Abstract:
A surface inspecting apparatus for inspecting a shape of an inspected surface of an object to be inspected, the surface inspecting apparatus includes: a mounting base for mounting the object; positioning means for positioning the object to an inspecting position on the mounting base; a memory for storing position specifying information for specifying a two-dimensional position of the object when the object is positioned; inputting means for inputting an outer shape data of the object; and edge position determining means for acquiring an edge position of the object based on the stored position specifying information and the inputted outer shape data.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a surface inspecting apparatus for inspecting a surface shape of an object to be inspected.  
           [0002]    In a thin plate such as a semiconductor wafer, an optical disk, a magnetic disk or the like, a surface shape (flatness of surface etc.) effects significant influence on quality. Further, a rapid change in a surface shape is liable to emerge at an edge portion of a thin plate. Hence, when a surface shape of the thin plate which is an object to be inspected is inspected by an interference fringe, or the like, it is requested to accurately grasp an edge position of the shin plate.  
         SUMMARY OF THE INVENTION  
         [0003]    In view of the above-described problem of the related art, it is a technical object of the invention to provide a surface inspecting apparatus capable of inspecting a surface shape with high accuracy by accurately grasping an edge position of an object to be inspected.  
           [0004]    In order to resolve the above-described problem, it is a characteristic of the invention to provide the following constitution.  
           [0005]    (1) A surface inspecting apparatus for inspecting a shape of a surface to be inspected of an object to be inspected comprising:  
           [0006]    a mounting base on which the object is mounted;  
           [0007]    positioning means for positioning the object to an inspecting position on the mounting base;  
           [0008]    a memory which stores position specifying information for specifying a two-dimensional position of the object when the object is positioned;  
           [0009]    inputting means for inputting an outer shape data of the object; and  
           [0010]    edge position determining means for determining an edge position of the object based on the stored position specifying information and the inputted outer shape data.  
           [0011]    (2) The surface inspecting apparatus according to (1), wherein the positioning means includes a guide member attached to the mounting base, with which the object is positioned to the inspecting position by being brought into contact with an edge of the object, and  
           [0012]    wherein the memory stores the position specifying information for specifying the two-dimensional position of the object when the edge of the object is brought into contact with the guide member.  
           [0013]    (3) The surface inspecting apparatus according to (2), further comprising:  
           [0014]    an image taking unit which takes an image of a mark provided for a predetermined position with respect to the guide member; and  
           [0015]    reference position determining means for determining a reference position by processing the taken image including the image of the mark;  
           [0016]    wherein the memory stores the determined reference position information as the position specifying information.  
           [0017]    (4) The surface inspecting apparatus according to (3), wherein the image taking unit takes an image of an interference fringe formed by the inspected surface of the positioned object and a reference surface.  
           [0018]    (5) The surface inspecting apparatus according to (1), further comprising:  
           [0019]    existing region determining means for determining an existing region of the object based on the determined edge position.  
           [0020]    (6) The surface inspecting apparatus according to (1), further comprising:  
           [0021]    analyzing means for determining a three-dimensional shape of the surface of the object; and  
           [0022]    outputting means for outputting information of a positional relationship between the determined edge position and an analyzing region of the analyzing means.  
           [0023]    (7) The surface inspecting apparatus according to (1), further comprising:  
           [0024]    analyzing means for determining a three-dimensional shape of the surface of the object;  
           [0025]    effective region determining means for determining an effective region achieving a predetermined inspection accuracy from a result of analysis by the analyzing means; and  
           [0026]    outputting means for outputting information of a positional relationship between the determined edge position and the determined effective region.  
