Abstract:
A laser direct imaging apparatus which can expose photosensitive materials having various sensitivities and which can correct an imaging position in accordance with deformation of a workpiece. In the laser direct imaging apparatus, the workpiece is moved in a sub-scanning direction while a cylindrical lens is used to converge a laser beam, which has been modulated based on raster data, in the sub-scanning direction and deflect the laser beam toward a main scanning direction so as to image a desired pattern on the workpiece. The cylindrical axis of the cylindrical lens is designed to be able to rotate horizontally and to be able to change an angle with respect to the main scanning direction.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a laser direct imaging (LDI) apparatus for moving a workpiece in a sub-scanning direction while using a cylindrical lens to condense a laser beam, which has been modulated based on raster data, in the sub-scanning direction and deflect the laser beam toward a main scanning direction so as to image a desired pattern on the workpiece. 
       BACKGROUND OF THE INVENTION 
       [0002]    In an LDI apparatus, CAD data used for designing a circuit pattern are converted into vector data format, and then contours are calculated from the vector data. After that, the contours are further converted into raster data for imaging. From the raster data, ON and OFF pixels for a laser beam are obtained. The ON pixels are irradiated with the laser beam. 
         [0003]      FIG. 7  is a view showing a configuration of background-art LDI apparatus. 
         [0004]    A laser source  1  is mounted on an optical table  16 . The optical table  16  is disposed on a column  17  on a bed  18 . A laser beam  5  emitted from the laser source  1  enters an acousto-optic modulator (hereinafter referred to as “AOM”)  4  reflected by mirrors  2  and an expander  3 . A laser beam  5   a  modulated by the AOM  4  is deflected by a polygon mirror  6  and enters an fθ lens  7 . The laser beam  5   a  emerged from the fθ lens  7  is deflected toward the downward direction of  FIG. 7  by a reflection mirror  8 , and enters a cylindrical lens  9 . The laser beam  5   a  emerged from the cylindrical lens  9  is incident on a workpiece  10 . A dry film resist (hereinafter referred to as “DFR”), a photo-resist or the like on the workpiece  10  is exposed to the laser beam  5   a . On this occasion, a table  12  where the workpiece  10  is mounted moves in a sub-scanning direction (Y-axis direction in  FIG. 7 . The X-axis direction in  FIG. 7  is a main scanning direction.) at a constant speed. A linear motor  14  moves the table  12 . A pair of guides  13  guide the table  12  (Patent Document 1). 
         [0005]    Here, the anterior focal point of the fθ lens  7  is positioned on the reflection plane of the polygon mirror  6 . Of the laser beam  5  reflected by the polygon mirror  6 , components parallel to the XY plane are parallel rays, and components perpendicular to the XY plane are divergent rays starting at a reflection point of the polygon mirror  6 . Accordingly, the components of the laser beam  5  parallel to the XY plane are converged by the fθ lens  7  but passed through the cylindrical lens  9  as they are. On the other hand, the components of the laser beam  5  perpendicular to the XY plane are converted into parallel rays by the fθ lens  7 , and converged by the cylindrical lens  9 . 
         [0006]      FIGS. 8A and 8B  are views showing the position of a start sensor.  FIG. 8A  is a view in the X-axis direction of  FIG. 7 , and  FIG. 8B  is a view in the Y-axis direction of  FIG. 7 . 
         [0007]    A mirror  11  is disposed under the left end portion of the cylindrical lens  9  in  FIG. 7 . A start sensor  15  is disposed in the direction of reflected laser beam from the mirror  11 . In order to align the imaging start positions of rows, which mean the rows of the exposed pixels by the main scanning (X-axis direction), imaging in each scan in the main scanning direction is started when a predetermined time has passed after the start sensor  15  has detected the laser beam  5   a  reflected by the mirror  11  (the distance between the detection position and the imaging start position is 10 mm in the illustrated case). 
         [0008]    The table  12  on which the workpiece  10  is mounted moves in the sub-scanning direction when the laser beam is scanning in the main scanning direction. Accordingly, when the laser beam  5  is scanned in the X direction, the scanning line by irradiation (exposure) with the laser beam  5  tilts clockwise at an angle α with respect to the X direction (main scanning direction) as shown in  FIG. 9 . The angle α will be referred to as “scanning angle”. 
         [0009]    In the background art, therefore, an irradiation optics is disposed so that the scanning angle α is set to 0 with respect to the moving direction of the table  12 , and an irradiation system is disposed so that the scanning line of exposure is perpendicular to the Y direction (sub-scanning direction). 
         [0010]    Patent Document 1: JP-A-2007-94122 
         [0011]    If the sensitivity of a photosensitive material to light (hereinafter referred to as “sensitivity” simply) is uniform, the scanning angle α can be made constant. However, some DFR (Dry Film Resist) may have a variation in its resist sensitivity. For example, assume that the output of a laser is constant, and the resist sensitivity is 50 mJ/cm 2 . In this case, the scanning speed of the laser beam (the number of revolutions of the polygon mirror) and the moving speed of the table must be made  1 / 5  of that when the resist sensitivity is 10 mJ/cm 2 . 
