Patent Publication Number: US-8994957-B2

Title: Detection method and detection apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of, and claims priority to, U.S. patent application Ser. No. 13/568,897, filed Aug. 7, 2012, now U.S. Pat. No. 8,547,559, which is a continuation of PCT/JP2011/000700, filed Feb. 8, 2011, which claims the benefit of Japanese Patent Application No, 2010-025935 filed Feb. 8, 2010, and the disclosures of all three applications of which are incorporated herein by reference, 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a detection method and a detection apparatus. 
     2. Related Art 
     Of a particular interest is a layered semiconductor device in which a plurality of substrates with electronic circuits formed thereon are stacked on each other in order to provide increased mount density for the semiconductor device. To stack a plurality of substrates on each other, a substrate bonding apparatus may be used to align and bond the substrates (see, for example, Japanese Patent Application Publication No. 2009-231671). 
     To stack a plurality of substrates on each other, the substrates may be appropriately positioned by referring to the outlines of the respective substrates. In this case, the outlines are detected by means of a transmissive optical system. However, when such an optical system is used to detect the outline of a layered substrate having a plurality of substrates stacked on each other and, in particular, the upper substrate is smaller in outline than the lower substrate, it is difficult to detect an accurate outline of the upper substrate. 
     SUMMARY 
     Therefore, it is an object of an aspect of the innovations herein to provide a detection method and a detection apparatus, which are capable of overcoming the above drawbacks accompanying the related art. The above and other objects can be achieved by combinations described in the claims. A first aspect of the innovations may include a detection method of detecting a position of an uppermost substrate of a plurality of substrates stacked on each other. The detection method includes applying illumination to a region covering a portion of an edge of the uppermost substrate and a portion of a lower substrate stacked with the uppermost substrate, identifying a position of the edge of the uppermost substrate based on a position of a step-like portion present in the region due to a step formed between the uppermost substrate and the lower substrate, and identifying a position of the uppermost substrate based on the position of the edge of the uppermost substrate. 
     A second aspect of the innovations may include a detection apparatus for detecting a position of an uppermost substrate of a plurality of substrates stacked on each other. The detection apparatus includes an illuminating section that applies illumination to a region covering a portion of an edge of the uppermost substrate and a portion of a lower substrate stacked with the uppermost substrate, and a position identifying section that identifies a position of the edge of the uppermost substrate based on a position of a step-like portion present in the region due to a step formed between the uppermost substrate and the lower substrate. 
     The summary clause does not necessarily describe all necessary features of the embodiments of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating the structure of a detection apparatus  100 . 
         FIG. 2  is an explanatory view illustrating an image  106  of a portion of an edge of a substrate obtained by an image obtaining section. 
         FIG. 3  illustrates how to identify the position of the portion of the edge of the substrate by means of a position identifying section. 
         FIG. 4  shows a curve to illustrate how luminance varies at a step-like portion E. 
         FIG. 5  is an explanatory view illustrating the detection conditions under which the detection apparatus operates. 
         FIG. 6  is an explanatory view illustrating how to obtain images of three different portions of the edge of the substrate. 
         FIG. 7  is an explanatory view illustrating how to obtain images while moving substrates. 
         FIG. 8  is an explanatory view illustrating how to obtain images while moving substrates. 
         FIG. 9  is an explanatory view illustrating how to judge the outline and position of a substrate based on the detected position of the edge of the substrate. 
         FIG. 10  is a front view illustrating an embodiment of scanning incident light. 
         FIG. 11  is a front view illustrating the embodiment of scanning incident light. 
         FIG. 12  is a front view illustrating another embodiment of scanning incident light. 
         FIG. 13  is an explanatory view illustrating how to obtain images of four different portions of the edge of the substrate. 
         FIG. 14  is an explanatory view showing an image of a portion of edges of substrates of a three-layered substrate. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, some embodiments of the present invention will be described. The embodiments does not limit the invention according to the claims, and all the combinations of the features described in the embodiments are not necessarily essential to means provided by aspects of the invention. 
       FIG. 1  is a perspective view schematically illustrating the structure of a detection apparatus  100  relating to an embodiment. The detection apparatus  100  is configured to detect the position of an upper substrate  104 , which is stacked on a lower substrate  102 . The detection apparatus  100  includes a stage  101 , an illuminating section  108 , an image obtaining section  110 , and a position identifying section  120 . 
