Patent Publication Number: US-11654525-B2

Title: Grinding apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a grinding apparatus. 
     Description of the Related Art 
     As disclosed in Japanese Patent Laid-open No. 2008-073785 and Japanese Patent Laid-open No. 2019-130607, a grinding apparatus for grinding a wafer held by a holding surface of a chuck table includes a first height gauge that measures the height of the holding surface, a second height gauge that measures the height of an upper surface of the wafer, and a calculation section that calculates the difference between the height of the holding surface measured by the first height gauge and the height of the upper surface of the wafer measured by the second height gauge, as the thickness of the wafer, and in the grinding apparatus, grinding is conducted until a predetermined thickness is reached while the thickness of the wafer is calculated. 
     For example, as illustrated in  FIG.  5   , a first height gauge  61  and a second height gauge  62  included in a conventional grinding apparatus are supported on a column member  70  erected on a base  10  on which a chuck table  2  and a grinding unit  3  are disposed, through an arm  71 , and the height of a wafer  17  is measured at a position spaced from a processing region where grindstones  340  and the wafer  17  come into contact with each other. Although the arm  71  extending in a horizontal direction from a column is provided such that the height can be measured at a position close to the processing region, lengthening the arm  71  generates such a problem that it becomes difficult to accurately measure the thickness due to thermal deformation or the like in the arm  71 . As a countermeasure, for example, as depicted in  FIG.  6   , an arm  72  may be provided on a column  11  on which a grinding feeding mechanism  4  for grinding feeding of the grinding unit  3  in the vertical direction is supported, and the arm  72  may be made short. 
     SUMMARY OF THE INVENTION 
     However, according to the abovementioned method, though the arm can be made short, it cannot be said that the thickness of the wafer can be accurately measured. The provision of the arm is considered to have a bad influence on measurement of the thickness of the wafer. 
     Accordingly, it is an object of the present invention to provide a novel grinding apparatus with which the thickness of the wafer can be accurately measured. 
     In accordance with an aspect of the present invention, there is provided a grinding apparatus including a chuck table that holds a wafer on a holding surface; a grinding unit that has a spindle unit in which a spindle with an annular grindstone mounted to a tip thereof is rotatably supported and that grinds the wafer by use of the grindstone; a grinding feeding mechanism that puts the grinding unit into grinding feeding in a grinding feeding direction perpendicular to the holding surface; a first height gauge that measures a height of the holding surface; a second height gauge that measures a height of an upper surface of the wafer held on the holding surface; and a calculation section that calculates a difference between the height of the holding surface measured by the first height gauge and the height of the upper surface of the wafer measured by the second height gauge, as a thickness of the wafer. In the grinding apparatus, the first height gauge and the second height gauge are disposed in the grinding unit. 
     Preferably, the grinding unit includes a holder having a support plate that has an opening for exposing a lower portion of the spindle and that supports the spindle unit and a side plate erected from a periphery of the support plate, and the first height gauge and the second height gauge are disposed on the side plate such that a first measurement point of the first height gauge and a second measurement point of the second height gauge are positioned in the vicinity of a processing region where the grindstone grinds the wafer. 
     In addition, preferably, when the grinding unit is lowered in a direction for approaching the holding surface by the grinding feeding mechanism, the first height gauge measures the height of the holding surface and the second height gauge measures the height of the upper surface of the wafer, before the grindstone comes into contact with the wafer. 
     In the grinding apparatus according to one aspect of the present invention, the first measurement point and the second measurement point can be positioned in the vicinity of the processing region where the upper surface of the wafer and the lower surface of the grindstone come into contact with each other, and, thus, the thickness of the wafer that is obtained immediately after grinding has started can be accurately measured, and fine variation in the thickness of the wafer that is recognized immediately after grinding has started can be recognized. 
     In addition, in the case where the first height gauge and the second height gauge are disposed on the side plate of the holder, it is possible, by causing the grindstone to approach the upper surface of the wafer by use of the grinding feeding mechanism, to simultaneously lower the first height gauge and the second height gauge. Further, since both height gauges are separated away from the upper surface of the wafer together with the grindstone when the grindstone is spaced away from the upper surface of the wafer by use of the grinding feeding mechanism, operability of maintenance work and the like can be enhanced. 
     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 a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a sectional view of a grinding apparatus before the start of grinding a wafer; 
         FIG.  2    is a plan view depicting the relation of horizontal positions of a first measurement point, a second measurement point, and a processing region; 
         FIG.  3    is a sectional view of the grinding apparatus grinding the wafer; 
         FIG.  4    is a sectional view of the grinding apparatus grinding the wafer; 
         FIG.  5    is a sectional view depicting an example of a conventional grinding apparatus; and 
         FIG.  6    is a sectional view depicting an example of a conventional grinding apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below with reference to the attached drawings. 
