Patent Publication Number: US-2006018560-A1

Title: Exposure device and exposure method

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority under 35 USC 119 from Japanese Patent Application Nos. 2004-203118 and 2005-010237, the disclosure of which is incorporated by reference herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an exposure device and an exposure method, and more particularly relates to an exposure device and exposure method which are capable of exposing an image with accurate focus, without “focal shift” occurring even if a workpiece features reference holes, land holes or the like.  
      2. Description of the Related Art  
      In recent years, as examples of image recording devices, various exposure devices have been proposed which perform image exposure with a light beam modulated in accordance with image data, utilizing a spatial light modulator (SLM) such as a digital micromirror device (DMD) or the like (see, for example Non-Patent References 1 and 2). A DMD has a structure in which, for example, a large number of very small micromirrors are provided on memory cells of an SRAM. Angles of reflective surfaces of the micromirrors are changed by electrostatic forces caused by charges accumulated at the memory cells. In practice, when imaging is to be performed, image data is written to the SRAM and, in this state, the micromirrors are set to predetermined angles and directions of reflection of light are set to desired directions.  
      A field of application of this exposure device is, for example, the fabrication of substrates of flat-panel displays such as liquid crystal displays, plasma displays and the like, or the fabrication of printed circuit boards.  
      As an exposure device for fabrication of panels or printed circuit boards or the like, there is a multi-head exposure device at which, with a view to widening an exposure range, exposure heads featuring DMDs are plurally arranged along a direction of conveyance of a substrate and along a direction intersecting the direction of conveyance.  
      At this multi-head exposure device, detection sections and an adjustment section are provided (see Japanese Patent No. 3,305,448). The detection sections measure displacements of the substrate at a plurality of measurement points. The adjustment section adjusts a positional relationship between an imaging plane of a projecting optical system, such as an exposure head, and the substrate on the basis of displacement data measured by the detection section. By maintaining focus using such means, correction is performed for exposure which responds to unevenness of the substrate surface, variations in thickness and the like.  
      Generally, reference holes are formed in the substrate as reference points for positioning the substrate at the multi-head exposure device. Further, holes, grooves and the like for mounting of various components at the workpiece, known as land holes, may be provided. In the present specification, the term “holes” includes such holes and indentation steps.  
      However, when a substrate in which these reference holes and the like are formed is exposed using the above-described multi-head exposure device, when displacements of the substrate in a Z direction (a substrate thickness direction) are measured with laser displacement meters provided at the detection sections, laser light irradiated from the laser displacement meters may pass through the reference holes and the like.  
      Furthermore, measurement ranges of the detection sections on the substrate are points which are set apart, with surroundings of the measurement points being focus-adjusted in accordance with the measurement results of the measurement points. In particular, in an X direction (the direction intersecting the direction of movement of the substrate), a spacing between measurement points is simply a spacing between detection sections. Consequently, spacings between respective measurement points are wider in the X direction.  
      In consequence, raw displacement measurement results measured by a detection section may include displacements of reference holes and the like. As a result, if displacement data is generated and focus adjustment performed using such displacement measurement results in the raw state, where a measurement point of the detection section is a hole, a recess portion or the like, a region peripheral thereto may be exposed with focusing which is matched to the measurement point. Moreover, in the conventional technology described above, there is a problem in that, depending on a degree of unevenness, it may be difficult to distinguish between machined holes, recess portions, etc. and warping of the substrate, and appropriate responses may not be possible.  
     SUMMARY OF THE INVENTION  
      An exposure device and exposure method are demanded, which are capable of exposing a workpiece such as a substrate or the like with accurate focus, even if the workpiece is provided with holes, such as reference holes and the like, and/or indentation portions and the like.  
      In order to solve the problems described above, a first aspect of the invention relates to an exposure device for exposing a photosensitive material with an exposure section which emits a light beam modulated in accordance with image data while the photosensitive material is relatively moved, the exposure device including: a hole position identification section, which determines a position of a hole in an exposure surface of the photosensitive material; a focusing section, which performs focusing control for causing a focusing position of the light beam from the exposure section to coincide with the exposure surface; and a displacement data generation section, which generates displacement data for the focusing control by the focusing section, excluding a position which is determined, on the basis of results of determination by the hole position identification section, to be the hole.  
      The holes may be, as described earlier, reference holes (alignment marks) which are used for alignment of a workpiece, land holes for mounting various components at the workpiece, and so forth. All of these are considered as holes. Further, in addition to holes, protrusion portions (which may be alignment marks) may also be considered thus. That is, it is possible for the displacement data generation section to generate displacement data for regions excluding portions of unevenness.  
      The workpiece may be a single-layer or multi-layer printed circuit board including a photosensitive layer, a flat panel display substrate, a rigid-flexible substrate (a flexible circuit board), a sheet-form or strip-form printed wiring board (PWB), a display device substrate, a liquid crystal cell formation structure, a filter or the like (these are hereafter referred to as the photosensitive material). Further, types of a photosensitive layer include photoresists, materials which are cured by light, materials which can be developed by light, and so forth.  
      A second aspect of the present application relates to an exposure method for exposing a photosensitive material by emitting a light beam which is modulated in accordance with image data while the photosensitive material is being relatively moved, the method including: determining a position of a hole in an exposure surface of the photosensitive material; performing focusing control for causing a focusing position of the light beam to coincide with the exposure surface; and generating displacement data for the focusing control, excluding a position which is determined, on the basis of results of determination of the hole position, to be the hole.  
      A third aspect of the present application relates to an exposure device for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure device including: a workpiece displacement measurement section, which measures displacements of an exposure surface of the workpiece; a hole co-ordinate measurement section, which finds a co-ordinate of a hole formed in the workpiece; a displacement data generation section, which generates displacement data of the exposure surface in accordance with results of measurement at the workpiece displacement measurement section; and a focusing section, which aligns a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation section, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected by the workpiece displacement measurement section, the displacement data generation section compares a position of detection of this displacement amount with a hole co-ordinate position found by the hole co-ordinate measurement section and, if the two positions coincide, determines that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, sets a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      A fourth aspect of the present application relates to an exposure device for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure device including: a workpiece displacement measurement section, which measures displacements of an exposure surface of the workpiece; a displacement data generation section, which generates displacement data of the exposure surface in accordance with results of measurement at the workpiece displacement measurement section; and a focusing section, which aligns a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation section, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected by the workpiece displacement measurement section, the displacement data generation section compares a position of detection of this displacement amount with a hole co-ordinate position inputted by a user beforehand and, if the two positions coincide, determines that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, sets a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      A fifth aspect of the present application relates to an exposure device for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure device including: a workpiece displacement measurement section, which measures displacements of an exposure surface of the workpiece; a hole co-ordinate measurement section, which finds a co-ordinate of a hole formed in the workpiece; a displacement data generation section, which generates displacement data of the exposure surface in accordance with results of measurement at the workpiece displacement measurement section; and a focusing section, which aligns a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation section, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected by the workpiece displacement measurement section, the displacement data generation section compares a position of detection of this displacement amount with a hole co-ordinate position found by the hole co-ordinate measurement section and a hole co-ordinate position inputted by a user beforehand, and, if the three positions coincide, determines that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, sets a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      A sixth aspect of the present application relates to an exposure method for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure method including: a workpiece displacement measurement step for measuring displacements of an exposure surface of the workpiece; a displacement data generation step for generating displacement data of the exposure surface in accordance with results of measurement in the workpiece displacement measurement step; a focusing step for aligning a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation step; and a hole co-ordinate measurement step for finding a co-ordinate of a hole formed in the workpiece, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected in the workpiece displacement measurement step, the displacement data generation step includes comparing a position of detection of this displacement amount with a hole co-ordinate position found by the hole co-ordinate measurement step and, if the two positions coincide, judging that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, setting a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      A seventh aspect of the present application relates to an exposure method for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure method including: a workpiece displacement measurement step for measuring displacements of an exposure surface of the workpiece; a displacement data generation step for generating displacement data of the exposure surface in accordance with results of measurement in the workpiece displacement measurement step; and a focusing step for aligning a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation step, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected in the workpiece displacement measurement step, the displacement data generation step includes comparing a position of detection of this displacement amount with a hole co-ordinate position inputted by a user beforehand and, if the two positions coincide, judging that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, setting a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      An eighth aspect of the present application relates to an exposure method for exposing a workpiece with one or a plurality of an exposure head, which relatively moves with respect to the workpiece, the exposure method including: a workpiece displacement measurement step for measuring displacement of an exposure surface of the workpiece; a hole co-ordinate measurement step for finding a co-ordinate of a hole formed in the workpiece; a displacement data generation step for generating displacement data of the exposure surface in accordance with results of measurement in the workpiece displacement measurement step; and a focusing step for aligning a focusing point of a light beam emitted from the exposure head with the exposure surface on the basis of the displacement data generated by the displacement data generation step, wherein, when a displacement amount equal to or greater than a predetermined magnitude is detected in the workpiece displacement measurement step, the displacement data generation step includes comparing a position of detection of this displacement amount by the workpiece displacement measurement step with a hole co-ordinate position found in the hole co-ordinate measurement step and a hole co-ordinate position inputted by a user beforehand, and, if the three positions coincide, first judging that a step corresponding to the displacement amount corresponds to the hole formed in the workpiece and, for a predetermined range about the hole, setting a displacement amount which differs from the measured displacement amount for generating the displacement data.  
