Method for grinding a workpiece

Abstract

A grinding method for a workpiece is provided, wherein a warped workpiece is held by a chuck table and ground appropriately. The grinding method involves grinding the workpiece in a grinding apparatus having a chuck table and a grinding unit. The chuck table has a first porous portion on its upper surface and a second porous portion in an annular shape surrounding the first porous portion. The grinding unit has a grinding tool. The grinding method comprises the following steps: a first grinding step, grinding the workpiece in which the central portion is held by the first porous portion of the chuck table; and a second grinding step, grinding the workpiece in which the central portion and the outer peripheral portion are held by the first and second porous portions of the chuck table.

Description

Technical Field

[0001] This invention relates to a grinding method for a workpiece that uses a chuck table to hold the workpiece and uses a grinding wheel to grind the workpiece to obtain a result of a specified thickness. Background Technology

[0002] In forming the device chip used in electronic devices, firstly, devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed on the front side of a wafer-shaped semiconductor wafer. At this point, multiple such devices are arranged in a matrix on the front side of the semiconductor wafer. Then, the semiconductor wafer is thinned by grinding from the back side, dividing the semiconductor wafer into individual devices to form a semiconductor chip.

[0003] Next, multiple semiconductor chips are mounted on a printed circuit board (PCB). At this time, the electrodes of each semiconductor chip are connected to the respective electrodes of the PCB. Then, when the PCB with the mounted semiconductor chips is sealed with resin, a flat package substrate is formed. When the package substrate is thinned by grinding from the back side and then divided into individual semiconductor chips, individual device chips are obtained.

[0004] Grinding of semiconductor wafers and packaging substrates is performed by a grinding apparatus (see Patent Document 1). The grinding apparatus includes a chuck stage for holding and gripping workpieces such as semiconductor wafers; and a grinding unit for grinding the workpiece held by the chuck stage. The grinding unit has an annular grinding wheel at its lower end. Furthermore, grinding tools arranged in a circular pattern are mounted on the lower surface of the grinding wheel, opposite the upper surface of the chuck stage.

[0005] When grinding a workpiece, firstly, the workpiece is placed on the chuck table, which holds it in place. At this point, the side not to be ground is brought into contact with the chuck table, so that the surface to be ground is exposed upwards. Then, the chuck table and the grinding wheel are rotated, causing the grinding wheel to descend. The grinding wheel, moving along a circular track, then contacts the surface to be ground on the workpiece, thus grinding it.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-200545

[0007] When multiple devices are formed on a semiconductor wafer, warping can sometimes occur on the semiconductor wafer due to forces generated on the various films constituting the devices. Additionally, warping can sometimes occur on the packaging substrate due to forces generated in the printed circuit board or sealing resin contained within the packaging substrate. In grinding apparatuses, it is sometimes desirable to grind workpieces with concave warped surfaces.

[0008] When a warped workpiece is placed on the chuck table, the central portion of the workpiece becomes lower than the outer periphery, causing the outer periphery to float. In this state, when the workpiece is pulled in place by the chuck table, negative pressure (attraction force) sometimes leaks out from the gap between the outer periphery and the chuck table, making it impossible to hold the workpiece. Therefore, when holding a warped workpiece in place by the chuck table, it is advisable to press down on the outer periphery from above to flatten the workpiece and suppress the leakage of negative pressure.

[0009] However, when the force causing the workpiece to warp is strong, it is not easy to press down the outer periphery of the workpiece with a force sufficient to deform it to the extent that it can be held by the chuck table. In addition, even if the workpiece can be deformed flat, the outer periphery of the workpiece may lift up again because a force is generated on the workpiece to restore its original shape. Summary of the Invention

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide a grinding method for a workpiece, wherein a warped workpiece is stably held by a chuck table and the workpiece is ground to a specified thickness.

[0011] According to one aspect of the present invention, a grinding method for a workpiece is provided, wherein the workpiece, which is concave and warped with a central portion lower than its outer peripheral portion, is ground from the back side in a grinding apparatus until a first thickness is achieved. The grinding apparatus comprises: a chuck table having a circular plate-shaped first porous portion, an annular second porous portion, a partition, and a frame on its upper surface; the outer diameter of the first porous portion is smaller than the diameter of the workpiece; the second porous portion surrounds the first porous portion and its outer diameter corresponds to the diameter of the workpiece; the partition is disposed between the first porous portion and the second porous portion; the frame surrounds the second porous portion; the chuck table rotates about a rotation axis penetrating the center of the upper surface and attracts and holds the workpiece; and a grinding unit having a zone above the center of the upper surface passing through the chuck table. A grinding wheel moving on a circular track in a domain provides grinding water to the workpiece held by the chuck table while grinding the exposed back side of the workpiece. The grinding method comprises the following steps: a first grinding step, in which the grinding wheel of the grinding unit grinds the workpiece from the back side, where the front side faces the upper surface of the chuck table and the central portion is held by the first perforated portion of the chuck table, until a second thickness greater than the first thickness is achieved; and a second grinding step, in which the grinding wheel of the grinding unit grinds the workpiece from the back side, where the central portion and the outer periphery are held by the first and second perforated portions of the chuck table, until the first thickness is achieved.

[0012] Additionally, according to another aspect of the present invention, a method for grinding a workpiece is provided, wherein the workpiece, which is concave and warped with a central portion lower than its outer peripheral portion, is ground from the back side in a grinding apparatus until a first thickness is achieved. The grinding apparatus comprises: a chuck table having a circular plate-shaped first porous portion, an annular second porous portion, a partition, and a frame on its upper surface; the outer diameter of the first porous portion is smaller than the diameter of the workpiece; the second porous portion surrounds the first porous portion and its outer diameter corresponds to the diameter of the workpiece; the partition is disposed between the first porous portion and the second porous portion; the frame surrounds the second porous portion; the chuck table rotates about a rotation axis penetrating the center of the upper surface and attracts and holds the workpiece; and a grinding unit having a grinding tool that moves on an annular track in a region above the center of the upper surface of the chuck table, while... The method of grinding a workpiece is characterized by providing grinding water to the workpiece held by the chuck table and grinding the exposed back side of the workpiece using a grinding tool, wherein the grinding method comprises the following steps: a first holding step in which the front side of the workpiece is positioned opposite the upper surface of the chuck table, and the central portion of the workpiece is held by suction using the first porous portion of the chuck table; a first grinding step in which the workpiece is ground from the back side using the grinding tool of the grinding unit until it reaches a second thickness greater than the first thickness; a second holding step in which the central portion and the outer peripheral portion of the workpiece are held by suction using the first porous portion and the second porous portion of the chuck table; and a second grinding step in which the workpiece is ground from the back side using the grinding tool of the grinding unit until it reaches the first thickness.

