Abstract:
A projection aligner comprises a projection optical system for radiating a luminous flux including ultraviolet rays onto a photomask, and projecting said luminous flux which has passed through the photomask onto a substrate to which photoresist is applied; a substrate table for mounting the substrate, and a light blocking means for covering the peripheral portion of the substrate to block luminous flux. The light blocking means ( 80 ) includes a first light blocking member ( 84 ) and a second light blocking member ( 86 ) each having a substantially semicircular opening, and moving means ( 82, 83 ) for moving the first light blocking means and the second light blocking means approaching each other and away from each other. As the first light blocking member and the second light blocking member are moved to approach each other, the first light blocking member and the second light blocking member form an annular shape and cover the peripheral portion of the substrate (CB).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a projection aligner with a light blocking device to block light on the edges of a substrate to which a photoresist has been applied while a predetermined pattern is formed on the surface of the substrate, e.g., of silicon by exposure. 
     BACKGROUND OF THE INVENTION 
     Photoresists are applied to substrates for semiconductors, e.g., silicon wafers, glass substrates for flat displays or kinds of substrates for electric circuits (hereinafter called substrate) but photoresists may not be uniform on the edges of the substrates. Due to this, the photoresist is not removed and remained on the edges and may cause the dust in the proceeding process. Therefore, the photoresist needs to be removed from the edges of the substrate before the process proceeds. 
     A negative-type photoresist is used in an electrode forming process of a plate process, and a positive-type photoresist is used to prevent resist film at the peripheral portion from separation. 
     Japan unexamined patent publication No. 2005-505147 discloses an apparatus having a ring-shaped light blocking body placing on a substrate to cover whole edges of the substrate. Since the light blocking body discloses in the publication No. 2005-505147 has a shape to cover whole edges of the substrate, when the substrate is loaded or unloaded, the substrate table is required to be moved to move the light blocking means in the waiting position so that the light blocking means is removed. Thereafter, the substrate table is moved to the substrate loading position and the substrate is changed, and the substrate table is moved to the waiting position to place the light blocking body on the substrate. Therefore, the moving distance of the substrate table is long, so that it takes time to load and unload the substrate. Moreover, the light blocking body is moved frequently, which causes the high possibility of dust filling up. 
     Japan unexamined patent publication No. 2005-045160 discloses a technique of an arc-shaped light blocking unit or a rectangular light blocking unit being placed near the edges of the wafer not to expose the peripheral region of the substrate. This technique requires the mechanism of moving the light blocking unit around the substrate and the mechanism of calculating and controlling the light blocking position. 
     Patent publication 1: Japan unexamined patent publication No. 2005-505147 
     Patent publication 2: Japan unexamined patent publication No. 2005-045160 
     SUMMARY OF THE INVENTION 
     Since the light blocking body covering the whole surface of the substrate as disclosed in the patent publication 1 increases in size, it takes time to load and unload the substrate, which lowers the processing ability of projection aligner. The light blocking unit disclosed in the patent publication 2 is small and handled easier but the control unit of the light blocking unit needs to calculate the insert position of the light blocking unit depending on the pattern drawn on the photomask in advance, so that the processing becomes complicated. 
     Therefore, the present invention provides a projection aligner utilizing a light blocking means so as to shorten time required for setting and removing the light blocking means during substrate conveyance. Further, the light blocking means can be applied for a variety of light blocking regions of the substrates. 
     A projection aligner of the first aspect of the present invention comprises a projection optical system for radiating a luminous flux including ultraviolet rays onto a photomask, and projecting the luminous flux which has passed through the photomask onto a substrate to which a photoresist is applied; a substrate table for mounting the substrate; and a light blocking means for covering peripheral portion of the substrate to block luminous flux. The light blocking means includes a first light blocking member and a second light blocking member each have a substantially semicircular opening; and moving means for moving the first light blocking member and the second light blocking member so as to approach each other and be away from each other. Accordingly, as the first light blocking member and the second light blocking member approach each other, the first light blocking member and the second light blocking member form an annular shape and cover the peripheral portion of the substrate. 
