Grinding device

Abstract

To provide a grinding device capable of expanding a measurement range in which measurement accuracy is guaranteed.SOLUTION: A grinding device includes a holding table, a grinding unit, first contact type height gauge and a second contact type height gauge each capable of acquiring displacement information in a thickness direction of a workpiece, and a calculation part which calculates a change in thicknesses of the workpiece by utilizing the displacement information. The calculation part calculates the change in thicknesses of the workpiece in a first range from an initial thickness of the workpiece before grinding to a first thickness smaller than the initial thickness based on displacement information which is acquired by using the first contact type height gauge, and calculates the change in the thickness of the workpiece in a second range containing a second thickness smaller than the first thickness based on displacement information which is acquired by using the second contact type height gauge. The first range is a range in which measurement accuracy is guaranteed in the first type height gauge, and the second range is a range in which measurement accuracy is guaranteed in the second type height gauge.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a grinding apparatus having two contact height gauges.

Background Art

[0002] When grinding a workpiece such as a semiconductor wafer with a grinding apparatus, for example, while sucking and holding the workpiece on the holding surface of a holding table and rotating the holding table around a predetermined rotation axis, a grinding wheel that rotates about the rotation axis is lowered, and the workpiece is ground and thinned with the grinding wheel of the grinding wheel.

[0003] In such a grinding apparatus, in a region different from the grinding region where the grinding wheel and the workpiece contact, the workpiece is ground while measuring the thickness of the workpiece with a pair of height gauges (see, for example, Patent Document 1).

[0004] Specifically, during grinding, the height position of the holding surface is measured with a first height gauge, and the height position of the upper surface (i.e., the surface to be ground) of the workpiece sucked and held on the holding surface is measured with a second height gauge. Then, the thickness of the workpiece is calculated from the difference between the height position of the upper surface of the workpiece and the height position of the holding surface.

[0005] By the way, each height gauge has a measurement range in which the measurement accuracy (also referred to as linearity accuracy) is guaranteed. For example, the measurement range in which the measurement accuracy is guaranteed is from 0 μm to 1800 μm or less. Therefore, even if measurement is performed outside the measurement range in which this measurement accuracy is guaranteed, the thickness of the workpiece cannot be accurately measured.

[0006] For example, when thinning a workpiece having a thickness of 3000 μm before grinding to 1000 μm, if the height position of the holding surface is set to 0 μm, the thickness of the workpiece cannot be accurately measured from the thickness of 3000 μm at the start of grinding until the thickness becomes 1800 μm as grinding progresses, and the thickness of the workpiece can be accurately measured only when the thickness becomes 1800 μm or less.

Prior Art Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2014-37045 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention has been made in view of the aforementioned problems, and aims to extend the measurement range in which measurement accuracy is guaranteed, in order to accurately measure the initial thickness of a relatively thick workpiece and also accurately measure the thickness of the workpiece after thinning. [Means for solving the problem]

[0009] According to one aspect of the present invention, the present invention comprises a holding table having a holding surface for suction holding a workpiece, a grinding unit having a spindle and grinding the workpiece held on the holding surface with a grinding wheel mounted on the spindle to thin the workpiece, a first contact type height gauge capable of acquiring displacement information corresponding to the displacement in the thickness direction of the workpiece held on the holding surface, a second contact type height gauge capable of acquiring the displacement information, and a calculation unit having a processor and memory and calculating the change in thickness of the workpiece using the displacement information, wherein the calculation unit obtains the first contact type height gauge A grinding apparatus is provided which, based on the displacement information obtained, calculates the change in the thickness of the workpiece in a first range from the initial thickness of the workpiece before grinding to a first thickness corresponding to a predetermined thickness of the workpiece that is thinner than the initial thickness, and, based on the displacement information obtained using the second contact height gauge, calculates the change in the thickness of the workpiece in a second range including a second thickness of the workpiece that is thinner than the first thickness, wherein the first range is the range in which the measurement accuracy is guaranteed by the first contact height gauge, and the second range is the range in which the measurement accuracy is guaranteed by the second contact height gauge.

