Patent Publication Number: US-2013250269-A1

Title: Exposure apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an exposure apparatus that guides coherent light beams to the surface of an exposure medium. 
     BACKGROUND ART 
     Exposure apparatuses, for example, photolithography used for pattern formation for semiconductor devices have adopted a technique of transferring a reticle (mask) pattern onto a substrate such as a semiconductor wafer. In this technique, a photosensitive photoresist is applied on a substrate, a reticle is placed on the photoresist, and a high pressure mercury lamp, a metal halide lamp, etc. is provided above the reticle to illuminate the reticle, thereby a radiated light image corresponding to the reticle (mask) pattern being formed on the photoresist. 
     Generally, in projection exposure apparatuses for example a stepper, a pattern to be transferred drawn on a reticle is projected onto a substrate via a projection optical module and formed thereon. 
     However, high intensity discharge lamps such as high pressure mercury lamps have a relatively short lifecycle and need to be frequently replaced. In addition, since these lamps are a diffusion light source with a plurality of wavelengths, it is required to use a relatively large and highly functional optical module for light convergence, reshaping and image formation, there is a problem in that the entire system becomes larger. 
     In order to cope with such problems, a system using a coherent light source such as a laser has also been proposed. For example, semiconductor lasers which have been widely used in industries have a very long lifecycle in comparison with high intensity discharge lamps such as high pressure mercury lamps. In addition, since semiconductor lasers are capable of generating light of high straightness and a single wavelength, an optical module can be compact and simple, so that there is an advantage in that the entire system becomes smaller and light utilization efficiency is improved. 
     On the other hand, in the unit using a coherent light source of laser beams or the like, there is another problem in that speckles are generated. Speckles are a spotted pattern which is formed when a coherent light beam such as a laser beam is emitted to a scattering plane. If speckles are generated on a screen, they are observed as spotted luminance unevenness, i.e. brightness unevenness, thus becoming a factor of having physiologically adverse affect on an observer. It is considered that the reason why speckles are generated in the case of using coherent light beams is that coherent light beams reflected from respective portions of a scattering and reflecting plane such as a screen have very high coherency so that coherent light beams interfere with one another to generate speckles. For example, a theoretical review of the generation of speckles is made in detail in Speckle Phenomena in Optics, Joseph W. Goodman, Roberts &amp; Co., 2006. 
     As discussed above, in the unit using a coherent light source, since there is a problem of generation of speckles unique to the coherent light source, techniques for suppressing the generation of speckles have been proposed. For example, Japanese Patent Laid-Open No. 6-208089 discloses a technique in which a laser beam is emitted to a scattering plate, scattered light beams obtained therefrom are guided to a spatial light modulator, and the scattering plate is driven to rotate by a motor, thus reducing speckles. 
     DISCLOSURE OF INVENTION 
     Conventionally, several techniques for reducing speckles have been proposed, however, the techniques proposed so far cannot effectively and sufficiently suppress the generation of speckles. For example, according to the method disclosed in Japanese Patent Laid-Open No. 6-208089 described above, laser beams irradiated to a scattering plate are scattered. Therefore, part of the laser beams is inevitably lost with no contribution to image display. In addition, a scattering plate needs to be rotated in order to reduce speckles. However, such a mechanical rotation mechanism becomes a relatively large apparatus, and power consumption is increased. Moreover, even if the scattering plate is rotated, the position of the optical axis of an illumination light beam is not changed, hence it is impossible to sufficiently suppress the generation of speckles caused by the diffusion on a screen. 
     Moreover, speckles are not a problem unique to projection apparatuses but a problem to various apparatuses having an illumination device incorporated therein for illuminating an illumination zone with coherent light beams. For example, scanners for reading image information have an illumination device incorporated therein for illuminating an object to be read. When speckles are generated due to light that illuminates an object to be read, it is impossible to read image information accurately. In order to avoid such inconvenience, scanners utilizing coherent light beams are required to perform a special process such as image correction. 
     Coherent light beams, for example laser beams as a typical example, have excellent straightness and can be emitted as a light of extremely high energy density. Therefore, it is preferable for illumination devices actually developed to design the optical path of coherent light beams in accordance with the characteristics of coherent light beams. 
     The inventors have extensively researched under consideration of the points discussed above, and as a result, the inventors have contrived the invention regarding an exposure apparatus which illuminates a region repeatedly with coherent light beams that are diffracted by a hologram recording medium or the like and guides the illumination light to an exposure medium, to make speckles inconspicuous on the exposure medium. Moreover, the inventors have proceeded with researches and succeeded in improvement in the exposure apparatus to constantly prevent the generation of a region extremely bright in the region illuminated with coherent light beams which have been diffracted by a hologram recording medium and superimposed on one another on the region. Namely, the purpose of the present invention is to provide an exposure apparatus capable of making speckles inconspicuous on an optical image formed on an exposure medium and effectively suppressing the generation of brightness unevenness in a region illuminated with coherent light beams which have been diffracted by a hologram recording medium and superimposed on one another on the region. 
     In order to solve the problems above, according to an aspect of the present invention, there is provided an exposure apparatus comprising: 
     an optical device configured to be capable of diffusing coherent light beams from respective points to an entire region of at least a specific zone; 
     an irradiation unit configured to irradiate the coherent light beams to the optical device so that the coherent light beams scan a surface of the optical device; and 
     a spatial light modulator that is provided at a location overlapped with the specific zone and illuminated by the illumination device, 
     wherein the irradiation unit makes the coherent light beams scan the surface of the optical device by changing propagation directions of the coherent light beams, and 
     coherent light beams modulated by the spatial light modulator are guided to a surface of a photosensitive medium. 
     According to the present invention, it is possible to make speckles inconspicuous effectively in a zone provided overlapping with a light modulator and on the surface of a photosensitive medium and also restrict brightness unevenness in the zone provided overlapping with the light modulator and on the surface of the photosensitive medium. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a schematic configuration of an exposure apparatus according to a basic embodiment of the present invention; 
         FIG. 2  is a view explaining an operational principle of an illumination device  40  of  FIG. 1 ; 
         FIG. 3  is a view explaining a state in which an image of a scattering plate is generated on a hologram recording medium  55  as interference fringes; 
         FIG. 4  is a view explaining a state in which an image of a scattering plate is reproduced using interference fringes formed in the hologram recording medium  55  obtained through an exposure process of  FIG. 3 ; 
         FIG. 5  is a view explaining a scanning route of a scanning device  65 ; 
         FIG. 6  is a view showing a schematic configuration of an exposure apparatus according to an applied embodiment of the present invention; 
         FIG. 7  is a view showing results of measuring speckle contrasts in the cases where the hologram recording medium  55  was used and not used; 
         FIG. 8  is a view showing a schematic configuration of an exposure apparatus according to a second embodiment of the present invention; 
         FIG. 9  is a view showing an example of a scanning device rotatable in two axes directions; 
         FIG. 10  is a view showing an example of making a parallel beam incident on the hologram recording medium  55 ; and 
         FIG. 11  is a view showing a schematic configuration of an irradiation unit  60  using a lens array according to a third embodiment. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention will be explained with reference to the drawings. In the accompanying drawings of the present description, in order for simplifying drawings and easy understanding, the scale, the ratio of height to width, etc., are appropriately modified or enlarged. 
     First Embodiment 
     An exposure apparatus according to a first embodiment of the present invention is capable of effectively preventing speckle, as a basic embodiment. Moreover, an exposure apparatus according to an applied embodiment of the present invention features an image forming module in addition to the configuration of the basic embodiment. Firstly, the basic embodiment of the present invention will be explained with reference to  FIGS. 1 to 5 . 
     Configuration of Basic Embodiment 
       FIG. 1  is a view showing a schematic configuration of an exposure apparatus according to the basic embodiment of the present invention. An exposure apparatus  10  shown in  FIG. 1  is provided with an optical device  50 , an irradiation unit  60 , and a spatial light modulator  30 . Coherent light beams modulated by the spatial light modulator  30  are guided to the surface of the exposure medium  15 . The optical device  50  and the irradiation unit  60  are included in an illumination device  40 . 
