METHOD OF SHAPING HOLDING SURFACE OF CHUCK TABLE

Abstract

A second relative speed where a spindle and a center of a holding surface are brought together in a grinding step is established such that the spindle and the outer circumferential edge of a surrounding region of the holding surface start being brought together other along a first direction and the spindle's rotational shaft and the holding surface's center start being brought together along a second direction simultaneously and that the spindle and the outer circumferential edge of the surrounding region finish being brought together along the first direction and the spindle's rotational shaft and the holding surface's center finish being brought together along the second direction simultaneously. Specifically, the second relative speed is established in view of parameters that are established as desired and the worn-off amount of the grindstones that is grasped prior to or during the grinding step (i.e., a change in thickness of the grindstones).

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of shaping a holding surface of a chuck table by grinding the holding surface.

Description of the Related Art

Chips including devices such as integrated circuits (ICs) are indispensable components for various pieces of electronic equipment such as mobile phones and personal computers. Such chips are manufactured by dividing wafers including a plurality of devices constructed in their face sides into individual pieces that include the respective devices.

For the purpose of reducing sizes of chips to be manufactured from wafers, the wafers may be thinned down before they are divided into the chips. A wafer is thinned down by, for example, a grinding apparatus having a chuck table having a circular holding surface that is larger than the wafer in diameter and a spindle having a distal end on which a grinding wheel having an annular array of grindstones is mounted. Specifically, the grinding apparatus thins down the wafer according to the following sequence of operation.

First, the wafer has its face side held on the holding surface of the chuck table. Then, while the grinding wheel whose outside diameter is larger than a radius of the wafer and the chuck table are being rotated, either one of the grindstones is brought into contact with a center of a reverse side of the wafer. Then, while the grinding wheel and the wafer are being rotated, the chuck table and the spindle are brought closer to each other. The grindstones grind the reverse side of the wafer by way of abrasive contact therewith, thinning down the wafer.

The wafer that has been thinned down tends to be reduced in rigidity, possibly making itself difficult to handle in subsequent processing steps. As a solution to this problem, there has been proposed in the art a grinding process known as TAIKO grinding in which a recess having a circular bottom surface is formed in the reverse side of a wafer (see, for example, Japanese Patent Laid-Open No. 2007-19461). Specifically, a grinding wheel, hereinafter referred to as a “TAIKO grinding wheel,” whose outside diameter is smaller than the radius of the wafer is used to form the recess by grinding a central portion of the reverse side of the wafer, leaving an outermost circumferential support ring on the wafer.

When the TAIKO grinding is performed on a wafer held on a chuck table having a flat holding surface by a grinding wheel including an annular array of grindstones, however, the wafer may have its surface blackened, i.e., burned, due to frictional engagement with the grindstones, and/or may develop iris-shaped grinding marks left on its surface. To alleviate these difficulties, it has been customary to carry out the TAIKO grinding while a rotational shaft of the TAIKO grinding wheel is tilted with respect to a rotational shaft of the chuck table.

However, when the rotational shaft of the TAIKO grinding wheel is tilted with respect to the rotational shaft of the chuck table and the TAIKO grinding is performed on the wafer held on the flat holding surface of the chuck table, a region of the wafer that is coextensive with the recess tends to be thicker in its portions underlying respective portions of the recess near the center and outer circumferential edge of the recess and tends to be thinner in its portion underlying an intermediate portion of the recess between the center and outer circumferential edge thereof.

In view of the above tendency of the wafer, there has been proposed a method of shaping the holding surface of a chuck table by grinding the same, prior to the TAIKO grinding (see, for example, Japanese Patent Laid-Open No. 2008-60470). According to the proposed method, specifically, a grinding wheel (hereinafter referred to as “holding surface grinding wheel”) grinds the holding surface of a chuck table while the rotational shaft of the holding surface grinding wheel is tilted with respect to the rotational shaft of the chuck table.

According to the proposed method, furthermore, the outside diameter of the holding surface grinding wheel is smaller than the radius of a wafer to be supported on the chuck table and the radius of the holding surface of the chuck table. When the holding surface grinding wheel grinds the holding surface of the chuck table, a region of the holding surface of the chuck table near its outer circumferential edge remains unground flatwise. Therefore, when the wafer is subsequently placed on the holding surface of the chuck table, a region of the wafer near its outer circumferential edge tends to ride on the flat region of the chuck table, making it difficult to perform the TAIKO grinding on the wafer.

The problem described above can be solved by making the outside diameter of the holding surface grinding wheel larger than the radius of the holding surface of the chuck table, i.e., by grinding the holding surface of the chuck table in a manner to curve the holding surface in its entirety. However, the solution may in turn lead to difficulty in uniformizing a thickness of a region of the wafer that underlies the recess in the wafer after the TAIKO grinding, on account of the difference between the outside diameters of the holding surface grinding wheel and the TAIKO grinding wheel.

There has been proposed a method of shaping a holding surface of a chuck table by grinding the holding surface of the chuck table to curve a central region of the holding surface of the chuck table and slanting a surrounding region of the holding surface that surrounds the central region thereof, by use of a grinding wheel that is equal in outside diameter to a grinding wheel used to grind a wafer to be held on the holding surface of the chuck table (see, for example, Japanese Patent Laid-Open No. 2018-69348).

SUMMARY OF THE INVENTION

When the holding surface of the chuck table is ground by the grinding wheel, the grindstones of the grinding wheel are worn and hence have their thicknesses reduced. If the holding surface of the chuck table is ground by the grinding wheel without concern over wear on the grinding stones, then the central region of the holding surface after it has been shaped is shallower as a whole than the central region of a holding surface suitable for the TAIKO grinding.

In contrast, if the central region of the holding surface of the chuck table is additionally ground to the same depth as the central region of the holding surface suitable for the TAIKO grinding, then a step is formed between the central region and the surrounding region that surrounds the central region. In this case, the step may be liable to make it difficult to perform the TAIKO grinding on a wafer placed on the holding surface of the chuck table thus shaped.

It is therefore an object of the present invention to provide a method of shaping a holding surface of a chuck table into a holding surface that is suitable for the TAIKO grinding without forming a step on the holding surface of the chuck table.

