METHOD FOR GRINDING PLATE-FORMED WORKPIECE AND GRINDING APPARATUS

Abstract

A method for grinding a plate-formed workpiece having a raised center with a grindstone is provided. The method includes a first holding process including suctioning and holding the plate-formed workpiece against a holder surface of a first chuck table, which is in a shape where a center is raised with respect to an outer circumference thereof; a reaction-force reducing grinding process including grinding a central part of the plate-formed workpiece with the grindstone to reduce a reaction force against a flattening force to be applied to the plate-formed workpiece; a second holding process including suctioning and holding the plate-formed workpiece against a holder surface of a second chuck table, which spreads in parallel to a lower surface of the grindstone; and a finish-grinding process including grinding to finish the plate-formed workpiece with the grindstone.

Claims

1. A method for grinding a plate-formed workpiece having a raised center with a grindstone, comprising: a first holding process including suctioning and holding the plate-formed workpiece against a holder surface of a first chuck table, the holder surface of the first chuck table being in a shape where a center is raised with respect to an outer circumference thereof; a reaction-force reducing grinding process including grinding a central part of the plate-formed workpiece with the grindstone to reduce a reaction force against a flattening force to be applied to the plate-formed workpiece; a second holding process including suctioning and holding the plate-formed workpiece against a holder surface of a second chuck table, the holder surface of the second chuck table spreading in parallel to a lower surface of the grindstone; and a finish-grinding process including grinding to finish the plate-formed workpiece with the grindstone.

2. A grinding apparatus configured to grind the plate-formed workpiece in the method according to claim 1, comprising at least: the first chuck table including the holder surface where the center is raised toward the lower surface of the grindstone; the second chuck table including the holder surface spreading in parallel to the lower surface of the grindstone; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with one of the first chuck table or the second chuck table.

3. A method for grinding a plate-formed workpiece having a raised center with a grindstone, comprising: a first holding process including suctioning and holding the plate-formed workpiece, in a state where a center of the plate-formed workpiece is raised, against a holder surface of a chuck table, the holder surface spreading in parallel to a lower surface of the grindstone; a reaction-force reducing grinding process including grinding a central part of the plate-formed workpiece with the grindstone to reduce a reaction force against a flattening force to be applied to the plate-formed workpiece; a second holding process including suctioning and holding the plate-formed workpiece against the holder surface of the chuck table without forming a gap between the holder surface and a lower surface of the plate-formed workpiece; and a finish-grinding process including grinding to finish the plate-formed workpiece with the grindstone.

4. A grinding apparatus configured to grind the plate-formed workpiece in the method according to claim 3, comprising at least: the chuck table including the holder surface; a suction path connecting the holder surface and a suction source; a pressure adjuster device arranged in the suction path, the pressure adjuster device being configured to adjust a negative pressure value of the holder surface; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with the chuck table.

5. A grinding apparatus configured to grind the plate-formed workpiece in the method according to claim 3, comprising at least: the chuck table having at least two holder surfaces including a central holder surface and an outer circumferential holder surface, the central holder surface and the outer circumferential holder surface being concentric; a central suction path connecting the central holder surface and a suction source; an outer circumferential suction path connecting the outer circumferential holder surface and the suction source; an area changeable device configured to change an area of the at least two holder surfaces; and a grinding assembly configured to grind the plate-formed workpiece suctioned and held with the chuck table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a cross-sectional view of a plate-formed workpiece.

[0013] FIG. 2 is a schematic perspective view of a grinding apparatus according to a first embodiment.

[0014] FIGS. 3A and 3B are schematic cross-sectional views of a first chuck table and surrounding thereof according to the first embodiment.

[0015] FIGS. 4A and 4B are schematic cross-sectional views of a second chuck table and surrounding thereof according to the first embodiment.

[0016] FIGS. 5A and 5B are schematic cross-sectional views of a chuck table and surrounding thereof according to a second embodiment.

[0017] FIGS. 6A and 6B are schematic cross-sectional views of the chuck table and surrounding thereof according to the second embodiment.

[0018] FIGS. 7A and 7B are schematic cross-sectional views of a universal chuck table and surrounding thereof according to a third embodiment.

[0019] FIGS. 8A and 8B are schematic cross-sectional views of the universal chuck table and surrounding thereof according to the third embodiment.

[0020] FIGS. 9A and 9B are schematic cross-sectional views of a chuck table and surrounding thereof according to a fourth embodiment.

[0021] FIGS. 10A and 10B are schematic cross-sectional views of the chuck table and surrounding thereof according to the fourth embodiment.

[0022] FIGS. 11A and 11B are schematic cross-sectional views of a chuck table and surrounding thereof according to a modified example.

DESCRIPTION OF EMBODIMENTS

First Embodiment

[0023] Hereinbelow, a grinding method and a grinding apparatus for a plate-formed workpiece according to a first embodiment will be described with reference to the accompanying drawings. First, a plate-formed workpiece W to be ground as shown in FIG. 1 is described. The plate-formed workpiece W is, for example, a disk-shaped wafer having a thickness of 2.5 mm. FIG. 1 is a cross-sectional view of the plate-formed workpiece W before grinding. As shown in FIG. 1, the plate-formed workpiece W is warped to rise at a center thereof, where a first surface W1 on one side in a direction of thickness is convex, and a second surface W2 on the other side in the direction of thickness is concave. For the plate-formed workpiece W in the present embodiment, although not specifically limited, a workpiece with resiliency that may exert a reaction force against a flattening force, when the flattening force to correct warpage is applied thereto before grinding, is used. For example, in a plate-formed workpiece W with a thickness of 2.5 mm, an amount of warpage, at a central part where the warpage is at its maximum extent, may be 2 mm.

