Grinding apparatus and method for grinding workpieces

Abstract

To reduce variations in thickness of a plurality of workpieces to be ground in order so as to each have a target finished thickness.SOLUTION: A method for grinding workpieces includes: identifying a correction thickness corresponding to an error between an actual thickness of each of the plurality of workpieces and a thickness measured by a measurement unit when a height of a surrounding region measured by a first gauge increases as the plurality of workpieces are ground; and then, grinding each of the plurality of workpieces until the thickness measured by the measurement unit becomes a thickness obtained by subtracting the correction thickness from a target finish thickness.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a grinding device for grinding a plurality of workpieces in sequence so that each of the workpieces has a target finishing thickness, and a grinding method for grinding a plurality of workpieces in sequence so that each of the workpieces has a target finishing thickness. [Background technology]

[0002] Device chips such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a workpiece such as a wafer having a plurality of devices formed on its surface into regions each including an individual device.

[0003] A workpiece is often thinned before being divided, for example to produce smaller chips. One method for thinning a workpiece is to grind the workpiece in a grinding device. The grinding device generally includes a chuck table having a holding surface including a holding area and an enclosing area surrounding the holding area, and a grinding unit having a spindle at the tip of which a grinding wheel including a plurality of grinding stones arranged in a circularly spaced manner is attached.

[0004] In a grinding machine, a workpiece is ground by bringing a plurality of grinding wheels into contact with the workpiece while rotating both the chuck table and the spindle in a state in which the workpiece is held in the holding area. In general, the grinding is performed while measuring the thickness of the workpiece, and is terminated when the measured thickness of the workpiece reaches the target finishing thickness.

[0005] The thickness of the workpiece is measured using a measurement unit including, for example, a first gauge for measuring the height of the enclosed area and a second gauge for measuring the height of the top surface of the workpiece held in the holding area. However, if the actual shape of the holding surface of the chuck table deviates from the expected shape, the thickness of the workpiece measured by this measurement unit may deviate from the actual thickness of the workpiece.

[0006] In consideration of this, in a grinding device, prior to grinding the workpiece, grinding (self-grinding) of the chuck table is sometimes performed to shape the holding surface (see, for example, Patent Document 1). This allows the shape of the holding surface of the chuck table to approach an expected shape. As a result, it is possible to reduce the error between the actual thickness of the workpiece and the thickness measured by the measurement unit.

[0007] In addition, in a grinding device, grinding water is supplied to the contact interface (processing point) between the workpiece and multiple grinding wheels, and / or cooling water is circulated through a flow path formed inside the chuck table while grinding the workpiece (see, for example, Patent Documents 2 and 3). This makes it possible to suppress deformation of the holding surface caused by thermal expansion of the chuck table, which is heated as the workpiece is ground. As a result, it is possible to reduce the error between the actual thickness of the workpiece and the thickness measured by the measurement unit. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2008-114336 A [Patent Document 2] JP 2009-113145 A [Patent Document 3] JP 2003-326458 A Summary of the Invention [Problem to be solved by the invention]

[0009] In a grinding device, it is preferable to grind a plurality of workpieces in sequence without interruption in order to improve throughput. However, in this case, deformation of the holding surface caused by thermal expansion of the chuck table heated in association with grinding of the workpieces cannot be sufficiently suppressed, and the finished thickness of the plurality of workpieces is likely to vary greatly.

[0010] In view of this, an object of the present invention is to reduce the variation in thickness of a plurality of workpieces that are ground in sequence to a target finish thickness. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided a grinding device for grinding a plurality of workpieces in sequence so that each of the workpieces has a target finishing thickness, the grinding device comprising: a chuck table having a holding surface including a holding area and an enclosing area surrounding the holding area, and for holding the plurality of workpieces in sequence in the holding area; a spindle having a grinding wheel including a plurality of grinding stones provided discretely in an annular shape attached to its tip, and for rotating the grinding wheel together with the spindle in order to grind each of the plurality of workpieces held in sequence in the holding area with the plurality of grinding stones; a moving mechanism for adjusting the distance between the chuck table and the grinding unit in order to bring the plurality of grinding stones into contact with each of the plurality of workpieces held in sequence in the holding area; a first gauge for measuring the height of the enclosing area; and a second gauge for measuring the height of an upper surface of each of the plurality of workpieces held in sequence in the holding area, the measuring unit including: a measuring unit for measuring the thickness of each of the plurality of workpieces; and a controller for controlling the measurement unit, the movement mechanism and the measurement unit, wherein the controller includes a memory for storing information indicating a relationship between an amount of change in height of the enclosed area caused by heating of the chuck table when the plurality of workpieces are ground in sequence and an error between an actual thickness of each of the plurality of workpieces and a thickness measured by the measurement unit, and a processor for controlling the measurement unit to measure the thickness of each of the plurality of workpieces when the plurality of workpieces are ground in sequence, and for specifying a correction thickness corresponding to the error by referring to the information when the height of the enclosed area measured by the first gauge when each of the plurality of workpieces is ground is higher than a reference height of the enclosed area measured by the first gauge before the plurality of workpieces are ground, and then controlling the grinding unit and the movement mechanism so that each of the plurality of workpieces is ground until the thickness measured by the measurement unit becomes a thickness obtained by subtracting the correction thickness from the target finish thickness.

