Abstract:
A reflective photolithography system includes an extreme ultraviolet light source, an illumination mirror system that reflects light generated by the light source, a blinder through which a portion of the reflected light is allowed to pass, a reticle stage equipped with a reflective reticle which receives the light passing through the blinder, and a projection mirror system configured that projects light reflected from the reflective reticle onto a wafer on a wafer stage. The illumination mirror system includes a control mirror module at its downstream end with respect to the optical axis of the apparatus. The control mirror module has a plurality of unit control mirrors which divide the light so as to illuminate a number of domains and such that the intensity of the light can be varied among the domains.

Description:
PRIORITY STATEMENT 
       [0001]    This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-0014398 filed on Feb. 13, 2012, the disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The inventive concept relates to photolithography. More particularly, the inventive concept relates to a reflective photolithography exposure apparatus. 
         [0003]    Photolithography is a process by which patterns, e.g., circuit patterns, can be transcribed onto a substrate such as a semiconductor wafer. In photolithography, an image of a pattern of a reticle is transferred to a photosensitive film (photoresist) on the substrate in an exposure process using light from a specific light source. Conventional transmissive types of reticles comprise a substrate and the pattern of the reticle is provided at a surface of the substrate. The substrate of the reticle is transparent with respect to the exposure light, and the pattern of the reticle may be opaque or partially opaque with respect to the exposure light. In an exposure process using a transmissive type of reticle, the light from the light source is directed through the reticle and onto the photoresist such that the photoresist is exposed to a virtual image of the reticle pattern. Then the photoresist is developed to remove either the exposed or unexposed portions thereof, thereby forming a photoresist pattern. Finally, underlying material is etched using the photoresist pattern as a mask. As a result, a pattern corresponding to that of the reticle is formed. 
         [0004]    Recently, extreme ultraviolet light (EUV) has been considered for use in photolithography because its short wavelength lends itself to the forming of ultrafine patterns of semiconductor devices. Photolithography using EUV requires a reflective reticle because most materials will absorb EUV instead of transmitting it due to the relatively short wavelength of EUV. 
       SUMMARY 
       [0005]    According to an aspect of the inventive concept, there is provided a reflective photolithography apparatus that includes a light source, an illumination mirror system having a plurality of illumination mirrors and a control mirror module, a reticle stage, a projection mirror system including a projection mirror, and a wafer stage, and in which the control mirror module includes a plurality of unit control mirrors having reflective surfaces, respectively, that are each adjustable. 
         [0006]    According to another aspect of the inventive concept, there is provided a reflective photolithography apparatus that includes a light source that generates extreme ultraviolet light, an illumination mirror system disposed in the apparatus to receive light generated by the light source and reflect the light, a blinder disposed in the apparatus to receive the light reflected by the illumination mirror system and configured to allow one portion of the light received thereby to pass therethrough and block the remainder of the light received thereby, a reticle stage configured to support a reflective reticle at the bottom thereof and positioned relative to the blinder such that the portion of the light passing through the blinder is received by the reticle supported by the reticle stage and reflected thereby back through the blinder, a projection mirror system disposed in the apparatus to receive the light reflected from the reflective reticle mounted on the reticle stage and passing back through the exposure slit and project the light in a given direction in the apparatus, and a wafer stage disposed in the apparatus in the path of the light projected by the projection mirror system such that a wafer mounted on the wafer stage will receive the light projected by the projection mirror system, and in which the illumination mirror system includes a control mirror module at an end thereof closest to the blinder with respect to the direction in which light is transmitted from the illumination mirror system in the apparatus. The control mirror module has a plurality of unit control mirrors which divide the light so as to illuminate a number of domains, respectively, and the unit control mirrors are adjustable to vary the intensity of the light among the domains. 