[0024] Next, a grinding apparatus 10 for grinding the plate-formed workpiece W will be described. FIG. 2 is a schematic perspective view of the grinding apparatus according to the first embodiment. An X-axis direction, a Y-axis direction, and a Z-axis direction shown in the drawings are orthogonal to one another. The X-axis direction and the Y-axis direction are substantially horizontal directions, and the Z-axis direction is an up-down direction (vertical direction). A +X side and a X side, which are one and the opposite sides as pointed by a bidirectional arrow along the X-axis direction, are a rightward side and a leftward side, respectively. A +Y side and a Y side, which are one and the opposite sides as pointed by a bidirectional arrow along the Y-axis direction, are a rearward side and a frontward side, respectively. A +Z side and a Z side, which are one and the opposite sides as pointed by a bidirectional arrow along the Z-axis direction, is an upper side and a lower side, respectively.

[0025] The grinding apparatus 10 is configured to perform a series of operations including a loading process, a grinding process, a cleaning process, and an unloading process with the plate-formed workpiece W fully automatically. The plate-formed workpiece W may be fed to the grinding apparatus 10 in a state where the plate-formed workpiece W is stored in a cassette 11.

[0026] On the Y direction side of a base 12 of the grinding apparatus 10, two cassettes 11 that may each store a plurality of plate-formed workpieces W are placed. One of the cassettes 11 may store the plate-formed workpieces W before grinding, and the other of the cassettes 11 may store the plate-formed workpieces W after grinding. At a rearward position with respect to the cassettes 11, a robot hand 14 that may pick up the plate-formed workpiece W from the one of the cassettes 11 or may place the plate-formed workpiece W back in the other of the cassettes 11 is provided.

[0027] The grinding apparatus 10 has a controller 16, including a processor to execute various processes and a memory storing programs. The grinding apparatus 10 is configured to perform the series of operations including the loading process, the grinding process, the cleaning process, and the unloading process with the plate-formed workpieces W fully automatically according to the programs stored in the memory of the controller 16 and controlling signals transmitted from the controller 16 to each component.

[0028] At a rightward-rear position and a leftward-rear position with respect to the robot hand 14, respectively, provided are a positioning assembly 18, on which the plate-formed workpiece W before grinding is placed, and a spinner-cleaning device 19, which may clean the plate-formed workpiece W after grinding. The robot hand 14 may convey the plate-formed workpiece W before grinding from the cassette 11 to the positioning assembly 18 and convey the plate-formed workpiece W after grinding from the spinner-cleaning device 19 to the cassette 11.

[0029] The positioning assembly 18 includes a plurality of positioning pins 23, which are arranged around a temporary placement table 22 and are movable inward toward or outward from a center of the temporary placement table 22. While the plate-formed workpiece W is on the temporary placement table 22 in the positioning assembly 21, by moving the plurality of positioning pins 23 to respectively contact an outer circumferential edge of the plate-formed workpiece W, a center of the plate-formed workpiece W is located at the center of the temporary placement table 22.

[0030] The spinner-cleaning device 19 may clean the plate-formed workpiece W having been ground by supplying a cleaning solution from a cleaning nozzle 25 to the plate-formed workpiece W and rotating a spinner table 26 holding the plate-formed workpiece W at a high speed by a motor, which is not shown.

[0031] At a position between the positioning assembly 18 and the spinner-cleaning device 19 on the base 12, a supporting block 28 extending in the Y-axis direction is provided, and at a rearward position on the base 12, a column 29 is provided to stand vertically. Moreover, the grinding apparatus 10 includes a conveyer assembly 30 arranged on the supporting block 28 and a holder device 40 located between the conveyer assembly 30 and the column 29 on the base 12. The holder device 40 includes a first chuck table 41 and a second chuck table 42 arranged on a turntable 43.

[0032] The conveyer assembly 30 may load the first chuck table 41 or the second chuck table 42 with the plate-formed workpiece W and unload the plate-formed workpiece W from the first chuck table 41 or the second chuck table 42. The conveyer assembly 30 may convey the plate-formed workpiece W among the first chuck table 41 or the second chuck table 42, which is located frontward at a load/unload position, the temporary placement table 22, and the spinner table 26.

[0033] The conveyer assembly 30 includes a conveyer pad 31, which may suction and hold an upper surface of the plate-formed workpiece W, and a rotating device 32, which may rotate (pivot) the conveyer pad 31 on an axis extending in the Z-axis direction. Moreover, the conveyer assembly 30 includes a lift/lower assembly 33, which supports the conveyer pad 31 movably upward or downward in the Z-axis direction, and a Y-axis movable assembly 34, which may move the conveyer pad 31 in the Y-axis direction. The rotating device 32 is supported by the lift/lower assembly 33, and the lift/lower assembly 33 is supported by a Y-axis movable device 37 of the Y-axis movable assembly 34, which will be described further below. The conveyer pad 31 is supported at an end of an arm 35, which extends horizontally from a lower end of the rotating device 32. The rotating device 32 and the lift/lower assembly 33 are each driven by a driving force from a motor and an actuator, which are not shown, to cause the arm 35 to rotate and move vertically.

[0034] The Y-axis movable assembly 34 includes a pair of guide rails 36 arranged on a surface of the supporting block 28 on the +X direction side and extending in the Y-axis direction, a Y-axis movable device 37 supported by the supporting block 28 through the pair of guide rails 36 movably in the Y-axis direction, a ball screw 38 extending in the Y-axis direction and screwed to a screw thread (not shown) in the Y-axis movable device 37, and a motor 39 to rotate the ball screw 38. As the motor 39 drives the ball screw 38 to rotate, the Y-axis movable device 37 moves in the Y-axis direction. As the Y-axis movable device 37 moves in the Y-axis direction, the arm 35 supported by the Y-axis movable device 37 through the rotating device 32 and the lift/lower assembly 33 moves in the Y-axis direction, and as a result, the position of the conveyer pad 31 may change in the Y-axis direction.

[0035] The conveyer assembly 30 may operate the rotating device 32 to rotate and the Y-axis movable assembly 34 to move in the Y-axis direction, thereby moving the conveyer pad 31 in the horizontal direction. Moreover, the conveyer assembly 30 may operate the lift/lower assembly 33 to move the conveyer pad 31 up or down in the Z-axis direction. With these operations, the plate-formed workpiece W may be conveyed among the first chuck table 41 or the second chuck table 42, which is located frontward at the load/unload position, the temporary placement table 22, and the spinner table 26.