           [0027]    (8) A surface inspecting apparatus for inspecting a shape of a surface to be inspected of an object to be inspected comprising:  
           [0028]    a mounting base on which the object is mounted;  
           [0029]    a guide member with which the object is positioned to an inspecting position on the mounting base by being brought into contact with an edge of the object;  
           [0030]    a mark provided for a predetermined position with respect to the guide member;  
           [0031]    an image taking unit which takes an image of an interference fringe formed by the inspected surface of the positioned object and a reference surface, and an image of the mark;  
           [0032]    analyzing means for determining a three-dimensional shape of the surface of the object based on the taken image of the interference fringe;  
           [0033]    reference position determining means for determining a reference position by processing the taken image including the image of the mark;  
           [0034]    inputting means for inputting an outer shape data of the object; and  
           [0035]    edge position determining means for determining an edge position of the object based on the determined reference position information and the inputted outer shape data.  
           [0036]    (9) The surface inspecting apparatus according to (8), further comprising:  
           [0037]    outputting means for outputting information on a positional relationship between the determined edge position and an analyzing region of the analyzing means.  
           [0038]    (10) The surface inspecting apparatus according to (8), further comprising:  
           [0039]    effective region determining means for determining an effective region achieving a predetermined inspection accuracy from a result of analysis by the analyzing means; and  
           [0040]    outputting means for outputting information of a positional relationship between the determined edge position and the determined effective region. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]    [0041]FIG. 1 is an outline constitution view of essential portions of an inspecting optical system and a control system of a surface inspecting apparatus.  
         [0042]    [0042]FIG. 2 is a view showing a guide mechanism of a glass plate to be inspected.  
         [0043]    [0043]FIGS. 3A and 3B illustrates views showing a way of determining a reference position (reference line).  
         [0044]    [0044]FIG. 4 is a view showing a guide mechanism of a wafer to be inspected.  
         [0045]    [0045]FIG. 5 is a view showing a vicinity of an edge of an object to be inspected.  
         [0046]    [0046]FIG. 6 is a view showing an existing region, an analyzing region and an effective region in which a result of inspection is reliable of a glass plate to be inspected. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0047]    An embodiment according to the invention will be described below with reference to the drawings. FIG. 1 is a view showing the schematic structure of the main parts of an inspecting optical system and a control system in a surface inspecting apparatus according to the invention. An oblique incidence interferometer is illustrated. A laser beam for an inspection which is emitted from an He—Ne laser beam source  1  as an inspecting light source passes through an expander lens  2  and is then changed into a parallel luminous flux by a collimator lens  3  and the parallel luminous flux is thereafter incident on a prism  4 . A part of the laser beam incident on the prism  4  is transmitted through a reference plane  4   a  and is reflected by a plane  6   a  to be inspected in a glass plate  6  to be inspected which is supported on a mounting base  7 , and passes through the prism  4  again and is transmitted through a lens  9  toward a camera  10 . Further, another part of the laser beam incident on the prism  4  is reflected by the reference plane  4   a  and passes through the lens  9  toward the camera  10 . The camera  10  picks up the image of an interference fringe formed by a laser beam reflected by the plane  6   a  and a laser beam reflected by the reference plane  4   a . The image of the interference fringe thus picked up is input as a video signal to an analyzer  11 . The analyzer  11  carries out an arithmetic analysis for the shape of a surface based on the input signal.  
         [0048]    Incidentally, an input section  11   a  such as a keyboard, a mouse, an inspection start switch and the like, a monitor  12  for displaying the picked-up image and a result of the analysis and a control section  13  are connected to the analyzer  11 . The control section  13  controls the driving operations of the laser beam source  1 , the motor for positioning, a piezo unit  5  and the like. The prism  4  is moved by the piezo unit  5  to change a distance between the reference plane  4   a  and the plane  6   a  so that the phase of a reference beam is varied in eight steps. Moreover, a memory  14  is connected to the control section  13 .  
         [0049]    The glass plate  6  is placed on the mounting base  7  as shown by FIG. 2. Numeral  25  designates a guide for positioning an edge  6   b  of the glass plate  6  at a reference position in X direction, and a mark  26  in a linear shape extending in Y direction is applied to the guide  25  by etching. Numerals  27  and  29  designate guides for positioning an edge  6   c  of the glass plate  6  at a reference position in Y direction and marks  28  and  30  in a linear shape extended in X direction similar to the mark  26  are applied to the guides  27  and  29 . Further, the mounting base  7  and the guides  25 ,  27  and  29  are designed such that heights of surfaces of the marks  26 ,  28  and  30  applied to the guides  25 ,  27  and  29  and a height of a surface of the glass plate  6  are equal to each other.  