         [0007]    According to still another aspect of the inventive concept, there is provided a reflective photolithography apparatus that includes a light source, a reticle stage, an optical illumination system interposed between the light source and the reticle stage along the optical axis of the apparatus so as to direct light from the light source in a direction along the optical axis towards the reticle stage whereby a reticle mounted to the stage can be illuminated with light from the light source, a wafer stage, and an optical projection system interposed between the reticle stage and the wafer stage along the optical axis of the apparatus so as to project light from a reticle mounted to the reticle in a direction along the optical axis towards the wafer stage, and in which the optical illumination system includes a control mirror module having a control mirror substrate, and a plurality of unit control mirrors supported by the mirror substrate so as to divide the light received by the optical illumination system from the light source, and reflect the light to illuminate a number of domains. The unit control mirrors are adjustable to vary the intensity of the light among the domains. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features and advantages of the inventive concept will be more apparent from the more detailed description of the preferred embodiments thereof, as illustrated in the accompanying drawings. In the drawings: 
           [0009]      FIG. 1  is a schematic diagram of a reflective photolithography apparatus in accordance with the inventive concept; 
           [0010]      FIG. 2A  is a bottom view of a reflective reticle mounted in the reflective photolithography apparatus; 
           [0011]      FIG. 2B  is a top view of a wafer mounted on a wafer stage of the reflective photolithography apparatus and together with  FIG. 2A  illustrates a step and scan exposure process; 
           [0012]      FIGS. 3A to 3F  are each a perspective view of an example of a control mirror module of a reflective photolithography apparatus in accordance with the inventive concept; 
           [0013]      FIGS. 4A and 4B  are each a sectional view of an example of a unit control mirror of a control mirror module in accordance with the inventive concept; 
           [0014]      FIGS. 5A to 5C  are schematic diagrams of a unit control mirror of a control mirror module in accordance with the inventive concept illustrating the operation of the mirror; 
           [0015]      FIGS. 6A and 6B  are perspective views of examples of different joints used to support the unit control mirrors in accordance with embodiments of the inventive concept; 
           [0016]      FIG. 7  is diagram perspective view of the control mirror module showing the unit control mirrors thereof tilted at various angles and in various directions; 
           [0017]      FIG. 8A  is a block diagram of a control device of the control mirror module in accordance with the inventive concept; 
           [0018]      FIGS. 8B and 8C  are each a circuit diagram of an example of components of the control device; 
           [0019]      FIGS. 9A to 9C  are each a conceptual diagram of an example of a way in which the intensity of EUV is controlled by the unit control mirrors of the control mirror module in accordance with the inventive concept; 
           [0020]      FIGS. 10A to 10D  are each a conceptual diagram of an example of a pattern of illumination that can be produced using the control mirror module in accordance with the inventive concept; 
           [0021]      FIG. 11A  is a diagram of a uniformity map of measured line widths of optical patterns of a reflective reticle in accordance the inventive concept; 
           [0022]      FIG. 11B  is a diagram of uniformity correction map for use in compensating for any non-uniformity of optical patterns of the reflective reticle; 
           [0023]      FIG. 12A  is a flowchart of an embodiment of an exposure process using the reflective photolithography apparatus in accordance with the inventive concept; 
           [0024]      FIG. 12B  is a flowchart of an inspection process for a wafer on which the exposure process has been performed in accordance with the inventive concept; and 
           [0025]      FIG. 12C  is a flowchart of a monitoring process for the exposure process in accordance with the inventive concept. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Various embodiments and examples of embodiments of the inventive concept will be described more fully hereinafter with reference to the accompanying drawings. Like numerals are used to designate like elements throughout the drawings. 
         [0027]    Furthermore, spatially relative terms, such as “upper,” and “lower” and “horizontally” are used to describe an element&#39;s and/or feature&#39;s relationship to another element(s) and/or feature(s) as illustrated in the figures. Thus, the spatially relative terms may apply to orientations in use which differ from the orientation depicted in the figures. Obviously, though, all such spatially relative terms refer to the orientation shown in the drawings for ease of description and are not necessarily limiting as embodiments according to the inventive concept can assume orientations different than those illustrated in the drawings when in use. 
         [0028]    Other terminology used herein for the purpose of describing particular examples or embodiments of the inventive concept is to be taken in context. For example, the term “pattern” generally refers to a series of similar features that are repeated at certain intervals but may at times refer to more than one series of features. The terms “comprises” or “comprising” when used in this specification specifies the presence of stated features but does not preclude the presence or additional features. 
         [0029]    A reflective photolithography apparatus in accordance with the inventive concept will now be described in detail with reference to  FIG. 1 . 
         [0030]    The reflective photolithography apparatus  100  includes a light source  10 , an illumination mirror system  20 , a reticle stage  40 , a blinder  60 , a projection mirror system  70 , and a wafer stage  80 . 
         [0031]    The light source  10  may be of a type that generates extreme ultraviolet light (EUV). For example, the light source  10  generates light having a wavelength of about 13.5 nanometers using carbon plasma. A light collector  15  may be integrated with the light source  10 . In this case, the collector  15  serves to collect the EUV generated by the light source  10  and transmit the EUV in a certain direction, i.e., along an optical axis of the apparatus  100 , to the illumination mirror system  20 . For example, the collector  15  may be a concave mirror such as a plano-concave mirror as shown in the figure. 