[0036] The turntable 43 in the holder device 40 is in a shape of a disk and is supported on the base 12 rotatably about an axis extending in the Z-axis direction. The turntable 43 may be driven to rotate by a motor in a turntable rotating assembly (not shown).

[0037] The first chuck table 41 and the second chuck table 42 are located symmetrically with respect to a rotation center of the turntable 43 (a center of the first chuck table 41 and a center of the second chuck table 42 are apart from each other by 180 degrees in a rotating direction of the turntable 43). The first chuck table 41 and the second chuck table 42 may be located at a grinding position, which is on the +Y direction side and the X direction side with respect to the rotation center of the turntable 43, or the load/unload position, which is on the Y direction side and the +X direction side with respect to the rotation center of the turntable 43. The grinding position is a position where a grinding assembly 90, which will be described later, may grind the first surface W1 of the plate-formed workpiece W.

[0038] The grinding apparatus 10 further includes a lift/lower assembly 80 arranged on the column 29 and the grinding assembly 90 movable up or down in the Z-axis direction.

[0039] The lift/lower assembly 80 includes a pair of guide rails 81 located on a frontward surface of the column 29 and extending in the Z-axis direction, a lift/lower table 82 arranged movably in the Z-axis direction with respect to the pair of guide rails 81, and a ball screw 83 extending in the Z-axis direction and screwed to a screw thread (not shown) in the lift/lower table 82. As a motor 84, which is coupled to one end of the ball screw 83, drives the ball screw 83 to rotate, the lift/lower table 82 moves in the Z-axis direction.

[0040] The grinding assembly 90 supports a spindle 93 rotatably with respect to a spindle housing 92, which is attached to a frontward surface of the lift/lower table 82 via a holder 91 and supported by the holder 91. The spindle 93 is driven by a driving force of a spindle motor 94 to rotate on an axis extending in the Z-axis direction.

[0041] A mount 95 is connected to a lower end of the spindle 93, and a grinding wheel 96 is attached to the mount 95. On a lower surface of the grinding wheel 96, an annular grindstone 97, including a plurality of grindstones arranged annularly, is provided. The grinding assembly 90 may grind the first surface W1 of the plate-formed workpiece W suctioned and held by the first chuck table 41 or the second chuck table 42 with the grindstone 97.

[0042] FIGS. 3A and 3B are schematic cross-sectional views of the first chuck table and surrounding thereof according to the first embodiment. FIGS. 4A and 4B are schematic cross-sectional views of the second chuck table and surrounding thereof according to the first embodiment. The first chuck table 41 and the second chuck table 42 have a substantially similar configuration except for shapes of holder surfaces 46, 56.

[0043] The first chuck table 41 as shown in FIGS. 3A and 3B includes a first frame 44 and a first porous sheet 45 in a shape of a disk mounted in a recess formed on an upper side of the first frame 44, and an upper surface of the first porous sheet 45 forms the holder surface 46. The second chuck table 42 as shown in FIGS. 4A and 4B includes a second frame 54 and a second porous sheet 55 in a shape of a disk mounted in a recess formed on an upper side of the second frame 54, and an upper surface of the second porous sheet 55 forms the holder surface 56. The first and second porous sheets 45, 55 are made of a porous material such as ceramics and have fine pores formed throughout.

[0044] The holder device 40 further includes a first table-rotating assembly 47 and a second table-rotating assembly 57. The first and second table-rotating assemblies 47, 57 are each composed of, for example, a motor and a pulley mechanism, which are not shown. The first table-rotating assembly 47 may drive the first chuck table 41 to rotate on a center axis C1 of the holder surface 46, and the second table-rotating assembly 57 may drive the second chuck table 42 to rotate on a center axis C2 of the holder surface 56.

[0045] The holder device 40 includes a suction source 60, a first suction path (suction path) 61 connected to the first porous sheet 45 of the first chuck table 41 and continuous with the holder surface 46, and a second suction path (suction path) 62 connected to the second porous sheet 55 of the second chuck table 42 and continuous with the holder surface 56. The suction source 60 may be composed of, for example, a vacuum generator such as a vacuum pump or an ejector.

[0046] The first suction path 61 is connected to the suction source 60 through a first open/close valve 63, and the second suction path 62 is connected to the suction source 60 through a second open/close valve 64. When the first open/close valve 63 is open, the suction source 60 and the holder surface 46 of the first chuck table 41 communicate through the first suction path 61, and the air is suctioned through the holder surface 46 to generate negative pressure, thereby the plate-formed workpiece W may be suctioned and held against the holder surface 46. When the second open/close valve 64 is open, the suction source 60 and the holder surface 56 of the second chuck table 42 communicate through the second suction path 62, and the air is suctioned through the holder surface 56 to generate negative pressure, thereby the plate-formed workpiece W may be suctioned and held against the holder surface 56. Optionally, the suction source 60 may be a common configuration to be connected with both the first and suction paths 61, 62, or may be provided separately to each of the first and second suction paths 61, 62.

[0047] Next, shapes of the holder surface 56 of the second chuck table 42 and the holder surface 46 of the first chuck table 41 will be described below in this given order.

[0048] The holder surface 56 of the second chuck table 42 is formed as a conical surface, of which apex is located on the center axis C2 that is a rotation axis of the second chuck table 42, and which descends gradually toward an outer periphery of the second chuck table 42. An inclination of the holder surface 56 is slight enough not to be visually recognizable. A radial range in the plate-formed workpiece W held on this holder surface 56 is a grinding range, where the plate-formed workpiece W contacts the annular grindstone 97. At an area directly below the grinding range, the holder surface 56 is formed to be parallel to a lower surface 971 of the grindstone 97.