In accordance with an aspect of the present invention, there is provided a method of shaping a holding surface of a chuck table of a grinding apparatus that includes the chuck table that is rotatable and has a circular holding surface and a spindle including a distal end portion on which a grinding wheel that has a plurality of grindstones disposed in an annular array is mounted, in which, when the spindle is rotated, the plurality of grindstones follow a track having an outside diameter smaller than a radius of the holding surface, and the method shapes the holding surface of the chuck table by grinding the holding surface of the chuck table such that a surrounding region of the holding surface that is positioned radially outwardly of a first concentric circle region of the holding surface that is radially spaced from a center of the holding surface by a distance that corresponds to the outside diameter of the track is slanted so as to be progressively deeper toward the first concentric circle region and that the center and the first concentric circle region are of a predetermined depth from an outer circumferential edge of the surrounding region and a second concentric circle region positioned radially between the center and the first concentric circle region is deeper than the center and the first concentric circle region. The method includes an adjusting step of adjusting a tilt of at least one of the spindle or the chuck table such that the plurality of grindstones will come into initial contact with a third concentric circle region of the holding surface that is radially positioned between the first concentric circle region and the second concentric circle region when the spindle and the holding surface are moved toward each other along a first direction, after the adjusting step, a contacting step of, while the spindle and the chuck table are being rotated, bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction until the plurality of grindstones contact the outer circumferential edge of the surrounding region, and after the contacting step, a grinding step of, while the spindle and the chuck table are being rotated and the spindle and the outer circumferential edge of the surrounding region are being brought toward each other at a first relative speed along the first direction, bringing a rotational shaft of the spindle and the center of the holding surface toward each other at a second relative speed along a second direction perpendicular to the first direction until the plurality of grindstones contact the center of the holding surface. In the grinding step, the spindle and the outer circumferential edge of the surrounding region are brought toward each other along the first direction by a first traveled distance represented by a sum of the predetermined depth and a worn-off amount of the plurality of grindstones that are worn by grinding the chuck table to the predetermined depth. In the grinding step, the rotational shaft of the spindle and the center of the holding surface are brought toward each other along the second direction by a second traveled distance equal to a width of the surrounding region along the second direction. The first relative speed is a constant speed established as desired. The second relative speed is a constant or variable speed established in view of the predetermined depth, the worn-off amount, the second traveled distance, and the first relative speed such that the spindle and the outer circumferential edge of the surrounding region start being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface start being brought toward each other along the second direction simultaneously and that the spindle and the outer circumferential edge of the surrounding region finish being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface finish being brought toward each other along the second direction simultaneously.

Preferably, the worn-off amount has been grasped prior to the contacting step, and the second relative speed is a speed that is obtained by dividing the second traveled distance by a time obtained by dividing the first traveled distance by the first relative speed.

Also, preferably, the surrounding region includes a first portion and a second portion positioned radially inwardly of the first portion and slanted with a larger gradient than the first portion, the grinding step includes a preliminary grinding step of forming the first portion in the surrounding region by bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction by a third traveled distance and bringing the rotational shaft of the spindle and the center of the holding surface toward each other along the second direction by a fourth traveled distance while the spindle and the chuck table are being rotated, after the preliminary grinding step, a measuring step of measuring a depth of an inner circumferential edge of the first portion from the outer circumferential edge of the surrounding region, and a main grinding step of forming the second portion in the surrounding region by bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction by a fifth traveled distance and bringing the rotational shaft of the spindle and the center of the holding surface toward each other along the second direction by a sixth traveled distance while the spindle and the chuck table are being rotated. The second relative speed in the preliminary grinding step is a speed that is obtained by dividing the second traveled distance by a time obtained by dividing the predetermined depth by the first relative speed. The third traveled distance represents a distance established as desired in a range smaller than the predetermined depth. The fourth traveled distance represents a distance that is obtained by multiplying the second relative speed in the preliminary grinding step by a time obtained by dividing the third traveled distance by the first relative speed. The worn-off amount represents a distance that is obtained by multiplying the predetermined depth by a value that is obtained by dividing a distance obtained by subtracting the depth of the inner circumferential edge of the first portion measured in the measuring step from the third traveled distance by the depth of the inner circumferential edge of the first portion measured in the measuring step. The fifth traveled distance represents a distance that is obtained by adding a distance obtained by subtracting the third traveled distance from the predetermined depth and the worn-off amount to each other. The sixth traveled distance represents a distance that is obtained by subtracting the fourth traveled distance from the second traveled distance. The second relative speed in the main grinding step is a speed that is obtained by dividing the sixth traveled distance by a time obtained by dividing the fifth traveled distance by the first relative speed.

According to the present invention, the second relative speed at which the spindle and the center of the holding surface of the spindle are brought toward each other in the grinding step is established such that the spindle and the outer circumferential edge of the surrounding region of the holding surface start being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface start being brought toward each other along the second direction simultaneously and that the spindle and the outer circumferential edge of the surrounding region finish being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface finish being brought toward each other along the second direction simultaneously.

Specifically, the second relative speed is established in view of parameters that are established as desired and the worn-off amount of the plurality of grindstones that is grasped prior to or during the grinding step (an absolute value of a change in thickness of the grindstones before and after the grinding step). According to the present invention, therefore, it is possible to shape the holding surface of the chuck table into a holding surface that is suitable for the TAIKO grinding without forming a step on the holding surface of the chuck table.

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 perspective view schematically illustrating an example of a grinding apparatus;

FIG. 2 is a side elevational view, partly in cross section, illustrating the example of the grinding apparatus depicted in FIG. 1;

FIG. 3 is a flowchart schematically illustrating an example of a method of shaping a holding surface of a chuck table;

FIG. 4 is a plan view schematically illustrating a chuck table depicted in FIGS. 1 and 2;

FIG. 5A is a plan view schematically illustrating an example of an adjusting step depicted in FIG. 3;

FIG. 5B is a front elevational view schematically illustrating the chuck table after the adjusting step illustrated in FIG. 5A;

FIG. 6A is a front elevational view schematically illustrating an example of a contacting step depicted in FIG. 3;

FIG. 6B is a cross-sectional view schematically illustrating the chuck table after the contacting step illustrated in FIG. 6A;

FIG. 7A is a plan view schematically illustrating an example of a grinding step depicted in FIG. 3;

FIG. 7B is a front elevational view schematically illustrating the example of the grinding step depicted in FIG. 3;

FIG. 7C is a cross-sectional view schematically illustrating the chuck table after the grinding step depicted in FIGS. 7A and 7B;

FIG. 8 is a flowchart schematically illustrating steps included in another example of the grinding step depicted in FIG. 3;

FIG. 9A is a plan view schematically illustrating an example of a preliminary grinding step depicted in FIG. 8;

FIG. 9B is a front elevational view schematically illustrating the example of the preliminary grinding step depicted in FIG. 8;

FIG. 9C is a cross-sectional view schematically illustrating the chuck table after the preliminary grinding step illustrated in FIGS. 9A and 9B;

FIG. 10A is a plan view schematically illustrating an example of a main grinding step depicted in FIG. 8;

FIG. 10B is a front elevational view schematically illustrating the example of the main grinding step depicted in FIG. 8; and

FIG. 10C is a cross-sectional view schematically illustrating the chuck table after the main grinding step illustrated in FIGS. 10A and 10B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically illustrates in perspective an example of a grinding apparatus, and FIG. 2 illustrates in side elevation, partly in cross section, the example of the grinding apparatus depicted in FIG. 1. In FIG. 1, some components of the grinding apparatus are illustrated in block form for illustrative purposes.