         [0032]    In this embodiment, the illumination mirror system  20  includes a plurality of illumination mirrors, e.g., three illumination mirrors  21 ,  22 ,  23 , and a control mirror module  30 , that direct the EUV to the reticle stage  40 . The illumination mirrors  21 ,  22 ,  23  themselves may be configured to condense the EUV in order to reduce loss in the apparatus, and such that the reflected light has a uniform intensity distribution. To these ends, each of the illumination mirrors  21 ,  22 ,  23  may be a concave or convex mirror arranged along the optical axis of the apparatus so as to change the direction along which the EUV propagates. In addition, the illumination mirror system  20  may shape the EUV, e.g., condense the EUV, into a beam having a square, circular, or bar-shaped cross section, and direct the beam of EUV to the reticle stage  40 . 
         [0033]    The control mirror module  30  controls the intensity distribution of the EUV, i.e., regulates the intensity of the EUV per unit area. For example, the control mirror module  30  may receive incident EUV having a uniform intensity distribution and reflect the incident EUV as a beam having a relatively high intensity across a first region thereof and a relatively low intensity across a second region thereof (as seen in a cross section of the beam of EUV). That is, the illumination mirror system  20  may output a beam of EUV whose intensity varies across respective areas thereof and direct such an altered beam of EUV to the reticle stage  40 . 
         [0034]    Still referring to  FIG. 1 , the control mirror module  30  is preferably disposed at the end of the illumination mirror system  20  with respect to the optical axis of the apparatus  100 . Thus, the control mirror module  30  may receive the EUV from the illumination mirrors  21 ,  22 ,  23  and reflect the EUV directly to the reticle stage  40 . The control mirror module  30  will be described in further detail below. 
         [0035]    The reticle stage  40  can support a reflective reticle  50  at the bottom thereof. For example, the reticle stage  40  may include a plate, and an electrostatic chuck (ESC) to secure the reticle  50  to the bottom of the plate. The reticle stage  40  may also be moveable in the apparatus  100  back and forth along a horizontal axis as shown by the arrows. 
         [0036]    The reflective reticle  50  has reflective optical patterns  52  that face downwardly when the reticle is mounted to the stage  40 . 
         [0037]    The blinder  60  is disposed below the reticle stage  40 . The blinder  60  comprises a plate  64  having an exposure slit  62  extending therethrough. The EUV transmitted from the illumination mirror system  20  passes through the exposure slit  62  so as to irradiate the reflective reticle  50  on the reticle stage  40 . The exposure slit  62  is elongated in a horizontal direction. In this embodiment, the cross-sectional area of the exposure slit  62  (in the plane of the plate  64 ) is bar-shaped and extremely narrow. Thus, the plate  64  intercepts one portion of the beam of EUV reflected by the illumination mirror system  20  whereas the exposure slit  62  allows another limited portion of the beam of EUV to pass through the blinder  60  to the reflective reticle  50 . The EUV reflected from the reticle  50  passes back through the exposure slit  62  to the projection mirror system  70 . 
         [0038]    The projection mirror system  70  of this embodiment includes a plurality of projection mirrors  71 - 76  that can correct various aberrations. The mirrors  71 - 76  of the projection mirror system  70  receive the EUV which is reflected from the reflective reticle  50  through the exposure slit  62 , and then direct the EUV along the optical axis of the apparatus  100  to a wafer stage  80  where the EUV irradiates a wafer  90  on the stage. More specifically, a photoresist layer of a certain thickness is formed on the wafer  90 , and the focus of the projection mirror system  70  is located above the surface of the wafer  90  so that the EUV is focused to a location within the photoresist layer. In this way, the photoresist layer can be irradiated with EUV bearing a virtual image of the optical patterns  52  of the reflective reticle  50  and shaped by the exposure slit  62 . 
         [0039]    Still referring to  FIG. 1 , it should be noted that the optical axis along which the EUV propagates is shown conceptually for ease in understanding the general purposes behind the various components of the apparatus  100  described above. 
         [0040]    The wafer stage  80  may be supported in the apparatus, like the reticle stage  40 , so as to be movable back and forth along a horizontal axis, as shown by the arrows in  FIG. 1 . Also, the wafer stage  80  and the reticle stage  40  may be linked to move simultaneously in the same direction but at a different rates, the ratio of which will be referred to hereinafter as a “movement ratio”. Furthermore, the apparatus  100  may be configured so that the movement ratio may be adjusted. For example, when the movement ratio is set to 10:1, if the reticle stage  40  is moved 10 μm left or right, the wafer stage  80  is simultaneously moved 1 μm in the same direction over the same period of time. Or, when the movement ratio is set to 5:1, if the reticle stage  40  is moved 10 μm to the left or right, the wafer stage  80  is moved 2 μm in the same direction over the same period of time. 