[0013] Furthermore, according to another aspect of the present invention, a grinding method for a workpiece is provided, wherein the workpiece, which is concave and warped with a central portion lower than its outer peripheral portion, is ground from the back side in a grinding apparatus until a first thickness is achieved. The grinding apparatus comprises: a chuck table having a circular plate-shaped first porous portion, an annular second porous portion, a partition portion, and a frame on its upper surface; the outer diameter of the first porous portion is smaller than the diameter of the workpiece; the second porous portion surrounds the first porous portion and its outer diameter corresponds to the diameter of the workpiece; the partition portion is disposed between the first porous portion and the second porous portion; the frame surrounds the second porous portion; the chuck table rotates about a rotation axis penetrating the center of the upper surface and attracts and holds the workpiece; and a grinding unit having a grinding surface passing through the chuck table. A grinding tool moving on a ring track in the area above the center of the workpiece, while providing grinding water to the workpiece held by the chuck table, grinds the exposed back side of the workpiece using the grinding tool. The grinding method for the workpiece is characterized by the following steps: a first holding step, in which the front side of the workpiece is positioned opposite the upper surface of the chuck table, and the central portion of the workpiece is held by suction using the first perforated portion of the chuck table; and a grinding step, in which the workpiece is ground from the back side using the grinding tool of the grinding unit until it reaches the first thickness; and during the grinding step, a second holding step is performed, in which the outer peripheral portion of the workpiece is held by suction using the second perforated portion of the chuck table.

[0014] Preferably, during the grinding of the workpiece, the grinding tool contacts the back side of the workpiece as it travels from the region above the center of the upper surface of the chuck table of the annular track to the region above the frame of the upper surface of the chuck table.

[0015] Furthermore, it is preferable that when the workpiece is held by suction using the second porous portion of the chuck table, the grinding water reaching the outer periphery of the second porous portion prevents leakage of the suction force exerted on the workpiece by the second porous portion.

[0016] In one aspect of the workpiece grinding method of the present invention, a grinding apparatus having a chuck table is used. The chuck table has a first porous portion in the shape of a circular plate and a second porous portion in the shape of an annular region surrounding the first porous portion on its upper surface. Furthermore, the workpiece is placed on the upper surface of the chuck table, and firstly, the central portion of the workpiece is attracted and held using the first porous portion. Even if warping occurs in the workpiece, it is relatively easy to attract and hold only the central portion of the workpiece.

[0017] When the workpiece is ground in this state, the outer peripheral portion is ground more concentratedly. Furthermore, the force causing the workpiece to warp is weakened, and the force required to restore the workpiece to its original shape after deformation is reduced. This change becomes significant in the outer peripheral portion of the workpiece.

[0018] Therefore, when the workpiece is ground to a certain extent, the outer periphery of the workpiece is held by suction using the second porous section, thereby holding the entire area of ​​the workpiece by suction using the chuck table. This suction holding is easier than holding the entire area of ​​the workpiece before grinding. Furthermore, the possibility of the outer periphery of the workpiece lifting again is reduced. Therefore, the workpiece is held stably and appropriately by suction, enabling stable grinding until the final thickness reaches the target first thickness.

[0019] Therefore, according to the present invention, a grinding method for a workpiece is provided, which uses a chuck table to stably hold a warped workpiece and grinds the workpiece to a specified thickness. Attached Figure Description

[0020] Figure 1 It is a schematic three-dimensional view of the grinding device.

[0021] Figure 2 It is a schematic three-dimensional view showing the chuck table and the workpiece.

[0022] Figure 3 It is a cross-sectional view schematically showing the situation where the central part of the workpiece is attracted and held by the first perforated part of the chuck table.

[0023] Figure 4 It is a cross-sectional view schematically showing the grinding of a workpiece whose central part is held by the suction of the first multi-hole section of the chuck table using a grinding wheel.

[0024] Figure 5 It is a cross-sectional view schematically showing the case where the outer periphery of the workpiece is attracted and held using the second perforated section of the chuck table.

[0025] Figure 6 It is a cross-sectional view schematically showing the grinding of a workpiece held by the first and second bore sections of the chuck table.

[0026] Figure 7 It is a top view schematically showing the area where the grinding tool contacts the workpiece.

[0027] Figure 8 (A) is a flowchart illustrating the steps in one method of grinding a workpiece. Figure 8(B) is a flowchart illustrating the steps in another method of grinding a workpiece.

[0028] Label Explanation

[0029] 1: Workpiece; 1a: Front side; 1b: Back side; 1c: Central part; 1d: Outer periphery; 2: Grinding device; 4: Device base; 4a: Opening; 6: Chuck table; 6a: First multi-hole section; 6b: Second multi-hole section; 6c: Partition; 6d: Frame; 6e: Table base; 8: X-axis moving table; 10: Loading / unloading area; 12: Machining area; 14: Grinding unit; 16: Support; 18: Z-axis guide rail; 20: Z-axis movement Plate; 22: Z-axis ball screw; 24: Z-axis pulse motor; 26: spindle housing; 28: spindle; 30: wheel mounting seat; 32: grinding wheel; 34: grinding tool; 36a: first suction path; 36b: second suction path; 38a: first suction source; 38b: second suction source; 40a: first switching part; 40b: second switching part; 42: rotary shaft; 44: grinding water; 46a, 46b: thickness; 48: annular track; 50: contact area. Detailed Implementation

[0030] Embodiments of the present invention will be described with reference to the accompanying drawings. In the grinding method for the workpiece of this embodiment, a grinding apparatus is used to grind a workpiece that has developed warping, thereby thinning it. First, the workpiece that is the object of grinding will be described. Figure 2 In the example of workpiece 1, a disc-shaped wafer is schematically shown.

[0031] The workpiece 1 is, for example, a generally circular substrate made of materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductor materials, or materials such as sapphire, glass, or quartz. The glass is, for example, alkali glass, alkali-free glass, soda lime glass, lead glass, borosilicate glass, or quartz glass.

[0032] Multiple devices, such as ICs or LSIs, are arranged in a matrix on the front side 1a of the workpiece 1. When the workpiece 1 is thinned by grinding from the back side 1b and then divided into individual devices, individual semiconductor chips are obtained. Each semiconductor chip is used in electronic devices such as mobile phones or personal computers. The semiconductor chips are used, for example, in a state sealed with molding resin (sealing resin).