[0049] The holder surface 46 of the first chuck table 41 has a central area 461 and a circumferential area 462 formed on an outer side of the central area 461. The central area 461 forms a conical surface, of which apex is located on a center axis C1 that is a rotation axis of the first chuck table 41, and which descends gradually toward an outer circumference of the first chuck table 41. An inclination of the holder surface 46 is substantially equal to the inclination of the holder surface 56. The circumferential area 462 forms a conical surface, which descends gradually toward the outer circumference of the first chuck table 41, of which taper angle is different from a taper angle of the conical surface of the central area 461. In particular, the circumferential area 462 forms a smaller taper angle than the taper angle of the central area 461.

[0050] As such, compared to the holder surface 56 of the second chuck table 42, the holder surface 46 of the first chuck table 41 is in a form such that the center is raised steeply than the circumference. Moreover, the holder surface 46 of the first chuck table 41 is in a positional relation such that the circumferential area 462 is farther from the lower surface 971 of the grindstone 97 than the central area 461 (see FIG. 3B), so that the holder surface 46 is raised toward the lower surface 971 of the grindstone 97.

[0051] Operations of the components in the grinding apparatus 10 are controlled by the controller 16 (see FIG. 2). The memory device in the controller 16 may store, as a part of controlling programs, for example, programs for controlling the operations of the holder device 40 and the grinding assembly 90. For example, the controller 16 may control open/close behaviors of the first and second open/close valves 63, 64 and suctioning behaviors with the holder surfaces 46, 56. For the operation of each component in the grinding apparatus 10 described below, when no explicit entity is specified as a subject to control the operation, it is assumed that the operation is controlled by signals output from the controller 16.

[0052] Hereinbelow, a method for grinding a plate-formed workpiece according to the present embodiment will be described. The method for grinding the plate-formed workpiece according to the present embodiment may be implemented by performing steps including a first holding process, a reaction-force reducing grinding process, a second holding process, and a finish-grinding process in this given order. FIG. 3A illustrates the first holding process, FIG. 3B illustrates the reaction-force reducing grinding process, FIG. 4 illustrates the second holding process, and FIG. 4B illustrates the finish-grinding process.

First Holding Process

[0053] In the first holding process, the conveyer assembly 30 (see FIG. 2) is operated to convey and place the plate-formed workpiece W onto the first chuck table 41. The plate-formed workpiece W with warpage is, as shown in FIG. 3A, set in an orientation such that the convex first surface W1 faces upward, and the concave second surface W2 faces downward. Next, the first open/close valve 63 is opened to connect the suction source 60 with the holder surface 46 of the first chuck table 41, and the air is suctioned through the holder surface 46 to generate negative pressure, thereby suctioning and holding the plate-formed workpiece W against the holder surface 46.

[0054] The holder surface 46 of the first chuck table 41 is in the form such that the center is raised, and the second surface W2 of the plate-formed workpiece W faces downward; therefore, in the state where the plate-formed workpiece W is placed on the holder surface 46, the second surface W2 of the plate-formed workpiece W generally fits with the holder surface 46. Moreover, as the negative pressure from the holder surface 46 acts on the plate-formed workpiece W, the holder surface 46 and the second surface W2 of the plate-formed workpiece W being suctioned and held thereon contact each other by the surfaces, and the shape of the plate-formed workpiece W with the center being raised may be maintained.

Reaction-Force Reducing Grinding Process

[0055] After the first holding process, the reaction-force reducing grinding process, for reducing a reaction force that may be generated when flattening the plate-formed workpiece W, is performed. The reaction-force reducing grinding process is, as shown in FIG. 3B, performed by grinding the first surface W1, which is the upper surface of the plate-formed workpiece W, with the grinding assembly 90.

[0056] In the reaction-force reducing grinding process, by rotating the turntable 43 (see FIG. 2), the first chuck table 41 is located below the grinding wheel 96 in the grinding assembly 90. In this location, the annular grindstone 97 is arranged such that an outer circumferential edge thereof passes through the center axis C1 of the first chuck table 41.

[0057] In this state, the first table-rotating assembly 47 is operated to rotate the first chuck table 41 and the plate-formed workpiece W held thereon, and the lift/lower assembly 80 (see FIG. 2) is operated to lower the grinding assembly 90 and rotate the grindstone 97 via the spindle 93. As such, the grindstone 97 and the plate-formed workpiece W suctioned and held against the first chuck table 41 approach and contact each other while rotating respectively.

[0058] In this arrangement, the holder surface 46 of the first chuck table 41 and the plate-formed workpiece W are raised at the center thereof; therefore, the grinding range where the plate-formed workpiece W contacts the grindstone 97 is a partial range that coincides straight above with the central area 461. In other words, the area coinciding straight above with the circumferential area 462 of the holder surface 46 has the smaller taper angle and thereby is not in contact with the lower surface 971 of the grindstone 97. Therefore, in the reaction-force reducing grinding process, the plate-formed workpiece W is ground partly, i.e., at a central part W3 of the first surface W1, and is not ground at the outer area outside the central part W3. Accordingly, the central part W3 of the plate-formed workpiece W is ground to be thinner than the outer area, and the reaction force that may be produced against the flattening correcting force may be reduced.

Second Holding Process

[0059] After the reaction-force reducing grinding process, the second holding process, in which the chuck table to hold the plate-formed workpiece W is changed from the first chuck table 41 to the second chuck table 42, is performed. In the second holding process, the plate-formed workpiece W on the first chuck table 41 is picked up by the conveyer pad 31 of the conveyer assembly 30 (see FIG. 2), the turntable 43 is operated to rotate by 180 degrees, and the plate-formed workpiece W is placed on the second chuck table 42. When placed on the second chuck table 42, the plate-formed workpiece W is maintained in the orientation where the first surface W1 faces upward and the second surface W2 faces downward. Thereafter, the second open/close valve 64 is opened, the suction source 60 and the holder surface 56 of the second chuck table 42 communicate, and the air is suctioned through the holder surface 56 to generate negative pressure, thereby suctioning and holding the plate-formed workpiece W against the holder surface 56.

