams having substantially parallel paths and substantially identical densities includes passing the light beams through a reticle blind for the reticle. Redirecting the light beams to bypass the reticle and expose a second object on the microelectronic substrate may include redirecting the light beams after passage through the reticle blind. The light from the illumination source may be passed through a concave lens, a convex lens and a reticle blind to obtain the substantially parallel paths and substantially identical densities. The light beams may be focused using an aperture. Redirecting the light beams to bypass the reticle and expose a second object may include reflecting the light beams away from the reticle and towards the second object, e.g., by tilting a light-reflecting mirror arranged in line with the reticle. Exposure of the second object may include directing the reflected light beams to a blank blind having a light-transmitting region and irradiating the second object through the blank blind.  
      In additional embodiments of the present invention, a photolithography exposure apparatus includes a first light-supplying unit configured to direct light to a first object on a microelectronic structure through a reticle in a primary exposure process. The first light-supplying unit is further configured to produce light beams having substantially parallel paths and substantially identical densities. A second light-supplying unit is configured to redirect the light beams produced by the first light-supplying unit to bypass the reticle and irradiate a second object on the microelectronic substrate in a secondary exposure process. The first light-supplying unit may include a first optical unit configured to produce light beams having substantially parallel paths, a second optical unit configured to process the light beams having substantially parallel paths to produce light beams having substantially parallel paths and substantially identical densities, an illumination unit configured to irradiate the light beams produced from the second optical unit onto the reticle, and a first projecting unit configured to irradiate light beams passing through the reticle onto the first object. The first optical unit may include a fly eye lens, and the second optical unit may include a concave lens, a convex lens, a reticle blind and a condensing lens. The first light-supplying unit may further include a third optical unit arranged between the first and second optical units and including an aperture configured to focus light beams that pass through the second optical unit.  
      The second light-supplying unit may include a first tiltable mirror configured to reflect light beams produced from the first light-supplying unit and a second mirror configured to reflect light beams reflected from the first mirror. A second projecting unit may be configured to irradiate the second object with light beams reflected from the second mirror. The second projecting unit may include a blank blind having a light-transmitting region therein.  
      The apparatus may further include a controller configured to control the first and second light-supplying units to selectively perform the primary and secondary exposure processes. The controller may include a first optical measuring unit configured to detect an initial point and an endpoint of a first exposure process and a drive unit configured to position the first tiltable mirror in respective first and second positions in response to detection of the initial point and the endpoint. The controller may further include a second optical measuring unit for measuring an intensity of light beams reflected from the second object and may be configured to control a speed of a secondary exposure process in accordance with the intensity of the light beams. The apparatus may further include a stage configured to support the microelectronic substrate and controlled by the controller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:  
       FIG. 1  is a flow chart illustrating exposure operations in accordance with some exemplary embodiments of the present invention;  
       FIG. 2  is a front view illustrating an exposure apparatus for performing the operations of  FIG. 1 ;  
       FIG. 3  is a perspective view illustrating a blank blind system of the apparatus of  FIG. 2 ; and  
       FIG. 4  is a plan view illustrating a semiconductor substrate processed using the apparatus of  FIG. 2 .  
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity.  
      It will be understood that when an element or a layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.  
      It will be understood that, although the terms first, second, 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 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 of the present invention.  
      Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.  
      The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.  
      Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.  
       FIG. 1  is a flow chart illustrating exemplary exposure operations in accordance with some exemplary embodiments of the present invention,  FIG. 2  is a front view illustrating an exposure apparatus configured to perform the operations of  FIG. 1 ,  FIG. 3  is a perspective view illustrating a blank blind system used in the apparatus of  FIG. 2  and  FIG. 4  is a plan view illustrating a semiconductor substrate processed using the operations and apparatus in  FIG. 2 . Referring to  FIGS. 2 and 4 , photoresist is coated on a semiconductor substrate W. The photoresist is soft baked to form a photoresist film PR on the semiconductor substrate W. A plurality of shot regions S 0  is defined on the semiconductor substrate W having the photoresist film PR.  