         [0041]    In an example of this embodiment, the wafer stage  80  is supported so as to be moveable along horizontal X- and Y-axes that orthogonal to each other. For example, the X-axis extends along the same direction of movement as the reticle stage  40  and corresponds to a scan direction and the Y-axis corresponds to a step direction. Accordingly, the apparatus  100  can execute a step-and-scan process which will be described in more detail below. 
         [0042]    The wafer stage  80  may also be supported in the apparatus  100  so as to be vertically moveable, in whole or in part, such that the focus of the apparatus can be adjusted and maintained at a certain level relative to a wafer supported on the wafer stage  80 . 
         [0043]    An additional optical component or components, e.g., a blinder, beam shaper, and/or aperture, etc., may be provided above the wafer stage  80 , i.e., between the wafer stage  80  and the projection mirror system  70  with respect to the optical axis of the apparatus  100 . 
         [0044]    An example of an exposure process using the reflective photolithography apparatus  100  in accordance with the inventive concept will now be described with reference to  FIGS. 2A and 2B .  FIG. 2A  is a bottom view of the reflective reticle  50  and  FIG. 2B  is a top view of the wafer  90 . 
         [0045]    Referring to  FIG. 2A , the exposure process comprises moving the reflective reticle  50  relative to the exposure slit  62 . More specifically, in a process employing the above-described embodiment of a reflective photolithography apparatus, the reticle stage  40  is moved along the X-axis, that is, in a direction perpendicular to the lengthwise direction of the elongated exposure slit  62 . Thus, the reflective reticle  50  is moved horizontally by the reticle stage  40  while the aperture  60  remains fixed. As a result, the exposure slit  62  is, in effect, scanned across the surface of the reflective reticle  50 . 
         [0046]    The reflective reticle  50  has a pattern area  54  and a peripheral area  56  in this example. The pattern area  54  is the area occupied by the optical patterns  52  of the reticle  50  and the peripheral area  56  surrounds the pattern area  54 . The exposure slit  62  scans only the pattern area  54  of the reflective reticle  50  in this example. 
         [0047]    Referring to  FIG. 2B , the EUV from the light source  10  is directed through the exposure slit  62  of the blinder  60  by the illumination mirror system  20 . As a result, the surface of the reflective reticle  50  is scanned with the EUV, and the EUV reflected from the reflective reticle  50  through the exposure slit  62  contains a virtual aerial image of the optical patterns  52 . The aerial image of the optical patterns  52  is projected by the projection mirror system  70  onto the wafer  90  to form optical virtual image  92  on the (photoresist layer on the) wafer  90 . 
         [0048]    Also, in this example, the projection mirror system  70  projects the EUV containing the aerial image of the optical patterns  52  to a fixed location above the wafer stage  80 , while the wafer stage  80  is moved horizontally at a rate that is a fraction of that of the reticle stage  64  (refer to the description above pertaining to the “movement ratio”). At this time, the wafer  90  is fixed on the stage  80  with its flat zone (FZ) facing in a given direction (the direction of the Y-axis in this example). 
         [0049]    After the reticle  50  has been scanned once and an aerial image of the optical patterns  52  of the reticle  50  has been transferred to a region of the wafer  90 , the wafer stage  80  is moved to bring another region of the wafer  90  to the location at which the projection mirror system  70  focuses the EUV in the apparatus. Then the reticle  50  is scanned again with the EUV, and an aerial image of the optical patterns  52  of the reticle is transferred to that region of the wafer  90 .  FIG. 2B  shows an example in which the aerial image is being transferred for a tenth time to the wafer  90  in this way. Typically, these regions are demarcated by scribe lanes. In the process described above, a photoresist layer on the wafer  90  is irradiated with the EUV and hence, exposed to the aerial images. Therefore, such scribe lanes and other features at the upper surface of the wafer  90  can not be seen in the plan view of  FIG. 2B . However, the virtual images of the patterns transferred to the photoresist are illustrated for ease in understanding. 
         [0050]    Examples of the control mirror module  30  will now be described in more detail. 
         [0051]    Referring to  FIGS. 3A to 3F , the control mirror module  30 A- 30 F includes a mirror substrate  35 A- 35 F, and a plurality of unit control mirrors  200 A- 200 F arranged in a cellular array or matrix on the mirror substrate  35 A- 35 F. 
