Abstract:
Disclosed herein is an inspecting apparatus including an illuminating unit adapted to be positioned in the periphery of a transparent member for illuminating the transparent member from the outside of the circumference thereof, an imaging unit adapted to be opposed to the transparent member for imaging the transparent member illuminated by the illuminating unit, and a displaying monitor for displaying an image obtained by the imaging unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to an inspecting apparatus capable of detecting a crack present in a test piece formed of a transparent material, and also to a laser processing apparatus capable of detecting a crack present in a workpiece formed of a transparent material. 
         [0003]    Description of the Related Art 
         [0004]    There is disclosed in Japanese Patent Laid-open No. 2012-195472 a laser processing method for forming a laser processed groove on a wafer formed of a transparent material such as lithium tantalate (LiTaO 3 ) and lithium niobate (LiNbO 3 ), the front side of the wafer being partitioned by a plurality of division lines to define a plurality of separate regions where a plurality of surface acoustic wave (SAW) devices are individually formed. In this laser processing method, a pulsed laser beam is applied to the front side of the wafer along each division line, wherein the pulse width of the pulsed laser beam is set to 200 ps or less and the repetition frequency of the pulsed laser beam is set to 50 kHz or less. According to this laser processing method, a laser processed groove can be formed on the front side of the wafer along each division line without generating a crack in the wafer. After forming the laser processed groove on the front side of the wafer along each division line, an external force is applied along each division line to thereby divide the wafer into the individual SAW devices. 
       SUMMARY OF THE INVENTION 
       [0005]    In the case of using the laser processing method disclosed in Japanese Patent Laid-open No. 2012-195472, any new crack is not generated in the wafer by the application of the laser beam. However, in the case that a minute crack has already been present in a certain device, there is a case that this minute crack may be extended by the application of the laser beam. In this case, there is a possibility that the crack may extend to the devices having no cracks at the time before the application of the laser beam. 
         [0006]    It is therefore an object of the present invention to provide an inspecting apparatus having a simple configuration which can detect a crack present in a test piece formed of a transparent material. It is another object of the present invention to provide a laser processing apparatus having a simple configuration which can detect a crack present in a workpiece formed of a transparent material. 
         [0007]    In accordance with an aspect of the present invention, there is provided an inspecting apparatus including illuminating means adapted to be positioned in the periphery of a transparent member for illuminating the transparent member from the outside of the circumference thereof; imaging means adapted to be opposed to the transparent member for imaging the transparent member illuminated by the illuminating means; and displaying means for displaying an image obtained by the imaging means. 
         [0008]    Preferably, the inspecting apparatus further includes storing means for storing the image obtained by the imaging means and the position of a crack present in the transparent member, the crack being detected according to the image obtained by the imaging means. 
         [0009]    In accordance with another aspect of the present invention, there is provided a laser processing apparatus including a chuck table for holding a transparent member; moving means for moving the chuck table in an X direction and a Y direction perpendicular to the X direction; laser beam applying means for applying a laser beam to the transparent member held on the chuck table; illuminating means adapted to be positioned in the periphery of the transparent member held on the chuck table for illuminating the transparent member from the outside of the circumference thereof; imaging means adapted to be opposed to the transparent member held on the chuck table for imaging the transparent member illuminated by the illuminating means; and displaying means for displaying an image obtained by the imaging means. 
         [0010]    Preferably, while the chuck table holding the transparent member is being moved by the moving means, the whole area of one side of the transparent member is imaged by the imaging means. Preferably, the transparent member includes a wafer formed of lithium tantalate or lithium niobate. 
         [0011]    According to the present invention, the illuminating means positioned in the periphery of the transparent member functions to illuminate the transparent member from the outside of the circumference thereof, and the imaging means opposed to the transparent member functions to image the transparent member illuminated by the illuminating means. Accordingly, a crack present in the transparent member can be imaged by the imaging means and an image obtained by the imaging means is displayed by the displaying means. Accordingly, the crack of the transparent member can be detected according to the image displayed by the displaying means. 