[0012] According to another aspect of the present invention, a grinding device includes a chuck table having a holding surface including a holding area and an enclosing area surrounding the holding area, and for holding a plurality of workpieces in sequence in the holding area; a grinding unit having a spindle having a grinding wheel attached to its tip, the grinding wheel including a plurality of grinding wheels spaced apart in an annular shape, and for rotating the grinding wheel together with the spindle to grind each of the plurality of workpieces held in sequence in the holding area with the plurality of grinding wheels; a moving mechanism for adjusting a distance between the chuck table and the grinding unit to bring the plurality of grinding wheels into contact with each of the plurality of workpieces held in sequence in the holding area; a first gauge for measuring a height of the enclosing area; and a second gauge for measuring the height of an upper surface of each of the plurality of workpieces held in sequence in the holding area, and a measuring unit for measuring a thickness of each of the plurality of workpieces. a reference height measuring step of measuring a reference height of the enclosed area with the first gauge, and a grinding step of grinding each of the plurality of workpieces until the thickness measured by the measuring unit becomes the target finish thickness or a thickness obtained by subtracting a correction thickness from the target finish thickness, after the reference height measuring step, wherein the correction thickness corresponds to an error between the actual thickness of each of the plurality of workpieces and the thickness measured by the measuring unit, and in the grinding step, if the height of the enclosed area measured by the first gauge when each of the plurality of workpieces is ground is higher than the reference height, the correction thickness is specified by referring to information indicating a relationship between the error and an amount of change in the height of the enclosed area caused by heating of the chuck table when the plurality of workpieces are ground in sequence, and then each of the plurality of workpieces is ground until the thickness measured by the measuring unit becomes the thickness obtained by subtracting the correction thickness from the target finish thickness.

[0013] In the present invention, the information is preferably a coefficient indicating the ratio between the amount of change and the error. Effect of the Invention

[0014] In the present invention, when the height of the enclosed area measured by the first gauge increases as the multiple workpieces are ground, a correction thickness corresponding to the error between the actual thickness of each of the multiple workpieces and the thickness measured by the measuring unit is identified, and each of the multiple workpieces is ground until the thickness measured by the measuring unit becomes the thickness obtained by subtracting the correction thickness from the target finishing thickness.

[0015] Therefore, in the present invention, even if it is not possible to sufficiently suppress deformation of the holding surface caused by the thermal expansion of the chuck table which is heated in conjunction with grinding of the workpieces, it is possible to reduce the variation in thickness of multiple workpieces which are ground in sequence so that each of them reaches the target finishing thickness. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view that illustrates an example of a grinding device. [Diagram 2] FIG. 2 is a perspective view that illustrates an example of a workpiece. [Diagram 3] FIG. 3 is a partial cross-sectional side view that typically shows a chuck table maintained at room temperature. [Figure 4] FIG. 4 is a partially sectional side view that typically shows the tip portion of the spindle, etc. FIG. [Diagram 5] FIG. 5 is a schematic partial cross-sectional side view of a heated chuck table. [Figure 6] FIG. 6 is a flow chart that illustrates an example of a method for grinding workpieces in which a plurality of workpieces are ground in sequence in a grinding device so that each workpiece has a target finish thickness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing a schematic diagram of an example of a grinding device. In Fig. 1, some components of the grinding device are shown in functional blocks. In Fig. 1, the X-axis direction (left direction) and the Y-axis direction (rear direction) are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (upward direction) is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

[0018] 1 includes a base 4 that supports or houses each of the components. A pair of cassette mounting areas 6a, 6b is provided on the upper surface of the front end of the base 4. Cassettes 8a, 8b, each capable of housing a plurality of workpieces, are placed on the cassette mounting areas 6a, 6b, spaced apart from each other in the Z-axis direction.

[0019] That is, each of the cassettes 8a and 8b is provided with a storage area having multiple stages capable of storing the workpieces. Fig. 2 is a perspective view showing an example of the workpieces stored in the cassettes 8a and 8b. The workpiece 11 shown in Fig. 2 is, for example, a wafer having a circular front surface 11a and a back surface 11b, and made of a semiconductor material such as silicon (Si).

[0020] This workpiece 11 is partitioned into a plurality of regions by a plurality of planned division lines 13 set in a lattice pattern, and devices 15 such as ICs are formed on the front surface 11a side of each region. The workpiece 11 may also include a film-like tape provided so as to cover the devices 15. This tape has a diameter approximately equal to the diameter of the wafer on which the devices 15 are formed, and is made of, for example, resin.

[0021] This tape protects the device 15 by absorbing the impact applied to the front surface 11a side when the back surface 11b side of the workpiece 11 is ground. There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be made of a semiconductor material other than silicon, ceramics, resin, or metal.

[0022] 1, a recess 4a is formed behind the cassette placement areas 6a, 6b, and a transport unit 10 is provided inside this recess 4a. This transport unit 10 is used to transport the workpiece 11 before grinding from one of the multiple storage areas (original storage area) of the cassettes 8a, 8b, and to transport the workpiece 11 after grinding, for example, into the original storage area.

[0023] Specifically, the transport unit 10 has, for example, a plurality of joints and a robot hand. In the transport unit 10, it is possible to suck and hold the workpiece 11 by applying a suction force to a space on one side of the robot hand, and to separate the workpiece 11 from the one side of the robot hand by making the pressure in the space normal pressure.

[0024] Furthermore, a motor is connected to the base end of the robot hand for rotating the robot hand about a straight line perpendicular to the Z-axis direction as a rotation axis. In the transport unit 10, by operating this motor, the robot hand holding the workpiece 11 can be inverted, that is, the workpiece 11 can be turned upside down.