[0010] Preferably, the lower limit of the first range is greater than or equal to the upper limit of the second range.

[0011] Preferably, the first contact portion of the first contact-type height gauge and the second contact portion of the second contact-type height gauge are positioned above the porous plate of the holding table so as to be able to contact the workpiece. [Effects of the Invention]

[0012] In a grinding apparatus according to one aspect of the present invention, the change in the thickness of the workpiece is calculated in a first range, from the initial thickness of the workpiece before grinding to a first thickness corresponding to a predetermined thickness of the workpiece that has been thinned beyond the initial thickness, based on displacement information obtained using a first contact-type height gauge. This first range is the range in which the measurement accuracy of the first contact-type height gauge is guaranteed.

[0013] Furthermore, based on the displacement information obtained using the second contact height gauge, the change in the thickness of the workpiece is calculated in a second range that includes the second thickness of the workpiece, which is thinner than the first thickness. This second range is the range in which the measurement accuracy is guaranteed by the second contact height gauge.

[0014] In this way, instead of measuring the thickness of the workpiece by the difference in height positions measured by two contact-type height gauges, each contact-type height gauge is responsible for measuring different ranges of workpiece thickness. This allows for grinding the workpiece while measuring a wide range of thicknesses that exceeds the range in which the measurement accuracy of a single contact-type height gauge is guaranteed. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view of a grinding machine. [Figure 2] This is a perspective view of a grinding machine with a chuck table positioned at the grinding location. [Figure 3] Figure 3(A) is a top view showing the arrangement of the two height gauges, and Figure 3(B) is a graph showing the range in which measurement accuracy is guaranteed. [Figure 4] This is a diagram showing how to set the reference height position of the second height gauge. [Figure 5] This is a diagram showing how to set the reference height position of the first height gauge. [Figure 6] This is a diagram showing how to grind a workpiece. [Figure 7] This is a diagram showing how to grind a workpiece.

Embodiments for Carrying out the Invention

[0016] Embodiments according to an aspect of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of a grinding apparatus 2. The X-axis direction, Y-axis direction, and Z-axis direction shown in FIG. 1 are directions orthogonal to each other.

[0017] The grinding apparatus 2 has a base 4 that supports a plurality of components. The base 4 has a rectangular parallelepiped shape including a long portion along the X-axis direction. On the upper surface of the base 4, a rectangular opening 4a is formed in which the long portion is arranged along the X-axis direction.

[0018] A rectangular table cover 6 is provided in the opening 4a. On both sides of the table cover 6 in the X-axis direction, bellows-shaped cover members 8 that can expand and contract along the X-axis direction are provided. Below the table cover 6 and the pair of cover members 8, an X-axis direction movement mechanism 10 is provided.

[0019] In FIG. 1, the approximate position of the X-axis direction movement mechanism 10 is indicated by an arrow, and the specific structure is omitted. The X-axis direction movement mechanism 10 has a pair of guide rails (not shown) arranged along the X-axis direction.

[0020] On the pair of guide rails, a rectangular plate-shaped moving table (not shown) is slidably attached along the X-axis direction. A nut portion (not shown) is provided on the lower surface side of the moving table.

[0021] A screw shaft (not shown), positioned along the X-axis, is rotatably connected to the nut via multiple balls (not shown). A drive source (not shown), such as a stepping motor, is connected to one end of the screw shaft.

[0022] When the drive source is activated, the moving table moves along the X-axis. A disc-shaped chuck table (holding table) 12 is provided on the table cover 6. As shown in Figure 4, the chuck table 12 has a disc-shaped frame 14 made of non-porous ceramics.

[0023] A disc-shaped porous plate 16 made of porous ceramics is fixed to the upper surface of the frame 14. Multiple first channels are formed radially in the recesses of the frame 14. In addition, a second channel is formed at the radial center of the recess, penetrating the frame 14 in the thickness direction.