     In a projection aligner of the second aspect of the present invention, the first light blocking member and the second light blocking members each comprise a removable first light blocking blade and a removable second light blocking blade for blocking the illumination flux, respectively, and a first light blocking base and a second light blocking base provided with the first light blocking blade and the second light blocking blade, respectively. The first light blocking base and the second light blocking base are connected to the moving means and connected to a lifting means for moving the first light blocking base and the second light blocking base up and down. 
     In a projection aligner of the third aspect of the present invention, the first light blocking blade and the second light blocking blade each have a distal end of thin portion so as to overlap each other in thickness direction as the first light blocking blade and the second light blocking blade approach each other. 
     In a projection aligner of the fourth aspect of the present invention, the substrate is loaded on the substrate table by a substrate conveyance means, and the moving means moves the first light blocking member and the second light blocking member so as to be moved straight in parallel with the direction where the accuracy of positioning is lower than the other directions. 
     In a projection aligner of the fifth aspect of the present invention, at least one of the first light blocking member and the second light blocking member is fixed at a rotary shaft at an end thereof, and the moving means moves at least one of the first light blocking member and the second light blocking member in a rotating direction. 
     A projection exposure method of the sixth aspect of the present invention radiates a luminous flux including ultraviolet rays onto a photomask, blocks the luminous flux having passed through the photomask at the peripheral portion of the substrate applied with a photoresist by light blocking means covering the peripheral portion of the substrate so that the peripheral portion of the substrate applied with a photoresist is not irradiated with the luminous flux but the central portion where the center side from the peripheral portion is radiated. The projection exposure method comprises a step of mounting the substrate on a substrate stage by a substrate convey means, a step of arranging the light blocking means above and closer to the substrate, a step of calculating a position of the substrate mounted on the substrate stage and a position of the light blocking means, and a step of in a case of the position of the light blocking means respect to the position of the substrate displaced out of the range of the predetermined range, moving the light blocking means so that the displacement is within the predetermined range. 
     In a projection exposure method of the seventh aspect of the present invention, the position of the substrate is calculated by measuring several alignment marks, and the position of light blocking means is calculated by measuring at least one alignment mark provided at the light blocking means. 
     According to the projection aligner of the present invention, the projection aligner comprises the separated first light blocking member and second light blocking member, so that the setting and unsetting of the light blocking means can easily be processed during the substrate loading or unloading. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a projection aligner  100 . 
         FIG. 2  is a schematic perspective view of the reflection-type exposure device  100  from which the illumination optical system  30  is excluded. 
         FIG. 3  is a plan view of a first light blocking device  80  as viewed in the Z-axis direction. 
         FIG. 4  is a perspective view showing a state where the substrate CB is loaded by a conveyance arm. 
         FIG. 5  is an operation flowchart of the first light blocking device  80 . 
         FIG. 6A  is a view showing a state where the substrate CB is loaded on or is unloaded from a vacuum chuck  69 . 
         FIG. 6B  is a view showing a state where the peripheral portion of the substrate CB is covered with the light blocking blades  86 . 
         FIG. 7A  is a view showing the light blocking blades  86  having an annular shape and a light blocking base. 
         FIG. 7B  is an enlarged cross-sectional view taken along a line B-B in  FIG. 7A . 
         FIGS. 8A ,  8 B,  8 C and  8 D are views showing modifications relating to a shape of the light blocking blade. 
         FIG. 9  is a view showing a second light blocking device  180 . 
         FIG. 10  is a view showing a third light blocking device  280 . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     &lt;Schematic Constitution of Protection Aligner  100 &gt; 
       FIG. 1  is a schematic side view of a projection aligner  100 . 
     The projection aligner  100  substantially includes: a light source  10  which radiates a luminous flux of a wavelength range containing ultraviolet rays; an illumination optical system  30  which converges a luminous flux from the light source  10 ; a mask stage  40  which holds a photomask H; a projection optical system  50 ; and a substrate stage  60 . 