[0025] Further, a position adjustment mechanism 12 for adjusting the position of the workpiece 11 is provided diagonally behind the recess 4a. This position adjustment mechanism 12 includes a disk-shaped position adjustment table and a number of pins arranged around the position adjustment table. Then, the workpiece 11 carried out from the cassettes 8a and 8b by the transport unit 10 is carried into this position adjustment table, and its center is aligned to a predetermined position.

[0026] Specifically, the workpiece 11 is carried onto the position adjustment table so that its back surface 11b faces upward. Then, multiple pins approach the position adjustment table along the radial direction of the position adjustment table. As a result, the multiple pins come into contact with the side surfaces of the workpiece 11 and move the workpiece 11 slightly. As a result, the center of the workpiece 11 is aligned to a predetermined position.

[0027] A transport unit 14 that holds the workpiece 11 and transports it rearward is provided on the side of the position adjustment mechanism 12. This transport unit 14 has, for example, a support shaft extending along the Z-axis direction, an arm whose base end is fixed to the upper end of the support shaft and extends along a direction perpendicular to the Z-axis direction, and a suction pad fixed to the underside of the tip of the arm.

[0028] In this conveying unit 14, it is possible to suck and hold the workpiece 11 by applying suction force to the space near the suction pad, and to separate the workpiece 11 from the suction pad by returning the pressure in that space to normal pressure.

[0029] Furthermore, the support shaft of the transport unit 14 is connected to a motor. When the motor is operated, the support shaft rotates about a straight line along the Z-axis direction as a rotation axis, that is, the suction pad revolves around the support shaft.

[0030] The support shaft of the transport unit 14 is connected to, for example, a ball screw type moving mechanism (not shown). When this moving mechanism is operated, the support shaft, the arm, and the suction pad move along the Z-axis direction, that is, the support shaft, the arm, and the suction pad move up and down.

[0031] For example, the transport unit 14 holds the workpiece 11 and transports it backward in the following order: First, the support shaft is rotated so that the suction pad is positioned directly above the workpiece 11 whose center has been adjusted to a predetermined position by the position adjustment mechanism 12. Next, the support shaft is lowered so that the suction pad comes into contact with the back surface (upper surface) 11b of the workpiece 11.

[0032] Next, the back surface (upper surface) 11b of the workpiece 11 is sucked and held by the suction pad. Next, the support shaft is raised so as to raise the suction pad holding the workpiece 11. Next, the support shaft is rotated so as to rotate the suction pad holding the workpiece 11. As a result, the workpiece 11 is transported backward.

[0033] A disk-shaped turntable 16 is provided behind the transport unit 14. The turntable 16 is connected to a motor. When the motor is operated, the turntable 16 rotates about a rotation axis that passes through the center of the upper surface of the turntable 16 and is aligned in the Z-axis direction.

[0034] In addition, three chuck tables 18a, 18b, and 18c are provided on the turntable 16 at approximately equal angular intervals along the circumferential direction of the turntable 16. Fig. 3 is a partial cross-sectional side view that shows each of the chuck tables 18a, 18b, and 18c maintained at room temperature.

[0035] Each of the chuck tables 18a, 18b, and 18c has a disk-shaped frame 20 made of, for example, ceramics. The frame 20 has a disk-shaped bottom wall 20a and a cylindrical side wall 20b standing on the outer periphery of the bottom wall 20a. That is, a recess defined by the bottom wall 20a and the side wall 20b is formed on the upper surface side of the frame 20.

[0036] A disk-shaped porous plate 22 made of porous ceramics or the like is fixed in this recess. The outer diameter of the side wall 20b of the frame 20 is slightly larger than the diameter of the workpiece 11, and the inner diameter (diameter of the porous plate 22) is slightly smaller than the diameter of the workpiece 11. The upper surface of the side wall 20b of the frame 20 and the upper surface of the porous plate 22 are configured to have a shape corresponding to the side surface of a cone, and function as a holding surface for holding the workpiece 11.

[0037] In addition, a flow path (not shown) is formed in the bottom wall 20a, which opens at the bottom surface of the recess and penetrates the bottom wall 20a. This flow path is connected to a suction source (not shown) via a valve (not shown) or the like, and is also connected to an air supply source (not shown) via a valve (not shown) or the like.

[0038] The suction source includes, for example, an ejector, etc. The air supply source includes, for example, a tank for storing high-pressure air, a filter for removing foreign matter mixed in the gas supplied from the tank, and a regulator for adjusting the pressure of the gas supplied from the tank.

[0039] When the suction source is operated with the flow path formed in the bottom wall 20a in communication with the suction source, the pressure in the flow path becomes negative, and a suction force acts on the space near the upper surface of the porous plate 22. Therefore, when the workpiece 11 is held on the holding surfaces of the chuck tables 18a, 18b, and 18c, the upper surface of the porous plate 22 becomes the holding region R1, and the upper surface of the side wall 20b of the frame 20 becomes the surrounding region R2 that surrounds the holding region R1.

[0040] Furthermore, each of the chuck tables 18a, 18b, and 18c is connected to a rotation mechanism (not shown). This rotation mechanism includes, for example, a motor and a pulley. When this rotation mechanism is operated, each of the chuck tables 18a, 18b, and 18c rotates about a straight line L passing through the center of each holding surface as a rotation axis.

[0041] Each of the chuck tables 18a, 18b, and 18c is supported by a table base 24 via bearings (not shown) or the like. The table base 24 is made of a metal material such as stainless steel. The table base 24 is connected to an inclination adjustment mechanism (not shown).