[0024] A suction source 18, such as a vacuum pump, is connected to the second channel via a solenoid valve 18a. When the solenoid valve 18a is opened while the suction source 18 is operating, negative pressure is transmitted to the upper surface of the porous plate 16 via the first channel, the second channel, etc.

[0025] The upper surfaces of the frame 14 and the porous plate 16 are substantially flush and function as a holding surface 12a that suctions and holds the workpiece 11 (see Figure 1). As shown in Figure 4, the holding surface 12a has a conical shape in which the central part protrudes compared to the outer periphery. The amount of protrusion is, for example, about 10 μm to 20 μm, but in Figure 4, the amount of protrusion is exaggerated for the sake of explanation.

[0026] An annular table base 20 is fixed to the underside of the chuck table 12 with fixing members (not shown) such as bolts. An annular support base (not shown) with approximately the same diameter as the table base 20 is provided on the underside of the table base 20.

[0027] An annular bearing (not shown) is provided inside a through hole located in the radial center of the support base, and a cylindrical rotating shaft 22 is fixed inside the bearing. In other words, the chuck table 12 is supported by the support base via the bearing.

[0028] The support base is supported by a tilt adjustment mechanism (not shown). The tilt adjustment mechanism adjusts the tilt of the chuck table 12 by adjusting the spatial tilt of the support base, making a portion of the holding surface 12a approximately parallel to the grinding surface 50d (see Figure 6), which will be described later.

[0029] The tilt adjustment mechanism includes one fixed axis (not shown) whose length in the Z-axis direction is constant, and two movable axes (not shown) whose length in the Z-axis direction is variable. The one fixed axis and the two movable axes are arranged at approximately equal intervals along the circumferential direction of the chuck table 12. The tilt adjustment mechanism is also supported by a movable plate of the X-axis direction movement mechanism 10.

[0030] The upper end of the aforementioned rotating shaft 22 is connected to the lower surface of the chuck table 12. A third flow path is formed in the rotating shaft 22 for transmitting negative pressure to the chuck table 12. In Figure 4, for the sake of explanation, the third flow path of the rotating shaft 22 is shown in a simplified manner, but the third flow path is connected to the suction source 18 via a rotary joint in order to achieve both high-speed rotation of about 100 rpm to 300 rpm and prevention of vacuum leakage.

[0031] A driven pulley (not shown) is fixed to the outer circumference of the rotating shaft 22. A rotational drive source (not shown), such as a servo motor, is placed on the moving plate of the X-axis movement mechanism 10, and a drive pulley (not shown) is fixed to the output shaft of the rotational drive source.

[0032] An endless belt (not shown) is attached to the driven pulley and the drive pulley. When the rotational drive source is operated, the power from the rotational drive source is transmitted, and the chuck table 12 rotates around the rotation axis 22. In Figure 4, the rotation center 12b of the chuck table 12 is shown by a dashed line. The rotation center 12b passes through the center of the holding surface 12a.

[0033] Returning to Figure 1, a support column 24 is provided on the rear side (one side in the X-axis direction) of the base 4, with its longitudinal portion aligned along the Z-axis direction. A Z-axis direction movement mechanism 26 is provided on one side of the support column 24. The Z-axis direction movement mechanism 26 has a pair of guide rails 28, each arranged substantially parallel to the Z-axis direction.

[0034] A movable plate 30 is slidably fixed to a pair of guide rails 28. A nut portion (not shown) is provided on the back side of the movable plate 30, and a screw shaft 32, which is arranged along the Z-axis direction, is rotatably connected to this nut portion via a plurality of balls (not shown).

[0035] A drive source 34, such as a stepping motor, is connected to the upper end of the screw shaft 32. By rotating the screw shaft 32 with the drive source 34, the movable plate 30 moves along the Z-axis direction.

[0036] A grinding unit 40 is provided on the surface side of the movable plate 30. The grinding unit 40 has a cylindrical support 42 fixed to the surface side of the movable plate 30. Inside the support 42 is a cylindrical spindle housing 44 whose longitudinal portion is arranged along the Z-axis direction.