      A ninth aspect of the present application relates to an exposure device for exposing a photosensitive material with an exposure section which emits a light beam modulated in accordance with image data while the photosensitive material is relatively moved, the exposure device including: an unevenness portion position identification section, which determines a position of an unevenness portion of an exposure surface of the photosensitive material; a focusing section, which performs focusing control for causing a focusing position of the light beam from the exposure section to coincide with the exposure surface; and a displacement data generation section, which generates displacement data for the focusing control by the focusing section, excluding a position which is determined, on the basis of results of determination by the unevenness portion position identification section, to be the unevenness portion.  
      A tenth aspect of the present application relates to an exposure method for exposing a photosensitive material by emitting a light beam which is modulated in accordance with image data while the photosensitive material is being relatively moved, the method including: determining a position of an unevenness portion of an exposure surface of the photosensitive material; performing focusing control for causing a focusing position of the light beam to coincide with the exposure surface; and generating displacement data for the focusing control, excluding a position which is determined, on the basis of results of determination of the unevenness portion position, to be the unevenness portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic perspective view showing overall structure of an exposure device relating to an embodiment.  
       FIG. 2  is a schematic side view showing overall structure of the exposure device relating to the embodiment.  
       FIG. 3  is a perspective view showing structure of an exposure unit provided at the exposure device relating to the embodiment.  
       FIG. 4A  is a plan view showing exposed regions which are formed on a photosensitive material.  
       FIG. 4B  is a schematic view showing an arrangement of exposure areas due to respective exposure heads.  
       FIG. 5  is a perspective view showing general structure of an exposure head provided at the exposure device relating to the embodiment.  
       FIGS. 6A and 6B  are sectional views, cut in a scanning direction along an optical axis, showing structure of the exposure head shown in  FIG. 5 .  
       FIG. 7  is a schematic plan view showing relative positional relationships of the exposure heads, displacement measurement units and alignment detection units.  
       FIG. 8  is a partial enlarged view showing structure of a digital micromirror device (DMD) provided at the exposure head shown in  FIG. 5 .  
       FIGS. 9A and 9B  are explanatory views showing operation of the DMD shown in  FIG. 8 .  
       FIG. 10  is a perspective view showing the exterior of a focusing mechanism provided at an exposure head which is provided at the exposure device shown in  FIG. 1 .  
       FIGS. 11A and 11B  are explanatory views showing operation of a focusing mechanism shown in  FIG. 10 .  
       FIG. 12  is a block diagram showing structure of a controller provided at the exposure device of  FIG. 1 .  
       FIG. 13  is a plan view showing an example of reference holes formed in a photosensitive material which is to be exposed by the exposure device of  FIG. 1 .  
       FIG. 14  is a graph showing an example of displacement data at a displacement measurement unit when it is determined that a hole is present.  
       FIG. 15  is a side view showing a relationship between a photosensitive material and laser displacement meters at a time of displacement measurement.  
       FIG. 16  is a block diagram showing a method of determining a hole position from a substrate machining process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      (1) Structure of Exposure Device  
      An exposure device  100  relating to a present embodiment is of a “flat-bed type”. As shown in  FIGS. 1 and 2 , the exposure device  100  is provided with a thick board-form equipment pedestal  156 , which is supported at four leg portions  154 , two guides  158  at an upper face of the equipment pedestal  156 , which extend in a stage movement direction shown by an arrow in  FIG. 1 , and an exposure stage  152 , which is supported by the guides  158  to be reciprocally movable. The exposure stage  152  is a pedestal on which a workpiece, such as a photosensitive material  150  or the like, is placed. The exposure stage  152  is disposed such that a length direction thereof is oriented in the stage movement direction. The exposure stage  152  can be moved along the guides  158  by a driving mechanism (not shown), and height of the exposure stage  152  can be adjusted.  
      The photosensitive material  150 , as mentioned earlier, is an item at which a photosensitive layer is applied to a surface of a substrate or the like.  
      At a central portion of the equipment pedestal  156 , an ‘n’-like gate  160  and gate  161  are provided so as to straddle a movement path of the exposure stage  152 . Respective end portions of the gate  160  and the gate  161  are fixed at two side faces of the equipment pedestal  156 . A detection unit  180  is provided at the gate  160 . The detection unit  180  is formed with an alignment detection unit  182 , which is provided at one side of the gate  160 , and a displacement measurement unit  184 , which is provided at the other side, sandwiching the gate  160 . The alignment detection unit  182  and the displacement measurement unit  184  correspond to a hole co-ordinate measurement section and a distance measurement section, respectively, of the present invention. As the alignment detection unit  182 , for example, CCD cameras are employed.  
      An exposure unit  162  is provided at the gate  161 . The exposure unit  162  is equipped with, for example, eight exposure heads  166 , which will be described later.  
      The exposure unit  162  and the detection unit  180  are connected to a controller  190 . The controller  190  corresponds to a displacement data generation section of the present invention. The controller  190  prepares displacement data in accordance with displacements of an exposure surface of the photosensitive material, which are measured by the displacement measurement unit  184 , and position co-ordinates of reference holes, which are found by photography by the alignment detection unit  182 . The controller  190  includes a function for performing focusing by controlling autofocus units  59 , which are provided at the respective exposure heads  166 , in accordance with the generated displacement data. Thus, the controller  190  corresponds to the displacement data generation section and the focusing section of the present invention.  
      Herein, the exposure stage  152 , the guides  158 , the gate  160 , the gate  161 , the exposure unit  162  and the detection unit  180  are structured so as to be accommodated inside a casing  110 , and the photosensitive material  150  is exposed without being affected by external light.  