     The projection aligner  100  includes the illumination optical system  30  for uniformly illuminating the photomask M which is supported on the mask stage  40  parallel to an X-Y plane. The illumination optical system  30  includes the light source  10  which is formed of a mercury short arc lamp similar to a positional light source, for example. The light source  10  is arranged at a first focal point of an elliptical mirror  11  and hence, an illumination luminous flux radiated from the light source  10  forms a light source image at a second focal point of the elliptical mirror via a dichroic mirror  12 . The dichroic mirror  12  does not reflect light other than light within a predetermined wavelength range. Here, the light source  10  which the illumination optical system  30  includes may be an ultraviolet-irradiation-type LED (Light Emitting Diode) or a laser. 
     Exposure light which reaches a substrate CB is blocked by a shutter  13 . Diverging light from a light source image is converted into a parallel luminous flux by a collimate lens  31  and, thereafter, is incident on a wavelength selection part  15 . The wavelength selection part  15  is constituted such that the wavelength selection part  15  can be inserted into or removed from an optical path formed between the light source  10  and the photomask M. 
     A fly-eye lens  32  is arranged at the second focal point of the elliptical mirror. A luminous flux which passes through the wavelength selection part  15  passes through the fly-eye lens  32  and a condenser lens  33  sequentially. 
     The luminous flux which passes through the wavelength selection part  15  is incident on the fly-eye lens  32 . The fly-eye lens  32  is constituted such that a large number of positive lens elements are densely arranged in a matrix array in a state where a center axis of each positive lens element extends along an optical axis OA. Accordingly, the luminous flux which is incident on the fly-eye lens  32  is divided by the large number of lens elements by wavefront dividing thus forming secondary light sources which is formed of light sources the number of which is equal to the number of lens elements on a rear focal plane of the fly-eye lens  32  (that is, in the vicinity of an irradiation surface of the fly-eye lens  32 ). 
     A luminous flux from the large number of secondary light sources formed on the rear focal plane of the fly-eye lens  32  is incident on the condenser lens  33 . The luminous flux which passes through the condenser lens  33  illuminates the patterned photomask M in a superposed manner. The luminous flux which illuminates the photomask M by exposure light and passes through the photomask M advances toward the projection optical system  50  and, thereafter, is radiated to the substrate CB which is an object to be exposed. 
       FIG. 2  is a schematic perspective view of the reflection-type exposure device  100  from which the illumination optical system  30  is excluded, wherein the mask stage  40 , the reflection-type projection optical system  50  and the substrate stage  60  are shown in an exploded manner. The substrate stage  60  is shown in a state where a first light blocking device  80  is mounted on the substrate stage  60 . 
     The mask stage  40  includes a Y stage  41  for moving the photomask M along the Y-axis direction which is the scanning direction. The Y stage  41  is driven at a high speed and with high accuracy by linear motors  42  which are arranged on both sides of the Y stage  41  respectively. An Xθ stage  45  which moves in the X-axis direction and in the direction rotated by θ with respect to a Z axis is mounted on the Y stage  41 . 
     The projection optical system  50  is a reflection-type projection optical system which is referred to as an Ophner type reflection-type projection optical system. The projection optical system  50  is supported on a support base  74 . On the reflection-type projection optical system  50 , in addition to a reflection mirror, a fixed mirror which performs the measurement using a laser interferometer is mounted. A catadioptric Dyson-type projection optic system or a refraction-type projection optical system may be used in place of the Ophner type projection optical system. 
     The substrate stage  60  is arranged on an upper surface of a base  72 . The substrate stage  60  includes XY stages  62  which are movable in the XY scanning directions. The substrate stage  60  is also configured to be movable in the Z axis direction in the same manner as the mask stage  40 . The XY stages  62  are driven at a high speed and with high accuracy by linear motors arranged on both sides of the XY stages  62 . 