     The lower substrate  102  and the upper substrate  104  are stacked in the thickness direction by means of a substrate bonding apparatus or the like. The upper substrate  104  is smaller in outline than the lower substrate  102 . Therefore, at the edge of the upper substrate  104 , a step is formed between the upper surface of the upper substrate  104  and the upper surface of the lower substrate  102 . 
     The stage  101  is configured to have the lower substrate  102  and the upper substrate  104  placed thereon for edge detection. The stage  101  is translated along the X, Y and Z axes. The stage  101  may be a stage for use in an apparatus configured to bond another substrate onto the upper substrate  104  or the like. In this case, the stage  101  may be configured to rotate with respect to the X, Y and Z axes. On the upper surface of the stage  101 , a reference mark  103  is provided. In the perspective views including  FIG. 1 , the X and Y axes respectively extend in the left-right direction and back-forth directions within the upper surface of the stage  101 . The Z axis extends upwards perpendicularly to the X and Y axes. 
     The reference mark  103  is used to, for example, adjust the illuminating section  108  and the image obtaining section  110 . For example, prior to the task of detecting the position of a substrate, the reference mark  103  is used to bring an optical system into a focus to enable an image capturing section  105  to form a sharp image of the reference mark  103  when a slit image  114  is applied to the reference mark  103 . Furthermore, the reference mark  103  is used to associate a position on the stage  101  with a position on the image captured by the image capturing section  105 . 
     The illuminating section  108  provides the slit image  114  used to detect a position of a substrate. The illuminating section  108  includes a light source  119 , a lens  118 , a slit  116 , and a lens  115  in the stated order. 
     The light source  119  emits light having a wavelength that can be detected by the image capturing section  105 , for example, emits visible light when the image capturing section  105  is capable of imaging visible light. The lens  118  collects the light from the light source  119 . The slit  116  delimits the illumination used to detect the position of the upper substrate  104 . The lens  115  collects the light that has passed through the slit  116  to form the slit image  114  on the upper surface of the lower substrate  102  and the upper surface of the upper substrate  104 . 
     The illuminating section  108  illuminates the lower substrate  102  and the upper substrate  104  at angle with respect to the plane orientation of the lower substrate  102  and the upper substrate  104 , for example, obliquely downward from top left in  FIG. 1 . The slit image  114  provided by the illuminating section  108  has, on the lower substrate  102  and the upper substrate  104 , an elongated shape extending in the radial direction of the disk-like lower substrate  102  and the upper substrate  104 . The area illuminated by the slit image  114  covers a portion of the edge of the upper substrate  104 . The illuminating section  108  stores in advance the position where the edge is expected to be positioned when the layered substrate is correctly placed at a predetermined position on the stage  101  and applies illumination to the expected position. The edge is a circumference when the lower substrate  102  and the like are shaped as a disk. The edge may have a characteristic such as a notch. 
     The image obtaining section  110  includes an image capturing section  105  and a lens  112 . The image obtaining section  110  images a region covering a portion of the edge of the upper substrate  104  at angle with respect to the plane orientation of the upper substrate  104  and the like, obliquely downward from top right in  FIG. 1 . In this case, the image obtaining section  110  also stores in advance the position where the edge is expected to be positioned when the layered substrate is correctly placed at a predetermined position on the stage  101  and images a region covering the expected position. 
     The lens  112  focuses the light reflected from the upper surfaces of the lower substrate  102  and the upper substrate  104  onto the image capturing section  105 . The examples of the image capturing section  105  include a CCD, a CMOS or the like having two-dimensionally arranged pixels. The image capturing section  105  produces an image  106  by, on the pixel basis, converting the optical signals of the image formed on the image capturing surface into electrical signals. The position identifying section  120  analyzes the image  106  and identifies the position of the edge of the upper substrate  104  based on the position of the step-like portion present in the image  106 . 
     The optical systems of the illuminating section  108  and the image obtaining section  110  are not limited to the structures shown in  FIG. 1 . For example, the lenses  118 ,  115  and  112  only schematically represent the optical systems and each is not limited to a single lens. The optical system of the image obtaining section  110  may be a non-tilted lens optics or tilted lens optics. If a tilted lens optics is employed, the image obtaining section  110  can focus incoming light within a large region on the surfaces of the upper substrate  104  and the lower substrate  102  that are at angle with respect to the main light ray by tilting the image capturing section  105 . 