[0042] The tilt adjustment mechanism includes, for example, two movable shafts and one fixed shaft that are arranged at approximately equal angular intervals along the circumferential direction of each of the chuck tables 18a, 18b, and 18c. When at least one of the two movable shafts partially raises or lowers the table base 24, the tilt of the rotation axis of each of the chuck tables 18a, 18b, and 18c is adjusted.

[0043] 1 via a table base 24, and rotates with the rotation of the turntable 16. This allows each of the chuck tables 18a, 18b, 18c to be positioned in sequence at, for example, a load / unload position A adjacent to the transport unit 14, a rough grinding position B diagonally behind the load / unload position A, and a finish grinding position C to the side of the rough grinding position B.

[0044] Then, the workpiece 11 transported rearward by the transport unit 14 is loaded onto one of the chuck tables 18a, 18b, and 18c (hereinafter, for convenience, referred to as chuck table 18a) positioned at the loading / unloading position A. The workpiece 11 is loaded onto the chuck table 18a, for example, in the following order.

[0045] First, the support shaft of the transport unit 14 is lowered so that the workpiece 11, which is held by suction on the back surface (upper surface) 11b side by the suction pad of the transport unit 14, approaches the holding surface of the chuck table 18a. Next, the pressure in the space near the suction pad of the transport unit 14 is returned to normal pressure, thereby separating the workpiece 11 from the suction pad.

[0046] Next, the suction source is operated in a state where the flow path formed in the bottom wall 20a of the frame 20 is in communication with the suction source so that the workpiece 11 is held in the holding area R1 of the holding surface of the chuck table 18a. This completes the loading of the workpiece 11 onto the chuck table 18a.

[0047] Then, when the workpiece 11 has been carried onto the chuck table 18a, the turntable 16 is rotated so as to position the chuck table 18a at the rough grinding position B or the finish grinding position C. Behind the rough grinding position B and the finish grinding position C, pillar-shaped support structures 30a, 30b are provided, respectively.

[0048] A moving mechanism 32 is provided on the front side of each of the support structures 30a, 30b. The moving mechanism 32 includes a pair of guide rails 34 extending along the Z-axis direction. Furthermore, a moving plate 36 is attached to the pair of guide rails 34 in a slidable manner.

[0049] A ball screw nut (not shown) is fixed to the rear surface of the moving plate 36, and a screw shaft 38 extending along the Z-axis direction is rotatably connected to this nut. The nut also houses a large number of balls that roll on the surface of the screw shaft 38 as the screw shaft 38 rotates.

[0050] Furthermore, a motor 40 is connected to one end (upper end) of the screw shaft 38. When the screw shaft 38 is rotated by the motor 40, a large number of balls circulate inside the nut, and the moving plate 36 moves along the Z-axis direction together with the nut.

[0051] A grinding unit 42 is provided on the front surface (surface) of the movable plate 36. The grinding unit 42 has a spindle housing 44 fixed to the movable plate 36. Furthermore, a spindle (not shown in FIG. 1) extending along the Z-axis direction is housed in the spindle housing 44 in a rotatable manner.

[0052] 4 is a partially sectional side view showing the tip (lower end) of the spindle, etc. The spindle 46 protrudes downward through a through hole formed in the bottom of the spindle housing 44, and its tip is a disk-shaped mount 48.

[0053] In the grinding unit 42 on the rough grinding position B side, a grinding wheel 50a for rough grinding is attached to the underside of the mount 48. Similarly, in the grinding unit 42 on the finish grinding position C side, a grinding wheel 50b for finish grinding is attached to the underside of the mount 48.

[0054] Each of the grinding wheels 50a, 50b includes an annular wheel base 52 made of a metal such as stainless steel or aluminum. A plurality of grinding stones 54 are fixed to the underside of the wheel base 52 at approximately equal angular intervals along the circumferential direction of the wheel base 52.

[0055] Each of the grinding wheels 54 contains a binder such as vitrified or resinoid, and abrasive grains such as diamond dispersed in the binder. The average grain size of the abrasive grains contained in the grinding wheel 54 included in the grinding wheel 50b for finish grinding is smaller than the average grain size of the abrasive grains contained in the grinding wheel 54 included in the grinding wheel 50a for rough grinding.

[0056] Further, a grinding fluid supply unit 56 is provided near each of the grinding wheels 50a, 50b. The grinding fluid supply unit 56 has, for example, a nozzle 58 located inside each of the grinding wheels 50a, 50b in a plan view, and a pump (not shown) that supplies liquid (grinding fluid) such as pure water to the nozzle 58.

[0057] When the pump operates, the grinding fluid is supplied from the nozzle 58 to the back surface (upper surface) 11b of the workpiece 11 held in the holding area R1 of the holding surface of the chuck table 18a positioned at the rough grinding position B or the finish grinding position C. The grinding fluid supply unit 56 may supply the grinding fluid through flow paths (not shown) formed in each of the grinding wheels 50a, 50b instead of or in addition to the nozzle 58.

[0058] 1 is connected to the base end (upper end) of the spindle 46. When the motor 60 is operated, the grinding wheels 50a, 50b rotate together with the spindle 46 around a straight line along the Z-axis direction as the rotation axis.

[0059] Measuring units 62a and 62b are provided on both sides of the turntable 16. The measuring unit 62a measures the thickness of the workpiece 11 held in the holding area R1 of the holding surface of each of the chuck tables 18a, 18b, and 18c positioned at the rough grinding position B. The measuring unit 62b measures the thickness of the workpiece 11 held in the holding area R1 of the holding surface of each of the chuck tables 18a, 18b, and 18c positioned at the finish grinding position C.