     The substrate table  60  includes a vacuum chuck  69  which sucks the substrate CB. The term “substrate CB” covers an electronic printed circuit board, a glass substrate for a liquid crystal element, or a glass element substrate for a PDP, for example. The vacuum chuck  69  is formed using ceramic, and the vacuum chuck  69  can hold the substrate CB by sucking using a vacuum pump not shown in the drawing. The substrate table  60  is movable also in the Z axis direction. Due to such a constitution, a luminous flux which is reflected on the Ophner type reflection-type projection optical system  50  is incident on the substrate CB and forms an image on the substrate CB. That is, a patterned image of the photomask M is formed on the substrate CB, and this image is transferred onto the substrate CB by a photoresist applied to the substrate CB. 
     An alignment camera AC is mounted on the support base  74  which supports the projection optical system  50  thereon. The alignment camera AC detects an alignment mark formed on the substrate CB. The alignment camera AC also detects a blade alignment mark formed on a light blocking blade described later. 
     The substrate table  60  includes a first light blocking device  80  around the vacuum chuck  69 . The first light blocking device  80  can shield a peripheral portion of the substrate CB which is held by the vacuum chuck  69  from light. The first light blocking device  80  is mounted on the substrate stage  60 . Accordingly, the first light blocking device  80  is movable in the X-axis direction, in the Y-axis direction and in the Z axis direction with respect to the optical axis OA of the projection optical system  50 . 
     &lt;Schematic Constitution of First Light Blocking Device  80 &gt; 
       FIG. 3  is a plan view of the XY stages  62  and the first light blocking device  80  as viewed in the Z axis direction.  FIG. 3  shows a state where the substrate CB is placed on the vacuum chuck  69 , and light blocking blades  86  of the first light blocking device  80  described later are opened. 
     The vacuum chuck  69  is arranged at the approximately center of the XY plane on the XY stages  62 . A pair of substrate lifters  68  is arranged in the Y-axis direction in a state where the pair of substrate lifters  68  sandwiches the vacuum chuck  69  therebetween. The substrate lifters  68  move the substrate CB in the vertical direction (Z-axis direction) at the time of loading or unloading the substrate CB. 
     Moving bases  81  of the moving device are arranged outside the pair of substrate lifters  68  in the Y-axis direction respectively. A moving guide  82  and an actuator  83  such as a drive motor are arranged on each moving base  81 . Lifting guides  88  are arranged on both sides of the moving base  81  in the X-axis direction, and a lifting actuator  89  is arranged at the approximately center of the moving base  81 . The lifting guides  88  and the lifting actuator  89  are provided for elevating or lowering the moving base  81  in the Z axis direction. 
     A pair of light blocking bases  84  ( 84 A,  84 B) is mounted on the pair of moving guides  82  and the actuators  83 . A pair of light blocking blades  86  ( 86 A,  86 B) is mounted on the pair of light blocking bases  84  respectively. Positioning pins  85  are mounted on the light blocking base  84 . The light blocking blade  86  includes a semicircular opening portion which conforms to, for example, the size of the substrate CB such as 6 inches or 8 inches or a size of a light blocking area. The light blocking blades  86  which differ in size or shape depending on a usage are suitably mounted on or removed from the light blocking base  84 . The positioning pins  85  are used for positioning the light blocking blade  86  at the time of mounting the light blocking blades  86  on the light blocking base  84 . 
     The light blocking blade  86 A and the light blocking blade  86 B approach each other or are moved away from each other as indicated by an arrow AR along with the movement of the moving guides  82  and the actuator  83  in the X-axis direction. When the light blocking blade  86 A and the light blocking blade  86 B approach each other, the light blocking blade  86 A and the light blocking blade  86 B form an annular shape and cover the peripheral portion of the substrate CB. 