     1. Configuration of Grinding Apparatus 
     A grinding apparatus  1  illustrated in  FIG.  1    is a grinding apparatus for grinding a wafer  17  by use of a grinding unit  3 . The configuration of the grinding apparatus  1  will be described below. 
     As depicted in  FIG.  1   , the grinding apparatus  1  includes a base  10  extending in a Y-axis direction and a column  11  erected on a +Y direction side of the base  10 . 
     A chuck table  2  is disposed on the base  10 . The chuck table  2  includes a suction section  20  that has a porous member and a frame body  21  that supports the suction section  20 . An upper surface of the suction section  20  is a holding surface  200  that holds the wafer  17 , and is formed in a comparatively gentle conical surface. In addition, an upper surface  210  of the frame body  21  is formed flush with the holding surface  200 . 
     An unillustrated suction source is connected to the holding surface  200 . With the suction source operated, a suction force generated is transmitted to the holding surface  200 . For example, in a state in which the wafer  17  is mounted on the holding surface  200 , the suction force generated by operation of the suction source is transmitted to the holding surface  200 , whereby the wafer  17  can be held under suction on the holding surface  200 . In this instance, the wafer  17  is held on the holding surface  200  so as to be along the conical surface of the holding surface  200 , so that, in the state in which the wafer  17  is held on the holding surface  200 , an upper surface  170  of the wafer  17  is substantially conical in shape. 
     The chuck table  2  is detachably mounted to a base  23 . The base  23  is rotatably supported by an annular connection member  29 , and the connection member  29  is supported by three support shafts  291  (two of which are depicted in  FIG.  1   ) erected on a support member  240 . 
     The support member  240  is opened, and a rotating mechanism  26  that rotates the chuck table  2  is disposed at the opening part of the support member  240 . The rotating mechanism  26  is, for example, a pulley mechanism, and includes a driving shaft  262  configured to be rotatable by a motor  260  around an axis  25  substantially in a Z-axis direction, a driving pulley  263  connected to an upper end of the driving shaft  262 , a transmission belt  264  that is wound around the driving pulley  263  to transmit a driving force of the driving pulley  263  to a driven pulley  265 , the driven pulley  265  wound by the transmission belt  264  together with the driving pulley  263 , a driven shaft  266  connected to the driven pulley  265 , and a rotary joint  267  connected to a lower end of the driven shaft  266 . The driven shaft  266  is connected to the base  23 . 
     When the driving shaft  262  is rotated by use of the motor  260 , the driving pulley  263  is rotated, and a rotating force of the driving pulley  263  is transmitted by the transmission belt  264  to the driven pulley  265 , whereby the driven pulley  265  is rotated. As a result, the driven shaft  266  connected to the driven pulley  265  is rotated around the axis  25 , to rotate the base  23  connected to the driven shaft  266  and the chuck table  2  mounted to the base  23 , around the axis  25 . 
     On a side surface on a −Y direction side of the column  11 , a grinding feeding mechanism  4  that puts the grinding unit  3  into grinding feeding in a grinding feeding direction perpendicular to the holding surface  200  is disposed. 
     The grinding unit  3  includes a spindle unit  35  having a spindle  30  having an axis in the Z-axis direction, a spindle housing  31  supporting the spindle  30  in a rotatable manner, and a spindle motor  32  driving, in a rotational manner, the spindle  30  around an axis in the Z-axis direction. 
     In addition, the grinding unit  3  includes a mount  33  connected to a lower end of the spindle  30  and a grinding wheel  34  detachably mounted to a lower surface of the mount  33 . 
     The grinding wheel  34  includes a wheel base  341  and a plurality of substantially rectangular parallelepiped grindstones  340  arranged in an annular pattern on a lower surface of the wheel base  341 . Lower surfaces  342  of the grindstones  340  are grinding surfaces that come into contact with the wafer  17 . 
     With the spindle  30  is rotated by use of the spindle motor  32 , the mount  33  connected to the spindle  30  and the grinding wheel  34  mounted to the lower surface of the mount  33  are rotated as one body. 
     In addition, the spindle  30 , the mount  33 , and the wheel base  341  are formed with a grinding water channel  80  in a penetrating manner. The grinding water channel  80  is connected to a grinding water source  8 , and, with grinding water supplied from the grinding water source  8 , the grinding water is passed through the inside of the spindle  30 , the mount  33 , and the wheel base  341  to be supplied through the lower end of the wheel base  341  to the lower side of the grindstones  340 . 