         [0012]    The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of a wafer supported through an adhesive tape to an annular frame; 
           [0014]      FIG. 2  is a schematic perspective view of an inspecting apparatus according to the present invention; 
           [0015]      FIG. 3  is a perspective view of a laser processing apparatus according to the present invention; and 
           [0016]      FIG. 4  is a schematic side view showing a condition that inspection is being performed by the laser processing apparatus shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    A preferred embodiment of the inspecting apparatus according to the present invention will now be described with reference to  FIGS. 1 and 2 , wherein a wafer  2  is used as a test piece to be inspected. The wafer  2  as the test piece shown in  FIG. 1  is formed of a transparent hard and brittle material such as lithium tantalate and lithium niobate. The wafer  2  is circular in shape. The wafer  2  has a front side  4  and a back side  5 . A plurality of crossing division lines  6  are formed on the front side  4  of the wafer  2  to thereby define a plurality of separate regions where a plurality of SAW devices  8  are individually formed. In this preferred embodiment, an adhesive tape  12  is fixed at its peripheral portion to an annular frame  10 , and the back side  5  of the wafer  2  is attached to the adhesive tape  12 . As a modification, the front side  4  of the wafer  2  may be attached to the adhesive tape  12 . 
         [0018]    Referring to  FIG. 2 , there is shown an inspecting apparatus  14  according to this preferred embodiment. The inspecting apparatus  14  includes illuminating means  16 , imaging means  18 , and displaying means  20 . The illuminating means  16  includes an annular plate  22  having an inner diameter larger than the diameter of the wafer  2  and a plurality of light sources  24  provided on one side (upper surface) of the annular plate  22  so as to be spaced in the circumferential direction of the annular plate  22 . Preferably, the outer diameter of the annular plate  22  is smaller than the inner diameter of the annular frame  10 . Each light source  24  functions to apply white light in the radially inward direction of the wafer  2 . The imaging means  18  includes an ordinary imaging device (charge coupled device (CCD)) for imaging the wafer  2  by using visible light. An image signal obtained by the imaging means  18  is output to the displaying means  20  having a screen. 
         [0019]    The inspecting apparatus  14  preferably further includes storing means. As shown in  FIG. 2 , control means  26  configured by a computer is connected to the imaging means  18 . The control means  26  includes a central processing unit (CPU)  28  for performing operational processing according to a control program, a read only memory (ROM)  30  preliminarily storing the control program, and a random access memory (RAM)  32  for storing the results of computation etc. In this preferred embodiment, the storing means in the inspecting apparatus  14  is configured by the RAM  32  of the control means  26 . 
         [0020]    An inspecting step using the inspecting apparatus  14  will now be described. In inspecting the wafer  2 , the wafer  2  supported through the adhesive tape  12  to the annular frame  10  is first placed on a suitable support  34  as shown in  FIG. 2 . Thereafter, the illuminating means  16  is set around the wafer  2 , and the imaging means  18  is set above the wafer  2  so as to face the front side  4  of the wafer  2 . Thereafter, the illuminating means  16  is operated to illuminate the wafer  2  from the outside of the outer circumference thereof, and the imaging means  18  is operated to image the wafer  2  illuminated above. By setting the illuminating means  16  and the imaging means  18  as mentioned above, it is possible to image a crack present in the wafer  2  formed of a transparent hard and brittle material. In imaging the wafer  2 , the imaging means  18  is suitably moved to thereby image the whole area of the front side  4  of the wafer  2 . An image obtained by the imaging means  18  is displayed on the screen of the displaying means  20 . Accordingly, the crack (shown by reference numeral  36  in  FIG. 2 ) in the wafer  2  can be detected according to the image displayed above. This inspection can be performed to the wafer  2  before dividing the wafer  2  into the SAW devices  8 . Accordingly, the inspection in this preferred embodiment can be performed more efficiently as compared with the case of performing the inspection after dividing the wafer  2  into the SAW devices  8 . 