[0060] The holder surface 56 of the second chuck table 42 spreads parallel to the lower surface 971 of the grindstone 97; therefore, in the state where the plate-formed workpiece W is held on the holder surface 56, the second surface W2 may be in the convex shape, which may create a space between the holder surface 56 and the second surface W2. In such a case, by suctioning the air through the holder surface 56, a force to attract the second surface W2 toward the holder surface 56 is applied to the plate-formed workpiece W, and moreover, the reaction force against this attracting force is reduced as the result of grinding the central part W3. Therefore, the second surface W2 of the plate-formed workpiece W may contact the holder surface 56 by the surface to be suctioned and held thereon.

Finish-Grinding Process

[0061] After the second holding process, as shown in FIG. 4B, the finish-grinding process is performed. The finish-grinding process is performed with the grinding assembly 90, in the same manner as the reaction-force reducing grinding process except that the chuck table to hold the plate-formed workpiece W has been changed from the first chuck table 41 to the second chuck table 42. In the finish-grinding process, the plate-formed workpiece W is ground by the grindstone 97 to a predetermined even thickness.

[0062] In particular, after being ground in the reaction-force reducing grinding process, the plate-formed workpiece W is thinner at the central part W3 than the outer area; therefore, an amount to grind in the finish-grinding process is larger at the outer area than the central part W3 of the plate-formed workpiece W. As the plate-formed workpiece W is ground to a thickness where the lower surface 971 of the grindstone 97 contacts an entire radial range of the plate-formed workpiece W, the first surface W1 of the plate-formed workpiece W may align in parallel to the lower surface 971 of the grindstone 97. As such, the second surface W2 of the plate-formed workpiece W is in surface contact with the holder surface 56 of the second chuck table 42 and suctioned to be held thereon, aligning in parallel to the lower surface 971 of the grindstone 97. Therefore, the first surface W1 and the second surface W2 of the plate-formed workpiece W align in parallel to each other, and the plate-formed workpiece W may be formed in the even thickness.

[0063] According to the first embodiment described above, the plate-formed workpiece W is, after being suctioned and held in the shape where the center is raised to be higher with respect to the outer circumference, ground at the central part W3 in the reaction-force reducing grinding process. Therefore, before the plate-formed workpiece W is suctioned and held in the second holding process, the reaction force that may be produced when the plate-formed workpiece W is flattened against the holder surface 56 may be reduced, and in the finish-grinding process, the second surface W2 of the plate-formed workpiece W is enabled to be ground to the form where the second surface W2 of the plate-formed workpiece W aligns parallel to the lower surface 971 of the grindstone 97. Accordingly, for grinding the plate-formed workpiece W having the center being raised, a process to adhere a tape to form a space between a concave surface of a plate-formed workpiece and the tape is eliminated. As a result, in the first embodiment described above, a working efficiency for grinding a plate-formed workpiece W with warpage, which is raised at the center, may be improved.

[0064] Next, embodiments other than the above-described embodiment will be described. In the description below, items that are identical or equivalent to those described earlier may be referred to by the same reference sings, and description of those may be omitted or simplified.

Second Embodiment

[0065] A second embodiment of the present disclosure will be described with reference to FIGS. 5A-5B and 6A-6B. FIGS. 5A-5B and 6A-6B are schematic cross-sectional views of a chuck table and surrounding thereof according to the second embodiment. FIG. 5A illustrates a first holding process, FIG. 5B illustrates a reaction-force reducing grinding process, FIG. 6A illustrates a second holding process, and FIG. 6B illustrates a finish-grinding process.

[0066] As shown in FIGS. 5A-5B and 6A-6B, in the second embodiment, the warped plate-formed workpiece W is ground, not using the first chuck table 41 described in the first embodiment, but using a chuck table 101, which is in the same configuration as the second chuck table 42. Therefore, in the description below, items in the chuck table 101 common with the second chuck table 42 are referred to by the same reference signs.

[0067] The holder device 40 in the second embodiment further has a pressure adjuster device 102, which is located in the second suction path 62 and may adjust a negative pressure value of the holder surface 56 of the chuck table 101. The pressure adjuster device 102 includes an air source 104, a second open/close valve 64, an air supply path 105 connected to the second suction path 62 between the second open/close valve 64 and the chuck table 101, and an adjuster valve 106 composed of, for example, a throttle valve, provided in the air supply path 105. The pressure adjuster device 102 may open the second open/close valve 64 and adjust an opening amount of the adjuster valve 106 to adjust a flow rate of the air to be supplied from the air source 104, and thereby adjusting the negative pressure value in the second suction path 62 and on the holder surface 56.

[0068] The adjustment of the negative pressure by the pressure adjuster device 102 may be controlled by the controller 16 (see FIG. 2) based on the negative pressure value in the second suction path 62 and on the holder surface 56 measured by a pressure gauge 107. For example, the controller 16 may have a predetermined first range for forming a gap S, which will be described further below, and a predetermined second range, which is higher than the first range in a direction of the negative pressure, stored in advance, and may control the adjuster valve 106 to operate such that the negative pressure value measured by the pressure gauge 107 may fall within either of the ranges.

[0069] In the first holding process according to the second embodiment, the plate-formed workpiece W having the raised center is placed on the holder surface 46 of the chuck table 101 with the second surface W2 facing downward. In this orientation of the plate-formed workpiece W, the gap S is formed between the holder surface 56, which is parallel to the lower surface 971 of the grindstone 97, and the concave shape of the second surface W2 of the plate-formed workpiece W.

[0070] With the gap S being formed, by opening the second open/close valve 64, the suction source 60 and the holder surface 56 of the chuck table 101 are connected through the second suction path 62. Meanwhile, the flow rate of the air to be supplied from the air source 104 to the second suction path 62 may be adjusted by the adjuster valve 106 of the pressure adjuster device 102.