      The shot regions S 0  are divided into a first shot region S 1  and a second shot region S 2 . The photoresist film PR on the first shot region S 1  is exposed and developed to form a photoresist pattern PT. The second shot region S 2  includes the rest of the shot regions S 0  except for the first shot region S 1 . The second shot region S 2  borders an edge E of the semiconductor substrate W. The photoresist film PR on the second shot region S 2  is removed by exposure and developing processes. The first shot region S 1  may have a size that varies in accordance with kinds of semiconductor devices being formed. Also, the configuration of the second shot region S 2  may vary in accordance with the configuration of the first shot region S 1 . In the illustrated embodiments, the photoresist film PR on the first shot region S 1  corresponds to a first object to be exposed and the photoresist film PR on the second shot region S 2  corresponds to a second object to be exposed.  
      An exposure apparatus  100  includes a light source  110 , a first light-supplying unit  120 , a second light-supplying unit  140 , a controlling unit  160  and a stage unit  180 . The light source  110  emits light beams (or rays) for exposing the first and second shot regions S 1  and S 2 . Examples of the light source  110  may include, but are not limited to, a mercury lamp, an ArF laser emitter, a KrF laser emitter, an extreme ultraviolet beam emitter, and an electron beam emitter. The light source  110  is connected to the first light-supplying unit  120 .  
      The first light-supplying unit  120  includes a first optical unit  120   a , a second optical unit  120   b , a third optical unit  120   c  and a first projecting unit  120   d . A first stage  182  for supporting a reticle R is arranged between the second optical unit  120   b  and the first projecting unit  120   d . The reticle R is positioned on the first stage  182 . A second stage  184  for supporting the semiconductor substrate W is positioned under the first projecting unit  120   d . The semiconductor substrate W is placed on the second stage  184 .  
      The first optical unit  120   a  includes a variable beam attenuator  121 , a beam shaping optical system  122 , a first mirror  123 , a first fly-eye lens  124 , a second mirror  125 , a condensing lens  126  and a second fly-eye lens  127 . The second optical unit  120   b  includes a beam splitter  131 , a first alignment system  132 , a reticle blind  135 , a second alignment system  136  and a third mirror  139 . The first alignment system  132  includes a first concave mirror  133  and a first convex mirror  134 . The second alignment system  136  includes a second concave mirror  137  and a second convex mirror  138  having sizes greater than those of the respective first concave mirror  133  and first convex mirror  134 .  
      The third optical unit  120   c  includes an aperture  128 . The third optical unit  120   c  is arranged between the first and second optical units  120   a  and  120   b . A housing  129  encloses the first, second and third optical units  120   a ,  120   b  and  120   c.    
      The light beams emitted from the light source  110  have substantially parallel paths and substantially identical densities. In particular, the light beams emitted from the light source  110  pass through the first optical unit  120   a  to produce the parallel paths. The light beams passing through the first optical unit  120   a  pass through the third optical unit  120   c  so that the light beams are focused. The light beams passing through the third optical unit  120   c  are aligned by the first alignment system  132  of the second optical unit  120   b  to have the substantially identical densities. The light beams aligned by the first alignment system  132  pass through the reticle blind  135  to produce a specific wavelength and a transmittance area. Values accurately reflecting image information of a reticle pattern on the reticle R may be selected as the specific wavelength and the transmittance area of the light beams. The light beams interfered by the reticle blind  135  are re-aligned by the second alignment system  136 . The light beams passing through the second alignment system  136  have substantially identical paths, substantially identical wavelengths and substantially identical densities. That is, the light beams that pass through the first optical unit  120   a , the third optical unit  120   c  and the second optical unit  120   b  may have optimal characteristics, such as a quantity of a light, an intensity of a light, and/or a density of a light, for forming the photoresist pattern PT. The optimal characteristics may be selected in accordance with an aspect ratio and an etching selectivity of a structure to be formed on the semiconductor substrate W.  