      As shown in  FIGS. 3 and 4 B, the exposure unit  162  is provided with the plurality of exposure heads  166 , which are arranged substantially in a matrix pattern of m columns and n rows (for example, two columns and four rows).  
      As shown in  FIG. 3 , exposure regions  168 , which are regions exposed by the exposure heads  166 , have rectangular shapes with short sides thereof in a scanning direction, and are inclined by a predetermined inclination angle θ with respect to the scanning direction. Hence, in accordance with movement of the exposure stage  152 , band-form exposed regions  170  are formed at the photosensitive material  150  by the respective exposure heads  166 . Note that, as shown in  FIGS. 1 and 3 , the scanning direction and the stage movement direction are opposite directions.  
      As shown in  FIGS. 4A and 4B , in each row, the respective exposure heads  166 , which are arranged in a line, are disposed to be offset by a predetermined interval in a row arrangement direction (which interval is an integer multiple (one in the present embodiment) of the long dimension of the exposure regions), such that each of the band-form exposed regions  170  will be partially superposed with the neighboring exposed regions  170 . Consequently, a portion that cannot be exposed between, for example, an exposure region  168 A disposed at a leftmost side of a first column and an exposure region  168 C disposed neighboring the exposure region  168 A at the right thereof will be covered by an exposure region  168 B disposed at the leftmost side of the second column. Similarly, a portion that cannot be exposed between the exposure region  168 B and an exposure region  168 D disposed neighboring the exposure region  168 B at the right thereof will be covered by the exposure region  168 C. Herein, the exposure region  168 A is exposed by exposure head  166 A and the exposure region  168 B is exposed by exposure head  166 B. Similarly, the exposure region  168 C and exposure regions  168 D,  168 E,  168 F,  168 G and  168 H are exposed by exposure heads  166 C,  166 D,  166 E,  166 F,  166 G and  166 H, respectively.  
      As shown in  FIG. 5  and  FIGS. 6A and 6B , each of the exposure heads  166 A to  166 H serves as a spatial light modulator for modulating an incident light beam at each of pixels in accordance with image data, and is equipped with a digital micromirror device (DMD)  50 . The DMD  50  is connected with the controller  190 , which is provided with a data processing section and a mirror driving control section. At the data processing section of the controller  190 , control signals are generated, on the basis of inputted image data, for driving control of each micromirror in a region, of the DMD  50  at the exposure head  166 , that is to be controlled.  
      The mirror driving control section controls the angles of the reflection surfaces of the micromirrors of the DMD  50  at each exposure head  166  in accordance with the control signals generated by the image data processing section. Control of the angles of the reflection surfaces will be described later.  
      A fiber array light source  66 , a lens system  67  and a reflection mirror  69  are arranged, in this order, at a light incidence side of the DMD  50 . The fiber array light source  66  is provided with a laser emission portion, at which emission end portions (light emission points) of optical fibers are arranged in a row along a direction corresponding to a length direction of an imaging region P. The lens system  67  corrects laser light emitted from the fiber array light source  66  and focuses the laser light on the DMD. The reflection mirror  69  reflects laser light that has passed through the lens system  67  toward the DMD  50 .  
      The lens system  67  is structured with a single pair of combination lenses  71 , which make the laser light that has been emitted from the fiber array light source  66  parallel, a single pair of combination lenses  73 , which correct the laser light that has been made parallel such that a light amount distribution is more uniform, and a condensing lens  75 , which focuses the laser light whose light amount distribution has been corrected onto the DMD. The combination lenses  73  have the functions of, in the direction of arrangement of the laser emission ends, broadening portions of light flux that are close to an optical axis of the lenses and constricting portions of the light flux that are distant from the optical axis, and in a direction intersecting this direction of arrangement, transmitting the light unaltered. Thus, the laser light is corrected such that the light amount distribution is uniform.  
      A lens system  54  and a lens system  58  are disposed at a light reflection side of the DMD  50 . The lens systems  54  and  58  focus the laser light that has been reflected at the DMD  50  onto a scanning surface (an exposure surface)  56  of the photosensitive material  150 . The lens systems  54  and  58  are disposed such that the DMD  50  and the exposure surface  56  have a conjugative relationship.  
      The present embodiment is specified such that, after the laser light emitted from the fiber array light source  66  has been made uniform and is incident on the DMD  50 , each pixel is broadened substantially by a factor of five and focused, by the lens system  54  and the lens system  58 .  
      The autofocus unit  59  is further provided at the emission side of the lens system  58 . The autofocus unit  59  aligns a focusing point of the laser light emitted from the fiber array light source  66  with the exposure surface  56 . The autofocus unit  59  corresponds to the focusing section of the present invention.  
       FIG. 7  shows relative positional relationships of the exposure head  166 , the alignment detection unit  182  and the displacement measurement unit  184 , viewed from above. As shown in  FIG. 7 , the alignment detection unit  182  is formed with four CCD cameras, alignment camera No. 1, alignment camera No. 2, alignment camera No. 3 and alignment camera No. 4, along a width direction of the photosensitive material  150 . Alignment camera No. 1 photographs the exposure region  168 A and the exposure region  168 B, and alignment camera No. 2 photographs the exposure region  168 C and the exposure region  168 D. Further, alignment camera No. 3 photographs the exposure region  168 E and the exposure region  168 F, and alignment camera No. 4 photographs the exposure region  168 G and the exposure region  168 H.  
      The displacement measurement unit  184  is disposed at a downstream side of the alignment detection unit  182  with respect to a conveyance direction during exposure, which is a Y-axis direction. The displacement measurement unit  184  is structured by laser alignment meters from laser alignment meter No. 1 to laser alignment meter No. 8. The laser alignment meters No. 1 to No. 8 are disposed so as to measure displacements of the exposure regions  168 A to  168 H, respectively.  
      Below, the DMD  50  will be described.  
      As shown in  FIG. 8 , at the DMD  50 , very small mirrors (micromirrors)  62 , which are supported by support columns, are arranged on an SRAM cell (a memory cell)  60 . The DMD  50  is a mirror device which is structured with a large number (for example, 1024 by 768, with a pitch of 13.68 μm) of these extremely small mirrors, which structure image elements (pixels), arranged in a checkerboard pattern. At each pixel, the micromirror  62  is provided so as to be supported at an uppermost portion of the support column. A material with high reflectivity, such as aluminium or the like, is applied by vapor deposition at a surface of the micromirror  62 . Here, the reflectivity of the micromirror  62  is at least 90%. The SRAM cell  60  with CMOS silicon gates, which is fabricated by a usual semiconductor memory production line, is disposed directly under the micromirror  62 , with the support column, which includes a hinge and a yoke, interposed therebetween. Overall, this structure is monolithic (an integrated form).  
      When digital signals representing inclination states (modulation states) of the micromirrors  62  are written to the SRAM cell  60  of the DMD  50 , and digital signals are outputted from the SRAM cell  60  to the micromirrors  62 , the micromirrors  62  supported at the support columns are inclined, about a diagonal, within a range of ±α° (for example, ±10°) relative to a side of a substrate on which the DMD  50  is disposed.  FIG. 9A  shows a state in which the micromirror  62  is inclined at +α°, which is an ‘on’ state, and  FIG. 9B  shows a state in which the micromirror  62  is inclined at −α°, which is an ‘off’ state. Accordingly, as a result of control of the inclinations of the micromirrors  62  at the pixels of the DMD  50  in accordance with image signals, as shown in  FIGS. 9A and 9B , light that is incident at the DMD  50  is reflected in directions of inclination of the respective micromirrors  62 .  