In FIGS. 1 and 2, a +X-axis direction (forward direction) indicated by the arrow+X and a +Y-axis direction (leftward direction) indicated by the arrow+Y are directions perpendicular to each other in a horizontal plane, and a +Z-axis direction (upward direction) indicated by the arrow+Z is a direction perpendicular to the +X-axis direction and the +Y-axis direction.

Also, a −X-axis direction (rearward direction) indicated by the arrow −X is opposite to the +X-axis direction, a −Y-axis direction (rightward direction) indicated by the arrow −Y is opposite the +Y-axis direction, and a −Z-axis direction (downward direction) indicated by the arrow −Z is opposite the +Z-axis direction. In addition, in the following description, the +X-axis direction and the −X-axis direction will also be collectively referred to as X-axis directions extending along an X-axis, the +Y-axis direction and the −Y-axis direction will also be collectively referred to as Y-axis directions extending along a Y-axis, and the +Z-axis direction and the −Z-axis direction will also be collectively referred to as Z-axis directions extending along a Z-axis. The grinding apparatus, denoted by 2 in FIGS. 1 and 2, is illustrated in reference to a three-dimensional XYZ coordinate system having the X-axis, the Y-axis, and the Z-axis.

As illustrated in FIGS. 1 and 2, the grinding apparatus 2 has a base 4 on which various components thereof are supported. The base 4 has a groove 4a defined in an upper surface thereof and extending along the X-axis directions. The groove 4a has a contour shaped as a rectangular parallelepiped. The groove 4a has a bottom on which there is mounted an X-axis moving mechanism 6 (see FIG. 2) for moving a chuck table 28, to be described later, along the X-axis directions.

The X-axis moving mechanism 6 has a pair of guide rails 8 extending along the X-axis directions and spaced from each other along the Y-axis directions. The X-axis moving mechanism 6 also has an X-axis movable plate 10 slidably mounted on the guide rails 8 for sliding movement along the X-axis directions and having a contour shaped as a rectangular parallelepiped, and a screw shaft 12 disposed between the guide rails 8 and extending along the X-axis directions.

The screw shaft 12 has a rear end coupled to a stepping motor 14 mounted on the bottom of the groove 4a for rotating the screw shaft 12 about its central axis. The screw shaft 12 has an externally threaded outer circumferential surface that is threaded through a nut 16 housing a large number of balls, not depicted, therein. The balls are held in operative engagement with the externally threaded outer circumferential surface of the screw shaft 12, and circulate through the nut 16 in response to rotation of the screw shaft 12. The screw shaft 12, the nut 16, and the balls jointly function as a ball screw mechanism.

Also, the nut 16 is fixed to a lower surface of the X-axis movable plate 10. Therefore, when the stepping motor 14 is energized, it rotates the screw shaft 12, moving the nut 16 and the X-axis movable plate 10 along the X-axis directions.

A rotating mechanism 18 for rotating the chuck table 28 to be described later is mounted on an upper surface of the X-axis movable plate 10. The rotating mechanism 18 has a support shaft 20 extending along the Z-axis directions and a rotary actuator, not depicted, such as a stepping motor that is operatively coupled to the support shaft 20 by pulleys.

The pulleys include a driven pulley 22 connected to the lower end of the support shaft 20 and a drive pulley, not depicted, connected to the rotary actuator. Also, an endless belt, not depicted, is trained around the driven pulley 22 and the drive pulley.

Moreover, a tilt adjusting mechanism for adjusting the tilt of the chuck table 28 to be described later is disposed on the X-axis movable plate 10. Also, the tilt adjusting mechanism has a fixed shaft, not depicted, and two movable shafts 24 whose lengths along the Z-axis directions are variable.

Also, the fixed shaft and the two movable shafts 24 have respective lower ends coupled to the X-axis movable plate 10 and respective upper ends fixed to a table base 26 disposed above the X-axis movable plate 10. Also, the table base 26 has a through hole defined centrally therein with the support shaft 20 rotatably fitted in and extending through the through hole in the table base 26.

Further, the chuck table 28, which is shaped as a circular plate, is mounted on the upper end of the support shaft 20. The chuck table 28 is rotatable independently of the table base 26 and supported on the table base 26 by a bearing, not depicted, for example.

When the rotating mechanism 18 is actuated, it rotates the chuck table 28. When the X-axis moving mechanism 6 is actuated, i.e., when the stepping motor 14 is energized, it moves the table base 26 and hence the chuck table 28 along the X-axis directions.

The chuck table 28 has a frame 30 shaped as a circular plate and made of ceramic, for example. The frame 30 has a circular bottom wall and a hollow cylindrical side wall extending upwardly from the outer circumferential edge of the bottom wall. Specifically, the bottom wall and the side wall jointly define a circular recess in an upper surface of the frame 30.

Note that the side wall of the frame 30 has an inside diameter slightly smaller than the diameter of a wafer 11 to be described later and an outside diameter slightly larger than the diameter of the wafer 11. Also, the bottom wall of the frame 30 has a fluid channel, not depicted, defined therein that is opened in the bottom of the recess. The fluid channel is held in fluid communication with a suction source, not depicted, such as an ejector.

Moreover, the recess in the upper surface of the frame 30 houses a circular porous plate 32 (see FIG. 1) fixedly disposed therein that is generally equal in diameter to the recess. The porous plate 32 is made of porous ceramic, for example. In addition, the porous plate 32 has an upper surface that lies generally parallel to the X-axis directions and the Y-axis directions. The side wall of the frame 30 has an upper surface that also lies generally parallel to the X-axis directions and the Y-axis directions.

When the suction source fluidly connected to the fluid channel defined in the bottom wall of the frame 30 is actuated, it generates and transmits a suction force through the fluid channel and the porous plate 32 to a space above the upper surface of the porous plate 32. The upper surface of the porous plate 32 and the upper surface of the side wall of the frame 30 function as a holding surface of the chuck table 28 for holding the wafer 11 under suction thereon.