     The following describes a detection method of detecting the position of the upper substrate  104  using the detection apparatus  100  shown in  FIG. 1 . The detection method includes a step of obtaining an image and a step of identifying the position. The step of obtaining an image includes a step of applying, by the illuminating section  108 , illumination from top left to a region covering a portion of the edge of the upper substrate  104  to form the slit image  114 , and a step of imaging, by the image capturing section  105 , at angle with respect to the plane orientation of the lower substrate  102  and the upper substrate  104 , the slit image  114  reflected by the upper surfaces of the lower substrate  102  and the upper substrate  104  to obtain the image  106 . 
       FIG. 2  is an explanatory view illustrating the image  106  of a portion of the edge of the substrate obtained by the image obtaining section  110 . In the image  106 , an upper substrate reflected image  132  corresponds to a portion of the slit image  114  that is reflected by the upper substrate  104 . On the other hand, a lower substrate reflected image  134  corresponds to a portion of the slit image  114  that is reflected by the lower substrate  102 . 
     The step of identifying the position includes a step of forwarding the image  106  from the image capturing section  105  to the position identifying section  120  and a step of performing image analysis by the position identifying section  120  to identify the position of the edge of the upper substrate  104  based on the position of the step-like portion E present between the upper substrate reflected image  132  and the lower substrate reflected image  134 . 
     The position of the step-like portion E in the image  106  corresponds to the position of the edge of the upper substrate  104 . In  FIG. 1 , when the edge of the upper substrate  104  is moved toward the back within the region illuminated by the slit image  114 , the position of the step-like portion E is moved to the left in the image  106 . On the other hand, when the edge of the upper substrate  104  is moved toward the front in  FIG. 1 , the position of the step-like portion E is moved to the right in the image  106 . Thus, the position of the edge of the upper substrate  104  can be identified by analyzing the position of the step-like portion E. 
     The position identifying section  120  stores thereon in advance the vertical width D of the upper substrate reflected image  132  based on the size of the slit  116 , the optical magnifications of the illuminating section  108  and the image obtaining section  110 , and the like. The position identifying section  120  stores thereon in advance a maximum value L max  of the horizontal width L of the upper substrate reflected image  132  based on the size of the slit  116 , the optical magnifications of the illuminating section  108  and the image obtaining section  110  and the like. 
     To analyze the image  106 , a selection window  136  is first used to select a region of the image to be analyzed. In order to identify the upper and lower boundaries of the upper substrate reflected image  132  in the image  106 , the vertical width b of the selection window  136  is preferably larger than the width D and the horizontal width a of the selection window  136  is preferably smaller than the width L max . Since the upper substrate reflected image  132  has higher luminance than the surrounding, the position identifying section  120  can identify the upper and lower boundaries and the width D of the upper substrate reflected image  132  by analyzing the vertical luminance variation in the image selected by the selection window  136 . 
       FIG. 3  illustrates how to identify the position of the step-like portion. In order to identify the position of the step-like portion E, the horizontal width a of the selection window  136  is preferably larger than the width L max , and the vertical width b of the selection window  136  is preferably smaller than the width D. The position identifying section  120  can identify the position of the step-like portion E by analyzing the horizontal luminance variation in the image selected by the selection window  136 . The position of the step-like portion E in the image  106  can be used to identify the position, on the stage  101 , the edge of the upper substrate  104  in the region illuminated by the slit image  114 . 
       FIG. 4  is a curve to illustrate how the luminance varies at the step-like portion E of the upper substrate reflected image  132  present in the image  106 . In  FIG. 4 , the horizontal axis represents the horizontal coordinates in the image  106  shown in  FIG. 2  and the like, and the vertical axis represents the luminance.  FIG. 4  shows the luminance variation in the upper substrate reflected image  132 . The upper substrate reflected image  132  is ideally expected to exhibit sharp luminance variation at the step-like portion E as indicated by a polygonal line  142 . In reality, however, the luminance of the upper substrate reflected image  132  gradually varies around the step-like portion E as shown by a curve  144  due to the aberration of the optical systems and the like. Here, the half width Sx of the region in which the luminance gradually varies is referred to as a blurring amount. 