[0033] In manufacturing packaged device chips, firstly, semiconductor chips are mounted on a printed circuit board (PCB). At this time, the electrodes of each semiconductor chip are connected to the respective electrodes of the PCB. Then, when the PCB with the mounted semiconductor chips is sealed using molding resin, a package substrate is formed. When the package substrate is thinned by grinding from the back side and divided into individual semiconductor chips, individual device chips are obtained.

[0034] On the front side of a semiconductor wafer on which multiple devices are formed, multiple metal films and insulating films constituting the devices are stacked. Furthermore, warping sometimes occurs on the semiconductor wafer due to forces generated on the stacked films. Additionally, warping sometimes occurs on the packaging substrate due to forces generated in the printed circuit board or sealing resin contained within the packaging substrate.

[0035] In the grinding method of this embodiment, a workpiece 1 that has warped, such as a semiconductor wafer or a packaging substrate, is ground. Hereinafter, the grinding method of this embodiment will be described using the case where the workpiece 1 is a semiconductor wafer as an example.

[0036] Next, the grinding apparatus for thinning the workpiece 1 will be described. Figure 1 An example of the grinding device 2 is shown schematically. Figure 1 The grinding apparatus 2 shown has an apparatus base 4 that supports the various structural elements. An opening 4a is provided on the upper surface of the apparatus base 4. An X-axis movable worktable 8 is provided in the opening 4a, and a chuck worktable 6 that attracts and holds the workpiece 1 and a worktable base 6e that supports the chuck worktable 1 are mounted on the upper surface of the X-axis movable worktable 8.

[0037] The X-axis moving table 8 can move along the X-axis direction via an X-axis moving mechanism (not shown). The X-axis moving table 8 is positioned by the X-axis moving mechanism in the loading / unloading area 10 for loading and unloading the workpiece 1 and the processing area 12 for grinding the workpiece 1.

[0038] A chuck table 6 is mounted on the upper surface of the table base 6e. The upper surface of the chuck table 6 serves as a holding surface for the workpiece 1. The chuck table 6 applies a negative pressure to the workpiece 1 held on the holding surface, thereby attracting and holding the workpiece 1. The table base 6e, on which the chuck table 6 is mounted, can rotate about an axis substantially perpendicular to the holding surface. Furthermore, the grinding apparatus 2 grinds the workpiece 1 while it is held by the chuck table 6. The detailed structure of the chuck table 6 will be described later.

[0039] A grinding unit 14 for grinding the workpiece 1 is disposed above the processing area 12. A support part 16 is erected on the rear side of the device base 4 to support the grinding unit 14. A pair of Z-axis guide rails 18 extending in the Z-axis direction are provided on the front surface of the support part 16, and a Z-axis moving plate 20 is slidably mounted on each Z-axis guide rail 18.

[0040] A nut portion (not shown) is provided on the back side (rear surface side) of the Z-axis moving plate 20, and a Z-axis ball screw 22 parallel to the Z-axis guide rail 18 is screwed onto this nut portion. A Z-axis pulse motor 24 is connected to one end of the Z-axis ball screw 22. If the Z-axis ball screw 22 is rotated by the Z-axis pulse motor 24, the Z-axis moving plate 20 moves along the Z-axis guide rail 18 in the Z-axis direction.

[0041] A grinding unit 14 for performing grinding operations on the workpiece 1 is fixed to the lower part of the front surface side of the Z-axis moving plate 20. If the Z-axis moving plate 20 is moved along the Z-axis direction, the grinding unit 14 can move along the Z-axis direction (machining feed direction).

[0042] The grinding unit 14 has a spindle 28 that rotates via a motor connected to the base end side. This motor is housed within the spindle housing 26. A circular wheel mounting base 30 is provided at the lower end (rear end) of the spindle 28, and an annular grinding wheel 32, which rotates with the spindle 28, is mounted on the lower surface of the wheel mounting base 30. Grinding tools 34 are arranged in a circular pattern on the lower surface of the grinding wheel 32.

[0043] The grinding wheel 34 comprises abrasive grains such as diamond and a bonding material that disperses and fixes the abrasive grains. When the spindle 28 is rotated, causing the grinding wheel 32 to rotate, the grinding wheel 34 rotates and moves along a ring track. When grinding the workpiece 1, in the machining area 12 where the X-axis moving table 8 is located, the center of the upper surface of the chuck table 6 is positioned below the ring track on which the grinding wheel 34 moves. In other words, the grinding wheel 34 moves along this ring track in the area above the center of the upper surface of the chuck table 6.

[0044] When grinding the upper surface of the workpiece 1 held by the chuck table 6, such as Figure 4 As shown, the chuck table 6 is rotated, and the grinding unit 14 is lowered while the grinding wheel 32 is rotating. Then, the grinding tool 34, which moves on the annular track, contacts the upper surface of the workpiece 1 to grind the workpiece 1.

[0045] Furthermore, when the grinding wheel 34 contacts the workpiece 1 and grinds the workpiece 1, grinding chips are generated from both the workpiece 1 and the grinding wheel 34, and heat is generated, causing the temperature of the workpiece 1 to rise. Therefore, in order to quickly remove the grinding chips and heat from the workpiece 1, a liquid called grinding water is provided to the workpiece 1 when grinding it with the grinding wheel 34. The grinding water is, for example, pure water.

[0046] Furthermore, when the X-axis moving table 8 is positioned in the loading / unloading area 10 and the workpiece 1 is loaded onto the chuck table 6, a negative pressure is applied to the workpiece 1 from the chuck table 6, and the workpiece 1 is held in place by the chuck table 6. At this time, if no warping occurs on the workpiece 1, the negative pressure will not leak, and the workpiece 1 will be stably held in place.

[0047] However, as mentioned above, warping sometimes occurs on the workpiece 1, which is the object of grinding. Figure 2 The diagram includes a perspective view schematically showing a warped, disc-shaped workpiece 1. The central portion 1c of the workpiece 1 is lower than the outer peripheral portion 1d, exhibiting a concave warping.

[0048] Furthermore, the central portion 1c and the outer peripheral portion 1d of the workpiece 1 are arbitrarily set on the warped workpiece 1, and their boundaries are not necessarily clearly defined. The central portion 1c is the portion that includes the center of the workpiece 1, and the outer peripheral portion 1d is the portion surrounding the central portion 1c. Moreover, the area outside the central portion 1c of the workpiece 1 is the outer peripheral portion 1d of the workpiece 1.