     The optical device  50  has a hologram recording medium  55  that can reproduce an image of a scattering plate in an illumination zone (a specific zone) LZ. The details of the hologram recording medium  55  will be explained later. 
     The irradiation unit  60  irradiates the optical device  50  with coherent light beams so that the coherent light beams scan the surface of the optical device  50 . The irradiation unit  60  has a laser source  61  that emits coherent light beams and a scanning device  65  that scans the surface of the optical device  50  with the coherent light beams emitted from the laser source  61 . 
     The spatial light modulator  30  is, for example, a reticle (mask) of transmission-type or reflection-type. In this case, an optical image corresponding to a reticle pattern is formed on the surface of the exposure medium  15 , which can be used as an exposure apparatus for fabricating a semiconductor device. 
     Or the spatial light modulator  30  may be a transmission-type liquid crystal microdisplay. In this case, the spatial light modulator  30  is illuminated by the illumination device  40  in the plane direction and coherent light beams pass through the spatial light modulator  30  selectively per pixel. In this way, a modulated image (an optical image) of a fine pattern can be formed on the exposure medium  15 . 
     Moreover, it is preferable that the incidence plane of the spatial light modulator  30  has the same shape and size as the illumination zone LZ that is illuminated with coherent light beams by the illumination device  40 . In this case, coherent light beams from the illumination device  40  can be used for exposure of the exposure medium  15  at high efficiency. 
     The exposure medium  15  is, for example, a semiconductor wafer applied with a resist pattern. However, there is no limitation on the type of the exposure medium  15 . The exposure medium  15  may be a film applied with a photosensitizer. 
     The exposure medium  15  is provided as close as possible to the spatial light modulator  30 . Hereinbelow, the reason will be explained in detail. If the spatial light modulator  30  is, for example, a mask, and when coherent light beams are incident on an edge of the mask, the coherent light beams are diffracted at this edge, thereby a diffracted image is obtained. The effect of the diffracted image becomes larger as the gap between the spatial light modulator  30  and the exposure medium  15  becomes larger, so that an optical image originally from the mask becomes blurry. Therefore, in this basic embodiment, in order to reduce the effect of a diffracted image, the exposure medium  15  is provided as close as possible to the spatial light modulator  30 . 
     As explained above, since the exposure medium  15  has to be provided as close as possible to the spatial light modulator  30 , the spatial light modulator  30  is limited to a transmission-type element, such as a reticle or liquid crystal microdisplay, a reflection-type element being difficult to be installed. 
       FIG. 2  is a view explaining an operational principle of the illumination device  40  of  FIG. 1 . In  FIG. 2 , in order for easy explanation, only some components of the illumination device  40  are shown. Hereinafter, the basic operational principle of the illumination device  40  of  FIG. 1  will be explained using  FIG. 2 . 
     The hologram recording medium  55  of the optical device  50  can receive coherent light beams emitted from the irradiation unit  60  as reproduction illumination light beams La and diffract the coherent light beams at high efficiency. Above all, the hologram recording medium  55  is configured to be capable of reproducing an image  5  of a scattering plate  6  in the illumination zone LZ by diffracting coherent light beams incident on its respective positions, in other words, respective micro zones which should be called respective points. 
     The irradiation unit  60  is configured so that the scanning device  65  uses coherent light beams emitted to the hologram recording medium  55  to scan the hologram recording medium  55 . Therefore, at a moment, the irradiation unit  60  irradiates a micro zone on the surface of the hologram recording medium  55  with a coherent light beam. 
     Coherent light beams emitted from the irradiation unit  60  to scan the hologram recording medium  55  are incident on respective positions, i.e. respective points or respective zones on the hologram recording medium  55  at an incident angle that satisfies diffraction conditions of the hologram recording medium  55 . Coherent light beams incident on respective positions of the hologram recording medium  55  from the irradiation unit  60  are diffracted by the hologram recording medium  55  to illuminate the specific zones that are overlapped with one another at least partially. Above all in the embodiment described here, coherent light beams incident on respective positions of the hologram recording medium  55  from the irradiation unit  60  are diffracted by the hologram recording medium  55  to illuminate the same illumination zone LZ. In more detail, as shown in  FIG. 2 , the coherent light beams incident on respective positions of the hologram recording medium  55  from the irradiation unit  60  reproduce the image  5  of the scattering plate  6  in a manner that the image  5  is superimposed on the illumination zone LZ. Namely, each coherent light beam incident on each position of the hologram recording medium  55  from the irradiation unit  60  is diffused, i.e. spread by the optical device  50  to be incident on the illumination zone LZ. 
     As for the hologram recording medium  55  that enables the diffraction of coherent light beams described above, in the example shown, a transmission-type volume hologram using photopolymer is used.  FIG. 3  is a view explaining a state in which an image of a scattering plate is generated on the hologram recording medium  55  as interference fringes. Here, the scattering plate  6  is a reference member for scattering light and it does not matter what a configuration the scattering plate  6  has. 
     As shown in  FIG. 3 , the hologram recording medium  55  is produced using scattered light beams from an actual scattering plate  6  as object beams Lo.  FIG. 3  shows a state in which a hologram photosensitive material  58  that has photosensitivity to become the hologram recording medium  55  is exposed by reference beams Lr and object beams Lo, both being coherent light beams that show coherence to each other. 
     As for the reference beams Lr, for example, laser beams from a laser source that oscillates laser beams in a specific wavelength range are used. The reference beams Lr pass through a condenser element  7  made of a lens and are incident on the hologram photosensitive material  58 . In the example shown in  FIG. 3 , laser beams to become the reference beams Lr are incident on the condenser element  7  as a parallel light flux that is parallel with the optical axis of the condenser element  7 . By passing through the condenser element  7 , the reference beams Lr are shaped, i.e. converted, from a parallel light flux into a convergent light flux and incident on the hologram photosensitive material  58 . On this occasion, a focal point FP of the convergent light flux Lr is located at a position beyond the hologram photosensitive material  58 . In other words, the hologram photosensitive material  58  is located between the condenser element  7  and the focal point FP of the convergent light flux Lr converged by the condenser element  7 . 
     Next, the object beams Lo are incident on the hologram photosensitive material  58  as scattered light from the scattering plate  6  made of opal glass, for example. In the example shown in  FIG. 3 , the hologram recording medium  55  to be produced is a reflection type and the object beams Lo are incident on the hologram photosensitive material  58  on the opposite side to the reference beams Lr. It is a precondition that the object beams Lo are coherent with the reference beams Lr. Therefore, for example, it is possible to separate laser beams oscillated by the same laser source and use one of the separated ones as the reference beams Lr and the other as the object beams Lo. 
     In the example shown in  FIG. 3 , a parallel light flux that is parallel with the direction of normal to the plate surface of the scattering plate  6  is incident on the scattering plate  6  and scattered, and then the scatted beams that have passed through the scattering plate  6  are incident on the hologram photosensitive material  58  as the object beams Lo. According to this method, when an isotropic scattering plate available at usually low cost is used as the scattering plate  6 , the object beams Lo from the scattering plate  6  can be incident on the hologram photosensitive material  58  at roughly constant intensity distribution. Moreover, according to this method, although depending on the degree of scattering by the scattering plate  6 , the object beams Lo can be easily incident on respective positions of the hologram photosensitive material  58  at roughly constant intensity from the entire region of a light-emitting surface  6   a  of the scattering plate  6 . In such a case, it is achievable that light beams incident on respective positions of the obtained hologram recording medium  55  reproduce images  5  of the scattering plate  6  at similar brightness and reproduced images  5  of the scattering plate  6  are observed at roughly constant brightness. 
     As described above, when the hologram photosensitive material  58  is exposed by the reference beams Lr and object beams Lo, interference fringes caused by the interference between the reference beams Lr and object beams Lo are generated and interference fringes of these light beams are recorded in the hologram photosensitive material  58  as some form of pattern, i.e. an refractive index modulation pattern, as one example in a volume hologram. Thereafter, an appropriate post-treatment corresponding to the type of the hologram photosensitive material  58  is applied, thereby obtaining the hologram recording medium  55 . 