      The quantity and the density of the light beams passing through the second alignment system  136  is less than those of the light beams emitted from the light source  110 . The light beams emitted from the light source  110  are inappropriate for the exposure process. For example, because the light beams emitted from the light source  110  may have a high luminance, a thin photoresist pattern PT may not be formed using the light beams. Also, because the light beams emitted from the light source  110  may have irregular paths having a high reflexibility, an efficiency of the exposure process may be decreased and a pre-formed photoresist pattern PT may be damaged.  
      The light beams passing through the second alignment system  136  are reflected from the third mirror  139 . The reflected light beams are irradiated onto the reticle R through the illumination unit  150 . The illumination unit  150  includes a condensing lens (not shown). The illumination unit  150  is positioned over the reticle R.  
      The light beams passing through the reticle R have the image information of the reticle pattern. The light beams passing through the reticle R are projected onto the first shot region S 1  through the first projecting unit  120   d . Here, the light beams passing through the reticle R are focused to have a size corresponding to that of the first shot region S 1 . Thus, a reduced image of the reticle pattern is transcribed into the first shot region S 1 .  
      When a primary exposure process is performed on the photoresist film PR on the first shot region S 1 , the primary exposure process may be carried out by a scanning process in which the reticle R and the semiconductor substrate W are moved in opposite directions. The reticle R is moved using the first stage  182  and the semiconductor substrate W is moved using the second stage  184 . The controlling unit  160  controls the first and second stages  182  and  184 . Alternatively, the primary exposure process may be performed by a stepper process.  
      To accurately perform the primary exposure process, movement velocities of the first and second stages  182  and  184  are controlled in accordance with an intensity of light beams reflected from the semiconductor substrate W. A first optical measuring unit  191  measures the intensity of the light beams reflected from the semiconductor substrate W.  
      The first optical measuring unit  191  is mounted on the first projecting unit  120   d  to face the semiconductor substrate W. The controlling unit  160  controls the movement velocities of the first and second stages  182  and  184  in accordance with a reflexibility of the light beams measured by the first optical measuring unit  191 . The first optical measuring unit detects an initial point and an endpoint of the first exposure process.  
      The second light-supplying unit  140  includes a light path-changing unit  140   a  and a second projecting unit  140   b . The light path-changing unit  140   a  is arranged between the third mirror  139  and the illumination unit  150 . The second projecting unit  140   b  is positioned over the second stage  184  in parallel with the first projecting unit  120   d.    
      The light-path changing unit  140   a  includes a first light-reflecting mirror  141 , a second light-reflecting mirror  142  and a driving unit  143 . The first light-reflecting mirror  141  is tiltably positioned on a path of the light beams reflected from the third mirror  139 . The driving unit  143  controls a tilting angle of the first light-reflecting mirror  141 . The controlling unit  160  controls the driving unit  143 . The driving unit  143  positions the first light reflecting mirror  141  on the region at the initial point of the first exposure process. The driving unit  143  removes the first light-reflecting mirror  141  from the region at an initial point of another first exposure process after having successively carried out the first exposure process.  
      When the first light-reflecting mirror  141  is tilted to a first position, the light beams reflected from the third mirror  139  are irradiated to the illumination unit  150  without being interfered with by the first light-reflecting mirror  141 . When the first light-reflecting mirror  141  is tilted to a second position, the light beams reflected from the third mirror  139  are reflected from the first light-reflecting mirror  141  toward the second light-reflecting mirror  142 . The light beams reflected from the second light-reflecting mirror  142  are irradiated to the second projecting unit  140   b . The light beams passing through the second projecting unit  140   b  are irradiated onto the second shot region S 2 . Additionally, the second projecting unit  140   b  may include a light-condensing member (not shown).  