         [0021]    The inspection using the inspecting apparatus  14  may be performed before and after laser processing of applying a laser beam to each division line  6  to form a strength reduced portion along each division line  6 . Accordingly, by performing the inspection using the inspecting apparatus  14  before and after laser processing, it is possible to verify the effect of the application of the laser beam on the extension of the crack. More specifically, in the case that the crack in the wafer  2  is detected by the inspection before laser processing, the image of an area including the crack and the position of the crack are stored into the RAM  32 . Further, in performing the inspection after laser processing, the same area as the area (the area including the crack) stored into the RAM  32  before laser processing is imaged. Then, the image of this area and the position of the crack are stored into the RAM  32 . Thereafter, the image stored before laser processing and the image stored after laser processing are compared with each other, thereby verifying the effect of the application of the laser beam on the extension of the crack. 
         [0022]    After dividing the wafer  2  into the individual SAW devices  8 , a screening operation is performed to separate the devices not including the cracks and the devices including the cracks. In performing this screening operation, the position of the crack stored in the RAM  32  is referred to, thereby eliminating the need for inspecting the presence or absence of the crack in each device. Accordingly, the efficiency of the screening operation can be improved. 
         [0023]    While the inspection using the inspecting apparatus  14  is performed in the condition where the wafer  2  is supported through the adhesive tape  12  to the annular frame  10  in this preferred embodiment, the inspection using the inspecting apparatus  14  may be performed in the condition where the wafer  2  is not supported to the annular frame  10 , but directly placed on a suitable support. 
         [0024]    A preferred embodiment of the laser processing apparatus according to the present invention will now be described with reference to  FIGS. 3 and 4 , wherein the wafer  2  is used as a workpiece to be processed. In the following description, substantially the same parts as those of the inspecting apparatus  14  will be denoted by the same reference symbols, and the description thereof will be omitted. 
         [0025]    Referring to  FIG. 3 , there is shown a laser processing apparatus  40  according to this preferred embodiment. The laser processing apparatus  40  includes a base  42 , holding means  44  for holding a workpiece, moving means  46  for moving the holding means  44 , laser beam applying means  48  for applying a laser beam to the workpiece held on the holding means  44 , imaging means  50 , displaying means  52 , and illuminating means  16 . The laser processing apparatus  40  preferably further includes storing means. As shown in  FIG. 4 , the laser processing apparatus  40  further includes control means  54  configured by a computer. The storing means is configured by a RAM  90  constituting the control means  54  as will be hereinafter described. 
         [0026]    The holding means  44  includes a rectangular X movable plate  56  mounted on the base  42  so as to be movable in an X direction, a rectangular Y movable plate  58  mounted on the X movable plate  56  so as to be movable in a Y direction, a cylindrical support  60  fixed to the upper surface of the Y movable plate  58 , and a rectangular cover plate  62  fixed to the upper end of the support  60 . The cover plate  62  is formed with an elongated hole  62   a  extending in the Y direction. A circular chuck table  64  is rotatably mounted on the upper end of the support  60  so as to extend upward through the elongated hole  62   a  of the cover plate  62 . A circular vacuum chuck  66  is provided on the upper surface of the chuck table  64 . The vacuum chuck  66  has a substantially horizontal holding surface. The vacuum chuck  66  is formed of a porous material. The vacuum chuck  66  is connected through a suction passage (not shown) formed in the support  60  to suction means (not shown). A plurality of clamps  68  are provided on the outer circumference of the chuck table  64  so as to be spaced in the circumferential direction thereof. The X direction is defined as the direction shown by an arrow X in  FIG. 3 , and the Y direction is defined as the direction shown by an arrow Y in  FIG. 3 , which is perpendicular to the X direction in an XY plane. The XY plane defined by the X direction and the Y direction is a substantially horizontal plane. 