       FIG. 4  is a view explaining a state in which an image of a scattering plate is reproduced using interference fringes formed in the hologram recording medium  55  obtained through an exposure process of  FIG. 3 . As shown in  FIG. 4 , the hologram recording medium  55  produced with the hologram photosensitive material  58  of  FIG. 3  meets its Bragg condition by means of light beams that have the same wavelength as the laser beams used in the exposure process and travel in a reverse direction of the reference beams Lr along an optical path of the reference beams Lr in the exposure process. Namely, as shown in  FIG. 4 , a diverging light flux that diverges from a reference point SP located with respect to the hologram recording medium  55  so as to have the same positional relationship as the relative position of the focal point FP in  FIG. 3  with respect to the hologram photosensitive material  58  in the exposure process and that has the same wavelength as the reference beams Lr in the exposure process is diffracted by the hologram recording medium  55  as the reproduction illumination light beams La, thereby creating the reproduced image  5  of the scattering plate  6  at a specific location with respect to the hologram recording medium  50  so as to have the same positional relationship as the relative position of the scattering plate  6  in  FIG. 3  with respect to the hologram photosensitive material  58  in the exposure process. 
     In this occasion, reproduction beams Lb. i.e. beams obtained by diffracting the reproduction illumination light beams La by the hologram recording medium  55 , for creating the reproduced image  5  of the scattering plate  6  reproduce respective points of the image  5  of the scattering plate  6  as beams travelling in the reverse direction of the optical path of the object beams Lo traveled towards the hologram photosensitive material  58  from the scattering plate  6  in the exposure process. As shown in  FIG. 3 , scattered beams Lo emitted from respective points of the light-emitting surface  6   a  of the scattering plate  6  in the exposure process are diffused, i.e. spread, to be incident on roughly entire region of the hologram photosensitive material  58 . Namely, on respective points of the hologram photosensitive material  58 , the object beams Lo from the entire region of the light-emitting surface  6   a  of the scattering plate  6  are incident. As a result, information of the entire light-emitting surface  6   a  is recorded at respective points of the hologram recording medium  55 . It is therefore possible that beams which form a diverging light flux from the reference point SP and function as the reproduction illumination light beams La are incident on respective points of the hologram recording medium  55  to reproduce the images  5  of the scattering plate  5  having the same contour as one another at the same location, i.e. the illumination zone LZ, respectively. 
     The light beams incident on the hologram recording medium  55  are diffracted in the direction of the illumination zone LZ, hence useless scattered light can be effectively restricted. Therefore, all of the reproduction illumination beams La incident on the hologram recording medium  55  can be effectively used for creating the image of the scattering plate  6 . 
     Next, the configuration of the irradiation unit  60  that emits coherent light beams to the optical device  50  made of the hologram recording medium  55  described above will be explained. In the example shown in  FIGS. 1 and 2 , the irradiation unit  60  is provided with the laser sources  61  generating coherent light beams and the scanning device  65  that changes the propagation direction of coherent light beams from the laser sources  61 . 
     The laser source  61  emits, for example, ultraviolet light. Or a plurality of laser sources  61  that emit laser beams of different wavelength ranges may be used. When a plurality of laser sources  61  are used, it is arranged that the same point on the scanning device  65  is irradiated with a laser beam from each laser source  61 . With this arrangement, the hologram recording medium  55  is illuminated with reproduction illumination light beams having illumination colors of the laser sources  61  mixed with one another. 
     Coherent light beams from the laser source  61  reflected by the scanning device  65  are incident on the hologram recording medium  55 , thereby an image  5  of the scattering plate  6  of an illumination color in accordance with a wavelength range of the laser source  61  being created on the entire region of the illumination zone LZ. 
     The scanning device  65  changes the propagation direction of a coherent light beam with time to direct the coherent light beam in different directions so that the coherent light beam does not travel in the same direction. This results in that the coherent light beam, the propagation direction of which is changed by the scanning device  65 , scans the incidence surface of the hologram recording medium  55  of the optical device  50 . 
     In the example shown in  FIG. 2 , the scanning device  65  includes a reflection device  66  having a reflection surface  66   a  rotatable about one axis line RA 1 .  FIG. 5  is a view explaining a scanning route of the scanning device  65 . As understood from  FIG. 5 , the reflection device  66  has a mirror device that has a mirror as the reflection surface  66   a  rotatable about one axis line RA 1 . The reflection device  66  is configured to change the orientation of the mirror  66   a  to change the propagation direction of the coherent light beams from the laser source  61 . In this occasion, as shown in  FIG. 2 , the mirror device  66  is provided so as to receive the coherent light beams from the laser source  61  roughly at the reference point SP. 
     A coherent light beam, for which final adjustments were made to its propagation direction by the mirror device  66 , can be incident on the hologram recording medium  55  of the optical device  50  as a reproduction illumination light beam La that can become one beam included in a diverging light flux from the reference point SP in  FIG. 4 . As a result, coherent light beams from the irradiation unit  60  scan the hologram recording medium  55  and coherent light beams incident on respective positions of the hologram recording medium  55  reproduce images  5  of the scattering plate  6  having the same contour on the same location, i.e. the illumination zone LZ. 
     As shown in  FIG. 5 , the reflection device  66  is configured to rotate the mirror  66   a  about one axis line RA 1 . In the example shown in  FIG. 5 , the rotation axis line RA 1  of the mirror  66   a  extends in parallel with the y-axis of the x-y axis unit, that is, the x-y axis unit having the x-y plane in parallel with the surface of the hologram recording medium  55 , defined on the surface of the hologram recording medium  55 . Then, the mirror  66   a  rotates about the axis line RA 1  that is in parallel with the y-axis of the x-y axis unit defined on the surface of the hologram recording medium  55 . Therefore, an incidence point IP of a coherent light beam from the irradiation unit  60  on the optical device  50  moves in a reciprocating motion in the direction parallel with the x-axis of the x-y axis unit defined on the surface of the hologram recording medium  55 . Namely, in the example shown in  FIG. 5 , the irradiation unit  60  emits a coherent light beam to the optical device  50  to scan the hologram recording medium  55  along a straight route. 
     The scanning device  65  including the mirror device  66  and other components is, as described above, a member rotatable about at least the axis line A 1  and configured with a MEMS, for example. The scanning device  65  periodically moves in rotational motion, however, there is no particular limitation on its rotational frequency as far as it can scan the optical device  50  with coherent light beams for at least one cycle or more during one exposure time. 
     As a practical problem, the hologram photosensitive material  58  may shrink when the hologram recording medium  55  is produced. In such a case, it is preferable to adjust the recording angles of coherent light beams to be entered to the optical device  50  from the irradiation unit  60  under consideration of the shrinkage of the hologram photosensitive material  58 . The wavelength of coherent light beams generated by the laser source  61  does not need to be precisely the same as the wavelength of the light beam used in the recording process of  FIG. 3  but may be roughly the same. 
     In a similar reason, even if the propagation direction of a light beam to be incident on the hologram recording medium  55  of the optical device  50  does not take precisely the same route as one beam included in a diverging light flux from the reference point SP, an image  5  can be reproduced in the illumination zone LZ. Actually, in the examples shown in  FIGS. 2 and 5 , the mirror, i.e. reflection plane  66   a  of the mirror device  66  of the scanning device  65  is inevitably displaced from its rotational axis line RA 1 . Therefore, when the mirror  66   a  is rotated about the rotational axis line RA 1  that does not pass through the reference point SP, a light beam to be incident on the hologram recording medium  55  may not be one of the beams that form a diverging light flux from the reference point SP. However, practically, an image  5  can be substantially reproduced in a manner that the image  5  is superimposed on the illumination zone LZ by means of coherent lights from the irradiation unit  60  having the shown configuration. 
     The scanning device  65  may not always necessarily reflect coherent light beams, but may refract or diffract coherent light beams, to scan the optical device  50  with the coherent light beams. 
     Effects of Basic Embodiment 
     Next, the functions of the exposure apparatus having the configurations described above will be explained. 