     In general, alignment marks AM 1  are formed on the substrate CB by exposure. A blade-use alignment mark AM 2  is also formed on the light blocking blades  86 . When the XY stages  62  move in the XY-axis directions, the alignment marks AM 1  or the blade-use alignment marks AM 2  move to an area directly below the alignment camera AC. The alignment camera AC performs the global alignment where the extension and the shrinkage of the whole substrate CB or the position of the substrate CB is measured by imaging three to ten and several alignment marks AM 1 . At this point of time, the alignment camera AC can also calculate the center position of the substrate CB on the XY plane. Further, the alignment camera AC confirms positions of the light blocking blade  86 A and the light blocking blade  86 B by imaging the blade-use alignment marks AM 2 . 
     &lt;Direction of Conveyance (Loading and Unloading) of Substrate using Conveyance Arm&gt; 
       FIG. 4  is a perspective view showing a state where the substrate CB is placed on the vacuum chuck  69  of the substrate table  60  by the conveyance arm. In  FIG. 4 , a conveyance robot RB 1  and a conveyance robot RB 2  convey the substrate CB. 
     Both the conveyance robot RB 1  and the conveyance robot RB 2  are formed of a so-called scalar-type conveyance robot which includes a plurality of rotational axes. A conveyance arm  92  having a distal end on which the substrate CB is placed is mounted on the conveyance robot RB 1 , and a conveyance arm  94  having a distal end on which the substrate CB is placed is mounted on the conveyance robot RB 2 . The conveyance arms  92 ,  94  hold the substrate CB by sucking such as vacuum sucking. Although it is not always necessary to provide two conveyance robots, for example, the conveyance robot RB 1  plays a role of loading the substrate CB in the vacuum chuck  69 , and the conveyance robot RB 2  plays a role of unloading the substrate CB from the vacuum chuck  69 . 
     Here, assume that the conveyance robot RB has the positioning accuracy of ±2 mm in the X-axis direction with respect to the vacuum chuck  69 , and has the positioning accuracy of ±1 mm in the Y-axis direction with respect to the vacuum chuck  69 . That is, the conveyance robot RB 1  is liable to be displaced in the X-axis direction compared to in the Y-axis direction. Accordingly, there exists a high possibility that the substrate CB is displaced in the X-axis direction with respect to the center position of the vacuum chuck  69 . 
     Here, the moving guide  82  and the actuator  83  are arranged to be movable in the X-axis direction. Although the conveyance robot RB 1  is liable to be displaced in the X-axis direction compared to in the Y-axis direction, such displacement can be minimized by such movement of the guides  82  and the actuator  83  in the X-axis direction. 
     &lt;Manner of Operation of First Light Blocking Device  80 &gt; 
       FIG. 5  is an operation flowchart of the first light blocking device  80 . The manner of operation of the first light blocking device  80  is explained in conjunction with  FIG. 6 .  FIG. 6A  is a view showing a state where the substrate CB is loaded on or is unloaded from the vacuum chuck  69 .  FIG. 6B  is a view showing a state where the peripheral portion of the substrate CB is covered with the light blocking blades  86 . 
     In step S 101 , the conveyance arm  92  (see  FIG. 4 ) loads the substrate CB on the vacuum chuck  69  from the X-axis direction. In this embodiment, assume that the positioning accuracy of the conveyance arm  92  in the X-axis direction is lower than the positioning accuracy of the conveyance arm  92  in the Y-axis direction. Accordingly, the moving guide  82  and the actuator  83  which are arranged on the moving base  81  are arranged to be movable in the X-axis direction. Further, at the time of loading the substrate CB, the light blocking blades  86  are in an open state, and the moving base  81  is in a lowered state. A state shown in  FIG. 6A  is a state taken in step S 101 . 
     In step S 102 , the conveyance arm  92  loads the substrate CB on the vacuum chuck  69  from the X-axis direction. Here, the substrate lifter  68  is in an elevated state, and the substrate CB is transferred from the conveyance arm  92  to the substrate lifter  68 . Then, the substrate lifter  68  is lowered and the substrate CB is placed on the vacuum chuck  69 . Thereafter, the vacuum chuck  69  holds the substrate CB by vacuum chucking so that the substrate CB is fixed. After finishing the transfer of the substrate CB, the conveyance arm  92  retracts. 