[0037] A portion of a cylindrical spindle 46, whose longitudinal portion is aligned along the Z-axis, is rotatably housed in the spindle housing 44. A rotational drive source (not shown), such as a servo motor, is provided near the upper end of the spindle 46.

[0038] The lower end of the spindle 46 protrudes below the lower ends of the support 42 and the spindle housing 44. The upper side of a disc-shaped mount 48 made of metal is fixed to the lower end of the spindle 46.

[0039] An annular grinding wheel 50 is fixed to the lower side of the mount 48 using fixing members (not shown), such as bolts. In this way, the grinding wheel 50 is mounted on the spindle 46 via the mount 48.

[0040] The grinding wheel 50 has an annular wheel base 50a made of a metal such as an aluminum alloy (see Figure 4). On the lower surface of the wheel base 50a, multiple segment-shaped grinding wheels 50b are arranged at approximately equal intervals along the circumferential direction of the wheel base 50a.

[0041] When the spindle 46 is rotated, the grinding wheel 50 rotates around the spindle 46 as its axis of rotation. At this time, as shown in Figure 6, the grinding surface 50d is formed by the trajectories of the lower surfaces 50c of the multiple grinding wheels 50b.

[0042] Returning to Figure 1, the chuck table 12 moves between the loading / unloading position A1, located on the front side (the other side in the X-axis direction) of the base 4, and the grinding position A2, by the X-axis movement mechanism 10.

[0043] When the chuck table 12 is positioned at loading / unloading position A1, an unground workpiece 11 is loaded into the chuck table 12, or a ground workpiece 11 is unloaded from the chuck table 12.

[0044] In this embodiment, the workpiece 11 to be ground has a thickness greater than the thickness corresponding to a predetermined diameter of a silicon wafer as defined by the SEMI (Semiconductor Equipment and Materials International) standard.

[0045] The workpiece 11 in this embodiment has a diameter of 8 inches (200 mm ± 0.2 mm), but a thickness of 3600 μm, which is sufficiently thicker than the thickness of an 8-inch silicon wafer specified in the SEMI standard (i.e., 725 ± 20 μm).

[0046] However, the thickness of the workpiece 11 may be a predetermined value of 2.0 mm or more and 20.0 mm or less. In this embodiment, the workpiece 11 is a single disc-shaped substrate made of glass. However, the workpiece 11 may also be a so-called laminated wafer, which is made up of multiple silicon wafers stacked on top of each other.

[0047] The workpiece 11 has one surface 11a that is attracted by the holding surface 12a and another surface 11b that becomes the grinding surface. The distance between the one surface 11a and the other surface 11b is the thickness of the workpiece 11. In this embodiment, the direction from the one surface 11a to the other surface 11b is conveniently referred to as the thickness direction 11c of the workpiece 11.

[0048] When grinding the workpiece 11, first, the chuck table 12, which holds the workpiece 11 by suction on its holding surface 12a, is positioned at the grinding position A2 as shown in Figure 2. Figure 2 is a perspective view of the grinding apparatus 2 with the chuck table 12 positioned at the grinding position A2.

[0049] Near the chuck table 12 located at grinding position A2, two contact-type height gauges are provided. The first height gauge (first contact-type height gauge) 52 is positioned closer to the support column 24 in the X-axis direction than the second height gauge (second contact-type height gauge) 54.

[0050] However, the positions of the first height gauge 52 and the second height gauge 54 may be swapped. In other words, the second height gauge 54 may be positioned closer to the support column 24 than the first height gauge 52.

[0051] As shown in Figure 3(A), the first height gauge 52 has a main body 52a fixed to the base 4. The base end of a cantilevered arm 52b is connected to the main body 52a. The tip of the arm 52b is provided with a cylindrical head portion 52c made of metal.

[0052] The head section 52c and arm 52b are attached to the main body section 52a so that they droop downwards under their own weight and assume a forward-leaning posture. In addition, a lifting mechanism (not shown) including a motor (not shown) is provided at the base end of the arm 52b to raise and lower the head section 52c relatively significantly as needed.