[0049] When grinding the workpiece 1 from the back side 1b, the workpiece 1 is placed on the chuck table 6 with the front side 1a facing downwards. When the warped workpiece 1 is placed on the chuck table 6, the central portion 1c of the workpiece 1 is lower than the outer peripheral portion 1d, and the outer peripheral portion 1d of the workpiece 1 floats up. In this state, when the workpiece 1 is attracted by the chuck table 6, sometimes the negative pressure (attraction force) leaks from the gap between the floating outer peripheral portion 1d of the workpiece 1 and the upper surface of the chuck table 6, making it impossible to attract and hold the workpiece 1.

[0050] If the workpiece 1 cannot be held properly, grinding on the back side 1b of the workpiece 1 cannot be performed properly. Therefore, it is also possible to press the outer peripheral portion 1d of the workpiece 1 from above when the workpiece 1 is placed on the chuck table 6, and apply negative pressure to the workpiece 1 while deforming it flat.

[0051] However, in this case, because a force is generated on the workpiece 1 to restore it to its original shape, the outer peripheral portion 1d of the workpiece 1 held by the chuck table 6 may float up again. In addition, if the force that warps the workpiece 1 is strong, it is not easy to press down the outer peripheral portion 1d.

[0052] Therefore, in the grinding method of the workpiece in this embodiment, firstly, negative pressure is applied only to the central portion 1c of the workpiece 1, and the workpiece 1 is ground while the central portion 1c is held by the chuck table 6. Then, the workpiece 1 is further ground while the outer peripheral portion 1d of the workpiece 1 is held by the chuck table 6, so that the workpiece 1 is thinned to the finished thickness.

[0053] The chuck table 6, which is capable of partially attracting and holding the workpiece 1, will be described. Figure 2 A chuck table 6 is schematically shown, capable of applying negative pressure to the central portion 1c and the outer peripheral portion 1d of the workpiece 1, respectively. The chuck table 6 has on its upper surface: a first porous portion 6a in the shape of a circular plate, the outer diameter of which is smaller than the diameter of the workpiece 1; and a second porous portion 6b in the shape of an annulus surrounding the first porous portion 6a, the outer diameter of which corresponds to the diameter of the workpiece 1.

[0054] The chuck table 6 also has the following on its upper surface: a partition 6c disposed between the first porous portion 6a and the second porous portion 6b; and a frame 6d surrounding the second porous portion 6b. The first porous portion 6a, the partition 6c, and the second porous portion 6b are housed in the frame 6d. When the workpiece 1 is placed on the chuck table 6, the central portion 1c of the workpiece 1 faces the first porous portion 6a, and the outer peripheral portion 1d of the workpiece 1 faces the second porous portion 6b.

[0055] The first porous section 6a, the second porous section 6b, the partition section 6c, and the frame 6d are components made of metals such as SUS (stainless steel) or ceramics. Numerous holes are formed in the first porous section 6a and the second porous section 6b, serving as transmission paths for negative pressure (attraction). The partition section 6c functions to suppress leakage of negative pressure (attraction) and is either a component without holes or a component with holes smaller than those in the first porous section 6a and the second porous section 6b.

[0056] exist Figure 3The diagram includes a schematic cross-sectional view of the chuck worktable 6. One end of the first suction path 36a is connected to the lower part of the first porous section 6a, and the other end of the first suction path 36a is connected to the first suction source 38a via the first switching section 40a. Additionally, one end of the second suction path 36b is connected to the lower part of the second porous section 6b, and the other end of the second suction path 36b is connected to the second suction source 38b via the second switching section 40b.

[0057] The first switching unit 40a has the function of switching the connected state and the disconnected state of the first suction path 36a. When the first suction path 36a is in the connected state, the negative pressure generated by the first suction source 38a acts on the central part 1c of the workpiece 1 placed on the chuck worktable 6 through the first suction path 36a and the first porous part 6a.

[0058] The second switching unit 40b has the function of switching the connected state and the disconnected state of the second suction path 36b. When the second suction path 36b is in the connected state, the negative pressure generated by the second suction source 38b acts on the outer peripheral portion 1d of the workpiece 1 placed on the chuck table 6 through the second suction path 36b and the second porous part 6b.

[0059] The center of the upper surface of the chuck table 6 coincides with the center of the first perforated portion 6a in the shape of a circular plate, and the chuck table 6 rotates about a rotation axis 42 that passes through the center of the upper surface. In addition, the grinding wheel 34 of the grinding unit 14 moves on an annular track above the center of the upper surface of the chuck table 6.

[0060] In the workpiece grinding method of this embodiment, when the workpiece 1 is ground using the grinding tool 34 of the grinding unit 14, the central portion 1c of the workpiece 1 is first held by the first porous portion 6a. The upper surface of the first porous portion 6a is covered by the central portion 1c of the workpiece 1, and a partition portion 6c is provided between the first porous portion 6a and the second porous portion 6b, so the negative pressure acting on the central portion 1c of the workpiece 1 from the first porous portion 6a is not easily leaked to the outside. Therefore, the workpiece 1 is properly held by the chuck table 6.

[0061] When the workpiece 1 is held in a drawn position, grinding can be performed on the back side 1b of the workpiece 1. In this case, since the workpiece 1 is ground while the outer peripheral portion 1d is in a floating state, the outer peripheral portion 1d is ground thinner in a concentrated manner. As a result, the outer peripheral portion 1d becomes thinner than the central portion 1c. Then, the grinding tool 34 also contacts the central portion 1c, causing the entire workpiece 1 to gradually become thinner.

[0062] When the workpiece 1 is thinned by grinding, the force causing it to warp weakens. Furthermore, the force required to restore the workpiece 1 to its original shape during deformation decreases. Therefore, during the grinding of the workpiece 1, the outer peripheral portion 1d of the workpiece 1 is held by suction using the second porous portion 6b, thereby holding the entire area of ​​the workpiece 1 by suction using the chuck table 6.

[0063] Compared to the case where the entire area of ​​the workpiece 1 before grinding is held by the chuck table 6, it is easier to hold the entire area of ​​the workpiece 1, which has been thinned to a certain extent by grinding. Furthermore, the possibility of the outer periphery 1d floating up again is also smaller. Therefore, the entire area of ​​the workpiece 1 is stably and appropriately held by the chuck table 6, enabling stable grinding of the workpiece 1.

[0064] The following describes each step of the grinding method for the workpiece according to this embodiment. Figure 8 (A) is a flowchart illustrating the steps of an example of the grinding method for a workpiece according to this embodiment.

[0065] In this grinding method, firstly, a first holding step S10 is performed, in which the central portion 1c of the workpiece 1 is attracted and adsorbed by the first porous portion 6a of the chuck table 6. In the first holding step S10, firstly, the X-axis moving table 8 is moved to the transfer-in / exit area 10, so that the front side 1a of the workpiece 1 is opposite to the upper surface of the chuck table 6. Figure 2 This is a perspective view schematically showing the workpiece 1 with its front 1a side facing the upper surface of the chuck table 6. At this time, the central portion 1c of the workpiece 1 is positioned above the first porous portion 6a.