     Firstly, the irradiation unit  60  emits coherent light beams to the optical device  50  so as to scan the hologram recording medium  55  of the optical device  50 . Specifically, the laser source  61  generates coherent light beams having a specific wavelength that travel along a unidirection. These coherent light beams are emitted to the scanning device  65  to change their propagation directions. More specifically, the coherent light beams travel towards the hologram recording medium  55  at reflection angles in accordance with incident angles from the laser source  61 , respectively. 
     The scanning device  65  makes coherent light beams incident on respective positions on the hologram recording medium  55  at an incident angle that meets the Bragg conditions on the respective positions. As a result, the coherent light beams incident on the respective positions reproduce images  5  of the scattering plate  6  in a manner that the images  5  are superimposed on one another on the entire region of the illumination zone LZ by diffraction caused by interference fringes recorded in the hologram recording medium  55 . Namely, the coherent light beams incident on respective positions of the hologram recording medium  55  from the irradiation unit  60  are diffused, i.e. spread, by the optical device  50  to be incident on the entire region of the illumination zone LZ. In this way, the irradiation unit  60  illuminates the illumination zone LZ with coherent light beams. For example, if the laser source  61  has a plurality of laser sources  61  each emitting own color, an image  5  of the scattering plate  6  is reproduced at each color on the illumination zone LZ. Therefore, when these laser sources  61  emit light simultaneously, the illumination zone LZ is illuminated with white that is a mixture of three colors. 
     The position of incidence on the hologram recording medium  55  of coherent light beams from the scanning device  65  is shifted with time in each position by the operation of the scanning device  65 . 
     In this basic embodiment, an optical image can be created on the exposure medium  15  with speckles inconspicuous, as explained below. 
     According to Speckle Phenomena in Optics, Joseph W. Goodman, Roberts &amp; Co., 2006 cited above, it is effective to integrate parameters such as polarization, phase, angle and time to increase modes. The modes here are speckle patterns with no correlation one another. For example, when coherent light beams are projected onto the same screen in different directions from a plurality of laser sources  61 , modes exist in the same number as the laser sources  61 . Moreover, when coherent light beams are projected onto a screen in different directions per unit of time from the same laser source  61 , modes exist by the number of changes in the incidence direction of the coherent light beams during the time that is not covered by the resolution of human eyes. It is assumed that, if there are many of this mode, the interference patterns of light are superimposed on one another and averaged with no correlation, and as a result, speckles to be observed by eyes of an observer are inconspicuous. 
     In the irradiation unit  60  described above, coherent light beams are emitted to the optical device  50  to scan the hologram recording medium  55 . Although coherent light beams incident on respective locations of the hologram recording medium  55  from the irradiation unit  60  illuminate the entire region of the same illumination zone LZ, the illuminating direction of the coherent light beams to illuminate the illumination zone LZ are different from one another. And, since the position on the hologram recording medium  55  on which a coherent light beam is incident changes with time, the incidence direction of the coherent light beam on the illumination zone LZ also changes with time. 
     When considering the illumination zone LZ as the reference, a coherent light beam is always incident on each location of the illumination zone LZ, however, its incidence direction always changes. As a result, a light beam modulated by the spatial light modulator  30  is incident on the exposure medium  15  provided close to the spatial light modulator  30  that overlaps with the illumination zone LZ, while changing its optical path with time. 
     As described above, in this basic embodiment, a coherent light beam continuously scans the hologram recording medium  55 . Following to this, the incidence direction of a coherent light beam incident on the illumination zone LZ from the irradiation unit  60  via the optical device  50  also continuously changes. When the incidence direction of a coherent light beam to the illumination zone LZ from the optical device  50  changes slightly, for example, an angle less than 1°, a speckle pattern generated on the illumination zone LZ changes greatly, resulting in superimposition of speckle patterns with no correlation. In addition, the frequency of a scanning device  65  such as a MEMS mirror and a polygonal mirror actually on the market is usually several hundred Hz or higher and a scanning device  65  of frequency reaching several ten thousands Hz is not rare. 
     Accordingly, according to the basic embodiment, the incidence direction of a coherent light beam changes with time on each location on the illumination zone LZ and this change occurs at a speed that is not covered by the resolution of human eyes. Therefore, if a screen is placed in the illumination zone LZ, speckle patterns generated corresponding to respective scattering patterns are superimposed on one another and averaged to be observed by an observer. Accordingly, speckles become inconspicuous effectively to an observer who observes an image displayed on the screen. 
     According to the reason above, in this basic embodiment, the spatial light modulator  30  is provided at the location overlapping with the illumination zone LZ. Therefore, speckles become inconspicuous at any position on the spatial light modulator  30 . 
     Moreover, the exposure medium  15  is provided as closer to the spatial light modulator  30  as much as possible. Therefore, an optical image modulated by the spatial light modulator  30  can be guided to the surface of the exposure medium  15  as it is as much as possible. 
     However, if the surface of the spatial light modulator  30  is a mirror surface, coherent light beams from the hologram recording medium  55  are reflected at this mirror surface. If this reflected image is viewed by human eyes or taken by an imaging apparatus, the hologram recording medium  55  itself is viewed by an observer, hence speckles are viewed by the observer. The reason why speckles are viewed is that coherent light beams from the hologram recording medium  55  are diffused at a mirror surface, and hence a plurality of new speckles patterns cannot be generated. In other words, wavefronts from the hologram recording medium on which an identical wavefront is always generated at each point are returned and viewed by an observer as they are. 
     It is not so desirable that reflected light containing speckles are emitted from the spatial light modulator  30 . This is because such reflected light may give a bad effect to human eyes depending on laser intensity. 
     In order to avoid such reflected light, as indicated by a broken line in  FIG. 1 , a light diffusion device  21  may be provided between the hologram recording medium  55  and the spatial light modulator  30 . A representative example of the light diffusion device  21  is a relief-type or volume hologram recording medium. However, there is no particular limitation to the material of the light diffusion device  21 , as far as the surface is a diffusion surface. For example, glass formed into frosted glass, i.e. opaque on its one side may be used. Moreover, the light diffusion device  21  may be opal glass, a relief diffusion plate, a microlens array, etc. 
     With the light diffusion device  21  provided as described above, coherent light beams diffused by the light diffusion device  21  are incident on the spatial light modulator  30 , and hence speckles become inconspicuous on the surfaces of the spatial light modulator  30  and the exposure medium  15 , even if the surfaces are a mirror surface. 
     To each point on the hologram recording medium  55 , a coherent light beam always having a constant wavefront is emitted. However, on each point on the light diffusion device  21 , coherent light beams are incident from respective points of the hologram recording medium  55  at an angle varying with time. Therefore, the scattering characteristics are changing with time at each point of the light diffusion device  21 . That is, wavefronts that are different from one another with time can be successively generated. In contrast, on the spatial light modulator  30 , coherent light beams having wavefronts varying with time generated by the light diffusion device  21  are incident. Therefore, on the spatial light modulator  30 , scattering patterns of coherent light beams from the light diffusion device  21  are changing with time. As a result, even if a spatial light modulator having a mirror at its part is directly observed, speckles are superimposed on one another with time, and hence speckles become inconspicuous. 
     Conventionally, speckles observed by humans are not only speckles at the exposure medium  15  side caused by the scattering of coherent light beams on the exposure medium  15  but also speckles at the optical device  50  side that could occur due to the scattering of coherent light beams before being projected onto the exposure medium  15 . The speckle pattern generated at the optical device  50  side is also recognizable to an observer by being projected onto the exposure medium  15  via the spatial light modulator  30 . However, according to the basic embodiment described above, coherent light beams continuously scan the hologram recording medium  55  and each of the coherent light beams incident on respective locations on the hologram recording medium  55  illuminates the entire region of the illumination zone LZ on which the spatial light modulator  30  is provided. Namely, the hologram recording medium  55  creates new wavefronts different from the prior wavefronts that have formed speckle patterns, thereby illuminating a screen in a complex manner and uniformly via the illumination zone LZ and further the spatial light modulator  30 . By the creation of new wavefronts at the hologram recording medium  55 , speckle patterns generated at the optical device  50  side become invisible. 