      Referring to  FIG. 3 , a blank blind system  170  includes a first blank blind  271 , a second blank blind  272  and a rotary driving unit  281 . The first and second blank blinds  271  and  272  each have a plate shape and have a light-transmitting region therein. In particular, the first blank blind  271  has a first light-transmitting region  275  and the second blank blind  272  has a second light-transmitting region  276 . The first light-transmitting region  275  has a size different from that of the second light-transmitting region  276 . The sizes of the first and second light-transmitting regions  275  and  276  may vary in accordance with the size of the second shot region S 2 , that is, the first and second blank blinds  271  and  272  correspond to reticles for exposing the second shot region S 2 .  
      The first and second blank blinds  271  and  272  are detachably secured to both sides of the rotary driving unit  281 . The first and second blank blinds  271  and  272  rotate with respect to a central axis of the rotary driving unit  281 . A secondary exposure process may be performed using one of the first and second blank blinds  271  and  272  that has a size corresponding to that of the second shot region S 2  to be exposed. As a result, the exposure process may be completed in a relatively short time. In the illustrated embodiment, the blank blind system  170  includes the first and second blank blinds  271  and  272 . Alternatively, the blank blinds system  170  may vary in accordance with a size of the exposure apparatus  100 .  
      To reduce damage to the photoresist pattern PT, a quantity and an intensity of the light beams irradiated onto the second shot region S 2  may be controlled in accordance with an intensity of the light beams reflected from the semiconductor substrate W. A second optical measuring unit  192  measures the intensity of the light beams reflected from the semiconductor substrate W. The second optical measuring unit  192  is mounted on the second projecting unit  140   b  to face the semiconductor substrate W. The controlling unit  160  controls a velocity of the second stage  184  in accordance with the reflexibility of the light beams measured by the second optical measuring unit  192 .  
      Korean Patent Laid Open Publication No. 1999-017136 discloses a method of reducing a time required for an exposure process. According to the above Korean Publication, all of the light beams emitted from a light source may be used for exposing a second shot region. However, because the light beams may have a high luminance and a high reflexibility, an efficiency of the exposure process may be decreased and a photoresist pattern on a first shot region may be damaged.  
      On the contrary, according to the present embodiment, the light beams used for exposing the first shot region S 1  are substantially identical to those used for exposing the second shot region S 2 . Thus, the light beams for exposing the second shot region S 2  have a reflexibility lower than that of the light beams disclosed in the above Korean Publication so that damage to the photoresist pattern PT on the first shot region S 1  may be limited in the secondary exposure process. As a result, the first and second exposure processes may be rapidly completed and efficiencies of the first and second exposure processes may be improved.  
       FIG. 1  is a flow chart illustrating an exposing method using the apparatus in  FIG. 2 . Referring to  FIG. 1 , in step S 10 , the reticle R and the semiconductor substrate W are placed on the first stage  182  and the second stage  184 , respectively. The semiconductor substrate W has a photoresist film PR formed thereon. A plurality of shot regions S 0  is defined on the semiconductor substrate W having the photoresist film PR.  
      The shot regions S 0  are divided into the first shot region S 1  and the second shot region S 2 . The first shot region S 1  corresponds to the first object and the second shot region S 2  corresponds to the second object. The photoresist film PR on the first shot region S 1  is exposed and developed to form the photoresist pattern PT. The second shot region S 2  borders the edge E of the semiconductor substrate W. The photoresist film PR on the second shot region S 2  is removed by exposure and developing processes.  
      In step S 115 , the light beams emitted from the light source  110  are processed to provide substantially parallel paths for the light beams. Here, the light beams emitted from the light source  110  may include, for example, a mercury light, a laser beam, an extreme ultraviolet beam, or an electron beam. To provide the paths for the light beams, the first optical unit  120   a  including the variable beam attenuator  121 , the beam shaping optical system  122 , the first mirror  123 , the first fly-eye lens  124 , the second mirror  125 , the condensing lens  126  and the second fly-eye lens  127  may be used.  