[0060] Specifically, each measuring unit 62a, 62b includes a first gauge 64a, 64b for measuring the height of the enclosed area R2 of the holding surface of the chuck table 18a, and a second gauge 66a, 66b for measuring the height of the holding area R1 of this holding surface or the back surface (top surface) 11b of the workpiece 11 held in the holding area R1.

[0061] Each of the first gauges 64a, 64b has a probe capable of contacting a point P1 (see FIG. 3) included in the surrounding region R2, and can measure the height of the position where the probe comes into contact. Also, each of the second gauges 66a, 66b has a probe capable of contacting a point P2 included in the holding region R1 or a point on the back surface 11b of the workpiece 11 located directly above point P2, and can measure the height of the position where the probe comes into contact.

[0062] Note that point P2 is positioned higher than point P1, for example. Point P1 is set so that the distance between the center of the holding surface and point P1 is longer than the radius of the workpiece 11 so that point P1 is not covered by the workpiece 11 when the workpiece 11 is held in the holding area R1 of the holding surface of each of the chuck tables 18a, 18b, and 18c. Point P2 is set so that the distance between the center of the holding surface and point P2 is, for example, half the radius of the workpiece 11.

[0063] Each of the first gauges 64a, 64b can measure a height (reference height) H1 of point P1 in a state before the workpiece 11 is ground, i.e., in a state in which each of the chuck tables 18a, 18b, 18c is maintained at room temperature. Similarly, each of the second gauges 66a, 66b can measure a height H2 of point P2 in a state in which each of the chuck tables 18a, 18b, 18c is maintained at room temperature.

[0064] Furthermore, each measuring unit 62a, 62b outputs as the thickness of the workpiece 11 a value obtained by subtracting the difference between height H1 and height H2 from the difference between the height measured by the first gauge 64a, 64b and the height measured by the second gauge 66a, 66b.

[0065] Therefore, in the grinding device 2, it is possible to roughly grind the back surface (top surface) 11b side of the workpiece 11 while measuring the thickness of the workpiece 11 with the measuring unit 62a, and to finish grind the back surface (top surface) 11b side of the workpiece 11 while measuring the thickness of the workpiece 11 with the measuring unit 62b.

[0066] When the workpiece 11 is rough ground or finish ground in this manner, the chuck tables 18a, 18b, and 18c and the table base 24 are heated. Fig. 5 is a partial cross-sectional side view that typically shows the heated chuck tables 18a, 18b, and 18c and the table base 24.

[0067] When the chuck tables 18a, 18b, and 18c and the table base 24 are heated, they thermally expand. However, the thermal expansion coefficient of the table base 24, which is made of a metal material, is greater than the thermal expansion coefficient of the chuck tables 18a, 18b, and 18c, which are made of ceramics.

[0068] Therefore, when each chuck table 18a, 18b, 18c and the table base 24 are heated, the so-called bimetal effect causes the holding surface of each chuck table 18a, 18b, 18c to curve overall so that the surrounded area R2 of the holding surface protrudes, and the positions of the above-mentioned points P1 and P2 also become higher.

[0069] That is, the height H1' of point P1 on each of the heated chuck tables 18a, 18b, 18c is higher than the height H1 of point P1 on each of the chuck tables 18a, 18b, 18c maintained at room temperature. Similarly, the height H2' of point P2 on each of the heated chuck tables 18a, 18b, 18c is higher than the height H2 of point P2 on each of the chuck tables 18a, 18b, 18c maintained at room temperature.

[0070] Furthermore, when each chuck table 18a, 18b, 18c and the table base 24 are heated, the change in height ΔH1 of point P1 (i.e., the value obtained by subtracting height H1 from height H1') becomes greater than the change in height ΔH2 of point P2 (i.e., the value obtained by subtracting height H2 from height H2').

[0071] Therefore, when the thickness of the workpiece 11 held in the holding area R1 of the holding surface of each of the chuck tables 18a, 18b, and 18c shown in Fig. 5 is measured by each of the measuring units 62a and 62b, the difference between the amount of change ΔH1 and the amount of change ΔH2 becomes an error. That is, in this case, each of the measuring units 62a and 62b outputs, as the thickness of the workpiece 11, a thickness that is larger than the actual thickness of the workpiece 11 by the amount of the error.

[0072] When the rough grinding and finish grinding of the workpiece 11 are completed, the turntable 16 is rotated so as to position the chuck table 18a at the load / unload position A. When the chuck table 18a is positioned at the load / unload position A, the pressure in the flow path formed in the bottom wall 20a of the frame 20 is set to normal pressure.

[0073] Specifically, first, the flow path is disconnected from the suction source, and then the air supply source is operated while the flow path is in communication with the air supply source, so that the workpiece 11 is not sucked toward the chuck table 18a but is simply placed on the chuck table 18a.

[0074] A transport unit 74 that holds the workpiece 11 and transports it forward is provided in front of the loading / unloading position A and to the side of the transport unit 14. This transport unit 74 has, for example, the same structure as the transport unit 14, and holds the workpiece 11 and transports it forward in the following order.

[0075] First, the support shaft is rotated so that the suction pad is positioned directly above the workpiece 11 placed on the chuck table 18a. Next, the support shaft is lowered so that the suction pad comes into contact with the back surface (upper surface) 11b of the workpiece 11.