     In step S 103 , the moving base  81  is elevated in the Z axis direction by the lifting guides  88  and the lifting actuator  89 . Then, the moving base  81  is moved to a height approximately equal to a height of the substrate CB in the Z axis direction. 
     In step S 104 , the alignment camera AC images approximately three to ten and several alignment marks AM 1  on the substrate CB. It is not always necessary to image all alignment marks AM 1 . Then, positions of respective shots exposed on the substrate CB or the like are calculated, and the center position of the substrate CB is calculated. 
     In step S 105 , the alignment camera AC images the blade-use alignment marks AM 2  on the light blocking blade  86 A and the light blocking blade  86 B. Then, positions of the light blocking blade  86 A and the light blocking blade  86 B are calculated. A height of the substrate CB in the Z axis direction and a height of the light blocking blades  86  in the Z axis direction are approximately equal and hence, the alignment camera AC can image the alignment marks AM 1  and the blade-use alignment marks AM 2  continuously. The processing in step S 104  may be performed after the processing in step S 105 . 
     In step S 106 , it is determined whether the center position of the substrate CB is largely displaced from the center position of the vacuum chuck  69  by an amount exceeding a predetermined amount. When the center position of the substrate CB is at the center position of the vacuum chuck  69  almost accurately, the processing advances to step S 107 . On the other hand, when the center position of the substrate CB is largely displaced by an amount exceeding the predetermined amount, the processing advances to step S 108 . 
     In step S 107 , the moving guides  82  and the actuator  83  move the light blocking blade  86 A and the light blocking blade  86 B in the X-axis direction. A moving amount (distance) of the light blocking blade  86 A and a moving amount (distance) of the light blocking blade  86 B are equal, that is, the moving amount is a distance which the light blocking blade  86 A and the light blocking blade  86 B move to the reference position at which the light blocking blade  86 A and the light blocking blade  86 B form an annular shape. When positions of the light blocking blade  86 A and the light blocking blade  86 B calculated in step S 105  are displaced from normal positions, the actuator  83  moves the light blocking blade  86 A and the light blocking blade  86 B to the reference position by taking into account an error caused by such displacement. 
     In step S 108 , the moving guides  82  and the actuator  83  move the light blocking blade  86 A and the light blocking blade  86 B in the X-axis direction by taking into account a displacement amount of the center position of the substrate CB from the center position of the vacuum chuck  69 . In this embodiment, the positional accuracy of the conveyance arm  92  is low in the X-axis direction. Therefore, the moving amounts of the light blocking blade  86 A and the light blocking blade  86 B are adjusted to properly shield the peripheral portion of the substrate CB from light. 
     A state shown in  FIG. 6B  is a state taken in step S 107  or in step S 108 . 
     In step S 109 , on the substrate CB, exposure is performed in conformity a pattern of the photomask M. 
     In step S 110 , the moving guides  82  and the actuator  83  retract the light blocking blade  86 A and the light blocking blade  86 B from an area above the substrate CB by moving the light blocking blade  86 A and the light blocking blade  86 B in the X-axis direction. 
     In step S 111 , the moving base  81  is lowered in the Z axis direction by the lifting guides  88  and the lifting actuator  89 . 
     In step S 112 , the substrate lifter  68  is elevated so that the substrate CB is lifted from the vacuum chuck  69 . The conveyance arm  92  enters a space formed below the substrate CB from the X-axis direction and, then, the substrate CB is unloaded. 
     In this embodiment, the substrate lifter  68  of the projection aligner  100  is elevated and lowered in the Z axis direction. Accordingly, the respective steps of the above-mentioned flowchart are taken. However, the first light blocking device  80  may be configured such that the substrate lifter  68  is fixed and the vacuum chuck  69  is elevated and lowered in the Z axis direction. 