[0071] The adjustment is controlled by the controller 16 operating the adjuster valve 106 so that the negative pressure value of the holder surface 56 measured by the pressure gauge 107 may fall within the first range described above. Thereby, the air is suctioned through the holder surface 56, and the pressure in the gap S is lowered. Accordingly, while the force to correct the warpage of the plate-formed workpiece W may be applied, the plate-formed workpiece W is, in the shape with the warpage being maintained or corrected to some extent, suctioned and held against the holder surface 56. In other words, the first range is set to pressure values (for example, 50 through 40 Mpa) that enable the plate-formed workpiece W to warp to form the gap S while being suctioned and held against the holder surface 56. Therefore, in the first holding process in the second embodiment, similarly to the first embodiment, the plate-formed workpiece W suctioned and held against the holder surface 56 may be maintained in the shape having the raised center.

[0072] In the second embodiment, after the first holding process, as shown in FIG. 5B, the reaction-force reducing grinding process is performed in the same manner as that in the first embodiment. In the reaction-force reducing grinding process, as it is in the first holding process, the plate-formed workpiece W is maintained in the state where the plate-formed workpiece W is warped and the gap S is formed. After the reaction-force reducing grinding process, as shown in FIG. 6A, the second holding process is performed with the chuck table 101, as well as the first holding process. In the second holding process, the adjuster valve 106 is operated so that the negative pressure value of the holder surface 56 measured by the pressure gauge 107 may fall within the second range described above. Accordingly, the air in the gap S is suctioned through the holder surface 56, and the gap S between the holder surface 56 and the second surface W2 of the plate-formed workpiece W is eliminated. As such, the holder surface 56 and the second surface W2 of the plate-formed workpiece W contact each other, and the plate-formed workpiece W may be suctioned and held against the holder surface 56. In other words, the second range is set to pressure values (for example, 90 through 80 Mpa) that enables suctioning and holding the plate-formed workpiece W in a manner such that the warpage of the plate-formed workpiece W after the reaction-force reducing grinding process is corrected and causing the holder surface 56 and the second surface W2 of the plate-formed workpiece W to contact each other.

[0073] Thereafter, according to the second embodiment, similarly to the first embodiment, the plate-formed workpiece W may as well be ground in the form such that the second surface W2 is flattened, as shown in FIG. 6B, in the finish-grinding process. Thereby, a working efficiency for grinding a plate-formed workpiece W with warpage, which is raised at the center, may be improved. Moreover, the first holding process, the reaction-force reducing grinding process, the second holding process, and the finish-grinding process may be performed with the single chuck table 101.

Third Embodiment

[0074] A third embodiment of the present disclosure will be described with reference to FIGS. 7A-7B and 8A-8B. FIGS. 7A-7B and 8A-8B are schematic cross-sectional views of a universal chuck table and surrounding thereof according to the third embodiment. FIG. 7A illustrates a first holding process, FIG. 7B illustrates a reaction-force reducing grinding process, FIG. 8A illustrates a second holding process, and FIG. 8B illustrates a finish-grinding process.

[0075] As shown in FIGS. 7A-7B and 8A-8B, in the third embodiment, a universal chuck table 110 may suction and hold the plate-formed workpiece W. The universal chuck table 110 includes a frame 111 and a disk-shaped porous sheet 112 arranged in in a recess in the frame 111.

[0076] The universal chuck table 110 has a partition 115 dividing the porous sheet 112 into sections in a radial direction. The partition 115 is made of a non-permeable material and is arranged concentrically about a center axis C2 of the universal chuck table 110 to divide the porous sheet 112 into a central section and an outer section that encircles the central region in a Baumkuchen fashion. The universal chuck table 110 being divided has two concentric holder surfaces. In particular, the universal chuck table 110 has a central holder surface 116, which is formed of an upper surface of the porous sheet 112 on the inner side of the partition 115, and an outer circumferential holder surface 117, which is formed of the upper surface of the porous sheet 112 on the outer side of the partition 115. The central holder surface 116 and the outer circumferential holder surface 117 are, similarly to the holder surface 56 of the first embodiment, formed to spread in parallel to the lower surface 941 of the grindstone 97.

[0077] The holder device 40 in the third embodiment has, further to the suction source 60, a central suction path 121, an outer circumferential suction path 122, and an area changeable device 123. The central suction path 121 is connected to the suction source 60 and the porous sheet 112 on the inner side of the partition 115, and thereby the central holder surface 116 and the suction source 60 communicate. The outer circumferential suction path 122 is connected to the suction source 60 and the porous sheet 112 on the outer side of the partition 115, and thereby the outer circumferential holder surface 117 and the suction source 60 communicate.

[0078] The area changeable device 123 includes a central open/close valve 125 provided in the central suction path 121 and an outer circumference open/close valve 126 provided in the outer circumferential suction path 122. As the central open/close valve 125 is opened, the suction source 60 and the central holder surface 116 communicate via the central suction path 121, and the air is suctioned through the central holder surface 116 to generate negative pressure, thereby causing the plate-formed workpiece W to be suctioned and held against the central holder surface 116. As the outer circumference open/close valve 126 is opened, the suction source 60 and the outer circumferential holder surface 117 communicate via the outer circumferential suction path 122, and the air is suctioned through the outer circumferential holder surface 117 to generate negative pressure, thereby causing the plate-formed workpiece W to be suctioned and held against the outer circumferential holder surface 117.

[0079] The area changeable device 123 may change an area of the holder surface of the universal chuck table 110 as a whole between a case where either one of the central open/close valve 125 or the outer circumference open/close valve 126 is opened and a case where both the central open/close valve 125 and the outer circumference open/close valve 126 are opened. The area of the holder surface may be changed by the controller 16 (see FIG. 2) controlling the central open/close valve 125 and/or the outer circumference open/close valve 126 to open or close, respectively.

[0080] In the first holding process according to the third embodiment, similarly to the second embodiment, the plate-formed workpiece W having the raised center is placed on the holder surfaces 116, 117 of the chuck table 110 with the second surface W2 facing downward. In this orientation of the plate-formed workpiece W, the gap S is formed between the holder surfaces 116, 117, which are parallel to the lower surface 971 of the grindstone 97, and the concave shape of the second surface W2 of the plate-formed workpiece W.