         [0027]    The moving means  46  includes X moving means  70 , Y moving means  72 , and rotating means (not shown). The X moving means  70  includes a ball screw  74  extending in the X direction on the base  42  and a motor  76  connected to one end of the ball screw  74 . The ball screw  74  has a nut portion (not shown), which is fixed to the lower surface of the X movable plate  56 . The X moving means  70  is operated in such a manner that the rotational motion of the motor  76  is converted into a linear motion by the ball screw  74  and this linear motion is transmitted to the X movable plate  56 , so that the X movable plate  56  is moved in the X direction along a pair of guide rails  42   a  provided on the base  42 . Similarly, the Y moving means  72  includes a ball screw  78  extending in the Y direction on the X movable plate  56  and a motor  80  connected to one end of the ball screw  78 . The ball screw  78  has a nut portion (not shown), which is fixed to the lower surface of the Y movable plate  58 . The Y moving means  72  is operated in such a manner that the rotational motion of the motor  80  is converted into a linear motion by the ball screw  78  and this linear motion is transmitted to the Y movable plate  58 , so that the Y movable plate  58  is moved in the Y direction along a pair of guide rails  56   a  provided on the X movable plate  56 . The rotating means is built in the support  60  to rotate the chuck table  64  with respect to the support  60 . 
         [0028]    An L-shaped casing  82  is provided on the base  42  at its rear end portion. The L-shaped casing  82  is composed of a vertical portion extending upward from the upper surface of the base  42  and a horizontal portion extending from the upper end of the vertical portion in a substantially horizontal direction. The laser beam applying means  48  includes pulsed laser beam oscillating means (not shown) built in the casing  82  and focusing means  84  provided on the lower surface of the front end portion of the casing  82 . The imaging means  50  is also provided on the lower surface of the front end portion of the casing  82  so as to be spaced from the focusing means  84  in the X direction. The focusing means  84  and the imaging means  50  are positioned above the chuck table  64 . The imaging means  50  includes an ordinary imaging device (CCD) for imaging a workpiece by using visible light, infrared light applying means for applying infrared light to the workpiece, an optical system for capturing the infrared light applied by the infrared light applying means, and an imaging device (infrared CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system (all the components being not shown). An image signal obtained by the imaging means  50  is output to the displaying means  52 , which is mounted on the upper surface of the front end portion of the casing  82 . As shown in  FIG. 4 , the control means  54  includes a CPU  86  for performing operational processing according to a control program, a ROM  88  preliminarily storing the control program, and the RAM  90  for storing the results of computation etc. The control means  54  is connected to the moving means  46 , the laser beam applying means  48 , the imaging means  50 , and the displaying means  52  and functions to control the operation of these components. 
         [0029]    An inspecting step and processing step using the laser processing apparatus  40  will now be described. A holding step is first performed in such a manner that the wafer  2  as a workpiece is held by the holding means  44 . In the holding step, the wafer  2  supported through the adhesive tape  12  to the annular frame  10  is placed on the upper surface (holding surface) of the vacuum chuck  66  in the condition where the front side  4  of the wafer  2  is oriented upward. Thereafter, the suction means is operated to apply a vacuum to the upper surface of the vacuum chuck  66 , thereby holding the back side  5  of the wafer  2  through the adhesive tape  12  on the upper surface of the vacuum chuck  66 . Further, the annular frame  10  is fixed at its peripheral portion by the plural clamps  68 . As similar to the case of the inspecting apparatus  14  mentioned above, the back side  5  of the wafer  2  is attached to the adhesive tape  12  fixed at its peripheral portion to the annular frame  10 . However, the front side  4  of the wafer  2  may be attached to the adhesive tape  12 . 