         [0050]    Numerals  22  and  24  designate eccentric cams which are respectively fixed to a shaft  21   a  of a motor  21  and a shaft  23   a  of a motor  23 . The control section  13  rotates the cam  22  by driving and rotating the motor  21  and positions the glass plate  6  in X direction by pressing the glass plate  6  (edge  6   b ) to the guide  25 . Similarly, the control section  13  rotates the cam  24  by driving and rotating the motor  23  and positions the glass plate  6  in Y direction by pressing the glass plate  6  (edge  6   c ) to the guides  27  and  29 .  
         [0051]    Numerals  31 ,  32  and  33  are adjusting screws for adjusting relative positions and a relative angle of the mounting base  7  and the reference surface  4   a  of the prism  4 .  
         [0052]    In the surface inspecting apparatus having the above-described constitution, operation thereof will be described as follows. First, dimension (size) data (a×b) of an outer shape of the glass plate  6  is inputted through the input section  11   a . The dimension data of the outer shape of the plate glass  6  is provided as a design value or a measured value. The control section  13  stores the inputted dimension data of the outer shape to the memory  14 .  
         [0053]    Next, when a positioning switch of the input section  11   a  is depressed after mounting the glass plate  6  on the mounting base  7 , the control section  13  drives and rotates the motors  21  and  22  to respectively press the cams  22  and  24  to the edges  6   d  and  6   e  of the glass plate  6 . Thereby, the edges  6   b  and  6   c  of the glass plate  6  are respectively brought into contact with the guides  25 ,  27  and  29  and the glass plate  6  is placed at a predetermined inspecting position. Thereafter, the control section  13  drives and rotates the motors  21  and  23  in the reverse direction to thereby nullify press force by the cams  22  and  24 . Inspection in a natural state in which the glass plate  6  is not exerted with external force can be carried out.  
         [0054]    After positioning of the glass plate  6  has been finished, an image of the interference fringe formed by a laser beam reflected by the reference surface  4   a , the surface  6   a  and surfaces of the guides  25 ,  27  and  29  is taken by the camera  10  and the image of the interference fridge is displayed on the monitor  12 . Further, the relative positions and relative angles of the surfaces of the guides  25 ,  27  and  29  and the reference surface  4   a  are adjusted by rotating the adjusting screws  31 ,  32  and  33  such that the image of the interference fringe of the guides  25 ,  27  and  29  attached with the marks  26 ,  28  and  30  is displayed clearly. Thereafter, when a mark measuring switch of the input section  11   a  is depressed, images of the marks  26 ,  28  and  30  on the guides  25 ,  27  and  29  are taken and based on positions of the marks  26 ,  28  and  30  acquired by processing the images, reference lines (reference positions) A and B are determined and stored to the memory  14  by the control section  13  as information for specifying a two-dimensional position of the glass plate  6 .  
         [0055]    The reference lines A and B are determined as follows. As shown by FIG. 3A, an amount of light on a scanning line X 1  acquired by taking the image of the mark  26  on the guide  25  is accumulated by an amount of eight steps. According to a distribution of the accumulated amount of light, as shown by FIG. 3B, the amount of light at a portion of the mark  25  is reduced and increased at other portion. In FIG. 3B, a line L horizontally traversing a portion of a valley of the amount of light of the mark  25  is drawn and intersections of the line L and the distribution of the amount of light are designated by notations P and Q. Next, when a length of a line segment PQ is designated by notation m, a portion of m/2 is set to a center line S in a length direction of the mark  26 . A distance x between the center line S and an edge  25   a  of the guide  25  has previously been obtained and stored to the memory  14 . Meanwhile, similarly with regard to the marks  28  and  30 , a distance y between a center line T and an edge  27   a  of the guide  27  (or an edge  29   a  of the guide  29 ) has previously been obtained and stored to the memory  14 . The control section  13  sets a position offset from the center line S by the distance x as the reference line B in x direction, and sets a position offset from the center line T by the distance y as the reference line A in Y direction to respectively store to the memory  14  as information for specifying the two-dimensional position of the glass plate  6 .  