[0066] Then, the workpiece 1 is lowered and placed on the upper surface of the chuck table 6. Next, as... Figure 3 As shown, the first switching unit 40a is activated to connect the first suction path 36a, causing the negative pressure generated by the first suction source 38a to act on the central portion 1c of the workpiece 1 via the first suction path 36a and the first porous part 6a. Thus, the central portion 1c of the workpiece 1 can be attracted and held using the first porous part 6a of the chuck table 6.

[0067] Furthermore, multiple devices such as ICs or LSIs (not shown) are formed on the front side 1a of the workpiece 1. Therefore, in order to protect these devices during the grinding of the workpiece 1, a protective tape (not shown) can be attached to the front side 1a of the workpiece 1 before performing the first holding step S10. This protective tape is peeled off from the workpiece 1 after the grinding of the workpiece 1 is completed.

[0068] After the first holding step S10, a first grinding step S20 is performed, in which the workpiece 1 is ground using the grinding wheel 34 of the grinding unit 14. In the first grinding step S20, the chuck table 6 is rotated about the rotation axis 42, and the spindle 28 of the grinding unit 14 is rotated. Then, while supplying grinding water to the grinding wheel 34 and the workpiece 1, the grinding unit 14 is lowered, so that the grinding wheel 34 contacts the back surface 1b of the workpiece 1. Thus, the workpiece 1 is ground from the back surface 1b side.

[0069] Figure 4 A schematic cross-sectional view of the workpiece 1 being ground in the first grinding step S20 is shown. In the first grinding step S20, the workpiece 1 is ground until it reaches a first thickness 46a (see reference). Figure 6 The second thickness 46b. Then, by using the second porous portion 6b to attract and hold the outer peripheral portion 1d of the workpiece 1, the second holding step S30, which uses the chuck table 6 to attract and hold the entire area of ​​the workpiece 1, is carried out.

[0070] The grinding apparatus 2 may also have a thickness measuring unit (not shown) for measuring the thickness of the workpiece 1 being ground. This thickness measuring unit, for example, has a probe that contacts the back surface 1b of the workpiece 1. If this measuring unit is used, the gradually thinning thickness of the workpiece 1 can be measured and monitored during the first grinding step S20.

[0071] In the first grinding step S20, for example, it is determined whether the thickness of the workpiece 1 has reached the second thickness 46b (S21). If the thickness of the workpiece 1 has not reached the second thickness 46b, the first grinding step S20 continues, and if the thickness of the workpiece 1 has reached the second thickness 46b, the second holding step S30 is performed.

[0072] Here, the second thickness 46b will be explained. The second thickness 46b is appropriately set to a value larger than the first thickness 46a, which is the final finished thickness of the workpiece 1 in the workpiece grinding method of this embodiment.

[0073] When the first grinding step S20 is performed to grind the workpiece 1, as described above, the force that warps the workpiece 1 is weakened, and the force required to restore the workpiece 1 to its original shape when it is deformed is reduced. As a result, the outer peripheral portion 1d of the workpiece 1 can be attracted and held by the second porous portion 6b. That is, the second holding step S30 can be performed.

[0074] Therefore, the second thickness 46b, which is the target thickness of the workpiece 1 in the first grinding step S20, is set to the thickness of the workpiece 1 such that the outer peripheral portion 1d of the workpiece 1 can be attracted and held by the second porous portion 6b. The second thickness 46b is a value appropriately set according to the type of workpiece 1 and the grinding conditions performed. Alternatively, it is also possible to determine, by other methods, that the thickness of the workpiece 1 has reached the second thickness 46b, thus enabling the second holding step S30 to be performed.

[0075] For example, the decision to perform the second holding step S30 can be determined based on the amount of descent of the grinding unit 14 after the grinding wheel 34 contacts the back surface 1b of the workpiece 1 to begin grinding. Alternatively, the decision to perform the second holding step S30 can be determined based on the elapsed time since the start of grinding of the workpiece 1. Furthermore, the output of the motor that rotates the spindle 28 can be monitored, and the decision can be made based on changes in that output. Alternatively, the magnitude of the load applied to the table base 6e can be monitored, and the decision can be made based on changes in that load.

[0076] In these methods, knowledge about the degree of grinding progress of the workpiece 1 is obtained. Furthermore, it is determined whether the second holding step S30 can be performed based on this degree of progress. Thus, the determination of whether the second holding step S30 can be performed, i.e., whether the thickness of the workpiece 1 has reached the second thickness 46b, can also be performed by methods other than measuring the thickness of the workpiece 1 (S21).

[0077] Therefore, grinding the workpiece 1 to a second thickness 46b in the first grinding step S20 is synonymous with reaching a state where the second holding step S30 can be performed. That is, it does not necessarily mean confirming that the thickness of the workpiece 1 has reached a specific thickness, and it is not necessary to directly measure the thickness of the workpiece 1. In the first grinding step S20, if the state where the second holding step S30 can be performed is reached, it can be said that the workpiece 1 has been ground to a second thickness 46b.

[0078] Furthermore, in the first grinding step S20, it is not necessary to determine whether the second holding step S30 can be performed. Grinding of the workpiece 1 begins, and if the outer peripheral portion 1d of the workpiece 1 can be attracted and held by the second porous portion 6b of the chuck table 6, then the first grinding step S20 can be said to be completed.

[0079] However, when multiple workpieces 1 are ground sequentially using the grinding device 2, the degree of warping generated on each workpiece 1 is not necessarily the same. Moreover, the criteria used to determine whether the second holding step S30 can be performed sometimes have to reflect the degree of warping of the workpiece 1.

[0080] Therefore, it is preferable that the grinding apparatus 2 has a mechanism capable of measuring the degree of warping of the workpiece 1. Alternatively, a warping measurement step can be performed before performing the first grinding step S20 to measure the degree of warping of the workpiece 1. Furthermore, the second thickness 46b, which serves as a criterion for determining whether the second holding step S30 can be performed, is, for example, set to a value that reflects the degree of warping of the workpiece 1.

[0081] Here, the degree of warpage of the workpiece 1 is expressed, for example, by indicators such as the curvature of the front side 1a or the back side 1b of the workpiece 1, the height difference between the lowest and highest points of the workpiece 1, and the difference between the lowest and highest points of the back side 1b of the workpiece 1. Moreover, the mechanism capable of measuring the degree of warpage of the workpiece 1 is, for example, a three-dimensional measuring device capable of irradiating light onto various parts of the workpiece 1 and detecting the reflected light, or a height measuring device having a probe capable of contacting the upper surface of the workpiece 1.