As illustrated in FIG. 1, the wafer 11 has a face side 11a, illustrated as facing downwardly, to which a protective tape 13 is affixed and a reverse side 11b, illustrated as facing upwardly, opposite the face side 11a. The wafer 11 is placed on the holding surface of the chuck table 28 with the protective tape 13 interposed therebetween. When the suction source fluidly connected to the fluid channel of the frame 30 is actuated, the wafer 11 with the reverse side 11b exposed upwardly is held under suction on the holding surface of the chuck table 28.

The wafer 11 is made of a semiconductor material such as silicon, for example, and has a plurality of devices, not depicted, constructed in the face side 11a thereof. Also, the protective tape 13, which is made of resin, for example, protects the devices against damage at a time at which the reverse side 11b of the wafer 11 is ground by the grinding apparatus 2.

The chuck table 28 is surrounded by a table cover 34 that extends around the chuck table 28. The table cover 34 is disposed in the groove 4a defined in the base 4 and has a width along the Y-axis directions that is substantially the same as the width of the groove 4a along the Y-axis directions. Also, a pair of dust-proof, drip-proof covers 36 each expansible and shrinkable along the X-axis directions are disposed in the groove 4a respectively in front of and behind the table cover 34 in sandwiching relation thereto.

When the X-axis moving mechanism 6 is actuated, i.e., when the stepping motor 14 is energized, to move the chuck table 28 along the X-axis directions, the table cover 34 is also moved together with the chuck table 28 along the X-axis directions, expanding one of the covers 36 and shrinking the other.

The grinding apparatus 2 further includes a support structure 38 shaped as a quadrangular prism that is disposed on an area of the upper surface of the base 4 positioned behind the groove 4a. A Z-axis moving mechanism 40 for vertically moving, i.e., lifting and lowering, a grinding unit 54 to be described later is mounted on a front surface of the support structure 38. The Z-axis moving mechanism 40 has a pair of guide rails 42 extending along the Z-axis directions and spaced from each other along the Y-axis directions.

The Z-axis moving mechanism 40 also has sliders 44 (see FIG. 2) slidably mounted on the guide rails 42 for sliding movement along the Z-axis directions. The sliders 44 have respective front ends fixed to a rear surface of a Z-axis movable plate 46 having a contour shaped as a rectangular parallelepiped, and a screw shaft 48 disposed between the guide rails 42 and extending along the Z-axis directions.

The screw shaft 48 has an upper end coupled to a stepping motor 50, the stepping motor 50 for rotating the screw shaft 48 about its vertical central axis. The screw shaft 48 has an externally threaded outer circumferential surface that is threaded through a nut 52 (see FIG. 2) housing a large number of balls, not depicted, therein. The balls are held in operative engagement with the externally threaded outer circumferential surface of the screw shaft 48, and circulate through the nut 52 in response to rotation of the screw shaft 48. The screw shaft 48, the nut 52, and the balls jointly function as a ball screw mechanism.

Also, the nut 52 is fixed to a rear surface of the Z-axis movable plate 46. Therefore, when the stepping motor 50 is energized, it rotates the screw shaft 48, moving the nut 52 and the Z-axis movable plate 46 along the Z-axis directions. The grinding unit 54 is mounted on a front surface of the Z-axis movable plate 46.

The grinding unit 54 has a hollow cylindrical holder 56 fixed to the front surface of the Z-axis movable plate 46. The holder 56 holds therein a hollow cylindrical housing 58 that extends along the Z-axis directions. The housing 58 accommodates therein a rotating mechanism for rotating a grinding wheel 64 to be described later about its vertical central axis.

The rotating mechanism has a spindle 60 extending along the Z-axis directions and having a distal end portion, i.e., a lower end portion, exposed downwardly from the housing 58. Note that the spindle 60 is rotatably supported by the housing 58 and has a proximal end portion, i.e., an upper end portion, coupled to a rotary actuator such as a servomotor.

Moreover, the spindle 60 includes a wheel mount 62 shaped as a circular plate and disposed on its distal end portion. The grinding unit 54 includes an annular grinding wheel 64 mounted on a lower surface of the wheel mount 62 by fasteners, not depicted, such as bolts, for example. The grinding wheel 64 has an outside diameter substantially equal to the diameter of the wheel mount 62.

The grinding wheel 64 has a plurality of grindstones 64a and a wheel base 64b having a lower surface on which the grindstones 64a are mounted at spaced intervals in an annular array. When the rotary actuator coupled to the proximal end portion of the spindle 60 is energized, it rotates the spindle 60 and hence the wheel mount 62 and the grinding wheel 64 about the vertical central axis along the Z-axis directions.

Also, the grinding wheel 64 has an outside diameter equal to the outside diameter of a TAIKO grinding wheel, i.e., a grinding wheel for forming a recess having a circular bottom surface in the reverse side 11b of the wafer 11. Therefore, the outside diameter of a track followed by the grindstones 64a at a time at which the grinding wheel 64 is rotated together with the spindle 60 is smaller than the radius of the wafer 11 and smaller than the radius of the holding surface of the chuck table 28.

Note that each of the grindstones 64a contains abrasive grains of diamond or cBN dispersed in a bond material such as a vitrified bond or a resin bond. The wheel base 64b is made of a metal material such as stainless steel or aluminum, for example.

Also, the grinding apparatus 2 includes a measurement unit 66 disposed on the upper surface of the base 4 alongside of the groove 4a. The measurement unit 66 has a pair of height gauges 66a and 66b for measuring the respective heights of surfaces at positions where their probes contact the surfaces. The probes of the height gauges 66a and 66b can be positioned so as to contact the holding surface of the chuck table 28 when or before or after the holding surface of the chuck table 28 is ground.

The grinding apparatus 2 further includes a controller 68 (see FIG. 1) for controlling the X-axis moving mechanism 6, the rotating mechanism 18, the Z-axis moving mechanism 40, the rotating mechanism accommodated in the housing 58, the measurement unit 66, and the like. The controller 68 includes a processor 68a and a memory 68b.

The processor 68a includes a central processing unit (CPU) and the like, for example. The memory 68b includes a volatile memory such as a dynamic random access memory (DRAM) or a static random access memory (SRAM) and a nonvolatile memory such as a solid state drive (SSD) also known as a NAND-type flash memory or a hard disk drive (HDD) also known as a magnetic storage device, for example.