     As described above, in the basic embodiment of the present invention, the scanning device  65  makes coherent light beams scan the hologram recording medium  55 , and coherent light beams emitted from the hologram recording medium  55  are incident on the spatial light modulator  30  that overlaps with the illumination zone LZ. Moreover, the exposure medium  15  is provided closer to the spatial light modulator  30 . Therefore, with an extremely simple configuration, coherent light beams can be guided to the exposure medium  15 , with speckles inconspicuous. 
     Moreover, with the light diffusion device  21  provided between the irradiation unit  60  and the spatial light modulator  30 , speckles can be inconspicuous to reflected light at the spatial light modulator  30 . 
     Applied Embodiment 
     It is a precondition in the exposure apparatus of  FIG. 1  that close exposure is performed without providing an image forming optical module between the spatial light modulator  30  and the exposure medium  15 . In contrast, an applied embodiment which will be explained below has a feature in that an image forming (projection) optical module is provided. 
       FIG. 6  is a view showing a schematic configuration of an exposure apparatus according to an applied embodiment of the present invention. In  FIG. 6 , the components common with  FIG. 1  are denoted by the same reference numerals, and different points will be mainly explained. 
     An exposure apparatus  10   a  of  FIG. 6  is provided with, like  FIG. 1 , the optical device  50 , the irradiation unit  60 , and the spatial light modulator  30 , and in addition, provided with an image forming module  25  disposed between the spatial light modulator  30  and the exposure medium  15 , and a light diffusion device  21  disposed between the irradiation unit  60  and the spatial light modulator  30 . 
     The image forming module  25  is to form an image of coherent light beams modulated by the spatial light modulator  30  on the exposure medium  15 . Having the image forming module  25  provided, scale-up or -down exposure is possible. 
     The light diffusion device  21  may not necessarily be essential in the exposure apparatus  10  of  FIG. 1  but essential in the exposure apparatus  10   a  of  FIG. 6 . Hereinbelow, the reason will be explained in detail. 
     Coherent light beams continuously scan the hologram recording medium  55 . Therefore, the incident angle of coherent light beams from the irradiation unit  60  to the illumination zone LZ continuously varies and the incident angle of coherent light beams from the optical device  50  to the exposure medium  15  also continuously varies. Therefore, when the surface of the exposure medium  15  is viewed by a human at a remote place, superimposed scattering patterns of coherent light beams having no correlation are viewed by human eyes. Accordingly, speckles generated corresponding to respective scattering patterns are superimposed on one another and averaged when observed by an observer, hence the speckles being inconspicuous. 
     However, different from a screen, the exposure medium  15  is to record an optical image from the spatial light modulator  30 . Recording an optical image on the exposure medium  15  is equivalent to recording an image viewed by human eyes when the hologram recording medium  55  is seen from the exposure medium  15 . The image forming module  25  exists between the exposure medium  15  and the spatial light modulator  30 . The points on the exposure medium  15  having an image formed thereon correspond to the respective points on the hologram recording medium  55  via the image forming module  25  and the spatial light modulator  30 , respectively. As described above, a coherent light beam always having a constant wavefront irrespective of time is emitted. Therefore, when the hologram recording medium  55  is seen from a point on the exposure medium  15 , a coherent light beam always having a constant wavefront is viewed, and since there is no factor to generate speckle patterns having no correlation, speckles being conspicuous. That is, an optical image containing speckles is undesirably recorded on the exposure medium  15 . 
     On the contrary, when the light diffusion device  21  is provided between the hologram recording medium  55  and the spatial light modulator  30 , coherent light beams are incident on each point of the light diffusion device  21  with the incident angle varying with time and light beams having scattering characteristics changing with time, that is, different wavefronts, are emitted from the light diffusion device  21 . This results in that coherent light beams emitted from respective points of the light diffusion device  21  have wavefronts changing with time. Therefore, coherent light beams having wavefronts changing with time are viewed when the light diffusion device  21  side is seen from respective points on the exposure medium  15 . Accordingly, speckles patterns having no correlation are superimposed on one another on the exposure medium  15 , hence speckles become inconspicuous. 
     For the reason above, in this applied embodiment, the light diffusion device  21  is provided between the hologram recording medium  55  and the spatial light modulator  30 . Ideally, it is preferable that an illumination zone for coherent light beams diffused by the optical device  50  is provided on the light diffusion device  21 . With this arrangement, diffused light beams from respective points of the optical device  50  are naturally incident on the light diffusion device  21 , as varying with time, hence speckles being inconspicuous when the optical device  50  side is seen from the exposure medium  15 . 
     It does not mean that the light diffusion device  21  can be provided at any place between the irradiation unit  60  and the spatial light modulator  30 . For example, if the light diffusion device  21  is provided close to the spatial light modulator  30 , in more specifically, provided within the length of a depth of field of the image forming module from the spatial light modulator  30 , an optical image of the light diffusion device  21  is inevitably recorded on the exposure medium  15 . On the other hand, if the light diffusion device  21  is provided out of the length of the depth of field of the image forming module  25  from the spatial light modulator  30 , an optical image of the light diffusion device  21  becomes completely blur, hence no possibility of forming an image on the exposure medium  15 . Therefore, it is desirable that the light diffusion device  21  is provided between the irradiation unit  60  and the spatial light modulator  30  but out of the length of the depth of field of the image forming module  25  from the spatial light modulator  30 . 
     However, when the light diffusion device  21  has a flat surface with relatively constant illuminance, such as opal glass, even if the light diffusion device  21  is provided within the length of the depth of field of the image forming module  25 , an image of the light diffusion device  21  may not affect the quality of exposure to the exposure medium  15 . Therefore, it is not essential to provide the light diffusion device  21  out of the length of the depth of field of the image forming module  25 . 
     As described above, in the applied embodiment of the present invention, the scanning device  65  makes coherent light beams scan the hologram recording medium  55 , and coherent light beams emitted from the hologram recording medium  55  are diffused by the light diffusion device  21 . Accordingly, the interference pattern of coherent light beams emitted from respective points of the light diffusion device  21  varies. Since coherent light beams emitted from the light diffusion device  21  are incident on the spatial light modulator  30 , speckles being inconspicuous on the spatial light modulator  30 . Therefore, even if the image forming module  25  is provided between the spatial light modulator  30  and the exposure medium  15 , speckles become inconspicuous. 
     (Other features of Exposure Apparatuses  10  and  10   a ) 
     The following are common to the exposure apparatuses  10  and  10   a  described above, which are referred to as an “exposure apparatus according to the present embodiment”, hereinbelow. 
     In Speckle Phenomena in Optics, Joseph W. Goodman, Roberts &amp; Co., 2006 mentioned above, a method using a numerical value corresponding to a speckle contrast (%) as a parameter to indicate the degree of speckles generated on a screen is proposed. The speckle contrast is the quantity defined as a value obtained by dividing the standard deviation of variation in intensity actually occurred on a screen by an average value of the intensity when a test-pattern image to originally show uniform intensity distribution is displayed. A larger value of the speckle contrast means a larger degree of generation of speckles on a screen and indicates to an observer that a spotted luminance-unevenness pattern is more remarkable. 
       FIG. 7  is a view showing results of measuring speckle contrasts in the cases where the hologram recording medium  55  described above was used and not used.  FIG. 7(   a ) shows a result obtained when a laser beam was directly emitted to the illumination zone LZ with no use of the scanning device  65  and the optical device  50 .  FIG. 7(   b ) shows a result obtained when a volume hologram produced having a diffusion angle of 20° was used as the optical device  50 .  FIG. 7(   c ) shows a result obtained when a relief diffusion plate was used as the optical device  50 .  FIG. 7(   d ) shows a result obtained when a singe-color LED light beam was directly emitted to the illumination zone LZ with the use of a singe-color LED, instead of the laser source  61 , as the irradiation device  60 . 
     When it is considered that a speckle contrast of 5 or lower is a reference index indicating an allowable speckle noise in a display apparatus or the like, in the present embodiment of the present invention shown in  FIG. 7(   b ), a speckle contrast was lower than 4, and hence extremely favorable result was obtained. 