[0053] The lower end of the head portion 52c is provided with a hemispherical contact portion (first contact portion) 52d made of diamond (see Figure 4). When grinding the workpiece 11, the main body portion 52a is positioned in a lowered position, and the contact portion 52d is brought into contact with the workpiece 11 which is held by the holding surface 12a (see Figure 6).

[0054] This allows the displacement of the height position of the other surface 11b of the workpiece 11 in the thickness direction 11c to be obtained. During grinding, the contact portion 52d continuously contacts the other surface 11b, thereby obtaining displacement information of the other surface 11b in real time.

[0055] When setting the reference height position of the first height gauge 52, the main body 52a is positioned in the lowered position (see Figure 5). Conversely, when the first height gauge 52 does not acquire displacement information of the other surface 11b, the main body 52a is positioned in the raised position (see Figure 4).

[0056] Incidentally, the head portion 52c is configured to be rotatable relative to the arm 52b. The axis of rotation of the head portion 52c is positioned along a direction approximately perpendicular to the plane of the paper in Figure 3(A). If a portion of the contact portion 52d continues to contact the workpiece 11, only this portion will wear down, causing uneven wear of the contact portion 52d.

[0057] If the contact portion 52d becomes unevenly worn, the operator can adjust the rotation angle of the head portion 52c to bring the area that is not unevenly worn into contact with the workpiece 11. This prevents the metal head portion 52c from coming into contact with the workpiece 11.

[0058] The second height gauge 54 also has a main body 54a, an arm 54b, and a head 54c. The head 54c and arm 54b are attached to the main body 54a so that they droop downwards under their own weight and tilt forward.

[0059] The lower end of the head portion 54c is also provided with a hemispherical contact portion (second contact portion) 54d (see Figure 4) made of diamond. When the head portion 54c contacts the other surface 11b, displacement information of the other surface 11b can be acquired in real time, similar to the head portion 52c.

[0060] The head section 54c, like the head section 52c, is configured to be able to move up and down by a lifting mechanism (not shown). When acquiring displacement information of the other surface 11b with the second height gauge 54, the main body section 54a is placed in the lowered position, and the contact section 54d is brought into contact with the workpiece 11, which is held in place by the holding surface 12a due to its own weight (see Figure 7).

[0061] When setting the reference height position of the second height gauge 54, the main body 54a is positioned in the lowered position (see Figure 4). In contrast, when displacement information is not acquired by the second height gauge 54, the main body 54a is positioned in the raised position so that the contact portion 54d is sufficiently far from the other surface 11b (see Figure 5).

[0062] The head portion 54c is also configured to rotate relative to the arm 54b. Therefore, by adjusting the rotation angle of the head portion 54c, the operator can bring the area of ​​the contact portion 54d that is not unevenly worn into contact with the workpiece 11.

[0063] FIG. 3(A) is a top view showing the arrangement of the first height gauge 52 and the second height gauge 54. The contact portion 52d and the contact portion 54d are arranged above the porous plate 16 of the chuck table 12 so as to be able to contact the workpiece 11, respectively.

[0064] In FIG. 3(A), the contact portions 52d, 54d are arranged between the rotation center 12b of the chuck table 12 and the radius of the porous plate 16 (i.e., the inner radius of the frame body 14). However, the distances from the rotation center 12b to the contact portions 52d, 54d are different.

[0065] Specifically, the distance B1 from the contact portion 52d (refer to the position of the head portion 52c) to the rotation center 12b is smaller than the distance B2 from the contact portion 54d (refer to the position of the head portion 54c) to the rotation center 12b (B1 < B2). However, the distances from the rotation center 12b to each of the contact portions 52d, 54d may be the same (B1 = B2).

[0066] If the distances from each of the contact portions 52d, 54d to the rotation center 12b are the same, the influence of the in-plane variation in the thickness of the workpiece 11 on the displacement information can be reduced as compared with the case where the distance B1 is made smaller than the distance B2.

[0067] As shown in FIG. 3(B), the first height gauge 52 has a range in which the measurement accuracy is guaranteed in advance so that the change in the thickness of the workpiece 11 can be accurately detected in a predetermined thickness range (the first range 52e). The first range 52e in this embodiment is a range of 1800 μm or more and 3600 μm or less.