[0076] Next, the back surface (upper surface) 11b of the workpiece 11 is sucked and held by the suction pad. Next, the support shaft is raised so as to raise the suction pad holding the workpiece 11. Next, the support shaft is rotated so as to rotate the suction pad holding the workpiece 11. As a result, the workpiece 11 is transported forward.

[0077] A cleaning device 76 for cleaning the workpiece 11 is provided on the side of the transport unit 74. This cleaning device 76 includes, for example, a spinner table for holding the workpiece 11, and a cleaning unit including a nozzle for supplying a liquid (cleaning liquid) such as pure water to the back surface (upper surface) 11b side of the workpiece 11 held by the spinner table.

[0078] The spinner table is connected to a suction source (not shown), an air supply source (not shown), and a rotation mechanism (not shown) in the same manner as the chuck tables 18a, 18b, and 18c. The workpiece 11 transported forward by the transport unit 74 is loaded onto the spinner table.

[0079] For example, the workpiece 11 is carried into the spinner table in the following order: First, the support shaft is rotated so that the workpiece 11 held by the suction pad of the transport unit 74 is positioned directly above the spinner table. Next, the support shaft of the transport unit 74 is lowered so that the workpiece 11 approaches the holding surface of the spinner table.

[0080] Next, the pressure in the space near the suction pad of the transport unit 74 is returned to normal pressure to separate the workpiece 11 from the suction pad. Next, the suction source communicating with the pinner table is operated so that the workpiece 11 is held on the holding surface of the spinner table. This completes the loading of the workpiece 11 onto the spinner table.

[0081] In this cleaning device 76, the workpiece 11 is cleaned by operating a cleaning unit to supply cleaning liquid to the back surface (top surface) 11b of the workpiece 11 while operating a rotation mechanism to rotate the spinner table that holds the workpiece 11 so as to expose its back surface (top surface) 11b.

[0082] Then, when cleaning of workpiece 11 in cleaning device 76 is completed, the communication between the spinner table and the suction source is cut off, and the air supply source is operated with the spinner table and the air supply source in communication with each other. As a result, workpiece 11 is not sucked to the spinner table but is simply placed on the spinner table.

[0083] Then, the cleaned workpiece 11 is carried out from the cleaning device 76 by the transport unit 10, and is carried into one of the plurality of accommodation areas of the cassettes 8a, 8b (for example, the original accommodation area).

[0084] The components of the grinding device 2 described above are controlled by a controller 78 built into the grinding device 2. The controller 78 includes a processor 78a and a memory 78b. The processor 78a is configured, for example, by a central processing unit (CPU). The memory 78b is configured, for example, by a volatile memory such as a dynamic random access memory (DRAM) or a static random access memory (SRAM), and a non-volatile memory such as a solid state drive (SSD) (NAND flash memory) or a hard disk drive (HDD) (magnetic storage device).

[0085] The memory 78b stores various information (data, programs, etc.) used by the processor 78a. The memory 78b stores information indicating the relationship between the amount of change in height of the surrounded region R2 caused by heating of the chuck table 18a when the multiple workpieces 11 are ground in sequence (in short, the above-mentioned amount of change ΔH1) and the error between the actual thickness of each of the multiple workpieces 11 and the thickness measured by the measuring units 62a, 62b (in short, the difference between the above-mentioned amount of change ΔH1 and the amount of change ΔH2).

[0086] This information may be, for example, a coefficient indicating the ratio between the amount of change in the height of the surrounding region R2 and the error (simply put, a value obtained by dividing the difference between the amount of change ΔH1 and the amount of change ΔH2 by the amount of change ΔH1), or may be a function for calculating the error using the amount of change in the height of the surrounding region R2 as a variable.

[0087] Furthermore, the processor 78a controls the components of the grinding device 2 to, for example, read from the memory 78b and execute a program for grinding a plurality of workpieces 11 in sequence so that each of the workpieces has a target finish thickness.

[0088] 6 is a flow chart showing a schematic example of a method for grinding a plurality of workpieces 11 in order to have a target finishing thickness by the grinding device 2. In this method, first, the reference height of the surrounding region R2 is measured by the first gauge 64b (reference height measurement step S1).

[0089] In this reference height measuring step S1, for example, the processor 78a controls the measuring unit 62b and the like so as to measure, by the first gauge 64b, the height (reference height) of a point P1 included in the enclosed region R2 of each holding surface of the chuck tables 18a, 18b, 18c which are sequentially positioned at the finish grinding position C. Then, the processor 78a stores the measured reference height in the memory 78b.

[0090] After the reference height measuring step S1, each of the multiple (e.g., N (N is a natural number of 5 or more)) workpieces 11 is ground until the thickness measured by the measuring unit 62b becomes the target finish thickness or a thickness obtained by subtracting the correction thickness from the target finish thickness (grinding step S2). Note that the correction thickness corresponds to the error between the actual thickness of each of the multiple workpieces 11 and the thickness measured by the measuring unit 62b.

[0091] In this grinding step S2, first, the workpiece 11 (first workpiece) is loaded onto the chuck table 18a. When the first workpiece is loaded onto the chuck table 18a, the processor 78a controls the motor connected to the turntable 16 so as to position the chuck table 18a at the loading / unloading position A.

[0092] Next, the processor 78a controls the transport units 10, 14, etc., so as to transport the first workpiece with its back surface 11b facing upward from the cassettes 8a, 8b to the chuck table 18a. Next, the processor 78a operates the suction source communicating with a flow path formed in the bottom wall 20a of the frame 20 of the chuck table 18a so that the first workpiece is held in the holding area R1 of the holding surface of the chuck table 18a.