The memory 68b stores various pieces of information including data and programs to be used by the processor 68a. The processor 68a controls the X-axis moving mechanism 6, the rotating mechanism 18, the Z-axis moving mechanism 40, the rotating mechanism accommodated in the housing 58, and/or the measurement unit 66 in order to read programs for carrying out a method of shaping the holding surface of a chuck table to be described below from the memory 68b and execute the read programs.

FIG. 3 is a flowchart schematically illustrating an example of a method of shaping the holding surface of the chuck table 28 into a holding surface that is suitable for the TAIKO grinding on the grinding apparatus 2.

Here, the holding surface that is suitable for the TAIKO grinding will be described below with reference to FIG. 4. FIG. 4 schematically illustrates the chuck table 28 in plan. The holding surface suitable for the TAIKO grinding should meet conditions set forth below.

First, the holding surface of the chuck table 28 includes a first concentric circle region C1 and a surrounding region S positioned radially outwardly of the first concentric circle region C1. The surrounding region S is slanted so as to be progressively deeper toward the first concentric circle region C1. Note that the first concentric circle region C1 represents an annular region that is radially spaced from a center C0 of the holding surface by a distance that corresponds to the outside diameter of a track to be followed by the grindstones 64a at a time at which the grinding wheel 64 is rotated.

Also, the center C0 and the first concentric circle region C1 of the holding surface are of a predetermined depth from an outer circumferential edge of the surrounding region S, e.g., an outer circumferential edge of the holding surface. Also, the holding surface of the chuck table 28 also has a second concentric circle region C2 positioned radially between the center C0 and the first concentric circle region C1 of the holding surface. The second concentric circle region C2 is deeper than the center C0 and the first concentric circle region C1.

According to the method of shaping the holding surface of the chuck table 28 illustrated in FIG. 3, the tilt of the chuck table 28 is first adjusted by the tilt adjusting mechanism (adjusting step S1). FIG. 5A schematically illustrates in plan an example of the adjusting step S1, and FIG. 5B schematically illustrates in front elevation the chuck table 28 and the like after the adjusting step S1 illustrated in FIG. 5A.

In the adjusting step S1, the tilt of the chuck table 28 is adjusted such that the grindstones 64a will come into initial contact with a third concentric circle region C3 of the holding surface that is radially positioned between the first concentric circle region C1 and the second concentric circle region C2 when the spindle 60 is lowered while the spindle 60 and the chuck table 28 are being rotated.

For example, in the adjusting step S1, the chuck table 28 is moved along the X-axis directions to position a rear end of the holding surface of the chuck table 28 directly below a rear end R of the track followed by the grindstones 64a at a time at which the grinding wheel 64 is rotated (see FIG. 5A).

Then, the tilt of the chuck table 28 is adjusted such that a left end L, as viewed along the forward direction, of the track will come into initial contact with the holding surface of the chuck table 28 at a time at which the spindle 60 is lowered. Hence, the adjusting step S1 is completed. Specifically, the tilt of the chuck table 28 is adjusted to make a left side, as viewed along the forward direction, of the chuck table 28 higher than a right side of the chuck table 28 (see FIG. 5B). The adjusting step S1 is completed when the tilt of the chuck table 28 has thus been adjusted.

After the adjusting step S1, the spindle 60 is lowered until the grindstones 64a contact the outer circumferential edge of the surrounding region S of the holding surface of the chuck table 28, while the spindle 60 and the chuck table 28 are being rotated (contacting step S2). FIG. 6A schematically illustrates in plan an example of the contacting step S2, and FIG. 6B schematically illustrates in cross section the chuck table 28 after the contacting step S2 illustrated in FIG. 6A.

In the contacting step S2, some of the grindstones 64a that are successively positioned at the left end L of the track contact the third concentric circle region C3 (see FIG. 6A). The grindstones 64a now grind the third concentric circle region C3, making the third concentric circle region C3 deeper than the center C0 and the outer circumferential edge of the holding surface of the chuck table 28.

Moreover, as the spindle 60 is progressively lowered, the area of the holding surface that is being ground by the grindstones 64a spreads radially inwardly and outwardly over the holding surface. Accordingly, the grindstones 64a also grind the first concentric circle region C1 and the second concentric circle region C2, making them deeper than the center C0 and the outer circumferential edge of the holding surface of the chuck table 28. When the spindle 60 has been lowered until the grindstones 64a come into contact with the outer circumferential edge of the surrounding region S of the holding surface of the chuck table 28, the contacting step S2 is completed (see FIG. 6B).

After the contacting step S2, the chuck table 28 is retracted until the grindstones 64a contact the center C0 of the holding surface, while the spindle 60 and the chuck table 28 are being rotated and the spindle 60 is being lowered (grinding step S3).

Here, in the grinding step S3, the spindle 60 is moved along the Z-axis directions, i.e., lowered, by a first traveled distance represented by the sum of the predetermined depth described above, i.e., the depth of the center C0 and the first concentric circle region C1 of the holding surface from the outer circumferential edge of the surrounding region S after the method of shaping the holding surface of the chuck table 28 illustrated in FIG. 3 has been carried out, and the worn-off amount of the grindstones 64a that has been caused by grinding the holding surface of the chuck table 28 to the predetermined depth.

Also, in the grinding step S3, the chuck table 28 is moved along the X-axis directions by a second traveled distance equal to the width of the surrounding region S that extends radially over the holding surface of the chuck table 28, e.g., the distance between the first concentric circle region C1 and the outer circumferential edge of the holding surface.

In the grinding step S3, the spindle 60 is lowered at a speed referred to as a first relative speed. In general, the first relative speed greatly affects the accuracy with which the holding surface of the chuck table 28 is processed, i.e., ground. In the grinding step S3, therefore, the first relative speed is set to a constant speed suitable for the grinding of the holding surface of the chuck table 28.

In the grinding step S3, furthermore, the chuck table 28 is retracted at a speed referred to as a second relative speed. Different processes are performed to establish the second relative speed, depending on whether the worn-off amount of the grindstones 64a has been grasped or not.

First, a process of establishing the second relative speed if the worn-off amount of the grindstones 64a has been grasped prior to the grinding step S3 will be described below with reference to FIGS. 7A, 7B, and 7C.

FIG. 7A schematically illustrates in plan an example of the grinding step S3. FIG. 7B schematically illustrates in front elevation the grinding step S3. FIG. 7C schematically illustrates in cross section the chuck table 28 after the grinding step S3.