     The problem of generation of speckles is practically a problem unique to the case of using a coherent light source of a laser beam or the like, and thus, the problem needs not be considered in the case of an apparatus using an incoherent light source such as an LED. However, according to  FIG. 7 , the present embodiment is superior to the case using a singe-color LED concerning the speckle contrast. The reason may be that the light diffusion device  21  is not used for illumination for a singe-color LED. As described above, It can be said that the exposure apparatuses  10  and  10   a  according to the present embodiment sufficiently dealt with the speckle defect. 
     In addition, according to the present embodiment described above, the following advantages can be obtained. 
     According to the present embodiment described above, the optical device  50  for making speckles inconspicuous can also function as an optical member for reshaping and adjusting the beam shape of a coherent light beam emitted from the irradiation device  60 . Therefore, it is possible to miniaturize and simplify the optical module. 
     Moreover, according to the present embodiment described above, coherent light beams incident on specific points in respective recording areas of the hologram recording medium  55  create images  5  of the scattering plate  6  in respective colors on the entire region of the illumination zone LZ and the spatial light modulator  30  is provided so that it is overlapped with the image  5 . Therefore, it is possible to utilize all of the light beams diffracted by the hologram recording medium  55  for image creation, thus excellent in utilization efficiency of light beams from the laser sources  61 . 
     The spatial light modulator  30  according the applied embodiment may be a transmission-type or reflection-type photomask, a micro-mirror device or a reflective-type LCOS (Liquid Crystal On Silicon). 
     Second Embodiment 
       FIG. 8  is a view showing a schematic configuration of an exposure apparatus according to a second embodiment of the present invention. An exposure apparatus  10  of  FIG. 8  is provided with an irradiation unit  60 , an optical device  50 , a first diaphragm  31 , a condensing optical module  32 , a spatial light modulator  30 , and an image forming module  25 , for exposing an image formed on the spatial light modulator  30  on an exposure member (exposure medium)  15 . It is defined in  FIG. 8  that the surface of the exposure member  15  is an X-Y plain and the axis orthogonal to the surface is a Z-axis. 
     The irradiation unit  60  is an optical module for illuminating the optical device  50  as an illumination zone. The irradiation unit  60  illuminates the optical device  50  with illumination light beams Lb that are emitted in a direction varying with time, at a varying incident angle with respect to the effective area of the optical device  50 . In this case, it is required that, by varying the direction of the illumination light beams Lb with time, the illumination light beams Lb emitted at respective times are superimposed on one another with time, thereby illuminating the entire region of the effective area of the optical device  50 . However, preferably, the illumination light beams Lb always illuminate the effective area of the optical device  50 , that is, the entire region in the optical device  50  required for forming an image to the exposure member  15 , irrespective of the emitting direction of the illumination light beams Lb. Accordingly, it is possible to give uniform brightness to an image to be formed. A variety of types of configuration can be adopted to the detailed configuration of the irradiation unit  60 , which will be explained later.  FIG. 8  shows illumination light beams Lb(t 1 ) and Lb(t 2 ) around the outermost section. Actually, the direction of the illumination light beams Lb continuously varies between Lb(t 1 ) and Lb(t 2 ). 
     The optical device  50  is an optical device for diffusing incident light. For example, glass formed into frosted glass, i.e. opaque on its one side, opal glass or a random phase diffusion plate is used as the optical device  50 . Moreover, a hologram, a microlens array, etc. may be used as the optical device  50 . In the present embodiment, by providing such optical device  50 , coherent light beams diffused by the optical device  50  are incident on the spatial light modulator  30 , thereby speckles generated at the spatial light modulator  30  and other optical components becoming inconspicuous. 
     The condensing optical module  32  is an optical device for converging coherent light beams emitted from the optical device  50  onto an illumination zone of the spatial light modulator  30 . In the present embodiment, light utilization efficiency is improved by converging coherent light beams emitted from the optical device  50  onto an illumination zone. With the first diaphragm  32  provided near the optical device  50  and a second diaphragm  25   b  provided near the image forming module  25  as a pair, the condensing optical module  32  gives uniform image-forming characteristics to all positions of the spatial light modulator  30 . The first diaphragm  32  may be formed with the optical device  50  or the edge of the effective area of the optical device  50 . 
     The spatial light modulator  30  is, for example, a transmission-type or a reflection-type reticle (photomask). In this case, an optical image corresponding to a reticle pattern is formed on the surface of the exposure member  15 , thus being able to be used as an exposure apparatus for fabricating a semiconductor device. Instead of a photomask, a display device, such as a liquid crystal microdisplay, for forming an image based on an input video signal may be used as the spatial light modulator  30 . Also in this case, the display device may be a transmission-type or a reflection-type. The spatial light modulator  30  illuminated by the optical device  50  selects coherent light beams to pass therethrough or to be reflected per pixel, thereby forming a modulated image (optical image) of a fine pattern on the exposure member  15 . 
     The exposure member  15  is, for example, a semiconductor wafer for forming a resist pattern. There is no particular limitation on the type of the exposure member  15 . The exposure medium  15  may be a film applied with a photosensitizer. 
     The image forming module  25  is an optical device for forming an image created on the spatial light modulator  30  on the exposure member  15  and exposing the formed image. In the present embodiment, the image forming module  25  includes a pair of convex lenses  25   a  and  25   c , and the second diaphragm  25   b  provided therebetween. As described above, the second diaphragm  25   b  is used as a pair with the first diaphragm  31  provided near the optical device  50 . 
     The irradiation unit  60  of the exposure apparatus in  FIG. 8  illuminates the entire region of the effective area of the optical device  50 , with the incident angle varying with time. It is preferable for realizing uniform brightness that the effective area of the optical device  50  is set to be an area that is always illuminated, irrespective of the direction of the illumination light beams Lb emitted from the irradiation unit  60 . 
     Emitted beams from the optical device  50  illuminate spatial light modulator  30  via the condensing optical module  32 . In this occasion, the condensing optical module  32  illuminates the entire region of the illumination zone of the spatial light modulator  30 . Illumination light beams Lb are incident on the optical device  50  at an incident angle varying with time. Therefore, diffused light beams emitted from the optical device  50  illuminate the spatial light modulator  30  at an angle also varying with time. Accordingly, speckles generated on the illumination zone of the spatial light modulator  30  are superimposed on one another and averaged within an exposure time that is an illumination time to the exposure member  15 . As a result, it is possible to restrict illumination unevenness occurred on the exposure member  15  so that an image created on the spatial light modulator  30  can be exposed on the exposure member  15  at high accuracy. 
     [Avoidance of Zero-Order Light] 
     Part of coherent light beams from the irradiation unit  60  is not diffracted by the hologram recording medium  55  but passes though it. This type of light is called zero-order light. When zero-order light is incident on the illumination zone LZ, an abnormal region, i.e. a spotted region, a line region, and a plane region, inevitably appears in which brightness, i.e. intensity, is rapidly increased compared with the surroundings. 
     When the reflection-type hologram recording medium  55 , hereinafter, “reflection-type holograms”, is used, the spatial light modulator  30  and the projection optical module  25  are not arranged in a propagation direction of zero-order light, hence it is relatively easy to avoid zero-order light. However, when the transmission-type hologram recording medium  55 , hereinafter, “transmission-type holograms” is used, it is highly likely that the spatial light modulator  30  and the projection optical module  25  are arranged in a propagation direction of zero-order light, hence care must be taken. Specifically, it is required to design the location of the scanning device  65 , the spatial light modulator  30 , and the projection optical module  25  so as to be arranged in accordance with the propagation path of zero-order light so that the zero-order light does not pass through the spatial light modulator  30 , the projection optical module  25 , etc. 
     [Reflection- and Transmission-type Hologram Recording Media] 
     Reflection-type holograms show higher wavelength selectivity than transmission-type holograms. In other words, in reflection-type holograms, although interference fringes corresponding to different wavelengths are superimposed on one another in layers, a coherent light beam having a desired wavelength can be diffracted by a desired layer only. In addition, reflection-type holograms are excellent in that the influence of zero-order light can be easily removed. 
     On the other hand, although transmission-type holograms have a wide spectrum range for diffraction and a high acceptable level to the laser source  61 , if interference fringes corresponding to different wavelengths are superimposed on one another in layers, layers other than a desired layer also diffract coherent light of a desired wavelength. Therefore, in general, it is difficult to configure transmission-type holograms in a layered structure. 