[0068] On the other hand, the second height gauge 54 has a range in which the measurement accuracy is guaranteed in advance so that the change in the thickness of the workpiece 11 can be accurately detected in a predetermined thickness range (the second range 54e) different from the first range 52e. The second range 54e in this embodiment is a range of 0 μm or more and 1800 μm or less.

[0069] Figure 3(B) is a graph showing the range in which measurement accuracy is guaranteed for the first height gauge 52 and the second height gauge 54. Measurement accuracy is evaluated, for example, by the linearity of a graph created with the displacement of the height gauge on the horizontal axis and the voltage value output from the height gauge on the vertical axis.

[0070] In this embodiment, the linearity of the first height gauge 52 and the second height gauge 54 is specified as ±0.3%FS (Full Scale). That is, ±0.3%FS is guaranteed in each of the first range 52e and the second range 54e described above.

[0071] Although each of the contact portions 52d and 54d can be physically moved within a range from -1000 μm to +6000 μm with a predetermined height position (0 μm) as the reference in a predetermined direction, as described above, the range in which accurate measurement precision is guaranteed is limited, as shown in the first range 52e and the second range 54e.

[0072] In this way, instead of measuring the thickness of the workpiece 11 by the difference in height positions measured by the two height gauges, the first height gauge 52 and the second height gauge 54 each measure different ranges of the workpiece 11's thickness, allowing the workpiece 11 to be ground while measuring a wide range of thicknesses that exceeds the range in which the measurement accuracy of a single height gauge is guaranteed.

[0073] In this embodiment, the lower limit of the first range 52e is equal to the upper limit of the second range 54e. By setting the first range 52e and the second range 54e continuously in this way, a wider range can be measured continuously compared to the case where the first range 52e and the second range 54e overlap in a fixed area.

[0074] Furthermore, if the lower limit of the first range 52e is greater than or equal to the upper limit of the second range 54e, the first range 52e does not need to be continuous with the second range 54e. For example, the first range 52e and the second range 54e may be discontinuous. However, in this case, there will be a measurement range between the first range 52e and the second range 54e where measurement accuracy is not guaranteed.

[0075] Furthermore, using three or more height gauges, the thickness of the workpiece 11 can be measured with guaranteed accuracy in three or more continuous or discontinuous measurement ranges. This further extends the measurement range with guaranteed accuracy.

[0076] Referring to Figures 1 and 2, other elements of the grinding apparatus 2 will be described. The grinding apparatus 2 includes an X-axis movement mechanism 10, a rotation drive source for the chuck table 12, a suction source 18, a solenoid valve 18a, a Z-axis movement mechanism 26, a grinding unit 40, a first height gauge 52 and a second height gauge 54, and a control unit 56 that controls their operation.

[0077] The control unit 56 is composed of a computer that includes, for example, a processor (processing unit) 58, such as a CPU (Central Processing Unit), and a memory (storage device) 60.

[0078] The memory 60 includes main memory such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and ROM (Read Only Memory), and auxiliary memory such as flash memory, hard disk drives, and solid-state drives.

[0079] The auxiliary storage device stores software, including a predetermined program. The functions of the control unit 56 are realized by operating the processing unit and other components according to this software.

[0080] By executing a predetermined program in the processor 58, the control unit 56 functions as a calculation unit 62 that calculates the change in the thickness of the workpiece 11 using displacement information from the first height gauge 52 and the second height gauge 54.

[0081] Next, referring to Figures 4 to 7, a method for grinding the workpiece 11 while calculating its thickness in the calculation unit 62 will be described. First, as shown in Figure 4, the reference height position of the second height gauge 54 is set. Figure 4 shows the process of setting the reference height position of the second height gauge 54.

[0082] Specifically, the chuck table 12, in which the workpiece 11 is not held by suction on the holding surface 12a, is moved to the grinding position A2, and the chuck table 12 is rotated around the rotation axis 22 while the contact portion 54d of the second height gauge 54 is brought into contact with the holding surface 12a.