       FIG. 8  shows a portion of the DMD  50  enlarged, and shows an example of a state in which the micromirrors  62  are controlled to +α° and −α°. The on-off control of the respective micromirrors  62  is carried out by the controller  190  connected to the DMD  50 . A light-absorbing body (which is not shown) is disposed in the direction in which light beams are reflected by the micromirrors  62  that are in the off state.  
      Next, the autofocus unit  59  will be described.  
      As shown in  FIG. 10 , the autofocus unit  59  is equipped with paired glass wedges  210  and  212 , which are a pair of glass members formed in wedge shapes (trapezoid prism shapes) of a transparent glass material. In the present embodiment, the paired glass wedges  210  and  212  are specified with a refractive index n=1.53, and are disposed adjacent to one another along an optical axis of the laser light, with mutually opposite orientations. The paired glass wedges  210  and  212  correspond to wedge-form optical members of the present invention.  
      Of the pair of paired glass wedges  210  and  212 , the paired glass wedge  210  is arranged at the side of incidence of the laser light (the DMD  50  side). Further, a face of the paired glass wedge  210  at a side which is formed perpendicularly to two side faces thereof serves as the face of the side at which laser light is incident, that is, a light incidence face  210 A. The light incidence face  210 A is arranged so as to be perpendicular with respect to the direction of incidence of the laser light. Correspondingly, a face of a side of the paired glass wedge  210  which is opposite from the light incidence face  210 A serves as a light emission face  210 B, from which the laser light is emitted. The light emission face  210 B is angled relative to the side faces of the paired glass wedge  210 .  
      The paired glass wedge  212  is adjacent to the paired glass wedge  210  and is disposed at a laser light emission side (the exposure surface  56  side) thereof. The paired glass wedge  212  is arranged such that a face thereof at a side which is angled with respect to two side faces thereof serves as a light incidence face  212 A, and a side which is perpendicular to the two side faces serves as a light emission face  212 B. Thus, the light emission face  212 B of the paired glass wedge  212  is substantially perpendicular to the optical axis of the laser light and the light incidence face  212 A is arranged at an inclined orientation.  
      In a non-contacting state of the paired glass wedges  210  and  212 , in which, as shown in  FIGS. 11A and 11B , the light emission face  210 B of the paired glass wedge  210  and the light incidence face  212 A of the paired glass wedge  212  form a small gap therebetween, the light incidence face  210 A of the paired glass wedge  210  and the light emission face  212 B of the paired glass wedge  212  are parallel and are substantially perpendicular to the optical axis of the laser light as mentioned above. In the present embodiment, the gap between the light emission face  210 B of the paired glass wedge  210  and the light incidence face  212 A of the paired glass wedge  212  is set to 0.1 mm.  
      As shown in  FIG. 10 , the autofocus unit  59  is equipped with a base holder  214  and a sliding holder  216 , which respectively separately retain the two paired glass wedges  210  and  212 . The base holder  214  and the sliding holder  216  correspond to an optical member support portion of the present invention. The paired glass wedge  212  is retained by the base holder  214  and the paired glass wedge  210  is retained by the  216 .  
      The base holder  214  is formed in a wedge shape with a form substantially similar to the paired glass wedge  212 . Rectangular aperture portions  218  and  220  are formed in an upper face (inclined face)  214 A and a lower face  214 B of the base holder  214 . A cavity portion (accommodation portion)  222  for accommodating the paired glass wedge  212  is formed inside the base holder  214 .  
      The cavity portion  222  has a recessed form, which is hollowed in from the upper face  214 A side of the base holder  214 , with the size of the aperture portion  218  and a predetermined depth dimension substantially perpendicularly downward. The paired glass wedge  212  is accommodated inside the cavity portion  222 . The cavity portion  222  is formed such that, when the paired glass wedge  212  is accommodated inside the cavity portion  222 , a lower face and interior periphery faces of the cavity portion  222  touch a lower face (i.e., the light emission face  212 B) and outer periphery faces of the paired glass wedge  212 , substantially without gaps.  
      The aperture portion  220  is formed at a central portion of the lower face  214 B of the base holder  214 . The aperture portion  220  is formed to be a little smaller than the opening forms of the aperture portion  218  of the upper face  214 A and the cavity portion  222 . At a left side end portion of the lower face  214 B, a fixing portion  224  is protrudingly provided for fixing the autofocus unit  59  as a whole to a frame (not shown) of the exposure unit  162 , by screw-fastening.  
      The sliding holder  216  is formed in a wedge shape with a form substantially similar to the paired glass wedge  210 . Rectangular aperture portions  226  and  228  are formed in, respectively, an upper face  216 A and a lower face  216 B of the sliding holder  216 . The sliding holder  216  is a substantially frame-like member inside which a cavity portion (accommodation portion)  230  for accommodating the paired glass wedge  210  is formed. Here, the lower face  216 B is an inclined face.  
      The cavity portion  230  is the same size as the aperture portion  226 , and has the form of a through-hole penetrating toward the aperture portion  228 . The cavity portion  230  is formed with a size such that, when the paired glass wedge  210  is accommodated, interior periphery faces of the cavity portion  230  touch outer periphery faces of the paired glass wedge  210 , substantially without gaps.  
      A paired glass wedge-restraining plate  234  with a rectangular frame form is fitted in at the aperture portion  226  of the sliding holder  216 . Thus, the paired glass wedge  210  is mounted so as to not fall out from the cavity portion  230 . A rectangular aperture portion  236  is formed substantially at the middle of the paired glass wedge-restraining plate  234 . The aperture portion  236  is substantially the same size as the aperture portion  220  at the lower face  214 B side of the base holder  214 . When the sliding holder  216  has been moved to a position of mounting of the paired glass wedge  210 , the aperture portion  236  is disposed at a position which is substantially superposed with the aperture portion  220 .  
      As shown in  FIG. 10 , the sliding holder  216  is disposed on the base holder  214  such that the lower face  216 B is fitted to face the upper face  214 A of the base holder  214  with a direction of inclination of the lower face  216 B being opposite to a direction of inclination of the upper face  214 A of the base holder  214 . Then, the sliding holder  216  is assembled to the base holder  214  by a pair of guide rails  232 , which are provided between the upper face  214 A of the base holder  214  and the lower face  216 B of the sliding holder  216 , thus forming a unit.  
      The sliding holder  216  is disposed to be substantially parallel with the base holder  214 , with a predetermined gap therebetween, by the pair of guide rails  232 . The sliding holder  216  is assembled to the base holder  214  to be relatively movable in a substantially left-right direction (the direction of arrow S in  FIG. 10 ) along the direction of inclination of the lower face  216 B and the upper face  214 A.  
      In order to assemble the paired glass wedges  210  and  212  and the paired glass wedge-restraining plate  234  to the base holder  214  and sliding holder  216 , the sliding holder  216  may be moved to a position for assembly of the paired glass wedges  210  and  212 , the cavity portion  230  of the sliding holder  216  aligned with the cavity portion  222  of the base holder  214 , and the paired glass wedge  212 , paired glass wedge  210  and paired glass wedge-restraining plate  234  assembled, in this order from below to above, into the cavity portion  222  and the cavity portion  230 .  
      As shown in  FIG. 10 , an actuator mounting plate  238  is fixed by screw-fastening at a substantially central position of a right side face  214 C of the base holder  214 . The right side face  214 C of the base holder  214  is formed to be substantially perpendicular to the upper face  214 A. The actuator mounting plate  238  which is assembled to this right side face  214 C protrudes upward from a mounting portion (lower portion), with an orientation which is substantially perpendicular to the upper face  214 A of the base holder  214 . A focusing motor  240  is mounted at an outer side face of an upper portion of the actuator mounting plate  238 . The focusing motor  240  corresponds to an optical member traversal section of the present invention.  