[0093] Next, while the first workpiece is being roughly ground, another workpiece 11 (second workpiece) is loaded onto the chuck table 18b. The second workpiece is loaded onto the chuck table 18b in the same manner as the first workpiece is loaded onto the chuck table 18a.

[0094] When rough grinding the first workpiece, first, the processor 78a controls the motor connected to the turntable 16 to position the chuck table 18a at the rough grinding position B, i.e., to position the chuck table 18b at the loading / unloading position A.

[0095] Then, the processor 78a controls the measuring unit 62a to measure the thickness of the first workpiece. Then, the processor 78a controls the rotation mechanism connected to the chuck table 18a and the grinding unit 42 (specifically, the motor 60) on the rough grinding position B side to rotate both the chuck table 18a and the grinding wheel 50a.

[0096] Next, the thickness of the first workpiece is measured by the measuring unit 62a, and while both the chuck table 18a and the grinding wheel 50a are rotating, the grinding wheel 50a is lowered and the processor 78a controls the moving mechanism 32 (specifically, the motor 40) on the rough grinding position B side and the grinding fluid supply unit 56 so that grinding fluid is supplied to the back surface of the first workpiece.

[0097] This causes the back surface side of the first workpiece to be roughly ground. This rough grinding is continued until the thickness of the first workpiece measured by the measuring unit 62a reaches a predetermined thickness that is thicker than the target finishing thickness.

[0098] Next, while the first workpiece is finish-ground, the second workpiece is rough-ground and another workpiece 11 (third workpiece) is loaded onto the chuck table 18c. The second workpiece is rough-ground in the same manner as the first workpiece. The third workpiece is loaded onto the chuck table 18c in the same manner as the first workpiece is loaded onto the chuck table 18a.

[0099] When finish grinding the first workpiece, first, the processor 78a controls the motor connected to the turntable 16 to position the chuck table 18a at the finish grinding position C, i.e., to position the chuck tables 18b, 18c at the rough grinding position B and the loading / unloading position A, respectively.

[0100] Then, the processor 78a controls the measuring unit 62b to measure the thickness of the first workpiece. Then, the processor 78a controls the rotation mechanism connected to the chuck table 18a and the grinding unit 42 (specifically, the motor 60) on the finish grinding position C side to rotate both the chuck table 18a and the grinding wheel 50b.

[0101] Next, the thickness of the first workpiece is measured by the measuring unit 62b, and while both the chuck table 18a and the grinding wheel 50b are rotating, the grinding wheel 50b is lowered and the processor 78a controls the moving mechanism 32 (specifically, the motor 40) on the finish grinding position C side and the grinding fluid supply unit 56 so that grinding fluid is supplied to the back surface of the first workpiece.

[0102] This finish grinding is continued until the thickness measured by the measuring unit 62b becomes the target finish thickness or the thickness obtained by subtracting the above-mentioned correction thickness from the target finish thickness.

[0103] Specifically, if the height of point P1 measured by the first gauge 64b during this finish grinding is equal to the reference height stored in the memory 78b, the finish grinding of the first workpiece is continued until the thickness measured by the measuring unit 62b becomes the target finish thickness.

[0104] Furthermore, if the height of point P1 measured by the first gauge 64b during this finish grinding is higher than the reference height stored in memory 78b, the correction thickness is identified by referring to the above information stored in memory 78b (i.e., information indicating the relationship between the above change amount ΔH1 and the difference between the above change amount ΔH1 and the change amount ΔH2), and then finish grinding of the first workpiece is continued until the thickness measured by the measuring unit 62b becomes the thickness obtained by subtracting the correction thickness from the target finish thickness.

[0105] Next, the first workpiece is removed from the chuck table 18a and a new workpiece 11 (fourth workpiece) is carried in, while finish grinding of the second workpiece and rough grinding of the third workpiece are performed. The finish grinding of the second workpiece is performed in the same manner as the finish grinding of the first workpiece. The rough grinding of the third workpiece is performed in the same manner as the rough grinding of the first workpiece. The fourth workpiece is carried in to the chuck table 18a in the same manner as the first workpiece is carried in to the chuck table 18a.

[0106] When removing the first workpiece from the chuck table 18a, the processor 78a first controls the motor connected to the turntable 16 to position the chuck table 18a at the loading / unloading position A, i.e., to position the chuck tables 18b, 18c at the finish grinding position C and the rough grinding position B, respectively.

[0107] Next, the processor 78a operates an air supply source communicating with a flow path formed in the bottom wall 20a of the frame 20 of the chuck table 18a so that the workpiece 11 is not sucked toward the chuck table 18a but simply placed on the chuck table 18a. Next, the processor 78a controls the transport unit 74 to transport the first workpiece from the chuck table 18a to the cleaning device 76.

[0108] When the first workpiece is carried into the cleaning device 76, the processor 78a controls the cleaning device 76 and the transport unit 10 so that the first workpiece is washed before being carried into the cassettes 8a, 8b. Furthermore, in the grinding step S2, the above-mentioned operations are repeated until finish grinding of the Nth workpiece (Nth workpiece) 11 is completed.

[0109] In the grinding apparatus 2, when the height of the surrounding region R2 measured by the first gauge 64b increases as the multiple workpieces 11 are ground, a correction thickness corresponding to the error between the actual thickness of each of the multiple workpieces 11 and the thickness measured by the measuring unit 62b is identified, and each of the multiple workpieces 11 is ground until the thickness measured by the measuring unit 62b becomes equal to the thickness obtained by subtracting the correction thickness from the target finishing thickness.