         [0052]    The mirror substrate  35 A- 35 F may be ceramic, glass, or metal substrates, or may be constituted by a printed circuit board (PCB). The mirror substrate  35 A- 35 F may be circular or polygonal. Also, the mirror substrate  35 A- 35 F may be planar (as illustrated) or may be concave or convex. Examples of control mirror modules having circular substrates are shown in  FIGS. 3A and 3C  to  3 F, whereas an example of a control mirror module having a polygonal substrate (in this case a rectangular substrate) is shown in  FIG. 3B . 
         [0053]    Preferably, the greatest dimension of the mirror substrate  35 A- 35 F is on the order of tens of centimeters. For example, the diameter of the mirror substrate  35 A,  35 C- 35 F is preferably on the order of tens of centimeters, and more preferably in a range of 30 to 60 centimeters. When the mirror substrate  35 B is polygonal, the length of its longest side or of its diagonal is preferably on the order of tens of centimeters, and more preferably in a range of 30 to 60 centimeters. 
         [0054]    The size (longest dimension) of each of the unit control mirrors  200 A- 200 F is on the order of tens to hundreds of micrometers. The shape of each of the unit control mirrors  200 A- 200 F may be polygonal such as rectangular, rhombic, or hexagonal, or circular or oval or elliptical as shown in  FIGS. 3A-3F . In some cases, such as when the unit control mirrors are elliptical as shown in  FIG. 3F , the control mirrors  200 F may be arranged in rows, with the mirrors  200 F in each row being offset relative to the mirrors  200 F in each row adjacent thereto. 
         [0055]    Examples of structures of the unit control mirrors  200  in accordance with the inventive concept are shown in  FIGS. 4A and 4B . 
         [0056]    In the example shown in  FIG. 4A , each unit control mirror  200  includes a unit mirror substrate  210  and a reflective stack  220  disposed on the unit mirror substrate  210 . The unit mirror substrate  210  may comprise any of a variety of magnetic substances or metals such as chromium, nickel, cobalt, molybdenum, aluminum, or iron. The reflective stack  220  is made up of pairs of unit reflective layers  222 , i.e., a first unit reflective layer  224  and a second unit reflective layer  226 . As one example, the first unit reflective layer  224  is a layer of silicon having a thickness of approximately 4.1 nm and the second unit reflective layer  226  is a layer of molybdenum having a thickness of approximately 2.7 nm. The reflective stack  220  may include approximately forty pairs of unit reflective layers  222 . The reflective layer  220  may also include a capping layer  228  (a mono-layer or a laminate) disposed on the pairs of unit reflective layers  222 . The capping layer  228  may comprise a layer of silicon or silicon oxide. In the case in which capping layer  228  comprises a layer of silicon oxide, the thickness of the silicon oxide layer is approximately 5 to 13 nm. 
         [0057]    In the example shown in  FIG. 4B , the unit mirror substrate  210  includes a silicon layer  214  and a metal layer  212  disposed on the bottom surface of the silicon layer  214 . The metal layer  212  is magnetic. 
         [0058]    Referring to  FIGS. 5A to 5C , the control mirror module  30  also includes supports  230  disposed on the mirror substrate  35  and supporting the unit control mirrors  200 . In  FIGS. 5A-5C , for the same of simplicity only one such support  230  and unit control mirror  200  is shown, and the components of the control mirror module  30  including the mirror substrate  35  are not shown to scale. 
         [0059]    The support  230  includes a joint  240 , at an upper portion thereof, that allows the unit control mirrors  200  to rotate or tilt relative to the mirror substrate  35 . The control mirror module  30  also has a plurality of electromagnets  250  integrated with the mirror substrate  35 . The electromagnets  250  are disposed at or near (adjacent) an upper surface of the mirror substrate  35  as juxtaposed with the unit mirror substrates  210  of the unit control mirrors  200 . More specifically, at least two respective electromagnets  250  are juxtaposed with each unit mirror substrate  210 . The electromagnets  250  are operable form a magnetic field that attracts or repels the unit mirror substrate  210 . Thus, the unit control mirrors  200  can be tilted at various angles by the magnetic field of the electromagnets  250 . In this respect, the control mirror module  30  also has control circuits  260  integrated with the mirror substrate  35 , in this example, to control the magnetic field of the electromagnets  250 . The control circuits  260  may include a MOS transistor  270 . Each of the control circuits may be operated independently. As an example,  FIGS. 5B and 5C  show the tilting of a unit control mirror  200  by two of the control circuits  260 . 