     The blurring amount Sx caused by the diffraction on the image capturing surface is on the order of βλ/NA, where β denotes the imaging magnification ratio of the optical system, λ denotes the wavelength of the incident light and NA denotes the numerical aperture of the lens. To accurately identify the step-like portion E, three or more measurements are preferably included within the range of the blurring amount. For example, when the image capturing section  105  is formed by using a CCD, three or more pixels are included within the range of Sx under the condition of (βλ/NA)&gt;3 u, where u denotes the size of the pixel of the CCD. In other words, the condition is transformed into NA&lt;(βλ/3 u). 
     For example, when β=1, u=5 μm, and λ=0.67 μm, NA&lt;0.045. This conditional expression for NA represents the preferable upper limit for NA when the variables β, u and λ take the above-mentioned values. When a tilted lens optics is used, the variable β is replaced with the lateral magnification β′ of the tilted lens optics. 
       FIG. 5  is an explanatory view illustrating other conditions. In addition to the blurring amount Sx shown in  FIG. 4 , there is a blurring amount Sy in the vertical direction of the upper substrate reflected image  132  and the lower substrate reflected image  134 . In order to identify the step-like portion E, the height H of the step-like portion E is preferably larger than (Sy+mu), where m denotes the number of pixels used to identify the step-like portion E and thus is an integer of 1 or more. Considering that the blurring amount Sy is also on the order of βλ/NA, the following expression is preferably satisfied
 
 H &gt;(βλ/ NA )+ mu   (1)
 
     The height H of the step-like portion E corresponds to the interval h between the upper surface of the lower substrate  102  and the upper surface of the upper substrate  104 , in other words, to the thickness of the upper substrate  104 . The value of the height H is defined by the following expression.
 
 H= 2 h β sin θ i   (2)
 
     Here, h denotes the distance between the upper surface of the lower substrate  102  and the upper surface of the upper substrate  104 , and θ i  denotes the incident angle of the incident light. When a tilted lens optics is used, the variable β is replaced with the lateral magnification β′ of the tilted lens optics. 
     When θ i  is 90°, sin θ i  takes a maximum value of 1. Thus, the maximum value of H can be represented by the following expression.
 
 H   max =2 hβ   (3)
 
     By substituting Expression (3) into Expression (1), the following expression is obtained.
 
2 h β&gt;(βλ/ NA )+ mu   (4)
 
     For example, when β=1, u=5 μm, λ=0.67 μm and m=1, the condition of NA&gt;0.0012 should be satisfied in order to detect a distance h of 30 μm. This conditional expression for NA represents the preferable lower limit for NA when the variables β, u, λ and m take the above-mentioned values. 
     In order to more accurately detect the shape of the upper substrate  104 , the incident plane including the incident light and the reflected light is preferably in contact with the edge of the upper substrate  104 . If the incident plane is off the tangential line direction of the substrate, the detected results may contain errors. In order to reduce such errors to fall within the acceptable range, the angle formed between the incident plane and the tangential line direction of the upper substrate  104  is preferably adjusted to be 5° or less. 
       FIG. 6  illustrates another embodiment of how to identify the position of the edge of the upper substrate  104 . According to this embodiment, the position of the upper substrate  104  is identified by applying slit images  114 ,  172  and  174  to three different portions on the edge of the upper substrate  104  and obtaining images formed by the reflections from the respective portions. In this case, detection apparatuses  100  corresponding to the slit images  114 ,  172  and  174  are provided. Each of the detection apparatuses  100  can identify the position of the edge of a corresponding one of the portions in accordance with the above-described detection method. 
     In this embodiment, provided that the shape of the upper substrate  104  is known in advance, the position of the upper substrate  104  on the stage  101  can be more accurately detected by identifying the positions of three different portions of the edge of the upper substrate  104  in the image  106 . For example, if the upper substrate  104  is shaped like a disk, the position of the center of the upper substrate  104  and the radius of the upper substrate  104  can be identified by identifying the positions of three different portions of the edge of the upper substrate  104 . Thus, the position of the upper substrate  104  can be accurately detected. This embodiment can not only achieve highly efficient detection but also reduce the errors that may occur when a plurality of portions of a substrate are detected by moving the substrate. 