[0083] This sets the reference height position of the second height gauge 54 to the holding surface 12a. In this embodiment, the second height gauge 54 is guaranteed to have measurement accuracy in the Z-axis direction from a thickness of 0 μm (i.e., the height position corresponding to the holding surface 12a) to a thickness of 1800 μm, and is responsible for measuring this thickness range.

[0084] Next, the chuck table 12 is returned to the loading / unloading position A1, and one side 64a of the disc-shaped jig plate 64 is held in place by the holding surface 12a. The jig plate 64 is made of ceramics such as alumina and has a thickness of 1800 μm. After holding in place by suction, the chuck table 12 is moved to the grinding position A2.

[0085] Next, as shown in Figure 5, the reference height position of the first height gauge 52 is set to the other side (top surface) 64b of the jig plate 64. Figure 5 shows the process of setting the reference height position of the first height gauge 52.

[0086] Specifically, the chuck table 12, which holds the jig plate 64 by suction, is moved to the grinding position A2, and the chuck table 12 is rotated around the rotation axis 22 while the contact portion 52d of the first height gauge 52 is brought into contact with the other surface 64b of the jig plate 64. This sets the reference height position of the first height gauge 52 to the other surface 64b of the jig plate 64.

[0087] The first height gauge 52 of this embodiment is guaranteed to have measurement accuracy in the Z-axis direction from a thickness of 1800 μm of the workpiece 11 (i.e., the height position corresponding to the other surface 64b of the jig plate 64) to a thickness of 3600 μm (i.e., the initial thickness of the workpiece 11 before grinding), and is responsible for measuring this thickness range.

[0088] Next, the chuck table 12 is returned to the loading / unloading position A1, the jig plate 64 is swapped with the workpiece 11, and the workpiece 11 is held in place by suction on the holding surface 12a. Then, the chuck table 12, with the workpiece 11 held in place by suction, is moved to the grinding position A2, and grinding is started.

[0089] Figure 6 shows the grinding process of the workpiece 11 when its thickness falls within a first range 52e, from an initial thickness 11c0 (3600 μm in this embodiment) before grinding to a predetermined first thickness 11c1 (1800 μm in this embodiment), which is thinner than the initial thickness 11c0.

[0090] During grinding, the chuck table 12, which holds the workpiece 11 by suction, is rotated around the rotation axis 22 at a predetermined speed, and the grinding wheel 50, which rotates around the spindle 46 as the rotation axis, is lowered along the Z-axis at a predetermined machining feed rate (infeed grinding).

[0091] When the grinding surface 50d comes into contact with the other surface 11b of the workpiece 11, the other surface 11b is ground. During grinding, the area where multiple grinding wheels 50b and the other surface 11b come into contact becomes a predetermined arc-shaped region 50e (see Figure 2). Grinding water such as pure water is supplied to the vicinity of this arc-shaped region 50e from a nozzle (not shown) at a predetermined flow rate.

[0092] During grinding, both contact portions 52d and 54d are in contact with the other surface 11b, but only the first height gauge 52, whose measurement accuracy is guaranteed in the first range 52e described above, can accurately measure the thickness.

[0093] Therefore, when the workpiece 11 is relatively thick, the calculation unit 62 calculates the change in the thickness of the workpiece 11 based on the displacement information obtained using the first height gauge 52. On the other hand, when the workpiece 11 gradually becomes thinner, the first height gauge 52 can no longer accurately measure the thickness of the workpiece 11.

[0094] Therefore, as shown in Figure 7, in the second range 54e which includes the second thickness 11c2 (i.e., the target thickness achieved by grinding) of the workpiece 11 that is thinner than the first thickness 11c1, the calculation unit 62 calculates the change in the thickness of the workpiece 11 based on the displacement information obtained using the second height gauge 54.

[0095] Figure 7 shows the grinding process of the workpiece 11 when its thickness is within the second range 54e. In this case, both contact portions 52d and 54d are in contact with the other surface 11b, but only the second height gauge 54, whose measurement accuracy is guaranteed within the second range 54e, can accurately measure the thickness.