         [0060]    The above-described components of the control mirror module  30  may be configured such that each unit control mirror  200  may be tilted to a maximum angle of 30 degrees from its home position at which it is level with respect to the mirror substrate  35 . It has been determined experimentally that the intensity of the EUV can be controlled sufficiently if the unit control mirrors  200  are tilted only by approximately 10 degrees. 
         [0061]      FIGS. 6A and 6B  show examples of the joints  240 . 
         [0062]    Referring to  FIG. 6A , the joint comprises a hinge  241 . For example, the hinge  241  includes a pivot housing  242  mounted to the bottom of the unit mirror substrate  210  and a pivot shaft  243  received in the pivot housing  242 . The pivot housing  242  and hence, the unit mirror  200 , can pivot about the longitudinal axis of the pivot shaft  243 . 
         [0063]    Referring to  FIG. 6B , the joint comprises a ball joint  246 . For example, the ball joint  246  include a socket  247  mounted to the bottom of the unit mirror substrate  210  and a ball  248  received in the socket  247 . The socket  247  and hence, the unit mirror  200 , can tilt in various directions about the ball  248 . 
         [0064]      FIG. 7  shows an example of the control mirror module  30  in which the unit control mirrors  200  thereof are tilted at various angles. That is  FIG. 7 , shows that the unit control mirrors  200  may be inclined independently in various directions and at various angles. 
         [0065]    Examples of the control circuits of the control mirror module  30  in accordance with the inventive concept will now be described in detail with reference to  FIGS. 8A to 8C . Referring to  FIG. 8A , each control circuit includes a MOS transistor  270  which has a source electrode connected to a bit line driver  285 , a drain electrode connected to an electromagnet  250 , and a gate electrode connected to a word line driver  280 . The word line driver  280  and the bit line driver  285  are connected to a controller  290 . Thus, in this example, when the MOS transistor  270  is turned on by the word line driver  280 , the current supplied from the bit line driver  285  is transferred to the electromagnet  250  such that the electromagnet  250  produces a magnetic field. 
         [0066]    Referring to  FIGS. 8B to 8C , each control circuit may also include a voltage regulator, e.g., a coupling capacitor  295   a  or diode  295   b , connected to the drain electrode. The voltage regulator  295   a  and  295   b  ensures that the electromagnet  250  produces a uniform discrete magnetic field. 
         [0067]      FIGS. 9A to 9C  conceptually illustrate ways in which the intensity of EUV illuminating the reticle can be controlled by the reflective photolithography apparatus in accordance with the inventive concept. 
         [0068]    Referring to  FIG. 9A , the unit control mirrors  200  are oriented horizontally (or with all of their reflective surfaces being disposed in the same plane). As a result, the intensity of the EUV is uniform across the exposure slit  62 . 
         [0069]    Referring to  FIG. 9B , some of the unit control mirrors  200  are tilted such that the intensity distribution of the EUV across the exposure slit  62  is biased or has gray levels. For instance, as shown in this example, central ones of the unit control mirrors  200  are tilted to toward the outer periphery of the mirror substrate  35  of the control mirror module  30 . As a result, the intensity of the EUV becomes lower at the center of the exposure slit  62 , and higher at the ends of the exposure slit  62 . 
         [0070]    Referring to  FIG. 9C , a set of the unit control mirrors  200  are tilted in the same direction toward one side of the mirror substrate  35  of the control mirror module  30 . As a result, the intensity of the EUV becomes lowest at one end of the exposure slit  62   k , lower at the center of the exposure slit  62 , and highest at the other end of the exposure slit  62 . 
         [0071]    As can be fully appreciated from  FIGS. 9A to 9C , the control mirror module  30  in accordance with the inventive concept can adjust the intensity of the EUV in a plurality of areas, e.g. cells, in various ways to obtain virtually any desired intensity distribution (profile) across the reflective reticle and wafer. 
         [0072]      FIGS. 10A to 10D  illustrate ways in which the intensity distribution of the EUV can be controlled by reflecting the EUV onto domains (areas in space) using the unit control mirrors. For example, these domains coincide with the blinder  60  in this embodiment. 
         [0073]    Referring to  FIG. 10A , areas IR 1  of the blinder  60  illuminated with EUV by the unit control mirrors  200 , respectively, overlap only other areas IR 1  along their peripheries (or not at all). For simplicity, the shapes of areas IR 1  are illustrated as having rounded corners. Therefore, intensity distribution of the EUV reflected by the control mirror module  30  will be entirely uniform. 