       FIGS. 7 and 8  illustrate further different embodiments of identifying the position of the edge of the upper substrate  104 .  FIGS. 7 and 8  illustrate operations performed after the operation shown in  FIG. 6 . According to this embodiment, the upper substrate  104  and the like are moved relative to the regions to be imaged and the illumination to be applied to the upper substrate  104  and the like, in order to obtain images of a plurality of portions and identify a characteristic such as a notch. 
     In this case, as shown in  FIG. 7 , the slit image  114  illuminates the region that includes the notch of the upper substrate  104 , the slit image  172  illuminates the position 90 degrees rotated away from the notch, and the slit image  174  illuminates the position 180 degrees rotated away from the notch. The slit images  114 ,  172  and  174  provide elongated illumination extending in the radial direction of the upper substrate  104  at their respective positions. Each of the detection apparatuses  100  obtains an image of a corresponding one of the regions and identifies the position of a corresponding portion of the edge. As shown in  FIG. 7 , the identification of the notch of the upper substrate  104  can identify how much the upper substrate  104  has rotated. 
     In  FIGS. 6 to 8 , the slit images  114  and  174  longitudinally extend in the Y axis and the slit image  172  longitudinally extents in the X axis. In this case, the incident plane of the slit image  114  or  174  is vertical to the Y axis. The incident plane of the slit image  172  is vertical to the X axis. 
     In  FIGS. 7 and 8 , the stage  101  is moved in the X direction, or to the right in  FIGS. 7 and 8 , from the position of the upper substrate  104  and the like shown in  FIG. 6 , as a result of which the upper substrate  104  and the lower substrate  102  are moved and a plurality of different portions of the edge are thus detected. In this case, the image obtaining section  110  captures a plurality of images  106 , while the illuminating section  108  and the image obtaining section  110  remains stationary and the stage  101  is moved at a constant rate. Here, the stage  101  may be moved intermittently and the images  106  may be obtained while the stage  101  is temporarily stationary. 
       FIG. 9  illustrates, as an example, the information about the plurality of different portions of the edge that is obtained by the embodiment shown in  FIGS. 6 to 8 .  FIG. 9  shows the position (Y1, Y2, . . . ) of the step-like portion in the image  106  corresponding to the slit image  114  in  FIGS. 6 to 8  and the associated position (X1, X2, . . . ) on the X axis of the stage  101 . Based on the shown information, the position of the notch on the stage  101  can be identified in the X and Y axes. 
     The method in which a plurality of portions of the edge are identified by moving the upper substrate  104  and the like is not limited to the case shown in  FIGS. 6 to 8  where three slit images are applied to the layered substrate, in other words, the case where the three detection apparatuses  100  are used to identify three different points on the layered substrate. This method is applicable to a case where a single point is identified as shown in  FIG. 1 , and to a case where more or less than three points are identified. In the case where a single point is identified, the position and shape of the upper substrate  104  can be detected by moving the upper substrate  104  and the like to identify a plurality of portions of the edge. 
     When the stage  101  is moved, vibration and the like may occur and change the relative positions of the stage  101  and the image capturing section  105  during the movement. This may lead to erroneously identified positions. When a plurality of portions are identified as shown in  FIGS. 6 to 8 , on the other hand, the detection apparatuses  100  associated with the slit images  114  and  174  detect the variation in position resulting from the vibration in the Y axis. The detected variation in position resulting from the vibration in the Y axis is used to correct the value in the Y axis included in the position information identified by using the slit image  172 . Similarly, the detection apparatus  100  associated with the slit image  172  detects the variation in position resulting from the vibration in the X axis. The detected variation in position resulting from the vibration in the X axis is used to correct the value in the X axis included in the position information identified by using the slit images  114  and  174 . Such correction enables the shape and position of the upper substrate  104  to be more accurately detected. 
       FIGS. 10 and 11  are front views to illustrate an embodiment of scanning the illumination. According to the embodiment shown in  FIGS. 10 and 11 , a plurality of portions of the edge are detected by moving the illumination to illuminate different regions, instead of moving the stage  101 . 
     As shown in  FIG. 10 , the illuminating section  108  has a parallel plate glass  182  on the side of the image with respect to the lens  115 , in other words, between the lens  115  and the layered substrate. Since the entrance surface of the parallel plate glass  182  is oriented vertical to the principal light ray in  FIG. 10 , the illumination is applied to the position x 1  after transmitting through the parallel plate glass  182 . Here, the position x 1  is on the extended line from the center of the lens in the direction of the principal light ray. 