         [0056]    Next, based on the dimension data (a×b) of the outer shape of the glass plate  6  inputted from the input section  11   a , the control section  13  sets a line remote from the reference line B by the dimension of b and in parallel with the reference line B as a reference line Bb. Similarly, a line remote from the reference line A by the dimension of a and in parallel with the reference line A is set as a reference line Aa. Further, the control section B sets positions of the reference lines B, A, Bb, and Aa in the photographed image respectively as edge positions of the edges  6   b ,  6   c ,  6   d  and  6   e  and sets a region surrounded by the reference lines B-A-Bb-Aa as an existing region U of the glass plate  6 .  
         [0057]    Next, the relative positions and the relative angle of the surface  6   a  of the glass plate  6  and the reference surface  4   a  are adjusted by rotating the adjusting screws  31 ,  32  and  33  such that the image of the interference fringe of the glass plate  6  is excellently displayed. Thereafter, when the inspection start switch of the input section  11   a  is depressed, the control section  13  changes the phase of the interference fringe by changing a distance between the reference surface  4   a  and the surface  6   a  by applying voltage to the piezo unit  5 . According to the apparatus, a number of phase shift is constituted by eight steps. In this way, the image of the interference fringe the phase of which is changed is taken by the camera  10  and respective image data is inputted to a memory at inside of the analyzer  11 .  
         [0058]    The analyzer  11  determines an analyzing region by a threshold processing after acquiring a contrast image by subjecting the plurality of images of the interference fringe having different phases inputted to the memory to well-known processings of removing noise and the like. Further, by converting the phase data of the image of the interference fringe into height data, a three-dimensional shape of the surface  6   a  is acquired. By the three-dimensional shape provided in the analyzing region, the edge positions of the glass plate  6  can accurately be known and the surface shape information can be acquired with high accuracy. Further, the three-dimensional shape is related to at which position of the existing region U the three-dimensional shape is disposed and displayed on the monitor  12  by a perspective view, a contour view or the like. Thereby, the flatness of the surface  6   a  can be evaluated based on the edge positions.  
         [0059]    Incidentally, although according to the embodiment, the dimension data (a×b) of the outer shape of the glass plate  6  is inputted from the input section  11   a , the motors  21  and  23  may be attached with encoders and the dimension data of the outer shape of the glass plate  6  maybe measured from rotational angles of the cams  22  and  24  to input it.  
         [0060]    Further, although according to the above-described embodiment, in order to acquire the edge positions of the glass plate  6 , the images of the marks  26 ,  28  and  30  on the guides  25 ,  27  and  29  are taken, the positions may be acquired by other method. For example, lines in a shape of a cross orthogonal to each other in XY directions or the like are applied onto a surface of other than a peripheral portion of a reference glass plate having a shape the same as that of the glass plate  6 , an image of an interference fringe of the cross lines is taken previously before inspecting the glass plate  6  and positions of the cross lines are calculated by subjecting the image to image processing. Then, based on distances from the edges of the cross lines which have been acquired previously, the reference lines A and B are determined as information for specifying the two-dimensional position of the glass plate  6  to store to the memory  14 .  
         [0061]    Further, although according to the above-described embodiment, the object to be inspected is constituted by the glass plate  6  in a quadrangular shape, the object to be inspected is not limited to the shape but may be a wafer  60  to be inspected in a circular shape as shown by, for example, FIG. 4. In the case of the wafer  60  in the circular shape, guides  55  and  57  and marks  56  and  58  are provided on a mounting base  50  as shown by FIG. 4. Further, an eccentric cam  52  and a motor  51  (notation  51   a  designates a shaft of the motor  51 ) are provided at positions shown in FIG. 4.  