     (Irradiation Device  60 ) 
     The embodiments described above show an example in which the irradiation unit  60  includes the laser sources  61  and the scanning device  65 . In the example, the scanning device  65  includes the one-axis-rotation type mirror device  66  that changes the propagation direction of a coherent light beam by reflection. However, the scanning device  65  is not limited thereto. As shown in  FIG. 9 , the scanning device  65  may be configured so that the mirror, i.e. reflection plane  66   a , of the mirror device  66  can rotate about the first rotation axis line RA 1  as well as about a second rotation axis line RA 2  intersecting the first rotation axis line RA 1 . In the example shown in  FIG. 9 , the second rotation axis line RA 2  of the mirror  66   a  is perpendicular to the first rotation axis line RA 1  which is extended in parallel to the Y axis of the XY coordinate unit defined on the plate plane of the hologram recording medium  55 . Then, since the mirror  66   a  can rotate about both of the first axis line RA 1  and the second axis line RA 2 , the incidence point IP of a coherent light beam of the irradiation unit  60  incident on the optical device  50  can be shifted on the plate plane of the hologram recording medium  55  in two-dimensional directions. Therefore, as an example, as shown in  FIG. 9 , the incidence point IP of a coherent light beam incident on the optical device  50  can be shifted along a circumference. 
     Moreover, the scanning device  65  may include two or more mirror devices  66 . In this case, although the mirror  66   a  of the mirror device  66  can rotate about only a single axis line, the incidence point IP of a coherent light beam from the irradiation device  60  incident on the optical device  50  can be shifted on the plate plane of the hologram recording medium  55  in two-dimensional directions. 
     As a concrete example of the mirror device  66   a  included in the scanning device  65 , there are a MEMS mirror, a polygonal mirror, and the like. 
     Moreover, the scanning device  65  may be configured to include other devices other than a reflection device, for example, the mirror device  66  described above, which changes the propagation direction of a coherent light beam by reflection. For example, the scanning device  65  may include a refraction prism, a lens, etc. 
     Essentially, the scanning device  65  is not a necessary component. The light source  61  of the irradiation device  60  may be configured so that it can be displaced, i.e. moved, oscillated, and rotated, with respect to the optical device  50 . Coherent light beams emitted from the light source  61  may scan the hologram recording medium  55  in accordance with the displacement of the light sources  61  with respect to the optical device  50 . 
     Moreover, although the description hereinbefore is made on condition that the light sources  61  of the irradiation device  60  oscillate a laser beam shaped into a line beam, the preset invention is not limited thereto. Particularly, in the embodiments described above, coherent light beams emitted to respective positions of the optical device  50  are shaped by the optical device  50  into a light flux which is incident on the entire region of the illumination region LZ. Therefore, no problem occurs even if coherent light beams emitted from the light sources  61  of the irradiation device  60  to the optical device  50  are not accurately shaped. For this reason, coherent light beams generated from the light sources  61  may be diverging light. In addition, the shape of coherent light beams, in cross section, generated from the light sources  61  may be an ellipse or the like instead of a circle. In addition, the transverse mode of coherent light beams generated from the light sources  61  may be a multi-mode. 
     In addition, when the light source  61  generates a diverging light flux, coherent light beams are incident on the hologram recording medium  55  of the optical device  50  not on a spot but on a region having a certain area. In this case, light beams which are diffracted by the hologram recording medium  55  and incident on respective positions of the illumination region LZ are angularly-multiplexed. In other words, in each instant, on respective positions of the illumination region LZ, coherent light beams are incident from directions within a certain angle range. Due to the angle-multiplexing, it is possible to more effectively make speckles inconspicuous. 
     Moreover, in the embodiments described above, although the example is described in which the irradiation unit  60  emits a coherent light beam to the optical device  50  so that the coherent light beam traces the optical path of one beam included in a light flux, the present invention is not limited thereto. For example, in the above embodiments, as shown in  FIG. 10 , the scanning device  65  may further include a condenser lens  67  disposed at the downstream side of the mirror device  66  along the optical path of a coherent light beam. In this case, a light beam from the mirror device  66 , which propagates along the optical path of light beams of a light flux, becomes a light beam that propagates in a certain direction through the condenser lens  67 . In other words, the irradiation device  60  emits a coherent light beam to the optical device  50  so that the coherent light beam traces the optical path of one beam included in a light flux. In this kind of example, instead of a converging light flux described above, a parallel light flux is used as the reference light beam Lr in the recording process in the production of the hologram recording medium  55 . The hologram recording medium  55  described above can be more simply produced and replicated. 
     (Optical Device  50 ) 
     In the embodiments described above, although the example in which the optical device  50  is configured with a reflection-type volume hologram recording medium  55  using photopolymer has been described, the present invention is not limited thereto. Moreover, the optical device  50  may include a volume hologram recording medium that is a type in which recording is performed by using a photosensitive medium including a silver halide material. Moreover, the optical device  50  may include a transmission-type volume hologram recording medium  55  or a relief-type, i.e. emboss-type hologram recording medium  55 . 
     With respect to the relief-type, i.e. emboss-type, hologram recording medium, a hologram interference fringe is recorded using a convex-concave structure of the surface thereof. However, in the case of the relief-type hologram recording medium, scattering due to the convex-concave structure of the surface may cause generation of new speckles, hence in this respect, the volume hologram recording medium is preferable. In the case of the volume hologram recording medium, a hologram interference fringe is recorded as a refractive index modulation pattern, i.e. refractive index distribution, of an inner portion of the medium, hence there is no influence of scattering because of the convex-concave structure of the surface. 
     However, even when the volume hologram recording medium is used, a type in which recording is performed using a photosensitive medium including a silver halide material may become a cause of generating new speckles due to scattering of silver halide particles. In this respect, the volume hologram recording medium using a photopolymer is preferable as the hologram recording medium  55 . 
     Moreover, in the recording process shown in  FIG. 3 , although a so-called Fresnel-type hologram recording medium  55  is produced, a Fourier transform-type hologram recording medium  55  which can be obtained through recording using lenses may be produced. When the Fourier transform-type hologram recording medium  55  is used, lenses can also be used for image reproduction. 
     In addition, a striped pattern, i.e. refractive index modulation pattern or convex-concave pattern, which is to be formed on the hologram recording medium  55  may be designed by using a computer based on a planned wavelength or incidence direction of a reproduction illumination light beam La, a shape or position of an image to be reproduced, and the like, without use of an actual object light beam Lo and reference light beam Lr. The hologram recording medium  55  obtained in this manner is called a computer generated hologram recording medium. Moreover, when a plurality of coherent light beams having mutually different wavelength ranges are emitted from the irradiation device  60  in a similar manner in the modification described above, the hologram recording medium  55  as a computer generated hologram recording medium may be partitioned two-dimensionally into a plurality of regions provided corresponding to coherent light beams of respective wavelength ranges so that the coherent light beams of the respective wavelength ranges are diffracted in the corresponding regions to reproduce images. 
     Moreover, in the embodiments described above, although the example is described in which the optical device  50  includes the hologram recording medium  55  by which coherent light beams emitted to respective positions thereof are spread to illuminate the entire region of the illumination region LZ, the present invention is not limited thereto. Instead of the hologram recording medium  55  or in addition to the hologram recording medium  55 , the optical device  50  may include a lens array as an optical device by which the propagation directions of coherent light beams incident on respective positions thereof are changed and the coherent light beams are diffused to illuminate the entire region of the illumination region LZ. As a concrete example of the lens array, a total reflection-type or refraction-type Fresnel lens having a diffusing function, a fly-eye lens, and the like may be exemplified. In this type of illumination device  40 , the irradiation device  60  and the optical device  50  may be configured so that the irradiation device  60  emits coherent light beams to the optical device  50  so that the coherent light beams scan the lens array and the coherent light beams incident on respective positions of the optical device  50  from the irradiation device  60  illuminate the illumination region LZ while the propagation directions of the coherent light beams are changed by the lens array, thus effectively making speckles inconspicuous. 