[0096] After grinding the workpiece 11 in this manner and thinning it to a second thickness 11c2, grinding is terminated and the chuck table 12 is returned to the loading / unloading position A1.

[0097] In this embodiment, instead of measuring the thickness of the workpiece 11 by the difference in height positions measured by two height gauges, the first height gauge 52 and the second height gauge 54 are each responsible for measuring different ranges of the workpiece 11's thickness. This allows the workpiece 11 to be ground while measuring a wide range of thicknesses that exceeds the range in which the measurement accuracy of a single height gauge is guaranteed.

[0098] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the object of the present invention. For example, multiple workpieces 11 can be ground by sequentially feeding them into the grinding device 2.

[0099] In this case, since the reference height position set on the second height gauge 54 (see Figure 4) and the reference height position set on the first height gauge 52 (see Figure 5) can be used, it is not necessarily required to set the reference height position each time before grinding a workpiece 11. [Explanation of symbols]

[0100] 2: Grinding device, 4: Base, 4a: Opening 6: Table cover, 8: Cover member, 10: X-axis movement mechanism 11: Workpiece, 11a: One side, 11b: Other side, 11c: Thickness direction 11c0: Initial thickness, 11c1: First thickness, 11c2: Second thickness 12: Chuck table (holding table), 12a: Holding surface, 12b: Center of rotation 14: Frame, 16: Porous plate, 18: Suction source, 18a: Solenoid valve 20: Table base, 22: Rotation axis 24: Support column, 26: Z-axis movement mechanism, 28: Guide rail, 30: Moving plate 32: Screw shaft, 34: Drive source 40: Grinding unit, 42: Support, 44: Spindle housing, 46: Spindle 48: Mount, 50: Grinding wheel, 50a: Wheel base, 50b: Grinding wheel 50c: Bottom surface, 50d: Grinding surface, 50e: Arc-shaped area 52: First height gauge (first contact type height gauge), 52a: Main body, 52b: Arm 52c: Head portion, 52d: Contact portion (first contact portion), 52e: First range 54: Second height gauge (second contact type height gauge), 54a: Main body, 54b: Arm 54c: Head section, 54d: Contact section (second contact section), 54e: Second range 56: Control unit, 58: Processor, 60: Memory, 62: Calculation unit 64: Jig plate, 64a: one side, 64b: other side A1: Loading / unloading location, A2: Grinding location B1,B2:Distance

Claims

1. A holding table having a holding surface for suction and holding a workpiece, A grinding unit having a spindle, which grinds the workpiece held on the holding surface with a grinding wheel mounted on the spindle to thin the workpiece, A first contact-type height gauge capable of acquiring displacement information corresponding to the displacement in the thickness direction of the workpiece held by suction on the holding surface, A second contact-type height gauge capable of acquiring the displacement information, A calculation unit having a processor and memory, which uses the displacement information to calculate the change in the thickness of the workpiece, Equipped with, The calculation unit is, Based on the displacement information obtained using the first contact-type height gauge, the change in the thickness of the workpiece is calculated within a first range, from the initial thickness of the workpiece before grinding to a first thickness corresponding to a predetermined thickness of the workpiece that has been thinned beyond the initial thickness. Based on the displacement information obtained using the second contact-type height gauge, the change in the thickness of the workpiece is calculated in a second range that includes a second thickness of the workpiece that is thinner than the first thickness. The first range is the range in which measurement accuracy is guaranteed in the first contact-type height gauge. The grinding apparatus is characterized in that the second range is a range in which measurement accuracy is guaranteed in the second contact-type height gauge.

2. The grinding apparatus according to claim 1, characterized in that the lower limit of the first range is greater than or equal to the upper limit of the second range.

3. The grinding apparatus according to claim 1 or 2, characterized in that the first contact portion of the first contact type height gauge and the second contact portion of the second contact type height gauge are arranged above the porous plate of the holding table so as to be able to contact the workpiece.

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