      Because the light beams emitted from the light source  110  may have a high luminance, the light beams emitted from the light source  110  may be inappropriate for the exposure process. Particularly, the light beams emitted from the light beam source may be inappropriate for forming a thin photoresist pattern or a structure having a high aspect ratio.  
      In step S 120 , the light beams are then focused to provide uniform sizes to the light beams. Here, to provide the uniform sizes to the light beams, the third optical unit  120   c  including the aperture  128  may be used.  
      In step S 125 , the focused light beams are processed to provide substantially identical densities for the focused light beams. The second optical unit  120   b  including the beam splitter  131 , the first alignment system  132 , the reticle blind  135 , the second alignment system  136  and the third mirror  139  provide the densities to the focused light beams. The first alignment system  132  includes the first concave mirror  133  and the first convex mirror  134 . The second alignment system  136  includes the second concave mirror  137  and the second convex mirror  138 .  
      The light beams have a specific wavelength and transmittance area. Here, the values accurately reflecting the image information of the reticle pattern on the reticle R may be selected as the specific wavelength and the transmittance area of the light beams. That is, the light beams may have optimal characteristics such as a quantity of a light, an intensity of a light, and/or a density of light, for forming the photoresist pattern PT. The optimal characteristics may be selected in accordance with a thickness of the desired photoresist pattern PT, an aspect ratio and an etching selectivity of a structure to be formed on the semiconductor substrate W.  
      In step S 130 , the light beams are irradiated to the reticle R. The light beams passing through the reticle R include the image information of the reticle pattern.  
      In step S 135 , the light beams including the image information are irradiated onto the first shot region S 1  to form the photoresist pattern PT. When the primary exposure process is performed on the photoresist film PR on the first shot region S 1 , the primary exposure process may be carried out by a scanning type in which the reticle R and the semiconductor substrate W are moved in opposite directions.  
      In step S 140 , an endpoint of the primary exposure process is detected. The endpoint may correspond to a point of time for alternatively performing the primary and secondary exposure processes. For example, when the second shot region S 2  is positioned under the second projecting unit  140   b  in moving the semiconductor substrate W, a point of time at which the primary exposure process on the first shot region S 1  is completed may be selected as the endpoint.  
      In the illustrated embodiments, the endpoint corresponds to a point of time for exposing the first and second shot regions S 1  and S 2  with the semiconductor substrate W being minimally moved. Alternatively, after the entire shot region S 1  is exposed, the second shot region S 2  may be exposed.  
      In step S 145 , the light beams having the paths and the densities are redirected to the second shot region S 2  using the light path-changing unit  140   a.    
      In step S 150 , to limit damage of the photoresist pattern PT on the first shot region S 1  in performing the secondary exposure process, the redirected light beams are processed using the blank blind system  170  to provide a size corresponding to that of the second shot region S 2 , for the redirected light beams. Here, the light beams used in the primary exposure process are substantially identical to those used in the secondary exposure process. Thus, the light beams used in the secondary exposure process have a relatively low reflexibility, such that the damage of the photoresist pattern PT on the first shot region S 1  may be limited. In step S 55 , the redirected light beams are irradiated onto the second shot region S 2  to perform the secondary exposure process.  
      Although the light beams emitted from the light source are used in the secondary exposure process, the light beams, if unprocessed, might damage the photoresist pattern due to the high luminance of the light beams. However, in the illustrated embodiments, the light beams substantially identical to each other are used in the primary and secondary exposure processes so that the damage of the photoresist pattern PT may be limited. Also, the primary and secondary exposure processes may be completed in a short time so that an efficiency of the exposure process may be improved.  
      According to some embodiments of the present invention, the primary and secondary exposure processes may be performed without exchanging reticles so that the primary and secondary exposure processes may be completed in a short time. Also, because light beams having the substantially parallel paths and densities by unit area are used in the primary and secondary exposure processes, the damage of the photoresist pattern may be limited.  
      Having described exemplary embodiments of the present invention, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiment of the present invention disclosed which is within the scope and the spirit of the invention outlined by the appended claims.