     Third Embodiment 
       FIG. 11  is a view showing a schematic configuration of an irradiation unit  60  using a lens array according to a third embodiment. The irradiation unit  60  in the present embodiment has a light source  61 , a scanning device  65 , a first light-path converting module  62 , a lens array  63 , and a second light-path converting module  64 . Also in the embodiment, an exposure apparatus can be configured by using components of the irradiation unit  60  except for the light source  61 . In this case, the first light-path converting module  62  is not an essential component. 
     The detailed configurations of the light source  61 , the scanning device  65 , etc. are similar to those of the embodiments described above, hence the explanation thereof is omitted. It is preferable to provide a beam shaping means for making intensity distribution uniform in the cross section of coherent light beams emitted from the light source  61 . As an design example, the beam shaping means may be provided to make intensity distribution uniform on a plane in the vicinity of the scanning device  65 , with this plane and a one-dimensional light modulator plane being set as a pair to function in conjunction with each other, thereby possible to illuminate an illumination zone with constant intensity. 
     The scanning device  65  in the present embodiment has a rotation center Ra in the a direction of the y-axis, to perform one-dimensional scanning of coherent light beams in the X-Z plane. Also in this case, it is required to scan the incidence plane of the lens array  63  and, as a result, sufficiently illuminate an illumination zone. 
     Coherent light beams incident on the scanning device  65  from the light source  61  become scanning light beams La having the direction varying with time and are incident on the lens array  63  via the first light-path converting module  62 .  FIG. 11  shows scanning light beams La(t 1 ) and La(t 2 ) in the vicinity of the outermost edge. However, practically, the scanning light beams La are shifted continuously between La(t 1 ) and La(t 2 ). 
     The first light-path converting module  62  is an optical device to change the light path of the scanning light beams La from the scanning device  65  so that the scanning light beams La are incident on the incidence plane of the lens array  63  roughly vertically. The first light-path converting module  62  is configured with a convex lens or the like having a light converging function. Scanning light beams La′ for which the light path has been changed are incident on respective lens elements of the lens array  63  vertically so that the scanning light beams La′ are incident on the respective lens elements under the same condition. Therefore, it is possible to reduce the burden of design such as designing the lens elements of the lens array  63  equally. The first light-path converting module  62  may not always necessarily be provided. The first light-path converting module  62  can be omitted by modifying the lens elements of the lens array  63  or the later-stage optical module in accordance with the state of incident light. 
     The lens array  63  is an optical device having a plurality of lens elements arranged on scanning positions (X-Y plane) of light beams by the scanning device  65 , to convert a scanning light beam La′ incident on each lens element to a diffused light beam. The size and shape of each lens element of the lens array  63  can be set freely according to need. For example, a cylindrical lens array having cylindrical lenses as the lens elements or a micro lens array having very small lens elements can be used. 
     In the present embodiment, a plurality of stages (two stages) of lens elements are arranged in the optical-axis direction (Z-axis direction). Coherent light beams emitted from the light source  61  may not always be a parallel beam but may contain scattering components little bit deviated from a parallel state. In the present embodiment, scattering components can be restricted by arranging a plurality of stages of lens elements in the optical-axis direction. The lens elements arranged in the optical-axis direction have an equal diameter and center axes all equally oriented in the light propagating direction. The lens array  63  may have lens elements each with one stage of lens element in the in the optical-axis direction. 
     The second light-path converting module  64  (a light-path converting module in the present invention) is an optical device for illuminating the optical device  50  as an illumination zone with illumination light beams Lb emitted from the lens array  63 . Illumination light beams Lb emitted from respective points of the lens array  63  caused by optical scanning of the scanning device  65  illuminate the illumination zone as superimposed on one another with time via the second light-path converting module  64 . It is preferable that the second light-path converting module  64  has a light converging function so that diffused light beams Lb′ emitted from the lens array  63  illuminate the effective area of the optical device  50  as an illumination zone. The utilization efficiency of light beams is improved by restricting the diffusion angle of diffused light beams Lb diffused by the lens array  63  so that the light beams are converged on the effective area of the optical device  50 . Moreover, it is preferable that the second light-path converting module  64  converts the diffused light beams into a parallel beam or a roughly parallel beam. By illuminating the effective area of the optical device  50  with a parallel beam or an almost parallel beam, it is possible to illuminate respective points of the effective area under almost same condition. For example, it is possible to uniformly illuminate the entire region of the effective area. 
     It is sufficient for the second light-path converting module  64  to have a function of restricting the diffusion angle. The second light-path converting module  64  is configured with a combination of lenses, concave mirrors, mirrors, prisms, etc. The second light-path converting module  64  may further be configured with a hologram device, a diffraction device, etc. having the equivalent function to above or may be configured with a combination of these devices. 
     It is sufficient for illumination light beams Lb emitted from the second light-path converting module  64  to illuminate at least part of the effective area of the optical device  50  at each instant and illuminate the entire region of the effective area by scanning of the scanning device  65 . However, it is preferable that the illumination light beams Lb illuminate the entire region of the effective area at each instant. With such configuration, it is possible to have uniform luminance distribution on the effective area of the optical device  50 . 
     Also with the irradiation unit  60  in the present embodiment, it is possible to illuminate the effective area of the optical device  50  with coherent light beams superimposed on one another with time, having the incident angle to each point of the effective area varying with time. As a result, diffused light beams emitted from the optical device  50  are averaged on the spatial light modulator  30  to restrict the generation of speckles which results in that irradiation unevenness of an image formed on the exposure member  15  is prevented and an image formed on the spatial light modulator  30  is accurately exposed by the exposure member  15 . 
     (Illuminating Method) 
     In the first to third embodiments described above, an example is shown in which the irradiation device  60  is configured to be able to scan the optical device  50  in a one-dimensional direction with coherent light beams and the hologram recording medium  55  or the lens array of the optical device  50  is configured to diffuse, i.e. spread and diverge the coherent light beams incident on respective positions of the hologram recording medium  55  in a two-dimensional direction, so that the illumination device  40  illuminates the two-dimensional illumination region LZ. However, as described above, the present invention is not limited to such example. For example, the irradiation device  60  may be configured to be able to scan the optical device  50  in a two dimensional direction with coherent light beams and the hologram recording medium  55  or the lens array of the optical device  50  may be configured to diffuse, i.e. spread and diverge, the coherent light beams incident on respective positions of the hologram recording medium  55  in a two-dimensional direction, so that the illumination device  40  illuminates the two-dimensional illumination region LZ, as shown in  FIG. 9 . 
     Moreover, as already described, the irradiation device  60  may be configured to be able to scan the optical device  50  in a one-dimensional direction with coherent light beams and the hologram recording medium  55  or the lens array of the optical device  50  may be configured to diffuse, i.e. spread and diverge, the coherent light beams incident on respective positions of the hologram recording medium  55  in a one-dimensional direction, so that the illumination device  40  illuminates the one-dimensional illumination region LZ. In this configuration, the scanning direction of a coherent light beam from the irradiation unit  60  and the diffusing direction, i.e. spreading direction, by the hologram recording medium  55  or the lens array of the optical device  50  may be parallel with each other. 
     Furthermore, the irradiation device  60  may be configured to be able to scan the optical device  50  in a one- or two-dimensional direction with coherent light beams and the hologram recording medium  55  or the lens array of the optical device  50  may be configured to diffuse, i.e. spread and diverge, the coherent light beams incident on respective positions of the hologram recording medium  55  in a one-dimensional direction. In this configuration, as already described, the optical device  50  may have a plurality of hologram recording media  55  or lens arrays to illuminate illumination zones LZ corresponding to the hologram recording media  55  or lens arrays successively, so that the illumination device  40  illuminates a two-dimensional region. In this occasion, the illumination zones LZ may be successively illuminated at a speed felt like as if simultaneously illuminated for human eyes or at a low speed so that human eyes can recognize that the illumination zones LZ are successively illuminated. 
     The present invention is not limited to the embodiments described above but includes various modifications conceivable by those skilled in the art. The effects of the present invention are also not limited to those described above. Namely, various additions, modifications and partial omissions may be made without departing from the conceptual idea and gist of present invention derived from those defined in the accompanying claims and their equivalents.