     For example, supplying the grinding water from the grinding water source  8  during grinding of the wafer  17  to a portion between the lower surfaces  342  of the grindstones  340  and the upper surface  170  of the wafer  17  makes it possible to cool the grindstones  340  and clean the swarf generated on the upper surface  170  of the wafer  17  and the like, with running water. 
     The grinding unit  3  includes a holder  37  which has a support plate  370  having an opening  372  for exposing a lower portion of the spindle  30  on the lower side; and a side plate  374  erected on a peripheral portion of the support plate  370 . The support plate  370  supports the spindle housing  31 . 
     The grinding feeding mechanism  4  includes a ball screw  40  having a rotational axis in the Z-axis direction, a pair of guide rails  41  disposed in parallel to the ball screw  40 , a Z-axis motor  42  for rotating the ball screw  40 , and an encoder  420  for measuring the rotation amount of the ball screw  40  rotated by the Z-axis motor  42 . The ball screw  40  is in screw engagement with a nut  400 , and a slider  38  is connected to the nut  400 . In addition, the slider  38  supports the side plate  374 . 
     When the ball screw  40  is driven by the Z-axis motor  42  and the ball screw  40  is rotated, the nut  400  in screw engagement with the ball screw  40  is lifted upward or downward in the Z-axis direction while sliding on the ball screw  40 . Attendant on this, the slider  38  connected to the nut  400  is lifted upward or downward in the Z-axis direction while being guided by the guide rails  41 , whereby the grinding unit  3  is moved in the Z-axis direction. 
     A connection section  60  is supported by the side plate  374  of the holder  37 , and the first height gauge  61  and the second height gauge  62  are supported by the connection section  60 . A first contact element  610  making contact with the upper surface  210  of the frame body  21  is provided at a lower portion of the first height gauge  61 , and a second contact element  620  making contact with the upper surface  170  of the wafer  17  is provided at a lower portion of the second height gauge  62 . 
     By bringing the first contact element  610  of the first height gauge  61  into contact with the upper surface  210  of the frame body  21 , it is possible to measure the height of the holding surface  200  which is flush with the upper surface  210  of the frame body  21 . In addition, by bringing the second contact element  620  of the second height gauge  62  into contact with the upper surface  170  of the wafer  17 , it is possible to measure the height of the upper surface  170  of the wafer  17 . 
     The first contact element  610  and the second contact element  620  are disposed at positions lower than the lower surfaces  342  of the grindstones  340 . Thus, when the grinding unit  3  is moved in a −Z direction by use of the grinding feeding mechanism  4  in a state in which the wafer  17  is held on the holding surface  200 , the first contact element  610  comes into contact with the upper surface  210  of the frame body  21  and the second contact element  620  comes into contact with the upper surface  170  of the wafer  17  before the grindstones  340  come into contact with the upper surface  170  of the wafer  17 . 
     As depicted in  FIG.  1   , the first height gauge  61  and the second height gauge  62  are connected to a calculation section  63 . The calculation section  63  is, for example, a calculating device having a central processing unit (CPU), a memory, and the like, and has a function of calculating the difference between the height value of the holding surface  200  measured by the first height gauge  61  and the height value of the upper surface  170  of the wafer  17  measured by the second height gauge  62 , as the thickness of the wafer  17 . 
     A first measurement point  611  which is a point where the first contact element  610  of the first height gauge  61  and the upper surface  210  of the frame body  21  come into contact each other and a second measurement point  621  which is a point where the second contact element  620  of the second height gauge  62  and the upper surface  170  of the wafer  17  held on the holding surface  200  come into contact each other are located in the vicinity of a processing region  9  where the lower surfaces  342  of the grindstones  340  and the upper surface  170  of the wafer  17  come into contact with each other in a positional relation of horizontal positions. Here, the vicinity of the processing region  9  is a position sufficiently close to the processing region  9  within such a range that interference with the grindstones  340  is not caused during grinding. 
     2. Operation of Grinding Apparatus 
     At the time of grinding the wafer  17  by use of the grinding apparatus  1 , first, the wafer  17  is mounted on the holding surface  200  of the chuck table  2 , and thereafter, the suction source connected to the holding surface  200  is operated. As a result, a suction force generated by the suction source is transmitted to the holding surface  200 , whereby the wafer  17  is held under suction by the holding surface  200 . Then, for example, the chuck table  2  is rotated in the direction of an arrow  27  depicted in  FIG.  2   . 
     In addition, for example, the grindstones  340  are preliminarily rotated in the direction of an arrow  39  depicted in  FIG.  2   . Then, in a state in which the grindstones  340  are rotating, the grindstones  340  are lowered in the direction of approaching the holding surface  200 , by use of the grinding feeding mechanism  4 . 