The second relative speed is established so as to be equal to a speed that is obtained by dividing the second traveled distance by a time obtained by dividing the first traveled distance by the first relative speed. Specifically, if it is assumed that the predetermined depth is represented by D, the worn-off amount of the grindstones 64a by W, the second traveled distance by X0, and the first relative speed by Zv, then the second relative speed, denoted by Xv, is expressed by the following equation (1):

$\begin{array}{cc}\mathrm{Xv}=\frac{X0}{\left(D+W\right)/\mathrm{Zv}}& \left(1\right)\end{array}$

When the grinding step S3 is started with the second relative speed thus established, the spindle 60 will finish its descent and the chuck table 28 will finish its movement simultaneously. According to the above process of establishing a second relative speed, the holding surface of the chuck table 28 is now shaped such that the depths of the center C0 and the first concentric circle region C1 are equal to the predetermined depth D and that the surrounding region S is of a shape represented by the side surface of an inverted truncated cone.

Then, a process of establishing the second relative speed if the worn-off amount of the grindstones 64a has not been grasped prior to the grinding step S3 will be described below with reference to FIGS. 8, 9A, 9B, 9C, 10A, 10B, and 10C. FIG. 8 is a flowchart schematically illustrating steps included in another example of the grinding step S3 depicted in FIG. 3.

In the other example of the grinding step S3 illustrated in FIG. 8, to put it simply, the holding surface of the chuck table 28 is slightly ground to form a portion, i.e., a first portion, represented by the side surface of an inverted truncated cone in the surrounding region S, after which the worn-off amount of the grindstones 64a is calculated in view of the depth of an inner circumferential edge of the first portion. Then, in the other example of the grinding step S3, in view of the calculated worn-off amount of the grindstones 64a, the second relative speed is established again, and the holding surface of the chuck table 28 is further ground to form a portion, i.e., a second portion, represented by the side surface of an inverted truncated cone and slanted with a larger gradient than the first portion, radially inwardly of the first portion.

Specifically, in the other example of the grinding step S3, the first portion is formed in the surrounding region S by lowering the spindle 60 by a third traveled distance and retracting the chuck table 28 by a fourth traveled distance while the spindle 60 and the chuck table 28 are being rotated (preliminary grinding step S31).

FIG. 9A schematically illustrates in plan an example of the preliminary grinding step S31. FIG. 9B schematically illustrates in front elevation the example of the preliminary grinding step S31. FIG. 9C schematically illustrates in cross section the chuck table 28 after the preliminary grinding step S31.

In the preliminary grinding step S31, a second relative speed is established so as to be equal to a speed that is obtained by dividing the second traveled distance X0 by a time that is obtained by dividing the predetermined depth D by the first relative speed Zv. Specifically, the second relative speed, denoted by Xv1, in preliminary grinding step S31 is expressed by the following equation (2):

$\begin{array}{cc}\mathrm{Xv}1=\frac{X0}{D/\mathrm{Zv}}=\frac{X0\times \mathrm{Zv}}{D}& \left(2\right)\end{array}$

Also, the third traveled distance refers to a distance established as desired in a range smaller than the predetermined depth D. In addition, the fourth traveled distance refers to a distance that is obtained by multiplying the second relative speed Xv1 in the preliminary grinding step S31 by a time that is obtained by dividing the third traveled distance by the first relative speed Zv.

Specifically, if it is assumed that the third traveled distance is represented by Z1, then the fourth traveled distance, represented by X1, is expressed by the following equation (3):

$\begin{array}{cc}X1=\mathrm{Xv}1\times \frac{Z1}{\mathrm{Zv}}=\frac{X0\times \mathrm{Zv}}{D}\times \frac{Z1}{\mathrm{Zv}}=\frac{X0}{D}\times Z1& \left(3\right)\end{array}$

When the spindle 60 starts being lowered and the chuck table 28 starts being retracted simultaneously with the second relative speed thus established, the spindle 60 will finish its descent and the chuck table 28 will finish its movement simultaneously. In the preliminary grinding step S31, therefore, the holding surface of the chuck table 28 is shaped such that the portion, i.e., the first portion, whose shape is represented by the side surface of an inverted truncated cone is formed in the surrounding region S.

Then, the depth of the inner circumferential edge of the first portion, represented by P1 in FIG. 9C, is measured (measuring step S32). Specifically, the depth of the inner circumferential edge of the first portion P1 is measured by the measurement unit 66 while the probe of the height gauge 66a is in contact with the outer circumferential edge of the surrounding region S and the probe of the height gauge 66b is in contact with the inner circumferential edge of the first portion P1.

Once the depth of the inner circumferential edge of the first portion P1 has been measured, the worn-off amount W of the grindstones 64a at a time at which the holding surface of the chuck table 28 has been ground to the predetermined depth D can be calculated. Specifically, the worn-off amount W refers to a distance that is obtained by multiplying the predetermined depth D by a value that is obtained by dividing a distance obtained by subtracting the depth of the inner circumferential edge of the first portion P1 from the third traveled distance Z1 by the depth of the inner circumferential edge of the first portion P1.

Stated otherwise, if it is assumed that the depth of the inner circumferential edge of the first portion P1 is represented by D1, then the worn-off amount W is expressed by the following equation (4):

$\begin{array}{cc}W=D\times \frac{\left(Z1-D1\right)}{D1}=\frac{D\times Z1-D\times D1}{D1}& \left(4\right)\end{array}$

Note that the measuring step S32 is carried out after the spindle 60 has been lifted to space the grindstones 64a and the chuck table 28 from each other, for example. Alternatively, the measuring step S32 may be carried out immediately after preliminary grinding step S31 without lifting the spindle 60. Further alternatively, the measuring step S32 may be carried out either while the spindle 60 and the chuck table 28 are being rotated or held at rest against rotation.

In a case where the grindstones 64a and the chuck table 28 have been spaced from each other in the measuring step S32, the spindle 60 is lowered until the grindstones 64a have their lower surfaces contacting the holding surface of the chuck table 28 again, prior to a main grinding step S33 to be described later. Similarly, in a case where the spindle 60 and the chuck table 28 have been held at rest against rotation in the measuring step S32, they are rotated again, prior to the main grinding step S33.

Then, the spindle 60 is lowered by a fifth traveled distance and the chuck table 28 is retracted by a sixth traveled distance while the spindle 60 and the chuck table 28 are being rotated, thereby forming the second portion in the surrounding region S (main grinding step S33).

FIG. 10A schematically illustrates in plan an example of the main grinding step S33. FIG. 10B schematically illustrates in front elevation the example of the main grinding step S33. FIG. 10C schematically illustrates in cross section the chuck table 28 after the main grinding step S33.