         [0030]    After performing the holding step, an inspecting-before-processing step is performed in such a manner that the inspection of the wafer  2  is performed before laser processing. In performing the inspecting-before-processing step, the illuminating means  16  is placed through the adhesive tape  12  on the vacuum chuck  66  so as to surround the wafer  2  as shown in  FIG. 4 . Thereafter, the holding means  44  is moved by the moving means  46  so that the imaging means  50  comes into opposition to the front side  4  of the wafer  2 . Thereafter, the illuminating means  16  is operated to illuminate the wafer  2  from the outside of the outer circumference thereof, and the imaging means  50  is next operated to image the wafer  2  illuminated above. By setting the illuminating means  16  and the imaging means  50  as mentioned above, it is possible to image a crack present in the wafer  2  formed of a transparent hard and brittle material. In imaging the wafer  2 , the holding means  44  is suitably moved by the moving means  46  to thereby allow the imaging means  50  to image the whole area of the front side  4  of the wafer  2 . An image obtained by the imaging means  50  is displayed on the screen of the displaying means  52 . Accordingly, the crack in the wafer  2  can be detected according to the image displayed above. This inspection can be performed to the wafer  2  before dividing the wafer  2  into the SAW devices  8 . Accordingly, the inspection can be performed more efficiently as compared with the case of performing the inspection after dividing the wafer  2  into the SAW devices  8 . In the case that the crack in the wafer  2  is detected in this inspecting-before-processing step, the image of an area including the crack and the position of the crack are stored into the RAM  90  of the control means  54 . 
         [0031]    After performing the inspecting-before-processing step, the illuminating means  16  is removed from the vacuum chuck  66 , and an alignment step is then performed to detect a laser beam applying position. In this alignment step, image processing such as pattern matching is performed by the control means  54 . More specifically, the control means  54  suitably operates the moving means  46  according to the image of the wafer  2  obtained by the imaging means  50 , thereby making the directions of the crossing division lines  6  parallel to the X direction and the Y direction and also making the alignment between the division lines  6  and the focusing means  84 . 
         [0032]    After performing the alignment step, a laser processing step is performed in the following manner. In performing the laser processing step, the moving means  46  is operated to move the holding means  44  to thereby position one end of a predetermined one of the division lines  6  directly below the focusing means  84 . Thereafter, the laser beam applying means  48  is operated to apply a pulsed laser beam from the focusing means  84  to the predetermined division line  6 , and at the same time the X moving means  70  is operated to move the holding means  44  in the X direction at a predetermined feed speed. When the other end of the predetermined division line  6  has reached the position directly below the focusing means  84 , the operation of the laser beam applying means  48  is stopped and the operation of the X moving means  70  is also stopped. Accordingly, a strength reduced portion is formed along the predetermined division line  6 . Thereafter, a plurality of strength reduced portions are similarly formed along all the other division lines  6 . 
         [0033]    In the case that the crack in the wafer  2  is detected in the inspecting-before-processing step mentioned above, an inspecting-after-processing step is performed after performing the laser processing step. In performing the inspecting-after-processing step, the moving means  46  is operated to move the holding means  44  to such a position that the imaging means  50  is opposed to the front side  4  of the wafer  2 . Thereafter, the illuminating means  16  is operated to illuminate the wafer  2  from the outside of the outer circumference thereof. In this condition, the imaging means  50  is operated to image the same area as the area (the area including the crack) whose image has already been stored into the RAM  90  in the inspecting-before-processing step. Thereafter, the image of this area and the position of the crack are stored into the RAM  90 . Thereafter, the image stored in the inspecting-before-processing step and the image stored in the inspecting-after-processing step are compared with each other, thereby verifying the effect of the application of the laser beam on the extension of the crack. Further, by referring to the position of the crack stored in the RAM  90 , the efficiency of the screening operation can be improved in screening the individual SAW devices  8  divided from the wafer  2 . 
         [0034]    While the illuminating means  16  in the laser processing apparatus  40  is similar to that of the inspecting apparatus  14  in this preferred embodiment, a plurality of light sources may be provided on the cover plate  62  radially outside the chuck table  64  so as to be spaced in the circumferential direction thereof. 
         [0035]    The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.