[0082] When measuring the degree of warpage of workpiece 1 using a three-dimensional measuring instrument, firstly, the three-dimensional shape of workpiece 1 is measured. Then, the degree of warpage of workpiece 1 is evaluated based on the information obtained related to the three-dimensional shape of workpiece 1. Furthermore, other information related to the shape of workpiece 1 can be obtained based on the measurement results of the three-dimensional measuring instrument. Therefore, the grinding conditions for workpiece 1 can be determined based on this other information related to the shape of workpiece 1. Additionally, the finished thickness of workpiece 1 can be corrected based on the information obtained related to the three-dimensional shape of workpiece 1.

[0083] For example, when using a three-dimensional measuring instrument, the height of the highest point of the workpiece 1 can be determined. Therefore, the height of the grinding unit 14 at the start of the first grinding step S20 can also be determined based on the height of the highest point of the workpiece 1. The height position of the grinding unit 14 at the start of the first grinding step S20 is, for example, a position that is higher than the height of the highest point of the workpiece 1 by a predetermined allowance height (air cutting amount).

[0084] Next, the second holding step S30 will be explained. Figure 5 A schematic cross-sectional view of the workpiece 1 during the second holding step S30 is shown. In the second holding step S30, the central portion 1c and the outer peripheral portion 1d of the workpiece 1 are held by suction using the first porous portion 6a and the second porous portion 6b of the chuck table 6. More specifically, the second switching portion 40b is activated to connect the second suction path 36b, so that the negative pressure generated by the second suction source 38b acts on the outer peripheral portion 1d of the workpiece 1 via the second suction path 36b and the second porous portion 6b.

[0085] As described above, the force causing the workpiece 1, which is thinned by grinding in the first grinding step S20, to warp is reduced, and the force required to restore the workpiece 1 to its original shape when it is deformed is also reduced. Furthermore, when the workpiece 1 is thinned, the degree of warping of the workpiece 1 is reduced compared to before grinding, and the distance between the outer peripheral portion 1d of the workpiece 1 and the upper surface of the chuck table 6 is reduced. Therefore, when negative pressure (attraction force) is applied to the workpiece 1 via the second porous portion 6b, this negative pressure is less likely to leak to the outside.

[0086] In particular, since grinding water is supplied to the grinding wheel 34 and the workpiece 1 during grinding, the gap between the outer peripheral portion 1d of the workpiece 1 and the second porous portion 6b of the chuck table 6 is partially or entirely sealed by the grinding water 44. That is, the negative pressure (attraction force) is less likely to leak to the outside through the grinding water 44.

[0087] Therefore, when negative pressure is applied to the workpiece 1 via the second porous portion 6b, the workpiece 1 deforms such that its outer peripheral portion 1d approaches the second porous portion 6b of the chuck table 6. Then, the entire area of ​​the workpiece 1 comes into contact with the upper surface of the chuck table 6. When the workpiece 1 is further ground in this state, the central portion 1c and the outer peripheral portion 1d of the workpiece 1 can be ground to the same thickness.

[0088] Next, the second grinding step S40 is performed. Figure 6 This is a schematic cross-sectional view of the workpiece 1 during the second grinding step S40. In the second grinding step S40, the grinding unit 14 is lowered, and the workpiece 1 is ground from the back side 1b using the grinding tool 34 of the grinding unit 14 until it reaches a first thickness 46a.

[0089] The grinding apparatus 2 includes, for example, the aforementioned thickness measuring unit (not shown) for measuring the thickness of the workpiece 1. Furthermore, in the second grinding step S40, the thickness of the workpiece 1 is monitored using this thickness measuring unit, and it is determined whether the thickness of the workpiece 1 has reached the first thickness 46a (S41). If the thickness of the workpiece 1 has not reached the first thickness 46a, the second grinding step S40 continues; if the thickness of the workpiece 1 has reached the first thickness 46a, the second grinding step S40 ends.

[0090] Here, the first thickness 46a is, for example, the finished thickness that serves as the final target thickness of the workpiece 1. However, the first thickness 46a is not limited to this. For example, the grinding apparatus 2 may also perform grinding on the workpiece 1 in two stages: rough grinding and fine grinding. Here, rough grinding refers to the process of grinding the workpiece 1 at high speed to a thickness that has not yet reached the finished thickness, while fine grinding refers to the process of grinding the workpiece 1 to the finished thickness with a relatively small processing load.

[0091] When grinding the workpiece 1 in two stages in the grinding apparatus 2, the grinding apparatus 2 may also have multiple grinding units. For example, the workpiece 1 may be rough ground using the first grinding unit and fine ground using the second grinding unit.

[0092] In this case, the grinding method for the workpiece of this embodiment can also be implemented in one or both of the first grinding unit and the second grinding unit. Moreover, the first thickness 46a in the grinding method implemented by the first grinding unit is set as the target thickness of the workpiece 1 in rough grinding, rather than the final finished thickness of the workpiece 1.

[0093] As explained above, in the workpiece grinding method of this embodiment, the workpiece 1 is ground by attracting and holding the central portion 1c of the workpiece 1, which has warped, using the first porous portion 6a of the chuck table 6. Furthermore, after the workpiece 1 has been ground to a certain extent, the outer peripheral portion 1d of the workpiece 1, which has reduced warping, is ground by attracting and holding it using the second porous portion 6b of the chuck table. Therefore, it is possible to appropriately grind a workpiece 1 that has warped to a degree that makes it difficult to attract and hold the entire area using the chuck table 6.

[0094] Alternatively, in the grinding method for the workpiece in this embodiment, after the first grinding step S20 is performed and the thickness of the workpiece 1 reaches the second thickness 46b, the second holding step S30 may be performed while the grinding of the workpiece 1 is interrupted by stopping the descent of the grinding unit 14. Alternatively, after the grinding of the workpiece 1 begins and the thickness of the workpiece 1 reaches the second thickness 46b, the descent of the grinding unit 14 may continue and the second holding step S30 may be performed.

[0095] In other words, in the grinding method of the workpiece in this embodiment, when the outer peripheral portion 1d of the workpiece 1 is held by suction using the second porous portion 6b, the grinding of the workpiece 1 can be stopped or continued. Therefore, the grinding method of the workpiece in this embodiment only needs to have the following two steps.