[0110] Therefore, in the grinding device 2, even if it is not possible to fully suppress deformation of the holding surface caused by thermal expansion of each chuck table 18a, 18b, 18c which is heated in conjunction with grinding of the workpiece 11, it is possible to reduce the variation in thickness of multiple workpieces 11 which are ground in sequence so that each reaches the target finishing thickness.

[0111] The above is one aspect of the present invention, and the present invention is not limited to the above. For example, the grinding device of the present invention may be a grinding device including a number of chuck tables other than three. In addition, in the grinding device of the present invention, only finish grinding may be performed without performing rough grinding of the workpiece 11.

[0112] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0113] 2: Grinding equipment 4: Base (4a: recess) 6a, 6b: Cassette placement area 8a, 8b: Cassette 10: Transport unit 11: Workpiece (11a: front side, 11b: back side) 12:Position adjustment mechanism 13: Planned division line 14: Transport unit 15: Device 16: Turntable 18a, 18b, 18c: Chuck table 20: Frame (20a: bottom wall, 20b: side wall) 22: Porous plate 24: Table base 30a, 30b: Support structure 32: Movement mechanism 34: Guide rail 36: Moving plate 38: Screw shaft 40: Motor 42: Grinding unit 44: Spindle housing 46: Spindle 48: Mount 50a, 50b: Grinding wheels 52: Wheel base 54: Grinding wheel 56: Grinding fluid supply unit 58: Nozzle 60: Motor 62a, 62b: measuring unit 64a, 64b: First gauge 66a, 66b: 2nd gauge 74: Transport unit 76: Cleaning equipment 78: Controller (78a: processor, 78b: memory)

Claims

1. A grinding apparatus for grinding a plurality of workpieces in sequence so that each of the workpieces has a target finishing thickness, comprising: a chuck table having a holding surface including a holding area and an enclosing area surrounding the holding area, for holding the plurality of workpieces in order in the holding area; a grinding unit having a spindle with a grinding wheel attached to its tip, the grinding wheel including a plurality of grinding stones arranged in a circularly spaced manner, for rotating the grinding wheel together with the spindle in order to grind each of the plurality of workpieces held in the holding area in order with the plurality of grinding stones; a moving mechanism for adjusting a distance between the chuck table and the grinding unit so that the grinding wheels come into contact with each of the workpieces held in sequence in the holding area; a measuring unit including a first gauge for measuring the height of the surrounding area and a second gauge for measuring the height of the upper surface of each of the plurality of workpieces held in the holding area in sequence, and for measuring the thickness of each of the plurality of workpieces; a controller for controlling the grinding unit, the moving mechanism and the measuring unit; The controller a memory that stores information indicating a relationship between an amount of change in height of the enclosed area caused by heating of the chuck table when the plurality of workpieces are ground in sequence, and an error between an actual thickness of each of the plurality of workpieces and a thickness measured by the measuring unit; a processor that controls the measuring unit to measure the thickness of each of the plurality of workpieces as the plurality of workpieces are ground in sequence, and when a height of the enclosed area measured by the first gauge when each of the plurality of workpieces is ground is higher than a reference height of the enclosed area measured by the first gauge before the plurality of workpieces are ground, identifies a correction thickness corresponding to the error by referring to the information, and then controls the grinding unit and the moving mechanism so that each of the plurality of workpieces is ground until the thickness measured by the measuring unit becomes a thickness obtained by subtracting the correction thickness from the target finish thickness.

2. 2. The grinding apparatus according to claim 1, wherein said information is a coefficient indicating a ratio between said amount of change and said error.

3. a chuck table having a holding surface including a holding area and an enclosing area surrounding the holding area, for holding a plurality of workpieces in sequence in the holding area; a grinding unit having a spindle with a grinding wheel attached to its tip, the grinding wheel including a plurality of grinding stones arranged in a circularly spaced manner, for rotating the grinding wheel together with the spindle in order to grind each of the plurality of workpieces held in the holding area in order with the plurality of grinding stones; a moving mechanism for adjusting a distance between the chuck table and the grinding unit so that the grinding wheels come into contact with each of the workpieces held in sequence in the holding area; a measuring unit including a first gauge for measuring the height of the surrounding area and a second gauge for measuring the height of the upper surface of each of the plurality of workpieces held in the holding area in sequence, and for measuring the thickness of each of the plurality of workpieces; A method for grinding a plurality of workpieces in order to grind each of the workpieces to a target finishing thickness in a grinding apparatus comprising: a reference height measuring step of measuring a reference height of the enclosed area by the first gauge; a grinding step of grinding each of the plurality of workpieces until a thickness measured by the measuring unit after the reference height measuring step becomes the target finishing thickness or a thickness obtained by subtracting a correction thickness from the target finishing thickness, the correction thickness corresponds to an error between an actual thickness of each of the plurality of workpieces and a thickness measured by the measurement unit; In the grinding step, when the height of the enclosed area measured by the first gauge when each of the plurality of workpieces is ground is higher than the reference height, the correction thickness is identified by referring to information indicating the relationship between the error and the amount of change in the height of the enclosed area caused by heating of the chuck table when the plurality of workpieces are ground in sequence, and then each of the plurality of workpieces is ground until the thickness measured by the measuring unit becomes the thickness obtained by subtracting the correction thickness from the target finishing thickness.

4. 4. The method for grinding a workpiece according to claim 3, wherein said information is a coefficient indicating a ratio between said amount of change and said error.

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