         [0062]    After mounting the wafer  60  on the mounting base  50 , the wafer  60  is positioned by the cam  52  and the guides  55  and  57 . The control section  13  sets a position offset from the center line S of the mark  56  by the distance of x as a reference line D in X direction and sets a position offset from the center line T of the mark  58  by the distance of y as a reference line C in Y direction to respectively stored to the memory  14  as information for specifying two-dimensional position of the wafer  60 . Next, based on a radius r which is dimension data of an outer shape of the wafer  60  inputted from the input section  11   a , a line remote from the reference line D by a dimension of r and in parallel with the reference line D is set as a reference line Dd. Similarly, a line remote from the reference line C by the dimension of r and in parallel with the reference line C is set to a reference line Cc. Further, the control section  13  sets a position remote from an intersection F of the reference line Cc and the reference line Dd in the image by the radius r as an edge position and sets a region within the edge as an existing region W of the wafer  60 . By a three-dimensional shape provided within an analyzing region, the edge position of the wafer  60  can accurately be known, further, information of the surface shape can be acquired with high accuracy. Further, the three-dimensional shape is related to at which position of the existing region W the three-dimensional shape is disposed and displayed on the monitor  12  by a perspective view, a contour view or the like. Thereby, the flatness of the wafer  60  can be evaluated based on the edge position.  
         [0063]    Further, the flatness is poor at a vicinity of the edge of the object to be inspected by sagging or the like in view of fabrication and is inclined as compared with a central portion as shown by FIG. 5. In this case, when a degree of inclination becomes steep, accuracy of the result of inspection is not reliable.  
         [0064]    Therefore, according to the apparatus, reliability of the result of inspection is determined from the degree of inclination. The control section  13  acquires an amount of inclination (flatness) of a surface from the three-dimensional shape of the surface  6   a  of the glass plate  6  and determines an effective region where the result of inspection is reliable when an amount of inclination is within a predetermined amount of inclination. For example, as shown by FIG. 5, when a reliable amount of inclination is constituted by up to an inclination of a height difference of a vertical distance of 0.02 μm relative to a horizontal distance of 0.1 mm, the control section  13  determines whether an amount of inclination of each pixel falls within the height difference of the vertical distance of 0.02 μm relative to the horizontal distance of 0.1 m and displays the result on the monitor  12  as shown by FIG. 6. In FIG. 6, notation U designates the existing region of the glass plate  6 , notation T designates the analyzing region where the image of the interference fringe is obtained and numeral  41  designates the effective region where the result of inspection is reliable. According to a surface inspecting apparatus of a related art, the edge of the object to be inspected cannot be detected and therefore, it cannot be specified at which position the effective region in which the result of inspection is reliable is disposed. According to the apparatus, the edges of the object to be inspected can be detected as described above and therefore, it can visually be grasped at which position the effective region in which the result of inspection is reliable is disposed.  
         [0065]    Further, although according to the above-described embodiment, there are provided two of the guides  27  and  29  for matching the edge  6   c  of the glass plate  6  to the reference position in Y direction, a single one thereof will do. However, by providing a plurality of guides in one direction, positional shift of the glass plate  6  is not brought about and the center line can further accurately be acquired. Further, contrary, there may be provided two of guides of matching the edge  6   b  of the glass plate  6  to the reference position in X direction. Further, it is preferable that a length to some degree is ded to the length of the guide (mark). In this way, positions, a number of pieces, shapes and the like of the guides can pertinently be selected to match to the outer shape of the object to be inspected. Further, positions, a number of pieces and the like of the eccentric cams can pertinently be selected to much to the outer shape of the object to be inspected.  
         [0066]    As has been explained above, according to the invention, the surface shape can be inspected with high accuracy by accurately grasping the edge positions of the object to be inspected.