         [0012]    However, the polygon mirror has a narrow range of stable revolution speed (which is, for example, as wide as or ½ as wide as the rated revolution speed). Accordingly, the range of possible scanning angle α is so narrow that the workpieces which can be exposed are limited in variety. 
       SUMMARY OF THE INVENTION 
       [0013]    An object of the present invention is to solve the foregoing problem. Another object of the present invention is to provide a laser direct imaging apparatus which can expose photosensitive materials having various sensitivities and which can correct an imaging position in accordance with deformation of a workpiece. 
         [0014]    In order to attain the foregoing objects, the present invention provides a laser direct imaging apparatus for moving a workpiece in a sub-scanning direction while using a cylindrical lens to converge a laser beam, which has been modulated based on raster data, in the sub-scanning direction and deflect the laser beam toward a main scanning direction so as to image a desired pattern on the workpiece. The laser direct imaging apparatus is characterized in that the cylindrical axis of the cylindrical lens is designed to be able to rotate horizontally and to be able to change an angle with respect to the main scanning direction. 
         [0015]    In this case, the axis of rotation of the cylindrical lens may be brought into line with a imaging start point of the laser beam. 
         [0016]    The angle (scanning angle α) of the cylindrical axis of the cylindrical lens with respect to the main scanning direction can be set easier. Accordingly, photosensitive materials having various sensitivities can be exposed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIGS. 1A and 1B  are views showing a configuration of a laser direct imaging apparatus according to the present invention; 
           [0018]      FIGS. 2A and 2B  are enlarged fragmentary views of a portion A in  FIG. 1A ; 
           [0019]      FIG. 3  is a fragmentary sectional view of a main portion of the laser direct imaging apparatus according to the present invention; 
           [0020]      FIG. 4  is a sectional view taken on the line B-B in  FIG. 2A ; 
           [0021]      FIG. 5  is a sectional view perpendicular to the cylindrical axis of a cylindrical lens; 
           [0022]      FIGS. 6A and 6B  are views showing a modification of the present invention; 
           [0023]      FIG. 7  is a view showing a configuration of a background-art laser direct imaging apparatus; 
           [0024]      FIGS. 8A and 8B  are diagrams for explaining the background-art laser direct imaging apparatus; and 
           [0025]      FIG. 9  is a diagram for explaining a scanning angle. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    The present invention will be described below with reference to the drawings. 
         [0027]      FIGS. 1A and 1B  are views showing a configuration of a laser direct imaging apparatus according to the present invention.  FIG. 1A  is a plan view, and  FIG. 1B  is a side view.  FIGS. 2A and 2B  are enlarged fragmentary view of a portion A in  FIG. 1A .  FIG. 2A  is a plan view, and  FIG. 2B  is a side view. For convenience of representation,  FIGS. 2A and 2B  show the state where the same as that in  FIGS. 1A and 1B  has been rotated at an angle of 90°.  FIG. 3  is a fragmentary sectional view of the vicinities of a pin  44  which will be described later.  FIG. 4  is a sectional view taken on the line B-B in  FIG. 2A . Parts the same as or having the same functions as those in  FIG. 7  are designated with the same reference numeral and a description thereof is omitted. 
         [0028]    A bracket  23  is fixed to a column  17 . A base plate  43  is fixed onto the bracket  23  by bolts  49 . A hollow hinge pin  34  has a hollow horseshoe boss portion  34   a . The boss portion  34   a  is annular and partially notched. The hollow hinge pin  34  is fixed to the base plate  43 . The center of the boss portion  34   a  is positioned above an imaging start point so that the axis of rotation of a cylindrical lens  9  passes through both the center and the imaging start point. As will be described later, the reason why the boss portion  34   a  is notched is to prevent the boss portion  34   a  from interfering with a laser beam  5   a  emerged from the cylindrical lens  9 . The inside radius of the boss portion  34   a  is a radius (here, 15 mm) large enough not to block the laser beam  5   a.    
         [0029]    The cylindrical lens  9  is supported on a lens holder  35 . A circular portion  38  provided in the lens holder  35  is fitted to the outer circumference of the boss portion  34   a  so as to allow the cylindrical axis of the cylindrical lens  9  to pass through the center of boss portion  34   a . Accordingly, the lens holder  35 , that is, the cylindrical lens  9  can be positioned desirably near and around the center of the boss portion  34   a , that is, the imaging start point. A hole  37  and three holes  50  are formed in the lens holder  35 . The hole  37  is formed to be large enough to allow the lens holder  35  to rotate without blocking the laser beam  5   a  emerged from the cylindrical lens  9 . 
         [0030]    As shown in  FIG. 3 , pins  44  are screwed down to the base plate  43  through the holes  50  respectively. Belleville springs  41  press the lens holder  35  against the base plate  43  so as to prevent the lens holder  35  from moving up from the base plate  43 . The pressure force of the Belleville springs  41  is too weak for the lens holder  35  to rotate around the axis passing through the imaging start point. The outer diameter of each pin  44  is smaller than the diameter of each hole  50 , so that the lens holder  35  can rotate around the axis passing through the imaging start point. 