         [0074]    Referring to  FIG. 10B , areas IR 2  on the blinder  60  illuminated with EUV by the unit control mirrors  200  overlap to a larger extent than the areas IR 1  in the example shown in and described above with reference to  FIG. 10A . For example, the areas IR 2  overlap substantially at the center of the blinder  60 . Therefore, intensity distribution of the EUV reflected by the control mirror module  30  will be higher at the center than at the periphery of the blinder  60 . 
         [0075]    Referring to  FIG. 10C , areas IR 3  on the blinder  60  illuminated with the EUV by the unit control mirrors  200  overlap asymmetrically. For example, an overlapping area OL 1  between first and second columns of the EUV is larger than an overlapping area OL 2  between the second column and a third column of the EUV (OL 1 &gt;OL 2 ). In addition, an overlapping area OL 3  between the third column of the EUV and a fourth column of the EUV is larger than the overlapping area OL 2  (OL 3 &lt;OL 2 ). Also, the overlapping area OL 3  may be larger than the overlapping area OL 1 . 
         [0076]    Referring to  FIG. 10D , each area IR 4  of the blinder  60  illuminated with EUV by a unit control mirror  200  overlaps several of the other areas IR 4 . This pattern of illumination can be achieved when, for example, the unit control mirrors  200  are convex mirrors or when the unit control mirrors  200  are planar mirrors and the mirror substrate  35  is concave. 
         [0077]    Thus, it can be appreciated from  FIGS. 10A to 10D  that various patterns of illumination of the EUV may be provided by the control mirror module according to the inventive concept. 
         [0078]    An example of an exposure process using the reflective photolithography apparatus  100  according to the inventive concept will now be described with reference to  FIG. 11A-12C . In this example, the optical patterns  52  of the reflective reticle  50  are line and space patterns and the uniformity of the optical patterns  52  is a measure of the uniformity of the line widths of the line and space patterns. 
         [0079]      FIG. 11A  is a uniformity map  410  of measured line widths of the optical patterns  52  of the reflective reticle  50 , and  FIG. 11B  is a uniformity correction map  420  for use in correcting the uniformity of the optical patterns  52  of the reflective reticle  50 . 
         [0080]    Referring to  FIG. 11A , the uniformity map  410  of the optical patterns  52  is a grid showing the uniformity of the line widths of the optical patterns  52  according to an average value of the line widths in areas of the reticle  50 . The areas are demarcated according to the level of the average value of the line widths. For example, the uniformity map  410  may include an area H 1  in which the average value of the line widths of the optical patterns  52  is lowest and areas H 2  to H 5  in which the average values of the line widths of the optical patterns  52  progressively increase. Although in this example the uniformity map  410  has classifies the average values of the line widths into five different levels, the map  410  may classify the average values of the line widths into more or fewer levels as needed. 
         [0081]    Referring to  FIG. 11B , the uniformity correction map  420  has an area L 1  in which the intensity of the EUV should be increased and areas L 2  to L 5  in which the intensity of EUV should be progressively decreased, to compensate for the differences in uniformity of the optical patterns  52  of the reflective reticle  50  shown in the map  410  in  FIG. 11A . More specifically, in this example, because the average value of the line widths of the optical patterns  52  is relatively high in area L 1 , the control mirror module  30  will be controlled to decrease the intensity of the EUV illuminating an area of the reticle corresponding to area L 1  on the map  420 . Conversely, because the average value of the line widths of the optical patterns  52  is relatively low in area L 5 , the control mirror module  30  will be controlled to increase the intensity of the EUV illuminating that area of the reticle corresponding to area L 5  on the map  420 . 
         [0082]    Referring to  FIG. 12A , the exposure process in accordance with the inventive concept includes generating a uniformity map  410  of the optical patterns  52  of the reflective reticle  50  (S 110 ). The generation of the uniformity map  410  may include measuring the line widths of the optical patterns  52  on the reflective reticle using, for example, a critical dimension-scanning electron microscope (CD-SEM) or aerial image measurement system (AIMS), calculating the average values, and classifying and displaying the average values in each of the unit areas of the grid. The unit areas may be of various sizes. For example, they may be several micrometers to hundreds of micrometers square. Basically, the size of the unit areas will depend on the tolerance of the optical patterns  52 . 
         [0083]    Next, a uniformity correction map  420  is produced based on the uniformity map  410  (S 120 ). The uniformity correction map  420  may display several demarcated areas corresponding to areas of the reticle  50  at which the intensity of the EUV should be raised and lowered. 