     &lt;Constitution of Light Blocking Blades  86 &gt; 
     The constitution of the light blocking blades  86  is explained. As shown in  FIG. 6B , the light blocking blade  86 A and the light blocking blade  86 B form an annular shape when the light blocking blade  86 A and the light blocking blade  86 B approach each other, and cover the peripheral portion of the substrate CB.  FIG. 7A  is a view showing the light blocking blades  86  having an annular shape and the light blocking base.  FIG. 7B  is an enlarged cross-sectional view taken along a line B-B in  FIG. 7A . 
     As shown in  FIG. 7A , the pair of light blocking blades  86  ( 86 A,  86 B) which is positioned by the positioning pins  85  is mounted on the pair of light blocking bases  84  ( 84 A,  84 B). The light blocking blade  86  is formed of a metal plate or a non-metal plate which is light in weight and has a high strength such as a stainless steel (SUS) plate, a titanium plate or a ceramics plate. A surface of the light blocking blade  86  is plated with black chromium or is subjected to a KEPLA-COAT (trade mark) treatment so that light resistance of the light blocking blade  86  is enhanced. The substrate CB usually has a circular shape and hence, the respective light blocking blades  86  have a semicircular opening portion. 
     When the light blocking blade  86 A and the light blocking blade  86 B approach each other, a distal end  86 AT of the light blocking blade  86 A and a distal end  86 BT of the light blocking blade  86 B overlap each other in the Z axis direction. As shown in  FIG. 7B , a thickness of the light blocking blade  86 A and a thickness of the light blocking blade  86 B are approximately 0.3 mm, and the distal ends  86 AT,  86 BT are formed into a thin wall portion having a thickness of 0.1 mm. It is preferable that a thickness of the light blocking blade  86  ( 86 A,  86 B) be as small as possible for enabling the formation of a clear light blocking area at the time of exposure. It is particularly preferable that a thickness of the light blocking blade  86  is 0.5 mm or less. The distal end  86 AT of the light blocking blade  86 A is formed in the +Z axis direction and the distal end  86 BT of the light blocking blade  86 B is formed in the −Z axis direction and hence, the distal end  86 AT and the distal end  86 BT overlap each other without colliding with each other. 
     &lt;Shape of Light Blocking Blade&gt; 
       FIG. 8  shows modifications relating to a shape of a light blocking blade  86 . A shape of the light blocking blade  86  in this embodiment can takes various shapes as described hereinafter. 
     A light blocking blade  86  shown in  FIG. 8A  is constituted of light blocking blades  86 C,  86 D. A light blocking portion  86 Nt for a notch is formed on the light blocking blade  86 C in conformity with a shape of a notch formed on a substrate CB. 
     A light blocking blade  86  shown in  FIG. 8B  is constituted of light blocking blades  86 E,  86 F. A light blocking portion  86 Nt for a notch is formed on one distal end of the light blocking blade  86 E and one distal end of the light blocking blade  86 F respectively in conformity with a shape of a notch formed on a substrate CB. 
     A light blocking blade  86  shown in  FIG. 8C  is constituted of light blocking blades  86 G,  86 H. A light blocking portion  86 Of for an orientation flat portion is formed on the light blocking blade  86 H in conformity with a shape of an orientation flat portion formed on a substrate CB. 
     A light blocking blade  86  shown in  FIG. 8D  is constituted of light blocking blades  86 I,  86 J. A light blocking portion  860   f  for an orientation flat portion is formed on one distal end of the light blocking blade  86 I and one distal end of the light blocking blade  86 J in conformity with a shape of an orientation flat portion formed on a substrate CB. 
     As described above, the shape of the light blocking blade  86  can be suitably changed in conformity with the shape of the substrate CB. Further, cutaway portions  86 Z which are aligned with the positioning pins  85  (see  FIG. 3  and  FIG. 7 ) are formed on the respective light blocking blades  86  and hence, the shape of the light blocking blade  86  can be suitably changed in conformity with the shape of the substrate CB. Further, even when the light blocking blades  86  are not positioned by the positioning pins  85 , the blade-use alignment marks AM 2  are formed on the light blocking blades  86  and hence, the positions of the light blocking blades  86  can be surely grasped. 