[0081] With the gap S being formed, by opening the outer circumference open/close valve 126, the suction source 60 and the outer circumferential holder surface 117 of the chuck table 110 are connected through the outer circumferential suction path 122. Thereby, an outer circumferential part W4 of the plate-formed workpiece W that overlaps the outer circumferential holder surface 117 vertically is suctioned and held against the outer circumferential holder surface 117.

[0082] Meanwhile, the central open/close valve 125 remains closed; therefore, a central part W3 of the plate-formed workpiece W that overlaps the central holder surface 116 vertically is neither subjected to the negative pressure on the central holder surface 116 nor suctioned thereby. Accordingly, while the warpage of the plate-formed workpiece W may be maintained or may be corrected to some extent, the outer circumferential part W4 of the plate-formed workpiece W is suctioned and held against the outer circumferential holder surface 117. As such, in the first holding process according to the third embodiment, as that in the first and second embodiments, the plate-formed workpiece W is maintained in the state with the center being raised.

[0083] In the third embodiment, after the first holding process, as shown in FIG. 7B, the reaction-force reducing grinding process is performed in the same manner as that in the first embodiment. In the reaction-force reducing grinding process, as it is in the first holding process, the plate-formed workpiece W is maintained in the state where the plate-formed workpiece W is warped and the gap S is formed.

[0084] After the reaction-force reducing grinding process, as shown in FIG. 8A, a second holding process is performed with the universal chuck table 110, as well as the first holding process. In the second holding process, the central open/close valve 125 and the outer circumference open/close valve 126 are operated to both open so that the suction source 60 and both the central holder surface 116 and the outer circumferential holder surface 117 communicate. Thereby, the air in the gap S is suctioned through the central holder surface 116, and the gap S between the holder surfaces 116, 117 and the second surface W2 of the plate-formed workpiece W is eliminated. As such, both of the holder surface 116, 117 and the second surface W2 of the plate-formed workpiece W contact each other, and the plate-formed workpiece W may be suctioned and held against both of the holder surfaces 116, 117.

[0085] According to the third embodiment, similarly to the first and second embodiments, as shown in FIG. 8B, the plate-formed workpiece W may as well be ground in the form such that the second surface W2 is flattened, in the finish-grinding process. Thereby, a working efficiency for grinding a plate-formed workpiece W with warpage, which is raised at the center, may be improved. Moreover, the first holding process, the reaction-force reducing grinding process, the second holding process, and the finish-grinding process may be performed with the single chuck table 110.

Fourth Embodiment

[0086] A fourth embodiment of the present disclosure will be described with reference to FIGS. 9A-9B and 10A-10B. FIGS. 9A-9B and 10A-10B are schematic cross-sectional views of a chuck table and surrounding thereof according to the fourth embodiment. FIG. 9A illustrates a first holding process, FIG. 9B illustrates a reaction-force reducing grinding process, FIG. 10A illustrates a second holding process, and FIG. 10B illustrates a finish-grinding process.

[0087] As shown in FIGS. 9A-9B and 10A-10B, a pressure adjuster device 102 according to the fourth embodiment has a third open/close valve 131 in an air supply path 105 in place of the air source 104 in the second embodiment. Moreover, in the fourth embodiment, an end of the air supply path 105 is open to the atmosphere, and by opening or closing the third open/close valve 131, suctioning or not suctioning the air into the second suction path 62 may be switched.

[0088] The pressure adjuster device 102 in the fourth embodiment may operate the suction source 60 to suction the air from the air supply path 105 and adjust a flow rate of the air in the second suction path 62 by opening the second open/close valve 64 and the third open/close valve 131 and adjusting an opening amount of the adjuster valve 106. As such, the negative pressure value in the second suction path 62 and the holder surface 56 may be adjusted.

[0089] In the first holding process according to the fourth embodiment, with the plate-formed workpiece W placed on the holder surface 56 of the chuck table 101, the second open/close valve 64 and the third open/close valve 131 are opened. Thereby, the suction source 60 and the holder surface 56 of the chuck table 101 are connected through the second suction path 62, and meanwhile, a flow rate of the air to be drawn from the atmosphere through the air supply path 105 to the second suction path 62 is adjusted by the adjuster valve 106.

[0090] The adjustment is controlled by the controller 16 operating the adjuster valve 106 so that the negative pressure value of the holder surface 56 measured by the pressure gauge 107 may fall within the first range (for example, 50 through 40 MPa). Accordingly, as shown in FIG. 9B, the gap S is formed between the warped plate-formed workpiece W and the holder surface 56, the plate-formed workpiece W is suctioned and held against the holder surface 56, and, similarly to the second embodiment, the plate-formed workpiece W suctioned and held against the holder surface 56 may be maintained in the shape having the raised center.

[0091] In this state, after the first holding process, the reaction-force reducing grinding process in the same manner as that in the first embodiment is performed. In the second holding process after the reduced reaction-force grinding process, the third open/close valve 131 is closed, and the adjuster valve 106 is controlled such that the negative pressure value of the holder surface 56 measured by the pressure gauge 107 falls within the second range (for example, 90 through 80 MPa). Accordingly, as shown in FIG. 10A, the warpage of the plate-formed workpiece W after the reaction-force reducing grinding process may be corrected, and the plate-formed workpiece W may be suctioned and held against the holder surface 56 in the way such that the holder surface 56 and the second surface W2 are in surface contact with each other.

[0092] Thereafter, according to the fourth embodiment, the plate-formed workpiece W may be ground in the form such that the second surface W2 is flattened, as shown in FIG. 10B, in the finish-grinding process. Thereby, similarly to the second embodiment, a working efficiency for grinding a plate-formed workpiece W with warpage, which is raised at the center, may be improved. Moreover, the first holding process, the reaction-force reducing grinding process, the second holding process, and the finish-grinding process may be performed with the single chuck table 101.