      A direction of protrusion and a direction of movement (the direction of arrow D) of a driving shaft  242  of the focusing motor  240  is matched with the movement direction (the direction of arrow S) of the sliding holder  216 , and the focusing motor  240  is assembled to the actuator mounting plate  238 . A distal end portion  242 A of the driving shaft  242  is coupled to a right side face  216 C of the sliding holder  216 . The focusing motor  240  is also connected to a focusing mechanism control section of the controller  190 , and is controlled for operation by this focusing mechanism control section.  
      A cutaway portion  244  is formed at a front-right corner portion of the upper face  216 A of the sliding holder  216 . A pair of support pillars  246  and  248  are provided at a lower face of this cutaway portion  244  and a front-right corner portion of the upper face  214 A of the base holder  214 , respectively. A tension coil spring  250 , whose spring force is set to be smaller than a driving force of the driving shaft  242  of the focusing motor  240 , spans between the pair of support pillars  246  and  248 . A pre-load is applied between the sliding holder  216  and the base holder  214 , which are coupled by the actuator mounting plate  238  and the focusing motor  240 , by this spring force of the tension coil spring  250 .  
      When the focusing motor  240  is operated, consequent to signals from a later-described head control section of the controller  190 , and the driving shaft  242  is moved in the direction of arrow D, the sliding holder  216  and the paired glass wedge  210  move in the direction of arrow S, guided by the pair of guide rails  232 . Even if there is a little play (looseness) at the driving shaft  242  of the focusing motor  240 , or at the guide rails  232  or the like, the sliding holder  216  and the paired glass wedge  210  are retained to be free of looseness in a rest state by the pre-load applied by the tension coil spring  250 . Furthermore, the sliding holder  216  and the paired glass wedge  210  operate smoothly during movements.  
      A rectangular sensor mounting plate  252  is fixed by screw-fastening at a front-right corner portion of the lower face  214 B of the base holder  214 . A protruding right side portion of the sensor mounting plate  252  extends rightward from a portion of mounting to the lower face  214 B of the base holder  214  (a left side portion of the sensor mounting plate  252 ). This right side portion is inflected relative to the portion of mounting so as to be substantially parallel with the upper face  214 A of the base holder  214 . A reference position sensor unit  254  is mounted at an upper face of the right side portion of the sensor mounting plate  252 , for detecting a reference position (i.e., a home position) of the sliding holder  216  at which the paired glass wedge  210  is retained.  
      At the reference position sensor unit  254 , an optical sensor  258  is mounted at an upper portion of a unit main body, which is formed in a cuboid shape. The reference position sensor unit  254  is provided with a circuit board (not shown), which amplifies electronic signals (detection signals), which are outputted from the optical sensor  258  into the unit main body. At the optical sensor  258 , a light projecting-receiving element (not shown) is provided at an inner wall face of a slit portion  256 . The optical sensor  258  is arranged such that the slit portion  256  is oriented to be substantially parallel with the movement direction of the sliding holder  216  (the direction of arrow S). Further, the reference position sensor unit  254  is connected to the head control section of the controller  190 .  
      At a front end portion of the right side face  216 C of the sliding holder  216 , a reference position detection plate  260 , to correspond with the reference position sensor unit  254 , is fixed by screw-fastening. The reference position detection plate  260  is ‘L’-shaped and is inflected substantially perpendicularly from a portion for mounting to the right side face  216 C of the sliding holder  216  (a left side portion of the reference position detection plate  260 ). A right side portion of the reference position detection plate  260 , which extends rightward with a predetermined length dimension, is a detection portion (a light sensor-shading portion). The reference position detection plate  260  is arranged at a position at which it is capable, in accordance with movement of the sliding holder  216 , of passing into the slit portion  256  of the optical sensor  258  and of withdrawing from the slit portion  256 .  
      When the distal end of the detection portion of the reference position detection plate  260  is moved into the slit portion  256  and withdrawn from the slit portion  256  in accordance with movements of the sliding holder  216 , the optical sensor  258  outputs high and low detection signals in accordance with respective states of detection of a light-blocking state and a light-non-blocking state according to the light projecting-receiving element. Hence, the reference position sensor unit  254  amplifies these detection signals with the circuit board and outputs the detection signals to the head control section of the controller  190 .  
      A position of switching of the output level of a detection signal inputted from the reference position sensor unit  254  between high and low, when the head control section of the controller  190  controls for driving the focusing motor  240  and the sliding holder  216  is moved, is verified as a reference position of the sliding holder  216  and the paired glass wedge  210 . Information of this reference position is stored in memory. Hence, for driving control of the focusing motor  240 , control signals which control driving of the focusing motor  240  are generated in accordance with the reference position information, control signals for applying correction to the reference position information are generated as necessary, and these signals are outputted to the focusing motor  240 .  
      When the focusing motor  240  of the autofocus unit  59  is controlled for driving by signals from the controller  190 , the paired glass wedge  210  retained at the sliding holder  216  moves, as shown in  FIGS. 11A and 11B , from the reference position shown by broken lines in the drawings, in the direction of arrow SA shown in  FIG. 11A  or the direction of arrow SB shown in  FIG. 11B .  
      Now, when the paired glass wedge  210  is at the reference position, a distance between the light incidence face  210 A of the paired glass wedge  210  and the light emission face  212 B of the paired glass wedge  212 , that is, a total thickness dimension of the paired glass wedges  210  and  212  including the small gap formed therebetween, is ‘t’. Hence, the thickness dimension t decreases by Δt (changes by −Δt) when the paired glass wedge  210  moves a certain distance from the reference position in the direction of arrow SA, and increases by Δt (changes by +Δt) when the paired glass wedge  210  moves the certain distance from the reference position in the direction of arrow SB.  
      When the thickness dimension t of the paired glass wedges  210  and  212  changes thus (by ±Δt), a transmission distance of the laser light passing through the paired glass wedges  210  and  212  changes, and a focusing distance of the laser light FD changes (by ±ΔFD). Here, the planes PS shown in  FIGS. 11A and 11B  represent focusing planes.  
      If the refractive index of the paired glass wedges  210  and  212  is ‘n’ (n=1.53 in the present embodiment), amounts of changes in the focusing distance FD of the laser light corresponding to amounts of changes in the thickness dimension t of the paired glass wedges  210  and  212  can be found by the following equations. 
 
+Δ FD=+Δt −(+Δ t )/ n  
 
−Δ FD=−Δt −(−Δ t )/ n  
 
      Below, structure of the controller  190  will be described with reference to  FIG. 12 .  
      The controller  190  features functions for controlling the exposure device  100  in accordance with inputs from a control computer  197 , and is constituted with the following units.  
      A. Exposure head driving units  191 A,  191 B,  191 C,  191 D,  191 E,  191 F,  191 G and  191 H, for driving the exposure heads  166 A to  166 H.  
      B. Image processing units  193 A,  193 B,  193 C,  193 D,  193 E,  193 F,  193 G and  193 H, for dividing image data inputted from the control computer  197  into image data of images that are to be exposed at the eight exposure regions  168 A to  168 H, and for inputting the divided image data to the exposure head driving units  191 A to  191 H, respectively.  
      C. An alignment measurement unit  194 , for processing image data from the alignment cameras Nos. 1 to 4, which are provided at the alignment detection unit  182 , and inputting the processed image data to a main control unit, which will be described later.  
      D. An alignment adjustment unit  196 , for adjusting alignment of the exposure stage  152  on the basis of alignment data obtained by the alignment measurement unit  194 .  