         [0031]    A cam follower  33  is rotatably supported on one side surface of the lens holder  35 . Alinear guide unit  39  constituted by a bearing  39   a  and a track  39   b  is disposed on the base plate  43 . The track  39   b  is fixed to a holder  51  so as to guide the bearing  39   a  in the X direction. The holder  51  is fixed to the base plate  43  by bolts  52 . A linear cam  32  is fixed to the bearing  39   a . An end surface of the linear cam  32  facing the cam follower  33  is tapered with its thick end placed downward in  FIG. 2A . 
         [0032]    The linear cam  32  is connected to a shaft  31   a  of a linear actuator  31 . A motor  30  drives the linear actuator  31  so as to move the shaft  31   a  in the X direction. The motor  30  is fixed to the base plate  43  with an L-shaped support  55 . A bolt  56  fixes the support  55  to the base plate  43 . 
         [0033]    A spring  36  presses the lens holder  35  to the left in  FIG. 2A  so as to bring the cam follower  33  into contact with a face  32   a  of the linear cam  32  opposed thereto. 
         [0034]    With the configuration mentioned thus, the linear cam  32  moves in the X direction when the motor  30  is rotated. The lens holder  35  rotates around the axis passing through the imaging start point (that is, the value of the scanning angle a increases and decreases) with the X-direction motion of the cam follower  33  in contact with the linear cam  32 . Then, the guide  39  is positioned to set the scanning angle α to a desired value. 
         [0035]    Next, the operation of the present invention will be described. 
         [0036]    First, description will be made about the scanning angle α. 
         [0037]    When the rotational speed+ of a polygon mirror is N [rpm] and the number of facets thereof is m, scanning time tm on every one facet of the polygon mirror and scanning time ts through a deflection angle  2 θ [degrees] can be expressed by Equations 1 and 2. 
         [0000]        tm= 60/ N/m [s]   (Equation 1) 
         [0000]        ts=tm ×θ/(360/ m ) [ s]   (Equation 2) 
         [0038]    When the deflection angle of the polygon mirror is θ, the maximum incident angle of the laser beam  5   a  incident on an fθ lens  7  is θ. When f designates the focal length of the fθ lens  7  and V designates the feed speed of a table (exposure speed), the scanning angle α can be expressed by Equation 3. 
         [0000]      α=tan −1 ( ts×V /(2× f× θ))   (Equation 3) 
         [0000]    where the angle θ is converted to radians. 
         [0039]      FIG. 5  is a sectional view perpendicular to the cylindrical axis of the cylindrical lens  9 . The reference sign P represents the cylindrical axis of the cylindrical lens  9 . 
         [0040]    As described previously, of the laser beam  5   a  incident on the cylindrical lens  9 , the component in the width direction of the cylindrical lens  9  is collimated. Accordingly, when the central axis of the laser beam  5   a  incident on the cylindrical lens  9  perpendicularly thereto passes through the axis P, the laser beam  5   a  is converged to a position F 0  which is at a distance F (F designates the focal length of the cylindrical lens  9 ) from the axis P. Here, assume that the cylindrical lens  9  is moved to the right in  FIG. 5  by a distance δ (that is, the axis P is moved to the right in  FIG. 5  by the distance δ) as shown by the alternately long- and double short-dashed line in  FIG. 5  while the central axis of the laser beam  5   a  is fixed. In this case, the laser beam  5   a  is converged to a position F 1  which is δ on the right of the position F in  FIG. 5 . That is, though the central axis of the laser beam  5   a  is on the same, the position where the laser beam  5   a  is converged is shifted by a distance with which the position of the axis P of the cylindrical lens  9  is shifted in parallel to the surface of a workpiece  10 . To say other words, when the axis P of the cylindrical lens  9  is tilted at an angle α with respect to the running direction of the workpiece, the position where the laser beam  5   a  is condensed is also tilted at the angle α with respect to the running direction. It is therefore possible to set the scanning angle as an angle of the axis P of the cylindrical lens  9  with respect to the scanning direction. 
         [0041]    In this embodiment, the cylindrical lens  9  is rotated around the axis passing through the imaging start point. Accordingly, there is no fear that the imaging start point is shifted in the X direction. It is therefore possible to perform imaging with high quality. 
         [0042]      FIGS. 6A and 6B  are views showing a modification of the present invention. 
         [0043]    The lens holder  35  is disposed on the base plate  43  so that the lens holder  35  can rotate around a hinge pin  42 . 
         [0044]    According to this modification, the axis of the hinge pin  42  does not pass through the imaging start point. Therefore, the imaging start point is shifted in the Y direction by a distance tan α. However, the scanning angle α can be known in advance. When the position where the workpiece  10  is placed on the table is shifted in the Y direction by the distance tan α, an image can be drawn in a desired position of the workpiece. 
         [0045]    The operation in this embodiment is substantially the same as that in the aforementioned embodiment. Therefore, redundant description will be omitted. 
         [0046]    Although a laser beam is modulated by an AOM in the aforementioned embodiments, the present invention can be also applied to a laser direct imaging apparatus in which a laser diode is used as a light source, and the laser diode is ON/OFF-controlled directly.