[0093] It may be noted that embodiment of the present disclosure may not necessarily be limited to the configurations described above but may be modified in various ways. In the embodiments described above, sizes or forms of the components illustrated in the accompanying drawings are not limited thereto but may be modified optionally within the scope of the effects of the present disclosure. Moreover, the embodiment may be modified optionally without departing from the scope of the object of the present disclosure.

[0094] For example, in the embodiments described above, in the reaction-force reducing grinding process, the central part W3 including the center of the plate-formed workpiece W is ground in a circle, but the form of grinding is not necessarily limited thereto. For example, a central area in the central part W3 may not be ground, but the plate-formed workpiece W may be ground annularly concentrically with the shape of the circumference of the plate-formed workpiece W to reduce the reaction force that may act against the correcting force to flatten the plate-formed workpiece W. In the case where the plate-formed workpiece W is ground annularly, the inclinations of the axes of the chuck tables 41, 11, 110 and/or the inclination of the axis of the spindle 93 may be adjusted so that the contact area between the grindstone 97 and the first surface W1 of the plate-formed workpiece W may be adjusted.

[0095] For another example, the form of the holder surface 46 of the first chuck table 41 in the first embodiment may be modified as long as the holder surface has the form where the center thereof is raised. For example, the holder surface may have a gradually curved form where the center is raised to be higher than the circumference thereof.

[0096] Meanwhile, the shape of the plate-formed workpiece W to be held and ground in the embodiments described above is merely an example and may be modified into a different shape other than circle such as rectangle, polygon having other shape than rectangle, or a shape with curved contours.

[0097] For another example, the two chuck tables 41, 42 are arranged on the turntable 43 in the first embodiment described above, but, optionally, three or more chuck tables may be arranged on a chuck table.

[0098] For another example, in the second and the fourth embodiments, the amount to open the adjuster valve 106 is adjusted by the controller 16, but, optionally, the amount to open the adjuster valve 106 may be adjusted manually by an operator.

[0099] For another example, the adjuster valve 106 described in the second and fourth embodiments may be replaced with a fixed throttle valve where an orifice diameter is fixed to a predetermined opening amount. In the arrangement where the adjuster valve 106 is replaced with the fixed throttle valve in the second or fourth embodiment, an open/close valve may be additionally provided in the air supply path 105, and the negative pressure value applied to the holder surface 56 may be adjusted by the additional open/close valve.

[0100] For another example, the first chuck table 41 in the first embodiment may be replaced with a chuck table as shown in FIGS. 11A-11B. FIGS. 11A-11B are schematic cross-sectional views of a first chuck table and surrounding thereof according to a modified example of the first embodiment. FIG. 11A illustrates a first holding process, and FIG. 11B illustrates a reaction-force reducing grinding process.

[0101] In the modified example shown in FIGS. 11A and 11B, the holder surface 46 of the first chuck table 41 is formed similarly to the holder surface 56 of the second chuck table 42 in the first embodiment, and a pressure adjuster device 132 is provided. The pressure adjuster device 132 includes an air supply path 133 provided to the first frame 44 of the first chuck table 41 and an adjuster valve 134 provided in the air supply path 133. In the modified example shown in FIGS. 11A-11B, the air supply path 133 is not equipped with an open/close valve, but optionally, the air supply path 133 may be equipped with an open/close valve.

[0102] The air supply path 133 is connected to the first porous sheet 45 at one end thereof, thereby communicating with the holder surface 46, and is open to the atmosphere at the other end. The adjuster valve 134 may function equally to the adjuster valve 106 in the fourth embodiment. As such, in the modified embodiment, the pressure adjuster device 132 may open the first open/close valve 63 and adjust the amount of opening of the adjuster valve 134, thereby adjusting the air to be suctioned by the suction source 60 from the atmosphere through the air supply path 133. Accordingly, the pressure adjuster device 132 may adjust the negative pressure value in the first suction path 61 and the holder surface 46.

[0103] In the first holding process with the first chuck table 41 according to the modified example, as shown in FIGS. 11A-11B, with the plate-formed workpiece W being placed on the holder surface 46, the first open/close valve 63 is opened. Thereby, the suction source 60 and the holder surface 46 are connected through the first suction path 61, and meanwhile, a flow rate of the air to be drawn from the atmosphere through the air supply path 133 and the first porous sheet 45 to the holder surface 46 is adjusted by the adjuster valve 134.

[0104] The adjustment is controlled by the controller 16 operating the adjuster valve 134 so that the negative pressure value on the holder surface 46 measured by the pressure gauge 107 may fall within the first range (for example, 50 through 40 MPa). Accordingly, the gap S is formed between the warped plate-formed workpiece W and the holder surface 46, the plate-formed workpiece W is suctioned and held against the holder surface 46, and, similarly to the second and fourth embodiments, the plate-formed workpiece W suctioned and held against the holder surface 46 may be maintained in the shape having the raised center (see FIG. 11B). In this state, the reaction-force reducing grinding process is performed in the same manner as that in the second and fourth embodiments, and thereafter, the second holding process and the finish-grinding process is performed in the same manner as those in the first embodiment.

[0105] Optionally, in the second or fourth embodiment, in the first holding process and the reaction-force reducing grinding process, the first chuck table 41 and the pressure adjuster device 132 in FIGS. 11A-11B may be used, and in the second holding process and the finish-grinding process, similarly to those described above, the chuck table 101 may be used. In this arrangement, the pressure adjuster device 102 in the second or fourth embodiment may be omitted, and further, a configuration where the adjuster valve 134 is replaced with a fixed throttle valve may be employed. In such a configuration, when the plate-formed workpiece W is held against the holder surface 46 of the first chuck table 41, the pressure value to act on the holder surface 46 may be lowered by the amount of opening of the fixed throttle valve. As such, the pressure between the holder surface 46 and the plate-formed workpiece W may be set to a pressure value, by which the warped plate-formed workpiece W may form the gap S, and by which the plate-formed workpiece W may be suctioned and held against the holder surface 46.