      E. Focusing control units  192 A,  192 B,  192 C,  192 D,  192 E,  192 F,  192 G and  192 H, provided at the exposure head driving units  191 A to  191 H, respectively, for controlling the autofocus units  59  on the basis of displacement measurement results, from the laser displacement meters provided at the displacement measurement unit  184 , and suchlike.  
      F. A main control unit  195 , which adjusts alignment of the exposure stage  152 , via the alignment adjustment unit  196 , in accordance with inputs of image data from the alignment measurement unit  194 , controls lifting and Y-axis direction conveyance of the exposure stage  152 , and controls the exposure head driving units  191 A to  191 H via the image processing units  193 A to  193 H.  
      CANPCIs are provided at the image processing units  193 A to  193 H and the alignment measurement unit  194 . The CANPCIs mutually exchange data between the image processing units  193 A to  193 H and the alignment measurement unit  194  and, at the same time, send and receive data, instructions and the like to and from the main control unit  195 .  
      Instructions and data from the control computer  197  are inputted, through the CANPCIs provided at the image processing units  193 A to  193 H and the alignment measurement unit  194 , to the main control unit  195 .  
      (2) Operation of the Exposure Device  100   
      Below, a sequence of operations from setting of the photosensitive material  150  at the exposure device  100  to completion of exposure will be described.  
     (2-1) EXAMPLE 1  
      The photosensitive material  150  is placed at the exposure stage  152  in a state in which the exposure stage  152  is at the position shown in  FIG. 1 . When an operator inputs an instruction to commence exposure, a command to the effect that the exposure stage  152  should be moved in a measurement direction while the alignment detection unit  182  and the displacement measurement unit  184  are started up is inputted from the control computer  197  provided at the controller  190  to the main control unit  195 .  
      When this command is inputted to the main control unit  195 , the alignment cameras Nos. 1 to 4 at the alignment detection unit  182  are activated, and measurements of position co-ordinates of a reference hole (X1,Y1), a reference hole (X2,Y2), a reference hole (X3,Y3) and a reference hole (X4,Y4) formed at the photosensitive material  150  are performed. At the same time, the laser displacement meters Nos. 1 to 8 at the displacement measurement unit  184  are started up, and measurements of displacements of the exposure surface of the photosensitive material  150  are performed. Note that an example of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4) formed at the photosensitive material  150  is shown in  FIG. 13 .  
      The results of measurements of displacement measured by the laser displacement meters Nos. 1 to 8 are inputted to the focusing control units  192 A to  192 H, respectively. The results of measurement of the position co-ordinates of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4) are inputted to the main control unit  195  via the CANPCIs of the alignment measurement unit  194  and the image processing unit  193 A, and are inputted from the main control unit  195  to the focusing control units  192 A to  192 H via the exposure head driving units  191 A to  191 H.  
      If a user has inputted X and Y co-ordinates of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4) at the control computer  197  beforehand, these X and Y co-ordinates are also inputted to the focusing control units  192 A to  192 H.  
      At the focusing control units  192 A to  192 H, from the displacement data measured by the laser displacement meters Nos. 1 to 8, differences between the displacement data and displacement data of previous measurements are found. Then, as shown in  FIG. 14 , when a difference from the previous data is more than a predetermined value for two or more successive cycles, for example, when differences of more than +100 digit occur, it is judged that there is a step in the photosensitive material  150 , and this displacement data is considered to possibly be a reference hole.  
      Next, a range of the hole is determined from the displacement data. As a specific example, to start, a point corresponding to displacement data three points previous from a position at which a difference of +100 digit or more occurs is considered to be the beginning of a hole and, to finish, a point corresponding to displacement data three points subsequent from a position at which a difference of +100 digit or more occurs is considered to be the end of the hole.  
      Y co-ordinates of a hole are found from the data, in which points corresponding to the start and end of the hole are represented by counts of points from an origin point, and a spacing between any two adjacent measurement points. X co-ordinates are found from mounting positions of the laser displacement meters Nos. 1 to 8.  
      Thereafter, the X co-ordinates and Y co-ordinates of the holes which have been found thus are compared with the position co-ordinates of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4) which have been measured at the alignment detection unit  182  and the position co-ordinates of the same which have been inputted by the user. Then, when these three match, it is judged that the steps detected by the laser displacement meters Nos. 1 to 8 are one or other of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4).  
      When the focusing control units  192 A to  192 H determines that step are one or other of the reference hole (X1,Y1), the reference hole (X2,Y2), the reference hole (X3,Y3) and the reference hole (X4,Y4), similarly to the determination of the start and end of the hole, a range from the point corresponding to displacement data three points previous to the position at which a difference of +100 digit or more initially occurs to the point corresponding to displacement data three points subsequent to the position at which a difference of +100 digit or more finally occurs is treated as a range across which these two points are joined by a straight line. In addition, the data obtained by the laser displacement meters Nos. 1 to 8 is subjected to moving average processing to remove a noise component. Thus, a focusing map is generated for each of the exposure regions  168 A to  168 H.  
      At the focusing control units  192 A to  192 H, the focusing motors  240  of the autofocus units  59  at the exposure heads  166 A to  166 H are driven to perform focusing in accordance with the focusing maps which are generated for each of the exposure regions  168 A to  168 H by the procedure described above.  
      Thus, in the exposure device  100  relating to the present embodiment, it is determined that positions at which the three sets of data—reference hole positions measured by the alignment cameras, measurement values from the laser displacement meters, and data inputted to the control computer by a user—match are hole positions. When a hole is detected, then, for example, the hole is excluded in creating a focusing map, displacement data of a hole portion is subjected to moving average processing and recreated as new displacement data, and focusing is carried out in accordance with this focusing map. Consequently, there will be no error in focusing positions of laser light from the exposure heads  166 . As a result, a sharp image free of mis-focusing will be obtained.  
     (2-2) EXAMPLE 2  
      The photosensitive material  150  is placed at the exposure stage  152  in a state in which the exposure stage  152  is at the position shown in  FIG. 1 . When an operator inputs an instruction to commence exposure, a command to the effect that the exposure stage  152  should be moved in the measurement direction while the displacement measurement unit  184  is started up is inputted from the control computer  197  provided at the controller  190  to the main control unit  195 .  
      When this command is inputted to the main control unit  195 , the laser displacement meters Nos. 1 to 8 at the displacement measurement unit  184  are started up, and measurements of displacements of the exposure surface of the photosensitive material  150  are performed.  
      The results of measurement of displacements measured by the laser displacement meters Nos. 1 to 8 are inputted to the focusing control units  192 A to  192 H, respectively.  
       FIG. 15  is a side view showing a relationship between the photosensitive material  150  and the laser displacement meters Nos. 1 to 8 during displacement measurement.  
      At the focusing control units  192 A to  192 H, from the displacement data measured by the laser displacement meters Nos. 1 to 8, differences between neighboring data, which is displacement data measured at the same time by neighboring laser displacement meters, are found. Then, when a difference between neighboring data is more than a predetermined value, for example, when a difference of more than +100 digit occurs, it is judged that there is a step in the photosensitive material  150 , and this displacement data is considered to possibly be a hole.  
      Next, a range of the hole is determined from the displacement data. Specifically, differences, such as a difference between the laser displacement meter No. 1 and the laser displacement meter No. 2 and a difference between the laser displacement meter No. 2 and the laser displacement meter No. 3, are progressively calculated. To start, a point corresponding to displacement data at a position at which a difference of +100 digit or more occurs is considered to be the beginning of a hole and, to finish, a point corresponding to displacement data at a position at which a difference of +100 digit or more occurs is considered to be the end of the hole. In  FIG. 15 , there are differences between No. 2 and No. 3 and between No. 3 and No. 4. Accordingly, No. 3 is judged to be at a hole position.  