     As shown in  FIG. 11 , if the parallel plate glass  182  is tilted at angle with respect to the principal light ray through the lens, the position to which the illumination is applied can be moved from x 1  to x 2  without changing the angle at which the illumination is incident on the layered substrate. In this way, a plurality of portions of the edge can be detected by changing the angle of the parallel plate glass  182  to scan the layered substrate with the illumination. 
       FIG. 12  is a front view illustrating another embodiment of scanning the illumination. In  FIG. 12 , the illuminating section  108  has a mirror  184  at the position of the pupil. The slit image  114  can be applied to different positions by changing the angle of the mirror  184 . 
     According to the embodiments shown in  FIGS. 10 to 12 , it is not necessary to move the stage  101  having the layered substrate placed thereon. As a result, the detection apparatus  100  as a whole can be made more compact. 
     In order to more accurately detect the shape of the upper substrate  104 , the incident plane including the incident light and the reflected light is preferably in contact with the edge of the upper substrate  104 . If the stage  101  or incident light is moved within a large area, a large angle may be formed between the edge and the incident plane within the detectable region, in which case the detected result may be less accurate (see  FIGS. 6 to 8 ). Therefore, if the measurement is performed while the stage  101  or incident light is moved, it is preferable to limit the movable range of the stage  101  or incident light. For example, when the slit  116  having a width of 0.065 mm is used to detect the edge of the upper substrate  104  having a size of approximately 300 mm, the upper substrate  104  is pre-aligned in such a manner that the notch is oriented in the Y direction with respect to the center of the substrate and then arranged on the stage  101 , and the edge of the upper substrate  104  may be accurately detected while the stage  101  or incident light is moved within 5 mm or less. 
       FIG. 13  illustrates an embodiment of identifying four different portions. In addition to the slit images  114 ,  172  and  174  shown in  FIG. 6 , a slit image  188  is additionally provided that is applied to the position 180 degrees rotated away from the slit image  172 . In this way, four different portions of the edge can be identified simultaneously. In this case, if one of the four slit images is applied to the position of the notch of the upper substrate  104 , the other three slit images can be used to simultaneously detect the position of the center of the upper substrate  104 . 
       FIG. 14  is an explanatory view showing an image of a portion of edges of substrates that can be obtained by means of the detection apparatus  100  shown in  FIG. 1  when three substrates with different sizes are stacked on each other. For example, when a substrate larger than the lower substrate  102  is placed under the lower substrate  102  in  FIG. 1 , the three substrates produce, in the image  106 , the upper substrate reflected image  132 , the lower substrate reflected image  134  and a three-layered substrate reflected image  192  from the above. In this case, the above-described method can be used to detect the position of the edge of the uppermost upper substrate  104  as long as a sufficiently distinguishable step-like portion E is present in association with the edge of the upper substrate  104  in the upper substrate reflected image  132 . 
     As is apparent from the above, the present embodiment enables an apparatus configured to manufacture a layered semiconductor apparatus by bonding a plurality of substrates together to accurately detect the outlines and positions of the substrates to be bonded together. In this way, the substrates to be bonded together can be accurately aligned with each other. 
     In the above-described embodiment, the image obtaining section  110  is positioned to obtain an image formed by the specular reflection of the illumination applied at angle by the illuminating section  108 . However, the arrangement of the illuminating section  108  and the image obtaining section  110  is not limited to such. As an alternative example, the illuminating section  108  may be at angle with respect to the plane of the substrate, and the image obtaining section  110  may obtain an image in the normal direction of the plane orientation of the substrate. As a further alternative example, the illuminating section  108  may apply the illumination in the normal direction to the plane of the substrate, and the image obtaining section  110  may obtain an image at angle with respect to the plane orientation of the substrate. As a yet further alternative example, the illuminating section  108  and the image obtaining section  110  may be both positioned at angle with respect to the plane of the substrate and off the specular reflection. 
     In the above-described embodiment, the slit image  114  is used as the illumination. However, the examples of the illumination are not limited to such. As an alternative, the negative-positive relation between the slit image  114  and the surrounding may be reversed. In other words, the illumination may be designed to have a slit-like shade surrounded by light. In this case, the illumination is preferably patterned to extend in the radial direction of the substrate when the substrate is circular. 
     While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention. 
     The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order.