     In this instance, since the first contact element  610  and the second contact element  620  are disposed at positions lower than the grindstones  340 , the first contact element  610  comes into contact with the upper surface  210  of the frame body  21  and the second contact element  620  comes into contact with the upper surface  170  of the wafer  17  before the grindstones  340  come into contact with the upper surface  170  of the wafer  17 . 
     As a result, the height of the holding surface  200  is measured by the first height gauge  61 , and the height of the upper surface  170  of the wafer  17  is measured by the second height gauge  62 . 
     Then, the height value of the holding surface  200  and the height value of the upper surface  170  of the wafer  17  thus measured are transmitted to the calculation section  63 , and the thickness of the wafer  17  that is yet to be ground is calculated. 
     In a state in which the first contact element  610  is in contact with the upper surface  210  of the frame body  21  and the second contact element  620  is in contact with the upper surface  170  of the wafer  17 , the grinding unit  3  is further lowered in the −Z direction by use of the grinding feeding mechanism  4 . As a result, as depicted in  FIG.  3   , the lower surfaces  342  of the grindstones  340  make contact with the upper surface  170  of the wafer  17 . Here, the contact part between the lower surfaces  342  of the grindstones  340  and the upper surface  170  of the wafer  17  is the processing region  9  depicted in  FIG.  2   . In a state in which the lower surfaces  342  of the grindstones  340  are in contact with the upper surface  170  of the wafer  17 , the grindstones  340  are further lowered in the −Z direction by use of the grinding feeding mechanism  4 , whereby the wafer  17  is ground. 
     During grinding of the wafer  17 , the measurement of the height of the holding surface  200  by the first height gauge  61  and the measurement of the height of the upper surface  170  of the wafer  17  by the second height gauge  62  are continued, and calculation of the thickness of the wafer  17  performed by the calculation section  63  on the basis of the difference between the two heights is continued. 
     In the grinding apparatus  1 , the first measurement point  611  and the second measurement point  621  are located in the vicinity of the processing region  9  where the upper surface  170  of the wafer  17  and the lower surfaces  342  of the grindstones  340  make contact as depicted in  FIG.  2   , and, thus, the thickness of the vicinity of the ground part of the wafer  17  can be measured, and fine variation in the thickness of the wafer  17  can be recognized, enabling accurate measurement of the thickness. Particularly, as depicted in  FIG.  2   , when the first measurement point  611  and the second measurement point  621  are located on the downstream side in regard of the rotating direction of the chuck table  2  as compared to the processing region  9 , the thickness of the ground part that is obtained immediately after grinding can be measured, and, thus, formation of the wafer  17  in a predetermined thickness can be recognized by the calculation section  63  immediately after such measurement, and the wafer  17  can be finished to a predetermined thickness. 
     In addition, since the first height gauge  61  and the second height gauge  62  are disposed on the side plate  374  of the holder  37 , it is possible, by bringing the grindstones  340  close to the upper surface  170  of the wafer  17  by use of the grinding feeding mechanism  4 , to simultaneously lower the first height gauge  61  and the second height gauge  62 . Further, since both height gauges are separated away from the upper surface  170  of the wafer  17  together with the grindstones  340  when the grindstones  340  are separated away from the upper surface  170  of the wafer  17  by use of the grinding feeding mechanism  4 , operability of maintenance work and the like can be enhanced. 
     When the wafer  17  has been ground to a predetermined thickness, the grinding unit  3  is moved in the +Z direction by use of the grinding feeding mechanism  4  to separate away the grindstones  340  from the upper surface  170  of the wafer  17 , and the grinding of the wafer  17  is ended. 
     Instead of the configuration in which the first height gauge  61  and the second height gauge  62  are provided at the connection section  60  supported by the side plate  374  of the holder  37 , the grinding apparatus  1  may have a configuration in which, as depicted in  FIG.  4   , an arm  69  fixed to the slider  38  is provided, and the first height gauge  61  and the second height gauge  62  are supported by the arm  69 . In this configuration, also, the first height gauge  61  and the second height gauge  62  supported by the arm  69  are located at horizontal positions similar to the horizontal position of the first height gauge  61  and the horizontal position of the second height gauge  62  that are depicted in  FIG.  1   . Thus, the first height gauge  61  and the second height gauge  62  are located in the vicinity of the processing region  9  depicted in  FIG.  2   , and, accordingly, the thickness of the vicinity of the ground part of the wafer  17  can be measured, enabling accurate measurement of the thickness of the wafer  17 . 
     The present invention is not limited to the details of the above described preferred embodiment. 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.