      Y co-ordinates of a hole are found from the data, in which points corresponding to the start and end of the hole are represented by counts of points from an origin point, and a spacing between any two adjacent measurement points. X co-ordinates are found from mounting positions of the laser displacement meters Nos. 1 to 8.  
      When the focusing control units  192 A to  192 H determine that step are a hole, similarly to the determination of the start and end of the hole, a range from the point corresponding to the position at which a difference of +100 digit or more initially occurs to the point corresponding to the position at which a difference of +100 digit or more finally occurs is treated as a range across which these two points are joined by a straight line. In addition, data obtained by a laser displacement meter immediately prior to a hole position serves as displacement data of the hole position. Thus, a focusing map is generated for each of the exposure regions  168 A to  168 H.  
      At the focusing control units  192 A to  192 H, the focusing motors  240  of the autofocus units  59  at the exposure heads  166 A to  166 H are driven to perform focusing in accordance with the focusing maps which are generated for each of the exposure regions  168 A to  168 H by the procedure described above.  
      Thus, in the exposure device  100  relating to the present embodiment, determinations of hole positions are carried out on the basis of differences in the measurement data between neighboring laser displacement meters. When a hole is detected, the hole is excluded in creating the focusing map, displacement data of a hole portion is substituted with displacement data of a position peripheral to the hole, and focusing is carried out in accordance with this focusing map. Consequently, there will be no error in focusing positions of laser light from the exposure heads  166 . As a result, a sharp image free of mis-focusing will be obtained.  
     (2-3) EXAMPLE 3  
      When a hole is to be formed in the photosensitive material  150 , before exposure, an operation is executed to form the hole with a drill, in a substrate machining process. Hole position information at such a time (X-Y co-ordinates) is transmitted to the exposure device from a device such as a raster image processor (RIP) or the like, and is respectively inputted to the focusing control units  192 A to  192 H. At a position of the hole position information, it is judged that there will be a step in the photosensitive material  150 , and it is determined that the displacement data will be a hole.  
       FIG. 16  is a block diagram showing a method for judging hole positions from the substrate machining process.  
      When operations for forming holes are executed by a drill in a substrate machining process  302 , information of hole positions at the photosensitive material  150  is passed to an RIP  300 . Thereafter, image data for exposure and the hole position information is transmitted from the RIP  300  to the controller  190  of the exposure device  100  before exposure.  
      The focusing control units  192 A to  192 H provided at the exposure device  100  determine the positions of the holes at the photosensitive material  150  from the hole position information that has been transmitted, and create focusing maps for each of the exposure regions  168 A to  168 H, with displacement data obtained by the laser displacement meters Nos. 1 to 8 immediately prior to the hole positions serving as displacement data for the hole positions.  
      At the focusing control units  192 A to  192 H, the focusing motors  240  of the autofocus units  59  at the exposure heads  166 A to  166 H are driven to perform focusing in accordance with the focusing maps generated for each of the exposure regions  168 A to  168 H by the procedure described above.  
      Thus, in the exposure device  100  relating to the present embodiment, determination of hole positions is carried out on the basis of data of hole positions that have been machined in a substrate machining process. When a hole is detected, the hole is excluded in creating a focusing map, displacement data of a hole portion is substituted with displacement data of a position peripheral to the hole, and focusing is carried out in accordance with this focusing map. Consequently, there will be no error in focusing positions of laser light from the exposure heads  166 . As a result, a sharp image free of mis-focusing will be obtained.  
      In the present invention, a hole position identification section may determine the position of a hole in an exposure surface of a photosensitive material on the basis of measurement data of heights of positions of the exposure surface of the photosensitive material from a distance measurement section, which measures the heights of positions of the exposure surface of the photosensitive material. Further, a displacement data generation section may generate displacement data without utilizing the measurement data for the position which is determined to be the position of the hole in the exposure surface of the photosensitive material.  
      In the present invention, the displacement data generation section may compare the measurement data at a first measurement position according to the distance measurement section with the measurement data at a measurement position near the first measurement position according to the distance measurement section and, if a difference between values of these measurement data exceeds a predetermined value, may correct or disregard the measurement data at the first measurement position according to the distance measurement section.  
      In the present invention, the hole position identification section may include a hole formation position information acquisition section, which acquires data of an occasion of hole formation in the photosensitive material by a hole formation section, and the disposition data generation section may identify the position of the hole at the photosensitive material on the basis of the data of the occasion of hole formation in the photosensitive material by the hole formation section, and correct or disregard the measurement data at that position.  
      The present invention may include, in addition to the distance measurement section and the focusing section, a hole co-ordinate measurement section for identifying the position of the hole at the photosensitive material, and, if second measurement data at a second measurement position, which is acquired by the distance measurement section, includes a value equal to or greater than a predetermined value, the displacement data generation section may compare the second measurement position at which the second measurement data is acquired with a hole co-ordinate position obtained by the hole co-ordinate measurement section and, if these two positions coincide, judge that the second measurement position at which the second measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the second measurement position, correct or disregard the second measurement data.  
      At this exposure device, position co-ordinates of holes formed in the photosensitive material are found by the hole co-ordinate measurement section. At the same time, at the displacement data generation section, presence/absence of holes is judged on the basis of the results of displacement measurements at the distance measurement section and the position co-ordinates found by the hole co-ordinate measurement section. When a hole is present, position co-ordinates thereof are identified, displacement measurement values of the hole and surroundings thereof are excluded, and displacement data is generated with displacement amounts which differ from these measured displacement amounts. Hence, the focusing section is controlled on the basis of this displacement data.  
      Therefore, even with a photosensitive material in which holes are formed, errors will not be included in the displacement data consequent to detection of the holes. As a result, it is possible to accurately align focusing of the light beam(s) from the exposure head(s) with the exposure surface of the photosensitive material.  
      Alignment cameras, which photograph the photosensitive material to find the positions of reference holes, or the like are examples of the hole co-ordinate measurement section.  
      The present invention may include, in addition to the distance measurement section and the focusing section, a hole position co-ordinate input section for identification by a user of the position of the hole at the photosensitive material. If third measurement data at a third measurement position, which is acquired by the distance measurement section, includes a value equal to or greater than a predetermined value, the displacement data generation section may compare the third measurement position at which the third measurement data is acquired with a hole co-ordinate position inputted by the user beforehand and, if these two positions coincide, judge that the third measurement position at which the third measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the third measurement position, correct or disregard the third measurement data.  
      At this exposure device, when a hole such as a reference hole or the like is formed in the photosensitive material, at the displacement data generation section, on the basis of the results of measurement of displacement at the distance measurement section and of position co-ordinates of the hole inputted by a user beforehand, displacement measurement values of the hole and surroundings thereof are excluded, and displacement data is generated with displacement amounts which differ from these measured displacement amounts. Hence, the focusing section is controlled on the basis of this displacement data.  
      Consequently, it is possible to accurately align focusing of the light beam from the exposure head with the exposure surface of the photosensitive material.  
      Furthermore, in this exposure device, because the section at which the positions of holes that are formed in the photosensitive material are inputted by a user is employed, the hole co-ordinate measurement section can be omitted, and structure can be simplified.  