         [0084]    Next, a control program for controlling the unit control mirrors  200  of the control mirror module  30  is generated based on the uniformity correction map  420  (S 130 ). The control program includes commands controlling the unit control mirrors  200  such that the control mirror module  30  reflect a greater amount of the EUV to the areas at which the intensity of the EUV should be higher and reflect less of the EUV to the areas at which the intensity of the EUV should be lower. 
         [0085]    Next, the reflective reticle  50  and the wafer  90  are loaded into the reflective photolithography apparatus  100  (S 140 ). For example, the reflective reticle  50  is mounted on the reticle stage  40  such that the surface on which the optical patterns  52  are formed faces down, and the wafer  90  is mounted on the wafer stage  80 . 
         [0086]    Next, an aerial image of the optical patterns  52  of the reflective reticle  50  is projected onto the wafer  90  (S 150 ). In particular, a photoresist layer formed on the wafer  90  is exposed to the aerial image of the optical patterns  52  of the reflective reticle  50  while the unit control mirrors  200  of the control mirror module  30  are positioned according to the control program. The exposure process may be executed in a step-and-scan manner. That is, as was described with reference to  FIGS. 2A and 2B , the wafer stage  80  on which the wafer  90  is mounted is moved in a step-wise manner to bring respective semiconductor chips on the wafer  90  into alignment with (the optical axis of) the apparatus, and an aerial image of the optical patterns  52  is projected onto each of the chips by a scanning method in which the reticle stage  40  and the wafer stage  80  are moved horizontally at different rates. 
         [0087]    Next, the wafer  90  is removed from the reflective photolithography apparatus  100  (S 160 ). Then the wafer  90  is inspected. 
         [0088]    Referring to  FIG. 12B , the inspection process includes forming patterns on the wafer  90  corresponding to the optical patterns  52  (S 210 ). Specifically, the photoresist layer exposed to the aerial image of the optical patterns  52  is developed to form a photoresist pattern. In addition, material (a target layer) under the photoresist pattern is itself patterned (etched) using the photoresist pattern as a mask. Then, the photoresist pattern may be removed. 
         [0089]    In addition, the line widths of the patterns formed on the wafer  90  are measured (S 220 ). This process may include measuring the line widths of the photoresist patterns and the line widths of the patterned target layer, and generating data representative of the measured line widths of the photoresist patterns and/or target layer patterns formed on the wafer  90 . 
         [0090]    Next, a uniformity measurement map based on the data of the measured line widths is produced (S 230 ). The uniformity measurement map maps the uniformity of the photoresist patterns and/or target layer patterns. 
         [0091]    Next, determining determination is made as to whether to proceed with the process (S 240 ). Such a determination may be based on whether the uniformity of the measured photoresist patterns or target layer patterns meets a certain tolerance, i.e., is within a range of predetermined values. 
         [0092]    The exposure process may also include a self-monitoring process in accordance with the inventive concept. 
         [0093]    Referring to  FIG. 12C , the monitoring process may include comparing the uniformity map  410  of the optical patterns  52  of the reflective reticle  50  to the uniformity measurement map produced after the target layer is patterned (S 310 ). Data representative of the comparison of the uniformity maps is generated. The comparative data may be data of domain-specific differences between the uniformity map  410  and the uniformity measurement map. 
         [0094]    Next, the uniformity correction map  420  is corrected based on the comparative data (S 320 ). Therefore, the correction map  420  may be corrected based on domain-specific differences between the uniformity map  410  and the uniformity measurement map. 
         [0095]    Next, the control program is corrected (overwritten) based on the corrected uniformity correction map  420  (S 330 ). 
         [0096]    As a result, the next exposure process is carried out according to the corrected control program. 
         [0097]    As described above, according to an aspect of the inventive concept, the reflective photolithography apparatus can control the intensity distribution of the exposure light, and compensate for any non-uniformity in an optical pattern(s) of a reflective reticle in real time. 
         [0098]    In addition, according to an aspect of the inventive concept, the reflective photolithography apparatus according to the inventive concept can perform exposure processes without the need to reproduce or correct a reflective reticle. Therefore, a reflective photolithography apparatus according to the inventive concept can help to reduce manufacturing costs and keep production time to a minimum. 
         [0099]    Finally, embodiments of the inventive concept and examples thereof have been described above in detail. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments described above. Rather, these embodiments were described so that this disclosure is thorough and complete, and fully conveys the inventive concept to those skilled in the art. Thus, the true spirit and scope of the inventive concept is not limited by the embodiment and examples described above but by the following claims.