[0096] That is, in the first grinding step S20, the grinding tool 34 of the grinding unit 14 grinds the workpiece 1, whose central portion 1c is held by the first porous portion 6a of the chuck table 6, from the back side 1b until it becomes a second thickness 46b, which is thicker than the first thickness 46a. Furthermore, in the second grinding step S40, the grinding tool 34 of the grinding unit 14 grinds the workpiece 1, whose central portion 1c and outer peripheral portion 1d are held by the first porous portion 6a and the second porous portion 6b of the chuck table 6, from the back side 1b until it becomes a first thickness 46a.

[0097] Next, the following situation will be described in detail: the central part 1c of the workpiece 1 is attracted and held by the first porous part 6a of the chuck table 6 and grinding begins, and the outer peripheral part 1d of the workpiece 1 is attracted and held by the second porous part 6b without stopping grinding. Figure 8 (B) is a flowchart showing the steps of the grinding method for the workpiece in this case. Figure 8 The grinding method of the workpiece shown in (B) is Figure 8 A variation of the grinding method for the workpiece shown in (A).

[0098] exist Figure 8 In the grinding method of the workpiece shown in (B), firstly, the front surface 1a of the workpiece 1 is brought face to face with the upper surface of the chuck table 6, and a first holding step S50 is performed to attract and hold the central portion 1c of the workpiece 1 using the first perforated portion 6a of the chuck table 6. This first holding step S50 is the same as the first holding step S10 described above, so its description is omitted.

[0099] After the first holding step S50 is performed, the workpiece 1 is ground from the back side 1b side using the grinding tool 34 of the grinding unit 14 until it reaches the first thickness 46a (S60). Moreover, during the grinding step, a second holding step S70 is performed in which the outer peripheral portion 1d of the workpiece 1 is attracted and held using the second porous portion 6b of the chuck table 6.

[0100] The second holding step S70, for example, is when the thickness of the workpiece 1, which has been thinned by grinding, reaches the aforementioned second thickness 46b (see reference). Figure 4 When the workpiece 1 reaches the second thickness 46b, the second switching part 40b is activated to apply negative pressure to the outer peripheral portion 1d of the workpiece 1, thereby attracting and holding the outer peripheral portion 1d of the workpiece 1 using the second porous part 6b.

[0101] Furthermore, the timing of performing the second holding step S70 is not limited to this. For example, the second switching unit 40b can be activated to switch the second suction path 36b to the connected state after the grinding of the workpiece 1 begins (S60) and before the thickness of the workpiece 1 reaches the second thickness 46b.

[0102] In this case, negative pressure (attraction force) continuously leaks from the gap between the second porous portion 6b and the outer peripheral portion 1d until the outer peripheral portion 1d of the workpiece 1 can be attracted and held by the second porous portion 6b (i.e., the thickness of the workpiece 1 reaches the second thickness 46b). Moreover, when the thickness of the workpiece 1 reaches the second thickness 46b, the workpiece 1 deforms due to the negative pressure, and the outer peripheral portion 1d comes into contact with the second porous portion 6b, thereby being attracted and held by the second porous portion 6b.

[0103] In other words, when the workpiece 1 is sufficiently thinned by grinding, the outer peripheral portion 1d is attracted and held by the second porous portion 6b when negative pressure is applied to the workpiece 1 through the second porous portion 6b. On the other hand, when the workpiece 1 is not sufficiently thinned (i.e., when the thickness of the workpiece 1 has not reached the second thickness 46b), the outer peripheral portion 1d is automatically attracted and held by the second porous portion 6b when the workpiece 1 is further ground and the thickness reaches the second thickness 46b.

[0104] Even if grinding of the workpiece 1 begins with only the central portion 1c of the workpiece 1 being attracted and held, if the entire area of ​​the workpiece 1 is eventually attracted and held by the chuck table 6, the workpiece 1 will also be appropriately ground until the thickness becomes the first thickness 46a. In this way, grinding of the workpiece 1 can be continued without stopping when the outer peripheral portion 1d of the workpiece 1 is attracted and held using the second porous portion 6b.

[0105] Here, the direction of movement of the grinding wheel 34 during the grinding of the workpiece 1 and the contact area between the workpiece 1 and the grinding wheel 34 will be explained. In the figures, the upper surface of the chuck table 6 is depicted as flat. However, in order to grind the surface of the workpiece 1 evenly, the upper surface of the chuck table 6 is a cone shape with a very small height, forming a very small slope from the outer periphery towards the center.

[0106] The rotation axis 42 of the chuck table 6 and the axis of the spindle 28 of the grinding unit 14 are slightly offset from each other in a direction that is parallel to each other. Moreover, the generatrix at the highest position of the conical generatrix constituting the upper surface of the chuck table 6 is approximately parallel to the lower surface of the grinding wheel 32 of the grinding unit 14. When the workpiece 1 is held by the chuck table 6, and the grinding unit 14 is lowered while the chuck table 6 and the grinding wheel 32 are rotated respectively, the grinding tool 34 contacts the workpiece 1 along the highest generatrix.

[0107] Figure 7 It is a top view schematically showing the workpiece 1 held by the chuck table 6 and the annular track 48 that becomes the path for the movement of the grinding wheel 34. Figure 7 The diagram schematically shows the back surface 1b of the workpiece 1, the annular track 48, and the contact area 50 in contact with the workpiece 1 during grinding. (Example) Figure 7 As shown, the grinding wheel 34 begins to contact the back surface 1b of the workpiece 1 when it passes above the center of the chuck table 6, and stops contacting the back surface 1b of the workpiece 1 when it passes above the outer periphery of the workpiece 1.

[0108] Here, when grinding a warped workpiece 1, the grinding wheel 34, which contacts the back surface 1b of the workpiece 1, moves along the annular track 48 and approaches the outer periphery of the workpiece 1. The grinding wheel 34 presses down on the raised outer periphery portion 1d from above. This reduces the gap between the workpiece 1 and the upper surface of the chuck table 6. Consequently, the outer periphery portion 1d of the workpiece 1 can be easily attracted and held using the second perforated portion 6b.

[0109] However, the situation changes when the grinding wheel 34 moves in the opposite direction—that is, when the grinding wheel 34 contacts the workpiece 1 from the outer periphery of the workpiece 1 in the contact area 50, and then stops contacting the workpiece 1 after passing above the center of the workpiece 1. Specifically, in the outer peripheral portion 1d of the workpiece 1, sometimes a force acts in the direction in which the workpiece 1 is drawn into the grinding wheel 34, causing the outer peripheral portion 1d of the workpiece 1 to be further lifted. In this case, the outer peripheral portion 1d of the workpiece 1 is difficult to be attracted and held by the second porous portion 6b.