      The present invention may include, in addition to the distance measurement section and the focusing section, the hole co-ordinate measurement section for identifying the position of the hole at the photosensitive material and the hole position co-ordinate input section for identification by a user of the position of the hole at the photosensitive material. If fourth measurement data at a fourth measurement position, which is acquired by the distance measurement section, includes a value equal to or greater than a predetermined value, the displacement data generation section may compare the fourth measurement position at which the fourth measurement data is acquired with a hole co-ordinate first position obtained by the hole co-ordinate measurement section and a hole co-ordinate second position inputted by the user beforehand and, if these three positions coincide, judge that the fourth measurement position at which the fourth measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the fourth measurement position, correct or disregard the fourth measurement data.  
      At this exposure device, position co-ordinates of holes formed in the photosensitive material are found by the hole co-ordinate measurement section. At the same time, at the displacement data generation section, presence/absence of holes is judged on the basis of the results of measurement of displacement at the distance measurement section, hole position co-ordinates found by the hole co-ordinate measurement section and hole position co-ordinates inputted by a user. When a hole is present, position co-ordinates thereof are identified.  
      As a result, judgments of presence/absence of holes and identifications of position co-ordinates are carried out with greater accuracy.  
      In the present invention, for a predetermined range about a co-ordinate position which is determined to be a hole, the displacement data generation section may specify data which differs from measurement data measured at a measurement position in the range to serve as measurement data peripheral to the co-ordinate position which is determined to be the hole.  
      At this exposure device, displacement amounts of a predetermined range around a co-ordinate position which is judged to be a hole are set to a displacement amount of the surroundings of the co-ordinate position judged to be a hole.  
      In the present invention, the displacement data generation section may subject measurement data acquired by the distance measurement section to moving average processing and update the measurement data.  
      When the displacement data includes noise with high frequency components, it is not preferable to use the raw data for performing focusing with the focusing section.  
      Accordingly, at this exposure device, high frequency components are removed from the displacement data and processing is performed such that focusing control by the focusing section is more satisfactory.  
      In the present invention, the focusing section may include: a plurality of optical members disposed at a respective emission side of at least one exposure head structuring an exposure section, the optical members being formed with wedge shapes of light-transmissive material and being arranged adjacent to one another, along an optical axis of a light beam emitted from the exposure head, with mutually opposite orientations; an optical member support section, which supports one optical member of the plurality of optical members to be movable along a face thereof which opposes another optical member of the plurality; and an optical member traversal section, which causes the one optical member to move along the opposing face relative to the other optical member.  
      In this exposure device, the plurality of wedge-form optical members provided at the focusing section are disposed adjacent to one another on the optical axis of the light beam, with mutually opposite orientations. The one wedge-form optical member is relatively moved with respect to the other wedge-form optical member, along a face thereof which opposes the other wedge-form optical member, by the optical member traversal section. As a result, a relative distance in the optical axis direction of the light beam between an incidence face, at which the light beam is incident on one wedge-form optical member, and a light emission face, from which the light beam which has passed through the plurality of wedge-form optical members after incidence is emitted from another one of the wedge-form optical members, consequently changes. In other words, a transmission path along which the light beam is transmitted through the plurality of wedge-form optical members is altered. As a result, a focusing distance of the light beam changes.  
      This focusing section has a structure which is simple, and can be compactly structured. Thus, it is easy to incorporate the focusing section at the emission side of each exposure head.  
      At the exposure device of the present invention, besides the form described hereabove, a structure which changes a distance of the photosensitive material from the exposure head by moving the photosensitive material itself in a focusing depth direction could also be employed as the focusing section.  
      In the present invention, the exposure head may perform imaging by altering modulation states of respective pixels to turn the pixels on and off in accordance with inputted image information.  
      At this exposure head, modulation states of pixels are changed to set the pixels to on and off. Therefore, it is not necessary to turn a light source itself on and off to turn the pixels on and off, and the light source can be maintained in an illuminating state during imaging. Accordingly, because a mechanism for turning the light source on and off with a high frequency cycle is not required, it is possible to simplify structure of the exposure head and reduce the frequency of breakdowns. Further, the pixels can be set to on and off more rapidly than in a case of turning a light source on and off directly. Therefore, a better quality image can be obtained. Further yet, it is easier to perform imaging onto the whole of a photosensitive material with a large surface area.  
      The present invention may include: measuring heights of positions of the exposure surface of the photosensitive material; and determining the position of the hole in the exposure surface of the photosensitive material on the basis of measurement data of the heights of positions of the exposure surface of the photosensitive material, with a step of generating displacement data generating the displacement data without utilizing the measurement data for the position which is determined to be the position of the hole in the exposure surface of the photosensitive material.  
      The present invention may include: comparing the measurement data at a first measurement position with the measurement data at a measurement position near the first measurement position; and, if a difference between values of these measurement data exceeds a predetermined value, one of correcting and disregarding the measurement data at the first measurement position.  
      The present invention may include: performing identification of the hole position by acquiring data of an occasion of hole formation in the photosensitive material; identifying the position of the hole at the photosensitive material on the basis of the data of the occasion of hole formation in the photosensitive material; and one of correcting and disregarding the measurement data at that position.  
      The present invention may include, if second measurement data at a second measurement position includes a value equal to or greater than a predetermined value: comparing the second measurement position at which the second measurement data is acquired with a hole co-ordinate position obtained by measurement of a hole co-ordinate; and, if these two positions coincide, judging that the second measurement position at which the second measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the second measurement position, one of correcting and disregarding the second measurement data.  
      In the exposure process too, when a hole formed in the photosensitive material is detected, the displacement data is generated with the hole and surroundings thereof excluded, and focusing is performed on the basis of this displacement data. Thus, even in a case in which holes are formed in the photosensitive material, it is possible to expose in a state in which focusing of laser light from an exposure head is precisely fitted to the exposure surface of the photosensitive material.  
      The present invention may include, if third measurement data at a third measurement position includes a value equal to or greater than a predetermined value: comparing the third measurement position at which the third measurement data is acquired with a hole co-ordinate position inputted by a user beforehand; and, if these two positions coincide, judging that the third measurement position at which the third measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the third measurement position, one of correcting and disregarding the third measurement data.  
      In this exposure process, instead of providing a hole co-ordinate measurement step for finding co-ordinates of holes formed in the photosensitive material, hole co-ordinates which have been inputted beforehand by a user are employed for identifying presence/absence and positions of holes in the photosensitive material.  
      Therefore, for this exposure process, an exposure device whose structure is simplified can be employed.  
      The present invention may include, if fourth measurement data at a fourth measurement position includes a value equal to or greater than a predetermined value: comparing the fourth measurement position at which the fourth measurement data is acquired with a hole co-ordinate first position and a hole co-ordinate second position, which is inputted by a user beforehand; and, if these three positions coincide, judging that the fourth measurement position at which the fourth measurement data is acquired corresponds to the position of the hole at the photosensitive material and, for a predetermined range about the fourth measurement position, one of correcting and disregarding the fourth measurement data.  
      In this exposure process, the presence/absence of holes is judged on the basis of displacement measurement results, hole position co-ordinates, and hole co-ordinate positions inputted by a user. When a hole is present, position co-ordinates thereof are identified.  
      As a result, judgments of the presence/absence of holes and identifications of position co-ordinates can be performed with higher accuracy.  
      According to the present invention as described above, an exposure device and exposure process which are capable of exposure which is accurately focused on a photosensitive material, even when holes are formed in the photosensitive material and/or grooves or the like are formed, are provided.  
      Hereabove, an exposure device of the present invention has been described in detail. However, the present invention is not limited to the embodiment described above. Naturally, various modifications and alterations may be implemented within a scope which does not depart from the spirit of the present invention.