Here, the fifth traveled distance refers to a distance that is obtained by adding a distance obtained by subtracting the third traveled distance Z1 from the predetermined depth D and the worn-off amount W of the grindstones 64a to each other at a time at which the holding surface of the chuck table 28 has been ground to the predetermined depth D. Specifically, the fifth traveled distance, represented by Z2, is expressed by the following equation (5):

$\begin{array}{cc}\begin{array}{c}Z2=\left(D-Z1\right)+W=\left(D-Z1\right)+\frac{D\times Z1-D\times D1}{D1}=\\ \frac{D\times D1-Z1\times D1+D\times Z1-D\times D1}{D1}\\ =\left(D-D1\right)\times \frac{Z1}{D1}\end{array}& \left(5\right)\end{array}$

Also, the sixth traveled distance refers to a distance that is obtained by subtracting the fourth traveled distance X1 from the second traveled distance X0. Specifically, the sixth traveled distance, denoted by X2, is expressed by the following equation (6):

$\begin{array}{cc}X2=X0-X1=X0-\left(\frac{X0}{D}\times Z1\right)=X0\times \frac{\left(D-Z1\right)}{D}& \left(6\right)\end{array}$

Further, the second relative speed in the main grinding step S33 refers to a speed that is obtained by dividing the sixth traveled distance X2 by a time obtained by dividing the fifth traveled distance Z2 by the first relative speed Zv. Specifically, the second relative speed, denoted by Xv2, in the main grinding step S33 is expressed by the following equation (7):

$\begin{array}{cc}\begin{array}{c}\mathrm{Xv}2=\frac{X2}{Z2/\mathrm{Zv}}=\frac{X0\times \left(D-Z1\right)}{D}\times \frac{D1}{\left(D-D1\right)\times Z1}\times \mathrm{Zv}=\\ \frac{D1\times \left(D-Z1\right)}{Z1\times \left(D-D1\right)}\times \frac{X0\times \mathrm{Zv}}{D}\\ =\frac{D1\times \left(D-Z1\right)}{Z1\times \left(D-D1\right)}\times \mathrm{Xv}1=\alpha \times \mathrm{Xv}1\end{array}& \left(7\right)\end{array}$

When the spindle 60 starts being lowered and the chuck table 28 starts being retracted simultaneously with the second relative speed thus established, the spindle 60 will finish its descent and the chuck table 28 will finish its movement simultaneously. In the main grinding step S33, therefore, the holding surface of the chuck table 28 is shaped such that the depth of the inner circumferential edge of the first portion P1 is equal to the predetermined depth D and the second portion, denoted by P2, whose shape is represented by the side surface of an inverted truncated cone is formed radially inwardly of the first portion P1.

Note that the second portion P2 is slanted with a larger gradient than the first portion P1. Specifically, since the third traveled distance Z1 is a distance longer than the depth D1 (see FIG. 9C) of the inner circumferential edge of the first portion P1 (Z1>D1), a distance obtained by subtracting the third traveled distance Z1 from the predetermined depth D is shorter than a distance obtained by subtracting the depth D1 of the inner circumferential edge of the first portion P1 from the predetermined depth D (D−Z1<D−D1).

The product of the third traveled distance Z1 and the distance obtained by subtracting the depth D1 of the inner circumferential edge of the first portion P1 from the predetermined depth D is larger than the product of the depth D1 of the inner circumferential edge of the first portion P1 and the distance obtained by subtracting the third traveled distance Z1 from the predetermined depth D (Z1×(D−D1)>D1×(D−Z1).

Consequently, as the value a in the above equation (7) is smaller than 1, the second relative speed Xv2 in the main grinding step S33 is lower than the second relative speed Xv2 in the preliminary grinding step S31. Moreover, because the first relative speed Zv is common in the preliminary grinding step S31 and the main grinding step S33, the second portion P2 is slanted with a larger gradient than the first portion P1.

In the above method of shaping the holding surface of the chuck table, the speed (second relative speed) at which the chuck table 28 is retracted in the grinding step S3 is established such that the spindle 60 starts being lowered and the chuck table 28 starts being retracted simultaneously and the spindle 60 finishes its descent and the chuck table 28 finishes its movement simultaneously.

Specifically, the second relative speed is established in view of parameters that are established as desired and the worn-off amount W of the grindstones 64a that is grasped prior to or during the grinding step S3 (the absolute value of a change in thickness of the grindstones 64a before and after the grinding step S3). Consequently, the above method of shaping the holding surface of the chuck table makes it possible to shape the holding surface of the chuck table 28 into a holding surface suitable for the TAIKO grinding without forming a step on the holding surface of the chuck table 28.

Note that the details described above represent certain aspects of the present invention, and the present invention is not limited to any of the above features. In the adjusting step S1 according to the present invention, for example, the front end of the holding surface of the chuck table 28 may be positioned directly below the front end of the track followed by the grindstones 64a at a time at which the grinding wheel 64 is rotated. Note that specific other details according to the present invention in this case remain the same as those described above except that the chuck table 28 is not retracted but moved forward in the grinding step S3.

Also, in the adjusting step S1 according to the present invention, the tilt of the chuck table 28 may be adjusted such that a right end, as viewed along the forward direction, of the track will come into initial contact with the holding surface of the chuck table 28 at a time at which the spindle 60 is lowered. Note that specific other details according to the present invention in this case remain the same as those described above.

Further the present invention may be applicable to a grinding apparatus having an X-axis moving mechanism for moving the spindle 60 along the X-axis directions in addition to or in place of the X-axis moving mechanism 6. Furthermore, the present invention may be applicable to a grinding apparatus having a Y-axis moving mechanism for moving the chuck table 28 or the spindle 60 along the Y-axis directions in addition to or in place of the X-axis moving mechanism 6. In other words, the present invention is not limited to any structural details of arrangements capable of relatively moving the rotational shaft of the spindle 60 and the center of the holding surface of the chuck table 28 in the horizontal plane.

In a case where the present invention is applied to a grinding apparatus including a Y-axis moving mechanism, the left end of the holding surface of the chuck table 28 may be positioned directly below the left end of the track followed by the grindstones 64a in the adjusting step S1, for example. Alternatively, the right end of the holding surface of the chuck table 28 may be positioned directly below the right end of the track followed by the grindstones 64a in the adjusting step S1.