     &lt;Modification of Light Blocking Device&gt; 
       FIG. 9  is a view showing a second light blocking device  180 . In the first light blocking device  80  shown in  FIG. 3  and  FIG. 6 , the light blocking blades  86  are elevated and lowered by elevating and lowering the moving base  81  in the Z axis direction, and the light blocking blades  86  are moved in the X-axis direction by moving the light blocking base  84  in the X-axis direction. In the second light blocking device  180 , light blocking blades  86  are moved simultaneously in the Z axis direction as well as in the X-axis direction by a rotary mechanism which includes a rotary shaft extending in the Y-axis direction. 
     In the second light blocking device  180  shown in  FIG. 9 , only a light blocking blade  86 A is shown. A light blocking blade  86 B has the substantially same constitution as the light blocking blade  86 A. The light blocking blade  86 A is arranged on a light blocking base  182  while being positioned in place. The light blocking base  182  is mounted on a rotary arm  186  by way of a pin  183 . An actuator  187  is also mounted on the rotary arm  186  by way of a pin  185 . The rotary arm  186  is mounted in a rotatable manner about a rotary shaft  184 . Also the actuator  187  is rotatable by way of a rotary pin  188 . 
     When the rotary arm  186  is rotated by about a half turn about the rotary shaft  184  as indicated by a chained line, the light blocking blade  86 A is elevated and lowered in the Z axis direction as indicated by a double-dashed chained line and is moved in the X-axis direction. The second light blocking device  180  makes the light blocking blade  86 A cover the peripheral portion of the substrate CB or retract from the substrate CB by operating the light blocking blade  86 A in such a manner. 
     Here, when the loaded substrate CB is displaced from the center of a vacuum chuck  69 , the light blocking blade  86 A is moved to the reference position by adjusting a drive amount of the actuator  187 . 
       FIG. 10  is a view showing a third light blocking device  280 . The third light blocking device  280  moves light blocking blades  86  by a rotary mechanism which includes a rotary shaft extending in the Z axis direction. 
     As shown in  FIG. 10A , the third light blocking device  280  includes a moving base  281 , and a rotary shaft  282  and a pair of actuators  285  are arranged on the moving base  281 . With respect to the pair of actuators  285 , each actuator  285  has one end thereof connected to a pin  286  mounted on the moving base  281  and has the other end thereof connected to a pin  287  mounted on a light blocking base  284 . 
     The moving base  281  is movable in the Y-axis direction by an actuator and guides not shown in the drawing. Further, a pair of light blocking bases  284  is rotatably mounted on the rotary shaft  282  of the moving base  281 . The pair of light blocking bases  284  can be opened or closed along with the expansion or the shrinkage of the actuator  285 . 
     Along with the movement of the moving base  281  in the Y-axis direction as indicated by an arrow AR 1  in  FIG. 10B , the light blocking blade  86 A and the light blocking blade  86 B retract from the substrate CB. Simultaneously, along with the shrinkage of the actuator  285 , the light blocking blade  86 A and the light blocking blade  86 B are opened as indicated by an arrow AR 2 . The operation opposite to the above-mentioned operation is taken when the substrate CB is to be shielded from light. 
     When the loaded substrate CB is displaced from the center of the vacuum chuck  69 , the light blocking blades  86 A,  86 B are moved to the reference position by adjusting a drive amount of the pair of actuators  285 . 
     Thus, as described above, an operation of setting and changing the light blocking unit can be omitted from the exposure process if plural kinds of light blocking blades are prepared for each size of the substrates CB or each shape of the light blocking regions. The first light blocking device  80 , the second light blocking device  180  and the third light blocking device  280  can be used properly by considering the displacement amount of the conveyance arm (robot) or other conditions.