[0110] Therefore, when grinding the workpiece 1, it is preferable that the grinding wheel 34 contacts the back surface 1b of the workpiece 1 during its travel from the region above the center of the upper surface of the chuck table 6 of the annular track 48 to the region above the frame 6d of the upper surface of the chuck table 6. The rotation direction of the spindle 28 can be set to achieve this purpose.

[0111] As explained above, in the workpiece grinding method of this embodiment, the workpiece 1 is ground while the chuck table 6 is used to hold and attract each region of the workpiece 1 that is warping in stages. Therefore, the workpiece 1 can be stably held by the chuck table 6 from the beginning to the end of the grinding process, and the workpiece 1 can be ground to a specified thickness.

[0112] Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be made to implement it. For example, in the above embodiments, the case where two porous portions, a first porous portion 6a and a second porous portion 6b, are provided on the upper surface of the chuck table 6 has been described. However, one aspect of the present invention is not limited to this. That is, three or more porous portions may be provided on the upper surface of the chuck table 6.

[0113] For example, one or more annular porous portions may be further configured between the first porous portion 6a and the second porous portion 6b. In this case, the warped workpiece 1 can be attracted and held by the chuck table 6 in more than three stages, thus making it easier to deform the workpiece 1 into a flat plate shape.

[0114] The structure and method of the above embodiments can be implemented with appropriate modifications without departing from the purpose of the present invention.

Claims

1. A grinding method of a workpiece, which grinds the workpiece that is warped in a concave shape with a central portion lower than an outer peripheral portion from a back surface to a first thickness in a grinding device having: a chuck table that has a first porous portion of a circular plate shape, a second porous portion of an annular shape, a partition portion, and a frame body on an upper surface, an outer diameter of the first porous portion is smaller than a diameter of the workpiece, the second porous portion surrounds the first porous portion and an outer diameter thereof corresponds to the diameter of the workpiece, the partition portion is provided between the first porous portion and the second porous portion, and the frame body surrounds the second porous portion, the chuck table rotates around a rotation axis that passes through a center of the upper surface and attracts and holds the workpiece; and a grinding unit that has a grinding tool that moves on an annular track of an area above the center of the upper surface of the chuck table, provides grinding water to the workpiece attracted and held by the chuck table, and grinds an exposed back surface side of the workpiece using the grinding tool, characterized by comprising: a first grinding step of grinding the workpiece whose front surface side is opposed to the upper surface of the chuck table and whose central portion is attracted and held by the first porous portion of the chuck table from the back surface side using the grinding tool of the grinding unit to a second thickness that is thicker than the first thickness; and a second grinding step of grinding the workpiece whose central portion and outer peripheral portion are attracted and held by the first porous portion and the second porous portion of the chuck table from the back surface side using the grinding tool of the grinding unit to the first thickness.

2. A grinding method of a workpiece, which grinds the workpiece that is warped in a concave shape with a central portion lower than an outer peripheral portion from a back surface to a first thickness in a grinding device having: a chuck table that has a first porous portion of a circular plate shape, a second porous portion of an annular shape, a partition portion, and a frame body on an upper surface, an outer diameter of the first porous portion is smaller than a diameter of the workpiece, the second porous portion surrounds the first porous portion and an outer diameter thereof corresponds to the diameter of the workpiece, the partition portion is provided between the first porous portion and the second porous portion, and the frame body surrounds the second porous portion, the chuck table rotates around a rotation axis that passes through a center of the upper surface and attracts and holds the workpiece; and a grinding unit that has a grinding tool that moves on an annular track of an area above the center of the upper surface of the chuck table, provides grinding water to the workpiece attracted and held by the chuck table, and grinds an exposed back surface side of the workpiece using the grinding tool, characterized by comprising: a first holding step of opposing a front surface side of the workpiece to the upper surface of the chuck table and attracting and holding a central portion of the workpiece by the first porous portion of the chuck table; a first grinding step of grinding the workpiece from a back surface side using the grinding tool of the grinding unit to a second thickness that is thicker than the first thickness; a second holding step of attracting and holding the central portion and the outer peripheral portion of the workpiece by the first porous portion and the second porous portion of the chuck table; and a second grinding step of grinding the workpiece from the back surface side using the grinding tool of the grinding unit to the first thickness. ​ ​ ​ ​ ​ ​ A chuck table having a first porous portion in the form of a circular plate on an upper surface, a second porous portion in the form of a ring surrounding the first porous portion and having an outer diameter corresponding to the diameter of the workpiece, a partition portion disposed between the first porous portion and the second porous portion, and a frame surrounding the second porous portion, the chuck table being rotatable about a rotation axis passing through the center of the upper surface and capable of attracting and holding the workpiece; ​ ​ ​ ​ ​ ​ ​ ​ ​ 3. A grinding method of a workpiece, which grinds the workpiece that is warped in a concave shape with a central portion lower than an outer peripheral portion from a back surface to a first thickness in a grinding device having: A chuck table having a first porous portion in the form of a circular plate on an upper surface, a second porous portion in the form of a ring surrounding the first porous portion and having an outer diameter corresponding to the diameter of the workpiece, a partition portion disposed between the first porous portion and the second porous portion, and a frame surrounding the second porous portion, the chuck table being rotatable about a rotation axis passing through the center of the upper surface and capable of attracting and holding the workpiece; and a grinding unit that has a grinding stone that moves on a ring-shaped track of a region above the center of the upper surface of the chuck table, grinds the exposed back surface side of the workpiece with the grinding stone while supplying grinding water to the workpiece held by suction to the chuck table, characterized in that the grinding method of the workpiece has steps of: a first holding step of opposing the front surface side of the workpiece to the upper surface of the chuck table and holding the central portion of the workpiece by suction with the first porous portion of the chuck table; and a grinding step of grinding the workpiece from the back surface side to the first thickness with the grinding stone of the grinding unit, during the implementation of the grinding step, a second holding step of holding the outer peripheral portion of the workpiece by suction with the second porous portion of the chuck table is implemented.

4. The grinding method of the workpiece according to any one of claims 1 to 3, characterized in that the grinding stone contacts the back surface of the workpiece during the travel of the grinding stone from the region above the center of the upper surface of the chuck table of the ring-shaped track to the region above the frame of the upper surface of the chuck table when the grinding of the workpiece is implemented.

5. The grinding method of the workpiece according to any one of claims 1 to 3, characterized in that the grinding water that reaches the outer periphery of the second porous portion suppresses the leakage of the suction force from the second porous portion to the workpiece when the workpiece is held by suction with the second porous portion of the chuck table.

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