Note that specific other details according to the present invention in these cases remain the same as those described above except that the chuck table 28 moves not in forward and rearward directions but in leftward and rightward directions in the grinding step S3 and that the tilt of the chuck table 28 is adjusted such that the front or rear end of the track followed by the grindstones 64a comes into initial contact with the holding surface of the chuck table 28 when the spindle 60 is lowered.

Also, according to the present invention, providing the spacing between the outer circumferential edge of the surrounding region S and the center C0 of the holding surface is equal to or larger than the radius of the wafer 11, the outer circumferential edge of the surrounding region S may be positioned radially inwardly of the outer circumferential edge of the holding surface of the chuck table 28. Specific other details according to the present invention of this case remains the same as those described above except that a point on the track that is farthest from the center C0 of the holding surface as viewed in plan is positioned slightly radially inwardly of the outer circumferential edge of the holding surface in the adjusting step S3.

Furthermore, the present invention may be applicable to a grinding apparatus having a tilt adjusting mechanism for adjusting the tilt of the spindle 60 in addition to or in place of the tilt adjusting mechanism for adjusting the tilt of the chuck table 28. In other words, the present invention is not limited to any structural details of arrangements capable of adjusting the angle formed between the rotational shaft of the spindle 60 and the rotational shaft of the chuck table 28.

Moreover, the present invention may also be applicable to a grinding apparatus free of the measurement unit 66, in a case in which the worn-off amount of the grindstones 64a has been grasped in advance. Alternatively, the present invention may be applicable to a grinding apparatus having a non-contact-type measurement unit instead of the measurement unit 66. In other words, the present invention is not limited to any structural details of arrangements capable of measuring a depth of a desired point on the holding surface of the chuck table 28.

The structure, the method, and the like according to the above embodiment can appropriately be changed or modified without departing from the scope of the present invention.

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.

Claims

1. A method of shaping a holding surface of a chuck table of a grinding apparatus that includes the chuck table that is rotatable and has a circular holding surface and a spindle including a distal end portion on which a grinding wheel that has a plurality of grindstones disposed in an annular array is mounted, in which, when the spindle is rotated, the plurality of grindstones follow a track having an outside diameter smaller than a radius of the holding surface, and the method shapes the holding surface of the chuck table by grinding the holding surface of the chuck table such that a surrounding region of the holding surface that is positioned radially outwardly of a first concentric circle region of the holding surface that is radially spaced from a center of the holding surface by a distance that corresponds to the outside diameter of the track is slanted so as to be progressively deeper toward the first concentric circle region and that the center and the first concentric circle region are of a predetermined depth from an outer circumferential edge of the surrounding region and a second concentric circle region positioned radially between the center and the first concentric circle region is deeper than the center and the first concentric circle region, the method comprising: an adjusting step of adjusting a tilt of at least one of the spindle or the chuck table such that the plurality of grindstones will come into initial contact with a third concentric circle region of the holding surface that is radially positioned between the first concentric circle region and the second concentric circle region when the spindle and the holding surface are moved toward each other along a first direction;after the adjusting step, a contacting step of, while the spindle and the chuck table are being rotated, bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction until the plurality of grindstones contact the outer circumferential edge of the surrounding region; andafter the contacting step, a grinding step of, while the spindle and the chuck table are being rotated and the spindle and the outer circumferential edge of the surrounding region are being brought toward each other at a first relative speed along the first direction, bringing a rotational shaft of the spindle and the center of the holding surface toward each other at a second relative speed along a second direction perpendicular to the first direction until the plurality of grindstones contact the center of the holding surface,wherein, in the grinding step, the spindle and the outer circumferential edge of the surrounding region are brought toward each other along the first direction by a first traveled distance represented by a sum of the predetermined depth and a worn-off amount of the plurality of grindstones that are worn by grinding the chuck table to the predetermined depth,in the grinding step, the rotational shaft of the spindle and the center of the holding surface are brought toward each other along the second direction by a second traveled distance equal to a width of the surrounding region along the second direction,the first relative speed is a constant speed established as desired, andthe second relative speed is a constant or variable speed established in view of the predetermined depth, the worn-off amount, the second traveled distance, and the first relative speed such that the spindle and the outer circumferential edge of the surrounding region start being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface start being brought toward each other along the second direction simultaneously and that the spindle and the outer circumferential edge of the surrounding region finish being brought toward each other along the first direction and the rotational shaft of the spindle and the center of the holding surface finish being brought toward each other along the second direction simultaneously.

2. The method of shaping a holding surface of a chuck table according to claim 1, wherein the worn-off amount has been grasped prior to the contacting step, andthe second relative speed is a speed that is obtained by dividing the second traveled distance by a time obtained by dividing the first traveled distance by the first relative speed.

3. The method of shaping a holding surface of a chuck table according to claim 1, wherein the surrounding region includes a first portion and a second portion positioned radially inwardly of the first portion and slanted with a larger gradient than the first portion,the grinding step includes a preliminary grinding step of forming the first portion in the surrounding region by bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction by a third traveled distance and bringing the rotational shaft of the spindle and the center of the holding surface toward each other along the second direction by a fourth traveled distance while the spindle and the chuck table are being rotated,after the preliminary grinding step, a measuring step of measuring a depth of an inner circumferential edge of the first portion from the outer circumferential edge of the surrounding region, anda main grinding step of forming the second portion in the surrounding region by bringing the spindle and the outer circumferential edge of the surrounding region toward each other along the first direction by a fifth traveled distance and bringing the rotational shaft of the spindle and the center of the holding surface toward each other along the second direction by a sixth traveled distance while the spindle and the chuck table are being rotated,the second relative speed in the preliminary grinding step is a speed that is obtained by dividing the second traveled distance by a time obtained by dividing the predetermined depth by the first relative speed,the third traveled distance represents a distance established as desired in a range smaller than the predetermined depth,the fourth traveled distance represents a distance that is obtained by multiplying the second relative speed in the preliminary grinding step by a time obtained by dividing the third traveled distance by the first relative speed,the worn-off amount represents a distance that is obtained by multiplying the predetermined depth by a value that is obtained by dividing a distance obtained by subtracting the depth of the inner circumferential edge of the first portion measured in the measuring step from the third traveled distance by the depth of the inner circumferential edge of the first portion measured in the measuring step,the fifth traveled distance represents a distance that is obtained by adding a distance obtained by subtracting the third traveled distance from the predetermined depth and the worn-off amount to each other,the sixth traveled distance represents a distance that is obtained by subtracting the fourth traveled distance from the second traveled distance, andthe second relative speed in the main grinding step is a speed that is obtained by dividing the sixth traveled distance by a time obtained by dividing the fifth traveled distance by the first relative speed.